sys/netinet/tcp_input.c

   1 /*-
   2  * SPDX-License-Identifier: BSD-3-Clause
   3  *
   4  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
   5  *      The Regents of the University of California.  All rights reserved.
   6  * Copyright (c) 2007-2008,2010
   7  *      Swinburne University of Technology, Melbourne, Australia.
   8  * Copyright (c) 2009-2010 Lawrence Stewart <lstewart@freebsd.org>
   9  * Copyright (c) 2010 The FreeBSD Foundation
  10  * Copyright (c) 2010-2011 Juniper Networks, Inc.
  11  * All rights reserved.
  12  *
  13  * Portions of this software were developed at the Centre for Advanced Internet
  14  * Architectures, Swinburne University of Technology, by Lawrence Stewart,
  15  * James Healy and David Hayes, made possible in part by a grant from the Cisco
  16  * University Research Program Fund at Community Foundation Silicon Valley.
  17  *
  18  * Portions of this software were developed at the Centre for Advanced
  19  * Internet Architectures, Swinburne University of Technology, Melbourne,
  20  * Australia by David Hayes under sponsorship from the FreeBSD Foundation.
  21  *
  22  * Portions of this software were developed by Robert N. M. Watson under
  23  * contract to Juniper Networks, Inc.
  24  *
  25  * Redistribution and use in source and binary forms, with or without
  26  * modification, are permitted provided that the following conditions
  27  * are met:
  28  * 1. Redistributions of source code must retain the above copyright
  29  *    notice, this list of conditions and the following disclaimer.
  30  * 2. Redistributions in binary form must reproduce the above copyright
  31  *    notice, this list of conditions and the following disclaimer in the
  32  *    documentation and/or other materials provided with the distribution.
  33  * 3. Neither the name of the University nor the names of its contributors
  34  *    may be used to endorse or promote products derived from this software
  35  *    without specific prior written permission.
  36  *
  37  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  38  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  39  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  40  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  41  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  42  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  43  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  44  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  45  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  46  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  47  * SUCH DAMAGE.
  48  *
  49  *      @(#)tcp_input.c 8.12 (Berkeley) 5/24/95
  50  */
  51
  52 #include <sys/cdefs.h>
  53 __FBSDID("$FreeBSD$");
  54
  55 #include "opt_inet.h"
  56 #include "opt_inet6.h"
  57 #include "opt_ipsec.h"
  58 #include "opt_tcpdebug.h"
  59
  60 #include <sys/param.h>
  61 #include <sys/kernel.h>
  62 #ifdef TCP_HHOOK
  63 #include <sys/hhook.h>
  64 #endif
  65 #include <sys/malloc.h>
  66 #include <sys/mbuf.h>
  67 #include <sys/proc.h>           /* for proc0 declaration */
  68 #include <sys/protosw.h>
  69 #include <sys/sdt.h>
  70 #include <sys/signalvar.h>
  71 #include <sys/socket.h>
  72 #include <sys/socketvar.h>
  73 #include <sys/sysctl.h>
  74 #include <sys/syslog.h>
  75 #include <sys/systm.h>
  76
  77 #include <machine/cpu.h>        /* before tcp_seq.h, for tcp_random18() */
  78
  79 #include <vm/uma.h>
  80
  81 #include <net/if.h>
  82 #include <net/if_var.h>
  83 #include <net/route.h>
  84 #include <net/vnet.h>
  85
  86 #define TCPSTATES               /* for logging */
  87
  88 #include <netinet/in.h>
  89 #include <netinet/in_kdtrace.h>
  90 #include <netinet/in_pcb.h>
  91 #include <netinet/in_systm.h>
  92 #include <netinet/ip.h>
  93 #include <netinet/ip_icmp.h>    /* required for icmp_var.h */
  94 #include <netinet/icmp_var.h>   /* for ICMP_BANDLIM */
  95 #include <netinet/ip_var.h>
  96 #include <netinet/ip_options.h>
  97 #include <netinet/ip6.h>
  98 #include <netinet/icmp6.h>
  99 #include <netinet6/in6_pcb.h>
 100 #include <netinet6/in6_var.h>
 101 #include <netinet6/ip6_var.h>
 102 #include <netinet6/nd6.h>
 103 #include <netinet/tcp.h>
 104 #include <netinet/tcp_fsm.h>
 105 #include <netinet/tcp_log_buf.h>
 106 #include <netinet/tcp_seq.h>
 107 #include <netinet/tcp_timer.h>
 108 #include <netinet/tcp_var.h>
 109 #include <netinet6/tcp6_var.h>
 110 #include <netinet/tcpip.h>
 111 #include <netinet/cc/cc.h>
 112 #include <netinet/tcp_fastopen.h>
 113 #ifdef TCPPCAP
 114 #include <netinet/tcp_pcap.h>
 115 #endif
 116 #include <netinet/tcp_syncache.h>
 117 #ifdef TCPDEBUG
 118 #include <netinet/tcp_debug.h>
 119 #endif /* TCPDEBUG */
 120 #ifdef TCP_OFFLOAD
 121 #include <netinet/tcp_offload.h>
 122 #endif
 123
 124 #include <netipsec/ipsec_support.h>
 125
 126 #include <machine/in_cksum.h>
 127
 128 #include <security/mac/mac_framework.h>
 129
 130 const int tcprexmtthresh = 3;
 131
 132 int tcp_log_in_vain = 0;
 133 SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW,
 134     &tcp_log_in_vain, 0,
 135     "Log all incoming TCP segments to closed ports");
 136
 137 VNET_DEFINE(int, blackhole) = 0;
 138 #define V_blackhole             VNET(blackhole)
 139 SYSCTL_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_VNET | CTLFLAG_RW,
 140     &VNET_NAME(blackhole), 0,
 141     "Do not send RST on segments to closed ports");
 142
 143 VNET_DEFINE(int, tcp_delack_enabled) = 1;
 144 SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_VNET | CTLFLAG_RW,
 145     &VNET_NAME(tcp_delack_enabled), 0,
 146     "Delay ACK to try and piggyback it onto a data packet");
 147
 148 VNET_DEFINE(int, drop_synfin) = 0;
 149 SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_VNET | CTLFLAG_RW,
 150     &VNET_NAME(drop_synfin), 0,
 151     "Drop TCP packets with SYN+FIN set");
 152
 153 VNET_DEFINE(int, tcp_do_rfc6675_pipe) = 0;
 154 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc6675_pipe, CTLFLAG_VNET | CTLFLAG_RW,
 155     &VNET_NAME(tcp_do_rfc6675_pipe), 0,
 156     "Use calculated pipe/in-flight bytes per RFC 6675");
 157
 158 VNET_DEFINE(int, tcp_do_rfc3042) = 1;
 159 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3042, CTLFLAG_VNET | CTLFLAG_RW,
 160     &VNET_NAME(tcp_do_rfc3042), 0,
 161     "Enable RFC 3042 (Limited Transmit)");
 162
 163 VNET_DEFINE(int, tcp_do_rfc3390) = 1;
 164 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3390, CTLFLAG_VNET | CTLFLAG_RW,
 165     &VNET_NAME(tcp_do_rfc3390), 0,
 166     "Enable RFC 3390 (Increasing TCP's Initial Congestion Window)");
 167
 168 VNET_DEFINE(int, tcp_initcwnd_segments) = 10;
 169 SYSCTL_INT(_net_inet_tcp, OID_AUTO, initcwnd_segments,
 170     CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_initcwnd_segments), 0,
 171     "Slow-start flight size (initial congestion window) in number of segments");
 172
 173 VNET_DEFINE(int, tcp_do_rfc3465) = 1;
 174 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3465, CTLFLAG_VNET | CTLFLAG_RW,
 175     &VNET_NAME(tcp_do_rfc3465), 0,
 176     "Enable RFC 3465 (Appropriate Byte Counting)");
 177
 178 VNET_DEFINE(int, tcp_abc_l_var) = 2;
 179 SYSCTL_INT(_net_inet_tcp, OID_AUTO, abc_l_var, CTLFLAG_VNET | CTLFLAG_RW,
 180     &VNET_NAME(tcp_abc_l_var), 2,
 181     "Cap the max cwnd increment during slow-start to this number of segments");
 182
 183 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, ecn, CTLFLAG_RW, 0, "TCP ECN");
 184
 185 VNET_DEFINE(int, tcp_do_ecn) = 2;
 186 SYSCTL_INT(_net_inet_tcp_ecn, OID_AUTO, enable, CTLFLAG_VNET | CTLFLAG_RW,
 187     &VNET_NAME(tcp_do_ecn), 0,
 188     "TCP ECN support");
 189
 190 VNET_DEFINE(int, tcp_ecn_maxretries) = 1;
 191 SYSCTL_INT(_net_inet_tcp_ecn, OID_AUTO, maxretries, CTLFLAG_VNET | CTLFLAG_RW,
 192     &VNET_NAME(tcp_ecn_maxretries), 0,
 193     "Max retries before giving up on ECN");
 194
 195 VNET_DEFINE(int, tcp_insecure_syn) = 0;
 196 SYSCTL_INT(_net_inet_tcp, OID_AUTO, insecure_syn, CTLFLAG_VNET | CTLFLAG_RW,
 197     &VNET_NAME(tcp_insecure_syn), 0,
 198     "Follow RFC793 instead of RFC5961 criteria for accepting SYN packets");
 199
 200 VNET_DEFINE(int, tcp_insecure_rst) = 0;
 201 SYSCTL_INT(_net_inet_tcp, OID_AUTO, insecure_rst, CTLFLAG_VNET | CTLFLAG_RW,
 202     &VNET_NAME(tcp_insecure_rst), 0,
 203     "Follow RFC793 instead of RFC5961 criteria for accepting RST packets");
 204
 205 VNET_DEFINE(int, tcp_recvspace) = 1024*64;
 206 #define V_tcp_recvspace VNET(tcp_recvspace)
 207 SYSCTL_INT(_net_inet_tcp, TCPCTL_RECVSPACE, recvspace, CTLFLAG_VNET | CTLFLAG_RW,
 208     &VNET_NAME(tcp_recvspace), 0, "Initial receive socket buffer size");
 209
 210 VNET_DEFINE(int, tcp_do_autorcvbuf) = 1;
 211 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_auto, CTLFLAG_VNET | CTLFLAG_RW,
 212     &VNET_NAME(tcp_do_autorcvbuf), 0,
 213     "Enable automatic receive buffer sizing");
 214
 215 VNET_DEFINE(int, tcp_autorcvbuf_max) = 2*1024*1024;
 216 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_max, CTLFLAG_VNET | CTLFLAG_RW,
 217     &VNET_NAME(tcp_autorcvbuf_max), 0,
 218     "Max size of automatic receive buffer");
 219
 220 VNET_DEFINE(struct inpcbhead, tcb);
 221 #define tcb6    tcb  /* for KAME src sync over BSD*'s */
 222 VNET_DEFINE(struct inpcbinfo, tcbinfo);
 223
 224 /*
 225  * TCP statistics are stored in an array of counter(9)s, which size matches
 226  * size of struct tcpstat.  TCP running connection count is a regular array.
 227  */
 228 VNET_PCPUSTAT_DEFINE(struct tcpstat, tcpstat);
 229 SYSCTL_VNET_PCPUSTAT(_net_inet_tcp, TCPCTL_STATS, stats, struct tcpstat,
 230     tcpstat, "TCP statistics (struct tcpstat, netinet/tcp_var.h)");
 231 VNET_DEFINE(counter_u64_t, tcps_states[TCP_NSTATES]);
 232 SYSCTL_COUNTER_U64_ARRAY(_net_inet_tcp, TCPCTL_STATES, states, CTLFLAG_RD |
 233     CTLFLAG_VNET, &VNET_NAME(tcps_states)[0], TCP_NSTATES,
 234     "TCP connection counts by TCP state");
 235
 236 static void
 237 tcp_vnet_init(const void *unused)
 238 {
 239
 240         COUNTER_ARRAY_ALLOC(V_tcps_states, TCP_NSTATES, M_WAITOK);
 241         VNET_PCPUSTAT_ALLOC(tcpstat, M_WAITOK);
 242 }
 243 VNET_SYSINIT(tcp_vnet_init, SI_SUB_PROTO_IFATTACHDOMAIN, SI_ORDER_ANY,
 244     tcp_vnet_init, NULL);
 245
 246 #ifdef VIMAGE
 247 static void
 248 tcp_vnet_uninit(const void *unused)
 249 {
 250
 251         COUNTER_ARRAY_FREE(V_tcps_states, TCP_NSTATES);
 252         VNET_PCPUSTAT_FREE(tcpstat);
 253 }
 254 VNET_SYSUNINIT(tcp_vnet_uninit, SI_SUB_PROTO_IFATTACHDOMAIN, SI_ORDER_ANY,
 255     tcp_vnet_uninit, NULL);
 256 #endif /* VIMAGE */
 257
 258 /*
 259  * Kernel module interface for updating tcpstat.  The argument is an index
 260  * into tcpstat treated as an array.
 261  */
 262 void
 263 kmod_tcpstat_inc(int statnum)
 264 {
 265
 266         counter_u64_add(VNET(tcpstat)[statnum], 1);
 267 }
 268
 269 #ifdef TCP_HHOOK
 270 /*
 271  * Wrapper for the TCP established input helper hook.
 272  */
 273 void
 274 hhook_run_tcp_est_in(struct tcpcb *tp, struct tcphdr *th, struct tcpopt *to)
 275 {
 276         struct tcp_hhook_data hhook_data;
 277
 278         if (V_tcp_hhh[HHOOK_TCP_EST_IN]->hhh_nhooks > 0) {
 279                 hhook_data.tp = tp;
 280                 hhook_data.th = th;
 281                 hhook_data.to = to;
 282
 283                 hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_IN], &hhook_data,
 284                     tp->osd);
 285         }
 286 }
 287 #endif
 288
 289 /*
 290  * CC wrapper hook functions
 291  */
 292 void
 293 cc_ack_received(struct tcpcb *tp, struct tcphdr *th, uint16_t nsegs,
 294     uint16_t type)
 295 {
 296         INP_WLOCK_ASSERT(tp->t_inpcb);
 297
 298         tp->ccv->nsegs = nsegs;
 299         tp->ccv->bytes_this_ack = BYTES_THIS_ACK(tp, th);
 300         if (tp->snd_cwnd <= tp->snd_wnd)
 301                 tp->ccv->flags |= CCF_CWND_LIMITED;
 302         else
 303                 tp->ccv->flags &= ~CCF_CWND_LIMITED;
 304
 305         if (type == CC_ACK) {
 306                 if (tp->snd_cwnd > tp->snd_ssthresh) {
 307                         tp->t_bytes_acked += min(tp->ccv->bytes_this_ack,
 308                              nsegs * V_tcp_abc_l_var * tcp_maxseg(tp));
 309                         if (tp->t_bytes_acked >= tp->snd_cwnd) {
 310                                 tp->t_bytes_acked -= tp->snd_cwnd;
 311                                 tp->ccv->flags |= CCF_ABC_SENTAWND;
 312                         }
 313                 } else {
 314                                 tp->ccv->flags &= ~CCF_ABC_SENTAWND;
 315                                 tp->t_bytes_acked = 0;
 316                 }
 317         }
 318
 319         if (CC_ALGO(tp)->ack_received != NULL) {
 320                 /* XXXLAS: Find a way to live without this */
 321                 tp->ccv->curack = th->th_ack;
 322                 CC_ALGO(tp)->ack_received(tp->ccv, type);
 323         }
 324 }
 325
 326 void
 327 cc_conn_init(struct tcpcb *tp)
 328 {
 329         struct hc_metrics_lite metrics;
 330         struct inpcb *inp = tp->t_inpcb;
 331         u_int maxseg;
 332         int rtt;
 333
 334         INP_WLOCK_ASSERT(tp->t_inpcb);
 335
 336         tcp_hc_get(&inp->inp_inc, &metrics);
 337         maxseg = tcp_maxseg(tp);
 338
 339         if (tp->t_srtt == 0 && (rtt = metrics.rmx_rtt)) {
 340                 tp->t_srtt = rtt;
 341                 tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
 342                 TCPSTAT_INC(tcps_usedrtt);
 343                 if (metrics.rmx_rttvar) {
 344                         tp->t_rttvar = metrics.rmx_rttvar;
 345                         TCPSTAT_INC(tcps_usedrttvar);
 346                 } else {
 347                         /* default variation is +- 1 rtt */
 348                         tp->t_rttvar =
 349                             tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
 350                 }
 351                 TCPT_RANGESET(tp->t_rxtcur,
 352                     ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
 353                     tp->t_rttmin, TCPTV_REXMTMAX);
 354         }
 355         if (metrics.rmx_ssthresh) {
 356                 /*
 357                  * There's some sort of gateway or interface
 358                  * buffer limit on the path.  Use this to set
 359                  * the slow start threshold, but set the
 360                  * threshold to no less than 2*mss.
 361                  */
 362                 tp->snd_ssthresh = max(2 * maxseg, metrics.rmx_ssthresh);
 363                 TCPSTAT_INC(tcps_usedssthresh);
 364         }
 365
 366         /*
 367          * Set the initial slow-start flight size.
 368          *
 369          * If a SYN or SYN/ACK was lost and retransmitted, we have to
 370          * reduce the initial CWND to one segment as congestion is likely
 371          * requiring us to be cautious.
 372          */
 373         if (tp->snd_cwnd == 1)
 374                 tp->snd_cwnd = maxseg;          /* SYN(-ACK) lost */
 375         else
 376                 tp->snd_cwnd = tcp_compute_initwnd(maxseg);
 377
 378         if (CC_ALGO(tp)->conn_init != NULL)
 379                 CC_ALGO(tp)->conn_init(tp->ccv);
 380 }
 381
 382 void inline
 383 cc_cong_signal(struct tcpcb *tp, struct tcphdr *th, uint32_t type)
 384 {
 385         u_int maxseg;
 386
 387         INP_WLOCK_ASSERT(tp->t_inpcb);
 388
 389         switch(type) {
 390         case CC_NDUPACK:
 391                 if (!IN_FASTRECOVERY(tp->t_flags)) {
 392                         tp->snd_recover = tp->snd_max;
 393                         if (tp->t_flags & TF_ECN_PERMIT)
 394                                 tp->t_flags |= TF_ECN_SND_CWR;
 395                 }
 396                 break;
 397         case CC_ECN:
 398                 if (!IN_CONGRECOVERY(tp->t_flags)) {
 399                         TCPSTAT_INC(tcps_ecn_rcwnd);
 400                         tp->snd_recover = tp->snd_max;
 401                         if (tp->t_flags & TF_ECN_PERMIT)
 402                                 tp->t_flags |= TF_ECN_SND_CWR;
 403                 }
 404                 break;
 405         case CC_RTO:
 406                 maxseg = tcp_maxseg(tp);
 407                 tp->t_dupacks = 0;
 408                 tp->t_bytes_acked = 0;
 409                 EXIT_RECOVERY(tp->t_flags);
 410                 tp->snd_ssthresh = max(2, min(tp->snd_wnd, tp->snd_cwnd) / 2 /
 411                     maxseg) * maxseg;
 412                 tp->snd_cwnd = maxseg;
 413                 break;
 414         case CC_RTO_ERR:
 415                 TCPSTAT_INC(tcps_sndrexmitbad);
 416                 /* RTO was unnecessary, so reset everything. */
 417                 tp->snd_cwnd = tp->snd_cwnd_prev;
 418                 tp->snd_ssthresh = tp->snd_ssthresh_prev;
 419                 tp->snd_recover = tp->snd_recover_prev;
 420                 if (tp->t_flags & TF_WASFRECOVERY)
 421                         ENTER_FASTRECOVERY(tp->t_flags);
 422                 if (tp->t_flags & TF_WASCRECOVERY)
 423                         ENTER_CONGRECOVERY(tp->t_flags);
 424                 tp->snd_nxt = tp->snd_max;
 425                 tp->t_flags &= ~TF_PREVVALID;
 426                 tp->t_badrxtwin = 0;
 427                 break;
 428         }
 429
 430         if (CC_ALGO(tp)->cong_signal != NULL) {
 431                 if (th != NULL)
 432                         tp->ccv->curack = th->th_ack;
 433                 CC_ALGO(tp)->cong_signal(tp->ccv, type);
 434         }
 435 }
 436
 437 void inline
 438 cc_post_recovery(struct tcpcb *tp, struct tcphdr *th)
 439 {
 440         INP_WLOCK_ASSERT(tp->t_inpcb);
 441
 442         /* XXXLAS: KASSERT that we're in recovery? */
 443
 444         if (CC_ALGO(tp)->post_recovery != NULL) {
 445                 tp->ccv->curack = th->th_ack;
 446                 CC_ALGO(tp)->post_recovery(tp->ccv);
 447         }
 448         /* XXXLAS: EXIT_RECOVERY ? */
 449         tp->t_bytes_acked = 0;
 450 }
 451
 452 /*
 453  * Indicate whether this ack should be delayed.  We can delay the ack if
 454  * following conditions are met:
 455  *      - There is no delayed ack timer in progress.
 456  *      - Our last ack wasn't a 0-sized window. We never want to delay
 457  *        the ack that opens up a 0-sized window.
 458  *      - LRO wasn't used for this segment. We make sure by checking that the
 459  *        segment size is not larger than the MSS.
 460  */
 461 #define DELAY_ACK(tp, tlen)                                             \
 462         ((!tcp_timer_active(tp, TT_DELACK) &&                           \
 463             (tp->t_flags & TF_RXWIN0SENT) == 0) &&                      \
 464             (tlen <= tp->t_maxseg) &&                                   \
 465             (V_tcp_delack_enabled || (tp->t_flags & TF_NEEDSYN)))
 466
 467 static void inline
 468 cc_ecnpkt_handler(struct tcpcb *tp, struct tcphdr *th, uint8_t iptos)
 469 {
 470         INP_WLOCK_ASSERT(tp->t_inpcb);
 471
 472         if (CC_ALGO(tp)->ecnpkt_handler != NULL) {
 473                 switch (iptos & IPTOS_ECN_MASK) {
 474                 case IPTOS_ECN_CE:
 475                     tp->ccv->flags |= CCF_IPHDR_CE;
 476                     break;
 477                 case IPTOS_ECN_ECT0:
 478                     tp->ccv->flags &= ~CCF_IPHDR_CE;
 479                     break;
 480                 case IPTOS_ECN_ECT1:
 481                     tp->ccv->flags &= ~CCF_IPHDR_CE;
 482                     break;
 483                 }
 484
 485                 if (th->th_flags & TH_CWR)
 486                         tp->ccv->flags |= CCF_TCPHDR_CWR;
 487                 else
 488                         tp->ccv->flags &= ~CCF_TCPHDR_CWR;
 489
 490                 if (tp->t_flags & TF_DELACK)
 491                         tp->ccv->flags |= CCF_DELACK;
 492                 else
 493                         tp->ccv->flags &= ~CCF_DELACK;
 494
 495                 CC_ALGO(tp)->ecnpkt_handler(tp->ccv);
 496
 497                 if (tp->ccv->flags & CCF_ACKNOW)
 498                         tcp_timer_activate(tp, TT_DELACK, tcp_delacktime);
 499         }
 500 }
 501
 502 /*
 503  * TCP input handling is split into multiple parts:
 504  *   tcp6_input is a thin wrapper around tcp_input for the extended
 505  *      ip6_protox[] call format in ip6_input
 506  *   tcp_input handles primary segment validation, inpcb lookup and
 507  *      SYN processing on listen sockets
 508  *   tcp_do_segment processes the ACK and text of the segment for
 509  *      establishing, established and closing connections
 510  */
 511 #ifdef INET6
 512 int
 513 tcp6_input(struct mbuf **mp, int *offp, int proto)
 514 {
 515         struct mbuf *m = *mp;
 516         struct in6_ifaddr *ia6;
 517         struct ip6_hdr *ip6;
 518
 519         IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
 520
 521         /*
 522          * draft-itojun-ipv6-tcp-to-anycast
 523          * better place to put this in?
 524          */
 525         ip6 = mtod(m, struct ip6_hdr *);
 526         ia6 = in6ifa_ifwithaddr(&ip6->ip6_dst, 0 /* XXX */);
 527         if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
 528                 struct ip6_hdr *ip6;
 529
 530                 ifa_free(&ia6->ia_ifa);
 531                 ip6 = mtod(m, struct ip6_hdr *);
 532                 icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
 533                             (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
 534                 return (IPPROTO_DONE);
 535         }
 536         if (ia6)
 537                 ifa_free(&ia6->ia_ifa);
 538
 539         return (tcp_input(mp, offp, proto));
 540 }
 541 #endif /* INET6 */
 542
 543 int
 544 tcp_input(struct mbuf **mp, int *offp, int proto)
 545 {
 546         struct mbuf *m = *mp;
 547         struct tcphdr *th = NULL;
 548         struct ip *ip = NULL;
 549         struct inpcb *inp = NULL;
 550         struct tcpcb *tp = NULL;
 551         struct socket *so = NULL;
 552         u_char *optp = NULL;
 553         int off0;
 554         int optlen = 0;
 555 #ifdef INET
 556         int len;
 557         uint8_t ipttl;
 558 #endif
 559         int tlen = 0, off;
 560         int drop_hdrlen;
 561         int thflags;
 562         int rstreason = 0;      /* For badport_bandlim accounting purposes */
 563         uint8_t iptos;
 564         struct m_tag *fwd_tag = NULL;
 565         struct epoch_tracker et;
 566 #ifdef INET6
 567         struct ip6_hdr *ip6 = NULL;
 568         int isipv6;
 569 #else
 570         const void *ip6 = NULL;
 571 #endif /* INET6 */
 572         struct tcpopt to;               /* options in this segment */
 573         char *s = NULL;                 /* address and port logging */
 574         int ti_locked;
 575 #ifdef TCPDEBUG
 576         /*
 577          * The size of tcp_saveipgen must be the size of the max ip header,
 578          * now IPv6.
 579          */
 580         u_char tcp_saveipgen[IP6_HDR_LEN];
 581         struct tcphdr tcp_savetcp;
 582         short ostate = 0;
 583 #endif
 584
 585 #ifdef INET6
 586         isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
 587 #endif
 588
 589         off0 = *offp;
 590         m = *mp;
 591         *mp = NULL;
 592         to.to_flags = 0;
 593         TCPSTAT_INC(tcps_rcvtotal);
 594
 595 #ifdef INET6
 596         if (isipv6) {
 597                 /* IP6_EXTHDR_CHECK() is already done at tcp6_input(). */
 598
 599                 if (m->m_len < (sizeof(*ip6) + sizeof(*th))) {
 600                         m = m_pullup(m, sizeof(*ip6) + sizeof(*th));
 601                         if (m == NULL) {
 602                                 TCPSTAT_INC(tcps_rcvshort);
 603                                 return (IPPROTO_DONE);
 604                         }
 605                 }
 606
 607                 ip6 = mtod(m, struct ip6_hdr *);
 608                 th = (struct tcphdr *)((caddr_t)ip6 + off0);
 609                 tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
 610                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID_IPV6) {
 611                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
 612                                 th->th_sum = m->m_pkthdr.csum_data;
 613                         else
 614                                 th->th_sum = in6_cksum_pseudo(ip6, tlen,
 615                                     IPPROTO_TCP, m->m_pkthdr.csum_data);
 616                         th->th_sum ^= 0xffff;
 617                 } else
 618                         th->th_sum = in6_cksum(m, IPPROTO_TCP, off0, tlen);
 619                 if (th->th_sum) {
 620                         TCPSTAT_INC(tcps_rcvbadsum);
 621                         goto drop;
 622                 }
 623
 624                 /*
 625                  * Be proactive about unspecified IPv6 address in source.
 626                  * As we use all-zero to indicate unbounded/unconnected pcb,
 627                  * unspecified IPv6 address can be used to confuse us.
 628                  *
 629                  * Note that packets with unspecified IPv6 destination is
 630                  * already dropped in ip6_input.
 631                  */
 632                 if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
 633                         /* XXX stat */
 634                         goto drop;
 635                 }
 636                 iptos = (ntohl(ip6->ip6_flow) >> 20) & 0xff;
 637         }
 638 #endif
 639 #if defined(INET) && defined(INET6)
 640         else
 641 #endif
 642 #ifdef INET
 643         {
 644                 /*
 645                  * Get IP and TCP header together in first mbuf.
 646                  * Note: IP leaves IP header in first mbuf.
 647                  */
 648                 if (off0 > sizeof (struct ip)) {
 649                         ip_stripoptions(m);
 650                         off0 = sizeof(struct ip);
 651                 }
 652                 if (m->m_len < sizeof (struct tcpiphdr)) {
 653                         if ((m = m_pullup(m, sizeof (struct tcpiphdr)))
 654                             == NULL) {
 655                                 TCPSTAT_INC(tcps_rcvshort);
 656                                 return (IPPROTO_DONE);
 657                         }
 658                 }
 659                 ip = mtod(m, struct ip *);
 660                 th = (struct tcphdr *)((caddr_t)ip + off0);
 661                 tlen = ntohs(ip->ip_len) - off0;
 662
 663                 iptos = ip->ip_tos;
 664                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
 665                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
 666                                 th->th_sum = m->m_pkthdr.csum_data;
 667                         else
 668                                 th->th_sum = in_pseudo(ip->ip_src.s_addr,
 669                                     ip->ip_dst.s_addr,
 670                                     htonl(m->m_pkthdr.csum_data + tlen +
 671                                     IPPROTO_TCP));
 672                         th->th_sum ^= 0xffff;
 673                 } else {
 674                         struct ipovly *ipov = (struct ipovly *)ip;
 675
 676                         /*
 677                          * Checksum extended TCP header and data.
 678                          */
 679                         len = off0 + tlen;
 680                         ipttl = ip->ip_ttl;
 681                         bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
 682                         ipov->ih_len = htons(tlen);
 683                         th->th_sum = in_cksum(m, len);
 684                         /* Reset length for SDT probes. */
 685                         ip->ip_len = htons(len);
 686                         /* Reset TOS bits */
 687                         ip->ip_tos = iptos;
 688                         /* Re-initialization for later version check */
 689                         ip->ip_ttl = ipttl;
 690                         ip->ip_v = IPVERSION;
 691                         ip->ip_hl = off0 >> 2;
 692                 }
 693
 694                 if (th->th_sum) {
 695                         TCPSTAT_INC(tcps_rcvbadsum);
 696                         goto drop;
 697                 }
 698         }
 699 #endif /* INET */
 700
 701         /*
 702          * Check that TCP offset makes sense,
 703          * pull out TCP options and adjust length.              XXX
 704          */
 705         off = th->th_off << 2;
 706         if (off < sizeof (struct tcphdr) || off > tlen) {
 707                 TCPSTAT_INC(tcps_rcvbadoff);
 708                 goto drop;
 709         }
 710         tlen -= off;    /* tlen is used instead of ti->ti_len */
 711         if (off > sizeof (struct tcphdr)) {
 712 #ifdef INET6
 713                 if (isipv6) {
 714                         IP6_EXTHDR_CHECK(m, off0, off, IPPROTO_DONE);
 715                         ip6 = mtod(m, struct ip6_hdr *);
 716                         th = (struct tcphdr *)((caddr_t)ip6 + off0);
 717                 }
 718 #endif
 719 #if defined(INET) && defined(INET6)
 720                 else
 721 #endif
 722 #ifdef INET
 723                 {
 724                         if (m->m_len < sizeof(struct ip) + off) {
 725                                 if ((m = m_pullup(m, sizeof (struct ip) + off))
 726                                     == NULL) {
 727                                         TCPSTAT_INC(tcps_rcvshort);
 728                                         return (IPPROTO_DONE);
 729                                 }
 730                                 ip = mtod(m, struct ip *);
 731                                 th = (struct tcphdr *)((caddr_t)ip + off0);
 732                         }
 733                 }
 734 #endif
 735                 optlen = off - sizeof (struct tcphdr);
 736                 optp = (u_char *)(th + 1);
 737         }
 738         thflags = th->th_flags;
 739
 740         /*
 741          * Convert TCP protocol specific fields to host format.
 742          */
 743         tcp_fields_to_host(th);
 744
 745         /*
 746          * Delay dropping TCP, IP headers, IPv6 ext headers, and TCP options.
 747          */
 748         drop_hdrlen = off0 + off;
 749
 750         /*
 751          * Locate pcb for segment; if we're likely to add or remove a
 752          * connection then first acquire pcbinfo lock.  There are three cases
 753          * where we might discover later we need a write lock despite the
 754          * flags: ACKs moving a connection out of the syncache, ACKs for a
 755          * connection in TIMEWAIT and SYNs not targeting a listening socket.
 756          */
 757         if ((thflags & (TH_FIN | TH_RST)) != 0) {
 758                 INP_INFO_RLOCK_ET(&V_tcbinfo, et);
 759                 ti_locked = TI_RLOCKED;
 760         } else
 761                 ti_locked = TI_UNLOCKED;
 762
 763         /*
 764          * Grab info from PACKET_TAG_IPFORWARD tag prepended to the chain.
 765          */
 766         if (
 767 #ifdef INET6
 768             (isipv6 && (m->m_flags & M_IP6_NEXTHOP))
 769 #ifdef INET
 770             || (!isipv6 && (m->m_flags & M_IP_NEXTHOP))
 771 #endif
 772 #endif
 773 #if defined(INET) && !defined(INET6)
 774             (m->m_flags & M_IP_NEXTHOP)
 775 #endif
 776             )
 777                 fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
 778
 779 findpcb:
 780 #ifdef INVARIANTS
 781         if (ti_locked == TI_RLOCKED) {
 782                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 783         } else {
 784                 INP_INFO_WUNLOCK_ASSERT(&V_tcbinfo);
 785         }
 786 #endif
 787 #ifdef INET6
 788         if (isipv6 && fwd_tag != NULL) {
 789                 struct sockaddr_in6 *next_hop6;
 790
 791                 next_hop6 = (struct sockaddr_in6 *)(fwd_tag + 1);
 792                 /*
 793                  * Transparently forwarded. Pretend to be the destination.
 794                  * Already got one like this?
 795                  */
 796                 inp = in6_pcblookup_mbuf(&V_tcbinfo,
 797                     &ip6->ip6_src, th->th_sport, &ip6->ip6_dst, th->th_dport,
 798                     INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif, m);
 799                 if (!inp) {
 800                         /*
 801                          * It's new.  Try to find the ambushing socket.
 802                          * Because we've rewritten the destination address,
 803                          * any hardware-generated hash is ignored.
 804                          */
 805                         inp = in6_pcblookup(&V_tcbinfo, &ip6->ip6_src,
 806                             th->th_sport, &next_hop6->sin6_addr,
 807                             next_hop6->sin6_port ? ntohs(next_hop6->sin6_port) :
 808                             th->th_dport, INPLOOKUP_WILDCARD |
 809                             INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif);
 810                 }
 811         } else if (isipv6) {
 812                 inp = in6_pcblookup_mbuf(&V_tcbinfo, &ip6->ip6_src,
 813                     th->th_sport, &ip6->ip6_dst, th->th_dport,
 814                     INPLOOKUP_WILDCARD | INPLOOKUP_WLOCKPCB,
 815                     m->m_pkthdr.rcvif, m);
 816         }
 817 #endif /* INET6 */
 818 #if defined(INET6) && defined(INET)
 819         else
 820 #endif
 821 #ifdef INET
 822         if (fwd_tag != NULL) {
 823                 struct sockaddr_in *next_hop;
 824
 825                 next_hop = (struct sockaddr_in *)(fwd_tag+1);
 826                 /*
 827                  * Transparently forwarded. Pretend to be the destination.
 828                  * already got one like this?
 829                  */
 830                 inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src, th->th_sport,
 831                     ip->ip_dst, th->th_dport, INPLOOKUP_WLOCKPCB,
 832                     m->m_pkthdr.rcvif, m);
 833                 if (!inp) {
 834                         /*
 835                          * It's new.  Try to find the ambushing socket.
 836                          * Because we've rewritten the destination address,
 837                          * any hardware-generated hash is ignored.
 838                          */
 839                         inp = in_pcblookup(&V_tcbinfo, ip->ip_src,
 840                             th->th_sport, next_hop->sin_addr,
 841                             next_hop->sin_port ? ntohs(next_hop->sin_port) :
 842                             th->th_dport, INPLOOKUP_WILDCARD |
 843                             INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif);
 844                 }
 845         } else
 846                 inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src,
 847                     th->th_sport, ip->ip_dst, th->th_dport,
 848                     INPLOOKUP_WILDCARD | INPLOOKUP_WLOCKPCB,
 849                     m->m_pkthdr.rcvif, m);
 850 #endif /* INET */
 851
 852         /*
 853          * If the INPCB does not exist then all data in the incoming
 854          * segment is discarded and an appropriate RST is sent back.
 855          * XXX MRT Send RST using which routing table?
 856          */
 857         if (inp == NULL) {
 858                 /*
 859                  * Log communication attempts to ports that are not
 860                  * in use.
 861                  */
 862                 if ((tcp_log_in_vain == 1 && (thflags & TH_SYN)) ||
 863                     tcp_log_in_vain == 2) {
 864                         if ((s = tcp_log_vain(NULL, th, (void *)ip, ip6)))
 865                                 log(LOG_INFO, "%s; %s: Connection attempt "
 866                                     "to closed port\n", s, __func__);
 867                 }
 868                 /*
 869                  * When blackholing do not respond with a RST but
 870                  * completely ignore the segment and drop it.
 871                  */
 872                 if ((V_blackhole == 1 && (thflags & TH_SYN)) ||
 873                     V_blackhole == 2)
 874                         goto dropunlock;
 875
 876                 rstreason = BANDLIM_RST_CLOSEDPORT;
 877                 goto dropwithreset;
 878         }
 879         INP_WLOCK_ASSERT(inp);
 880         /*
 881          * While waiting for inp lock during the lookup, another thread
 882          * can have dropped the inpcb, in which case we need to loop back
 883          * and try to find a new inpcb to deliver to.
 884          */
 885         if (inp->inp_flags & INP_DROPPED) {
 886                 INP_WUNLOCK(inp);
 887                 inp = NULL;
 888                 goto findpcb;
 889         }
 890         if ((inp->inp_flowtype == M_HASHTYPE_NONE) &&
 891             (M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) &&
 892             ((inp->inp_socket == NULL) ||
 893             (inp->inp_socket->so_options & SO_ACCEPTCONN) == 0)) {
 894                 inp->inp_flowid = m->m_pkthdr.flowid;
 895                 inp->inp_flowtype = M_HASHTYPE_GET(m);
 896         }
 897 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
 898 #ifdef INET6
 899         if (isipv6 && IPSEC_ENABLED(ipv6) &&
 900             IPSEC_CHECK_POLICY(ipv6, m, inp) != 0) {
 901                 goto dropunlock;
 902         }
 903 #ifdef INET
 904         else
 905 #endif
 906 #endif /* INET6 */
 907 #ifdef INET
 908         if (IPSEC_ENABLED(ipv4) &&
 909             IPSEC_CHECK_POLICY(ipv4, m, inp) != 0) {
 910                 goto dropunlock;
 911         }
 912 #endif /* INET */
 913 #endif /* IPSEC */
 914
 915         /*
 916          * Check the minimum TTL for socket.
 917          */
 918         if (inp->inp_ip_minttl != 0) {
 919 #ifdef INET6
 920                 if (isipv6) {
 921                         if (inp->inp_ip_minttl > ip6->ip6_hlim)
 922                                 goto dropunlock;
 923                 } else
 924 #endif
 925                 if (inp->inp_ip_minttl > ip->ip_ttl)
 926                         goto dropunlock;
 927         }
 928
 929         /*
 930          * A previous connection in TIMEWAIT state is supposed to catch stray
 931          * or duplicate segments arriving late.  If this segment was a
 932          * legitimate new connection attempt, the old INPCB gets removed and
 933          * we can try again to find a listening socket.
 934          *
 935          * At this point, due to earlier optimism, we may hold only an inpcb
 936          * lock, and not the inpcbinfo write lock.  If so, we need to try to
 937          * acquire it, or if that fails, acquire a reference on the inpcb,
 938          * drop all locks, acquire a global write lock, and then re-acquire
 939          * the inpcb lock.  We may at that point discover that another thread
 940          * has tried to free the inpcb, in which case we need to loop back
 941          * and try to find a new inpcb to deliver to.
 942          *
 943          * XXXRW: It may be time to rethink timewait locking.
 944          */
 945         if (inp->inp_flags & INP_TIMEWAIT) {
 946                 if (ti_locked == TI_UNLOCKED) {
 947                         INP_INFO_RLOCK_ET(&V_tcbinfo, et);
 948                         ti_locked = TI_RLOCKED;
 949                 }
 950                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 951
 952                 if (thflags & TH_SYN)
 953                         tcp_dooptions(&to, optp, optlen, TO_SYN);
 954                 /*
 955                  * NB: tcp_twcheck unlocks the INP and frees the mbuf.
 956                  */
 957                 if (tcp_twcheck(inp, &to, th, m, tlen))
 958                         goto findpcb;
 959                 INP_INFO_RUNLOCK_ET(&V_tcbinfo, et);
 960                 return (IPPROTO_DONE);
 961         }
 962         /*
 963          * The TCPCB may no longer exist if the connection is winding
 964          * down or it is in the CLOSED state.  Either way we drop the
 965          * segment and send an appropriate response.
 966          */
 967         tp = intotcpcb(inp);
 968         if (tp == NULL || tp->t_state == TCPS_CLOSED) {
 969                 rstreason = BANDLIM_RST_CLOSEDPORT;
 970                 goto dropwithreset;
 971         }
 972
 973 #ifdef TCP_OFFLOAD
 974         if (tp->t_flags & TF_TOE) {
 975                 tcp_offload_input(tp, m);
 976                 m = NULL;       /* consumed by the TOE driver */
 977                 goto dropunlock;
 978         }
 979 #endif
 980
 981         /*
 982          * We've identified a valid inpcb, but it could be that we need an
 983          * inpcbinfo write lock but don't hold it.  In this case, attempt to
 984          * acquire using the same strategy as the TIMEWAIT case above.  If we
 985          * relock, we have to jump back to 'relocked' as the connection might
 986          * now be in TIMEWAIT.
 987          */
 988 #ifdef INVARIANTS
 989         if ((thflags & (TH_FIN | TH_RST)) != 0)
 990                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 991 #endif
 992         if (!((tp->t_state == TCPS_ESTABLISHED && (thflags & TH_SYN) == 0) ||
 993               (tp->t_state == TCPS_LISTEN && (thflags & TH_SYN) &&
 994                !IS_FASTOPEN(tp->t_flags)))) {
 995                 if (ti_locked == TI_UNLOCKED) {
 996                         INP_INFO_RLOCK_ET(&V_tcbinfo, et);
 997                         ti_locked = TI_RLOCKED;
 998                 }
 999                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
1000         }
1001
1002 #ifdef MAC
1003         INP_WLOCK_ASSERT(inp);
1004         if (mac_inpcb_check_deliver(inp, m))
1005                 goto dropunlock;
1006 #endif
1007         so = inp->inp_socket;
1008         KASSERT(so != NULL, ("%s: so == NULL", __func__));
1009 #ifdef TCPDEBUG
1010         if (so->so_options & SO_DEBUG) {
1011                 ostate = tp->t_state;
1012 #ifdef INET6
1013                 if (isipv6) {
1014                         bcopy((char *)ip6, (char *)tcp_saveipgen, sizeof(*ip6));
1015                 } else
1016 #endif
1017                         bcopy((char *)ip, (char *)tcp_saveipgen, sizeof(*ip));
1018                 tcp_savetcp = *th;
1019         }
1020 #endif /* TCPDEBUG */
1021         /*
1022          * When the socket is accepting connections (the INPCB is in LISTEN
1023          * state) we look into the SYN cache if this is a new connection
1024          * attempt or the completion of a previous one.
1025          */
1026         KASSERT(tp->t_state == TCPS_LISTEN || !(so->so_options & SO_ACCEPTCONN),
1027             ("%s: so accepting but tp %p not listening", __func__, tp));
1028         if (tp->t_state == TCPS_LISTEN && (so->so_options & SO_ACCEPTCONN)) {
1029                 struct in_conninfo inc;
1030
1031                 bzero(&inc, sizeof(inc));
1032 #ifdef INET6
1033                 if (isipv6) {
1034                         inc.inc_flags |= INC_ISIPV6;
1035                         if (inp->inp_inc.inc_flags & INC_IPV6MINMTU)
1036                                 inc.inc_flags |= INC_IPV6MINMTU;
1037                         inc.inc6_faddr = ip6->ip6_src;
1038                         inc.inc6_laddr = ip6->ip6_dst;
1039                 } else
1040 #endif
1041                 {
1042                         inc.inc_faddr = ip->ip_src;
1043                         inc.inc_laddr = ip->ip_dst;
1044                 }
1045                 inc.inc_fport = th->th_sport;
1046                 inc.inc_lport = th->th_dport;
1047                 inc.inc_fibnum = so->so_fibnum;
1048
1049                 /*
1050                  * Check for an existing connection attempt in syncache if
1051                  * the flag is only ACK.  A successful lookup creates a new
1052                  * socket appended to the listen queue in SYN_RECEIVED state.
1053                  */
1054                 if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
1055
1056                         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
1057                         /*
1058                          * Parse the TCP options here because
1059                          * syncookies need access to the reflected
1060                          * timestamp.
1061                          */
1062                         tcp_dooptions(&to, optp, optlen, 0);
1063                         /*
1064                          * NB: syncache_expand() doesn't unlock
1065                          * inp and tcpinfo locks.
1066                          */
1067                         rstreason = syncache_expand(&inc, &to, th, &so, m);
1068                         if (rstreason < 0) {
1069                                 /*
1070                                  * A failing TCP MD5 signature comparison
1071                                  * must result in the segment being dropped
1072                                  * and must not produce any response back
1073                                  * to the sender.
1074                                  */
1075                                 goto dropunlock;
1076                         } else if (rstreason == 0) {
1077                                 /*
1078                                  * No syncache entry or ACK was not
1079                                  * for our SYN/ACK.  Send a RST.
1080                                  * NB: syncache did its own logging
1081                                  * of the failure cause.
1082                                  */
1083                                 rstreason = BANDLIM_RST_OPENPORT;
1084                                 goto dropwithreset;
1085                         }
1086 tfo_socket_result:
1087                         if (so == NULL) {
1088                                 /*
1089                                  * We completed the 3-way handshake
1090                                  * but could not allocate a socket
1091                                  * either due to memory shortage,
1092                                  * listen queue length limits or
1093                                  * global socket limits.  Send RST
1094                                  * or wait and have the remote end
1095                                  * retransmit the ACK for another
1096                                  * try.
1097                                  */
1098                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1099                                         log(LOG_DEBUG, "%s; %s: Listen socket: "
1100                                             "Socket allocation failed due to "
1101                                             "limits or memory shortage, %s\n",
1102                                             s, __func__,
1103                                             V_tcp_sc_rst_sock_fail ?
1104                                             "sending RST" : "try again");
1105                                 if (V_tcp_sc_rst_sock_fail) {
1106                                         rstreason = BANDLIM_UNLIMITED;
1107                                         goto dropwithreset;
1108                                 } else
1109                                         goto dropunlock;
1110                         }
1111                         /*
1112                          * Socket is created in state SYN_RECEIVED.
1113                          * Unlock the listen socket, lock the newly
1114                          * created socket and update the tp variable.
1115                          */
1116                         INP_WUNLOCK(inp);       /* listen socket */
1117                         inp = sotoinpcb(so);
1118                         /*
1119                          * New connection inpcb is already locked by
1120                          * syncache_expand().
1121                          */
1122                         INP_WLOCK_ASSERT(inp);
1123                         tp = intotcpcb(inp);
1124                         KASSERT(tp->t_state == TCPS_SYN_RECEIVED,
1125                             ("%s: ", __func__));
1126                         /*
1127                          * Process the segment and the data it
1128                          * contains.  tcp_do_segment() consumes
1129                          * the mbuf chain and unlocks the inpcb.
1130                          */
1131                         TCP_PROBE5(receive, NULL, tp, m, tp, th);
1132                         tp->t_fb->tfb_tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen,
1133                             iptos);
1134                         if (ti_locked == TI_RLOCKED)
1135                                 INP_INFO_RUNLOCK_ET(&V_tcbinfo, et);
1136                         return (IPPROTO_DONE);
1137                 }
1138                 /*
1139                  * Segment flag validation for new connection attempts:
1140                  *
1141                  * Our (SYN|ACK) response was rejected.
1142                  * Check with syncache and remove entry to prevent
1143                  * retransmits.
1144                  *
1145                  * NB: syncache_chkrst does its own logging of failure
1146                  * causes.
1147                  */
1148                 if (thflags & TH_RST) {
1149                         syncache_chkrst(&inc, th, m);
1150                         goto dropunlock;
1151                 }
1152                 /*
1153                  * We can't do anything without SYN.
1154                  */
1155                 if ((thflags & TH_SYN) == 0) {
1156                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1157                                 log(LOG_DEBUG, "%s; %s: Listen socket: "
1158                                     "SYN is missing, segment ignored\n",
1159                                     s, __func__);
1160                         TCPSTAT_INC(tcps_badsyn);
1161                         goto dropunlock;
1162                 }
1163                 /*
1164                  * (SYN|ACK) is bogus on a listen socket.
1165                  */
1166                 if (thflags & TH_ACK) {
1167                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1168                                 log(LOG_DEBUG, "%s; %s: Listen socket: "
1169                                     "SYN|ACK invalid, segment rejected\n",
1170                                     s, __func__);
1171                         syncache_badack(&inc);  /* XXX: Not needed! */
1172                         TCPSTAT_INC(tcps_badsyn);
1173                         rstreason = BANDLIM_RST_OPENPORT;
1174                         goto dropwithreset;
1175                 }
1176                 /*
1177                  * If the drop_synfin option is enabled, drop all
1178                  * segments with both the SYN and FIN bits set.
1179                  * This prevents e.g. nmap from identifying the
1180                  * TCP/IP stack.
1181                  * XXX: Poor reasoning.  nmap has other methods
1182                  * and is constantly refining its stack detection
1183                  * strategies.
1184                  * XXX: This is a violation of the TCP specification
1185                  * and was used by RFC1644.
1186                  */
1187                 if ((thflags & TH_FIN) && V_drop_synfin) {
1188                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1189                                 log(LOG_DEBUG, "%s; %s: Listen socket: "
1190                                     "SYN|FIN segment ignored (based on "
1191                                     "sysctl setting)\n", s, __func__);
1192                         TCPSTAT_INC(tcps_badsyn);
1193                         goto dropunlock;
1194                 }
1195                 /*
1196                  * Segment's flags are (SYN) or (SYN|FIN).
1197                  *
1198                  * TH_PUSH, TH_URG, TH_ECE, TH_CWR are ignored
1199                  * as they do not affect the state of the TCP FSM.
1200                  * The data pointed to by TH_URG and th_urp is ignored.
1201                  */
1202                 KASSERT((thflags & (TH_RST|TH_ACK)) == 0,
1203                     ("%s: Listen socket: TH_RST or TH_ACK set", __func__));
1204                 KASSERT(thflags & (TH_SYN),
1205                     ("%s: Listen socket: TH_SYN not set", __func__));
1206 #ifdef INET6
1207                 /*
1208                  * If deprecated address is forbidden,
1209                  * we do not accept SYN to deprecated interface
1210                  * address to prevent any new inbound connection from
1211                  * getting established.
1212                  * When we do not accept SYN, we send a TCP RST,
1213                  * with deprecated source address (instead of dropping
1214                  * it).  We compromise it as it is much better for peer
1215                  * to send a RST, and RST will be the final packet
1216                  * for the exchange.
1217                  *
1218                  * If we do not forbid deprecated addresses, we accept
1219                  * the SYN packet.  RFC2462 does not suggest dropping
1220                  * SYN in this case.
1221                  * If we decipher RFC2462 5.5.4, it says like this:
1222                  * 1. use of deprecated addr with existing
1223                  *    communication is okay - "SHOULD continue to be
1224                  *    used"
1225                  * 2. use of it with new communication:
1226                  *   (2a) "SHOULD NOT be used if alternate address
1227                  *        with sufficient scope is available"
1228                  *   (2b) nothing mentioned otherwise.
1229                  * Here we fall into (2b) case as we have no choice in
1230                  * our source address selection - we must obey the peer.
1231                  *
1232                  * The wording in RFC2462 is confusing, and there are
1233                  * multiple description text for deprecated address
1234                  * handling - worse, they are not exactly the same.
1235                  * I believe 5.5.4 is the best one, so we follow 5.5.4.
1236                  */
1237                 if (isipv6 && !V_ip6_use_deprecated) {
1238                         struct in6_ifaddr *ia6;
1239
1240                         ia6 = in6ifa_ifwithaddr(&ip6->ip6_dst, 0 /* XXX */);
1241                         if (ia6 != NULL &&
1242                             (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
1243                                 ifa_free(&ia6->ia_ifa);
1244                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1245                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
1246                                         "Connection attempt to deprecated "
1247                                         "IPv6 address rejected\n",
1248                                         s, __func__);
1249                                 rstreason = BANDLIM_RST_OPENPORT;
1250                                 goto dropwithreset;
1251                         }
1252                         if (ia6)
1253                                 ifa_free(&ia6->ia_ifa);
1254                 }
1255 #endif /* INET6 */
1256                 /*
1257                  * Basic sanity checks on incoming SYN requests:
1258                  *   Don't respond if the destination is a link layer
1259                  *      broadcast according to RFC1122 4.2.3.10, p. 104.
1260                  *   If it is from this socket it must be forged.
1261                  *   Don't respond if the source or destination is a
1262                  *      global or subnet broad- or multicast address.
1263                  *   Note that it is quite possible to receive unicast
1264                  *      link-layer packets with a broadcast IP address. Use
1265                  *      in_broadcast() to find them.
1266                  */
1267                 if (m->m_flags & (M_BCAST|M_MCAST)) {
1268                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1269                             log(LOG_DEBUG, "%s; %s: Listen socket: "
1270                                 "Connection attempt from broad- or multicast "
1271                                 "link layer address ignored\n", s, __func__);
1272                         goto dropunlock;
1273                 }
1274 #ifdef INET6
1275                 if (isipv6) {
1276                         if (th->th_dport == th->th_sport &&
1277                             IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &ip6->ip6_src)) {
1278                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1279                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
1280                                         "Connection attempt to/from self "
1281                                         "ignored\n", s, __func__);
1282                                 goto dropunlock;
1283                         }
1284                         if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
1285                             IN6_IS_ADDR_MULTICAST(&ip6->ip6_src)) {
1286                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1287                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
1288                                         "Connection attempt from/to multicast "
1289                                         "address ignored\n", s, __func__);
1290                                 goto dropunlock;
1291                         }
1292                 }
1293 #endif
1294 #if defined(INET) && defined(INET6)
1295                 else
1296 #endif
1297 #ifdef INET
1298                 {
1299                         if (th->th_dport == th->th_sport &&
1300                             ip->ip_dst.s_addr == ip->ip_src.s_addr) {
1301                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1302                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
1303                                         "Connection attempt from/to self "
1304                                         "ignored\n", s, __func__);
1305                                 goto dropunlock;
1306                         }
1307                         if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
1308                             IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
1309                             ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
1310                             in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif)) {
1311                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1312                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
1313                                         "Connection attempt from/to broad- "
1314                                         "or multicast address ignored\n",
1315                                         s, __func__);
1316                                 goto dropunlock;
1317                         }
1318                 }
1319 #endif
1320                 /*
1321                  * SYN appears to be valid.  Create compressed TCP state
1322                  * for syncache.
1323                  */
1324 #ifdef TCPDEBUG
1325                 if (so->so_options & SO_DEBUG)
1326                         tcp_trace(TA_INPUT, ostate, tp,
1327                             (void *)tcp_saveipgen, &tcp_savetcp, 0);
1328 #endif
1329                 TCP_PROBE3(debug__input, tp, th, m);
1330                 tcp_dooptions(&to, optp, optlen, TO_SYN);
1331                 if (syncache_add(&inc, &to, th, inp, &so, m, NULL, NULL))
1332                         goto tfo_socket_result;
1333
1334                 /*
1335                  * Entry added to syncache and mbuf consumed.
1336                  * Only the listen socket is unlocked by syncache_add().
1337                  */
1338                 if (ti_locked == TI_RLOCKED) {
1339                         INP_INFO_RUNLOCK_ET(&V_tcbinfo, et);
1340                         ti_locked = TI_UNLOCKED;
1341                 }
1342                 INP_INFO_WUNLOCK_ASSERT(&V_tcbinfo);
1343                 return (IPPROTO_DONE);
1344         } else if (tp->t_state == TCPS_LISTEN) {
1345                 /*
1346                  * When a listen socket is torn down the SO_ACCEPTCONN
1347                  * flag is removed first while connections are drained
1348                  * from the accept queue in a unlock/lock cycle of the
1349                  * ACCEPT_LOCK, opening a race condition allowing a SYN
1350                  * attempt go through unhandled.
1351                  */
1352                 goto dropunlock;
1353         }
1354 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1355         if (tp->t_flags & TF_SIGNATURE) {
1356                 tcp_dooptions(&to, optp, optlen, thflags);
1357                 if ((to.to_flags & TOF_SIGNATURE) == 0) {
1358                         TCPSTAT_INC(tcps_sig_err_nosigopt);
1359                         goto dropunlock;
1360                 }
1361                 if (!TCPMD5_ENABLED() ||
1362                     TCPMD5_INPUT(m, th, to.to_signature) != 0)
1363                         goto dropunlock;
1364         }
1365 #endif
1366         TCP_PROBE5(receive, NULL, tp, m, tp, th);
1367
1368         /*
1369          * Segment belongs to a connection in SYN_SENT, ESTABLISHED or later
1370          * state.  tcp_do_segment() always consumes the mbuf chain, unlocks
1371          * the inpcb, and unlocks pcbinfo.
1372          */
1373         tp->t_fb->tfb_tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen, iptos);
1374         if (ti_locked == TI_RLOCKED)
1375                 INP_INFO_RUNLOCK_ET(&V_tcbinfo, et);
1376         return (IPPROTO_DONE);
1377
1378 dropwithreset:
1379         TCP_PROBE5(receive, NULL, tp, m, tp, th);
1380
1381         if (ti_locked == TI_RLOCKED) {
1382                 INP_INFO_RUNLOCK_ET(&V_tcbinfo, et);
1383                 ti_locked = TI_UNLOCKED;
1384         }
1385 #ifdef INVARIANTS
1386         else {
1387                 KASSERT(ti_locked == TI_UNLOCKED, ("%s: dropwithreset "
1388                     "ti_locked: %d", __func__, ti_locked));
1389                 INP_INFO_WUNLOCK_ASSERT(&V_tcbinfo);
1390         }
1391 #endif
1392
1393         if (inp != NULL) {
1394                 tcp_dropwithreset(m, th, tp, tlen, rstreason);
1395                 INP_WUNLOCK(inp);
1396         } else
1397                 tcp_dropwithreset(m, th, NULL, tlen, rstreason);
1398         m = NULL;       /* mbuf chain got consumed. */
1399         goto drop;
1400
1401 dropunlock:
1402         if (m != NULL)
1403                 TCP_PROBE5(receive, NULL, tp, m, tp, th);
1404
1405         if (ti_locked == TI_RLOCKED) {
1406                 INP_INFO_RUNLOCK_ET(&V_tcbinfo, et);
1407                 ti_locked = TI_UNLOCKED;
1408         }
1409 #ifdef INVARIANTS
1410         else {
1411                 KASSERT(ti_locked == TI_UNLOCKED, ("%s: dropunlock "
1412                     "ti_locked: %d", __func__, ti_locked));
1413                 INP_INFO_WUNLOCK_ASSERT(&V_tcbinfo);
1414         }
1415 #endif
1416
1417         if (inp != NULL)
1418                 INP_WUNLOCK(inp);
1419
1420 drop:
1421         INP_INFO_WUNLOCK_ASSERT(&V_tcbinfo);
1422         if (s != NULL)
1423                 free(s, M_TCPLOG);
1424         if (m != NULL)
1425                 m_freem(m);
1426         return (IPPROTO_DONE);
1427 }
1428
1429 /*
1430  * Automatic sizing of receive socket buffer.  Often the send
1431  * buffer size is not optimally adjusted to the actual network
1432  * conditions at hand (delay bandwidth product).  Setting the
1433  * buffer size too small limits throughput on links with high
1434  * bandwidth and high delay (eg. trans-continental/oceanic links).
1435  *
1436  * On the receive side the socket buffer memory is only rarely
1437  * used to any significant extent.  This allows us to be much
1438  * more aggressive in scaling the receive socket buffer.  For
1439  * the case that the buffer space is actually used to a large
1440  * extent and we run out of kernel memory we can simply drop
1441  * the new segments; TCP on the sender will just retransmit it
1442  * later.  Setting the buffer size too big may only consume too
1443  * much kernel memory if the application doesn't read() from
1444  * the socket or packet loss or reordering makes use of the
1445  * reassembly queue.
1446  *
1447  * The criteria to step up the receive buffer one notch are:
1448  *  1. Application has not set receive buffer size with
1449  *     SO_RCVBUF. Setting SO_RCVBUF clears SB_AUTOSIZE.
1450  *  2. the number of bytes received during 1/2 of an sRTT
1451  *     is at least 3/8 of the current socket buffer size.
1452  *  3. receive buffer size has not hit maximal automatic size;
1453  *
1454  * If all of the criteria are met we increaset the socket buffer
1455  * by a 1/2 (bounded by the max). This allows us to keep ahead
1456  * of slow-start but also makes it so our peer never gets limited
1457  * by our rwnd which we then open up causing a burst.
1458  *
1459  * This algorithm does two steps per RTT at most and only if
1460  * we receive a bulk stream w/o packet losses or reorderings.
1461  * Shrinking the buffer during idle times is not necessary as
1462  * it doesn't consume any memory when idle.
1463  *
1464  * TODO: Only step up if the application is actually serving
1465  * the buffer to better manage the socket buffer resources.
1466  */
1467 int
1468 tcp_autorcvbuf(struct mbuf *m, struct tcphdr *th, struct socket *so,
1469     struct tcpcb *tp, int tlen)
1470 {
1471         int newsize = 0;
1472
1473         if (V_tcp_do_autorcvbuf && (so->so_rcv.sb_flags & SB_AUTOSIZE) &&
1474             tp->t_srtt != 0 && tp->rfbuf_ts != 0 &&
1475             TCP_TS_TO_TICKS(tcp_ts_getticks() - tp->rfbuf_ts) >
1476             ((tp->t_srtt >> TCP_RTT_SHIFT)/2)) {
1477                 if (tp->rfbuf_cnt > ((so->so_rcv.sb_hiwat / 2)/ 4 * 3) &&
1478                     so->so_rcv.sb_hiwat < V_tcp_autorcvbuf_max) {
1479                         newsize = min((so->so_rcv.sb_hiwat + (so->so_rcv.sb_hiwat/2)), V_tcp_autorcvbuf_max);
1480                 }
1481                 TCP_PROBE6(receive__autoresize, NULL, tp, m, tp, th, newsize);
1482
1483                 /* Start over with next RTT. */
1484                 tp->rfbuf_ts = 0;
1485                 tp->rfbuf_cnt = 0;
1486         } else {
1487                 tp->rfbuf_cnt += tlen;  /* add up */
1488         }
1489         return (newsize);
1490 }
1491
1492 void
1493 tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
1494     struct tcpcb *tp, int drop_hdrlen, int tlen, uint8_t iptos)
1495 {
1496         int thflags, acked, ourfinisacked, needoutput = 0, sack_changed;
1497         int rstreason, todrop, win;
1498         uint32_t tiwin;
1499         uint16_t nsegs;
1500         char *s;
1501         struct in_conninfo *inc;
1502         struct mbuf *mfree;
1503         struct tcpopt to;
1504         int tfo_syn;
1505
1506 #ifdef TCPDEBUG
1507         /*
1508          * The size of tcp_saveipgen must be the size of the max ip header,
1509          * now IPv6.
1510          */
1511         u_char tcp_saveipgen[IP6_HDR_LEN];
1512         struct tcphdr tcp_savetcp;
1513         short ostate = 0;
1514 #endif
1515         thflags = th->th_flags;
1516         inc = &tp->t_inpcb->inp_inc;
1517         tp->sackhint.last_sack_ack = 0;
1518         sack_changed = 0;
1519         nsegs = max(1, m->m_pkthdr.lro_nsegs);
1520         /*
1521          * If this is either a state-changing packet or current state isn't
1522          * established, we require a write lock on tcbinfo.  Otherwise, we
1523          * allow the tcbinfo to be in either alocked or unlocked, as the
1524          * caller may have unnecessarily acquired a write lock due to a race.
1525          */
1526         if ((thflags & (TH_SYN | TH_FIN | TH_RST)) != 0 ||
1527             tp->t_state != TCPS_ESTABLISHED) {
1528                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
1529         }
1530         INP_WLOCK_ASSERT(tp->t_inpcb);
1531         KASSERT(tp->t_state > TCPS_LISTEN, ("%s: TCPS_LISTEN",
1532             __func__));
1533         KASSERT(tp->t_state != TCPS_TIME_WAIT, ("%s: TCPS_TIME_WAIT",
1534             __func__));
1535
1536 #ifdef TCPPCAP
1537         /* Save segment, if requested. */
1538         tcp_pcap_add(th, m, &(tp->t_inpkts));
1539 #endif
1540         TCP_LOG_EVENT(tp, th, &so->so_rcv, &so->so_snd, TCP_LOG_IN, 0,
1541             tlen, NULL, true);
1542
1543         if ((thflags & TH_SYN) && (thflags & TH_FIN) && V_drop_synfin) {
1544                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1545                         log(LOG_DEBUG, "%s; %s: "
1546                             "SYN|FIN segment ignored (based on "
1547                             "sysctl setting)\n", s, __func__);
1548                         free(s, M_TCPLOG);
1549                 }
1550                 goto drop;
1551         }
1552
1553         /*
1554          * If a segment with the ACK-bit set arrives in the SYN-SENT state
1555          * check SEQ.ACK first.
1556          */
1557         if ((tp->t_state == TCPS_SYN_SENT) && (thflags & TH_ACK) &&
1558             (SEQ_LEQ(th->th_ack, tp->iss) || SEQ_GT(th->th_ack, tp->snd_max))) {
1559                 rstreason = BANDLIM_UNLIMITED;
1560                 goto dropwithreset;
1561         }
1562
1563         /*
1564          * Segment received on connection.
1565          * Reset idle time and keep-alive timer.
1566          * XXX: This should be done after segment
1567          * validation to ignore broken/spoofed segs.
1568          */
1569         tp->t_rcvtime = ticks;
1570
1571         /*
1572          * Scale up the window into a 32-bit value.
1573          * For the SYN_SENT state the scale is zero.
1574          */
1575         tiwin = th->th_win << tp->snd_scale;
1576
1577         /*
1578          * TCP ECN processing.
1579          */
1580         if (tp->t_flags & TF_ECN_PERMIT) {
1581                 if (thflags & TH_CWR)
1582                         tp->t_flags &= ~TF_ECN_SND_ECE;
1583                 switch (iptos & IPTOS_ECN_MASK) {
1584                 case IPTOS_ECN_CE:
1585                         tp->t_flags |= TF_ECN_SND_ECE;
1586                         TCPSTAT_INC(tcps_ecn_ce);
1587                         break;
1588                 case IPTOS_ECN_ECT0:
1589                         TCPSTAT_INC(tcps_ecn_ect0);
1590                         break;
1591                 case IPTOS_ECN_ECT1:
1592                         TCPSTAT_INC(tcps_ecn_ect1);
1593                         break;
1594                 }
1595
1596                 /* Process a packet differently from RFC3168. */
1597                 cc_ecnpkt_handler(tp, th, iptos);
1598
1599                 /* Congestion experienced. */
1600                 if (thflags & TH_ECE) {
1601                         cc_cong_signal(tp, th, CC_ECN);
1602                 }
1603         }
1604
1605         /*
1606          * Parse options on any incoming segment.
1607          */
1608         tcp_dooptions(&to, (u_char *)(th + 1),
1609             (th->th_off << 2) - sizeof(struct tcphdr),
1610             (thflags & TH_SYN) ? TO_SYN : 0);
1611
1612 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1613         if ((tp->t_flags & TF_SIGNATURE) != 0 &&
1614             (to.to_flags & TOF_SIGNATURE) == 0) {
1615                 TCPSTAT_INC(tcps_sig_err_sigopt);
1616                 /* XXX: should drop? */
1617         }
1618 #endif
1619         /*
1620          * If echoed timestamp is later than the current time,
1621          * fall back to non RFC1323 RTT calculation.  Normalize
1622          * timestamp if syncookies were used when this connection
1623          * was established.
1624          */
1625         if ((to.to_flags & TOF_TS) && (to.to_tsecr != 0)) {
1626                 to.to_tsecr -= tp->ts_offset;
1627                 if (TSTMP_GT(to.to_tsecr, tcp_ts_getticks()))
1628                         to.to_tsecr = 0;
1629                 else if (tp->t_flags & TF_PREVVALID &&
1630                          tp->t_badrxtwin != 0 && SEQ_LT(to.to_tsecr, tp->t_badrxtwin))
1631                         cc_cong_signal(tp, th, CC_RTO_ERR);
1632         }
1633         /*
1634          * Process options only when we get SYN/ACK back. The SYN case
1635          * for incoming connections is handled in tcp_syncache.
1636          * According to RFC1323 the window field in a SYN (i.e., a <SYN>
1637          * or <SYN,ACK>) segment itself is never scaled.
1638          * XXX this is traditional behavior, may need to be cleaned up.
1639          */
1640         if (tp->t_state == TCPS_SYN_SENT && (thflags & TH_SYN)) {
1641                 if ((to.to_flags & TOF_SCALE) &&
1642                     (tp->t_flags & TF_REQ_SCALE)) {
1643                         tp->t_flags |= TF_RCVD_SCALE;
1644                         tp->snd_scale = to.to_wscale;
1645                 }
1646                 /*
1647                  * Initial send window.  It will be updated with
1648                  * the next incoming segment to the scaled value.
1649                  */
1650                 tp->snd_wnd = th->th_win;
1651                 if (to.to_flags & TOF_TS) {
1652                         tp->t_flags |= TF_RCVD_TSTMP;
1653                         tp->ts_recent = to.to_tsval;
1654                         tp->ts_recent_age = tcp_ts_getticks();
1655                 }
1656                 if (to.to_flags & TOF_MSS)
1657                         tcp_mss(tp, to.to_mss);
1658                 if ((tp->t_flags & TF_SACK_PERMIT) &&
1659                     (to.to_flags & TOF_SACKPERM) == 0)
1660                         tp->t_flags &= ~TF_SACK_PERMIT;
1661                 if (IS_FASTOPEN(tp->t_flags)) {
1662                         if (to.to_flags & TOF_FASTOPEN) {
1663                                 uint16_t mss;
1664
1665                                 if (to.to_flags & TOF_MSS)
1666                                         mss = to.to_mss;
1667                                 else
1668                                         if ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0)
1669                                                 mss = TCP6_MSS;
1670                                         else
1671                                                 mss = TCP_MSS;
1672                                 tcp_fastopen_update_cache(tp, mss,
1673                                     to.to_tfo_len, to.to_tfo_cookie);
1674                         } else
1675                                 tcp_fastopen_disable_path(tp);
1676                 }
1677         }
1678
1679         /*
1680          * If timestamps were negotiated during SYN/ACK they should
1681          * appear on every segment during this session and vice versa.
1682          */
1683         if ((tp->t_flags & TF_RCVD_TSTMP) && !(to.to_flags & TOF_TS)) {
1684                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1685                         log(LOG_DEBUG, "%s; %s: Timestamp missing, "
1686                             "no action\n", s, __func__);
1687                         free(s, M_TCPLOG);
1688                 }
1689         }
1690         if (!(tp->t_flags & TF_RCVD_TSTMP) && (to.to_flags & TOF_TS)) {
1691                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1692                         log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
1693                             "no action\n", s, __func__);
1694                         free(s, M_TCPLOG);
1695                 }
1696         }
1697
1698         /*
1699          * Header prediction: check for the two common cases
1700          * of a uni-directional data xfer.  If the packet has
1701          * no control flags, is in-sequence, the window didn't
1702          * change and we're not retransmitting, it's a
1703          * candidate.  If the length is zero and the ack moved
1704          * forward, we're the sender side of the xfer.  Just
1705          * free the data acked & wake any higher level process
1706          * that was blocked waiting for space.  If the length
1707          * is non-zero and the ack didn't move, we're the
1708          * receiver side.  If we're getting packets in-order
1709          * (the reassembly queue is empty), add the data to
1710          * the socket buffer and note that we need a delayed ack.
1711          * Make sure that the hidden state-flags are also off.
1712          * Since we check for TCPS_ESTABLISHED first, it can only
1713          * be TH_NEEDSYN.
1714          */
1715         if (tp->t_state == TCPS_ESTABLISHED &&
1716             th->th_seq == tp->rcv_nxt &&
1717             (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
1718             tp->snd_nxt == tp->snd_max &&
1719             tiwin && tiwin == tp->snd_wnd &&
1720             ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
1721             SEGQ_EMPTY(tp) &&
1722             ((to.to_flags & TOF_TS) == 0 ||
1723              TSTMP_GEQ(to.to_tsval, tp->ts_recent)) ) {
1724
1725                 /*
1726                  * If last ACK falls within this segment's sequence numbers,
1727                  * record the timestamp.
1728                  * NOTE that the test is modified according to the latest
1729                  * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1730                  */
1731                 if ((to.to_flags & TOF_TS) != 0 &&
1732                     SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
1733                         tp->ts_recent_age = tcp_ts_getticks();
1734                         tp->ts_recent = to.to_tsval;
1735                 }
1736
1737                 if (tlen == 0) {
1738                         if (SEQ_GT(th->th_ack, tp->snd_una) &&
1739                             SEQ_LEQ(th->th_ack, tp->snd_max) &&
1740                             !IN_RECOVERY(tp->t_flags) &&
1741                             (to.to_flags & TOF_SACK) == 0 &&
1742                             TAILQ_EMPTY(&tp->snd_holes)) {
1743                                 /*
1744                                  * This is a pure ack for outstanding data.
1745                                  */
1746                                 TCPSTAT_INC(tcps_predack);
1747
1748                                 /*
1749                                  * "bad retransmit" recovery without timestamps.
1750                                  */
1751                                 if ((to.to_flags & TOF_TS) == 0 &&
1752                                     tp->t_rxtshift == 1 &&
1753                                     tp->t_flags & TF_PREVVALID &&
1754                                     (int)(ticks - tp->t_badrxtwin) < 0) {
1755                                         cc_cong_signal(tp, th, CC_RTO_ERR);
1756                                 }
1757
1758                                 /*
1759                                  * Recalculate the transmit timer / rtt.
1760                                  *
1761                                  * Some boxes send broken timestamp replies
1762                                  * during the SYN+ACK phase, ignore
1763                                  * timestamps of 0 or we could calculate a
1764                                  * huge RTT and blow up the retransmit timer.
1765                                  */
1766                                 if ((to.to_flags & TOF_TS) != 0 &&
1767                                     to.to_tsecr) {
1768                                         uint32_t t;
1769
1770                                         t = tcp_ts_getticks() - to.to_tsecr;
1771                                         if (!tp->t_rttlow || tp->t_rttlow > t)
1772                                                 tp->t_rttlow = t;
1773                                         tcp_xmit_timer(tp,
1774                                             TCP_TS_TO_TICKS(t) + 1);
1775                                 } else if (tp->t_rtttime &&
1776                                     SEQ_GT(th->th_ack, tp->t_rtseq)) {
1777                                         if (!tp->t_rttlow ||
1778                                             tp->t_rttlow > ticks - tp->t_rtttime)
1779                                                 tp->t_rttlow = ticks - tp->t_rtttime;
1780                                         tcp_xmit_timer(tp,
1781                                                         ticks - tp->t_rtttime);
1782                                 }
1783                                 acked = BYTES_THIS_ACK(tp, th);
1784
1785 #ifdef TCP_HHOOK
1786                                 /* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
1787                                 hhook_run_tcp_est_in(tp, th, &to);
1788 #endif
1789
1790                                 TCPSTAT_ADD(tcps_rcvackpack, nsegs);
1791                                 TCPSTAT_ADD(tcps_rcvackbyte, acked);
1792                                 sbdrop(&so->so_snd, acked);
1793                                 if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
1794                                     SEQ_LEQ(th->th_ack, tp->snd_recover))
1795                                         tp->snd_recover = th->th_ack - 1;
1796
1797                                 /*
1798                                  * Let the congestion control algorithm update
1799                                  * congestion control related information. This
1800                                  * typically means increasing the congestion
1801                                  * window.
1802                                  */
1803                                 cc_ack_received(tp, th, nsegs, CC_ACK);
1804
1805                                 tp->snd_una = th->th_ack;
1806                                 /*
1807                                  * Pull snd_wl2 up to prevent seq wrap relative
1808                                  * to th_ack.
1809                                  */
1810                                 tp->snd_wl2 = th->th_ack;
1811                                 tp->t_dupacks = 0;
1812                                 m_freem(m);
1813
1814                                 /*
1815                                  * If all outstanding data are acked, stop
1816                                  * retransmit timer, otherwise restart timer
1817                                  * using current (possibly backed-off) value.
1818                                  * If process is waiting for space,
1819                                  * wakeup/selwakeup/signal.  If data
1820                                  * are ready to send, let tcp_output
1821                                  * decide between more output or persist.
1822                                  */
1823 #ifdef TCPDEBUG
1824                                 if (so->so_options & SO_DEBUG)
1825                                         tcp_trace(TA_INPUT, ostate, tp,
1826                                             (void *)tcp_saveipgen,
1827                                             &tcp_savetcp, 0);
1828 #endif
1829                                 TCP_PROBE3(debug__input, tp, th, m);
1830                                 if (tp->snd_una == tp->snd_max)
1831                                         tcp_timer_activate(tp, TT_REXMT, 0);
1832                                 else if (!tcp_timer_active(tp, TT_PERSIST))
1833                                         tcp_timer_activate(tp, TT_REXMT,
1834                                                       tp->t_rxtcur);
1835                                 sowwakeup(so);
1836                                 if (sbavail(&so->so_snd))
1837                                         (void) tp->t_fb->tfb_tcp_output(tp);
1838                                 goto check_delack;
1839                         }
1840                 } else if (th->th_ack == tp->snd_una &&
1841                     tlen <= sbspace(&so->so_rcv)) {
1842                         int newsize = 0;        /* automatic sockbuf scaling */
1843
1844                         /*
1845                          * This is a pure, in-sequence data packet with
1846                          * nothing on the reassembly queue and we have enough
1847                          * buffer space to take it.
1848                          */
1849                         /* Clean receiver SACK report if present */
1850                         if ((tp->t_flags & TF_SACK_PERMIT) && tp->rcv_numsacks)
1851                                 tcp_clean_sackreport(tp);
1852                         TCPSTAT_INC(tcps_preddat);
1853                         tp->rcv_nxt += tlen;
1854                         /*
1855                          * Pull snd_wl1 up to prevent seq wrap relative to
1856                          * th_seq.
1857                          */
1858                         tp->snd_wl1 = th->th_seq;
1859                         /*
1860                          * Pull rcv_up up to prevent seq wrap relative to
1861                          * rcv_nxt.
1862                          */
1863                         tp->rcv_up = tp->rcv_nxt;
1864                         TCPSTAT_ADD(tcps_rcvpack, nsegs);
1865                         TCPSTAT_ADD(tcps_rcvbyte, tlen);
1866 #ifdef TCPDEBUG
1867                         if (so->so_options & SO_DEBUG)
1868                                 tcp_trace(TA_INPUT, ostate, tp,
1869                                     (void *)tcp_saveipgen, &tcp_savetcp, 0);
1870 #endif
1871                         TCP_PROBE3(debug__input, tp, th, m);
1872
1873                         newsize = tcp_autorcvbuf(m, th, so, tp, tlen);
1874
1875                         /* Add data to socket buffer. */
1876                         SOCKBUF_LOCK(&so->so_rcv);
1877                         if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
1878                                 m_freem(m);
1879                         } else {
1880                                 /*
1881                                  * Set new socket buffer size.
1882                                  * Give up when limit is reached.
1883                                  */
1884                                 if (newsize)
1885                                         if (!sbreserve_locked(&so->so_rcv,
1886                                             newsize, so, NULL))
1887                                                 so->so_rcv.sb_flags &= ~SB_AUTOSIZE;
1888                                 m_adj(m, drop_hdrlen);  /* delayed header drop */
1889                                 sbappendstream_locked(&so->so_rcv, m, 0);
1890                         }
1891                         /* NB: sorwakeup_locked() does an implicit unlock. */
1892                         sorwakeup_locked(so);
1893                         if (DELAY_ACK(tp, tlen)) {
1894                                 tp->t_flags |= TF_DELACK;
1895                         } else {
1896                                 tp->t_flags |= TF_ACKNOW;
1897                                 tp->t_fb->tfb_tcp_output(tp);
1898                         }
1899                         goto check_delack;
1900                 }
1901         }
1902
1903         /*
1904          * Calculate amount of space in receive window,
1905          * and then do TCP input processing.
1906          * Receive window is amount of space in rcv queue,
1907          * but not less than advertised window.
1908          */
1909         win = sbspace(&so->so_rcv);
1910         if (win < 0)
1911                 win = 0;
1912         tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
1913
1914         switch (tp->t_state) {
1915
1916         /*
1917          * If the state is SYN_RECEIVED:
1918          *      if seg contains an ACK, but not for our SYN/ACK, send a RST.
1919          */
1920         case TCPS_SYN_RECEIVED:
1921                 if ((thflags & TH_ACK) &&
1922                     (SEQ_LEQ(th->th_ack, tp->snd_una) ||
1923                      SEQ_GT(th->th_ack, tp->snd_max))) {
1924                                 rstreason = BANDLIM_RST_OPENPORT;
1925                                 goto dropwithreset;
1926                 }
1927                 if (IS_FASTOPEN(tp->t_flags)) {
1928                         /*
1929                          * When a TFO connection is in SYN_RECEIVED, the
1930                          * only valid packets are the initial SYN, a
1931                          * retransmit/copy of the initial SYN (possibly with
1932                          * a subset of the original data), a valid ACK, a
1933                          * FIN, or a RST.
1934                          */
1935                         if ((thflags & (TH_SYN|TH_ACK)) == (TH_SYN|TH_ACK)) {
1936                                 rstreason = BANDLIM_RST_OPENPORT;
1937                                 goto dropwithreset;
1938                         } else if (thflags & TH_SYN) {
1939                                 /* non-initial SYN is ignored */
1940                                 if ((tcp_timer_active(tp, TT_DELACK) ||
1941                                      tcp_timer_active(tp, TT_REXMT)))
1942                                         goto drop;
1943                         } else if (!(thflags & (TH_ACK|TH_FIN|TH_RST))) {
1944                                 goto drop;
1945                         }
1946                 }
1947                 break;
1948
1949         /*
1950          * If the state is SYN_SENT:
1951          *      if seg contains a RST with valid ACK (SEQ.ACK has already
1952          *          been verified), then drop the connection.
1953          *      if seg contains a RST without an ACK, drop the seg.
1954          *      if seg does not contain SYN, then drop the seg.
1955          * Otherwise this is an acceptable SYN segment
1956          *      initialize tp->rcv_nxt and tp->irs
1957          *      if seg contains ack then advance tp->snd_una
1958          *      if seg contains an ECE and ECN support is enabled, the stream
1959          *          is ECN capable.
1960          *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
1961          *      arrange for segment to be acked (eventually)
1962          *      continue processing rest of data/controls, beginning with URG
1963          */
1964         case TCPS_SYN_SENT:
1965                 if ((thflags & (TH_ACK|TH_RST)) == (TH_ACK|TH_RST)) {
1966                         TCP_PROBE5(connect__refused, NULL, tp,
1967                             m, tp, th);
1968                         tp = tcp_drop(tp, ECONNREFUSED);
1969                 }
1970                 if (thflags & TH_RST)
1971                         goto drop;
1972                 if (!(thflags & TH_SYN))
1973                         goto drop;
1974
1975                 tp->irs = th->th_seq;
1976                 tcp_rcvseqinit(tp);
1977                 if (thflags & TH_ACK) {
1978                         int tfo_partial_ack = 0;
1979
1980                         TCPSTAT_INC(tcps_connects);
1981                         soisconnected(so);
1982 #ifdef MAC
1983                         mac_socketpeer_set_from_mbuf(m, so);
1984 #endif
1985                         /* Do window scaling on this connection? */
1986                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1987                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1988                                 tp->rcv_scale = tp->request_r_scale;
1989                         }
1990                         tp->rcv_adv += min(tp->rcv_wnd,
1991                             TCP_MAXWIN << tp->rcv_scale);
1992                         tp->snd_una++;          /* SYN is acked */
1993                         /*
1994                          * If not all the data that was sent in the TFO SYN
1995                          * has been acked, resend the remainder right away.
1996                          */
1997                         if (IS_FASTOPEN(tp->t_flags) &&
1998                             (tp->snd_una != tp->snd_max)) {
1999                                 tp->snd_nxt = th->th_ack;
2000                                 tfo_partial_ack = 1;
2001                         }
2002                         /*
2003                          * If there's data, delay ACK; if there's also a FIN
2004                          * ACKNOW will be turned on later.
2005                          */
2006                         if (DELAY_ACK(tp, tlen) && tlen != 0 && !tfo_partial_ack)
2007                                 tcp_timer_activate(tp, TT_DELACK,
2008                                     tcp_delacktime);
2009                         else
2010                                 tp->t_flags |= TF_ACKNOW;
2011
2012                         if (((thflags & (TH_CWR | TH_ECE)) == TH_ECE) &&
2013                             V_tcp_do_ecn) {
2014                                 tp->t_flags |= TF_ECN_PERMIT;
2015                                 TCPSTAT_INC(tcps_ecn_shs);
2016                         }
2017
2018                         /*
2019                          * Received <SYN,ACK> in SYN_SENT[*] state.
2020                          * Transitions:
2021                          *      SYN_SENT  --> ESTABLISHED
2022                          *      SYN_SENT* --> FIN_WAIT_1
2023                          */
2024                         tp->t_starttime = ticks;
2025                         if (tp->t_flags & TF_NEEDFIN) {
2026                                 tcp_state_change(tp, TCPS_FIN_WAIT_1);
2027                                 tp->t_flags &= ~TF_NEEDFIN;
2028                                 thflags &= ~TH_SYN;
2029                         } else {
2030                                 tcp_state_change(tp, TCPS_ESTABLISHED);
2031                                 TCP_PROBE5(connect__established, NULL, tp,
2032                                     m, tp, th);
2033                                 cc_conn_init(tp);
2034                                 tcp_timer_activate(tp, TT_KEEP,
2035                                     TP_KEEPIDLE(tp));
2036                         }
2037                 } else {
2038                         /*
2039                          * Received initial SYN in SYN-SENT[*] state =>
2040                          * simultaneous open.
2041                          * If it succeeds, connection is * half-synchronized.
2042                          * Otherwise, do 3-way handshake:
2043                          *        SYN-SENT -> SYN-RECEIVED
2044                          *        SYN-SENT* -> SYN-RECEIVED*
2045                          */
2046                         tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
2047                         tcp_timer_activate(tp, TT_REXMT, 0);
2048                         tcp_state_change(tp, TCPS_SYN_RECEIVED);
2049                 }
2050
2051                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
2052                 INP_WLOCK_ASSERT(tp->t_inpcb);
2053
2054                 /*
2055                  * Advance th->th_seq to correspond to first data byte.
2056                  * If data, trim to stay within window,
2057                  * dropping FIN if necessary.
2058                  */
2059                 th->th_seq++;
2060                 if (tlen > tp->rcv_wnd) {
2061                         todrop = tlen - tp->rcv_wnd;
2062                         m_adj(m, -todrop);
2063                         tlen = tp->rcv_wnd;
2064                         thflags &= ~TH_FIN;
2065                         TCPSTAT_INC(tcps_rcvpackafterwin);
2066                         TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
2067                 }
2068                 tp->snd_wl1 = th->th_seq - 1;
2069                 tp->rcv_up = th->th_seq;
2070                 /*
2071                  * Client side of transaction: already sent SYN and data.
2072                  * If the remote host used T/TCP to validate the SYN,
2073                  * our data will be ACK'd; if so, enter normal data segment
2074                  * processing in the middle of step 5, ack processing.
2075                  * Otherwise, goto step 6.
2076                  */
2077                 if (thflags & TH_ACK)
2078                         goto process_ACK;
2079
2080                 goto step6;
2081
2082         /*
2083          * If the state is LAST_ACK or CLOSING or TIME_WAIT:
2084          *      do normal processing.
2085          *
2086          * NB: Leftover from RFC1644 T/TCP.  Cases to be reused later.
2087          */
2088         case TCPS_LAST_ACK:
2089         case TCPS_CLOSING:
2090                 break;  /* continue normal processing */
2091         }
2092
2093         /*
2094          * States other than LISTEN or SYN_SENT.
2095          * First check the RST flag and sequence number since reset segments
2096          * are exempt from the timestamp and connection count tests.  This
2097          * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
2098          * below which allowed reset segments in half the sequence space
2099          * to fall though and be processed (which gives forged reset
2100          * segments with a random sequence number a 50 percent chance of
2101          * killing a connection).
2102          * Then check timestamp, if present.
2103          * Then check the connection count, if present.
2104          * Then check that at least some bytes of segment are within
2105          * receive window.  If segment begins before rcv_nxt,
2106          * drop leading data (and SYN); if nothing left, just ack.
2107          */
2108         if (thflags & TH_RST) {
2109                 /*
2110                  * RFC5961 Section 3.2
2111                  *
2112                  * - RST drops connection only if SEG.SEQ == RCV.NXT.
2113                  * - If RST is in window, we send challenge ACK.
2114                  *
2115                  * Note: to take into account delayed ACKs, we should
2116                  *   test against last_ack_sent instead of rcv_nxt.
2117                  * Note 2: we handle special case of closed window, not
2118                  *   covered by the RFC.
2119                  */
2120                 if ((SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
2121                     SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) ||
2122                     (tp->rcv_wnd == 0 && tp->last_ack_sent == th->th_seq)) {
2123
2124                         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
2125                         KASSERT(tp->t_state != TCPS_SYN_SENT,
2126                             ("%s: TH_RST for TCPS_SYN_SENT th %p tp %p",
2127                             __func__, th, tp));
2128
2129                         if (V_tcp_insecure_rst ||
2130                             tp->last_ack_sent == th->th_seq) {
2131                                 TCPSTAT_INC(tcps_drops);
2132                                 /* Drop the connection. */
2133                                 switch (tp->t_state) {
2134                                 case TCPS_SYN_RECEIVED:
2135                                         so->so_error = ECONNREFUSED;
2136                                         goto close;
2137                                 case TCPS_ESTABLISHED:
2138                                 case TCPS_FIN_WAIT_1:
2139                                 case TCPS_FIN_WAIT_2:
2140                                 case TCPS_CLOSE_WAIT:
2141                                 case TCPS_CLOSING:
2142                                 case TCPS_LAST_ACK:
2143                                         so->so_error = ECONNRESET;
2144                                 close:
2145                                         /* FALLTHROUGH */
2146                                 default:
2147                                         tp = tcp_close(tp);
2148                                 }
2149                         } else {
2150                                 TCPSTAT_INC(tcps_badrst);
2151                                 /* Send challenge ACK. */
2152                                 tcp_respond(tp, mtod(m, void *), th, m,
2153                                     tp->rcv_nxt, tp->snd_nxt, TH_ACK);
2154                                 tp->last_ack_sent = tp->rcv_nxt;
2155                                 m = NULL;
2156                         }
2157                 }
2158                 goto drop;
2159         }
2160
2161         /*
2162          * RFC5961 Section 4.2
2163          * Send challenge ACK for any SYN in synchronized state.
2164          */
2165         if ((thflags & TH_SYN) && tp->t_state != TCPS_SYN_SENT &&
2166             tp->t_state != TCPS_SYN_RECEIVED) {
2167                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
2168
2169                 TCPSTAT_INC(tcps_badsyn);
2170                 if (V_tcp_insecure_syn &&
2171                     SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
2172                     SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
2173                         tp = tcp_drop(tp, ECONNRESET);
2174                         rstreason = BANDLIM_UNLIMITED;
2175                 } else {
2176                         /* Send challenge ACK. */
2177                         tcp_respond(tp, mtod(m, void *), th, m, tp->rcv_nxt,
2178                             tp->snd_nxt, TH_ACK);
2179                         tp->last_ack_sent = tp->rcv_nxt;
2180                         m = NULL;
2181                 }
2182                 goto drop;
2183         }
2184
2185         /*
2186          * RFC 1323 PAWS: If we have a timestamp reply on this segment
2187          * and it's less than ts_recent, drop it.
2188          */
2189         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
2190             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
2191
2192                 /* Check to see if ts_recent is over 24 days old.  */
2193                 if (tcp_ts_getticks() - tp->ts_recent_age > TCP_PAWS_IDLE) {
2194                         /*
2195                          * Invalidate ts_recent.  If this segment updates
2196                          * ts_recent, the age will be reset later and ts_recent
2197                          * will get a valid value.  If it does not, setting
2198                          * ts_recent to zero will at least satisfy the
2199                          * requirement that zero be placed in the timestamp
2200                          * echo reply when ts_recent isn't valid.  The
2201                          * age isn't reset until we get a valid ts_recent
2202                          * because we don't want out-of-order segments to be
2203                          * dropped when ts_recent is old.
2204                          */
2205                         tp->ts_recent = 0;
2206                 } else {
2207                         TCPSTAT_INC(tcps_rcvduppack);
2208                         TCPSTAT_ADD(tcps_rcvdupbyte, tlen);
2209                         TCPSTAT_INC(tcps_pawsdrop);
2210                         if (tlen)
2211                                 goto dropafterack;
2212                         goto drop;
2213                 }
2214         }
2215
2216         /*
2217          * In the SYN-RECEIVED state, validate that the packet belongs to
2218          * this connection before trimming the data to fit the receive
2219          * window.  Check the sequence number versus IRS since we know
2220          * the sequence numbers haven't wrapped.  This is a partial fix
2221          * for the "LAND" DoS attack.
2222          */
2223         if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
2224                 rstreason = BANDLIM_RST_OPENPORT;
2225                 goto dropwithreset;
2226         }
2227
2228         todrop = tp->rcv_nxt - th->th_seq;
2229         if (todrop > 0) {
2230                 if (thflags & TH_SYN) {
2231                         thflags &= ~TH_SYN;
2232                         th->th_seq++;
2233                         if (th->th_urp > 1)
2234                                 th->th_urp--;
2235                         else
2236                                 thflags &= ~TH_URG;
2237                         todrop--;
2238                 }
2239                 /*
2240                  * Following if statement from Stevens, vol. 2, p. 960.
2241                  */
2242                 if (todrop > tlen
2243                     || (todrop == tlen && (thflags & TH_FIN) == 0)) {
2244                         /*
2245                          * Any valid FIN must be to the left of the window.
2246                          * At this point the FIN must be a duplicate or out
2247                          * of sequence; drop it.
2248                          */
2249                         thflags &= ~TH_FIN;
2250
2251                         /*
2252                          * Send an ACK to resynchronize and drop any data.
2253                          * But keep on processing for RST or ACK.
2254                          */
2255                         tp->t_flags |= TF_ACKNOW;
2256                         todrop = tlen;
2257                         TCPSTAT_INC(tcps_rcvduppack);
2258                         TCPSTAT_ADD(tcps_rcvdupbyte, todrop);
2259                 } else {
2260                         TCPSTAT_INC(tcps_rcvpartduppack);
2261                         TCPSTAT_ADD(tcps_rcvpartdupbyte, todrop);
2262                 }
2263                 /*
2264                  * DSACK - add SACK block for dropped range
2265                  */
2266                 if (tp->t_flags & TF_SACK_PERMIT) {
2267                         tcp_update_sack_list(tp, th->th_seq,
2268                             th->th_seq + todrop);
2269                         /*
2270                          * ACK now, as the next in-sequence segment
2271                          * will clear the DSACK block again
2272                          */
2273                         tp->t_flags |= TF_ACKNOW;
2274                 }
2275                 drop_hdrlen += todrop;  /* drop from the top afterwards */
2276                 th->th_seq += todrop;
2277                 tlen -= todrop;
2278                 if (th->th_urp > todrop)
2279                         th->th_urp -= todrop;
2280                 else {
2281                         thflags &= ~TH_URG;
2282                         th->th_urp = 0;
2283                 }
2284         }
2285
2286         /*
2287          * If new data are received on a connection after the
2288          * user processes are gone, then RST the other end.
2289          */
2290         if ((so->so_state & SS_NOFDREF) &&
2291             tp->t_state > TCPS_CLOSE_WAIT && tlen) {
2292                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
2293
2294                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
2295                         log(LOG_DEBUG, "%s; %s: %s: Received %d bytes of data "
2296                             "after socket was closed, "
2297                             "sending RST and removing tcpcb\n",
2298                             s, __func__, tcpstates[tp->t_state], tlen);
2299                         free(s, M_TCPLOG);
2300                 }
2301                 tp = tcp_close(tp);
2302                 TCPSTAT_INC(tcps_rcvafterclose);
2303                 rstreason = BANDLIM_UNLIMITED;
2304                 goto dropwithreset;
2305         }
2306
2307         /*
2308          * If segment ends after window, drop trailing data
2309          * (and PUSH and FIN); if nothing left, just ACK.
2310          */
2311         todrop = (th->th_seq + tlen) - (tp->rcv_nxt + tp->rcv_wnd);
2312         if (todrop > 0) {
2313                 TCPSTAT_INC(tcps_rcvpackafterwin);
2314                 if (todrop >= tlen) {
2315                         TCPSTAT_ADD(tcps_rcvbyteafterwin, tlen);
2316                         /*
2317                          * If window is closed can only take segments at
2318                          * window edge, and have to drop data and PUSH from
2319                          * incoming segments.  Continue processing, but
2320                          * remember to ack.  Otherwise, drop segment
2321                          * and ack.
2322                          */
2323                         if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
2324                                 tp->t_flags |= TF_ACKNOW;
2325                                 TCPSTAT_INC(tcps_rcvwinprobe);
2326                         } else
2327                                 goto dropafterack;
2328                 } else
2329                         TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
2330                 m_adj(m, -todrop);
2331                 tlen -= todrop;
2332                 thflags &= ~(TH_PUSH|TH_FIN);
2333         }
2334
2335         /*
2336          * If last ACK falls within this segment's sequence numbers,
2337          * record its timestamp.
2338          * NOTE:
2339          * 1) That the test incorporates suggestions from the latest
2340          *    proposal of the tcplw@cray.com list (Braden 1993/04/26).
2341          * 2) That updating only on newer timestamps interferes with
2342          *    our earlier PAWS tests, so this check should be solely
2343          *    predicated on the sequence space of this segment.
2344          * 3) That we modify the segment boundary check to be
2345          *        Last.ACK.Sent <= SEG.SEQ + SEG.Len
2346          *    instead of RFC1323's
2347          *        Last.ACK.Sent < SEG.SEQ + SEG.Len,
2348          *    This modified check allows us to overcome RFC1323's
2349          *    limitations as described in Stevens TCP/IP Illustrated
2350          *    Vol. 2 p.869. In such cases, we can still calculate the
2351          *    RTT correctly when RCV.NXT == Last.ACK.Sent.
2352          */
2353         if ((to.to_flags & TOF_TS) != 0 &&
2354             SEQ_LEQ(th->th_seq, tp->last_ack_sent) &&
2355             SEQ_LEQ(tp->last_ack_sent, th->th_seq + tlen +
2356                 ((thflags & (TH_SYN|TH_FIN)) != 0))) {
2357                 tp->ts_recent_age = tcp_ts_getticks();
2358                 tp->ts_recent = to.to_tsval;
2359         }
2360
2361         /*
2362          * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
2363          * flag is on (half-synchronized state), then queue data for
2364          * later processing; else drop segment and return.
2365          */
2366         if ((thflags & TH_ACK) == 0) {
2367                 if (tp->t_state == TCPS_SYN_RECEIVED ||
2368                     (tp->t_flags & TF_NEEDSYN)) {
2369                         if (tp->t_state == TCPS_SYN_RECEIVED &&
2370                             IS_FASTOPEN(tp->t_flags)) {
2371                                 tp->snd_wnd = tiwin;
2372                                 cc_conn_init(tp);
2373                         }
2374                         goto step6;
2375                 } else if (tp->t_flags & TF_ACKNOW)
2376                         goto dropafterack;
2377                 else
2378                         goto drop;
2379         }
2380
2381         /*
2382          * Ack processing.
2383          */
2384         switch (tp->t_state) {
2385
2386         /*
2387          * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
2388          * ESTABLISHED state and continue processing.
2389          * The ACK was checked above.
2390          */
2391         case TCPS_SYN_RECEIVED:
2392
2393                 TCPSTAT_INC(tcps_connects);
2394                 soisconnected(so);
2395                 /* Do window scaling? */
2396                 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
2397                         (TF_RCVD_SCALE|TF_REQ_SCALE)) {
2398                         tp->rcv_scale = tp->request_r_scale;
2399                 }
2400                 tp->snd_wnd = tiwin;
2401                 /*
2402                  * Make transitions:
2403                  *      SYN-RECEIVED  -> ESTABLISHED
2404                  *      SYN-RECEIVED* -> FIN-WAIT-1
2405                  */
2406                 tp->t_starttime = ticks;
2407                 if (IS_FASTOPEN(tp->t_flags) && tp->t_tfo_pending) {
2408                         tcp_fastopen_decrement_counter(tp->t_tfo_pending);
2409                         tp->t_tfo_pending = NULL;
2410
2411                         /*
2412                          * Account for the ACK of our SYN prior to
2413                          * regular ACK processing below.
2414                          */
2415                         tp->snd_una++;
2416                 }
2417                 if (tp->t_flags & TF_NEEDFIN) {
2418                         tcp_state_change(tp, TCPS_FIN_WAIT_1);
2419                         tp->t_flags &= ~TF_NEEDFIN;
2420                 } else {
2421                         tcp_state_change(tp, TCPS_ESTABLISHED);
2422                         TCP_PROBE5(accept__established, NULL, tp,
2423                             m, tp, th);
2424                         /*
2425                          * TFO connections call cc_conn_init() during SYN
2426                          * processing.  Calling it again here for such
2427                          * connections is not harmless as it would undo the
2428                          * snd_cwnd reduction that occurs when a TFO SYN|ACK
2429                          * is retransmitted.
2430                          */
2431                         if (!IS_FASTOPEN(tp->t_flags))
2432                                 cc_conn_init(tp);
2433                         tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
2434                 }
2435                 /*
2436                  * If segment contains data or ACK, will call tcp_reass()
2437                  * later; if not, do so now to pass queued data to user.
2438                  */
2439                 if (tlen == 0 && (thflags & TH_FIN) == 0)
2440                         (void) tcp_reass(tp, (struct tcphdr *)0, NULL, 0,
2441                             (struct mbuf *)0);
2442                 tp->snd_wl1 = th->th_seq - 1;
2443                 /* FALLTHROUGH */
2444
2445         /*
2446          * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
2447          * ACKs.  If the ack is in the range
2448          *      tp->snd_una < th->th_ack <= tp->snd_max
2449          * then advance tp->snd_una to th->th_ack and drop
2450          * data from the retransmission queue.  If this ACK reflects
2451          * more up to date window information we update our window information.
2452          */
2453         case TCPS_ESTABLISHED:
2454         case TCPS_FIN_WAIT_1:
2455         case TCPS_FIN_WAIT_2:
2456         case TCPS_CLOSE_WAIT:
2457         case TCPS_CLOSING:
2458         case TCPS_LAST_ACK:
2459                 if (SEQ_GT(th->th_ack, tp->snd_max)) {
2460                         TCPSTAT_INC(tcps_rcvacktoomuch);
2461                         goto dropafterack;
2462                 }
2463                 if ((tp->t_flags & TF_SACK_PERMIT) &&
2464                     ((to.to_flags & TOF_SACK) ||
2465                      !TAILQ_EMPTY(&tp->snd_holes)))
2466                         sack_changed = tcp_sack_doack(tp, &to, th->th_ack);
2467                 else
2468                         /*
2469                          * Reset the value so that previous (valid) value
2470                          * from the last ack with SACK doesn't get used.
2471                          */
2472                         tp->sackhint.sacked_bytes = 0;
2473
2474 #ifdef TCP_HHOOK
2475                 /* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
2476                 hhook_run_tcp_est_in(tp, th, &to);
2477 #endif
2478
2479                 if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
2480                         u_int maxseg;
2481
2482                         maxseg = tcp_maxseg(tp);
2483                         if (tlen == 0 &&
2484                             (tiwin == tp->snd_wnd ||
2485                             (tp->t_flags & TF_SACK_PERMIT))) {
2486                                 /*
2487                                  * If this is the first time we've seen a
2488                                  * FIN from the remote, this is not a
2489                                  * duplicate and it needs to be processed
2490                                  * normally.  This happens during a
2491                                  * simultaneous close.
2492                                  */
2493                                 if ((thflags & TH_FIN) &&
2494                                     (TCPS_HAVERCVDFIN(tp->t_state) == 0)) {
2495                                         tp->t_dupacks = 0;
2496                                         break;
2497                                 }
2498                                 TCPSTAT_INC(tcps_rcvdupack);
2499                                 /*
2500                                  * If we have outstanding data (other than
2501                                  * a window probe), this is a completely
2502                                  * duplicate ack (ie, window info didn't
2503                                  * change and FIN isn't set),
2504                                  * the ack is the biggest we've
2505                                  * seen and we've seen exactly our rexmt
2506                                  * threshold of them, assume a packet
2507                                  * has been dropped and retransmit it.
2508                                  * Kludge snd_nxt & the congestion
2509                                  * window so we send only this one
2510                                  * packet.
2511                                  *
2512                                  * We know we're losing at the current
2513                                  * window size so do congestion avoidance
2514                                  * (set ssthresh to half the current window
2515                                  * and pull our congestion window back to
2516                                  * the new ssthresh).
2517                                  *
2518                                  * Dup acks mean that packets have left the
2519                                  * network (they're now cached at the receiver)
2520                                  * so bump cwnd by the amount in the receiver
2521                                  * to keep a constant cwnd packets in the
2522                                  * network.
2523                                  *
2524                                  * When using TCP ECN, notify the peer that
2525                                  * we reduced the cwnd.
2526                                  */
2527                                 /*
2528                                  * Following 2 kinds of acks should not affect
2529                                  * dupack counting:
2530                                  * 1) Old acks
2531                                  * 2) Acks with SACK but without any new SACK
2532                                  * information in them. These could result from
2533                                  * any anomaly in the network like a switch
2534                                  * duplicating packets or a possible DoS attack.
2535                                  */
2536                                 if (th->th_ack != tp->snd_una ||
2537                                     ((tp->t_flags & TF_SACK_PERMIT) &&
2538                                     !sack_changed))
2539                                         break;
2540                                 else if (!tcp_timer_active(tp, TT_REXMT))
2541                                         tp->t_dupacks = 0;
2542                                 else if (++tp->t_dupacks > tcprexmtthresh ||
2543                                      IN_FASTRECOVERY(tp->t_flags)) {
2544                                         cc_ack_received(tp, th, nsegs,
2545                                             CC_DUPACK);
2546                                         if ((tp->t_flags & TF_SACK_PERMIT) &&
2547                                             IN_FASTRECOVERY(tp->t_flags)) {
2548                                                 int awnd;
2549
2550                                                 /*
2551                                                  * Compute the amount of data in flight first.
2552                                                  * We can inject new data into the pipe iff
2553                                                  * we have less than 1/2 the original window's
2554                                                  * worth of data in flight.
2555                                                  */
2556                                                 if (V_tcp_do_rfc6675_pipe)
2557                                                         awnd = tcp_compute_pipe(tp);
2558                                                 else
2559                                                         awnd = (tp->snd_nxt - tp->snd_fack) +
2560                                                                 tp->sackhint.sack_bytes_rexmit;
2561
2562                                                 if (awnd < tp->snd_ssthresh) {
2563                                                         tp->snd_cwnd += maxseg;
2564                                                         if (tp->snd_cwnd > tp->snd_ssthresh)
2565                                                                 tp->snd_cwnd = tp->snd_ssthresh;
2566                                                 }
2567                                         } else
2568                                                 tp->snd_cwnd += maxseg;
2569                                         (void) tp->t_fb->tfb_tcp_output(tp);
2570                                         goto drop;
2571                                 } else if (tp->t_dupacks == tcprexmtthresh) {
2572                                         tcp_seq onxt = tp->snd_nxt;
2573
2574                                         /*
2575                                          * If we're doing sack, check to
2576                                          * see if we're already in sack
2577                                          * recovery. If we're not doing sack,
2578                                          * check to see if we're in newreno
2579                                          * recovery.
2580                                          */
2581                                         if (tp->t_flags & TF_SACK_PERMIT) {
2582                                                 if (IN_FASTRECOVERY(tp->t_flags)) {
2583                                                         tp->t_dupacks = 0;
2584                                                         break;
2585                                                 }
2586                                         } else {
2587                                                 if (SEQ_LEQ(th->th_ack,
2588                                                     tp->snd_recover)) {
2589                                                         tp->t_dupacks = 0;
2590                                                         break;
2591                                                 }
2592                                         }
2593                                         /* Congestion signal before ack. */
2594                                         cc_cong_signal(tp, th, CC_NDUPACK);
2595                                         cc_ack_received(tp, th, nsegs,
2596                                             CC_DUPACK);
2597                                         tcp_timer_activate(tp, TT_REXMT, 0);
2598                                         tp->t_rtttime = 0;
2599                                         if (tp->t_flags & TF_SACK_PERMIT) {
2600                                                 TCPSTAT_INC(
2601                                                     tcps_sack_recovery_episode);
2602                                                 tp->sack_newdata = tp->snd_nxt;
2603                                                 tp->snd_cwnd = maxseg;
2604                                                 (void) tp->t_fb->tfb_tcp_output(tp);
2605                                                 goto drop;
2606                                         }
2607                                         tp->snd_nxt = th->th_ack;
2608                                         tp->snd_cwnd = maxseg;
2609                                         (void) tp->t_fb->tfb_tcp_output(tp);
2610                                         KASSERT(tp->snd_limited <= 2,
2611                                             ("%s: tp->snd_limited too big",
2612                                             __func__));
2613                                         tp->snd_cwnd = tp->snd_ssthresh +
2614                                              maxseg *
2615                                              (tp->t_dupacks - tp->snd_limited);
2616                                         if (SEQ_GT(onxt, tp->snd_nxt))
2617                                                 tp->snd_nxt = onxt;
2618                                         goto drop;
2619                                 } else if (V_tcp_do_rfc3042) {
2620                                         /*
2621                                          * Process first and second duplicate
2622                                          * ACKs. Each indicates a segment
2623                                          * leaving the network, creating room
2624                                          * for more. Make sure we can send a
2625                                          * packet on reception of each duplicate
2626                                          * ACK by increasing snd_cwnd by one
2627                                          * segment. Restore the original
2628                                          * snd_cwnd after packet transmission.
2629                                          */
2630                                         cc_ack_received(tp, th, nsegs,
2631                                             CC_DUPACK);
2632                                         uint32_t oldcwnd = tp->snd_cwnd;
2633                                         tcp_seq oldsndmax = tp->snd_max;
2634                                         u_int sent;
2635                                         int avail;
2636
2637                                         KASSERT(tp->t_dupacks == 1 ||
2638                                             tp->t_dupacks == 2,
2639                                             ("%s: dupacks not 1 or 2",
2640                                             __func__));
2641                                         if (tp->t_dupacks == 1)
2642                                                 tp->snd_limited = 0;
2643                                         tp->snd_cwnd =
2644                                             (tp->snd_nxt - tp->snd_una) +
2645                                             (tp->t_dupacks - tp->snd_limited) *
2646                                             maxseg;
2647                                         /*
2648                                          * Only call tcp_output when there
2649                                          * is new data available to be sent.
2650                                          * Otherwise we would send pure ACKs.
2651                                          */
2652                                         SOCKBUF_LOCK(&so->so_snd);
2653                                         avail = sbavail(&so->so_snd) -
2654                                             (tp->snd_nxt - tp->snd_una);
2655                                         SOCKBUF_UNLOCK(&so->so_snd);
2656                                         if (avail > 0)
2657                                                 (void) tp->t_fb->tfb_tcp_output(tp);
2658                                         sent = tp->snd_max - oldsndmax;
2659                                         if (sent > maxseg) {
2660                                                 KASSERT((tp->t_dupacks == 2 &&
2661                                                     tp->snd_limited == 0) ||
2662                                                    (sent == maxseg + 1 &&
2663                                                     tp->t_flags & TF_SENTFIN),
2664                                                     ("%s: sent too much",
2665                                                     __func__));
2666                                                 tp->snd_limited = 2;
2667                                         } else if (sent > 0)
2668                                                 ++tp->snd_limited;
2669                                         tp->snd_cwnd = oldcwnd;
2670                                         goto drop;
2671                                 }
2672                         }
2673                         break;
2674                 } else {
2675                         /*
2676                          * This ack is advancing the left edge, reset the
2677                          * counter.
2678                          */
2679                         tp->t_dupacks = 0;
2680                         /*
2681                          * If this ack also has new SACK info, increment the
2682                          * counter as per rfc6675.
2683                          */
2684                         if ((tp->t_flags & TF_SACK_PERMIT) && sack_changed)
2685                                 tp->t_dupacks++;
2686                 }
2687
2688                 KASSERT(SEQ_GT(th->th_ack, tp->snd_una),
2689                     ("%s: th_ack <= snd_una", __func__));
2690
2691                 /*
2692                  * If the congestion window was inflated to account
2693                  * for the other side's cached packets, retract it.
2694                  */
2695                 if (IN_FASTRECOVERY(tp->t_flags)) {
2696                         if (SEQ_LT(th->th_ack, tp->snd_recover)) {
2697                                 if (tp->t_flags & TF_SACK_PERMIT)
2698                                         tcp_sack_partialack(tp, th);
2699                                 else
2700                                         tcp_newreno_partial_ack(tp, th);
2701                         } else
2702                                 cc_post_recovery(tp, th);
2703                 }
2704                 /*
2705                  * If we reach this point, ACK is not a duplicate,
2706                  *     i.e., it ACKs something we sent.
2707                  */
2708                 if (tp->t_flags & TF_NEEDSYN) {
2709                         /*
2710                          * T/TCP: Connection was half-synchronized, and our
2711                          * SYN has been ACK'd (so connection is now fully
2712                          * synchronized).  Go to non-starred state,
2713                          * increment snd_una for ACK of SYN, and check if
2714                          * we can do window scaling.
2715                          */
2716                         tp->t_flags &= ~TF_NEEDSYN;
2717                         tp->snd_una++;
2718                         /* Do window scaling? */
2719                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
2720                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
2721                                 tp->rcv_scale = tp->request_r_scale;
2722                                 /* Send window already scaled. */
2723                         }
2724                 }
2725
2726 process_ACK:
2727                 INP_WLOCK_ASSERT(tp->t_inpcb);
2728
2729                 acked = BYTES_THIS_ACK(tp, th);
2730                 KASSERT(acked >= 0, ("%s: acked unexepectedly negative "
2731                     "(tp->snd_una=%u, th->th_ack=%u, tp=%p, m=%p)", __func__,
2732                     tp->snd_una, th->th_ack, tp, m));
2733                 TCPSTAT_ADD(tcps_rcvackpack, nsegs);
2734                 TCPSTAT_ADD(tcps_rcvackbyte, acked);
2735
2736                 /*
2737                  * If we just performed our first retransmit, and the ACK
2738                  * arrives within our recovery window, then it was a mistake
2739                  * to do the retransmit in the first place.  Recover our
2740                  * original cwnd and ssthresh, and proceed to transmit where
2741                  * we left off.
2742                  */
2743                 if (tp->t_rxtshift == 1 &&
2744                     tp->t_flags & TF_PREVVALID &&
2745                     tp->t_badrxtwin &&
2746                     SEQ_LT(to.to_tsecr, tp->t_badrxtwin))
2747                         cc_cong_signal(tp, th, CC_RTO_ERR);
2748
2749                 /*
2750                  * If we have a timestamp reply, update smoothed
2751                  * round trip time.  If no timestamp is present but
2752                  * transmit timer is running and timed sequence
2753                  * number was acked, update smoothed round trip time.
2754                  * Since we now have an rtt measurement, cancel the
2755                  * timer backoff (cf., Phil Karn's retransmit alg.).
2756                  * Recompute the initial retransmit timer.
2757                  *
2758                  * Some boxes send broken timestamp replies
2759                  * during the SYN+ACK phase, ignore
2760                  * timestamps of 0 or we could calculate a
2761                  * huge RTT and blow up the retransmit timer.
2762                  */
2763                 if ((to.to_flags & TOF_TS) != 0 && to.to_tsecr) {
2764                         uint32_t t;
2765
2766                         t = tcp_ts_getticks() - to.to_tsecr;
2767                         if (!tp->t_rttlow || tp->t_rttlow > t)
2768                                 tp->t_rttlow = t;
2769                         tcp_xmit_timer(tp, TCP_TS_TO_TICKS(t) + 1);
2770                 } else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
2771                         if (!tp->t_rttlow || tp->t_rttlow > ticks - tp->t_rtttime)
2772                                 tp->t_rttlow = ticks - tp->t_rtttime;
2773                         tcp_xmit_timer(tp, ticks - tp->t_rtttime);
2774                 }
2775
2776                 /*
2777                  * If all outstanding data is acked, stop retransmit
2778                  * timer and remember to restart (more output or persist).
2779                  * If there is more data to be acked, restart retransmit
2780                  * timer, using current (possibly backed-off) value.
2781                  */
2782                 if (th->th_ack == tp->snd_max) {
2783                         tcp_timer_activate(tp, TT_REXMT, 0);
2784                         needoutput = 1;
2785                 } else if (!tcp_timer_active(tp, TT_PERSIST))
2786                         tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
2787
2788                 /*
2789                  * If no data (only SYN) was ACK'd,
2790                  *    skip rest of ACK processing.
2791                  */
2792                 if (acked == 0)
2793                         goto step6;
2794
2795                 /*
2796                  * Let the congestion control algorithm update congestion
2797                  * control related information. This typically means increasing
2798                  * the congestion window.
2799                  */
2800                 cc_ack_received(tp, th, nsegs, CC_ACK);
2801
2802                 SOCKBUF_LOCK(&so->so_snd);
2803                 if (acked > sbavail(&so->so_snd)) {
2804                         if (tp->snd_wnd >= sbavail(&so->so_snd))
2805                                 tp->snd_wnd -= sbavail(&so->so_snd);
2806                         else
2807                                 tp->snd_wnd = 0;
2808                         mfree = sbcut_locked(&so->so_snd,
2809                             (int)sbavail(&so->so_snd));
2810                         ourfinisacked = 1;
2811                 } else {
2812                         mfree = sbcut_locked(&so->so_snd, acked);
2813                         if (tp->snd_wnd >= (uint32_t) acked)
2814                                 tp->snd_wnd -= acked;
2815                         else
2816                                 tp->snd_wnd = 0;
2817                         ourfinisacked = 0;
2818                 }
2819                 /* NB: sowwakeup_locked() does an implicit unlock. */
2820                 sowwakeup_locked(so);
2821                 m_freem(mfree);
2822                 /* Detect una wraparound. */
2823                 if (!IN_RECOVERY(tp->t_flags) &&
2824                     SEQ_GT(tp->snd_una, tp->snd_recover) &&
2825                     SEQ_LEQ(th->th_ack, tp->snd_recover))
2826                         tp->snd_recover = th->th_ack - 1;
2827                 /* XXXLAS: Can this be moved up into cc_post_recovery? */
2828                 if (IN_RECOVERY(tp->t_flags) &&
2829                     SEQ_GEQ(th->th_ack, tp->snd_recover)) {
2830                         EXIT_RECOVERY(tp->t_flags);
2831                 }
2832                 tp->snd_una = th->th_ack;
2833                 if (tp->t_flags & TF_SACK_PERMIT) {
2834                         if (SEQ_GT(tp->snd_una, tp->snd_recover))
2835                                 tp->snd_recover = tp->snd_una;
2836                 }
2837                 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
2838                         tp->snd_nxt = tp->snd_una;
2839
2840                 switch (tp->t_state) {
2841
2842                 /*
2843                  * In FIN_WAIT_1 STATE in addition to the processing
2844                  * for the ESTABLISHED state if our FIN is now acknowledged
2845                  * then enter FIN_WAIT_2.
2846                  */
2847                 case TCPS_FIN_WAIT_1:
2848                         if (ourfinisacked) {
2849                                 /*
2850                                  * If we can't receive any more
2851                                  * data, then closing user can proceed.
2852                                  * Starting the timer is contrary to the
2853                                  * specification, but if we don't get a FIN
2854                                  * we'll hang forever.
2855                                  *
2856                                  * XXXjl:
2857                                  * we should release the tp also, and use a
2858                                  * compressed state.
2859                                  */
2860                                 if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
2861                                         soisdisconnected(so);
2862                                         tcp_timer_activate(tp, TT_2MSL,
2863                                             (tcp_fast_finwait2_recycle ?
2864                                             tcp_finwait2_timeout :
2865                                             TP_MAXIDLE(tp)));
2866                                 }
2867                                 tcp_state_change(tp, TCPS_FIN_WAIT_2);
2868                         }
2869                         break;
2870
2871                 /*
2872                  * In CLOSING STATE in addition to the processing for
2873                  * the ESTABLISHED state if the ACK acknowledges our FIN
2874                  * then enter the TIME-WAIT state, otherwise ignore
2875                  * the segment.
2876                  */
2877                 case TCPS_CLOSING:
2878                         if (ourfinisacked) {
2879                                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
2880                                 tcp_twstart(tp);
2881                                 m_freem(m);
2882                                 return;
2883                         }
2884                         break;
2885
2886                 /*
2887                  * In LAST_ACK, we may still be waiting for data to drain
2888                  * and/or to be acked, as well as for the ack of our FIN.
2889                  * If our FIN is now acknowledged, delete the TCB,
2890                  * enter the closed state and return.
2891                  */
2892                 case TCPS_LAST_ACK:
2893                         if (ourfinisacked) {
2894                                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
2895                                 tp = tcp_close(tp);
2896                                 goto drop;
2897                         }
2898                         break;
2899                 }
2900         }
2901
2902 step6:
2903         INP_WLOCK_ASSERT(tp->t_inpcb);
2904
2905         /*
2906          * Update window information.
2907          * Don't look at window if no ACK: TAC's send garbage on first SYN.
2908          */
2909         if ((thflags & TH_ACK) &&
2910             (SEQ_LT(tp->snd_wl1, th->th_seq) ||
2911             (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
2912              (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
2913                 /* keep track of pure window updates */
2914                 if (tlen == 0 &&
2915                     tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
2916                         TCPSTAT_INC(tcps_rcvwinupd);
2917                 tp->snd_wnd = tiwin;
2918                 tp->snd_wl1 = th->th_seq;
2919                 tp->snd_wl2 = th->th_ack;
2920                 if (tp->snd_wnd > tp->max_sndwnd)
2921                         tp->max_sndwnd = tp->snd_wnd;
2922                 needoutput = 1;
2923         }
2924
2925         /*
2926          * Process segments with URG.
2927          */
2928         if ((thflags & TH_URG) && th->th_urp &&
2929             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2930                 /*
2931                  * This is a kludge, but if we receive and accept
2932                  * random urgent pointers, we'll crash in
2933                  * soreceive.  It's hard to imagine someone
2934                  * actually wanting to send this much urgent data.
2935                  */
2936                 SOCKBUF_LOCK(&so->so_rcv);
2937                 if (th->th_urp + sbavail(&so->so_rcv) > sb_max) {
2938                         th->th_urp = 0;                 /* XXX */
2939                         thflags &= ~TH_URG;             /* XXX */
2940                         SOCKBUF_UNLOCK(&so->so_rcv);    /* XXX */
2941                         goto dodata;                    /* XXX */
2942                 }
2943                 /*
2944                  * If this segment advances the known urgent pointer,
2945                  * then mark the data stream.  This should not happen
2946                  * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
2947                  * a FIN has been received from the remote side.
2948                  * In these states we ignore the URG.
2949                  *
2950                  * According to RFC961 (Assigned Protocols),
2951                  * the urgent pointer points to the last octet
2952                  * of urgent data.  We continue, however,
2953                  * to consider it to indicate the first octet
2954                  * of data past the urgent section as the original
2955                  * spec states (in one of two places).
2956                  */
2957                 if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
2958                         tp->rcv_up = th->th_seq + th->th_urp;
2959                         so->so_oobmark = sbavail(&so->so_rcv) +
2960                             (tp->rcv_up - tp->rcv_nxt) - 1;
2961                         if (so->so_oobmark == 0)
2962                                 so->so_rcv.sb_state |= SBS_RCVATMARK;
2963                         sohasoutofband(so);
2964                         tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
2965                 }
2966                 SOCKBUF_UNLOCK(&so->so_rcv);
2967                 /*
2968                  * Remove out of band data so doesn't get presented to user.
2969                  * This can happen independent of advancing the URG pointer,
2970                  * but if two URG's are pending at once, some out-of-band
2971                  * data may creep in... ick.
2972                  */
2973                 if (th->th_urp <= (uint32_t)tlen &&
2974                     !(so->so_options & SO_OOBINLINE)) {
2975                         /* hdr drop is delayed */
2976                         tcp_pulloutofband(so, th, m, drop_hdrlen);
2977                 }
2978         } else {
2979                 /*
2980                  * If no out of band data is expected,
2981                  * pull receive urgent pointer along
2982                  * with the receive window.
2983                  */
2984                 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
2985                         tp->rcv_up = tp->rcv_nxt;
2986         }
2987 dodata:                                                 /* XXX */
2988         INP_WLOCK_ASSERT(tp->t_inpcb);
2989
2990         /*
2991          * Process the segment text, merging it into the TCP sequencing queue,
2992          * and arranging for acknowledgment of receipt if necessary.
2993          * This process logically involves adjusting tp->rcv_wnd as data
2994          * is presented to the user (this happens in tcp_usrreq.c,
2995          * case PRU_RCVD).  If a FIN has already been received on this
2996          * connection then we just ignore the text.
2997          */
2998         tfo_syn = ((tp->t_state == TCPS_SYN_RECEIVED) &&
2999                    IS_FASTOPEN(tp->t_flags));
3000         if ((tlen || (thflags & TH_FIN) || tfo_syn) &&
3001             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
3002                 tcp_seq save_start = th->th_seq;
3003                 tcp_seq save_rnxt  = tp->rcv_nxt;
3004                 int     save_tlen  = tlen;
3005                 m_adj(m, drop_hdrlen);  /* delayed header drop */
3006                 /*
3007                  * Insert segment which includes th into TCP reassembly queue
3008                  * with control block tp.  Set thflags to whether reassembly now
3009                  * includes a segment with FIN.  This handles the common case
3010                  * inline (segment is the next to be received on an established
3011                  * connection, and the queue is empty), avoiding linkage into
3012                  * and removal from the queue and repetition of various
3013                  * conversions.
3014                  * Set DELACK for segments received in order, but ack
3015                  * immediately when segments are out of order (so
3016                  * fast retransmit can work).
3017                  */
3018                 if (th->th_seq == tp->rcv_nxt &&
3019                     SEGQ_EMPTY(tp) &&
3020                     (TCPS_HAVEESTABLISHED(tp->t_state) ||
3021                      tfo_syn)) {
3022                         if (DELAY_ACK(tp, tlen) || tfo_syn)
3023                                 tp->t_flags |= TF_DELACK;
3024                         else
3025                                 tp->t_flags |= TF_ACKNOW;
3026                         tp->rcv_nxt += tlen;
3027                         thflags = th->th_flags & TH_FIN;
3028                         TCPSTAT_INC(tcps_rcvpack);
3029                         TCPSTAT_ADD(tcps_rcvbyte, tlen);
3030                         SOCKBUF_LOCK(&so->so_rcv);
3031                         if (so->so_rcv.sb_state & SBS_CANTRCVMORE)
3032                                 m_freem(m);
3033                         else
3034                                 sbappendstream_locked(&so->so_rcv, m, 0);
3035                         /* NB: sorwakeup_locked() does an implicit unlock. */
3036                         sorwakeup_locked(so);
3037                 } else {
3038                         /*
3039                          * XXX: Due to the header drop above "th" is
3040                          * theoretically invalid by now.  Fortunately
3041                          * m_adj() doesn't actually frees any mbufs
3042                          * when trimming from the head.
3043                          */
3044                         tcp_seq temp = save_start;
3045                         thflags = tcp_reass(tp, th, &temp, &tlen, m);
3046                         tp->t_flags |= TF_ACKNOW;
3047                 }
3048                 if ((tp->t_flags & TF_SACK_PERMIT) && (save_tlen > 0)) {
3049                         if ((tlen == 0) && (SEQ_LT(save_start, save_rnxt))) {
3050                                 /*
3051                                  * DSACK actually handled in the fastpath
3052                                  * above.
3053                                  */
3054                                 tcp_update_sack_list(tp, save_start,
3055                                     save_start + save_tlen);
3056                         } else if ((tlen > 0) && SEQ_GT(tp->rcv_nxt, save_rnxt)) {
3057                                 if ((tp->rcv_numsacks >= 1) &&
3058                                     (tp->sackblks[0].end == save_start)) {
3059                                         /*
3060                                          * Partial overlap, recorded at todrop
3061                                          * above.
3062                                          */
3063                                         tcp_update_sack_list(tp,
3064                                             tp->sackblks[0].start,
3065                                             tp->sackblks[0].end);
3066                                 } else {
3067                                         tcp_update_dsack_list(tp, save_start,
3068                                             save_start + save_tlen);
3069                                 }
3070                         } else if (tlen >= save_tlen) {
3071                                 /* Update of sackblks. */
3072                                 tcp_update_dsack_list(tp, save_start,
3073                                     save_start + save_tlen);
3074                         } else if (tlen > 0) {
3075                                 tcp_update_dsack_list(tp, save_start,
3076                                     save_start + tlen);
3077                         }
3078                 }
3079 #if 0
3080                 /*
3081                  * Note the amount of data that peer has sent into
3082                  * our window, in order to estimate the sender's
3083                  * buffer size.
3084                  * XXX: Unused.
3085                  */
3086                 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt))
3087                         len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
3088                 else
3089                         len = so->so_rcv.sb_hiwat;
3090 #endif
3091         } else {
3092                 m_freem(m);
3093                 thflags &= ~TH_FIN;
3094         }
3095
3096         /*
3097          * If FIN is received ACK the FIN and let the user know
3098          * that the connection is closing.
3099          */
3100         if (thflags & TH_FIN) {
3101                 if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
3102                         socantrcvmore(so);
3103                         /*
3104                          * If connection is half-synchronized
3105                          * (ie NEEDSYN flag on) then delay ACK,
3106                          * so it may be piggybacked when SYN is sent.
3107                          * Otherwise, since we received a FIN then no
3108                          * more input can be expected, send ACK now.
3109                          */
3110                         if (tp->t_flags & TF_NEEDSYN)
3111                                 tp->t_flags |= TF_DELACK;
3112                         else
3113                                 tp->t_flags |= TF_ACKNOW;
3114                         tp->rcv_nxt++;
3115                 }
3116                 switch (tp->t_state) {
3117
3118                 /*
3119                  * In SYN_RECEIVED and ESTABLISHED STATES
3120                  * enter the CLOSE_WAIT state.
3121                  */
3122                 case TCPS_SYN_RECEIVED:
3123                         tp->t_starttime = ticks;
3124                         /* FALLTHROUGH */
3125                 case TCPS_ESTABLISHED:
3126                         tcp_state_change(tp, TCPS_CLOSE_WAIT);
3127                         break;
3128
3129                 /*
3130                  * If still in FIN_WAIT_1 STATE FIN has not been acked so
3131                  * enter the CLOSING state.
3132                  */
3133                 case TCPS_FIN_WAIT_1:
3134                         tcp_state_change(tp, TCPS_CLOSING);
3135                         break;
3136
3137                 /*
3138                  * In FIN_WAIT_2 state enter the TIME_WAIT state,
3139                  * starting the time-wait timer, turning off the other
3140                  * standard timers.
3141                  */
3142                 case TCPS_FIN_WAIT_2:
3143                         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
3144
3145                         tcp_twstart(tp);
3146                         return;
3147                 }
3148         }
3149 #ifdef TCPDEBUG
3150         if (so->so_options & SO_DEBUG)
3151                 tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
3152                           &tcp_savetcp, 0);
3153 #endif
3154         TCP_PROBE3(debug__input, tp, th, m);
3155
3156         /*
3157          * Return any desired output.
3158          */
3159         if (needoutput || (tp->t_flags & TF_ACKNOW))
3160                 (void) tp->t_fb->tfb_tcp_output(tp);
3161
3162 check_delack:
3163         INP_WLOCK_ASSERT(tp->t_inpcb);
3164
3165         if (tp->t_flags & TF_DELACK) {
3166                 tp->t_flags &= ~TF_DELACK;
3167                 tcp_timer_activate(tp, TT_DELACK, tcp_delacktime);
3168         }
3169         INP_WUNLOCK(tp->t_inpcb);
3170         return;
3171
3172 dropafterack:
3173         /*
3174          * Generate an ACK dropping incoming segment if it occupies
3175          * sequence space, where the ACK reflects our state.
3176          *
3177          * We can now skip the test for the RST flag since all
3178          * paths to this code happen after packets containing
3179          * RST have been dropped.
3180          *
3181          * In the SYN-RECEIVED state, don't send an ACK unless the
3182          * segment we received passes the SYN-RECEIVED ACK test.
3183          * If it fails send a RST.  This breaks the loop in the
3184          * "LAND" DoS attack, and also prevents an ACK storm
3185          * between two listening ports that have been sent forged
3186          * SYN segments, each with the source address of the other.
3187          */
3188         if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
3189             (SEQ_GT(tp->snd_una, th->th_ack) ||
3190              SEQ_GT(th->th_ack, tp->snd_max)) ) {
3191                 rstreason = BANDLIM_RST_OPENPORT;
3192                 goto dropwithreset;
3193         }
3194 #ifdef TCPDEBUG
3195         if (so->so_options & SO_DEBUG)
3196                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
3197                           &tcp_savetcp, 0);
3198 #endif
3199         TCP_PROBE3(debug__input, tp, th, m);
3200         tp->t_flags |= TF_ACKNOW;
3201         (void) tp->t_fb->tfb_tcp_output(tp);
3202         INP_WUNLOCK(tp->t_inpcb);
3203         m_freem(m);
3204         return;
3205
3206 dropwithreset:
3207         if (tp != NULL) {
3208                 tcp_dropwithreset(m, th, tp, tlen, rstreason);
3209                 INP_WUNLOCK(tp->t_inpcb);
3210         } else
3211                 tcp_dropwithreset(m, th, NULL, tlen, rstreason);
3212         return;
3213
3214 drop:
3215         /*
3216          * Drop space held by incoming segment and return.
3217          */
3218 #ifdef TCPDEBUG
3219         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
3220                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
3221                           &tcp_savetcp, 0);
3222 #endif
3223         TCP_PROBE3(debug__input, tp, th, m);
3224         if (tp != NULL)
3225                 INP_WUNLOCK(tp->t_inpcb);
3226         m_freem(m);
3227 }
3228
3229 /*
3230  * Issue RST and make ACK acceptable to originator of segment.
3231  * The mbuf must still include the original packet header.
3232  * tp may be NULL.
3233  */
3234 void
3235 tcp_dropwithreset(struct mbuf *m, struct tcphdr *th, struct tcpcb *tp,
3236     int tlen, int rstreason)
3237 {
3238 #ifdef INET
3239         struct ip *ip;
3240 #endif
3241 #ifdef INET6
3242         struct ip6_hdr *ip6;
3243 #endif
3244
3245         if (tp != NULL) {
3246                 INP_WLOCK_ASSERT(tp->t_inpcb);
3247         }
3248
3249         /* Don't bother if destination was broadcast/multicast. */
3250         if ((th->th_flags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
3251                 goto drop;
3252 #ifdef INET6
3253         if (mtod(m, struct ip *)->ip_v == 6) {
3254                 ip6 = mtod(m, struct ip6_hdr *);
3255                 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
3256                     IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
3257                         goto drop;
3258                 /* IPv6 anycast check is done at tcp6_input() */
3259         }
3260 #endif
3261 #if defined(INET) && defined(INET6)
3262         else
3263 #endif
3264 #ifdef INET
3265         {
3266                 ip = mtod(m, struct ip *);
3267                 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
3268                     IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
3269                     ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
3270                     in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
3271                         goto drop;
3272         }
3273 #endif
3274
3275         /* Perform bandwidth limiting. */
3276         if (badport_bandlim(rstreason) < 0)
3277                 goto drop;
3278
3279         /* tcp_respond consumes the mbuf chain. */
3280         if (th->th_flags & TH_ACK) {
3281                 tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0,
3282                     th->th_ack, TH_RST);
3283         } else {
3284                 if (th->th_flags & TH_SYN)
3285                         tlen++;
3286                 if (th->th_flags & TH_FIN)
3287                         tlen++;
3288                 tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
3289                     (tcp_seq)0, TH_RST|TH_ACK);
3290         }
3291         return;
3292 drop:
3293         m_freem(m);
3294 }
3295
3296 /*
3297  * Parse TCP options and place in tcpopt.
3298  */
3299 void
3300 tcp_dooptions(struct tcpopt *to, u_char *cp, int cnt, int flags)
3301 {
3302         int opt, optlen;
3303
3304         to->to_flags = 0;
3305         for (; cnt > 0; cnt -= optlen, cp += optlen) {
3306                 opt = cp[0];
3307                 if (opt == TCPOPT_EOL)
3308                         break;
3309                 if (opt == TCPOPT_NOP)
3310                         optlen = 1;
3311                 else {
3312                         if (cnt < 2)
3313                                 break;
3314                         optlen = cp[1];
3315                         if (optlen < 2 || optlen > cnt)
3316                                 break;
3317                 }
3318                 switch (opt) {
3319                 case TCPOPT_MAXSEG:
3320                         if (optlen != TCPOLEN_MAXSEG)
3321                                 continue;
3322                         if (!(flags & TO_SYN))
3323                                 continue;
3324                         to->to_flags |= TOF_MSS;
3325                         bcopy((char *)cp + 2,
3326                             (char *)&to->to_mss, sizeof(to->to_mss));
3327                         to->to_mss = ntohs(to->to_mss);
3328                         break;
3329                 case TCPOPT_WINDOW:
3330                         if (optlen != TCPOLEN_WINDOW)
3331                                 continue;
3332                         if (!(flags & TO_SYN))
3333                                 continue;
3334                         to->to_flags |= TOF_SCALE;
3335                         to->to_wscale = min(cp[2], TCP_MAX_WINSHIFT);
3336                         break;
3337                 case TCPOPT_TIMESTAMP:
3338                         if (optlen != TCPOLEN_TIMESTAMP)
3339                                 continue;
3340                         to->to_flags |= TOF_TS;
3341                         bcopy((char *)cp + 2,
3342                             (char *)&to->to_tsval, sizeof(to->to_tsval));
3343                         to->to_tsval = ntohl(to->to_tsval);
3344                         bcopy((char *)cp + 6,
3345                             (char *)&to->to_tsecr, sizeof(to->to_tsecr));
3346                         to->to_tsecr = ntohl(to->to_tsecr);
3347                         break;
3348                 case TCPOPT_SIGNATURE:
3349                         /*
3350                          * In order to reply to a host which has set the
3351                          * TCP_SIGNATURE option in its initial SYN, we have
3352                          * to record the fact that the option was observed
3353                          * here for the syncache code to perform the correct
3354                          * response.
3355                          */
3356                         if (optlen != TCPOLEN_SIGNATURE)
3357                                 continue;
3358                         to->to_flags |= TOF_SIGNATURE;
3359                         to->to_signature = cp + 2;
3360                         break;
3361                 case TCPOPT_SACK_PERMITTED:
3362                         if (optlen != TCPOLEN_SACK_PERMITTED)
3363                                 continue;
3364                         if (!(flags & TO_SYN))
3365                                 continue;
3366                         if (!V_tcp_do_sack)
3367                                 continue;
3368                         to->to_flags |= TOF_SACKPERM;
3369                         break;
3370                 case TCPOPT_SACK:
3371                         if (optlen <= 2 || (optlen - 2) % TCPOLEN_SACK != 0)
3372                                 continue;
3373                         if (flags & TO_SYN)
3374                                 continue;
3375                         to->to_flags |= TOF_SACK;
3376                         to->to_nsacks = (optlen - 2) / TCPOLEN_SACK;
3377                         to->to_sacks = cp + 2;
3378                         TCPSTAT_INC(tcps_sack_rcv_blocks);
3379                         break;
3380                 case TCPOPT_FAST_OPEN:
3381                         /*
3382                          * Cookie length validation is performed by the
3383                          * server side cookie checking code or the client
3384                          * side cookie cache update code.
3385                          */
3386                         if (!(flags & TO_SYN))
3387                                 continue;
3388                         if (!V_tcp_fastopen_client_enable &&
3389                             !V_tcp_fastopen_server_enable)
3390                                 continue;
3391                         to->to_flags |= TOF_FASTOPEN;
3392                         to->to_tfo_len = optlen - 2;
3393                         to->to_tfo_cookie = to->to_tfo_len ? cp + 2 : NULL;
3394                         break;
3395                 default:
3396                         continue;
3397                 }
3398         }
3399 }
3400
3401 /*
3402  * Pull out of band byte out of a segment so
3403  * it doesn't appear in the user's data queue.
3404  * It is still reflected in the segment length for
3405  * sequencing purposes.
3406  */
3407 void
3408 tcp_pulloutofband(struct socket *so, struct tcphdr *th, struct mbuf *m,
3409     int off)
3410 {
3411         int cnt = off + th->th_urp - 1;
3412
3413         while (cnt >= 0) {
3414                 if (m->m_len > cnt) {
3415                         char *cp = mtod(m, caddr_t) + cnt;
3416                         struct tcpcb *tp = sototcpcb(so);
3417
3418                         INP_WLOCK_ASSERT(tp->t_inpcb);
3419
3420                         tp->t_iobc = *cp;
3421                         tp->t_oobflags |= TCPOOB_HAVEDATA;
3422                         bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
3423                         m->m_len--;
3424                         if (m->m_flags & M_PKTHDR)
3425                                 m->m_pkthdr.len--;
3426                         return;
3427                 }
3428                 cnt -= m->m_len;
3429                 m = m->m_next;
3430                 if (m == NULL)
3431                         break;
3432         }
3433         panic("tcp_pulloutofband");
3434 }
3435
3436 /*
3437  * Collect new round-trip time estimate
3438  * and update averages and current timeout.
3439  */
3440 void
3441 tcp_xmit_timer(struct tcpcb *tp, int rtt)
3442 {
3443         int delta;
3444
3445         INP_WLOCK_ASSERT(tp->t_inpcb);
3446
3447         TCPSTAT_INC(tcps_rttupdated);
3448         tp->t_rttupdated++;
3449         if ((tp->t_srtt != 0) && (tp->t_rxtshift <= TCP_RTT_INVALIDATE)) {
3450                 /*
3451                  * srtt is stored as fixed point with 5 bits after the
3452                  * binary point (i.e., scaled by 8).  The following magic
3453                  * is equivalent to the smoothing algorithm in rfc793 with
3454                  * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
3455                  * point).  Adjust rtt to origin 0.
3456                  */
3457                 delta = ((rtt - 1) << TCP_DELTA_SHIFT)
3458                         - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
3459
3460                 if ((tp->t_srtt += delta) <= 0)
3461                         tp->t_srtt = 1;
3462
3463                 /*
3464                  * We accumulate a smoothed rtt variance (actually, a
3465                  * smoothed mean difference), then set the retransmit
3466                  * timer to smoothed rtt + 4 times the smoothed variance.
3467                  * rttvar is stored as fixed point with 4 bits after the
3468                  * binary point (scaled by 16).  The following is
3469                  * equivalent to rfc793 smoothing with an alpha of .75
3470                  * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
3471                  * rfc793's wired-in beta.
3472                  */
3473                 if (delta < 0)
3474                         delta = -delta;
3475                 delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
3476                 if ((tp->t_rttvar += delta) <= 0)
3477                         tp->t_rttvar = 1;
3478                 if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
3479                     tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
3480         } else {
3481                 /*
3482                  * No rtt measurement yet - use the unsmoothed rtt.
3483                  * Set the variance to half the rtt (so our first
3484                  * retransmit happens at 3*rtt).
3485                  */
3486                 tp->t_srtt = rtt << TCP_RTT_SHIFT;
3487                 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
3488                 tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
3489         }
3490         tp->t_rtttime = 0;
3491         tp->t_rxtshift = 0;
3492
3493         /*
3494          * the retransmit should happen at rtt + 4 * rttvar.
3495          * Because of the way we do the smoothing, srtt and rttvar
3496          * will each average +1/2 tick of bias.  When we compute
3497          * the retransmit timer, we want 1/2 tick of rounding and
3498          * 1 extra tick because of +-1/2 tick uncertainty in the
3499          * firing of the timer.  The bias will give us exactly the
3500          * 1.5 tick we need.  But, because the bias is
3501          * statistical, we have to test that we don't drop below
3502          * the minimum feasible timer (which is 2 ticks).
3503          */
3504         TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
3505                       max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
3506
3507         /*
3508          * We received an ack for a packet that wasn't retransmitted;
3509          * it is probably safe to discard any error indications we've
3510          * received recently.  This isn't quite right, but close enough
3511          * for now (a route might have failed after we sent a segment,
3512          * and the return path might not be symmetrical).
3513          */
3514         tp->t_softerror = 0;
3515 }
3516
3517 /*
3518  * Determine a reasonable value for maxseg size.
3519  * If the route is known, check route for mtu.
3520  * If none, use an mss that can be handled on the outgoing interface
3521  * without forcing IP to fragment.  If no route is found, route has no mtu,
3522  * or the destination isn't local, use a default, hopefully conservative
3523  * size (usually 512 or the default IP max size, but no more than the mtu
3524  * of the interface), as we can't discover anything about intervening
3525  * gateways or networks.  We also initialize the congestion/slow start
3526  * window to be a single segment if the destination isn't local.
3527  * While looking at the routing entry, we also initialize other path-dependent
3528  * parameters from pre-set or cached values in the routing entry.
3529  *
3530  * NOTE that resulting t_maxseg doesn't include space for TCP options or
3531  * IP options, e.g. IPSEC data, since length of this data may vary, and
3532  * thus it is calculated for every segment separately in tcp_output().
3533  *
3534  * NOTE that this routine is only called when we process an incoming
3535  * segment, or an ICMP need fragmentation datagram. Outgoing SYN/ACK MSS
3536  * settings are handled in tcp_mssopt().
3537  */
3538 void
3539 tcp_mss_update(struct tcpcb *tp, int offer, int mtuoffer,
3540     struct hc_metrics_lite *metricptr, struct tcp_ifcap *cap)
3541 {
3542         int mss = 0;
3543         uint32_t maxmtu = 0;
3544         struct inpcb *inp = tp->t_inpcb;
3545         struct hc_metrics_lite metrics;
3546 #ifdef INET6
3547         int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
3548         size_t min_protoh = isipv6 ?
3549                             sizeof (struct ip6_hdr) + sizeof (struct tcphdr) :
3550                             sizeof (struct tcpiphdr);
3551 #else
3552         const size_t min_protoh = sizeof(struct tcpiphdr);
3553 #endif
3554
3555         INP_WLOCK_ASSERT(tp->t_inpcb);
3556
3557         if (mtuoffer != -1) {
3558                 KASSERT(offer == -1, ("%s: conflict", __func__));
3559                 offer = mtuoffer - min_protoh;
3560         }
3561
3562         /* Initialize. */
3563 #ifdef INET6
3564         if (isipv6) {
3565                 maxmtu = tcp_maxmtu6(&inp->inp_inc, cap);
3566                 tp->t_maxseg = V_tcp_v6mssdflt;
3567         }
3568 #endif
3569 #if defined(INET) && defined(INET6)
3570         else
3571 #endif
3572 #ifdef INET
3573         {
3574                 maxmtu = tcp_maxmtu(&inp->inp_inc, cap);
3575                 tp->t_maxseg = V_tcp_mssdflt;
3576         }
3577 #endif
3578
3579         /*
3580          * No route to sender, stay with default mss and return.
3581          */
3582         if (maxmtu == 0) {
3583                 /*
3584                  * In case we return early we need to initialize metrics
3585                  * to a defined state as tcp_hc_get() would do for us
3586                  * if there was no cache hit.
3587                  */
3588                 if (metricptr != NULL)
3589                         bzero(metricptr, sizeof(struct hc_metrics_lite));
3590                 return;
3591         }
3592
3593         /* What have we got? */
3594         switch (offer) {
3595                 case 0:
3596                         /*
3597                          * Offer == 0 means that there was no MSS on the SYN
3598                          * segment, in this case we use tcp_mssdflt as
3599                          * already assigned to t_maxseg above.
3600                          */
3601                         offer = tp->t_maxseg;
3602                         break;
3603
3604                 case -1:
3605                         /*
3606                          * Offer == -1 means that we didn't receive SYN yet.
3607                          */
3608                         /* FALLTHROUGH */
3609
3610                 default:
3611                         /*
3612                          * Prevent DoS attack with too small MSS. Round up
3613                          * to at least minmss.
3614                          */
3615                         offer = max(offer, V_tcp_minmss);
3616         }
3617
3618         /*
3619          * rmx information is now retrieved from tcp_hostcache.
3620          */
3621         tcp_hc_get(&inp->inp_inc, &metrics);
3622         if (metricptr != NULL)
3623                 bcopy(&metrics, metricptr, sizeof(struct hc_metrics_lite));
3624
3625         /*
3626          * If there's a discovered mtu in tcp hostcache, use it.
3627          * Else, use the link mtu.
3628          */
3629         if (metrics.rmx_mtu)
3630                 mss = min(metrics.rmx_mtu, maxmtu) - min_protoh;
3631         else {
3632 #ifdef INET6
3633                 if (isipv6) {
3634                         mss = maxmtu - min_protoh;
3635                         if (!V_path_mtu_discovery &&
3636                             !in6_localaddr(&inp->in6p_faddr))
3637                                 mss = min(mss, V_tcp_v6mssdflt);
3638                 }
3639 #endif
3640 #if defined(INET) && defined(INET6)
3641                 else
3642 #endif
3643 #ifdef INET
3644                 {
3645                         mss = maxmtu - min_protoh;
3646                         if (!V_path_mtu_discovery &&
3647                             !in_localaddr(inp->inp_faddr))
3648                                 mss = min(mss, V_tcp_mssdflt);
3649                 }
3650 #endif
3651                 /*
3652                  * XXX - The above conditional (mss = maxmtu - min_protoh)
3653                  * probably violates the TCP spec.
3654                  * The problem is that, since we don't know the
3655                  * other end's MSS, we are supposed to use a conservative
3656                  * default.  But, if we do that, then MTU discovery will
3657                  * never actually take place, because the conservative
3658                  * default is much less than the MTUs typically seen
3659                  * on the Internet today.  For the moment, we'll sweep
3660                  * this under the carpet.
3661                  *
3662                  * The conservative default might not actually be a problem
3663                  * if the only case this occurs is when sending an initial
3664                  * SYN with options and data to a host we've never talked
3665                  * to before.  Then, they will reply with an MSS value which
3666                  * will get recorded and the new parameters should get
3667                  * recomputed.  For Further Study.
3668                  */
3669         }
3670         mss = min(mss, offer);
3671
3672         /*
3673          * Sanity check: make sure that maxseg will be large
3674          * enough to allow some data on segments even if the
3675          * all the option space is used (40bytes).  Otherwise
3676          * funny things may happen in tcp_output.
3677          *
3678          * XXXGL: shouldn't we reserve space for IP/IPv6 options?
3679          */
3680         mss = max(mss, 64);
3681
3682         tp->t_maxseg = mss;
3683 }
3684
3685 void
3686 tcp_mss(struct tcpcb *tp, int offer)
3687 {
3688         int mss;
3689         uint32_t bufsize;
3690         struct inpcb *inp;
3691         struct socket *so;
3692         struct hc_metrics_lite metrics;
3693         struct tcp_ifcap cap;
3694
3695         KASSERT(tp != NULL, ("%s: tp == NULL", __func__));
3696
3697         bzero(&cap, sizeof(cap));
3698         tcp_mss_update(tp, offer, -1, &metrics, &cap);
3699
3700         mss = tp->t_maxseg;
3701         inp = tp->t_inpcb;
3702
3703         /*
3704          * If there's a pipesize, change the socket buffer to that size,
3705          * don't change if sb_hiwat is different than default (then it
3706          * has been changed on purpose with setsockopt).
3707          * Make the socket buffers an integral number of mss units;
3708          * if the mss is larger than the socket buffer, decrease the mss.
3709          */
3710         so = inp->inp_socket;
3711         SOCKBUF_LOCK(&so->so_snd);
3712         if ((so->so_snd.sb_hiwat == V_tcp_sendspace) && metrics.rmx_sendpipe)
3713                 bufsize = metrics.rmx_sendpipe;
3714         else
3715                 bufsize = so->so_snd.sb_hiwat;
3716         if (bufsize < mss)
3717                 mss = bufsize;
3718         else {
3719                 bufsize = roundup(bufsize, mss);
3720                 if (bufsize > sb_max)
3721                         bufsize = sb_max;
3722                 if (bufsize > so->so_snd.sb_hiwat)
3723                         (void)sbreserve_locked(&so->so_snd, bufsize, so, NULL);
3724         }
3725         SOCKBUF_UNLOCK(&so->so_snd);
3726         /*
3727          * Sanity check: make sure that maxseg will be large
3728          * enough to allow some data on segments even if the
3729          * all the option space is used (40bytes).  Otherwise
3730          * funny things may happen in tcp_output.
3731          *
3732          * XXXGL: shouldn't we reserve space for IP/IPv6 options?
3733          */
3734         tp->t_maxseg = max(mss, 64);
3735
3736         SOCKBUF_LOCK(&so->so_rcv);
3737         if ((so->so_rcv.sb_hiwat == V_tcp_recvspace) && metrics.rmx_recvpipe)
3738                 bufsize = metrics.rmx_recvpipe;
3739         else
3740                 bufsize = so->so_rcv.sb_hiwat;
3741         if (bufsize > mss) {
3742                 bufsize = roundup(bufsize, mss);
3743                 if (bufsize > sb_max)
3744                         bufsize = sb_max;
3745                 if (bufsize > so->so_rcv.sb_hiwat)
3746                         (void)sbreserve_locked(&so->so_rcv, bufsize, so, NULL);
3747         }
3748         SOCKBUF_UNLOCK(&so->so_rcv);
3749
3750         /* Check the interface for TSO capabilities. */
3751         if (cap.ifcap & CSUM_TSO) {
3752                 tp->t_flags |= TF_TSO;
3753                 tp->t_tsomax = cap.tsomax;
3754                 tp->t_tsomaxsegcount = cap.tsomaxsegcount;
3755                 tp->t_tsomaxsegsize = cap.tsomaxsegsize;
3756         }
3757 }
3758
3759 /*
3760  * Determine the MSS option to send on an outgoing SYN.
3761  */
3762 int
3763 tcp_mssopt(struct in_conninfo *inc)
3764 {
3765         int mss = 0;
3766         uint32_t thcmtu = 0;
3767         uint32_t maxmtu = 0;
3768         size_t min_protoh;
3769
3770         KASSERT(inc != NULL, ("tcp_mssopt with NULL in_conninfo pointer"));
3771
3772 #ifdef INET6
3773         if (inc->inc_flags & INC_ISIPV6) {
3774                 mss = V_tcp_v6mssdflt;
3775                 maxmtu = tcp_maxmtu6(inc, NULL);
3776                 min_protoh = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
3777         }
3778 #endif
3779 #if defined(INET) && defined(INET6)
3780         else
3781 #endif
3782 #ifdef INET
3783         {
3784                 mss = V_tcp_mssdflt;
3785                 maxmtu = tcp_maxmtu(inc, NULL);
3786                 min_protoh = sizeof(struct tcpiphdr);
3787         }
3788 #endif
3789 #if defined(INET6) || defined(INET)
3790         thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */
3791 #endif
3792
3793         if (maxmtu && thcmtu)
3794                 mss = min(maxmtu, thcmtu) - min_protoh;
3795         else if (maxmtu || thcmtu)
3796                 mss = max(maxmtu, thcmtu) - min_protoh;
3797
3798         return (mss);
3799 }
3800
3801
3802 /*
3803  * On a partial ack arrives, force the retransmission of the
3804  * next unacknowledged segment.  Do not clear tp->t_dupacks.
3805  * By setting snd_nxt to ti_ack, this forces retransmission timer to
3806  * be started again.
3807  */
3808 void
3809 tcp_newreno_partial_ack(struct tcpcb *tp, struct tcphdr *th)
3810 {
3811         tcp_seq onxt = tp->snd_nxt;
3812         uint32_t ocwnd = tp->snd_cwnd;
3813         u_int maxseg = tcp_maxseg(tp);
3814
3815         INP_WLOCK_ASSERT(tp->t_inpcb);
3816
3817         tcp_timer_activate(tp, TT_REXMT, 0);
3818         tp->t_rtttime = 0;
3819         tp->snd_nxt = th->th_ack;
3820         /*
3821          * Set snd_cwnd to one segment beyond acknowledged offset.
3822          * (tp->snd_una has not yet been updated when this function is called.)
3823          */
3824         tp->snd_cwnd = maxseg + BYTES_THIS_ACK(tp, th);
3825         tp->t_flags |= TF_ACKNOW;
3826         (void) tp->t_fb->tfb_tcp_output(tp);
3827         tp->snd_cwnd = ocwnd;
3828         if (SEQ_GT(onxt, tp->snd_nxt))
3829                 tp->snd_nxt = onxt;
3830         /*
3831          * Partial window deflation.  Relies on fact that tp->snd_una
3832          * not updated yet.
3833          */
3834         if (tp->snd_cwnd > BYTES_THIS_ACK(tp, th))
3835                 tp->snd_cwnd -= BYTES_THIS_ACK(tp, th);
3836         else
3837                 tp->snd_cwnd = 0;
3838         tp->snd_cwnd += maxseg;
3839 }
3840
3841 int
3842 tcp_compute_pipe(struct tcpcb *tp)
3843 {
3844         return (tp->snd_max - tp->snd_una +
3845                 tp->sackhint.sack_bytes_rexmit -
3846                 tp->sackhint.sacked_bytes);
3847 }
3848
3849 uint32_t
3850 tcp_compute_initwnd(uint32_t maxseg)
3851 {
3852         /*
3853          * Calculate the Initial Window, also used as Restart Window
3854          *
3855          * RFC5681 Section 3.1 specifies the default conservative values.
3856          * RFC3390 specifies slightly more aggressive values.
3857          * RFC6928 increases it to ten segments.
3858          * Support for user specified value for initial flight size.
3859          */
3860         if (V_tcp_initcwnd_segments)
3861                 return min(V_tcp_initcwnd_segments * maxseg,
3862                     max(2 * maxseg, V_tcp_initcwnd_segments * 1460));
3863         else if (V_tcp_do_rfc3390)
3864                 return min(4 * maxseg, max(2 * maxseg, 4380));
3865         else {
3866                 /* Per RFC5681 Section 3.1 */
3867                 if (maxseg > 2190)
3868                         return (2 * maxseg);
3869                 else if (maxseg > 1095)
3870                         return (3 * maxseg);
3871                 else
3872                         return (4 * maxseg);
3873         }
3874 }