sys/netinet/tcp_input.c

   1 /*-
   2  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
   3  *      The Regents of the University of California.  All rights reserved.
   4  * Copyright (c) 2007-2008,2010
   5  *      Swinburne University of Technology, Melbourne, Australia.
   6  * Copyright (c) 2009-2010 Lawrence Stewart <lstewart@freebsd.org>
   7  * Copyright (c) 2010 The FreeBSD Foundation
   8  * Copyright (c) 2010-2011 Juniper Networks, Inc.
   9  * All rights reserved.
  10  *
  11  * Portions of this software were developed at the Centre for Advanced Internet
  12  * Architectures, Swinburne University of Technology, by Lawrence Stewart,
  13  * James Healy and David Hayes, made possible in part by a grant from the Cisco
  14  * University Research Program Fund at Community Foundation Silicon Valley.
  15  *
  16  * Portions of this software were developed at the Centre for Advanced
  17  * Internet Architectures, Swinburne University of Technology, Melbourne,
  18  * Australia by David Hayes under sponsorship from the FreeBSD Foundation.
  19  *
  20  * Portions of this software were developed by Robert N. M. Watson under
  21  * contract to Juniper Networks, Inc.
  22  *
  23  * Redistribution and use in source and binary forms, with or without
  24  * modification, are permitted provided that the following conditions
  25  * are met:
  26  * 1. Redistributions of source code must retain the above copyright
  27  *    notice, this list of conditions and the following disclaimer.
  28  * 2. Redistributions in binary form must reproduce the above copyright
  29  *    notice, this list of conditions and the following disclaimer in the
  30  *    documentation and/or other materials provided with the distribution.
  31  * 4. Neither the name of the University nor the names of its contributors
  32  *    may be used to endorse or promote products derived from this software
  33  *    without specific prior written permission.
  34  *
  35  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  36  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  37  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  38  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  39  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  40  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  41  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  42  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  43  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  44  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  45  * SUCH DAMAGE.
  46  *
  47  *      @(#)tcp_input.c 8.12 (Berkeley) 5/24/95
  48  */
  49
  50 #include <sys/cdefs.h>
  51 __FBSDID("$FreeBSD$");
  52
  53 #include "opt_ipfw.h"           /* for ipfw_fwd */
  54 #include "opt_inet.h"
  55 #include "opt_inet6.h"
  56 #include "opt_ipsec.h"
  57 #include "opt_kdtrace.h"
  58 #include "opt_tcpdebug.h"
  59
  60 #include <sys/param.h>
  61 #include <sys/kernel.h>
  62 #include <sys/hhook.h>
  63 #include <sys/malloc.h>
  64 #include <sys/mbuf.h>
  65 #include <sys/proc.h>           /* for proc0 declaration */
  66 #include <sys/protosw.h>
  67 #include <sys/sdt.h>
  68 #include <sys/signalvar.h>
  69 #include <sys/socket.h>
  70 #include <sys/socketvar.h>
  71 #include <sys/sysctl.h>
  72 #include <sys/syslog.h>
  73 #include <sys/systm.h>
  74
  75 #include <machine/cpu.h>        /* before tcp_seq.h, for tcp_random18() */
  76
  77 #include <vm/uma.h>
  78
  79 #include <net/if.h>
  80 #include <net/route.h>
  81 #include <net/vnet.h>
  82
  83 #define TCPSTATES               /* for logging */
  84
  85 #include <netinet/cc.h>
  86 #include <netinet/in.h>
  87 #include <netinet/in_kdtrace.h>
  88 #include <netinet/in_pcb.h>
  89 #include <netinet/in_systm.h>
  90 #include <netinet/in_var.h>
  91 #include <netinet/ip.h>
  92 #include <netinet/ip_icmp.h>    /* required for icmp_var.h */
  93 #include <netinet/icmp_var.h>   /* for ICMP_BANDLIM */
  94 #include <netinet/ip_var.h>
  95 #include <netinet/ip_options.h>
  96 #include <netinet/ip6.h>
  97 #include <netinet/icmp6.h>
  98 #include <netinet6/in6_pcb.h>
  99 #include <netinet6/ip6_var.h>
 100 #include <netinet6/nd6.h>
 101 #ifdef TCP_RFC7413
 102 #include <netinet/tcp_fastopen.h>
 103 #endif
 104 #include <netinet/tcp_fsm.h>
 105 #include <netinet/tcp_seq.h>
 106 #include <netinet/tcp_timer.h>
 107 #include <netinet/tcp_var.h>
 108 #include <netinet6/tcp6_var.h>
 109 #include <netinet/tcpip.h>
 110 #include <netinet/tcp_syncache.h>
 111 #ifdef TCPDEBUG
 112 #include <netinet/tcp_debug.h>
 113 #endif /* TCPDEBUG */
 114 #ifdef TCP_OFFLOAD
 115 #include <netinet/tcp_offload.h>
 116 #endif
 117
 118 #ifdef IPSEC
 119 #include <netipsec/ipsec.h>
 120 #include <netipsec/ipsec6.h>
 121 #endif /*IPSEC*/
 122
 123 #include <machine/in_cksum.h>
 124
 125 #include <security/mac/mac_framework.h>
 126
 127 const int tcprexmtthresh = 3;
 128
 129 int tcp_log_in_vain = 0;
 130 SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW,
 131     &tcp_log_in_vain, 0,
 132     "Log all incoming TCP segments to closed ports");
 133
 134 VNET_DEFINE(int, blackhole) = 0;
 135 #define V_blackhole             VNET(blackhole)
 136 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_RW,
 137     &VNET_NAME(blackhole), 0,
 138     "Do not send RST on segments to closed ports");
 139
 140 VNET_DEFINE(int, tcp_delack_enabled) = 1;
 141 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_RW,
 142     &VNET_NAME(tcp_delack_enabled), 0,
 143     "Delay ACK to try and piggyback it onto a data packet");
 144
 145 VNET_DEFINE(int, drop_synfin) = 0;
 146 #define V_drop_synfin           VNET(drop_synfin)
 147 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_RW,
 148     &VNET_NAME(drop_synfin), 0,
 149     "Drop TCP packets with SYN+FIN set");
 150
 151 VNET_DEFINE(int, tcp_do_rfc6675_pipe) = 0;
 152 SYSCTL_INT(_net_inet_tcp, OID_AUTO, do_pipe, CTLFLAG_VNET | CTLFLAG_RW,
 153     &VNET_NAME(tcp_do_rfc6675_pipe), 0,
 154     "Use calculated pipe/in-flight bytes per RFC 6675");
 155
 156 VNET_DEFINE(int, tcp_do_rfc3042) = 1;
 157 #define V_tcp_do_rfc3042        VNET(tcp_do_rfc3042)
 158 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, rfc3042, CTLFLAG_RW,
 159     &VNET_NAME(tcp_do_rfc3042), 0,
 160     "Enable RFC 3042 (Limited Transmit)");
 161
 162 VNET_DEFINE(int, tcp_do_rfc3390) = 1;
 163 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, rfc3390, CTLFLAG_RW,
 164     &VNET_NAME(tcp_do_rfc3390), 0,
 165     "Enable RFC 3390 (Increasing TCP's Initial Congestion Window)");
 166
 167 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, experimental, CTLFLAG_RW, 0,
 168     "Experimental TCP extensions");
 169
 170 VNET_DEFINE(int, tcp_do_initcwnd10) = 1;
 171 SYSCTL_VNET_INT(_net_inet_tcp_experimental, OID_AUTO, initcwnd10, CTLFLAG_RW,
 172     &VNET_NAME(tcp_do_initcwnd10), 0,
 173     "Enable RFC 6928 (Increasing initial CWND to 10)");
 174
 175 VNET_DEFINE(int, tcp_do_rfc3465) = 1;
 176 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, rfc3465, CTLFLAG_RW,
 177     &VNET_NAME(tcp_do_rfc3465), 0,
 178     "Enable RFC 3465 (Appropriate Byte Counting)");
 179
 180 VNET_DEFINE(int, tcp_abc_l_var) = 2;
 181 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, abc_l_var, CTLFLAG_RW,
 182     &VNET_NAME(tcp_abc_l_var), 2,
 183     "Cap the max cwnd increment during slow-start to this number of segments");
 184
 185 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, ecn, CTLFLAG_RW, 0, "TCP ECN");
 186
 187 VNET_DEFINE(int, tcp_do_ecn) = 0;
 188 SYSCTL_VNET_INT(_net_inet_tcp_ecn, OID_AUTO, enable, CTLFLAG_RW,
 189     &VNET_NAME(tcp_do_ecn), 0,
 190     "TCP ECN support");
 191
 192 VNET_DEFINE(int, tcp_ecn_maxretries) = 1;
 193 SYSCTL_VNET_INT(_net_inet_tcp_ecn, OID_AUTO, maxretries, CTLFLAG_RW,
 194     &VNET_NAME(tcp_ecn_maxretries), 0,
 195     "Max retries before giving up on ECN");
 196
 197 VNET_DEFINE(int, tcp_insecure_rst) = 0;
 198 #define V_tcp_insecure_rst      VNET(tcp_insecure_rst)
 199 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, insecure_rst, CTLFLAG_RW,
 200     &VNET_NAME(tcp_insecure_rst), 0,
 201     "Follow the old (insecure) criteria for accepting RST packets");
 202
 203 VNET_DEFINE(int, tcp_recvspace) = 1024*64;
 204 #define V_tcp_recvspace VNET(tcp_recvspace)
 205 SYSCTL_VNET_INT(_net_inet_tcp, TCPCTL_RECVSPACE, recvspace, CTLFLAG_RW,
 206     &VNET_NAME(tcp_recvspace), 0, "Initial receive socket buffer size");
 207
 208 VNET_DEFINE(int, tcp_do_autorcvbuf) = 1;
 209 #define V_tcp_do_autorcvbuf     VNET(tcp_do_autorcvbuf)
 210 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, recvbuf_auto, CTLFLAG_RW,
 211     &VNET_NAME(tcp_do_autorcvbuf), 0,
 212     "Enable automatic receive buffer sizing");
 213
 214 VNET_DEFINE(int, tcp_autorcvbuf_inc) = 16*1024;
 215 #define V_tcp_autorcvbuf_inc    VNET(tcp_autorcvbuf_inc)
 216 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, recvbuf_inc, CTLFLAG_RW,
 217     &VNET_NAME(tcp_autorcvbuf_inc), 0,
 218     "Incrementor step size of automatic receive buffer");
 219
 220 VNET_DEFINE(int, tcp_autorcvbuf_max) = 2*1024*1024;
 221 #define V_tcp_autorcvbuf_max    VNET(tcp_autorcvbuf_max)
 222 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, recvbuf_max, CTLFLAG_RW,
 223     &VNET_NAME(tcp_autorcvbuf_max), 0,
 224     "Max size of automatic receive buffer");
 225
 226 VNET_DEFINE(struct inpcbhead, tcb);
 227 #define tcb6    tcb  /* for KAME src sync over BSD*'s */
 228 VNET_DEFINE(struct inpcbinfo, tcbinfo);
 229
 230 static void      tcp_dooptions(struct tcpopt *, u_char *, int, int);
 231 static void      tcp_do_segment(struct mbuf *, struct tcphdr *,
 232                      struct socket *, struct tcpcb *, int, int, uint8_t,
 233                      int);
 234 static void      tcp_dropwithreset(struct mbuf *, struct tcphdr *,
 235                      struct tcpcb *, int, int);
 236 static void      tcp_pulloutofband(struct socket *,
 237                      struct tcphdr *, struct mbuf *, int);
 238 static void      tcp_xmit_timer(struct tcpcb *, int);
 239 static void      tcp_newreno_partial_ack(struct tcpcb *, struct tcphdr *);
 240 static void inline      cc_ack_received(struct tcpcb *tp, struct tcphdr *th,
 241                             uint16_t type);
 242 static void inline      cc_conn_init(struct tcpcb *tp);
 243 static void inline      cc_post_recovery(struct tcpcb *tp, struct tcphdr *th);
 244 static void inline      hhook_run_tcp_est_in(struct tcpcb *tp,
 245                             struct tcphdr *th, struct tcpopt *to);
 246
 247 /*
 248  * TCP statistics are stored in an "array" of counter(9)s.
 249  */
 250 VNET_PCPUSTAT_DEFINE(struct tcpstat, tcpstat);
 251 VNET_PCPUSTAT_SYSINIT(tcpstat);
 252 SYSCTL_VNET_PCPUSTAT(_net_inet_tcp, TCPCTL_STATS, stats, struct tcpstat,
 253     tcpstat, "TCP statistics (struct tcpstat, netinet/tcp_var.h)");
 254
 255 #ifdef VIMAGE
 256 VNET_PCPUSTAT_SYSUNINIT(tcpstat);
 257 #endif /* VIMAGE */
 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 /*
 270  * Wrapper for the TCP established input helper hook.
 271  */
 272 static void inline
 273 hhook_run_tcp_est_in(struct tcpcb *tp, struct tcphdr *th, struct tcpopt *to)
 274 {
 275         struct tcp_hhook_data hhook_data;
 276
 277         if (V_tcp_hhh[HHOOK_TCP_EST_IN]->hhh_nhooks > 0) {
 278                 hhook_data.tp = tp;
 279                 hhook_data.th = th;
 280                 hhook_data.to = to;
 281
 282                 hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_IN], &hhook_data,
 283                     tp->osd);
 284         }
 285 }
 286
 287 /*
 288  * CC wrapper hook functions
 289  */
 290 static void inline
 291 cc_ack_received(struct tcpcb *tp, struct tcphdr *th, uint16_t type)
 292 {
 293         INP_WLOCK_ASSERT(tp->t_inpcb);
 294
 295         tp->ccv->bytes_this_ack = BYTES_THIS_ACK(tp, th);
 296         if (tp->snd_cwnd <= tp->snd_wnd)
 297                 tp->ccv->flags |= CCF_CWND_LIMITED;
 298         else
 299                 tp->ccv->flags &= ~CCF_CWND_LIMITED;
 300
 301         if (type == CC_ACK) {
 302                 if (tp->snd_cwnd > tp->snd_ssthresh) {
 303                         tp->t_bytes_acked += min(tp->ccv->bytes_this_ack,
 304                              V_tcp_abc_l_var * tp->t_maxseg);
 305                         if (tp->t_bytes_acked >= tp->snd_cwnd) {
 306                                 tp->t_bytes_acked -= tp->snd_cwnd;
 307                                 tp->ccv->flags |= CCF_ABC_SENTAWND;
 308                         }
 309                 } else {
 310                                 tp->ccv->flags &= ~CCF_ABC_SENTAWND;
 311                                 tp->t_bytes_acked = 0;
 312                 }
 313         }
 314
 315         if (CC_ALGO(tp)->ack_received != NULL) {
 316                 /* XXXLAS: Find a way to live without this */
 317                 tp->ccv->curack = th->th_ack;
 318                 CC_ALGO(tp)->ack_received(tp->ccv, type);
 319         }
 320 }
 321
 322 static void inline
 323 cc_conn_init(struct tcpcb *tp)
 324 {
 325         struct hc_metrics_lite metrics;
 326         struct inpcb *inp = tp->t_inpcb;
 327         int rtt;
 328
 329         INP_WLOCK_ASSERT(tp->t_inpcb);
 330
 331         tcp_hc_get(&inp->inp_inc, &metrics);
 332
 333         if (tp->t_srtt == 0 && (rtt = metrics.rmx_rtt)) {
 334                 tp->t_srtt = rtt;
 335                 tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
 336                 TCPSTAT_INC(tcps_usedrtt);
 337                 if (metrics.rmx_rttvar) {
 338                         tp->t_rttvar = metrics.rmx_rttvar;
 339                         TCPSTAT_INC(tcps_usedrttvar);
 340                 } else {
 341                         /* default variation is +- 1 rtt */
 342                         tp->t_rttvar =
 343                             tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
 344                 }
 345                 TCPT_RANGESET(tp->t_rxtcur,
 346                     ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
 347                     tp->t_rttmin, TCPTV_REXMTMAX);
 348         }
 349         if (metrics.rmx_ssthresh) {
 350                 /*
 351                  * There's some sort of gateway or interface
 352                  * buffer limit on the path.  Use this to set
 353                  * the slow start threshhold, but set the
 354                  * threshold to no less than 2*mss.
 355                  */
 356                 tp->snd_ssthresh = max(2 * tp->t_maxseg, metrics.rmx_ssthresh);
 357                 TCPSTAT_INC(tcps_usedssthresh);
 358         }
 359
 360         /*
 361          * Set the initial slow-start flight size.
 362          *
 363          * RFC5681 Section 3.1 specifies the default conservative values.
 364          * RFC3390 specifies slightly more aggressive values.
 365          * RFC6928 increases it to ten segments.
 366          *
 367          * If a SYN or SYN/ACK was lost and retransmitted, we have to
 368          * reduce the initial CWND to one segment as congestion is likely
 369          * requiring us to be cautious.
 370          */
 371         if (tp->snd_cwnd == 1)
 372                 tp->snd_cwnd = tp->t_maxseg;            /* SYN(-ACK) lost */
 373         else if (V_tcp_do_initcwnd10)
 374                 tp->snd_cwnd = min(10 * tp->t_maxseg,
 375                     max(2 * tp->t_maxseg, 14600));
 376         else if (V_tcp_do_rfc3390)
 377                 tp->snd_cwnd = min(4 * tp->t_maxseg,
 378                     max(2 * tp->t_maxseg, 4380));
 379         else {
 380                 /* Per RFC5681 Section 3.1 */
 381                 if (tp->t_maxseg > 2190)
 382                         tp->snd_cwnd = 2 * tp->t_maxseg;
 383                 else if (tp->t_maxseg > 1095)
 384                         tp->snd_cwnd = 3 * tp->t_maxseg;
 385                 else
 386                         tp->snd_cwnd = 4 * tp->t_maxseg;
 387         }
 388
 389         if (CC_ALGO(tp)->conn_init != NULL)
 390                 CC_ALGO(tp)->conn_init(tp->ccv);
 391 }
 392
 393 void inline
 394 cc_cong_signal(struct tcpcb *tp, struct tcphdr *th, uint32_t type)
 395 {
 396         INP_WLOCK_ASSERT(tp->t_inpcb);
 397
 398         switch(type) {
 399         case CC_NDUPACK:
 400                 if (!IN_FASTRECOVERY(tp->t_flags)) {
 401                         tp->snd_recover = tp->snd_max;
 402                         if (tp->t_flags & TF_ECN_PERMIT)
 403                                 tp->t_flags |= TF_ECN_SND_CWR;
 404                 }
 405                 break;
 406         case CC_ECN:
 407                 if (!IN_CONGRECOVERY(tp->t_flags)) {
 408                         TCPSTAT_INC(tcps_ecn_rcwnd);
 409                         tp->snd_recover = tp->snd_max;
 410                         if (tp->t_flags & TF_ECN_PERMIT)
 411                                 tp->t_flags |= TF_ECN_SND_CWR;
 412                 }
 413                 break;
 414         case CC_RTO:
 415                 tp->t_dupacks = 0;
 416                 tp->t_bytes_acked = 0;
 417                 EXIT_RECOVERY(tp->t_flags);
 418                 tp->snd_ssthresh = max(2, min(tp->snd_wnd, tp->snd_cwnd) / 2 /
 419                     tp->t_maxseg) * tp->t_maxseg;
 420                 tp->snd_cwnd = tp->t_maxseg;
 421                 break;
 422         case CC_RTO_ERR:
 423                 TCPSTAT_INC(tcps_sndrexmitbad);
 424                 /* RTO was unnecessary, so reset everything. */
 425                 tp->snd_cwnd = tp->snd_cwnd_prev;
 426                 tp->snd_ssthresh = tp->snd_ssthresh_prev;
 427                 tp->snd_recover = tp->snd_recover_prev;
 428                 if (tp->t_flags & TF_WASFRECOVERY)
 429                         ENTER_FASTRECOVERY(tp->t_flags);
 430                 if (tp->t_flags & TF_WASCRECOVERY)
 431                         ENTER_CONGRECOVERY(tp->t_flags);
 432                 tp->snd_nxt = tp->snd_max;
 433                 tp->t_flags &= ~TF_PREVVALID;
 434                 tp->t_badrxtwin = 0;
 435                 break;
 436         }
 437
 438         if (CC_ALGO(tp)->cong_signal != NULL) {
 439                 if (th != NULL)
 440                         tp->ccv->curack = th->th_ack;
 441                 CC_ALGO(tp)->cong_signal(tp->ccv, type);
 442         }
 443 }
 444
 445 static void inline
 446 cc_post_recovery(struct tcpcb *tp, struct tcphdr *th)
 447 {
 448         INP_WLOCK_ASSERT(tp->t_inpcb);
 449
 450         /* XXXLAS: KASSERT that we're in recovery? */
 451
 452         if (CC_ALGO(tp)->post_recovery != NULL) {
 453                 tp->ccv->curack = th->th_ack;
 454                 CC_ALGO(tp)->post_recovery(tp->ccv);
 455         }
 456         /* XXXLAS: EXIT_RECOVERY ? */
 457         tp->t_bytes_acked = 0;
 458 }
 459
 460 #ifdef TCP_SIGNATURE
 461 static inline int
 462 tcp_signature_verify_input(struct mbuf *m, int off0, int tlen, int optlen,
 463     struct tcpopt *to, struct tcphdr *th, u_int tcpbflag)
 464 {
 465         int ret;
 466
 467         tcp_fields_to_net(th);
 468         ret = tcp_signature_verify(m, off0, tlen, optlen, to, th, tcpbflag);
 469         tcp_fields_to_host(th);
 470         return (ret);
 471 }
 472 #endif
 473
 474 /* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */
 475 #ifdef INET6
 476 #define ND6_HINT(tp) \
 477 do { \
 478         if ((tp) && (tp)->t_inpcb && \
 479             ((tp)->t_inpcb->inp_vflag & INP_IPV6) != 0) \
 480                 nd6_nud_hint(NULL, NULL, 0); \
 481 } while (0)
 482 #else
 483 #define ND6_HINT(tp)
 484 #endif
 485
 486 /*
 487  * Indicate whether this ack should be delayed.  We can delay the ack if
 488  *      - there is no delayed ack timer in progress and
 489  *      - our last ack wasn't a 0-sized window.  We never want to delay
 490  *        the ack that opens up a 0-sized window and
 491  *              - delayed acks are enabled or
 492  *              - this is a half-synchronized T/TCP connection.
 493  *      - the segment size is not larger than the MSS and LRO wasn't used
 494  *        for this segment.
 495  */
 496 #define DELAY_ACK(tp, tlen)                                             \
 497         ((!tcp_timer_active(tp, TT_DELACK) &&                           \
 498             (tp->t_flags & TF_RXWIN0SENT) == 0) &&                      \
 499             (tlen <= tp->t_maxopd) &&                                   \
 500             (V_tcp_delack_enabled || (tp->t_flags & TF_NEEDSYN)))
 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
 518         IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
 519
 520         /*
 521          * draft-itojun-ipv6-tcp-to-anycast
 522          * better place to put this in?
 523          */
 524         ia6 = ip6_getdstifaddr(m);
 525         if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
 526                 struct ip6_hdr *ip6;
 527
 528                 ifa_free(&ia6->ia_ifa);
 529                 ip6 = mtod(m, struct ip6_hdr *);
 530                 icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
 531                             (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
 532                 return IPPROTO_DONE;
 533         }
 534         if (ia6)
 535                 ifa_free(&ia6->ia_ifa);
 536
 537         tcp_input(m, *offp);
 538         return IPPROTO_DONE;
 539 }
 540 #endif /* INET6 */
 541
 542 void
 543 tcp_input(struct mbuf *m, int off0)
 544 {
 545         struct tcphdr *th = NULL;
 546         struct ip *ip = NULL;
 547         struct inpcb *inp = NULL;
 548         struct tcpcb *tp = NULL;
 549         struct socket *so = NULL;
 550         u_char *optp = NULL;
 551         int optlen = 0;
 552 #ifdef INET
 553         int len;
 554 #endif
 555         int tlen = 0, off;
 556         int drop_hdrlen;
 557         int thflags;
 558         int rstreason = 0;      /* For badport_bandlim accounting purposes */
 559 #ifdef TCP_SIGNATURE
 560         uint8_t sig_checked = 0;
 561 #endif
 562         uint8_t iptos = 0;
 563         struct m_tag *fwd_tag = NULL;
 564 #ifdef INET6
 565         struct ip6_hdr *ip6 = NULL;
 566         int isipv6;
 567 #else
 568         const void *ip6 = NULL;
 569 #endif /* INET6 */
 570         struct tcpopt to;               /* options in this segment */
 571         char *s = NULL;                 /* address and port logging */
 572         int ti_locked;
 573 #define TI_UNLOCKED     1
 574 #define TI_WLOCKED      2
 575
 576 #ifdef TCPDEBUG
 577         /*
 578          * The size of tcp_saveipgen must be the size of the max ip header,
 579          * now IPv6.
 580          */
 581         u_char tcp_saveipgen[IP6_HDR_LEN];
 582         struct tcphdr tcp_savetcp;
 583         short ostate = 0;
 584 #endif
 585
 586 #ifdef INET6
 587         isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
 588 #endif
 589
 590         to.to_flags = 0;
 591         TCPSTAT_INC(tcps_rcvtotal);
 592
 593 #ifdef INET6
 594         if (isipv6) {
 595                 /* IP6_EXTHDR_CHECK() is already done at tcp6_input(). */
 596
 597                 if (m->m_len < (sizeof(*ip6) + sizeof(*th))) {
 598                         m = m_pullup(m, sizeof(*ip6) + sizeof(*th));
 599                         if (m == NULL) {
 600                                 TCPSTAT_INC(tcps_rcvshort);
 601                                 return;
 602                         }
 603                 }
 604
 605                 ip6 = mtod(m, struct ip6_hdr *);
 606                 th = (struct tcphdr *)((caddr_t)ip6 + off0);
 607                 tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
 608                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID_IPV6) {
 609                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
 610                                 th->th_sum = m->m_pkthdr.csum_data;
 611                         else
 612                                 th->th_sum = in6_cksum_pseudo(ip6, tlen,
 613                                     IPPROTO_TCP, m->m_pkthdr.csum_data);
 614                         th->th_sum ^= 0xffff;
 615                 } else
 616                         th->th_sum = in6_cksum(m, IPPROTO_TCP, off0, tlen);
 617                 if (th->th_sum) {
 618                         TCPSTAT_INC(tcps_rcvbadsum);
 619                         goto drop;
 620                 }
 621
 622                 /*
 623                  * Be proactive about unspecified IPv6 address in source.
 624                  * As we use all-zero to indicate unbounded/unconnected pcb,
 625                  * unspecified IPv6 address can be used to confuse us.
 626                  *
 627                  * Note that packets with unspecified IPv6 destination is
 628                  * already dropped in ip6_input.
 629                  */
 630                 if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
 631                         /* XXX stat */
 632                         goto drop;
 633                 }
 634         }
 635 #endif
 636 #if defined(INET) && defined(INET6)
 637         else
 638 #endif
 639 #ifdef INET
 640         {
 641                 /*
 642                  * Get IP and TCP header together in first mbuf.
 643                  * Note: IP leaves IP header in first mbuf.
 644                  */
 645                 if (off0 > sizeof (struct ip)) {
 646                         ip_stripoptions(m);
 647                         off0 = sizeof(struct ip);
 648                 }
 649                 if (m->m_len < sizeof (struct tcpiphdr)) {
 650                         if ((m = m_pullup(m, sizeof (struct tcpiphdr)))
 651                             == NULL) {
 652                                 TCPSTAT_INC(tcps_rcvshort);
 653                                 return;
 654                         }
 655                 }
 656                 ip = mtod(m, struct ip *);
 657                 th = (struct tcphdr *)((caddr_t)ip + off0);
 658                 tlen = ntohs(ip->ip_len) - off0;
 659
 660                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
 661                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
 662                                 th->th_sum = m->m_pkthdr.csum_data;
 663                         else
 664                                 th->th_sum = in_pseudo(ip->ip_src.s_addr,
 665                                     ip->ip_dst.s_addr,
 666                                     htonl(m->m_pkthdr.csum_data + tlen +
 667                                     IPPROTO_TCP));
 668                         th->th_sum ^= 0xffff;
 669                 } else {
 670                         struct ipovly *ipov = (struct ipovly *)ip;
 671
 672                         /*
 673                          * Checksum extended TCP header and data.
 674                          */
 675                         len = off0 + tlen;
 676                         bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
 677                         ipov->ih_len = htons(tlen);
 678                         th->th_sum = in_cksum(m, len);
 679                         /* Reset length for SDT probes. */
 680                         ip->ip_len = htons(tlen + off0);
 681                 }
 682
 683                 if (th->th_sum) {
 684                         TCPSTAT_INC(tcps_rcvbadsum);
 685                         goto drop;
 686                 }
 687                 /* Re-initialization for later version check */
 688                 ip->ip_v = IPVERSION;
 689         }
 690 #endif /* INET */
 691
 692 #ifdef INET6
 693         if (isipv6)
 694                 iptos = (ntohl(ip6->ip6_flow) >> 20) & 0xff;
 695 #endif
 696 #if defined(INET) && defined(INET6)
 697         else
 698 #endif
 699 #ifdef INET
 700                 iptos = ip->ip_tos;
 701 #endif
 702
 703         /*
 704          * Check that TCP offset makes sense,
 705          * pull out TCP options and adjust length.              XXX
 706          */
 707         off = th->th_off << 2;
 708         if (off < sizeof (struct tcphdr) || off > tlen) {
 709                 TCPSTAT_INC(tcps_rcvbadoff);
 710                 goto drop;
 711         }
 712         tlen -= off;    /* tlen is used instead of ti->ti_len */
 713         if (off > sizeof (struct tcphdr)) {
 714 #ifdef INET6
 715                 if (isipv6) {
 716                         IP6_EXTHDR_CHECK(m, off0, off, );
 717                         ip6 = mtod(m, struct ip6_hdr *);
 718                         th = (struct tcphdr *)((caddr_t)ip6 + off0);
 719                 }
 720 #endif
 721 #if defined(INET) && defined(INET6)
 722                 else
 723 #endif
 724 #ifdef INET
 725                 {
 726                         if (m->m_len < sizeof(struct ip) + off) {
 727                                 if ((m = m_pullup(m, sizeof (struct ip) + off))
 728                                     == NULL) {
 729                                         TCPSTAT_INC(tcps_rcvshort);
 730                                         return;
 731                                 }
 732                                 ip = mtod(m, struct ip *);
 733                                 th = (struct tcphdr *)((caddr_t)ip + off0);
 734                         }
 735                 }
 736 #endif
 737                 optlen = off - sizeof (struct tcphdr);
 738                 optp = (u_char *)(th + 1);
 739         }
 740         thflags = th->th_flags;
 741
 742         /*
 743          * Convert TCP protocol specific fields to host format.
 744          */
 745         tcp_fields_to_host(th);
 746
 747         /*
 748          * Delay dropping TCP, IP headers, IPv6 ext headers, and TCP options.
 749          */
 750         drop_hdrlen = off0 + off;
 751
 752         /*
 753          * Locate pcb for segment; if we're likely to add or remove a
 754          * connection then first acquire pcbinfo lock.  There are two cases
 755          * where we might discover later we need a write lock despite the
 756          * flags: ACKs moving a connection out of the syncache, and ACKs for
 757          * a connection in TIMEWAIT.
 758          */
 759         if ((thflags & (TH_SYN | TH_FIN | TH_RST)) != 0) {
 760                 INP_INFO_WLOCK(&V_tcbinfo);
 761                 ti_locked = TI_WLOCKED;
 762         } else
 763                 ti_locked = TI_UNLOCKED;
 764
 765         /*
 766          * Grab info from PACKET_TAG_IPFORWARD tag prepended to the chain.
 767          */
 768         if (
 769 #ifdef INET6
 770             (isipv6 && (m->m_flags & M_IP6_NEXTHOP))
 771 #ifdef INET
 772             || (!isipv6 && (m->m_flags & M_IP_NEXTHOP))
 773 #endif
 774 #endif
 775 #if defined(INET) && !defined(INET6)
 776             (m->m_flags & M_IP_NEXTHOP)
 777 #endif
 778             )
 779                 fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
 780
 781 findpcb:
 782 #ifdef INVARIANTS
 783         if (ti_locked == TI_WLOCKED) {
 784                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 785         } else {
 786                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 787         }
 788 #endif
 789 #ifdef INET6
 790         if (isipv6 && fwd_tag != NULL) {
 791                 struct sockaddr_in6 *next_hop6;
 792
 793                 next_hop6 = (struct sockaddr_in6 *)(fwd_tag + 1);
 794                 /*
 795                  * Transparently forwarded. Pretend to be the destination.
 796                  * Already got one like this?
 797                  */
 798                 inp = in6_pcblookup_mbuf(&V_tcbinfo,
 799                     &ip6->ip6_src, th->th_sport, &ip6->ip6_dst, th->th_dport,
 800                     INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif, m);
 801                 if (!inp) {
 802                         /*
 803                          * It's new.  Try to find the ambushing socket.
 804                          * Because we've rewritten the destination address,
 805                          * any hardware-generated hash is ignored.
 806                          */
 807                         inp = in6_pcblookup(&V_tcbinfo, &ip6->ip6_src,
 808                             th->th_sport, &next_hop6->sin6_addr,
 809                             next_hop6->sin6_port ? ntohs(next_hop6->sin6_port) :
 810                             th->th_dport, INPLOOKUP_WILDCARD |
 811                             INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif);
 812                 }
 813         } else if (isipv6) {
 814                 inp = in6_pcblookup_mbuf(&V_tcbinfo, &ip6->ip6_src,
 815                     th->th_sport, &ip6->ip6_dst, th->th_dport,
 816                     INPLOOKUP_WILDCARD | INPLOOKUP_WLOCKPCB,
 817                     m->m_pkthdr.rcvif, m);
 818         }
 819 #endif /* INET6 */
 820 #if defined(INET6) && defined(INET)
 821         else
 822 #endif
 823 #ifdef INET
 824         if (fwd_tag != NULL) {
 825                 struct sockaddr_in *next_hop;
 826
 827                 next_hop = (struct sockaddr_in *)(fwd_tag+1);
 828                 /*
 829                  * Transparently forwarded. Pretend to be the destination.
 830                  * already got one like this?
 831                  */
 832                 inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src, th->th_sport,
 833                     ip->ip_dst, th->th_dport, INPLOOKUP_WLOCKPCB,
 834                     m->m_pkthdr.rcvif, m);
 835                 if (!inp) {
 836                         /*
 837                          * It's new.  Try to find the ambushing socket.
 838                          * Because we've rewritten the destination address,
 839                          * any hardware-generated hash is ignored.
 840                          */
 841                         inp = in_pcblookup(&V_tcbinfo, ip->ip_src,
 842                             th->th_sport, next_hop->sin_addr,
 843                             next_hop->sin_port ? ntohs(next_hop->sin_port) :
 844                             th->th_dport, INPLOOKUP_WILDCARD |
 845                             INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif);
 846                 }
 847         } else
 848                 inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src,
 849                     th->th_sport, ip->ip_dst, th->th_dport,
 850                     INPLOOKUP_WILDCARD | INPLOOKUP_WLOCKPCB,
 851                     m->m_pkthdr.rcvif, m);
 852 #endif /* INET */
 853
 854         /*
 855          * If the INPCB does not exist then all data in the incoming
 856          * segment is discarded and an appropriate RST is sent back.
 857          * XXX MRT Send RST using which routing table?
 858          */
 859         if (inp == NULL) {
 860                 /*
 861                  * Log communication attempts to ports that are not
 862                  * in use.
 863                  */
 864                 if ((tcp_log_in_vain == 1 && (thflags & TH_SYN)) ||
 865                     tcp_log_in_vain == 2) {
 866                         if ((s = tcp_log_vain(NULL, th, (void *)ip, ip6)))
 867                                 log(LOG_INFO, "%s; %s: Connection attempt "
 868                                     "to closed port\n", s, __func__);
 869                 }
 870                 /*
 871                  * When blackholing do not respond with a RST but
 872                  * completely ignore the segment and drop it.
 873                  */
 874                 if ((V_blackhole == 1 && (thflags & TH_SYN)) ||
 875                     V_blackhole == 2)
 876                         goto dropunlock;
 877
 878                 rstreason = BANDLIM_RST_CLOSEDPORT;
 879                 goto dropwithreset;
 880         }
 881         INP_WLOCK_ASSERT(inp);
 882         if ((inp->inp_flowtype == M_HASHTYPE_NONE) &&
 883             (M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) &&
 884             ((inp->inp_socket == NULL) ||
 885             (inp->inp_socket->so_options & SO_ACCEPTCONN) == 0)) {
 886                 inp->inp_flowid = m->m_pkthdr.flowid;
 887                 inp->inp_flowtype = M_HASHTYPE_GET(m);
 888         }
 889 #ifdef IPSEC
 890 #ifdef INET6
 891         if (isipv6 && ipsec6_in_reject(m, inp)) {
 892                 IPSEC6STAT_INC(ips_in_polvio);
 893                 goto dropunlock;
 894         } else
 895 #endif /* INET6 */
 896         if (ipsec4_in_reject(m, inp) != 0) {
 897                 IPSECSTAT_INC(ips_in_polvio);
 898                 goto dropunlock;
 899         }
 900 #endif /* IPSEC */
 901
 902         /*
 903          * Check the minimum TTL for socket.
 904          */
 905         if (inp->inp_ip_minttl != 0) {
 906 #ifdef INET6
 907                 if (isipv6 && inp->inp_ip_minttl > ip6->ip6_hlim)
 908                         goto dropunlock;
 909                 else
 910 #endif
 911                 if (inp->inp_ip_minttl > ip->ip_ttl)
 912                         goto dropunlock;
 913         }
 914
 915         /*
 916          * A previous connection in TIMEWAIT state is supposed to catch stray
 917          * or duplicate segments arriving late.  If this segment was a
 918          * legitimate new connection attempt, the old INPCB gets removed and
 919          * we can try again to find a listening socket.
 920          *
 921          * At this point, due to earlier optimism, we may hold only an inpcb
 922          * lock, and not the inpcbinfo write lock.  If so, we need to try to
 923          * acquire it, or if that fails, acquire a reference on the inpcb,
 924          * drop all locks, acquire a global write lock, and then re-acquire
 925          * the inpcb lock.  We may at that point discover that another thread
 926          * has tried to free the inpcb, in which case we need to loop back
 927          * and try to find a new inpcb to deliver to.
 928          *
 929          * XXXRW: It may be time to rethink timewait locking.
 930          */
 931 relocked:
 932         if (inp->inp_flags & INP_TIMEWAIT) {
 933                 if (ti_locked == TI_UNLOCKED) {
 934                         if (INP_INFO_TRY_WLOCK(&V_tcbinfo) == 0) {
 935                                 in_pcbref(inp);
 936                                 INP_WUNLOCK(inp);
 937                                 INP_INFO_WLOCK(&V_tcbinfo);
 938                                 ti_locked = TI_WLOCKED;
 939                                 INP_WLOCK(inp);
 940                                 if (in_pcbrele_wlocked(inp)) {
 941                                         inp = NULL;
 942                                         goto findpcb;
 943                                 }
 944                         } else
 945                                 ti_locked = TI_WLOCKED;
 946                 }
 947                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 948
 949                 if (thflags & TH_SYN)
 950                         tcp_dooptions(&to, optp, optlen, TO_SYN);
 951                 /*
 952                  * NB: tcp_twcheck unlocks the INP and frees the mbuf.
 953                  */
 954                 if (tcp_twcheck(inp, &to, th, m, tlen))
 955                         goto findpcb;
 956                 INP_INFO_WUNLOCK(&V_tcbinfo);
 957                 return;
 958         }
 959         /*
 960          * The TCPCB may no longer exist if the connection is winding
 961          * down or it is in the CLOSED state.  Either way we drop the
 962          * segment and send an appropriate response.
 963          */
 964         tp = intotcpcb(inp);
 965         if (tp == NULL || tp->t_state == TCPS_CLOSED) {
 966                 rstreason = BANDLIM_RST_CLOSEDPORT;
 967                 goto dropwithreset;
 968         }
 969
 970 #ifdef TCP_OFFLOAD
 971         if (tp->t_flags & TF_TOE) {
 972                 tcp_offload_input(tp, m);
 973                 m = NULL;       /* consumed by the TOE driver */
 974                 goto dropunlock;
 975         }
 976 #endif
 977
 978         /*
 979          * We've identified a valid inpcb, but it could be that we need an
 980          * inpcbinfo write lock but don't hold it.  In this case, attempt to
 981          * acquire using the same strategy as the TIMEWAIT case above.  If we
 982          * relock, we have to jump back to 'relocked' as the connection might
 983          * now be in TIMEWAIT.
 984          */
 985 #ifdef INVARIANTS
 986         if ((thflags & (TH_SYN | TH_FIN | TH_RST)) != 0)
 987                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 988 #endif
 989         if (tp->t_state != TCPS_ESTABLISHED) {
 990                 if (ti_locked == TI_UNLOCKED) {
 991                         if (INP_INFO_TRY_WLOCK(&V_tcbinfo) == 0) {
 992                                 in_pcbref(inp);
 993                                 INP_WUNLOCK(inp);
 994                                 INP_INFO_WLOCK(&V_tcbinfo);
 995                                 ti_locked = TI_WLOCKED;
 996                                 INP_WLOCK(inp);
 997                                 if (in_pcbrele_wlocked(inp)) {
 998                                         inp = NULL;
 999                                         goto findpcb;
1000                                 }
1001                                 goto relocked;
1002                         } else
1003                                 ti_locked = TI_WLOCKED;
1004                 }
1005                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
1006         }
1007
1008 #ifdef MAC
1009         INP_WLOCK_ASSERT(inp);
1010         if (mac_inpcb_check_deliver(inp, m))
1011                 goto dropunlock;
1012 #endif
1013         so = inp->inp_socket;
1014         KASSERT(so != NULL, ("%s: so == NULL", __func__));
1015 #ifdef TCPDEBUG
1016         if (so->so_options & SO_DEBUG) {
1017                 ostate = tp->t_state;
1018 #ifdef INET6
1019                 if (isipv6) {
1020                         bcopy((char *)ip6, (char *)tcp_saveipgen, sizeof(*ip6));
1021                 } else
1022 #endif
1023                         bcopy((char *)ip, (char *)tcp_saveipgen, sizeof(*ip));
1024                 tcp_savetcp = *th;
1025         }
1026 #endif /* TCPDEBUG */
1027         /*
1028          * When the socket is accepting connections (the INPCB is in LISTEN
1029          * state) we look into the SYN cache if this is a new connection
1030          * attempt or the completion of a previous one.  Because listen
1031          * sockets are never in TCPS_ESTABLISHED, the V_tcbinfo lock will be
1032          * held in this case.
1033          */
1034         if (so->so_options & SO_ACCEPTCONN) {
1035                 struct in_conninfo inc;
1036
1037                 KASSERT(tp->t_state == TCPS_LISTEN, ("%s: so accepting but "
1038                     "tp not listening", __func__));
1039                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
1040
1041                 bzero(&inc, sizeof(inc));
1042 #ifdef INET6
1043                 if (isipv6) {
1044                         inc.inc_flags |= INC_ISIPV6;
1045                         inc.inc6_faddr = ip6->ip6_src;
1046                         inc.inc6_laddr = ip6->ip6_dst;
1047                 } else
1048 #endif
1049                 {
1050                         inc.inc_faddr = ip->ip_src;
1051                         inc.inc_laddr = ip->ip_dst;
1052                 }
1053                 inc.inc_fport = th->th_sport;
1054                 inc.inc_lport = th->th_dport;
1055                 inc.inc_fibnum = so->so_fibnum;
1056
1057                 /*
1058                  * Check for an existing connection attempt in syncache if
1059                  * the flag is only ACK.  A successful lookup creates a new
1060                  * socket appended to the listen queue in SYN_RECEIVED state.
1061                  */
1062                 if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
1063                         /*
1064                          * Parse the TCP options here because
1065                          * syncookies need access to the reflected
1066                          * timestamp.
1067                          */
1068                         tcp_dooptions(&to, optp, optlen, 0);
1069                         /*
1070                          * NB: syncache_expand() doesn't unlock
1071                          * inp and tcpinfo locks.
1072                          */
1073                         if (!syncache_expand(&inc, &to, th, &so, m)) {
1074                                 /*
1075                                  * No syncache entry or ACK was not
1076                                  * for our SYN/ACK.  Send a RST.
1077                                  * NB: syncache did its own logging
1078                                  * of the failure cause.
1079                                  */
1080                                 rstreason = BANDLIM_RST_OPENPORT;
1081                                 goto dropwithreset;
1082                         }
1083 #ifdef TCP_RFC7413
1084 new_tfo_socket:
1085 #endif
1086                         if (so == NULL) {
1087                                 /*
1088                                  * We completed the 3-way handshake
1089                                  * but could not allocate a socket
1090                                  * either due to memory shortage,
1091                                  * listen queue length limits or
1092                                  * global socket limits.  Send RST
1093                                  * or wait and have the remote end
1094                                  * retransmit the ACK for another
1095                                  * try.
1096                                  */
1097                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1098                                         log(LOG_DEBUG, "%s; %s: Listen socket: "
1099                                             "Socket allocation failed due to "
1100                                             "limits or memory shortage, %s\n",
1101                                             s, __func__,
1102                                             V_tcp_sc_rst_sock_fail ?
1103                                             "sending RST" : "try again");
1104                                 if (V_tcp_sc_rst_sock_fail) {
1105                                         rstreason = BANDLIM_UNLIMITED;
1106                                         goto dropwithreset;
1107                                 } else
1108                                         goto dropunlock;
1109                         }
1110                         /*
1111                          * Socket is created in state SYN_RECEIVED.
1112                          * Unlock the listen socket, lock the newly
1113                          * created socket and update the tp variable.
1114                          */
1115                         INP_WUNLOCK(inp);       /* listen socket */
1116                         inp = sotoinpcb(so);
1117                         INP_WLOCK(inp);         /* new connection */
1118                         tp = intotcpcb(inp);
1119                         KASSERT(tp->t_state == TCPS_SYN_RECEIVED,
1120                             ("%s: ", __func__));
1121 #ifdef TCP_SIGNATURE
1122                         if (sig_checked == 0)  {
1123                                 tcp_dooptions(&to, optp, optlen,
1124                                     (thflags & TH_SYN) ? TO_SYN : 0);
1125                                 if (!tcp_signature_verify_input(m, off0, tlen,
1126                                     optlen, &to, th, tp->t_flags)) {
1127
1128                                         /*
1129                                          * In SYN_SENT state if it receives an
1130                                          * RST, it is allowed for further
1131                                          * processing.
1132                                          */
1133                                         if ((thflags & TH_RST) == 0 ||
1134                                             (tp->t_state == TCPS_SYN_SENT) == 0)
1135                                                 goto dropunlock;
1136                                 }
1137                                 sig_checked = 1;
1138                         }
1139 #endif
1140
1141                         /*
1142                          * Process the segment and the data it
1143                          * contains.  tcp_do_segment() consumes
1144                          * the mbuf chain and unlocks the inpcb.
1145                          */
1146                         tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen,
1147                             iptos, ti_locked);
1148                         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1149                         return;
1150                 }
1151                 /*
1152                  * Segment flag validation for new connection attempts:
1153                  *
1154                  * Our (SYN|ACK) response was rejected.
1155                  * Check with syncache and remove entry to prevent
1156                  * retransmits.
1157                  *
1158                  * NB: syncache_chkrst does its own logging of failure
1159                  * causes.
1160                  */
1161                 if (thflags & TH_RST) {
1162                         syncache_chkrst(&inc, th);
1163                         goto dropunlock;
1164                 }
1165                 /*
1166                  * We can't do anything without SYN.
1167                  */
1168                 if ((thflags & TH_SYN) == 0) {
1169                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1170                                 log(LOG_DEBUG, "%s; %s: Listen socket: "
1171                                     "SYN is missing, segment ignored\n",
1172                                     s, __func__);
1173                         TCPSTAT_INC(tcps_badsyn);
1174                         goto dropunlock;
1175                 }
1176                 /*
1177                  * (SYN|ACK) is bogus on a listen socket.
1178                  */
1179                 if (thflags & TH_ACK) {
1180                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1181                                 log(LOG_DEBUG, "%s; %s: Listen socket: "
1182                                     "SYN|ACK invalid, segment rejected\n",
1183                                     s, __func__);
1184                         syncache_badack(&inc);  /* XXX: Not needed! */
1185                         TCPSTAT_INC(tcps_badsyn);
1186                         rstreason = BANDLIM_RST_OPENPORT;
1187                         goto dropwithreset;
1188                 }
1189                 /*
1190                  * If the drop_synfin option is enabled, drop all
1191                  * segments with both the SYN and FIN bits set.
1192                  * This prevents e.g. nmap from identifying the
1193                  * TCP/IP stack.
1194                  * XXX: Poor reasoning.  nmap has other methods
1195                  * and is constantly refining its stack detection
1196                  * strategies.
1197                  * XXX: This is a violation of the TCP specification
1198                  * and was used by RFC1644.
1199                  */
1200                 if ((thflags & TH_FIN) && V_drop_synfin) {
1201                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1202                                 log(LOG_DEBUG, "%s; %s: Listen socket: "
1203                                     "SYN|FIN segment ignored (based on "
1204                                     "sysctl setting)\n", s, __func__);
1205                         TCPSTAT_INC(tcps_badsyn);
1206                         goto dropunlock;
1207                 }
1208                 /*
1209                  * Segment's flags are (SYN) or (SYN|FIN).
1210                  *
1211                  * TH_PUSH, TH_URG, TH_ECE, TH_CWR are ignored
1212                  * as they do not affect the state of the TCP FSM.
1213                  * The data pointed to by TH_URG and th_urp is ignored.
1214                  */
1215                 KASSERT((thflags & (TH_RST|TH_ACK)) == 0,
1216                     ("%s: Listen socket: TH_RST or TH_ACK set", __func__));
1217                 KASSERT(thflags & (TH_SYN),
1218                     ("%s: Listen socket: TH_SYN not set", __func__));
1219 #ifdef INET6
1220                 /*
1221                  * If deprecated address is forbidden,
1222                  * we do not accept SYN to deprecated interface
1223                  * address to prevent any new inbound connection from
1224                  * getting established.
1225                  * When we do not accept SYN, we send a TCP RST,
1226                  * with deprecated source address (instead of dropping
1227                  * it).  We compromise it as it is much better for peer
1228                  * to send a RST, and RST will be the final packet
1229                  * for the exchange.
1230                  *
1231                  * If we do not forbid deprecated addresses, we accept
1232                  * the SYN packet.  RFC2462 does not suggest dropping
1233                  * SYN in this case.
1234                  * If we decipher RFC2462 5.5.4, it says like this:
1235                  * 1. use of deprecated addr with existing
1236                  *    communication is okay - "SHOULD continue to be
1237                  *    used"
1238                  * 2. use of it with new communication:
1239                  *   (2a) "SHOULD NOT be used if alternate address
1240                  *        with sufficient scope is available"
1241                  *   (2b) nothing mentioned otherwise.
1242                  * Here we fall into (2b) case as we have no choice in
1243                  * our source address selection - we must obey the peer.
1244                  *
1245                  * The wording in RFC2462 is confusing, and there are
1246                  * multiple description text for deprecated address
1247                  * handling - worse, they are not exactly the same.
1248                  * I believe 5.5.4 is the best one, so we follow 5.5.4.
1249                  */
1250                 if (isipv6 && !V_ip6_use_deprecated) {
1251                         struct in6_ifaddr *ia6;
1252
1253                         ia6 = ip6_getdstifaddr(m);
1254                         if (ia6 != NULL &&
1255                             (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
1256                                 ifa_free(&ia6->ia_ifa);
1257                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1258                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
1259                                         "Connection attempt to deprecated "
1260                                         "IPv6 address rejected\n",
1261                                         s, __func__);
1262                                 rstreason = BANDLIM_RST_OPENPORT;
1263                                 goto dropwithreset;
1264                         }
1265                         if (ia6)
1266                                 ifa_free(&ia6->ia_ifa);
1267                 }
1268 #endif /* INET6 */
1269                 /*
1270                  * Basic sanity checks on incoming SYN requests:
1271                  *   Don't respond if the destination is a link layer
1272                  *      broadcast according to RFC1122 4.2.3.10, p. 104.
1273                  *   If it is from this socket it must be forged.
1274                  *   Don't respond if the source or destination is a
1275                  *      global or subnet broad- or multicast address.
1276                  *   Note that it is quite possible to receive unicast
1277                  *      link-layer packets with a broadcast IP address. Use
1278                  *      in_broadcast() to find them.
1279                  */
1280                 if (m->m_flags & (M_BCAST|M_MCAST)) {
1281                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1282                             log(LOG_DEBUG, "%s; %s: Listen socket: "
1283                                 "Connection attempt from broad- or multicast "
1284                                 "link layer address ignored\n", s, __func__);
1285                         goto dropunlock;
1286                 }
1287 #ifdef INET6
1288                 if (isipv6) {
1289                         if (th->th_dport == th->th_sport &&
1290                             IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &ip6->ip6_src)) {
1291                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1292                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
1293                                         "Connection attempt to/from self "
1294                                         "ignored\n", s, __func__);
1295                                 goto dropunlock;
1296                         }
1297                         if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
1298                             IN6_IS_ADDR_MULTICAST(&ip6->ip6_src)) {
1299                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1300                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
1301                                         "Connection attempt from/to multicast "
1302                                         "address ignored\n", s, __func__);
1303                                 goto dropunlock;
1304                         }
1305                 }
1306 #endif
1307 #if defined(INET) && defined(INET6)
1308                 else
1309 #endif
1310 #ifdef INET
1311                 {
1312                         if (th->th_dport == th->th_sport &&
1313                             ip->ip_dst.s_addr == ip->ip_src.s_addr) {
1314                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1315                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
1316                                         "Connection attempt from/to self "
1317                                         "ignored\n", s, __func__);
1318                                 goto dropunlock;
1319                         }
1320                         if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
1321                             IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
1322                             ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
1323                             in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif)) {
1324                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1325                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
1326                                         "Connection attempt from/to broad- "
1327                                         "or multicast address ignored\n",
1328                                         s, __func__);
1329                                 goto dropunlock;
1330                         }
1331                 }
1332 #endif
1333                 /*
1334                  * SYN appears to be valid.  Create compressed TCP state
1335                  * for syncache.
1336                  */
1337 #ifdef TCPDEBUG
1338                 if (so->so_options & SO_DEBUG)
1339                         tcp_trace(TA_INPUT, ostate, tp,
1340                             (void *)tcp_saveipgen, &tcp_savetcp, 0);
1341 #endif
1342                 tcp_dooptions(&to, optp, optlen, TO_SYN);
1343 #ifdef TCP_RFC7413
1344                 if (syncache_add(&inc, &to, th, inp, &so, m, NULL, NULL))
1345                         goto new_tfo_socket;
1346 #else
1347                 syncache_add(&inc, &to, th, inp, &so, m, NULL, NULL);
1348 #endif
1349                 /*
1350                  * Entry added to syncache and mbuf consumed.
1351                  * Everything already unlocked by syncache_add().
1352                  */
1353                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1354                 return;
1355         } else if (tp->t_state == TCPS_LISTEN) {
1356                 /*
1357                  * When a listen socket is torn down the SO_ACCEPTCONN
1358                  * flag is removed first while connections are drained
1359                  * from the accept queue in a unlock/lock cycle of the
1360                  * ACCEPT_LOCK, opening a race condition allowing a SYN
1361                  * attempt go through unhandled.
1362                  */
1363                 goto dropunlock;
1364         }
1365
1366 #ifdef TCP_SIGNATURE
1367         if (sig_checked == 0)  {
1368                 tcp_dooptions(&to, optp, optlen,
1369                     (thflags & TH_SYN) ? TO_SYN : 0);
1370                 if (!tcp_signature_verify_input(m, off0, tlen, optlen, &to,
1371                     th, tp->t_flags)) {
1372
1373                         /*
1374                          * In SYN_SENT state if it receives an RST, it is
1375                          * allowed for further processing.
1376                          */
1377                         if ((thflags & TH_RST) == 0 ||
1378                             (tp->t_state == TCPS_SYN_SENT) == 0)
1379                                 goto dropunlock;
1380                 }
1381                 sig_checked = 1;
1382         }
1383 #endif
1384
1385         TCP_PROBE5(receive, NULL, tp, mtod(m, const char *), tp, th);
1386
1387         /*
1388          * Segment belongs to a connection in SYN_SENT, ESTABLISHED or later
1389          * state.  tcp_do_segment() always consumes the mbuf chain, unlocks
1390          * the inpcb, and unlocks pcbinfo.
1391          */
1392         tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen, iptos, ti_locked);
1393         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1394         return;
1395
1396 dropwithreset:
1397         TCP_PROBE5(receive, NULL, tp, mtod(m, const char *), tp, th);
1398
1399         if (ti_locked == TI_WLOCKED) {
1400                 INP_INFO_WUNLOCK(&V_tcbinfo);
1401                 ti_locked = TI_UNLOCKED;
1402         }
1403 #ifdef INVARIANTS
1404         else {
1405                 KASSERT(ti_locked == TI_UNLOCKED, ("%s: dropwithreset "
1406                     "ti_locked: %d", __func__, ti_locked));
1407                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1408         }
1409 #endif
1410
1411         if (inp != NULL) {
1412                 tcp_dropwithreset(m, th, tp, tlen, rstreason);
1413                 INP_WUNLOCK(inp);
1414         } else
1415                 tcp_dropwithreset(m, th, NULL, tlen, rstreason);
1416         m = NULL;       /* mbuf chain got consumed. */
1417         goto drop;
1418
1419 dropunlock:
1420         if (m != NULL)
1421                 TCP_PROBE5(receive, NULL, tp, mtod(m, const char *), tp, th);
1422
1423         if (ti_locked == TI_WLOCKED) {
1424                 INP_INFO_WUNLOCK(&V_tcbinfo);
1425                 ti_locked = TI_UNLOCKED;
1426         }
1427 #ifdef INVARIANTS
1428         else {
1429                 KASSERT(ti_locked == TI_UNLOCKED, ("%s: dropunlock "
1430                     "ti_locked: %d", __func__, ti_locked));
1431                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1432         }
1433 #endif
1434
1435         if (inp != NULL)
1436                 INP_WUNLOCK(inp);
1437
1438 drop:
1439         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1440         if (s != NULL)
1441                 free(s, M_TCPLOG);
1442         if (m != NULL)
1443                 m_freem(m);
1444 }
1445
1446 static void
1447 tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
1448     struct tcpcb *tp, int drop_hdrlen, int tlen, uint8_t iptos,
1449     int ti_locked)
1450 {
1451         int thflags, acked, ourfinisacked, needoutput = 0, sack_changed;
1452         int rstreason, todrop, win;
1453         u_long tiwin;
1454         char *s;
1455         struct in_conninfo *inc;
1456         struct mbuf *mfree;
1457         struct tcpopt to;
1458         int tfo_syn;
1459
1460 #ifdef TCPDEBUG
1461         /*
1462          * The size of tcp_saveipgen must be the size of the max ip header,
1463          * now IPv6.
1464          */
1465         u_char tcp_saveipgen[IP6_HDR_LEN];
1466         struct tcphdr tcp_savetcp;
1467         short ostate = 0;
1468 #endif
1469         thflags = th->th_flags;
1470         inc = &tp->t_inpcb->inp_inc;
1471         tp->sackhint.last_sack_ack = 0;
1472         sack_changed = 0;
1473
1474         /*
1475          * If this is either a state-changing packet or current state isn't
1476          * established, we require a write lock on tcbinfo.  Otherwise, we
1477          * allow the tcbinfo to be in either alocked or unlocked, as the
1478          * caller may have unnecessarily acquired a write lock due to a race.
1479          */
1480         if ((thflags & (TH_SYN | TH_FIN | TH_RST)) != 0 ||
1481             tp->t_state != TCPS_ESTABLISHED) {
1482                 KASSERT(ti_locked == TI_WLOCKED, ("%s ti_locked %d for "
1483                     "SYN/FIN/RST/!EST", __func__, ti_locked));
1484                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
1485         } else {
1486 #ifdef INVARIANTS
1487                 if (ti_locked == TI_WLOCKED)
1488                         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
1489                 else {
1490                         KASSERT(ti_locked == TI_UNLOCKED, ("%s: EST "
1491                             "ti_locked: %d", __func__, ti_locked));
1492                         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1493                 }
1494 #endif
1495         }
1496         INP_WLOCK_ASSERT(tp->t_inpcb);
1497         KASSERT(tp->t_state > TCPS_LISTEN, ("%s: TCPS_LISTEN",
1498             __func__));
1499         KASSERT(tp->t_state != TCPS_TIME_WAIT, ("%s: TCPS_TIME_WAIT",
1500             __func__));
1501
1502         /*
1503          * Segment received on connection.
1504          * Reset idle time and keep-alive timer.
1505          * XXX: This should be done after segment
1506          * validation to ignore broken/spoofed segs.
1507          */
1508         tp->t_rcvtime = ticks;
1509         if (TCPS_HAVEESTABLISHED(tp->t_state))
1510                 tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
1511
1512         /*
1513          * Unscale the window into a 32-bit value.
1514          * For the SYN_SENT state the scale is zero.
1515          */
1516         tiwin = th->th_win << tp->snd_scale;
1517
1518         /*
1519          * TCP ECN processing.
1520          */
1521         if (tp->t_flags & TF_ECN_PERMIT) {
1522                 if (thflags & TH_CWR)
1523                         tp->t_flags &= ~TF_ECN_SND_ECE;
1524                 switch (iptos & IPTOS_ECN_MASK) {
1525                 case IPTOS_ECN_CE:
1526                         tp->t_flags |= TF_ECN_SND_ECE;
1527                         TCPSTAT_INC(tcps_ecn_ce);
1528                         break;
1529                 case IPTOS_ECN_ECT0:
1530                         TCPSTAT_INC(tcps_ecn_ect0);
1531                         break;
1532                 case IPTOS_ECN_ECT1:
1533                         TCPSTAT_INC(tcps_ecn_ect1);
1534                         break;
1535                 }
1536                 /* Congestion experienced. */
1537                 if (thflags & TH_ECE) {
1538                         cc_cong_signal(tp, th, CC_ECN);
1539                 }
1540         }
1541
1542         /*
1543          * Parse options on any incoming segment.
1544          */
1545         tcp_dooptions(&to, (u_char *)(th + 1),
1546             (th->th_off << 2) - sizeof(struct tcphdr),
1547             (thflags & TH_SYN) ? TO_SYN : 0);
1548
1549         /*
1550          * If echoed timestamp is later than the current time,
1551          * fall back to non RFC1323 RTT calculation.  Normalize
1552          * timestamp if syncookies were used when this connection
1553          * was established.
1554          */
1555         if ((to.to_flags & TOF_TS) && (to.to_tsecr != 0)) {
1556                 to.to_tsecr -= tp->ts_offset;
1557                 if (TSTMP_GT(to.to_tsecr, tcp_ts_getticks()))
1558                         to.to_tsecr = 0;
1559         }
1560         /*
1561          * If timestamps were negotiated during SYN/ACK they should
1562          * appear on every segment during this session and vice versa.
1563          */
1564         if ((tp->t_flags & TF_RCVD_TSTMP) && !(to.to_flags & TOF_TS)) {
1565                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1566                         log(LOG_DEBUG, "%s; %s: Timestamp missing, "
1567                             "no action\n", s, __func__);
1568                         free(s, M_TCPLOG);
1569                 }
1570         }
1571         if (!(tp->t_flags & TF_RCVD_TSTMP) && (to.to_flags & TOF_TS)) {
1572                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1573                         log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
1574                             "no action\n", s, __func__);
1575                         free(s, M_TCPLOG);
1576                 }
1577         }
1578
1579         /*
1580          * Process options only when we get SYN/ACK back. The SYN case
1581          * for incoming connections is handled in tcp_syncache.
1582          * According to RFC1323 the window field in a SYN (i.e., a <SYN>
1583          * or <SYN,ACK>) segment itself is never scaled.
1584          * XXX this is traditional behavior, may need to be cleaned up.
1585          */
1586         if (tp->t_state == TCPS_SYN_SENT && (thflags & TH_SYN)) {
1587                 if ((to.to_flags & TOF_SCALE) &&
1588                     (tp->t_flags & TF_REQ_SCALE)) {
1589                         tp->t_flags |= TF_RCVD_SCALE;
1590                         tp->snd_scale = to.to_wscale;
1591                 }
1592                 /*
1593                  * Initial send window.  It will be updated with
1594                  * the next incoming segment to the scaled value.
1595                  */
1596                 tp->snd_wnd = th->th_win;
1597                 if (to.to_flags & TOF_TS) {
1598                         tp->t_flags |= TF_RCVD_TSTMP;
1599                         tp->ts_recent = to.to_tsval;
1600                         tp->ts_recent_age = tcp_ts_getticks();
1601                 }
1602                 if (to.to_flags & TOF_MSS)
1603                         tcp_mss(tp, to.to_mss);
1604                 if ((tp->t_flags & TF_SACK_PERMIT) &&
1605                     (to.to_flags & TOF_SACKPERM) == 0)
1606                         tp->t_flags &= ~TF_SACK_PERMIT;
1607         }
1608
1609         /*
1610          * Header prediction: check for the two common cases
1611          * of a uni-directional data xfer.  If the packet has
1612          * no control flags, is in-sequence, the window didn't
1613          * change and we're not retransmitting, it's a
1614          * candidate.  If the length is zero and the ack moved
1615          * forward, we're the sender side of the xfer.  Just
1616          * free the data acked & wake any higher level process
1617          * that was blocked waiting for space.  If the length
1618          * is non-zero and the ack didn't move, we're the
1619          * receiver side.  If we're getting packets in-order
1620          * (the reassembly queue is empty), add the data to
1621          * the socket buffer and note that we need a delayed ack.
1622          * Make sure that the hidden state-flags are also off.
1623          * Since we check for TCPS_ESTABLISHED first, it can only
1624          * be TH_NEEDSYN.
1625          */
1626         if (tp->t_state == TCPS_ESTABLISHED &&
1627             th->th_seq == tp->rcv_nxt &&
1628             (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
1629             tp->snd_nxt == tp->snd_max &&
1630             tiwin && tiwin == tp->snd_wnd &&
1631             ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
1632             LIST_EMPTY(&tp->t_segq) &&
1633             ((to.to_flags & TOF_TS) == 0 ||
1634              TSTMP_GEQ(to.to_tsval, tp->ts_recent)) ) {
1635
1636                 /*
1637                  * If last ACK falls within this segment's sequence numbers,
1638                  * record the timestamp.
1639                  * NOTE that the test is modified according to the latest
1640                  * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1641                  */
1642                 if ((to.to_flags & TOF_TS) != 0 &&
1643                     SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
1644                         tp->ts_recent_age = tcp_ts_getticks();
1645                         tp->ts_recent = to.to_tsval;
1646                 }
1647
1648                 if (tlen == 0) {
1649                         if (SEQ_GT(th->th_ack, tp->snd_una) &&
1650                             SEQ_LEQ(th->th_ack, tp->snd_max) &&
1651                             !IN_RECOVERY(tp->t_flags) &&
1652                             (to.to_flags & TOF_SACK) == 0 &&
1653                             TAILQ_EMPTY(&tp->snd_holes)) {
1654                                 /*
1655                                  * This is a pure ack for outstanding data.
1656                                  */
1657                                 if (ti_locked == TI_WLOCKED)
1658                                         INP_INFO_WUNLOCK(&V_tcbinfo);
1659                                 ti_locked = TI_UNLOCKED;
1660
1661                                 TCPSTAT_INC(tcps_predack);
1662
1663                                 /*
1664                                  * "bad retransmit" recovery.
1665                                  */
1666                                 if (tp->t_rxtshift == 1 &&
1667                                     tp->t_flags & TF_PREVVALID &&
1668                                     (int)(ticks - tp->t_badrxtwin) < 0) {
1669                                         cc_cong_signal(tp, th, CC_RTO_ERR);
1670                                 }
1671
1672                                 /*
1673                                  * Recalculate the transmit timer / rtt.
1674                                  *
1675                                  * Some boxes send broken timestamp replies
1676                                  * during the SYN+ACK phase, ignore
1677                                  * timestamps of 0 or we could calculate a
1678                                  * huge RTT and blow up the retransmit timer.
1679                                  */
1680                                 if ((to.to_flags & TOF_TS) != 0 &&
1681                                     to.to_tsecr) {
1682                                         u_int t;
1683
1684                                         t = tcp_ts_getticks() - to.to_tsecr;
1685                                         if (!tp->t_rttlow || tp->t_rttlow > t)
1686                                                 tp->t_rttlow = t;
1687                                         tcp_xmit_timer(tp,
1688                                             TCP_TS_TO_TICKS(t) + 1);
1689                                 } else if (tp->t_rtttime &&
1690                                     SEQ_GT(th->th_ack, tp->t_rtseq)) {
1691                                         if (!tp->t_rttlow ||
1692                                             tp->t_rttlow > ticks - tp->t_rtttime)
1693                                                 tp->t_rttlow = ticks - tp->t_rtttime;
1694                                         tcp_xmit_timer(tp,
1695                                                         ticks - tp->t_rtttime);
1696                                 }
1697                                 acked = BYTES_THIS_ACK(tp, th);
1698
1699                                 /* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
1700                                 hhook_run_tcp_est_in(tp, th, &to);
1701
1702                                 TCPSTAT_INC(tcps_rcvackpack);
1703                                 TCPSTAT_ADD(tcps_rcvackbyte, acked);
1704                                 sbdrop(&so->so_snd, acked);
1705                                 if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
1706                                     SEQ_LEQ(th->th_ack, tp->snd_recover))
1707                                         tp->snd_recover = th->th_ack - 1;
1708
1709                                 /*
1710                                  * Let the congestion control algorithm update
1711                                  * congestion control related information. This
1712                                  * typically means increasing the congestion
1713                                  * window.
1714                                  */
1715                                 cc_ack_received(tp, th, CC_ACK);
1716
1717                                 tp->snd_una = th->th_ack;
1718                                 /*
1719                                  * Pull snd_wl2 up to prevent seq wrap relative
1720                                  * to th_ack.
1721                                  */
1722                                 tp->snd_wl2 = th->th_ack;
1723                                 tp->t_dupacks = 0;
1724                                 m_freem(m);
1725                                 ND6_HINT(tp); /* Some progress has been made. */
1726
1727                                 /*
1728                                  * If all outstanding data are acked, stop
1729                                  * retransmit timer, otherwise restart timer
1730                                  * using current (possibly backed-off) value.
1731                                  * If process is waiting for space,
1732                                  * wakeup/selwakeup/signal.  If data
1733                                  * are ready to send, let tcp_output
1734                                  * decide between more output or persist.
1735                                  */
1736 #ifdef TCPDEBUG
1737                                 if (so->so_options & SO_DEBUG)
1738                                         tcp_trace(TA_INPUT, ostate, tp,
1739                                             (void *)tcp_saveipgen,
1740                                             &tcp_savetcp, 0);
1741 #endif
1742                                 if (tp->snd_una == tp->snd_max)
1743                                         tcp_timer_activate(tp, TT_REXMT, 0);
1744                                 else if (!tcp_timer_active(tp, TT_PERSIST))
1745                                         tcp_timer_activate(tp, TT_REXMT,
1746                                                       tp->t_rxtcur);
1747                                 sowwakeup(so);
1748                                 if (so->so_snd.sb_cc)
1749                                         (void) tcp_output(tp);
1750                                 goto check_delack;
1751                         }
1752                 } else if (th->th_ack == tp->snd_una &&
1753                     tlen <= sbspace(&so->so_rcv)) {
1754                         int newsize = 0;        /* automatic sockbuf scaling */
1755
1756                         /*
1757                          * This is a pure, in-sequence data packet with
1758                          * nothing on the reassembly queue and we have enough
1759                          * buffer space to take it.
1760                          */
1761                         if (ti_locked == TI_WLOCKED)
1762                                 INP_INFO_WUNLOCK(&V_tcbinfo);
1763                         ti_locked = TI_UNLOCKED;
1764
1765                         /* Clean receiver SACK report if present */
1766                         if ((tp->t_flags & TF_SACK_PERMIT) && tp->rcv_numsacks)
1767                                 tcp_clean_sackreport(tp);
1768                         TCPSTAT_INC(tcps_preddat);
1769                         tp->rcv_nxt += tlen;
1770                         /*
1771                          * Pull snd_wl1 up to prevent seq wrap relative to
1772                          * th_seq.
1773                          */
1774                         tp->snd_wl1 = th->th_seq;
1775                         /*
1776                          * Pull rcv_up up to prevent seq wrap relative to
1777                          * rcv_nxt.
1778                          */
1779                         tp->rcv_up = tp->rcv_nxt;
1780                         TCPSTAT_INC(tcps_rcvpack);
1781                         TCPSTAT_ADD(tcps_rcvbyte, tlen);
1782                         ND6_HINT(tp);   /* Some progress has been made */
1783 #ifdef TCPDEBUG
1784                         if (so->so_options & SO_DEBUG)
1785                                 tcp_trace(TA_INPUT, ostate, tp,
1786                                     (void *)tcp_saveipgen, &tcp_savetcp, 0);
1787 #endif
1788                 /*
1789                  * Automatic sizing of receive socket buffer.  Often the send
1790                  * buffer size is not optimally adjusted to the actual network
1791                  * conditions at hand (delay bandwidth product).  Setting the
1792                  * buffer size too small limits throughput on links with high
1793                  * bandwidth and high delay (eg. trans-continental/oceanic links).
1794                  *
1795                  * On the receive side the socket buffer memory is only rarely
1796                  * used to any significant extent.  This allows us to be much
1797                  * more aggressive in scaling the receive socket buffer.  For
1798                  * the case that the buffer space is actually used to a large
1799                  * extent and we run out of kernel memory we can simply drop
1800                  * the new segments; TCP on the sender will just retransmit it
1801                  * later.  Setting the buffer size too big may only consume too
1802                  * much kernel memory if the application doesn't read() from
1803                  * the socket or packet loss or reordering makes use of the
1804                  * reassembly queue.
1805                  *
1806                  * The criteria to step up the receive buffer one notch are:
1807                  *  1. the number of bytes received during the time it takes
1808                  *     one timestamp to be reflected back to us (the RTT);
1809                  *  2. received bytes per RTT is within seven eighth of the
1810                  *     current socket buffer size;
1811                  *  3. receive buffer size has not hit maximal automatic size;
1812                  *
1813                  * This algorithm does one step per RTT at most and only if
1814                  * we receive a bulk stream w/o packet losses or reorderings.
1815                  * Shrinking the buffer during idle times is not necessary as
1816                  * it doesn't consume any memory when idle.
1817                  *
1818                  * TODO: Only step up if the application is actually serving
1819                  * the buffer to better manage the socket buffer resources.
1820                  */
1821                         if (V_tcp_do_autorcvbuf &&
1822                             (to.to_flags & TOF_TS) &&
1823                             to.to_tsecr &&
1824                             (so->so_rcv.sb_flags & SB_AUTOSIZE)) {
1825                                 if (TSTMP_GT(to.to_tsecr, tp->rfbuf_ts) &&
1826                                     to.to_tsecr - tp->rfbuf_ts < hz) {
1827                                         if (tp->rfbuf_cnt >
1828                                             (so->so_rcv.sb_hiwat / 8 * 7) &&
1829                                             so->so_rcv.sb_hiwat <
1830                                             V_tcp_autorcvbuf_max) {
1831                                                 newsize =
1832                                                     min(so->so_rcv.sb_hiwat +
1833                                                     V_tcp_autorcvbuf_inc,
1834                                                     V_tcp_autorcvbuf_max);
1835                                         }
1836                                         /* Start over with next RTT. */
1837                                         tp->rfbuf_ts = 0;
1838                                         tp->rfbuf_cnt = 0;
1839                                 } else
1840                                         tp->rfbuf_cnt += tlen;  /* add up */
1841                         }
1842
1843                         /* Add data to socket buffer. */
1844                         SOCKBUF_LOCK(&so->so_rcv);
1845                         if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
1846                                 m_freem(m);
1847                         } else {
1848                                 /*
1849                                  * Set new socket buffer size.
1850                                  * Give up when limit is reached.
1851                                  */
1852                                 if (newsize)
1853                                         if (!sbreserve_locked(&so->so_rcv,
1854                                             newsize, so, NULL))
1855                                                 so->so_rcv.sb_flags &= ~SB_AUTOSIZE;
1856                                 m_adj(m, drop_hdrlen);  /* delayed header drop */
1857                                 sbappendstream_locked(&so->so_rcv, m);
1858                         }
1859                         /* NB: sorwakeup_locked() does an implicit unlock. */
1860                         sorwakeup_locked(so);
1861                         if (DELAY_ACK(tp, tlen)) {
1862                                 tp->t_flags |= TF_DELACK;
1863                         } else {
1864                                 tp->t_flags |= TF_ACKNOW;
1865                                 tcp_output(tp);
1866                         }
1867                         goto check_delack;
1868                 }
1869         }
1870
1871         /*
1872          * Calculate amount of space in receive window,
1873          * and then do TCP input processing.
1874          * Receive window is amount of space in rcv queue,
1875          * but not less than advertised window.
1876          */
1877         win = sbspace(&so->so_rcv);
1878         if (win < 0)
1879                 win = 0;
1880         tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
1881
1882         /* Reset receive buffer auto scaling when not in bulk receive mode. */
1883         tp->rfbuf_ts = 0;
1884         tp->rfbuf_cnt = 0;
1885
1886         switch (tp->t_state) {
1887
1888         /*
1889          * If the state is SYN_RECEIVED:
1890          *      if seg contains an ACK, but not for our SYN/ACK, send a RST.
1891          */
1892         case TCPS_SYN_RECEIVED:
1893                 if ((thflags & TH_ACK) &&
1894                     (SEQ_LEQ(th->th_ack, tp->snd_una) ||
1895                      SEQ_GT(th->th_ack, tp->snd_max))) {
1896                                 rstreason = BANDLIM_RST_OPENPORT;
1897                                 goto dropwithreset;
1898                 }
1899 #ifdef TCP_RFC7413
1900                 if (tp->t_flags & TF_FASTOPEN) {
1901                         /*
1902                          * When a TFO connection is in SYN_RECEIVED, the
1903                          * only valid packets are the initial SYN, a
1904                          * retransmit/copy of the initial SYN (possibly with
1905                          * a subset of the original data), a valid ACK, a
1906                          * FIN, or a RST.
1907                          */
1908                         if ((thflags & (TH_SYN|TH_ACK)) == (TH_SYN|TH_ACK)) {
1909                                 rstreason = BANDLIM_RST_OPENPORT;
1910                                 goto dropwithreset;
1911                         } else if (thflags & TH_SYN) {
1912                                 /* non-initial SYN is ignored */
1913                                 if ((tcp_timer_active(tp, TT_DELACK) ||
1914                                      tcp_timer_active(tp, TT_REXMT)))
1915                                         goto drop;
1916                         } else if (!(thflags & (TH_ACK|TH_FIN|TH_RST))) {
1917                                 goto drop;
1918                         }
1919                 }
1920 #endif
1921                 break;
1922
1923         /*
1924          * If the state is SYN_SENT:
1925          *      if seg contains an ACK, but not for our SYN, drop the input.
1926          *      if seg contains a RST, then drop the connection.
1927          *      if seg does not contain SYN, then drop it.
1928          * Otherwise this is an acceptable SYN segment
1929          *      initialize tp->rcv_nxt and tp->irs
1930          *      if seg contains ack then advance tp->snd_una
1931          *      if seg contains an ECE and ECN support is enabled, the stream
1932          *          is ECN capable.
1933          *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
1934          *      arrange for segment to be acked (eventually)
1935          *      continue processing rest of data/controls, beginning with URG
1936          */
1937         case TCPS_SYN_SENT:
1938                 if ((thflags & TH_ACK) &&
1939                     (SEQ_LEQ(th->th_ack, tp->iss) ||
1940                      SEQ_GT(th->th_ack, tp->snd_max))) {
1941                         rstreason = BANDLIM_UNLIMITED;
1942                         goto dropwithreset;
1943                 }
1944                 if ((thflags & (TH_ACK|TH_RST)) == (TH_ACK|TH_RST)) {
1945                         TCP_PROBE5(connect__refused, NULL, tp,
1946                             mtod(m, const char *), tp, th);
1947                         tp = tcp_drop(tp, ECONNREFUSED);
1948                 }
1949                 if (thflags & TH_RST)
1950                         goto drop;
1951                 if (!(thflags & TH_SYN))
1952                         goto drop;
1953
1954                 tp->irs = th->th_seq;
1955                 tcp_rcvseqinit(tp);
1956                 if (thflags & TH_ACK) {
1957                         TCPSTAT_INC(tcps_connects);
1958                         soisconnected(so);
1959 #ifdef MAC
1960                         mac_socketpeer_set_from_mbuf(m, so);
1961 #endif
1962                         /* Do window scaling on this connection? */
1963                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1964                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1965                                 tp->rcv_scale = tp->request_r_scale;
1966                         }
1967                         tp->rcv_adv += imin(tp->rcv_wnd,
1968                             TCP_MAXWIN << tp->rcv_scale);
1969                         tp->snd_una++;          /* SYN is acked */
1970                         /*
1971                          * If there's data, delay ACK; if there's also a FIN
1972                          * ACKNOW will be turned on later.
1973                          */
1974                         if (DELAY_ACK(tp, tlen) && tlen != 0)
1975                                 tcp_timer_activate(tp, TT_DELACK,
1976                                     tcp_delacktime);
1977                         else
1978                                 tp->t_flags |= TF_ACKNOW;
1979
1980                         if ((thflags & TH_ECE) && V_tcp_do_ecn) {
1981                                 tp->t_flags |= TF_ECN_PERMIT;
1982                                 TCPSTAT_INC(tcps_ecn_shs);
1983                         }
1984
1985                         /*
1986                          * Received <SYN,ACK> in SYN_SENT[*] state.
1987                          * Transitions:
1988                          *      SYN_SENT  --> ESTABLISHED
1989                          *      SYN_SENT* --> FIN_WAIT_1
1990                          */
1991                         tp->t_starttime = ticks;
1992                         if (tp->t_flags & TF_NEEDFIN) {
1993                                 tcp_state_change(tp, TCPS_FIN_WAIT_1);
1994                                 tp->t_flags &= ~TF_NEEDFIN;
1995                                 thflags &= ~TH_SYN;
1996                         } else {
1997                                 tcp_state_change(tp, TCPS_ESTABLISHED);
1998                                 TCP_PROBE5(connect__established, NULL, tp,
1999                                     mtod(m, const char *), tp, th);
2000                                 cc_conn_init(tp);
2001                                 tcp_timer_activate(tp, TT_KEEP,
2002                                     TP_KEEPIDLE(tp));
2003                         }
2004                 } else {
2005                         /*
2006                          * Received initial SYN in SYN-SENT[*] state =>
2007                          * simultaneous open.  If segment contains CC option
2008                          * and there is a cached CC, apply TAO test.
2009                          * If it succeeds, connection is * half-synchronized.
2010                          * Otherwise, do 3-way handshake:
2011                          *        SYN-SENT -> SYN-RECEIVED
2012                          *        SYN-SENT* -> SYN-RECEIVED*
2013                          * If there was no CC option, clear cached CC value.
2014                          */
2015                         tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
2016                         tcp_timer_activate(tp, TT_REXMT, 0);
2017                         tcp_state_change(tp, TCPS_SYN_RECEIVED);
2018                 }
2019
2020                 KASSERT(ti_locked == TI_WLOCKED, ("%s: trimthenstep6: "
2021                     "ti_locked %d", __func__, ti_locked));
2022                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
2023                 INP_WLOCK_ASSERT(tp->t_inpcb);
2024
2025                 /*
2026                  * Advance th->th_seq to correspond to first data byte.
2027                  * If data, trim to stay within window,
2028                  * dropping FIN if necessary.
2029                  */
2030                 th->th_seq++;
2031                 if (tlen > tp->rcv_wnd) {
2032                         todrop = tlen - tp->rcv_wnd;
2033                         m_adj(m, -todrop);
2034                         tlen = tp->rcv_wnd;
2035                         thflags &= ~TH_FIN;
2036                         TCPSTAT_INC(tcps_rcvpackafterwin);
2037                         TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
2038                 }
2039                 tp->snd_wl1 = th->th_seq - 1;
2040                 tp->rcv_up = th->th_seq;
2041                 /*
2042                  * Client side of transaction: already sent SYN and data.
2043                  * If the remote host used T/TCP to validate the SYN,
2044                  * our data will be ACK'd; if so, enter normal data segment
2045                  * processing in the middle of step 5, ack processing.
2046                  * Otherwise, goto step 6.
2047                  */
2048                 if (thflags & TH_ACK)
2049                         goto process_ACK;
2050
2051                 goto step6;
2052
2053         /*
2054          * If the state is LAST_ACK or CLOSING or TIME_WAIT:
2055          *      do normal processing.
2056          *
2057          * NB: Leftover from RFC1644 T/TCP.  Cases to be reused later.
2058          */
2059         case TCPS_LAST_ACK:
2060         case TCPS_CLOSING:
2061                 break;  /* continue normal processing */
2062         }
2063
2064         /*
2065          * States other than LISTEN or SYN_SENT.
2066          * First check the RST flag and sequence number since reset segments
2067          * are exempt from the timestamp and connection count tests.  This
2068          * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
2069          * below which allowed reset segments in half the sequence space
2070          * to fall though and be processed (which gives forged reset
2071          * segments with a random sequence number a 50 percent chance of
2072          * killing a connection).
2073          * Then check timestamp, if present.
2074          * Then check the connection count, if present.
2075          * Then check that at least some bytes of segment are within
2076          * receive window.  If segment begins before rcv_nxt,
2077          * drop leading data (and SYN); if nothing left, just ack.
2078          *
2079          *
2080          * If the RST bit is set, check the sequence number to see
2081          * if this is a valid reset segment.
2082          * RFC 793 page 37:
2083          *   In all states except SYN-SENT, all reset (RST) segments
2084          *   are validated by checking their SEQ-fields.  A reset is
2085          *   valid if its sequence number is in the window.
2086          * Note: this does not take into account delayed ACKs, so
2087          *   we should test against last_ack_sent instead of rcv_nxt.
2088          *   The sequence number in the reset segment is normally an
2089          *   echo of our outgoing acknowlegement numbers, but some hosts
2090          *   send a reset with the sequence number at the rightmost edge
2091          *   of our receive window, and we have to handle this case.
2092          * Note 2: Paul Watson's paper "Slipping in the Window" has shown
2093          *   that brute force RST attacks are possible.  To combat this,
2094          *   we use a much stricter check while in the ESTABLISHED state,
2095          *   only accepting RSTs where the sequence number is equal to
2096          *   last_ack_sent.  In all other states (the states in which a
2097          *   RST is more likely), the more permissive check is used.
2098          * If we have multiple segments in flight, the initial reset
2099          * segment sequence numbers will be to the left of last_ack_sent,
2100          * but they will eventually catch up.
2101          * In any case, it never made sense to trim reset segments to
2102          * fit the receive window since RFC 1122 says:
2103          *   4.2.2.12  RST Segment: RFC-793 Section 3.4
2104          *
2105          *    A TCP SHOULD allow a received RST segment to include data.
2106          *
2107          *    DISCUSSION
2108          *         It has been suggested that a RST segment could contain
2109          *         ASCII text that encoded and explained the cause of the
2110          *         RST.  No standard has yet been established for such
2111          *         data.
2112          *
2113          * If the reset segment passes the sequence number test examine
2114          * the state:
2115          *    SYN_RECEIVED STATE:
2116          *      If passive open, return to LISTEN state.
2117          *      If active open, inform user that connection was refused.
2118          *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, CLOSE_WAIT STATES:
2119          *      Inform user that connection was reset, and close tcb.
2120          *    CLOSING, LAST_ACK STATES:
2121          *      Close the tcb.
2122          *    TIME_WAIT STATE:
2123          *      Drop the segment - see Stevens, vol. 2, p. 964 and
2124          *      RFC 1337.
2125          */
2126         if (thflags & TH_RST) {
2127                 if (SEQ_GEQ(th->th_seq, tp->last_ack_sent - 1) &&
2128                     SEQ_LEQ(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
2129                         switch (tp->t_state) {
2130
2131                         case TCPS_SYN_RECEIVED:
2132                                 so->so_error = ECONNREFUSED;
2133                                 goto close;
2134
2135                         case TCPS_ESTABLISHED:
2136                                 if (V_tcp_insecure_rst == 0 &&
2137                                     !(SEQ_GEQ(th->th_seq, tp->rcv_nxt - 1) &&
2138                                     SEQ_LEQ(th->th_seq, tp->rcv_nxt + 1)) &&
2139                                     !(SEQ_GEQ(th->th_seq, tp->last_ack_sent - 1) &&
2140                                     SEQ_LEQ(th->th_seq, tp->last_ack_sent + 1))) {
2141                                         TCPSTAT_INC(tcps_badrst);
2142                                         goto drop;
2143                                 }
2144                                 /* FALLTHROUGH */
2145                         case TCPS_FIN_WAIT_1:
2146                         case TCPS_FIN_WAIT_2:
2147                         case TCPS_CLOSE_WAIT:
2148                                 so->so_error = ECONNRESET;
2149                         close:
2150                                 KASSERT(ti_locked == TI_WLOCKED,
2151                                     ("tcp_do_segment: TH_RST 1 ti_locked %d",
2152                                     ti_locked));
2153                                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
2154
2155                                 tcp_state_change(tp, TCPS_CLOSED);
2156                                 TCPSTAT_INC(tcps_drops);
2157                                 tp = tcp_close(tp);
2158                                 break;
2159
2160                         case TCPS_CLOSING:
2161                         case TCPS_LAST_ACK:
2162                                 KASSERT(ti_locked == TI_WLOCKED,
2163                                     ("tcp_do_segment: TH_RST 2 ti_locked %d",
2164                                     ti_locked));
2165                                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
2166
2167                                 tp = tcp_close(tp);
2168                                 break;
2169                         }
2170                 }
2171                 goto drop;
2172         }
2173
2174         /*
2175          * RFC 1323 PAWS: If we have a timestamp reply on this segment
2176          * and it's less than ts_recent, drop it.
2177          */
2178         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
2179             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
2180
2181                 /* Check to see if ts_recent is over 24 days old.  */
2182                 if (tcp_ts_getticks() - tp->ts_recent_age > TCP_PAWS_IDLE) {
2183                         /*
2184                          * Invalidate ts_recent.  If this segment updates
2185                          * ts_recent, the age will be reset later and ts_recent
2186                          * will get a valid value.  If it does not, setting
2187                          * ts_recent to zero will at least satisfy the
2188                          * requirement that zero be placed in the timestamp
2189                          * echo reply when ts_recent isn't valid.  The
2190                          * age isn't reset until we get a valid ts_recent
2191                          * because we don't want out-of-order segments to be
2192                          * dropped when ts_recent is old.
2193                          */
2194                         tp->ts_recent = 0;
2195                 } else {
2196                         TCPSTAT_INC(tcps_rcvduppack);
2197                         TCPSTAT_ADD(tcps_rcvdupbyte, tlen);
2198                         TCPSTAT_INC(tcps_pawsdrop);
2199                         if (tlen)
2200                                 goto dropafterack;
2201                         goto drop;
2202                 }
2203         }
2204
2205         /*
2206          * In the SYN-RECEIVED state, validate that the packet belongs to
2207          * this connection before trimming the data to fit the receive
2208          * window.  Check the sequence number versus IRS since we know
2209          * the sequence numbers haven't wrapped.  This is a partial fix
2210          * for the "LAND" DoS attack.
2211          */
2212         if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
2213                 rstreason = BANDLIM_RST_OPENPORT;
2214                 goto dropwithreset;
2215         }
2216
2217         todrop = tp->rcv_nxt - th->th_seq;
2218         if (todrop > 0) {
2219                 if (thflags & TH_SYN) {
2220                         thflags &= ~TH_SYN;
2221                         th->th_seq++;
2222                         if (th->th_urp > 1)
2223                                 th->th_urp--;
2224                         else
2225                                 thflags &= ~TH_URG;
2226                         todrop--;
2227                 }
2228                 /*
2229                  * Following if statement from Stevens, vol. 2, p. 960.
2230                  */
2231                 if (todrop > tlen
2232                     || (todrop == tlen && (thflags & TH_FIN) == 0)) {
2233                         /*
2234                          * Any valid FIN must be to the left of the window.
2235                          * At this point the FIN must be a duplicate or out
2236                          * of sequence; drop it.
2237                          */
2238                         thflags &= ~TH_FIN;
2239
2240                         /*
2241                          * Send an ACK to resynchronize and drop any data.
2242                          * But keep on processing for RST or ACK.
2243                          */
2244                         tp->t_flags |= TF_ACKNOW;
2245                         todrop = tlen;
2246                         TCPSTAT_INC(tcps_rcvduppack);
2247                         TCPSTAT_ADD(tcps_rcvdupbyte, todrop);
2248                 } else {
2249                         TCPSTAT_INC(tcps_rcvpartduppack);
2250                         TCPSTAT_ADD(tcps_rcvpartdupbyte, todrop);
2251                 }
2252                 drop_hdrlen += todrop;  /* drop from the top afterwards */
2253                 th->th_seq += todrop;
2254                 tlen -= todrop;
2255                 if (th->th_urp > todrop)
2256                         th->th_urp -= todrop;
2257                 else {
2258                         thflags &= ~TH_URG;
2259                         th->th_urp = 0;
2260                 }
2261         }
2262
2263         /*
2264          * If new data are received on a connection after the
2265          * user processes are gone, then RST the other end.
2266          */
2267         if ((so->so_state & SS_NOFDREF) &&
2268             tp->t_state > TCPS_CLOSE_WAIT && tlen) {
2269                 KASSERT(ti_locked == TI_WLOCKED, ("%s: SS_NOFDEREF && "
2270                     "CLOSE_WAIT && tlen ti_locked %d", __func__, ti_locked));
2271                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
2272
2273                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
2274                         log(LOG_DEBUG, "%s; %s: %s: Received %d bytes of data "
2275                             "after socket was closed, "
2276                             "sending RST and removing tcpcb\n",
2277                             s, __func__, tcpstates[tp->t_state], tlen);
2278                         free(s, M_TCPLOG);
2279                 }
2280                 tp = tcp_close(tp);
2281                 TCPSTAT_INC(tcps_rcvafterclose);
2282                 rstreason = BANDLIM_UNLIMITED;
2283                 goto dropwithreset;
2284         }
2285
2286         /*
2287          * If segment ends after window, drop trailing data
2288          * (and PUSH and FIN); if nothing left, just ACK.
2289          */
2290         todrop = (th->th_seq + tlen) - (tp->rcv_nxt + tp->rcv_wnd);
2291         if (todrop > 0) {
2292                 TCPSTAT_INC(tcps_rcvpackafterwin);
2293                 if (todrop >= tlen) {
2294                         TCPSTAT_ADD(tcps_rcvbyteafterwin, tlen);
2295                         /*
2296                          * If window is closed can only take segments at
2297                          * window edge, and have to drop data and PUSH from
2298                          * incoming segments.  Continue processing, but
2299                          * remember to ack.  Otherwise, drop segment
2300                          * and ack.
2301                          */
2302                         if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
2303                                 tp->t_flags |= TF_ACKNOW;
2304                                 TCPSTAT_INC(tcps_rcvwinprobe);
2305                         } else
2306                                 goto dropafterack;
2307                 } else
2308                         TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
2309                 m_adj(m, -todrop);
2310                 tlen -= todrop;
2311                 thflags &= ~(TH_PUSH|TH_FIN);
2312         }
2313
2314         /*
2315          * If last ACK falls within this segment's sequence numbers,
2316          * record its timestamp.
2317          * NOTE:
2318          * 1) That the test incorporates suggestions from the latest
2319          *    proposal of the tcplw@cray.com list (Braden 1993/04/26).
2320          * 2) That updating only on newer timestamps interferes with
2321          *    our earlier PAWS tests, so this check should be solely
2322          *    predicated on the sequence space of this segment.
2323          * 3) That we modify the segment boundary check to be
2324          *        Last.ACK.Sent <= SEG.SEQ + SEG.Len
2325          *    instead of RFC1323's
2326          *        Last.ACK.Sent < SEG.SEQ + SEG.Len,
2327          *    This modified check allows us to overcome RFC1323's
2328          *    limitations as described in Stevens TCP/IP Illustrated
2329          *    Vol. 2 p.869. In such cases, we can still calculate the
2330          *    RTT correctly when RCV.NXT == Last.ACK.Sent.
2331          */
2332         if ((to.to_flags & TOF_TS) != 0 &&
2333             SEQ_LEQ(th->th_seq, tp->last_ack_sent) &&
2334             SEQ_LEQ(tp->last_ack_sent, th->th_seq + tlen +
2335                 ((thflags & (TH_SYN|TH_FIN)) != 0))) {
2336                 tp->ts_recent_age = tcp_ts_getticks();
2337                 tp->ts_recent = to.to_tsval;
2338         }
2339
2340         /*
2341          * If a SYN is in the window, then this is an
2342          * error and we send an RST and drop the connection.
2343          */
2344         if (thflags & TH_SYN) {
2345                 KASSERT(ti_locked == TI_WLOCKED,
2346                     ("tcp_do_segment: TH_SYN ti_locked %d", ti_locked));
2347                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
2348
2349                 tp = tcp_drop(tp, ECONNRESET);
2350                 rstreason = BANDLIM_UNLIMITED;
2351                 goto drop;
2352         }
2353
2354         /*
2355          * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
2356          * flag is on (half-synchronized state), then queue data for
2357          * later processing; else drop segment and return.
2358          */
2359         if ((thflags & TH_ACK) == 0) {
2360                 if (tp->t_state == TCPS_SYN_RECEIVED ||
2361                     (tp->t_flags & TF_NEEDSYN)) {
2362 #ifdef TCP_RFC7413
2363                         if (tp->t_state == TCPS_SYN_RECEIVED &&
2364                             tp->t_flags & TF_FASTOPEN) {
2365                                 tp->snd_wnd = tiwin;
2366                                 cc_conn_init(tp);
2367                         }
2368 #endif
2369                         goto step6;
2370                 } else if (tp->t_flags & TF_ACKNOW)
2371                         goto dropafterack;
2372                 else
2373                         goto drop;
2374         }
2375
2376         /*
2377          * Ack processing.
2378          */
2379         switch (tp->t_state) {
2380
2381         /*
2382          * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
2383          * ESTABLISHED state and continue processing.
2384          * The ACK was checked above.
2385          */
2386         case TCPS_SYN_RECEIVED:
2387
2388                 TCPSTAT_INC(tcps_connects);
2389                 soisconnected(so);
2390                 /* Do window scaling? */
2391                 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
2392                         (TF_RCVD_SCALE|TF_REQ_SCALE)) {
2393                         tp->rcv_scale = tp->request_r_scale;
2394                         tp->snd_wnd = tiwin;
2395                 }
2396                 /*
2397                  * Make transitions:
2398                  *      SYN-RECEIVED  -> ESTABLISHED
2399                  *      SYN-RECEIVED* -> FIN-WAIT-1
2400                  */
2401                 tp->t_starttime = ticks;
2402                 if (tp->t_flags & TF_NEEDFIN) {
2403                         tcp_state_change(tp, TCPS_FIN_WAIT_1);
2404                         tp->t_flags &= ~TF_NEEDFIN;
2405                 } else {
2406                         tcp_state_change(tp, TCPS_ESTABLISHED);
2407                         TCP_PROBE5(accept__established, NULL, tp,
2408                             mtod(m, const char *), tp, th);
2409 #ifdef TCP_RFC7413
2410                         if (tp->t_tfo_pending) {
2411                                 tcp_fastopen_decrement_counter(tp->t_tfo_pending);
2412                                 tp->t_tfo_pending = NULL;
2413
2414                                 /*
2415                                  * Account for the ACK of our SYN prior to
2416                                  * regular ACK processing below.
2417                                  */
2418                                 tp->snd_una++;
2419                         }
2420                         /*
2421                          * TFO connections call cc_conn_init() during SYN
2422                          * processing.  Calling it again here for such
2423                          * connections is not harmless as it would undo the
2424                          * snd_cwnd reduction that occurs when a TFO SYN|ACK
2425                          * is retransmitted.
2426                          */
2427                         if (!(tp->t_flags & TF_FASTOPEN))
2428 #endif
2429                                 cc_conn_init(tp);
2430                         tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
2431                 }
2432                 /*
2433                  * If segment contains data or ACK, will call tcp_reass()
2434                  * later; if not, do so now to pass queued data to user.
2435                  */
2436                 if (tlen == 0 && (thflags & TH_FIN) == 0)
2437                         (void) tcp_reass(tp, (struct tcphdr *)0, 0,
2438                             (struct mbuf *)0);
2439                 tp->snd_wl1 = th->th_seq - 1;
2440                 /* FALLTHROUGH */
2441
2442         /*
2443          * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
2444          * ACKs.  If the ack is in the range
2445          *      tp->snd_una < th->th_ack <= tp->snd_max
2446          * then advance tp->snd_una to th->th_ack and drop
2447          * data from the retransmission queue.  If this ACK reflects
2448          * more up to date window information we update our window information.
2449          */
2450         case TCPS_ESTABLISHED:
2451         case TCPS_FIN_WAIT_1:
2452         case TCPS_FIN_WAIT_2:
2453         case TCPS_CLOSE_WAIT:
2454         case TCPS_CLOSING:
2455         case TCPS_LAST_ACK:
2456                 if (SEQ_GT(th->th_ack, tp->snd_max)) {
2457                         TCPSTAT_INC(tcps_rcvacktoomuch);
2458                         goto dropafterack;
2459                 }
2460                 if ((tp->t_flags & TF_SACK_PERMIT) &&
2461                     ((to.to_flags & TOF_SACK) ||
2462                      !TAILQ_EMPTY(&tp->snd_holes)))
2463                         sack_changed = tcp_sack_doack(tp, &to, th->th_ack);
2464                 else
2465                         /*
2466                          * Reset the value so that previous (valid) value
2467                          * from the last ack with SACK doesn't get used.
2468                          */
2469                         tp->sackhint.sacked_bytes = 0;
2470
2471                 /* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
2472                 hhook_run_tcp_est_in(tp, th, &to);
2473
2474                 if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
2475                         if (tlen == 0 &&
2476                             (tiwin == tp->snd_wnd ||
2477                             (tp->t_flags & TF_SACK_PERMIT))) {
2478                                 TCPSTAT_INC(tcps_rcvdupack);
2479                                 /*
2480                                  * If we have outstanding data (other than
2481                                  * a window probe), this is a completely
2482                                  * duplicate ack (ie, window info didn't
2483                                  * change), the ack is the biggest we've
2484                                  * seen and we've seen exactly our rexmt
2485                                  * threshhold of them, assume a packet
2486                                  * has been dropped and retransmit it.
2487                                  * Kludge snd_nxt & the congestion
2488                                  * window so we send only this one
2489                                  * packet.
2490                                  *
2491                                  * We know we're losing at the current
2492                                  * window size so do congestion avoidance
2493                                  * (set ssthresh to half the current window
2494                                  * and pull our congestion window back to
2495                                  * the new ssthresh).
2496                                  *
2497                                  * Dup acks mean that packets have left the
2498                                  * network (they're now cached at the receiver)
2499                                  * so bump cwnd by the amount in the receiver
2500                                  * to keep a constant cwnd packets in the
2501                                  * network.
2502                                  *
2503                                  * When using TCP ECN, notify the peer that
2504                                  * we reduced the cwnd.
2505                                  */
2506                                 /*
2507                                  * Following 2 kinds of acks should not affect
2508                                  * dupack counting:
2509                                  * 1) Old acks
2510                                  * 2) Acks with SACK but without any new SACK
2511                                  * information in them. These could result from
2512                                  * any anomaly in the network like a switch
2513                                  * duplicating packets or a possible DoS attack.
2514                                  */
2515                                 if (th->th_ack != tp->snd_una ||
2516                                     ((tp->t_flags & TF_SACK_PERMIT) &&
2517                                     !sack_changed))
2518                                         break;
2519                                 else if (!tcp_timer_active(tp, TT_REXMT))
2520                                         tp->t_dupacks = 0;
2521                                 else if (++tp->t_dupacks > tcprexmtthresh ||
2522                                      IN_FASTRECOVERY(tp->t_flags)) {
2523                                         cc_ack_received(tp, th, CC_DUPACK);
2524                                         if ((tp->t_flags & TF_SACK_PERMIT) &&
2525                                             IN_FASTRECOVERY(tp->t_flags)) {
2526                                                 int awnd;
2527
2528                                                 /*
2529                                                  * Compute the amount of data in flight first.
2530                                                  * We can inject new data into the pipe iff
2531                                                  * we have less than 1/2 the original window's
2532                                                  * worth of data in flight.
2533                                                  */
2534                                                 if (V_tcp_do_rfc6675_pipe)
2535                                                         awnd = tcp_compute_pipe(tp);
2536                                                 else
2537                                                         awnd = (tp->snd_nxt - tp->snd_fack) +
2538                                                                 tp->sackhint.sack_bytes_rexmit;
2539
2540                                                 if (awnd < tp->snd_ssthresh) {
2541                                                         tp->snd_cwnd += tp->t_maxseg;
2542                                                         if (tp->snd_cwnd > tp->snd_ssthresh)
2543                                                                 tp->snd_cwnd = tp->snd_ssthresh;
2544                                                 }
2545                                         } else
2546                                                 tp->snd_cwnd += tp->t_maxseg;
2547                                         if ((thflags & TH_FIN) &&
2548                                             (TCPS_HAVERCVDFIN(tp->t_state) == 0)) {
2549                                                 /*
2550                                                  * If its a fin we need to process
2551                                                  * it to avoid a race where both
2552                                                  * sides enter FIN-WAIT and send FIN|ACK
2553                                                  * at the same time.
2554                                                  */
2555                                                 break;
2556                                         }
2557                                         (void) tcp_output(tp);
2558                                         goto drop;
2559                                 } else if (tp->t_dupacks == tcprexmtthresh) {
2560                                         tcp_seq onxt = tp->snd_nxt;
2561
2562                                         /*
2563                                          * If we're doing sack, check to
2564                                          * see if we're already in sack
2565                                          * recovery. If we're not doing sack,
2566                                          * check to see if we're in newreno
2567                                          * recovery.
2568                                          */
2569                                         if (tp->t_flags & TF_SACK_PERMIT) {
2570                                                 if (IN_FASTRECOVERY(tp->t_flags)) {
2571                                                         tp->t_dupacks = 0;
2572                                                         break;
2573                                                 }
2574                                         } else {
2575                                                 if (SEQ_LEQ(th->th_ack,
2576                                                     tp->snd_recover)) {
2577                                                         tp->t_dupacks = 0;
2578                                                         break;
2579                                                 }
2580                                         }
2581                                         /* Congestion signal before ack. */
2582                                         cc_cong_signal(tp, th, CC_NDUPACK);
2583                                         cc_ack_received(tp, th, CC_DUPACK);
2584                                         tcp_timer_activate(tp, TT_REXMT, 0);
2585                                         tp->t_rtttime = 0;
2586                                         if (tp->t_flags & TF_SACK_PERMIT) {
2587                                                 TCPSTAT_INC(
2588                                                     tcps_sack_recovery_episode);
2589                                                 tp->sack_newdata = tp->snd_nxt;
2590                                                 tp->snd_cwnd = tp->t_maxseg;
2591                                                 (void) tcp_output(tp);
2592                                                 goto drop;
2593                                         }
2594                                         tp->snd_nxt = th->th_ack;
2595                                         tp->snd_cwnd = tp->t_maxseg;
2596                                         if ((thflags & TH_FIN) &&
2597                                             (TCPS_HAVERCVDFIN(tp->t_state) == 0)) {
2598                                                 /*
2599                                                  * If its a fin we need to process
2600                                                  * it to avoid a race where both
2601                                                  * sides enter FIN-WAIT and send FIN|ACK
2602                                                  * at the same time.
2603                                                  */
2604                                                 break;
2605                                         }
2606                                         (void) tcp_output(tp);
2607                                         KASSERT(tp->snd_limited <= 2,
2608                                             ("%s: tp->snd_limited too big",
2609                                             __func__));
2610                                         tp->snd_cwnd = tp->snd_ssthresh +
2611                                              tp->t_maxseg *
2612                                              (tp->t_dupacks - tp->snd_limited);
2613                                         if (SEQ_GT(onxt, tp->snd_nxt))
2614                                                 tp->snd_nxt = onxt;
2615                                         goto drop;
2616                                 } else if (V_tcp_do_rfc3042) {
2617                                         /*
2618                                          * Process first and second duplicate
2619                                          * ACKs. Each indicates a segment
2620                                          * leaving the network, creating room
2621                                          * for more. Make sure we can send a
2622                                          * packet on reception of each duplicate
2623                                          * ACK by increasing snd_cwnd by one
2624                                          * segment. Restore the original
2625                                          * snd_cwnd after packet transmission.
2626                                          */
2627                                         cc_ack_received(tp, th, CC_DUPACK);
2628                                         u_long oldcwnd = tp->snd_cwnd;
2629                                         tcp_seq oldsndmax = tp->snd_max;
2630                                         u_int sent;
2631                                         int avail;
2632
2633                                         KASSERT(tp->t_dupacks == 1 ||
2634                                             tp->t_dupacks == 2,
2635                                             ("%s: dupacks not 1 or 2",
2636                                             __func__));
2637                                         if (tp->t_dupacks == 1)
2638                                                 tp->snd_limited = 0;
2639                                         tp->snd_cwnd =
2640                                             (tp->snd_nxt - tp->snd_una) +
2641                                             (tp->t_dupacks - tp->snd_limited) *
2642                                             tp->t_maxseg;
2643                                         if ((thflags & TH_FIN) &&
2644                                             (TCPS_HAVERCVDFIN(tp->t_state) == 0)) {
2645                                                 /*
2646                                                  * If its a fin we need to process
2647                                                  * it to avoid a race where both
2648                                                  * sides enter FIN-WAIT and send FIN|ACK
2649                                                  * at the same time.
2650                                                  */
2651                                                 break;
2652                                         }
2653                                         /*
2654                                          * Only call tcp_output when there
2655                                          * is new data available to be sent.
2656                                          * Otherwise we would send pure ACKs.
2657                                          */
2658                                         SOCKBUF_LOCK(&so->so_snd);
2659                                         avail = so->so_snd.sb_cc -
2660                                             (tp->snd_nxt - tp->snd_una);
2661                                         SOCKBUF_UNLOCK(&so->so_snd);
2662                                         if (avail > 0)
2663                                                 (void) tcp_output(tp);
2664                                         sent = tp->snd_max - oldsndmax;
2665                                         if (sent > tp->t_maxseg) {
2666                                                 KASSERT((tp->t_dupacks == 2 &&
2667                                                     tp->snd_limited == 0) ||
2668                                                    (sent == tp->t_maxseg + 1 &&
2669                                                     tp->t_flags & TF_SENTFIN),
2670                                                     ("%s: sent too much",
2671                                                     __func__));
2672                                                 tp->snd_limited = 2;
2673                                         } else if (sent > 0)
2674                                                 ++tp->snd_limited;
2675                                         tp->snd_cwnd = oldcwnd;
2676                                         goto drop;
2677                                 }
2678                         }
2679                         break;
2680                 } else {
2681                         /*
2682                          * This ack is advancing the left edge, reset the
2683                          * counter.
2684                          */
2685                         tp->t_dupacks = 0;
2686                         /*
2687                          * If this ack also has new SACK info, increment the
2688                          * counter as per rfc6675.
2689                          */
2690                         if ((tp->t_flags & TF_SACK_PERMIT) && sack_changed)
2691                                 tp->t_dupacks++;
2692                 }
2693
2694                 KASSERT(SEQ_GT(th->th_ack, tp->snd_una),
2695                     ("%s: th_ack <= snd_una", __func__));
2696
2697                 /*
2698                  * If the congestion window was inflated to account
2699                  * for the other side's cached packets, retract it.
2700                  */
2701                 if (IN_FASTRECOVERY(tp->t_flags)) {
2702                         if (SEQ_LT(th->th_ack, tp->snd_recover)) {
2703                                 if (tp->t_flags & TF_SACK_PERMIT)
2704                                         tcp_sack_partialack(tp, th);
2705                                 else
2706                                         tcp_newreno_partial_ack(tp, th);
2707                         } else
2708                                 cc_post_recovery(tp, th);
2709                 }
2710                 /*
2711                  * If we reach this point, ACK is not a duplicate,
2712                  *     i.e., it ACKs something we sent.
2713                  */
2714                 if (tp->t_flags & TF_NEEDSYN) {
2715                         /*
2716                          * T/TCP: Connection was half-synchronized, and our
2717                          * SYN has been ACK'd (so connection is now fully
2718                          * synchronized).  Go to non-starred state,
2719                          * increment snd_una for ACK of SYN, and check if
2720                          * we can do window scaling.
2721                          */
2722                         tp->t_flags &= ~TF_NEEDSYN;
2723                         tp->snd_una++;
2724                         /* Do window scaling? */
2725                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
2726                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
2727                                 tp->rcv_scale = tp->request_r_scale;
2728                                 /* Send window already scaled. */
2729                         }
2730                 }
2731
2732 process_ACK:
2733                 INP_WLOCK_ASSERT(tp->t_inpcb);
2734
2735                 acked = BYTES_THIS_ACK(tp, th);
2736                 TCPSTAT_INC(tcps_rcvackpack);
2737                 TCPSTAT_ADD(tcps_rcvackbyte, acked);
2738
2739                 /*
2740                  * If we just performed our first retransmit, and the ACK
2741                  * arrives within our recovery window, then it was a mistake
2742                  * to do the retransmit in the first place.  Recover our
2743                  * original cwnd and ssthresh, and proceed to transmit where
2744                  * we left off.
2745                  */
2746                 if (tp->t_rxtshift == 1 && tp->t_flags & TF_PREVVALID &&
2747                     (int)(ticks - tp->t_badrxtwin) < 0)
2748                         cc_cong_signal(tp, th, CC_RTO_ERR);
2749
2750                 /*
2751                  * If we have a timestamp reply, update smoothed
2752                  * round trip time.  If no timestamp is present but
2753                  * transmit timer is running and timed sequence
2754                  * number was acked, update smoothed round trip time.
2755                  * Since we now have an rtt measurement, cancel the
2756                  * timer backoff (cf., Phil Karn's retransmit alg.).
2757                  * Recompute the initial retransmit timer.
2758                  *
2759                  * Some boxes send broken timestamp replies
2760                  * during the SYN+ACK phase, ignore
2761                  * timestamps of 0 or we could calculate a
2762                  * huge RTT and blow up the retransmit timer.
2763                  */
2764                 if ((to.to_flags & TOF_TS) != 0 && to.to_tsecr) {
2765                         u_int t;
2766
2767                         t = tcp_ts_getticks() - to.to_tsecr;
2768                         if (!tp->t_rttlow || tp->t_rttlow > t)
2769                                 tp->t_rttlow = t;
2770                         tcp_xmit_timer(tp, TCP_TS_TO_TICKS(t) + 1);
2771                 } else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
2772                         if (!tp->t_rttlow || tp->t_rttlow > ticks - tp->t_rtttime)
2773                                 tp->t_rttlow = ticks - tp->t_rtttime;
2774                         tcp_xmit_timer(tp, ticks - tp->t_rtttime);
2775                 }
2776
2777                 /*
2778                  * If all outstanding data is acked, stop retransmit
2779                  * timer and remember to restart (more output or persist).
2780                  * If there is more data to be acked, restart retransmit
2781                  * timer, using current (possibly backed-off) value.
2782                  */
2783                 if (th->th_ack == tp->snd_max) {
2784                         tcp_timer_activate(tp, TT_REXMT, 0);
2785                         needoutput = 1;
2786                 } else if (!tcp_timer_active(tp, TT_PERSIST))
2787                         tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
2788
2789                 /*
2790                  * If no data (only SYN) was ACK'd,
2791                  *    skip rest of ACK processing.
2792                  */
2793                 if (acked == 0)
2794                         goto step6;
2795
2796                 /*
2797                  * Let the congestion control algorithm update congestion
2798                  * control related information. This typically means increasing
2799                  * the congestion window.
2800                  */
2801                 cc_ack_received(tp, th, CC_ACK);
2802
2803                 SOCKBUF_LOCK(&so->so_snd);
2804                 if (acked > so->so_snd.sb_cc) {
2805                         tp->snd_wnd -= so->so_snd.sb_cc;
2806                         mfree = sbcut_locked(&so->so_snd,
2807                             (int)so->so_snd.sb_cc);
2808                         ourfinisacked = 1;
2809                 } else {
2810                         mfree = sbcut_locked(&so->so_snd, acked);
2811                         tp->snd_wnd -= acked;
2812                         ourfinisacked = 0;
2813                 }
2814                 /* NB: sowwakeup_locked() does an implicit unlock. */
2815                 sowwakeup_locked(so);
2816                 m_freem(mfree);
2817                 /* Detect una wraparound. */
2818                 if (!IN_RECOVERY(tp->t_flags) &&
2819                     SEQ_GT(tp->snd_una, tp->snd_recover) &&
2820                     SEQ_LEQ(th->th_ack, tp->snd_recover))
2821                         tp->snd_recover = th->th_ack - 1;
2822                 /* XXXLAS: Can this be moved up into cc_post_recovery? */
2823                 if (IN_RECOVERY(tp->t_flags) &&
2824                     SEQ_GEQ(th->th_ack, tp->snd_recover)) {
2825                         EXIT_RECOVERY(tp->t_flags);
2826                 }
2827                 tp->snd_una = th->th_ack;
2828                 if (tp->t_flags & TF_SACK_PERMIT) {
2829                         if (SEQ_GT(tp->snd_una, tp->snd_recover))
2830                                 tp->snd_recover = tp->snd_una;
2831                 }
2832                 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
2833                         tp->snd_nxt = tp->snd_una;
2834
2835                 switch (tp->t_state) {
2836
2837                 /*
2838                  * In FIN_WAIT_1 STATE in addition to the processing
2839                  * for the ESTABLISHED state if our FIN is now acknowledged
2840                  * then enter FIN_WAIT_2.
2841                  */
2842                 case TCPS_FIN_WAIT_1:
2843                         if (ourfinisacked) {
2844                                 /*
2845                                  * If we can't receive any more
2846                                  * data, then closing user can proceed.
2847                                  * Starting the timer is contrary to the
2848                                  * specification, but if we don't get a FIN
2849                                  * we'll hang forever.
2850                                  *
2851                                  * XXXjl:
2852                                  * we should release the tp also, and use a
2853                                  * compressed state.
2854                                  */
2855                                 if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
2856                                         soisdisconnected(so);
2857                                         tcp_timer_activate(tp, TT_2MSL,
2858                                             (tcp_fast_finwait2_recycle ?
2859                                             tcp_finwait2_timeout :
2860                                             TP_MAXIDLE(tp)));
2861                                 }
2862                                 tcp_state_change(tp, TCPS_FIN_WAIT_2);
2863                         }
2864                         break;
2865
2866                 /*
2867                  * In CLOSING STATE in addition to the processing for
2868                  * the ESTABLISHED state if the ACK acknowledges our FIN
2869                  * then enter the TIME-WAIT state, otherwise ignore
2870                  * the segment.
2871                  */
2872                 case TCPS_CLOSING:
2873                         if (ourfinisacked) {
2874                                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
2875                                 tcp_twstart(tp);
2876                                 INP_INFO_WUNLOCK(&V_tcbinfo);
2877                                 m_freem(m);
2878                                 return;
2879                         }
2880                         break;
2881
2882                 /*
2883                  * In LAST_ACK, we may still be waiting for data to drain
2884                  * and/or to be acked, as well as for the ack of our FIN.
2885                  * If our FIN is now acknowledged, delete the TCB,
2886                  * enter the closed state and return.
2887                  */
2888                 case TCPS_LAST_ACK:
2889                         if (ourfinisacked) {
2890                                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
2891                                 tp = tcp_close(tp);
2892                                 goto drop;
2893                         }
2894                         break;
2895                 }
2896         }
2897
2898 step6:
2899         INP_WLOCK_ASSERT(tp->t_inpcb);
2900
2901         /*
2902          * Update window information.
2903          * Don't look at window if no ACK: TAC's send garbage on first SYN.
2904          */
2905         if ((thflags & TH_ACK) &&
2906             (SEQ_LT(tp->snd_wl1, th->th_seq) ||
2907             (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
2908              (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
2909                 /* keep track of pure window updates */
2910                 if (tlen == 0 &&
2911                     tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
2912                         TCPSTAT_INC(tcps_rcvwinupd);
2913                 tp->snd_wnd = tiwin;
2914                 tp->snd_wl1 = th->th_seq;
2915                 tp->snd_wl2 = th->th_ack;
2916                 if (tp->snd_wnd > tp->max_sndwnd)
2917                         tp->max_sndwnd = tp->snd_wnd;
2918                 needoutput = 1;
2919         }
2920
2921         /*
2922          * Process segments with URG.
2923          */
2924         if ((thflags & TH_URG) && th->th_urp &&
2925             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2926                 /*
2927                  * This is a kludge, but if we receive and accept
2928                  * random urgent pointers, we'll crash in
2929                  * soreceive.  It's hard to imagine someone
2930                  * actually wanting to send this much urgent data.
2931                  */
2932                 SOCKBUF_LOCK(&so->so_rcv);
2933                 if (th->th_urp + so->so_rcv.sb_cc > sb_max) {
2934                         th->th_urp = 0;                 /* XXX */
2935                         thflags &= ~TH_URG;             /* XXX */
2936                         SOCKBUF_UNLOCK(&so->so_rcv);    /* XXX */
2937                         goto dodata;                    /* XXX */
2938                 }
2939                 /*
2940                  * If this segment advances the known urgent pointer,
2941                  * then mark the data stream.  This should not happen
2942                  * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
2943                  * a FIN has been received from the remote side.
2944                  * In these states we ignore the URG.
2945                  *
2946                  * According to RFC961 (Assigned Protocols),
2947                  * the urgent pointer points to the last octet
2948                  * of urgent data.  We continue, however,
2949                  * to consider it to indicate the first octet
2950                  * of data past the urgent section as the original
2951                  * spec states (in one of two places).
2952                  */
2953                 if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
2954                         tp->rcv_up = th->th_seq + th->th_urp;
2955                         so->so_oobmark = so->so_rcv.sb_cc +
2956                             (tp->rcv_up - tp->rcv_nxt) - 1;
2957                         if (so->so_oobmark == 0)
2958                                 so->so_rcv.sb_state |= SBS_RCVATMARK;
2959                         sohasoutofband(so);
2960                         tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
2961                 }
2962                 SOCKBUF_UNLOCK(&so->so_rcv);
2963                 /*
2964                  * Remove out of band data so doesn't get presented to user.
2965                  * This can happen independent of advancing the URG pointer,
2966                  * but if two URG's are pending at once, some out-of-band
2967                  * data may creep in... ick.
2968                  */
2969                 if (th->th_urp <= (u_long)tlen &&
2970                     !(so->so_options & SO_OOBINLINE)) {
2971                         /* hdr drop is delayed */
2972                         tcp_pulloutofband(so, th, m, drop_hdrlen);
2973                 }
2974         } else {
2975                 /*
2976                  * If no out of band data is expected,
2977                  * pull receive urgent pointer along
2978                  * with the receive window.
2979                  */
2980                 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
2981                         tp->rcv_up = tp->rcv_nxt;
2982         }
2983 dodata:                                                 /* XXX */
2984         INP_WLOCK_ASSERT(tp->t_inpcb);
2985
2986         /*
2987          * Process the segment text, merging it into the TCP sequencing queue,
2988          * and arranging for acknowledgment of receipt if necessary.
2989          * This process logically involves adjusting tp->rcv_wnd as data
2990          * is presented to the user (this happens in tcp_usrreq.c,
2991          * case PRU_RCVD).  If a FIN has already been received on this
2992          * connection then we just ignore the text.
2993          */
2994         tfo_syn = ((tp->t_state == TCPS_SYN_RECEIVED) &&
2995                    (tp->t_flags & TF_FASTOPEN));
2996         if ((tlen || (thflags & TH_FIN) || tfo_syn) &&
2997             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2998                 tcp_seq save_start = th->th_seq;
2999
3000                 m_adj(m, drop_hdrlen);  /* delayed header drop */
3001                 /*
3002                  * Insert segment which includes th into TCP reassembly queue
3003                  * with control block tp.  Set thflags to whether reassembly now
3004                  * includes a segment with FIN.  This handles the common case
3005                  * inline (segment is the next to be received on an established
3006                  * connection, and the queue is empty), avoiding linkage into
3007                  * and removal from the queue and repetition of various
3008                  * conversions.
3009                  * Set DELACK for segments received in order, but ack
3010                  * immediately when segments are out of order (so
3011                  * fast retransmit can work).
3012                  */
3013                 if (th->th_seq == tp->rcv_nxt &&
3014                     LIST_EMPTY(&tp->t_segq) &&
3015                     (TCPS_HAVEESTABLISHED(tp->t_state) ||
3016                      tfo_syn)) {
3017                         if (DELAY_ACK(tp, tlen) || tfo_syn)
3018                                 tp->t_flags |= TF_DELACK;
3019                         else
3020                                 tp->t_flags |= TF_ACKNOW;
3021                         tp->rcv_nxt += tlen;
3022                         thflags = th->th_flags & TH_FIN;
3023                         TCPSTAT_INC(tcps_rcvpack);
3024                         TCPSTAT_ADD(tcps_rcvbyte, tlen);
3025                         ND6_HINT(tp);
3026                         SOCKBUF_LOCK(&so->so_rcv);
3027                         if (so->so_rcv.sb_state & SBS_CANTRCVMORE)
3028                                 m_freem(m);
3029                         else
3030                                 sbappendstream_locked(&so->so_rcv, m);
3031                         /* NB: sorwakeup_locked() does an implicit unlock. */
3032                         sorwakeup_locked(so);
3033                 } else {
3034                         /*
3035                          * XXX: Due to the header drop above "th" is
3036                          * theoretically invalid by now.  Fortunately
3037                          * m_adj() doesn't actually frees any mbufs
3038                          * when trimming from the head.
3039                          */
3040                         thflags = tcp_reass(tp, th, &tlen, m);
3041                         tp->t_flags |= TF_ACKNOW;
3042                 }
3043                 if (tlen > 0 && (tp->t_flags & TF_SACK_PERMIT))
3044                         tcp_update_sack_list(tp, save_start, save_start + tlen);
3045 #if 0
3046                 /*
3047                  * Note the amount of data that peer has sent into
3048                  * our window, in order to estimate the sender's
3049                  * buffer size.
3050                  * XXX: Unused.
3051                  */
3052                 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt))
3053                         len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
3054                 else
3055                         len = so->so_rcv.sb_hiwat;
3056 #endif
3057         } else {
3058                 m_freem(m);
3059                 thflags &= ~TH_FIN;
3060         }
3061
3062         /*
3063          * If FIN is received ACK the FIN and let the user know
3064          * that the connection is closing.
3065          */
3066         if (thflags & TH_FIN) {
3067                 if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
3068                         socantrcvmore(so);
3069                         /*
3070                          * If connection is half-synchronized
3071                          * (ie NEEDSYN flag on) then delay ACK,
3072                          * so it may be piggybacked when SYN is sent.
3073                          * Otherwise, since we received a FIN then no
3074                          * more input can be expected, send ACK now.
3075                          */
3076                         if (tp->t_flags & TF_NEEDSYN)
3077                                 tp->t_flags |= TF_DELACK;
3078                         else
3079                                 tp->t_flags |= TF_ACKNOW;
3080                         tp->rcv_nxt++;
3081                 }
3082                 switch (tp->t_state) {
3083
3084                 /*
3085                  * In SYN_RECEIVED and ESTABLISHED STATES
3086                  * enter the CLOSE_WAIT state.
3087                  */
3088                 case TCPS_SYN_RECEIVED:
3089                         tp->t_starttime = ticks;
3090                         /* FALLTHROUGH */
3091                 case TCPS_ESTABLISHED:
3092                         tcp_state_change(tp, TCPS_CLOSE_WAIT);
3093                         break;
3094
3095                 /*
3096                  * If still in FIN_WAIT_1 STATE FIN has not been acked so
3097                  * enter the CLOSING state.
3098                  */
3099                 case TCPS_FIN_WAIT_1:
3100                         tcp_state_change(tp, TCPS_CLOSING);
3101                         break;
3102
3103                 /*
3104                  * In FIN_WAIT_2 state enter the TIME_WAIT state,
3105                  * starting the time-wait timer, turning off the other
3106                  * standard timers.
3107                  */
3108                 case TCPS_FIN_WAIT_2:
3109                         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
3110                         KASSERT(ti_locked == TI_WLOCKED, ("%s: dodata "
3111                             "TCP_FIN_WAIT_2 ti_locked: %d", __func__,
3112                             ti_locked));
3113
3114                         tcp_twstart(tp);
3115                         INP_INFO_WUNLOCK(&V_tcbinfo);
3116                         return;
3117                 }
3118         }
3119         if (ti_locked == TI_WLOCKED)
3120                 INP_INFO_WUNLOCK(&V_tcbinfo);
3121         ti_locked = TI_UNLOCKED;
3122
3123 #ifdef TCPDEBUG
3124         if (so->so_options & SO_DEBUG)
3125                 tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
3126                           &tcp_savetcp, 0);
3127 #endif
3128
3129         /*
3130          * Return any desired output.
3131          */
3132         if (needoutput || (tp->t_flags & TF_ACKNOW))
3133                 (void) tcp_output(tp);
3134
3135 check_delack:
3136         KASSERT(ti_locked == TI_UNLOCKED, ("%s: check_delack ti_locked %d",
3137             __func__, ti_locked));
3138         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
3139         INP_WLOCK_ASSERT(tp->t_inpcb);
3140
3141         if (tp->t_flags & TF_DELACK) {
3142                 tp->t_flags &= ~TF_DELACK;
3143                 tcp_timer_activate(tp, TT_DELACK, tcp_delacktime);
3144         }
3145         INP_WUNLOCK(tp->t_inpcb);
3146         return;
3147
3148 dropafterack:
3149         /*
3150          * Generate an ACK dropping incoming segment if it occupies
3151          * sequence space, where the ACK reflects our state.
3152          *
3153          * We can now skip the test for the RST flag since all
3154          * paths to this code happen after packets containing
3155          * RST have been dropped.
3156          *
3157          * In the SYN-RECEIVED state, don't send an ACK unless the
3158          * segment we received passes the SYN-RECEIVED ACK test.
3159          * If it fails send a RST.  This breaks the loop in the
3160          * "LAND" DoS attack, and also prevents an ACK storm
3161          * between two listening ports that have been sent forged
3162          * SYN segments, each with the source address of the other.
3163          */
3164         if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
3165             (SEQ_GT(tp->snd_una, th->th_ack) ||
3166              SEQ_GT(th->th_ack, tp->snd_max)) ) {
3167                 rstreason = BANDLIM_RST_OPENPORT;
3168                 goto dropwithreset;
3169         }
3170 #ifdef TCPDEBUG
3171         if (so->so_options & SO_DEBUG)
3172                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
3173                           &tcp_savetcp, 0);
3174 #endif
3175         if (ti_locked == TI_WLOCKED)
3176                 INP_INFO_WUNLOCK(&V_tcbinfo);
3177         ti_locked = TI_UNLOCKED;
3178
3179         tp->t_flags |= TF_ACKNOW;
3180         (void) tcp_output(tp);
3181         INP_WUNLOCK(tp->t_inpcb);
3182         m_freem(m);
3183         return;
3184
3185 dropwithreset:
3186         if (ti_locked == TI_WLOCKED)
3187                 INP_INFO_WUNLOCK(&V_tcbinfo);
3188         ti_locked = TI_UNLOCKED;
3189
3190         if (tp != NULL) {
3191                 tcp_dropwithreset(m, th, tp, tlen, rstreason);
3192                 INP_WUNLOCK(tp->t_inpcb);
3193         } else
3194                 tcp_dropwithreset(m, th, NULL, tlen, rstreason);
3195         return;
3196
3197 drop:
3198         if (ti_locked == TI_WLOCKED) {
3199                 INP_INFO_WUNLOCK(&V_tcbinfo);
3200                 ti_locked = TI_UNLOCKED;
3201         }
3202 #ifdef INVARIANTS
3203         else
3204                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
3205 #endif
3206
3207         /*
3208          * Drop space held by incoming segment and return.
3209          */
3210 #ifdef TCPDEBUG
3211         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
3212                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
3213                           &tcp_savetcp, 0);
3214 #endif
3215         if (tp != NULL)
3216                 INP_WUNLOCK(tp->t_inpcb);
3217         m_freem(m);
3218 }
3219
3220 /*
3221  * Issue RST and make ACK acceptable to originator of segment.
3222  * The mbuf must still include the original packet header.
3223  * tp may be NULL.
3224  */
3225 static void
3226 tcp_dropwithreset(struct mbuf *m, struct tcphdr *th, struct tcpcb *tp,
3227     int tlen, int rstreason)
3228 {
3229 #ifdef INET
3230         struct ip *ip;
3231 #endif
3232 #ifdef INET6
3233         struct ip6_hdr *ip6;
3234 #endif
3235
3236         if (tp != NULL) {
3237                 INP_WLOCK_ASSERT(tp->t_inpcb);
3238         }
3239
3240         /* Don't bother if destination was broadcast/multicast. */
3241         if ((th->th_flags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
3242                 goto drop;
3243 #ifdef INET6
3244         if (mtod(m, struct ip *)->ip_v == 6) {
3245                 ip6 = mtod(m, struct ip6_hdr *);
3246                 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
3247                     IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
3248                         goto drop;
3249                 /* IPv6 anycast check is done at tcp6_input() */
3250         }
3251 #endif
3252 #if defined(INET) && defined(INET6)
3253         else
3254 #endif
3255 #ifdef INET
3256         {
3257                 ip = mtod(m, struct ip *);
3258                 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
3259                     IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
3260                     ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
3261                     in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
3262                         goto drop;
3263         }
3264 #endif
3265
3266         /* Perform bandwidth limiting. */
3267         if (badport_bandlim(rstreason) < 0)
3268                 goto drop;
3269
3270         /* tcp_respond consumes the mbuf chain. */
3271         if (th->th_flags & TH_ACK) {
3272                 tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0,
3273                     th->th_ack, TH_RST);
3274         } else {
3275                 if (th->th_flags & TH_SYN)
3276                         tlen++;
3277                 tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
3278                     (tcp_seq)0, TH_RST|TH_ACK);
3279         }
3280         return;
3281 drop:
3282         m_freem(m);
3283 }
3284
3285 /*
3286  * Parse TCP options and place in tcpopt.
3287  */
3288 static void
3289 tcp_dooptions(struct tcpopt *to, u_char *cp, int cnt, int flags)
3290 {
3291         int opt, optlen;
3292
3293         to->to_flags = 0;
3294         for (; cnt > 0; cnt -= optlen, cp += optlen) {
3295                 opt = cp[0];
3296                 if (opt == TCPOPT_EOL)
3297                         break;
3298                 if (opt == TCPOPT_NOP)
3299                         optlen = 1;
3300                 else {
3301                         if (cnt < 2)
3302                                 break;
3303                         optlen = cp[1];
3304                         if (optlen < 2 || optlen > cnt)
3305                                 break;
3306                 }
3307                 switch (opt) {
3308                 case TCPOPT_MAXSEG:
3309                         if (optlen != TCPOLEN_MAXSEG)
3310                                 continue;
3311                         if (!(flags & TO_SYN))
3312                                 continue;
3313                         to->to_flags |= TOF_MSS;
3314                         bcopy((char *)cp + 2,
3315                             (char *)&to->to_mss, sizeof(to->to_mss));
3316                         to->to_mss = ntohs(to->to_mss);
3317                         break;
3318                 case TCPOPT_WINDOW:
3319                         if (optlen != TCPOLEN_WINDOW)
3320                                 continue;
3321                         if (!(flags & TO_SYN))
3322                                 continue;
3323                         to->to_flags |= TOF_SCALE;
3324                         to->to_wscale = min(cp[2], TCP_MAX_WINSHIFT);
3325                         break;
3326                 case TCPOPT_TIMESTAMP:
3327                         if (optlen != TCPOLEN_TIMESTAMP)
3328                                 continue;
3329                         to->to_flags |= TOF_TS;
3330                         bcopy((char *)cp + 2,
3331                             (char *)&to->to_tsval, sizeof(to->to_tsval));
3332                         to->to_tsval = ntohl(to->to_tsval);
3333                         bcopy((char *)cp + 6,
3334                             (char *)&to->to_tsecr, sizeof(to->to_tsecr));
3335                         to->to_tsecr = ntohl(to->to_tsecr);
3336                         break;
3337 #ifdef TCP_SIGNATURE
3338                 /*
3339                  * XXX In order to reply to a host which has set the
3340                  * TCP_SIGNATURE option in its initial SYN, we have to
3341                  * record the fact that the option was observed here
3342                  * for the syncache code to perform the correct response.
3343                  */
3344                 case TCPOPT_SIGNATURE:
3345                         if (optlen != TCPOLEN_SIGNATURE)
3346                                 continue;
3347                         to->to_flags |= TOF_SIGNATURE;
3348                         to->to_signature = cp + 2;
3349                         break;
3350 #endif
3351                 case TCPOPT_SACK_PERMITTED:
3352                         if (optlen != TCPOLEN_SACK_PERMITTED)
3353                                 continue;
3354                         if (!(flags & TO_SYN))
3355                                 continue;
3356                         if (!V_tcp_do_sack)
3357                                 continue;
3358                         to->to_flags |= TOF_SACKPERM;
3359                         break;
3360                 case TCPOPT_SACK:
3361                         if (optlen <= 2 || (optlen - 2) % TCPOLEN_SACK != 0)
3362                                 continue;
3363                         if (flags & TO_SYN)
3364                                 continue;
3365                         to->to_flags |= TOF_SACK;
3366                         to->to_nsacks = (optlen - 2) / TCPOLEN_SACK;
3367                         to->to_sacks = cp + 2;
3368                         TCPSTAT_INC(tcps_sack_rcv_blocks);
3369                         break;
3370 #ifdef TCP_RFC7413
3371                 case TCPOPT_FAST_OPEN:
3372                         if ((optlen != TCPOLEN_FAST_OPEN_EMPTY) &&
3373                             (optlen < TCPOLEN_FAST_OPEN_MIN) &&
3374                             (optlen > TCPOLEN_FAST_OPEN_MAX))
3375                                 continue;
3376                         if (!(flags & TO_SYN))
3377                                 continue;
3378                         if (!V_tcp_fastopen_enabled)
3379                                 continue;
3380                         to->to_flags |= TOF_FASTOPEN;
3381                         to->to_tfo_len = optlen - 2;
3382                         to->to_tfo_cookie = to->to_tfo_len ? cp + 2 : NULL;
3383                         break;
3384 #endif
3385                 default:
3386                         continue;
3387                 }
3388         }
3389 }
3390
3391 /*
3392  * Pull out of band byte out of a segment so
3393  * it doesn't appear in the user's data queue.
3394  * It is still reflected in the segment length for
3395  * sequencing purposes.
3396  */
3397 static void
3398 tcp_pulloutofband(struct socket *so, struct tcphdr *th, struct mbuf *m,
3399     int off)
3400 {
3401         int cnt = off + th->th_urp - 1;
3402
3403         while (cnt >= 0) {
3404                 if (m->m_len > cnt) {
3405                         char *cp = mtod(m, caddr_t) + cnt;
3406                         struct tcpcb *tp = sototcpcb(so);
3407
3408                         INP_WLOCK_ASSERT(tp->t_inpcb);
3409
3410                         tp->t_iobc = *cp;
3411                         tp->t_oobflags |= TCPOOB_HAVEDATA;
3412                         bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
3413                         m->m_len--;
3414                         if (m->m_flags & M_PKTHDR)
3415                                 m->m_pkthdr.len--;
3416                         return;
3417                 }
3418                 cnt -= m->m_len;
3419                 m = m->m_next;
3420                 if (m == NULL)
3421                         break;
3422         }
3423         panic("tcp_pulloutofband");
3424 }
3425
3426 /*
3427  * Collect new round-trip time estimate
3428  * and update averages and current timeout.
3429  */
3430 static void
3431 tcp_xmit_timer(struct tcpcb *tp, int rtt)
3432 {
3433         int delta;
3434
3435         INP_WLOCK_ASSERT(tp->t_inpcb);
3436
3437         TCPSTAT_INC(tcps_rttupdated);
3438         tp->t_rttupdated++;
3439         if (tp->t_srtt != 0) {
3440                 /*
3441                  * srtt is stored as fixed point with 5 bits after the
3442                  * binary point (i.e., scaled by 8).  The following magic
3443                  * is equivalent to the smoothing algorithm in rfc793 with
3444                  * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
3445                  * point).  Adjust rtt to origin 0.
3446                  */
3447                 delta = ((rtt - 1) << TCP_DELTA_SHIFT)
3448                         - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
3449
3450                 if ((tp->t_srtt += delta) <= 0)
3451                         tp->t_srtt = 1;
3452
3453                 /*
3454                  * We accumulate a smoothed rtt variance (actually, a
3455                  * smoothed mean difference), then set the retransmit
3456                  * timer to smoothed rtt + 4 times the smoothed variance.
3457                  * rttvar is stored as fixed point with 4 bits after the
3458                  * binary point (scaled by 16).  The following is
3459                  * equivalent to rfc793 smoothing with an alpha of .75
3460                  * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
3461                  * rfc793's wired-in beta.
3462                  */
3463                 if (delta < 0)
3464                         delta = -delta;
3465                 delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
3466                 if ((tp->t_rttvar += delta) <= 0)
3467                         tp->t_rttvar = 1;
3468                 if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
3469                     tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
3470         } else {
3471                 /*
3472                  * No rtt measurement yet - use the unsmoothed rtt.
3473                  * Set the variance to half the rtt (so our first
3474                  * retransmit happens at 3*rtt).
3475                  */
3476                 tp->t_srtt = rtt << TCP_RTT_SHIFT;
3477                 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
3478                 tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
3479         }
3480         tp->t_rtttime = 0;
3481         tp->t_rxtshift = 0;
3482
3483         /*
3484          * the retransmit should happen at rtt + 4 * rttvar.
3485          * Because of the way we do the smoothing, srtt and rttvar
3486          * will each average +1/2 tick of bias.  When we compute
3487          * the retransmit timer, we want 1/2 tick of rounding and
3488          * 1 extra tick because of +-1/2 tick uncertainty in the
3489          * firing of the timer.  The bias will give us exactly the
3490          * 1.5 tick we need.  But, because the bias is
3491          * statistical, we have to test that we don't drop below
3492          * the minimum feasible timer (which is 2 ticks).
3493          */
3494         TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
3495                       max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
3496
3497         /*
3498          * We received an ack for a packet that wasn't retransmitted;
3499          * it is probably safe to discard any error indications we've
3500          * received recently.  This isn't quite right, but close enough
3501          * for now (a route might have failed after we sent a segment,
3502          * and the return path might not be symmetrical).
3503          */
3504         tp->t_softerror = 0;
3505 }
3506
3507 /*
3508  * Determine a reasonable value for maxseg size.
3509  * If the route is known, check route for mtu.
3510  * If none, use an mss that can be handled on the outgoing interface
3511  * without forcing IP to fragment.  If no route is found, route has no mtu,
3512  * or the destination isn't local, use a default, hopefully conservative
3513  * size (usually 512 or the default IP max size, but no more than the mtu
3514  * of the interface), as we can't discover anything about intervening
3515  * gateways or networks.  We also initialize the congestion/slow start
3516  * window to be a single segment if the destination isn't local.
3517  * While looking at the routing entry, we also initialize other path-dependent
3518  * parameters from pre-set or cached values in the routing entry.
3519  *
3520  * Also take into account the space needed for options that we
3521  * send regularly.  Make maxseg shorter by that amount to assure
3522  * that we can send maxseg amount of data even when the options
3523  * are present.  Store the upper limit of the length of options plus
3524  * data in maxopd.
3525  *
3526  * NOTE that this routine is only called when we process an incoming
3527  * segment, or an ICMP need fragmentation datagram. Outgoing SYN/ACK MSS
3528  * settings are handled in tcp_mssopt().
3529  */
3530 void
3531 tcp_mss_update(struct tcpcb *tp, int offer, int mtuoffer,
3532     struct hc_metrics_lite *metricptr, struct tcp_ifcap *cap)
3533 {
3534         int mss = 0;
3535         u_long maxmtu = 0;
3536         struct inpcb *inp = tp->t_inpcb;
3537         struct hc_metrics_lite metrics;
3538         int origoffer;
3539 #ifdef INET6
3540         int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
3541         size_t min_protoh = isipv6 ?
3542                             sizeof (struct ip6_hdr) + sizeof (struct tcphdr) :
3543                             sizeof (struct tcpiphdr);
3544 #else
3545         const size_t min_protoh = sizeof(struct tcpiphdr);
3546 #endif
3547
3548         INP_WLOCK_ASSERT(tp->t_inpcb);
3549
3550         if (mtuoffer != -1) {
3551                 KASSERT(offer == -1, ("%s: conflict", __func__));
3552                 offer = mtuoffer - min_protoh;
3553         }
3554         origoffer = offer;
3555
3556         /* Initialize. */
3557 #ifdef INET6
3558         if (isipv6) {
3559                 maxmtu = tcp_maxmtu6(&inp->inp_inc, cap);
3560                 tp->t_maxopd = tp->t_maxseg = V_tcp_v6mssdflt;
3561         }
3562 #endif
3563 #if defined(INET) && defined(INET6)
3564         else
3565 #endif
3566 #ifdef INET
3567         {
3568                 maxmtu = tcp_maxmtu(&inp->inp_inc, cap);
3569                 tp->t_maxopd = tp->t_maxseg = V_tcp_mssdflt;
3570         }
3571 #endif
3572
3573         /*
3574          * No route to sender, stay with default mss and return.
3575          */
3576         if (maxmtu == 0) {
3577                 /*
3578                  * In case we return early we need to initialize metrics
3579                  * to a defined state as tcp_hc_get() would do for us
3580                  * if there was no cache hit.
3581                  */
3582                 if (metricptr != NULL)
3583                         bzero(metricptr, sizeof(struct hc_metrics_lite));
3584                 return;
3585         }
3586
3587         /* What have we got? */
3588         switch (offer) {
3589                 case 0:
3590                         /*
3591                          * Offer == 0 means that there was no MSS on the SYN
3592                          * segment, in this case we use tcp_mssdflt as
3593                          * already assigned to t_maxopd above.
3594                          */
3595                         offer = tp->t_maxopd;
3596                         break;
3597
3598                 case -1:
3599                         /*
3600                          * Offer == -1 means that we didn't receive SYN yet.
3601                          */
3602                         /* FALLTHROUGH */
3603
3604                 default:
3605                         /*
3606                          * Prevent DoS attack with too small MSS. Round up
3607                          * to at least minmss.
3608                          */
3609                         offer = max(offer, V_tcp_minmss);
3610         }
3611
3612         /*
3613          * rmx information is now retrieved from tcp_hostcache.
3614          */
3615         tcp_hc_get(&inp->inp_inc, &metrics);
3616         if (metricptr != NULL)
3617                 bcopy(&metrics, metricptr, sizeof(struct hc_metrics_lite));
3618
3619         /*
3620          * If there's a discovered mtu int tcp hostcache, use it
3621          * else, use the link mtu.
3622          */
3623         if (metrics.rmx_mtu)
3624                 mss = min(metrics.rmx_mtu, maxmtu) - min_protoh;
3625         else {
3626 #ifdef INET6
3627                 if (isipv6) {
3628                         mss = maxmtu - min_protoh;
3629                         if (!V_path_mtu_discovery &&
3630                             !in6_localaddr(&inp->in6p_faddr))
3631                                 mss = min(mss, V_tcp_v6mssdflt);
3632                 }
3633 #endif
3634 #if defined(INET) && defined(INET6)
3635                 else
3636 #endif
3637 #ifdef INET
3638                 {
3639                         mss = maxmtu - min_protoh;
3640                         if (!V_path_mtu_discovery &&
3641                             !in_localaddr(inp->inp_faddr))
3642                                 mss = min(mss, V_tcp_mssdflt);
3643                 }
3644 #endif
3645                 /*
3646                  * XXX - The above conditional (mss = maxmtu - min_protoh)
3647                  * probably violates the TCP spec.
3648                  * The problem is that, since we don't know the
3649                  * other end's MSS, we are supposed to use a conservative
3650                  * default.  But, if we do that, then MTU discovery will
3651                  * never actually take place, because the conservative
3652                  * default is much less than the MTUs typically seen
3653                  * on the Internet today.  For the moment, we'll sweep
3654                  * this under the carpet.
3655                  *
3656                  * The conservative default might not actually be a problem
3657                  * if the only case this occurs is when sending an initial
3658                  * SYN with options and data to a host we've never talked
3659                  * to before.  Then, they will reply with an MSS value which
3660                  * will get recorded and the new parameters should get
3661                  * recomputed.  For Further Study.
3662                  */
3663         }
3664         mss = min(mss, offer);
3665
3666         /*
3667          * Sanity check: make sure that maxopd will be large
3668          * enough to allow some data on segments even if the
3669          * all the option space is used (40bytes).  Otherwise
3670          * funny things may happen in tcp_output.
3671          */
3672         mss = max(mss, 64);
3673
3674         /*
3675          * maxopd stores the maximum length of data AND options
3676          * in a segment; maxseg is the amount of data in a normal
3677          * segment.  We need to store this value (maxopd) apart
3678          * from maxseg, because now every segment carries options
3679          * and thus we normally have somewhat less data in segments.
3680          */
3681         tp->t_maxopd = mss;
3682
3683         /*
3684          * origoffer==-1 indicates that no segments were received yet.
3685          * In this case we just guess.
3686          */
3687         if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
3688             (origoffer == -1 ||
3689              (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
3690                 mss -= TCPOLEN_TSTAMP_APPA;
3691
3692         tp->t_maxseg = mss;
3693 }
3694
3695 void
3696 tcp_mss(struct tcpcb *tp, int offer)
3697 {
3698         int mss;
3699         u_long bufsize;
3700         struct inpcb *inp;
3701         struct socket *so;
3702         struct hc_metrics_lite metrics;
3703         struct tcp_ifcap cap;
3704
3705         KASSERT(tp != NULL, ("%s: tp == NULL", __func__));
3706
3707         bzero(&cap, sizeof(cap));
3708         tcp_mss_update(tp, offer, -1, &metrics, &cap);
3709
3710         mss = tp->t_maxseg;
3711         inp = tp->t_inpcb;
3712
3713         /*
3714          * If there's a pipesize, change the socket buffer to that size,
3715          * don't change if sb_hiwat is different than default (then it
3716          * has been changed on purpose with setsockopt).
3717          * Make the socket buffers an integral number of mss units;
3718          * if the mss is larger than the socket buffer, decrease the mss.
3719          */
3720         so = inp->inp_socket;
3721         SOCKBUF_LOCK(&so->so_snd);
3722         if ((so->so_snd.sb_hiwat == V_tcp_sendspace) && metrics.rmx_sendpipe)
3723                 bufsize = metrics.rmx_sendpipe;
3724         else
3725                 bufsize = so->so_snd.sb_hiwat;
3726         if (bufsize < mss)
3727                 mss = bufsize;
3728         else {
3729                 bufsize = roundup(bufsize, mss);
3730                 if (bufsize > sb_max)
3731                         bufsize = sb_max;
3732                 if (bufsize > so->so_snd.sb_hiwat)
3733                         (void)sbreserve_locked(&so->so_snd, bufsize, so, NULL);
3734         }
3735         SOCKBUF_UNLOCK(&so->so_snd);
3736         tp->t_maxseg = mss;
3737
3738         SOCKBUF_LOCK(&so->so_rcv);
3739         if ((so->so_rcv.sb_hiwat == V_tcp_recvspace) && metrics.rmx_recvpipe)
3740                 bufsize = metrics.rmx_recvpipe;
3741         else
3742                 bufsize = so->so_rcv.sb_hiwat;
3743         if (bufsize > mss) {
3744                 bufsize = roundup(bufsize, mss);
3745                 if (bufsize > sb_max)
3746                         bufsize = sb_max;
3747                 if (bufsize > so->so_rcv.sb_hiwat)
3748                         (void)sbreserve_locked(&so->so_rcv, bufsize, so, NULL);
3749         }
3750         SOCKBUF_UNLOCK(&so->so_rcv);
3751
3752         /* Check the interface for TSO capabilities. */
3753         if (cap.ifcap & CSUM_TSO) {
3754                 tp->t_flags |= TF_TSO;
3755                 tp->t_tsomax = cap.tsomax;
3756                 tp->t_tsomaxsegcount = cap.tsomaxsegcount;
3757                 tp->t_tsomaxsegsize = cap.tsomaxsegsize;
3758         }
3759 }
3760
3761 /*
3762  * Determine the MSS option to send on an outgoing SYN.
3763  */
3764 int
3765 tcp_mssopt(struct in_conninfo *inc)
3766 {
3767         int mss = 0;
3768         u_long maxmtu = 0;
3769         u_long thcmtu = 0;
3770         size_t min_protoh;
3771
3772         KASSERT(inc != NULL, ("tcp_mssopt with NULL in_conninfo pointer"));
3773
3774 #ifdef INET6
3775         if (inc->inc_flags & INC_ISIPV6) {
3776                 mss = V_tcp_v6mssdflt;
3777                 maxmtu = tcp_maxmtu6(inc, NULL);
3778                 min_protoh = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
3779         }
3780 #endif
3781 #if defined(INET) && defined(INET6)
3782         else
3783 #endif
3784 #ifdef INET
3785         {
3786                 mss = V_tcp_mssdflt;
3787                 maxmtu = tcp_maxmtu(inc, NULL);
3788                 min_protoh = sizeof(struct tcpiphdr);
3789         }
3790 #endif
3791 #if defined(INET6) || defined(INET)
3792         thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */
3793 #endif
3794
3795         if (maxmtu && thcmtu)
3796                 mss = min(maxmtu, thcmtu) - min_protoh;
3797         else if (maxmtu || thcmtu)
3798                 mss = max(maxmtu, thcmtu) - min_protoh;
3799
3800         return (mss);
3801 }
3802
3803
3804 /*
3805  * On a partial ack arrives, force the retransmission of the
3806  * next unacknowledged segment.  Do not clear tp->t_dupacks.
3807  * By setting snd_nxt to ti_ack, this forces retransmission timer to
3808  * be started again.
3809  */
3810 static void
3811 tcp_newreno_partial_ack(struct tcpcb *tp, struct tcphdr *th)
3812 {
3813         tcp_seq onxt = tp->snd_nxt;
3814         u_long  ocwnd = tp->snd_cwnd;
3815
3816         INP_WLOCK_ASSERT(tp->t_inpcb);
3817
3818         tcp_timer_activate(tp, TT_REXMT, 0);
3819         tp->t_rtttime = 0;
3820         tp->snd_nxt = th->th_ack;
3821         /*
3822          * Set snd_cwnd to one segment beyond acknowledged offset.
3823          * (tp->snd_una has not yet been updated when this function is called.)
3824          */
3825         tp->snd_cwnd = tp->t_maxseg + BYTES_THIS_ACK(tp, th);
3826         tp->t_flags |= TF_ACKNOW;
3827         (void) tcp_output(tp);
3828         tp->snd_cwnd = ocwnd;
3829         if (SEQ_GT(onxt, tp->snd_nxt))
3830                 tp->snd_nxt = onxt;
3831         /*
3832          * Partial window deflation.  Relies on fact that tp->snd_una
3833          * not updated yet.
3834          */
3835         if (tp->snd_cwnd > BYTES_THIS_ACK(tp, th))
3836                 tp->snd_cwnd -= BYTES_THIS_ACK(tp, th);
3837         else
3838                 tp->snd_cwnd = 0;
3839         tp->snd_cwnd += tp->t_maxseg;
3840 }
3841
3842 int
3843 tcp_compute_pipe(struct tcpcb *tp)
3844 {
3845         return (tp->snd_max - tp->snd_una +
3846                 tp->sackhint.sack_bytes_rexmit -
3847                 tp->sackhint.sacked_bytes);
3848 }