sys/netinet/tcp_reass.c

   1 /*-
   2  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 4. Neither the name of the University nor the names of its contributors
  14  *    may be used to endorse or promote products derived from this software
  15  *    without specific prior written permission.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  27  * SUCH DAMAGE.
  28  *
  29  *      @(#)tcp_input.c 8.12 (Berkeley) 5/24/95
  30  * $FreeBSD$
  31  */
  32
  33 #include "opt_ipfw.h"           /* for ipfw_fwd */
  34 #include "opt_inet.h"
  35 #include "opt_inet6.h"
  36 #include "opt_ipsec.h"
  37 #include "opt_mac.h"
  38 #include "opt_tcpdebug.h"
  39
  40 #include <sys/param.h>
  41 #include <sys/kernel.h>
  42 #include <sys/malloc.h>
  43 #include <sys/mbuf.h>
  44 #include <sys/proc.h>           /* for proc0 declaration */
  45 #include <sys/protosw.h>
  46 #include <sys/signalvar.h>
  47 #include <sys/socket.h>
  48 #include <sys/socketvar.h>
  49 #include <sys/sysctl.h>
  50 #include <sys/syslog.h>
  51 #include <sys/systm.h>
  52
  53 #include <machine/cpu.h>        /* before tcp_seq.h, for tcp_random18() */
  54
  55 #include <vm/uma.h>
  56
  57 #include <net/if.h>
  58 #include <net/route.h>
  59
  60 #include <netinet/in.h>
  61 #include <netinet/in_pcb.h>
  62 #include <netinet/in_systm.h>
  63 #include <netinet/in_var.h>
  64 #include <netinet/ip.h>
  65 #include <netinet/ip_icmp.h>    /* required for icmp_var.h */
  66 #include <netinet/icmp_var.h>   /* for ICMP_BANDLIM */
  67 #include <netinet/ip_var.h>
  68 #include <netinet/ip_options.h>
  69 #include <netinet/ip6.h>
  70 #include <netinet/icmp6.h>
  71 #include <netinet6/in6_pcb.h>
  72 #include <netinet6/ip6_var.h>
  73 #include <netinet6/nd6.h>
  74 #include <netinet/tcp.h>
  75 #include <netinet/tcp_fsm.h>
  76 #include <netinet/tcp_seq.h>
  77 #include <netinet/tcp_timer.h>
  78 #include <netinet/tcp_var.h>
  79 #include <netinet6/tcp6_var.h>
  80 #include <netinet/tcpip.h>
  81 #ifdef TCPDEBUG
  82 #include <netinet/tcp_debug.h>
  83 #endif /* TCPDEBUG */
  84
  85 #ifdef FAST_IPSEC
  86 #include <netipsec/ipsec.h>
  87 #include <netipsec/ipsec6.h>
  88 #endif /*FAST_IPSEC*/
  89
  90 #ifdef IPSEC
  91 #include <netinet6/ipsec.h>
  92 #include <netinet6/ipsec6.h>
  93 #include <netkey/key.h>
  94 #endif /*IPSEC*/
  95
  96 #include <machine/in_cksum.h>
  97
  98 #include <security/mac/mac_framework.h>
  99
 100 static const int tcprexmtthresh = 3;
 101
 102 struct  tcpstat tcpstat;
 103 SYSCTL_STRUCT(_net_inet_tcp, TCPCTL_STATS, stats, CTLFLAG_RW,
 104     &tcpstat , tcpstat, "TCP statistics (struct tcpstat, netinet/tcp_var.h)");
 105
 106 static int tcp_log_in_vain = 0;
 107 SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW,
 108     &tcp_log_in_vain, 0, "Log all incoming TCP segments to closed ports");
 109
 110 static int blackhole = 0;
 111 SYSCTL_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_RW,
 112     &blackhole, 0, "Do not send RST on segments to closed ports");
 113
 114 int tcp_delack_enabled = 1;
 115 SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_RW,
 116     &tcp_delack_enabled, 0,
 117     "Delay ACK to try and piggyback it onto a data packet");
 118
 119 static int drop_synfin = 0;
 120 SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_RW,
 121     &drop_synfin, 0, "Drop TCP packets with SYN+FIN set");
 122
 123 static int tcp_do_rfc3042 = 1;
 124 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3042, CTLFLAG_RW,
 125     &tcp_do_rfc3042, 0, "Enable RFC 3042 (Limited Transmit)");
 126
 127 static int tcp_do_rfc3390 = 1;
 128 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3390, CTLFLAG_RW,
 129     &tcp_do_rfc3390, 0,
 130     "Enable RFC 3390 (Increasing TCP's Initial Congestion Window)");
 131
 132 static int tcp_insecure_rst = 0;
 133 SYSCTL_INT(_net_inet_tcp, OID_AUTO, insecure_rst, CTLFLAG_RW,
 134     &tcp_insecure_rst, 0,
 135     "Follow the old (insecure) criteria for accepting RST packets");
 136
 137 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, reass, CTLFLAG_RW, 0,
 138     "TCP Segment Reassembly Queue");
 139
 140 static int tcp_reass_maxseg = 0;
 141 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, maxsegments, CTLFLAG_RDTUN,
 142     &tcp_reass_maxseg, 0,
 143     "Global maximum number of TCP Segments in Reassembly Queue");
 144
 145 int tcp_reass_qsize = 0;
 146 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, cursegments, CTLFLAG_RD,
 147     &tcp_reass_qsize, 0,
 148     "Global number of TCP Segments currently in Reassembly Queue");
 149
 150 static int tcp_reass_maxqlen = 48;
 151 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, maxqlen, CTLFLAG_RW,
 152     &tcp_reass_maxqlen, 0,
 153     "Maximum number of TCP Segments per individual Reassembly Queue");
 154
 155 static int tcp_reass_overflows = 0;
 156 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, overflows, CTLFLAG_RD,
 157     &tcp_reass_overflows, 0,
 158     "Global number of TCP Segment Reassembly Queue Overflows");
 159
 160 int     tcp_do_autorcvbuf = 1;
 161 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_auto, CTLFLAG_RW,
 162     &tcp_do_autorcvbuf, 0, "Enable automatic receive buffer sizing");
 163
 164 int     tcp_autorcvbuf_inc = 16*1024;
 165 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_inc, CTLFLAG_RW,
 166     &tcp_autorcvbuf_inc, 0,
 167     "Incrementor step size of automatic receive buffer");
 168
 169 int     tcp_autorcvbuf_max = 256*1024;
 170 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_max, CTLFLAG_RW,
 171     &tcp_autorcvbuf_max, 0, "Max size of automatic receive buffer");
 172
 173 struct inpcbhead tcb;
 174 #define tcb6    tcb  /* for KAME src sync over BSD*'s */
 175 struct inpcbinfo tcbinfo;
 176 struct mtx      *tcbinfo_mtx;
 177
 178 static void      tcp_dooptions(struct tcpopt *, u_char *, int, int);
 179 static int       tcp_do_segment(struct mbuf *, struct tcphdr *,
 180                      struct socket *, struct tcpcb *, int, int);
 181 static void      tcp_dropwithreset(struct mbuf *, struct tcphdr *,
 182                      struct tcpcb *, int, int);
 183 static void      tcp_pulloutofband(struct socket *,
 184                      struct tcphdr *, struct mbuf *, int);
 185 static int       tcp_reass(struct tcpcb *, struct tcphdr *, int *,
 186                      struct mbuf *);
 187 static void      tcp_xmit_timer(struct tcpcb *, int);
 188 static void      tcp_newreno_partial_ack(struct tcpcb *, struct tcphdr *);
 189 static int       tcp_timewait(struct inpcb *, struct tcpopt *,
 190                      struct tcphdr *, struct mbuf *, int);
 191
 192 /* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */
 193 #ifdef INET6
 194 #define ND6_HINT(tp) \
 195 do { \
 196         if ((tp) && (tp)->t_inpcb && \
 197             ((tp)->t_inpcb->inp_vflag & INP_IPV6) != 0) \
 198                 nd6_nud_hint(NULL, NULL, 0); \
 199 } while (0)
 200 #else
 201 #define ND6_HINT(tp)
 202 #endif
 203
 204 /*
 205  * Indicate whether this ack should be delayed.  We can delay the ack if
 206  *      - there is no delayed ack timer in progress and
 207  *      - our last ack wasn't a 0-sized window.  We never want to delay
 208  *        the ack that opens up a 0-sized window and
 209  *              - delayed acks are enabled or
 210  *              - this is a half-synchronized T/TCP connection.
 211  */
 212 #define DELAY_ACK(tp)                                                   \
 213         ((!callout_active(tp->tt_delack) &&                             \
 214             (tp->t_flags & TF_RXWIN0SENT) == 0) &&                      \
 215             (tcp_delack_enabled || (tp->t_flags & TF_NEEDSYN)))
 216
 217 /* Initialize TCP reassembly queue */
 218 static void
 219 tcp_reass_zone_change(void *tag)
 220 {
 221
 222         tcp_reass_maxseg = nmbclusters / 16;
 223         uma_zone_set_max(tcp_reass_zone, tcp_reass_maxseg);
 224 }
 225
 226 uma_zone_t      tcp_reass_zone;
 227 void
 228 tcp_reass_init()
 229 {
 230         tcp_reass_maxseg = nmbclusters / 16;
 231         TUNABLE_INT_FETCH("net.inet.tcp.reass.maxsegments",
 232             &tcp_reass_maxseg);
 233         tcp_reass_zone = uma_zcreate("tcpreass", sizeof (struct tseg_qent),
 234             NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE);
 235         uma_zone_set_max(tcp_reass_zone, tcp_reass_maxseg);
 236         EVENTHANDLER_REGISTER(nmbclusters_change,
 237             tcp_reass_zone_change, NULL, EVENTHANDLER_PRI_ANY);
 238 }
 239
 240 static int
 241 tcp_reass(struct tcpcb *tp, struct tcphdr *th, int *tlenp, struct mbuf *m)
 242 {
 243         struct tseg_qent *q;
 244         struct tseg_qent *p = NULL;
 245         struct tseg_qent *nq;
 246         struct tseg_qent *te = NULL;
 247         struct socket *so = tp->t_inpcb->inp_socket;
 248         int flags;
 249
 250         INP_LOCK_ASSERT(tp->t_inpcb);
 251
 252         /*
 253          * XXX: tcp_reass() is rather inefficient with its data structures
 254          * and should be rewritten (see NetBSD for optimizations).  While
 255          * doing that it should move to its own file tcp_reass.c.
 256          */
 257
 258         /*
 259          * Call with th==NULL after become established to
 260          * force pre-ESTABLISHED data up to user socket.
 261          */
 262         if (th == NULL)
 263                 goto present;
 264
 265         /*
 266          * Limit the number of segments in the reassembly queue to prevent
 267          * holding on to too many segments (and thus running out of mbufs).
 268          * Make sure to let the missing segment through which caused this
 269          * queue.  Always keep one global queue entry spare to be able to
 270          * process the missing segment.
 271          */
 272         if (th->th_seq != tp->rcv_nxt &&
 273             (tcp_reass_qsize + 1 >= tcp_reass_maxseg ||
 274              tp->t_segqlen >= tcp_reass_maxqlen)) {
 275                 tcp_reass_overflows++;
 276                 tcpstat.tcps_rcvmemdrop++;
 277                 m_freem(m);
 278                 *tlenp = 0;
 279                 return (0);
 280         }
 281
 282         /*
 283          * Allocate a new queue entry. If we can't, or hit the zone limit
 284          * just drop the pkt.
 285          */
 286         te = uma_zalloc(tcp_reass_zone, M_NOWAIT);
 287         if (te == NULL) {
 288                 tcpstat.tcps_rcvmemdrop++;
 289                 m_freem(m);
 290                 *tlenp = 0;
 291                 return (0);
 292         }
 293         tp->t_segqlen++;
 294         tcp_reass_qsize++;
 295
 296         /*
 297          * Find a segment which begins after this one does.
 298          */
 299         LIST_FOREACH(q, &tp->t_segq, tqe_q) {
 300                 if (SEQ_GT(q->tqe_th->th_seq, th->th_seq))
 301                         break;
 302                 p = q;
 303         }
 304
 305         /*
 306          * If there is a preceding segment, it may provide some of
 307          * our data already.  If so, drop the data from the incoming
 308          * segment.  If it provides all of our data, drop us.
 309          */
 310         if (p != NULL) {
 311                 int i;
 312                 /* conversion to int (in i) handles seq wraparound */
 313                 i = p->tqe_th->th_seq + p->tqe_len - th->th_seq;
 314                 if (i > 0) {
 315                         if (i >= *tlenp) {
 316                                 tcpstat.tcps_rcvduppack++;
 317                                 tcpstat.tcps_rcvdupbyte += *tlenp;
 318                                 m_freem(m);
 319                                 uma_zfree(tcp_reass_zone, te);
 320                                 tp->t_segqlen--;
 321                                 tcp_reass_qsize--;
 322                                 /*
 323                                  * Try to present any queued data
 324                                  * at the left window edge to the user.
 325                                  * This is needed after the 3-WHS
 326                                  * completes.
 327                                  */
 328                                 goto present;   /* ??? */
 329                         }
 330                         m_adj(m, i);
 331                         *tlenp -= i;
 332                         th->th_seq += i;
 333                 }
 334         }
 335         tcpstat.tcps_rcvoopack++;
 336         tcpstat.tcps_rcvoobyte += *tlenp;
 337
 338         /*
 339          * While we overlap succeeding segments trim them or,
 340          * if they are completely covered, dequeue them.
 341          */
 342         while (q) {
 343                 int i = (th->th_seq + *tlenp) - q->tqe_th->th_seq;
 344                 if (i <= 0)
 345                         break;
 346                 if (i < q->tqe_len) {
 347                         q->tqe_th->th_seq += i;
 348                         q->tqe_len -= i;
 349                         m_adj(q->tqe_m, i);
 350                         break;
 351                 }
 352
 353                 nq = LIST_NEXT(q, tqe_q);
 354                 LIST_REMOVE(q, tqe_q);
 355                 m_freem(q->tqe_m);
 356                 uma_zfree(tcp_reass_zone, q);
 357                 tp->t_segqlen--;
 358                 tcp_reass_qsize--;
 359                 q = nq;
 360         }
 361
 362         /* Insert the new segment queue entry into place. */
 363         te->tqe_m = m;
 364         te->tqe_th = th;
 365         te->tqe_len = *tlenp;
 366
 367         if (p == NULL) {
 368                 LIST_INSERT_HEAD(&tp->t_segq, te, tqe_q);
 369         } else {
 370                 LIST_INSERT_AFTER(p, te, tqe_q);
 371         }
 372
 373 present:
 374         /*
 375          * Present data to user, advancing rcv_nxt through
 376          * completed sequence space.
 377          */
 378         if (!TCPS_HAVEESTABLISHED(tp->t_state))
 379                 return (0);
 380         q = LIST_FIRST(&tp->t_segq);
 381         if (!q || q->tqe_th->th_seq != tp->rcv_nxt)
 382                 return (0);
 383         SOCKBUF_LOCK(&so->so_rcv);
 384         do {
 385                 tp->rcv_nxt += q->tqe_len;
 386                 flags = q->tqe_th->th_flags & TH_FIN;
 387                 nq = LIST_NEXT(q, tqe_q);
 388                 LIST_REMOVE(q, tqe_q);
 389                 if (so->so_rcv.sb_state & SBS_CANTRCVMORE)
 390                         m_freem(q->tqe_m);
 391                 else
 392                         sbappendstream_locked(&so->so_rcv, q->tqe_m);
 393                 uma_zfree(tcp_reass_zone, q);
 394                 tp->t_segqlen--;
 395                 tcp_reass_qsize--;
 396                 q = nq;
 397         } while (q && q->tqe_th->th_seq == tp->rcv_nxt);
 398         ND6_HINT(tp);
 399         sorwakeup_locked(so);
 400         return (flags);
 401 }
 402
 403 /*
 404  * TCP input routine, follows pages 65-76 of the
 405  * protocol specification dated September, 1981 very closely.
 406  */
 407 #ifdef INET6
 408 int
 409 tcp6_input(struct mbuf **mp, int *offp, int proto)
 410 {
 411         struct mbuf *m = *mp;
 412         struct in6_ifaddr *ia6;
 413
 414         IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
 415
 416         /*
 417          * draft-itojun-ipv6-tcp-to-anycast
 418          * better place to put this in?
 419          */
 420         ia6 = ip6_getdstifaddr(m);
 421         if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
 422                 struct ip6_hdr *ip6;
 423
 424                 ip6 = mtod(m, struct ip6_hdr *);
 425                 icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
 426                             (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
 427                 return IPPROTO_DONE;
 428         }
 429
 430         tcp_input(m, *offp);
 431         return IPPROTO_DONE;
 432 }
 433 #endif
 434
 435 void
 436 tcp_input(struct mbuf *m, int off0)
 437 {
 438         struct tcphdr *th;
 439         struct ip *ip = NULL;
 440         struct ipovly *ipov;
 441         struct inpcb *inp = NULL;
 442         struct tcpcb *tp = NULL;
 443         struct socket *so = NULL;
 444         u_char *optp = NULL;
 445         int optlen = 0;
 446         int len, tlen, off;
 447         int drop_hdrlen;
 448         int thflags;
 449         int rstreason = 0;      /* For badport_bandlim accounting purposes */
 450 #ifdef IPFIREWALL_FORWARD
 451         struct m_tag *fwd_tag;
 452 #endif
 453 #ifdef INET6
 454         struct ip6_hdr *ip6 = NULL;
 455         int isipv6;
 456         char ip6buf[INET6_ADDRSTRLEN];
 457 #else
 458         const int isipv6 = 0;
 459 #endif
 460         struct tcpopt to;               /* options in this segment */
 461
 462 #ifdef TCPDEBUG
 463         /*
 464          * The size of tcp_saveipgen must be the size of the max ip header,
 465          * now IPv6.
 466          */
 467         u_char tcp_saveipgen[IP6_HDR_LEN];
 468         struct tcphdr tcp_savetcp;
 469         short ostate = 0;
 470 #endif
 471
 472 #ifdef INET6
 473         isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
 474 #endif
 475
 476         to.to_flags = 0;
 477         tcpstat.tcps_rcvtotal++;
 478
 479         if (isipv6) {
 480 #ifdef INET6
 481                 /* IP6_EXTHDR_CHECK() is already done at tcp6_input() */
 482                 ip6 = mtod(m, struct ip6_hdr *);
 483                 tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
 484                 if (in6_cksum(m, IPPROTO_TCP, off0, tlen)) {
 485                         tcpstat.tcps_rcvbadsum++;
 486                         goto drop;
 487                 }
 488                 th = (struct tcphdr *)((caddr_t)ip6 + off0);
 489
 490                 /*
 491                  * Be proactive about unspecified IPv6 address in source.
 492                  * As we use all-zero to indicate unbounded/unconnected pcb,
 493                  * unspecified IPv6 address can be used to confuse us.
 494                  *
 495                  * Note that packets with unspecified IPv6 destination is
 496                  * already dropped in ip6_input.
 497                  */
 498                 if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
 499                         /* XXX stat */
 500                         goto drop;
 501                 }
 502 #else
 503                 th = NULL;              /* XXX: avoid compiler warning */
 504 #endif
 505         } else {
 506                 /*
 507                  * Get IP and TCP header together in first mbuf.
 508                  * Note: IP leaves IP header in first mbuf.
 509                  */
 510                 if (off0 > sizeof (struct ip)) {
 511                         ip_stripoptions(m, (struct mbuf *)0);
 512                         off0 = sizeof(struct ip);
 513                 }
 514                 if (m->m_len < sizeof (struct tcpiphdr)) {
 515                         if ((m = m_pullup(m, sizeof (struct tcpiphdr)))
 516                             == NULL) {
 517                                 tcpstat.tcps_rcvshort++;
 518                                 return;
 519                         }
 520                 }
 521                 ip = mtod(m, struct ip *);
 522                 ipov = (struct ipovly *)ip;
 523                 th = (struct tcphdr *)((caddr_t)ip + off0);
 524                 tlen = ip->ip_len;
 525
 526                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
 527                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
 528                                 th->th_sum = m->m_pkthdr.csum_data;
 529                         else
 530                                 th->th_sum = in_pseudo(ip->ip_src.s_addr,
 531                                                 ip->ip_dst.s_addr,
 532                                                 htonl(m->m_pkthdr.csum_data +
 533                                                         ip->ip_len +
 534                                                         IPPROTO_TCP));
 535                         th->th_sum ^= 0xffff;
 536 #ifdef TCPDEBUG
 537                         ipov->ih_len = (u_short)tlen;
 538                         ipov->ih_len = htons(ipov->ih_len);
 539 #endif
 540                 } else {
 541                         /*
 542                          * Checksum extended TCP header and data.
 543                          */
 544                         len = sizeof (struct ip) + tlen;
 545                         bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
 546                         ipov->ih_len = (u_short)tlen;
 547                         ipov->ih_len = htons(ipov->ih_len);
 548                         th->th_sum = in_cksum(m, len);
 549                 }
 550                 if (th->th_sum) {
 551                         tcpstat.tcps_rcvbadsum++;
 552                         goto drop;
 553                 }
 554                 /* Re-initialization for later version check */
 555                 ip->ip_v = IPVERSION;
 556         }
 557
 558         /*
 559          * Check that TCP offset makes sense,
 560          * pull out TCP options and adjust length.              XXX
 561          */
 562         off = th->th_off << 2;
 563         if (off < sizeof (struct tcphdr) || off > tlen) {
 564                 tcpstat.tcps_rcvbadoff++;
 565                 goto drop;
 566         }
 567         tlen -= off;    /* tlen is used instead of ti->ti_len */
 568         if (off > sizeof (struct tcphdr)) {
 569                 if (isipv6) {
 570 #ifdef INET6
 571                         IP6_EXTHDR_CHECK(m, off0, off, );
 572                         ip6 = mtod(m, struct ip6_hdr *);
 573                         th = (struct tcphdr *)((caddr_t)ip6 + off0);
 574 #endif
 575                 } else {
 576                         if (m->m_len < sizeof(struct ip) + off) {
 577                                 if ((m = m_pullup(m, sizeof (struct ip) + off))
 578                                     == NULL) {
 579                                         tcpstat.tcps_rcvshort++;
 580                                         return;
 581                                 }
 582                                 ip = mtod(m, struct ip *);
 583                                 ipov = (struct ipovly *)ip;
 584                                 th = (struct tcphdr *)((caddr_t)ip + off0);
 585                         }
 586                 }
 587                 optlen = off - sizeof (struct tcphdr);
 588                 optp = (u_char *)(th + 1);
 589         }
 590         thflags = th->th_flags;
 591
 592         /*
 593          * If the drop_synfin option is enabled, drop all packets with
 594          * both the SYN and FIN bits set. This prevents e.g. nmap from
 595          * identifying the TCP/IP stack.
 596          *
 597          * This is a violation of the TCP specification.
 598          */
 599         if (drop_synfin && (thflags & (TH_SYN|TH_FIN)) == (TH_SYN|TH_FIN))
 600                 goto drop;
 601
 602         /*
 603          * Convert TCP protocol specific fields to host format.
 604          */
 605         th->th_seq = ntohl(th->th_seq);
 606         th->th_ack = ntohl(th->th_ack);
 607         th->th_win = ntohs(th->th_win);
 608         th->th_urp = ntohs(th->th_urp);
 609
 610         /*
 611          * Delay dropping TCP, IP headers, IPv6 ext headers, and TCP options.
 612          */
 613         drop_hdrlen = off0 + off;
 614
 615         /*
 616          * Locate pcb for segment.
 617          */
 618         INP_INFO_WLOCK(&tcbinfo);
 619 findpcb:
 620         INP_INFO_WLOCK_ASSERT(&tcbinfo);
 621 #ifdef IPFIREWALL_FORWARD
 622         /* Grab info from PACKET_TAG_IPFORWARD tag prepended to the chain. */
 623         fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
 624
 625         if (fwd_tag != NULL && isipv6 == 0) {   /* IPv6 support is not yet */
 626                 struct sockaddr_in *next_hop;
 627
 628                 next_hop = (struct sockaddr_in *)(fwd_tag+1);
 629                 /*
 630                  * Transparently forwarded. Pretend to be the destination.
 631                  * already got one like this?
 632                  */
 633                 inp = in_pcblookup_hash(&tcbinfo,
 634                                         ip->ip_src, th->th_sport,
 635                                         ip->ip_dst, th->th_dport,
 636                                         0, m->m_pkthdr.rcvif);
 637                 if (!inp) {
 638                         /* It's new.  Try to find the ambushing socket. */
 639                         inp = in_pcblookup_hash(&tcbinfo,
 640                                                 ip->ip_src, th->th_sport,
 641                                                 next_hop->sin_addr,
 642                                                 next_hop->sin_port ?
 643                                                     ntohs(next_hop->sin_port) :
 644                                                     th->th_dport,
 645                                                 INPLOOKUP_WILDCARD,
 646                                                 m->m_pkthdr.rcvif);
 647                 }
 648                 /* Remove the tag from the packet.  We don't need it anymore. */
 649                 m_tag_delete(m, fwd_tag);
 650         } else
 651 #endif /* IPFIREWALL_FORWARD */
 652         {
 653                 if (isipv6) {
 654 #ifdef INET6
 655                         inp = in6_pcblookup_hash(&tcbinfo,
 656                                                  &ip6->ip6_src, th->th_sport,
 657                                                  &ip6->ip6_dst, th->th_dport,
 658                                                  INPLOOKUP_WILDCARD,
 659                                                  m->m_pkthdr.rcvif);
 660 #endif
 661                 } else
 662                         inp = in_pcblookup_hash(&tcbinfo,
 663                                                 ip->ip_src, th->th_sport,
 664                                                 ip->ip_dst, th->th_dport,
 665                                                 INPLOOKUP_WILDCARD,
 666                                                 m->m_pkthdr.rcvif);
 667         }
 668
 669 #if defined(IPSEC) || defined(FAST_IPSEC)
 670 #ifdef INET6
 671         if (isipv6 && inp != NULL && ipsec6_in_reject(m, inp)) {
 672 #ifdef IPSEC
 673                 ipsec6stat.in_polvio++;
 674 #endif
 675                 goto dropunlock;
 676         } else
 677 #endif /* INET6 */
 678         if (inp != NULL && ipsec4_in_reject(m, inp)) {
 679 #ifdef IPSEC
 680                 ipsecstat.in_polvio++;
 681 #endif
 682                 goto dropunlock;
 683         }
 684 #endif /*IPSEC || FAST_IPSEC*/
 685
 686         /*
 687          * If the INPCB does not exist then all data in the incoming
 688          * segment is discarded and an appropriate RST is sent back.
 689          */
 690         if (inp == NULL) {
 691                 /*
 692                  * Log communication attempts to ports that are not
 693                  * in use.
 694                  */
 695                 if ((tcp_log_in_vain == 1 && (thflags & TH_SYN)) ||
 696                     tcp_log_in_vain == 2) {
 697 #ifndef INET6
 698                         char dbuf[4*sizeof "123"], sbuf[4*sizeof "123"];
 699 #else
 700                         char dbuf[INET6_ADDRSTRLEN+2], sbuf[INET6_ADDRSTRLEN+2];
 701                         if (isipv6) {
 702                                 strcpy(dbuf, "[");
 703                                 strcat(dbuf,
 704                                     ip6_sprintf(ip6buf, &ip6->ip6_dst));
 705                                 strcat(dbuf, "]");
 706                                 strcpy(sbuf, "[");
 707                                 strcat(sbuf,
 708                                     ip6_sprintf(ip6buf, &ip6->ip6_src));
 709                                 strcat(sbuf, "]");
 710                         } else
 711 #endif /* INET6 */
 712                         {
 713                                 strcpy(dbuf, inet_ntoa(ip->ip_dst));
 714                                 strcpy(sbuf, inet_ntoa(ip->ip_src));
 715                         }
 716                         log(LOG_INFO,
 717                             "Connection attempt to TCP %s:%d "
 718                             "from %s:%d flags:0x%02x\n",
 719                             dbuf, ntohs(th->th_dport), sbuf,
 720                             ntohs(th->th_sport), thflags);
 721                 }
 722                 /*
 723                  * When blackholing do not respond with a RST but
 724                  * completely ignore the segment and drop it.
 725                  */
 726                 if ((blackhole == 1 && (thflags & TH_SYN)) ||
 727                     blackhole == 2)
 728                         goto dropunlock;
 729
 730                 rstreason = BANDLIM_RST_CLOSEDPORT;
 731                 goto dropwithreset;
 732         }
 733         INP_LOCK(inp);
 734
 735         /* Check the minimum TTL for socket. */
 736         if (inp->inp_ip_minttl != 0) {
 737 #ifdef INET6
 738                 if (isipv6 && inp->inp_ip_minttl > ip6->ip6_hlim)
 739                         goto dropunlock;
 740                 else
 741 #endif
 742                 if (inp->inp_ip_minttl > ip->ip_ttl)
 743                         goto dropunlock;
 744         }
 745
 746         /*
 747          * A previous connection in TIMEWAIT state is supposed to catch
 748          * stray or duplicate segments arriving late.  If this segment
 749          * was a legitimate new connection attempt the old INPCB gets
 750          * removed and we can try again to find a listening socket.
 751          */
 752         if (inp->inp_vflag & INP_TIMEWAIT) {
 753                 if (thflags & TH_SYN)
 754                         tcp_dooptions(&to, optp, optlen, TO_SYN);
 755                 if (tcp_timewait(inp, &to, th, m, tlen))
 756                         goto findpcb;
 757                 /* tcp_timewait unlocks inp. */
 758                 INP_INFO_WUNLOCK(&tcbinfo);
 759                 return;
 760         }
 761         /*
 762          * The TCPCB may no longer exist if the connection is winding
 763          * down or it is in the CLOSED state.  Either way we drop the
 764          * segment and send an appropriate response.
 765          */
 766         tp = intotcpcb(inp);
 767         if (tp == NULL) {
 768                 INP_UNLOCK(inp);
 769                 rstreason = BANDLIM_RST_CLOSEDPORT;
 770                 goto dropwithreset;
 771         }
 772         if (tp->t_state == TCPS_CLOSED)
 773                 goto dropunlock;        /* XXX: dropwithreset??? */
 774
 775 #ifdef MAC
 776         INP_LOCK_ASSERT(inp);
 777         if (mac_check_inpcb_deliver(inp, m))
 778                 goto dropunlock;
 779 #endif
 780         so = inp->inp_socket;
 781         KASSERT(so != NULL, ("%s: so == NULL", __func__));
 782 #ifdef TCPDEBUG
 783         if (so->so_options & SO_DEBUG) {
 784                 ostate = tp->t_state;
 785                 if (isipv6)
 786                         bcopy((char *)ip6, (char *)tcp_saveipgen, sizeof(*ip6));
 787                 else
 788                         bcopy((char *)ip, (char *)tcp_saveipgen, sizeof(*ip));
 789                 tcp_savetcp = *th;
 790         }
 791 #endif
 792         /*
 793          * When the socket is accepting connections (the INPCB is in LISTEN
 794          * state) we look into the SYN cache if this is a new connection
 795          * attempt or the completion of a previous one.
 796          */
 797         if (so->so_options & SO_ACCEPTCONN) {
 798                 struct in_conninfo inc;
 799
 800                 bzero(&inc, sizeof(inc));
 801                 inc.inc_isipv6 = isipv6;
 802 #ifdef INET6
 803                 if (isipv6) {
 804                         inc.inc6_faddr = ip6->ip6_src;
 805                         inc.inc6_laddr = ip6->ip6_dst;
 806                 } else
 807 #endif
 808                 {
 809                         inc.inc_faddr = ip->ip_src;
 810                         inc.inc_laddr = ip->ip_dst;
 811                 }
 812                 inc.inc_fport = th->th_sport;
 813                 inc.inc_lport = th->th_dport;
 814
 815                 /*
 816                  * If the state is LISTEN then ignore segment if it contains
 817                  * a RST.  If the segment contains an ACK then it is bad and
 818                  * send a RST.  If it does not contain a SYN then it is not
 819                  * interesting; drop it.
 820                  *
 821                  * If the state is SYN_RECEIVED (syncache) and seg contains
 822                  * an ACK, but not for our SYN/ACK, send a RST.  If the seg
 823                  * contains a RST, check the sequence number to see if it
 824                  * is a valid reset segment.
 825                  */
 826                 if ((thflags & (TH_RST|TH_ACK|TH_SYN)) != TH_SYN) {
 827                         if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
 828                                 /*
 829                                  * Parse the TCP options here because
 830                                  * syncookies need access to the reflected
 831                                  * timestamp.
 832                                  */
 833                                 tcp_dooptions(&to, optp, optlen, 0);
 834                                 if (!syncache_expand(&inc, &to, th, &so, m)) {
 835                                         /*
 836                                          * No syncache entry, or ACK was not
 837                                          * for our SYN/ACK.  Send a RST.
 838                                          */
 839                                         tcpstat.tcps_badsyn++;
 840                                         rstreason = BANDLIM_RST_OPENPORT;
 841                                         goto dropwithreset;
 842                                 }
 843                                 if (so == NULL) {
 844                                         /*
 845                                          * Could not complete 3-way handshake,
 846                                          * connection is being closed down, and
 847                                          * syncache has free'd mbuf.
 848                                          */
 849                                         INP_UNLOCK(inp);
 850                                         INP_INFO_WUNLOCK(&tcbinfo);
 851                                         return;
 852                                 }
 853                                 /*
 854                                  * Socket is created in state SYN_RECEIVED.
 855                                  * Continue processing segment.
 856                                  */
 857                                 INP_UNLOCK(inp);        /* listen socket */
 858                                 inp = sotoinpcb(so);
 859                                 INP_LOCK(inp);          /* new connection */
 860                                 tp = intotcpcb(inp);
 861                                 /*
 862                                  * Process the segment and the data it
 863                                  * contains.  tcp_do_segment() consumes
 864                                  * the mbuf chain and unlocks the inpcb.
 865                                  * XXX: The potential return value of
 866                                  * TIME_WAIT nuked is supposed to be
 867                                  * handled above.
 868                                  */
 869                                 if (tcp_do_segment(m, th, so, tp,
 870                                                    drop_hdrlen, tlen))
 871                                         goto findpcb;   /* TIME_WAIT nuked */
 872                                 return;
 873                         }
 874                         if (thflags & TH_RST) {
 875                                 syncache_chkrst(&inc, th);
 876                                 goto dropunlock;
 877                         }
 878                         if (thflags & TH_ACK) {
 879                                 syncache_badack(&inc);
 880                                 tcpstat.tcps_badsyn++;
 881                                 rstreason = BANDLIM_RST_OPENPORT;
 882                                 goto dropwithreset;
 883                         }
 884                         goto dropunlock;
 885                 }
 886
 887                 /*
 888                  * Segment's flags are (SYN) or (SYN|FIN).
 889                  */
 890 #ifdef INET6
 891                 /*
 892                  * If deprecated address is forbidden,
 893                  * we do not accept SYN to deprecated interface
 894                  * address to prevent any new inbound connection from
 895                  * getting established.
 896                  * When we do not accept SYN, we send a TCP RST,
 897                  * with deprecated source address (instead of dropping
 898                  * it).  We compromise it as it is much better for peer
 899                  * to send a RST, and RST will be the final packet
 900                  * for the exchange.
 901                  *
 902                  * If we do not forbid deprecated addresses, we accept
 903                  * the SYN packet.  RFC2462 does not suggest dropping
 904                  * SYN in this case.
 905                  * If we decipher RFC2462 5.5.4, it says like this:
 906                  * 1. use of deprecated addr with existing
 907                  *    communication is okay - "SHOULD continue to be
 908                  *    used"
 909                  * 2. use of it with new communication:
 910                  *   (2a) "SHOULD NOT be used if alternate address
 911                  *        with sufficient scope is available"
 912                  *   (2b) nothing mentioned otherwise.
 913                  * Here we fall into (2b) case as we have no choice in
 914                  * our source address selection - we must obey the peer.
 915                  *
 916                  * The wording in RFC2462 is confusing, and there are
 917                  * multiple description text for deprecated address
 918                  * handling - worse, they are not exactly the same.
 919                  * I believe 5.5.4 is the best one, so we follow 5.5.4.
 920                  */
 921                 if (isipv6 && !ip6_use_deprecated) {
 922                         struct in6_ifaddr *ia6;
 923
 924                         if ((ia6 = ip6_getdstifaddr(m)) &&
 925                             (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
 926                                 INP_UNLOCK(inp);
 927                                 tp = NULL;
 928                                 rstreason = BANDLIM_RST_OPENPORT;
 929                                 goto dropwithreset;
 930                         }
 931                 }
 932 #endif
 933                 /*
 934                  * Basic sanity checks on incoming SYN requests:
 935                  *
 936                  * Don't bother responding if the destination was a
 937                  * broadcast according to RFC1122 4.2.3.10, p. 104.
 938                  *
 939                  * If it is from this socket, drop it, it must be forged.
 940                  *
 941                  * Note that it is quite possible to receive unicast
 942                  * link-layer packets with a broadcast IP address. Use
 943                  * in_broadcast() to find them.
 944                  */
 945                 if (m->m_flags & (M_BCAST|M_MCAST))
 946                         goto dropunlock;
 947                 if (isipv6) {
 948 #ifdef INET6
 949                         if (th->th_dport == th->th_sport &&
 950                             IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &ip6->ip6_src))
 951                                 goto dropunlock;
 952                         if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
 953                             IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
 954                                 goto dropunlock;
 955 #endif
 956                 } else {
 957                         if (th->th_dport == th->th_sport &&
 958                             ip->ip_dst.s_addr == ip->ip_src.s_addr)
 959                                 goto dropunlock;
 960                         if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
 961                             IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
 962                             ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
 963                             in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
 964                                 goto dropunlock;
 965                 }
 966                 /*
 967                  * SYN appears to be valid.  Create compressed TCP state
 968                  * for syncache.
 969                  */
 970                 if (so->so_qlen <= so->so_qlimit) {
 971 #ifdef TCPDEBUG
 972                         if (so->so_options & SO_DEBUG)
 973                                 tcp_trace(TA_INPUT, ostate, tp,
 974                                     (void *)tcp_saveipgen, &tcp_savetcp, 0);
 975 #endif
 976                         tcp_dooptions(&to, optp, optlen, TO_SYN);
 977                         if (!syncache_add(&inc, &to, th, inp, &so, m))
 978                                 goto dropunlock;
 979                         /*
 980                          * Entry added to syncache, mbuf used to
 981                          * send SYN-ACK packet.  Everything unlocked
 982                          * already.
 983                          */
 984                         return;
 985                 }
 986                 /* Catch all.  Everthing that makes it down here is junk. */
 987                 goto dropunlock;
 988         }
 989
 990         /*
 991          * Segment belongs to a connection in SYN_SENT, ESTABLISHED or
 992          * later state.  tcp_do_segment() always consumes the mbuf chain
 993          * and unlocks the inpcb.
 994          */
 995         if (tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen))
 996                 goto findpcb;   /* XXX: TIME_WAIT was nuked. */
 997         return;
 998
 999 dropwithreset:
1000         INP_INFO_WLOCK_ASSERT(&tcbinfo);
1001         tcp_dropwithreset(m, th, tp, tlen, rstreason);
1002         m = NULL;       /* mbuf chain got consumed. */
1003 dropunlock:
1004         INP_INFO_WLOCK_ASSERT(&tcbinfo);
1005         if (tp != NULL)
1006                 INP_UNLOCK(inp);
1007         INP_INFO_WUNLOCK(&tcbinfo);
1008 drop:
1009         INP_INFO_UNLOCK_ASSERT(&tcbinfo);
1010         if (m != NULL)
1011                 m_freem(m);
1012         return;
1013 }
1014
1015 static int
1016 tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
1017     struct tcpcb *tp, int drop_hdrlen, int tlen)
1018 {
1019         int thflags, acked, ourfinisacked, needoutput = 0;
1020         int headlocked = 1;
1021         int rstreason, todrop, win;
1022         u_long tiwin;
1023         struct tcpopt to;
1024
1025 #ifdef TCPDEBUG
1026         /*
1027          * The size of tcp_saveipgen must be the size of the max ip header,
1028          * now IPv6.
1029          */
1030         u_char tcp_saveipgen[IP6_HDR_LEN];
1031         struct tcphdr tcp_savetcp;
1032         short ostate = 0;
1033 #endif
1034         thflags = th->th_flags;
1035
1036         INP_INFO_WLOCK_ASSERT(&tcbinfo);
1037         INP_LOCK_ASSERT(tp->t_inpcb);
1038         KASSERT(tp->t_state > TCPS_LISTEN, ("%s: TCPS_LISTEN", __func__));
1039
1040         /*
1041          * Segment received on connection.
1042          * Reset idle time and keep-alive timer.
1043          */
1044         tp->t_rcvtime = ticks;
1045         if (TCPS_HAVEESTABLISHED(tp->t_state))
1046                 callout_reset(tp->tt_keep, tcp_keepidle, tcp_timer_keep, tp);
1047
1048         /*
1049          * Unscale the window into a 32-bit value.
1050          * This value is bogus for the TCPS_SYN_SENT state
1051          * and is overwritten later.
1052          */
1053         tiwin = th->th_win << tp->snd_scale;
1054
1055         /*
1056          * Parse options on any incoming segment.
1057          */
1058         tcp_dooptions(&to, (u_char *)(th + 1),
1059             (th->th_off << 2) - sizeof(struct tcphdr),
1060             (thflags & TH_SYN) ? TO_SYN : 0);
1061
1062         /*
1063          * If echoed timestamp is later than the current time,
1064          * fall back to non RFC1323 RTT calculation.  Normalize
1065          * timestamp if syncookies were used when this connection
1066          * was established.
1067          */
1068         if ((to.to_flags & TOF_TS) && (to.to_tsecr != 0)) {
1069                 to.to_tsecr -= tp->ts_offset;
1070                 if (TSTMP_GT(to.to_tsecr, ticks))
1071                         to.to_tsecr = 0;
1072         }
1073
1074         /*
1075          * Process options only when we get SYN/ACK back. The SYN case
1076          * for incoming connections is handled in tcp_syncache.
1077          * XXX this is traditional behavior, may need to be cleaned up.
1078          */
1079         if (tp->t_state == TCPS_SYN_SENT && (thflags & TH_SYN)) {
1080                 if ((to.to_flags & TOF_SCALE) &&
1081                     (tp->t_flags & TF_REQ_SCALE)) {
1082                         tp->t_flags |= TF_RCVD_SCALE;
1083                         tp->snd_scale = to.to_wscale;
1084                         tp->snd_wnd = th->th_win << tp->snd_scale;
1085                         tiwin = tp->snd_wnd;
1086                 }
1087                 if (to.to_flags & TOF_TS) {
1088                         tp->t_flags |= TF_RCVD_TSTMP;
1089                         tp->ts_recent = to.to_tsval;
1090                         tp->ts_recent_age = ticks;
1091                 }
1092                 /* Initial send window, already scaled. */
1093                 tp->snd_wnd = th->th_win;
1094                 if (to.to_flags & TOF_MSS)
1095                         tcp_mss(tp, to.to_mss);
1096                 if (tp->sack_enable) {
1097                         if (!(to.to_flags & TOF_SACKPERM))
1098                                 tp->sack_enable = 0;
1099                         else
1100                                 tp->t_flags |= TF_SACK_PERMIT;
1101                 }
1102
1103         }
1104
1105         /*
1106          * Header prediction: check for the two common cases
1107          * of a uni-directional data xfer.  If the packet has
1108          * no control flags, is in-sequence, the window didn't
1109          * change and we're not retransmitting, it's a
1110          * candidate.  If the length is zero and the ack moved
1111          * forward, we're the sender side of the xfer.  Just
1112          * free the data acked & wake any higher level process
1113          * that was blocked waiting for space.  If the length
1114          * is non-zero and the ack didn't move, we're the
1115          * receiver side.  If we're getting packets in-order
1116          * (the reassembly queue is empty), add the data to
1117          * the socket buffer and note that we need a delayed ack.
1118          * Make sure that the hidden state-flags are also off.
1119          * Since we check for TCPS_ESTABLISHED above, it can only
1120          * be TH_NEEDSYN.
1121          */
1122         if (tp->t_state == TCPS_ESTABLISHED &&
1123             (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
1124             ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
1125             ((to.to_flags & TOF_TS) == 0 ||
1126              TSTMP_GEQ(to.to_tsval, tp->ts_recent)) &&
1127              th->th_seq == tp->rcv_nxt && tiwin && tiwin == tp->snd_wnd &&
1128              tp->snd_nxt == tp->snd_max) {
1129
1130                 /*
1131                  * If last ACK falls within this segment's sequence numbers,
1132                  * record the timestamp.
1133                  * NOTE that the test is modified according to the latest
1134                  * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1135                  */
1136                 if ((to.to_flags & TOF_TS) != 0 &&
1137                     SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
1138                         tp->ts_recent_age = ticks;
1139                         tp->ts_recent = to.to_tsval;
1140                 }
1141
1142                 if (tlen == 0) {
1143                         if (SEQ_GT(th->th_ack, tp->snd_una) &&
1144                             SEQ_LEQ(th->th_ack, tp->snd_max) &&
1145                             tp->snd_cwnd >= tp->snd_wnd &&
1146                             ((!tcp_do_newreno && !tp->sack_enable &&
1147                               tp->t_dupacks < tcprexmtthresh) ||
1148                              ((tcp_do_newreno || tp->sack_enable) &&
1149                               !IN_FASTRECOVERY(tp) &&
1150                               (to.to_flags & TOF_SACK) == 0 &&
1151                               TAILQ_EMPTY(&tp->snd_holes)))) {
1152                                 KASSERT(headlocked,
1153                                     ("%s: headlocked", __func__));
1154                                 INP_INFO_WUNLOCK(&tcbinfo);
1155                                 headlocked = 0;
1156                                 /*
1157                                  * this is a pure ack for outstanding data.
1158                                  */
1159                                 ++tcpstat.tcps_predack;
1160                                 /*
1161                                  * "bad retransmit" recovery
1162                                  */
1163                                 if (tp->t_rxtshift == 1 &&
1164                                     ticks < tp->t_badrxtwin) {
1165                                         ++tcpstat.tcps_sndrexmitbad;
1166                                         tp->snd_cwnd = tp->snd_cwnd_prev;
1167                                         tp->snd_ssthresh =
1168                                             tp->snd_ssthresh_prev;
1169                                         tp->snd_recover = tp->snd_recover_prev;
1170                                         if (tp->t_flags & TF_WASFRECOVERY)
1171                                             ENTER_FASTRECOVERY(tp);
1172                                         tp->snd_nxt = tp->snd_max;
1173                                         tp->t_badrxtwin = 0;
1174                                 }
1175
1176                                 /*
1177                                  * Recalculate the transmit timer / rtt.
1178                                  *
1179                                  * Some boxes send broken timestamp replies
1180                                  * during the SYN+ACK phase, ignore
1181                                  * timestamps of 0 or we could calculate a
1182                                  * huge RTT and blow up the retransmit timer.
1183                                  */
1184                                 if ((to.to_flags & TOF_TS) != 0 &&
1185                                     to.to_tsecr) {
1186                                         if (!tp->t_rttlow ||
1187                                             tp->t_rttlow > ticks - to.to_tsecr)
1188                                                 tp->t_rttlow = ticks - to.to_tsecr;
1189                                         tcp_xmit_timer(tp,
1190                                             ticks - to.to_tsecr + 1);
1191                                 } else if (tp->t_rtttime &&
1192                                     SEQ_GT(th->th_ack, tp->t_rtseq)) {
1193                                         if (!tp->t_rttlow ||
1194                                             tp->t_rttlow > ticks - tp->t_rtttime)
1195                                                 tp->t_rttlow = ticks - tp->t_rtttime;
1196                                         tcp_xmit_timer(tp,
1197                                                         ticks - tp->t_rtttime);
1198                                 }
1199                                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
1200                                 acked = th->th_ack - tp->snd_una;
1201                                 tcpstat.tcps_rcvackpack++;
1202                                 tcpstat.tcps_rcvackbyte += acked;
1203                                 sbdrop(&so->so_snd, acked);
1204                                 if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
1205                                     SEQ_LEQ(th->th_ack, tp->snd_recover))
1206                                         tp->snd_recover = th->th_ack - 1;
1207                                 tp->snd_una = th->th_ack;
1208                                 /*
1209                                  * pull snd_wl2 up to prevent seq wrap relative
1210                                  * to th_ack.
1211                                  */
1212                                 tp->snd_wl2 = th->th_ack;
1213                                 tp->t_dupacks = 0;
1214                                 m_freem(m);
1215                                 ND6_HINT(tp); /* some progress has been done */
1216
1217                                 /*
1218                                  * If all outstanding data are acked, stop
1219                                  * retransmit timer, otherwise restart timer
1220                                  * using current (possibly backed-off) value.
1221                                  * If process is waiting for space,
1222                                  * wakeup/selwakeup/signal.  If data
1223                                  * are ready to send, let tcp_output
1224                                  * decide between more output or persist.
1225
1226 #ifdef TCPDEBUG
1227                                 if (so->so_options & SO_DEBUG)
1228                                         tcp_trace(TA_INPUT, ostate, tp,
1229                                             (void *)tcp_saveipgen,
1230                                             &tcp_savetcp, 0);
1231 #endif
1232                                  */
1233                                 if (tp->snd_una == tp->snd_max)
1234                                         callout_stop(tp->tt_rexmt);
1235                                 else if (!callout_active(tp->tt_persist))
1236                                         callout_reset(tp->tt_rexmt,
1237                                                       tp->t_rxtcur,
1238                                                       tcp_timer_rexmt, tp);
1239
1240                                 sowwakeup(so);
1241                                 if (so->so_snd.sb_cc)
1242                                         (void) tcp_output(tp);
1243                                 goto check_delack;
1244                         }
1245                 } else if (th->th_ack == tp->snd_una &&
1246                     LIST_EMPTY(&tp->t_segq) &&
1247                     tlen <= sbspace(&so->so_rcv)) {
1248                         int newsize = 0;        /* automatic sockbuf scaling */
1249
1250                         KASSERT(headlocked, ("%s: headlocked", __func__));
1251                         INP_INFO_WUNLOCK(&tcbinfo);
1252                         headlocked = 0;
1253                         /*
1254                          * this is a pure, in-sequence data packet
1255                          * with nothing on the reassembly queue and
1256                          * we have enough buffer space to take it.
1257                          */
1258                         /* Clean receiver SACK report if present */
1259                         if (tp->sack_enable && tp->rcv_numsacks)
1260                                 tcp_clean_sackreport(tp);
1261                         ++tcpstat.tcps_preddat;
1262                         tp->rcv_nxt += tlen;
1263                         /*
1264                          * Pull snd_wl1 up to prevent seq wrap relative to
1265                          * th_seq.
1266                          */
1267                         tp->snd_wl1 = th->th_seq;
1268                         /*
1269                          * Pull rcv_up up to prevent seq wrap relative to
1270                          * rcv_nxt.
1271                          */
1272                         tp->rcv_up = tp->rcv_nxt;
1273                         tcpstat.tcps_rcvpack++;
1274                         tcpstat.tcps_rcvbyte += tlen;
1275                         ND6_HINT(tp);   /* some progress has been done */
1276 #ifdef TCPDEBUG
1277                         if (so->so_options & SO_DEBUG)
1278                                 tcp_trace(TA_INPUT, ostate, tp,
1279                                     (void *)tcp_saveipgen, &tcp_savetcp, 0);
1280 #endif
1281                 /*
1282                  * Automatic sizing of receive socket buffer.  Often the send
1283                  * buffer size is not optimally adjusted to the actual network
1284                  * conditions at hand (delay bandwidth product).  Setting the
1285                  * buffer size too small limits throughput on links with high
1286                  * bandwidth and high delay (eg. trans-continental/oceanic links).
1287                  *
1288                  * On the receive side the socket buffer memory is only rarely
1289                  * used to any significant extent.  This allows us to be much
1290                  * more aggressive in scaling the receive socket buffer.  For
1291                  * the case that the buffer space is actually used to a large
1292                  * extent and we run out of kernel memory we can simply drop
1293                  * the new segments; TCP on the sender will just retransmit it
1294                  * later.  Setting the buffer size too big may only consume too
1295                  * much kernel memory if the application doesn't read() from
1296                  * the socket or packet loss or reordering makes use of the
1297                  * reassembly queue.
1298                  *
1299                  * The criteria to step up the receive buffer one notch are:
1300                  *  1. the number of bytes received during the time it takes
1301                  *     one timestamp to be reflected back to us (the RTT);
1302                  *  2. received bytes per RTT is within seven eighth of the
1303                  *     current socket buffer size;
1304                  *  3. receive buffer size has not hit maximal automatic size;
1305                  *
1306                  * This algorithm does one step per RTT at most and only if
1307                  * we receive a bulk stream w/o packet losses or reorderings.
1308                  * Shrinking the buffer during idle times is not necessary as
1309                  * it doesn't consume any memory when idle.
1310                  *
1311                  * TODO: Only step up if the application is actually serving
1312                  * the buffer to better manage the socket buffer resources.
1313                  */
1314                         if (tcp_do_autorcvbuf &&
1315                             to.to_tsecr &&
1316                             (so->so_rcv.sb_flags & SB_AUTOSIZE)) {
1317                                 if (to.to_tsecr > tp->rfbuf_ts &&
1318                                     to.to_tsecr - tp->rfbuf_ts < hz) {
1319                                         if (tp->rfbuf_cnt >
1320                                             (so->so_rcv.sb_hiwat / 8 * 7) &&
1321                                             so->so_rcv.sb_hiwat <
1322                                             tcp_autorcvbuf_max) {
1323                                                 newsize =
1324                                                     min(so->so_rcv.sb_hiwat +
1325                                                     tcp_autorcvbuf_inc,
1326                                                     tcp_autorcvbuf_max);
1327                                         }
1328                                         /* Start over with next RTT. */
1329                                         tp->rfbuf_ts = 0;
1330                                         tp->rfbuf_cnt = 0;
1331                                 } else
1332                                         tp->rfbuf_cnt += tlen;  /* add up */
1333                         }
1334
1335                         /* Add data to socket buffer. */
1336                         SOCKBUF_LOCK(&so->so_rcv);
1337                         if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
1338                                 m_freem(m);
1339                         } else {
1340                                 /*
1341                                  * Set new socket buffer size.
1342                                  * Give up when limit is reached.
1343                                  */
1344                                 if (newsize)
1345                                         if (!sbreserve_locked(&so->so_rcv,
1346                                             newsize, so, curthread))
1347                                                 so->so_rcv.sb_flags &= ~SB_AUTOSIZE;
1348                                 m_adj(m, drop_hdrlen);  /* delayed header drop */
1349                                 sbappendstream_locked(&so->so_rcv, m);
1350                         }
1351                         sorwakeup_locked(so);
1352                         if (DELAY_ACK(tp)) {
1353                                 tp->t_flags |= TF_DELACK;
1354                         } else {
1355                                 tp->t_flags |= TF_ACKNOW;
1356                                 tcp_output(tp);
1357                         }
1358                         goto check_delack;
1359                 }
1360         }
1361
1362         /*
1363          * Calculate amount of space in receive window,
1364          * and then do TCP input processing.
1365          * Receive window is amount of space in rcv queue,
1366          * but not less than advertised window.
1367          */
1368         win = sbspace(&so->so_rcv);
1369         if (win < 0)
1370                 win = 0;
1371         tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
1372
1373         /* Reset receive buffer auto scaling when not in bulk receive mode. */
1374         tp->rfbuf_ts = 0;
1375         tp->rfbuf_cnt = 0;
1376
1377         switch (tp->t_state) {
1378
1379         /*
1380          * If the state is SYN_RECEIVED:
1381          *      if seg contains an ACK, but not for our SYN/ACK, send a RST.
1382          */
1383         case TCPS_SYN_RECEIVED:
1384                 if ((thflags & TH_ACK) &&
1385                     (SEQ_LEQ(th->th_ack, tp->snd_una) ||
1386                      SEQ_GT(th->th_ack, tp->snd_max))) {
1387                                 rstreason = BANDLIM_RST_OPENPORT;
1388                                 goto dropwithreset;
1389                 }
1390                 break;
1391
1392         /*
1393          * If the state is SYN_SENT:
1394          *      if seg contains an ACK, but not for our SYN, drop the input.
1395          *      if seg contains a RST, then drop the connection.
1396          *      if seg does not contain SYN, then drop it.
1397          * Otherwise this is an acceptable SYN segment
1398          *      initialize tp->rcv_nxt and tp->irs
1399          *      if seg contains ack then advance tp->snd_una
1400          *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
1401          *      arrange for segment to be acked (eventually)
1402          *      continue processing rest of data/controls, beginning with URG
1403          */
1404         case TCPS_SYN_SENT:
1405                 if ((thflags & TH_ACK) &&
1406                     (SEQ_LEQ(th->th_ack, tp->iss) ||
1407                      SEQ_GT(th->th_ack, tp->snd_max))) {
1408                         rstreason = BANDLIM_UNLIMITED;
1409                         goto dropwithreset;
1410                 }
1411                 if (thflags & TH_RST) {
1412                         if (thflags & TH_ACK) {
1413                                 KASSERT(headlocked, ("%s: after_listen: "
1414                                     "tcp_drop.2: head not locked", __func__));
1415                                 tp = tcp_drop(tp, ECONNREFUSED);
1416                         }
1417                         goto drop;
1418                 }
1419                 if ((thflags & TH_SYN) == 0)
1420                         goto drop;
1421
1422                 tp->irs = th->th_seq;
1423                 tcp_rcvseqinit(tp);
1424                 if (thflags & TH_ACK) {
1425                         tcpstat.tcps_connects++;
1426                         soisconnected(so);
1427 #ifdef MAC
1428                         SOCK_LOCK(so);
1429                         mac_set_socket_peer_from_mbuf(m, so);
1430                         SOCK_UNLOCK(so);
1431 #endif
1432                         /* Do window scaling on this connection? */
1433                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1434                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1435                                 tp->rcv_scale = tp->request_r_scale;
1436                         }
1437                         tp->rcv_adv += tp->rcv_wnd;
1438                         tp->snd_una++;          /* SYN is acked */
1439                         /*
1440                          * If there's data, delay ACK; if there's also a FIN
1441                          * ACKNOW will be turned on later.
1442                          */
1443                         if (DELAY_ACK(tp) && tlen != 0)
1444                                 callout_reset(tp->tt_delack, tcp_delacktime,
1445                                     tcp_timer_delack, tp);
1446                         else
1447                                 tp->t_flags |= TF_ACKNOW;
1448                         /*
1449                          * Received <SYN,ACK> in SYN_SENT[*] state.
1450                          * Transitions:
1451                          *      SYN_SENT  --> ESTABLISHED
1452                          *      SYN_SENT* --> FIN_WAIT_1
1453                          */
1454                         tp->t_starttime = ticks;
1455                         if (tp->t_flags & TF_NEEDFIN) {
1456                                 tp->t_state = TCPS_FIN_WAIT_1;
1457                                 tp->t_flags &= ~TF_NEEDFIN;
1458                                 thflags &= ~TH_SYN;
1459                         } else {
1460                                 tp->t_state = TCPS_ESTABLISHED;
1461                                 callout_reset(tp->tt_keep, tcp_keepidle,
1462                                               tcp_timer_keep, tp);
1463                         }
1464                 } else {
1465                         /*
1466                          * Received initial SYN in SYN-SENT[*] state =>
1467                          * simultaneous open.  If segment contains CC option
1468                          * and there is a cached CC, apply TAO test.
1469                          * If it succeeds, connection is * half-synchronized.
1470                          * Otherwise, do 3-way handshake:
1471                          *        SYN-SENT -> SYN-RECEIVED
1472                          *        SYN-SENT* -> SYN-RECEIVED*
1473                          * If there was no CC option, clear cached CC value.
1474                          */
1475                         tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
1476                         callout_stop(tp->tt_rexmt);
1477                         tp->t_state = TCPS_SYN_RECEIVED;
1478                 }
1479
1480                 KASSERT(headlocked, ("%s: trimthenstep6: head not locked",
1481                     __func__));
1482                 INP_LOCK_ASSERT(tp->t_inpcb);
1483
1484                 /*
1485                  * Advance th->th_seq to correspond to first data byte.
1486                  * If data, trim to stay within window,
1487                  * dropping FIN if necessary.
1488                  */
1489                 th->th_seq++;
1490                 if (tlen > tp->rcv_wnd) {
1491                         todrop = tlen - tp->rcv_wnd;
1492                         m_adj(m, -todrop);
1493                         tlen = tp->rcv_wnd;
1494                         thflags &= ~TH_FIN;
1495                         tcpstat.tcps_rcvpackafterwin++;
1496                         tcpstat.tcps_rcvbyteafterwin += todrop;
1497                 }
1498                 tp->snd_wl1 = th->th_seq - 1;
1499                 tp->rcv_up = th->th_seq;
1500                 /*
1501                  * Client side of transaction: already sent SYN and data.
1502                  * If the remote host used T/TCP to validate the SYN,
1503                  * our data will be ACK'd; if so, enter normal data segment
1504                  * processing in the middle of step 5, ack processing.
1505                  * Otherwise, goto step 6.
1506                  */
1507                 if (thflags & TH_ACK)
1508                         goto process_ACK;
1509
1510                 goto step6;
1511
1512         /*
1513          * If the state is LAST_ACK or CLOSING or TIME_WAIT:
1514          *      do normal processing.
1515          *
1516          * NB: Leftover from RFC1644 T/TCP.  Cases to be reused later.
1517          */
1518         case TCPS_LAST_ACK:
1519         case TCPS_CLOSING:
1520         case TCPS_TIME_WAIT:
1521                 KASSERT(tp->t_state != TCPS_TIME_WAIT, ("%s: timewait",
1522                     __func__));
1523                 break;  /* continue normal processing */
1524         }
1525
1526         /*
1527          * States other than LISTEN or SYN_SENT.
1528          * First check the RST flag and sequence number since reset segments
1529          * are exempt from the timestamp and connection count tests.  This
1530          * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
1531          * below which allowed reset segments in half the sequence space
1532          * to fall though and be processed (which gives forged reset
1533          * segments with a random sequence number a 50 percent chance of
1534          * killing a connection).
1535          * Then check timestamp, if present.
1536          * Then check the connection count, if present.
1537          * Then check that at least some bytes of segment are within
1538          * receive window.  If segment begins before rcv_nxt,
1539          * drop leading data (and SYN); if nothing left, just ack.
1540          *
1541          *
1542          * If the RST bit is set, check the sequence number to see
1543          * if this is a valid reset segment.
1544          * RFC 793 page 37:
1545          *   In all states except SYN-SENT, all reset (RST) segments
1546          *   are validated by checking their SEQ-fields.  A reset is
1547          *   valid if its sequence number is in the window.
1548          * Note: this does not take into account delayed ACKs, so
1549          *   we should test against last_ack_sent instead of rcv_nxt.
1550          *   The sequence number in the reset segment is normally an
1551          *   echo of our outgoing acknowlegement numbers, but some hosts
1552          *   send a reset with the sequence number at the rightmost edge
1553          *   of our receive window, and we have to handle this case.
1554          * Note 2: Paul Watson's paper "Slipping in the Window" has shown
1555          *   that brute force RST attacks are possible.  To combat this,
1556          *   we use a much stricter check while in the ESTABLISHED state,
1557          *   only accepting RSTs where the sequence number is equal to
1558          *   last_ack_sent.  In all other states (the states in which a
1559          *   RST is more likely), the more permissive check is used.
1560          * If we have multiple segments in flight, the intial reset
1561          * segment sequence numbers will be to the left of last_ack_sent,
1562          * but they will eventually catch up.
1563          * In any case, it never made sense to trim reset segments to
1564          * fit the receive window since RFC 1122 says:
1565          *   4.2.2.12  RST Segment: RFC-793 Section 3.4
1566          *
1567          *    A TCP SHOULD allow a received RST segment to include data.
1568          *
1569          *    DISCUSSION
1570          *         It has been suggested that a RST segment could contain
1571          *         ASCII text that encoded and explained the cause of the
1572          *         RST.  No standard has yet been established for such
1573          *         data.
1574          *
1575          * If the reset segment passes the sequence number test examine
1576          * the state:
1577          *    SYN_RECEIVED STATE:
1578          *      If passive open, return to LISTEN state.
1579          *      If active open, inform user that connection was refused.
1580          *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, CLOSE_WAIT STATES:
1581          *      Inform user that connection was reset, and close tcb.
1582          *    CLOSING, LAST_ACK STATES:
1583          *      Close the tcb.
1584          *    TIME_WAIT STATE:
1585          *      Drop the segment - see Stevens, vol. 2, p. 964 and
1586          *      RFC 1337.
1587          */
1588         if (thflags & TH_RST) {
1589                 if (SEQ_GEQ(th->th_seq, tp->last_ack_sent - 1) &&
1590                     SEQ_LEQ(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
1591                         switch (tp->t_state) {
1592
1593                         case TCPS_SYN_RECEIVED:
1594                                 so->so_error = ECONNREFUSED;
1595                                 goto close;
1596
1597                         case TCPS_ESTABLISHED:
1598                                 if (tcp_insecure_rst == 0 &&
1599                                     !(SEQ_GEQ(th->th_seq, tp->rcv_nxt - 1) &&
1600                                     SEQ_LEQ(th->th_seq, tp->rcv_nxt + 1)) &&
1601                                     !(SEQ_GEQ(th->th_seq, tp->last_ack_sent - 1) &&
1602                                     SEQ_LEQ(th->th_seq, tp->last_ack_sent + 1))) {
1603                                         tcpstat.tcps_badrst++;
1604                                         goto drop;
1605                                 }
1606                         case TCPS_FIN_WAIT_1:
1607                         case TCPS_FIN_WAIT_2:
1608                         case TCPS_CLOSE_WAIT:
1609                                 so->so_error = ECONNRESET;
1610                         close:
1611                                 tp->t_state = TCPS_CLOSED;
1612                                 tcpstat.tcps_drops++;
1613                                 KASSERT(headlocked, ("%s: trimthenstep6: "
1614                                     "tcp_close: head not locked", __func__));
1615                                 tp = tcp_close(tp);
1616                                 break;
1617
1618                         case TCPS_CLOSING:
1619                         case TCPS_LAST_ACK:
1620                                 KASSERT(headlocked, ("%s: trimthenstep6: "
1621                                     "tcp_close.2: head not locked", __func__));
1622                                 tp = tcp_close(tp);
1623                                 break;
1624
1625                         case TCPS_TIME_WAIT:
1626                                 KASSERT(tp->t_state != TCPS_TIME_WAIT,
1627                                     ("%s: timewait", __func__));
1628                                 break;
1629                         }
1630                 }
1631                 goto drop;
1632         }
1633
1634         /*
1635          * RFC 1323 PAWS: If we have a timestamp reply on this segment
1636          * and it's less than ts_recent, drop it.
1637          */
1638         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
1639             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
1640
1641                 /* Check to see if ts_recent is over 24 days old.  */
1642                 if ((int)(ticks - tp->ts_recent_age) > TCP_PAWS_IDLE) {
1643                         /*
1644                          * Invalidate ts_recent.  If this segment updates
1645                          * ts_recent, the age will be reset later and ts_recent
1646                          * will get a valid value.  If it does not, setting
1647                          * ts_recent to zero will at least satisfy the
1648                          * requirement that zero be placed in the timestamp
1649                          * echo reply when ts_recent isn't valid.  The
1650                          * age isn't reset until we get a valid ts_recent
1651                          * because we don't want out-of-order segments to be
1652                          * dropped when ts_recent is old.
1653                          */
1654                         tp->ts_recent = 0;
1655                 } else {
1656                         tcpstat.tcps_rcvduppack++;
1657                         tcpstat.tcps_rcvdupbyte += tlen;
1658                         tcpstat.tcps_pawsdrop++;
1659                         if (tlen)
1660                                 goto dropafterack;
1661                         goto drop;
1662                 }
1663         }
1664
1665         /*
1666          * In the SYN-RECEIVED state, validate that the packet belongs to
1667          * this connection before trimming the data to fit the receive
1668          * window.  Check the sequence number versus IRS since we know
1669          * the sequence numbers haven't wrapped.  This is a partial fix
1670          * for the "LAND" DoS attack.
1671          */
1672         if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
1673                 rstreason = BANDLIM_RST_OPENPORT;
1674                 goto dropwithreset;
1675         }
1676
1677         todrop = tp->rcv_nxt - th->th_seq;
1678         if (todrop > 0) {
1679                 if (thflags & TH_SYN) {
1680                         thflags &= ~TH_SYN;
1681                         th->th_seq++;
1682                         if (th->th_urp > 1)
1683                                 th->th_urp--;
1684                         else
1685                                 thflags &= ~TH_URG;
1686                         todrop--;
1687                 }
1688                 /*
1689                  * Following if statement from Stevens, vol. 2, p. 960.
1690                  */
1691                 if (todrop > tlen
1692                     || (todrop == tlen && (thflags & TH_FIN) == 0)) {
1693                         /*
1694                          * Any valid FIN must be to the left of the window.
1695                          * At this point the FIN must be a duplicate or out
1696                          * of sequence; drop it.
1697                          */
1698                         thflags &= ~TH_FIN;
1699
1700                         /*
1701                          * Send an ACK to resynchronize and drop any data.
1702                          * But keep on processing for RST or ACK.
1703                          */
1704                         tp->t_flags |= TF_ACKNOW;
1705                         todrop = tlen;
1706                         tcpstat.tcps_rcvduppack++;
1707                         tcpstat.tcps_rcvdupbyte += todrop;
1708                 } else {
1709                         tcpstat.tcps_rcvpartduppack++;
1710                         tcpstat.tcps_rcvpartdupbyte += todrop;
1711                 }
1712                 drop_hdrlen += todrop;  /* drop from the top afterwards */
1713                 th->th_seq += todrop;
1714                 tlen -= todrop;
1715                 if (th->th_urp > todrop)
1716                         th->th_urp -= todrop;
1717                 else {
1718                         thflags &= ~TH_URG;
1719                         th->th_urp = 0;
1720                 }
1721         }
1722
1723         /*
1724          * If new data are received on a connection after the
1725          * user processes are gone, then RST the other end.
1726          */
1727         if ((so->so_state & SS_NOFDREF) &&
1728             tp->t_state > TCPS_CLOSE_WAIT && tlen) {
1729                 KASSERT(headlocked, ("%s: trimthenstep6: tcp_close.3: head "
1730                     "not locked", __func__));
1731                 tp = tcp_close(tp);
1732                 tcpstat.tcps_rcvafterclose++;
1733                 rstreason = BANDLIM_UNLIMITED;
1734                 goto dropwithreset;
1735         }
1736
1737         /*
1738          * If segment ends after window, drop trailing data
1739          * (and PUSH and FIN); if nothing left, just ACK.
1740          */
1741         todrop = (th->th_seq+tlen) - (tp->rcv_nxt+tp->rcv_wnd);
1742         if (todrop > 0) {
1743                 tcpstat.tcps_rcvpackafterwin++;
1744                 if (todrop >= tlen) {
1745                         tcpstat.tcps_rcvbyteafterwin += tlen;
1746                         /*
1747                          * If a new connection request is received
1748                          * while in TIME_WAIT, drop the old connection
1749                          * and start over if the sequence numbers
1750                          * are above the previous ones.
1751                          */
1752                         KASSERT(tp->t_state != TCPS_TIME_WAIT, ("%s: timewait",
1753                             __func__));
1754                         if (thflags & TH_SYN &&
1755                             tp->t_state == TCPS_TIME_WAIT &&
1756                             SEQ_GT(th->th_seq, tp->rcv_nxt)) {
1757                                 KASSERT(headlocked, ("%s: trimthenstep6: "
1758                                     "tcp_close.4: head not locked", __func__));
1759                                 tp = tcp_close(tp);
1760                                 /* XXX: Shouldn't be possible. */
1761                                 return (1);
1762                         }
1763                         /*
1764                          * If window is closed can only take segments at
1765                          * window edge, and have to drop data and PUSH from
1766                          * incoming segments.  Continue processing, but
1767                          * remember to ack.  Otherwise, drop segment
1768                          * and ack.
1769                          */
1770                         if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
1771                                 tp->t_flags |= TF_ACKNOW;
1772                                 tcpstat.tcps_rcvwinprobe++;
1773                         } else
1774                                 goto dropafterack;
1775                 } else
1776                         tcpstat.tcps_rcvbyteafterwin += todrop;
1777                 m_adj(m, -todrop);
1778                 tlen -= todrop;
1779                 thflags &= ~(TH_PUSH|TH_FIN);
1780         }
1781
1782         /*
1783          * If last ACK falls within this segment's sequence numbers,
1784          * record its timestamp.
1785          * NOTE:
1786          * 1) That the test incorporates suggestions from the latest
1787          *    proposal of the tcplw@cray.com list (Braden 1993/04/26).
1788          * 2) That updating only on newer timestamps interferes with
1789          *    our earlier PAWS tests, so this check should be solely
1790          *    predicated on the sequence space of this segment.
1791          * 3) That we modify the segment boundary check to be
1792          *        Last.ACK.Sent <= SEG.SEQ + SEG.Len
1793          *    instead of RFC1323's
1794          *        Last.ACK.Sent < SEG.SEQ + SEG.Len,
1795          *    This modified check allows us to overcome RFC1323's
1796          *    limitations as described in Stevens TCP/IP Illustrated
1797          *    Vol. 2 p.869. In such cases, we can still calculate the
1798          *    RTT correctly when RCV.NXT == Last.ACK.Sent.
1799          */
1800         if ((to.to_flags & TOF_TS) != 0 &&
1801             SEQ_LEQ(th->th_seq, tp->last_ack_sent) &&
1802             SEQ_LEQ(tp->last_ack_sent, th->th_seq + tlen +
1803                 ((thflags & (TH_SYN|TH_FIN)) != 0))) {
1804                 tp->ts_recent_age = ticks;
1805                 tp->ts_recent = to.to_tsval;
1806         }
1807
1808         /*
1809          * If a SYN is in the window, then this is an
1810          * error and we send an RST and drop the connection.
1811          */
1812         if (thflags & TH_SYN) {
1813                 KASSERT(headlocked, ("%s: tcp_drop: trimthenstep6: "
1814                     "head not locked", __func__));
1815                 tp = tcp_drop(tp, ECONNRESET);
1816                 rstreason = BANDLIM_UNLIMITED;
1817                 goto drop;
1818         }
1819
1820         /*
1821          * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
1822          * flag is on (half-synchronized state), then queue data for
1823          * later processing; else drop segment and return.
1824          */
1825         if ((thflags & TH_ACK) == 0) {
1826                 if (tp->t_state == TCPS_SYN_RECEIVED ||
1827                     (tp->t_flags & TF_NEEDSYN))
1828                         goto step6;
1829                 else if (tp->t_flags & TF_ACKNOW)
1830                         goto dropafterack;
1831                 else
1832                         goto drop;
1833         }
1834
1835         /*
1836          * Ack processing.
1837          */
1838         switch (tp->t_state) {
1839
1840         /*
1841          * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
1842          * ESTABLISHED state and continue processing.
1843          * The ACK was checked above.
1844          */
1845         case TCPS_SYN_RECEIVED:
1846
1847                 tcpstat.tcps_connects++;
1848                 soisconnected(so);
1849                 /* Do window scaling? */
1850                 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1851                         (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1852                         tp->rcv_scale = tp->request_r_scale;
1853                         tp->snd_wnd = tiwin;
1854                 }
1855                 /*
1856                  * Make transitions:
1857                  *      SYN-RECEIVED  -> ESTABLISHED
1858                  *      SYN-RECEIVED* -> FIN-WAIT-1
1859                  */
1860                 tp->t_starttime = ticks;
1861                 if (tp->t_flags & TF_NEEDFIN) {
1862                         tp->t_state = TCPS_FIN_WAIT_1;
1863                         tp->t_flags &= ~TF_NEEDFIN;
1864                 } else {
1865                         tp->t_state = TCPS_ESTABLISHED;
1866                         callout_reset(tp->tt_keep, tcp_keepidle,
1867                                       tcp_timer_keep, tp);
1868                 }
1869                 /*
1870                  * If segment contains data or ACK, will call tcp_reass()
1871                  * later; if not, do so now to pass queued data to user.
1872                  */
1873                 if (tlen == 0 && (thflags & TH_FIN) == 0)
1874                         (void) tcp_reass(tp, (struct tcphdr *)0, 0,
1875                             (struct mbuf *)0);
1876                 tp->snd_wl1 = th->th_seq - 1;
1877                 /* FALLTHROUGH */
1878
1879         /*
1880          * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
1881          * ACKs.  If the ack is in the range
1882          *      tp->snd_una < th->th_ack <= tp->snd_max
1883          * then advance tp->snd_una to th->th_ack and drop
1884          * data from the retransmission queue.  If this ACK reflects
1885          * more up to date window information we update our window information.
1886          */
1887         case TCPS_ESTABLISHED:
1888         case TCPS_FIN_WAIT_1:
1889         case TCPS_FIN_WAIT_2:
1890         case TCPS_CLOSE_WAIT:
1891         case TCPS_CLOSING:
1892         case TCPS_LAST_ACK:
1893         case TCPS_TIME_WAIT:
1894                 KASSERT(tp->t_state != TCPS_TIME_WAIT, ("%s: timewait",
1895                     __func__));
1896                 if (SEQ_GT(th->th_ack, tp->snd_max)) {
1897                         tcpstat.tcps_rcvacktoomuch++;
1898                         goto dropafterack;
1899                 }
1900                 if (tp->sack_enable &&
1901                     ((to.to_flags & TOF_SACK) ||
1902                      !TAILQ_EMPTY(&tp->snd_holes)))
1903                         tcp_sack_doack(tp, &to, th->th_ack);
1904                 if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
1905                         if (tlen == 0 && tiwin == tp->snd_wnd) {
1906                                 tcpstat.tcps_rcvdupack++;
1907                                 /*
1908                                  * If we have outstanding data (other than
1909                                  * a window probe), this is a completely
1910                                  * duplicate ack (ie, window info didn't
1911                                  * change), the ack is the biggest we've
1912                                  * seen and we've seen exactly our rexmt
1913                                  * threshhold of them, assume a packet
1914                                  * has been dropped and retransmit it.
1915                                  * Kludge snd_nxt & the congestion
1916                                  * window so we send only this one
1917                                  * packet.
1918                                  *
1919                                  * We know we're losing at the current
1920                                  * window size so do congestion avoidance
1921                                  * (set ssthresh to half the current window
1922                                  * and pull our congestion window back to
1923                                  * the new ssthresh).
1924                                  *
1925                                  * Dup acks mean that packets have left the
1926                                  * network (they're now cached at the receiver)
1927                                  * so bump cwnd by the amount in the receiver
1928                                  * to keep a constant cwnd packets in the
1929                                  * network.
1930                                  */
1931                                 if (!callout_active(tp->tt_rexmt) ||
1932                                     th->th_ack != tp->snd_una)
1933                                         tp->t_dupacks = 0;
1934                                 else if (++tp->t_dupacks > tcprexmtthresh ||
1935                                     ((tcp_do_newreno || tp->sack_enable) &&
1936                                      IN_FASTRECOVERY(tp))) {
1937                                         if (tp->sack_enable && IN_FASTRECOVERY(tp)) {
1938                                                 int awnd;
1939
1940                                                 /*
1941                                                  * Compute the amount of data in flight first.
1942                                                  * We can inject new data into the pipe iff
1943                                                  * we have less than 1/2 the original window's
1944                                                  * worth of data in flight.
1945                                                  */
1946                                                 awnd = (tp->snd_nxt - tp->snd_fack) +
1947                                                         tp->sackhint.sack_bytes_rexmit;
1948                                                 if (awnd < tp->snd_ssthresh) {
1949                                                         tp->snd_cwnd += tp->t_maxseg;
1950                                                         if (tp->snd_cwnd > tp->snd_ssthresh)
1951                                                                 tp->snd_cwnd = tp->snd_ssthresh;
1952                                                 }
1953                                         } else
1954                                                 tp->snd_cwnd += tp->t_maxseg;
1955                                         (void) tcp_output(tp);
1956                                         goto drop;
1957                                 } else if (tp->t_dupacks == tcprexmtthresh) {
1958                                         tcp_seq onxt = tp->snd_nxt;
1959                                         u_int win;
1960
1961                                         /*
1962                                          * If we're doing sack, check to
1963                                          * see if we're already in sack
1964                                          * recovery. If we're not doing sack,
1965                                          * check to see if we're in newreno
1966                                          * recovery.
1967                                          */
1968                                         if (tp->sack_enable) {
1969                                                 if (IN_FASTRECOVERY(tp)) {
1970                                                         tp->t_dupacks = 0;
1971                                                         break;
1972                                                 }
1973                                         } else if (tcp_do_newreno) {
1974                                                 if (SEQ_LEQ(th->th_ack,
1975                                                     tp->snd_recover)) {
1976                                                         tp->t_dupacks = 0;
1977                                                         break;
1978                                                 }
1979                                         }
1980                                         win = min(tp->snd_wnd, tp->snd_cwnd) /
1981                                             2 / tp->t_maxseg;
1982                                         if (win < 2)
1983                                                 win = 2;
1984                                         tp->snd_ssthresh = win * tp->t_maxseg;
1985                                         ENTER_FASTRECOVERY(tp);
1986                                         tp->snd_recover = tp->snd_max;
1987                                         callout_stop(tp->tt_rexmt);
1988                                         tp->t_rtttime = 0;
1989                                         if (tp->sack_enable) {
1990                                                 tcpstat.tcps_sack_recovery_episode++;
1991                                                 tp->sack_newdata = tp->snd_nxt;
1992                                                 tp->snd_cwnd = tp->t_maxseg;
1993                                                 (void) tcp_output(tp);
1994                                                 goto drop;
1995                                         }
1996                                         tp->snd_nxt = th->th_ack;
1997                                         tp->snd_cwnd = tp->t_maxseg;
1998                                         (void) tcp_output(tp);
1999                                         KASSERT(tp->snd_limited <= 2,
2000                                             ("%s: tp->snd_limited too big",
2001                                             __func__));
2002                                         tp->snd_cwnd = tp->snd_ssthresh +
2003                                              tp->t_maxseg *
2004                                              (tp->t_dupacks - tp->snd_limited);
2005                                         if (SEQ_GT(onxt, tp->snd_nxt))
2006                                                 tp->snd_nxt = onxt;
2007                                         goto drop;
2008                                 } else if (tcp_do_rfc3042) {
2009                                         u_long oldcwnd = tp->snd_cwnd;
2010                                         tcp_seq oldsndmax = tp->snd_max;
2011                                         u_int sent;
2012
2013                                         KASSERT(tp->t_dupacks == 1 ||
2014                                             tp->t_dupacks == 2,
2015                                             ("%s: dupacks not 1 or 2",
2016                                             __func__));
2017                                         if (tp->t_dupacks == 1)
2018                                                 tp->snd_limited = 0;
2019                                         tp->snd_cwnd =
2020                                             (tp->snd_nxt - tp->snd_una) +
2021                                             (tp->t_dupacks - tp->snd_limited) *
2022                                             tp->t_maxseg;
2023                                         (void) tcp_output(tp);
2024                                         sent = tp->snd_max - oldsndmax;
2025                                         if (sent > tp->t_maxseg) {
2026                                                 KASSERT((tp->t_dupacks == 2 &&
2027                                                     tp->snd_limited == 0) ||
2028                                                    (sent == tp->t_maxseg + 1 &&
2029                                                     tp->t_flags & TF_SENTFIN),
2030                                                     ("%s: sent too much",
2031                                                     __func__));
2032                                                 tp->snd_limited = 2;
2033                                         } else if (sent > 0)
2034                                                 ++tp->snd_limited;
2035                                         tp->snd_cwnd = oldcwnd;
2036                                         goto drop;
2037                                 }
2038                         } else
2039                                 tp->t_dupacks = 0;
2040                         break;
2041                 }
2042
2043                 KASSERT(SEQ_GT(th->th_ack, tp->snd_una),
2044                     ("%s: th_ack <= snd_una", __func__));
2045
2046                 /*
2047                  * If the congestion window was inflated to account
2048                  * for the other side's cached packets, retract it.
2049                  */
2050                 if (tcp_do_newreno || tp->sack_enable) {
2051                         if (IN_FASTRECOVERY(tp)) {
2052                                 if (SEQ_LT(th->th_ack, tp->snd_recover)) {
2053                                         if (tp->sack_enable)
2054                                                 tcp_sack_partialack(tp, th);
2055                                         else
2056                                                 tcp_newreno_partial_ack(tp, th);
2057                                 } else {
2058                                         /*
2059                                          * Out of fast recovery.
2060                                          * Window inflation should have left us
2061                                          * with approximately snd_ssthresh
2062                                          * outstanding data.
2063                                          * But in case we would be inclined to
2064                                          * send a burst, better to do it via
2065                                          * the slow start mechanism.
2066                                          */
2067                                         if (SEQ_GT(th->th_ack +
2068                                                         tp->snd_ssthresh,
2069                                                    tp->snd_max))
2070                                                 tp->snd_cwnd = tp->snd_max -
2071                                                                 th->th_ack +
2072                                                                 tp->t_maxseg;
2073                                         else
2074                                                 tp->snd_cwnd = tp->snd_ssthresh;
2075                                 }
2076                         }
2077                 } else {
2078                         if (tp->t_dupacks >= tcprexmtthresh &&
2079                             tp->snd_cwnd > tp->snd_ssthresh)
2080                                 tp->snd_cwnd = tp->snd_ssthresh;
2081                 }
2082                 tp->t_dupacks = 0;
2083                 /*
2084                  * If we reach this point, ACK is not a duplicate,
2085                  *     i.e., it ACKs something we sent.
2086                  */
2087                 if (tp->t_flags & TF_NEEDSYN) {
2088                         /*
2089                          * T/TCP: Connection was half-synchronized, and our
2090                          * SYN has been ACK'd (so connection is now fully
2091                          * synchronized).  Go to non-starred state,
2092                          * increment snd_una for ACK of SYN, and check if
2093                          * we can do window scaling.
2094                          */
2095                         tp->t_flags &= ~TF_NEEDSYN;
2096                         tp->snd_una++;
2097                         /* Do window scaling? */
2098                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
2099                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
2100                                 tp->rcv_scale = tp->request_r_scale;
2101                                 /* Send window already scaled. */
2102                         }
2103                 }
2104
2105 process_ACK:
2106                 KASSERT(headlocked, ("%s: process_ACK: head not locked",
2107                     __func__));
2108                 INP_LOCK_ASSERT(tp->t_inpcb);
2109
2110                 acked = th->th_ack - tp->snd_una;
2111                 tcpstat.tcps_rcvackpack++;
2112                 tcpstat.tcps_rcvackbyte += acked;
2113
2114                 /*
2115                  * If we just performed our first retransmit, and the ACK
2116                  * arrives within our recovery window, then it was a mistake
2117                  * to do the retransmit in the first place.  Recover our
2118                  * original cwnd and ssthresh, and proceed to transmit where
2119                  * we left off.
2120                  */
2121                 if (tp->t_rxtshift == 1 && ticks < tp->t_badrxtwin) {
2122                         ++tcpstat.tcps_sndrexmitbad;
2123                         tp->snd_cwnd = tp->snd_cwnd_prev;
2124                         tp->snd_ssthresh = tp->snd_ssthresh_prev;
2125                         tp->snd_recover = tp->snd_recover_prev;
2126                         if (tp->t_flags & TF_WASFRECOVERY)
2127                                 ENTER_FASTRECOVERY(tp);
2128                         tp->snd_nxt = tp->snd_max;
2129                         tp->t_badrxtwin = 0;    /* XXX probably not required */
2130                 }
2131
2132                 /*
2133                  * If we have a timestamp reply, update smoothed
2134                  * round trip time.  If no timestamp is present but
2135                  * transmit timer is running and timed sequence
2136                  * number was acked, update smoothed round trip time.
2137                  * Since we now have an rtt measurement, cancel the
2138                  * timer backoff (cf., Phil Karn's retransmit alg.).
2139                  * Recompute the initial retransmit timer.
2140                  *
2141                  * Some boxes send broken timestamp replies
2142                  * during the SYN+ACK phase, ignore
2143                  * timestamps of 0 or we could calculate a
2144                  * huge RTT and blow up the retransmit timer.
2145                  */
2146                 if ((to.to_flags & TOF_TS) != 0 &&
2147                     to.to_tsecr) {
2148                         if (!tp->t_rttlow || tp->t_rttlow > ticks - to.to_tsecr)
2149                                 tp->t_rttlow = ticks - to.to_tsecr;
2150                         tcp_xmit_timer(tp, ticks - to.to_tsecr + 1);
2151                 } else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
2152                         if (!tp->t_rttlow || tp->t_rttlow > ticks - tp->t_rtttime)
2153                                 tp->t_rttlow = ticks - tp->t_rtttime;
2154                         tcp_xmit_timer(tp, ticks - tp->t_rtttime);
2155                 }
2156                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
2157
2158                 /*
2159                  * If all outstanding data is acked, stop retransmit
2160                  * timer and remember to restart (more output or persist).
2161                  * If there is more data to be acked, restart retransmit
2162                  * timer, using current (possibly backed-off) value.
2163                  */
2164                 if (th->th_ack == tp->snd_max) {
2165                         callout_stop(tp->tt_rexmt);
2166                         needoutput = 1;
2167                 } else if (!callout_active(tp->tt_persist))
2168                         callout_reset(tp->tt_rexmt, tp->t_rxtcur,
2169                                       tcp_timer_rexmt, tp);
2170
2171                 /*
2172                  * If no data (only SYN) was ACK'd,
2173                  *    skip rest of ACK processing.
2174                  */
2175                 if (acked == 0)
2176                         goto step6;
2177
2178                 /*
2179                  * When new data is acked, open the congestion window.
2180                  * If the window gives us less than ssthresh packets
2181                  * in flight, open exponentially (maxseg per packet).
2182                  * Otherwise open linearly: maxseg per window
2183                  * (maxseg^2 / cwnd per packet).
2184                  */
2185                 if ((!tcp_do_newreno && !tp->sack_enable) ||
2186                     !IN_FASTRECOVERY(tp)) {
2187                         u_int cw = tp->snd_cwnd;
2188                         u_int incr = tp->t_maxseg;
2189                         if (cw > tp->snd_ssthresh)
2190                                 incr = incr * incr / cw;
2191                         tp->snd_cwnd = min(cw+incr, TCP_MAXWIN<<tp->snd_scale);
2192                 }
2193                 SOCKBUF_LOCK(&so->so_snd);
2194                 if (acked > so->so_snd.sb_cc) {
2195                         tp->snd_wnd -= so->so_snd.sb_cc;
2196                         sbdrop_locked(&so->so_snd, (int)so->so_snd.sb_cc);
2197                         ourfinisacked = 1;
2198                 } else {
2199                         sbdrop_locked(&so->so_snd, acked);
2200                         tp->snd_wnd -= acked;
2201                         ourfinisacked = 0;
2202                 }
2203                 sowwakeup_locked(so);
2204                 /* detect una wraparound */
2205                 if ((tcp_do_newreno || tp->sack_enable) &&
2206                     !IN_FASTRECOVERY(tp) &&
2207                     SEQ_GT(tp->snd_una, tp->snd_recover) &&
2208                     SEQ_LEQ(th->th_ack, tp->snd_recover))
2209                         tp->snd_recover = th->th_ack - 1;
2210                 if ((tcp_do_newreno || tp->sack_enable) &&
2211                     IN_FASTRECOVERY(tp) &&
2212                     SEQ_GEQ(th->th_ack, tp->snd_recover))
2213                         EXIT_FASTRECOVERY(tp);
2214                 tp->snd_una = th->th_ack;
2215                 if (tp->sack_enable) {
2216                         if (SEQ_GT(tp->snd_una, tp->snd_recover))
2217                                 tp->snd_recover = tp->snd_una;
2218                 }
2219                 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
2220                         tp->snd_nxt = tp->snd_una;
2221
2222                 switch (tp->t_state) {
2223
2224                 /*
2225                  * In FIN_WAIT_1 STATE in addition to the processing
2226                  * for the ESTABLISHED state if our FIN is now acknowledged
2227                  * then enter FIN_WAIT_2.
2228                  */
2229                 case TCPS_FIN_WAIT_1:
2230                         if (ourfinisacked) {
2231                                 /*
2232                                  * If we can't receive any more
2233                                  * data, then closing user can proceed.
2234                                  * Starting the timer is contrary to the
2235                                  * specification, but if we don't get a FIN
2236                                  * we'll hang forever.
2237                                  */
2238                 /* XXXjl
2239                  * we should release the tp also, and use a
2240                  * compressed state.
2241                  */
2242                                 if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
2243                                         int timeout;
2244
2245                                         soisdisconnected(so);
2246                                         timeout = (tcp_fast_finwait2_recycle) ?
2247                                                 tcp_finwait2_timeout : tcp_maxidle;
2248                                         callout_reset(tp->tt_2msl, timeout,
2249                                                       tcp_timer_2msl, tp);
2250                                 }
2251                                 tp->t_state = TCPS_FIN_WAIT_2;
2252                         }
2253                         break;
2254
2255                 /*
2256                  * In CLOSING STATE in addition to the processing for
2257                  * the ESTABLISHED state if the ACK acknowledges our FIN
2258                  * then enter the TIME-WAIT state, otherwise ignore
2259                  * the segment.
2260                  */
2261                 case TCPS_CLOSING:
2262                         if (ourfinisacked) {
2263                                 KASSERT(headlocked, ("%s: process_ACK: "
2264                                     "head not locked", __func__));
2265                                 tcp_twstart(tp);
2266                                 INP_INFO_WUNLOCK(&tcbinfo);
2267                                 headlocked = 0;
2268                                 m_freem(m);
2269                                 return (0);
2270                         }
2271                         break;
2272
2273                 /*
2274                  * In LAST_ACK, we may still be waiting for data to drain
2275                  * and/or to be acked, as well as for the ack of our FIN.
2276                  * If our FIN is now acknowledged, delete the TCB,
2277                  * enter the closed state and return.
2278                  */
2279                 case TCPS_LAST_ACK:
2280                         if (ourfinisacked) {
2281                                 KASSERT(headlocked, ("%s: process_ACK: "
2282                                     "tcp_close: head not locked", __func__));
2283                                 tp = tcp_close(tp);
2284                                 goto drop;
2285                         }
2286                         break;
2287
2288                 /*
2289                  * In TIME_WAIT state the only thing that should arrive
2290                  * is a retransmission of the remote FIN.  Acknowledge
2291                  * it and restart the finack timer.
2292                  */
2293                 case TCPS_TIME_WAIT:
2294                         KASSERT(tp->t_state != TCPS_TIME_WAIT,
2295                             ("%s: timewait", __func__));
2296                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
2297                                       tcp_timer_2msl, tp);
2298                         goto dropafterack;
2299                 }
2300         }
2301
2302 step6:
2303         KASSERT(headlocked, ("%s: step6: head not locked", __func__));
2304         INP_LOCK_ASSERT(tp->t_inpcb);
2305
2306         /*
2307          * Update window information.
2308          * Don't look at window if no ACK: TAC's send garbage on first SYN.
2309          */
2310         if ((thflags & TH_ACK) &&
2311             (SEQ_LT(tp->snd_wl1, th->th_seq) ||
2312             (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
2313              (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
2314                 /* keep track of pure window updates */
2315                 if (tlen == 0 &&
2316                     tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
2317                         tcpstat.tcps_rcvwinupd++;
2318                 tp->snd_wnd = tiwin;
2319                 tp->snd_wl1 = th->th_seq;
2320                 tp->snd_wl2 = th->th_ack;
2321                 if (tp->snd_wnd > tp->max_sndwnd)
2322                         tp->max_sndwnd = tp->snd_wnd;
2323                 needoutput = 1;
2324         }
2325
2326         /*
2327          * Process segments with URG.
2328          */
2329         if ((thflags & TH_URG) && th->th_urp &&
2330             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2331                 /*
2332                  * This is a kludge, but if we receive and accept
2333                  * random urgent pointers, we'll crash in
2334                  * soreceive.  It's hard to imagine someone
2335                  * actually wanting to send this much urgent data.
2336                  */
2337                 SOCKBUF_LOCK(&so->so_rcv);
2338                 if (th->th_urp + so->so_rcv.sb_cc > sb_max) {
2339                         th->th_urp = 0;                 /* XXX */
2340                         thflags &= ~TH_URG;             /* XXX */
2341                         SOCKBUF_UNLOCK(&so->so_rcv);    /* XXX */
2342                         goto dodata;                    /* XXX */
2343                 }
2344                 /*
2345                  * If this segment advances the known urgent pointer,
2346                  * then mark the data stream.  This should not happen
2347                  * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
2348                  * a FIN has been received from the remote side.
2349                  * In these states we ignore the URG.
2350                  *
2351                  * According to RFC961 (Assigned Protocols),
2352                  * the urgent pointer points to the last octet
2353                  * of urgent data.  We continue, however,
2354                  * to consider it to indicate the first octet
2355                  * of data past the urgent section as the original
2356                  * spec states (in one of two places).
2357                  */
2358                 if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
2359                         tp->rcv_up = th->th_seq + th->th_urp;
2360                         so->so_oobmark = so->so_rcv.sb_cc +
2361                             (tp->rcv_up - tp->rcv_nxt) - 1;
2362                         if (so->so_oobmark == 0)
2363                                 so->so_rcv.sb_state |= SBS_RCVATMARK;
2364                         sohasoutofband(so);
2365                         tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
2366                 }
2367                 SOCKBUF_UNLOCK(&so->so_rcv);
2368                 /*
2369                  * Remove out of band data so doesn't get presented to user.
2370                  * This can happen independent of advancing the URG pointer,
2371                  * but if two URG's are pending at once, some out-of-band
2372                  * data may creep in... ick.
2373                  */
2374                 if (th->th_urp <= (u_long)tlen &&
2375                     !(so->so_options & SO_OOBINLINE)) {
2376                         /* hdr drop is delayed */
2377                         tcp_pulloutofband(so, th, m, drop_hdrlen);
2378                 }
2379         } else {
2380                 /*
2381                  * If no out of band data is expected,
2382                  * pull receive urgent pointer along
2383                  * with the receive window.
2384                  */
2385                 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
2386                         tp->rcv_up = tp->rcv_nxt;
2387         }
2388 dodata:                                                 /* XXX */
2389         KASSERT(headlocked, ("%s: dodata: head not locked", __func__));
2390         INP_LOCK_ASSERT(tp->t_inpcb);
2391
2392         /*
2393          * Process the segment text, merging it into the TCP sequencing queue,
2394          * and arranging for acknowledgment of receipt if necessary.
2395          * This process logically involves adjusting tp->rcv_wnd as data
2396          * is presented to the user (this happens in tcp_usrreq.c,
2397          * case PRU_RCVD).  If a FIN has already been received on this
2398          * connection then we just ignore the text.
2399          */
2400         if ((tlen || (thflags & TH_FIN)) &&
2401             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2402                 tcp_seq save_start = th->th_seq;
2403                 tcp_seq save_end = th->th_seq + tlen;
2404                 m_adj(m, drop_hdrlen);  /* delayed header drop */
2405                 /*
2406                  * Insert segment which includes th into TCP reassembly queue
2407                  * with control block tp.  Set thflags to whether reassembly now
2408                  * includes a segment with FIN.  This handles the common case
2409                  * inline (segment is the next to be received on an established
2410                  * connection, and the queue is empty), avoiding linkage into
2411                  * and removal from the queue and repetition of various
2412                  * conversions.
2413                  * Set DELACK for segments received in order, but ack
2414                  * immediately when segments are out of order (so
2415                  * fast retransmit can work).
2416                  */
2417                 if (th->th_seq == tp->rcv_nxt &&
2418                     LIST_EMPTY(&tp->t_segq) &&
2419                     TCPS_HAVEESTABLISHED(tp->t_state)) {
2420                         if (DELAY_ACK(tp))
2421                                 tp->t_flags |= TF_DELACK;
2422                         else
2423                                 tp->t_flags |= TF_ACKNOW;
2424                         tp->rcv_nxt += tlen;
2425                         thflags = th->th_flags & TH_FIN;
2426                         tcpstat.tcps_rcvpack++;
2427                         tcpstat.tcps_rcvbyte += tlen;
2428                         ND6_HINT(tp);
2429                         SOCKBUF_LOCK(&so->so_rcv);
2430                         if (so->so_rcv.sb_state & SBS_CANTRCVMORE)
2431                                 m_freem(m);
2432                         else
2433                                 sbappendstream_locked(&so->so_rcv, m);
2434                         sorwakeup_locked(so);
2435                 } else {
2436                         thflags = tcp_reass(tp, th, &tlen, m);
2437                         tp->t_flags |= TF_ACKNOW;
2438                 }
2439                 if (tlen > 0 && tp->sack_enable)
2440                         tcp_update_sack_list(tp, save_start, save_end);
2441 #if 0
2442                 /*
2443                  * Note the amount of data that peer has sent into
2444                  * our window, in order to estimate the sender's
2445                  * buffer size.
2446                  * XXX: Unused.
2447                  */
2448                 len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
2449 #endif
2450         } else {
2451                 m_freem(m);
2452                 thflags &= ~TH_FIN;
2453         }
2454
2455         /*
2456          * If FIN is received ACK the FIN and let the user know
2457          * that the connection is closing.
2458          */
2459         if (thflags & TH_FIN) {
2460                 if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2461                         socantrcvmore(so);
2462                         /*
2463                          * If connection is half-synchronized
2464                          * (ie NEEDSYN flag on) then delay ACK,
2465                          * so it may be piggybacked when SYN is sent.
2466                          * Otherwise, since we received a FIN then no
2467                          * more input can be expected, send ACK now.
2468                          */
2469                         if (tp->t_flags & TF_NEEDSYN)
2470                                 tp->t_flags |= TF_DELACK;
2471                         else
2472                                 tp->t_flags |= TF_ACKNOW;
2473                         tp->rcv_nxt++;
2474                 }
2475                 switch (tp->t_state) {
2476
2477                 /*
2478                  * In SYN_RECEIVED and ESTABLISHED STATES
2479                  * enter the CLOSE_WAIT state.
2480                  */
2481                 case TCPS_SYN_RECEIVED:
2482                         tp->t_starttime = ticks;
2483                         /*FALLTHROUGH*/
2484                 case TCPS_ESTABLISHED:
2485                         tp->t_state = TCPS_CLOSE_WAIT;
2486                         break;
2487
2488                 /*
2489                  * If still in FIN_WAIT_1 STATE FIN has not been acked so
2490                  * enter the CLOSING state.
2491                  */
2492                 case TCPS_FIN_WAIT_1:
2493                         tp->t_state = TCPS_CLOSING;
2494                         break;
2495
2496                 /*
2497                  * In FIN_WAIT_2 state enter the TIME_WAIT state,
2498                  * starting the time-wait timer, turning off the other
2499                  * standard timers.
2500                  */
2501                 case TCPS_FIN_WAIT_2:
2502                         KASSERT(headlocked == 1, ("%s: dodata: "
2503                             "TCP_FIN_WAIT_2: head not locked", __func__));
2504                         tcp_twstart(tp);
2505                         INP_INFO_WUNLOCK(&tcbinfo);
2506                         return (0);
2507
2508                 /*
2509                  * In TIME_WAIT state restart the 2 MSL time_wait timer.
2510                  */
2511                 case TCPS_TIME_WAIT:
2512                         KASSERT(tp->t_state != TCPS_TIME_WAIT,
2513                             ("%s: timewait", __func__));
2514                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
2515                                       tcp_timer_2msl, tp);
2516                         break;
2517                 }
2518         }
2519         INP_INFO_WUNLOCK(&tcbinfo);
2520         headlocked = 0;
2521 #ifdef TCPDEBUG
2522         if (so->so_options & SO_DEBUG)
2523                 tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
2524                           &tcp_savetcp, 0);
2525 #endif
2526
2527         /*
2528          * Return any desired output.
2529          */
2530         if (needoutput || (tp->t_flags & TF_ACKNOW))
2531                 (void) tcp_output(tp);
2532
2533 check_delack:
2534         KASSERT(headlocked == 0, ("%s: check_delack: head locked",
2535             __func__));
2536         INP_LOCK_ASSERT(tp->t_inpcb);
2537         if (tp->t_flags & TF_DELACK) {
2538                 tp->t_flags &= ~TF_DELACK;
2539                 callout_reset(tp->tt_delack, tcp_delacktime,
2540                     tcp_timer_delack, tp);
2541         }
2542         INP_UNLOCK(tp->t_inpcb);
2543         return (0);
2544
2545 dropafterack:
2546         KASSERT(headlocked, ("%s: dropafterack: head not locked", __func__));
2547         /*
2548          * Generate an ACK dropping incoming segment if it occupies
2549          * sequence space, where the ACK reflects our state.
2550          *
2551          * We can now skip the test for the RST flag since all
2552          * paths to this code happen after packets containing
2553          * RST have been dropped.
2554          *
2555          * In the SYN-RECEIVED state, don't send an ACK unless the
2556          * segment we received passes the SYN-RECEIVED ACK test.
2557          * If it fails send a RST.  This breaks the loop in the
2558          * "LAND" DoS attack, and also prevents an ACK storm
2559          * between two listening ports that have been sent forged
2560          * SYN segments, each with the source address of the other.
2561          */
2562         if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
2563             (SEQ_GT(tp->snd_una, th->th_ack) ||
2564              SEQ_GT(th->th_ack, tp->snd_max)) ) {
2565                 rstreason = BANDLIM_RST_OPENPORT;
2566                 goto dropwithreset;
2567         }
2568 #ifdef TCPDEBUG
2569         if (so->so_options & SO_DEBUG)
2570                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2571                           &tcp_savetcp, 0);
2572 #endif
2573         KASSERT(headlocked, ("%s: headlocked should be 1", __func__));
2574         INP_INFO_WUNLOCK(&tcbinfo);
2575         tp->t_flags |= TF_ACKNOW;
2576         (void) tcp_output(tp);
2577         INP_UNLOCK(tp->t_inpcb);
2578         m_freem(m);
2579         return (0);
2580
2581 dropwithreset:
2582         KASSERT(headlocked, ("%s: dropwithreset: head not locked", __func__));
2583
2584         tcp_dropwithreset(m, th, tp, tlen, rstreason);
2585
2586         if (tp != NULL)
2587                 INP_UNLOCK(tp->t_inpcb);
2588         if (headlocked)
2589                 INP_INFO_WUNLOCK(&tcbinfo);
2590         return (0);
2591
2592 drop:
2593         /*
2594          * Drop space held by incoming segment and return.
2595          */
2596 #ifdef TCPDEBUG
2597         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2598                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2599                           &tcp_savetcp, 0);
2600 #endif
2601         if (tp != NULL)
2602                 INP_UNLOCK(tp->t_inpcb);
2603         if (headlocked)
2604                 INP_INFO_WUNLOCK(&tcbinfo);
2605         m_freem(m);
2606         return (0);
2607 }
2608
2609
2610 /*
2611  * Issue RST on TCP segment.  The mbuf must still include the original
2612  * packet header.
2613  */
2614 static void
2615 tcp_dropwithreset(struct mbuf *m, struct tcphdr *th, struct tcpcb *tp,
2616     int tlen, int rstreason)
2617 {
2618         struct ip *ip;
2619 #ifdef INET6
2620         struct ip6_hdr *ip6;
2621 #endif
2622
2623         /*
2624          * Generate a RST, dropping incoming segment.
2625          * Make ACK acceptable to originator of segment.
2626          * Don't bother to respond if destination was broadcast/multicast.
2627          */
2628         if ((th->th_flags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
2629                 goto drop;
2630 #ifdef INET6
2631         if (mtod(m, struct ip *)->ip_v == 6) {
2632                 ip6 = mtod(m, struct ip6_hdr *);
2633                 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
2634                     IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
2635                         goto drop;
2636                 /* IPv6 anycast check is done at tcp6_input() */
2637         } else
2638 #endif
2639         {
2640                 ip = mtod(m, struct ip *);
2641                 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
2642                     IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
2643                     ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
2644                     in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
2645                         goto drop;
2646         }
2647
2648         /* Perform bandwidth limiting. */
2649         if (badport_bandlim(rstreason) < 0)
2650                 goto drop;
2651
2652         /* tcp_respond consumes the mbuf chain. */
2653         if (th->th_flags & TH_ACK) {
2654                 tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0,
2655                     th->th_ack, TH_RST);
2656         } else {
2657                 if (th->th_flags & TH_SYN)
2658                         tlen++;
2659                 tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
2660                     (tcp_seq)0, TH_RST|TH_ACK);
2661         }
2662         return;
2663 drop:
2664         m_freem(m);
2665         return;
2666 }
2667
2668 /*
2669  * Parse TCP options and place in tcpopt.
2670  */
2671 static void
2672 tcp_dooptions(struct tcpopt *to, u_char *cp, int cnt, int flags)
2673 {
2674         int opt, optlen;
2675
2676         to->to_flags = 0;
2677         for (; cnt > 0; cnt -= optlen, cp += optlen) {
2678                 opt = cp[0];
2679                 if (opt == TCPOPT_EOL)
2680                         break;
2681                 if (opt == TCPOPT_NOP)
2682                         optlen = 1;
2683                 else {
2684                         if (cnt < 2)
2685                                 break;
2686                         optlen = cp[1];
2687                         if (optlen < 2 || optlen > cnt)
2688                                 break;
2689                 }
2690                 switch (opt) {
2691                 case TCPOPT_MAXSEG:
2692                         if (optlen != TCPOLEN_MAXSEG)
2693                                 continue;
2694                         if (!(flags & TO_SYN))
2695                                 continue;
2696                         to->to_flags |= TOF_MSS;
2697                         bcopy((char *)cp + 2,
2698                             (char *)&to->to_mss, sizeof(to->to_mss));
2699                         to->to_mss = ntohs(to->to_mss);
2700                         break;
2701                 case TCPOPT_WINDOW:
2702                         if (optlen != TCPOLEN_WINDOW)
2703                                 continue;
2704                         if (!(flags & TO_SYN))
2705                                 continue;
2706                         to->to_flags |= TOF_SCALE;
2707                         to->to_wscale = min(cp[2], TCP_MAX_WINSHIFT);
2708                         break;
2709                 case TCPOPT_TIMESTAMP:
2710                         if (optlen != TCPOLEN_TIMESTAMP)
2711                                 continue;
2712                         to->to_flags |= TOF_TS;
2713                         bcopy((char *)cp + 2,
2714                             (char *)&to->to_tsval, sizeof(to->to_tsval));
2715                         to->to_tsval = ntohl(to->to_tsval);
2716                         bcopy((char *)cp + 6,
2717                             (char *)&to->to_tsecr, sizeof(to->to_tsecr));
2718                         to->to_tsecr = ntohl(to->to_tsecr);
2719                         break;
2720 #ifdef TCP_SIGNATURE
2721                 /*
2722                  * XXX In order to reply to a host which has set the
2723                  * TCP_SIGNATURE option in its initial SYN, we have to
2724                  * record the fact that the option was observed here
2725                  * for the syncache code to perform the correct response.
2726                  */
2727                 case TCPOPT_SIGNATURE:
2728                         if (optlen != TCPOLEN_SIGNATURE)
2729                                 continue;
2730                         to->to_flags |= (TOF_SIGNATURE | TOF_SIGLEN);
2731                         break;
2732 #endif
2733                 case TCPOPT_SACK_PERMITTED:
2734                         if (optlen != TCPOLEN_SACK_PERMITTED)
2735                                 continue;
2736                         if (!(flags & TO_SYN))
2737                                 continue;
2738                         if (!tcp_do_sack)
2739                                 continue;
2740                         to->to_flags |= TOF_SACKPERM;
2741                         break;
2742                 case TCPOPT_SACK:
2743                         if (optlen <= 2 || (optlen - 2) % TCPOLEN_SACK != 0)
2744                                 continue;
2745                         if (flags & TO_SYN)
2746                                 continue;
2747                         to->to_flags |= TOF_SACK;
2748                         to->to_nsacks = (optlen - 2) / TCPOLEN_SACK;
2749                         to->to_sacks = cp + 2;
2750                         tcpstat.tcps_sack_rcv_blocks++;
2751                         break;
2752                 default:
2753                         continue;
2754                 }
2755         }
2756 }
2757
2758 /*
2759  * Pull out of band byte out of a segment so
2760  * it doesn't appear in the user's data queue.
2761  * It is still reflected in the segment length for
2762  * sequencing purposes.
2763  */
2764 static void
2765 tcp_pulloutofband(struct socket *so, struct tcphdr *th, struct mbuf *m,
2766     int off)
2767 {
2768         int cnt = off + th->th_urp - 1;
2769
2770         while (cnt >= 0) {
2771                 if (m->m_len > cnt) {
2772                         char *cp = mtod(m, caddr_t) + cnt;
2773                         struct tcpcb *tp = sototcpcb(so);
2774
2775                         tp->t_iobc = *cp;
2776                         tp->t_oobflags |= TCPOOB_HAVEDATA;
2777                         bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
2778                         m->m_len--;
2779                         if (m->m_flags & M_PKTHDR)
2780                                 m->m_pkthdr.len--;
2781                         return;
2782                 }
2783                 cnt -= m->m_len;
2784                 m = m->m_next;
2785                 if (m == NULL)
2786                         break;
2787         }
2788         panic("tcp_pulloutofband");
2789 }
2790
2791 /*
2792  * Collect new round-trip time estimate
2793  * and update averages and current timeout.
2794  */
2795 static void
2796 tcp_xmit_timer(struct tcpcb *tp, int rtt)
2797 {
2798         int delta;
2799
2800         INP_LOCK_ASSERT(tp->t_inpcb);
2801
2802         tcpstat.tcps_rttupdated++;
2803         tp->t_rttupdated++;
2804         if (tp->t_srtt != 0) {
2805                 /*
2806                  * srtt is stored as fixed point with 5 bits after the
2807                  * binary point (i.e., scaled by 8).  The following magic
2808                  * is equivalent to the smoothing algorithm in rfc793 with
2809                  * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
2810                  * point).  Adjust rtt to origin 0.
2811                  */
2812                 delta = ((rtt - 1) << TCP_DELTA_SHIFT)
2813                         - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
2814
2815                 if ((tp->t_srtt += delta) <= 0)
2816                         tp->t_srtt = 1;
2817
2818                 /*
2819                  * We accumulate a smoothed rtt variance (actually, a
2820                  * smoothed mean difference), then set the retransmit
2821                  * timer to smoothed rtt + 4 times the smoothed variance.
2822                  * rttvar is stored as fixed point with 4 bits after the
2823                  * binary point (scaled by 16).  The following is
2824                  * equivalent to rfc793 smoothing with an alpha of .75
2825                  * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
2826                  * rfc793's wired-in beta.
2827                  */
2828                 if (delta < 0)
2829                         delta = -delta;
2830                 delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
2831                 if ((tp->t_rttvar += delta) <= 0)
2832                         tp->t_rttvar = 1;
2833                 if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
2834                     tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2835         } else {
2836                 /*
2837                  * No rtt measurement yet - use the unsmoothed rtt.
2838                  * Set the variance to half the rtt (so our first
2839                  * retransmit happens at 3*rtt).
2840                  */
2841                 tp->t_srtt = rtt << TCP_RTT_SHIFT;
2842                 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
2843                 tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2844         }
2845         tp->t_rtttime = 0;
2846         tp->t_rxtshift = 0;
2847
2848         /*
2849          * the retransmit should happen at rtt + 4 * rttvar.
2850          * Because of the way we do the smoothing, srtt and rttvar
2851          * will each average +1/2 tick of bias.  When we compute
2852          * the retransmit timer, we want 1/2 tick of rounding and
2853          * 1 extra tick because of +-1/2 tick uncertainty in the
2854          * firing of the timer.  The bias will give us exactly the
2855          * 1.5 tick we need.  But, because the bias is
2856          * statistical, we have to test that we don't drop below
2857          * the minimum feasible timer (which is 2 ticks).
2858          */
2859         TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
2860                       max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
2861
2862         /*
2863          * We received an ack for a packet that wasn't retransmitted;
2864          * it is probably safe to discard any error indications we've
2865          * received recently.  This isn't quite right, but close enough
2866          * for now (a route might have failed after we sent a segment,
2867          * and the return path might not be symmetrical).
2868          */
2869         tp->t_softerror = 0;
2870 }
2871
2872 /*
2873  * Determine a reasonable value for maxseg size.
2874  * If the route is known, check route for mtu.
2875  * If none, use an mss that can be handled on the outgoing
2876  * interface without forcing IP to fragment; if bigger than
2877  * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
2878  * to utilize large mbufs.  If no route is found, route has no mtu,
2879  * or the destination isn't local, use a default, hopefully conservative
2880  * size (usually 512 or the default IP max size, but no more than the mtu
2881  * of the interface), as we can't discover anything about intervening
2882  * gateways or networks.  We also initialize the congestion/slow start
2883  * window to be a single segment if the destination isn't local.
2884  * While looking at the routing entry, we also initialize other path-dependent
2885  * parameters from pre-set or cached values in the routing entry.
2886  *
2887  * Also take into account the space needed for options that we
2888  * send regularly.  Make maxseg shorter by that amount to assure
2889  * that we can send maxseg amount of data even when the options
2890  * are present.  Store the upper limit of the length of options plus
2891  * data in maxopd.
2892  *
2893  *
2894  * In case of T/TCP, we call this routine during implicit connection
2895  * setup as well (offer = -1), to initialize maxseg from the cached
2896  * MSS of our peer.
2897  *
2898  * NOTE that this routine is only called when we process an incoming
2899  * segment. Outgoing SYN/ACK MSS settings are handled in tcp_mssopt().
2900  */
2901 void
2902 tcp_mss(struct tcpcb *tp, int offer)
2903 {
2904         int rtt, mss;
2905         u_long bufsize;
2906         u_long maxmtu;
2907         struct inpcb *inp = tp->t_inpcb;
2908         struct socket *so;
2909         struct hc_metrics_lite metrics;
2910         int origoffer = offer;
2911         int mtuflags = 0;
2912 #ifdef INET6
2913         int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
2914         size_t min_protoh = isipv6 ?
2915                             sizeof (struct ip6_hdr) + sizeof (struct tcphdr) :
2916                             sizeof (struct tcpiphdr);
2917 #else
2918         const size_t min_protoh = sizeof(struct tcpiphdr);
2919 #endif
2920
2921         /* initialize */
2922 #ifdef INET6
2923         if (isipv6) {
2924                 maxmtu = tcp_maxmtu6(&inp->inp_inc, &mtuflags);
2925                 tp->t_maxopd = tp->t_maxseg = tcp_v6mssdflt;
2926         } else
2927 #endif
2928         {
2929                 maxmtu = tcp_maxmtu(&inp->inp_inc, &mtuflags);
2930                 tp->t_maxopd = tp->t_maxseg = tcp_mssdflt;
2931         }
2932         so = inp->inp_socket;
2933
2934         /*
2935          * no route to sender, stay with default mss and return
2936          */
2937         if (maxmtu == 0)
2938                 return;
2939
2940         /* what have we got? */
2941         switch (offer) {
2942                 case 0:
2943                         /*
2944                          * Offer == 0 means that there was no MSS on the SYN
2945                          * segment, in this case we use tcp_mssdflt.
2946                          */
2947                         offer =
2948 #ifdef INET6
2949                                 isipv6 ? tcp_v6mssdflt :
2950 #endif
2951                                 tcp_mssdflt;
2952                         break;
2953
2954                 case -1:
2955                         /*
2956                          * Offer == -1 means that we didn't receive SYN yet.
2957                          */
2958                         /* FALLTHROUGH */
2959
2960                 default:
2961                         /*
2962                          * Prevent DoS attack with too small MSS. Round up
2963                          * to at least minmss.
2964                          */
2965                         offer = max(offer, tcp_minmss);
2966                         /*
2967                          * Sanity check: make sure that maxopd will be large
2968                          * enough to allow some data on segments even if the
2969                          * all the option space is used (40bytes).  Otherwise
2970                          * funny things may happen in tcp_output.
2971                          */
2972                         offer = max(offer, 64);
2973         }
2974
2975         /*
2976          * rmx information is now retrieved from tcp_hostcache
2977          */
2978         tcp_hc_get(&inp->inp_inc, &metrics);
2979
2980         /*
2981          * if there's a discovered mtu int tcp hostcache, use it
2982          * else, use the link mtu.
2983          */
2984         if (metrics.rmx_mtu)
2985                 mss = min(metrics.rmx_mtu, maxmtu) - min_protoh;
2986         else {
2987 #ifdef INET6
2988                 if (isipv6) {
2989                         mss = maxmtu - min_protoh;
2990                         if (!path_mtu_discovery &&
2991                             !in6_localaddr(&inp->in6p_faddr))
2992                                 mss = min(mss, tcp_v6mssdflt);
2993                 } else
2994 #endif
2995                 {
2996                         mss = maxmtu - min_protoh;
2997                         if (!path_mtu_discovery &&
2998                             !in_localaddr(inp->inp_faddr))
2999                                 mss = min(mss, tcp_mssdflt);
3000                 }
3001         }
3002         mss = min(mss, offer);
3003
3004         /*
3005          * maxopd stores the maximum length of data AND options
3006          * in a segment; maxseg is the amount of data in a normal
3007          * segment.  We need to store this value (maxopd) apart
3008          * from maxseg, because now every segment carries options
3009          * and thus we normally have somewhat less data in segments.
3010          */
3011         tp->t_maxopd = mss;
3012
3013         /*
3014          * origoffer==-1 indicates, that no segments were received yet.
3015          * In this case we just guess.
3016          */
3017         if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
3018             (origoffer == -1 ||
3019              (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
3020                 mss -= TCPOLEN_TSTAMP_APPA;
3021         tp->t_maxseg = mss;
3022
3023 #if     (MCLBYTES & (MCLBYTES - 1)) == 0
3024                 if (mss > MCLBYTES)
3025                         mss &= ~(MCLBYTES-1);
3026 #else
3027                 if (mss > MCLBYTES)
3028                         mss = mss / MCLBYTES * MCLBYTES;
3029 #endif
3030         tp->t_maxseg = mss;
3031
3032         /*
3033          * If there's a pipesize, change the socket buffer to that size,
3034          * don't change if sb_hiwat is different than default (then it
3035          * has been changed on purpose with setsockopt).
3036          * Make the socket buffers an integral number of mss units;
3037          * if the mss is larger than the socket buffer, decrease the mss.
3038          */
3039         SOCKBUF_LOCK(&so->so_snd);
3040         if ((so->so_snd.sb_hiwat == tcp_sendspace) && metrics.rmx_sendpipe)
3041                 bufsize = metrics.rmx_sendpipe;
3042         else
3043                 bufsize = so->so_snd.sb_hiwat;
3044         if (bufsize < mss)
3045                 mss = bufsize;
3046         else {
3047                 bufsize = roundup(bufsize, mss);
3048                 if (bufsize > sb_max)
3049                         bufsize = sb_max;
3050                 if (bufsize > so->so_snd.sb_hiwat)
3051                         (void)sbreserve_locked(&so->so_snd, bufsize, so, NULL);
3052         }
3053         SOCKBUF_UNLOCK(&so->so_snd);
3054         tp->t_maxseg = mss;
3055
3056         SOCKBUF_LOCK(&so->so_rcv);
3057         if ((so->so_rcv.sb_hiwat == tcp_recvspace) && metrics.rmx_recvpipe)
3058                 bufsize = metrics.rmx_recvpipe;
3059         else
3060                 bufsize = so->so_rcv.sb_hiwat;
3061         if (bufsize > mss) {
3062                 bufsize = roundup(bufsize, mss);
3063                 if (bufsize > sb_max)
3064                         bufsize = sb_max;
3065                 if (bufsize > so->so_rcv.sb_hiwat)
3066                         (void)sbreserve_locked(&so->so_rcv, bufsize, so, NULL);
3067         }
3068         SOCKBUF_UNLOCK(&so->so_rcv);
3069         /*
3070          * While we're here, check the others too
3071          */
3072         if (tp->t_srtt == 0 && (rtt = metrics.rmx_rtt)) {
3073                 tp->t_srtt = rtt;
3074                 tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
3075                 tcpstat.tcps_usedrtt++;
3076                 if (metrics.rmx_rttvar) {
3077                         tp->t_rttvar = metrics.rmx_rttvar;
3078                         tcpstat.tcps_usedrttvar++;
3079                 } else {
3080                         /* default variation is +- 1 rtt */
3081                         tp->t_rttvar =
3082                             tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
3083                 }
3084                 TCPT_RANGESET(tp->t_rxtcur,
3085                               ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
3086                               tp->t_rttmin, TCPTV_REXMTMAX);
3087         }
3088         if (metrics.rmx_ssthresh) {
3089                 /*
3090                  * There's some sort of gateway or interface
3091                  * buffer limit on the path.  Use this to set
3092                  * the slow start threshhold, but set the
3093                  * threshold to no less than 2*mss.
3094                  */
3095                 tp->snd_ssthresh = max(2 * mss, metrics.rmx_ssthresh);
3096                 tcpstat.tcps_usedssthresh++;
3097         }
3098         if (metrics.rmx_bandwidth)
3099                 tp->snd_bandwidth = metrics.rmx_bandwidth;
3100
3101         /*
3102          * Set the slow-start flight size depending on whether this
3103          * is a local network or not.
3104          *
3105          * Extend this so we cache the cwnd too and retrieve it here.
3106          * Make cwnd even bigger than RFC3390 suggests but only if we
3107          * have previous experience with the remote host. Be careful
3108          * not make cwnd bigger than remote receive window or our own
3109          * send socket buffer. Maybe put some additional upper bound
3110          * on the retrieved cwnd. Should do incremental updates to
3111          * hostcache when cwnd collapses so next connection doesn't
3112          * overloads the path again.
3113          *
3114          * RFC3390 says only do this if SYN or SYN/ACK didn't got lost.
3115          * We currently check only in syncache_socket for that.
3116          */
3117 #define TCP_METRICS_CWND
3118 #ifdef TCP_METRICS_CWND
3119         if (metrics.rmx_cwnd)
3120                 tp->snd_cwnd = max(mss,
3121                                 min(metrics.rmx_cwnd / 2,
3122                                  min(tp->snd_wnd, so->so_snd.sb_hiwat)));
3123         else
3124 #endif
3125         if (tcp_do_rfc3390)
3126                 tp->snd_cwnd = min(4 * mss, max(2 * mss, 4380));
3127 #ifdef INET6
3128         else if ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
3129                  (!isipv6 && in_localaddr(inp->inp_faddr)))
3130 #else
3131         else if (in_localaddr(inp->inp_faddr))
3132 #endif
3133                 tp->snd_cwnd = mss * ss_fltsz_local;
3134         else
3135                 tp->snd_cwnd = mss * ss_fltsz;
3136
3137         /* Check the interface for TSO capabilities. */
3138         if (mtuflags & CSUM_TSO)
3139                 tp->t_flags |= TF_TSO;
3140 }
3141
3142 /*
3143  * Determine the MSS option to send on an outgoing SYN.
3144  */
3145 int
3146 tcp_mssopt(struct in_conninfo *inc)
3147 {
3148         int mss = 0;
3149         u_long maxmtu = 0;
3150         u_long thcmtu = 0;
3151         size_t min_protoh;
3152 #ifdef INET6
3153         int isipv6 = inc->inc_isipv6 ? 1 : 0;
3154 #endif
3155
3156         KASSERT(inc != NULL, ("tcp_mssopt with NULL in_conninfo pointer"));
3157
3158 #ifdef INET6
3159         if (isipv6) {
3160                 mss = tcp_v6mssdflt;
3161                 maxmtu = tcp_maxmtu6(inc, NULL);
3162                 thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */
3163                 min_protoh = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
3164         } else
3165 #endif
3166         {
3167                 mss = tcp_mssdflt;
3168                 maxmtu = tcp_maxmtu(inc, NULL);
3169                 thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */
3170                 min_protoh = sizeof(struct tcpiphdr);
3171         }
3172         if (maxmtu && thcmtu)
3173                 mss = min(maxmtu, thcmtu) - min_protoh;
3174         else if (maxmtu || thcmtu)
3175                 mss = max(maxmtu, thcmtu) - min_protoh;
3176
3177         return (mss);
3178 }
3179
3180
3181 /*
3182  * On a partial ack arrives, force the retransmission of the
3183  * next unacknowledged segment.  Do not clear tp->t_dupacks.
3184  * By setting snd_nxt to ti_ack, this forces retransmission timer to
3185  * be started again.
3186  */
3187 static void
3188 tcp_newreno_partial_ack(struct tcpcb *tp, struct tcphdr *th)
3189 {
3190         tcp_seq onxt = tp->snd_nxt;
3191         u_long  ocwnd = tp->snd_cwnd;
3192
3193         callout_stop(tp->tt_rexmt);
3194         tp->t_rtttime = 0;
3195         tp->snd_nxt = th->th_ack;
3196         /*
3197          * Set snd_cwnd to one segment beyond acknowledged offset.
3198          * (tp->snd_una has not yet been updated when this function is called.)
3199          */
3200         tp->snd_cwnd = tp->t_maxseg + (th->th_ack - tp->snd_una);
3201         tp->t_flags |= TF_ACKNOW;
3202         (void) tcp_output(tp);
3203         tp->snd_cwnd = ocwnd;
3204         if (SEQ_GT(onxt, tp->snd_nxt))
3205                 tp->snd_nxt = onxt;
3206         /*
3207          * Partial window deflation.  Relies on fact that tp->snd_una
3208          * not updated yet.
3209          */
3210         if (tp->snd_cwnd > th->th_ack - tp->snd_una)
3211                 tp->snd_cwnd -= th->th_ack - tp->snd_una;
3212         else
3213                 tp->snd_cwnd = 0;
3214         tp->snd_cwnd += tp->t_maxseg;
3215 }
3216
3217 /*
3218  * Returns 1 if the TIME_WAIT state was killed and we should start over,
3219  * looking for a pcb in the listen state.  Returns 0 otherwise.
3220  */
3221 static int
3222 tcp_timewait(struct inpcb *inp, struct tcpopt *to, struct tcphdr *th,
3223     struct mbuf *m, int tlen)
3224 {
3225         struct tcptw *tw;
3226         int thflags;
3227         tcp_seq seq;
3228 #ifdef INET6
3229         int isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
3230 #else
3231         const int isipv6 = 0;
3232 #endif
3233
3234         /* tcbinfo lock required for tcp_twclose(), tcp_timer_2msl_reset(). */
3235         INP_INFO_WLOCK_ASSERT(&tcbinfo);
3236         INP_LOCK_ASSERT(inp);
3237
3238         /*
3239          * XXXRW: Time wait state for inpcb has been recycled, but inpcb is
3240          * still present.  This is undesirable, but temporarily necessary
3241          * until we work out how to handle inpcb's who's timewait state has
3242          * been removed.
3243          */
3244         tw = intotw(inp);
3245         if (tw == NULL)
3246                 goto drop;
3247
3248         thflags = th->th_flags;
3249
3250         /*
3251          * NOTE: for FIN_WAIT_2 (to be added later),
3252          * must validate sequence number before accepting RST
3253          */
3254
3255         /*
3256          * If the segment contains RST:
3257          *      Drop the segment - see Stevens, vol. 2, p. 964 and
3258          *      RFC 1337.
3259          */
3260         if (thflags & TH_RST)
3261                 goto drop;
3262
3263 #if 0
3264 /* PAWS not needed at the moment */
3265         /*
3266          * RFC 1323 PAWS: If we have a timestamp reply on this segment
3267          * and it's less than ts_recent, drop it.
3268          */
3269         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
3270             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
3271                 if ((thflags & TH_ACK) == 0)
3272                         goto drop;
3273                 goto ack;
3274         }
3275         /*
3276          * ts_recent is never updated because we never accept new segments.
3277          */
3278 #endif
3279
3280         /*
3281          * If a new connection request is received
3282          * while in TIME_WAIT, drop the old connection
3283          * and start over if the sequence numbers
3284          * are above the previous ones.
3285          */
3286         if ((thflags & TH_SYN) && SEQ_GT(th->th_seq, tw->rcv_nxt)) {
3287                 tcp_twclose(tw, 0);
3288                 return (1);
3289         }
3290
3291         /*
3292          * Drop the the segment if it does not contain an ACK.
3293          */
3294         if ((thflags & TH_ACK) == 0)
3295                 goto drop;
3296
3297         /*
3298          * Reset the 2MSL timer if this is a duplicate FIN.
3299          */
3300         if (thflags & TH_FIN) {
3301                 seq = th->th_seq + tlen + (thflags & TH_SYN ? 1 : 0);
3302                 if (seq + 1 == tw->rcv_nxt)
3303                         tcp_timer_2msl_reset(tw, 1);
3304         }
3305
3306         /*
3307          * Acknowledge the segment if it has data or is not a duplicate ACK.
3308          */
3309         if (thflags != TH_ACK || tlen != 0 ||
3310             th->th_seq != tw->rcv_nxt || th->th_ack != tw->snd_nxt)
3311                 tcp_twrespond(tw, TH_ACK);
3312         goto drop;
3313
3314         /*
3315          * Generate a RST, dropping incoming segment.
3316          * Make ACK acceptable to originator of segment.
3317          * Don't bother to respond if destination was broadcast/multicast.
3318          */
3319         if (m->m_flags & (M_BCAST|M_MCAST))
3320                 goto drop;
3321         if (isipv6) {
3322                 struct ip6_hdr *ip6;
3323
3324                 /* IPv6 anycast check is done at tcp6_input() */
3325                 ip6 = mtod(m, struct ip6_hdr *);
3326                 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
3327                     IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
3328                         goto drop;
3329         } else {
3330                 struct ip *ip;
3331
3332                 ip = mtod(m, struct ip *);
3333                 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
3334                     IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
3335                     ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
3336                     in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
3337                         goto drop;
3338         }
3339         if (thflags & TH_ACK) {
3340                 tcp_respond(NULL,
3341                     mtod(m, void *), th, m, 0, th->th_ack, TH_RST);
3342         } else {
3343                 seq = th->th_seq + (thflags & TH_SYN ? 1 : 0);
3344                 tcp_respond(NULL,
3345                     mtod(m, void *), th, m, seq, 0, TH_RST|TH_ACK);
3346         }
3347         INP_UNLOCK(inp);
3348         return (0);
3349
3350 drop:
3351         INP_UNLOCK(inp);
3352         m_freem(m);
3353         return (0);
3354 }