packages/net/bsd_tcpip/v2_0/src/sys/netinet/tcp_input.c

   1 //==========================================================================
   2 //
   3 //      src/sys/netinet/tcp_input.c
   4 //
   5 //==========================================================================
   6 //####BSDCOPYRIGHTBEGIN####
   7 //
   8 // -------------------------------------------
   9 //
  10 // Portions of this software may have been derived from OpenBSD,
  11 // FreeBSD or other sources, and are covered by the appropriate
  12 // copyright disclaimers included herein.
  13 //
  14 // Portions created by Red Hat are
  15 // Copyright (C) 2002 Red Hat, Inc. All Rights Reserved.
  16 //
  17 // -------------------------------------------
  18 //
  19 //####BSDCOPYRIGHTEND####
  20 //==========================================================================
  21
  22 /*
  23  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
  24  *      The Regents of the University of California.  All rights reserved.
  25  *
  26  * Redistribution and use in source and binary forms, with or without
  27  * modification, are permitted provided that the following conditions
  28  * are met:
  29  * 1. Redistributions of source code must retain the above copyright
  30  *    notice, this list of conditions and the following disclaimer.
  31  * 2. Redistributions in binary form must reproduce the above copyright
  32  *    notice, this list of conditions and the following disclaimer in the
  33  *    documentation and/or other materials provided with the distribution.
  34  * 3. All advertising materials mentioning features or use of this software
  35  *    must display the following acknowledgement:
  36  *      This product includes software developed by the University of
  37  *      California, Berkeley and its contributors.
  38  * 4. Neither the name of the University nor the names of its contributors
  39  *    may be used to endorse or promote products derived from this software
  40  *    without specific prior written permission.
  41  *
  42  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  43  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  44  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  45  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  46  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  47  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  48  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  49  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  50  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  51  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  52  * SUCH DAMAGE.
  53  *
  54  *      @(#)tcp_input.c 8.12 (Berkeley) 5/24/95
  55  * $FreeBSD: src/sys/netinet/tcp_input.c,v 1.107.2.16 2001/08/22 00:59:12 silby Exp $
  56  */
  57
  58 #include <sys/param.h>
  59 #include <sys/malloc.h>
  60 #include <sys/mbuf.h>
  61 #include <sys/protosw.h>
  62 #include <sys/socket.h>
  63 #include <sys/sysctl.h>
  64 #include <sys/socketvar.h>
  65
  66 #include <net/if.h>
  67 #include <net/route.h>
  68
  69 #include <netinet/in.h>
  70 #include <netinet/in_systm.h>
  71 #include <netinet/ip.h>
  72 #include <netinet/ip_icmp.h>    /* for ICMP_BANDLIM             */
  73 #include <netinet/in_var.h>
  74 #include <netinet/icmp_var.h>   /* for ICMP_BANDLIM             */
  75 #include <netinet/in_pcb.h>
  76 #include <netinet/ip_var.h>
  77 #ifdef INET6
  78 #include <netinet/ip6.h>
  79 #include <netinet/icmp6.h>
  80 #include <netinet6/nd6.h>
  81 #include <netinet6/ip6_var.h>
  82 #include <netinet6/in6_pcb.h>
  83 #endif
  84 #include <netinet/tcp.h>
  85 #include <netinet/tcp_fsm.h>
  86 #include <netinet/tcp_seq.h>
  87 #include <netinet/tcp_timer.h>
  88 #include <netinet/tcp_var.h>
  89
  90 #ifdef INET6
  91 #include <netinet6/tcp6_var.h>
  92 #endif
  93 #include <netinet/tcpip.h>
  94 #ifdef TCPDEBUG
  95 #include <netinet/tcp_debug.h>
  96
  97 u_char tcp_saveipgen[40]; /* the size must be of max ip header, now IPv6 */
  98 struct tcphdr tcp_savetcp;
  99 #endif /* TCPDEBUG */
 100
 101 #ifdef IPSEC
 102 #include <netinet6/ipsec.h>
 103 #include <netkey/key.h>
 104 #endif /*IPSEC*/
 105
 106 static int      tcprexmtthresh = 3;
 107 tcp_cc  tcp_ccgen;
 108
 109 struct  tcpstat tcpstat;
 110 SYSCTL_STRUCT(_net_inet_tcp, TCPCTL_STATS, stats, CTLFLAG_RD,
 111     &tcpstat , tcpstat, "TCP statistics (struct tcpstat, netinet/tcp_var.h)");
 112
 113 static int log_in_vain = 0;
 114 SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW,
 115     &log_in_vain, 0, "Log all incoming TCP connections");
 116
 117 static int blackhole = 0;
 118 SYSCTL_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_RW,
 119         &blackhole, 0, "Do not send RST when dropping refused connections");
 120
 121 int tcp_delack_enabled = 1;
 122 SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_RW,
 123     &tcp_delack_enabled, 0,
 124     "Delay ACK to try and piggyback it onto a data packet");
 125
 126 int tcp_lq_overflow = 1;
 127 SYSCTL_INT(_net_inet_tcp, OID_AUTO, tcp_lq_overflow, CTLFLAG_RW,
 128     &tcp_lq_overflow, 0,
 129     "Listen Queue Overflow");
 130
 131 #ifdef TCP_DROP_SYNFIN
 132 static int drop_synfin = 0;
 133 SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_RW,
 134     &drop_synfin, 0, "Drop TCP packets with SYN+FIN set");
 135 #endif
 136
 137 struct inpcbhead tcb;
 138 #define tcb6    tcb  /* for KAME src sync over BSD*'s */
 139 struct inpcbinfo tcbinfo;
 140
 141 static void      tcp_dooptions __P((struct tcpcb *,
 142             u_char *, int, struct tcphdr *, struct tcpopt *));
 143 static void      tcp_pulloutofband __P((struct socket *,
 144             struct tcphdr *, struct mbuf *, int));
 145 static int       tcp_reass __P((struct tcpcb *, struct tcphdr *, int *,
 146                                 struct mbuf *));
 147 static void      tcp_xmit_timer __P((struct tcpcb *, int));
 148 static int       tcp_newreno __P((struct tcpcb *, struct tcphdr *));
 149
 150 /* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */
 151 #ifdef INET6
 152 #define ND6_HINT(tp) \
 153 do { \
 154         if ((tp) && (tp)->t_inpcb && \
 155             ((tp)->t_inpcb->inp_vflag & INP_IPV6) != 0 && \
 156             (tp)->t_inpcb->in6p_route.ro_rt) \
 157                 nd6_nud_hint((tp)->t_inpcb->in6p_route.ro_rt, NULL, 0); \
 158 } while (0)
 159 #else
 160 #define ND6_HINT(tp)
 161 #endif
 162
 163 /*
 164  * Indicate whether this ack should be delayed.
 165  */
 166 #define DELAY_ACK(tp) \
 167         (tcp_delack_enabled && !callout_pending(tp->tt_delack))
 168
 169 static int
 170 tcp_reass(tp, th, tlenp, m)
 171         register struct tcpcb *tp;
 172         register struct tcphdr *th;
 173         int *tlenp;
 174         struct mbuf *m;
 175 {
 176         struct tseg_qent *q;
 177         struct tseg_qent *p = NULL;
 178         struct tseg_qent *nq;
 179         struct tseg_qent *te;
 180         struct socket *so = tp->t_inpcb->inp_socket;
 181         int flags;
 182
 183         /*
 184          * Call with th==0 after become established to
 185          * force pre-ESTABLISHED data up to user socket.
 186          */
 187         if (th == 0)
 188                 goto present;
 189
 190         /* Allocate a new queue entry. If we can't, just drop the pkt. XXX */
 191         MALLOC(te, struct tseg_qent *, sizeof (struct tseg_qent), M_TSEGQ,
 192                M_NOWAIT);
 193         if (te == NULL) {
 194                 tcpstat.tcps_rcvmemdrop++;
 195                 m_freem(m);
 196                 return (0);
 197         }
 198
 199         /*
 200          * Find a segment which begins after this one does.
 201          */
 202         LIST_FOREACH(q, &tp->t_segq, tqe_q) {
 203                 if (SEQ_GT(q->tqe_th->th_seq, th->th_seq))
 204                         break;
 205                 p = q;
 206         }
 207
 208         /*
 209          * If there is a preceding segment, it may provide some of
 210          * our data already.  If so, drop the data from the incoming
 211          * segment.  If it provides all of our data, drop us.
 212          */
 213         if (p != NULL) {
 214                 register int i;
 215                 /* conversion to int (in i) handles seq wraparound */
 216                 i = p->tqe_th->th_seq + p->tqe_len - th->th_seq;
 217                 if (i > 0) {
 218                         if (i >= *tlenp) {
 219                                 tcpstat.tcps_rcvduppack++;
 220                                 tcpstat.tcps_rcvdupbyte += *tlenp;
 221                                 m_freem(m);
 222                                 FREE(te, M_TSEGQ);
 223                                 /*
 224                                  * Try to present any queued data
 225                                  * at the left window edge to the user.
 226                                  * This is needed after the 3-WHS
 227                                  * completes.
 228                                  */
 229                                 goto present;   /* ??? */
 230                         }
 231                         m_adj(m, i);
 232                         *tlenp -= i;
 233                         th->th_seq += i;
 234                 }
 235         }
 236         tcpstat.tcps_rcvoopack++;
 237         tcpstat.tcps_rcvoobyte += *tlenp;
 238
 239         /*
 240          * While we overlap succeeding segments trim them or,
 241          * if they are completely covered, dequeue them.
 242          */
 243         while (q) {
 244                 register int i = (th->th_seq + *tlenp) - q->tqe_th->th_seq;
 245                 if (i <= 0)
 246                         break;
 247                 if (i < q->tqe_len) {
 248                         q->tqe_th->th_seq += i;
 249                         q->tqe_len -= i;
 250                         m_adj(q->tqe_m, i);
 251                         break;
 252                 }
 253
 254                 nq = LIST_NEXT(q, tqe_q);
 255                 LIST_REMOVE(q, tqe_q);
 256                 m_freem(q->tqe_m);
 257                 FREE(q, M_TSEGQ);
 258                 q = nq;
 259         }
 260
 261         /* Insert the new segment queue entry into place. */
 262         te->tqe_m = m;
 263         te->tqe_th = th;
 264         te->tqe_len = *tlenp;
 265
 266         if (p == NULL) {
 267                 LIST_INSERT_HEAD(&tp->t_segq, te, tqe_q);
 268         } else {
 269                 LIST_INSERT_AFTER(p, te, tqe_q);
 270         }
 271
 272 present:
 273         /*
 274          * Present data to user, advancing rcv_nxt through
 275          * completed sequence space.
 276          */
 277         if (!TCPS_HAVEESTABLISHED(tp->t_state))
 278                 return (0);
 279         q = LIST_FIRST(&tp->t_segq);
 280         if (!q || q->tqe_th->th_seq != tp->rcv_nxt)
 281                 return (0);
 282         do {
 283                 tp->rcv_nxt += q->tqe_len;
 284                 flags = q->tqe_th->th_flags & TH_FIN;
 285                 nq = LIST_NEXT(q, tqe_q);
 286                 LIST_REMOVE(q, tqe_q);
 287                 if (so->so_state & SS_CANTRCVMORE)
 288                         m_freem(q->tqe_m);
 289                 else
 290                         sbappend(&so->so_rcv, q->tqe_m);
 291                 FREE(q, M_TSEGQ);
 292                 q = nq;
 293         } while (q && q->tqe_th->th_seq == tp->rcv_nxt);
 294         ND6_HINT(tp);
 295         sorwakeup(so);
 296         return (flags);
 297 }
 298
 299 /*
 300  * TCP input routine, follows pages 65-76 of the
 301  * protocol specification dated September, 1981 very closely.
 302  */
 303 #ifdef INET6
 304 int
 305 tcp6_input(mp, offp, proto)
 306         struct mbuf **mp;
 307         int *offp, proto;
 308 {
 309         register struct mbuf *m = *mp;
 310         struct in6_ifaddr *ia6;
 311
 312         IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
 313
 314         /*
 315          * draft-itojun-ipv6-tcp-to-anycast
 316          * better place to put this in?
 317          */
 318         ia6 = ip6_getdstifaddr(m);
 319         if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
 320                 struct ip6_hdr *ip6;
 321
 322                 ip6 = mtod(m, struct ip6_hdr *);
 323                 icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
 324                             (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
 325                 return IPPROTO_DONE;
 326         }
 327
 328         tcp_input(m, *offp);
 329         return IPPROTO_DONE;
 330 }
 331 #endif
 332
 333 void
 334 tcp_input(m, off0)
 335         register struct mbuf *m;
 336         int off0;
 337 {
 338         register struct tcphdr *th;
 339         register struct ip *ip = NULL;
 340         register struct ipovly *ipov;
 341         register struct inpcb *inp;
 342         u_char *optp = NULL;
 343         int optlen = 0;
 344         int len, tlen, off;
 345         int drop_hdrlen;
 346         register struct tcpcb *tp = 0;
 347         register int thflags;
 348         struct socket *so = 0;
 349         int todrop, acked, ourfinisacked, needoutput = 0;
 350         struct in_addr laddr;
 351 #ifdef INET6
 352         struct in6_addr laddr6;
 353 #endif
 354         int dropsocket = 0;
 355         int iss = 0;
 356         u_long tiwin;
 357         struct tcpopt to;               /* options in this segment */
 358         struct rmxp_tao *taop;          /* pointer to our TAO cache entry */
 359         struct rmxp_tao tao_noncached;  /* in case there's no cached entry */
 360 #ifdef TCPDEBUG
 361         short ostate = 0;
 362 #endif
 363 #ifdef INET6
 364         struct ip6_hdr *ip6 = NULL;
 365         int isipv6;
 366 #endif /* INET6 */
 367         int rstreason; /* For badport_bandlim accounting purposes */
 368
 369 #ifdef INET6
 370         isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
 371 #endif
 372         bzero((char *)&to, sizeof(to));
 373
 374         tcpstat.tcps_rcvtotal++;
 375
 376 #ifdef INET6
 377         if (isipv6) {
 378                 /* IP6_EXTHDR_CHECK() is already done at tcp6_input() */
 379                 ip6 = mtod(m, struct ip6_hdr *);
 380                 tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
 381                 if (in6_cksum(m, IPPROTO_TCP, off0, tlen)) {
 382                         tcpstat.tcps_rcvbadsum++;
 383                         goto drop;
 384                 }
 385                 th = (struct tcphdr *)((caddr_t)ip6 + off0);
 386
 387                 /*
 388                  * Be proactive about unspecified IPv6 address in source.
 389                  * As we use all-zero to indicate unbounded/unconnected pcb,
 390                  * unspecified IPv6 address can be used to confuse us.
 391                  *
 392                  * Note that packets with unspecified IPv6 destination is
 393                  * already dropped in ip6_input.
 394                  */
 395                 if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
 396                         /* XXX stat */
 397                         goto drop;
 398                 }
 399         } else
 400 #endif /* INET6 */
 401       {
 402         /*
 403          * Get IP and TCP header together in first mbuf.
 404          * Note: IP leaves IP header in first mbuf.
 405          */
 406         if (off0 > sizeof (struct ip)) {
 407                 ip_stripoptions(m, (struct mbuf *)0);
 408                 off0 = sizeof(struct ip);
 409         }
 410         if (m->m_len < sizeof (struct tcpiphdr)) {
 411                 if ((m = m_pullup(m, sizeof (struct tcpiphdr))) == 0) {
 412                         tcpstat.tcps_rcvshort++;
 413                         return;
 414                 }
 415         }
 416         ip = mtod(m, struct ip *);
 417         ipov = (struct ipovly *)ip;
 418         th = (struct tcphdr *)((caddr_t)ip + off0);
 419         tlen = ip->ip_len;
 420
 421         if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
 422                 if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
 423                         th->th_sum = m->m_pkthdr.csum_data;
 424                 else
 425                         th->th_sum = in_pseudo(ip->ip_src.s_addr,
 426                             ip->ip_dst.s_addr, htonl(m->m_pkthdr.csum_data +
 427                             ip->ip_len + IPPROTO_TCP));
 428                 th->th_sum ^= 0xffff;
 429         } else {
 430                 /*
 431                  * Checksum extended TCP header and data.
 432                  */
 433                 len = sizeof (struct ip) + tlen;
 434                 bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
 435                 ipov->ih_len = (u_short)tlen;
 436                 HTONS(ipov->ih_len);
 437                 th->th_sum = in_cksum(m, len);
 438         }
 439         if (th->th_sum) {
 440                 tcpstat.tcps_rcvbadsum++;
 441                 goto drop;
 442         }
 443 #ifdef INET6
 444         /* Re-initialization for later version check */
 445         ip->ip_v = IPVERSION;
 446 #endif
 447       }
 448
 449         /*
 450          * Check that TCP offset makes sense,
 451          * pull out TCP options and adjust length.              XXX
 452          */
 453         off = th->th_off << 2;
 454         if (off < sizeof (struct tcphdr) || off > tlen) {
 455                 tcpstat.tcps_rcvbadoff++;
 456                 goto drop;
 457         }
 458         tlen -= off;    /* tlen is used instead of ti->ti_len */
 459         if (off > sizeof (struct tcphdr)) {
 460 #ifdef INET6
 461                 if (isipv6) {
 462                         IP6_EXTHDR_CHECK(m, off0, off, );
 463                         ip6 = mtod(m, struct ip6_hdr *);
 464                         th = (struct tcphdr *)((caddr_t)ip6 + off0);
 465                 } else
 466 #endif /* INET6 */
 467               {
 468                 if (m->m_len < sizeof(struct ip) + off) {
 469                         if ((m = m_pullup(m, sizeof (struct ip) + off)) == 0) {
 470                                 tcpstat.tcps_rcvshort++;
 471                                 return;
 472                         }
 473                         ip = mtod(m, struct ip *);
 474                         ipov = (struct ipovly *)ip;
 475                         th = (struct tcphdr *)((caddr_t)ip + off0);
 476                 }
 477               }
 478                 optlen = off - sizeof (struct tcphdr);
 479                 optp = (u_char *)(th + 1);
 480         }
 481         thflags = th->th_flags;
 482
 483 #ifdef TCP_DROP_SYNFIN
 484         /*
 485          * If the drop_synfin option is enabled, drop all packets with
 486          * both the SYN and FIN bits set. This prevents e.g. nmap from
 487          * identifying the TCP/IP stack.
 488          *
 489          * This is incompatible with RFC1644 extensions (T/TCP).
 490          */
 491         if (drop_synfin && (thflags & (TH_SYN|TH_FIN)) == (TH_SYN|TH_FIN))
 492                 goto drop;
 493 #endif
 494
 495         /*
 496          * Convert TCP protocol specific fields to host format.
 497          */
 498         NTOHL(th->th_seq);
 499         NTOHL(th->th_ack);
 500         NTOHS(th->th_win);
 501         NTOHS(th->th_urp);
 502
 503         /*
 504          * Delay droping TCP, IP headers, IPv6 ext headers, and TCP options,
 505          * until after ip6_savecontrol() is called and before other functions
 506          * which don't want those proto headers.
 507          * Because ip6_savecontrol() is going to parse the mbuf to
 508          * search for data to be passed up to user-land, it wants mbuf
 509          * parameters to be unchanged.
 510          */
 511         drop_hdrlen = off0 + off;
 512
 513         /*
 514          * Locate pcb for segment.
 515          */
 516 findpcb:
 517 #ifdef IPFIREWALL_FORWARD
 518         if (ip_fw_fwd_addr != NULL
 519 #ifdef INET6
 520             && isipv6 == NULL /* IPv6 support is not yet */
 521 #endif /* INET6 */
 522             ) {
 523                 /*
 524                  * Diverted. Pretend to be the destination.
 525                  * already got one like this?
 526                  */
 527                 inp = in_pcblookup_hash(&tcbinfo, ip->ip_src, th->th_sport,
 528                         ip->ip_dst, th->th_dport, 0, m->m_pkthdr.rcvif);
 529                 if (!inp) {
 530                         /*
 531                          * No, then it's new. Try find the ambushing socket
 532                          */
 533                         if (!ip_fw_fwd_addr->sin_port) {
 534                                 inp = in_pcblookup_hash(&tcbinfo, ip->ip_src,
 535                                     th->th_sport, ip_fw_fwd_addr->sin_addr,
 536                                     th->th_dport, 1, m->m_pkthdr.rcvif);
 537                         } else {
 538                                 inp = in_pcblookup_hash(&tcbinfo,
 539                                     ip->ip_src, th->th_sport,
 540                                     ip_fw_fwd_addr->sin_addr,
 541                                     ntohs(ip_fw_fwd_addr->sin_port), 1,
 542                                     m->m_pkthdr.rcvif);
 543                         }
 544                 }
 545                 ip_fw_fwd_addr = NULL;
 546         } else
 547 #endif  /* IPFIREWALL_FORWARD */
 548       {
 549 #ifdef INET6
 550         if (isipv6)
 551                 inp = in6_pcblookup_hash(&tcbinfo, &ip6->ip6_src, th->th_sport,
 552                                          &ip6->ip6_dst, th->th_dport, 1,
 553                                          m->m_pkthdr.rcvif);
 554         else
 555 #endif /* INET6 */
 556         inp = in_pcblookup_hash(&tcbinfo, ip->ip_src, th->th_sport,
 557             ip->ip_dst, th->th_dport, 1, m->m_pkthdr.rcvif);
 558       }
 559
 560 #ifdef IPSEC
 561 #ifdef INET6
 562         if (isipv6) {
 563                 if (inp != NULL && ipsec6_in_reject_so(m, inp->inp_socket)) {
 564                         ipsec6stat.in_polvio++;
 565                         goto drop;
 566                 }
 567         } else
 568 #endif /* INET6 */
 569         if (inp != NULL && ipsec4_in_reject_so(m, inp->inp_socket)) {
 570                 ipsecstat.in_polvio++;
 571                 goto drop;
 572         }
 573 #endif /*IPSEC*/
 574
 575         /*
 576          * If the state is CLOSED (i.e., TCB does not exist) then
 577          * all data in the incoming segment is discarded.
 578          * If the TCB exists but is in CLOSED state, it is embryonic,
 579          * but should either do a listen or a connect soon.
 580          */
 581         if (inp == NULL) {
 582                 if (log_in_vain) {
 583 #ifdef INET6
 584                         char dbuf[INET6_ADDRSTRLEN], sbuf[INET6_ADDRSTRLEN];
 585 #else /* INET6 */
 586                         char dbuf[4*sizeof "123"], sbuf[4*sizeof "123"];
 587 #endif /* INET6 */
 588
 589 #ifdef INET6
 590                         if (isipv6) {
 591                                 strcpy(dbuf, ip6_sprintf(&ip6->ip6_dst));
 592                                 strcpy(sbuf, ip6_sprintf(&ip6->ip6_src));
 593                         } else
 594 #endif
 595                       {
 596                         strcpy(dbuf, inet_ntoa(ip->ip_dst));
 597                         strcpy(sbuf, inet_ntoa(ip->ip_src));
 598                       }
 599                         switch (log_in_vain) {
 600                         case 1:
 601                                 if(thflags & TH_SYN)
 602                                         log(LOG_INFO,
 603                                         "Connection attempt to TCP %s:%d from %s:%d\n",
 604                                         dbuf, ntohs(th->th_dport),
 605                                         sbuf,
 606                                         ntohs(th->th_sport));
 607                                 break;
 608                         case 2:
 609                                 log(LOG_INFO,
 610                                 "Connection attempt to TCP %s:%d from %s:%d flags:0x%x\n",
 611                                 dbuf, ntohs(th->th_dport), sbuf,
 612                                 ntohs(th->th_sport), thflags);
 613                                 break;
 614                         default:
 615                                 break;
 616                         }
 617                 }
 618                 if (blackhole) {
 619                         switch (blackhole) {
 620                         case 1:
 621                                 if (thflags & TH_SYN)
 622                                         goto drop;
 623                                 break;
 624                         case 2:
 625                                 goto drop;
 626                         default:
 627                                 goto drop;
 628                         }
 629                 }
 630                 rstreason = BANDLIM_RST_CLOSEDPORT;
 631                 goto dropwithreset;
 632         }
 633         tp = intotcpcb(inp);
 634         if (tp == 0) {
 635                 rstreason = BANDLIM_RST_CLOSEDPORT;
 636                 goto dropwithreset;
 637         }
 638         if (tp->t_state == TCPS_CLOSED)
 639                 goto drop;
 640
 641         /* Unscale the window into a 32-bit value. */
 642         if ((thflags & TH_SYN) == 0)
 643                 tiwin = th->th_win << tp->snd_scale;
 644         else
 645                 tiwin = th->th_win;
 646
 647         so = inp->inp_socket;
 648         if (so->so_options & (SO_DEBUG|SO_ACCEPTCONN)) {
 649 #ifdef TCPDEBUG
 650                 if (so->so_options & SO_DEBUG) {
 651                         ostate = tp->t_state;
 652 #ifdef INET6
 653                         if (isipv6)
 654                                 bcopy((char *)ip6, (char *)tcp_saveipgen,
 655                                       sizeof(*ip6));
 656                         else
 657 #endif /* INET6 */
 658                         bcopy((char *)ip, (char *)tcp_saveipgen, sizeof(*ip));
 659                         tcp_savetcp = *th;
 660                 }
 661 #endif
 662                 if (so->so_options & SO_ACCEPTCONN) {
 663                         register struct tcpcb *tp0 = tp;
 664                         struct socket *so2;
 665 #ifdef IPSEC
 666                         struct socket *oso;
 667 #endif
 668 #ifdef INET6
 669                         struct inpcb *oinp = sotoinpcb(so);
 670 #endif /* INET6 */
 671
 672 #ifndef IPSEC
 673                         /*
 674                          * Current IPsec implementation makes incorrect IPsec
 675                          * cache if this check is done here.
 676                          * So delay this until duplicated socket is created.
 677                          */
 678                         if ((thflags & (TH_RST|TH_ACK|TH_SYN)) != TH_SYN) {
 679                                 /*
 680                                  * Note: dropwithreset makes sure we don't
 681                                  * send a RST in response to a RST.
 682                                  */
 683                                 if (thflags & TH_ACK) {
 684                                         tcpstat.tcps_badsyn++;
 685                                         rstreason = BANDLIM_RST_OPENPORT;
 686                                         goto dropwithreset;
 687                                 }
 688                                 goto drop;
 689                         }
 690 #endif
 691
 692 #ifdef INET6
 693                         /*
 694                          * If deprecated address is forbidden,
 695                          * we do not accept SYN to deprecated interface
 696                          * address to prevent any new inbound connection from
 697                          * getting established.
 698                          * When we do not accept SYN, we send a TCP RST,
 699                          * with deprecated source address (instead of dropping
 700                          * it).  We compromise it as it is much better for peer
 701                          * to send a RST, and RST will be the final packet
 702                          * for the exchange.
 703                          *
 704                          * If we do not forbid deprecated addresses, we accept
 705                          * the SYN packet.  RFC2462 does not suggest dropping
 706                          * SYN in this case.
 707                          * If we decipher RFC2462 5.5.4, it says like this:
 708                          * 1. use of deprecated addr with existing
 709                          *    communication is okay - "SHOULD continue to be
 710                          *    used"
 711                          * 2. use of it with new communication:
 712                          *   (2a) "SHOULD NOT be used if alternate address
 713                          *        with sufficient scope is available"
 714                          *   (2b) nothing mentioned otherwise.
 715                          * Here we fall into (2b) case as we have no choice in
 716                          * our source address selection - we must obey the peer.
 717                          *
 718                          * The wording in RFC2462 is confusing, and there are
 719                          * multiple description text for deprecated address
 720                          * handling - worse, they are not exactly the same.
 721                          * I believe 5.5.4 is the best one, so we follow 5.5.4.
 722                          */
 723                         if (isipv6 && !ip6_use_deprecated) {
 724                                 struct in6_ifaddr *ia6;
 725
 726                                 if ((ia6 = ip6_getdstifaddr(m)) &&
 727                                     (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
 728                                         tp = NULL;
 729                                         rstreason = BANDLIM_RST_OPENPORT;
 730                                         goto dropwithreset;
 731                                 }
 732                         }
 733 #endif
 734
 735                         so2 = sonewconn(so, 0);
 736                         if (so2 == 0) {
 737                                 tcpstat.tcps_listendrop++;
 738                                 so2 = sodropablereq(so);
 739                                 if (so2) {
 740                                         if (tcp_lq_overflow)
 741                                                 sototcpcb(so2)->t_flags |=
 742                                                     TF_LQ_OVERFLOW;
 743                                         tcp_drop(sototcpcb(so2), ETIMEDOUT);
 744                                         so2 = sonewconn(so, 0);
 745                                 }
 746                                 if (!so2)
 747                                         goto drop;
 748                         }
 749 #ifdef IPSEC
 750                         oso = so;
 751 #endif
 752                         so = so2;
 753                         /*
 754                          * This is ugly, but ....
 755                          *
 756                          * Mark socket as temporary until we're
 757                          * committed to keeping it.  The code at
 758                          * ``drop'' and ``dropwithreset'' check the
 759                          * flag dropsocket to see if the temporary
 760                          * socket created here should be discarded.
 761                          * We mark the socket as discardable until
 762                          * we're committed to it below in TCPS_LISTEN.
 763                          */
 764                         dropsocket++;
 765                         inp = (struct inpcb *)so->so_pcb;
 766 #ifdef INET6
 767                         if (isipv6)
 768                                 inp->in6p_laddr = ip6->ip6_dst;
 769                         else {
 770                                 inp->inp_vflag &= ~INP_IPV6;
 771                                 inp->inp_vflag |= INP_IPV4;
 772 #endif /* INET6 */
 773                         inp->inp_laddr = ip->ip_dst;
 774 #ifdef INET6
 775                         }
 776 #endif /* INET6 */
 777                         inp->inp_lport = th->th_dport;
 778                         if (in_pcbinshash(inp) != 0) {
 779                                 /*
 780                                  * Undo the assignments above if we failed to
 781                                  * put the PCB on the hash lists.
 782                                  */
 783 #ifdef INET6
 784                                 if (isipv6)
 785                                         inp->in6p_laddr = in6addr_any;
 786                                 else
 787 #endif /* INET6 */
 788                                 inp->inp_laddr.s_addr = INADDR_ANY;
 789                                 inp->inp_lport = 0;
 790                                 goto drop;
 791                         }
 792 #ifdef IPSEC
 793                         /*
 794                          * To avoid creating incorrectly cached IPsec
 795                          * association, this is need to be done here.
 796                          *
 797                          * Subject: (KAME-snap 748)
 798                          * From: Wayne Knowles <w.knowles@niwa.cri.nz>
 799                          * ftp://ftp.kame.net/pub/mail-list/snap-users/748
 800                          */
 801                         if ((thflags & (TH_RST|TH_ACK|TH_SYN)) != TH_SYN) {
 802                                 /*
 803                                  * Note: dropwithreset makes sure we don't
 804                                  * send a RST in response to a RST.
 805                                  */
 806                                 if (thflags & TH_ACK) {
 807                                         tcpstat.tcps_badsyn++;
 808                                         rstreason = BANDLIM_RST_OPENPORT;
 809                                         goto dropwithreset;
 810                                 }
 811                                 goto drop;
 812                         }
 813 #endif
 814 #ifdef INET6
 815                         if (isipv6) {
 816                                 /*
 817                                  * Inherit socket options from the listening
 818                                  * socket.
 819                                  * Note that in6p_inputopts are not (even
 820                                  * should not be) copied, since it stores
 821                                  * previously received options and is used to
 822                                  * detect if each new option is different than
 823                                  * the previous one and hence should be passed
 824                                  * to a user.
 825                                  * If we copied in6p_inputopts, a user would
 826                                  * not be able to receive options just after
 827                                  * calling the accept system call.
 828                                  */
 829                                 inp->inp_flags |=
 830                                         oinp->inp_flags & INP_CONTROLOPTS;
 831                                 if (oinp->in6p_outputopts)
 832                                         inp->in6p_outputopts =
 833                                                 ip6_copypktopts(oinp->in6p_outputopts,
 834                                                                 M_NOWAIT);
 835                         } else
 836 #endif /* INET6 */
 837                         inp->inp_options = ip_srcroute();
 838 #ifdef IPSEC
 839                         /* copy old policy into new socket's */
 840                         if (ipsec_copy_policy(sotoinpcb(oso)->inp_sp,
 841                                               inp->inp_sp))
 842                                 printf("tcp_input: could not copy policy\n");
 843 #endif
 844                         tp = intotcpcb(inp);
 845                         tp->t_state = TCPS_LISTEN;
 846                         tp->t_flags |= tp0->t_flags & (TF_NOPUSH|TF_NOOPT);
 847
 848                         /* Compute proper scaling value from buffer space */
 849                         while (tp->request_r_scale < TCP_MAX_WINSHIFT &&
 850                            TCP_MAXWIN << tp->request_r_scale <
 851                            so->so_rcv.sb_hiwat)
 852                                 tp->request_r_scale++;
 853                 }
 854         }
 855
 856 #ifdef INET6
 857         /* save packet options if user wanted */
 858         if (isipv6 && (inp->in6p_flags & INP_CONTROLOPTS) != 0) {
 859                 struct ip6_recvpktopts opts6;
 860
 861                 /*
 862                  * Temporarily re-adjusting the mbuf before ip6_savecontrol(),
 863                  * which is necessary for FreeBSD only due to difference from
 864                  * other BSD stacks.
 865                  * XXX: we'll soon make a more natural fix after getting a
 866                  *      consensus.
 867                  */
 868                 ip6_savecontrol(inp, ip6, m, &opts6, &inp->in6p_inputopts);
 869                 if (inp->in6p_inputopts)
 870                         ip6_update_recvpcbopt(inp->in6p_inputopts, &opts6);
 871                 if (opts6.head) {
 872                         if (sbappendcontrol(&inp->in6p_socket->so_rcv,
 873                                             NULL, opts6.head)
 874                             == 0)
 875                                 m_freem(opts6.head);
 876                 }
 877         }
 878 #endif /* INET6 */
 879
 880         /*
 881          * Segment received on connection.
 882          * Reset idle time and keep-alive timer.
 883          */
 884         tp->t_rcvtime = ticks;
 885         if (TCPS_HAVEESTABLISHED(tp->t_state))
 886                 callout_reset(tp->tt_keep, tcp_keepidle, tcp_timer_keep, tp);
 887
 888         /*
 889          * Process options if not in LISTEN state,
 890          * else do it below (after getting remote address).
 891          */
 892         if (tp->t_state != TCPS_LISTEN)
 893                 tcp_dooptions(tp, optp, optlen, th, &to);
 894
 895         /*
 896          * Header prediction: check for the two common cases
 897          * of a uni-directional data xfer.  If the packet has
 898          * no control flags, is in-sequence, the window didn't
 899          * change and we're not retransmitting, it's a
 900          * candidate.  If the length is zero and the ack moved
 901          * forward, we're the sender side of the xfer.  Just
 902          * free the data acked & wake any higher level process
 903          * that was blocked waiting for space.  If the length
 904          * is non-zero and the ack didn't move, we're the
 905          * receiver side.  If we're getting packets in-order
 906          * (the reassembly queue is empty), add the data to
 907          * the socket buffer and note that we need a delayed ack.
 908          * Make sure that the hidden state-flags are also off.
 909          * Since we check for TCPS_ESTABLISHED above, it can only
 910          * be TH_NEEDSYN.
 911          */
 912         if (tp->t_state == TCPS_ESTABLISHED &&
 913             (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
 914             ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
 915             ((to.to_flag & TOF_TS) == 0 ||
 916              TSTMP_GEQ(to.to_tsval, tp->ts_recent)) &&
 917             /*
 918              * Using the CC option is compulsory if once started:
 919              *   the segment is OK if no T/TCP was negotiated or
 920              *   if the segment has a CC option equal to CCrecv
 921              */
 922             ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) != (TF_REQ_CC|TF_RCVD_CC) ||
 923              ((to.to_flag & TOF_CC) != 0 && to.to_cc == tp->cc_recv)) &&
 924             th->th_seq == tp->rcv_nxt &&
 925             tiwin && tiwin == tp->snd_wnd &&
 926             tp->snd_nxt == tp->snd_max) {
 927
 928                 /*
 929                  * If last ACK falls within this segment's sequence numbers,
 930                  * record the timestamp.
 931                  * NOTE that the test is modified according to the latest
 932                  * proposal of the tcplw@cray.com list (Braden 1993/04/26).
 933                  */
 934                 if ((to.to_flag & TOF_TS) != 0 &&
 935                    SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
 936                         tp->ts_recent_age = ticks;
 937                         tp->ts_recent = to.to_tsval;
 938                 }
 939
 940                 if (tlen == 0) {
 941                         if (SEQ_GT(th->th_ack, tp->snd_una) &&
 942                             SEQ_LEQ(th->th_ack, tp->snd_max) &&
 943                             tp->snd_cwnd >= tp->snd_wnd &&
 944                             tp->t_dupacks < tcprexmtthresh) {
 945                                 /*
 946                                  * this is a pure ack for outstanding data.
 947                                  */
 948                                 ++tcpstat.tcps_predack;
 949                                 /*
 950                                  * "bad retransmit" recovery
 951                                  */
 952                                 if (tp->t_rxtshift == 1 &&
 953                                     ticks < tp->t_badrxtwin) {
 954                                         tp->snd_cwnd = tp->snd_cwnd_prev;
 955                                         tp->snd_ssthresh =
 956                                             tp->snd_ssthresh_prev;
 957                                         tp->snd_nxt = tp->snd_max;
 958                                         tp->t_badrxtwin = 0;
 959                                 }
 960                                 if ((to.to_flag & TOF_TS) != 0)
 961                                         tcp_xmit_timer(tp,
 962                                             ticks - to.to_tsecr + 1);
 963                                 else if (tp->t_rtttime &&
 964                                             SEQ_GT(th->th_ack, tp->t_rtseq))
 965                                         tcp_xmit_timer(tp, ticks - tp->t_rtttime);
 966                                 acked = th->th_ack - tp->snd_una;
 967                                 tcpstat.tcps_rcvackpack++;
 968                                 tcpstat.tcps_rcvackbyte += acked;
 969                                 sbdrop(&so->so_snd, acked);
 970                                 tp->snd_una = th->th_ack;
 971                                 m_freem(m);
 972                                 ND6_HINT(tp); /* some progress has been done */
 973
 974                                 /*
 975                                  * If all outstanding data are acked, stop
 976                                  * retransmit timer, otherwise restart timer
 977                                  * using current (possibly backed-off) value.
 978                                  * If process is waiting for space,
 979                                  * wakeup/selwakeup/signal.  If data
 980                                  * are ready to send, let tcp_output
 981                                  * decide between more output or persist.
 982                                  */
 983                                 if (tp->snd_una == tp->snd_max)
 984                                         callout_stop(tp->tt_rexmt);
 985                                 else if (!callout_active(tp->tt_persist))
 986                                         callout_reset(tp->tt_rexmt,
 987                                                       tp->t_rxtcur,
 988                                                       tcp_timer_rexmt, tp);
 989
 990                                 sowwakeup(so);
 991                                 if (so->so_snd.sb_cc)
 992                                         (void) tcp_output(tp);
 993                                 return;
 994                         }
 995                 } else if (th->th_ack == tp->snd_una &&
 996                     LIST_EMPTY(&tp->t_segq) &&
 997                     tlen <= sbspace(&so->so_rcv)) {
 998                         /*
 999                          * this is a pure, in-sequence data packet
1000                          * with nothing on the reassembly queue and
1001                          * we have enough buffer space to take it.
1002                          */
1003                         ++tcpstat.tcps_preddat;
1004                         tp->rcv_nxt += tlen;
1005                         tcpstat.tcps_rcvpack++;
1006                         tcpstat.tcps_rcvbyte += tlen;
1007                         ND6_HINT(tp);   /* some progress has been done */
1008                         /*
1009                          * Add data to socket buffer.
1010                          */
1011                         m_adj(m, drop_hdrlen);  /* delayed header drop */
1012                         sbappend(&so->so_rcv, m);
1013                         sorwakeup(so);
1014                         if (DELAY_ACK(tp)) {
1015                                 callout_reset(tp->tt_delack, tcp_delacktime,
1016                                     tcp_timer_delack, tp);
1017                         } else {
1018                                 tp->t_flags |= TF_ACKNOW;
1019                                 tcp_output(tp);
1020                         }
1021                         return;
1022                 }
1023         }
1024
1025         /*
1026          * Calculate amount of space in receive window,
1027          * and then do TCP input processing.
1028          * Receive window is amount of space in rcv queue,
1029          * but not less than advertised window.
1030          */
1031         { int win;
1032
1033         win = sbspace(&so->so_rcv);
1034         if (win < 0)
1035                 win = 0;
1036         tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
1037         }
1038
1039         switch (tp->t_state) {
1040
1041         /*
1042          * If the state is LISTEN then ignore segment if it contains an RST.
1043          * If the segment contains an ACK then it is bad and send a RST.
1044          * If it does not contain a SYN then it is not interesting; drop it.
1045          * If it is from this socket, drop it, it must be forged.
1046          * Don't bother responding if the destination was a broadcast.
1047          * Otherwise initialize tp->rcv_nxt, and tp->irs, select an initial
1048          * tp->iss, and send a segment:
1049          *     <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
1050          * Also initialize tp->snd_nxt to tp->iss+1 and tp->snd_una to tp->iss.
1051          * Fill in remote peer address fields if not previously specified.
1052          * Enter SYN_RECEIVED state, and process any other fields of this
1053          * segment in this state.
1054          */
1055         case TCPS_LISTEN: {
1056                 register struct sockaddr_in *sin;
1057 #ifdef INET6
1058                 register struct sockaddr_in6 *sin6;
1059 #endif
1060
1061                 if (thflags & TH_RST)
1062                         goto drop;
1063                 if (thflags & TH_ACK) {
1064                         rstreason = BANDLIM_RST_OPENPORT;
1065                         goto dropwithreset;
1066                 }
1067                 if ((thflags & TH_SYN) == 0)
1068                         goto drop;
1069                 if (th->th_dport == th->th_sport) {
1070 #ifdef INET6
1071                         if (isipv6) {
1072                                 if (IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst,
1073                                                        &ip6->ip6_src))
1074                                         goto drop;
1075                         } else
1076 #endif /* INET6 */
1077                         if (ip->ip_dst.s_addr == ip->ip_src.s_addr)
1078                                 goto drop;
1079                 }
1080                 /*
1081                  * RFC1122 4.2.3.10, p. 104: discard bcast/mcast SYN
1082                  * in_broadcast() should never return true on a received
1083                  * packet with M_BCAST not set.
1084                  *
1085                  * Packets with a multicast source address should also
1086                  * be discarded.
1087                  */
1088                 if (m->m_flags & (M_BCAST|M_MCAST))
1089                         goto drop;
1090 #ifdef INET6
1091                 if (isipv6) {
1092                         if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
1093                             IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
1094                                 goto drop;
1095                 } else
1096 #endif
1097                 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
1098                     IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
1099                     ip->ip_src.s_addr == htonl(INADDR_BROADCAST))
1100                         goto drop;
1101 #ifdef INET6
1102                 if (isipv6) {
1103                         MALLOC(sin6, struct sockaddr_in6 *, sizeof *sin6,
1104                                M_SONAME, M_NOWAIT);
1105                         if (sin6 == NULL)
1106                                 goto drop;
1107                         bzero(sin6, sizeof(*sin6));
1108                         sin6->sin6_family = AF_INET6;
1109                         sin6->sin6_len = sizeof(*sin6);
1110                         sin6->sin6_addr = ip6->ip6_src;
1111                         sin6->sin6_port = th->th_sport;
1112                         laddr6 = inp->in6p_laddr;
1113                         if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
1114                                 inp->in6p_laddr = ip6->ip6_dst;
1115                         if (in6_pcbconnect(inp, (struct sockaddr *)sin6,
1116                                            (struct proc *)&proc0)) {
1117                                 inp->in6p_laddr = laddr6;
1118                                 FREE(sin6, M_SONAME);
1119                                 goto drop;
1120                         }
1121                         FREE(sin6, M_SONAME);
1122                 } else
1123 #endif
1124               {
1125                 MALLOC(sin, struct sockaddr_in *, sizeof *sin, M_SONAME,
1126                        M_NOWAIT);
1127                 if (sin == NULL)
1128                         goto drop;
1129                 sin->sin_family = AF_INET;
1130                 sin->sin_len = sizeof(*sin);
1131                 sin->sin_addr = ip->ip_src;
1132                 sin->sin_port = th->th_sport;
1133                 bzero((caddr_t)sin->sin_zero, sizeof(sin->sin_zero));
1134                 laddr = inp->inp_laddr;
1135                 if (inp->inp_laddr.s_addr == INADDR_ANY)
1136                         inp->inp_laddr = ip->ip_dst;
1137                 if (in_pcbconnect(inp, (struct sockaddr *)sin, proc0)) {
1138                         inp->inp_laddr = laddr;
1139                         FREE(sin, M_SONAME);
1140                         goto drop;
1141                 }
1142                 FREE(sin, M_SONAME);
1143               }
1144                 if ((taop = tcp_gettaocache(inp)) == NULL) {
1145                         taop = &tao_noncached;
1146                         bzero(taop, sizeof(*taop));
1147                 }
1148                 tcp_dooptions(tp, optp, optlen, th, &to);
1149                 if (iss)
1150                         tp->iss = iss;
1151                 else {
1152                         tp->iss = tcp_new_isn(tp);
1153                 }
1154                 tp->irs = th->th_seq;
1155                 tcp_sendseqinit(tp);
1156                 tcp_rcvseqinit(tp);
1157                 tp->snd_recover = tp->snd_una;
1158                 /*
1159                  * Initialization of the tcpcb for transaction;
1160                  *   set SND.WND = SEG.WND,
1161                  *   initialize CCsend and CCrecv.
1162                  */
1163                 tp->snd_wnd = tiwin;    /* initial send-window */
1164                 tp->cc_send = CC_INC(tcp_ccgen);
1165                 tp->cc_recv = to.to_cc;
1166                 /*
1167                  * Perform TAO test on incoming CC (SEG.CC) option, if any.
1168                  * - compare SEG.CC against cached CC from the same host,
1169                  *      if any.
1170                  * - if SEG.CC > chached value, SYN must be new and is accepted
1171                  *      immediately: save new CC in the cache, mark the socket
1172                  *      connected, enter ESTABLISHED state, turn on flag to
1173                  *      send a SYN in the next segment.
1174                  *      A virtual advertised window is set in rcv_adv to
1175                  *      initialize SWS prevention.  Then enter normal segment
1176                  *      processing: drop SYN, process data and FIN.
1177                  * - otherwise do a normal 3-way handshake.
1178                  */
1179                 if ((to.to_flag & TOF_CC) != 0) {
1180                     if (((tp->t_flags & TF_NOPUSH) != 0) &&
1181                         taop->tao_cc != 0 && CC_GT(to.to_cc, taop->tao_cc)) {
1182
1183                         taop->tao_cc = to.to_cc;
1184                         tp->t_starttime = ticks;
1185                         tp->t_state = TCPS_ESTABLISHED;
1186
1187                         /*
1188                          * If there is a FIN, or if there is data and the
1189                          * connection is local, then delay SYN,ACK(SYN) in
1190                          * the hope of piggy-backing it on a response
1191                          * segment.  Otherwise must send ACK now in case
1192                          * the other side is slow starting.
1193                          */
1194                         if (DELAY_ACK(tp) && ((thflags & TH_FIN) ||
1195                             (tlen != 0 &&
1196 #ifdef INET6
1197                               ((isipv6 && in6_localaddr(&inp->in6p_faddr))
1198                               ||
1199                               (!isipv6 &&
1200 #endif
1201                             in_localaddr(inp->inp_faddr)
1202 #ifdef INET6
1203                                ))
1204 #endif
1205                              ))) {
1206                                 callout_reset(tp->tt_delack, tcp_delacktime,
1207                                     tcp_timer_delack, tp);
1208                                 tp->t_flags |= TF_NEEDSYN;
1209                         } else
1210                                 tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
1211
1212                         /*
1213                          * Limit the `virtual advertised window' to TCP_MAXWIN
1214                          * here.  Even if we requested window scaling, it will
1215                          * become effective only later when our SYN is acked.
1216                          */
1217                         tp->rcv_adv += min(tp->rcv_wnd, TCP_MAXWIN);
1218                         tcpstat.tcps_connects++;
1219                         soisconnected(so);
1220                         callout_reset(tp->tt_keep, tcp_keepinit,
1221                                       tcp_timer_keep, tp);
1222                         dropsocket = 0;         /* committed to socket */
1223                         tcpstat.tcps_accepts++;
1224                         goto trimthenstep6;
1225                     }
1226                 /* else do standard 3-way handshake */
1227                 } else {
1228                     /*
1229                      * No CC option, but maybe CC.NEW:
1230                      *   invalidate cached value.
1231                      */
1232                      taop->tao_cc = 0;
1233                 }
1234                 /*
1235                  * TAO test failed or there was no CC option,
1236                  *    do a standard 3-way handshake.
1237                  */
1238                 tp->t_flags |= TF_ACKNOW;
1239                 tp->t_state = TCPS_SYN_RECEIVED;
1240                 callout_reset(tp->tt_keep, tcp_keepinit, tcp_timer_keep, tp);
1241                 dropsocket = 0;         /* committed to socket */
1242                 tcpstat.tcps_accepts++;
1243                 goto trimthenstep6;
1244                 }
1245
1246         /*
1247          * If the state is SYN_RECEIVED:
1248          *      if seg contains an ACK, but not for our SYN/ACK, send a RST.
1249          */
1250         case TCPS_SYN_RECEIVED:
1251                 if ((thflags & TH_ACK) &&
1252                     (SEQ_LEQ(th->th_ack, tp->snd_una) ||
1253                      SEQ_GT(th->th_ack, tp->snd_max))) {
1254                                 rstreason = BANDLIM_RST_OPENPORT;
1255                                 goto dropwithreset;
1256                 }
1257                 break;
1258
1259         /*
1260          * If the state is SYN_SENT:
1261          *      if seg contains an ACK, but not for our SYN, drop the input.
1262          *      if seg contains a RST, then drop the connection.
1263          *      if seg does not contain SYN, then drop it.
1264          * Otherwise this is an acceptable SYN segment
1265          *      initialize tp->rcv_nxt and tp->irs
1266          *      if seg contains ack then advance tp->snd_una
1267          *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
1268          *      arrange for segment to be acked (eventually)
1269          *      continue processing rest of data/controls, beginning with URG
1270          */
1271         case TCPS_SYN_SENT:
1272                 if ((taop = tcp_gettaocache(inp)) == NULL) {
1273                         taop = &tao_noncached;
1274                         bzero(taop, sizeof(*taop));
1275                 }
1276
1277                 if ((thflags & TH_ACK) &&
1278                     (SEQ_LEQ(th->th_ack, tp->iss) ||
1279                      SEQ_GT(th->th_ack, tp->snd_max))) {
1280                         /*
1281                          * If we have a cached CCsent for the remote host,
1282                          * hence we haven't just crashed and restarted,
1283                          * do not send a RST.  This may be a retransmission
1284                          * from the other side after our earlier ACK was lost.
1285                          * Our new SYN, when it arrives, will serve as the
1286                          * needed ACK.
1287                          */
1288                         if (taop->tao_ccsent != 0)
1289                                 goto drop;
1290                         else {
1291                                 rstreason = BANDLIM_UNLIMITED;
1292                                 goto dropwithreset;
1293                         }
1294                 }
1295                 if (thflags & TH_RST) {
1296                         if (thflags & TH_ACK)
1297                                 tp = tcp_drop(tp, ECONNREFUSED);
1298                         goto drop;
1299                 }
1300                 if ((thflags & TH_SYN) == 0)
1301                         goto drop;
1302                 tp->snd_wnd = th->th_win;       /* initial send window */
1303                 tp->cc_recv = to.to_cc;         /* foreign CC */
1304
1305                 tp->irs = th->th_seq;
1306                 tcp_rcvseqinit(tp);
1307                 if (thflags & TH_ACK) {
1308                         /*
1309                          * Our SYN was acked.  If segment contains CC.ECHO
1310                          * option, check it to make sure this segment really
1311                          * matches our SYN.  If not, just drop it as old
1312                          * duplicate, but send an RST if we're still playing
1313                          * by the old rules.  If no CC.ECHO option, make sure
1314                          * we don't get fooled into using T/TCP.
1315                          */
1316                         if (to.to_flag & TOF_CCECHO) {
1317                                 if (tp->cc_send != to.to_ccecho) {
1318                                         if (taop->tao_ccsent != 0)
1319                                                 goto drop;
1320                                         else {
1321                                                 rstreason = BANDLIM_UNLIMITED;
1322                                                 goto dropwithreset;
1323                                         }
1324                                 }
1325                         } else
1326                                 tp->t_flags &= ~TF_RCVD_CC;
1327                         tcpstat.tcps_connects++;
1328                         soisconnected(so);
1329                         /* Do window scaling on this connection? */
1330                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1331                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1332                                 tp->snd_scale = tp->requested_s_scale;
1333                                 tp->rcv_scale = tp->request_r_scale;
1334                         }
1335                         /* Segment is acceptable, update cache if undefined. */
1336                         if (taop->tao_ccsent == 0)
1337                                 taop->tao_ccsent = to.to_ccecho;
1338
1339                         tp->rcv_adv += tp->rcv_wnd;
1340                         tp->snd_una++;          /* SYN is acked */
1341                         /*
1342                          * If there's data, delay ACK; if there's also a FIN
1343                          * ACKNOW will be turned on later.
1344                          */
1345                         if (DELAY_ACK(tp) && tlen != 0)
1346                                 callout_reset(tp->tt_delack, tcp_delacktime,
1347                                     tcp_timer_delack, tp);
1348                         else
1349                                 tp->t_flags |= TF_ACKNOW;
1350                         /*
1351                          * Received <SYN,ACK> in SYN_SENT[*] state.
1352                          * Transitions:
1353                          *      SYN_SENT  --> ESTABLISHED
1354                          *      SYN_SENT* --> FIN_WAIT_1
1355                          */
1356                         tp->t_starttime = ticks;
1357                         if (tp->t_flags & TF_NEEDFIN) {
1358                                 tp->t_state = TCPS_FIN_WAIT_1;
1359                                 tp->t_flags &= ~TF_NEEDFIN;
1360                                 thflags &= ~TH_SYN;
1361                         } else {
1362                                 tp->t_state = TCPS_ESTABLISHED;
1363                                 callout_reset(tp->tt_keep, tcp_keepidle,
1364                                               tcp_timer_keep, tp);
1365                         }
1366                 } else {
1367                 /*
1368                  *  Received initial SYN in SYN-SENT[*] state => simul-
1369                  *  taneous open.  If segment contains CC option and there is
1370                  *  a cached CC, apply TAO test; if it succeeds, connection is
1371                  *  half-synchronized.  Otherwise, do 3-way handshake:
1372                  *        SYN-SENT -> SYN-RECEIVED
1373                  *        SYN-SENT* -> SYN-RECEIVED*
1374                  *  If there was no CC option, clear cached CC value.
1375                  */
1376                         tp->t_flags |= TF_ACKNOW;
1377                         callout_stop(tp->tt_rexmt);
1378                         if (to.to_flag & TOF_CC) {
1379                                 if (taop->tao_cc != 0 &&
1380                                     CC_GT(to.to_cc, taop->tao_cc)) {
1381                                         /*
1382                                          * update cache and make transition:
1383                                          *        SYN-SENT -> ESTABLISHED*
1384                                          *        SYN-SENT* -> FIN-WAIT-1*
1385                                          */
1386                                         taop->tao_cc = to.to_cc;
1387                                         tp->t_starttime = ticks;
1388                                         if (tp->t_flags & TF_NEEDFIN) {
1389                                                 tp->t_state = TCPS_FIN_WAIT_1;
1390                                                 tp->t_flags &= ~TF_NEEDFIN;
1391                                         } else {
1392                                                 tp->t_state = TCPS_ESTABLISHED;
1393                                                 callout_reset(tp->tt_keep,
1394                                                               tcp_keepidle,
1395                                                               tcp_timer_keep,
1396                                                               tp);
1397                                         }
1398                                         tp->t_flags |= TF_NEEDSYN;
1399                                 } else
1400                                         tp->t_state = TCPS_SYN_RECEIVED;
1401                         } else {
1402                                 /* CC.NEW or no option => invalidate cache */
1403                                 taop->tao_cc = 0;
1404                                 tp->t_state = TCPS_SYN_RECEIVED;
1405                         }
1406                 }
1407
1408 trimthenstep6:
1409                 /*
1410                  * Advance th->th_seq to correspond to first data byte.
1411                  * If data, trim to stay within window,
1412                  * dropping FIN if necessary.
1413                  */
1414                 th->th_seq++;
1415                 if (tlen > tp->rcv_wnd) {
1416                         todrop = tlen - tp->rcv_wnd;
1417                         m_adj(m, -todrop);
1418                         tlen = tp->rcv_wnd;
1419                         thflags &= ~TH_FIN;
1420                         tcpstat.tcps_rcvpackafterwin++;
1421                         tcpstat.tcps_rcvbyteafterwin += todrop;
1422                 }
1423                 tp->snd_wl1 = th->th_seq - 1;
1424                 tp->rcv_up = th->th_seq;
1425                 /*
1426                  *  Client side of transaction: already sent SYN and data.
1427                  *  If the remote host used T/TCP to validate the SYN,
1428                  *  our data will be ACK'd; if so, enter normal data segment
1429                  *  processing in the middle of step 5, ack processing.
1430                  *  Otherwise, goto step 6.
1431                  */
1432                 if (thflags & TH_ACK)
1433                         goto process_ACK;
1434                 goto step6;
1435         /*
1436          * If the state is LAST_ACK or CLOSING or TIME_WAIT:
1437          *      if segment contains a SYN and CC [not CC.NEW] option:
1438          *              if state == TIME_WAIT and connection duration > MSL,
1439          *                  drop packet and send RST;
1440          *
1441          *              if SEG.CC > CCrecv then is new SYN, and can implicitly
1442          *                  ack the FIN (and data) in retransmission queue.
1443          *                  Complete close and delete TCPCB.  Then reprocess
1444          *                  segment, hoping to find new TCPCB in LISTEN state;
1445          *
1446          *              else must be old SYN; drop it.
1447          *      else do normal processing.
1448          */
1449         case TCPS_LAST_ACK:
1450         case TCPS_CLOSING:
1451         case TCPS_TIME_WAIT:
1452                 if ((thflags & TH_SYN) &&
1453                     (to.to_flag & TOF_CC) && tp->cc_recv != 0) {
1454                         if (tp->t_state == TCPS_TIME_WAIT &&
1455                                         (ticks - tp->t_starttime) > tcp_msl) {
1456                                 rstreason = BANDLIM_UNLIMITED;
1457                                 goto dropwithreset;
1458                         }
1459                         if (CC_GT(to.to_cc, tp->cc_recv)) {
1460                                 tp = tcp_close(tp);
1461                                 goto findpcb;
1462                         }
1463                         else
1464                                 goto drop;
1465                 }
1466                 break;  /* continue normal processing */
1467         }
1468
1469         /*
1470          * States other than LISTEN or SYN_SENT.
1471          * First check the RST flag and sequence number since reset segments
1472          * are exempt from the timestamp and connection count tests.  This
1473          * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
1474          * below which allowed reset segments in half the sequence space
1475          * to fall though and be processed (which gives forged reset
1476          * segments with a random sequence number a 50 percent chance of
1477          * killing a connection).
1478          * Then check timestamp, if present.
1479          * Then check the connection count, if present.
1480          * Then check that at least some bytes of segment are within
1481          * receive window.  If segment begins before rcv_nxt,
1482          * drop leading data (and SYN); if nothing left, just ack.
1483          *
1484          *
1485          * If the RST bit is set, check the sequence number to see
1486          * if this is a valid reset segment.
1487          * RFC 793 page 37:
1488          *   In all states except SYN-SENT, all reset (RST) segments
1489          *   are validated by checking their SEQ-fields.  A reset is
1490          *   valid if its sequence number is in the window.
1491          * Note: this does not take into account delayed ACKs, so
1492          *   we should test against last_ack_sent instead of rcv_nxt.
1493          *   The sequence number in the reset segment is normally an
1494          *   echo of our outgoing acknowlegement numbers, but some hosts
1495          *   send a reset with the sequence number at the rightmost edge
1496          *   of our receive window, and we have to handle this case.
1497          * If we have multiple segments in flight, the intial reset
1498          * segment sequence numbers will be to the left of last_ack_sent,
1499          * but they will eventually catch up.
1500          * In any case, it never made sense to trim reset segments to
1501          * fit the receive window since RFC 1122 says:
1502          *   4.2.2.12  RST Segment: RFC-793 Section 3.4
1503          *
1504          *    A TCP SHOULD allow a received RST segment to include data.
1505          *
1506          *    DISCUSSION
1507          *         It has been suggested that a RST segment could contain
1508          *         ASCII text that encoded and explained the cause of the
1509          *         RST.  No standard has yet been established for such
1510          *         data.
1511          *
1512          * If the reset segment passes the sequence number test examine
1513          * the state:
1514          *    SYN_RECEIVED STATE:
1515          *      If passive open, return to LISTEN state.
1516          *      If active open, inform user that connection was refused.
1517          *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT2, CLOSE_WAIT STATES:
1518          *      Inform user that connection was reset, and close tcb.
1519          *    CLOSING, LAST_ACK STATES:
1520          *      Close the tcb.
1521          *    TIME_WAIT STATE:
1522          *      Drop the segment - see Stevens, vol. 2, p. 964 and
1523          *      RFC 1337.
1524          */
1525         if (thflags & TH_RST) {
1526                 if (SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
1527                     SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
1528                         switch (tp->t_state) {
1529
1530                         case TCPS_SYN_RECEIVED:
1531                                 so->so_error = ECONNREFUSED;
1532                                 goto close;
1533
1534                         case TCPS_ESTABLISHED:
1535                         case TCPS_FIN_WAIT_1:
1536                         case TCPS_FIN_WAIT_2:
1537                         case TCPS_CLOSE_WAIT:
1538                                 so->so_error = ECONNRESET;
1539                         close:
1540                                 tp->t_state = TCPS_CLOSED;
1541                                 tcpstat.tcps_drops++;
1542                                 tp = tcp_close(tp);
1543                                 break;
1544
1545                         case TCPS_CLOSING:
1546                         case TCPS_LAST_ACK:
1547                                 tp = tcp_close(tp);
1548                                 break;
1549
1550                         case TCPS_TIME_WAIT:
1551                                 break;
1552                         }
1553                 }
1554                 goto drop;
1555         }
1556
1557         /*
1558          * RFC 1323 PAWS: If we have a timestamp reply on this segment
1559          * and it's less than ts_recent, drop it.
1560          */
1561         if ((to.to_flag & TOF_TS) != 0 && tp->ts_recent &&
1562             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
1563
1564                 /* Check to see if ts_recent is over 24 days old.  */
1565                 if ((int)(ticks - tp->ts_recent_age) > TCP_PAWS_IDLE) {
1566                         /*
1567                          * Invalidate ts_recent.  If this segment updates
1568                          * ts_recent, the age will be reset later and ts_recent
1569                          * will get a valid value.  If it does not, setting
1570                          * ts_recent to zero will at least satisfy the
1571                          * requirement that zero be placed in the timestamp
1572                          * echo reply when ts_recent isn't valid.  The
1573                          * age isn't reset until we get a valid ts_recent
1574                          * because we don't want out-of-order segments to be
1575                          * dropped when ts_recent is old.
1576                          */
1577                         tp->ts_recent = 0;
1578                 } else {
1579                         tcpstat.tcps_rcvduppack++;
1580                         tcpstat.tcps_rcvdupbyte += tlen;
1581                         tcpstat.tcps_pawsdrop++;
1582                         goto dropafterack;
1583                 }
1584         }
1585
1586         /*
1587          * T/TCP mechanism
1588          *   If T/TCP was negotiated and the segment doesn't have CC,
1589          *   or if its CC is wrong then drop the segment.
1590          *   RST segments do not have to comply with this.
1591          */
1592         if ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) == (TF_REQ_CC|TF_RCVD_CC) &&
1593             ((to.to_flag & TOF_CC) == 0 || tp->cc_recv != to.to_cc))
1594                 goto dropafterack;
1595
1596         /*
1597          * In the SYN-RECEIVED state, validate that the packet belongs to
1598          * this connection before trimming the data to fit the receive
1599          * window.  Check the sequence number versus IRS since we know
1600          * the sequence numbers haven't wrapped.  This is a partial fix
1601          * for the "LAND" DoS attack.
1602          */
1603         if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
1604                 rstreason = BANDLIM_UNLIMITED;
1605                 goto dropwithreset;
1606         }
1607
1608         todrop = tp->rcv_nxt - th->th_seq;
1609         if (todrop > 0) {
1610                 if (thflags & TH_SYN) {
1611                         thflags &= ~TH_SYN;
1612                         th->th_seq++;
1613                         if (th->th_urp > 1)
1614                                 th->th_urp--;
1615                         else
1616                                 thflags &= ~TH_URG;
1617                         todrop--;
1618                 }
1619                 /*
1620                  * Following if statement from Stevens, vol. 2, p. 960.
1621                  */
1622                 if (todrop > tlen
1623                     || (todrop == tlen && (thflags & TH_FIN) == 0)) {
1624                         /*
1625                          * Any valid FIN must be to the left of the window.
1626                          * At this point the FIN must be a duplicate or out
1627                          * of sequence; drop it.
1628                          */
1629                         thflags &= ~TH_FIN;
1630
1631                         /*
1632                          * Send an ACK to resynchronize and drop any data.
1633                          * But keep on processing for RST or ACK.
1634                          */
1635                         tp->t_flags |= TF_ACKNOW;
1636                         todrop = tlen;
1637                         tcpstat.tcps_rcvduppack++;
1638                         tcpstat.tcps_rcvdupbyte += todrop;
1639                 } else {
1640                         tcpstat.tcps_rcvpartduppack++;
1641                         tcpstat.tcps_rcvpartdupbyte += todrop;
1642                 }
1643                 drop_hdrlen += todrop;  /* drop from the top afterwards */
1644                 th->th_seq += todrop;
1645                 tlen -= todrop;
1646                 if (th->th_urp > todrop)
1647                         th->th_urp -= todrop;
1648                 else {
1649                         thflags &= ~TH_URG;
1650                         th->th_urp = 0;
1651                 }
1652         }
1653
1654         /*
1655          * If new data are received on a connection after the
1656          * user processes are gone, then RST the other end.
1657          */
1658         if ((so->so_state & SS_NOFDREF) &&
1659             tp->t_state > TCPS_CLOSE_WAIT && tlen) {
1660                 tp = tcp_close(tp);
1661                 tcpstat.tcps_rcvafterclose++;
1662                 rstreason = BANDLIM_UNLIMITED;
1663                 goto dropwithreset;
1664         }
1665
1666         /*
1667          * If segment ends after window, drop trailing data
1668          * (and PUSH and FIN); if nothing left, just ACK.
1669          */
1670         todrop = (th->th_seq+tlen) - (tp->rcv_nxt+tp->rcv_wnd);
1671         if (todrop > 0) {
1672                 tcpstat.tcps_rcvpackafterwin++;
1673                 if (todrop >= tlen) {
1674                         tcpstat.tcps_rcvbyteafterwin += tlen;
1675                         /*
1676                          * If a new connection request is received
1677                          * while in TIME_WAIT, drop the old connection
1678                          * and start over if the sequence numbers
1679                          * are above the previous ones.
1680                          */
1681                         if (thflags & TH_SYN &&
1682                             tp->t_state == TCPS_TIME_WAIT &&
1683                             SEQ_GT(th->th_seq, tp->rcv_nxt)) {
1684                                 iss = tcp_new_isn(tp);
1685                                 tp = tcp_close(tp);
1686                                 goto findpcb;
1687                         }
1688                         /*
1689                          * If window is closed can only take segments at
1690                          * window edge, and have to drop data and PUSH from
1691                          * incoming segments.  Continue processing, but
1692                          * remember to ack.  Otherwise, drop segment
1693                          * and ack.
1694                          */
1695                         if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
1696                                 tp->t_flags |= TF_ACKNOW;
1697                                 tcpstat.tcps_rcvwinprobe++;
1698                         } else
1699                                 goto dropafterack;
1700                 } else
1701                         tcpstat.tcps_rcvbyteafterwin += todrop;
1702                 m_adj(m, -todrop);
1703                 tlen -= todrop;
1704                 thflags &= ~(TH_PUSH|TH_FIN);
1705         }
1706
1707         /*
1708          * If last ACK falls within this segment's sequence numbers,
1709          * record its timestamp.
1710          * NOTE that the test is modified according to the latest
1711          * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1712          */
1713         if ((to.to_flag & TOF_TS) != 0 &&
1714             SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
1715                 tp->ts_recent_age = ticks;
1716                 tp->ts_recent = to.to_tsval;
1717         }
1718
1719         /*
1720          * If a SYN is in the window, then this is an
1721          * error and we send an RST and drop the connection.
1722          */
1723         if (thflags & TH_SYN) {
1724                 tp = tcp_drop(tp, ECONNRESET);
1725                 rstreason = BANDLIM_UNLIMITED;
1726                 goto dropwithreset;
1727         }
1728
1729         /*
1730          * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
1731          * flag is on (half-synchronized state), then queue data for
1732          * later processing; else drop segment and return.
1733          */
1734         if ((thflags & TH_ACK) == 0) {
1735                 if (tp->t_state == TCPS_SYN_RECEIVED ||
1736                     (tp->t_flags & TF_NEEDSYN))
1737                         goto step6;
1738                 else
1739                         goto drop;
1740         }
1741
1742         /*
1743          * Ack processing.
1744          */
1745         switch (tp->t_state) {
1746
1747         /*
1748          * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
1749          * ESTABLISHED state and continue processing.
1750          * The ACK was checked above.
1751          */
1752         case TCPS_SYN_RECEIVED:
1753
1754                 tcpstat.tcps_connects++;
1755                 soisconnected(so);
1756                 /* Do window scaling? */
1757                 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1758                         (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1759                         tp->snd_scale = tp->requested_s_scale;
1760                         tp->rcv_scale = tp->request_r_scale;
1761                 }
1762                 /*
1763                  * Upon successful completion of 3-way handshake,
1764                  * update cache.CC if it was undefined, pass any queued
1765                  * data to the user, and advance state appropriately.
1766                  */
1767                 if ((taop = tcp_gettaocache(inp)) != NULL &&
1768                     taop->tao_cc == 0)
1769                         taop->tao_cc = tp->cc_recv;
1770
1771                 /*
1772                  * Make transitions:
1773                  *      SYN-RECEIVED  -> ESTABLISHED
1774                  *      SYN-RECEIVED* -> FIN-WAIT-1
1775                  */
1776                 tp->t_starttime = ticks;
1777                 if (tp->t_flags & TF_NEEDFIN) {
1778                         tp->t_state = TCPS_FIN_WAIT_1;
1779                         tp->t_flags &= ~TF_NEEDFIN;
1780                 } else {
1781                         tp->t_state = TCPS_ESTABLISHED;
1782                         callout_reset(tp->tt_keep, tcp_keepidle,
1783                                       tcp_timer_keep, tp);
1784                 }
1785                 /*
1786                  * If segment contains data or ACK, will call tcp_reass()
1787                  * later; if not, do so now to pass queued data to user.
1788                  */
1789                 if (tlen == 0 && (thflags & TH_FIN) == 0)
1790                         (void) tcp_reass(tp, (struct tcphdr *)0, 0,
1791                             (struct mbuf *)0);
1792                 tp->snd_wl1 = th->th_seq - 1;
1793                 /* fall into ... */
1794
1795         /*
1796          * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
1797          * ACKs.  If the ack is in the range
1798          *      tp->snd_una < th->th_ack <= tp->snd_max
1799          * then advance tp->snd_una to th->th_ack and drop
1800          * data from the retransmission queue.  If this ACK reflects
1801          * more up to date window information we update our window information.
1802          */
1803         case TCPS_ESTABLISHED:
1804         case TCPS_FIN_WAIT_1:
1805         case TCPS_FIN_WAIT_2:
1806         case TCPS_CLOSE_WAIT:
1807         case TCPS_CLOSING:
1808         case TCPS_LAST_ACK:
1809         case TCPS_TIME_WAIT:
1810
1811                 if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
1812                         if (tlen == 0 && tiwin == tp->snd_wnd) {
1813                                 tcpstat.tcps_rcvdupack++;
1814                                 /*
1815                                  * If we have outstanding data (other than
1816                                  * a window probe), this is a completely
1817                                  * duplicate ack (ie, window info didn't
1818                                  * change), the ack is the biggest we've
1819                                  * seen and we've seen exactly our rexmt
1820                                  * threshhold of them, assume a packet
1821                                  * has been dropped and retransmit it.
1822                                  * Kludge snd_nxt & the congestion
1823                                  * window so we send only this one
1824                                  * packet.
1825                                  *
1826                                  * We know we're losing at the current
1827                                  * window size so do congestion avoidance
1828                                  * (set ssthresh to half the current window
1829                                  * and pull our congestion window back to
1830                                  * the new ssthresh).
1831                                  *
1832                                  * Dup acks mean that packets have left the
1833                                  * network (they're now cached at the receiver)
1834                                  * so bump cwnd by the amount in the receiver
1835                                  * to keep a constant cwnd packets in the
1836                                  * network.
1837                                  */
1838                                 if (!callout_active(tp->tt_rexmt) ||
1839                                     th->th_ack != tp->snd_una)
1840                                         tp->t_dupacks = 0;
1841                                 else if (++tp->t_dupacks == tcprexmtthresh) {
1842                                         tcp_seq onxt = tp->snd_nxt;
1843                                         u_int win =
1844                                             min(tp->snd_wnd, tp->snd_cwnd) / 2 /
1845                                                 tp->t_maxseg;
1846                                         if (tcp_do_newreno && SEQ_LT(th->th_ack,
1847                                             tp->snd_recover)) {
1848                                                 /* False retransmit, should not
1849                                                  * cut window
1850                                                  */
1851                                                 tp->snd_cwnd += tp->t_maxseg;
1852                                                 tp->t_dupacks = 0;
1853                                                 (void) tcp_output(tp);
1854                                                 goto drop;
1855                                         }
1856                                         if (win < 2)
1857                                                 win = 2;
1858                                         tp->snd_ssthresh = win * tp->t_maxseg;
1859                                         tp->snd_recover = tp->snd_max;
1860                                         callout_stop(tp->tt_rexmt);
1861                                         tp->t_rtttime = 0;
1862                                         tp->snd_nxt = th->th_ack;
1863                                         tp->snd_cwnd = tp->t_maxseg;
1864                                         (void) tcp_output(tp);
1865                                         tp->snd_cwnd = tp->snd_ssthresh +
1866                                                tp->t_maxseg * tp->t_dupacks;
1867                                         if (SEQ_GT(onxt, tp->snd_nxt))
1868                                                 tp->snd_nxt = onxt;
1869                                         goto drop;
1870                                 } else if (tp->t_dupacks > tcprexmtthresh) {
1871                                         tp->snd_cwnd += tp->t_maxseg;
1872                                         (void) tcp_output(tp);
1873                                         goto drop;
1874                                 }
1875                         } else
1876                                 tp->t_dupacks = 0;
1877                         break;
1878                 }
1879                 /*
1880                  * If the congestion window was inflated to account
1881                  * for the other side's cached packets, retract it.
1882                  */
1883                 if (tcp_do_newreno == 0) {
1884                         if (tp->t_dupacks >= tcprexmtthresh &&
1885                                 tp->snd_cwnd > tp->snd_ssthresh)
1886                                 tp->snd_cwnd = tp->snd_ssthresh;
1887                         tp->t_dupacks = 0;
1888                 } else if (tp->t_dupacks >= tcprexmtthresh &&
1889                     !tcp_newreno(tp, th)) {
1890                         /*
1891                          * Window inflation should have left us with approx.
1892                          * snd_ssthresh outstanding data.  But in case we
1893                          * would be inclined to send a burst, better to do
1894                          * it via the slow start mechanism.
1895                          */
1896                         if (SEQ_GT(th->th_ack + tp->snd_ssthresh, tp->snd_max))
1897                                 tp->snd_cwnd =
1898                                     tp->snd_max - th->th_ack + tp->t_maxseg;
1899                         else
1900                                 tp->snd_cwnd = tp->snd_ssthresh;
1901                         tp->t_dupacks = 0;
1902                 }
1903                 if (SEQ_GT(th->th_ack, tp->snd_max)) {
1904                         tcpstat.tcps_rcvacktoomuch++;
1905                         goto dropafterack;
1906                 }
1907                 /*
1908                  *  If we reach this point, ACK is not a duplicate,
1909                  *     i.e., it ACKs something we sent.
1910                  */
1911                 if (tp->t_flags & TF_NEEDSYN) {
1912                         /*
1913                          * T/TCP: Connection was half-synchronized, and our
1914                          * SYN has been ACK'd (so connection is now fully
1915                          * synchronized).  Go to non-starred state,
1916                          * increment snd_una for ACK of SYN, and check if
1917                          * we can do window scaling.
1918                          */
1919                         tp->t_flags &= ~TF_NEEDSYN;
1920                         tp->snd_una++;
1921                         /* Do window scaling? */
1922                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1923                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1924                                 tp->snd_scale = tp->requested_s_scale;
1925                                 tp->rcv_scale = tp->request_r_scale;
1926                         }
1927                 }
1928
1929 process_ACK:
1930                 acked = th->th_ack - tp->snd_una;
1931                 tcpstat.tcps_rcvackpack++;
1932                 tcpstat.tcps_rcvackbyte += acked;
1933
1934                 /*
1935                  * If we just performed our first retransmit, and the ACK
1936                  * arrives within our recovery window, then it was a mistake
1937                  * to do the retransmit in the first place.  Recover our
1938                  * original cwnd and ssthresh, and proceed to transmit where
1939                  * we left off.
1940                  */
1941                 if (tp->t_rxtshift == 1 && ticks < tp->t_badrxtwin) {
1942                         tp->snd_cwnd = tp->snd_cwnd_prev;
1943                         tp->snd_ssthresh = tp->snd_ssthresh_prev;
1944                         tp->snd_nxt = tp->snd_max;
1945                         tp->t_badrxtwin = 0;    /* XXX probably not required */
1946                 }
1947
1948                 /*
1949                  * If we have a timestamp reply, update smoothed
1950                  * round trip time.  If no timestamp is present but
1951                  * transmit timer is running and timed sequence
1952                  * number was acked, update smoothed round trip time.
1953                  * Since we now have an rtt measurement, cancel the
1954                  * timer backoff (cf., Phil Karn's retransmit alg.).
1955                  * Recompute the initial retransmit timer.
1956                  */
1957                 if (to.to_flag & TOF_TS)
1958                         tcp_xmit_timer(tp, ticks - to.to_tsecr + 1);
1959                 else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq))
1960                         tcp_xmit_timer(tp, ticks - tp->t_rtttime);
1961
1962                 /*
1963                  * If all outstanding data is acked, stop retransmit
1964                  * timer and remember to restart (more output or persist).
1965                  * If there is more data to be acked, restart retransmit
1966                  * timer, using current (possibly backed-off) value.
1967                  */
1968                 if (th->th_ack == tp->snd_max) {
1969                         callout_stop(tp->tt_rexmt);
1970                         needoutput = 1;
1971                 } else if (!callout_active(tp->tt_persist))
1972                         callout_reset(tp->tt_rexmt, tp->t_rxtcur,
1973                                       tcp_timer_rexmt, tp);
1974
1975                 /*
1976                  * If no data (only SYN) was ACK'd,
1977                  *    skip rest of ACK processing.
1978                  */
1979                 if (acked == 0)
1980                         goto step6;
1981
1982                 /*
1983                  * When new data is acked, open the congestion window.
1984                  * If the window gives us less than ssthresh packets
1985                  * in flight, open exponentially (maxseg per packet).
1986                  * Otherwise open linearly: maxseg per window
1987                  * (maxseg^2 / cwnd per packet).
1988                  */
1989                 {
1990                 register u_int cw = tp->snd_cwnd;
1991                 register u_int incr = tp->t_maxseg;
1992
1993                 if (cw > tp->snd_ssthresh)
1994                         incr = incr * incr / cw;
1995                 /*
1996                  * If t_dupacks != 0 here, it indicates that we are still
1997                  * in NewReno fast recovery mode, so we leave the congestion
1998                  * window alone.
1999                  */
2000                 if (tcp_do_newreno == 0 || tp->t_dupacks == 0)
2001                         tp->snd_cwnd = min(cw + incr,TCP_MAXWIN<<tp->snd_scale);
2002                 }
2003                 if (acked > so->so_snd.sb_cc) {
2004                         tp->snd_wnd -= so->so_snd.sb_cc;
2005                         sbdrop(&so->so_snd, (int)so->so_snd.sb_cc);
2006                         ourfinisacked = 1;
2007                 } else {
2008                         sbdrop(&so->so_snd, acked);
2009                         tp->snd_wnd -= acked;
2010                         ourfinisacked = 0;
2011                 }
2012                 sowwakeup(so);
2013                 tp->snd_una = th->th_ack;
2014                 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
2015                         tp->snd_nxt = tp->snd_una;
2016
2017                 switch (tp->t_state) {
2018
2019                 /*
2020                  * In FIN_WAIT_1 STATE in addition to the processing
2021                  * for the ESTABLISHED state if our FIN is now acknowledged
2022                  * then enter FIN_WAIT_2.
2023                  */
2024                 case TCPS_FIN_WAIT_1:
2025                         if (ourfinisacked) {
2026                                 /*
2027                                  * If we can't receive any more
2028                                  * data, then closing user can proceed.
2029                                  * Starting the timer is contrary to the
2030                                  * specification, but if we don't get a FIN
2031                                  * we'll hang forever.
2032                                  */
2033                                 if (so->so_state & SS_CANTRCVMORE) {
2034                                         soisdisconnected(so);
2035                                         callout_reset(tp->tt_2msl, tcp_maxidle,
2036                                                       tcp_timer_2msl, tp);
2037                                 }
2038                                 tp->t_state = TCPS_FIN_WAIT_2;
2039                         }
2040                         break;
2041
2042                 /*
2043                  * In CLOSING STATE in addition to the processing for
2044                  * the ESTABLISHED state if the ACK acknowledges our FIN
2045                  * then enter the TIME-WAIT state, otherwise ignore
2046                  * the segment.
2047                  */
2048                 case TCPS_CLOSING:
2049                         if (ourfinisacked) {
2050                                 tp->t_state = TCPS_TIME_WAIT;
2051                                 tcp_canceltimers(tp);
2052                                 /* Shorten TIME_WAIT [RFC-1644, p.28] */
2053                                 if (tp->cc_recv != 0 &&
2054                                     (ticks - tp->t_starttime) < tcp_msl) {
2055                                         callout_reset(tp->tt_2msl,
2056                                                       tp->t_rxtcur *
2057                                                       TCPTV_TWTRUNC,
2058                                                       tcp_timer_2msl, tp);
2059                                 }
2060                                 else {
2061                                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
2062                                                       tcp_timer_2msl, tp);
2063                                 }
2064                                 soisdisconnected(so);
2065                         }
2066                         break;
2067
2068                 /*
2069                  * In LAST_ACK, we may still be waiting for data to drain
2070                  * and/or to be acked, as well as for the ack of our FIN.
2071                  * If our FIN is now acknowledged, delete the TCB,
2072                  * enter the closed state and return.
2073                  */
2074                 case TCPS_LAST_ACK:
2075                         if (ourfinisacked) {
2076                                 tp = tcp_close(tp);
2077                                 goto drop;
2078                         }
2079                         break;
2080
2081                 /*
2082                  * In TIME_WAIT state the only thing that should arrive
2083                  * is a retransmission of the remote FIN.  Acknowledge
2084                  * it and restart the finack timer.
2085                  */
2086                 case TCPS_TIME_WAIT:
2087                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
2088                                       tcp_timer_2msl, tp);
2089                         goto dropafterack;
2090                 }
2091         }
2092
2093 step6:
2094         /*
2095          * Update window information.
2096          * Don't look at window if no ACK: TAC's send garbage on first SYN.
2097          */
2098         if ((thflags & TH_ACK) &&
2099             (SEQ_LT(tp->snd_wl1, th->th_seq) ||
2100             (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
2101              (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
2102                 /* keep track of pure window updates */
2103                 if (tlen == 0 &&
2104                     tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
2105                         tcpstat.tcps_rcvwinupd++;
2106                 tp->snd_wnd = tiwin;
2107                 tp->snd_wl1 = th->th_seq;
2108                 tp->snd_wl2 = th->th_ack;
2109                 if (tp->snd_wnd > tp->max_sndwnd)
2110                         tp->max_sndwnd = tp->snd_wnd;
2111                 needoutput = 1;
2112         }
2113
2114         /*
2115          * Process segments with URG.
2116          */
2117         if ((thflags & TH_URG) && th->th_urp &&
2118             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2119                 /*
2120                  * This is a kludge, but if we receive and accept
2121                  * random urgent pointers, we'll crash in
2122                  * soreceive.  It's hard to imagine someone
2123                  * actually wanting to send this much urgent data.
2124                  */
2125                 if (th->th_urp + so->so_rcv.sb_cc > sb_max) {
2126                         th->th_urp = 0;                 /* XXX */
2127                         thflags &= ~TH_URG;             /* XXX */
2128                         goto dodata;                    /* XXX */
2129                 }
2130                 /*
2131                  * If this segment advances the known urgent pointer,
2132                  * then mark the data stream.  This should not happen
2133                  * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
2134                  * a FIN has been received from the remote side.
2135                  * In these states we ignore the URG.
2136                  *
2137                  * According to RFC961 (Assigned Protocols),
2138                  * the urgent pointer points to the last octet
2139                  * of urgent data.  We continue, however,
2140                  * to consider it to indicate the first octet
2141                  * of data past the urgent section as the original
2142                  * spec states (in one of two places).
2143                  */
2144                 if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
2145                         tp->rcv_up = th->th_seq + th->th_urp;
2146                         so->so_oobmark = so->so_rcv.sb_cc +
2147                             (tp->rcv_up - tp->rcv_nxt) - 1;
2148                         if (so->so_oobmark == 0)
2149                                 so->so_state |= SS_RCVATMARK;
2150                         sohasoutofband(so);
2151                         tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
2152                 }
2153                 /*
2154                  * Remove out of band data so doesn't get presented to user.
2155                  * This can happen independent of advancing the URG pointer,
2156                  * but if two URG's are pending at once, some out-of-band
2157                  * data may creep in... ick.
2158                  */
2159                 if (th->th_urp <= (u_long)tlen
2160 #ifdef SO_OOBINLINE
2161                      && (so->so_options & SO_OOBINLINE) == 0
2162 #endif
2163                      )
2164                         tcp_pulloutofband(so, th, m,
2165                                 drop_hdrlen);   /* hdr drop is delayed */
2166         } else
2167                 /*
2168                  * If no out of band data is expected,
2169                  * pull receive urgent pointer along
2170                  * with the receive window.
2171                  */
2172                 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
2173                         tp->rcv_up = tp->rcv_nxt;
2174 dodata:                                                 /* XXX */
2175
2176         /*
2177          * Process the segment text, merging it into the TCP sequencing queue,
2178          * and arranging for acknowledgment of receipt if necessary.
2179          * This process logically involves adjusting tp->rcv_wnd as data
2180          * is presented to the user (this happens in tcp_usrreq.c,
2181          * case PRU_RCVD).  If a FIN has already been received on this
2182          * connection then we just ignore the text.
2183          */
2184         if ((tlen || (thflags&TH_FIN)) &&
2185             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2186                 m_adj(m, drop_hdrlen);  /* delayed header drop */
2187                 /*
2188                  * Insert segment which inludes th into reassembly queue of tcp with
2189                  * control block tp.  Return TH_FIN if reassembly now includes
2190                  * a segment with FIN.  This handle the common case inline (segment
2191                  * is the next to be received on an established connection, and the
2192                  * queue is empty), avoiding linkage into and removal from the queue
2193                  * and repetition of various conversions.
2194                  * Set DELACK for segments received in order, but ack immediately
2195                  * when segments are out of order (so fast retransmit can work).
2196                  */
2197                 if (th->th_seq == tp->rcv_nxt &&
2198                     LIST_EMPTY(&tp->t_segq) &&
2199                     TCPS_HAVEESTABLISHED(tp->t_state)) {
2200                         if (DELAY_ACK(tp))
2201                                 callout_reset(tp->tt_delack, tcp_delacktime,
2202                                     tcp_timer_delack, tp);
2203                         else
2204                                 tp->t_flags |= TF_ACKNOW;
2205                         tp->rcv_nxt += tlen;
2206                         thflags = th->th_flags & TH_FIN;
2207                         tcpstat.tcps_rcvpack++;
2208                         tcpstat.tcps_rcvbyte += tlen;
2209                         ND6_HINT(tp);
2210                         sbappend(&so->so_rcv, m);
2211                         sorwakeup(so);
2212                 } else {
2213                         thflags = tcp_reass(tp, th, &tlen, m);
2214                         tp->t_flags |= TF_ACKNOW;
2215                 }
2216
2217                 /*
2218                  * Note the amount of data that peer has sent into
2219                  * our window, in order to estimate the sender's
2220                  * buffer size.
2221                  */
2222                 len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
2223         } else {
2224                 m_freem(m);
2225                 thflags &= ~TH_FIN;
2226         }
2227
2228         /*
2229          * If FIN is received ACK the FIN and let the user know
2230          * that the connection is closing.
2231          */
2232         if (thflags & TH_FIN) {
2233                 if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2234                         socantrcvmore(so);
2235                         /*
2236                          *  If connection is half-synchronized
2237                          *  (ie NEEDSYN flag on) then delay ACK,
2238                          *  so it may be piggybacked when SYN is sent.
2239                          *  Otherwise, since we received a FIN then no
2240                          *  more input can be expected, send ACK now.
2241                          */
2242                         if (DELAY_ACK(tp) && (tp->t_flags & TF_NEEDSYN))
2243                                 callout_reset(tp->tt_delack, tcp_delacktime,
2244                                     tcp_timer_delack, tp);
2245                         else
2246                                 tp->t_flags |= TF_ACKNOW;
2247                         tp->rcv_nxt++;
2248                 }
2249                 switch (tp->t_state) {
2250
2251                 /*
2252                  * In SYN_RECEIVED and ESTABLISHED STATES
2253                  * enter the CLOSE_WAIT state.
2254                  */
2255                 case TCPS_SYN_RECEIVED:
2256                         tp->t_starttime = ticks;
2257                         /*FALLTHROUGH*/
2258                 case TCPS_ESTABLISHED:
2259                         tp->t_state = TCPS_CLOSE_WAIT;
2260                         break;
2261
2262                 /*
2263                  * If still in FIN_WAIT_1 STATE FIN has not been acked so
2264                  * enter the CLOSING state.
2265                  */
2266                 case TCPS_FIN_WAIT_1:
2267                         tp->t_state = TCPS_CLOSING;
2268                         break;
2269
2270                 /*
2271                  * In FIN_WAIT_2 state enter the TIME_WAIT state,
2272                  * starting the time-wait timer, turning off the other
2273                  * standard timers.
2274                  */
2275                 case TCPS_FIN_WAIT_2:
2276                         tp->t_state = TCPS_TIME_WAIT;
2277                         tcp_canceltimers(tp);
2278                         /* Shorten TIME_WAIT [RFC-1644, p.28] */
2279                         if (tp->cc_recv != 0 &&
2280                             (ticks - tp->t_starttime) < tcp_msl) {
2281                                 callout_reset(tp->tt_2msl,
2282                                               tp->t_rxtcur * TCPTV_TWTRUNC,
2283                                               tcp_timer_2msl, tp);
2284                                 /* For transaction client, force ACK now. */
2285                                 tp->t_flags |= TF_ACKNOW;
2286                         }
2287                         else {
2288                                 callout_reset(tp->tt_2msl, 2 * tcp_msl,
2289                                               tcp_timer_2msl, tp);
2290                         }
2291                         soisdisconnected(so);
2292                         break;
2293
2294                 /*
2295                  * In TIME_WAIT state restart the 2 MSL time_wait timer.
2296                  */
2297                 case TCPS_TIME_WAIT:
2298                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
2299                                       tcp_timer_2msl, tp);
2300                         break;
2301                 }
2302         }
2303 #ifdef TCPDEBUG
2304         if (so->so_options & SO_DEBUG)
2305                 tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
2306                           &tcp_savetcp, 0);
2307 #endif
2308
2309         /*
2310          * Return any desired output.
2311          */
2312         if (needoutput || (tp->t_flags & TF_ACKNOW))
2313                 (void) tcp_output(tp);
2314         return;
2315
2316 dropafterack:
2317         /*
2318          * Generate an ACK dropping incoming segment if it occupies
2319          * sequence space, where the ACK reflects our state.
2320          *
2321          * We can now skip the test for the RST flag since all
2322          * paths to this code happen after packets containing
2323          * RST have been dropped.
2324          *
2325          * In the SYN-RECEIVED state, don't send an ACK unless the
2326          * segment we received passes the SYN-RECEIVED ACK test.
2327          * If it fails send a RST.  This breaks the loop in the
2328          * "LAND" DoS attack, and also prevents an ACK storm
2329          * between two listening ports that have been sent forged
2330          * SYN segments, each with the source address of the other.
2331          */
2332         if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
2333             (SEQ_GT(tp->snd_una, th->th_ack) ||
2334              SEQ_GT(th->th_ack, tp->snd_max)) ) {
2335                 rstreason = BANDLIM_RST_OPENPORT;
2336                 goto dropwithreset;
2337         }
2338 #ifdef TCPDEBUG
2339         if (so->so_options & SO_DEBUG)
2340                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2341                           &tcp_savetcp, 0);
2342 #endif
2343         m_freem(m);
2344         tp->t_flags |= TF_ACKNOW;
2345         (void) tcp_output(tp);
2346         return;
2347
2348 dropwithreset:
2349         /*
2350          * Generate a RST, dropping incoming segment.
2351          * Make ACK acceptable to originator of segment.
2352          * Don't bother to respond if destination was broadcast/multicast.
2353          */
2354         if ((thflags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
2355                 goto drop;
2356 #ifdef INET6
2357         if (isipv6) {
2358                 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
2359                     IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
2360                         goto drop;
2361         } else
2362 #endif /* INET6 */
2363         if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
2364             IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
2365             ip->ip_src.s_addr == htonl(INADDR_BROADCAST))
2366                 goto drop;
2367         /* IPv6 anycast check is done at tcp6_input() */
2368
2369         /*
2370          * Perform bandwidth limiting.
2371          */
2372 #ifdef ICMP_BANDLIM
2373         if (badport_bandlim(rstreason) < 0)
2374                 goto drop;
2375 #endif
2376
2377 #ifdef TCPDEBUG
2378         if (tp == 0 || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2379                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2380                           &tcp_savetcp, 0);
2381 #endif
2382         if (thflags & TH_ACK)
2383                 /* mtod() below is safe as long as hdr dropping is delayed */
2384                 tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0, th->th_ack,
2385                             TH_RST);
2386         else {
2387                 if (thflags & TH_SYN)
2388                         tlen++;
2389                 /* mtod() below is safe as long as hdr dropping is delayed */
2390                 tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
2391                             (tcp_seq)0, TH_RST|TH_ACK);
2392         }
2393         /* destroy temporarily created socket */
2394         if (dropsocket)
2395                 (void) soabort(so);
2396         return;
2397
2398 drop:
2399         /*
2400          * Drop space held by incoming segment and return.
2401          */
2402 #ifdef TCPDEBUG
2403         if (tp == 0 || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2404                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2405                           &tcp_savetcp, 0);
2406 #endif
2407         m_freem(m);
2408         /* destroy temporarily created socket */
2409         if (dropsocket)
2410                 (void) soabort(so);
2411         return;
2412 }
2413
2414 static void
2415 tcp_dooptions(tp, cp, cnt, th, to)
2416         struct tcpcb *tp;
2417         u_char *cp;
2418         int cnt;
2419         struct tcphdr *th;
2420         struct tcpopt *to;
2421 {
2422         u_short mss = 0;
2423         int opt, optlen;
2424
2425         for (; cnt > 0; cnt -= optlen, cp += optlen) {
2426                 opt = cp[0];
2427                 if (opt == TCPOPT_EOL)
2428                         break;
2429                 if (opt == TCPOPT_NOP)
2430                         optlen = 1;
2431                 else {
2432                         if (cnt < 2)
2433                                 break;
2434                         optlen = cp[1];
2435                         if (optlen < 2 || optlen > cnt)
2436                                 break;
2437                 }
2438                 switch (opt) {
2439
2440                 default:
2441                         continue;
2442
2443                 case TCPOPT_MAXSEG:
2444                         if (optlen != TCPOLEN_MAXSEG)
2445                                 continue;
2446                         if (!(th->th_flags & TH_SYN))
2447                                 continue;
2448                         bcopy((char *) cp + 2, (char *) &mss, sizeof(mss));
2449                         NTOHS(mss);
2450                         break;
2451
2452                 case TCPOPT_WINDOW:
2453                         if (optlen != TCPOLEN_WINDOW)
2454                                 continue;
2455                         if (!(th->th_flags & TH_SYN))
2456                                 continue;
2457                         tp->t_flags |= TF_RCVD_SCALE;
2458                         tp->requested_s_scale = min(cp[2], TCP_MAX_WINSHIFT);
2459                         break;
2460
2461                 case TCPOPT_TIMESTAMP:
2462                         if (optlen != TCPOLEN_TIMESTAMP)
2463                                 continue;
2464                         to->to_flag |= TOF_TS;
2465                         bcopy((char *)cp + 2,
2466                             (char *)&to->to_tsval, sizeof(to->to_tsval));
2467                         NTOHL(to->to_tsval);
2468                         bcopy((char *)cp + 6,
2469                             (char *)&to->to_tsecr, sizeof(to->to_tsecr));
2470                         NTOHL(to->to_tsecr);
2471
2472                         /*
2473                          * A timestamp received in a SYN makes
2474                          * it ok to send timestamp requests and replies.
2475                          */
2476                         if (th->th_flags & TH_SYN) {
2477                                 tp->t_flags |= TF_RCVD_TSTMP;
2478                                 tp->ts_recent = to->to_tsval;
2479                                 tp->ts_recent_age = ticks;
2480                         }
2481                         break;
2482                 case TCPOPT_CC:
2483                         if (optlen != TCPOLEN_CC)
2484                                 continue;
2485                         to->to_flag |= TOF_CC;
2486                         bcopy((char *)cp + 2,
2487                             (char *)&to->to_cc, sizeof(to->to_cc));
2488                         NTOHL(to->to_cc);
2489                         /*
2490                          * A CC or CC.new option received in a SYN makes
2491                          * it ok to send CC in subsequent segments.
2492                          */
2493                         if (th->th_flags & TH_SYN)
2494                                 tp->t_flags |= TF_RCVD_CC;
2495                         break;
2496                 case TCPOPT_CCNEW:
2497                         if (optlen != TCPOLEN_CC)
2498                                 continue;
2499                         if (!(th->th_flags & TH_SYN))
2500                                 continue;
2501                         to->to_flag |= TOF_CCNEW;
2502                         bcopy((char *)cp + 2,
2503                             (char *)&to->to_cc, sizeof(to->to_cc));
2504                         NTOHL(to->to_cc);
2505                         /*
2506                          * A CC or CC.new option received in a SYN makes
2507                          * it ok to send CC in subsequent segments.
2508                          */
2509                         tp->t_flags |= TF_RCVD_CC;
2510                         break;
2511                 case TCPOPT_CCECHO:
2512                         if (optlen != TCPOLEN_CC)
2513                                 continue;
2514                         if (!(th->th_flags & TH_SYN))
2515                                 continue;
2516                         to->to_flag |= TOF_CCECHO;
2517                         bcopy((char *)cp + 2,
2518                             (char *)&to->to_ccecho, sizeof(to->to_ccecho));
2519                         NTOHL(to->to_ccecho);
2520                         break;
2521                 }
2522         }
2523         if (th->th_flags & TH_SYN)
2524                 tcp_mss(tp, mss);       /* sets t_maxseg */
2525 }
2526
2527 /*
2528  * Pull out of band byte out of a segment so
2529  * it doesn't appear in the user's data queue.
2530  * It is still reflected in the segment length for
2531  * sequencing purposes.
2532  */
2533 static void
2534 tcp_pulloutofband(so, th, m, off)
2535         struct socket *so;
2536         struct tcphdr *th;
2537         register struct mbuf *m;
2538         int off;                /* delayed to be droped hdrlen */
2539 {
2540         int cnt = off + th->th_urp - 1;
2541
2542         while (cnt >= 0) {
2543                 if (m->m_len > cnt) {
2544                         char *cp = mtod(m, caddr_t) + cnt;
2545                         struct tcpcb *tp = sototcpcb(so);
2546
2547                         tp->t_iobc = *cp;
2548                         tp->t_oobflags |= TCPOOB_HAVEDATA;
2549                         bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
2550                         m->m_len--;
2551                         if (m->m_flags & M_PKTHDR)
2552                                 m->m_pkthdr.len--;
2553                         return;
2554                 }
2555                 cnt -= m->m_len;
2556                 m = m->m_next;
2557                 if (m == 0)
2558                         break;
2559         }
2560         panic("tcp_pulloutofband");
2561 }
2562
2563 /*
2564  * Collect new round-trip time estimate
2565  * and update averages and current timeout.
2566  */
2567 static void
2568 tcp_xmit_timer(tp, rtt)
2569         register struct tcpcb *tp;
2570         int rtt;
2571 {
2572         register int delta;
2573
2574         tcpstat.tcps_rttupdated++;
2575         tp->t_rttupdated++;
2576         if (tp->t_srtt != 0) {
2577                 /*
2578                  * srtt is stored as fixed point with 5 bits after the
2579                  * binary point (i.e., scaled by 8).  The following magic
2580                  * is equivalent to the smoothing algorithm in rfc793 with
2581                  * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
2582                  * point).  Adjust rtt to origin 0.
2583                  */
2584                 delta = ((rtt - 1) << TCP_DELTA_SHIFT)
2585                         - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
2586
2587                 if ((tp->t_srtt += delta) <= 0)
2588                         tp->t_srtt = 1;
2589
2590                 /*
2591                  * We accumulate a smoothed rtt variance (actually, a
2592                  * smoothed mean difference), then set the retransmit
2593                  * timer to smoothed rtt + 4 times the smoothed variance.
2594                  * rttvar is stored as fixed point with 4 bits after the
2595                  * binary point (scaled by 16).  The following is
2596                  * equivalent to rfc793 smoothing with an alpha of .75
2597                  * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
2598                  * rfc793's wired-in beta.
2599                  */
2600                 if (delta < 0)
2601                         delta = -delta;
2602                 delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
2603                 if ((tp->t_rttvar += delta) <= 0)
2604                         tp->t_rttvar = 1;
2605         } else {
2606                 /*
2607                  * No rtt measurement yet - use the unsmoothed rtt.
2608                  * Set the variance to half the rtt (so our first
2609                  * retransmit happens at 3*rtt).
2610                  */
2611                 tp->t_srtt = rtt << TCP_RTT_SHIFT;
2612                 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
2613         }
2614         tp->t_rtttime = 0;
2615         tp->t_rxtshift = 0;
2616
2617         /*
2618          * the retransmit should happen at rtt + 4 * rttvar.
2619          * Because of the way we do the smoothing, srtt and rttvar
2620          * will each average +1/2 tick of bias.  When we compute
2621          * the retransmit timer, we want 1/2 tick of rounding and
2622          * 1 extra tick because of +-1/2 tick uncertainty in the
2623          * firing of the timer.  The bias will give us exactly the
2624          * 1.5 tick we need.  But, because the bias is
2625          * statistical, we have to test that we don't drop below
2626          * the minimum feasible timer (which is 2 ticks).
2627          */
2628         TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
2629                       max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
2630
2631         /*
2632          * We received an ack for a packet that wasn't retransmitted;
2633          * it is probably safe to discard any error indications we've
2634          * received recently.  This isn't quite right, but close enough
2635          * for now (a route might have failed after we sent a segment,
2636          * and the return path might not be symmetrical).
2637          */
2638         tp->t_softerror = 0;
2639 }
2640
2641 /*
2642  * Determine a reasonable value for maxseg size.
2643  * If the route is known, check route for mtu.
2644  * If none, use an mss that can be handled on the outgoing
2645  * interface without forcing IP to fragment; if bigger than
2646  * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
2647  * to utilize large mbufs.  If no route is found, route has no mtu,
2648  * or the destination isn't local, use a default, hopefully conservative
2649  * size (usually 512 or the default IP max size, but no more than the mtu
2650  * of the interface), as we can't discover anything about intervening
2651  * gateways or networks.  We also initialize the congestion/slow start
2652  * window to be a single segment if the destination isn't local.
2653  * While looking at the routing entry, we also initialize other path-dependent
2654  * parameters from pre-set or cached values in the routing entry.
2655  *
2656  * Also take into account the space needed for options that we
2657  * send regularly.  Make maxseg shorter by that amount to assure
2658  * that we can send maxseg amount of data even when the options
2659  * are present.  Store the upper limit of the length of options plus
2660  * data in maxopd.
2661  *
2662  * NOTE that this routine is only called when we process an incoming
2663  * segment, for outgoing segments only tcp_mssopt is called.
2664  *
2665  * In case of T/TCP, we call this routine during implicit connection
2666  * setup as well (offer = -1), to initialize maxseg from the cached
2667  * MSS of our peer.
2668  */
2669 void
2670 tcp_mss(tp, offer)
2671         struct tcpcb *tp;
2672         int offer;
2673 {
2674         register struct rtentry *rt;
2675         struct ifnet *ifp;
2676         register int rtt, mss;
2677         u_long bufsize;
2678         struct inpcb *inp;
2679         struct socket *so;
2680         struct rmxp_tao *taop;
2681         int origoffer = offer;
2682 #ifdef INET6
2683         int isipv6;
2684         int min_protoh;
2685 #endif
2686
2687         inp = tp->t_inpcb;
2688 #ifdef INET6
2689         isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
2690         min_protoh = isipv6 ? sizeof (struct ip6_hdr) + sizeof (struct tcphdr)
2691                             : sizeof (struct tcpiphdr);
2692 #else
2693 #define min_protoh  (sizeof (struct tcpiphdr))
2694 #endif
2695 #ifdef INET6
2696         if (isipv6)
2697                 rt = tcp_rtlookup6(inp);
2698         else
2699 #endif
2700         rt = tcp_rtlookup(inp);
2701         if (rt == NULL) {
2702                 tp->t_maxopd = tp->t_maxseg =
2703 #ifdef INET6
2704                 isipv6 ? tcp_v6mssdflt :
2705 #endif /* INET6 */
2706                 tcp_mssdflt;
2707                 return;
2708         }
2709         ifp = rt->rt_ifp;
2710         so = inp->inp_socket;
2711
2712         taop = rmx_taop(rt->rt_rmx);
2713         /*
2714          * Offer == -1 means that we didn't receive SYN yet,
2715          * use cached value in that case;
2716          */
2717         if (offer == -1)
2718                 offer = taop->tao_mssopt;
2719         /*
2720          * Offer == 0 means that there was no MSS on the SYN segment,
2721          * in this case we use tcp_mssdflt.
2722          */
2723         if (offer == 0)
2724                 offer =
2725 #ifdef INET6
2726                         isipv6 ? tcp_v6mssdflt :
2727 #endif /* INET6 */
2728                         tcp_mssdflt;
2729         else
2730                 /*
2731                  * Sanity check: make sure that maxopd will be large
2732                  * enough to allow some data on segments even is the
2733                  * all the option space is used (40bytes).  Otherwise
2734                  * funny things may happen in tcp_output.
2735                  */
2736                 offer = max(offer, 64);
2737         taop->tao_mssopt = offer;
2738
2739         /*
2740          * While we're here, check if there's an initial rtt
2741          * or rttvar.  Convert from the route-table units
2742          * to scaled multiples of the slow timeout timer.
2743          */
2744         if (tp->t_srtt == 0 && (rtt = rt->rt_rmx.rmx_rtt)) {
2745                 /*
2746                  * XXX the lock bit for RTT indicates that the value
2747                  * is also a minimum value; this is subject to time.
2748                  */
2749                 if (rt->rt_rmx.rmx_locks & RTV_RTT)
2750                         tp->t_rttmin = rtt / (RTM_RTTUNIT / hz);
2751                 tp->t_srtt = rtt / (RTM_RTTUNIT / (hz * TCP_RTT_SCALE));
2752                 tcpstat.tcps_usedrtt++;
2753                 if (rt->rt_rmx.rmx_rttvar) {
2754                         tp->t_rttvar = rt->rt_rmx.rmx_rttvar /
2755                             (RTM_RTTUNIT / (hz * TCP_RTTVAR_SCALE));
2756                         tcpstat.tcps_usedrttvar++;
2757                 } else {
2758                         /* default variation is +- 1 rtt */
2759                         tp->t_rttvar =
2760                             tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
2761                 }
2762                 TCPT_RANGESET(tp->t_rxtcur,
2763                               ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
2764                               tp->t_rttmin, TCPTV_REXMTMAX);
2765         }
2766         /*
2767          * if there's an mtu associated with the route, use it
2768          * else, use the link mtu.
2769          */
2770         if (rt->rt_rmx.rmx_mtu)
2771                 mss = rt->rt_rmx.rmx_mtu - min_protoh;
2772         else
2773         {
2774                 mss =
2775 #ifdef INET6
2776                         (isipv6 ? nd_ifinfo[rt->rt_ifp->if_index].linkmtu :
2777 #endif
2778                          ifp->if_mtu
2779 #ifdef INET6
2780                          )
2781 #endif
2782                         - min_protoh;
2783 #ifdef INET6
2784                 if (isipv6) {
2785                         if (!in6_localaddr(&inp->in6p_faddr))
2786                                 mss = min(mss, tcp_v6mssdflt);
2787                 } else
2788 #endif
2789                 if (!in_localaddr(inp->inp_faddr))
2790                         mss = min(mss, tcp_mssdflt);
2791         }
2792         mss = min(mss, offer);
2793         /*
2794          * maxopd stores the maximum length of data AND options
2795          * in a segment; maxseg is the amount of data in a normal
2796          * segment.  We need to store this value (maxopd) apart
2797          * from maxseg, because now every segment carries options
2798          * and thus we normally have somewhat less data in segments.
2799          */
2800         tp->t_maxopd = mss;
2801
2802         /*
2803          * In case of T/TCP, origoffer==-1 indicates, that no segments
2804          * were received yet.  In this case we just guess, otherwise
2805          * we do the same as before T/TCP.
2806          */
2807         if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
2808             (origoffer == -1 ||
2809              (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
2810                 mss -= TCPOLEN_TSTAMP_APPA;
2811         if ((tp->t_flags & (TF_REQ_CC|TF_NOOPT)) == TF_REQ_CC &&
2812             (origoffer == -1 ||
2813              (tp->t_flags & TF_RCVD_CC) == TF_RCVD_CC))
2814                 mss -= TCPOLEN_CC_APPA;
2815
2816 #if     (MCLBYTES & (MCLBYTES - 1)) == 0
2817                 if (mss > MCLBYTES)
2818                         mss &= ~(MCLBYTES-1);
2819 #else
2820                 if (mss > MCLBYTES)
2821                         mss = mss / MCLBYTES * MCLBYTES;
2822 #endif
2823         /*
2824          * If there's a pipesize, change the socket buffer
2825          * to that size.  Make the socket buffers an integral
2826          * number of mss units; if the mss is larger than
2827          * the socket buffer, decrease the mss.
2828          */
2829 #ifdef RTV_SPIPE
2830         if ((bufsize = rt->rt_rmx.rmx_sendpipe) == 0)
2831 #endif
2832                 bufsize = so->so_snd.sb_hiwat;
2833         if (bufsize < mss)
2834                 mss = bufsize;
2835         else {
2836                 bufsize = roundup(bufsize, mss);
2837                 if (bufsize > sb_max)
2838                         bufsize = sb_max;
2839                 (void)sbreserve(&so->so_snd, bufsize, so, NULL);
2840         }
2841         tp->t_maxseg = mss;
2842
2843 #ifdef RTV_RPIPE
2844         if ((bufsize = rt->rt_rmx.rmx_recvpipe) == 0)
2845 #endif
2846                 bufsize = so->so_rcv.sb_hiwat;
2847         if (bufsize > mss) {
2848                 bufsize = roundup(bufsize, mss);
2849                 if (bufsize > sb_max)
2850                         bufsize = sb_max;
2851                 (void)sbreserve(&so->so_rcv, bufsize, so, NULL);
2852         }
2853
2854         /*
2855          * Set the slow-start flight size depending on whether this
2856          * is a local network or not.
2857          */
2858         if (
2859 #ifdef INET6
2860             (isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
2861             (!isipv6 &&
2862 #endif
2863              in_localaddr(inp->inp_faddr)
2864 #ifdef INET6
2865              )
2866 #endif
2867             )
2868                 tp->snd_cwnd = mss * ss_fltsz_local;
2869         else
2870                 tp->snd_cwnd = mss * ss_fltsz;
2871
2872         if (rt->rt_rmx.rmx_ssthresh) {
2873                 /*
2874                  * There's some sort of gateway or interface
2875                  * buffer limit on the path.  Use this to set
2876                  * the slow start threshhold, but set the
2877                  * threshold to no less than 2*mss.
2878                  */
2879                 tp->snd_ssthresh = max(2 * mss, rt->rt_rmx.rmx_ssthresh);
2880                 tcpstat.tcps_usedssthresh++;
2881         }
2882 }
2883
2884 /*
2885  * Determine the MSS option to send on an outgoing SYN.
2886  */
2887 int
2888 tcp_mssopt(tp)
2889         struct tcpcb *tp;
2890 {
2891         struct rtentry *rt;
2892 #ifdef INET6
2893         int isipv6;
2894         int min_protoh;
2895 #endif
2896
2897 #ifdef INET6
2898         isipv6 = ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
2899         min_protoh = isipv6 ? sizeof (struct ip6_hdr) + sizeof (struct tcphdr)
2900                             : sizeof (struct tcpiphdr);
2901 #else
2902 #define min_protoh  (sizeof (struct tcpiphdr))
2903 #endif
2904 #ifdef INET6
2905         if (isipv6)
2906                 rt = tcp_rtlookup6(tp->t_inpcb);
2907         else
2908 #endif /* INET6 */
2909         rt = tcp_rtlookup(tp->t_inpcb);
2910         if (rt == NULL)
2911                 return
2912 #ifdef INET6
2913                         isipv6 ? tcp_v6mssdflt :
2914 #endif /* INET6 */
2915                         tcp_mssdflt;
2916
2917         return rt->rt_ifp->if_mtu - min_protoh;
2918 }
2919
2920
2921 /*
2922  * Checks for partial ack.  If partial ack arrives, force the retransmission
2923  * of the next unacknowledged segment, do not clear tp->t_dupacks, and return
2924  * 1.  By setting snd_nxt to ti_ack, this forces retransmission timer to
2925  * be started again.  If the ack advances at least to tp->snd_recover, return 0.
2926  */
2927 static int
2928 tcp_newreno(tp, th)
2929         struct tcpcb *tp;
2930         struct tcphdr *th;
2931 {
2932         if (SEQ_LT(th->th_ack, tp->snd_recover)) {
2933                 tcp_seq onxt = tp->snd_nxt;
2934                 u_long  ocwnd = tp->snd_cwnd;
2935
2936                 callout_stop(tp->tt_rexmt);
2937                 tp->t_rtttime = 0;
2938                 tp->snd_nxt = th->th_ack;
2939                 /*
2940                  * Set snd_cwnd to one segment beyond acknowledged offset
2941                  * (tp->snd_una has not yet been updated when this function
2942                  *  is called)
2943                  */
2944                 tp->snd_cwnd = tp->t_maxseg + (th->th_ack - tp->snd_una);
2945                 (void) tcp_output(tp);
2946                 tp->snd_cwnd = ocwnd;
2947                 if (SEQ_GT(onxt, tp->snd_nxt))
2948                         tp->snd_nxt = onxt;
2949                 /*
2950                  * Partial window deflation.  Relies on fact that tp->snd_una
2951                  * not updated yet.
2952                  */
2953                 tp->snd_cwnd -= (th->th_ack - tp->snd_una - tp->t_maxseg);
2954                 return (1);
2955         }
2956         return (0);
2957 }