sys/netinet/tcp_input.c

   1 /*
   2  * Copyright (c) 2002-2004 Jeffrey Hsu.  All rights reserved.
   3  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
   4  *      The Regents of the University of California.  All rights reserved.
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions
   8  * are met:
   9  * 1. Redistributions of source code must retain the above copyright
  10  *    notice, this list of conditions and the following disclaimer.
  11  * 2. Redistributions in binary form must reproduce the above copyright
  12  *    notice, this list of conditions and the following disclaimer in the
  13  *    documentation and/or other materials provided with the distribution.
  14  * 3. All advertising materials mentioning features or use of this software
  15  *    must display the following acknowledgement:
  16  *      This product includes software developed by the University of
  17  *      California, Berkeley and its contributors.
  18  * 4. Neither the name of the University nor the names of its contributors
  19  *    may be used to endorse or promote products derived from this software
  20  *    without specific prior written permission.
  21  *
  22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  32  * SUCH DAMAGE.
  33  *
  34  *      @(#)tcp_input.c 8.12 (Berkeley) 5/24/95
  35  * $FreeBSD: src/sys/netinet/tcp_input.c,v 1.107.2.38 2003/05/21 04:46:41 cjc Exp $
  36  * $DragonFly: src/sys/netinet/tcp_input.c,v 1.20 2004/03/09 21:21:54 hsu Exp $
  37  */
  38
  39 #include "opt_ipfw.h"           /* for ipfw_fwd         */
  40 #include "opt_inet6.h"
  41 #include "opt_ipsec.h"
  42 #include "opt_tcpdebug.h"
  43 #include "opt_tcp_input.h"
  44
  45 #include <sys/param.h>
  46 #include <sys/systm.h>
  47 #include <sys/kernel.h>
  48 #include <sys/sysctl.h>
  49 #include <sys/malloc.h>
  50 #include <sys/mbuf.h>
  51 #include <sys/proc.h>           /* for proc0 declaration */
  52 #include <sys/protosw.h>
  53 #include <sys/socket.h>
  54 #include <sys/socketvar.h>
  55 #include <sys/syslog.h>
  56 #include <sys/in_cksum.h>
  57
  58 #include <machine/cpu.h>        /* before tcp_seq.h, for tcp_random18() */
  59
  60 #include <net/if.h>
  61 #include <net/route.h>
  62
  63 #include <netinet/in.h>
  64 #include <netinet/in_systm.h>
  65 #include <netinet/ip.h>
  66 #include <netinet/ip_icmp.h>    /* for ICMP_BANDLIM             */
  67 #include <netinet/in_var.h>
  68 #include <netinet/icmp_var.h>   /* for ICMP_BANDLIM             */
  69 #include <netinet/in_pcb.h>
  70 #include <netinet/ip_var.h>
  71 #include <netinet/ip6.h>
  72 #include <netinet/icmp6.h>
  73 #include <netinet6/nd6.h>
  74 #include <netinet6/ip6_var.h>
  75 #include <netinet6/in6_pcb.h>
  76 #include <netinet/tcp.h>
  77 #include <netinet/tcp_fsm.h>
  78 #include <netinet/tcp_seq.h>
  79 #include <netinet/tcp_timer.h>
  80 #include <netinet/tcp_var.h>
  81 #include <netinet6/tcp6_var.h>
  82 #include <netinet/tcpip.h>
  83 #ifdef TCPDEBUG
  84 #include <netinet/tcp_debug.h>
  85
  86 u_char tcp_saveipgen[40]; /* the size must be of max ip header, now IPv6 */
  87 struct tcphdr tcp_savetcp;
  88 #endif /* TCPDEBUG */
  89
  90 #ifdef FAST_IPSEC
  91 #include <netipsec/ipsec.h>
  92 #include <netipsec/ipsec6.h>
  93 #endif
  94
  95 #ifdef IPSEC
  96 #include <netinet6/ipsec.h>
  97 #include <netinet6/ipsec6.h>
  98 #include <netproto/key/key.h>
  99 #endif /*IPSEC*/
 100
 101 MALLOC_DEFINE(M_TSEGQ, "tseg_qent", "TCP segment queue entry");
 102
 103 static const int tcprexmtthresh = 3;
 104 tcp_cc  tcp_ccgen;
 105
 106 struct  tcpstat tcpstat;
 107 SYSCTL_STRUCT(_net_inet_tcp, TCPCTL_STATS, stats, CTLFLAG_RW,
 108     &tcpstat , tcpstat, "TCP statistics (struct tcpstat, netinet/tcp_var.h)");
 109
 110 static int log_in_vain = 0;
 111 SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW,
 112     &log_in_vain, 0, "Log all incoming TCP connections");
 113
 114 static int blackhole = 0;
 115 SYSCTL_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_RW,
 116     &blackhole, 0, "Do not send RST when dropping refused connections");
 117
 118 int tcp_delack_enabled = 1;
 119 SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_RW,
 120     &tcp_delack_enabled, 0,
 121     "Delay ACK to try and piggyback it onto a data packet");
 122
 123 #ifdef TCP_DROP_SYNFIN
 124 static int drop_synfin = 0;
 125 SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_RW,
 126     &drop_synfin, 0, "Drop TCP packets with SYN+FIN set");
 127 #endif
 128
 129 static int tcp_do_limitedtransmit = 1;
 130 SYSCTL_INT(_net_inet_tcp, OID_AUTO, limitedtransmit, CTLFLAG_RW,
 131     &tcp_do_limitedtransmit, 0, "Enable RFC 3042 (Limited Transmit)");
 132
 133 static int tcp_do_early_retransmit = 0;
 134 SYSCTL_INT(_net_inet_tcp, OID_AUTO, earlyretransmit, CTLFLAG_RW,
 135     &tcp_do_early_retransmit, 0, "Early retransmit");
 136
 137 static int tcp_do_rfc3390 = 1;
 138 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3390, CTLFLAG_RW,
 139     &tcp_do_rfc3390, 0,
 140     "Enable RFC 3390 (Increasing TCP's Initial Congestion Window)");
 141
 142 static int tcp_do_eifel_detect = 1;
 143 SYSCTL_INT(_net_inet_tcp, OID_AUTO, eifel, CTLFLAG_RW,
 144     &tcp_do_eifel_detect, 0, "Eifel detection algorithm (RFC 3522)");
 145
 146 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, reass, CTLFLAG_RW, 0,
 147     "TCP Segment Reassembly Queue");
 148
 149 int tcp_reass_maxseg = 0;
 150 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, maxsegments, CTLFLAG_RD,
 151     &tcp_reass_maxseg, 0,
 152     "Global maximum number of TCP Segments in Reassembly Queue");
 153
 154 int tcp_reass_qsize = 0;
 155 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, cursegments, CTLFLAG_RD,
 156     &tcp_reass_qsize, 0,
 157     "Global number of TCP Segments currently in Reassembly Queue");
 158
 159 static int tcp_reass_overflows = 0;
 160 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, overflows, CTLFLAG_RD,
 161     &tcp_reass_overflows, 0,
 162     "Global number of TCP Segment Reassembly Queue Overflows");
 163
 164 struct inpcbinfo tcbinfo[MAXCPU];
 165
 166 static void      tcp_dooptions(struct tcpopt *, u_char *, int, int);
 167 static void      tcp_pulloutofband(struct socket *,
 168                      struct tcphdr *, struct mbuf *, int);
 169 static int       tcp_reass(struct tcpcb *, struct tcphdr *, int *,
 170                      struct mbuf *);
 171 static void      tcp_xmit_timer(struct tcpcb *, int);
 172 static void      tcp_newreno_partial_ack(struct tcpcb *, struct tcphdr *);
 173
 174 /* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */
 175 #ifdef INET6
 176 #define ND6_HINT(tp) \
 177 do { \
 178         if ((tp) && (tp)->t_inpcb && \
 179             ((tp)->t_inpcb->inp_vflag & INP_IPV6) != 0 && \
 180             (tp)->t_inpcb->in6p_route.ro_rt) \
 181                 nd6_nud_hint((tp)->t_inpcb->in6p_route.ro_rt, NULL, 0); \
 182 } while (0)
 183 #else
 184 #define ND6_HINT(tp)
 185 #endif
 186
 187 /*
 188  * Indicate whether this ack should be delayed.  We can delay the ack if
 189  *      - delayed acks are enabled and
 190  *      - there is no delayed ack timer in progress and
 191  *      - our last ack wasn't a 0-sized window.  We never want to delay
 192  *        the ack that opens up a 0-sized window.
 193  */
 194 #define DELAY_ACK(tp) \
 195         (tcp_delack_enabled && !callout_pending(tp->tt_delack) && \
 196         (tp->t_flags & TF_RXWIN0SENT) == 0)
 197
 198 static int
 199 tcp_reass(tp, th, tlenp, m)
 200         struct tcpcb *tp;
 201         struct tcphdr *th;
 202         int *tlenp;
 203         struct mbuf *m;
 204 {
 205         struct tseg_qent *q;
 206         struct tseg_qent *p = NULL;
 207         struct tseg_qent *nq;
 208         struct tseg_qent *te;
 209         struct socket *so = tp->t_inpcb->inp_socket;
 210         int flags;
 211
 212         /*
 213          * Call with th==0 after become established to
 214          * force pre-ESTABLISHED data up to user socket.
 215          */
 216         if (th == 0)
 217                 goto present;
 218
 219         /*
 220          * Limit the number of segments in the reassembly queue to prevent
 221          * holding on to too many segments (and thus running out of mbufs).
 222          * Make sure to let the missing segment through which caused this
 223          * queue.  Always keep one global queue entry spare to be able to
 224          * process the missing segment.
 225          */
 226         if (th->th_seq != tp->rcv_nxt &&
 227             tcp_reass_qsize + 1 >= tcp_reass_maxseg) {
 228                 tcp_reass_overflows++;
 229                 tcpstat.tcps_rcvmemdrop++;
 230                 m_freem(m);
 231                 return (0);
 232         }
 233
 234         /* Allocate a new queue entry. If we can't, just drop the pkt. XXX */
 235         MALLOC(te, struct tseg_qent *, sizeof(struct tseg_qent), M_TSEGQ,
 236                M_NOWAIT);
 237         if (te == NULL) {
 238                 tcpstat.tcps_rcvmemdrop++;
 239                 m_freem(m);
 240                 return (0);
 241         }
 242         tcp_reass_qsize++;
 243
 244         /*
 245          * Find a segment which begins after this one does.
 246          */
 247         LIST_FOREACH(q, &tp->t_segq, tqe_q) {
 248                 if (SEQ_GT(q->tqe_th->th_seq, th->th_seq))
 249                         break;
 250                 p = q;
 251         }
 252
 253         /*
 254          * If there is a preceding segment, it may provide some of
 255          * our data already.  If so, drop the data from the incoming
 256          * segment.  If it provides all of our data, drop us.
 257          */
 258         if (p != NULL) {
 259                 int i;
 260                 /* conversion to int (in i) handles seq wraparound */
 261                 i = p->tqe_th->th_seq + p->tqe_len - th->th_seq;
 262                 if (i > 0) {
 263                         if (i >= *tlenp) {
 264                                 tcpstat.tcps_rcvduppack++;
 265                                 tcpstat.tcps_rcvdupbyte += *tlenp;
 266                                 m_freem(m);
 267                                 free(te, M_TSEGQ);
 268                                 tcp_reass_qsize--;
 269                                 /*
 270                                  * Try to present any queued data
 271                                  * at the left window edge to the user.
 272                                  * This is needed after the 3-WHS
 273                                  * completes.
 274                                  */
 275                                 goto present;   /* ??? */
 276                         }
 277                         m_adj(m, i);
 278                         *tlenp -= i;
 279                         th->th_seq += i;
 280                 }
 281         }
 282         tcpstat.tcps_rcvoopack++;
 283         tcpstat.tcps_rcvoobyte += *tlenp;
 284
 285         /*
 286          * While we overlap succeeding segments trim them or,
 287          * if they are completely covered, dequeue them.
 288          */
 289         while (q) {
 290                 int i = (th->th_seq + *tlenp) - q->tqe_th->th_seq;
 291                 if (i <= 0)
 292                         break;
 293                 if (i < q->tqe_len) {
 294                         q->tqe_th->th_seq += i;
 295                         q->tqe_len -= i;
 296                         m_adj(q->tqe_m, i);
 297                         break;
 298                 }
 299
 300                 nq = LIST_NEXT(q, tqe_q);
 301                 LIST_REMOVE(q, tqe_q);
 302                 m_freem(q->tqe_m);
 303                 free(q, M_TSEGQ);
 304                 tcp_reass_qsize--;
 305                 q = nq;
 306         }
 307
 308         /* Insert the new segment queue entry into place. */
 309         te->tqe_m = m;
 310         te->tqe_th = th;
 311         te->tqe_len = *tlenp;
 312
 313         if (p == NULL) {
 314                 LIST_INSERT_HEAD(&tp->t_segq, te, tqe_q);
 315         } else {
 316                 LIST_INSERT_AFTER(p, te, tqe_q);
 317         }
 318
 319 present:
 320         /*
 321          * Present data to user, advancing rcv_nxt through
 322          * completed sequence space.
 323          */
 324         if (!TCPS_HAVEESTABLISHED(tp->t_state))
 325                 return (0);
 326         q = LIST_FIRST(&tp->t_segq);
 327         if (!q || q->tqe_th->th_seq != tp->rcv_nxt)
 328                 return (0);
 329         do {
 330                 tp->rcv_nxt += q->tqe_len;
 331                 flags = q->tqe_th->th_flags & TH_FIN;
 332                 nq = LIST_NEXT(q, tqe_q);
 333                 LIST_REMOVE(q, tqe_q);
 334                 if (so->so_state & SS_CANTRCVMORE)
 335                         m_freem(q->tqe_m);
 336                 else
 337                         sbappend(&so->so_rcv, q->tqe_m);
 338                 free(q, M_TSEGQ);
 339                 tcp_reass_qsize--;
 340                 q = nq;
 341         } while (q && q->tqe_th->th_seq == tp->rcv_nxt);
 342         ND6_HINT(tp);
 343         sorwakeup(so);
 344         return (flags);
 345 }
 346
 347 /*
 348  * TCP input routine, follows pages 65-76 of the
 349  * protocol specification dated September, 1981 very closely.
 350  */
 351 #ifdef INET6
 352 int
 353 tcp6_input(mp, offp, proto)
 354         struct mbuf **mp;
 355         int *offp, proto;
 356 {
 357         struct mbuf *m = *mp;
 358         struct in6_ifaddr *ia6;
 359
 360         IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
 361
 362         /*
 363          * draft-itojun-ipv6-tcp-to-anycast
 364          * better place to put this in?
 365          */
 366         ia6 = ip6_getdstifaddr(m);
 367         if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
 368                 struct ip6_hdr *ip6;
 369
 370                 ip6 = mtod(m, struct ip6_hdr *);
 371                 icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
 372                             (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
 373                 return IPPROTO_DONE;
 374         }
 375
 376         tcp_input(m, *offp, proto);
 377         return IPPROTO_DONE;
 378 }
 379 #endif
 380
 381 void
 382 tcp_input(m, off0, proto)
 383         struct mbuf *m;
 384         int off0, proto;
 385 {
 386         struct tcphdr *th;
 387         struct ip *ip = NULL;
 388         struct ipovly *ipov;
 389         struct inpcb *inp = NULL;
 390         u_char *optp = NULL;
 391         int optlen = 0;
 392         int len, tlen, off;
 393         int drop_hdrlen;
 394         struct tcpcb *tp = NULL;
 395         int thflags;
 396         struct socket *so = 0;
 397         int todrop, acked, ourfinisacked, needoutput = 0;
 398         u_long tiwin;
 399         struct tcpopt to;               /* options in this segment */
 400         struct rmxp_tao *taop;          /* pointer to our TAO cache entry */
 401         struct rmxp_tao tao_noncached;  /* in case there's no cached entry */
 402         struct sockaddr_in *next_hop = NULL;
 403         int rstreason; /* For badport_bandlim accounting purposes */
 404         int cpu;
 405         struct ip6_hdr *ip6 = NULL;
 406 #ifdef INET6
 407         int isipv6;
 408 #else
 409         const int isipv6 = 0;
 410 #endif
 411 #ifdef TCPDEBUG
 412         short ostate = 0;
 413 #endif
 414
 415         /* Grab info from MT_TAG mbufs prepended to the chain. */
 416         for (;m && m->m_type == MT_TAG; m = m->m_next) {
 417                 if (m->_m_tag_id == PACKET_TAG_IPFORWARD)
 418                         next_hop = (struct sockaddr_in *)m->m_hdr.mh_data;
 419         }
 420 #ifdef INET6
 421         isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
 422 #endif
 423         bzero((char *)&to, sizeof(to));
 424
 425         tcpstat.tcps_rcvtotal++;
 426
 427         if (isipv6) {
 428                 /* IP6_EXTHDR_CHECK() is already done at tcp6_input() */
 429                 ip6 = mtod(m, struct ip6_hdr *);
 430                 tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
 431                 if (in6_cksum(m, IPPROTO_TCP, off0, tlen)) {
 432                         tcpstat.tcps_rcvbadsum++;
 433                         goto drop;
 434                 }
 435                 th = (struct tcphdr *)((caddr_t)ip6 + off0);
 436
 437                 /*
 438                  * Be proactive about unspecified IPv6 address in source.
 439                  * As we use all-zero to indicate unbounded/unconnected pcb,
 440                  * unspecified IPv6 address can be used to confuse us.
 441                  *
 442                  * Note that packets with unspecified IPv6 destination is
 443                  * already dropped in ip6_input.
 444                  */
 445                 if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
 446                         /* XXX stat */
 447                         goto drop;
 448                 }
 449         } else {
 450                 /*
 451                  * Get IP and TCP header together in first mbuf.
 452                  * Note: IP leaves IP header in first mbuf.
 453                  */
 454                 if (off0 > sizeof(struct ip)) {
 455                         ip_stripoptions(m);
 456                         off0 = sizeof(struct ip);
 457                 }
 458                 if (m->m_len < sizeof(struct tcpiphdr)) {
 459                         if ((m = m_pullup(m, sizeof(struct tcpiphdr))) == 0) {
 460                                 tcpstat.tcps_rcvshort++;
 461                                 return;
 462                         }
 463                 }
 464                 ip = mtod(m, struct ip *);
 465                 ipov = (struct ipovly *)ip;
 466                 th = (struct tcphdr *)((caddr_t)ip + off0);
 467                 tlen = ip->ip_len;
 468
 469                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
 470                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
 471                                 th->th_sum = m->m_pkthdr.csum_data;
 472                         else
 473                                 th->th_sum = in_pseudo(ip->ip_src.s_addr,
 474                                                 ip->ip_dst.s_addr,
 475                                                 htonl(m->m_pkthdr.csum_data +
 476                                                         ip->ip_len +
 477                                                         IPPROTO_TCP));
 478                         th->th_sum ^= 0xffff;
 479                 } else {
 480                         /*
 481                          * Checksum extended TCP header and data.
 482                          */
 483                         len = sizeof(struct ip) + tlen;
 484                         bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
 485                         ipov->ih_len = (u_short)tlen;
 486                         ipov->ih_len = htons(ipov->ih_len);
 487                         th->th_sum = in_cksum(m, len);
 488                 }
 489                 if (th->th_sum) {
 490                         tcpstat.tcps_rcvbadsum++;
 491                         goto drop;
 492                 }
 493 #ifdef INET6
 494                 /* Re-initialization for later version check */
 495                 ip->ip_v = IPVERSION;
 496 #endif
 497         }
 498
 499         /*
 500          * Check that TCP offset makes sense,
 501          * pull out TCP options and adjust length.              XXX
 502          */
 503         off = th->th_off << 2;
 504         if (off < sizeof(struct tcphdr) || off > tlen) {
 505                 tcpstat.tcps_rcvbadoff++;
 506                 goto drop;
 507         }
 508         tlen -= off;    /* tlen is used instead of ti->ti_len */
 509         if (off > sizeof(struct tcphdr)) {
 510                 if (isipv6) {
 511                         IP6_EXTHDR_CHECK(m, off0, off, );
 512                         ip6 = mtod(m, struct ip6_hdr *);
 513                         th = (struct tcphdr *)((caddr_t)ip6 + off0);
 514                 } else {
 515                         if (m->m_len < sizeof(struct ip) + off) {
 516                                 if ((m = m_pullup(m, sizeof(struct ip) + off))
 517                                                 == 0) {
 518                                         tcpstat.tcps_rcvshort++;
 519                                         return;
 520                                 }
 521                                 ip = mtod(m, struct ip *);
 522                                 ipov = (struct ipovly *)ip;
 523                                 th = (struct tcphdr *)((caddr_t)ip + off0);
 524                         }
 525                 }
 526                 optlen = off - sizeof(struct tcphdr);
 527                 optp = (u_char *)(th + 1);
 528         }
 529         thflags = th->th_flags;
 530
 531 #ifdef TCP_DROP_SYNFIN
 532         /*
 533          * If the drop_synfin option is enabled, drop all packets with
 534          * both the SYN and FIN bits set. This prevents e.g. nmap from
 535          * identifying the TCP/IP stack.
 536          *
 537          * This is a violation of the TCP specification.
 538          */
 539         if (drop_synfin && (thflags & (TH_SYN|TH_FIN)) == (TH_SYN|TH_FIN))
 540                 goto drop;
 541 #endif
 542
 543         /*
 544          * Convert TCP protocol specific fields to host format.
 545          */
 546         th->th_seq = ntohl(th->th_seq);
 547         th->th_ack = ntohl(th->th_ack);
 548         th->th_win = ntohs(th->th_win);
 549         th->th_urp = ntohs(th->th_urp);
 550
 551         /*
 552          * Delay droping TCP, IP headers, IPv6 ext headers, and TCP options,
 553          * until after ip6_savecontrol() is called and before other functions
 554          * which don't want those proto headers.
 555          * Because ip6_savecontrol() is going to parse the mbuf to
 556          * search for data to be passed up to user-land, it wants mbuf
 557          * parameters to be unchanged.
 558          * XXX: the call of ip6_savecontrol() has been obsoleted based on
 559          * latest version of the advanced API (20020110).
 560          */
 561         drop_hdrlen = off0 + off;
 562
 563         /*
 564          * Locate pcb for segment.
 565          */
 566 findpcb:
 567         /* IPFIREWALL_FORWARD section */
 568         if (next_hop != NULL && isipv6 == 0) {  /* IPv6 support is not yet */
 569                 /*
 570                  * Transparently forwarded. Pretend to be the destination.
 571                  * already got one like this?
 572                  */
 573                 inp = in_pcblookup_hash(&tcbinfo[mycpu->gd_cpuid],
 574                                         ip->ip_src, th->th_sport,
 575                                         ip->ip_dst, th->th_dport,
 576                                         0, m->m_pkthdr.rcvif);
 577                 if (!inp) {
 578                         /*
 579                          * It's new.  Try to find the ambushing socket.
 580                          */
 581
 582                         /*
 583                          * The rest of the ipfw code stores the port in
 584                          * host order.  XXX
 585                          * (The IP address is still in network order.)
 586                          */
 587                         in_port_t dport = next_hop->sin_port ?
 588                                                 htons(next_hop->sin_port) :
 589                                                 th->th_dport;
 590
 591                         cpu = tcp_addrcpu(ip->ip_src.s_addr, th->th_sport,
 592                                           next_hop->sin_addr.s_addr, dport);
 593                         inp = in_pcblookup_hash(&tcbinfo[cpu],
 594                                                 ip->ip_src, th->th_sport,
 595                                                 next_hop->sin_addr, dport,
 596                                                 1, m->m_pkthdr.rcvif);
 597                 }
 598         } else {
 599                 if (isipv6)
 600                         inp = in6_pcblookup_hash(&tcbinfo[0],
 601                                                  &ip6->ip6_src, th->th_sport,
 602                                                  &ip6->ip6_dst, th->th_dport,
 603                                                  1, m->m_pkthdr.rcvif);
 604                 else
 605                         inp = in_pcblookup_hash(&tcbinfo[mycpu->gd_cpuid],
 606                                                 ip->ip_src, th->th_sport,
 607                                                 ip->ip_dst, th->th_dport,
 608                                                 1, m->m_pkthdr.rcvif);
 609       }
 610
 611 #ifdef IPSEC
 612         if (isipv6) {
 613                 if (inp != NULL && ipsec6_in_reject_so(m, inp->inp_socket)) {
 614                         ipsec6stat.in_polvio++;
 615                         goto drop;
 616                 }
 617         } else {
 618                 if (inp != NULL && ipsec4_in_reject_so(m, inp->inp_socket)) {
 619                         ipsecstat.in_polvio++;
 620                         goto drop;
 621                 }
 622         }
 623 #endif
 624 #ifdef FAST_IPSEC
 625         if (isipv6) {
 626                 if (inp != NULL && ipsec6_in_reject(m, inp)) {
 627                         goto drop;
 628                 }
 629         } else {
 630                 if (inp != NULL && ipsec4_in_reject(m, inp)) {
 631                         goto drop;
 632                 }
 633         }
 634 #endif
 635
 636         /*
 637          * If the state is CLOSED (i.e., TCB does not exist) then
 638          * all data in the incoming segment is discarded.
 639          * If the TCB exists but is in CLOSED state, it is embryonic,
 640          * but should either do a listen or a connect soon.
 641          */
 642         if (inp == NULL) {
 643                 if (log_in_vain) {
 644 #ifdef INET6
 645                         char dbuf[INET6_ADDRSTRLEN+2], sbuf[INET6_ADDRSTRLEN+2];
 646 #else
 647                         char dbuf[4*sizeof "123"], sbuf[4*sizeof "123"];
 648 #endif
 649                         if (isipv6) {
 650                                 strcpy(dbuf, "[");
 651                                 strcpy(sbuf, "[");
 652                                 strcat(dbuf, ip6_sprintf(&ip6->ip6_dst));
 653                                 strcat(sbuf, ip6_sprintf(&ip6->ip6_src));
 654                                 strcat(dbuf, "]");
 655                                 strcat(sbuf, "]");
 656                         } else {
 657                                 strcpy(dbuf, inet_ntoa(ip->ip_dst));
 658                                 strcpy(sbuf, inet_ntoa(ip->ip_src));
 659                         }
 660                         switch (log_in_vain) {
 661                         case 1:
 662                                 if ((thflags & TH_SYN) == 0)
 663                                         break;
 664                         case 2:
 665                                 log(LOG_INFO,
 666                                     "Connection attempt to TCP %s:%d "
 667                                     "from %s:%d flags:0x%02x\n",
 668                                     dbuf, ntohs(th->th_dport), sbuf,
 669                                     ntohs(th->th_sport), thflags);
 670                                 break;
 671                         default:
 672                                 break;
 673                         }
 674                 }
 675                 if (blackhole) {
 676                         switch (blackhole) {
 677                         case 1:
 678                                 if (thflags & TH_SYN)
 679                                         goto drop;
 680                                 break;
 681                         case 2:
 682                                 goto drop;
 683                         default:
 684                                 goto drop;
 685                         }
 686                 }
 687                 rstreason = BANDLIM_RST_CLOSEDPORT;
 688                 goto dropwithreset;
 689         }
 690         tp = intotcpcb(inp);
 691         if (tp == NULL) {
 692                 rstreason = BANDLIM_RST_CLOSEDPORT;
 693                 goto dropwithreset;
 694         }
 695         if (tp->t_state == TCPS_CLOSED)
 696                 goto drop;
 697
 698         /* Unscale the window into a 32-bit value. */
 699         if ((thflags & TH_SYN) == 0)
 700                 tiwin = th->th_win << tp->snd_scale;
 701         else
 702                 tiwin = th->th_win;
 703
 704         so = inp->inp_socket;
 705
 706 #ifdef TCPDEBUG
 707         if (so->so_options & SO_DEBUG) {
 708                 ostate = tp->t_state;
 709                 if (isipv6)
 710                         bcopy((char *)ip6, (char *)tcp_saveipgen, sizeof(*ip6));
 711                 else
 712                         bcopy((char *)ip, (char *)tcp_saveipgen, sizeof(*ip));
 713                 tcp_savetcp = *th;
 714         }
 715 #endif
 716
 717         if (so->so_options & SO_ACCEPTCONN) {
 718                 struct in_conninfo inc;
 719
 720 #ifdef INET6
 721                 inc.inc_isipv6 = isipv6;
 722 #endif
 723                 if (isipv6) {
 724                         inc.inc6_faddr = ip6->ip6_src;
 725                         inc.inc6_laddr = ip6->ip6_dst;
 726                         inc.inc6_route.ro_rt = NULL;            /* XXX */
 727                 } else {
 728                         inc.inc_faddr = ip->ip_src;
 729                         inc.inc_laddr = ip->ip_dst;
 730                         inc.inc_route.ro_rt = NULL;             /* XXX */
 731                 }
 732                 inc.inc_fport = th->th_sport;
 733                 inc.inc_lport = th->th_dport;
 734
 735                 /*
 736                  * If the state is LISTEN then ignore segment if it contains
 737                  * a RST.  If the segment contains an ACK then it is bad and
 738                  * send a RST.  If it does not contain a SYN then it is not
 739                  * interesting; drop it.
 740                  *
 741                  * If the state is SYN_RECEIVED (syncache) and seg contains
 742                  * an ACK, but not for our SYN/ACK, send a RST.  If the seg
 743                  * contains a RST, check the sequence number to see if it
 744                  * is a valid reset segment.
 745                  */
 746                 if ((thflags & (TH_RST|TH_ACK|TH_SYN)) != TH_SYN) {
 747                         if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
 748                                 if (!syncache_expand(&inc, th, &so, m)) {
 749                                         /*
 750                                          * No syncache entry, or ACK was not
 751                                          * for our SYN/ACK.  Send a RST.
 752                                          */
 753                                         tcpstat.tcps_badsyn++;
 754                                         rstreason = BANDLIM_RST_OPENPORT;
 755                                         goto dropwithreset;
 756                                 }
 757                                 if (so == NULL)
 758                                         /*
 759                                          * Could not complete 3-way handshake,
 760                                          * connection is being closed down, and
 761                                          * syncache will free mbuf.
 762                                          */
 763                                         return;
 764                                 /*
 765                                  * Socket is created in state SYN_RECEIVED.
 766                                  * Continue processing segment.
 767                                  */
 768                                 inp = sotoinpcb(so);
 769                                 tp = intotcpcb(inp);
 770                                 /*
 771                                  * This is what would have happened in
 772                                  * tcp_output() when the SYN,ACK was sent.
 773                                  */
 774                                 tp->snd_up = tp->snd_una;
 775                                 tp->snd_max = tp->snd_nxt = tp->iss + 1;
 776                                 tp->last_ack_sent = tp->rcv_nxt;
 777 /*
 778  * XXX possible bug - it doesn't appear that tp->snd_wnd is unscaled
 779  * until the _second_ ACK is received:
 780  *    rcv SYN (set wscale opts)  --> send SYN/ACK, set snd_wnd = window.
 781  *    rcv ACK, calculate tiwin --> process SYN_RECEIVED, determine wscale,
 782  *        move to ESTAB, set snd_wnd to tiwin.
 783  */
 784                                 tp->snd_wnd = tiwin;    /* unscaled */
 785                                 goto after_listen;
 786                         }
 787                         if (thflags & TH_RST) {
 788                                 syncache_chkrst(&inc, th);
 789                                 goto drop;
 790                         }
 791                         if (thflags & TH_ACK) {
 792                                 syncache_badack(&inc);
 793                                 tcpstat.tcps_badsyn++;
 794                                 rstreason = BANDLIM_RST_OPENPORT;
 795                                 goto dropwithreset;
 796                         }
 797                         goto drop;
 798                 }
 799
 800                 /*
 801                  * Segment's flags are (SYN) or (SYN|FIN).
 802                  */
 803 #ifdef INET6
 804                 /*
 805                  * If deprecated address is forbidden,
 806                  * we do not accept SYN to deprecated interface
 807                  * address to prevent any new inbound connection from
 808                  * getting established.
 809                  * When we do not accept SYN, we send a TCP RST,
 810                  * with deprecated source address (instead of dropping
 811                  * it).  We compromise it as it is much better for peer
 812                  * to send a RST, and RST will be the final packet
 813                  * for the exchange.
 814                  *
 815                  * If we do not forbid deprecated addresses, we accept
 816                  * the SYN packet.  RFC2462 does not suggest dropping
 817                  * SYN in this case.
 818                  * If we decipher RFC2462 5.5.4, it says like this:
 819                  * 1. use of deprecated addr with existing
 820                  *    communication is okay - "SHOULD continue to be
 821                  *    used"
 822                  * 2. use of it with new communication:
 823                  *   (2a) "SHOULD NOT be used if alternate address
 824                  *        with sufficient scope is available"
 825                  *   (2b) nothing mentioned otherwise.
 826                  * Here we fall into (2b) case as we have no choice in
 827                  * our source address selection - we must obey the peer.
 828                  *
 829                  * The wording in RFC2462 is confusing, and there are
 830                  * multiple description text for deprecated address
 831                  * handling - worse, they are not exactly the same.
 832                  * I believe 5.5.4 is the best one, so we follow 5.5.4.
 833                  */
 834                 if (isipv6 && !ip6_use_deprecated) {
 835                         struct in6_ifaddr *ia6;
 836
 837                         if ((ia6 = ip6_getdstifaddr(m)) &&
 838                             (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
 839                                 tp = NULL;
 840                                 rstreason = BANDLIM_RST_OPENPORT;
 841                                 goto dropwithreset;
 842                         }
 843                 }
 844 #endif
 845                 /*
 846                  * If it is from this socket, drop it, it must be forged.
 847                  * Don't bother responding if the destination was a broadcast.
 848                  */
 849                 if (th->th_dport == th->th_sport) {
 850                         if (isipv6) {
 851                                 if (IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst,
 852                                                        &ip6->ip6_src))
 853                                         goto drop;
 854                         } else {
 855                                 if (ip->ip_dst.s_addr == ip->ip_src.s_addr)
 856                                         goto drop;
 857                         }
 858                 }
 859                 /*
 860                  * RFC1122 4.2.3.10, p. 104: discard bcast/mcast SYN
 861                  *
 862                  * Note that it is quite possible to receive unicast
 863                  * link-layer packets with a broadcast IP address. Use
 864                  * in_broadcast() to find them.
 865                  */
 866                 if (m->m_flags & (M_BCAST|M_MCAST))
 867                         goto drop;
 868                 if (isipv6) {
 869                         if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
 870                             IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
 871                                 goto drop;
 872                 } else {
 873                         if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
 874                             IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
 875                             ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
 876                             in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
 877                                 goto drop;
 878                 }
 879                 /*
 880                  * SYN appears to be valid; create compressed TCP state
 881                  * for syncache, or perform t/tcp connection.
 882                  */
 883                 if (so->so_qlen <= so->so_qlimit) {
 884                         tcp_dooptions(&to, optp, optlen, 1);
 885                         if (!syncache_add(&inc, &to, th, &so, m))
 886                                 goto drop;
 887                         if (so == NULL)
 888                                 /*
 889                                  * Entry added to syncache, mbuf used to
 890                                  * send SYN,ACK packet.
 891                                  */
 892                                 return;
 893                         /*
 894                          * Segment passed TAO tests.
 895                          */
 896                         inp = sotoinpcb(so);
 897                         tp = intotcpcb(inp);
 898                         tp->snd_wnd = tiwin;
 899                         tp->t_starttime = ticks;
 900                         tp->t_state = TCPS_ESTABLISHED;
 901
 902                         /*
 903                          * If there is a FIN, or if there is data and the
 904                          * connection is local, then delay SYN,ACK(SYN) in
 905                          * the hope of piggy-backing it on a response
 906                          * segment.  Otherwise must send ACK now in case
 907                          * the other side is slow starting.
 908                          */
 909                         if (DELAY_ACK(tp) &&
 910                             ((thflags & TH_FIN) ||
 911                              (tlen != 0 &&
 912                               ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
 913                                (!isipv6 && in_localaddr(inp->inp_faddr)))))) {
 914                                 callout_reset(tp->tt_delack, tcp_delacktime,
 915                                                 tcp_timer_delack, tp);
 916                                 tp->t_flags |= TF_NEEDSYN;
 917                         } else
 918                                 tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
 919
 920                         tcpstat.tcps_connects++;
 921                         soisconnected(so);
 922                         goto trimthenstep6;
 923                 }
 924                 goto drop;
 925         }
 926 after_listen:
 927
 928 /* XXX temp debugging */
 929         /* should not happen - syncache should pick up these connections */
 930         if (tp->t_state == TCPS_LISTEN)
 931                 panic("tcp_input: TCPS_LISTEN");
 932
 933         /*
 934          * Segment received on connection.
 935          * Reset idle time and keep-alive timer.
 936          */
 937         tp->t_rcvtime = ticks;
 938         if (TCPS_HAVEESTABLISHED(tp->t_state))
 939                 callout_reset(tp->tt_keep, tcp_keepidle, tcp_timer_keep, tp);
 940
 941         /*
 942          * Process options.
 943          * XXX this is tradtitional behavior, may need to be cleaned up.
 944          */
 945         tcp_dooptions(&to, optp, optlen, thflags & TH_SYN);
 946         if (thflags & TH_SYN) {
 947                 if (to.to_flags & TOF_SCALE) {
 948                         tp->t_flags |= TF_RCVD_SCALE;
 949                         tp->requested_s_scale = to.to_requested_s_scale;
 950                 }
 951                 if (to.to_flags & TOF_TS) {
 952                         tp->t_flags |= TF_RCVD_TSTMP;
 953                         tp->ts_recent = to.to_tsval;
 954                         tp->ts_recent_age = ticks;
 955                 }
 956                 if (to.to_flags & (TOF_CC|TOF_CCNEW))
 957                         tp->t_flags |= TF_RCVD_CC;
 958                 if (to.to_flags & TOF_MSS)
 959                         tcp_mss(tp, to.to_mss);
 960         }
 961
 962         /*
 963          * Header prediction: check for the two common cases
 964          * of a uni-directional data xfer.  If the packet has
 965          * no control flags, is in-sequence, the window didn't
 966          * change and we're not retransmitting, it's a
 967          * candidate.  If the length is zero and the ack moved
 968          * forward, we're the sender side of the xfer.  Just
 969          * free the data acked & wake any higher level process
 970          * that was blocked waiting for space.  If the length
 971          * is non-zero and the ack didn't move, we're the
 972          * receiver side.  If we're getting packets in-order
 973          * (the reassembly queue is empty), add the data to
 974          * the socket buffer and note that we need a delayed ack.
 975          * Make sure that the hidden state-flags are also off.
 976          * Since we check for TCPS_ESTABLISHED above, it can only
 977          * be TH_NEEDSYN.
 978          */
 979         if (tp->t_state == TCPS_ESTABLISHED &&
 980             (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
 981             ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
 982             ((to.to_flags & TOF_TS) == 0 ||
 983              TSTMP_GEQ(to.to_tsval, tp->ts_recent)) &&
 984             /*
 985              * Using the CC option is compulsory if once started:
 986              *   the segment is OK if no T/TCP was negotiated or
 987              *   if the segment has a CC option equal to CCrecv
 988              */
 989             ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) != (TF_REQ_CC|TF_RCVD_CC) ||
 990              ((to.to_flags & TOF_CC) != 0 && to.to_cc == tp->cc_recv)) &&
 991             th->th_seq == tp->rcv_nxt &&
 992             tiwin && tiwin == tp->snd_wnd &&
 993             tp->snd_nxt == tp->snd_max) {
 994
 995                 /*
 996                  * If last ACK falls within this segment's sequence numbers,
 997                  * record the timestamp.
 998                  * NOTE that the test is modified according to the latest
 999                  * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1000                  */
1001                 if ((to.to_flags & TOF_TS) != 0 &&
1002                     SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
1003                         tp->ts_recent_age = ticks;
1004                         tp->ts_recent = to.to_tsval;
1005                 }
1006
1007                 if (tlen == 0) {
1008                         if (SEQ_GT(th->th_ack, tp->snd_una) &&
1009                             SEQ_LEQ(th->th_ack, tp->snd_max) &&
1010                             tp->snd_cwnd >= tp->snd_wnd &&
1011                             ((!tcp_do_newreno &&
1012                               tp->t_dupacks < tcprexmtthresh) ||
1013                              (tcp_do_newreno && !IN_FASTRECOVERY(tp)))) {
1014                                 /*
1015                                  * this is a pure ack for outstanding data.
1016                                  */
1017                                 ++tcpstat.tcps_predack;
1018                                 /*
1019                                  * "bad retransmit" recovery
1020                                  *
1021                                  * If Eifel detection applies, then
1022                                  * it is deterministic, so use it
1023                                  * unconditionally over the old heuristic.
1024                                  * Otherwise, fall back to the old heuristic.
1025                                  */
1026                                 if (tcp_do_eifel_detect &&
1027                                     (to.to_flags & TOF_TS) && to.to_tsecr &&
1028                                     (tp->t_flags & TF_FIRSTACCACK)) {
1029                                         /* Eifel detection applicable. */
1030                                         if (to.to_tsecr < tp->t_rexmtTS) {
1031                                                 tcp_revert_congestion_state(tp);
1032                                                 ++tcpstat.tcps_eifeldetected;
1033                                         }
1034                                 } else if (tp->t_rxtshift == 1 &&
1035                                            ticks < tp->t_badrxtwin) {
1036                                         tcp_revert_congestion_state(tp);
1037                                         ++tcpstat.tcps_rttdetected;
1038                                 }
1039                                 tp->t_flags &= ~(TF_FIRSTACCACK |
1040                                                  TF_FASTREXMT | TF_EARLYREXMT);
1041                                 /*
1042                                  * Recalculate the retransmit timer / rtt.
1043                                  *
1044                                  * Some machines (certain windows boxes)
1045                                  * send broken timestamp replies during the
1046                                  * SYN+ACK phase, ignore timestamps of 0.
1047                                  */
1048                                 if ((to.to_flags & TOF_TS) != 0 &&
1049                                     to.to_tsecr) {
1050                                         tcp_xmit_timer(tp,
1051                                             ticks - to.to_tsecr + 1);
1052                                 } else if (tp->t_rtttime &&
1053                                             SEQ_GT(th->th_ack, tp->t_rtseq)) {
1054                                         tcp_xmit_timer(tp,
1055                                                        ticks - tp->t_rtttime);
1056                                 }
1057                                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
1058                                 acked = th->th_ack - tp->snd_una;
1059                                 tcpstat.tcps_rcvackpack++;
1060                                 tcpstat.tcps_rcvackbyte += acked;
1061                                 sbdrop(&so->so_snd, acked);
1062                                 if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
1063                                     SEQ_LEQ(th->th_ack, tp->snd_recover))
1064                                         tp->snd_recover = th->th_ack - 1;
1065                                 tp->snd_una = th->th_ack;
1066                                 tp->t_dupacks = 0;
1067                                 m_freem(m);
1068                                 ND6_HINT(tp); /* some progress has been done */
1069
1070                                 /*
1071                                  * If all outstanding data are acked, stop
1072                                  * retransmit timer, otherwise restart timer
1073                                  * using current (possibly backed-off) value.
1074                                  * If process is waiting for space,
1075                                  * wakeup/selwakeup/signal.  If data
1076                                  * are ready to send, let tcp_output
1077                                  * decide between more output or persist.
1078                                  */
1079                                 if (tp->snd_una == tp->snd_max)
1080                                         callout_stop(tp->tt_rexmt);
1081                                 else if (!callout_active(tp->tt_persist))
1082                                         callout_reset(tp->tt_rexmt,
1083                                                       tp->t_rxtcur,
1084                                                       tcp_timer_rexmt, tp);
1085
1086                                 sowwakeup(so);
1087                                 if (so->so_snd.sb_cc)
1088                                         (void) tcp_output(tp);
1089                                 return;
1090                         }
1091                 } else if (th->th_ack == tp->snd_una &&
1092                     LIST_EMPTY(&tp->t_segq) &&
1093                     tlen <= sbspace(&so->so_rcv)) {
1094                         /*
1095                          * this is a pure, in-sequence data packet
1096                          * with nothing on the reassembly queue and
1097                          * we have enough buffer space to take it.
1098                          */
1099                         ++tcpstat.tcps_preddat;
1100                         tp->rcv_nxt += tlen;
1101                         tcpstat.tcps_rcvpack++;
1102                         tcpstat.tcps_rcvbyte += tlen;
1103                         ND6_HINT(tp);   /* some progress has been done */
1104                         /*
1105                          * Add data to socket buffer.
1106                          */
1107                         if (so->so_state & SS_CANTRCVMORE) {
1108                                 m_freem(m);
1109                         } else {
1110                                 m_adj(m, drop_hdrlen);  /* delayed header drop */
1111                                 sbappend(&so->so_rcv, m);
1112                         }
1113                         sorwakeup(so);
1114                         if (DELAY_ACK(tp)) {
1115                                 callout_reset(tp->tt_delack, tcp_delacktime,
1116                                     tcp_timer_delack, tp);
1117                         } else {
1118                                 tp->t_flags |= TF_ACKNOW;
1119                                 tcp_output(tp);
1120                         }
1121                         return;
1122                 }
1123         }
1124
1125         /*
1126          * Calculate amount of space in receive window,
1127          * and then do TCP input processing.
1128          * Receive window is amount of space in rcv queue,
1129          * but not less than advertised window.
1130          */
1131         { int win;
1132
1133         win = sbspace(&so->so_rcv);
1134         if (win < 0)
1135                 win = 0;
1136         tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
1137         }
1138
1139         switch (tp->t_state) {
1140
1141         /*
1142          * If the state is SYN_RECEIVED:
1143          *      if seg contains an ACK, but not for our SYN/ACK, send a RST.
1144          */
1145         case TCPS_SYN_RECEIVED:
1146                 if ((thflags & TH_ACK) &&
1147                     (SEQ_LEQ(th->th_ack, tp->snd_una) ||
1148                      SEQ_GT(th->th_ack, tp->snd_max))) {
1149                                 rstreason = BANDLIM_RST_OPENPORT;
1150                                 goto dropwithreset;
1151                 }
1152                 break;
1153
1154         /*
1155          * If the state is SYN_SENT:
1156          *      if seg contains an ACK, but not for our SYN, drop the input.
1157          *      if seg contains a RST, then drop the connection.
1158          *      if seg does not contain SYN, then drop it.
1159          * Otherwise this is an acceptable SYN segment
1160          *      initialize tp->rcv_nxt and tp->irs
1161          *      if seg contains ack then advance tp->snd_una
1162          *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
1163          *      arrange for segment to be acked (eventually)
1164          *      continue processing rest of data/controls, beginning with URG
1165          */
1166         case TCPS_SYN_SENT:
1167                 if ((taop = tcp_gettaocache(&inp->inp_inc)) == NULL) {
1168                         taop = &tao_noncached;
1169                         bzero(taop, sizeof(*taop));
1170                 }
1171
1172                 if ((thflags & TH_ACK) &&
1173                     (SEQ_LEQ(th->th_ack, tp->iss) ||
1174                      SEQ_GT(th->th_ack, tp->snd_max))) {
1175                         /*
1176                          * If we have a cached CCsent for the remote host,
1177                          * hence we haven't just crashed and restarted,
1178                          * do not send a RST.  This may be a retransmission
1179                          * from the other side after our earlier ACK was lost.
1180                          * Our new SYN, when it arrives, will serve as the
1181                          * needed ACK.
1182                          */
1183                         if (taop->tao_ccsent != 0)
1184                                 goto drop;
1185                         else {
1186                                 rstreason = BANDLIM_UNLIMITED;
1187                                 goto dropwithreset;
1188                         }
1189                 }
1190                 if (thflags & TH_RST) {
1191                         if (thflags & TH_ACK)
1192                                 tp = tcp_drop(tp, ECONNREFUSED);
1193                         goto drop;
1194                 }
1195                 if ((thflags & TH_SYN) == 0)
1196                         goto drop;
1197                 tp->snd_wnd = th->th_win;       /* initial send window */
1198                 tp->cc_recv = to.to_cc;         /* foreign CC */
1199
1200                 tp->irs = th->th_seq;
1201                 tcp_rcvseqinit(tp);
1202                 if (thflags & TH_ACK) {
1203                         /*
1204                          * Our SYN was acked.  If segment contains CC.ECHO
1205                          * option, check it to make sure this segment really
1206                          * matches our SYN.  If not, just drop it as old
1207                          * duplicate, but send an RST if we're still playing
1208                          * by the old rules.  If no CC.ECHO option, make sure
1209                          * we don't get fooled into using T/TCP.
1210                          */
1211                         if (to.to_flags & TOF_CCECHO) {
1212                                 if (tp->cc_send != to.to_ccecho) {
1213                                         if (taop->tao_ccsent != 0)
1214                                                 goto drop;
1215                                         else {
1216                                                 rstreason = BANDLIM_UNLIMITED;
1217                                                 goto dropwithreset;
1218                                         }
1219                                 }
1220                         } else
1221                                 tp->t_flags &= ~TF_RCVD_CC;
1222                         tcpstat.tcps_connects++;
1223                         soisconnected(so);
1224                         /* Do window scaling on this connection? */
1225                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1226                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1227                                 tp->snd_scale = tp->requested_s_scale;
1228                                 tp->rcv_scale = tp->request_r_scale;
1229                         }
1230                         /* Segment is acceptable, update cache if undefined. */
1231                         if (taop->tao_ccsent == 0)
1232                                 taop->tao_ccsent = to.to_ccecho;
1233
1234                         tp->rcv_adv += tp->rcv_wnd;
1235                         tp->snd_una++;          /* SYN is acked */
1236                         /*
1237                          * If there's data, delay ACK; if there's also a FIN
1238                          * ACKNOW will be turned on later.
1239                          */
1240                         if (DELAY_ACK(tp) && tlen != 0)
1241                                 callout_reset(tp->tt_delack, tcp_delacktime,
1242                                     tcp_timer_delack, tp);
1243                         else
1244                                 tp->t_flags |= TF_ACKNOW;
1245                         /*
1246                          * Received <SYN,ACK> in SYN_SENT[*] state.
1247                          * Transitions:
1248                          *      SYN_SENT  --> ESTABLISHED
1249                          *      SYN_SENT* --> FIN_WAIT_1
1250                          */
1251                         tp->t_starttime = ticks;
1252                         if (tp->t_flags & TF_NEEDFIN) {
1253                                 tp->t_state = TCPS_FIN_WAIT_1;
1254                                 tp->t_flags &= ~TF_NEEDFIN;
1255                                 thflags &= ~TH_SYN;
1256                         } else {
1257                                 tp->t_state = TCPS_ESTABLISHED;
1258                                 callout_reset(tp->tt_keep, tcp_keepidle,
1259                                               tcp_timer_keep, tp);
1260                         }
1261                 } else {
1262                         /*
1263                          * Received initial SYN in SYN-SENT[*] state =>
1264                          * simultaneous open.  If segment contains CC option
1265                          * and there is a cached CC, apply TAO test.
1266                          * If it succeeds, connection is * half-synchronized.
1267                          * Otherwise, do 3-way handshake:
1268                          *        SYN-SENT -> SYN-RECEIVED
1269                          *        SYN-SENT* -> SYN-RECEIVED*
1270                          * If there was no CC option, clear cached CC value.
1271                          */
1272                         tp->t_flags |= TF_ACKNOW;
1273                         callout_stop(tp->tt_rexmt);
1274                         if (to.to_flags & TOF_CC) {
1275                                 if (taop->tao_cc != 0 &&
1276                                     CC_GT(to.to_cc, taop->tao_cc)) {
1277                                         /*
1278                                          * update cache and make transition:
1279                                          *        SYN-SENT -> ESTABLISHED*
1280                                          *        SYN-SENT* -> FIN-WAIT-1*
1281                                          */
1282                                         taop->tao_cc = to.to_cc;
1283                                         tp->t_starttime = ticks;
1284                                         if (tp->t_flags & TF_NEEDFIN) {
1285                                                 tp->t_state = TCPS_FIN_WAIT_1;
1286                                                 tp->t_flags &= ~TF_NEEDFIN;
1287                                         } else {
1288                                                 tp->t_state = TCPS_ESTABLISHED;
1289                                                 callout_reset(tp->tt_keep,
1290                                                               tcp_keepidle,
1291                                                               tcp_timer_keep,
1292                                                               tp);
1293                                         }
1294                                         tp->t_flags |= TF_NEEDSYN;
1295                                 } else
1296                                         tp->t_state = TCPS_SYN_RECEIVED;
1297                         } else {
1298                                 /* CC.NEW or no option => invalidate cache */
1299                                 taop->tao_cc = 0;
1300                                 tp->t_state = TCPS_SYN_RECEIVED;
1301                         }
1302                 }
1303
1304 trimthenstep6:
1305                 /*
1306                  * Advance th->th_seq to correspond to first data byte.
1307                  * If data, trim to stay within window,
1308                  * dropping FIN if necessary.
1309                  */
1310                 th->th_seq++;
1311                 if (tlen > tp->rcv_wnd) {
1312                         todrop = tlen - tp->rcv_wnd;
1313                         m_adj(m, -todrop);
1314                         tlen = tp->rcv_wnd;
1315                         thflags &= ~TH_FIN;
1316                         tcpstat.tcps_rcvpackafterwin++;
1317                         tcpstat.tcps_rcvbyteafterwin += todrop;
1318                 }
1319                 tp->snd_wl1 = th->th_seq - 1;
1320                 tp->rcv_up = th->th_seq;
1321                 /*
1322                  * Client side of transaction: already sent SYN and data.
1323                  * If the remote host used T/TCP to validate the SYN,
1324                  * our data will be ACK'd; if so, enter normal data segment
1325                  * processing in the middle of step 5, ack processing.
1326                  * Otherwise, goto step 6.
1327                  */
1328                 if (thflags & TH_ACK)
1329                         goto process_ACK;
1330
1331                 goto step6;
1332
1333         /*
1334          * If the state is LAST_ACK or CLOSING or TIME_WAIT:
1335          *      if segment contains a SYN and CC [not CC.NEW] option:
1336          *              if state == TIME_WAIT and connection duration > MSL,
1337          *                  drop packet and send RST;
1338          *
1339          *              if SEG.CC > CCrecv then is new SYN, and can implicitly
1340          *                  ack the FIN (and data) in retransmission queue.
1341          *                  Complete close and delete TCPCB.  Then reprocess
1342          *                  segment, hoping to find new TCPCB in LISTEN state;
1343          *
1344          *              else must be old SYN; drop it.
1345          *      else do normal processing.
1346          */
1347         case TCPS_LAST_ACK:
1348         case TCPS_CLOSING:
1349         case TCPS_TIME_WAIT:
1350                 if ((thflags & TH_SYN) &&
1351                     (to.to_flags & TOF_CC) && tp->cc_recv != 0) {
1352                         if (tp->t_state == TCPS_TIME_WAIT &&
1353                                         (ticks - tp->t_starttime) > tcp_msl) {
1354                                 rstreason = BANDLIM_UNLIMITED;
1355                                 goto dropwithreset;
1356                         }
1357                         if (CC_GT(to.to_cc, tp->cc_recv)) {
1358                                 tp = tcp_close(tp);
1359                                 goto findpcb;
1360                         }
1361                         else
1362                                 goto drop;
1363                 }
1364                 break;  /* continue normal processing */
1365         }
1366
1367         /*
1368          * States other than LISTEN or SYN_SENT.
1369          * First check the RST flag and sequence number since reset segments
1370          * are exempt from the timestamp and connection count tests.  This
1371          * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
1372          * below which allowed reset segments in half the sequence space
1373          * to fall though and be processed (which gives forged reset
1374          * segments with a random sequence number a 50 percent chance of
1375          * killing a connection).
1376          * Then check timestamp, if present.
1377          * Then check the connection count, if present.
1378          * Then check that at least some bytes of segment are within
1379          * receive window.  If segment begins before rcv_nxt,
1380          * drop leading data (and SYN); if nothing left, just ack.
1381          *
1382          *
1383          * If the RST bit is set, check the sequence number to see
1384          * if this is a valid reset segment.
1385          * RFC 793 page 37:
1386          *   In all states except SYN-SENT, all reset (RST) segments
1387          *   are validated by checking their SEQ-fields.  A reset is
1388          *   valid if its sequence number is in the window.
1389          * Note: this does not take into account delayed ACKs, so
1390          *   we should test against last_ack_sent instead of rcv_nxt.
1391          *   The sequence number in the reset segment is normally an
1392          *   echo of our outgoing acknowlegement numbers, but some hosts
1393          *   send a reset with the sequence number at the rightmost edge
1394          *   of our receive window, and we have to handle this case.
1395          * If we have multiple segments in flight, the intial reset
1396          * segment sequence numbers will be to the left of last_ack_sent,
1397          * but they will eventually catch up.
1398          * In any case, it never made sense to trim reset segments to
1399          * fit the receive window since RFC 1122 says:
1400          *   4.2.2.12  RST Segment: RFC-793 Section 3.4
1401          *
1402          *    A TCP SHOULD allow a received RST segment to include data.
1403          *
1404          *    DISCUSSION
1405          *         It has been suggested that a RST segment could contain
1406          *         ASCII text that encoded and explained the cause of the
1407          *         RST.  No standard has yet been established for such
1408          *         data.
1409          *
1410          * If the reset segment passes the sequence number test examine
1411          * the state:
1412          *    SYN_RECEIVED STATE:
1413          *      If passive open, return to LISTEN state.
1414          *      If active open, inform user that connection was refused.
1415          *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, CLOSE_WAIT STATES:
1416          *      Inform user that connection was reset, and close tcb.
1417          *    CLOSING, LAST_ACK STATES:
1418          *      Close the tcb.
1419          *    TIME_WAIT STATE:
1420          *      Drop the segment - see Stevens, vol. 2, p. 964 and
1421          *      RFC 1337.
1422          */
1423         if (thflags & TH_RST) {
1424                 if (SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
1425                     SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
1426                         switch (tp->t_state) {
1427
1428                         case TCPS_SYN_RECEIVED:
1429                                 so->so_error = ECONNREFUSED;
1430                                 goto close;
1431
1432                         case TCPS_ESTABLISHED:
1433                         case TCPS_FIN_WAIT_1:
1434                         case TCPS_FIN_WAIT_2:
1435                         case TCPS_CLOSE_WAIT:
1436                                 so->so_error = ECONNRESET;
1437                         close:
1438                                 tp->t_state = TCPS_CLOSED;
1439                                 tcpstat.tcps_drops++;
1440                                 tp = tcp_close(tp);
1441                                 break;
1442
1443                         case TCPS_CLOSING:
1444                         case TCPS_LAST_ACK:
1445                                 tp = tcp_close(tp);
1446                                 break;
1447
1448                         case TCPS_TIME_WAIT:
1449                                 break;
1450                         }
1451                 }
1452                 goto drop;
1453         }
1454
1455         /*
1456          * RFC 1323 PAWS: If we have a timestamp reply on this segment
1457          * and it's less than ts_recent, drop it.
1458          */
1459         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
1460             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
1461
1462                 /* Check to see if ts_recent is over 24 days old.  */
1463                 if ((int)(ticks - tp->ts_recent_age) > TCP_PAWS_IDLE) {
1464                         /*
1465                          * Invalidate ts_recent.  If this segment updates
1466                          * ts_recent, the age will be reset later and ts_recent
1467                          * will get a valid value.  If it does not, setting
1468                          * ts_recent to zero will at least satisfy the
1469                          * requirement that zero be placed in the timestamp
1470                          * echo reply when ts_recent isn't valid.  The
1471                          * age isn't reset until we get a valid ts_recent
1472                          * because we don't want out-of-order segments to be
1473                          * dropped when ts_recent is old.
1474                          */
1475                         tp->ts_recent = 0;
1476                 } else {
1477                         tcpstat.tcps_rcvduppack++;
1478                         tcpstat.tcps_rcvdupbyte += tlen;
1479                         tcpstat.tcps_pawsdrop++;
1480                         if (tlen)
1481                                 goto dropafterack;
1482                         goto drop;
1483                 }
1484         }
1485
1486         /*
1487          * T/TCP mechanism
1488          *   If T/TCP was negotiated and the segment doesn't have CC,
1489          *   or if its CC is wrong then drop the segment.
1490          *   RST segments do not have to comply with this.
1491          */
1492         if ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) == (TF_REQ_CC|TF_RCVD_CC) &&
1493             ((to.to_flags & TOF_CC) == 0 || tp->cc_recv != to.to_cc))
1494                 goto dropafterack;
1495
1496         /*
1497          * In the SYN-RECEIVED state, validate that the packet belongs to
1498          * this connection before trimming the data to fit the receive
1499          * window.  Check the sequence number versus IRS since we know
1500          * the sequence numbers haven't wrapped.  This is a partial fix
1501          * for the "LAND" DoS attack.
1502          */
1503         if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
1504                 rstreason = BANDLIM_RST_OPENPORT;
1505                 goto dropwithreset;
1506         }
1507
1508         todrop = tp->rcv_nxt - th->th_seq;
1509         if (todrop > 0) {
1510                 if (thflags & TH_SYN) {
1511                         thflags &= ~TH_SYN;
1512                         th->th_seq++;
1513                         if (th->th_urp > 1)
1514                                 th->th_urp--;
1515                         else
1516                                 thflags &= ~TH_URG;
1517                         todrop--;
1518                 }
1519                 /*
1520                  * Following if statement from Stevens, vol. 2, p. 960.
1521                  */
1522                 if (todrop > tlen
1523                     || (todrop == tlen && (thflags & TH_FIN) == 0)) {
1524                         /*
1525                          * Any valid FIN must be to the left of the window.
1526                          * At this point the FIN must be a duplicate or out
1527                          * of sequence; drop it.
1528                          */
1529                         thflags &= ~TH_FIN;
1530
1531                         /*
1532                          * Send an ACK to resynchronize and drop any data.
1533                          * But keep on processing for RST or ACK.
1534                          */
1535                         tp->t_flags |= TF_ACKNOW;
1536                         todrop = tlen;
1537                         tcpstat.tcps_rcvduppack++;
1538                         tcpstat.tcps_rcvdupbyte += todrop;
1539                 } else {
1540                         tcpstat.tcps_rcvpartduppack++;
1541                         tcpstat.tcps_rcvpartdupbyte += todrop;
1542                 }
1543                 drop_hdrlen += todrop;  /* drop from the top afterwards */
1544                 th->th_seq += todrop;
1545                 tlen -= todrop;
1546                 if (th->th_urp > todrop)
1547                         th->th_urp -= todrop;
1548                 else {
1549                         thflags &= ~TH_URG;
1550                         th->th_urp = 0;
1551                 }
1552         }
1553
1554         /*
1555          * If new data are received on a connection after the
1556          * user processes are gone, then RST the other end.
1557          */
1558         if ((so->so_state & SS_NOFDREF) &&
1559             tp->t_state > TCPS_CLOSE_WAIT && tlen) {
1560                 tp = tcp_close(tp);
1561                 tcpstat.tcps_rcvafterclose++;
1562                 rstreason = BANDLIM_UNLIMITED;
1563                 goto dropwithreset;
1564         }
1565
1566         /*
1567          * If segment ends after window, drop trailing data
1568          * (and PUSH and FIN); if nothing left, just ACK.
1569          */
1570         todrop = (th->th_seq+tlen) - (tp->rcv_nxt+tp->rcv_wnd);
1571         if (todrop > 0) {
1572                 tcpstat.tcps_rcvpackafterwin++;
1573                 if (todrop >= tlen) {
1574                         tcpstat.tcps_rcvbyteafterwin += tlen;
1575                         /*
1576                          * If a new connection request is received
1577                          * while in TIME_WAIT, drop the old connection
1578                          * and start over if the sequence numbers
1579                          * are above the previous ones.
1580                          */
1581                         if (thflags & TH_SYN &&
1582                             tp->t_state == TCPS_TIME_WAIT &&
1583                             SEQ_GT(th->th_seq, tp->rcv_nxt)) {
1584                                 tp = tcp_close(tp);
1585                                 goto findpcb;
1586                         }
1587                         /*
1588                          * If window is closed can only take segments at
1589                          * window edge, and have to drop data and PUSH from
1590                          * incoming segments.  Continue processing, but
1591                          * remember to ack.  Otherwise, drop segment
1592                          * and ack.
1593                          */
1594                         if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
1595                                 tp->t_flags |= TF_ACKNOW;
1596                                 tcpstat.tcps_rcvwinprobe++;
1597                         } else
1598                                 goto dropafterack;
1599                 } else
1600                         tcpstat.tcps_rcvbyteafterwin += todrop;
1601                 m_adj(m, -todrop);
1602                 tlen -= todrop;
1603                 thflags &= ~(TH_PUSH|TH_FIN);
1604         }
1605
1606         /*
1607          * If last ACK falls within this segment's sequence numbers,
1608          * record its timestamp.
1609          * NOTE that the test is modified according to the latest
1610          * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1611          */
1612         if ((to.to_flags & TOF_TS) != 0 &&
1613             SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
1614                 tp->ts_recent_age = ticks;
1615                 tp->ts_recent = to.to_tsval;
1616         }
1617
1618         /*
1619          * If a SYN is in the window, then this is an
1620          * error and we send an RST and drop the connection.
1621          */
1622         if (thflags & TH_SYN) {
1623                 tp = tcp_drop(tp, ECONNRESET);
1624                 rstreason = BANDLIM_UNLIMITED;
1625                 goto dropwithreset;
1626         }
1627
1628         /*
1629          * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
1630          * flag is on (half-synchronized state), then queue data for
1631          * later processing; else drop segment and return.
1632          */
1633         if ((thflags & TH_ACK) == 0) {
1634                 if (tp->t_state == TCPS_SYN_RECEIVED ||
1635                     (tp->t_flags & TF_NEEDSYN))
1636                         goto step6;
1637                 else
1638                         goto drop;
1639         }
1640
1641         /*
1642          * Ack processing.
1643          */
1644         switch (tp->t_state) {
1645
1646         /*
1647          * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
1648          * ESTABLISHED state and continue processing.
1649          * The ACK was checked above.
1650          */
1651         case TCPS_SYN_RECEIVED:
1652
1653                 tcpstat.tcps_connects++;
1654                 soisconnected(so);
1655                 /* Do window scaling? */
1656                 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1657                         (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1658                         tp->snd_scale = tp->requested_s_scale;
1659                         tp->rcv_scale = tp->request_r_scale;
1660                 }
1661                 /*
1662                  * Upon successful completion of 3-way handshake,
1663                  * update cache.CC if it was undefined, pass any queued
1664                  * data to the user, and advance state appropriately.
1665                  */
1666                 if ((taop = tcp_gettaocache(&inp->inp_inc)) != NULL &&
1667                     taop->tao_cc == 0)
1668                         taop->tao_cc = tp->cc_recv;
1669
1670                 /*
1671                  * Make transitions:
1672                  *      SYN-RECEIVED  -> ESTABLISHED
1673                  *      SYN-RECEIVED* -> FIN-WAIT-1
1674                  */
1675                 tp->t_starttime = ticks;
1676                 if (tp->t_flags & TF_NEEDFIN) {
1677                         tp->t_state = TCPS_FIN_WAIT_1;
1678                         tp->t_flags &= ~TF_NEEDFIN;
1679                 } else {
1680                         tp->t_state = TCPS_ESTABLISHED;
1681                         callout_reset(tp->tt_keep, tcp_keepidle,
1682                                       tcp_timer_keep, tp);
1683                 }
1684                 /*
1685                  * If segment contains data or ACK, will call tcp_reass()
1686                  * later; if not, do so now to pass queued data to user.
1687                  */
1688                 if (tlen == 0 && (thflags & TH_FIN) == 0)
1689                         (void) tcp_reass(tp, (struct tcphdr *)0, 0,
1690                             (struct mbuf *)0);
1691                 tp->snd_wl1 = th->th_seq - 1;
1692                 /* fall into ... */
1693
1694         /*
1695          * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
1696          * ACKs.  If the ack is in the range
1697          *      tp->snd_una < th->th_ack <= tp->snd_max
1698          * then advance tp->snd_una to th->th_ack and drop
1699          * data from the retransmission queue.  If this ACK reflects
1700          * more up to date window information we update our window information.
1701          */
1702         case TCPS_ESTABLISHED:
1703         case TCPS_FIN_WAIT_1:
1704         case TCPS_FIN_WAIT_2:
1705         case TCPS_CLOSE_WAIT:
1706         case TCPS_CLOSING:
1707         case TCPS_LAST_ACK:
1708         case TCPS_TIME_WAIT:
1709
1710                 if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
1711                         if (tlen == 0 && tiwin == tp->snd_wnd) {
1712                                 tcpstat.tcps_rcvdupack++;
1713                                 /*
1714                                  * If we have outstanding data (other than
1715                                  * a window probe), this is a completely
1716                                  * duplicate ack (ie, window info didn't
1717                                  * change), the ack is the biggest we've
1718                                  * seen and we've seen exactly our rexmt
1719                                  * threshhold of them, assume a packet
1720                                  * has been dropped and retransmit it.
1721                                  * Kludge snd_nxt & the congestion
1722                                  * window so we send only this one
1723                                  * packet.
1724                                  *
1725                                  * We know we're losing at the current
1726                                  * window size so do congestion avoidance
1727                                  * (set ssthresh to half the current window
1728                                  * and pull our congestion window back to
1729                                  * the new ssthresh).
1730                                  *
1731                                  * Dup acks mean that packets have left the
1732                                  * network (they're now cached at the receiver)
1733                                  * so bump cwnd by the amount in the receiver
1734                                  * to keep a constant cwnd packets in the
1735                                  * network.
1736                                  */
1737                                 if (!callout_active(tp->tt_rexmt) ||
1738                                     th->th_ack != tp->snd_una)
1739                                         tp->t_dupacks = 0;
1740                                 else if (++tp->t_dupacks > tcprexmtthresh ||
1741                                          (tcp_do_newreno &&
1742                                           IN_FASTRECOVERY(tp))) {
1743                                         tp->snd_cwnd += tp->t_maxseg;
1744                                         (void) tcp_output(tp);
1745                                         goto drop;
1746                                 } else if (tp->t_dupacks == tcprexmtthresh) {
1747                                         tcp_seq onxt;
1748                                         u_int win;
1749
1750                                         if (tcp_do_newreno &&
1751                                             SEQ_LEQ(th->th_ack,
1752                                                     tp->snd_recover)) {
1753                                                 tp->t_dupacks = 0;
1754                                                 break;
1755                                         }
1756 fastretransmit:
1757                                         if (tcp_do_eifel_detect &&
1758                                             (tp->t_flags & TF_RCVD_TSTMP)) {
1759                                                 tcp_save_congestion_state(tp);
1760                                                 tp->t_flags |= TF_FASTREXMT;
1761                                         }
1762                                         win = min(tp->snd_wnd, tp->snd_cwnd) /
1763                                             2 / tp->t_maxseg;
1764                                         if (win < 2)
1765                                                 win = 2;
1766                                         tp->snd_ssthresh = win * tp->t_maxseg;
1767                                         ENTER_FASTRECOVERY(tp);
1768                                         tp->snd_recover = tp->snd_max;
1769                                         callout_stop(tp->tt_rexmt);
1770                                         tp->t_rtttime = 0;
1771                                         onxt = tp->snd_nxt;
1772                                         tp->snd_nxt = th->th_ack;
1773                                         tp->snd_cwnd = tp->t_maxseg;
1774                                         (void) tcp_output(tp);
1775                                         ++tcpstat.tcps_sndfastrexmit;
1776                                         KASSERT(tp->snd_limited <= 2,
1777                                             ("tp->snd_limited too big"));
1778                                         tp->snd_cwnd = tp->snd_ssthresh +
1779                                             (tp->t_maxseg *
1780                                              (tp->t_dupacks - tp->snd_limited));
1781                                         if (SEQ_GT(onxt, tp->snd_nxt))
1782                                                 tp->snd_nxt = onxt;
1783                                         goto drop;
1784                                 } else if (tcp_do_limitedtransmit) {
1785                                         u_long oldcwnd = tp->snd_cwnd;
1786                                         tcp_seq oldsndmax = tp->snd_max;
1787                                         /* outstanding data */
1788                                         uint32_t ownd =
1789                                             tp->snd_max - tp->snd_una;
1790                                         u_int sent;
1791
1792 #define iceildiv(n, d)          (((n)+(d)-1) / (d))
1793
1794                                         KASSERT(tp->t_dupacks == 1 ||
1795                                             tp->t_dupacks == 2,
1796                                             ("dupacks not 1 or 2"));
1797                                         if (tp->t_dupacks == 1)
1798                                                 tp->snd_limited = 0;
1799                                         tp->snd_cwnd = ownd +
1800                                             (tp->t_dupacks - tp->snd_limited) *
1801                                             tp->t_maxseg;
1802                                         (void) tcp_output(tp);
1803                                         tp->snd_cwnd = oldcwnd;
1804                                         sent = tp->snd_max - oldsndmax;
1805                                         if (sent > tp->t_maxseg) {
1806                                                 KASSERT((tp->t_dupacks == 2 &&
1807                                                     tp->snd_limited == 0) ||
1808                                                    (sent == tp->t_maxseg + 1 &&
1809                                                     tp->t_flags & TF_SENTFIN),
1810                                                     ("sent too much"));
1811                                                 KASSERT(sent <=
1812                                                         tp->t_maxseg * 2,
1813                                                     ("sent too many segments"));
1814                                                 tp->snd_limited = 2;
1815                                                 tcpstat.tcps_sndlimited += 2;
1816                                         } else if (sent > 0) {
1817                                                 ++tp->snd_limited;
1818                                                 ++tcpstat.tcps_sndlimited;
1819                                         } else if (tcp_do_early_retransmit &&
1820                                             (tcp_do_eifel_detect &&
1821                                              (tp->t_flags & TF_RCVD_TSTMP)) &&
1822                                             tcp_do_newreno &&
1823                                             tp->t_dupacks + 1 >=
1824                                               iceildiv(ownd, tp->t_maxseg)) {
1825                                                 ++tcpstat.tcps_sndearlyrexmit;
1826                                                 tp->t_flags |= TF_EARLYREXMT;
1827                                                 goto fastretransmit;
1828                                         }
1829                                         goto drop;
1830                                 }
1831                         } else
1832                                 tp->t_dupacks = 0;
1833                         break;
1834                 }
1835
1836                 KASSERT(SEQ_GT(th->th_ack, tp->snd_una), ("th_ack <= snd_una"));
1837
1838                 /*
1839                  * If the congestion window was inflated to account
1840                  * for the other side's cached packets, retract it.
1841                  */
1842                 if (tcp_do_newreno) {
1843                         if (IN_FASTRECOVERY(tp)) {
1844                                 if (SEQ_LT(th->th_ack, tp->snd_recover)) {
1845                                         tcp_newreno_partial_ack(tp, th);
1846                                 } else {
1847                                         /*
1848                                          * Window inflation should have left us
1849                                          * with approximately snd_ssthresh
1850                                          * outstanding data.
1851                                          * But in case we would be inclined to
1852                                          * send a burst, better to do it via
1853                                          * the slow start mechanism.
1854                                          */
1855                                         if (SEQ_GT(th->th_ack +
1856                                                         tp->snd_ssthresh,
1857                                                    tp->snd_max))
1858                                                 tp->snd_cwnd = tp->snd_max -
1859                                                                 th->th_ack +
1860                                                                 tp->t_maxseg;
1861                                         else
1862                                                 tp->snd_cwnd = tp->snd_ssthresh;
1863                                 }
1864                         }
1865                 } else {
1866                         if (tp->t_dupacks >= tcprexmtthresh &&
1867                             tp->snd_cwnd > tp->snd_ssthresh)
1868                                 tp->snd_cwnd = tp->snd_ssthresh;
1869                 }
1870                 tp->t_dupacks = 0;
1871                 if (SEQ_GT(th->th_ack, tp->snd_max)) {
1872                         tcpstat.tcps_rcvacktoomuch++;
1873                         goto dropafterack;
1874                 }
1875                 /*
1876                  * If we reach this point, ACK is not a duplicate,
1877                  *     i.e., it ACKs something we sent.
1878                  */
1879                 if (tp->t_flags & TF_NEEDSYN) {
1880                         /*
1881                          * T/TCP: Connection was half-synchronized, and our
1882                          * SYN has been ACK'd (so connection is now fully
1883                          * synchronized).  Go to non-starred state,
1884                          * increment snd_una for ACK of SYN, and check if
1885                          * we can do window scaling.
1886                          */
1887                         tp->t_flags &= ~TF_NEEDSYN;
1888                         tp->snd_una++;
1889                         /* Do window scaling? */
1890                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1891                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1892                                 tp->snd_scale = tp->requested_s_scale;
1893                                 tp->rcv_scale = tp->request_r_scale;
1894                         }
1895                 }
1896
1897 process_ACK:
1898                 acked = th->th_ack - tp->snd_una;
1899                 tcpstat.tcps_rcvackpack++;
1900                 tcpstat.tcps_rcvackbyte += acked;
1901
1902                 /*
1903                  * If we just performed our first retransmit, and the ACK
1904                  * arrives within our recovery window, then it was a mistake
1905                  * to do the retransmit in the first place.  Recover our
1906                  * original cwnd and ssthresh, and proceed to transmit where
1907                  * we left off.
1908                  */
1909                 if (tcp_do_eifel_detect && acked &&
1910                     (to.to_flags & TOF_TS) && to.to_tsecr &&
1911                     (tp->t_flags & TF_FIRSTACCACK)) {
1912                         /* Eifel detection applicable. */
1913                         if (to.to_tsecr < tp->t_rexmtTS) {
1914                                 ++tcpstat.tcps_eifeldetected;
1915                                 tcp_revert_congestion_state(tp);
1916                                 if (tp->t_rxtshift == 1 &&
1917                                     ticks >= tp->t_badrxtwin)
1918                                         ++tcpstat.tcps_rttcantdetect;
1919                         }
1920                 } else if (tp->t_rxtshift == 1 && ticks < tp->t_badrxtwin) {
1921                         tcp_revert_congestion_state(tp);
1922                         ++tcpstat.tcps_rttdetected;
1923                 }
1924
1925                 /*
1926                  * If we have a timestamp reply, update smoothed
1927                  * round trip time.  If no timestamp is present but
1928                  * transmit timer is running and timed sequence
1929                  * number was acked, update smoothed round trip time.
1930                  * Since we now have an rtt measurement, cancel the
1931                  * timer backoff (cf., Phil Karn's retransmit alg.).
1932                  * Recompute the initial retransmit timer.
1933                  *
1934                  * Some machines (certain windows boxes) send broken
1935                  * timestamp replies during the SYN+ACK phase, ignore
1936                  * timestamps of 0.
1937                  */
1938                 if ((to.to_flags & TOF_TS) != 0 &&
1939                     to.to_tsecr) {
1940                         tcp_xmit_timer(tp, ticks - to.to_tsecr + 1);
1941                 } else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
1942                         tcp_xmit_timer(tp, ticks - tp->t_rtttime);
1943                 }
1944                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
1945
1946                 /*
1947                  * If all outstanding data is acked, stop retransmit
1948                  * timer and remember to restart (more output or persist).
1949                  * If there is more data to be acked, restart retransmit
1950                  * timer, using current (possibly backed-off) value.
1951                  */
1952                 if (th->th_ack == tp->snd_max) {
1953                         callout_stop(tp->tt_rexmt);
1954                         needoutput = 1;
1955                 } else if (!callout_active(tp->tt_persist))
1956                         callout_reset(tp->tt_rexmt, tp->t_rxtcur,
1957                                       tcp_timer_rexmt, tp);
1958
1959                 /*
1960                  * If no data (only SYN) was ACK'd,
1961                  *    skip rest of ACK processing.
1962                  */
1963                 if (acked == 0)
1964                         goto step6;
1965
1966                 /* Stop looking for an acceptable ACK since one was received. */
1967                 tp->t_flags &= ~(TF_FIRSTACCACK | TF_FASTREXMT | TF_EARLYREXMT);
1968
1969                 /*
1970                  * When new data is acked, open the congestion window.
1971                  * If the window gives us less than ssthresh packets
1972                  * in flight, open exponentially (maxseg per packet).
1973                  * Otherwise open linearly: maxseg per window
1974                  * (maxseg^2 / cwnd per packet).
1975                  */
1976                 if (!tcp_do_newreno || !IN_FASTRECOVERY(tp)) {
1977                         u_int cw = tp->snd_cwnd;
1978                         u_int incr = tp->t_maxseg;
1979                         if (cw > tp->snd_ssthresh)
1980                                 incr = incr * incr / cw;
1981                         tp->snd_cwnd = min(cw+incr, TCP_MAXWIN<<tp->snd_scale);
1982                 }
1983                 if (acked > so->so_snd.sb_cc) {
1984                         tp->snd_wnd -= so->so_snd.sb_cc;
1985                         sbdrop(&so->so_snd, (int)so->so_snd.sb_cc);
1986                         ourfinisacked = 1;
1987                 } else {
1988                         sbdrop(&so->so_snd, acked);
1989                         tp->snd_wnd -= acked;
1990                         ourfinisacked = 0;
1991                 }
1992                 sowwakeup(so);
1993                 /* detect una wraparound */
1994                 if (tcp_do_newreno && !IN_FASTRECOVERY(tp) &&
1995                     SEQ_GT(tp->snd_una, tp->snd_recover) &&
1996                     SEQ_LEQ(th->th_ack, tp->snd_recover))
1997                         tp->snd_recover = th->th_ack - 1;
1998                 if (tcp_do_newreno && IN_FASTRECOVERY(tp) &&
1999                     SEQ_GEQ(th->th_ack, tp->snd_recover))
2000                         EXIT_FASTRECOVERY(tp);
2001                 tp->snd_una = th->th_ack;
2002                 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
2003                         tp->snd_nxt = tp->snd_una;
2004
2005                 switch (tp->t_state) {
2006
2007                 /*
2008                  * In FIN_WAIT_1 STATE in addition to the processing
2009                  * for the ESTABLISHED state if our FIN is now acknowledged
2010                  * then enter FIN_WAIT_2.
2011                  */
2012                 case TCPS_FIN_WAIT_1:
2013                         if (ourfinisacked) {
2014                                 /*
2015                                  * If we can't receive any more
2016                                  * data, then closing user can proceed.
2017                                  * Starting the timer is contrary to the
2018                                  * specification, but if we don't get a FIN
2019                                  * we'll hang forever.
2020                                  */
2021                                 if (so->so_state & SS_CANTRCVMORE) {
2022                                         soisdisconnected(so);
2023                                         callout_reset(tp->tt_2msl, tcp_maxidle,
2024                                                       tcp_timer_2msl, tp);
2025                                 }
2026                                 tp->t_state = TCPS_FIN_WAIT_2;
2027                         }
2028                         break;
2029
2030                 /*
2031                  * In CLOSING STATE in addition to the processing for
2032                  * the ESTABLISHED state if the ACK acknowledges our FIN
2033                  * then enter the TIME-WAIT state, otherwise ignore
2034                  * the segment.
2035                  */
2036                 case TCPS_CLOSING:
2037                         if (ourfinisacked) {
2038                                 tp->t_state = TCPS_TIME_WAIT;
2039                                 tcp_canceltimers(tp);
2040                                 /* Shorten TIME_WAIT [RFC-1644, p.28] */
2041                                 if (tp->cc_recv != 0 &&
2042                                     (ticks - tp->t_starttime) < tcp_msl)
2043                                         callout_reset(tp->tt_2msl,
2044                                                       tp->t_rxtcur *
2045                                                       TCPTV_TWTRUNC,
2046                                                       tcp_timer_2msl, tp);
2047                                 else
2048                                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
2049                                                       tcp_timer_2msl, tp);
2050                                 soisdisconnected(so);
2051                         }
2052                         break;
2053
2054                 /*
2055                  * In LAST_ACK, we may still be waiting for data to drain
2056                  * and/or to be acked, as well as for the ack of our FIN.
2057                  * If our FIN is now acknowledged, delete the TCB,
2058                  * enter the closed state and return.
2059                  */
2060                 case TCPS_LAST_ACK:
2061                         if (ourfinisacked) {
2062                                 tp = tcp_close(tp);
2063                                 goto drop;
2064                         }
2065                         break;
2066
2067                 /*
2068                  * In TIME_WAIT state the only thing that should arrive
2069                  * is a retransmission of the remote FIN.  Acknowledge
2070                  * it and restart the finack timer.
2071                  */
2072                 case TCPS_TIME_WAIT:
2073                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
2074                                       tcp_timer_2msl, tp);
2075                         goto dropafterack;
2076                 }
2077         }
2078
2079 step6:
2080         /*
2081          * Update window information.
2082          * Don't look at window if no ACK: TAC's send garbage on first SYN.
2083          */
2084         if ((thflags & TH_ACK) &&
2085             (SEQ_LT(tp->snd_wl1, th->th_seq) ||
2086             (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
2087              (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
2088                 /* keep track of pure window updates */
2089                 if (tlen == 0 &&
2090                     tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
2091                         tcpstat.tcps_rcvwinupd++;
2092                 tp->snd_wnd = tiwin;
2093                 tp->snd_wl1 = th->th_seq;
2094                 tp->snd_wl2 = th->th_ack;
2095                 if (tp->snd_wnd > tp->max_sndwnd)
2096                         tp->max_sndwnd = tp->snd_wnd;
2097                 needoutput = 1;
2098         }
2099
2100         /*
2101          * Process segments with URG.
2102          */
2103         if ((thflags & TH_URG) && th->th_urp &&
2104             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2105                 /*
2106                  * This is a kludge, but if we receive and accept
2107                  * random urgent pointers, we'll crash in
2108                  * soreceive.  It's hard to imagine someone
2109                  * actually wanting to send this much urgent data.
2110                  */
2111                 if (th->th_urp + so->so_rcv.sb_cc > sb_max) {
2112                         th->th_urp = 0;                 /* XXX */
2113                         thflags &= ~TH_URG;             /* XXX */
2114                         goto dodata;                    /* XXX */
2115                 }
2116                 /*
2117                  * If this segment advances the known urgent pointer,
2118                  * then mark the data stream.  This should not happen
2119                  * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
2120                  * a FIN has been received from the remote side.
2121                  * In these states we ignore the URG.
2122                  *
2123                  * According to RFC961 (Assigned Protocols),
2124                  * the urgent pointer points to the last octet
2125                  * of urgent data.  We continue, however,
2126                  * to consider it to indicate the first octet
2127                  * of data past the urgent section as the original
2128                  * spec states (in one of two places).
2129                  */
2130                 if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
2131                         tp->rcv_up = th->th_seq + th->th_urp;
2132                         so->so_oobmark = so->so_rcv.sb_cc +
2133                             (tp->rcv_up - tp->rcv_nxt) - 1;
2134                         if (so->so_oobmark == 0)
2135                                 so->so_state |= SS_RCVATMARK;
2136                         sohasoutofband(so);
2137                         tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
2138                 }
2139                 /*
2140                  * Remove out of band data so doesn't get presented to user.
2141                  * This can happen independent of advancing the URG pointer,
2142                  * but if two URG's are pending at once, some out-of-band
2143                  * data may creep in... ick.
2144                  */
2145                 if (th->th_urp <= (u_long)tlen
2146 #ifdef SO_OOBINLINE
2147                      && (so->so_options & SO_OOBINLINE) == 0
2148 #endif
2149                      )
2150                         tcp_pulloutofband(so, th, m,
2151                                 drop_hdrlen);   /* hdr drop is delayed */
2152         } else {
2153                 /*
2154                  * If no out of band data is expected,
2155                  * pull receive urgent pointer along
2156                  * with the receive window.
2157                  */
2158                 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
2159                         tp->rcv_up = tp->rcv_nxt;
2160         }
2161 dodata:                                                 /* XXX */
2162
2163         /*
2164          * Process the segment text, merging it into the TCP sequencing queue,
2165          * and arranging for acknowledgment of receipt if necessary.
2166          * This process logically involves adjusting tp->rcv_wnd as data
2167          * is presented to the user (this happens in tcp_usrreq.c,
2168          * case PRU_RCVD).  If a FIN has already been received on this
2169          * connection then we just ignore the text.
2170          */
2171         if ((tlen || (thflags & TH_FIN)) &&
2172             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2173                 m_adj(m, drop_hdrlen);  /* delayed header drop */
2174                 /*
2175                  * Insert segment which includes th into TCP reassembly queue
2176                  * with control block tp.  Set thflags to whether reassembly now
2177                  * includes a segment with FIN.  This handles the common case
2178                  * inline (segment is the next to be received on an established
2179                  * connection, and the queue is empty), avoiding linkage into
2180                  * and removal from the queue and repetition of various
2181                  * conversions.
2182                  * Set DELACK for segments received in order, but ack
2183                  * immediately when segments are out of order (so
2184                  * fast retransmit can work).
2185                  */
2186                 if (th->th_seq == tp->rcv_nxt &&
2187                     LIST_EMPTY(&tp->t_segq) &&
2188                     TCPS_HAVEESTABLISHED(tp->t_state)) {
2189                         if (DELAY_ACK(tp))
2190                                 callout_reset(tp->tt_delack, tcp_delacktime,
2191                                               tcp_timer_delack, tp);
2192                         else
2193                                 tp->t_flags |= TF_ACKNOW;
2194                         tp->rcv_nxt += tlen;
2195                         thflags = th->th_flags & TH_FIN;
2196                         tcpstat.tcps_rcvpack++;
2197                         tcpstat.tcps_rcvbyte += tlen;
2198                         ND6_HINT(tp);
2199                         if (so->so_state & SS_CANTRCVMORE)
2200                                 m_freem(m);
2201                         else
2202                                 sbappend(&so->so_rcv, m);
2203                         sorwakeup(so);
2204                 } else {
2205                         thflags = tcp_reass(tp, th, &tlen, m);
2206                         tp->t_flags |= TF_ACKNOW;
2207                 }
2208
2209                 /*
2210                  * Note the amount of data that peer has sent into
2211                  * our window, in order to estimate the sender's
2212                  * buffer size.
2213                  */
2214                 len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
2215         } else {
2216                 m_freem(m);
2217                 thflags &= ~TH_FIN;
2218         }
2219
2220         /*
2221          * If FIN is received ACK the FIN and let the user know
2222          * that the connection is closing.
2223          */
2224         if (thflags & TH_FIN) {
2225                 if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2226                         socantrcvmore(so);
2227                         /*
2228                          * If connection is half-synchronized
2229                          * (ie NEEDSYN flag on) then delay ACK,
2230                          * so it may be piggybacked when SYN is sent.
2231                          * Otherwise, since we received a FIN then no
2232                          * more input can be expected, send ACK now.
2233                          */
2234                         if (DELAY_ACK(tp) && (tp->t_flags & TF_NEEDSYN))
2235                                 callout_reset(tp->tt_delack, tcp_delacktime,
2236                                     tcp_timer_delack, tp);
2237                         else
2238                                 tp->t_flags |= TF_ACKNOW;
2239                         tp->rcv_nxt++;
2240                 }
2241                 switch (tp->t_state) {
2242
2243                 /*
2244                  * In SYN_RECEIVED and ESTABLISHED STATES
2245                  * enter the CLOSE_WAIT state.
2246                  */
2247                 case TCPS_SYN_RECEIVED:
2248                         tp->t_starttime = ticks;
2249                         /*FALLTHROUGH*/
2250                 case TCPS_ESTABLISHED:
2251                         tp->t_state = TCPS_CLOSE_WAIT;
2252                         break;
2253
2254                 /*
2255                  * If still in FIN_WAIT_1 STATE FIN has not been acked so
2256                  * enter the CLOSING state.
2257                  */
2258                 case TCPS_FIN_WAIT_1:
2259                         tp->t_state = TCPS_CLOSING;
2260                         break;
2261
2262                 /*
2263                  * In FIN_WAIT_2 state enter the TIME_WAIT state,
2264                  * starting the time-wait timer, turning off the other
2265                  * standard timers.
2266                  */
2267                 case TCPS_FIN_WAIT_2:
2268                         tp->t_state = TCPS_TIME_WAIT;
2269                         tcp_canceltimers(tp);
2270                         /* Shorten TIME_WAIT [RFC-1644, p.28] */
2271                         if (tp->cc_recv != 0 &&
2272                             (ticks - tp->t_starttime) < tcp_msl) {
2273                                 callout_reset(tp->tt_2msl,
2274                                               tp->t_rxtcur * TCPTV_TWTRUNC,
2275                                               tcp_timer_2msl, tp);
2276                                 /* For transaction client, force ACK now. */
2277                                 tp->t_flags |= TF_ACKNOW;
2278                         }
2279                         else
2280                                 callout_reset(tp->tt_2msl, 2 * tcp_msl,
2281                                               tcp_timer_2msl, tp);
2282                         soisdisconnected(so);
2283                         break;
2284
2285                 /*
2286                  * In TIME_WAIT state restart the 2 MSL time_wait timer.
2287                  */
2288                 case TCPS_TIME_WAIT:
2289                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
2290                                       tcp_timer_2msl, tp);
2291                         break;
2292                 }
2293         }
2294 #ifdef TCPDEBUG
2295         if (so->so_options & SO_DEBUG)
2296                 tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
2297                           &tcp_savetcp, 0);
2298 #endif
2299
2300         /*
2301          * Return any desired output.
2302          */
2303         if (needoutput || (tp->t_flags & TF_ACKNOW))
2304                 (void) tcp_output(tp);
2305         return;
2306
2307 dropafterack:
2308         /*
2309          * Generate an ACK dropping incoming segment if it occupies
2310          * sequence space, where the ACK reflects our state.
2311          *
2312          * We can now skip the test for the RST flag since all
2313          * paths to this code happen after packets containing
2314          * RST have been dropped.
2315          *
2316          * In the SYN-RECEIVED state, don't send an ACK unless the
2317          * segment we received passes the SYN-RECEIVED ACK test.
2318          * If it fails send a RST.  This breaks the loop in the
2319          * "LAND" DoS attack, and also prevents an ACK storm
2320          * between two listening ports that have been sent forged
2321          * SYN segments, each with the source address of the other.
2322          */
2323         if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
2324             (SEQ_GT(tp->snd_una, th->th_ack) ||
2325              SEQ_GT(th->th_ack, tp->snd_max)) ) {
2326                 rstreason = BANDLIM_RST_OPENPORT;
2327                 goto dropwithreset;
2328         }
2329 #ifdef TCPDEBUG
2330         if (so->so_options & SO_DEBUG)
2331                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2332                           &tcp_savetcp, 0);
2333 #endif
2334         m_freem(m);
2335         tp->t_flags |= TF_ACKNOW;
2336         (void) tcp_output(tp);
2337         return;
2338
2339 dropwithreset:
2340         /*
2341          * Generate a RST, dropping incoming segment.
2342          * Make ACK acceptable to originator of segment.
2343          * Don't bother to respond if destination was broadcast/multicast.
2344          */
2345         if ((thflags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
2346                 goto drop;
2347         if (isipv6) {
2348                 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
2349                     IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
2350                         goto drop;
2351         } else {
2352                 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
2353                     IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
2354                     ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
2355                     in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
2356                         goto drop;
2357         }
2358         /* IPv6 anycast check is done at tcp6_input() */
2359
2360         /*
2361          * Perform bandwidth limiting.
2362          */
2363 #ifdef ICMP_BANDLIM
2364         if (badport_bandlim(rstreason) < 0)
2365                 goto drop;
2366 #endif
2367
2368 #ifdef TCPDEBUG
2369         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2370                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2371                           &tcp_savetcp, 0);
2372 #endif
2373         if (thflags & TH_ACK)
2374                 /* mtod() below is safe as long as hdr dropping is delayed */
2375                 tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0, th->th_ack,
2376                             TH_RST);
2377         else {
2378                 if (thflags & TH_SYN)
2379                         tlen++;
2380                 /* mtod() below is safe as long as hdr dropping is delayed */
2381                 tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
2382                             (tcp_seq)0, TH_RST|TH_ACK);
2383         }
2384         return;
2385
2386 drop:
2387         /*
2388          * Drop space held by incoming segment and return.
2389          */
2390 #ifdef TCPDEBUG
2391         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2392                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2393                           &tcp_savetcp, 0);
2394 #endif
2395         m_freem(m);
2396         return;
2397 }
2398
2399 /*
2400  * Parse TCP options and place in tcpopt.
2401  */
2402 static void
2403 tcp_dooptions(to, cp, cnt, is_syn)
2404         struct tcpopt *to;
2405         u_char *cp;
2406         int cnt;
2407 {
2408         int opt, optlen;
2409
2410         to->to_flags = 0;
2411         for (; cnt > 0; cnt -= optlen, cp += optlen) {
2412                 opt = cp[0];
2413                 if (opt == TCPOPT_EOL)
2414                         break;
2415                 if (opt == TCPOPT_NOP)
2416                         optlen = 1;
2417                 else {
2418                         if (cnt < 2)
2419                                 break;
2420                         optlen = cp[1];
2421                         if (optlen < 2 || optlen > cnt)
2422                                 break;
2423                 }
2424                 switch (opt) {
2425                 case TCPOPT_MAXSEG:
2426                         if (optlen != TCPOLEN_MAXSEG)
2427                                 continue;
2428                         if (!is_syn)
2429                                 continue;
2430                         to->to_flags |= TOF_MSS;
2431                         bcopy((char *)cp + 2,
2432                             (char *)&to->to_mss, sizeof(to->to_mss));
2433                         to->to_mss = ntohs(to->to_mss);
2434                         break;
2435                 case TCPOPT_WINDOW:
2436                         if (optlen != TCPOLEN_WINDOW)
2437                                 continue;
2438                         if (! is_syn)
2439                                 continue;
2440                         to->to_flags |= TOF_SCALE;
2441                         to->to_requested_s_scale = min(cp[2], TCP_MAX_WINSHIFT);
2442                         break;
2443                 case TCPOPT_TIMESTAMP:
2444                         if (optlen != TCPOLEN_TIMESTAMP)
2445                                 continue;
2446                         to->to_flags |= TOF_TS;
2447                         bcopy((char *)cp + 2,
2448                             (char *)&to->to_tsval, sizeof(to->to_tsval));
2449                         to->to_tsval = ntohl(to->to_tsval);
2450                         bcopy((char *)cp + 6,
2451                             (char *)&to->to_tsecr, sizeof(to->to_tsecr));
2452                         to->to_tsecr = ntohl(to->to_tsecr);
2453                         break;
2454                 case TCPOPT_CC:
2455                         if (optlen != TCPOLEN_CC)
2456                                 continue;
2457                         to->to_flags |= TOF_CC;
2458                         bcopy((char *)cp + 2,
2459                             (char *)&to->to_cc, sizeof(to->to_cc));
2460                         to->to_cc = ntohl(to->to_cc);
2461                         break;
2462                 case TCPOPT_CCNEW:
2463                         if (optlen != TCPOLEN_CC)
2464                                 continue;
2465                         if (!is_syn)
2466                                 continue;
2467                         to->to_flags |= TOF_CCNEW;
2468                         bcopy((char *)cp + 2,
2469                             (char *)&to->to_cc, sizeof(to->to_cc));
2470                         to->to_cc = ntohl(to->to_cc);
2471                         break;
2472                 case TCPOPT_CCECHO:
2473                         if (optlen != TCPOLEN_CC)
2474                                 continue;
2475                         if (!is_syn)
2476                                 continue;
2477                         to->to_flags |= TOF_CCECHO;
2478                         bcopy((char *)cp + 2,
2479                             (char *)&to->to_ccecho, sizeof(to->to_ccecho));
2480                         to->to_ccecho = ntohl(to->to_ccecho);
2481                         break;
2482                 default:
2483                         continue;
2484                 }
2485         }
2486 }
2487
2488 /*
2489  * Pull out of band byte out of a segment so
2490  * it doesn't appear in the user's data queue.
2491  * It is still reflected in the segment length for
2492  * sequencing purposes.
2493  */
2494 static void
2495 tcp_pulloutofband(so, th, m, off)
2496         struct socket *so;
2497         struct tcphdr *th;
2498         struct mbuf *m;
2499         int off;                /* delayed to be droped hdrlen */
2500 {
2501         int cnt = off + th->th_urp - 1;
2502
2503         while (cnt >= 0) {
2504                 if (m->m_len > cnt) {
2505                         char *cp = mtod(m, caddr_t) + cnt;
2506                         struct tcpcb *tp = sototcpcb(so);
2507
2508                         tp->t_iobc = *cp;
2509                         tp->t_oobflags |= TCPOOB_HAVEDATA;
2510                         bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
2511                         m->m_len--;
2512                         if (m->m_flags & M_PKTHDR)
2513                                 m->m_pkthdr.len--;
2514                         return;
2515                 }
2516                 cnt -= m->m_len;
2517                 m = m->m_next;
2518                 if (m == 0)
2519                         break;
2520         }
2521         panic("tcp_pulloutofband");
2522 }
2523
2524 /*
2525  * Collect new round-trip time estimate
2526  * and update averages and current timeout.
2527  */
2528 static void
2529 tcp_xmit_timer(tp, rtt)
2530         struct tcpcb *tp;
2531         int rtt;
2532 {
2533         int delta;
2534
2535         tcpstat.tcps_rttupdated++;
2536         tp->t_rttupdated++;
2537         if (tp->t_srtt != 0) {
2538                 /*
2539                  * srtt is stored as fixed point with 5 bits after the
2540                  * binary point (i.e., scaled by 8).  The following magic
2541                  * is equivalent to the smoothing algorithm in rfc793 with
2542                  * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
2543                  * point).  Adjust rtt to origin 0.
2544                  */
2545                 delta = ((rtt - 1) << TCP_DELTA_SHIFT)
2546                         - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
2547
2548                 if ((tp->t_srtt += delta) <= 0)
2549                         tp->t_srtt = 1;
2550
2551                 /*
2552                  * We accumulate a smoothed rtt variance (actually, a
2553                  * smoothed mean difference), then set the retransmit
2554                  * timer to smoothed rtt + 4 times the smoothed variance.
2555                  * rttvar is stored as fixed point with 4 bits after the
2556                  * binary point (scaled by 16).  The following is
2557                  * equivalent to rfc793 smoothing with an alpha of .75
2558                  * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
2559                  * rfc793's wired-in beta.
2560                  */
2561                 if (delta < 0)
2562                         delta = -delta;
2563                 delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
2564                 if ((tp->t_rttvar += delta) <= 0)
2565                         tp->t_rttvar = 1;
2566                 if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
2567                         tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2568         } else {
2569                 /*
2570                  * No rtt measurement yet - use the unsmoothed rtt.
2571                  * Set the variance to half the rtt (so our first
2572                  * retransmit happens at 3*rtt).
2573                  */
2574                 tp->t_srtt = rtt << TCP_RTT_SHIFT;
2575                 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
2576                 tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2577         }
2578         tp->t_rtttime = 0;
2579         tp->t_rxtshift = 0;
2580
2581         /*
2582          * the retransmit should happen at rtt + 4 * rttvar.
2583          * Because of the way we do the smoothing, srtt and rttvar
2584          * will each average +1/2 tick of bias.  When we compute
2585          * the retransmit timer, we want 1/2 tick of rounding and
2586          * 1 extra tick because of +-1/2 tick uncertainty in the
2587          * firing of the timer.  The bias will give us exactly the
2588          * 1.5 tick we need.  But, because the bias is
2589          * statistical, we have to test that we don't drop below
2590          * the minimum feasible timer (which is 2 ticks).
2591          */
2592         TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
2593                       max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
2594
2595         /*
2596          * We received an ack for a packet that wasn't retransmitted;
2597          * it is probably safe to discard any error indications we've
2598          * received recently.  This isn't quite right, but close enough
2599          * for now (a route might have failed after we sent a segment,
2600          * and the return path might not be symmetrical).
2601          */
2602         tp->t_softerror = 0;
2603 }
2604
2605 /*
2606  * Determine a reasonable value for maxseg size.
2607  * If the route is known, check route for mtu.
2608  * If none, use an mss that can be handled on the outgoing
2609  * interface without forcing IP to fragment; if bigger than
2610  * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
2611  * to utilize large mbufs.  If no route is found, route has no mtu,
2612  * or the destination isn't local, use a default, hopefully conservative
2613  * size (usually 512 or the default IP max size, but no more than the mtu
2614  * of the interface), as we can't discover anything about intervening
2615  * gateways or networks.  We also initialize the congestion/slow start
2616  * window to be a single segment if the destination isn't local.
2617  * While looking at the routing entry, we also initialize other path-dependent
2618  * parameters from pre-set or cached values in the routing entry.
2619  *
2620  * Also take into account the space needed for options that we
2621  * send regularly.  Make maxseg shorter by that amount to assure
2622  * that we can send maxseg amount of data even when the options
2623  * are present.  Store the upper limit of the length of options plus
2624  * data in maxopd.
2625  *
2626  * NOTE that this routine is only called when we process an incoming
2627  * segment, for outgoing segments only tcp_mssopt is called.
2628  *
2629  * In case of T/TCP, we call this routine during implicit connection
2630  * setup as well (offer = -1), to initialize maxseg from the cached
2631  * MSS of our peer.
2632  */
2633 void
2634 tcp_mss(tp, offer)
2635         struct tcpcb *tp;
2636         int offer;
2637 {
2638         struct rtentry *rt;
2639         struct ifnet *ifp;
2640         int rtt, mss;
2641         u_long bufsize;
2642         struct inpcb *inp = tp->t_inpcb;
2643         struct socket *so;
2644         struct rmxp_tao *taop;
2645         int origoffer = offer;
2646 #ifdef INET6
2647         int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
2648         size_t min_protoh = isipv6 ?
2649                             sizeof(struct ip6_hdr) + sizeof(struct tcphdr) :
2650                             sizeof(struct tcpiphdr);
2651 #else
2652         const int isipv6 = 0;
2653         const size_t min_protoh = sizeof(struct tcpiphdr);
2654 #endif
2655
2656         if (isipv6)
2657                 rt = tcp_rtlookup6(&inp->inp_inc);
2658         else
2659                 rt = tcp_rtlookup(&inp->inp_inc);
2660         if (rt == NULL) {
2661                 tp->t_maxopd = tp->t_maxseg =
2662                                 isipv6 ? tcp_v6mssdflt : tcp_mssdflt;
2663                 return;
2664         }
2665         ifp = rt->rt_ifp;
2666         so = inp->inp_socket;
2667
2668         taop = rmx_taop(rt->rt_rmx);
2669         /*
2670          * Offer == -1 means that we didn't receive SYN yet,
2671          * use cached value in that case;
2672          */
2673         if (offer == -1)
2674                 offer = taop->tao_mssopt;
2675         /*
2676          * Offer == 0 means that there was no MSS on the SYN segment,
2677          * in this case we use tcp_mssdflt.
2678          */
2679         if (offer == 0)
2680                 offer = isipv6 ? tcp_v6mssdflt : tcp_mssdflt;
2681         else
2682                 /*
2683                  * Sanity check: make sure that maxopd will be large
2684                  * enough to allow some data on segments even is the
2685                  * all the option space is used (40bytes).  Otherwise
2686                  * funny things may happen in tcp_output.
2687                  */
2688                 offer = max(offer, 64);
2689         taop->tao_mssopt = offer;
2690
2691         /*
2692          * While we're here, check if there's an initial rtt
2693          * or rttvar.  Convert from the route-table units
2694          * to scaled multiples of the slow timeout timer.
2695          */
2696         if (tp->t_srtt == 0 && (rtt = rt->rt_rmx.rmx_rtt)) {
2697                 /*
2698                  * XXX the lock bit for RTT indicates that the value
2699                  * is also a minimum value; this is subject to time.
2700                  */
2701                 if (rt->rt_rmx.rmx_locks & RTV_RTT)
2702                         tp->t_rttmin = rtt / (RTM_RTTUNIT / hz);
2703                 tp->t_srtt = rtt / (RTM_RTTUNIT / (hz * TCP_RTT_SCALE));
2704                 tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
2705                 tcpstat.tcps_usedrtt++;
2706                 if (rt->rt_rmx.rmx_rttvar) {
2707                         tp->t_rttvar = rt->rt_rmx.rmx_rttvar /
2708                             (RTM_RTTUNIT / (hz * TCP_RTTVAR_SCALE));
2709                         tcpstat.tcps_usedrttvar++;
2710                 } else {
2711                         /* default variation is +- 1 rtt */
2712                         tp->t_rttvar =
2713                             tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
2714                 }
2715                 TCPT_RANGESET(tp->t_rxtcur,
2716                               ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
2717                               tp->t_rttmin, TCPTV_REXMTMAX);
2718         }
2719         /*
2720          * if there's an mtu associated with the route, use it
2721          * else, use the link mtu.
2722          */
2723         if (rt->rt_rmx.rmx_mtu)
2724                 mss = rt->rt_rmx.rmx_mtu - min_protoh;
2725         else {
2726                 if (isipv6) {
2727                         mss = nd_ifinfo[rt->rt_ifp->if_index].linkmtu -
2728                                 min_protoh;
2729                         if (!in6_localaddr(&inp->in6p_faddr))
2730                                 mss = min(mss, tcp_v6mssdflt);
2731                 } else {
2732                         mss = ifp->if_mtu - min_protoh;
2733                         if (!in_localaddr(inp->inp_faddr))
2734                                 mss = min(mss, tcp_mssdflt);
2735                 }
2736         }
2737         mss = min(mss, offer);
2738         /*
2739          * maxopd stores the maximum length of data AND options
2740          * in a segment; maxseg is the amount of data in a normal
2741          * segment.  We need to store this value (maxopd) apart
2742          * from maxseg, because now every segment carries options
2743          * and thus we normally have somewhat less data in segments.
2744          */
2745         tp->t_maxopd = mss;
2746
2747         /*
2748          * In case of T/TCP, origoffer==-1 indicates, that no segments
2749          * were received yet.  In this case we just guess, otherwise
2750          * we do the same as before T/TCP.
2751          */
2752         if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
2753             (origoffer == -1 ||
2754              (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
2755                 mss -= TCPOLEN_TSTAMP_APPA;
2756         if ((tp->t_flags & (TF_REQ_CC|TF_NOOPT)) == TF_REQ_CC &&
2757             (origoffer == -1 ||
2758              (tp->t_flags & TF_RCVD_CC) == TF_RCVD_CC))
2759                 mss -= TCPOLEN_CC_APPA;
2760
2761 #if     (MCLBYTES & (MCLBYTES - 1)) == 0
2762                 if (mss > MCLBYTES)
2763                         mss &= ~(MCLBYTES-1);
2764 #else
2765                 if (mss > MCLBYTES)
2766                         mss = mss / MCLBYTES * MCLBYTES;
2767 #endif
2768         /*
2769          * If there's a pipesize, change the socket buffer
2770          * to that size.  Make the socket buffers an integral
2771          * number of mss units; if the mss is larger than
2772          * the socket buffer, decrease the mss.
2773          */
2774 #ifdef RTV_SPIPE
2775         if ((bufsize = rt->rt_rmx.rmx_sendpipe) == 0)
2776 #endif
2777                 bufsize = so->so_snd.sb_hiwat;
2778         if (bufsize < mss)
2779                 mss = bufsize;
2780         else {
2781                 bufsize = roundup(bufsize, mss);
2782                 if (bufsize > sb_max)
2783                         bufsize = sb_max;
2784                 if (bufsize > so->so_snd.sb_hiwat)
2785                         (void)sbreserve(&so->so_snd, bufsize, so, NULL);
2786         }
2787         tp->t_maxseg = mss;
2788
2789 #ifdef RTV_RPIPE
2790         if ((bufsize = rt->rt_rmx.rmx_recvpipe) == 0)
2791 #endif
2792                 bufsize = so->so_rcv.sb_hiwat;
2793         if (bufsize > mss) {
2794                 bufsize = roundup(bufsize, mss);
2795                 if (bufsize > sb_max)
2796                         bufsize = sb_max;
2797                 if (bufsize > so->so_rcv.sb_hiwat)
2798                         (void)sbreserve(&so->so_rcv, bufsize, so, NULL);
2799         }
2800
2801         /*
2802          * Set the slow-start flight size depending on whether this
2803          * is a local network or not.
2804          */
2805         if (tcp_do_rfc3390)
2806                 tp->snd_cwnd = min(4 * mss, max(2 * mss, 4380));
2807         else if ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
2808                  (!isipv6 && in_localaddr(inp->inp_faddr)))
2809                 tp->snd_cwnd = mss * ss_fltsz_local;
2810         else
2811                 tp->snd_cwnd = mss * ss_fltsz;
2812
2813         if (rt->rt_rmx.rmx_ssthresh) {
2814                 /*
2815                  * There's some sort of gateway or interface
2816                  * buffer limit on the path.  Use this to set
2817                  * the slow start threshhold, but set the
2818                  * threshold to no less than 2*mss.
2819                  */
2820                 tp->snd_ssthresh = max(2 * mss, rt->rt_rmx.rmx_ssthresh);
2821                 tcpstat.tcps_usedssthresh++;
2822         }
2823 }
2824
2825 /*
2826  * Determine the MSS option to send on an outgoing SYN.
2827  */
2828 int
2829 tcp_mssopt(tp)
2830         struct tcpcb *tp;
2831 {
2832         struct rtentry *rt;
2833 #ifdef INET6
2834         int isipv6 = ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
2835         int min_protoh = isipv6 ?
2836                              sizeof(struct ip6_hdr) + sizeof(struct tcphdr) :
2837                              sizeof(struct tcpiphdr);
2838 #else
2839         const int isipv6 = 0;
2840         const size_t min_protoh = sizeof(struct tcpiphdr);
2841 #endif
2842
2843         if (isipv6)
2844                 rt = tcp_rtlookup6(&tp->t_inpcb->inp_inc);
2845         else
2846                 rt = tcp_rtlookup(&tp->t_inpcb->inp_inc);
2847         if (rt == NULL)
2848                 return (isipv6 ? tcp_v6mssdflt : tcp_mssdflt);
2849
2850         return (rt->rt_ifp->if_mtu - min_protoh);
2851 }
2852
2853
2854 /*
2855  * When a partial ack arrives, force the retransmission of the
2856  * next unacknowledged segment.  Do not clear tp->t_dupacks.
2857  * By setting snd_nxt to ti_ack, this forces retransmission timer to
2858  * be started again.
2859  */
2860 static void
2861 tcp_newreno_partial_ack(tp, th)
2862         struct tcpcb *tp;
2863         struct tcphdr *th;
2864 {
2865         tcp_seq onxt = tp->snd_nxt;
2866         u_long  ocwnd = tp->snd_cwnd;
2867
2868         callout_stop(tp->tt_rexmt);
2869         tp->t_rtttime = 0;
2870         tp->snd_nxt = th->th_ack;
2871         /*
2872          * Set snd_cwnd to one segment beyond acknowledged offset
2873          * (tp->snd_una has not yet been updated when this function is called.)
2874          */
2875         tp->snd_cwnd = tp->t_maxseg + (th->th_ack - tp->snd_una);
2876         tp->t_flags |= TF_ACKNOW;
2877         (void) tcp_output(tp);
2878         tp->snd_cwnd = ocwnd;
2879         if (SEQ_GT(onxt, tp->snd_nxt))
2880                 tp->snd_nxt = onxt;
2881         /*
2882          * Partial window deflation.  Relies on fact that tp->snd_una
2883          * not updated yet.
2884          */
2885         tp->snd_cwnd -= (th->th_ack - tp->snd_una - tp->t_maxseg);
2886 }