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 1.22 2004/03/22 06:38:17 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         boolean_t isipv6;
 408 #else
 409         const boolean_t isipv6 = FALSE;
 410 #endif
 411 #ifdef TCPDEBUG
 412         short ostate = 0;
 413 #endif
 414
 415         tcpstat.tcps_rcvtotal++;
 416
 417         /* Grab info from and strip MT_TAG mbufs prepended to the chain. */
 418         while  (m->m_type == MT_TAG) {
 419                 if (m->_m_tag_id == PACKET_TAG_IPFORWARD)
 420                         next_hop = (struct sockaddr_in *)m->m_hdr.mh_data;
 421                 m = m->m_next;
 422         }
 423
 424 #ifdef INET6
 425         isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? TRUE : FALSE;
 426 #endif
 427
 428         if (isipv6) {
 429                 /* IP6_EXTHDR_CHECK() is already done at tcp6_input() */
 430                 ip6 = mtod(m, struct ip6_hdr *);
 431                 tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
 432                 if (in6_cksum(m, IPPROTO_TCP, off0, tlen)) {
 433                         tcpstat.tcps_rcvbadsum++;
 434                         goto drop;
 435                 }
 436                 th = (struct tcphdr *)((caddr_t)ip6 + off0);
 437
 438                 /*
 439                  * Be proactive about unspecified IPv6 address in source.
 440                  * As we use all-zero to indicate unbounded/unconnected pcb,
 441                  * unspecified IPv6 address can be used to confuse us.
 442                  *
 443                  * Note that packets with unspecified IPv6 destination is
 444                  * already dropped in ip6_input.
 445                  */
 446                 if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
 447                         /* XXX stat */
 448                         goto drop;
 449                 }
 450         } else {
 451                 /*
 452                  * Get IP and TCP header together in first mbuf.
 453                  * Note: IP leaves IP header in first mbuf.
 454                  */
 455                 if (off0 > sizeof(struct ip)) {
 456                         ip_stripoptions(m);
 457                         off0 = sizeof(struct ip);
 458                 }
 459                 /* already checked and pulled up in ip_demux() */
 460                 KASSERT(m->m_len >= sizeof(struct tcpiphdr),
 461                     ("TCP header not in one mbuf"));
 462                 ip = mtod(m, struct ip *);
 463                 ipov = (struct ipovly *)ip;
 464                 th = (struct tcphdr *)((caddr_t)ip + off0);
 465                 tlen = ip->ip_len;
 466
 467                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
 468                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
 469                                 th->th_sum = m->m_pkthdr.csum_data;
 470                         else
 471                                 th->th_sum = in_pseudo(ip->ip_src.s_addr,
 472                                                 ip->ip_dst.s_addr,
 473                                                 htonl(m->m_pkthdr.csum_data +
 474                                                         ip->ip_len +
 475                                                         IPPROTO_TCP));
 476                         th->th_sum ^= 0xffff;
 477                 } else {
 478                         /*
 479                          * Checksum extended TCP header and data.
 480                          */
 481                         len = sizeof(struct ip) + tlen;
 482                         bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
 483                         ipov->ih_len = (u_short)tlen;
 484                         ipov->ih_len = htons(ipov->ih_len);
 485                         th->th_sum = in_cksum(m, len);
 486                 }
 487                 if (th->th_sum) {
 488                         tcpstat.tcps_rcvbadsum++;
 489                         goto drop;
 490                 }
 491 #ifdef INET6
 492                 /* Re-initialization for later version check */
 493                 ip->ip_v = IPVERSION;
 494 #endif
 495         }
 496
 497         /*
 498          * Check that TCP offset makes sense,
 499          * pull out TCP options and adjust length.              XXX
 500          */
 501         off = th->th_off << 2;
 502         /* already checked and pulled up in ip_demux() */
 503         KASSERT(off >= sizeof(struct tcphdr) && off <= tlen,
 504             ("bad TCP data offset"));
 505         tlen -= off;    /* tlen is used instead of ti->ti_len */
 506         if (off > sizeof(struct tcphdr)) {
 507                 if (isipv6) {
 508                         IP6_EXTHDR_CHECK(m, off0, off, );
 509                         ip6 = mtod(m, struct ip6_hdr *);
 510                         th = (struct tcphdr *)((caddr_t)ip6 + off0);
 511                 } else {
 512                         /* already pulled up in ip_demux() */
 513                         KASSERT(m->m_len >= sizeof(struct ip) + off,
 514                             ("TCP header and options not in one mbuf"));
 515                 }
 516                 optlen = off - sizeof(struct tcphdr);
 517                 optp = (u_char *)(th + 1);
 518         }
 519         thflags = th->th_flags;
 520
 521 #ifdef TCP_DROP_SYNFIN
 522         /*
 523          * If the drop_synfin option is enabled, drop all packets with
 524          * both the SYN and FIN bits set. This prevents e.g. nmap from
 525          * identifying the TCP/IP stack.
 526          *
 527          * This is a violation of the TCP specification.
 528          */
 529         if (drop_synfin && (thflags & (TH_SYN|TH_FIN)) == (TH_SYN|TH_FIN))
 530                 goto drop;
 531 #endif
 532
 533         /*
 534          * Convert TCP protocol specific fields to host format.
 535          */
 536         th->th_seq = ntohl(th->th_seq);
 537         th->th_ack = ntohl(th->th_ack);
 538         th->th_win = ntohs(th->th_win);
 539         th->th_urp = ntohs(th->th_urp);
 540
 541         /*
 542          * Delay dropping TCP, IP headers, IPv6 ext headers, and TCP options,
 543          * until after ip6_savecontrol() is called and before other functions
 544          * which don't want those proto headers.
 545          * Because ip6_savecontrol() is going to parse the mbuf to
 546          * search for data to be passed up to user-land, it wants mbuf
 547          * parameters to be unchanged.
 548          * XXX: the call of ip6_savecontrol() has been obsoleted based on
 549          * latest version of the advanced API (20020110).
 550          */
 551         drop_hdrlen = off0 + off;
 552
 553         /*
 554          * Locate pcb for segment.
 555          */
 556 findpcb:
 557         /* IPFIREWALL_FORWARD section */
 558         if (next_hop != NULL && !isipv6) {  /* IPv6 support is not there yet */
 559                 /*
 560                  * Transparently forwarded. Pretend to be the destination.
 561                  * already got one like this?
 562                  */
 563                 inp = in_pcblookup_hash(&tcbinfo[mycpu->gd_cpuid],
 564                                         ip->ip_src, th->th_sport,
 565                                         ip->ip_dst, th->th_dport,
 566                                         0, m->m_pkthdr.rcvif);
 567                 if (!inp) {
 568                         /*
 569                          * It's new.  Try to find the ambushing socket.
 570                          */
 571
 572                         /*
 573                          * The rest of the ipfw code stores the port in
 574                          * host order.  XXX
 575                          * (The IP address is still in network order.)
 576                          */
 577                         in_port_t dport = next_hop->sin_port ?
 578                                                 htons(next_hop->sin_port) :
 579                                                 th->th_dport;
 580
 581                         cpu = tcp_addrcpu(ip->ip_src.s_addr, th->th_sport,
 582                                           next_hop->sin_addr.s_addr, dport);
 583                         inp = in_pcblookup_hash(&tcbinfo[cpu],
 584                                                 ip->ip_src, th->th_sport,
 585                                                 next_hop->sin_addr, dport,
 586                                                 1, m->m_pkthdr.rcvif);
 587                 }
 588         } else {
 589                 if (isipv6)
 590                         inp = in6_pcblookup_hash(&tcbinfo[0],
 591                                                  &ip6->ip6_src, th->th_sport,
 592                                                  &ip6->ip6_dst, th->th_dport,
 593                                                  1, m->m_pkthdr.rcvif);
 594                 else
 595                         inp = in_pcblookup_hash(&tcbinfo[mycpu->gd_cpuid],
 596                                                 ip->ip_src, th->th_sport,
 597                                                 ip->ip_dst, th->th_dport,
 598                                                 1, m->m_pkthdr.rcvif);
 599       }
 600
 601 #ifdef IPSEC
 602         if (isipv6) {
 603                 if (inp != NULL && ipsec6_in_reject_so(m, inp->inp_socket)) {
 604                         ipsec6stat.in_polvio++;
 605                         goto drop;
 606                 }
 607         } else {
 608                 if (inp != NULL && ipsec4_in_reject_so(m, inp->inp_socket)) {
 609                         ipsecstat.in_polvio++;
 610                         goto drop;
 611                 }
 612         }
 613 #endif
 614 #ifdef FAST_IPSEC
 615         if (isipv6) {
 616                 if (inp != NULL && ipsec6_in_reject(m, inp)) {
 617                         goto drop;
 618                 }
 619         } else {
 620                 if (inp != NULL && ipsec4_in_reject(m, inp)) {
 621                         goto drop;
 622                 }
 623         }
 624 #endif
 625
 626         /*
 627          * If the state is CLOSED (i.e., TCB does not exist) then
 628          * all data in the incoming segment is discarded.
 629          * If the TCB exists but is in CLOSED state, it is embryonic,
 630          * but should either do a listen or a connect soon.
 631          */
 632         if (inp == NULL) {
 633                 if (log_in_vain) {
 634 #ifdef INET6
 635                         char dbuf[INET6_ADDRSTRLEN+2], sbuf[INET6_ADDRSTRLEN+2];
 636 #else
 637                         char dbuf[4 * sizeof "123"], sbuf[4 * sizeof "123"];
 638 #endif
 639                         if (isipv6) {
 640                                 strcpy(dbuf, "[");
 641                                 strcpy(sbuf, "[");
 642                                 strcat(dbuf, ip6_sprintf(&ip6->ip6_dst));
 643                                 strcat(sbuf, ip6_sprintf(&ip6->ip6_src));
 644                                 strcat(dbuf, "]");
 645                                 strcat(sbuf, "]");
 646                         } else {
 647                                 strcpy(dbuf, inet_ntoa(ip->ip_dst));
 648                                 strcpy(sbuf, inet_ntoa(ip->ip_src));
 649                         }
 650                         switch (log_in_vain) {
 651                         case 1:
 652                                 if ((thflags & TH_SYN) == 0)
 653                                         break;
 654                         case 2:
 655                                 log(LOG_INFO,
 656                                     "Connection attempt to TCP %s:%d "
 657                                     "from %s:%d flags:0x%02x\n",
 658                                     dbuf, ntohs(th->th_dport), sbuf,
 659                                     ntohs(th->th_sport), thflags);
 660                                 break;
 661                         default:
 662                                 break;
 663                         }
 664                 }
 665                 if (blackhole) {
 666                         switch (blackhole) {
 667                         case 1:
 668                                 if (thflags & TH_SYN)
 669                                         goto drop;
 670                                 break;
 671                         case 2:
 672                                 goto drop;
 673                         default:
 674                                 goto drop;
 675                         }
 676                 }
 677                 rstreason = BANDLIM_RST_CLOSEDPORT;
 678                 goto dropwithreset;
 679         }
 680         tp = intotcpcb(inp);
 681         if (tp == NULL) {
 682                 rstreason = BANDLIM_RST_CLOSEDPORT;
 683                 goto dropwithreset;
 684         }
 685         if (tp->t_state == TCPS_CLOSED)
 686                 goto drop;
 687
 688         /* Unscale the window into a 32-bit value. */
 689         if ((thflags & TH_SYN) == 0)
 690                 tiwin = th->th_win << tp->snd_scale;
 691         else
 692                 tiwin = th->th_win;
 693
 694         so = inp->inp_socket;
 695
 696 #ifdef TCPDEBUG
 697         if (so->so_options & SO_DEBUG) {
 698                 ostate = tp->t_state;
 699                 if (isipv6)
 700                         bcopy((char *)ip6, (char *)tcp_saveipgen, sizeof(*ip6));
 701                 else
 702                         bcopy((char *)ip, (char *)tcp_saveipgen, sizeof(*ip));
 703                 tcp_savetcp = *th;
 704         }
 705 #endif
 706
 707         bzero((char *)&to, sizeof(to));
 708
 709         if (so->so_options & SO_ACCEPTCONN) {
 710                 struct in_conninfo inc;
 711
 712 #ifdef INET6
 713                 inc.inc_isipv6 = (isipv6 == TRUE);
 714 #endif
 715                 if (isipv6) {
 716                         inc.inc6_faddr = ip6->ip6_src;
 717                         inc.inc6_laddr = ip6->ip6_dst;
 718                         inc.inc6_route.ro_rt = NULL;            /* XXX */
 719                 } else {
 720                         inc.inc_faddr = ip->ip_src;
 721                         inc.inc_laddr = ip->ip_dst;
 722                         inc.inc_route.ro_rt = NULL;             /* XXX */
 723                 }
 724                 inc.inc_fport = th->th_sport;
 725                 inc.inc_lport = th->th_dport;
 726
 727                 /*
 728                  * If the state is LISTEN then ignore segment if it contains
 729                  * a RST.  If the segment contains an ACK then it is bad and
 730                  * send a RST.  If it does not contain a SYN then it is not
 731                  * interesting; drop it.
 732                  *
 733                  * If the state is SYN_RECEIVED (syncache) and seg contains
 734                  * an ACK, but not for our SYN/ACK, send a RST.  If the seg
 735                  * contains a RST, check the sequence number to see if it
 736                  * is a valid reset segment.
 737                  */
 738                 if ((thflags & (TH_RST|TH_ACK|TH_SYN)) != TH_SYN) {
 739                         if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
 740                                 if (!syncache_expand(&inc, th, &so, m)) {
 741                                         /*
 742                                          * No syncache entry, or ACK was not
 743                                          * for our SYN/ACK.  Send a RST.
 744                                          */
 745                                         tcpstat.tcps_badsyn++;
 746                                         rstreason = BANDLIM_RST_OPENPORT;
 747                                         goto dropwithreset;
 748                                 }
 749                                 if (so == NULL)
 750                                         /*
 751                                          * Could not complete 3-way handshake,
 752                                          * connection is being closed down, and
 753                                          * syncache will free mbuf.
 754                                          */
 755                                         return;
 756                                 /*
 757                                  * Socket is created in state SYN_RECEIVED.
 758                                  * Continue processing segment.
 759                                  */
 760                                 inp = sotoinpcb(so);
 761                                 tp = intotcpcb(inp);
 762                                 /*
 763                                  * This is what would have happened in
 764                                  * tcp_output() when the SYN,ACK was sent.
 765                                  */
 766                                 tp->snd_up = tp->snd_una;
 767                                 tp->snd_max = tp->snd_nxt = tp->iss + 1;
 768                                 tp->last_ack_sent = tp->rcv_nxt;
 769 /*
 770  * XXX possible bug - it doesn't appear that tp->snd_wnd is unscaled
 771  * until the _second_ ACK is received:
 772  *    rcv SYN (set wscale opts)  --> send SYN/ACK, set snd_wnd = window.
 773  *    rcv ACK, calculate tiwin --> process SYN_RECEIVED, determine wscale,
 774  *        move to ESTAB, set snd_wnd to tiwin.
 775  */
 776                                 tp->snd_wnd = tiwin;    /* unscaled */
 777                                 goto after_listen;
 778                         }
 779                         if (thflags & TH_RST) {
 780                                 syncache_chkrst(&inc, th);
 781                                 goto drop;
 782                         }
 783                         if (thflags & TH_ACK) {
 784                                 syncache_badack(&inc);
 785                                 tcpstat.tcps_badsyn++;
 786                                 rstreason = BANDLIM_RST_OPENPORT;
 787                                 goto dropwithreset;
 788                         }
 789                         goto drop;
 790                 }
 791
 792                 /*
 793                  * Segment's flags are (SYN) or (SYN|FIN).
 794                  */
 795 #ifdef INET6
 796                 /*
 797                  * If deprecated address is forbidden,
 798                  * we do not accept SYN to deprecated interface
 799                  * address to prevent any new inbound connection from
 800                  * getting established.
 801                  * When we do not accept SYN, we send a TCP RST,
 802                  * with deprecated source address (instead of dropping
 803                  * it).  We compromise it as it is much better for peer
 804                  * to send a RST, and RST will be the final packet
 805                  * for the exchange.
 806                  *
 807                  * If we do not forbid deprecated addresses, we accept
 808                  * the SYN packet.  RFC2462 does not suggest dropping
 809                  * SYN in this case.
 810                  * If we decipher RFC2462 5.5.4, it says like this:
 811                  * 1. use of deprecated addr with existing
 812                  *    communication is okay - "SHOULD continue to be
 813                  *    used"
 814                  * 2. use of it with new communication:
 815                  *   (2a) "SHOULD NOT be used if alternate address
 816                  *        with sufficient scope is available"
 817                  *   (2b) nothing mentioned otherwise.
 818                  * Here we fall into (2b) case as we have no choice in
 819                  * our source address selection - we must obey the peer.
 820                  *
 821                  * The wording in RFC2462 is confusing, and there are
 822                  * multiple description text for deprecated address
 823                  * handling - worse, they are not exactly the same.
 824                  * I believe 5.5.4 is the best one, so we follow 5.5.4.
 825                  */
 826                 if (isipv6 && !ip6_use_deprecated) {
 827                         struct in6_ifaddr *ia6;
 828
 829                         if ((ia6 = ip6_getdstifaddr(m)) &&
 830                             (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
 831                                 tp = NULL;
 832                                 rstreason = BANDLIM_RST_OPENPORT;
 833                                 goto dropwithreset;
 834                         }
 835                 }
 836 #endif
 837                 /*
 838                  * If it is from this socket, drop it, it must be forged.
 839                  * Don't bother responding if the destination was a broadcast.
 840                  */
 841                 if (th->th_dport == th->th_sport) {
 842                         if (isipv6) {
 843                                 if (IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst,
 844                                                        &ip6->ip6_src))
 845                                         goto drop;
 846                         } else {
 847                                 if (ip->ip_dst.s_addr == ip->ip_src.s_addr)
 848                                         goto drop;
 849                         }
 850                 }
 851                 /*
 852                  * RFC1122 4.2.3.10, p. 104: discard bcast/mcast SYN
 853                  *
 854                  * Note that it is quite possible to receive unicast
 855                  * link-layer packets with a broadcast IP address. Use
 856                  * in_broadcast() to find them.
 857                  */
 858                 if (m->m_flags & (M_BCAST|M_MCAST))
 859                         goto drop;
 860                 if (isipv6) {
 861                         if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
 862                             IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
 863                                 goto drop;
 864                 } else {
 865                         if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
 866                             IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
 867                             ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
 868                             in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
 869                                 goto drop;
 870                 }
 871                 /*
 872                  * SYN appears to be valid; create compressed TCP state
 873                  * for syncache, or perform t/tcp connection.
 874                  */
 875                 if (so->so_qlen <= so->so_qlimit) {
 876                         tcp_dooptions(&to, optp, optlen, 1);
 877                         if (!syncache_add(&inc, &to, th, &so, m))
 878                                 goto drop;
 879                         if (so == NULL)
 880                                 /*
 881                                  * Entry added to syncache, mbuf used to
 882                                  * send SYN,ACK packet.
 883                                  */
 884                                 return;
 885                         /*
 886                          * Segment passed TAO tests.
 887                          */
 888                         inp = sotoinpcb(so);
 889                         tp = intotcpcb(inp);
 890                         tp->snd_wnd = tiwin;
 891                         tp->t_starttime = ticks;
 892                         tp->t_state = TCPS_ESTABLISHED;
 893
 894                         /*
 895                          * If there is a FIN, or if there is data and the
 896                          * connection is local, then delay SYN,ACK(SYN) in
 897                          * the hope of piggy-backing it on a response
 898                          * segment.  Otherwise must send ACK now in case
 899                          * the other side is slow starting.
 900                          */
 901                         if (DELAY_ACK(tp) &&
 902                             ((thflags & TH_FIN) ||
 903                              (tlen != 0 &&
 904                               ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
 905                                (!isipv6 && in_localaddr(inp->inp_faddr)))))) {
 906                                 callout_reset(tp->tt_delack, tcp_delacktime,
 907                                                 tcp_timer_delack, tp);
 908                                 tp->t_flags |= TF_NEEDSYN;
 909                         } else
 910                                 tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
 911
 912                         tcpstat.tcps_connects++;
 913                         soisconnected(so);
 914                         goto trimthenstep6;
 915                 }
 916                 goto drop;
 917         }
 918 after_listen:
 919
 920 /* XXX temp debugging */
 921         /* should not happen - syncache should pick up these connections */
 922         if (tp->t_state == TCPS_LISTEN)
 923                 panic("tcp_input: TCPS_LISTEN");
 924
 925         /*
 926          * Segment received on connection.
 927          * Reset idle time and keep-alive timer.
 928          */
 929         tp->t_rcvtime = ticks;
 930         if (TCPS_HAVEESTABLISHED(tp->t_state))
 931                 callout_reset(tp->tt_keep, tcp_keepidle, tcp_timer_keep, tp);
 932
 933         /*
 934          * Process options.
 935          * XXX this is tradtitional behavior, may need to be cleaned up.
 936          */
 937         tcp_dooptions(&to, optp, optlen, thflags & TH_SYN);
 938         if (thflags & TH_SYN) {
 939                 if (to.to_flags & TOF_SCALE) {
 940                         tp->t_flags |= TF_RCVD_SCALE;
 941                         tp->requested_s_scale = to.to_requested_s_scale;
 942                 }
 943                 if (to.to_flags & TOF_TS) {
 944                         tp->t_flags |= TF_RCVD_TSTMP;
 945                         tp->ts_recent = to.to_tsval;
 946                         tp->ts_recent_age = ticks;
 947                 }
 948                 if (to.to_flags & (TOF_CC|TOF_CCNEW))
 949                         tp->t_flags |= TF_RCVD_CC;
 950                 if (to.to_flags & TOF_MSS)
 951                         tcp_mss(tp, to.to_mss);
 952         }
 953
 954         /*
 955          * Header prediction: check for the two common cases
 956          * of a uni-directional data xfer.  If the packet has
 957          * no control flags, is in-sequence, the window didn't
 958          * change and we're not retransmitting, it's a
 959          * candidate.  If the length is zero and the ack moved
 960          * forward, we're the sender side of the xfer.  Just
 961          * free the data acked & wake any higher level process
 962          * that was blocked waiting for space.  If the length
 963          * is non-zero and the ack didn't move, we're the
 964          * receiver side.  If we're getting packets in-order
 965          * (the reassembly queue is empty), add the data to
 966          * the socket buffer and note that we need a delayed ack.
 967          * Make sure that the hidden state-flags are also off.
 968          * Since we check for TCPS_ESTABLISHED above, it can only
 969          * be TH_NEEDSYN.
 970          */
 971         if (tp->t_state == TCPS_ESTABLISHED &&
 972             (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
 973             ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
 974             ((to.to_flags & TOF_TS) == 0 ||
 975              TSTMP_GEQ(to.to_tsval, tp->ts_recent)) &&
 976             /*
 977              * Using the CC option is compulsory if once started:
 978              *   the segment is OK if no T/TCP was negotiated or
 979              *   if the segment has a CC option equal to CCrecv
 980              */
 981             ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) != (TF_REQ_CC|TF_RCVD_CC) ||
 982              ((to.to_flags & TOF_CC) != 0 && to.to_cc == tp->cc_recv)) &&
 983             th->th_seq == tp->rcv_nxt &&
 984             tiwin && tiwin == tp->snd_wnd &&
 985             tp->snd_nxt == tp->snd_max) {
 986
 987                 /*
 988                  * If last ACK falls within this segment's sequence numbers,
 989                  * record the timestamp.
 990                  * NOTE that the test is modified according to the latest
 991                  * proposal of the tcplw@cray.com list (Braden 1993/04/26).
 992                  */
 993                 if ((to.to_flags & TOF_TS) != 0 &&
 994                     SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
 995                         tp->ts_recent_age = ticks;
 996                         tp->ts_recent = to.to_tsval;
 997                 }
 998
 999                 if (tlen == 0) {
1000                         if (SEQ_GT(th->th_ack, tp->snd_una) &&
1001                             SEQ_LEQ(th->th_ack, tp->snd_max) &&
1002                             tp->snd_cwnd >= tp->snd_wnd &&
1003                             ((!tcp_do_newreno &&
1004                               tp->t_dupacks < tcprexmtthresh) ||
1005                              (tcp_do_newreno && !IN_FASTRECOVERY(tp)))) {
1006                                 /*
1007                                  * this is a pure ack for outstanding data.
1008                                  */
1009                                 ++tcpstat.tcps_predack;
1010                                 /*
1011                                  * "bad retransmit" recovery
1012                                  *
1013                                  * If Eifel detection applies, then
1014                                  * it is deterministic, so use it
1015                                  * unconditionally over the old heuristic.
1016                                  * Otherwise, fall back to the old heuristic.
1017                                  */
1018                                 if (tcp_do_eifel_detect &&
1019                                     (to.to_flags & TOF_TS) && to.to_tsecr &&
1020                                     (tp->t_flags & TF_FIRSTACCACK)) {
1021                                         /* Eifel detection applicable. */
1022                                         if (to.to_tsecr < tp->t_rexmtTS) {
1023                                                 tcp_revert_congestion_state(tp);
1024                                                 ++tcpstat.tcps_eifeldetected;
1025                                         }
1026                                 } else if (tp->t_rxtshift == 1 &&
1027                                            ticks < tp->t_badrxtwin) {
1028                                         tcp_revert_congestion_state(tp);
1029                                         ++tcpstat.tcps_rttdetected;
1030                                 }
1031                                 tp->t_flags &= ~(TF_FIRSTACCACK |
1032                                                  TF_FASTREXMT | TF_EARLYREXMT);
1033                                 /*
1034                                  * Recalculate the retransmit timer / rtt.
1035                                  *
1036                                  * Some machines (certain windows boxes)
1037                                  * send broken timestamp replies during the
1038                                  * SYN+ACK phase, ignore timestamps of 0.
1039                                  */
1040                                 if ((to.to_flags & TOF_TS) != 0 &&
1041                                     to.to_tsecr) {
1042                                         tcp_xmit_timer(tp,
1043                                             ticks - to.to_tsecr + 1);
1044                                 } else if (tp->t_rtttime &&
1045                                             SEQ_GT(th->th_ack, tp->t_rtseq)) {
1046                                         tcp_xmit_timer(tp,
1047                                                        ticks - tp->t_rtttime);
1048                                 }
1049                                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
1050                                 acked = th->th_ack - tp->snd_una;
1051                                 tcpstat.tcps_rcvackpack++;
1052                                 tcpstat.tcps_rcvackbyte += acked;
1053                                 sbdrop(&so->so_snd, acked);
1054                                 if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
1055                                     SEQ_LEQ(th->th_ack, tp->snd_recover))
1056                                         tp->snd_recover = th->th_ack - 1;
1057                                 tp->snd_una = th->th_ack;
1058                                 tp->t_dupacks = 0;
1059                                 m_freem(m);
1060                                 ND6_HINT(tp); /* some progress has been done */
1061
1062                                 /*
1063                                  * If all outstanding data are acked, stop
1064                                  * retransmit timer, otherwise restart timer
1065                                  * using current (possibly backed-off) value.
1066                                  * If process is waiting for space,
1067                                  * wakeup/selwakeup/signal.  If data
1068                                  * are ready to send, let tcp_output
1069                                  * decide between more output or persist.
1070                                  */
1071                                 if (tp->snd_una == tp->snd_max)
1072                                         callout_stop(tp->tt_rexmt);
1073                                 else if (!callout_active(tp->tt_persist))
1074                                         callout_reset(tp->tt_rexmt,
1075                                                       tp->t_rxtcur,
1076                                                       tcp_timer_rexmt, tp);
1077
1078                                 sowwakeup(so);
1079                                 if (so->so_snd.sb_cc)
1080                                         (void) tcp_output(tp);
1081                                 return;
1082                         }
1083                 } else if (th->th_ack == tp->snd_una &&
1084                     LIST_EMPTY(&tp->t_segq) &&
1085                     tlen <= sbspace(&so->so_rcv)) {
1086                         /*
1087                          * this is a pure, in-sequence data packet
1088                          * with nothing on the reassembly queue and
1089                          * we have enough buffer space to take it.
1090                          */
1091                         ++tcpstat.tcps_preddat;
1092                         tp->rcv_nxt += tlen;
1093                         tcpstat.tcps_rcvpack++;
1094                         tcpstat.tcps_rcvbyte += tlen;
1095                         ND6_HINT(tp);   /* some progress has been done */
1096                         /*
1097                          * Add data to socket buffer.
1098                          */
1099                         if (so->so_state & SS_CANTRCVMORE) {
1100                                 m_freem(m);
1101                         } else {
1102                                 m_adj(m, drop_hdrlen);  /* delayed header drop */
1103                                 sbappend(&so->so_rcv, m);
1104                         }
1105                         sorwakeup(so);
1106                         if (DELAY_ACK(tp)) {
1107                                 callout_reset(tp->tt_delack, tcp_delacktime,
1108                                     tcp_timer_delack, tp);
1109                         } else {
1110                                 tp->t_flags |= TF_ACKNOW;
1111                                 tcp_output(tp);
1112                         }
1113                         return;
1114                 }
1115         }
1116
1117         /*
1118          * Calculate amount of space in receive window,
1119          * and then do TCP input processing.
1120          * Receive window is amount of space in rcv queue,
1121          * but not less than advertised window.
1122          */
1123         { int win;
1124
1125         win = sbspace(&so->so_rcv);
1126         if (win < 0)
1127                 win = 0;
1128         tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
1129         }
1130
1131         switch (tp->t_state) {
1132
1133         /*
1134          * If the state is SYN_RECEIVED:
1135          *      if seg contains an ACK, but not for our SYN/ACK, send a RST.
1136          */
1137         case TCPS_SYN_RECEIVED:
1138                 if ((thflags & TH_ACK) &&
1139                     (SEQ_LEQ(th->th_ack, tp->snd_una) ||
1140                      SEQ_GT(th->th_ack, tp->snd_max))) {
1141                                 rstreason = BANDLIM_RST_OPENPORT;
1142                                 goto dropwithreset;
1143                 }
1144                 break;
1145
1146         /*
1147          * If the state is SYN_SENT:
1148          *      if seg contains an ACK, but not for our SYN, drop the input.
1149          *      if seg contains a RST, then drop the connection.
1150          *      if seg does not contain SYN, then drop it.
1151          * Otherwise this is an acceptable SYN segment
1152          *      initialize tp->rcv_nxt and tp->irs
1153          *      if seg contains ack then advance tp->snd_una
1154          *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
1155          *      arrange for segment to be acked (eventually)
1156          *      continue processing rest of data/controls, beginning with URG
1157          */
1158         case TCPS_SYN_SENT:
1159                 if ((taop = tcp_gettaocache(&inp->inp_inc)) == NULL) {
1160                         taop = &tao_noncached;
1161                         bzero(taop, sizeof(*taop));
1162                 }
1163
1164                 if ((thflags & TH_ACK) &&
1165                     (SEQ_LEQ(th->th_ack, tp->iss) ||
1166                      SEQ_GT(th->th_ack, tp->snd_max))) {
1167                         /*
1168                          * If we have a cached CCsent for the remote host,
1169                          * hence we haven't just crashed and restarted,
1170                          * do not send a RST.  This may be a retransmission
1171                          * from the other side after our earlier ACK was lost.
1172                          * Our new SYN, when it arrives, will serve as the
1173                          * needed ACK.
1174                          */
1175                         if (taop->tao_ccsent != 0)
1176                                 goto drop;
1177                         else {
1178                                 rstreason = BANDLIM_UNLIMITED;
1179                                 goto dropwithreset;
1180                         }
1181                 }
1182                 if (thflags & TH_RST) {
1183                         if (thflags & TH_ACK)
1184                                 tp = tcp_drop(tp, ECONNREFUSED);
1185                         goto drop;
1186                 }
1187                 if ((thflags & TH_SYN) == 0)
1188                         goto drop;
1189                 tp->snd_wnd = th->th_win;       /* initial send window */
1190                 tp->cc_recv = to.to_cc;         /* foreign CC */
1191
1192                 tp->irs = th->th_seq;
1193                 tcp_rcvseqinit(tp);
1194                 if (thflags & TH_ACK) {
1195                         /*
1196                          * Our SYN was acked.  If segment contains CC.ECHO
1197                          * option, check it to make sure this segment really
1198                          * matches our SYN.  If not, just drop it as old
1199                          * duplicate, but send an RST if we're still playing
1200                          * by the old rules.  If no CC.ECHO option, make sure
1201                          * we don't get fooled into using T/TCP.
1202                          */
1203                         if (to.to_flags & TOF_CCECHO) {
1204                                 if (tp->cc_send != to.to_ccecho) {
1205                                         if (taop->tao_ccsent != 0)
1206                                                 goto drop;
1207                                         else {
1208                                                 rstreason = BANDLIM_UNLIMITED;
1209                                                 goto dropwithreset;
1210                                         }
1211                                 }
1212                         } else
1213                                 tp->t_flags &= ~TF_RCVD_CC;
1214                         tcpstat.tcps_connects++;
1215                         soisconnected(so);
1216                         /* Do window scaling on this connection? */
1217                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1218                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1219                                 tp->snd_scale = tp->requested_s_scale;
1220                                 tp->rcv_scale = tp->request_r_scale;
1221                         }
1222                         /* Segment is acceptable, update cache if undefined. */
1223                         if (taop->tao_ccsent == 0)
1224                                 taop->tao_ccsent = to.to_ccecho;
1225
1226                         tp->rcv_adv += tp->rcv_wnd;
1227                         tp->snd_una++;          /* SYN is acked */
1228                         /*
1229                          * If there's data, delay ACK; if there's also a FIN
1230                          * ACKNOW will be turned on later.
1231                          */
1232                         if (DELAY_ACK(tp) && tlen != 0)
1233                                 callout_reset(tp->tt_delack, tcp_delacktime,
1234                                     tcp_timer_delack, tp);
1235                         else
1236                                 tp->t_flags |= TF_ACKNOW;
1237                         /*
1238                          * Received <SYN,ACK> in SYN_SENT[*] state.
1239                          * Transitions:
1240                          *      SYN_SENT  --> ESTABLISHED
1241                          *      SYN_SENT* --> FIN_WAIT_1
1242                          */
1243                         tp->t_starttime = ticks;
1244                         if (tp->t_flags & TF_NEEDFIN) {
1245                                 tp->t_state = TCPS_FIN_WAIT_1;
1246                                 tp->t_flags &= ~TF_NEEDFIN;
1247                                 thflags &= ~TH_SYN;
1248                         } else {
1249                                 tp->t_state = TCPS_ESTABLISHED;
1250                                 callout_reset(tp->tt_keep, tcp_keepidle,
1251                                               tcp_timer_keep, tp);
1252                         }
1253                 } else {
1254                         /*
1255                          * Received initial SYN in SYN-SENT[*] state =>
1256                          * simultaneous open.  If segment contains CC option
1257                          * and there is a cached CC, apply TAO test.
1258                          * If it succeeds, connection is * half-synchronized.
1259                          * Otherwise, do 3-way handshake:
1260                          *        SYN-SENT -> SYN-RECEIVED
1261                          *        SYN-SENT* -> SYN-RECEIVED*
1262                          * If there was no CC option, clear cached CC value.
1263                          */
1264                         tp->t_flags |= TF_ACKNOW;
1265                         callout_stop(tp->tt_rexmt);
1266                         if (to.to_flags & TOF_CC) {
1267                                 if (taop->tao_cc != 0 &&
1268                                     CC_GT(to.to_cc, taop->tao_cc)) {
1269                                         /*
1270                                          * update cache and make transition:
1271                                          *        SYN-SENT -> ESTABLISHED*
1272                                          *        SYN-SENT* -> FIN-WAIT-1*
1273                                          */
1274                                         taop->tao_cc = to.to_cc;
1275                                         tp->t_starttime = ticks;
1276                                         if (tp->t_flags & TF_NEEDFIN) {
1277                                                 tp->t_state = TCPS_FIN_WAIT_1;
1278                                                 tp->t_flags &= ~TF_NEEDFIN;
1279                                         } else {
1280                                                 tp->t_state = TCPS_ESTABLISHED;
1281                                                 callout_reset(tp->tt_keep,
1282                                                               tcp_keepidle,
1283                                                               tcp_timer_keep,
1284                                                               tp);
1285                                         }
1286                                         tp->t_flags |= TF_NEEDSYN;
1287                                 } else
1288                                         tp->t_state = TCPS_SYN_RECEIVED;
1289                         } else {
1290                                 /* CC.NEW or no option => invalidate cache */
1291                                 taop->tao_cc = 0;
1292                                 tp->t_state = TCPS_SYN_RECEIVED;
1293                         }
1294                 }
1295
1296 trimthenstep6:
1297                 /*
1298                  * Advance th->th_seq to correspond to first data byte.
1299                  * If data, trim to stay within window,
1300                  * dropping FIN if necessary.
1301                  */
1302                 th->th_seq++;
1303                 if (tlen > tp->rcv_wnd) {
1304                         todrop = tlen - tp->rcv_wnd;
1305                         m_adj(m, -todrop);
1306                         tlen = tp->rcv_wnd;
1307                         thflags &= ~TH_FIN;
1308                         tcpstat.tcps_rcvpackafterwin++;
1309                         tcpstat.tcps_rcvbyteafterwin += todrop;
1310                 }
1311                 tp->snd_wl1 = th->th_seq - 1;
1312                 tp->rcv_up = th->th_seq;
1313                 /*
1314                  * Client side of transaction: already sent SYN and data.
1315                  * If the remote host used T/TCP to validate the SYN,
1316                  * our data will be ACK'd; if so, enter normal data segment
1317                  * processing in the middle of step 5, ack processing.
1318                  * Otherwise, goto step 6.
1319                  */
1320                 if (thflags & TH_ACK)
1321                         goto process_ACK;
1322
1323                 goto step6;
1324
1325         /*
1326          * If the state is LAST_ACK or CLOSING or TIME_WAIT:
1327          *      if segment contains a SYN and CC [not CC.NEW] option:
1328          *              if state == TIME_WAIT and connection duration > MSL,
1329          *                  drop packet and send RST;
1330          *
1331          *              if SEG.CC > CCrecv then is new SYN, and can implicitly
1332          *                  ack the FIN (and data) in retransmission queue.
1333          *                  Complete close and delete TCPCB.  Then reprocess
1334          *                  segment, hoping to find new TCPCB in LISTEN state;
1335          *
1336          *              else must be old SYN; drop it.
1337          *      else do normal processing.
1338          */
1339         case TCPS_LAST_ACK:
1340         case TCPS_CLOSING:
1341         case TCPS_TIME_WAIT:
1342                 if ((thflags & TH_SYN) &&
1343                     (to.to_flags & TOF_CC) && tp->cc_recv != 0) {
1344                         if (tp->t_state == TCPS_TIME_WAIT &&
1345                                         (ticks - tp->t_starttime) > tcp_msl) {
1346                                 rstreason = BANDLIM_UNLIMITED;
1347                                 goto dropwithreset;
1348                         }
1349                         if (CC_GT(to.to_cc, tp->cc_recv)) {
1350                                 tp = tcp_close(tp);
1351                                 goto findpcb;
1352                         }
1353                         else
1354                                 goto drop;
1355                 }
1356                 break;  /* continue normal processing */
1357         }
1358
1359         /*
1360          * States other than LISTEN or SYN_SENT.
1361          * First check the RST flag and sequence number since reset segments
1362          * are exempt from the timestamp and connection count tests.  This
1363          * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
1364          * below which allowed reset segments in half the sequence space
1365          * to fall though and be processed (which gives forged reset
1366          * segments with a random sequence number a 50 percent chance of
1367          * killing a connection).
1368          * Then check timestamp, if present.
1369          * Then check the connection count, if present.
1370          * Then check that at least some bytes of segment are within
1371          * receive window.  If segment begins before rcv_nxt,
1372          * drop leading data (and SYN); if nothing left, just ack.
1373          *
1374          *
1375          * If the RST bit is set, check the sequence number to see
1376          * if this is a valid reset segment.
1377          * RFC 793 page 37:
1378          *   In all states except SYN-SENT, all reset (RST) segments
1379          *   are validated by checking their SEQ-fields.  A reset is
1380          *   valid if its sequence number is in the window.
1381          * Note: this does not take into account delayed ACKs, so
1382          *   we should test against last_ack_sent instead of rcv_nxt.
1383          *   The sequence number in the reset segment is normally an
1384          *   echo of our outgoing acknowlegement numbers, but some hosts
1385          *   send a reset with the sequence number at the rightmost edge
1386          *   of our receive window, and we have to handle this case.
1387          * If we have multiple segments in flight, the intial reset
1388          * segment sequence numbers will be to the left of last_ack_sent,
1389          * but they will eventually catch up.
1390          * In any case, it never made sense to trim reset segments to
1391          * fit the receive window since RFC 1122 says:
1392          *   4.2.2.12  RST Segment: RFC-793 Section 3.4
1393          *
1394          *    A TCP SHOULD allow a received RST segment to include data.
1395          *
1396          *    DISCUSSION
1397          *         It has been suggested that a RST segment could contain
1398          *         ASCII text that encoded and explained the cause of the
1399          *         RST.  No standard has yet been established for such
1400          *         data.
1401          *
1402          * If the reset segment passes the sequence number test examine
1403          * the state:
1404          *    SYN_RECEIVED STATE:
1405          *      If passive open, return to LISTEN state.
1406          *      If active open, inform user that connection was refused.
1407          *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, CLOSE_WAIT STATES:
1408          *      Inform user that connection was reset, and close tcb.
1409          *    CLOSING, LAST_ACK STATES:
1410          *      Close the tcb.
1411          *    TIME_WAIT STATE:
1412          *      Drop the segment - see Stevens, vol. 2, p. 964 and
1413          *      RFC 1337.
1414          */
1415         if (thflags & TH_RST) {
1416                 if (SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
1417                     SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
1418                         switch (tp->t_state) {
1419
1420                         case TCPS_SYN_RECEIVED:
1421                                 so->so_error = ECONNREFUSED;
1422                                 goto close;
1423
1424                         case TCPS_ESTABLISHED:
1425                         case TCPS_FIN_WAIT_1:
1426                         case TCPS_FIN_WAIT_2:
1427                         case TCPS_CLOSE_WAIT:
1428                                 so->so_error = ECONNRESET;
1429                         close:
1430                                 tp->t_state = TCPS_CLOSED;
1431                                 tcpstat.tcps_drops++;
1432                                 tp = tcp_close(tp);
1433                                 break;
1434
1435                         case TCPS_CLOSING:
1436                         case TCPS_LAST_ACK:
1437                                 tp = tcp_close(tp);
1438                                 break;
1439
1440                         case TCPS_TIME_WAIT:
1441                                 break;
1442                         }
1443                 }
1444                 goto drop;
1445         }
1446
1447         /*
1448          * RFC 1323 PAWS: If we have a timestamp reply on this segment
1449          * and it's less than ts_recent, drop it.
1450          */
1451         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
1452             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
1453
1454                 /* Check to see if ts_recent is over 24 days old.  */
1455                 if ((int)(ticks - tp->ts_recent_age) > TCP_PAWS_IDLE) {
1456                         /*
1457                          * Invalidate ts_recent.  If this segment updates
1458                          * ts_recent, the age will be reset later and ts_recent
1459                          * will get a valid value.  If it does not, setting
1460                          * ts_recent to zero will at least satisfy the
1461                          * requirement that zero be placed in the timestamp
1462                          * echo reply when ts_recent isn't valid.  The
1463                          * age isn't reset until we get a valid ts_recent
1464                          * because we don't want out-of-order segments to be
1465                          * dropped when ts_recent is old.
1466                          */
1467                         tp->ts_recent = 0;
1468                 } else {
1469                         tcpstat.tcps_rcvduppack++;
1470                         tcpstat.tcps_rcvdupbyte += tlen;
1471                         tcpstat.tcps_pawsdrop++;
1472                         if (tlen)
1473                                 goto dropafterack;
1474                         goto drop;
1475                 }
1476         }
1477
1478         /*
1479          * T/TCP mechanism
1480          *   If T/TCP was negotiated and the segment doesn't have CC,
1481          *   or if its CC is wrong then drop the segment.
1482          *   RST segments do not have to comply with this.
1483          */
1484         if ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) == (TF_REQ_CC|TF_RCVD_CC) &&
1485             ((to.to_flags & TOF_CC) == 0 || tp->cc_recv != to.to_cc))
1486                 goto dropafterack;
1487
1488         /*
1489          * In the SYN-RECEIVED state, validate that the packet belongs to
1490          * this connection before trimming the data to fit the receive
1491          * window.  Check the sequence number versus IRS since we know
1492          * the sequence numbers haven't wrapped.  This is a partial fix
1493          * for the "LAND" DoS attack.
1494          */
1495         if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
1496                 rstreason = BANDLIM_RST_OPENPORT;
1497                 goto dropwithreset;
1498         }
1499
1500         todrop = tp->rcv_nxt - th->th_seq;
1501         if (todrop > 0) {
1502                 if (thflags & TH_SYN) {
1503                         thflags &= ~TH_SYN;
1504                         th->th_seq++;
1505                         if (th->th_urp > 1)
1506                                 th->th_urp--;
1507                         else
1508                                 thflags &= ~TH_URG;
1509                         todrop--;
1510                 }
1511                 /*
1512                  * Following if statement from Stevens, vol. 2, p. 960.
1513                  */
1514                 if (todrop > tlen
1515                     || (todrop == tlen && (thflags & TH_FIN) == 0)) {
1516                         /*
1517                          * Any valid FIN must be to the left of the window.
1518                          * At this point the FIN must be a duplicate or out
1519                          * of sequence; drop it.
1520                          */
1521                         thflags &= ~TH_FIN;
1522
1523                         /*
1524                          * Send an ACK to resynchronize and drop any data.
1525                          * But keep on processing for RST or ACK.
1526                          */
1527                         tp->t_flags |= TF_ACKNOW;
1528                         todrop = tlen;
1529                         tcpstat.tcps_rcvduppack++;
1530                         tcpstat.tcps_rcvdupbyte += todrop;
1531                 } else {
1532                         tcpstat.tcps_rcvpartduppack++;
1533                         tcpstat.tcps_rcvpartdupbyte += todrop;
1534                 }
1535                 drop_hdrlen += todrop;  /* drop from the top afterwards */
1536                 th->th_seq += todrop;
1537                 tlen -= todrop;
1538                 if (th->th_urp > todrop)
1539                         th->th_urp -= todrop;
1540                 else {
1541                         thflags &= ~TH_URG;
1542                         th->th_urp = 0;
1543                 }
1544         }
1545
1546         /*
1547          * If new data are received on a connection after the
1548          * user processes are gone, then RST the other end.
1549          */
1550         if ((so->so_state & SS_NOFDREF) &&
1551             tp->t_state > TCPS_CLOSE_WAIT && tlen) {
1552                 tp = tcp_close(tp);
1553                 tcpstat.tcps_rcvafterclose++;
1554                 rstreason = BANDLIM_UNLIMITED;
1555                 goto dropwithreset;
1556         }
1557
1558         /*
1559          * If segment ends after window, drop trailing data
1560          * (and PUSH and FIN); if nothing left, just ACK.
1561          */
1562         todrop = (th->th_seq+tlen) - (tp->rcv_nxt+tp->rcv_wnd);
1563         if (todrop > 0) {
1564                 tcpstat.tcps_rcvpackafterwin++;
1565                 if (todrop >= tlen) {
1566                         tcpstat.tcps_rcvbyteafterwin += tlen;
1567                         /*
1568                          * If a new connection request is received
1569                          * while in TIME_WAIT, drop the old connection
1570                          * and start over if the sequence numbers
1571                          * are above the previous ones.
1572                          */
1573                         if (thflags & TH_SYN &&
1574                             tp->t_state == TCPS_TIME_WAIT &&
1575                             SEQ_GT(th->th_seq, tp->rcv_nxt)) {
1576                                 tp = tcp_close(tp);
1577                                 goto findpcb;
1578                         }
1579                         /*
1580                          * If window is closed can only take segments at
1581                          * window edge, and have to drop data and PUSH from
1582                          * incoming segments.  Continue processing, but
1583                          * remember to ack.  Otherwise, drop segment
1584                          * and ack.
1585                          */
1586                         if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
1587                                 tp->t_flags |= TF_ACKNOW;
1588                                 tcpstat.tcps_rcvwinprobe++;
1589                         } else
1590                                 goto dropafterack;
1591                 } else
1592                         tcpstat.tcps_rcvbyteafterwin += todrop;
1593                 m_adj(m, -todrop);
1594                 tlen -= todrop;
1595                 thflags &= ~(TH_PUSH|TH_FIN);
1596         }
1597
1598         /*
1599          * If last ACK falls within this segment's sequence numbers,
1600          * record its timestamp.
1601          * NOTE that the test is modified according to the latest
1602          * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1603          */
1604         if ((to.to_flags & TOF_TS) != 0 &&
1605             SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
1606                 tp->ts_recent_age = ticks;
1607                 tp->ts_recent = to.to_tsval;
1608         }
1609
1610         /*
1611          * If a SYN is in the window, then this is an
1612          * error and we send an RST and drop the connection.
1613          */
1614         if (thflags & TH_SYN) {
1615                 tp = tcp_drop(tp, ECONNRESET);
1616                 rstreason = BANDLIM_UNLIMITED;
1617                 goto dropwithreset;
1618         }
1619
1620         /*
1621          * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
1622          * flag is on (half-synchronized state), then queue data for
1623          * later processing; else drop segment and return.
1624          */
1625         if ((thflags & TH_ACK) == 0) {
1626                 if (tp->t_state == TCPS_SYN_RECEIVED ||
1627                     (tp->t_flags & TF_NEEDSYN))
1628                         goto step6;
1629                 else
1630                         goto drop;
1631         }
1632
1633         /*
1634          * Ack processing.
1635          */
1636         switch (tp->t_state) {
1637
1638         /*
1639          * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
1640          * ESTABLISHED state and continue processing.
1641          * The ACK was checked above.
1642          */
1643         case TCPS_SYN_RECEIVED:
1644
1645                 tcpstat.tcps_connects++;
1646                 soisconnected(so);
1647                 /* Do window scaling? */
1648                 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1649                         (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1650                         tp->snd_scale = tp->requested_s_scale;
1651                         tp->rcv_scale = tp->request_r_scale;
1652                 }
1653                 /*
1654                  * Upon successful completion of 3-way handshake,
1655                  * update cache.CC if it was undefined, pass any queued
1656                  * data to the user, and advance state appropriately.
1657                  */
1658                 if ((taop = tcp_gettaocache(&inp->inp_inc)) != NULL &&
1659                     taop->tao_cc == 0)
1660                         taop->tao_cc = tp->cc_recv;
1661
1662                 /*
1663                  * Make transitions:
1664                  *      SYN-RECEIVED  -> ESTABLISHED
1665                  *      SYN-RECEIVED* -> FIN-WAIT-1
1666                  */
1667                 tp->t_starttime = ticks;
1668                 if (tp->t_flags & TF_NEEDFIN) {
1669                         tp->t_state = TCPS_FIN_WAIT_1;
1670                         tp->t_flags &= ~TF_NEEDFIN;
1671                 } else {
1672                         tp->t_state = TCPS_ESTABLISHED;
1673                         callout_reset(tp->tt_keep, tcp_keepidle,
1674                                       tcp_timer_keep, tp);
1675                 }
1676                 /*
1677                  * If segment contains data or ACK, will call tcp_reass()
1678                  * later; if not, do so now to pass queued data to user.
1679                  */
1680                 if (tlen == 0 && (thflags & TH_FIN) == 0)
1681                         (void) tcp_reass(tp, (struct tcphdr *)0, 0,
1682                             (struct mbuf *)0);
1683                 tp->snd_wl1 = th->th_seq - 1;
1684                 /* fall into ... */
1685
1686         /*
1687          * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
1688          * ACKs.  If the ack is in the range
1689          *      tp->snd_una < th->th_ack <= tp->snd_max
1690          * then advance tp->snd_una to th->th_ack and drop
1691          * data from the retransmission queue.  If this ACK reflects
1692          * more up to date window information we update our window information.
1693          */
1694         case TCPS_ESTABLISHED:
1695         case TCPS_FIN_WAIT_1:
1696         case TCPS_FIN_WAIT_2:
1697         case TCPS_CLOSE_WAIT:
1698         case TCPS_CLOSING:
1699         case TCPS_LAST_ACK:
1700         case TCPS_TIME_WAIT:
1701
1702                 if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
1703                         if (tlen == 0 && tiwin == tp->snd_wnd) {
1704                                 tcpstat.tcps_rcvdupack++;
1705                                 /*
1706                                  * If we have outstanding data (other than
1707                                  * a window probe), this is a completely
1708                                  * duplicate ack (ie, window info didn't
1709                                  * change), the ack is the biggest we've
1710                                  * seen and we've seen exactly our rexmt
1711                                  * threshhold of them, assume a packet
1712                                  * has been dropped and retransmit it.
1713                                  * Kludge snd_nxt & the congestion
1714                                  * window so we send only this one
1715                                  * packet.
1716                                  *
1717                                  * We know we're losing at the current
1718                                  * window size so do congestion avoidance
1719                                  * (set ssthresh to half the current window
1720                                  * and pull our congestion window back to
1721                                  * the new ssthresh).
1722                                  *
1723                                  * Dup acks mean that packets have left the
1724                                  * network (they're now cached at the receiver)
1725                                  * so bump cwnd by the amount in the receiver
1726                                  * to keep a constant cwnd packets in the
1727                                  * network.
1728                                  */
1729                                 if (!callout_active(tp->tt_rexmt) ||
1730                                     th->th_ack != tp->snd_una)
1731                                         tp->t_dupacks = 0;
1732                                 else if (++tp->t_dupacks > tcprexmtthresh ||
1733                                          (tcp_do_newreno &&
1734                                           IN_FASTRECOVERY(tp))) {
1735                                         tp->snd_cwnd += tp->t_maxseg;
1736                                         (void) tcp_output(tp);
1737                                         goto drop;
1738                                 } else if (tp->t_dupacks == tcprexmtthresh) {
1739                                         tcp_seq onxt;
1740                                         u_int win;
1741
1742                                         if (tcp_do_newreno &&
1743                                             SEQ_LEQ(th->th_ack,
1744                                                     tp->snd_recover)) {
1745                                                 tp->t_dupacks = 0;
1746                                                 break;
1747                                         }
1748 fastretransmit:
1749                                         if (tcp_do_eifel_detect &&
1750                                             (tp->t_flags & TF_RCVD_TSTMP)) {
1751                                                 tcp_save_congestion_state(tp);
1752                                                 tp->t_flags |= TF_FASTREXMT;
1753                                         }
1754                                         win = min(tp->snd_wnd, tp->snd_cwnd) /
1755                                             2 / tp->t_maxseg;
1756                                         if (win < 2)
1757                                                 win = 2;
1758                                         tp->snd_ssthresh = win * tp->t_maxseg;
1759                                         ENTER_FASTRECOVERY(tp);
1760                                         tp->snd_recover = tp->snd_max;
1761                                         callout_stop(tp->tt_rexmt);
1762                                         tp->t_rtttime = 0;
1763                                         onxt = tp->snd_nxt;
1764                                         tp->snd_nxt = th->th_ack;
1765                                         tp->snd_cwnd = tp->t_maxseg;
1766                                         (void) tcp_output(tp);
1767                                         ++tcpstat.tcps_sndfastrexmit;
1768                                         KASSERT(tp->snd_limited <= 2,
1769                                             ("tp->snd_limited too big"));
1770                                         tp->snd_cwnd = tp->snd_ssthresh +
1771                                             (tp->t_maxseg *
1772                                              (tp->t_dupacks - tp->snd_limited));
1773                                         if (SEQ_GT(onxt, tp->snd_nxt))
1774                                                 tp->snd_nxt = onxt;
1775                                         goto drop;
1776                                 } else if (tcp_do_limitedtransmit) {
1777                                         u_long oldcwnd = tp->snd_cwnd;
1778                                         tcp_seq oldsndmax = tp->snd_max;
1779                                         /* outstanding data */
1780                                         uint32_t ownd =
1781                                             tp->snd_max - tp->snd_una;
1782                                         u_int sent;
1783
1784 #define iceildiv(n, d)          (((n)+(d)-1) / (d))
1785
1786                                         KASSERT(tp->t_dupacks == 1 ||
1787                                             tp->t_dupacks == 2,
1788                                             ("dupacks not 1 or 2"));
1789                                         if (tp->t_dupacks == 1)
1790                                                 tp->snd_limited = 0;
1791                                         tp->snd_cwnd = ownd +
1792                                             (tp->t_dupacks - tp->snd_limited) *
1793                                             tp->t_maxseg;
1794                                         (void) tcp_output(tp);
1795                                         tp->snd_cwnd = oldcwnd;
1796                                         sent = tp->snd_max - oldsndmax;
1797                                         if (sent > tp->t_maxseg) {
1798                                                 KASSERT((tp->t_dupacks == 2 &&
1799                                                     tp->snd_limited == 0) ||
1800                                                    (sent == tp->t_maxseg + 1 &&
1801                                                     tp->t_flags & TF_SENTFIN),
1802                                                     ("sent too much"));
1803                                                 KASSERT(sent <=
1804                                                         tp->t_maxseg * 2,
1805                                                     ("sent too many segments"));
1806                                                 tp->snd_limited = 2;
1807                                                 tcpstat.tcps_sndlimited += 2;
1808                                         } else if (sent > 0) {
1809                                                 ++tp->snd_limited;
1810                                                 ++tcpstat.tcps_sndlimited;
1811                                         } else if (tcp_do_early_retransmit &&
1812                                             (tcp_do_eifel_detect &&
1813                                              (tp->t_flags & TF_RCVD_TSTMP)) &&
1814                                             tcp_do_newreno &&
1815                                             tp->t_dupacks + 1 >=
1816                                               iceildiv(ownd, tp->t_maxseg)) {
1817                                                 ++tcpstat.tcps_sndearlyrexmit;
1818                                                 tp->t_flags |= TF_EARLYREXMT;
1819                                                 goto fastretransmit;
1820                                         }
1821                                         goto drop;
1822                                 }
1823                         } else
1824                                 tp->t_dupacks = 0;
1825                         break;
1826                 }
1827
1828                 KASSERT(SEQ_GT(th->th_ack, tp->snd_una), ("th_ack <= snd_una"));
1829
1830                 /*
1831                  * If the congestion window was inflated to account
1832                  * for the other side's cached packets, retract it.
1833                  */
1834                 if (tcp_do_newreno) {
1835                         if (IN_FASTRECOVERY(tp)) {
1836                                 if (SEQ_LT(th->th_ack, tp->snd_recover)) {
1837                                         tcp_newreno_partial_ack(tp, th);
1838                                 } else {
1839                                         /*
1840                                          * Window inflation should have left us
1841                                          * with approximately snd_ssthresh
1842                                          * outstanding data.
1843                                          * But in case we would be inclined to
1844                                          * send a burst, better to do it via
1845                                          * the slow start mechanism.
1846                                          */
1847                                         if (SEQ_GT(th->th_ack +
1848                                                         tp->snd_ssthresh,
1849                                                    tp->snd_max))
1850                                                 tp->snd_cwnd = tp->snd_max -
1851                                                                 th->th_ack +
1852                                                                 tp->t_maxseg;
1853                                         else
1854                                                 tp->snd_cwnd = tp->snd_ssthresh;
1855                                 }
1856                         }
1857                 } else {
1858                         if (tp->t_dupacks >= tcprexmtthresh &&
1859                             tp->snd_cwnd > tp->snd_ssthresh)
1860                                 tp->snd_cwnd = tp->snd_ssthresh;
1861                 }
1862                 tp->t_dupacks = 0;
1863                 if (SEQ_GT(th->th_ack, tp->snd_max)) {
1864                         tcpstat.tcps_rcvacktoomuch++;
1865                         goto dropafterack;
1866                 }
1867                 /*
1868                  * If we reach this point, ACK is not a duplicate,
1869                  *     i.e., it ACKs something we sent.
1870                  */
1871                 if (tp->t_flags & TF_NEEDSYN) {
1872                         /*
1873                          * T/TCP: Connection was half-synchronized, and our
1874                          * SYN has been ACK'd (so connection is now fully
1875                          * synchronized).  Go to non-starred state,
1876                          * increment snd_una for ACK of SYN, and check if
1877                          * we can do window scaling.
1878                          */
1879                         tp->t_flags &= ~TF_NEEDSYN;
1880                         tp->snd_una++;
1881                         /* Do window scaling? */
1882                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1883                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1884                                 tp->snd_scale = tp->requested_s_scale;
1885                                 tp->rcv_scale = tp->request_r_scale;
1886                         }
1887                 }
1888
1889 process_ACK:
1890                 acked = th->th_ack - tp->snd_una;
1891                 tcpstat.tcps_rcvackpack++;
1892                 tcpstat.tcps_rcvackbyte += acked;
1893
1894                 /*
1895                  * If we just performed our first retransmit, and the ACK
1896                  * arrives within our recovery window, then it was a mistake
1897                  * to do the retransmit in the first place.  Recover our
1898                  * original cwnd and ssthresh, and proceed to transmit where
1899                  * we left off.
1900                  */
1901                 if (tcp_do_eifel_detect && acked &&
1902                     (to.to_flags & TOF_TS) && to.to_tsecr &&
1903                     (tp->t_flags & TF_FIRSTACCACK)) {
1904                         /* Eifel detection applicable. */
1905                         if (to.to_tsecr < tp->t_rexmtTS) {
1906                                 ++tcpstat.tcps_eifeldetected;
1907                                 tcp_revert_congestion_state(tp);
1908                                 if (tp->t_rxtshift == 1 &&
1909                                     ticks >= tp->t_badrxtwin)
1910                                         ++tcpstat.tcps_rttcantdetect;
1911                         }
1912                 } else if (tp->t_rxtshift == 1 && ticks < tp->t_badrxtwin) {
1913                         tcp_revert_congestion_state(tp);
1914                         ++tcpstat.tcps_rttdetected;
1915                 }
1916
1917                 /*
1918                  * If we have a timestamp reply, update smoothed
1919                  * round trip time.  If no timestamp is present but
1920                  * transmit timer is running and timed sequence
1921                  * number was acked, update smoothed round trip time.
1922                  * Since we now have an rtt measurement, cancel the
1923                  * timer backoff (cf., Phil Karn's retransmit alg.).
1924                  * Recompute the initial retransmit timer.
1925                  *
1926                  * Some machines (certain windows boxes) send broken
1927                  * timestamp replies during the SYN+ACK phase, ignore
1928                  * timestamps of 0.
1929                  */
1930                 if ((to.to_flags & TOF_TS) != 0 &&
1931                     to.to_tsecr) {
1932                         tcp_xmit_timer(tp, ticks - to.to_tsecr + 1);
1933                 } else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
1934                         tcp_xmit_timer(tp, ticks - tp->t_rtttime);
1935                 }
1936                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
1937
1938                 /*
1939                  * If all outstanding data is acked, stop retransmit
1940                  * timer and remember to restart (more output or persist).
1941                  * If there is more data to be acked, restart retransmit
1942                  * timer, using current (possibly backed-off) value.
1943                  */
1944                 if (th->th_ack == tp->snd_max) {
1945                         callout_stop(tp->tt_rexmt);
1946                         needoutput = 1;
1947                 } else if (!callout_active(tp->tt_persist))
1948                         callout_reset(tp->tt_rexmt, tp->t_rxtcur,
1949                                       tcp_timer_rexmt, tp);
1950
1951                 /*
1952                  * If no data (only SYN) was ACK'd,
1953                  *    skip rest of ACK processing.
1954                  */
1955                 if (acked == 0)
1956                         goto step6;
1957
1958                 /* Stop looking for an acceptable ACK since one was received. */
1959                 tp->t_flags &= ~(TF_FIRSTACCACK | TF_FASTREXMT | TF_EARLYREXMT);
1960
1961                 /*
1962                  * When new data is acked, open the congestion window.
1963                  * If the window gives us less than ssthresh packets
1964                  * in flight, open exponentially (maxseg per packet).
1965                  * Otherwise open linearly: maxseg per window
1966                  * (maxseg^2 / cwnd per packet).
1967                  */
1968                 if (!tcp_do_newreno || !IN_FASTRECOVERY(tp)) {
1969                         u_int cw = tp->snd_cwnd;
1970                         u_int incr = tp->t_maxseg;
1971                         if (cw > tp->snd_ssthresh)
1972                                 incr = incr * incr / cw;
1973                         tp->snd_cwnd = min(cw+incr, TCP_MAXWIN<<tp->snd_scale);
1974                 }
1975                 if (acked > so->so_snd.sb_cc) {
1976                         tp->snd_wnd -= so->so_snd.sb_cc;
1977                         sbdrop(&so->so_snd, (int)so->so_snd.sb_cc);
1978                         ourfinisacked = 1;
1979                 } else {
1980                         sbdrop(&so->so_snd, acked);
1981                         tp->snd_wnd -= acked;
1982                         ourfinisacked = 0;
1983                 }
1984                 sowwakeup(so);
1985                 /* detect una wraparound */
1986                 if (tcp_do_newreno && !IN_FASTRECOVERY(tp) &&
1987                     SEQ_GT(tp->snd_una, tp->snd_recover) &&
1988                     SEQ_LEQ(th->th_ack, tp->snd_recover))
1989                         tp->snd_recover = th->th_ack - 1;
1990                 if (tcp_do_newreno && IN_FASTRECOVERY(tp) &&
1991                     SEQ_GEQ(th->th_ack, tp->snd_recover))
1992                         EXIT_FASTRECOVERY(tp);
1993                 tp->snd_una = th->th_ack;
1994                 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
1995                         tp->snd_nxt = tp->snd_una;
1996
1997                 switch (tp->t_state) {
1998
1999                 /*
2000                  * In FIN_WAIT_1 STATE in addition to the processing
2001                  * for the ESTABLISHED state if our FIN is now acknowledged
2002                  * then enter FIN_WAIT_2.
2003                  */
2004                 case TCPS_FIN_WAIT_1:
2005                         if (ourfinisacked) {
2006                                 /*
2007                                  * If we can't receive any more
2008                                  * data, then closing user can proceed.
2009                                  * Starting the timer is contrary to the
2010                                  * specification, but if we don't get a FIN
2011                                  * we'll hang forever.
2012                                  */
2013                                 if (so->so_state & SS_CANTRCVMORE) {
2014                                         soisdisconnected(so);
2015                                         callout_reset(tp->tt_2msl, tcp_maxidle,
2016                                                       tcp_timer_2msl, tp);
2017                                 }
2018                                 tp->t_state = TCPS_FIN_WAIT_2;
2019                         }
2020                         break;
2021
2022                 /*
2023                  * In CLOSING STATE in addition to the processing for
2024                  * the ESTABLISHED state if the ACK acknowledges our FIN
2025                  * then enter the TIME-WAIT state, otherwise ignore
2026                  * the segment.
2027                  */
2028                 case TCPS_CLOSING:
2029                         if (ourfinisacked) {
2030                                 tp->t_state = TCPS_TIME_WAIT;
2031                                 tcp_canceltimers(tp);
2032                                 /* Shorten TIME_WAIT [RFC-1644, p.28] */
2033                                 if (tp->cc_recv != 0 &&
2034                                     (ticks - tp->t_starttime) < tcp_msl)
2035                                         callout_reset(tp->tt_2msl,
2036                                                       tp->t_rxtcur *
2037                                                       TCPTV_TWTRUNC,
2038                                                       tcp_timer_2msl, tp);
2039                                 else
2040                                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
2041                                                       tcp_timer_2msl, tp);
2042                                 soisdisconnected(so);
2043                         }
2044                         break;
2045
2046                 /*
2047                  * In LAST_ACK, we may still be waiting for data to drain
2048                  * and/or to be acked, as well as for the ack of our FIN.
2049                  * If our FIN is now acknowledged, delete the TCB,
2050                  * enter the closed state and return.
2051                  */
2052                 case TCPS_LAST_ACK:
2053                         if (ourfinisacked) {
2054                                 tp = tcp_close(tp);
2055                                 goto drop;
2056                         }
2057                         break;
2058
2059                 /*
2060                  * In TIME_WAIT state the only thing that should arrive
2061                  * is a retransmission of the remote FIN.  Acknowledge
2062                  * it and restart the finack timer.
2063                  */
2064                 case TCPS_TIME_WAIT:
2065                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
2066                                       tcp_timer_2msl, tp);
2067                         goto dropafterack;
2068                 }
2069         }
2070
2071 step6:
2072         /*
2073          * Update window information.
2074          * Don't look at window if no ACK: TAC's send garbage on first SYN.
2075          */
2076         if ((thflags & TH_ACK) &&
2077             (SEQ_LT(tp->snd_wl1, th->th_seq) ||
2078             (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
2079              (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
2080                 /* keep track of pure window updates */
2081                 if (tlen == 0 &&
2082                     tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
2083                         tcpstat.tcps_rcvwinupd++;
2084                 tp->snd_wnd = tiwin;
2085                 tp->snd_wl1 = th->th_seq;
2086                 tp->snd_wl2 = th->th_ack;
2087                 if (tp->snd_wnd > tp->max_sndwnd)
2088                         tp->max_sndwnd = tp->snd_wnd;
2089                 needoutput = 1;
2090         }
2091
2092         /*
2093          * Process segments with URG.
2094          */
2095         if ((thflags & TH_URG) && th->th_urp &&
2096             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2097                 /*
2098                  * This is a kludge, but if we receive and accept
2099                  * random urgent pointers, we'll crash in
2100                  * soreceive.  It's hard to imagine someone
2101                  * actually wanting to send this much urgent data.
2102                  */
2103                 if (th->th_urp + so->so_rcv.sb_cc > sb_max) {
2104                         th->th_urp = 0;                 /* XXX */
2105                         thflags &= ~TH_URG;             /* XXX */
2106                         goto dodata;                    /* XXX */
2107                 }
2108                 /*
2109                  * If this segment advances the known urgent pointer,
2110                  * then mark the data stream.  This should not happen
2111                  * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
2112                  * a FIN has been received from the remote side.
2113                  * In these states we ignore the URG.
2114                  *
2115                  * According to RFC961 (Assigned Protocols),
2116                  * the urgent pointer points to the last octet
2117                  * of urgent data.  We continue, however,
2118                  * to consider it to indicate the first octet
2119                  * of data past the urgent section as the original
2120                  * spec states (in one of two places).
2121                  */
2122                 if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
2123                         tp->rcv_up = th->th_seq + th->th_urp;
2124                         so->so_oobmark = so->so_rcv.sb_cc +
2125                             (tp->rcv_up - tp->rcv_nxt) - 1;
2126                         if (so->so_oobmark == 0)
2127                                 so->so_state |= SS_RCVATMARK;
2128                         sohasoutofband(so);
2129                         tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
2130                 }
2131                 /*
2132                  * Remove out of band data so doesn't get presented to user.
2133                  * This can happen independent of advancing the URG pointer,
2134                  * but if two URG's are pending at once, some out-of-band
2135                  * data may creep in... ick.
2136                  */
2137                 if (th->th_urp <= (u_long)tlen
2138 #ifdef SO_OOBINLINE
2139                      && (so->so_options & SO_OOBINLINE) == 0
2140 #endif
2141                      )
2142                         tcp_pulloutofband(so, th, m,
2143                                 drop_hdrlen);   /* hdr drop is delayed */
2144         } else {
2145                 /*
2146                  * If no out of band data is expected,
2147                  * pull receive urgent pointer along
2148                  * with the receive window.
2149                  */
2150                 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
2151                         tp->rcv_up = tp->rcv_nxt;
2152         }
2153 dodata:                                                 /* XXX */
2154
2155         /*
2156          * Process the segment text, merging it into the TCP sequencing queue,
2157          * and arranging for acknowledgment of receipt if necessary.
2158          * This process logically involves adjusting tp->rcv_wnd as data
2159          * is presented to the user (this happens in tcp_usrreq.c,
2160          * case PRU_RCVD).  If a FIN has already been received on this
2161          * connection then we just ignore the text.
2162          */
2163         if ((tlen || (thflags & TH_FIN)) &&
2164             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2165                 m_adj(m, drop_hdrlen);  /* delayed header drop */
2166                 /*
2167                  * Insert segment which includes th into TCP reassembly queue
2168                  * with control block tp.  Set thflags to whether reassembly now
2169                  * includes a segment with FIN.  This handles the common case
2170                  * inline (segment is the next to be received on an established
2171                  * connection, and the queue is empty), avoiding linkage into
2172                  * and removal from the queue and repetition of various
2173                  * conversions.
2174                  * Set DELACK for segments received in order, but ack
2175                  * immediately when segments are out of order (so
2176                  * fast retransmit can work).
2177                  */
2178                 if (th->th_seq == tp->rcv_nxt &&
2179                     LIST_EMPTY(&tp->t_segq) &&
2180                     TCPS_HAVEESTABLISHED(tp->t_state)) {
2181                         if (DELAY_ACK(tp))
2182                                 callout_reset(tp->tt_delack, tcp_delacktime,
2183                                               tcp_timer_delack, tp);
2184                         else
2185                                 tp->t_flags |= TF_ACKNOW;
2186                         tp->rcv_nxt += tlen;
2187                         thflags = th->th_flags & TH_FIN;
2188                         tcpstat.tcps_rcvpack++;
2189                         tcpstat.tcps_rcvbyte += tlen;
2190                         ND6_HINT(tp);
2191                         if (so->so_state & SS_CANTRCVMORE)
2192                                 m_freem(m);
2193                         else
2194                                 sbappend(&so->so_rcv, m);
2195                         sorwakeup(so);
2196                 } else {
2197                         thflags = tcp_reass(tp, th, &tlen, m);
2198                         tp->t_flags |= TF_ACKNOW;
2199                 }
2200
2201                 /*
2202                  * Note the amount of data that peer has sent into
2203                  * our window, in order to estimate the sender's
2204                  * buffer size.
2205                  */
2206                 len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
2207         } else {
2208                 m_freem(m);
2209                 thflags &= ~TH_FIN;
2210         }
2211
2212         /*
2213          * If FIN is received ACK the FIN and let the user know
2214          * that the connection is closing.
2215          */
2216         if (thflags & TH_FIN) {
2217                 if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2218                         socantrcvmore(so);
2219                         /*
2220                          * If connection is half-synchronized
2221                          * (ie NEEDSYN flag on) then delay ACK,
2222                          * so it may be piggybacked when SYN is sent.
2223                          * Otherwise, since we received a FIN then no
2224                          * more input can be expected, send ACK now.
2225                          */
2226                         if (DELAY_ACK(tp) && (tp->t_flags & TF_NEEDSYN))
2227                                 callout_reset(tp->tt_delack, tcp_delacktime,
2228                                     tcp_timer_delack, tp);
2229                         else
2230                                 tp->t_flags |= TF_ACKNOW;
2231                         tp->rcv_nxt++;
2232                 }
2233                 switch (tp->t_state) {
2234
2235                 /*
2236                  * In SYN_RECEIVED and ESTABLISHED STATES
2237                  * enter the CLOSE_WAIT state.
2238                  */
2239                 case TCPS_SYN_RECEIVED:
2240                         tp->t_starttime = ticks;
2241                         /*FALLTHROUGH*/
2242                 case TCPS_ESTABLISHED:
2243                         tp->t_state = TCPS_CLOSE_WAIT;
2244                         break;
2245
2246                 /*
2247                  * If still in FIN_WAIT_1 STATE FIN has not been acked so
2248                  * enter the CLOSING state.
2249                  */
2250                 case TCPS_FIN_WAIT_1:
2251                         tp->t_state = TCPS_CLOSING;
2252                         break;
2253
2254                 /*
2255                  * In FIN_WAIT_2 state enter the TIME_WAIT state,
2256                  * starting the time-wait timer, turning off the other
2257                  * standard timers.
2258                  */
2259                 case TCPS_FIN_WAIT_2:
2260                         tp->t_state = TCPS_TIME_WAIT;
2261                         tcp_canceltimers(tp);
2262                         /* Shorten TIME_WAIT [RFC-1644, p.28] */
2263                         if (tp->cc_recv != 0 &&
2264                             (ticks - tp->t_starttime) < tcp_msl) {
2265                                 callout_reset(tp->tt_2msl,
2266                                               tp->t_rxtcur * TCPTV_TWTRUNC,
2267                                               tcp_timer_2msl, tp);
2268                                 /* For transaction client, force ACK now. */
2269                                 tp->t_flags |= TF_ACKNOW;
2270                         }
2271                         else
2272                                 callout_reset(tp->tt_2msl, 2 * tcp_msl,
2273                                               tcp_timer_2msl, tp);
2274                         soisdisconnected(so);
2275                         break;
2276
2277                 /*
2278                  * In TIME_WAIT state restart the 2 MSL time_wait timer.
2279                  */
2280                 case TCPS_TIME_WAIT:
2281                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
2282                                       tcp_timer_2msl, tp);
2283                         break;
2284                 }
2285         }
2286 #ifdef TCPDEBUG
2287         if (so->so_options & SO_DEBUG)
2288                 tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
2289                           &tcp_savetcp, 0);
2290 #endif
2291
2292         /*
2293          * Return any desired output.
2294          */
2295         if (needoutput || (tp->t_flags & TF_ACKNOW))
2296                 (void) tcp_output(tp);
2297         return;
2298
2299 dropafterack:
2300         /*
2301          * Generate an ACK dropping incoming segment if it occupies
2302          * sequence space, where the ACK reflects our state.
2303          *
2304          * We can now skip the test for the RST flag since all
2305          * paths to this code happen after packets containing
2306          * RST have been dropped.
2307          *
2308          * In the SYN-RECEIVED state, don't send an ACK unless the
2309          * segment we received passes the SYN-RECEIVED ACK test.
2310          * If it fails send a RST.  This breaks the loop in the
2311          * "LAND" DoS attack, and also prevents an ACK storm
2312          * between two listening ports that have been sent forged
2313          * SYN segments, each with the source address of the other.
2314          */
2315         if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
2316             (SEQ_GT(tp->snd_una, th->th_ack) ||
2317              SEQ_GT(th->th_ack, tp->snd_max)) ) {
2318                 rstreason = BANDLIM_RST_OPENPORT;
2319                 goto dropwithreset;
2320         }
2321 #ifdef TCPDEBUG
2322         if (so->so_options & SO_DEBUG)
2323                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2324                           &tcp_savetcp, 0);
2325 #endif
2326         m_freem(m);
2327         tp->t_flags |= TF_ACKNOW;
2328         (void) tcp_output(tp);
2329         return;
2330
2331 dropwithreset:
2332         /*
2333          * Generate a RST, dropping incoming segment.
2334          * Make ACK acceptable to originator of segment.
2335          * Don't bother to respond if destination was broadcast/multicast.
2336          */
2337         if ((thflags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
2338                 goto drop;
2339         if (isipv6) {
2340                 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
2341                     IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
2342                         goto drop;
2343         } else {
2344                 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
2345                     IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
2346                     ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
2347                     in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
2348                         goto drop;
2349         }
2350         /* IPv6 anycast check is done at tcp6_input() */
2351
2352         /*
2353          * Perform bandwidth limiting.
2354          */
2355 #ifdef ICMP_BANDLIM
2356         if (badport_bandlim(rstreason) < 0)
2357                 goto drop;
2358 #endif
2359
2360 #ifdef TCPDEBUG
2361         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2362                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2363                           &tcp_savetcp, 0);
2364 #endif
2365         if (thflags & TH_ACK)
2366                 /* mtod() below is safe as long as hdr dropping is delayed */
2367                 tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0, th->th_ack,
2368                             TH_RST);
2369         else {
2370                 if (thflags & TH_SYN)
2371                         tlen++;
2372                 /* mtod() below is safe as long as hdr dropping is delayed */
2373                 tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
2374                             (tcp_seq)0, TH_RST|TH_ACK);
2375         }
2376         return;
2377
2378 drop:
2379         /*
2380          * Drop space held by incoming segment and return.
2381          */
2382 #ifdef TCPDEBUG
2383         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2384                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2385                           &tcp_savetcp, 0);
2386 #endif
2387         m_freem(m);
2388         return;
2389 }
2390
2391 /*
2392  * Parse TCP options and place in tcpopt.
2393  */
2394 static void
2395 tcp_dooptions(to, cp, cnt, is_syn)
2396         struct tcpopt *to;
2397         u_char *cp;
2398         int cnt;
2399 {
2400         int opt, optlen;
2401
2402         to->to_flags = 0;
2403         for (; cnt > 0; cnt -= optlen, cp += optlen) {
2404                 opt = cp[0];
2405                 if (opt == TCPOPT_EOL)
2406                         break;
2407                 if (opt == TCPOPT_NOP)
2408                         optlen = 1;
2409                 else {
2410                         if (cnt < 2)
2411                                 break;
2412                         optlen = cp[1];
2413                         if (optlen < 2 || optlen > cnt)
2414                                 break;
2415                 }
2416                 switch (opt) {
2417                 case TCPOPT_MAXSEG:
2418                         if (optlen != TCPOLEN_MAXSEG)
2419                                 continue;
2420                         if (!is_syn)
2421                                 continue;
2422                         to->to_flags |= TOF_MSS;
2423                         bcopy((char *)cp + 2,
2424                             (char *)&to->to_mss, sizeof(to->to_mss));
2425                         to->to_mss = ntohs(to->to_mss);
2426                         break;
2427                 case TCPOPT_WINDOW:
2428                         if (optlen != TCPOLEN_WINDOW)
2429                                 continue;
2430                         if (! is_syn)
2431                                 continue;
2432                         to->to_flags |= TOF_SCALE;
2433                         to->to_requested_s_scale = min(cp[2], TCP_MAX_WINSHIFT);
2434                         break;
2435                 case TCPOPT_TIMESTAMP:
2436                         if (optlen != TCPOLEN_TIMESTAMP)
2437                                 continue;
2438                         to->to_flags |= TOF_TS;
2439                         bcopy((char *)cp + 2,
2440                             (char *)&to->to_tsval, sizeof(to->to_tsval));
2441                         to->to_tsval = ntohl(to->to_tsval);
2442                         bcopy((char *)cp + 6,
2443                             (char *)&to->to_tsecr, sizeof(to->to_tsecr));
2444                         to->to_tsecr = ntohl(to->to_tsecr);
2445                         break;
2446                 case TCPOPT_CC:
2447                         if (optlen != TCPOLEN_CC)
2448                                 continue;
2449                         to->to_flags |= TOF_CC;
2450                         bcopy((char *)cp + 2,
2451                             (char *)&to->to_cc, sizeof(to->to_cc));
2452                         to->to_cc = ntohl(to->to_cc);
2453                         break;
2454                 case TCPOPT_CCNEW:
2455                         if (optlen != TCPOLEN_CC)
2456                                 continue;
2457                         if (!is_syn)
2458                                 continue;
2459                         to->to_flags |= TOF_CCNEW;
2460                         bcopy((char *)cp + 2,
2461                             (char *)&to->to_cc, sizeof(to->to_cc));
2462                         to->to_cc = ntohl(to->to_cc);
2463                         break;
2464                 case TCPOPT_CCECHO:
2465                         if (optlen != TCPOLEN_CC)
2466                                 continue;
2467                         if (!is_syn)
2468                                 continue;
2469                         to->to_flags |= TOF_CCECHO;
2470                         bcopy((char *)cp + 2,
2471                             (char *)&to->to_ccecho, sizeof(to->to_ccecho));
2472                         to->to_ccecho = ntohl(to->to_ccecho);
2473                         break;
2474                 default:
2475                         continue;
2476                 }
2477         }
2478 }
2479
2480 /*
2481  * Pull out of band byte out of a segment so
2482  * it doesn't appear in the user's data queue.
2483  * It is still reflected in the segment length for
2484  * sequencing purposes.
2485  */
2486 static void
2487 tcp_pulloutofband(so, th, m, off)
2488         struct socket *so;
2489         struct tcphdr *th;
2490         struct mbuf *m;
2491         int off;                /* delayed to be droped hdrlen */
2492 {
2493         int cnt = off + th->th_urp - 1;
2494
2495         while (cnt >= 0) {
2496                 if (m->m_len > cnt) {
2497                         char *cp = mtod(m, caddr_t) + cnt;
2498                         struct tcpcb *tp = sototcpcb(so);
2499
2500                         tp->t_iobc = *cp;
2501                         tp->t_oobflags |= TCPOOB_HAVEDATA;
2502                         bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
2503                         m->m_len--;
2504                         if (m->m_flags & M_PKTHDR)
2505                                 m->m_pkthdr.len--;
2506                         return;
2507                 }
2508                 cnt -= m->m_len;
2509                 m = m->m_next;
2510                 if (m == 0)
2511                         break;
2512         }
2513         panic("tcp_pulloutofband");
2514 }
2515
2516 /*
2517  * Collect new round-trip time estimate
2518  * and update averages and current timeout.
2519  */
2520 static void
2521 tcp_xmit_timer(tp, rtt)
2522         struct tcpcb *tp;
2523         int rtt;
2524 {
2525         int delta;
2526
2527         tcpstat.tcps_rttupdated++;
2528         tp->t_rttupdated++;
2529         if (tp->t_srtt != 0) {
2530                 /*
2531                  * srtt is stored as fixed point with 5 bits after the
2532                  * binary point (i.e., scaled by 8).  The following magic
2533                  * is equivalent to the smoothing algorithm in rfc793 with
2534                  * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
2535                  * point).  Adjust rtt to origin 0.
2536                  */
2537                 delta = ((rtt - 1) << TCP_DELTA_SHIFT)
2538                         - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
2539
2540                 if ((tp->t_srtt += delta) <= 0)
2541                         tp->t_srtt = 1;
2542
2543                 /*
2544                  * We accumulate a smoothed rtt variance (actually, a
2545                  * smoothed mean difference), then set the retransmit
2546                  * timer to smoothed rtt + 4 times the smoothed variance.
2547                  * rttvar is stored as fixed point with 4 bits after the
2548                  * binary point (scaled by 16).  The following is
2549                  * equivalent to rfc793 smoothing with an alpha of .75
2550                  * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
2551                  * rfc793's wired-in beta.
2552                  */
2553                 if (delta < 0)
2554                         delta = -delta;
2555                 delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
2556                 if ((tp->t_rttvar += delta) <= 0)
2557                         tp->t_rttvar = 1;
2558                 if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
2559                         tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2560         } else {
2561                 /*
2562                  * No rtt measurement yet - use the unsmoothed rtt.
2563                  * Set the variance to half the rtt (so our first
2564                  * retransmit happens at 3*rtt).
2565                  */
2566                 tp->t_srtt = rtt << TCP_RTT_SHIFT;
2567                 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
2568                 tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2569         }
2570         tp->t_rtttime = 0;
2571         tp->t_rxtshift = 0;
2572
2573         /*
2574          * the retransmit should happen at rtt + 4 * rttvar.
2575          * Because of the way we do the smoothing, srtt and rttvar
2576          * will each average +1/2 tick of bias.  When we compute
2577          * the retransmit timer, we want 1/2 tick of rounding and
2578          * 1 extra tick because of +-1/2 tick uncertainty in the
2579          * firing of the timer.  The bias will give us exactly the
2580          * 1.5 tick we need.  But, because the bias is
2581          * statistical, we have to test that we don't drop below
2582          * the minimum feasible timer (which is 2 ticks).
2583          */
2584         TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
2585                       max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
2586
2587         /*
2588          * We received an ack for a packet that wasn't retransmitted;
2589          * it is probably safe to discard any error indications we've
2590          * received recently.  This isn't quite right, but close enough
2591          * for now (a route might have failed after we sent a segment,
2592          * and the return path might not be symmetrical).
2593          */
2594         tp->t_softerror = 0;
2595 }
2596
2597 /*
2598  * Determine a reasonable value for maxseg size.
2599  * If the route is known, check route for mtu.
2600  * If none, use an mss that can be handled on the outgoing
2601  * interface without forcing IP to fragment; if bigger than
2602  * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
2603  * to utilize large mbufs.  If no route is found, route has no mtu,
2604  * or the destination isn't local, use a default, hopefully conservative
2605  * size (usually 512 or the default IP max size, but no more than the mtu
2606  * of the interface), as we can't discover anything about intervening
2607  * gateways or networks.  We also initialize the congestion/slow start
2608  * window to be a single segment if the destination isn't local.
2609  * While looking at the routing entry, we also initialize other path-dependent
2610  * parameters from pre-set or cached values in the routing entry.
2611  *
2612  * Also take into account the space needed for options that we
2613  * send regularly.  Make maxseg shorter by that amount to assure
2614  * that we can send maxseg amount of data even when the options
2615  * are present.  Store the upper limit of the length of options plus
2616  * data in maxopd.
2617  *
2618  * NOTE that this routine is only called when we process an incoming
2619  * segment, for outgoing segments only tcp_mssopt is called.
2620  *
2621  * In case of T/TCP, we call this routine during implicit connection
2622  * setup as well (offer = -1), to initialize maxseg from the cached
2623  * MSS of our peer.
2624  */
2625 void
2626 tcp_mss(tp, offer)
2627         struct tcpcb *tp;
2628         int offer;
2629 {
2630         struct rtentry *rt;
2631         struct ifnet *ifp;
2632         int rtt, mss;
2633         u_long bufsize;
2634         struct inpcb *inp = tp->t_inpcb;
2635         struct socket *so;
2636         struct rmxp_tao *taop;
2637         int origoffer = offer;
2638 #ifdef INET6
2639         boolean_t isipv6 = ((inp->inp_vflag & INP_IPV6) ? TRUE : FALSE);
2640         size_t min_protoh = isipv6 ?
2641                             sizeof(struct ip6_hdr) + sizeof(struct tcphdr) :
2642                             sizeof(struct tcpiphdr);
2643 #else
2644         const boolean_t isipv6 = FALSE;
2645         const size_t min_protoh = sizeof(struct tcpiphdr);
2646 #endif
2647
2648         if (isipv6)
2649                 rt = tcp_rtlookup6(&inp->inp_inc);
2650         else
2651                 rt = tcp_rtlookup(&inp->inp_inc);
2652         if (rt == NULL) {
2653                 tp->t_maxopd = tp->t_maxseg =
2654                     (isipv6 ? tcp_v6mssdflt : tcp_mssdflt);
2655                 return;
2656         }
2657         ifp = rt->rt_ifp;
2658         so = inp->inp_socket;
2659
2660         taop = rmx_taop(rt->rt_rmx);
2661         /*
2662          * Offer == -1 means that we didn't receive SYN yet,
2663          * use cached value in that case;
2664          */
2665         if (offer == -1)
2666                 offer = taop->tao_mssopt;
2667         /*
2668          * Offer == 0 means that there was no MSS on the SYN segment,
2669          * in this case we use tcp_mssdflt.
2670          */
2671         if (offer == 0)
2672                 offer = (isipv6 ? tcp_v6mssdflt : tcp_mssdflt);
2673         else
2674                 /*
2675                  * Sanity check: make sure that maxopd will be large
2676                  * enough to allow some data on segments even is the
2677                  * all the option space is used (40bytes).  Otherwise
2678                  * funny things may happen in tcp_output.
2679                  */
2680                 offer = max(offer, 64);
2681         taop->tao_mssopt = offer;
2682
2683         /*
2684          * While we're here, check if there's an initial rtt
2685          * or rttvar.  Convert from the route-table units
2686          * to scaled multiples of the slow timeout timer.
2687          */
2688         if (tp->t_srtt == 0 && (rtt = rt->rt_rmx.rmx_rtt)) {
2689                 /*
2690                  * XXX the lock bit for RTT indicates that the value
2691                  * is also a minimum value; this is subject to time.
2692                  */
2693                 if (rt->rt_rmx.rmx_locks & RTV_RTT)
2694                         tp->t_rttmin = rtt / (RTM_RTTUNIT / hz);
2695                 tp->t_srtt = rtt / (RTM_RTTUNIT / (hz * TCP_RTT_SCALE));
2696                 tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
2697                 tcpstat.tcps_usedrtt++;
2698                 if (rt->rt_rmx.rmx_rttvar) {
2699                         tp->t_rttvar = rt->rt_rmx.rmx_rttvar /
2700                             (RTM_RTTUNIT / (hz * TCP_RTTVAR_SCALE));
2701                         tcpstat.tcps_usedrttvar++;
2702                 } else {
2703                         /* default variation is +- 1 rtt */
2704                         tp->t_rttvar =
2705                             tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
2706                 }
2707                 TCPT_RANGESET(tp->t_rxtcur,
2708                               ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
2709                               tp->t_rttmin, TCPTV_REXMTMAX);
2710         }
2711         /*
2712          * if there's an mtu associated with the route, use it
2713          * else, use the link mtu.
2714          */
2715         if (rt->rt_rmx.rmx_mtu)
2716                 mss = rt->rt_rmx.rmx_mtu - min_protoh;
2717         else {
2718                 if (isipv6) {
2719                         mss = nd_ifinfo[rt->rt_ifp->if_index].linkmtu -
2720                                 min_protoh;
2721                         if (!in6_localaddr(&inp->in6p_faddr))
2722                                 mss = min(mss, tcp_v6mssdflt);
2723                 } else {
2724                         mss = ifp->if_mtu - min_protoh;
2725                         if (!in_localaddr(inp->inp_faddr))
2726                                 mss = min(mss, tcp_mssdflt);
2727                 }
2728         }
2729         mss = min(mss, offer);
2730         /*
2731          * maxopd stores the maximum length of data AND options
2732          * in a segment; maxseg is the amount of data in a normal
2733          * segment.  We need to store this value (maxopd) apart
2734          * from maxseg, because now every segment carries options
2735          * and thus we normally have somewhat less data in segments.
2736          */
2737         tp->t_maxopd = mss;
2738
2739         /*
2740          * In case of T/TCP, origoffer==-1 indicates, that no segments
2741          * were received yet.  In this case we just guess, otherwise
2742          * we do the same as before T/TCP.
2743          */
2744         if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
2745             (origoffer == -1 ||
2746              (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
2747                 mss -= TCPOLEN_TSTAMP_APPA;
2748         if ((tp->t_flags & (TF_REQ_CC|TF_NOOPT)) == TF_REQ_CC &&
2749             (origoffer == -1 ||
2750              (tp->t_flags & TF_RCVD_CC) == TF_RCVD_CC))
2751                 mss -= TCPOLEN_CC_APPA;
2752
2753 #if     (MCLBYTES & (MCLBYTES - 1)) == 0
2754                 if (mss > MCLBYTES)
2755                         mss &= ~(MCLBYTES-1);
2756 #else
2757                 if (mss > MCLBYTES)
2758                         mss = mss / MCLBYTES * MCLBYTES;
2759 #endif
2760         /*
2761          * If there's a pipesize, change the socket buffer
2762          * to that size.  Make the socket buffers an integral
2763          * number of mss units; if the mss is larger than
2764          * the socket buffer, decrease the mss.
2765          */
2766 #ifdef RTV_SPIPE
2767         if ((bufsize = rt->rt_rmx.rmx_sendpipe) == 0)
2768 #endif
2769                 bufsize = so->so_snd.sb_hiwat;
2770         if (bufsize < mss)
2771                 mss = bufsize;
2772         else {
2773                 bufsize = roundup(bufsize, mss);
2774                 if (bufsize > sb_max)
2775                         bufsize = sb_max;
2776                 if (bufsize > so->so_snd.sb_hiwat)
2777                         (void)sbreserve(&so->so_snd, bufsize, so, NULL);
2778         }
2779         tp->t_maxseg = mss;
2780
2781 #ifdef RTV_RPIPE
2782         if ((bufsize = rt->rt_rmx.rmx_recvpipe) == 0)
2783 #endif
2784                 bufsize = so->so_rcv.sb_hiwat;
2785         if (bufsize > mss) {
2786                 bufsize = roundup(bufsize, mss);
2787                 if (bufsize > sb_max)
2788                         bufsize = sb_max;
2789                 if (bufsize > so->so_rcv.sb_hiwat)
2790                         (void)sbreserve(&so->so_rcv, bufsize, so, NULL);
2791         }
2792
2793         /*
2794          * Set the slow-start flight size depending on whether this
2795          * is a local network or not.
2796          */
2797         if (tcp_do_rfc3390)
2798                 tp->snd_cwnd = min(4 * mss, max(2 * mss, 4380));
2799         else if ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
2800                  (!isipv6 && in_localaddr(inp->inp_faddr)))
2801                 tp->snd_cwnd = mss * ss_fltsz_local;
2802         else
2803                 tp->snd_cwnd = mss * ss_fltsz;
2804
2805         if (rt->rt_rmx.rmx_ssthresh) {
2806                 /*
2807                  * There's some sort of gateway or interface
2808                  * buffer limit on the path.  Use this to set
2809                  * the slow start threshhold, but set the
2810                  * threshold to no less than 2*mss.
2811                  */
2812                 tp->snd_ssthresh = max(2 * mss, rt->rt_rmx.rmx_ssthresh);
2813                 tcpstat.tcps_usedssthresh++;
2814         }
2815 }
2816
2817 /*
2818  * Determine the MSS option to send on an outgoing SYN.
2819  */
2820 int
2821 tcp_mssopt(tp)
2822         struct tcpcb *tp;
2823 {
2824         struct rtentry *rt;
2825 #ifdef INET6
2826         boolean_t isipv6 =
2827             ((tp->t_inpcb->inp_vflag & INP_IPV6) ? TRUE : FALSE);
2828         int min_protoh = isipv6 ?
2829                              sizeof(struct ip6_hdr) + sizeof(struct tcphdr) :
2830                              sizeof(struct tcpiphdr);
2831 #else
2832         const boolean_t isipv6 = FALSE;
2833         const size_t min_protoh = sizeof(struct tcpiphdr);
2834 #endif
2835
2836         if (isipv6)
2837                 rt = tcp_rtlookup6(&tp->t_inpcb->inp_inc);
2838         else
2839                 rt = tcp_rtlookup(&tp->t_inpcb->inp_inc);
2840         if (rt == NULL)
2841                 return (isipv6 ? tcp_v6mssdflt : tcp_mssdflt);
2842
2843         return (rt->rt_ifp->if_mtu - min_protoh);
2844 }
2845
2846
2847 /*
2848  * When a partial ack arrives, force the retransmission of the
2849  * next unacknowledged segment.  Do not clear tp->t_dupacks.
2850  * By setting snd_nxt to ti_ack, this forces retransmission timer to
2851  * be started again.
2852  */
2853 static void
2854 tcp_newreno_partial_ack(tp, th)
2855         struct tcpcb *tp;
2856         struct tcphdr *th;
2857 {
2858         tcp_seq onxt = tp->snd_nxt;
2859         u_long  ocwnd = tp->snd_cwnd;
2860
2861         callout_stop(tp->tt_rexmt);
2862         tp->t_rtttime = 0;
2863         tp->snd_nxt = th->th_ack;
2864         /*
2865          * Set snd_cwnd to one segment beyond acknowledged offset
2866          * (tp->snd_una has not yet been updated when this function is called.)
2867          */
2868         tp->snd_cwnd = tp->t_maxseg + (th->th_ack - tp->snd_una);
2869         tp->t_flags |= TF_ACKNOW;
2870         (void) tcp_output(tp);
2871         tp->snd_cwnd = ocwnd;
2872         if (SEQ_GT(onxt, tp->snd_nxt))
2873                 tp->snd_nxt = onxt;
2874         /*
2875          * Partial window deflation.  Relies on fact that tp->snd_una
2876          * not updated yet.
2877          */
2878         tp->snd_cwnd -= (th->th_ack - tp->snd_una - tp->t_maxseg);
2879 }