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 1.19 2004/03/08 19:44:32 hsu Exp $
  37  */
  38
  39 #include "opt_ipfw.h"           /* for ipfw_fwd         */
  40 #include "opt_inet6.h"
  41 #include "opt_ipsec.h"
  42 #include "opt_tcpdebug.h"
  43 #include "opt_tcp_input.h"
  44
  45 #include <sys/param.h>
  46 #include <sys/systm.h>
  47 #include <sys/kernel.h>
  48 #include <sys/sysctl.h>
  49 #include <sys/malloc.h>
  50 #include <sys/mbuf.h>
  51 #include <sys/proc.h>           /* for proc0 declaration */
  52 #include <sys/protosw.h>
  53 #include <sys/socket.h>
  54 #include <sys/socketvar.h>
  55 #include <sys/syslog.h>
  56 #include <sys/in_cksum.h>
  57
  58 #include <machine/cpu.h>        /* before tcp_seq.h, for tcp_random18() */
  59
  60 #include <net/if.h>
  61 #include <net/route.h>
  62
  63 #include <netinet/in.h>
  64 #include <netinet/in_systm.h>
  65 #include <netinet/ip.h>
  66 #include <netinet/ip_icmp.h>    /* for ICMP_BANDLIM             */
  67 #include <netinet/in_var.h>
  68 #include <netinet/icmp_var.h>   /* for ICMP_BANDLIM             */
  69 #include <netinet/in_pcb.h>
  70 #include <netinet/ip_var.h>
  71 #include <netinet/ip6.h>
  72 #include <netinet/icmp6.h>
  73 #include <netinet6/nd6.h>
  74 #include <netinet6/ip6_var.h>
  75 #include <netinet6/in6_pcb.h>
  76 #include <netinet/tcp.h>
  77 #include <netinet/tcp_fsm.h>
  78 #include <netinet/tcp_seq.h>
  79 #include <netinet/tcp_timer.h>
  80 #include <netinet/tcp_var.h>
  81 #include <netinet6/tcp6_var.h>
  82 #include <netinet/tcpip.h>
  83 #ifdef TCPDEBUG
  84 #include <netinet/tcp_debug.h>
  85
  86 u_char tcp_saveipgen[40]; /* the size must be of max ip header, now IPv6 */
  87 struct tcphdr tcp_savetcp;
  88 #endif /* TCPDEBUG */
  89
  90 #ifdef FAST_IPSEC
  91 #include <netipsec/ipsec.h>
  92 #include <netipsec/ipsec6.h>
  93 #endif
  94
  95 #ifdef IPSEC
  96 #include <netinet6/ipsec.h>
  97 #include <netinet6/ipsec6.h>
  98 #include <netproto/key/key.h>
  99 #endif /*IPSEC*/
 100
 101 MALLOC_DEFINE(M_TSEGQ, "tseg_qent", "TCP segment queue entry");
 102
 103 static const int tcprexmtthresh = 3;
 104 tcp_cc  tcp_ccgen;
 105
 106 struct  tcpstat tcpstat;
 107 SYSCTL_STRUCT(_net_inet_tcp, TCPCTL_STATS, stats, CTLFLAG_RW,
 108     &tcpstat , tcpstat, "TCP statistics (struct tcpstat, netinet/tcp_var.h)");
 109
 110 static int log_in_vain = 0;
 111 SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW,
 112     &log_in_vain, 0, "Log all incoming TCP connections");
 113
 114 static int blackhole = 0;
 115 SYSCTL_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_RW,
 116     &blackhole, 0, "Do not send RST when dropping refused connections");
 117
 118 int tcp_delack_enabled = 1;
 119 SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_RW,
 120     &tcp_delack_enabled, 0,
 121     "Delay ACK to try and piggyback it onto a data packet");
 122
 123 #ifdef TCP_DROP_SYNFIN
 124 static int drop_synfin = 0;
 125 SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_RW,
 126     &drop_synfin, 0, "Drop TCP packets with SYN+FIN set");
 127 #endif
 128
 129 static int tcp_do_limitedtransmit = 1;
 130 SYSCTL_INT(_net_inet_tcp, OID_AUTO, limitedtransmit, CTLFLAG_RW,
 131     &tcp_do_limitedtransmit, 0, "Enable RFC 3042 (Limited Transmit)");
 132
 133 static int tcp_do_early_retransmit = 0;
 134 SYSCTL_INT(_net_inet_tcp, OID_AUTO, earlyretransmit, CTLFLAG_RW,
 135     &tcp_do_early_retransmit, 0, "Early retransmit");
 136
 137 static int tcp_do_rfc3390 = 1;
 138 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3390, CTLFLAG_RW,
 139     &tcp_do_rfc3390, 0,
 140     "Enable RFC 3390 (Increasing TCP's Initial Congestion Window)");
 141
 142 static int tcp_do_eifel_detect = 1;
 143 SYSCTL_INT(_net_inet_tcp, OID_AUTO, eifel, CTLFLAG_RW,
 144     &tcp_do_eifel_detect, 0, "Eifel detection algorithm (RFC 3522)");
 145
 146 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, reass, CTLFLAG_RW, 0,
 147     "TCP Segment Reassembly Queue");
 148
 149 int tcp_reass_maxseg = 0;
 150 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, maxsegments, CTLFLAG_RD,
 151     &tcp_reass_maxseg, 0,
 152     "Global maximum number of TCP Segments in Reassembly Queue");
 153
 154 int tcp_reass_qsize = 0;
 155 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, cursegments, CTLFLAG_RD,
 156     &tcp_reass_qsize, 0,
 157     "Global number of TCP Segments currently in Reassembly Queue");
 158
 159 static int tcp_reass_overflows = 0;
 160 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, overflows, CTLFLAG_RD,
 161     &tcp_reass_overflows, 0,
 162     "Global number of TCP Segment Reassembly Queue Overflows");
 163
 164 struct inpcbinfo tcbinfo[MAXCPU];
 165
 166 static void      tcp_dooptions(struct tcpopt *, u_char *, int, int);
 167 static void      tcp_pulloutofband(struct socket *,
 168                      struct tcphdr *, struct mbuf *, int);
 169 static int       tcp_reass(struct tcpcb *, struct tcphdr *, int *,
 170                      struct mbuf *);
 171 static void      tcp_xmit_timer(struct tcpcb *, int);
 172 static void      tcp_newreno_partial_ack(struct tcpcb *, struct tcphdr *);
 173
 174 /* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */
 175 #ifdef INET6
 176 #define ND6_HINT(tp) \
 177 do { \
 178         if ((tp) && (tp)->t_inpcb && \
 179             ((tp)->t_inpcb->inp_vflag & INP_IPV6) != 0 && \
 180             (tp)->t_inpcb->in6p_route.ro_rt) \
 181                 nd6_nud_hint((tp)->t_inpcb->in6p_route.ro_rt, NULL, 0); \
 182 } while (0)
 183 #else
 184 #define ND6_HINT(tp)
 185 #endif
 186
 187 /*
 188  * Indicate whether this ack should be delayed.  We can delay the ack if
 189  *      - delayed acks are enabled and
 190  *      - there is no delayed ack timer in progress and
 191  *      - our last ack wasn't a 0-sized window.  We never want to delay
 192  *        the ack that opens up a 0-sized window.
 193  */
 194 #define DELAY_ACK(tp) \
 195         (tcp_delack_enabled && !callout_pending(tp->tt_delack) && \
 196         (tp->t_flags & TF_RXWIN0SENT) == 0)
 197
 198 static int
 199 tcp_reass(tp, th, tlenp, m)
 200         struct tcpcb *tp;
 201         struct tcphdr *th;
 202         int *tlenp;
 203         struct mbuf *m;
 204 {
 205         struct tseg_qent *q;
 206         struct tseg_qent *p = NULL;
 207         struct tseg_qent *nq;
 208         struct tseg_qent *te;
 209         struct socket *so = tp->t_inpcb->inp_socket;
 210         int flags;
 211
 212         /*
 213          * Call with th==0 after become established to
 214          * force pre-ESTABLISHED data up to user socket.
 215          */
 216         if (th == 0)
 217                 goto present;
 218
 219         /*
 220          * Limit the number of segments in the reassembly queue to prevent
 221          * holding on to too many segments (and thus running out of mbufs).
 222          * Make sure to let the missing segment through which caused this
 223          * queue.  Always keep one global queue entry spare to be able to
 224          * process the missing segment.
 225          */
 226         if (th->th_seq != tp->rcv_nxt &&
 227             tcp_reass_qsize + 1 >= tcp_reass_maxseg) {
 228                 tcp_reass_overflows++;
 229                 tcpstat.tcps_rcvmemdrop++;
 230                 m_freem(m);
 231                 return (0);
 232         }
 233
 234         /* Allocate a new queue entry. If we can't, just drop the pkt. XXX */
 235         MALLOC(te, struct tseg_qent *, sizeof(struct tseg_qent), M_TSEGQ,
 236                M_NOWAIT);
 237         if (te == NULL) {
 238                 tcpstat.tcps_rcvmemdrop++;
 239                 m_freem(m);
 240                 return (0);
 241         }
 242         tcp_reass_qsize++;
 243
 244         /*
 245          * Find a segment which begins after this one does.
 246          */
 247         LIST_FOREACH(q, &tp->t_segq, tqe_q) {
 248                 if (SEQ_GT(q->tqe_th->th_seq, th->th_seq))
 249                         break;
 250                 p = q;
 251         }
 252
 253         /*
 254          * If there is a preceding segment, it may provide some of
 255          * our data already.  If so, drop the data from the incoming
 256          * segment.  If it provides all of our data, drop us.
 257          */
 258         if (p != NULL) {
 259                 int i;
 260                 /* conversion to int (in i) handles seq wraparound */
 261                 i = p->tqe_th->th_seq + p->tqe_len - th->th_seq;
 262                 if (i > 0) {
 263                         if (i >= *tlenp) {
 264                                 tcpstat.tcps_rcvduppack++;
 265                                 tcpstat.tcps_rcvdupbyte += *tlenp;
 266                                 m_freem(m);
 267                                 free(te, M_TSEGQ);
 268                                 tcp_reass_qsize--;
 269                                 /*
 270                                  * Try to present any queued data
 271                                  * at the left window edge to the user.
 272                                  * This is needed after the 3-WHS
 273                                  * completes.
 274                                  */
 275                                 goto present;   /* ??? */
 276                         }
 277                         m_adj(m, i);
 278                         *tlenp -= i;
 279                         th->th_seq += i;
 280                 }
 281         }
 282         tcpstat.tcps_rcvoopack++;
 283         tcpstat.tcps_rcvoobyte += *tlenp;
 284
 285         /*
 286          * While we overlap succeeding segments trim them or,
 287          * if they are completely covered, dequeue them.
 288          */
 289         while (q) {
 290                 int i = (th->th_seq + *tlenp) - q->tqe_th->th_seq;
 291                 if (i <= 0)
 292                         break;
 293                 if (i < q->tqe_len) {
 294                         q->tqe_th->th_seq += i;
 295                         q->tqe_len -= i;
 296                         m_adj(q->tqe_m, i);
 297                         break;
 298                 }
 299
 300                 nq = LIST_NEXT(q, tqe_q);
 301                 LIST_REMOVE(q, tqe_q);
 302                 m_freem(q->tqe_m);
 303                 free(q, M_TSEGQ);
 304                 tcp_reass_qsize--;
 305                 q = nq;
 306         }
 307
 308         /* Insert the new segment queue entry into place. */
 309         te->tqe_m = m;
 310         te->tqe_th = th;
 311         te->tqe_len = *tlenp;
 312
 313         if (p == NULL) {
 314                 LIST_INSERT_HEAD(&tp->t_segq, te, tqe_q);
 315         } else {
 316                 LIST_INSERT_AFTER(p, te, tqe_q);
 317         }
 318
 319 present:
 320         /*
 321          * Present data to user, advancing rcv_nxt through
 322          * completed sequence space.
 323          */
 324         if (!TCPS_HAVEESTABLISHED(tp->t_state))
 325                 return (0);
 326         q = LIST_FIRST(&tp->t_segq);
 327         if (!q || q->tqe_th->th_seq != tp->rcv_nxt)
 328                 return (0);
 329         do {
 330                 tp->rcv_nxt += q->tqe_len;
 331                 flags = q->tqe_th->th_flags & TH_FIN;
 332                 nq = LIST_NEXT(q, tqe_q);
 333                 LIST_REMOVE(q, tqe_q);
 334                 if (so->so_state & SS_CANTRCVMORE)
 335                         m_freem(q->tqe_m);
 336                 else
 337                         sbappend(&so->so_rcv, q->tqe_m);
 338                 free(q, M_TSEGQ);
 339                 tcp_reass_qsize--;
 340                 q = nq;
 341         } while (q && q->tqe_th->th_seq == tp->rcv_nxt);
 342         ND6_HINT(tp);
 343         sorwakeup(so);
 344         return (flags);
 345 }
 346
 347 /*
 348  * TCP input routine, follows pages 65-76 of the
 349  * protocol specification dated September, 1981 very closely.
 350  */
 351 #ifdef INET6
 352 int
 353 tcp6_input(mp, offp, proto)
 354         struct mbuf **mp;
 355         int *offp, proto;
 356 {
 357         struct mbuf *m = *mp;
 358         struct in6_ifaddr *ia6;
 359
 360         IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
 361
 362         /*
 363          * draft-itojun-ipv6-tcp-to-anycast
 364          * better place to put this in?
 365          */
 366         ia6 = ip6_getdstifaddr(m);
 367         if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
 368                 struct ip6_hdr *ip6;
 369
 370                 ip6 = mtod(m, struct ip6_hdr *);
 371                 icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
 372                             (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
 373                 return IPPROTO_DONE;
 374         }
 375
 376         tcp_input(m, *offp, proto);
 377         return IPPROTO_DONE;
 378 }
 379 #endif
 380
 381 void
 382 tcp_input(m, off0, proto)
 383         struct mbuf *m;
 384         int off0, proto;
 385 {
 386         struct tcphdr *th;
 387         struct ip *ip = NULL;
 388         struct ipovly *ipov;
 389         struct inpcb *inp = NULL;
 390         u_char *optp = NULL;
 391         int optlen = 0;
 392         int len, tlen, off;
 393         int drop_hdrlen;
 394         struct tcpcb *tp = NULL;
 395         int thflags;
 396         struct socket *so = 0;
 397         int todrop, acked, ourfinisacked, needoutput = 0;
 398         u_long tiwin;
 399         struct tcpopt to;               /* options in this segment */
 400         struct rmxp_tao *taop;          /* pointer to our TAO cache entry */
 401         struct rmxp_tao tao_noncached;  /* in case there's no cached entry */
 402         struct sockaddr_in *next_hop = NULL;
 403         int rstreason; /* For badport_bandlim accounting purposes */
 404         int cpu;
 405         struct ip6_hdr *ip6 = NULL;
 406 #ifdef INET6
 407         int isipv6;
 408 #else
 409         const int isipv6 = 0;
 410 #endif
 411 #ifdef TCPDEBUG
 412         short ostate = 0;
 413 #endif
 414
 415         /* Grab info from MT_TAG mbufs prepended to the chain. */
 416         for (;m && m->m_type == MT_TAG; m = m->m_next) {
 417                 if (m->_m_tag_id == PACKET_TAG_IPFORWARD)
 418                         next_hop = (struct sockaddr_in *)m->m_hdr.mh_data;
 419         }
 420 #ifdef INET6
 421         isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
 422 #endif
 423         bzero((char *)&to, sizeof(to));
 424
 425         tcpstat.tcps_rcvtotal++;
 426
 427         if (isipv6) {
 428                 /* IP6_EXTHDR_CHECK() is already done at tcp6_input() */
 429                 ip6 = mtod(m, struct ip6_hdr *);
 430                 tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
 431                 if (in6_cksum(m, IPPROTO_TCP, off0, tlen)) {
 432                         tcpstat.tcps_rcvbadsum++;
 433                         goto drop;
 434                 }
 435                 th = (struct tcphdr *)((caddr_t)ip6 + off0);
 436
 437                 /*
 438                  * Be proactive about unspecified IPv6 address in source.
 439                  * As we use all-zero to indicate unbounded/unconnected pcb,
 440                  * unspecified IPv6 address can be used to confuse us.
 441                  *
 442                  * Note that packets with unspecified IPv6 destination is
 443                  * already dropped in ip6_input.
 444                  */
 445                 if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
 446                         /* XXX stat */
 447                         goto drop;
 448                 }
 449         } else {
 450                 /*
 451                  * Get IP and TCP header together in first mbuf.
 452                  * Note: IP leaves IP header in first mbuf.
 453                  */
 454                 if (off0 > sizeof(struct ip)) {
 455                         ip_stripoptions(m);
 456                         off0 = sizeof(struct ip);
 457                 }
 458                 if (m->m_len < sizeof(struct tcpiphdr)) {
 459                         if ((m = m_pullup(m, sizeof(struct tcpiphdr))) == 0) {
 460                                 tcpstat.tcps_rcvshort++;
 461                                 return;
 462                         }
 463                 }
 464                 ip = mtod(m, struct ip *);
 465                 ipov = (struct ipovly *)ip;
 466                 th = (struct tcphdr *)((caddr_t)ip + off0);
 467                 tlen = ip->ip_len;
 468
 469                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
 470                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
 471                                 th->th_sum = m->m_pkthdr.csum_data;
 472                         else
 473                                 th->th_sum = in_pseudo(ip->ip_src.s_addr,
 474                                                 ip->ip_dst.s_addr,
 475                                                 htonl(m->m_pkthdr.csum_data +
 476                                                         ip->ip_len +
 477                                                         IPPROTO_TCP));
 478                         th->th_sum ^= 0xffff;
 479                 } else {
 480                         /*
 481                          * Checksum extended TCP header and data.
 482                          */
 483                         len = sizeof(struct ip) + tlen;
 484                         bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
 485                         ipov->ih_len = (u_short)tlen;
 486                         ipov->ih_len = htons(ipov->ih_len);
 487                         th->th_sum = in_cksum(m, len);
 488                 }
 489                 if (th->th_sum) {
 490                         tcpstat.tcps_rcvbadsum++;
 491                         goto drop;
 492                 }
 493 #ifdef INET6
 494                 /* Re-initialization for later version check */
 495                 ip->ip_v = IPVERSION;
 496 #endif
 497         }
 498
 499         /*
 500          * Check that TCP offset makes sense,
 501          * pull out TCP options and adjust length.              XXX
 502          */
 503         off = th->th_off << 2;
 504         if (off < sizeof(struct tcphdr) || off > tlen) {
 505                 tcpstat.tcps_rcvbadoff++;
 506                 goto drop;
 507         }
 508         tlen -= off;    /* tlen is used instead of ti->ti_len */
 509         if (off > sizeof(struct tcphdr)) {
 510                 if (isipv6) {
 511                         IP6_EXTHDR_CHECK(m, off0, off, );
 512                         ip6 = mtod(m, struct ip6_hdr *);
 513                         th = (struct tcphdr *)((caddr_t)ip6 + off0);
 514                 } else {
 515                         if (m->m_len < sizeof(struct ip) + off) {
 516                                 if ((m = m_pullup(m, sizeof(struct ip) + off))
 517                                                 == 0) {
 518                                         tcpstat.tcps_rcvshort++;
 519                                         return;
 520                                 }
 521                                 ip = mtod(m, struct ip *);
 522                                 ipov = (struct ipovly *)ip;
 523                                 th = (struct tcphdr *)((caddr_t)ip + off0);
 524                         }
 525                 }
 526                 optlen = off - sizeof(struct tcphdr);
 527                 optp = (u_char *)(th + 1);
 528         }
 529         thflags = th->th_flags;
 530
 531 #ifdef TCP_DROP_SYNFIN
 532         /*
 533          * If the drop_synfin option is enabled, drop all packets with
 534          * both the SYN and FIN bits set. This prevents e.g. nmap from
 535          * identifying the TCP/IP stack.
 536          *
 537          * This is a violation of the TCP specification.
 538          */
 539         if (drop_synfin && (thflags & (TH_SYN|TH_FIN)) == (TH_SYN|TH_FIN))
 540                 goto drop;
 541 #endif
 542
 543         /*
 544          * Convert TCP protocol specific fields to host format.
 545          */
 546         th->th_seq = ntohl(th->th_seq);
 547         th->th_ack = ntohl(th->th_ack);
 548         th->th_win = ntohs(th->th_win);
 549         th->th_urp = ntohs(th->th_urp);
 550
 551         /*
 552          * Delay droping TCP, IP headers, IPv6 ext headers, and TCP options,
 553          * until after ip6_savecontrol() is called and before other functions
 554          * which don't want those proto headers.
 555          * Because ip6_savecontrol() is going to parse the mbuf to
 556          * search for data to be passed up to user-land, it wants mbuf
 557          * parameters to be unchanged.
 558          * XXX: the call of ip6_savecontrol() has been obsoleted based on
 559          * latest version of the advanced API (20020110).
 560          */
 561         drop_hdrlen = off0 + off;
 562
 563         /*
 564          * Locate pcb for segment.
 565          */
 566 findpcb:
 567         /* IPFIREWALL_FORWARD section */
 568         if (next_hop != NULL && isipv6 == 0) {  /* IPv6 support is not yet */
 569                 /*
 570                  * Transparently forwarded. Pretend to be the destination.
 571                  * already got one like this?
 572                  */
 573                 inp = in_pcblookup_hash(&tcbinfo[mycpu->gd_cpuid],
 574                                         ip->ip_src, th->th_sport,
 575                                         ip->ip_dst, th->th_dport,
 576                                         0, m->m_pkthdr.rcvif);
 577                 if (!inp) {
 578                         /* It's new.  Try find the ambushing socket. */
 579                         cpu = tcp_addrcpu(ip->ip_src.s_addr, th->th_sport,
 580                                           next_hop->sin_addr.s_addr,
 581                                           next_hop->sin_port ?
 582                                               ntohs(next_hop->sin_port) :
 583                                               th->th_dport);
 584                         inp = in_pcblookup_hash(&tcbinfo[cpu],
 585                                                 ip->ip_src, th->th_sport,
 586                                                 next_hop->sin_addr,
 587                                                 next_hop->sin_port ?
 588                                                     ntohs(next_hop->sin_port) :
 589                                                     th->th_dport,
 590                                                 1, m->m_pkthdr.rcvif);
 591                 }
 592         } else {
 593                 if (isipv6)
 594                         inp = in6_pcblookup_hash(&tcbinfo[0],
 595                                                  &ip6->ip6_src, th->th_sport,
 596                                                  &ip6->ip6_dst, th->th_dport,
 597                                                  1, m->m_pkthdr.rcvif);
 598                 else
 599                         inp = in_pcblookup_hash(&tcbinfo[mycpu->gd_cpuid],
 600                                                 ip->ip_src, th->th_sport,
 601                                                 ip->ip_dst, th->th_dport,
 602                                                 1, m->m_pkthdr.rcvif);
 603       }
 604
 605 #ifdef IPSEC
 606         if (isipv6) {
 607                 if (inp != NULL && ipsec6_in_reject_so(m, inp->inp_socket)) {
 608                         ipsec6stat.in_polvio++;
 609                         goto drop;
 610                 }
 611         } else {
 612                 if (inp != NULL && ipsec4_in_reject_so(m, inp->inp_socket)) {
 613                         ipsecstat.in_polvio++;
 614                         goto drop;
 615                 }
 616         }
 617 #endif
 618 #ifdef FAST_IPSEC
 619         if (isipv6) {
 620                 if (inp != NULL && ipsec6_in_reject(m, inp)) {
 621                         goto drop;
 622                 }
 623         } else {
 624                 if (inp != NULL && ipsec4_in_reject(m, inp)) {
 625                         goto drop;
 626                 }
 627         }
 628 #endif
 629
 630         /*
 631          * If the state is CLOSED (i.e., TCB does not exist) then
 632          * all data in the incoming segment is discarded.
 633          * If the TCB exists but is in CLOSED state, it is embryonic,
 634          * but should either do a listen or a connect soon.
 635          */
 636         if (inp == NULL) {
 637                 if (log_in_vain) {
 638 #ifdef INET6
 639                         char dbuf[INET6_ADDRSTRLEN+2], sbuf[INET6_ADDRSTRLEN+2];
 640 #else
 641                         char dbuf[4*sizeof "123"], sbuf[4*sizeof "123"];
 642 #endif
 643                         if (isipv6) {
 644                                 strcpy(dbuf, "[");
 645                                 strcpy(sbuf, "[");
 646                                 strcat(dbuf, ip6_sprintf(&ip6->ip6_dst));
 647                                 strcat(sbuf, ip6_sprintf(&ip6->ip6_src));
 648                                 strcat(dbuf, "]");
 649                                 strcat(sbuf, "]");
 650                         } else {
 651                                 strcpy(dbuf, inet_ntoa(ip->ip_dst));
 652                                 strcpy(sbuf, inet_ntoa(ip->ip_src));
 653                         }
 654                         switch (log_in_vain) {
 655                         case 1:
 656                                 if ((thflags & TH_SYN) == 0)
 657                                         break;
 658                         case 2:
 659                                 log(LOG_INFO,
 660                                     "Connection attempt to TCP %s:%d "
 661                                     "from %s:%d flags:0x%02x\n",
 662                                     dbuf, ntohs(th->th_dport), sbuf,
 663                                     ntohs(th->th_sport), thflags);
 664                                 break;
 665                         default:
 666                                 break;
 667                         }
 668                 }
 669                 if (blackhole) {
 670                         switch (blackhole) {
 671                         case 1:
 672                                 if (thflags & TH_SYN)
 673                                         goto drop;
 674                                 break;
 675                         case 2:
 676                                 goto drop;
 677                         default:
 678                                 goto drop;
 679                         }
 680                 }
 681                 rstreason = BANDLIM_RST_CLOSEDPORT;
 682                 goto dropwithreset;
 683         }
 684         tp = intotcpcb(inp);
 685         if (tp == NULL) {
 686                 rstreason = BANDLIM_RST_CLOSEDPORT;
 687                 goto dropwithreset;
 688         }
 689         if (tp->t_state == TCPS_CLOSED)
 690                 goto drop;
 691
 692         /* Unscale the window into a 32-bit value. */
 693         if ((thflags & TH_SYN) == 0)
 694                 tiwin = th->th_win << tp->snd_scale;
 695         else
 696                 tiwin = th->th_win;
 697
 698         so = inp->inp_socket;
 699
 700 #ifdef TCPDEBUG
 701         if (so->so_options & SO_DEBUG) {
 702                 ostate = tp->t_state;
 703                 if (isipv6)
 704                         bcopy((char *)ip6, (char *)tcp_saveipgen, sizeof(*ip6));
 705                 else
 706                         bcopy((char *)ip, (char *)tcp_saveipgen, sizeof(*ip));
 707                 tcp_savetcp = *th;
 708         }
 709 #endif
 710
 711         if (so->so_options & SO_ACCEPTCONN) {
 712                 struct in_conninfo inc;
 713
 714 #ifdef INET6
 715                 inc.inc_isipv6 = isipv6;
 716 #endif
 717                 if (isipv6) {
 718                         inc.inc6_faddr = ip6->ip6_src;
 719                         inc.inc6_laddr = ip6->ip6_dst;
 720                         inc.inc6_route.ro_rt = NULL;            /* XXX */
 721                 } else {
 722                         inc.inc_faddr = ip->ip_src;
 723                         inc.inc_laddr = ip->ip_dst;
 724                         inc.inc_route.ro_rt = NULL;             /* XXX */
 725                 }
 726                 inc.inc_fport = th->th_sport;
 727                 inc.inc_lport = th->th_dport;
 728
 729                 /*
 730                  * If the state is LISTEN then ignore segment if it contains
 731                  * a RST.  If the segment contains an ACK then it is bad and
 732                  * send a RST.  If it does not contain a SYN then it is not
 733                  * interesting; drop it.
 734                  *
 735                  * If the state is SYN_RECEIVED (syncache) and seg contains
 736                  * an ACK, but not for our SYN/ACK, send a RST.  If the seg
 737                  * contains a RST, check the sequence number to see if it
 738                  * is a valid reset segment.
 739                  */
 740                 if ((thflags & (TH_RST|TH_ACK|TH_SYN)) != TH_SYN) {
 741                         if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
 742                                 if (!syncache_expand(&inc, th, &so, m)) {
 743                                         /*
 744                                          * No syncache entry, or ACK was not
 745                                          * for our SYN/ACK.  Send a RST.
 746                                          */
 747                                         tcpstat.tcps_badsyn++;
 748                                         rstreason = BANDLIM_RST_OPENPORT;
 749                                         goto dropwithreset;
 750                                 }
 751                                 if (so == NULL)
 752                                         /*
 753                                          * Could not complete 3-way handshake,
 754                                          * connection is being closed down, and
 755                                          * syncache will free mbuf.
 756                                          */
 757                                         return;
 758                                 /*
 759                                  * Socket is created in state SYN_RECEIVED.
 760                                  * Continue processing segment.
 761                                  */
 762                                 inp = sotoinpcb(so);
 763                                 tp = intotcpcb(inp);
 764                                 /*
 765                                  * This is what would have happened in
 766                                  * tcp_output() when the SYN,ACK was sent.
 767                                  */
 768                                 tp->snd_up = tp->snd_una;
 769                                 tp->snd_max = tp->snd_nxt = tp->iss + 1;
 770                                 tp->last_ack_sent = tp->rcv_nxt;
 771 /*
 772  * XXX possible bug - it doesn't appear that tp->snd_wnd is unscaled
 773  * until the _second_ ACK is received:
 774  *    rcv SYN (set wscale opts)  --> send SYN/ACK, set snd_wnd = window.
 775  *    rcv ACK, calculate tiwin --> process SYN_RECEIVED, determine wscale,
 776  *        move to ESTAB, set snd_wnd to tiwin.
 777  */
 778                                 tp->snd_wnd = tiwin;    /* unscaled */
 779                                 goto after_listen;
 780                         }
 781                         if (thflags & TH_RST) {
 782                                 syncache_chkrst(&inc, th);
 783                                 goto drop;
 784                         }
 785                         if (thflags & TH_ACK) {
 786                                 syncache_badack(&inc);
 787                                 tcpstat.tcps_badsyn++;
 788                                 rstreason = BANDLIM_RST_OPENPORT;
 789                                 goto dropwithreset;
 790                         }
 791                         goto drop;
 792                 }
 793
 794                 /*
 795                  * Segment's flags are (SYN) or (SYN|FIN).
 796                  */
 797 #ifdef INET6
 798                 /*
 799                  * If deprecated address is forbidden,
 800                  * we do not accept SYN to deprecated interface
 801                  * address to prevent any new inbound connection from
 802                  * getting established.
 803                  * When we do not accept SYN, we send a TCP RST,
 804                  * with deprecated source address (instead of dropping
 805                  * it).  We compromise it as it is much better for peer
 806                  * to send a RST, and RST will be the final packet
 807                  * for the exchange.
 808                  *
 809                  * If we do not forbid deprecated addresses, we accept
 810                  * the SYN packet.  RFC2462 does not suggest dropping
 811                  * SYN in this case.
 812                  * If we decipher RFC2462 5.5.4, it says like this:
 813                  * 1. use of deprecated addr with existing
 814                  *    communication is okay - "SHOULD continue to be
 815                  *    used"
 816                  * 2. use of it with new communication:
 817                  *   (2a) "SHOULD NOT be used if alternate address
 818                  *        with sufficient scope is available"
 819                  *   (2b) nothing mentioned otherwise.
 820                  * Here we fall into (2b) case as we have no choice in
 821                  * our source address selection - we must obey the peer.
 822                  *
 823                  * The wording in RFC2462 is confusing, and there are
 824                  * multiple description text for deprecated address
 825                  * handling - worse, they are not exactly the same.
 826                  * I believe 5.5.4 is the best one, so we follow 5.5.4.
 827                  */
 828                 if (isipv6 && !ip6_use_deprecated) {
 829                         struct in6_ifaddr *ia6;
 830
 831                         if ((ia6 = ip6_getdstifaddr(m)) &&
 832                             (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
 833                                 tp = NULL;
 834                                 rstreason = BANDLIM_RST_OPENPORT;
 835                                 goto dropwithreset;
 836                         }
 837                 }
 838 #endif
 839                 /*
 840                  * If it is from this socket, drop it, it must be forged.
 841                  * Don't bother responding if the destination was a broadcast.
 842                  */
 843                 if (th->th_dport == th->th_sport) {
 844                         if (isipv6) {
 845                                 if (IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst,
 846                                                        &ip6->ip6_src))
 847                                         goto drop;
 848                         } else {
 849                                 if (ip->ip_dst.s_addr == ip->ip_src.s_addr)
 850                                         goto drop;
 851                         }
 852                 }
 853                 /*
 854                  * RFC1122 4.2.3.10, p. 104: discard bcast/mcast SYN
 855                  *
 856                  * Note that it is quite possible to receive unicast
 857                  * link-layer packets with a broadcast IP address. Use
 858                  * in_broadcast() to find them.
 859                  */
 860                 if (m->m_flags & (M_BCAST|M_MCAST))
 861                         goto drop;
 862                 if (isipv6) {
 863                         if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
 864                             IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
 865                                 goto drop;
 866                 } else {
 867                         if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
 868                             IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
 869                             ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
 870                             in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
 871                                 goto drop;
 872                 }
 873                 /*
 874                  * SYN appears to be valid; create compressed TCP state
 875                  * for syncache, or perform t/tcp connection.
 876                  */
 877                 if (so->so_qlen <= so->so_qlimit) {
 878                         tcp_dooptions(&to, optp, optlen, 1);
 879                         if (!syncache_add(&inc, &to, th, &so, m))
 880                                 goto drop;
 881                         if (so == NULL)
 882                                 /*
 883                                  * Entry added to syncache, mbuf used to
 884                                  * send SYN,ACK packet.
 885                                  */
 886                                 return;
 887                         /*
 888                          * Segment passed TAO tests.
 889                          */
 890                         inp = sotoinpcb(so);
 891                         tp = intotcpcb(inp);
 892                         tp->snd_wnd = tiwin;
 893                         tp->t_starttime = ticks;
 894                         tp->t_state = TCPS_ESTABLISHED;
 895
 896                         /*
 897                          * If there is a FIN, or if there is data and the
 898                          * connection is local, then delay SYN,ACK(SYN) in
 899                          * the hope of piggy-backing it on a response
 900                          * segment.  Otherwise must send ACK now in case
 901                          * the other side is slow starting.
 902                          */
 903                         if (DELAY_ACK(tp) &&
 904                             ((thflags & TH_FIN) ||
 905                              (tlen != 0 &&
 906                               ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
 907                                (!isipv6 && in_localaddr(inp->inp_faddr)))))) {
 908                                 callout_reset(tp->tt_delack, tcp_delacktime,
 909                                                 tcp_timer_delack, tp);
 910                                 tp->t_flags |= TF_NEEDSYN;
 911                         } else
 912                                 tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
 913
 914                         tcpstat.tcps_connects++;
 915                         soisconnected(so);
 916                         goto trimthenstep6;
 917                 }
 918                 goto drop;
 919         }
 920 after_listen:
 921
 922 /* XXX temp debugging */
 923         /* should not happen - syncache should pick up these connections */
 924         if (tp->t_state == TCPS_LISTEN)
 925                 panic("tcp_input: TCPS_LISTEN");
 926
 927         /*
 928          * Segment received on connection.
 929          * Reset idle time and keep-alive timer.
 930          */
 931         tp->t_rcvtime = ticks;
 932         if (TCPS_HAVEESTABLISHED(tp->t_state))
 933                 callout_reset(tp->tt_keep, tcp_keepidle, tcp_timer_keep, tp);
 934
 935         /*
 936          * Process options.
 937          * XXX this is tradtitional behavior, may need to be cleaned up.
 938          */
 939         tcp_dooptions(&to, optp, optlen, thflags & TH_SYN);
 940         if (thflags & TH_SYN) {
 941                 if (to.to_flags & TOF_SCALE) {
 942                         tp->t_flags |= TF_RCVD_SCALE;
 943                         tp->requested_s_scale = to.to_requested_s_scale;
 944                 }
 945                 if (to.to_flags & TOF_TS) {
 946                         tp->t_flags |= TF_RCVD_TSTMP;
 947                         tp->ts_recent = to.to_tsval;
 948                         tp->ts_recent_age = ticks;
 949                 }
 950                 if (to.to_flags & (TOF_CC|TOF_CCNEW))
 951                         tp->t_flags |= TF_RCVD_CC;
 952                 if (to.to_flags & TOF_MSS)
 953                         tcp_mss(tp, to.to_mss);
 954         }
 955
 956         /*
 957          * Header prediction: check for the two common cases
 958          * of a uni-directional data xfer.  If the packet has
 959          * no control flags, is in-sequence, the window didn't
 960          * change and we're not retransmitting, it's a
 961          * candidate.  If the length is zero and the ack moved
 962          * forward, we're the sender side of the xfer.  Just
 963          * free the data acked & wake any higher level process
 964          * that was blocked waiting for space.  If the length
 965          * is non-zero and the ack didn't move, we're the
 966          * receiver side.  If we're getting packets in-order
 967          * (the reassembly queue is empty), add the data to
 968          * the socket buffer and note that we need a delayed ack.
 969          * Make sure that the hidden state-flags are also off.
 970          * Since we check for TCPS_ESTABLISHED above, it can only
 971          * be TH_NEEDSYN.
 972          */
 973         if (tp->t_state == TCPS_ESTABLISHED &&
 974             (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
 975             ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
 976             ((to.to_flags & TOF_TS) == 0 ||
 977              TSTMP_GEQ(to.to_tsval, tp->ts_recent)) &&
 978             /*
 979              * Using the CC option is compulsory if once started:
 980              *   the segment is OK if no T/TCP was negotiated or
 981              *   if the segment has a CC option equal to CCrecv
 982              */
 983             ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) != (TF_REQ_CC|TF_RCVD_CC) ||
 984              ((to.to_flags & TOF_CC) != 0 && to.to_cc == tp->cc_recv)) &&
 985             th->th_seq == tp->rcv_nxt &&
 986             tiwin && tiwin == tp->snd_wnd &&
 987             tp->snd_nxt == tp->snd_max) {
 988
 989                 /*
 990                  * If last ACK falls within this segment's sequence numbers,
 991                  * record the timestamp.
 992                  * NOTE that the test is modified according to the latest
 993                  * proposal of the tcplw@cray.com list (Braden 1993/04/26).
 994                  */
 995                 if ((to.to_flags & TOF_TS) != 0 &&
 996                     SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
 997                         tp->ts_recent_age = ticks;
 998                         tp->ts_recent = to.to_tsval;
 999                 }
1000
1001                 if (tlen == 0) {
1002                         if (SEQ_GT(th->th_ack, tp->snd_una) &&
1003                             SEQ_LEQ(th->th_ack, tp->snd_max) &&
1004                             tp->snd_cwnd >= tp->snd_wnd &&
1005                             ((!tcp_do_newreno &&
1006                               tp->t_dupacks < tcprexmtthresh) ||
1007                              (tcp_do_newreno && !IN_FASTRECOVERY(tp)))) {
1008                                 /*
1009                                  * this is a pure ack for outstanding data.
1010                                  */
1011                                 ++tcpstat.tcps_predack;
1012                                 /*
1013                                  * "bad retransmit" recovery
1014                                  *
1015                                  * If Eifel detection applies, then
1016                                  * it is deterministic, so use it
1017                                  * unconditionally over the old heuristic.
1018                                  * Otherwise, fall back to the old heuristic.
1019                                  */
1020                                 if (tcp_do_eifel_detect &&
1021                                     (to.to_flags & TOF_TS) && to.to_tsecr &&
1022                                     (tp->t_flags & TF_FIRSTACCACK)) {
1023                                         /* Eifel detection applicable. */
1024                                         if (to.to_tsecr < tp->t_rexmtTS) {
1025                                                 tcp_revert_congestion_state(tp);
1026                                                 ++tcpstat.tcps_eifeldetected;
1027                                         }
1028                                 } else if (tp->t_rxtshift == 1 &&
1029                                            ticks < tp->t_badrxtwin) {
1030                                         tcp_revert_congestion_state(tp);
1031                                         ++tcpstat.tcps_rttdetected;
1032                                 }
1033                                 tp->t_flags &= ~(TF_FIRSTACCACK |
1034                                                  TF_FASTREXMT | TF_EARLYREXMT);
1035                                 /*
1036                                  * Recalculate the retransmit timer / rtt.
1037                                  *
1038                                  * Some machines (certain windows boxes)
1039                                  * send broken timestamp replies during the
1040                                  * SYN+ACK phase, ignore timestamps of 0.
1041                                  */
1042                                 if ((to.to_flags & TOF_TS) != 0 &&
1043                                     to.to_tsecr) {
1044                                         tcp_xmit_timer(tp,
1045                                             ticks - to.to_tsecr + 1);
1046                                 } else if (tp->t_rtttime &&
1047                                             SEQ_GT(th->th_ack, tp->t_rtseq)) {
1048                                         tcp_xmit_timer(tp,
1049                                                        ticks - tp->t_rtttime);
1050                                 }
1051                                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
1052                                 acked = th->th_ack - tp->snd_una;
1053                                 tcpstat.tcps_rcvackpack++;
1054                                 tcpstat.tcps_rcvackbyte += acked;
1055                                 sbdrop(&so->so_snd, acked);
1056                                 if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
1057                                     SEQ_LEQ(th->th_ack, tp->snd_recover))
1058                                         tp->snd_recover = th->th_ack - 1;
1059                                 tp->snd_una = th->th_ack;
1060                                 tp->t_dupacks = 0;
1061                                 m_freem(m);
1062                                 ND6_HINT(tp); /* some progress has been done */
1063
1064                                 /*
1065                                  * If all outstanding data are acked, stop
1066                                  * retransmit timer, otherwise restart timer
1067                                  * using current (possibly backed-off) value.
1068                                  * If process is waiting for space,
1069                                  * wakeup/selwakeup/signal.  If data
1070                                  * are ready to send, let tcp_output
1071                                  * decide between more output or persist.
1072                                  */
1073                                 if (tp->snd_una == tp->snd_max)
1074                                         callout_stop(tp->tt_rexmt);
1075                                 else if (!callout_active(tp->tt_persist))
1076                                         callout_reset(tp->tt_rexmt,
1077                                                       tp->t_rxtcur,
1078                                                       tcp_timer_rexmt, tp);
1079
1080                                 sowwakeup(so);
1081                                 if (so->so_snd.sb_cc)
1082                                         (void) tcp_output(tp);
1083                                 return;
1084                         }
1085                 } else if (th->th_ack == tp->snd_una &&
1086                     LIST_EMPTY(&tp->t_segq) &&
1087                     tlen <= sbspace(&so->so_rcv)) {
1088                         /*
1089                          * this is a pure, in-sequence data packet
1090                          * with nothing on the reassembly queue and
1091                          * we have enough buffer space to take it.
1092                          */
1093                         ++tcpstat.tcps_preddat;
1094                         tp->rcv_nxt += tlen;
1095                         tcpstat.tcps_rcvpack++;
1096                         tcpstat.tcps_rcvbyte += tlen;
1097                         ND6_HINT(tp);   /* some progress has been done */
1098                         /*
1099                          * Add data to socket buffer.
1100                          */
1101                         if (so->so_state & SS_CANTRCVMORE) {
1102                                 m_freem(m);
1103                         } else {
1104                                 m_adj(m, drop_hdrlen);  /* delayed header drop */
1105                                 sbappend(&so->so_rcv, m);
1106                         }
1107                         sorwakeup(so);
1108                         if (DELAY_ACK(tp)) {
1109                                 callout_reset(tp->tt_delack, tcp_delacktime,
1110                                     tcp_timer_delack, tp);
1111                         } else {
1112                                 tp->t_flags |= TF_ACKNOW;
1113                                 tcp_output(tp);
1114                         }
1115                         return;
1116                 }
1117         }
1118
1119         /*
1120          * Calculate amount of space in receive window,
1121          * and then do TCP input processing.
1122          * Receive window is amount of space in rcv queue,
1123          * but not less than advertised window.
1124          */
1125         { int win;
1126
1127         win = sbspace(&so->so_rcv);
1128         if (win < 0)
1129                 win = 0;
1130         tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
1131         }
1132
1133         switch (tp->t_state) {
1134
1135         /*
1136          * If the state is SYN_RECEIVED:
1137          *      if seg contains an ACK, but not for our SYN/ACK, send a RST.
1138          */
1139         case TCPS_SYN_RECEIVED:
1140                 if ((thflags & TH_ACK) &&
1141                     (SEQ_LEQ(th->th_ack, tp->snd_una) ||
1142                      SEQ_GT(th->th_ack, tp->snd_max))) {
1143                                 rstreason = BANDLIM_RST_OPENPORT;
1144                                 goto dropwithreset;
1145                 }
1146                 break;
1147
1148         /*
1149          * If the state is SYN_SENT:
1150          *      if seg contains an ACK, but not for our SYN, drop the input.
1151          *      if seg contains a RST, then drop the connection.
1152          *      if seg does not contain SYN, then drop it.
1153          * Otherwise this is an acceptable SYN segment
1154          *      initialize tp->rcv_nxt and tp->irs
1155          *      if seg contains ack then advance tp->snd_una
1156          *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
1157          *      arrange for segment to be acked (eventually)
1158          *      continue processing rest of data/controls, beginning with URG
1159          */
1160         case TCPS_SYN_SENT:
1161                 if ((taop = tcp_gettaocache(&inp->inp_inc)) == NULL) {
1162                         taop = &tao_noncached;
1163                         bzero(taop, sizeof(*taop));
1164                 }
1165
1166                 if ((thflags & TH_ACK) &&
1167                     (SEQ_LEQ(th->th_ack, tp->iss) ||
1168                      SEQ_GT(th->th_ack, tp->snd_max))) {
1169                         /*
1170                          * If we have a cached CCsent for the remote host,
1171                          * hence we haven't just crashed and restarted,
1172                          * do not send a RST.  This may be a retransmission
1173                          * from the other side after our earlier ACK was lost.
1174                          * Our new SYN, when it arrives, will serve as the
1175                          * needed ACK.
1176                          */
1177                         if (taop->tao_ccsent != 0)
1178                                 goto drop;
1179                         else {
1180                                 rstreason = BANDLIM_UNLIMITED;
1181                                 goto dropwithreset;
1182                         }
1183                 }
1184                 if (thflags & TH_RST) {
1185                         if (thflags & TH_ACK)
1186                                 tp = tcp_drop(tp, ECONNREFUSED);
1187                         goto drop;
1188                 }
1189                 if ((thflags & TH_SYN) == 0)
1190                         goto drop;
1191                 tp->snd_wnd = th->th_win;       /* initial send window */
1192                 tp->cc_recv = to.to_cc;         /* foreign CC */
1193
1194                 tp->irs = th->th_seq;
1195                 tcp_rcvseqinit(tp);
1196                 if (thflags & TH_ACK) {
1197                         /*
1198                          * Our SYN was acked.  If segment contains CC.ECHO
1199                          * option, check it to make sure this segment really
1200                          * matches our SYN.  If not, just drop it as old
1201                          * duplicate, but send an RST if we're still playing
1202                          * by the old rules.  If no CC.ECHO option, make sure
1203                          * we don't get fooled into using T/TCP.
1204                          */
1205                         if (to.to_flags & TOF_CCECHO) {
1206                                 if (tp->cc_send != to.to_ccecho) {
1207                                         if (taop->tao_ccsent != 0)
1208                                                 goto drop;
1209                                         else {
1210                                                 rstreason = BANDLIM_UNLIMITED;
1211                                                 goto dropwithreset;
1212                                         }
1213                                 }
1214                         } else
1215                                 tp->t_flags &= ~TF_RCVD_CC;
1216                         tcpstat.tcps_connects++;
1217                         soisconnected(so);
1218                         /* Do window scaling on this connection? */
1219                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1220                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1221                                 tp->snd_scale = tp->requested_s_scale;
1222                                 tp->rcv_scale = tp->request_r_scale;
1223                         }
1224                         /* Segment is acceptable, update cache if undefined. */
1225                         if (taop->tao_ccsent == 0)
1226                                 taop->tao_ccsent = to.to_ccecho;
1227
1228                         tp->rcv_adv += tp->rcv_wnd;
1229                         tp->snd_una++;          /* SYN is acked */
1230                         /*
1231                          * If there's data, delay ACK; if there's also a FIN
1232                          * ACKNOW will be turned on later.
1233                          */
1234                         if (DELAY_ACK(tp) && tlen != 0)
1235                                 callout_reset(tp->tt_delack, tcp_delacktime,
1236                                     tcp_timer_delack, tp);
1237                         else
1238                                 tp->t_flags |= TF_ACKNOW;
1239                         /*
1240                          * Received <SYN,ACK> in SYN_SENT[*] state.
1241                          * Transitions:
1242                          *      SYN_SENT  --> ESTABLISHED
1243                          *      SYN_SENT* --> FIN_WAIT_1
1244                          */
1245                         tp->t_starttime = ticks;
1246                         if (tp->t_flags & TF_NEEDFIN) {
1247                                 tp->t_state = TCPS_FIN_WAIT_1;
1248                                 tp->t_flags &= ~TF_NEEDFIN;
1249                                 thflags &= ~TH_SYN;
1250                         } else {
1251                                 tp->t_state = TCPS_ESTABLISHED;
1252                                 callout_reset(tp->tt_keep, tcp_keepidle,
1253                                               tcp_timer_keep, tp);
1254                         }
1255                 } else {
1256                         /*
1257                          * Received initial SYN in SYN-SENT[*] state =>
1258                          * simultaneous open.  If segment contains CC option
1259                          * and there is a cached CC, apply TAO test.
1260                          * If it succeeds, connection is * half-synchronized.
1261                          * Otherwise, do 3-way handshake:
1262                          *        SYN-SENT -> SYN-RECEIVED
1263                          *        SYN-SENT* -> SYN-RECEIVED*
1264                          * If there was no CC option, clear cached CC value.
1265                          */
1266                         tp->t_flags |= TF_ACKNOW;
1267                         callout_stop(tp->tt_rexmt);
1268                         if (to.to_flags & TOF_CC) {
1269                                 if (taop->tao_cc != 0 &&
1270                                     CC_GT(to.to_cc, taop->tao_cc)) {
1271                                         /*
1272                                          * update cache and make transition:
1273                                          *        SYN-SENT -> ESTABLISHED*
1274                                          *        SYN-SENT* -> FIN-WAIT-1*
1275                                          */
1276                                         taop->tao_cc = to.to_cc;
1277                                         tp->t_starttime = ticks;
1278                                         if (tp->t_flags & TF_NEEDFIN) {
1279                                                 tp->t_state = TCPS_FIN_WAIT_1;
1280                                                 tp->t_flags &= ~TF_NEEDFIN;
1281                                         } else {
1282                                                 tp->t_state = TCPS_ESTABLISHED;
1283                                                 callout_reset(tp->tt_keep,
1284                                                               tcp_keepidle,
1285                                                               tcp_timer_keep,
1286                                                               tp);
1287                                         }
1288                                         tp->t_flags |= TF_NEEDSYN;
1289                                 } else
1290                                         tp->t_state = TCPS_SYN_RECEIVED;
1291                         } else {
1292                                 /* CC.NEW or no option => invalidate cache */
1293                                 taop->tao_cc = 0;
1294                                 tp->t_state = TCPS_SYN_RECEIVED;
1295                         }
1296                 }
1297
1298 trimthenstep6:
1299                 /*
1300                  * Advance th->th_seq to correspond to first data byte.
1301                  * If data, trim to stay within window,
1302                  * dropping FIN if necessary.
1303                  */
1304                 th->th_seq++;
1305                 if (tlen > tp->rcv_wnd) {
1306                         todrop = tlen - tp->rcv_wnd;
1307                         m_adj(m, -todrop);
1308                         tlen = tp->rcv_wnd;
1309                         thflags &= ~TH_FIN;
1310                         tcpstat.tcps_rcvpackafterwin++;
1311                         tcpstat.tcps_rcvbyteafterwin += todrop;
1312                 }
1313                 tp->snd_wl1 = th->th_seq - 1;
1314                 tp->rcv_up = th->th_seq;
1315                 /*
1316                  * Client side of transaction: already sent SYN and data.
1317                  * If the remote host used T/TCP to validate the SYN,
1318                  * our data will be ACK'd; if so, enter normal data segment
1319                  * processing in the middle of step 5, ack processing.
1320                  * Otherwise, goto step 6.
1321                  */
1322                 if (thflags & TH_ACK)
1323                         goto process_ACK;
1324
1325                 goto step6;
1326
1327         /*
1328          * If the state is LAST_ACK or CLOSING or TIME_WAIT:
1329          *      if segment contains a SYN and CC [not CC.NEW] option:
1330          *              if state == TIME_WAIT and connection duration > MSL,
1331          *                  drop packet and send RST;
1332          *
1333          *              if SEG.CC > CCrecv then is new SYN, and can implicitly
1334          *                  ack the FIN (and data) in retransmission queue.
1335          *                  Complete close and delete TCPCB.  Then reprocess
1336          *                  segment, hoping to find new TCPCB in LISTEN state;
1337          *
1338          *              else must be old SYN; drop it.
1339          *      else do normal processing.
1340          */
1341         case TCPS_LAST_ACK:
1342         case TCPS_CLOSING:
1343         case TCPS_TIME_WAIT:
1344                 if ((thflags & TH_SYN) &&
1345                     (to.to_flags & TOF_CC) && tp->cc_recv != 0) {
1346                         if (tp->t_state == TCPS_TIME_WAIT &&
1347                                         (ticks - tp->t_starttime) > tcp_msl) {
1348                                 rstreason = BANDLIM_UNLIMITED;
1349                                 goto dropwithreset;
1350                         }
1351                         if (CC_GT(to.to_cc, tp->cc_recv)) {
1352                                 tp = tcp_close(tp);
1353                                 goto findpcb;
1354                         }
1355                         else
1356                                 goto drop;
1357                 }
1358                 break;  /* continue normal processing */
1359         }
1360
1361         /*
1362          * States other than LISTEN or SYN_SENT.
1363          * First check the RST flag and sequence number since reset segments
1364          * are exempt from the timestamp and connection count tests.  This
1365          * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
1366          * below which allowed reset segments in half the sequence space
1367          * to fall though and be processed (which gives forged reset
1368          * segments with a random sequence number a 50 percent chance of
1369          * killing a connection).
1370          * Then check timestamp, if present.
1371          * Then check the connection count, if present.
1372          * Then check that at least some bytes of segment are within
1373          * receive window.  If segment begins before rcv_nxt,
1374          * drop leading data (and SYN); if nothing left, just ack.
1375          *
1376          *
1377          * If the RST bit is set, check the sequence number to see
1378          * if this is a valid reset segment.
1379          * RFC 793 page 37:
1380          *   In all states except SYN-SENT, all reset (RST) segments
1381          *   are validated by checking their SEQ-fields.  A reset is
1382          *   valid if its sequence number is in the window.
1383          * Note: this does not take into account delayed ACKs, so
1384          *   we should test against last_ack_sent instead of rcv_nxt.
1385          *   The sequence number in the reset segment is normally an
1386          *   echo of our outgoing acknowlegement numbers, but some hosts
1387          *   send a reset with the sequence number at the rightmost edge
1388          *   of our receive window, and we have to handle this case.
1389          * If we have multiple segments in flight, the intial reset
1390          * segment sequence numbers will be to the left of last_ack_sent,
1391          * but they will eventually catch up.
1392          * In any case, it never made sense to trim reset segments to
1393          * fit the receive window since RFC 1122 says:
1394          *   4.2.2.12  RST Segment: RFC-793 Section 3.4
1395          *
1396          *    A TCP SHOULD allow a received RST segment to include data.
1397          *
1398          *    DISCUSSION
1399          *         It has been suggested that a RST segment could contain
1400          *         ASCII text that encoded and explained the cause of the
1401          *         RST.  No standard has yet been established for such
1402          *         data.
1403          *
1404          * If the reset segment passes the sequence number test examine
1405          * the state:
1406          *    SYN_RECEIVED STATE:
1407          *      If passive open, return to LISTEN state.
1408          *      If active open, inform user that connection was refused.
1409          *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, CLOSE_WAIT STATES:
1410          *      Inform user that connection was reset, and close tcb.
1411          *    CLOSING, LAST_ACK STATES:
1412          *      Close the tcb.
1413          *    TIME_WAIT STATE:
1414          *      Drop the segment - see Stevens, vol. 2, p. 964 and
1415          *      RFC 1337.
1416          */
1417         if (thflags & TH_RST) {
1418                 if (SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
1419                     SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
1420                         switch (tp->t_state) {
1421
1422                         case TCPS_SYN_RECEIVED:
1423                                 so->so_error = ECONNREFUSED;
1424                                 goto close;
1425
1426                         case TCPS_ESTABLISHED:
1427                         case TCPS_FIN_WAIT_1:
1428                         case TCPS_FIN_WAIT_2:
1429                         case TCPS_CLOSE_WAIT:
1430                                 so->so_error = ECONNRESET;
1431                         close:
1432                                 tp->t_state = TCPS_CLOSED;
1433                                 tcpstat.tcps_drops++;
1434                                 tp = tcp_close(tp);
1435                                 break;
1436
1437                         case TCPS_CLOSING:
1438                         case TCPS_LAST_ACK:
1439                                 tp = tcp_close(tp);
1440                                 break;
1441
1442                         case TCPS_TIME_WAIT:
1443                                 break;
1444                         }
1445                 }
1446                 goto drop;
1447         }
1448
1449         /*
1450          * RFC 1323 PAWS: If we have a timestamp reply on this segment
1451          * and it's less than ts_recent, drop it.
1452          */
1453         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
1454             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
1455
1456                 /* Check to see if ts_recent is over 24 days old.  */
1457                 if ((int)(ticks - tp->ts_recent_age) > TCP_PAWS_IDLE) {
1458                         /*
1459                          * Invalidate ts_recent.  If this segment updates
1460                          * ts_recent, the age will be reset later and ts_recent
1461                          * will get a valid value.  If it does not, setting
1462                          * ts_recent to zero will at least satisfy the
1463                          * requirement that zero be placed in the timestamp
1464                          * echo reply when ts_recent isn't valid.  The
1465                          * age isn't reset until we get a valid ts_recent
1466                          * because we don't want out-of-order segments to be
1467                          * dropped when ts_recent is old.
1468                          */
1469                         tp->ts_recent = 0;
1470                 } else {
1471                         tcpstat.tcps_rcvduppack++;
1472                         tcpstat.tcps_rcvdupbyte += tlen;
1473                         tcpstat.tcps_pawsdrop++;
1474                         if (tlen)
1475                                 goto dropafterack;
1476                         goto drop;
1477                 }
1478         }
1479
1480         /*
1481          * T/TCP mechanism
1482          *   If T/TCP was negotiated and the segment doesn't have CC,
1483          *   or if its CC is wrong then drop the segment.
1484          *   RST segments do not have to comply with this.
1485          */
1486         if ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) == (TF_REQ_CC|TF_RCVD_CC) &&
1487             ((to.to_flags & TOF_CC) == 0 || tp->cc_recv != to.to_cc))
1488                 goto dropafterack;
1489
1490         /*
1491          * In the SYN-RECEIVED state, validate that the packet belongs to
1492          * this connection before trimming the data to fit the receive
1493          * window.  Check the sequence number versus IRS since we know
1494          * the sequence numbers haven't wrapped.  This is a partial fix
1495          * for the "LAND" DoS attack.
1496          */
1497         if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
1498                 rstreason = BANDLIM_RST_OPENPORT;
1499                 goto dropwithreset;
1500         }
1501
1502         todrop = tp->rcv_nxt - th->th_seq;
1503         if (todrop > 0) {
1504                 if (thflags & TH_SYN) {
1505                         thflags &= ~TH_SYN;
1506                         th->th_seq++;
1507                         if (th->th_urp > 1)
1508                                 th->th_urp--;
1509                         else
1510                                 thflags &= ~TH_URG;
1511                         todrop--;
1512                 }
1513                 /*
1514                  * Following if statement from Stevens, vol. 2, p. 960.
1515                  */
1516                 if (todrop > tlen
1517                     || (todrop == tlen && (thflags & TH_FIN) == 0)) {
1518                         /*
1519                          * Any valid FIN must be to the left of the window.
1520                          * At this point the FIN must be a duplicate or out
1521                          * of sequence; drop it.
1522                          */
1523                         thflags &= ~TH_FIN;
1524
1525                         /*
1526                          * Send an ACK to resynchronize and drop any data.
1527                          * But keep on processing for RST or ACK.
1528                          */
1529                         tp->t_flags |= TF_ACKNOW;
1530                         todrop = tlen;
1531                         tcpstat.tcps_rcvduppack++;
1532                         tcpstat.tcps_rcvdupbyte += todrop;
1533                 } else {
1534                         tcpstat.tcps_rcvpartduppack++;
1535                         tcpstat.tcps_rcvpartdupbyte += todrop;
1536                 }
1537                 drop_hdrlen += todrop;  /* drop from the top afterwards */
1538                 th->th_seq += todrop;
1539                 tlen -= todrop;
1540                 if (th->th_urp > todrop)
1541                         th->th_urp -= todrop;
1542                 else {
1543                         thflags &= ~TH_URG;
1544                         th->th_urp = 0;
1545                 }
1546         }
1547
1548         /*
1549          * If new data are received on a connection after the
1550          * user processes are gone, then RST the other end.
1551          */
1552         if ((so->so_state & SS_NOFDREF) &&
1553             tp->t_state > TCPS_CLOSE_WAIT && tlen) {
1554                 tp = tcp_close(tp);
1555                 tcpstat.tcps_rcvafterclose++;
1556                 rstreason = BANDLIM_UNLIMITED;
1557                 goto dropwithreset;
1558         }
1559
1560         /*
1561          * If segment ends after window, drop trailing data
1562          * (and PUSH and FIN); if nothing left, just ACK.
1563          */
1564         todrop = (th->th_seq+tlen) - (tp->rcv_nxt+tp->rcv_wnd);
1565         if (todrop > 0) {
1566                 tcpstat.tcps_rcvpackafterwin++;
1567                 if (todrop >= tlen) {
1568                         tcpstat.tcps_rcvbyteafterwin += tlen;
1569                         /*
1570                          * If a new connection request is received
1571                          * while in TIME_WAIT, drop the old connection
1572                          * and start over if the sequence numbers
1573                          * are above the previous ones.
1574                          */
1575                         if (thflags & TH_SYN &&
1576                             tp->t_state == TCPS_TIME_WAIT &&
1577                             SEQ_GT(th->th_seq, tp->rcv_nxt)) {
1578                                 tp = tcp_close(tp);
1579                                 goto findpcb;
1580                         }
1581                         /*
1582                          * If window is closed can only take segments at
1583                          * window edge, and have to drop data and PUSH from
1584                          * incoming segments.  Continue processing, but
1585                          * remember to ack.  Otherwise, drop segment
1586                          * and ack.
1587                          */
1588                         if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
1589                                 tp->t_flags |= TF_ACKNOW;
1590                                 tcpstat.tcps_rcvwinprobe++;
1591                         } else
1592                                 goto dropafterack;
1593                 } else
1594                         tcpstat.tcps_rcvbyteafterwin += todrop;
1595                 m_adj(m, -todrop);
1596                 tlen -= todrop;
1597                 thflags &= ~(TH_PUSH|TH_FIN);
1598         }
1599
1600         /*
1601          * If last ACK falls within this segment's sequence numbers,
1602          * record its timestamp.
1603          * NOTE that the test is modified according to the latest
1604          * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1605          */
1606         if ((to.to_flags & TOF_TS) != 0 &&
1607             SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
1608                 tp->ts_recent_age = ticks;
1609                 tp->ts_recent = to.to_tsval;
1610         }
1611
1612         /*
1613          * If a SYN is in the window, then this is an
1614          * error and we send an RST and drop the connection.
1615          */
1616         if (thflags & TH_SYN) {
1617                 tp = tcp_drop(tp, ECONNRESET);
1618                 rstreason = BANDLIM_UNLIMITED;
1619                 goto dropwithreset;
1620         }
1621
1622         /*
1623          * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
1624          * flag is on (half-synchronized state), then queue data for
1625          * later processing; else drop segment and return.
1626          */
1627         if ((thflags & TH_ACK) == 0) {
1628                 if (tp->t_state == TCPS_SYN_RECEIVED ||
1629                     (tp->t_flags & TF_NEEDSYN))
1630                         goto step6;
1631                 else
1632                         goto drop;
1633         }
1634
1635         /*
1636          * Ack processing.
1637          */
1638         switch (tp->t_state) {
1639
1640         /*
1641          * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
1642          * ESTABLISHED state and continue processing.
1643          * The ACK was checked above.
1644          */
1645         case TCPS_SYN_RECEIVED:
1646
1647                 tcpstat.tcps_connects++;
1648                 soisconnected(so);
1649                 /* Do window scaling? */
1650                 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1651                         (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1652                         tp->snd_scale = tp->requested_s_scale;
1653                         tp->rcv_scale = tp->request_r_scale;
1654                 }
1655                 /*
1656                  * Upon successful completion of 3-way handshake,
1657                  * update cache.CC if it was undefined, pass any queued
1658                  * data to the user, and advance state appropriately.
1659                  */
1660                 if ((taop = tcp_gettaocache(&inp->inp_inc)) != NULL &&
1661                     taop->tao_cc == 0)
1662                         taop->tao_cc = tp->cc_recv;
1663
1664                 /*
1665                  * Make transitions:
1666                  *      SYN-RECEIVED  -> ESTABLISHED
1667                  *      SYN-RECEIVED* -> FIN-WAIT-1
1668                  */
1669                 tp->t_starttime = ticks;
1670                 if (tp->t_flags & TF_NEEDFIN) {
1671                         tp->t_state = TCPS_FIN_WAIT_1;
1672                         tp->t_flags &= ~TF_NEEDFIN;
1673                 } else {
1674                         tp->t_state = TCPS_ESTABLISHED;
1675                         callout_reset(tp->tt_keep, tcp_keepidle,
1676                                       tcp_timer_keep, tp);
1677                 }
1678                 /*
1679                  * If segment contains data or ACK, will call tcp_reass()
1680                  * later; if not, do so now to pass queued data to user.
1681                  */
1682                 if (tlen == 0 && (thflags & TH_FIN) == 0)
1683                         (void) tcp_reass(tp, (struct tcphdr *)0, 0,
1684                             (struct mbuf *)0);
1685                 tp->snd_wl1 = th->th_seq - 1;
1686                 /* fall into ... */
1687
1688         /*
1689          * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
1690          * ACKs.  If the ack is in the range
1691          *      tp->snd_una < th->th_ack <= tp->snd_max
1692          * then advance tp->snd_una to th->th_ack and drop
1693          * data from the retransmission queue.  If this ACK reflects
1694          * more up to date window information we update our window information.
1695          */
1696         case TCPS_ESTABLISHED:
1697         case TCPS_FIN_WAIT_1:
1698         case TCPS_FIN_WAIT_2:
1699         case TCPS_CLOSE_WAIT:
1700         case TCPS_CLOSING:
1701         case TCPS_LAST_ACK:
1702         case TCPS_TIME_WAIT:
1703
1704                 if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
1705                         if (tlen == 0 && tiwin == tp->snd_wnd) {
1706                                 tcpstat.tcps_rcvdupack++;
1707                                 /*
1708                                  * If we have outstanding data (other than
1709                                  * a window probe), this is a completely
1710                                  * duplicate ack (ie, window info didn't
1711                                  * change), the ack is the biggest we've
1712                                  * seen and we've seen exactly our rexmt
1713                                  * threshhold of them, assume a packet
1714                                  * has been dropped and retransmit it.
1715                                  * Kludge snd_nxt & the congestion
1716                                  * window so we send only this one
1717                                  * packet.
1718                                  *
1719                                  * We know we're losing at the current
1720                                  * window size so do congestion avoidance
1721                                  * (set ssthresh to half the current window
1722                                  * and pull our congestion window back to
1723                                  * the new ssthresh).
1724                                  *
1725                                  * Dup acks mean that packets have left the
1726                                  * network (they're now cached at the receiver)
1727                                  * so bump cwnd by the amount in the receiver
1728                                  * to keep a constant cwnd packets in the
1729                                  * network.
1730                                  */
1731                                 if (!callout_active(tp->tt_rexmt) ||
1732                                     th->th_ack != tp->snd_una)
1733                                         tp->t_dupacks = 0;
1734                                 else if (++tp->t_dupacks > tcprexmtthresh ||
1735                                          (tcp_do_newreno &&
1736                                           IN_FASTRECOVERY(tp))) {
1737                                         tp->snd_cwnd += tp->t_maxseg;
1738                                         (void) tcp_output(tp);
1739                                         goto drop;
1740                                 } else if (tp->t_dupacks == tcprexmtthresh) {
1741                                         tcp_seq onxt;
1742                                         u_int win;
1743
1744                                         if (tcp_do_newreno &&
1745                                             SEQ_LEQ(th->th_ack,
1746                                                     tp->snd_recover)) {
1747                                                 tp->t_dupacks = 0;
1748                                                 break;
1749                                         }
1750 fastretransmit:
1751                                         if (tcp_do_eifel_detect &&
1752                                             (tp->t_flags & TF_RCVD_TSTMP)) {
1753                                                 tcp_save_congestion_state(tp);
1754                                                 tp->t_flags |= TF_FASTREXMT;
1755                                         }
1756                                         win = min(tp->snd_wnd, tp->snd_cwnd) /
1757                                             2 / tp->t_maxseg;
1758                                         if (win < 2)
1759                                                 win = 2;
1760                                         tp->snd_ssthresh = win * tp->t_maxseg;
1761                                         ENTER_FASTRECOVERY(tp);
1762                                         tp->snd_recover = tp->snd_max;
1763                                         callout_stop(tp->tt_rexmt);
1764                                         tp->t_rtttime = 0;
1765                                         onxt = tp->snd_nxt;
1766                                         tp->snd_nxt = th->th_ack;
1767                                         tp->snd_cwnd = tp->t_maxseg;
1768                                         (void) tcp_output(tp);
1769                                         ++tcpstat.tcps_sndfastrexmit;
1770                                         KASSERT(tp->snd_limited <= 2,
1771                                             ("tp->snd_limited too big"));
1772                                         tp->snd_cwnd = tp->snd_ssthresh +
1773                                             (tp->t_maxseg *
1774                                              (tp->t_dupacks - tp->snd_limited));
1775                                         if (SEQ_GT(onxt, tp->snd_nxt))
1776                                                 tp->snd_nxt = onxt;
1777                                         goto drop;
1778                                 } else if (tcp_do_limitedtransmit) {
1779                                         u_long oldcwnd = tp->snd_cwnd;
1780                                         tcp_seq oldsndmax = tp->snd_max;
1781                                         /* outstanding data */
1782                                         uint32_t ownd =
1783                                             tp->snd_max - tp->snd_una;
1784                                         u_int sent;
1785
1786 #define iceildiv(n, d)          (((n)+(d)-1) / (d))
1787
1788                                         KASSERT(tp->t_dupacks == 1 ||
1789                                             tp->t_dupacks == 2,
1790                                             ("dupacks not 1 or 2"));
1791                                         if (tp->t_dupacks == 1)
1792                                                 tp->snd_limited = 0;
1793                                         tp->snd_cwnd = ownd +
1794                                             (tp->t_dupacks - tp->snd_limited) *
1795                                             tp->t_maxseg;
1796                                         (void) tcp_output(tp);
1797                                         tp->snd_cwnd = oldcwnd;
1798                                         sent = tp->snd_max - oldsndmax;
1799                                         if (sent > tp->t_maxseg) {
1800                                                 KASSERT((tp->t_dupacks == 2 &&
1801                                                     tp->snd_limited == 0) ||
1802                                                    (sent == tp->t_maxseg + 1 &&
1803                                                     tp->t_flags & TF_SENTFIN),
1804                                                     ("sent too much"));
1805                                                 KASSERT(sent <=
1806                                                         tp->t_maxseg * 2,
1807                                                     ("sent too many segments"));
1808                                                 tp->snd_limited = 2;
1809                                                 tcpstat.tcps_sndlimited += 2;
1810                                         } else if (sent > 0) {
1811                                                 ++tp->snd_limited;
1812                                                 ++tcpstat.tcps_sndlimited;
1813                                         } else if (tcp_do_early_retransmit &&
1814                                             (tcp_do_eifel_detect &&
1815                                              (tp->t_flags & TF_RCVD_TSTMP)) &&
1816                                             tcp_do_newreno &&
1817                                             tp->t_dupacks + 1 >=
1818                                               iceildiv(ownd, tp->t_maxseg)) {
1819                                                 ++tcpstat.tcps_sndearlyrexmit;
1820                                                 tp->t_flags |= TF_EARLYREXMT;
1821                                                 goto fastretransmit;
1822                                         }
1823                                         goto drop;
1824                                 }
1825                         } else
1826                                 tp->t_dupacks = 0;
1827                         break;
1828                 }
1829
1830                 KASSERT(SEQ_GT(th->th_ack, tp->snd_una), ("th_ack <= snd_una"));
1831
1832                 /*
1833                  * If the congestion window was inflated to account
1834                  * for the other side's cached packets, retract it.
1835                  */
1836                 if (tcp_do_newreno) {
1837                         if (IN_FASTRECOVERY(tp)) {
1838                                 if (SEQ_LT(th->th_ack, tp->snd_recover)) {
1839                                         tcp_newreno_partial_ack(tp, th);
1840                                 } else {
1841                                         /*
1842                                          * Window inflation should have left us
1843                                          * with approximately snd_ssthresh
1844                                          * outstanding data.
1845                                          * But in case we would be inclined to
1846                                          * send a burst, better to do it via
1847                                          * the slow start mechanism.
1848                                          */
1849                                         if (SEQ_GT(th->th_ack +
1850                                                         tp->snd_ssthresh,
1851                                                    tp->snd_max))
1852                                                 tp->snd_cwnd = tp->snd_max -
1853                                                                 th->th_ack +
1854                                                                 tp->t_maxseg;
1855                                         else
1856                                                 tp->snd_cwnd = tp->snd_ssthresh;
1857                                 }
1858                         }
1859                 } else {
1860                         if (tp->t_dupacks >= tcprexmtthresh &&
1861                             tp->snd_cwnd > tp->snd_ssthresh)
1862                                 tp->snd_cwnd = tp->snd_ssthresh;
1863                 }
1864                 tp->t_dupacks = 0;
1865                 if (SEQ_GT(th->th_ack, tp->snd_max)) {
1866                         tcpstat.tcps_rcvacktoomuch++;
1867                         goto dropafterack;
1868                 }
1869                 /*
1870                  * If we reach this point, ACK is not a duplicate,
1871                  *     i.e., it ACKs something we sent.
1872                  */
1873                 if (tp->t_flags & TF_NEEDSYN) {
1874                         /*
1875                          * T/TCP: Connection was half-synchronized, and our
1876                          * SYN has been ACK'd (so connection is now fully
1877                          * synchronized).  Go to non-starred state,
1878                          * increment snd_una for ACK of SYN, and check if
1879                          * we can do window scaling.
1880                          */
1881                         tp->t_flags &= ~TF_NEEDSYN;
1882                         tp->snd_una++;
1883                         /* Do window scaling? */
1884                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1885                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1886                                 tp->snd_scale = tp->requested_s_scale;
1887                                 tp->rcv_scale = tp->request_r_scale;
1888                         }
1889                 }
1890
1891 process_ACK:
1892                 acked = th->th_ack - tp->snd_una;
1893                 tcpstat.tcps_rcvackpack++;
1894                 tcpstat.tcps_rcvackbyte += acked;
1895
1896                 /*
1897                  * If we just performed our first retransmit, and the ACK
1898                  * arrives within our recovery window, then it was a mistake
1899                  * to do the retransmit in the first place.  Recover our
1900                  * original cwnd and ssthresh, and proceed to transmit where
1901                  * we left off.
1902                  */
1903                 if (tcp_do_eifel_detect && acked &&
1904                     (to.to_flags & TOF_TS) && to.to_tsecr &&
1905                     (tp->t_flags & TF_FIRSTACCACK)) {
1906                         /* Eifel detection applicable. */
1907                         if (to.to_tsecr < tp->t_rexmtTS) {
1908                                 ++tcpstat.tcps_eifeldetected;
1909                                 tcp_revert_congestion_state(tp);
1910                                 if (tp->t_rxtshift == 1 &&
1911                                     ticks >= tp->t_badrxtwin)
1912                                         ++tcpstat.tcps_rttcantdetect;
1913                         }
1914                 } else if (tp->t_rxtshift == 1 && ticks < tp->t_badrxtwin) {
1915                         tcp_revert_congestion_state(tp);
1916                         ++tcpstat.tcps_rttdetected;
1917                 }
1918
1919                 /*
1920                  * If we have a timestamp reply, update smoothed
1921                  * round trip time.  If no timestamp is present but
1922                  * transmit timer is running and timed sequence
1923                  * number was acked, update smoothed round trip time.
1924                  * Since we now have an rtt measurement, cancel the
1925                  * timer backoff (cf., Phil Karn's retransmit alg.).
1926                  * Recompute the initial retransmit timer.
1927                  *
1928                  * Some machines (certain windows boxes) send broken
1929                  * timestamp replies during the SYN+ACK phase, ignore
1930                  * timestamps of 0.
1931                  */
1932                 if ((to.to_flags & TOF_TS) != 0 &&
1933                     to.to_tsecr) {
1934                         tcp_xmit_timer(tp, ticks - to.to_tsecr + 1);
1935                 } else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
1936                         tcp_xmit_timer(tp, ticks - tp->t_rtttime);
1937                 }
1938                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
1939
1940                 /*
1941                  * If all outstanding data is acked, stop retransmit
1942                  * timer and remember to restart (more output or persist).
1943                  * If there is more data to be acked, restart retransmit
1944                  * timer, using current (possibly backed-off) value.
1945                  */
1946                 if (th->th_ack == tp->snd_max) {
1947                         callout_stop(tp->tt_rexmt);
1948                         needoutput = 1;
1949                 } else if (!callout_active(tp->tt_persist))
1950                         callout_reset(tp->tt_rexmt, tp->t_rxtcur,
1951                                       tcp_timer_rexmt, tp);
1952
1953                 /*
1954                  * If no data (only SYN) was ACK'd,
1955                  *    skip rest of ACK processing.
1956                  */
1957                 if (acked == 0)
1958                         goto step6;
1959
1960                 /* Stop looking for an acceptable ACK since one was received. */
1961                 tp->t_flags &= ~(TF_FIRSTACCACK | TF_FASTREXMT | TF_EARLYREXMT);
1962
1963                 /*
1964                  * When new data is acked, open the congestion window.
1965                  * If the window gives us less than ssthresh packets
1966                  * in flight, open exponentially (maxseg per packet).
1967                  * Otherwise open linearly: maxseg per window
1968                  * (maxseg^2 / cwnd per packet).
1969                  */
1970                 if (!tcp_do_newreno || !IN_FASTRECOVERY(tp)) {
1971                         u_int cw = tp->snd_cwnd;
1972                         u_int incr = tp->t_maxseg;
1973                         if (cw > tp->snd_ssthresh)
1974                                 incr = incr * incr / cw;
1975                         tp->snd_cwnd = min(cw+incr, TCP_MAXWIN<<tp->snd_scale);
1976                 }
1977                 if (acked > so->so_snd.sb_cc) {
1978                         tp->snd_wnd -= so->so_snd.sb_cc;
1979                         sbdrop(&so->so_snd, (int)so->so_snd.sb_cc);
1980                         ourfinisacked = 1;
1981                 } else {
1982                         sbdrop(&so->so_snd, acked);
1983                         tp->snd_wnd -= acked;
1984                         ourfinisacked = 0;
1985                 }
1986                 sowwakeup(so);
1987                 /* detect una wraparound */
1988                 if (tcp_do_newreno && !IN_FASTRECOVERY(tp) &&
1989                     SEQ_GT(tp->snd_una, tp->snd_recover) &&
1990                     SEQ_LEQ(th->th_ack, tp->snd_recover))
1991                         tp->snd_recover = th->th_ack - 1;
1992                 if (tcp_do_newreno && IN_FASTRECOVERY(tp) &&
1993                     SEQ_GEQ(th->th_ack, tp->snd_recover))
1994                         EXIT_FASTRECOVERY(tp);
1995                 tp->snd_una = th->th_ack;
1996                 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
1997                         tp->snd_nxt = tp->snd_una;
1998
1999                 switch (tp->t_state) {
2000
2001                 /*
2002                  * In FIN_WAIT_1 STATE in addition to the processing
2003                  * for the ESTABLISHED state if our FIN is now acknowledged
2004                  * then enter FIN_WAIT_2.
2005                  */
2006                 case TCPS_FIN_WAIT_1:
2007                         if (ourfinisacked) {
2008                                 /*
2009                                  * If we can't receive any more
2010                                  * data, then closing user can proceed.
2011                                  * Starting the timer is contrary to the
2012                                  * specification, but if we don't get a FIN
2013                                  * we'll hang forever.
2014                                  */
2015                                 if (so->so_state & SS_CANTRCVMORE) {
2016                                         soisdisconnected(so);
2017                                         callout_reset(tp->tt_2msl, tcp_maxidle,
2018                                                       tcp_timer_2msl, tp);
2019                                 }
2020                                 tp->t_state = TCPS_FIN_WAIT_2;
2021                         }
2022                         break;
2023
2024                 /*
2025                  * In CLOSING STATE in addition to the processing for
2026                  * the ESTABLISHED state if the ACK acknowledges our FIN
2027                  * then enter the TIME-WAIT state, otherwise ignore
2028                  * the segment.
2029                  */
2030                 case TCPS_CLOSING:
2031                         if (ourfinisacked) {
2032                                 tp->t_state = TCPS_TIME_WAIT;
2033                                 tcp_canceltimers(tp);
2034                                 /* Shorten TIME_WAIT [RFC-1644, p.28] */
2035                                 if (tp->cc_recv != 0 &&
2036                                     (ticks - tp->t_starttime) < tcp_msl)
2037                                         callout_reset(tp->tt_2msl,
2038                                                       tp->t_rxtcur *
2039                                                       TCPTV_TWTRUNC,
2040                                                       tcp_timer_2msl, tp);
2041                                 else
2042                                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
2043                                                       tcp_timer_2msl, tp);
2044                                 soisdisconnected(so);
2045                         }
2046                         break;
2047
2048                 /*
2049                  * In LAST_ACK, we may still be waiting for data to drain
2050                  * and/or to be acked, as well as for the ack of our FIN.
2051                  * If our FIN is now acknowledged, delete the TCB,
2052                  * enter the closed state and return.
2053                  */
2054                 case TCPS_LAST_ACK:
2055                         if (ourfinisacked) {
2056                                 tp = tcp_close(tp);
2057                                 goto drop;
2058                         }
2059                         break;
2060
2061                 /*
2062                  * In TIME_WAIT state the only thing that should arrive
2063                  * is a retransmission of the remote FIN.  Acknowledge
2064                  * it and restart the finack timer.
2065                  */
2066                 case TCPS_TIME_WAIT:
2067                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
2068                                       tcp_timer_2msl, tp);
2069                         goto dropafterack;
2070                 }
2071         }
2072
2073 step6:
2074         /*
2075          * Update window information.
2076          * Don't look at window if no ACK: TAC's send garbage on first SYN.
2077          */
2078         if ((thflags & TH_ACK) &&
2079             (SEQ_LT(tp->snd_wl1, th->th_seq) ||
2080             (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
2081              (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
2082                 /* keep track of pure window updates */
2083                 if (tlen == 0 &&
2084                     tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
2085                         tcpstat.tcps_rcvwinupd++;
2086                 tp->snd_wnd = tiwin;
2087                 tp->snd_wl1 = th->th_seq;
2088                 tp->snd_wl2 = th->th_ack;
2089                 if (tp->snd_wnd > tp->max_sndwnd)
2090                         tp->max_sndwnd = tp->snd_wnd;
2091                 needoutput = 1;
2092         }
2093
2094         /*
2095          * Process segments with URG.
2096          */
2097         if ((thflags & TH_URG) && th->th_urp &&
2098             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2099                 /*
2100                  * This is a kludge, but if we receive and accept
2101                  * random urgent pointers, we'll crash in
2102                  * soreceive.  It's hard to imagine someone
2103                  * actually wanting to send this much urgent data.
2104                  */
2105                 if (th->th_urp + so->so_rcv.sb_cc > sb_max) {
2106                         th->th_urp = 0;                 /* XXX */
2107                         thflags &= ~TH_URG;             /* XXX */
2108                         goto dodata;                    /* XXX */
2109                 }
2110                 /*
2111                  * If this segment advances the known urgent pointer,
2112                  * then mark the data stream.  This should not happen
2113                  * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
2114                  * a FIN has been received from the remote side.
2115                  * In these states we ignore the URG.
2116                  *
2117                  * According to RFC961 (Assigned Protocols),
2118                  * the urgent pointer points to the last octet
2119                  * of urgent data.  We continue, however,
2120                  * to consider it to indicate the first octet
2121                  * of data past the urgent section as the original
2122                  * spec states (in one of two places).
2123                  */
2124                 if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
2125                         tp->rcv_up = th->th_seq + th->th_urp;
2126                         so->so_oobmark = so->so_rcv.sb_cc +
2127                             (tp->rcv_up - tp->rcv_nxt) - 1;
2128                         if (so->so_oobmark == 0)
2129                                 so->so_state |= SS_RCVATMARK;
2130                         sohasoutofband(so);
2131                         tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
2132                 }
2133                 /*
2134                  * Remove out of band data so doesn't get presented to user.
2135                  * This can happen independent of advancing the URG pointer,
2136                  * but if two URG's are pending at once, some out-of-band
2137                  * data may creep in... ick.
2138                  */
2139                 if (th->th_urp <= (u_long)tlen
2140 #ifdef SO_OOBINLINE
2141                      && (so->so_options & SO_OOBINLINE) == 0
2142 #endif
2143                      )
2144                         tcp_pulloutofband(so, th, m,
2145                                 drop_hdrlen);   /* hdr drop is delayed */
2146         } else {
2147                 /*
2148                  * If no out of band data is expected,
2149                  * pull receive urgent pointer along
2150                  * with the receive window.
2151                  */
2152                 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
2153                         tp->rcv_up = tp->rcv_nxt;
2154         }
2155 dodata:                                                 /* XXX */
2156
2157         /*
2158          * Process the segment text, merging it into the TCP sequencing queue,
2159          * and arranging for acknowledgment of receipt if necessary.
2160          * This process logically involves adjusting tp->rcv_wnd as data
2161          * is presented to the user (this happens in tcp_usrreq.c,
2162          * case PRU_RCVD).  If a FIN has already been received on this
2163          * connection then we just ignore the text.
2164          */
2165         if ((tlen || (thflags & TH_FIN)) &&
2166             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2167                 m_adj(m, drop_hdrlen);  /* delayed header drop */
2168                 /*
2169                  * Insert segment which includes th into TCP reassembly queue
2170                  * with control block tp.  Set thflags to whether reassembly now
2171                  * includes a segment with FIN.  This handles the common case
2172                  * inline (segment is the next to be received on an established
2173                  * connection, and the queue is empty), avoiding linkage into
2174                  * and removal from the queue and repetition of various
2175                  * conversions.
2176                  * Set DELACK for segments received in order, but ack
2177                  * immediately when segments are out of order (so
2178                  * fast retransmit can work).
2179                  */
2180                 if (th->th_seq == tp->rcv_nxt &&
2181                     LIST_EMPTY(&tp->t_segq) &&
2182                     TCPS_HAVEESTABLISHED(tp->t_state)) {
2183                         if (DELAY_ACK(tp))
2184                                 callout_reset(tp->tt_delack, tcp_delacktime,
2185                                               tcp_timer_delack, tp);
2186                         else
2187                                 tp->t_flags |= TF_ACKNOW;
2188                         tp->rcv_nxt += tlen;
2189                         thflags = th->th_flags & TH_FIN;
2190                         tcpstat.tcps_rcvpack++;
2191                         tcpstat.tcps_rcvbyte += tlen;
2192                         ND6_HINT(tp);
2193                         if (so->so_state & SS_CANTRCVMORE)
2194                                 m_freem(m);
2195                         else
2196                                 sbappend(&so->so_rcv, m);
2197                         sorwakeup(so);
2198                 } else {
2199                         thflags = tcp_reass(tp, th, &tlen, m);
2200                         tp->t_flags |= TF_ACKNOW;
2201                 }
2202
2203                 /*
2204                  * Note the amount of data that peer has sent into
2205                  * our window, in order to estimate the sender's
2206                  * buffer size.
2207                  */
2208                 len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
2209         } else {
2210                 m_freem(m);
2211                 thflags &= ~TH_FIN;
2212         }
2213
2214         /*
2215          * If FIN is received ACK the FIN and let the user know
2216          * that the connection is closing.
2217          */
2218         if (thflags & TH_FIN) {
2219                 if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2220                         socantrcvmore(so);
2221                         /*
2222                          * If connection is half-synchronized
2223                          * (ie NEEDSYN flag on) then delay ACK,
2224                          * so it may be piggybacked when SYN is sent.
2225                          * Otherwise, since we received a FIN then no
2226                          * more input can be expected, send ACK now.
2227                          */
2228                         if (DELAY_ACK(tp) && (tp->t_flags & TF_NEEDSYN))
2229                                 callout_reset(tp->tt_delack, tcp_delacktime,
2230                                     tcp_timer_delack, tp);
2231                         else
2232                                 tp->t_flags |= TF_ACKNOW;
2233                         tp->rcv_nxt++;
2234                 }
2235                 switch (tp->t_state) {
2236
2237                 /*
2238                  * In SYN_RECEIVED and ESTABLISHED STATES
2239                  * enter the CLOSE_WAIT state.
2240                  */
2241                 case TCPS_SYN_RECEIVED:
2242                         tp->t_starttime = ticks;
2243                         /*FALLTHROUGH*/
2244                 case TCPS_ESTABLISHED:
2245                         tp->t_state = TCPS_CLOSE_WAIT;
2246                         break;
2247
2248                 /*
2249                  * If still in FIN_WAIT_1 STATE FIN has not been acked so
2250                  * enter the CLOSING state.
2251                  */
2252                 case TCPS_FIN_WAIT_1:
2253                         tp->t_state = TCPS_CLOSING;
2254                         break;
2255
2256                 /*
2257                  * In FIN_WAIT_2 state enter the TIME_WAIT state,
2258                  * starting the time-wait timer, turning off the other
2259                  * standard timers.
2260                  */
2261                 case TCPS_FIN_WAIT_2:
2262                         tp->t_state = TCPS_TIME_WAIT;
2263                         tcp_canceltimers(tp);
2264                         /* Shorten TIME_WAIT [RFC-1644, p.28] */
2265                         if (tp->cc_recv != 0 &&
2266                             (ticks - tp->t_starttime) < tcp_msl) {
2267                                 callout_reset(tp->tt_2msl,
2268                                               tp->t_rxtcur * TCPTV_TWTRUNC,
2269                                               tcp_timer_2msl, tp);
2270                                 /* For transaction client, force ACK now. */
2271                                 tp->t_flags |= TF_ACKNOW;
2272                         }
2273                         else
2274                                 callout_reset(tp->tt_2msl, 2 * tcp_msl,
2275                                               tcp_timer_2msl, tp);
2276                         soisdisconnected(so);
2277                         break;
2278
2279                 /*
2280                  * In TIME_WAIT state restart the 2 MSL time_wait timer.
2281                  */
2282                 case TCPS_TIME_WAIT:
2283                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
2284                                       tcp_timer_2msl, tp);
2285                         break;
2286                 }
2287         }
2288 #ifdef TCPDEBUG
2289         if (so->so_options & SO_DEBUG)
2290                 tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
2291                           &tcp_savetcp, 0);
2292 #endif
2293
2294         /*
2295          * Return any desired output.
2296          */
2297         if (needoutput || (tp->t_flags & TF_ACKNOW))
2298                 (void) tcp_output(tp);
2299         return;
2300
2301 dropafterack:
2302         /*
2303          * Generate an ACK dropping incoming segment if it occupies
2304          * sequence space, where the ACK reflects our state.
2305          *
2306          * We can now skip the test for the RST flag since all
2307          * paths to this code happen after packets containing
2308          * RST have been dropped.
2309          *
2310          * In the SYN-RECEIVED state, don't send an ACK unless the
2311          * segment we received passes the SYN-RECEIVED ACK test.
2312          * If it fails send a RST.  This breaks the loop in the
2313          * "LAND" DoS attack, and also prevents an ACK storm
2314          * between two listening ports that have been sent forged
2315          * SYN segments, each with the source address of the other.
2316          */
2317         if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
2318             (SEQ_GT(tp->snd_una, th->th_ack) ||
2319              SEQ_GT(th->th_ack, tp->snd_max)) ) {
2320                 rstreason = BANDLIM_RST_OPENPORT;
2321                 goto dropwithreset;
2322         }
2323 #ifdef TCPDEBUG
2324         if (so->so_options & SO_DEBUG)
2325                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2326                           &tcp_savetcp, 0);
2327 #endif
2328         m_freem(m);
2329         tp->t_flags |= TF_ACKNOW;
2330         (void) tcp_output(tp);
2331         return;
2332
2333 dropwithreset:
2334         /*
2335          * Generate a RST, dropping incoming segment.
2336          * Make ACK acceptable to originator of segment.
2337          * Don't bother to respond if destination was broadcast/multicast.
2338          */
2339         if ((thflags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
2340                 goto drop;
2341         if (isipv6) {
2342                 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
2343                     IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
2344                         goto drop;
2345         } else {
2346                 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
2347                     IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
2348                     ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
2349                     in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
2350                         goto drop;
2351         }
2352         /* IPv6 anycast check is done at tcp6_input() */
2353
2354         /*
2355          * Perform bandwidth limiting.
2356          */
2357 #ifdef ICMP_BANDLIM
2358         if (badport_bandlim(rstreason) < 0)
2359                 goto drop;
2360 #endif
2361
2362 #ifdef TCPDEBUG
2363         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2364                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2365                           &tcp_savetcp, 0);
2366 #endif
2367         if (thflags & TH_ACK)
2368                 /* mtod() below is safe as long as hdr dropping is delayed */
2369                 tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0, th->th_ack,
2370                             TH_RST);
2371         else {
2372                 if (thflags & TH_SYN)
2373                         tlen++;
2374                 /* mtod() below is safe as long as hdr dropping is delayed */
2375                 tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
2376                             (tcp_seq)0, TH_RST|TH_ACK);
2377         }
2378         return;
2379
2380 drop:
2381         /*
2382          * Drop space held by incoming segment and return.
2383          */
2384 #ifdef TCPDEBUG
2385         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2386                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2387                           &tcp_savetcp, 0);
2388 #endif
2389         m_freem(m);
2390         return;
2391 }
2392
2393 /*
2394  * Parse TCP options and place in tcpopt.
2395  */
2396 static void
2397 tcp_dooptions(to, cp, cnt, is_syn)
2398         struct tcpopt *to;
2399         u_char *cp;
2400         int cnt;
2401 {
2402         int opt, optlen;
2403
2404         to->to_flags = 0;
2405         for (; cnt > 0; cnt -= optlen, cp += optlen) {
2406                 opt = cp[0];
2407                 if (opt == TCPOPT_EOL)
2408                         break;
2409                 if (opt == TCPOPT_NOP)
2410                         optlen = 1;
2411                 else {
2412                         if (cnt < 2)
2413                                 break;
2414                         optlen = cp[1];
2415                         if (optlen < 2 || optlen > cnt)
2416                                 break;
2417                 }
2418                 switch (opt) {
2419                 case TCPOPT_MAXSEG:
2420                         if (optlen != TCPOLEN_MAXSEG)
2421                                 continue;
2422                         if (!is_syn)
2423                                 continue;
2424                         to->to_flags |= TOF_MSS;
2425                         bcopy((char *)cp + 2,
2426                             (char *)&to->to_mss, sizeof(to->to_mss));
2427                         to->to_mss = ntohs(to->to_mss);
2428                         break;
2429                 case TCPOPT_WINDOW:
2430                         if (optlen != TCPOLEN_WINDOW)
2431                                 continue;
2432                         if (! is_syn)
2433                                 continue;
2434                         to->to_flags |= TOF_SCALE;
2435                         to->to_requested_s_scale = min(cp[2], TCP_MAX_WINSHIFT);
2436                         break;
2437                 case TCPOPT_TIMESTAMP:
2438                         if (optlen != TCPOLEN_TIMESTAMP)
2439                                 continue;
2440                         to->to_flags |= TOF_TS;
2441                         bcopy((char *)cp + 2,
2442                             (char *)&to->to_tsval, sizeof(to->to_tsval));
2443                         to->to_tsval = ntohl(to->to_tsval);
2444                         bcopy((char *)cp + 6,
2445                             (char *)&to->to_tsecr, sizeof(to->to_tsecr));
2446                         to->to_tsecr = ntohl(to->to_tsecr);
2447                         break;
2448                 case TCPOPT_CC:
2449                         if (optlen != TCPOLEN_CC)
2450                                 continue;
2451                         to->to_flags |= TOF_CC;
2452                         bcopy((char *)cp + 2,
2453                             (char *)&to->to_cc, sizeof(to->to_cc));
2454                         to->to_cc = ntohl(to->to_cc);
2455                         break;
2456                 case TCPOPT_CCNEW:
2457                         if (optlen != TCPOLEN_CC)
2458                                 continue;
2459                         if (!is_syn)
2460                                 continue;
2461                         to->to_flags |= TOF_CCNEW;
2462                         bcopy((char *)cp + 2,
2463                             (char *)&to->to_cc, sizeof(to->to_cc));
2464                         to->to_cc = ntohl(to->to_cc);
2465                         break;
2466                 case TCPOPT_CCECHO:
2467                         if (optlen != TCPOLEN_CC)
2468                                 continue;
2469                         if (!is_syn)
2470                                 continue;
2471                         to->to_flags |= TOF_CCECHO;
2472                         bcopy((char *)cp + 2,
2473                             (char *)&to->to_ccecho, sizeof(to->to_ccecho));
2474                         to->to_ccecho = ntohl(to->to_ccecho);
2475                         break;
2476                 default:
2477                         continue;
2478                 }
2479         }
2480 }
2481
2482 /*
2483  * Pull out of band byte out of a segment so
2484  * it doesn't appear in the user's data queue.
2485  * It is still reflected in the segment length for
2486  * sequencing purposes.
2487  */
2488 static void
2489 tcp_pulloutofband(so, th, m, off)
2490         struct socket *so;
2491         struct tcphdr *th;
2492         struct mbuf *m;
2493         int off;                /* delayed to be droped hdrlen */
2494 {
2495         int cnt = off + th->th_urp - 1;
2496
2497         while (cnt >= 0) {
2498                 if (m->m_len > cnt) {
2499                         char *cp = mtod(m, caddr_t) + cnt;
2500                         struct tcpcb *tp = sototcpcb(so);
2501
2502                         tp->t_iobc = *cp;
2503                         tp->t_oobflags |= TCPOOB_HAVEDATA;
2504                         bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
2505                         m->m_len--;
2506                         if (m->m_flags & M_PKTHDR)
2507                                 m->m_pkthdr.len--;
2508                         return;
2509                 }
2510                 cnt -= m->m_len;
2511                 m = m->m_next;
2512                 if (m == 0)
2513                         break;
2514         }
2515         panic("tcp_pulloutofband");
2516 }
2517
2518 /*
2519  * Collect new round-trip time estimate
2520  * and update averages and current timeout.
2521  */
2522 static void
2523 tcp_xmit_timer(tp, rtt)
2524         struct tcpcb *tp;
2525         int rtt;
2526 {
2527         int delta;
2528
2529         tcpstat.tcps_rttupdated++;
2530         tp->t_rttupdated++;
2531         if (tp->t_srtt != 0) {
2532                 /*
2533                  * srtt is stored as fixed point with 5 bits after the
2534                  * binary point (i.e., scaled by 8).  The following magic
2535                  * is equivalent to the smoothing algorithm in rfc793 with
2536                  * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
2537                  * point).  Adjust rtt to origin 0.
2538                  */
2539                 delta = ((rtt - 1) << TCP_DELTA_SHIFT)
2540                         - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
2541
2542                 if ((tp->t_srtt += delta) <= 0)
2543                         tp->t_srtt = 1;
2544
2545                 /*
2546                  * We accumulate a smoothed rtt variance (actually, a
2547                  * smoothed mean difference), then set the retransmit
2548                  * timer to smoothed rtt + 4 times the smoothed variance.
2549                  * rttvar is stored as fixed point with 4 bits after the
2550                  * binary point (scaled by 16).  The following is
2551                  * equivalent to rfc793 smoothing with an alpha of .75
2552                  * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
2553                  * rfc793's wired-in beta.
2554                  */
2555                 if (delta < 0)
2556                         delta = -delta;
2557                 delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
2558                 if ((tp->t_rttvar += delta) <= 0)
2559                         tp->t_rttvar = 1;
2560                 if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
2561                         tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2562         } else {
2563                 /*
2564                  * No rtt measurement yet - use the unsmoothed rtt.
2565                  * Set the variance to half the rtt (so our first
2566                  * retransmit happens at 3*rtt).
2567                  */
2568                 tp->t_srtt = rtt << TCP_RTT_SHIFT;
2569                 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
2570                 tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2571         }
2572         tp->t_rtttime = 0;
2573         tp->t_rxtshift = 0;
2574
2575         /*
2576          * the retransmit should happen at rtt + 4 * rttvar.
2577          * Because of the way we do the smoothing, srtt and rttvar
2578          * will each average +1/2 tick of bias.  When we compute
2579          * the retransmit timer, we want 1/2 tick of rounding and
2580          * 1 extra tick because of +-1/2 tick uncertainty in the
2581          * firing of the timer.  The bias will give us exactly the
2582          * 1.5 tick we need.  But, because the bias is
2583          * statistical, we have to test that we don't drop below
2584          * the minimum feasible timer (which is 2 ticks).
2585          */
2586         TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
2587                       max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
2588
2589         /*
2590          * We received an ack for a packet that wasn't retransmitted;
2591          * it is probably safe to discard any error indications we've
2592          * received recently.  This isn't quite right, but close enough
2593          * for now (a route might have failed after we sent a segment,
2594          * and the return path might not be symmetrical).
2595          */
2596         tp->t_softerror = 0;
2597 }
2598
2599 /*
2600  * Determine a reasonable value for maxseg size.
2601  * If the route is known, check route for mtu.
2602  * If none, use an mss that can be handled on the outgoing
2603  * interface without forcing IP to fragment; if bigger than
2604  * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
2605  * to utilize large mbufs.  If no route is found, route has no mtu,
2606  * or the destination isn't local, use a default, hopefully conservative
2607  * size (usually 512 or the default IP max size, but no more than the mtu
2608  * of the interface), as we can't discover anything about intervening
2609  * gateways or networks.  We also initialize the congestion/slow start
2610  * window to be a single segment if the destination isn't local.
2611  * While looking at the routing entry, we also initialize other path-dependent
2612  * parameters from pre-set or cached values in the routing entry.
2613  *
2614  * Also take into account the space needed for options that we
2615  * send regularly.  Make maxseg shorter by that amount to assure
2616  * that we can send maxseg amount of data even when the options
2617  * are present.  Store the upper limit of the length of options plus
2618  * data in maxopd.
2619  *
2620  * NOTE that this routine is only called when we process an incoming
2621  * segment, for outgoing segments only tcp_mssopt is called.
2622  *
2623  * In case of T/TCP, we call this routine during implicit connection
2624  * setup as well (offer = -1), to initialize maxseg from the cached
2625  * MSS of our peer.
2626  */
2627 void
2628 tcp_mss(tp, offer)
2629         struct tcpcb *tp;
2630         int offer;
2631 {
2632         struct rtentry *rt;
2633         struct ifnet *ifp;
2634         int rtt, mss;
2635         u_long bufsize;
2636         struct inpcb *inp = tp->t_inpcb;
2637         struct socket *so;
2638         struct rmxp_tao *taop;
2639         int origoffer = offer;
2640 #ifdef INET6
2641         int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
2642         size_t min_protoh = isipv6 ?
2643                             sizeof(struct ip6_hdr) + sizeof(struct tcphdr) :
2644                             sizeof(struct tcpiphdr);
2645 #else
2646         const int isipv6 = 0;
2647         const size_t min_protoh = sizeof(struct tcpiphdr);
2648 #endif
2649
2650         if (isipv6)
2651                 rt = tcp_rtlookup6(&inp->inp_inc);
2652         else
2653                 rt = tcp_rtlookup(&inp->inp_inc);
2654         if (rt == NULL) {
2655                 tp->t_maxopd = tp->t_maxseg =
2656                                 isipv6 ? tcp_v6mssdflt : tcp_mssdflt;
2657                 return;
2658         }
2659         ifp = rt->rt_ifp;
2660         so = inp->inp_socket;
2661
2662         taop = rmx_taop(rt->rt_rmx);
2663         /*
2664          * Offer == -1 means that we didn't receive SYN yet,
2665          * use cached value in that case;
2666          */
2667         if (offer == -1)
2668                 offer = taop->tao_mssopt;
2669         /*
2670          * Offer == 0 means that there was no MSS on the SYN segment,
2671          * in this case we use tcp_mssdflt.
2672          */
2673         if (offer == 0)
2674                 offer = isipv6 ? tcp_v6mssdflt : tcp_mssdflt;
2675         else
2676                 /*
2677                  * Sanity check: make sure that maxopd will be large
2678                  * enough to allow some data on segments even is the
2679                  * all the option space is used (40bytes).  Otherwise
2680                  * funny things may happen in tcp_output.
2681                  */
2682                 offer = max(offer, 64);
2683         taop->tao_mssopt = offer;
2684
2685         /*
2686          * While we're here, check if there's an initial rtt
2687          * or rttvar.  Convert from the route-table units
2688          * to scaled multiples of the slow timeout timer.
2689          */
2690         if (tp->t_srtt == 0 && (rtt = rt->rt_rmx.rmx_rtt)) {
2691                 /*
2692                  * XXX the lock bit for RTT indicates that the value
2693                  * is also a minimum value; this is subject to time.
2694                  */
2695                 if (rt->rt_rmx.rmx_locks & RTV_RTT)
2696                         tp->t_rttmin = rtt / (RTM_RTTUNIT / hz);
2697                 tp->t_srtt = rtt / (RTM_RTTUNIT / (hz * TCP_RTT_SCALE));
2698                 tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
2699                 tcpstat.tcps_usedrtt++;
2700                 if (rt->rt_rmx.rmx_rttvar) {
2701                         tp->t_rttvar = rt->rt_rmx.rmx_rttvar /
2702                             (RTM_RTTUNIT / (hz * TCP_RTTVAR_SCALE));
2703                         tcpstat.tcps_usedrttvar++;
2704                 } else {
2705                         /* default variation is +- 1 rtt */
2706                         tp->t_rttvar =
2707                             tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
2708                 }
2709                 TCPT_RANGESET(tp->t_rxtcur,
2710                               ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
2711                               tp->t_rttmin, TCPTV_REXMTMAX);
2712         }
2713         /*
2714          * if there's an mtu associated with the route, use it
2715          * else, use the link mtu.
2716          */
2717         if (rt->rt_rmx.rmx_mtu)
2718                 mss = rt->rt_rmx.rmx_mtu - min_protoh;
2719         else {
2720                 if (isipv6) {
2721                         mss = nd_ifinfo[rt->rt_ifp->if_index].linkmtu -
2722                                 min_protoh;
2723                         if (!in6_localaddr(&inp->in6p_faddr))
2724                                 mss = min(mss, tcp_v6mssdflt);
2725                 } else {
2726                         mss = ifp->if_mtu - min_protoh;
2727                         if (!in_localaddr(inp->inp_faddr))
2728                                 mss = min(mss, tcp_mssdflt);
2729                 }
2730         }
2731         mss = min(mss, offer);
2732         /*
2733          * maxopd stores the maximum length of data AND options
2734          * in a segment; maxseg is the amount of data in a normal
2735          * segment.  We need to store this value (maxopd) apart
2736          * from maxseg, because now every segment carries options
2737          * and thus we normally have somewhat less data in segments.
2738          */
2739         tp->t_maxopd = mss;
2740
2741         /*
2742          * In case of T/TCP, origoffer==-1 indicates, that no segments
2743          * were received yet.  In this case we just guess, otherwise
2744          * we do the same as before T/TCP.
2745          */
2746         if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
2747             (origoffer == -1 ||
2748              (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
2749                 mss -= TCPOLEN_TSTAMP_APPA;
2750         if ((tp->t_flags & (TF_REQ_CC|TF_NOOPT)) == TF_REQ_CC &&
2751             (origoffer == -1 ||
2752              (tp->t_flags & TF_RCVD_CC) == TF_RCVD_CC))
2753                 mss -= TCPOLEN_CC_APPA;
2754
2755 #if     (MCLBYTES & (MCLBYTES - 1)) == 0
2756                 if (mss > MCLBYTES)
2757                         mss &= ~(MCLBYTES-1);
2758 #else
2759                 if (mss > MCLBYTES)
2760                         mss = mss / MCLBYTES * MCLBYTES;
2761 #endif
2762         /*
2763          * If there's a pipesize, change the socket buffer
2764          * to that size.  Make the socket buffers an integral
2765          * number of mss units; if the mss is larger than
2766          * the socket buffer, decrease the mss.
2767          */
2768 #ifdef RTV_SPIPE
2769         if ((bufsize = rt->rt_rmx.rmx_sendpipe) == 0)
2770 #endif
2771                 bufsize = so->so_snd.sb_hiwat;
2772         if (bufsize < mss)
2773                 mss = bufsize;
2774         else {
2775                 bufsize = roundup(bufsize, mss);
2776                 if (bufsize > sb_max)
2777                         bufsize = sb_max;
2778                 if (bufsize > so->so_snd.sb_hiwat)
2779                         (void)sbreserve(&so->so_snd, bufsize, so, NULL);
2780         }
2781         tp->t_maxseg = mss;
2782
2783 #ifdef RTV_RPIPE
2784         if ((bufsize = rt->rt_rmx.rmx_recvpipe) == 0)
2785 #endif
2786                 bufsize = so->so_rcv.sb_hiwat;
2787         if (bufsize > mss) {
2788                 bufsize = roundup(bufsize, mss);
2789                 if (bufsize > sb_max)
2790                         bufsize = sb_max;
2791                 if (bufsize > so->so_rcv.sb_hiwat)
2792                         (void)sbreserve(&so->so_rcv, bufsize, so, NULL);
2793         }
2794
2795         /*
2796          * Set the slow-start flight size depending on whether this
2797          * is a local network or not.
2798          */
2799         if (tcp_do_rfc3390)
2800                 tp->snd_cwnd = min(4 * mss, max(2 * mss, 4380));
2801         else if ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
2802                  (!isipv6 && in_localaddr(inp->inp_faddr)))
2803                 tp->snd_cwnd = mss * ss_fltsz_local;
2804         else
2805                 tp->snd_cwnd = mss * ss_fltsz;
2806
2807         if (rt->rt_rmx.rmx_ssthresh) {
2808                 /*
2809                  * There's some sort of gateway or interface
2810                  * buffer limit on the path.  Use this to set
2811                  * the slow start threshhold, but set the
2812                  * threshold to no less than 2*mss.
2813                  */
2814                 tp->snd_ssthresh = max(2 * mss, rt->rt_rmx.rmx_ssthresh);
2815                 tcpstat.tcps_usedssthresh++;
2816         }
2817 }
2818
2819 /*
2820  * Determine the MSS option to send on an outgoing SYN.
2821  */
2822 int
2823 tcp_mssopt(tp)
2824         struct tcpcb *tp;
2825 {
2826         struct rtentry *rt;
2827 #ifdef INET6
2828         int isipv6 = ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
2829         int min_protoh = isipv6 ?
2830                              sizeof(struct ip6_hdr) + sizeof(struct tcphdr) :
2831                              sizeof(struct tcpiphdr);
2832 #else
2833         const int isipv6 = 0;
2834         const size_t min_protoh = sizeof(struct tcpiphdr);
2835 #endif
2836
2837         if (isipv6)
2838                 rt = tcp_rtlookup6(&tp->t_inpcb->inp_inc);
2839         else
2840                 rt = tcp_rtlookup(&tp->t_inpcb->inp_inc);
2841         if (rt == NULL)
2842                 return (isipv6 ? tcp_v6mssdflt : tcp_mssdflt);
2843
2844         return (rt->rt_ifp->if_mtu - min_protoh);
2845 }
2846
2847
2848 /*
2849  * When a partial ack arrives, force the retransmission of the
2850  * next unacknowledged segment.  Do not clear tp->t_dupacks.
2851  * By setting snd_nxt to ti_ack, this forces retransmission timer to
2852  * be started again.
2853  */
2854 static void
2855 tcp_newreno_partial_ack(tp, th)
2856         struct tcpcb *tp;
2857         struct tcphdr *th;
2858 {
2859         tcp_seq onxt = tp->snd_nxt;
2860         u_long  ocwnd = tp->snd_cwnd;
2861
2862         callout_stop(tp->tt_rexmt);
2863         tp->t_rtttime = 0;
2864         tp->snd_nxt = th->th_ack;
2865         /*
2866          * Set snd_cwnd to one segment beyond acknowledged offset
2867          * (tp->snd_una has not yet been updated when this function is called.)
2868          */
2869         tp->snd_cwnd = tp->t_maxseg + (th->th_ack - tp->snd_una);
2870         tp->t_flags |= TF_ACKNOW;
2871         (void) tcp_output(tp);
2872         tp->snd_cwnd = ocwnd;
2873         if (SEQ_GT(onxt, tp->snd_nxt))
2874                 tp->snd_nxt = onxt;
2875         /*
2876          * Partial window deflation.  Relies on fact that tp->snd_una
2877          * not updated yet.
2878          */
2879         tp->snd_cwnd -= (th->th_ack - tp->snd_una - tp->t_maxseg);
2880 }