sys/netinet/tcp_input.c

   1 /*
   2  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. All advertising materials mentioning features or use of this software
  14  *    must display the following acknowledgement:
  15  *      This product includes software developed by the University of
  16  *      California, Berkeley and its contributors.
  17  * 4. Neither the name of the University nor the names of its contributors
  18  *    may be used to endorse or promote products derived from this software
  19  *    without specific prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  31  * SUCH DAMAGE.
  32  *
  33  *      @(#)tcp_input.c 8.12 (Berkeley) 5/24/95
  34  * $FreeBSD: src/sys/netinet/tcp_input.c,v 1.107.2.38 2003/05/21 04:46:41 cjc Exp $
  35  * $DragonFly: src/sys/netinet/tcp_input.c,v 1.4 2003/07/24 01:31:07 dillon Exp $
  36  */
  37
  38 #include "opt_ipfw.h"           /* for ipfw_fwd         */
  39 #include "opt_inet6.h"
  40 #include "opt_ipsec.h"
  41 #include "opt_tcpdebug.h"
  42 #include "opt_tcp_input.h"
  43
  44 #include <sys/param.h>
  45 #include <sys/systm.h>
  46 #include <sys/kernel.h>
  47 #include <sys/sysctl.h>
  48 #include <sys/malloc.h>
  49 #include <sys/mbuf.h>
  50 #include <sys/proc.h>           /* for proc0 declaration */
  51 #include <sys/protosw.h>
  52 #include <sys/socket.h>
  53 #include <sys/socketvar.h>
  54 #include <sys/syslog.h>
  55
  56 #include <machine/cpu.h>        /* before tcp_seq.h, for tcp_random18() */
  57
  58 #include <net/if.h>
  59 #include <net/route.h>
  60
  61 #include <netinet/in.h>
  62 #include <netinet/in_systm.h>
  63 #include <netinet/ip.h>
  64 #include <netinet/ip_icmp.h>    /* for ICMP_BANDLIM             */
  65 #include <netinet/in_var.h>
  66 #include <netinet/icmp_var.h>   /* for ICMP_BANDLIM             */
  67 #include <netinet/in_pcb.h>
  68 #include <netinet/ip_var.h>
  69 #include <netinet/ip6.h>
  70 #include <netinet/icmp6.h>
  71 #include <netinet6/nd6.h>
  72 #include <netinet6/ip6_var.h>
  73 #include <netinet6/in6_pcb.h>
  74 #include <netinet/tcp.h>
  75 #include <netinet/tcp_fsm.h>
  76 #include <netinet/tcp_seq.h>
  77 #include <netinet/tcp_timer.h>
  78 #include <netinet/tcp_var.h>
  79 #include <netinet6/tcp6_var.h>
  80 #include <netinet/tcpip.h>
  81 #ifdef TCPDEBUG
  82 #include <netinet/tcp_debug.h>
  83
  84 u_char tcp_saveipgen[40]; /* the size must be of max ip header, now IPv6 */
  85 struct tcphdr tcp_savetcp;
  86 #endif /* TCPDEBUG */
  87
  88 #ifdef FAST_IPSEC
  89 #include <netipsec/ipsec.h>
  90 #include <netipsec/ipsec6.h>
  91 #endif
  92
  93 #ifdef IPSEC
  94 #include <netinet6/ipsec.h>
  95 #include <netinet6/ipsec6.h>
  96 #include <netkey/key.h>
  97 #endif /*IPSEC*/
  98
  99 #include <machine/in_cksum.h>
 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 struct inpcbhead tcb;
 134 #define tcb6    tcb  /* for KAME src sync over BSD*'s */
 135 struct inpcbinfo tcbinfo;
 136
 137 static void      tcp_dooptions(struct tcpopt *, u_char *, int, int);
 138 static void      tcp_pulloutofband(struct socket *,
 139                      struct tcphdr *, struct mbuf *, int);
 140 static int       tcp_reass(struct tcpcb *, struct tcphdr *, int *,
 141                      struct mbuf *);
 142 static void      tcp_xmit_timer(struct tcpcb *, int);
 143 static void      tcp_newreno_partial_ack(struct tcpcb *, struct tcphdr *);
 144
 145 /* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */
 146 #ifdef INET6
 147 #define ND6_HINT(tp) \
 148 do { \
 149         if ((tp) && (tp)->t_inpcb && \
 150             ((tp)->t_inpcb->inp_vflag & INP_IPV6) != 0 && \
 151             (tp)->t_inpcb->in6p_route.ro_rt) \
 152                 nd6_nud_hint((tp)->t_inpcb->in6p_route.ro_rt, NULL, 0); \
 153 } while (0)
 154 #else
 155 #define ND6_HINT(tp)
 156 #endif
 157
 158 /*
 159  * Indicate whether this ack should be delayed.  We can delay the ack if
 160  *      - delayed acks are enabled and
 161  *      - there is no delayed ack timer in progress and
 162  *      - our last ack wasn't a 0-sized window.  We never want to delay
 163  *        the ack that opens up a 0-sized window.
 164  */
 165 #define DELAY_ACK(tp) \
 166         (tcp_delack_enabled && !callout_pending(tp->tt_delack) && \
 167         (tp->t_flags & TF_RXWIN0SENT) == 0)
 168
 169 static int
 170 tcp_reass(tp, th, tlenp, m)
 171         register struct tcpcb *tp;
 172         register struct tcphdr *th;
 173         int *tlenp;
 174         struct mbuf *m;
 175 {
 176         struct tseg_qent *q;
 177         struct tseg_qent *p = NULL;
 178         struct tseg_qent *nq;
 179         struct tseg_qent *te;
 180         struct socket *so = tp->t_inpcb->inp_socket;
 181         int flags;
 182
 183         /*
 184          * Call with th==0 after become established to
 185          * force pre-ESTABLISHED data up to user socket.
 186          */
 187         if (th == 0)
 188                 goto present;
 189
 190         /* Allocate a new queue entry. If we can't, just drop the pkt. XXX */
 191         MALLOC(te, struct tseg_qent *, sizeof(struct tseg_qent), M_TSEGQ,
 192                M_NOWAIT);
 193         if (te == NULL) {
 194                 tcpstat.tcps_rcvmemdrop++;
 195                 m_freem(m);
 196                 return (0);
 197         }
 198
 199         /*
 200          * Find a segment which begins after this one does.
 201          */
 202         LIST_FOREACH(q, &tp->t_segq, tqe_q) {
 203                 if (SEQ_GT(q->tqe_th->th_seq, th->th_seq))
 204                         break;
 205                 p = q;
 206         }
 207
 208         /*
 209          * If there is a preceding segment, it may provide some of
 210          * our data already.  If so, drop the data from the incoming
 211          * segment.  If it provides all of our data, drop us.
 212          */
 213         if (p != NULL) {
 214                 register int i;
 215                 /* conversion to int (in i) handles seq wraparound */
 216                 i = p->tqe_th->th_seq + p->tqe_len - th->th_seq;
 217                 if (i > 0) {
 218                         if (i >= *tlenp) {
 219                                 tcpstat.tcps_rcvduppack++;
 220                                 tcpstat.tcps_rcvdupbyte += *tlenp;
 221                                 m_freem(m);
 222                                 free(te, M_TSEGQ);
 223                                 /*
 224                                  * Try to present any queued data
 225                                  * at the left window edge to the user.
 226                                  * This is needed after the 3-WHS
 227                                  * completes.
 228                                  */
 229                                 goto present;   /* ??? */
 230                         }
 231                         m_adj(m, i);
 232                         *tlenp -= i;
 233                         th->th_seq += i;
 234                 }
 235         }
 236         tcpstat.tcps_rcvoopack++;
 237         tcpstat.tcps_rcvoobyte += *tlenp;
 238
 239         /*
 240          * While we overlap succeeding segments trim them or,
 241          * if they are completely covered, dequeue them.
 242          */
 243         while (q) {
 244                 register int i = (th->th_seq + *tlenp) - q->tqe_th->th_seq;
 245                 if (i <= 0)
 246                         break;
 247                 if (i < q->tqe_len) {
 248                         q->tqe_th->th_seq += i;
 249                         q->tqe_len -= i;
 250                         m_adj(q->tqe_m, i);
 251                         break;
 252                 }
 253
 254                 nq = LIST_NEXT(q, tqe_q);
 255                 LIST_REMOVE(q, tqe_q);
 256                 m_freem(q->tqe_m);
 257                 free(q, M_TSEGQ);
 258                 q = nq;
 259         }
 260
 261         /* Insert the new segment queue entry into place. */
 262         te->tqe_m = m;
 263         te->tqe_th = th;
 264         te->tqe_len = *tlenp;
 265
 266         if (p == NULL) {
 267                 LIST_INSERT_HEAD(&tp->t_segq, te, tqe_q);
 268         } else {
 269                 LIST_INSERT_AFTER(p, te, tqe_q);
 270         }
 271
 272 present:
 273         /*
 274          * Present data to user, advancing rcv_nxt through
 275          * completed sequence space.
 276          */
 277         if (!TCPS_HAVEESTABLISHED(tp->t_state))
 278                 return (0);
 279         q = LIST_FIRST(&tp->t_segq);
 280         if (!q || q->tqe_th->th_seq != tp->rcv_nxt)
 281                 return (0);
 282         do {
 283                 tp->rcv_nxt += q->tqe_len;
 284                 flags = q->tqe_th->th_flags & TH_FIN;
 285                 nq = LIST_NEXT(q, tqe_q);
 286                 LIST_REMOVE(q, tqe_q);
 287                 if (so->so_state & SS_CANTRCVMORE)
 288                         m_freem(q->tqe_m);
 289                 else
 290                         sbappend(&so->so_rcv, q->tqe_m);
 291                 free(q, M_TSEGQ);
 292                 q = nq;
 293         } while (q && q->tqe_th->th_seq == tp->rcv_nxt);
 294         ND6_HINT(tp);
 295         sorwakeup(so);
 296         return (flags);
 297 }
 298
 299 /*
 300  * TCP input routine, follows pages 65-76 of the
 301  * protocol specification dated September, 1981 very closely.
 302  */
 303 #ifdef INET6
 304 int
 305 tcp6_input(mp, offp, proto)
 306         struct mbuf **mp;
 307         int *offp, proto;
 308 {
 309         register struct mbuf *m = *mp;
 310         struct in6_ifaddr *ia6;
 311
 312         IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
 313
 314         /*
 315          * draft-itojun-ipv6-tcp-to-anycast
 316          * better place to put this in?
 317          */
 318         ia6 = ip6_getdstifaddr(m);
 319         if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
 320                 struct ip6_hdr *ip6;
 321
 322                 ip6 = mtod(m, struct ip6_hdr *);
 323                 icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
 324                             (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
 325                 return IPPROTO_DONE;
 326         }
 327
 328         tcp_input(m, *offp, proto);
 329         return IPPROTO_DONE;
 330 }
 331 #endif
 332
 333 void
 334 tcp_input(m, off0, proto)
 335         register struct mbuf *m;
 336         int off0, proto;
 337 {
 338         register struct tcphdr *th;
 339         register struct ip *ip = NULL;
 340         register struct ipovly *ipov;
 341         register struct inpcb *inp = NULL;
 342         u_char *optp = NULL;
 343         int optlen = 0;
 344         int len, tlen, off;
 345         int drop_hdrlen;
 346         register struct tcpcb *tp = NULL;
 347         register int thflags;
 348         struct socket *so = 0;
 349         int todrop, acked, ourfinisacked, needoutput = 0;
 350         u_long tiwin;
 351         struct tcpopt to;               /* options in this segment */
 352         struct rmxp_tao *taop;          /* pointer to our TAO cache entry */
 353         struct rmxp_tao tao_noncached;  /* in case there's no cached entry */
 354         struct sockaddr_in *next_hop = NULL;
 355         int rstreason; /* For badport_bandlim accounting purposes */
 356         struct ip6_hdr *ip6 = NULL;
 357 #ifdef INET6
 358         int isipv6;
 359 #else
 360         const int isipv6 = 0;
 361 #endif
 362 #ifdef TCPDEBUG
 363         short ostate = 0;
 364 #endif
 365
 366         /* Grab info from MT_TAG mbufs prepended to the chain. */
 367         for (;m && m->m_type == MT_TAG; m = m->m_next) {
 368                 if (m->_m_tag_id == PACKET_TAG_IPFORWARD)
 369                         next_hop = (struct sockaddr_in *)m->m_hdr.mh_data;
 370         }
 371 #ifdef INET6
 372         isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
 373 #endif
 374         bzero((char *)&to, sizeof(to));
 375
 376         tcpstat.tcps_rcvtotal++;
 377
 378         if (isipv6) {
 379                 /* IP6_EXTHDR_CHECK() is already done at tcp6_input() */
 380                 ip6 = mtod(m, struct ip6_hdr *);
 381                 tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
 382                 if (in6_cksum(m, IPPROTO_TCP, off0, tlen)) {
 383                         tcpstat.tcps_rcvbadsum++;
 384                         goto drop;
 385                 }
 386                 th = (struct tcphdr *)((caddr_t)ip6 + off0);
 387
 388                 /*
 389                  * Be proactive about unspecified IPv6 address in source.
 390                  * As we use all-zero to indicate unbounded/unconnected pcb,
 391                  * unspecified IPv6 address can be used to confuse us.
 392                  *
 393                  * Note that packets with unspecified IPv6 destination is
 394                  * already dropped in ip6_input.
 395                  */
 396                 if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
 397                         /* XXX stat */
 398                         goto drop;
 399                 }
 400         } else {
 401                 /*
 402                  * Get IP and TCP header together in first mbuf.
 403                  * Note: IP leaves IP header in first mbuf.
 404                  */
 405                 if (off0 > sizeof(struct ip)) {
 406                         ip_stripoptions(m, (struct mbuf *)0);
 407                         off0 = sizeof(struct ip);
 408                 }
 409                 if (m->m_len < sizeof(struct tcpiphdr)) {
 410                         if ((m = m_pullup(m, sizeof(struct tcpiphdr))) == 0) {
 411                                 tcpstat.tcps_rcvshort++;
 412                                 return;
 413                         }
 414                 }
 415                 ip = mtod(m, struct ip *);
 416                 ipov = (struct ipovly *)ip;
 417                 th = (struct tcphdr *)((caddr_t)ip + off0);
 418                 tlen = ip->ip_len;
 419
 420                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
 421                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
 422                                 th->th_sum = m->m_pkthdr.csum_data;
 423                         else
 424                                 th->th_sum = in_pseudo(ip->ip_src.s_addr,
 425                                                 ip->ip_dst.s_addr,
 426                                                 htonl(m->m_pkthdr.csum_data +
 427                                                         ip->ip_len +
 428                                                         IPPROTO_TCP));
 429                         th->th_sum ^= 0xffff;
 430                 } else {
 431                         /*
 432                          * Checksum extended TCP header and data.
 433                          */
 434                         len = sizeof(struct ip) + tlen;
 435                         bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
 436                         ipov->ih_len = (u_short)tlen;
 437                         ipov->ih_len = htons(ipov->ih_len);
 438                         th->th_sum = in_cksum(m, len);
 439                 }
 440                 if (th->th_sum) {
 441                         tcpstat.tcps_rcvbadsum++;
 442                         goto drop;
 443                 }
 444 #ifdef INET6
 445                 /* Re-initialization for later version check */
 446                 ip->ip_v = IPVERSION;
 447 #endif
 448         }
 449
 450         /*
 451          * Check that TCP offset makes sense,
 452          * pull out TCP options and adjust length.              XXX
 453          */
 454         off = th->th_off << 2;
 455         if (off < sizeof(struct tcphdr) || off > tlen) {
 456                 tcpstat.tcps_rcvbadoff++;
 457                 goto drop;
 458         }
 459         tlen -= off;    /* tlen is used instead of ti->ti_len */
 460         if (off > sizeof(struct tcphdr)) {
 461                 if (isipv6) {
 462                         IP6_EXTHDR_CHECK(m, off0, off, );
 463                         ip6 = mtod(m, struct ip6_hdr *);
 464                         th = (struct tcphdr *)((caddr_t)ip6 + off0);
 465                 } else {
 466                         if (m->m_len < sizeof(struct ip) + off) {
 467                                 if ((m = m_pullup(m, sizeof(struct ip) + off))
 468                                                 == 0) {
 469                                         tcpstat.tcps_rcvshort++;
 470                                         return;
 471                                 }
 472                                 ip = mtod(m, struct ip *);
 473                                 ipov = (struct ipovly *)ip;
 474                                 th = (struct tcphdr *)((caddr_t)ip + off0);
 475                         }
 476                 }
 477                 optlen = off - sizeof(struct tcphdr);
 478                 optp = (u_char *)(th + 1);
 479         }
 480         thflags = th->th_flags;
 481
 482 #ifdef TCP_DROP_SYNFIN
 483         /*
 484          * If the drop_synfin option is enabled, drop all packets with
 485          * both the SYN and FIN bits set. This prevents e.g. nmap from
 486          * identifying the TCP/IP stack.
 487          *
 488          * This is a violation of the TCP specification.
 489          */
 490         if (drop_synfin && (thflags & (TH_SYN|TH_FIN)) == (TH_SYN|TH_FIN))
 491                 goto drop;
 492 #endif
 493
 494         /*
 495          * Convert TCP protocol specific fields to host format.
 496          */
 497         th->th_seq = ntohl(th->th_seq);
 498         th->th_ack = ntohl(th->th_ack);
 499         th->th_win = ntohs(th->th_win);
 500         th->th_urp = ntohs(th->th_urp);
 501
 502         /*
 503          * Delay droping TCP, IP headers, IPv6 ext headers, and TCP options,
 504          * until after ip6_savecontrol() is called and before other functions
 505          * which don't want those proto headers.
 506          * Because ip6_savecontrol() is going to parse the mbuf to
 507          * search for data to be passed up to user-land, it wants mbuf
 508          * parameters to be unchanged.
 509          * XXX: the call of ip6_savecontrol() has been obsoleted based on
 510          * latest version of the advanced API (20020110).
 511          */
 512         drop_hdrlen = off0 + off;
 513
 514         /*
 515          * Locate pcb for segment.
 516          */
 517 findpcb:
 518         /* IPFIREWALL_FORWARD section */
 519         if (next_hop != NULL && isipv6 == 0) {  /* IPv6 support is not yet */
 520                 /*
 521                  * Transparently forwarded. Pretend to be the destination.
 522                  * already got one like this?
 523                  */
 524                 inp = in_pcblookup_hash(&tcbinfo, ip->ip_src, th->th_sport,
 525                                         ip->ip_dst, th->th_dport,
 526                                         0, m->m_pkthdr.rcvif);
 527                 if (!inp) {
 528                         /* It's new.  Try find the ambushing socket. */
 529                         inp = in_pcblookup_hash(&tcbinfo,
 530                                                 ip->ip_src, th->th_sport,
 531                                                 next_hop->sin_addr,
 532                                                 next_hop->sin_port ?
 533                                                     ntohs(next_hop->sin_port) :
 534                                                     th->th_dport,
 535                                                 1, m->m_pkthdr.rcvif);
 536                 }
 537         } else {
 538                 if (isipv6)
 539                         inp = in6_pcblookup_hash(&tcbinfo,
 540                                                  &ip6->ip6_src, th->th_sport,
 541                                                  &ip6->ip6_dst, th->th_dport,
 542                                                  1, m->m_pkthdr.rcvif);
 543                 else
 544                         inp = in_pcblookup_hash(&tcbinfo,
 545                                                 ip->ip_src, th->th_sport,
 546                                                 ip->ip_dst, th->th_dport,
 547                                                 1, m->m_pkthdr.rcvif);
 548       }
 549
 550 #ifdef IPSEC
 551         if (isipv6) {
 552                 if (inp != NULL && ipsec6_in_reject_so(m, inp->inp_socket)) {
 553                         ipsec6stat.in_polvio++;
 554                         goto drop;
 555                 }
 556         } else {
 557                 if (inp != NULL && ipsec4_in_reject_so(m, inp->inp_socket)) {
 558                         ipsecstat.in_polvio++;
 559                         goto drop;
 560                 }
 561         }
 562 #endif
 563 #ifdef FAST_IPSEC
 564         if (isipv6) {
 565                 if (inp != NULL && ipsec6_in_reject(m, inp)) {
 566                         goto drop;
 567                 }
 568         } else {
 569                 if (inp != NULL && ipsec4_in_reject(m, inp)) {
 570                         goto drop;
 571                 }
 572         }
 573 #endif
 574
 575         /*
 576          * If the state is CLOSED (i.e., TCB does not exist) then
 577          * all data in the incoming segment is discarded.
 578          * If the TCB exists but is in CLOSED state, it is embryonic,
 579          * but should either do a listen or a connect soon.
 580          */
 581         if (inp == NULL) {
 582                 if (log_in_vain) {
 583 #ifdef INET6
 584                         char dbuf[INET6_ADDRSTRLEN+2], sbuf[INET6_ADDRSTRLEN+2];
 585 #else
 586                         char dbuf[4*sizeof "123"], sbuf[4*sizeof "123"];
 587 #endif
 588                         if (isipv6) {
 589                                 strcpy(dbuf, "[");
 590                                 strcpy(sbuf, "[");
 591                                 strcat(dbuf, ip6_sprintf(&ip6->ip6_dst));
 592                                 strcat(sbuf, ip6_sprintf(&ip6->ip6_src));
 593                                 strcat(dbuf, "]");
 594                                 strcat(sbuf, "]");
 595                         } else {
 596                                 strcpy(dbuf, inet_ntoa(ip->ip_dst));
 597                                 strcpy(sbuf, inet_ntoa(ip->ip_src));
 598                         }
 599                         switch (log_in_vain) {
 600                         case 1:
 601                                 if ((thflags & TH_SYN) == 0)
 602                                         break;
 603                         case 2:
 604                                 log(LOG_INFO,
 605                                     "Connection attempt to TCP %s:%d "
 606                                     "from %s:%d flags:0x%02x\n",
 607                                     dbuf, ntohs(th->th_dport), sbuf,
 608                                     ntohs(th->th_sport), thflags);
 609                                 break;
 610                         default:
 611                                 break;
 612                         }
 613                 }
 614                 if (blackhole) {
 615                         switch (blackhole) {
 616                         case 1:
 617                                 if (thflags & TH_SYN)
 618                                         goto drop;
 619                                 break;
 620                         case 2:
 621                                 goto drop;
 622                         default:
 623                                 goto drop;
 624                         }
 625                 }
 626                 rstreason = BANDLIM_RST_CLOSEDPORT;
 627                 goto dropwithreset;
 628         }
 629         tp = intotcpcb(inp);
 630         if (tp == NULL) {
 631                 rstreason = BANDLIM_RST_CLOSEDPORT;
 632                 goto dropwithreset;
 633         }
 634         if (tp->t_state == TCPS_CLOSED)
 635                 goto drop;
 636
 637         /* Unscale the window into a 32-bit value. */
 638         if ((thflags & TH_SYN) == 0)
 639                 tiwin = th->th_win << tp->snd_scale;
 640         else
 641                 tiwin = th->th_win;
 642
 643         so = inp->inp_socket;
 644         if (so->so_options & (SO_DEBUG|SO_ACCEPTCONN)) {
 645                 struct in_conninfo inc;
 646 #ifdef TCPDEBUG
 647                 if (so->so_options & SO_DEBUG) {
 648                         ostate = tp->t_state;
 649                         if (isipv6)
 650                                 bcopy((char *)ip6, (char *)tcp_saveipgen,
 651                                     sizeof(*ip6));
 652                         else
 653                                 bcopy((char *)ip, (char *)tcp_saveipgen,
 654                                     sizeof(*ip));
 655                         tcp_savetcp = *th;
 656                 }
 657 #endif
 658                 /* skip if this isn't a listen socket */
 659                 if ((so->so_options & SO_ACCEPTCONN) == 0)
 660                         goto after_listen;
 661 #ifdef INET6
 662                 inc.inc_isipv6 = isipv6;
 663 #endif
 664                 if (isipv6) {
 665                         inc.inc6_faddr = ip6->ip6_src;
 666                         inc.inc6_laddr = ip6->ip6_dst;
 667                         inc.inc6_route.ro_rt = NULL;            /* XXX */
 668                 } else {
 669                         inc.inc_faddr = ip->ip_src;
 670                         inc.inc_laddr = ip->ip_dst;
 671                         inc.inc_route.ro_rt = NULL;             /* XXX */
 672                 }
 673                 inc.inc_fport = th->th_sport;
 674                 inc.inc_lport = th->th_dport;
 675
 676                 /*
 677                  * If the state is LISTEN then ignore segment if it contains
 678                  * a RST.  If the segment contains an ACK then it is bad and
 679                  * send a RST.  If it does not contain a SYN then it is not
 680                  * interesting; drop it.
 681                  *
 682                  * If the state is SYN_RECEIVED (syncache) and seg contains
 683                  * an ACK, but not for our SYN/ACK, send a RST.  If the seg
 684                  * contains a RST, check the sequence number to see if it
 685                  * is a valid reset segment.
 686                  */
 687                 if ((thflags & (TH_RST|TH_ACK|TH_SYN)) != TH_SYN) {
 688                         if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
 689                                 if (!syncache_expand(&inc, th, &so, m)) {
 690                                         /*
 691                                          * No syncache entry, or ACK was not
 692                                          * for our SYN/ACK.  Send a RST.
 693                                          */
 694                                         tcpstat.tcps_badsyn++;
 695                                         rstreason = BANDLIM_RST_OPENPORT;
 696                                         goto dropwithreset;
 697                                 }
 698                                 if (so == NULL)
 699                                         /*
 700                                          * Could not complete 3-way handshake,
 701                                          * connection is being closed down, and
 702                                          * syncache will free mbuf.
 703                                          */
 704                                         return;
 705                                 /*
 706                                  * Socket is created in state SYN_RECEIVED.
 707                                  * Continue processing segment.
 708                                  */
 709                                 inp = sotoinpcb(so);
 710                                 tp = intotcpcb(inp);
 711                                 /*
 712                                  * This is what would have happened in
 713                                  * tcp_output() when the SYN,ACK was sent.
 714                                  */
 715                                 tp->snd_up = tp->snd_una;
 716                                 tp->snd_max = tp->snd_nxt = tp->iss + 1;
 717                                 tp->last_ack_sent = tp->rcv_nxt;
 718 /*
 719  * XXX possible bug - it doesn't appear that tp->snd_wnd is unscaled
 720  * until the _second_ ACK is received:
 721  *    rcv SYN (set wscale opts)  --> send SYN/ACK, set snd_wnd = window.
 722  *    rcv ACK, calculate tiwin --> process SYN_RECEIVED, determine wscale,
 723  *        move to ESTAB, set snd_wnd to tiwin.
 724  */
 725                                 tp->snd_wnd = tiwin;    /* unscaled */
 726                                 goto after_listen;
 727                         }
 728                         if (thflags & TH_RST) {
 729                                 syncache_chkrst(&inc, th);
 730                                 goto drop;
 731                         }
 732                         if (thflags & TH_ACK) {
 733                                 syncache_badack(&inc);
 734                                 tcpstat.tcps_badsyn++;
 735                                 rstreason = BANDLIM_RST_OPENPORT;
 736                                 goto dropwithreset;
 737                         }
 738                         goto drop;
 739                 }
 740
 741                 /*
 742                  * Segment's flags are (SYN) or (SYN|FIN).
 743                  */
 744 #ifdef INET6
 745                 /*
 746                  * If deprecated address is forbidden,
 747                  * we do not accept SYN to deprecated interface
 748                  * address to prevent any new inbound connection from
 749                  * getting established.
 750                  * When we do not accept SYN, we send a TCP RST,
 751                  * with deprecated source address (instead of dropping
 752                  * it).  We compromise it as it is much better for peer
 753                  * to send a RST, and RST will be the final packet
 754                  * for the exchange.
 755                  *
 756                  * If we do not forbid deprecated addresses, we accept
 757                  * the SYN packet.  RFC2462 does not suggest dropping
 758                  * SYN in this case.
 759                  * If we decipher RFC2462 5.5.4, it says like this:
 760                  * 1. use of deprecated addr with existing
 761                  *    communication is okay - "SHOULD continue to be
 762                  *    used"
 763                  * 2. use of it with new communication:
 764                  *   (2a) "SHOULD NOT be used if alternate address
 765                  *        with sufficient scope is available"
 766                  *   (2b) nothing mentioned otherwise.
 767                  * Here we fall into (2b) case as we have no choice in
 768                  * our source address selection - we must obey the peer.
 769                  *
 770                  * The wording in RFC2462 is confusing, and there are
 771                  * multiple description text for deprecated address
 772                  * handling - worse, they are not exactly the same.
 773                  * I believe 5.5.4 is the best one, so we follow 5.5.4.
 774                  */
 775                 if (isipv6 && !ip6_use_deprecated) {
 776                         struct in6_ifaddr *ia6;
 777
 778                         if ((ia6 = ip6_getdstifaddr(m)) &&
 779                             (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
 780                                 tp = NULL;
 781                                 rstreason = BANDLIM_RST_OPENPORT;
 782                                 goto dropwithreset;
 783                         }
 784                 }
 785 #endif
 786                 /*
 787                  * If it is from this socket, drop it, it must be forged.
 788                  * Don't bother responding if the destination was a broadcast.
 789                  */
 790                 if (th->th_dport == th->th_sport) {
 791                         if (isipv6) {
 792                                 if (IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst,
 793                                                        &ip6->ip6_src))
 794                                         goto drop;
 795                         } else {
 796                                 if (ip->ip_dst.s_addr == ip->ip_src.s_addr)
 797                                         goto drop;
 798                         }
 799                 }
 800                 /*
 801                  * RFC1122 4.2.3.10, p. 104: discard bcast/mcast SYN
 802                  *
 803                  * Note that it is quite possible to receive unicast
 804                  * link-layer packets with a broadcast IP address. Use
 805                  * in_broadcast() to find them.
 806                  */
 807                 if (m->m_flags & (M_BCAST|M_MCAST))
 808                         goto drop;
 809                 if (isipv6) {
 810                         if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
 811                             IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
 812                                 goto drop;
 813                 } else {
 814                         if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
 815                             IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
 816                             ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
 817                             in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
 818                                 goto drop;
 819                 }
 820                 /*
 821                  * SYN appears to be valid; create compressed TCP state
 822                  * for syncache, or perform t/tcp connection.
 823                  */
 824                 if (so->so_qlen <= so->so_qlimit) {
 825                         tcp_dooptions(&to, optp, optlen, 1);
 826                         if (!syncache_add(&inc, &to, th, &so, m))
 827                                 goto drop;
 828                         if (so == NULL)
 829                                 /*
 830                                  * Entry added to syncache, mbuf used to
 831                                  * send SYN,ACK packet.
 832                                  */
 833                                 return;
 834                         /*
 835                          * Segment passed TAO tests.
 836                          */
 837                         inp = sotoinpcb(so);
 838                         tp = intotcpcb(inp);
 839                         tp->snd_wnd = tiwin;
 840                         tp->t_starttime = ticks;
 841                         tp->t_state = TCPS_ESTABLISHED;
 842
 843                         /*
 844                          * If there is a FIN, or if there is data and the
 845                          * connection is local, then delay SYN,ACK(SYN) in
 846                          * the hope of piggy-backing it on a response
 847                          * segment.  Otherwise must send ACK now in case
 848                          * the other side is slow starting.
 849                          */
 850                         if (DELAY_ACK(tp) &&
 851                             ((thflags & TH_FIN) ||
 852                              (tlen != 0 &&
 853                               ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
 854                                (!isipv6 && in_localaddr(inp->inp_faddr)))))) {
 855                                 callout_reset(tp->tt_delack, tcp_delacktime,
 856                                                 tcp_timer_delack, tp);
 857                                 tp->t_flags |= TF_NEEDSYN;
 858                         } else
 859                                 tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
 860
 861                         tcpstat.tcps_connects++;
 862                         soisconnected(so);
 863                         goto trimthenstep6;
 864                 }
 865                 goto drop;
 866         }
 867 after_listen:
 868
 869 /* XXX temp debugging */
 870         /* should not happen - syncache should pick up these connections */
 871         if (tp->t_state == TCPS_LISTEN)
 872                 panic("tcp_input: TCPS_LISTEN");
 873
 874         /*
 875          * Segment received on connection.
 876          * Reset idle time and keep-alive timer.
 877          */
 878         tp->t_rcvtime = ticks;
 879         if (TCPS_HAVEESTABLISHED(tp->t_state))
 880                 callout_reset(tp->tt_keep, tcp_keepidle, tcp_timer_keep, tp);
 881
 882         /*
 883          * Process options.
 884          * XXX this is tradtitional behavior, may need to be cleaned up.
 885          */
 886         tcp_dooptions(&to, optp, optlen, thflags & TH_SYN);
 887         if (thflags & TH_SYN) {
 888                 if (to.to_flags & TOF_SCALE) {
 889                         tp->t_flags |= TF_RCVD_SCALE;
 890                         tp->requested_s_scale = to.to_requested_s_scale;
 891                 }
 892                 if (to.to_flags & TOF_TS) {
 893                         tp->t_flags |= TF_RCVD_TSTMP;
 894                         tp->ts_recent = to.to_tsval;
 895                         tp->ts_recent_age = ticks;
 896                 }
 897                 if (to.to_flags & (TOF_CC|TOF_CCNEW))
 898                         tp->t_flags |= TF_RCVD_CC;
 899                 if (to.to_flags & TOF_MSS)
 900                         tcp_mss(tp, to.to_mss);
 901         }
 902
 903         /*
 904          * Header prediction: check for the two common cases
 905          * of a uni-directional data xfer.  If the packet has
 906          * no control flags, is in-sequence, the window didn't
 907          * change and we're not retransmitting, it's a
 908          * candidate.  If the length is zero and the ack moved
 909          * forward, we're the sender side of the xfer.  Just
 910          * free the data acked & wake any higher level process
 911          * that was blocked waiting for space.  If the length
 912          * is non-zero and the ack didn't move, we're the
 913          * receiver side.  If we're getting packets in-order
 914          * (the reassembly queue is empty), add the data to
 915          * the socket buffer and note that we need a delayed ack.
 916          * Make sure that the hidden state-flags are also off.
 917          * Since we check for TCPS_ESTABLISHED above, it can only
 918          * be TH_NEEDSYN.
 919          */
 920         if (tp->t_state == TCPS_ESTABLISHED &&
 921             (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
 922             ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
 923             ((to.to_flags & TOF_TS) == 0 ||
 924              TSTMP_GEQ(to.to_tsval, tp->ts_recent)) &&
 925             /*
 926              * Using the CC option is compulsory if once started:
 927              *   the segment is OK if no T/TCP was negotiated or
 928              *   if the segment has a CC option equal to CCrecv
 929              */
 930             ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) != (TF_REQ_CC|TF_RCVD_CC) ||
 931              ((to.to_flags & TOF_CC) != 0 && to.to_cc == tp->cc_recv)) &&
 932             th->th_seq == tp->rcv_nxt &&
 933             tiwin && tiwin == tp->snd_wnd &&
 934             tp->snd_nxt == tp->snd_max) {
 935
 936                 /*
 937                  * If last ACK falls within this segment's sequence numbers,
 938                  * record the timestamp.
 939                  * NOTE that the test is modified according to the latest
 940                  * proposal of the tcplw@cray.com list (Braden 1993/04/26).
 941                  */
 942                 if ((to.to_flags & TOF_TS) != 0 &&
 943                     SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
 944                         tp->ts_recent_age = ticks;
 945                         tp->ts_recent = to.to_tsval;
 946                 }
 947
 948                 if (tlen == 0) {
 949                         if (SEQ_GT(th->th_ack, tp->snd_una) &&
 950                             SEQ_LEQ(th->th_ack, tp->snd_max) &&
 951                             tp->snd_cwnd >= tp->snd_wnd &&
 952                             ((!tcp_do_newreno &&
 953                               tp->t_dupacks < tcprexmtthresh) ||
 954                              (tcp_do_newreno && !IN_FASTRECOVERY(tp)))) {
 955                                 /*
 956                                  * this is a pure ack for outstanding data.
 957                                  */
 958                                 ++tcpstat.tcps_predack;
 959                                 /*
 960                                  * "bad retransmit" recovery
 961                                  */
 962                                 if (tp->t_rxtshift == 1 &&
 963                                     ticks < tp->t_badrxtwin) {
 964                                         tp->snd_cwnd = tp->snd_cwnd_prev;
 965                                         tp->snd_ssthresh =
 966                                             tp->snd_ssthresh_prev;
 967                                         tp->snd_recover = tp->snd_recover_prev;
 968                                         if (tp->t_flags & TF_WASFRECOVERY)
 969                                             ENTER_FASTRECOVERY(tp);
 970                                         tp->snd_nxt = tp->snd_max;
 971                                         tp->t_badrxtwin = 0;
 972                                 }
 973                                 /*
 974                                  * Recalculate the retransmit timer / rtt.
 975                                  *
 976                                  * Some machines (certain windows boxes)
 977                                  * send broken timestamp replies during the
 978                                  * SYN+ACK phase, ignore timestamps of 0.
 979                                  */
 980                                 if ((to.to_flags & TOF_TS) != 0 &&
 981                                     to.to_tsecr) {
 982                                         tcp_xmit_timer(tp,
 983                                             ticks - to.to_tsecr + 1);
 984                                 } else if (tp->t_rtttime &&
 985                                             SEQ_GT(th->th_ack, tp->t_rtseq)) {
 986                                         tcp_xmit_timer(tp,
 987                                                        ticks - tp->t_rtttime);
 988                                 }
 989                                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
 990                                 acked = th->th_ack - tp->snd_una;
 991                                 tcpstat.tcps_rcvackpack++;
 992                                 tcpstat.tcps_rcvackbyte += acked;
 993                                 sbdrop(&so->so_snd, acked);
 994                                 if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
 995                                     SEQ_LEQ(th->th_ack, tp->snd_recover))
 996                                         tp->snd_recover = th->th_ack - 1;
 997                                 tp->snd_una = th->th_ack;
 998                                 tp->t_dupacks = 0;
 999                                 m_freem(m);
1000                                 ND6_HINT(tp); /* some progress has been done */
1001
1002                                 /*
1003                                  * If all outstanding data are acked, stop
1004                                  * retransmit timer, otherwise restart timer
1005                                  * using current (possibly backed-off) value.
1006                                  * If process is waiting for space,
1007                                  * wakeup/selwakeup/signal.  If data
1008                                  * are ready to send, let tcp_output
1009                                  * decide between more output or persist.
1010                                  */
1011                                 if (tp->snd_una == tp->snd_max)
1012                                         callout_stop(tp->tt_rexmt);
1013                                 else if (!callout_active(tp->tt_persist))
1014                                         callout_reset(tp->tt_rexmt,
1015                                                       tp->t_rxtcur,
1016                                                       tcp_timer_rexmt, tp);
1017
1018                                 sowwakeup(so);
1019                                 if (so->so_snd.sb_cc)
1020                                         (void) tcp_output(tp);
1021                                 return;
1022                         }
1023                 } else if (th->th_ack == tp->snd_una &&
1024                     LIST_EMPTY(&tp->t_segq) &&
1025                     tlen <= sbspace(&so->so_rcv)) {
1026                         /*
1027                          * this is a pure, in-sequence data packet
1028                          * with nothing on the reassembly queue and
1029                          * we have enough buffer space to take it.
1030                          */
1031                         ++tcpstat.tcps_preddat;
1032                         tp->rcv_nxt += tlen;
1033                         tcpstat.tcps_rcvpack++;
1034                         tcpstat.tcps_rcvbyte += tlen;
1035                         ND6_HINT(tp);   /* some progress has been done */
1036                         /*
1037                          * Add data to socket buffer.
1038                          */
1039                         if (so->so_state & SS_CANTRCVMORE) {
1040                                 m_freem(m);
1041                         } else {
1042                                 m_adj(m, drop_hdrlen);  /* delayed header drop */
1043                                 sbappend(&so->so_rcv, m);
1044                         }
1045                         sorwakeup(so);
1046                         if (DELAY_ACK(tp)) {
1047                                 callout_reset(tp->tt_delack, tcp_delacktime,
1048                                     tcp_timer_delack, tp);
1049                         } else {
1050                                 tp->t_flags |= TF_ACKNOW;
1051                                 tcp_output(tp);
1052                         }
1053                         return;
1054                 }
1055         }
1056
1057         /*
1058          * Calculate amount of space in receive window,
1059          * and then do TCP input processing.
1060          * Receive window is amount of space in rcv queue,
1061          * but not less than advertised window.
1062          */
1063         { int win;
1064
1065         win = sbspace(&so->so_rcv);
1066         if (win < 0)
1067                 win = 0;
1068         tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
1069         }
1070
1071         switch (tp->t_state) {
1072
1073         /*
1074          * If the state is SYN_RECEIVED:
1075          *      if seg contains an ACK, but not for our SYN/ACK, send a RST.
1076          */
1077         case TCPS_SYN_RECEIVED:
1078                 if ((thflags & TH_ACK) &&
1079                     (SEQ_LEQ(th->th_ack, tp->snd_una) ||
1080                      SEQ_GT(th->th_ack, tp->snd_max))) {
1081                                 rstreason = BANDLIM_RST_OPENPORT;
1082                                 goto dropwithreset;
1083                 }
1084                 break;
1085
1086         /*
1087          * If the state is SYN_SENT:
1088          *      if seg contains an ACK, but not for our SYN, drop the input.
1089          *      if seg contains a RST, then drop the connection.
1090          *      if seg does not contain SYN, then drop it.
1091          * Otherwise this is an acceptable SYN segment
1092          *      initialize tp->rcv_nxt and tp->irs
1093          *      if seg contains ack then advance tp->snd_una
1094          *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
1095          *      arrange for segment to be acked (eventually)
1096          *      continue processing rest of data/controls, beginning with URG
1097          */
1098         case TCPS_SYN_SENT:
1099                 if ((taop = tcp_gettaocache(&inp->inp_inc)) == NULL) {
1100                         taop = &tao_noncached;
1101                         bzero(taop, sizeof(*taop));
1102                 }
1103
1104                 if ((thflags & TH_ACK) &&
1105                     (SEQ_LEQ(th->th_ack, tp->iss) ||
1106                      SEQ_GT(th->th_ack, tp->snd_max))) {
1107                         /*
1108                          * If we have a cached CCsent for the remote host,
1109                          * hence we haven't just crashed and restarted,
1110                          * do not send a RST.  This may be a retransmission
1111                          * from the other side after our earlier ACK was lost.
1112                          * Our new SYN, when it arrives, will serve as the
1113                          * needed ACK.
1114                          */
1115                         if (taop->tao_ccsent != 0)
1116                                 goto drop;
1117                         else {
1118                                 rstreason = BANDLIM_UNLIMITED;
1119                                 goto dropwithreset;
1120                         }
1121                 }
1122                 if (thflags & TH_RST) {
1123                         if (thflags & TH_ACK)
1124                                 tp = tcp_drop(tp, ECONNREFUSED);
1125                         goto drop;
1126                 }
1127                 if ((thflags & TH_SYN) == 0)
1128                         goto drop;
1129                 tp->snd_wnd = th->th_win;       /* initial send window */
1130                 tp->cc_recv = to.to_cc;         /* foreign CC */
1131
1132                 tp->irs = th->th_seq;
1133                 tcp_rcvseqinit(tp);
1134                 if (thflags & TH_ACK) {
1135                         /*
1136                          * Our SYN was acked.  If segment contains CC.ECHO
1137                          * option, check it to make sure this segment really
1138                          * matches our SYN.  If not, just drop it as old
1139                          * duplicate, but send an RST if we're still playing
1140                          * by the old rules.  If no CC.ECHO option, make sure
1141                          * we don't get fooled into using T/TCP.
1142                          */
1143                         if (to.to_flags & TOF_CCECHO) {
1144                                 if (tp->cc_send != to.to_ccecho) {
1145                                         if (taop->tao_ccsent != 0)
1146                                                 goto drop;
1147                                         else {
1148                                                 rstreason = BANDLIM_UNLIMITED;
1149                                                 goto dropwithreset;
1150                                         }
1151                                 }
1152                         } else
1153                                 tp->t_flags &= ~TF_RCVD_CC;
1154                         tcpstat.tcps_connects++;
1155                         soisconnected(so);
1156                         /* Do window scaling on this connection? */
1157                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1158                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1159                                 tp->snd_scale = tp->requested_s_scale;
1160                                 tp->rcv_scale = tp->request_r_scale;
1161                         }
1162                         /* Segment is acceptable, update cache if undefined. */
1163                         if (taop->tao_ccsent == 0)
1164                                 taop->tao_ccsent = to.to_ccecho;
1165
1166                         tp->rcv_adv += tp->rcv_wnd;
1167                         tp->snd_una++;          /* SYN is acked */
1168                         /*
1169                          * If there's data, delay ACK; if there's also a FIN
1170                          * ACKNOW will be turned on later.
1171                          */
1172                         if (DELAY_ACK(tp) && tlen != 0)
1173                                 callout_reset(tp->tt_delack, tcp_delacktime,
1174                                     tcp_timer_delack, tp);
1175                         else
1176                                 tp->t_flags |= TF_ACKNOW;
1177                         /*
1178                          * Received <SYN,ACK> in SYN_SENT[*] state.
1179                          * Transitions:
1180                          *      SYN_SENT  --> ESTABLISHED
1181                          *      SYN_SENT* --> FIN_WAIT_1
1182                          */
1183                         tp->t_starttime = ticks;
1184                         if (tp->t_flags & TF_NEEDFIN) {
1185                                 tp->t_state = TCPS_FIN_WAIT_1;
1186                                 tp->t_flags &= ~TF_NEEDFIN;
1187                                 thflags &= ~TH_SYN;
1188                         } else {
1189                                 tp->t_state = TCPS_ESTABLISHED;
1190                                 callout_reset(tp->tt_keep, tcp_keepidle,
1191                                               tcp_timer_keep, tp);
1192                         }
1193                 } else {
1194                         /*
1195                          * Received initial SYN in SYN-SENT[*] state =>
1196                          * simultaneous open.  If segment contains CC option
1197                          * and there is a cached CC, apply TAO test.
1198                          * If it succeeds, connection is * half-synchronized.
1199                          * Otherwise, do 3-way handshake:
1200                          *        SYN-SENT -> SYN-RECEIVED
1201                          *        SYN-SENT* -> SYN-RECEIVED*
1202                          * If there was no CC option, clear cached CC value.
1203                          */
1204                         tp->t_flags |= TF_ACKNOW;
1205                         callout_stop(tp->tt_rexmt);
1206                         if (to.to_flags & TOF_CC) {
1207                                 if (taop->tao_cc != 0 &&
1208                                     CC_GT(to.to_cc, taop->tao_cc)) {
1209                                         /*
1210                                          * update cache and make transition:
1211                                          *        SYN-SENT -> ESTABLISHED*
1212                                          *        SYN-SENT* -> FIN-WAIT-1*
1213                                          */
1214                                         taop->tao_cc = to.to_cc;
1215                                         tp->t_starttime = ticks;
1216                                         if (tp->t_flags & TF_NEEDFIN) {
1217                                                 tp->t_state = TCPS_FIN_WAIT_1;
1218                                                 tp->t_flags &= ~TF_NEEDFIN;
1219                                         } else {
1220                                                 tp->t_state = TCPS_ESTABLISHED;
1221                                                 callout_reset(tp->tt_keep,
1222                                                               tcp_keepidle,
1223                                                               tcp_timer_keep,
1224                                                               tp);
1225                                         }
1226                                         tp->t_flags |= TF_NEEDSYN;
1227                                 } else
1228                                         tp->t_state = TCPS_SYN_RECEIVED;
1229                         } else {
1230                                 /* CC.NEW or no option => invalidate cache */
1231                                 taop->tao_cc = 0;
1232                                 tp->t_state = TCPS_SYN_RECEIVED;
1233                         }
1234                 }
1235
1236 trimthenstep6:
1237                 /*
1238                  * Advance th->th_seq to correspond to first data byte.
1239                  * If data, trim to stay within window,
1240                  * dropping FIN if necessary.
1241                  */
1242                 th->th_seq++;
1243                 if (tlen > tp->rcv_wnd) {
1244                         todrop = tlen - tp->rcv_wnd;
1245                         m_adj(m, -todrop);
1246                         tlen = tp->rcv_wnd;
1247                         thflags &= ~TH_FIN;
1248                         tcpstat.tcps_rcvpackafterwin++;
1249                         tcpstat.tcps_rcvbyteafterwin += todrop;
1250                 }
1251                 tp->snd_wl1 = th->th_seq - 1;
1252                 tp->rcv_up = th->th_seq;
1253                 /*
1254                  * Client side of transaction: already sent SYN and data.
1255                  * If the remote host used T/TCP to validate the SYN,
1256                  * our data will be ACK'd; if so, enter normal data segment
1257                  * processing in the middle of step 5, ack processing.
1258                  * Otherwise, goto step 6.
1259                  */
1260                 if (thflags & TH_ACK)
1261                         goto process_ACK;
1262
1263                 goto step6;
1264
1265         /*
1266          * If the state is LAST_ACK or CLOSING or TIME_WAIT:
1267          *      if segment contains a SYN and CC [not CC.NEW] option:
1268          *              if state == TIME_WAIT and connection duration > MSL,
1269          *                  drop packet and send RST;
1270          *
1271          *              if SEG.CC > CCrecv then is new SYN, and can implicitly
1272          *                  ack the FIN (and data) in retransmission queue.
1273          *                  Complete close and delete TCPCB.  Then reprocess
1274          *                  segment, hoping to find new TCPCB in LISTEN state;
1275          *
1276          *              else must be old SYN; drop it.
1277          *      else do normal processing.
1278          */
1279         case TCPS_LAST_ACK:
1280         case TCPS_CLOSING:
1281         case TCPS_TIME_WAIT:
1282                 if ((thflags & TH_SYN) &&
1283                     (to.to_flags & TOF_CC) && tp->cc_recv != 0) {
1284                         if (tp->t_state == TCPS_TIME_WAIT &&
1285                                         (ticks - tp->t_starttime) > tcp_msl) {
1286                                 rstreason = BANDLIM_UNLIMITED;
1287                                 goto dropwithreset;
1288                         }
1289                         if (CC_GT(to.to_cc, tp->cc_recv)) {
1290                                 tp = tcp_close(tp);
1291                                 goto findpcb;
1292                         }
1293                         else
1294                                 goto drop;
1295                 }
1296                 break;  /* continue normal processing */
1297         }
1298
1299         /*
1300          * States other than LISTEN or SYN_SENT.
1301          * First check the RST flag and sequence number since reset segments
1302          * are exempt from the timestamp and connection count tests.  This
1303          * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
1304          * below which allowed reset segments in half the sequence space
1305          * to fall though and be processed (which gives forged reset
1306          * segments with a random sequence number a 50 percent chance of
1307          * killing a connection).
1308          * Then check timestamp, if present.
1309          * Then check the connection count, if present.
1310          * Then check that at least some bytes of segment are within
1311          * receive window.  If segment begins before rcv_nxt,
1312          * drop leading data (and SYN); if nothing left, just ack.
1313          *
1314          *
1315          * If the RST bit is set, check the sequence number to see
1316          * if this is a valid reset segment.
1317          * RFC 793 page 37:
1318          *   In all states except SYN-SENT, all reset (RST) segments
1319          *   are validated by checking their SEQ-fields.  A reset is
1320          *   valid if its sequence number is in the window.
1321          * Note: this does not take into account delayed ACKs, so
1322          *   we should test against last_ack_sent instead of rcv_nxt.
1323          *   The sequence number in the reset segment is normally an
1324          *   echo of our outgoing acknowlegement numbers, but some hosts
1325          *   send a reset with the sequence number at the rightmost edge
1326          *   of our receive window, and we have to handle this case.
1327          * If we have multiple segments in flight, the intial reset
1328          * segment sequence numbers will be to the left of last_ack_sent,
1329          * but they will eventually catch up.
1330          * In any case, it never made sense to trim reset segments to
1331          * fit the receive window since RFC 1122 says:
1332          *   4.2.2.12  RST Segment: RFC-793 Section 3.4
1333          *
1334          *    A TCP SHOULD allow a received RST segment to include data.
1335          *
1336          *    DISCUSSION
1337          *         It has been suggested that a RST segment could contain
1338          *         ASCII text that encoded and explained the cause of the
1339          *         RST.  No standard has yet been established for such
1340          *         data.
1341          *
1342          * If the reset segment passes the sequence number test examine
1343          * the state:
1344          *    SYN_RECEIVED STATE:
1345          *      If passive open, return to LISTEN state.
1346          *      If active open, inform user that connection was refused.
1347          *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, CLOSE_WAIT STATES:
1348          *      Inform user that connection was reset, and close tcb.
1349          *    CLOSING, LAST_ACK STATES:
1350          *      Close the tcb.
1351          *    TIME_WAIT STATE:
1352          *      Drop the segment - see Stevens, vol. 2, p. 964 and
1353          *      RFC 1337.
1354          */
1355         if (thflags & TH_RST) {
1356                 if (SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
1357                     SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
1358                         switch (tp->t_state) {
1359
1360                         case TCPS_SYN_RECEIVED:
1361                                 so->so_error = ECONNREFUSED;
1362                                 goto close;
1363
1364                         case TCPS_ESTABLISHED:
1365                         case TCPS_FIN_WAIT_1:
1366                         case TCPS_FIN_WAIT_2:
1367                         case TCPS_CLOSE_WAIT:
1368                                 so->so_error = ECONNRESET;
1369                         close:
1370                                 tp->t_state = TCPS_CLOSED;
1371                                 tcpstat.tcps_drops++;
1372                                 tp = tcp_close(tp);
1373                                 break;
1374
1375                         case TCPS_CLOSING:
1376                         case TCPS_LAST_ACK:
1377                                 tp = tcp_close(tp);
1378                                 break;
1379
1380                         case TCPS_TIME_WAIT:
1381                                 break;
1382                         }
1383                 }
1384                 goto drop;
1385         }
1386
1387         /*
1388          * RFC 1323 PAWS: If we have a timestamp reply on this segment
1389          * and it's less than ts_recent, drop it.
1390          */
1391         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
1392             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
1393
1394                 /* Check to see if ts_recent is over 24 days old.  */
1395                 if ((int)(ticks - tp->ts_recent_age) > TCP_PAWS_IDLE) {
1396                         /*
1397                          * Invalidate ts_recent.  If this segment updates
1398                          * ts_recent, the age will be reset later and ts_recent
1399                          * will get a valid value.  If it does not, setting
1400                          * ts_recent to zero will at least satisfy the
1401                          * requirement that zero be placed in the timestamp
1402                          * echo reply when ts_recent isn't valid.  The
1403                          * age isn't reset until we get a valid ts_recent
1404                          * because we don't want out-of-order segments to be
1405                          * dropped when ts_recent is old.
1406                          */
1407                         tp->ts_recent = 0;
1408                 } else {
1409                         tcpstat.tcps_rcvduppack++;
1410                         tcpstat.tcps_rcvdupbyte += tlen;
1411                         tcpstat.tcps_pawsdrop++;
1412                         if (tlen)
1413                                 goto dropafterack;
1414                         goto drop;
1415                 }
1416         }
1417
1418         /*
1419          * T/TCP mechanism
1420          *   If T/TCP was negotiated and the segment doesn't have CC,
1421          *   or if its CC is wrong then drop the segment.
1422          *   RST segments do not have to comply with this.
1423          */
1424         if ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) == (TF_REQ_CC|TF_RCVD_CC) &&
1425             ((to.to_flags & TOF_CC) == 0 || tp->cc_recv != to.to_cc))
1426                 goto dropafterack;
1427
1428         /*
1429          * In the SYN-RECEIVED state, validate that the packet belongs to
1430          * this connection before trimming the data to fit the receive
1431          * window.  Check the sequence number versus IRS since we know
1432          * the sequence numbers haven't wrapped.  This is a partial fix
1433          * for the "LAND" DoS attack.
1434          */
1435         if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
1436                 rstreason = BANDLIM_RST_OPENPORT;
1437                 goto dropwithreset;
1438         }
1439
1440         todrop = tp->rcv_nxt - th->th_seq;
1441         if (todrop > 0) {
1442                 if (thflags & TH_SYN) {
1443                         thflags &= ~TH_SYN;
1444                         th->th_seq++;
1445                         if (th->th_urp > 1)
1446                                 th->th_urp--;
1447                         else
1448                                 thflags &= ~TH_URG;
1449                         todrop--;
1450                 }
1451                 /*
1452                  * Following if statement from Stevens, vol. 2, p. 960.
1453                  */
1454                 if (todrop > tlen
1455                     || (todrop == tlen && (thflags & TH_FIN) == 0)) {
1456                         /*
1457                          * Any valid FIN must be to the left of the window.
1458                          * At this point the FIN must be a duplicate or out
1459                          * of sequence; drop it.
1460                          */
1461                         thflags &= ~TH_FIN;
1462
1463                         /*
1464                          * Send an ACK to resynchronize and drop any data.
1465                          * But keep on processing for RST or ACK.
1466                          */
1467                         tp->t_flags |= TF_ACKNOW;
1468                         todrop = tlen;
1469                         tcpstat.tcps_rcvduppack++;
1470                         tcpstat.tcps_rcvdupbyte += todrop;
1471                 } else {
1472                         tcpstat.tcps_rcvpartduppack++;
1473                         tcpstat.tcps_rcvpartdupbyte += todrop;
1474                 }
1475                 drop_hdrlen += todrop;  /* drop from the top afterwards */
1476                 th->th_seq += todrop;
1477                 tlen -= todrop;
1478                 if (th->th_urp > todrop)
1479                         th->th_urp -= todrop;
1480                 else {
1481                         thflags &= ~TH_URG;
1482                         th->th_urp = 0;
1483                 }
1484         }
1485
1486         /*
1487          * If new data are received on a connection after the
1488          * user processes are gone, then RST the other end.
1489          */
1490         if ((so->so_state & SS_NOFDREF) &&
1491             tp->t_state > TCPS_CLOSE_WAIT && tlen) {
1492                 tp = tcp_close(tp);
1493                 tcpstat.tcps_rcvafterclose++;
1494                 rstreason = BANDLIM_UNLIMITED;
1495                 goto dropwithreset;
1496         }
1497
1498         /*
1499          * If segment ends after window, drop trailing data
1500          * (and PUSH and FIN); if nothing left, just ACK.
1501          */
1502         todrop = (th->th_seq+tlen) - (tp->rcv_nxt+tp->rcv_wnd);
1503         if (todrop > 0) {
1504                 tcpstat.tcps_rcvpackafterwin++;
1505                 if (todrop >= tlen) {
1506                         tcpstat.tcps_rcvbyteafterwin += tlen;
1507                         /*
1508                          * If a new connection request is received
1509                          * while in TIME_WAIT, drop the old connection
1510                          * and start over if the sequence numbers
1511                          * are above the previous ones.
1512                          */
1513                         if (thflags & TH_SYN &&
1514                             tp->t_state == TCPS_TIME_WAIT &&
1515                             SEQ_GT(th->th_seq, tp->rcv_nxt)) {
1516                                 tp = tcp_close(tp);
1517                                 goto findpcb;
1518                         }
1519                         /*
1520                          * If window is closed can only take segments at
1521                          * window edge, and have to drop data and PUSH from
1522                          * incoming segments.  Continue processing, but
1523                          * remember to ack.  Otherwise, drop segment
1524                          * and ack.
1525                          */
1526                         if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
1527                                 tp->t_flags |= TF_ACKNOW;
1528                                 tcpstat.tcps_rcvwinprobe++;
1529                         } else
1530                                 goto dropafterack;
1531                 } else
1532                         tcpstat.tcps_rcvbyteafterwin += todrop;
1533                 m_adj(m, -todrop);
1534                 tlen -= todrop;
1535                 thflags &= ~(TH_PUSH|TH_FIN);
1536         }
1537
1538         /*
1539          * If last ACK falls within this segment's sequence numbers,
1540          * record its timestamp.
1541          * NOTE that the test is modified according to the latest
1542          * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1543          */
1544         if ((to.to_flags & TOF_TS) != 0 &&
1545             SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
1546                 tp->ts_recent_age = ticks;
1547                 tp->ts_recent = to.to_tsval;
1548         }
1549
1550         /*
1551          * If a SYN is in the window, then this is an
1552          * error and we send an RST and drop the connection.
1553          */
1554         if (thflags & TH_SYN) {
1555                 tp = tcp_drop(tp, ECONNRESET);
1556                 rstreason = BANDLIM_UNLIMITED;
1557                 goto dropwithreset;
1558         }
1559
1560         /*
1561          * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
1562          * flag is on (half-synchronized state), then queue data for
1563          * later processing; else drop segment and return.
1564          */
1565         if ((thflags & TH_ACK) == 0) {
1566                 if (tp->t_state == TCPS_SYN_RECEIVED ||
1567                     (tp->t_flags & TF_NEEDSYN))
1568                         goto step6;
1569                 else
1570                         goto drop;
1571         }
1572
1573         /*
1574          * Ack processing.
1575          */
1576         switch (tp->t_state) {
1577
1578         /*
1579          * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
1580          * ESTABLISHED state and continue processing.
1581          * The ACK was checked above.
1582          */
1583         case TCPS_SYN_RECEIVED:
1584
1585                 tcpstat.tcps_connects++;
1586                 soisconnected(so);
1587                 /* Do window scaling? */
1588                 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1589                         (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1590                         tp->snd_scale = tp->requested_s_scale;
1591                         tp->rcv_scale = tp->request_r_scale;
1592                 }
1593                 /*
1594                  * Upon successful completion of 3-way handshake,
1595                  * update cache.CC if it was undefined, pass any queued
1596                  * data to the user, and advance state appropriately.
1597                  */
1598                 if ((taop = tcp_gettaocache(&inp->inp_inc)) != NULL &&
1599                     taop->tao_cc == 0)
1600                         taop->tao_cc = tp->cc_recv;
1601
1602                 /*
1603                  * Make transitions:
1604                  *      SYN-RECEIVED  -> ESTABLISHED
1605                  *      SYN-RECEIVED* -> FIN-WAIT-1
1606                  */
1607                 tp->t_starttime = ticks;
1608                 if (tp->t_flags & TF_NEEDFIN) {
1609                         tp->t_state = TCPS_FIN_WAIT_1;
1610                         tp->t_flags &= ~TF_NEEDFIN;
1611                 } else {
1612                         tp->t_state = TCPS_ESTABLISHED;
1613                         callout_reset(tp->tt_keep, tcp_keepidle,
1614                                       tcp_timer_keep, tp);
1615                 }
1616                 /*
1617                  * If segment contains data or ACK, will call tcp_reass()
1618                  * later; if not, do so now to pass queued data to user.
1619                  */
1620                 if (tlen == 0 && (thflags & TH_FIN) == 0)
1621                         (void) tcp_reass(tp, (struct tcphdr *)0, 0,
1622                             (struct mbuf *)0);
1623                 tp->snd_wl1 = th->th_seq - 1;
1624                 /* fall into ... */
1625
1626         /*
1627          * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
1628          * ACKs.  If the ack is in the range
1629          *      tp->snd_una < th->th_ack <= tp->snd_max
1630          * then advance tp->snd_una to th->th_ack and drop
1631          * data from the retransmission queue.  If this ACK reflects
1632          * more up to date window information we update our window information.
1633          */
1634         case TCPS_ESTABLISHED:
1635         case TCPS_FIN_WAIT_1:
1636         case TCPS_FIN_WAIT_2:
1637         case TCPS_CLOSE_WAIT:
1638         case TCPS_CLOSING:
1639         case TCPS_LAST_ACK:
1640         case TCPS_TIME_WAIT:
1641
1642                 if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
1643                         if (tlen == 0 && tiwin == tp->snd_wnd) {
1644                                 tcpstat.tcps_rcvdupack++;
1645                                 /*
1646                                  * If we have outstanding data (other than
1647                                  * a window probe), this is a completely
1648                                  * duplicate ack (ie, window info didn't
1649                                  * change), the ack is the biggest we've
1650                                  * seen and we've seen exactly our rexmt
1651                                  * threshhold of them, assume a packet
1652                                  * has been dropped and retransmit it.
1653                                  * Kludge snd_nxt & the congestion
1654                                  * window so we send only this one
1655                                  * packet.
1656                                  *
1657                                  * We know we're losing at the current
1658                                  * window size so do congestion avoidance
1659                                  * (set ssthresh to half the current window
1660                                  * and pull our congestion window back to
1661                                  * the new ssthresh).
1662                                  *
1663                                  * Dup acks mean that packets have left the
1664                                  * network (they're now cached at the receiver)
1665                                  * so bump cwnd by the amount in the receiver
1666                                  * to keep a constant cwnd packets in the
1667                                  * network.
1668                                  */
1669                                 if (!callout_active(tp->tt_rexmt) ||
1670                                     th->th_ack != tp->snd_una)
1671                                         tp->t_dupacks = 0;
1672                                 else if (++tp->t_dupacks > tcprexmtthresh ||
1673                                          (tcp_do_newreno &&
1674                                           IN_FASTRECOVERY(tp))) {
1675                                         tp->snd_cwnd += tp->t_maxseg;
1676                                         (void) tcp_output(tp);
1677                                         goto drop;
1678                                 } else if (tp->t_dupacks == tcprexmtthresh) {
1679                                         tcp_seq onxt = tp->snd_nxt;
1680                                         u_int win;
1681                                         if (tcp_do_newreno &&
1682                                             SEQ_LEQ(th->th_ack,
1683                                                     tp->snd_recover)) {
1684                                                 tp->t_dupacks = 0;
1685                                                 break;
1686                                         }
1687                                         win = min(tp->snd_wnd, tp->snd_cwnd) /
1688                                             2 / tp->t_maxseg;
1689                                         if (win < 2)
1690                                                 win = 2;
1691                                         tp->snd_ssthresh = win * tp->t_maxseg;
1692                                         ENTER_FASTRECOVERY(tp);
1693                                         tp->snd_recover = tp->snd_max;
1694                                         callout_stop(tp->tt_rexmt);
1695                                         tp->t_rtttime = 0;
1696                                         tp->snd_nxt = th->th_ack;
1697                                         tp->snd_cwnd = tp->t_maxseg;
1698                                         (void) tcp_output(tp);
1699                                         KASSERT(tp->snd_limited <= 2,
1700                                             ("tp->snd_limited too big"));
1701                                         tp->snd_cwnd = tp->snd_ssthresh +
1702                                             (tp->t_maxseg *
1703                                              (tp->t_dupacks - tp->snd_limited));
1704                                         if (SEQ_GT(onxt, tp->snd_nxt))
1705                                                 tp->snd_nxt = onxt;
1706                                         goto drop;
1707                                 } else if (tcp_do_limitedtransmit) {
1708                                         u_long oldcwnd = tp->snd_cwnd;
1709                                         tcp_seq oldsndmax = tp->snd_max;
1710                                         u_int sent;
1711                                         KASSERT(tp->t_dupacks == 1 ||
1712                                             tp->t_dupacks == 2,
1713                                             ("dupacks not 1 or 2"));
1714                                         if (tp->t_dupacks == 1) {
1715                                                 tp->snd_limited = 0;
1716                                                 tp->snd_cwnd += tp->t_maxseg;
1717                                         } else {
1718                                                 tp->snd_cwnd +=
1719                                                     tp->t_maxseg * 2;
1720                                         }
1721                                         (void) tcp_output(tp);
1722                                         sent = tp->snd_max - oldsndmax;
1723                                         if (sent > tp->t_maxseg) {
1724                                                 KASSERT(tp->snd_limited == 0 &&
1725                                                     tp->t_dupacks == 2,
1726                                                     ("sent too much"));
1727                                                 tp->snd_limited = 2;
1728                                         } else if (sent > 0)
1729                                                 ++tp->snd_limited;
1730                                         tp->snd_cwnd = oldcwnd;
1731                                         goto drop;
1732                                 }
1733                         } else
1734                                 tp->t_dupacks = 0;
1735                         break;
1736                 }
1737
1738                 KASSERT(SEQ_GT(th->th_ack, tp->snd_una), ("th_ack <= snd_una"));
1739
1740                 /*
1741                  * If the congestion window was inflated to account
1742                  * for the other side's cached packets, retract it.
1743                  */
1744                 if (tcp_do_newreno) {
1745                         if (IN_FASTRECOVERY(tp)) {
1746                                 if (SEQ_LT(th->th_ack, tp->snd_recover)) {
1747                                         tcp_newreno_partial_ack(tp, th);
1748                                 } else {
1749                                         /*
1750                                          * Window inflation should have left us
1751                                          * with approximately snd_ssthresh
1752                                          * outstanding data.
1753                                          * But in case we would be inclined to
1754                                          * send a burst, better to do it via
1755                                          * the slow start mechanism.
1756                                          */
1757                                         if (SEQ_GT(th->th_ack +
1758                                                         tp->snd_ssthresh,
1759                                                    tp->snd_max))
1760                                                 tp->snd_cwnd = tp->snd_max -
1761                                                                 th->th_ack +
1762                                                                 tp->t_maxseg;
1763                                         else
1764                                                 tp->snd_cwnd = tp->snd_ssthresh;
1765                                 }
1766                         }
1767                 } else {
1768                         if (tp->t_dupacks >= tcprexmtthresh &&
1769                             tp->snd_cwnd > tp->snd_ssthresh)
1770                                 tp->snd_cwnd = tp->snd_ssthresh;
1771                 }
1772                 tp->t_dupacks = 0;
1773                 if (SEQ_GT(th->th_ack, tp->snd_max)) {
1774                         tcpstat.tcps_rcvacktoomuch++;
1775                         goto dropafterack;
1776                 }
1777                 /*
1778                  * If we reach this point, ACK is not a duplicate,
1779                  *     i.e., it ACKs something we sent.
1780                  */
1781                 if (tp->t_flags & TF_NEEDSYN) {
1782                         /*
1783                          * T/TCP: Connection was half-synchronized, and our
1784                          * SYN has been ACK'd (so connection is now fully
1785                          * synchronized).  Go to non-starred state,
1786                          * increment snd_una for ACK of SYN, and check if
1787                          * we can do window scaling.
1788                          */
1789                         tp->t_flags &= ~TF_NEEDSYN;
1790                         tp->snd_una++;
1791                         /* Do window scaling? */
1792                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1793                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1794                                 tp->snd_scale = tp->requested_s_scale;
1795                                 tp->rcv_scale = tp->request_r_scale;
1796                         }
1797                 }
1798
1799 process_ACK:
1800                 acked = th->th_ack - tp->snd_una;
1801                 tcpstat.tcps_rcvackpack++;
1802                 tcpstat.tcps_rcvackbyte += acked;
1803
1804                 /*
1805                  * If we just performed our first retransmit, and the ACK
1806                  * arrives within our recovery window, then it was a mistake
1807                  * to do the retransmit in the first place.  Recover our
1808                  * original cwnd and ssthresh, and proceed to transmit where
1809                  * we left off.
1810                  */
1811                 if (tp->t_rxtshift == 1 && ticks < tp->t_badrxtwin) {
1812                         tp->snd_cwnd = tp->snd_cwnd_prev;
1813                         tp->snd_ssthresh = tp->snd_ssthresh_prev;
1814                         tp->snd_recover = tp->snd_recover_prev;
1815                         if (tp->t_flags & TF_WASFRECOVERY)
1816                                 ENTER_FASTRECOVERY(tp);
1817                         tp->snd_nxt = tp->snd_max;
1818                         tp->t_badrxtwin = 0;    /* XXX probably not required */
1819                 }
1820
1821                 /*
1822                  * If we have a timestamp reply, update smoothed
1823                  * round trip time.  If no timestamp is present but
1824                  * transmit timer is running and timed sequence
1825                  * number was acked, update smoothed round trip time.
1826                  * Since we now have an rtt measurement, cancel the
1827                  * timer backoff (cf., Phil Karn's retransmit alg.).
1828                  * Recompute the initial retransmit timer.
1829                  *
1830                  * Some machines (certain windows boxes) send broken
1831                  * timestamp replies during the SYN+ACK phase, ignore
1832                  * timestamps of 0.
1833                  */
1834                 if ((to.to_flags & TOF_TS) != 0 &&
1835                     to.to_tsecr) {
1836                         tcp_xmit_timer(tp, ticks - to.to_tsecr + 1);
1837                 } else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
1838                         tcp_xmit_timer(tp, ticks - tp->t_rtttime);
1839                 }
1840                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
1841
1842                 /*
1843                  * If all outstanding data is acked, stop retransmit
1844                  * timer and remember to restart (more output or persist).
1845                  * If there is more data to be acked, restart retransmit
1846                  * timer, using current (possibly backed-off) value.
1847                  */
1848                 if (th->th_ack == tp->snd_max) {
1849                         callout_stop(tp->tt_rexmt);
1850                         needoutput = 1;
1851                 } else if (!callout_active(tp->tt_persist))
1852                         callout_reset(tp->tt_rexmt, tp->t_rxtcur,
1853                                       tcp_timer_rexmt, tp);
1854
1855                 /*
1856                  * If no data (only SYN) was ACK'd,
1857                  *    skip rest of ACK processing.
1858                  */
1859                 if (acked == 0)
1860                         goto step6;
1861
1862                 /*
1863                  * When new data is acked, open the congestion window.
1864                  * If the window gives us less than ssthresh packets
1865                  * in flight, open exponentially (maxseg per packet).
1866                  * Otherwise open linearly: maxseg per window
1867                  * (maxseg^2 / cwnd per packet).
1868                  */
1869                 if (!tcp_do_newreno || !IN_FASTRECOVERY(tp)) {
1870                         register u_int cw = tp->snd_cwnd;
1871                         register u_int incr = tp->t_maxseg;
1872                         if (cw > tp->snd_ssthresh)
1873                                 incr = incr * incr / cw;
1874                         tp->snd_cwnd = min(cw+incr, TCP_MAXWIN<<tp->snd_scale);
1875                 }
1876                 if (acked > so->so_snd.sb_cc) {
1877                         tp->snd_wnd -= so->so_snd.sb_cc;
1878                         sbdrop(&so->so_snd, (int)so->so_snd.sb_cc);
1879                         ourfinisacked = 1;
1880                 } else {
1881                         sbdrop(&so->so_snd, acked);
1882                         tp->snd_wnd -= acked;
1883                         ourfinisacked = 0;
1884                 }
1885                 sowwakeup(so);
1886                 /* detect una wraparound */
1887                 if (tcp_do_newreno && !IN_FASTRECOVERY(tp) &&
1888                     SEQ_GT(tp->snd_una, tp->snd_recover) &&
1889                     SEQ_LEQ(th->th_ack, tp->snd_recover))
1890                         tp->snd_recover = th->th_ack - 1;
1891                 if (tcp_do_newreno && IN_FASTRECOVERY(tp) &&
1892                     SEQ_GEQ(th->th_ack, tp->snd_recover))
1893                         EXIT_FASTRECOVERY(tp);
1894                 tp->snd_una = th->th_ack;
1895                 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
1896                         tp->snd_nxt = tp->snd_una;
1897
1898                 switch (tp->t_state) {
1899
1900                 /*
1901                  * In FIN_WAIT_1 STATE in addition to the processing
1902                  * for the ESTABLISHED state if our FIN is now acknowledged
1903                  * then enter FIN_WAIT_2.
1904                  */
1905                 case TCPS_FIN_WAIT_1:
1906                         if (ourfinisacked) {
1907                                 /*
1908                                  * If we can't receive any more
1909                                  * data, then closing user can proceed.
1910                                  * Starting the timer is contrary to the
1911                                  * specification, but if we don't get a FIN
1912                                  * we'll hang forever.
1913                                  */
1914                                 if (so->so_state & SS_CANTRCVMORE) {
1915                                         soisdisconnected(so);
1916                                         callout_reset(tp->tt_2msl, tcp_maxidle,
1917                                                       tcp_timer_2msl, tp);
1918                                 }
1919                                 tp->t_state = TCPS_FIN_WAIT_2;
1920                         }
1921                         break;
1922
1923                 /*
1924                  * In CLOSING STATE in addition to the processing for
1925                  * the ESTABLISHED state if the ACK acknowledges our FIN
1926                  * then enter the TIME-WAIT state, otherwise ignore
1927                  * the segment.
1928                  */
1929                 case TCPS_CLOSING:
1930                         if (ourfinisacked) {
1931                                 tp->t_state = TCPS_TIME_WAIT;
1932                                 tcp_canceltimers(tp);
1933                                 /* Shorten TIME_WAIT [RFC-1644, p.28] */
1934                                 if (tp->cc_recv != 0 &&
1935                                     (ticks - tp->t_starttime) < tcp_msl)
1936                                         callout_reset(tp->tt_2msl,
1937                                                       tp->t_rxtcur *
1938                                                       TCPTV_TWTRUNC,
1939                                                       tcp_timer_2msl, tp);
1940                                 else
1941                                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
1942                                                       tcp_timer_2msl, tp);
1943                                 soisdisconnected(so);
1944                         }
1945                         break;
1946
1947                 /*
1948                  * In LAST_ACK, we may still be waiting for data to drain
1949                  * and/or to be acked, as well as for the ack of our FIN.
1950                  * If our FIN is now acknowledged, delete the TCB,
1951                  * enter the closed state and return.
1952                  */
1953                 case TCPS_LAST_ACK:
1954                         if (ourfinisacked) {
1955                                 tp = tcp_close(tp);
1956                                 goto drop;
1957                         }
1958                         break;
1959
1960                 /*
1961                  * In TIME_WAIT state the only thing that should arrive
1962                  * is a retransmission of the remote FIN.  Acknowledge
1963                  * it and restart the finack timer.
1964                  */
1965                 case TCPS_TIME_WAIT:
1966                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
1967                                       tcp_timer_2msl, tp);
1968                         goto dropafterack;
1969                 }
1970         }
1971
1972 step6:
1973         /*
1974          * Update window information.
1975          * Don't look at window if no ACK: TAC's send garbage on first SYN.
1976          */
1977         if ((thflags & TH_ACK) &&
1978             (SEQ_LT(tp->snd_wl1, th->th_seq) ||
1979             (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
1980              (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
1981                 /* keep track of pure window updates */
1982                 if (tlen == 0 &&
1983                     tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
1984                         tcpstat.tcps_rcvwinupd++;
1985                 tp->snd_wnd = tiwin;
1986                 tp->snd_wl1 = th->th_seq;
1987                 tp->snd_wl2 = th->th_ack;
1988                 if (tp->snd_wnd > tp->max_sndwnd)
1989                         tp->max_sndwnd = tp->snd_wnd;
1990                 needoutput = 1;
1991         }
1992
1993         /*
1994          * Process segments with URG.
1995          */
1996         if ((thflags & TH_URG) && th->th_urp &&
1997             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
1998                 /*
1999                  * This is a kludge, but if we receive and accept
2000                  * random urgent pointers, we'll crash in
2001                  * soreceive.  It's hard to imagine someone
2002                  * actually wanting to send this much urgent data.
2003                  */
2004                 if (th->th_urp + so->so_rcv.sb_cc > sb_max) {
2005                         th->th_urp = 0;                 /* XXX */
2006                         thflags &= ~TH_URG;             /* XXX */
2007                         goto dodata;                    /* XXX */
2008                 }
2009                 /*
2010                  * If this segment advances the known urgent pointer,
2011                  * then mark the data stream.  This should not happen
2012                  * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
2013                  * a FIN has been received from the remote side.
2014                  * In these states we ignore the URG.
2015                  *
2016                  * According to RFC961 (Assigned Protocols),
2017                  * the urgent pointer points to the last octet
2018                  * of urgent data.  We continue, however,
2019                  * to consider it to indicate the first octet
2020                  * of data past the urgent section as the original
2021                  * spec states (in one of two places).
2022                  */
2023                 if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
2024                         tp->rcv_up = th->th_seq + th->th_urp;
2025                         so->so_oobmark = so->so_rcv.sb_cc +
2026                             (tp->rcv_up - tp->rcv_nxt) - 1;
2027                         if (so->so_oobmark == 0)
2028                                 so->so_state |= SS_RCVATMARK;
2029                         sohasoutofband(so);
2030                         tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
2031                 }
2032                 /*
2033                  * Remove out of band data so doesn't get presented to user.
2034                  * This can happen independent of advancing the URG pointer,
2035                  * but if two URG's are pending at once, some out-of-band
2036                  * data may creep in... ick.
2037                  */
2038                 if (th->th_urp <= (u_long)tlen
2039 #ifdef SO_OOBINLINE
2040                      && (so->so_options & SO_OOBINLINE) == 0
2041 #endif
2042                      )
2043                         tcp_pulloutofband(so, th, m,
2044                                 drop_hdrlen);   /* hdr drop is delayed */
2045         } else {
2046                 /*
2047                  * If no out of band data is expected,
2048                  * pull receive urgent pointer along
2049                  * with the receive window.
2050                  */
2051                 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
2052                         tp->rcv_up = tp->rcv_nxt;
2053         }
2054 dodata:                                                 /* XXX */
2055
2056         /*
2057          * Process the segment text, merging it into the TCP sequencing queue,
2058          * and arranging for acknowledgment of receipt if necessary.
2059          * This process logically involves adjusting tp->rcv_wnd as data
2060          * is presented to the user (this happens in tcp_usrreq.c,
2061          * case PRU_RCVD).  If a FIN has already been received on this
2062          * connection then we just ignore the text.
2063          */
2064         if ((tlen || (thflags & TH_FIN)) &&
2065             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2066                 m_adj(m, drop_hdrlen);  /* delayed header drop */
2067                 /*
2068                  * Insert segment which includes th into TCP reassembly queue
2069                  * with control block tp.  Set thflags to whether reassembly now
2070                  * includes a segment with FIN.  This handles the common case
2071                  * inline (segment is the next to be received on an established
2072                  * connection, and the queue is empty), avoiding linkage into
2073                  * and removal from the queue and repetition of various
2074                  * conversions.
2075                  * Set DELACK for segments received in order, but ack
2076                  * immediately when segments are out of order (so
2077                  * fast retransmit can work).
2078                  */
2079                 if (th->th_seq == tp->rcv_nxt &&
2080                     LIST_EMPTY(&tp->t_segq) &&
2081                     TCPS_HAVEESTABLISHED(tp->t_state)) {
2082                         if (DELAY_ACK(tp))
2083                                 callout_reset(tp->tt_delack, tcp_delacktime,
2084                                               tcp_timer_delack, tp);
2085                         else
2086                                 tp->t_flags |= TF_ACKNOW;
2087                         tp->rcv_nxt += tlen;
2088                         thflags = th->th_flags & TH_FIN;
2089                         tcpstat.tcps_rcvpack++;
2090                         tcpstat.tcps_rcvbyte += tlen;
2091                         ND6_HINT(tp);
2092                         if (so->so_state & SS_CANTRCVMORE)
2093                                 m_freem(m);
2094                         else
2095                                 sbappend(&so->so_rcv, m);
2096                         sorwakeup(so);
2097                 } else {
2098                         thflags = tcp_reass(tp, th, &tlen, m);
2099                         tp->t_flags |= TF_ACKNOW;
2100                 }
2101
2102                 /*
2103                  * Note the amount of data that peer has sent into
2104                  * our window, in order to estimate the sender's
2105                  * buffer size.
2106                  */
2107                 len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
2108         } else {
2109                 m_freem(m);
2110                 thflags &= ~TH_FIN;
2111         }
2112
2113         /*
2114          * If FIN is received ACK the FIN and let the user know
2115          * that the connection is closing.
2116          */
2117         if (thflags & TH_FIN) {
2118                 if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2119                         socantrcvmore(so);
2120                         /*
2121                          * If connection is half-synchronized
2122                          * (ie NEEDSYN flag on) then delay ACK,
2123                          * so it may be piggybacked when SYN is sent.
2124                          * Otherwise, since we received a FIN then no
2125                          * more input can be expected, send ACK now.
2126                          */
2127                         if (DELAY_ACK(tp) && (tp->t_flags & TF_NEEDSYN))
2128                                 callout_reset(tp->tt_delack, tcp_delacktime,
2129                                     tcp_timer_delack, tp);
2130                         else
2131                                 tp->t_flags |= TF_ACKNOW;
2132                         tp->rcv_nxt++;
2133                 }
2134                 switch (tp->t_state) {
2135
2136                 /*
2137                  * In SYN_RECEIVED and ESTABLISHED STATES
2138                  * enter the CLOSE_WAIT state.
2139                  */
2140                 case TCPS_SYN_RECEIVED:
2141                         tp->t_starttime = ticks;
2142                         /*FALLTHROUGH*/
2143                 case TCPS_ESTABLISHED:
2144                         tp->t_state = TCPS_CLOSE_WAIT;
2145                         break;
2146
2147                 /*
2148                  * If still in FIN_WAIT_1 STATE FIN has not been acked so
2149                  * enter the CLOSING state.
2150                  */
2151                 case TCPS_FIN_WAIT_1:
2152                         tp->t_state = TCPS_CLOSING;
2153                         break;
2154
2155                 /*
2156                  * In FIN_WAIT_2 state enter the TIME_WAIT state,
2157                  * starting the time-wait timer, turning off the other
2158                  * standard timers.
2159                  */
2160                 case TCPS_FIN_WAIT_2:
2161                         tp->t_state = TCPS_TIME_WAIT;
2162                         tcp_canceltimers(tp);
2163                         /* Shorten TIME_WAIT [RFC-1644, p.28] */
2164                         if (tp->cc_recv != 0 &&
2165                             (ticks - tp->t_starttime) < tcp_msl) {
2166                                 callout_reset(tp->tt_2msl,
2167                                               tp->t_rxtcur * TCPTV_TWTRUNC,
2168                                               tcp_timer_2msl, tp);
2169                                 /* For transaction client, force ACK now. */
2170                                 tp->t_flags |= TF_ACKNOW;
2171                         }
2172                         else
2173                                 callout_reset(tp->tt_2msl, 2 * tcp_msl,
2174                                               tcp_timer_2msl, tp);
2175                         soisdisconnected(so);
2176                         break;
2177
2178                 /*
2179                  * In TIME_WAIT state restart the 2 MSL time_wait timer.
2180                  */
2181                 case TCPS_TIME_WAIT:
2182                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
2183                                       tcp_timer_2msl, tp);
2184                         break;
2185                 }
2186         }
2187 #ifdef TCPDEBUG
2188         if (so->so_options & SO_DEBUG)
2189                 tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
2190                           &tcp_savetcp, 0);
2191 #endif
2192
2193         /*
2194          * Return any desired output.
2195          */
2196         if (needoutput || (tp->t_flags & TF_ACKNOW))
2197                 (void) tcp_output(tp);
2198         return;
2199
2200 dropafterack:
2201         /*
2202          * Generate an ACK dropping incoming segment if it occupies
2203          * sequence space, where the ACK reflects our state.
2204          *
2205          * We can now skip the test for the RST flag since all
2206          * paths to this code happen after packets containing
2207          * RST have been dropped.
2208          *
2209          * In the SYN-RECEIVED state, don't send an ACK unless the
2210          * segment we received passes the SYN-RECEIVED ACK test.
2211          * If it fails send a RST.  This breaks the loop in the
2212          * "LAND" DoS attack, and also prevents an ACK storm
2213          * between two listening ports that have been sent forged
2214          * SYN segments, each with the source address of the other.
2215          */
2216         if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
2217             (SEQ_GT(tp->snd_una, th->th_ack) ||
2218              SEQ_GT(th->th_ack, tp->snd_max)) ) {
2219                 rstreason = BANDLIM_RST_OPENPORT;
2220                 goto dropwithreset;
2221         }
2222 #ifdef TCPDEBUG
2223         if (so->so_options & SO_DEBUG)
2224                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2225                           &tcp_savetcp, 0);
2226 #endif
2227         m_freem(m);
2228         tp->t_flags |= TF_ACKNOW;
2229         (void) tcp_output(tp);
2230         return;
2231
2232 dropwithreset:
2233         /*
2234          * Generate a RST, dropping incoming segment.
2235          * Make ACK acceptable to originator of segment.
2236          * Don't bother to respond if destination was broadcast/multicast.
2237          */
2238         if ((thflags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
2239                 goto drop;
2240         if (isipv6) {
2241                 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
2242                     IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
2243                         goto drop;
2244         } else {
2245                 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
2246                     IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
2247                     ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
2248                     in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
2249                         goto drop;
2250         }
2251         /* IPv6 anycast check is done at tcp6_input() */
2252
2253         /*
2254          * Perform bandwidth limiting.
2255          */
2256 #ifdef ICMP_BANDLIM
2257         if (badport_bandlim(rstreason) < 0)
2258                 goto drop;
2259 #endif
2260
2261 #ifdef TCPDEBUG
2262         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2263                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2264                           &tcp_savetcp, 0);
2265 #endif
2266         if (thflags & TH_ACK)
2267                 /* mtod() below is safe as long as hdr dropping is delayed */
2268                 tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0, th->th_ack,
2269                             TH_RST);
2270         else {
2271                 if (thflags & TH_SYN)
2272                         tlen++;
2273                 /* mtod() below is safe as long as hdr dropping is delayed */
2274                 tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
2275                             (tcp_seq)0, TH_RST|TH_ACK);
2276         }
2277         return;
2278
2279 drop:
2280         /*
2281          * Drop space held by incoming segment and return.
2282          */
2283 #ifdef TCPDEBUG
2284         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2285                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2286                           &tcp_savetcp, 0);
2287 #endif
2288         m_freem(m);
2289         return;
2290 }
2291
2292 /*
2293  * Parse TCP options and place in tcpopt.
2294  */
2295 static void
2296 tcp_dooptions(to, cp, cnt, is_syn)
2297         struct tcpopt *to;
2298         u_char *cp;
2299         int cnt;
2300 {
2301         int opt, optlen;
2302
2303         to->to_flags = 0;
2304         for (; cnt > 0; cnt -= optlen, cp += optlen) {
2305                 opt = cp[0];
2306                 if (opt == TCPOPT_EOL)
2307                         break;
2308                 if (opt == TCPOPT_NOP)
2309                         optlen = 1;
2310                 else {
2311                         if (cnt < 2)
2312                                 break;
2313                         optlen = cp[1];
2314                         if (optlen < 2 || optlen > cnt)
2315                                 break;
2316                 }
2317                 switch (opt) {
2318                 case TCPOPT_MAXSEG:
2319                         if (optlen != TCPOLEN_MAXSEG)
2320                                 continue;
2321                         if (!is_syn)
2322                                 continue;
2323                         to->to_flags |= TOF_MSS;
2324                         bcopy((char *)cp + 2,
2325                             (char *)&to->to_mss, sizeof(to->to_mss));
2326                         to->to_mss = ntohs(to->to_mss);
2327                         break;
2328                 case TCPOPT_WINDOW:
2329                         if (optlen != TCPOLEN_WINDOW)
2330                                 continue;
2331                         if (! is_syn)
2332                                 continue;
2333                         to->to_flags |= TOF_SCALE;
2334                         to->to_requested_s_scale = min(cp[2], TCP_MAX_WINSHIFT);
2335                         break;
2336                 case TCPOPT_TIMESTAMP:
2337                         if (optlen != TCPOLEN_TIMESTAMP)
2338                                 continue;
2339                         to->to_flags |= TOF_TS;
2340                         bcopy((char *)cp + 2,
2341                             (char *)&to->to_tsval, sizeof(to->to_tsval));
2342                         to->to_tsval = ntohl(to->to_tsval);
2343                         bcopy((char *)cp + 6,
2344                             (char *)&to->to_tsecr, sizeof(to->to_tsecr));
2345                         to->to_tsecr = ntohl(to->to_tsecr);
2346                         break;
2347                 case TCPOPT_CC:
2348                         if (optlen != TCPOLEN_CC)
2349                                 continue;
2350                         to->to_flags |= TOF_CC;
2351                         bcopy((char *)cp + 2,
2352                             (char *)&to->to_cc, sizeof(to->to_cc));
2353                         to->to_cc = ntohl(to->to_cc);
2354                         break;
2355                 case TCPOPT_CCNEW:
2356                         if (optlen != TCPOLEN_CC)
2357                                 continue;
2358                         if (!is_syn)
2359                                 continue;
2360                         to->to_flags |= TOF_CCNEW;
2361                         bcopy((char *)cp + 2,
2362                             (char *)&to->to_cc, sizeof(to->to_cc));
2363                         to->to_cc = ntohl(to->to_cc);
2364                         break;
2365                 case TCPOPT_CCECHO:
2366                         if (optlen != TCPOLEN_CC)
2367                                 continue;
2368                         if (!is_syn)
2369                                 continue;
2370                         to->to_flags |= TOF_CCECHO;
2371                         bcopy((char *)cp + 2,
2372                             (char *)&to->to_ccecho, sizeof(to->to_ccecho));
2373                         to->to_ccecho = ntohl(to->to_ccecho);
2374                         break;
2375                 default:
2376                         continue;
2377                 }
2378         }
2379 }
2380
2381 /*
2382  * Pull out of band byte out of a segment so
2383  * it doesn't appear in the user's data queue.
2384  * It is still reflected in the segment length for
2385  * sequencing purposes.
2386  */
2387 static void
2388 tcp_pulloutofband(so, th, m, off)
2389         struct socket *so;
2390         struct tcphdr *th;
2391         register struct mbuf *m;
2392         int off;                /* delayed to be droped hdrlen */
2393 {
2394         int cnt = off + th->th_urp - 1;
2395
2396         while (cnt >= 0) {
2397                 if (m->m_len > cnt) {
2398                         char *cp = mtod(m, caddr_t) + cnt;
2399                         struct tcpcb *tp = sototcpcb(so);
2400
2401                         tp->t_iobc = *cp;
2402                         tp->t_oobflags |= TCPOOB_HAVEDATA;
2403                         bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
2404                         m->m_len--;
2405                         if (m->m_flags & M_PKTHDR)
2406                                 m->m_pkthdr.len--;
2407                         return;
2408                 }
2409                 cnt -= m->m_len;
2410                 m = m->m_next;
2411                 if (m == 0)
2412                         break;
2413         }
2414         panic("tcp_pulloutofband");
2415 }
2416
2417 /*
2418  * Collect new round-trip time estimate
2419  * and update averages and current timeout.
2420  */
2421 static void
2422 tcp_xmit_timer(tp, rtt)
2423         register struct tcpcb *tp;
2424         int rtt;
2425 {
2426         register int delta;
2427
2428         tcpstat.tcps_rttupdated++;
2429         tp->t_rttupdated++;
2430         if (tp->t_srtt != 0) {
2431                 /*
2432                  * srtt is stored as fixed point with 5 bits after the
2433                  * binary point (i.e., scaled by 8).  The following magic
2434                  * is equivalent to the smoothing algorithm in rfc793 with
2435                  * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
2436                  * point).  Adjust rtt to origin 0.
2437                  */
2438                 delta = ((rtt - 1) << TCP_DELTA_SHIFT)
2439                         - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
2440
2441                 if ((tp->t_srtt += delta) <= 0)
2442                         tp->t_srtt = 1;
2443
2444                 /*
2445                  * We accumulate a smoothed rtt variance (actually, a
2446                  * smoothed mean difference), then set the retransmit
2447                  * timer to smoothed rtt + 4 times the smoothed variance.
2448                  * rttvar is stored as fixed point with 4 bits after the
2449                  * binary point (scaled by 16).  The following is
2450                  * equivalent to rfc793 smoothing with an alpha of .75
2451                  * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
2452                  * rfc793's wired-in beta.
2453                  */
2454                 if (delta < 0)
2455                         delta = -delta;
2456                 delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
2457                 if ((tp->t_rttvar += delta) <= 0)
2458                         tp->t_rttvar = 1;
2459                 if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
2460                         tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2461         } else {
2462                 /*
2463                  * No rtt measurement yet - use the unsmoothed rtt.
2464                  * Set the variance to half the rtt (so our first
2465                  * retransmit happens at 3*rtt).
2466                  */
2467                 tp->t_srtt = rtt << TCP_RTT_SHIFT;
2468                 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
2469                 tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2470         }
2471         tp->t_rtttime = 0;
2472         tp->t_rxtshift = 0;
2473
2474         /*
2475          * the retransmit should happen at rtt + 4 * rttvar.
2476          * Because of the way we do the smoothing, srtt and rttvar
2477          * will each average +1/2 tick of bias.  When we compute
2478          * the retransmit timer, we want 1/2 tick of rounding and
2479          * 1 extra tick because of +-1/2 tick uncertainty in the
2480          * firing of the timer.  The bias will give us exactly the
2481          * 1.5 tick we need.  But, because the bias is
2482          * statistical, we have to test that we don't drop below
2483          * the minimum feasible timer (which is 2 ticks).
2484          */
2485         TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
2486                       max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
2487
2488         /*
2489          * We received an ack for a packet that wasn't retransmitted;
2490          * it is probably safe to discard any error indications we've
2491          * received recently.  This isn't quite right, but close enough
2492          * for now (a route might have failed after we sent a segment,
2493          * and the return path might not be symmetrical).
2494          */
2495         tp->t_softerror = 0;
2496 }
2497
2498 /*
2499  * Determine a reasonable value for maxseg size.
2500  * If the route is known, check route for mtu.
2501  * If none, use an mss that can be handled on the outgoing
2502  * interface without forcing IP to fragment; if bigger than
2503  * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
2504  * to utilize large mbufs.  If no route is found, route has no mtu,
2505  * or the destination isn't local, use a default, hopefully conservative
2506  * size (usually 512 or the default IP max size, but no more than the mtu
2507  * of the interface), as we can't discover anything about intervening
2508  * gateways or networks.  We also initialize the congestion/slow start
2509  * window to be a single segment if the destination isn't local.
2510  * While looking at the routing entry, we also initialize other path-dependent
2511  * parameters from pre-set or cached values in the routing entry.
2512  *
2513  * Also take into account the space needed for options that we
2514  * send regularly.  Make maxseg shorter by that amount to assure
2515  * that we can send maxseg amount of data even when the options
2516  * are present.  Store the upper limit of the length of options plus
2517  * data in maxopd.
2518  *
2519  * NOTE that this routine is only called when we process an incoming
2520  * segment, for outgoing segments only tcp_mssopt is called.
2521  *
2522  * In case of T/TCP, we call this routine during implicit connection
2523  * setup as well (offer = -1), to initialize maxseg from the cached
2524  * MSS of our peer.
2525  */
2526 void
2527 tcp_mss(tp, offer)
2528         struct tcpcb *tp;
2529         int offer;
2530 {
2531         register struct rtentry *rt;
2532         struct ifnet *ifp;
2533         register int rtt, mss;
2534         u_long bufsize;
2535         struct inpcb *inp = tp->t_inpcb;
2536         struct socket *so;
2537         struct rmxp_tao *taop;
2538         int origoffer = offer;
2539 #ifdef INET6
2540         int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
2541         size_t min_protoh = isipv6 ?
2542                             sizeof(struct ip6_hdr) + sizeof(struct tcphdr) :
2543                             sizeof(struct tcpiphdr);
2544 #else
2545         const int isipv6 = 0;
2546         const size_t min_protoh = sizeof(struct tcpiphdr);
2547 #endif
2548
2549         if (isipv6)
2550                 rt = tcp_rtlookup6(&inp->inp_inc);
2551         else
2552                 rt = tcp_rtlookup(&inp->inp_inc);
2553         if (rt == NULL) {
2554                 tp->t_maxopd = tp->t_maxseg =
2555                                 isipv6 ? tcp_v6mssdflt : tcp_mssdflt;
2556                 return;
2557         }
2558         ifp = rt->rt_ifp;
2559         so = inp->inp_socket;
2560
2561         taop = rmx_taop(rt->rt_rmx);
2562         /*
2563          * Offer == -1 means that we didn't receive SYN yet,
2564          * use cached value in that case;
2565          */
2566         if (offer == -1)
2567                 offer = taop->tao_mssopt;
2568         /*
2569          * Offer == 0 means that there was no MSS on the SYN segment,
2570          * in this case we use tcp_mssdflt.
2571          */
2572         if (offer == 0)
2573                 offer = isipv6 ? tcp_v6mssdflt : tcp_mssdflt;
2574         else
2575                 /*
2576                  * Sanity check: make sure that maxopd will be large
2577                  * enough to allow some data on segments even is the
2578                  * all the option space is used (40bytes).  Otherwise
2579                  * funny things may happen in tcp_output.
2580                  */
2581                 offer = max(offer, 64);
2582         taop->tao_mssopt = offer;
2583
2584         /*
2585          * While we're here, check if there's an initial rtt
2586          * or rttvar.  Convert from the route-table units
2587          * to scaled multiples of the slow timeout timer.
2588          */
2589         if (tp->t_srtt == 0 && (rtt = rt->rt_rmx.rmx_rtt)) {
2590                 /*
2591                  * XXX the lock bit for RTT indicates that the value
2592                  * is also a minimum value; this is subject to time.
2593                  */
2594                 if (rt->rt_rmx.rmx_locks & RTV_RTT)
2595                         tp->t_rttmin = rtt / (RTM_RTTUNIT / hz);
2596                 tp->t_srtt = rtt / (RTM_RTTUNIT / (hz * TCP_RTT_SCALE));
2597                 tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
2598                 tcpstat.tcps_usedrtt++;
2599                 if (rt->rt_rmx.rmx_rttvar) {
2600                         tp->t_rttvar = rt->rt_rmx.rmx_rttvar /
2601                             (RTM_RTTUNIT / (hz * TCP_RTTVAR_SCALE));
2602                         tcpstat.tcps_usedrttvar++;
2603                 } else {
2604                         /* default variation is +- 1 rtt */
2605                         tp->t_rttvar =
2606                             tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
2607                 }
2608                 TCPT_RANGESET(tp->t_rxtcur,
2609                               ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
2610                               tp->t_rttmin, TCPTV_REXMTMAX);
2611         }
2612         /*
2613          * if there's an mtu associated with the route, use it
2614          * else, use the link mtu.
2615          */
2616         if (rt->rt_rmx.rmx_mtu)
2617                 mss = rt->rt_rmx.rmx_mtu - min_protoh;
2618         else {
2619                 if (isipv6) {
2620                         mss = nd_ifinfo[rt->rt_ifp->if_index].linkmtu -
2621                                 min_protoh;
2622                         if (!in6_localaddr(&inp->in6p_faddr))
2623                                 mss = min(mss, tcp_v6mssdflt);
2624                 } else {
2625                         mss = ifp->if_mtu - min_protoh;
2626                         if (!in_localaddr(inp->inp_faddr))
2627                                 mss = min(mss, tcp_mssdflt);
2628                 }
2629         }
2630         mss = min(mss, offer);
2631         /*
2632          * maxopd stores the maximum length of data AND options
2633          * in a segment; maxseg is the amount of data in a normal
2634          * segment.  We need to store this value (maxopd) apart
2635          * from maxseg, because now every segment carries options
2636          * and thus we normally have somewhat less data in segments.
2637          */
2638         tp->t_maxopd = mss;
2639
2640         /*
2641          * In case of T/TCP, origoffer==-1 indicates, that no segments
2642          * were received yet.  In this case we just guess, otherwise
2643          * we do the same as before T/TCP.
2644          */
2645         if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
2646             (origoffer == -1 ||
2647              (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
2648                 mss -= TCPOLEN_TSTAMP_APPA;
2649         if ((tp->t_flags & (TF_REQ_CC|TF_NOOPT)) == TF_REQ_CC &&
2650             (origoffer == -1 ||
2651              (tp->t_flags & TF_RCVD_CC) == TF_RCVD_CC))
2652                 mss -= TCPOLEN_CC_APPA;
2653
2654 #if     (MCLBYTES & (MCLBYTES - 1)) == 0
2655                 if (mss > MCLBYTES)
2656                         mss &= ~(MCLBYTES-1);
2657 #else
2658                 if (mss > MCLBYTES)
2659                         mss = mss / MCLBYTES * MCLBYTES;
2660 #endif
2661         /*
2662          * If there's a pipesize, change the socket buffer
2663          * to that size.  Make the socket buffers an integral
2664          * number of mss units; if the mss is larger than
2665          * the socket buffer, decrease the mss.
2666          */
2667 #ifdef RTV_SPIPE
2668         if ((bufsize = rt->rt_rmx.rmx_sendpipe) == 0)
2669 #endif
2670                 bufsize = so->so_snd.sb_hiwat;
2671         if (bufsize < mss)
2672                 mss = bufsize;
2673         else {
2674                 bufsize = roundup(bufsize, mss);
2675                 if (bufsize > sb_max)
2676                         bufsize = sb_max;
2677                 if (bufsize > so->so_snd.sb_hiwat)
2678                         (void)sbreserve(&so->so_snd, bufsize, so, NULL);
2679         }
2680         tp->t_maxseg = mss;
2681
2682 #ifdef RTV_RPIPE
2683         if ((bufsize = rt->rt_rmx.rmx_recvpipe) == 0)
2684 #endif
2685                 bufsize = so->so_rcv.sb_hiwat;
2686         if (bufsize > mss) {
2687                 bufsize = roundup(bufsize, mss);
2688                 if (bufsize > sb_max)
2689                         bufsize = sb_max;
2690                 if (bufsize > so->so_rcv.sb_hiwat)
2691                         (void)sbreserve(&so->so_rcv, bufsize, so, NULL);
2692         }
2693
2694         /*
2695          * Set the slow-start flight size depending on whether this
2696          * is a local network or not.
2697          */
2698         if ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
2699             (!isipv6 && in_localaddr(inp->inp_faddr)))
2700                 tp->snd_cwnd = mss * ss_fltsz_local;
2701         else
2702                 tp->snd_cwnd = mss * ss_fltsz;
2703
2704         if (rt->rt_rmx.rmx_ssthresh) {
2705                 /*
2706                  * There's some sort of gateway or interface
2707                  * buffer limit on the path.  Use this to set
2708                  * the slow start threshhold, but set the
2709                  * threshold to no less than 2*mss.
2710                  */
2711                 tp->snd_ssthresh = max(2 * mss, rt->rt_rmx.rmx_ssthresh);
2712                 tcpstat.tcps_usedssthresh++;
2713         }
2714 }
2715
2716 /*
2717  * Determine the MSS option to send on an outgoing SYN.
2718  */
2719 int
2720 tcp_mssopt(tp)
2721         struct tcpcb *tp;
2722 {
2723         struct rtentry *rt;
2724 #ifdef INET6
2725         int isipv6 = ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
2726         int min_protoh = isipv6 ?
2727                              sizeof(struct ip6_hdr) + sizeof(struct tcphdr) :
2728                              sizeof(struct tcpiphdr);
2729 #else
2730         const int isipv6 = 0;
2731         const size_t min_protoh = sizeof(struct tcpiphdr);
2732 #endif
2733
2734         if (isipv6)
2735                 rt = tcp_rtlookup6(&tp->t_inpcb->inp_inc);
2736         else
2737                 rt = tcp_rtlookup(&tp->t_inpcb->inp_inc);
2738         if (rt == NULL)
2739                 return (isipv6 ? tcp_v6mssdflt : tcp_mssdflt);
2740
2741         return (rt->rt_ifp->if_mtu - min_protoh);
2742 }
2743
2744
2745 /*
2746  * When a partial ack arrives, force the retransmission of the
2747  * next unacknowledged segment.  Do not clear tp->t_dupacks.
2748  * By setting snd_nxt to ti_ack, this forces retransmission timer to
2749  * be started again.
2750  */
2751 static void
2752 tcp_newreno_partial_ack(tp, th)
2753         struct tcpcb *tp;
2754         struct tcphdr *th;
2755 {
2756         tcp_seq onxt = tp->snd_nxt;
2757         u_long  ocwnd = tp->snd_cwnd;
2758
2759         callout_stop(tp->tt_rexmt);
2760         tp->t_rtttime = 0;
2761         tp->snd_nxt = th->th_ack;
2762         /*
2763          * Set snd_cwnd to one segment beyond acknowledged offset
2764          * (tp->snd_una has not yet been updated when this function is called.)
2765          */
2766         tp->snd_cwnd = tp->t_maxseg + (th->th_ack - tp->snd_una);
2767         tp->t_flags |= TF_ACKNOW;
2768         (void) tcp_output(tp);
2769         tp->snd_cwnd = ocwnd;
2770         if (SEQ_GT(onxt, tp->snd_nxt))
2771                 tp->snd_nxt = onxt;
2772         /*
2773          * Partial window deflation.  Relies on fact that tp->snd_una
2774          * not updated yet.
2775          */
2776         tp->snd_cwnd -= (th->th_ack - tp->snd_una - tp->t_maxseg);
2777 }