sys/netinet/tcp_input.c

   1 /*
   2  * Copyright (c) 2002-2003 Jeffrey Hsu
   3  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
   4  *      The Regents of the University of California.  All rights reserved.
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions
   8  * are met:
   9  * 1. Redistributions of source code must retain the above copyright
  10  *    notice, this list of conditions and the following disclaimer.
  11  * 2. Redistributions in binary form must reproduce the above copyright
  12  *    notice, this list of conditions and the following disclaimer in the
  13  *    documentation and/or other materials provided with the distribution.
  14  * 3. All advertising materials mentioning features or use of this software
  15  *    must display the following acknowledgement:
  16  *      This product includes software developed by the University of
  17  *      California, Berkeley and its contributors.
  18  * 4. Neither the name of the University nor the names of its contributors
  19  *    may be used to endorse or promote products derived from this software
  20  *    without specific prior written permission.
  21  *
  22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  32  * SUCH DAMAGE.
  33  *
  34  *      @(#)tcp_input.c 8.12 (Berkeley) 5/24/95
  35  * $FreeBSD: src/sys/netinet/tcp_input.c,v 1.107.2.38 2003/05/21 04:46:41 cjc Exp $
  36  * $DragonFly: src/sys/netinet/tcp_input.c,v 1.13 2004/02/14 21:12:39 dillon Exp $
  37  */
  38
  39 #include "opt_ipfw.h"           /* for ipfw_fwd         */
  40 #include "opt_inet6.h"
  41 #include "opt_ipsec.h"
  42 #include "opt_tcpdebug.h"
  43 #include "opt_tcp_input.h"
  44
  45 #include <sys/param.h>
  46 #include <sys/systm.h>
  47 #include <sys/kernel.h>
  48 #include <sys/sysctl.h>
  49 #include <sys/malloc.h>
  50 #include <sys/mbuf.h>
  51 #include <sys/proc.h>           /* for proc0 declaration */
  52 #include <sys/protosw.h>
  53 #include <sys/socket.h>
  54 #include <sys/socketvar.h>
  55 #include <sys/syslog.h>
  56 #include <sys/in_cksum.h>
  57
  58 #include <machine/cpu.h>        /* before tcp_seq.h, for tcp_random18() */
  59
  60 #include <net/if.h>
  61 #include <net/route.h>
  62
  63 #include <netinet/in.h>
  64 #include <netinet/in_systm.h>
  65 #include <netinet/ip.h>
  66 #include <netinet/ip_icmp.h>    /* for ICMP_BANDLIM             */
  67 #include <netinet/in_var.h>
  68 #include <netinet/icmp_var.h>   /* for ICMP_BANDLIM             */
  69 #include <netinet/in_pcb.h>
  70 #include <netinet/ip_var.h>
  71 #include <netinet/ip6.h>
  72 #include <netinet/icmp6.h>
  73 #include <netinet6/nd6.h>
  74 #include <netinet6/ip6_var.h>
  75 #include <netinet6/in6_pcb.h>
  76 #include <netinet/tcp.h>
  77 #include <netinet/tcp_fsm.h>
  78 #include <netinet/tcp_seq.h>
  79 #include <netinet/tcp_timer.h>
  80 #include <netinet/tcp_var.h>
  81 #include <netinet6/tcp6_var.h>
  82 #include <netinet/tcpip.h>
  83 #ifdef TCPDEBUG
  84 #include <netinet/tcp_debug.h>
  85
  86 u_char tcp_saveipgen[40]; /* the size must be of max ip header, now IPv6 */
  87 struct tcphdr tcp_savetcp;
  88 #endif /* TCPDEBUG */
  89
  90 #ifdef FAST_IPSEC
  91 #include <netipsec/ipsec.h>
  92 #include <netipsec/ipsec6.h>
  93 #endif
  94
  95 #ifdef IPSEC
  96 #include <netinet6/ipsec.h>
  97 #include <netinet6/ipsec6.h>
  98 #include <netproto/key/key.h>
  99 #endif /*IPSEC*/
 100
 101 MALLOC_DEFINE(M_TSEGQ, "tseg_qent", "TCP segment queue entry");
 102
 103 static const int tcprexmtthresh = 3;
 104 tcp_cc  tcp_ccgen;
 105
 106 struct  tcpstat tcpstat;
 107 SYSCTL_STRUCT(_net_inet_tcp, TCPCTL_STATS, stats, CTLFLAG_RW,
 108     &tcpstat , tcpstat, "TCP statistics (struct tcpstat, netinet/tcp_var.h)");
 109
 110 static int log_in_vain = 0;
 111 SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW,
 112     &log_in_vain, 0, "Log all incoming TCP connections");
 113
 114 static int blackhole = 0;
 115 SYSCTL_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_RW,
 116     &blackhole, 0, "Do not send RST when dropping refused connections");
 117
 118 int tcp_delack_enabled = 1;
 119 SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_RW,
 120     &tcp_delack_enabled, 0,
 121     "Delay ACK to try and piggyback it onto a data packet");
 122
 123 #ifdef TCP_DROP_SYNFIN
 124 static int drop_synfin = 0;
 125 SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_RW,
 126     &drop_synfin, 0, "Drop TCP packets with SYN+FIN set");
 127 #endif
 128
 129 static int tcp_do_limitedtransmit = 1;
 130 SYSCTL_INT(_net_inet_tcp, OID_AUTO, limitedtransmit, CTLFLAG_RW,
 131     &tcp_do_limitedtransmit, 0, "Enable RFC 3042 (Limited Transmit)");
 132
 133 static int tcp_do_rfc3390 = 1;
 134 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3390, CTLFLAG_RW,
 135     &tcp_do_rfc3390, 0,
 136     "Enable RFC 3390 (Increasing TCP's Initial Congestion Window)");
 137
 138 static int tcp_do_eifel_detect = 1;
 139 SYSCTL_INT(_net_inet_tcp, OID_AUTO, eifel, CTLFLAG_RW,
 140     &tcp_do_eifel_detect, 0, "Eifel detection algorithm (RFC 3522)");
 141
 142 struct inpcbhead tcb;
 143 #define tcb6    tcb  /* for KAME src sync over BSD*'s */
 144 struct inpcbinfo tcbinfo;
 145
 146 static void      tcp_dooptions(struct tcpopt *, u_char *, int, int);
 147 static void      tcp_pulloutofband(struct socket *,
 148                      struct tcphdr *, struct mbuf *, int);
 149 static int       tcp_reass(struct tcpcb *, struct tcphdr *, int *,
 150                      struct mbuf *);
 151 static void      tcp_xmit_timer(struct tcpcb *, int);
 152 static void      tcp_newreno_partial_ack(struct tcpcb *, struct tcphdr *);
 153
 154 /* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */
 155 #ifdef INET6
 156 #define ND6_HINT(tp) \
 157 do { \
 158         if ((tp) && (tp)->t_inpcb && \
 159             ((tp)->t_inpcb->inp_vflag & INP_IPV6) != 0 && \
 160             (tp)->t_inpcb->in6p_route.ro_rt) \
 161                 nd6_nud_hint((tp)->t_inpcb->in6p_route.ro_rt, NULL, 0); \
 162 } while (0)
 163 #else
 164 #define ND6_HINT(tp)
 165 #endif
 166
 167 /*
 168  * Indicate whether this ack should be delayed.  We can delay the ack if
 169  *      - delayed acks are enabled and
 170  *      - there is no delayed ack timer in progress and
 171  *      - our last ack wasn't a 0-sized window.  We never want to delay
 172  *        the ack that opens up a 0-sized window.
 173  */
 174 #define DELAY_ACK(tp) \
 175         (tcp_delack_enabled && !callout_pending(tp->tt_delack) && \
 176         (tp->t_flags & TF_RXWIN0SENT) == 0)
 177
 178 static int
 179 tcp_reass(tp, th, tlenp, m)
 180         struct tcpcb *tp;
 181         struct tcphdr *th;
 182         int *tlenp;
 183         struct mbuf *m;
 184 {
 185         struct tseg_qent *q;
 186         struct tseg_qent *p = NULL;
 187         struct tseg_qent *nq;
 188         struct tseg_qent *te;
 189         struct socket *so = tp->t_inpcb->inp_socket;
 190         int flags;
 191
 192         /*
 193          * Call with th==0 after become established to
 194          * force pre-ESTABLISHED data up to user socket.
 195          */
 196         if (th == 0)
 197                 goto present;
 198
 199         /* Allocate a new queue entry. If we can't, just drop the pkt. XXX */
 200         MALLOC(te, struct tseg_qent *, sizeof(struct tseg_qent), M_TSEGQ,
 201                M_NOWAIT);
 202         if (te == NULL) {
 203                 tcpstat.tcps_rcvmemdrop++;
 204                 m_freem(m);
 205                 return (0);
 206         }
 207
 208         /*
 209          * Find a segment which begins after this one does.
 210          */
 211         LIST_FOREACH(q, &tp->t_segq, tqe_q) {
 212                 if (SEQ_GT(q->tqe_th->th_seq, th->th_seq))
 213                         break;
 214                 p = q;
 215         }
 216
 217         /*
 218          * If there is a preceding segment, it may provide some of
 219          * our data already.  If so, drop the data from the incoming
 220          * segment.  If it provides all of our data, drop us.
 221          */
 222         if (p != NULL) {
 223                 int i;
 224                 /* conversion to int (in i) handles seq wraparound */
 225                 i = p->tqe_th->th_seq + p->tqe_len - th->th_seq;
 226                 if (i > 0) {
 227                         if (i >= *tlenp) {
 228                                 tcpstat.tcps_rcvduppack++;
 229                                 tcpstat.tcps_rcvdupbyte += *tlenp;
 230                                 m_freem(m);
 231                                 free(te, M_TSEGQ);
 232                                 /*
 233                                  * Try to present any queued data
 234                                  * at the left window edge to the user.
 235                                  * This is needed after the 3-WHS
 236                                  * completes.
 237                                  */
 238                                 goto present;   /* ??? */
 239                         }
 240                         m_adj(m, i);
 241                         *tlenp -= i;
 242                         th->th_seq += i;
 243                 }
 244         }
 245         tcpstat.tcps_rcvoopack++;
 246         tcpstat.tcps_rcvoobyte += *tlenp;
 247
 248         /*
 249          * While we overlap succeeding segments trim them or,
 250          * if they are completely covered, dequeue them.
 251          */
 252         while (q) {
 253                 int i = (th->th_seq + *tlenp) - q->tqe_th->th_seq;
 254                 if (i <= 0)
 255                         break;
 256                 if (i < q->tqe_len) {
 257                         q->tqe_th->th_seq += i;
 258                         q->tqe_len -= i;
 259                         m_adj(q->tqe_m, i);
 260                         break;
 261                 }
 262
 263                 nq = LIST_NEXT(q, tqe_q);
 264                 LIST_REMOVE(q, tqe_q);
 265                 m_freem(q->tqe_m);
 266                 free(q, M_TSEGQ);
 267                 q = nq;
 268         }
 269
 270         /* Insert the new segment queue entry into place. */
 271         te->tqe_m = m;
 272         te->tqe_th = th;
 273         te->tqe_len = *tlenp;
 274
 275         if (p == NULL) {
 276                 LIST_INSERT_HEAD(&tp->t_segq, te, tqe_q);
 277         } else {
 278                 LIST_INSERT_AFTER(p, te, tqe_q);
 279         }
 280
 281 present:
 282         /*
 283          * Present data to user, advancing rcv_nxt through
 284          * completed sequence space.
 285          */
 286         if (!TCPS_HAVEESTABLISHED(tp->t_state))
 287                 return (0);
 288         q = LIST_FIRST(&tp->t_segq);
 289         if (!q || q->tqe_th->th_seq != tp->rcv_nxt)
 290                 return (0);
 291         do {
 292                 tp->rcv_nxt += q->tqe_len;
 293                 flags = q->tqe_th->th_flags & TH_FIN;
 294                 nq = LIST_NEXT(q, tqe_q);
 295                 LIST_REMOVE(q, tqe_q);
 296                 if (so->so_state & SS_CANTRCVMORE)
 297                         m_freem(q->tqe_m);
 298                 else
 299                         sbappend(&so->so_rcv, q->tqe_m);
 300                 free(q, M_TSEGQ);
 301                 q = nq;
 302         } while (q && q->tqe_th->th_seq == tp->rcv_nxt);
 303         ND6_HINT(tp);
 304         sorwakeup(so);
 305         return (flags);
 306 }
 307
 308 /*
 309  * TCP input routine, follows pages 65-76 of the
 310  * protocol specification dated September, 1981 very closely.
 311  */
 312 #ifdef INET6
 313 int
 314 tcp6_input(mp, offp, proto)
 315         struct mbuf **mp;
 316         int *offp, proto;
 317 {
 318         struct mbuf *m = *mp;
 319         struct in6_ifaddr *ia6;
 320
 321         IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
 322
 323         /*
 324          * draft-itojun-ipv6-tcp-to-anycast
 325          * better place to put this in?
 326          */
 327         ia6 = ip6_getdstifaddr(m);
 328         if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
 329                 struct ip6_hdr *ip6;
 330
 331                 ip6 = mtod(m, struct ip6_hdr *);
 332                 icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
 333                             (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
 334                 return IPPROTO_DONE;
 335         }
 336
 337         tcp_input(m, *offp, proto);
 338         return IPPROTO_DONE;
 339 }
 340 #endif
 341
 342 void
 343 tcp_input(m, off0, proto)
 344         struct mbuf *m;
 345         int off0, proto;
 346 {
 347         struct tcphdr *th;
 348         struct ip *ip = NULL;
 349         struct ipovly *ipov;
 350         struct inpcb *inp = NULL;
 351         u_char *optp = NULL;
 352         int optlen = 0;
 353         int len, tlen, off;
 354         int drop_hdrlen;
 355         struct tcpcb *tp = NULL;
 356         int thflags;
 357         struct socket *so = 0;
 358         int todrop, acked, ourfinisacked, needoutput = 0;
 359         u_long tiwin;
 360         struct tcpopt to;               /* options in this segment */
 361         struct rmxp_tao *taop;          /* pointer to our TAO cache entry */
 362         struct rmxp_tao tao_noncached;  /* in case there's no cached entry */
 363         struct sockaddr_in *next_hop = NULL;
 364         int rstreason; /* For badport_bandlim accounting purposes */
 365         struct ip6_hdr *ip6 = NULL;
 366 #ifdef INET6
 367         int isipv6;
 368 #else
 369         const int isipv6 = 0;
 370 #endif
 371 #ifdef TCPDEBUG
 372         short ostate = 0;
 373 #endif
 374
 375         /* Grab info from MT_TAG mbufs prepended to the chain. */
 376         for (;m && m->m_type == MT_TAG; m = m->m_next) {
 377                 if (m->_m_tag_id == PACKET_TAG_IPFORWARD)
 378                         next_hop = (struct sockaddr_in *)m->m_hdr.mh_data;
 379         }
 380 #ifdef INET6
 381         isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
 382 #endif
 383         bzero((char *)&to, sizeof(to));
 384
 385         tcpstat.tcps_rcvtotal++;
 386
 387         if (isipv6) {
 388                 /* IP6_EXTHDR_CHECK() is already done at tcp6_input() */
 389                 ip6 = mtod(m, struct ip6_hdr *);
 390                 tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
 391                 if (in6_cksum(m, IPPROTO_TCP, off0, tlen)) {
 392                         tcpstat.tcps_rcvbadsum++;
 393                         goto drop;
 394                 }
 395                 th = (struct tcphdr *)((caddr_t)ip6 + off0);
 396
 397                 /*
 398                  * Be proactive about unspecified IPv6 address in source.
 399                  * As we use all-zero to indicate unbounded/unconnected pcb,
 400                  * unspecified IPv6 address can be used to confuse us.
 401                  *
 402                  * Note that packets with unspecified IPv6 destination is
 403                  * already dropped in ip6_input.
 404                  */
 405                 if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
 406                         /* XXX stat */
 407                         goto drop;
 408                 }
 409         } else {
 410                 /*
 411                  * Get IP and TCP header together in first mbuf.
 412                  * Note: IP leaves IP header in first mbuf.
 413                  */
 414                 if (off0 > sizeof(struct ip)) {
 415                         ip_stripoptions(m, (struct mbuf *)0);
 416                         off0 = sizeof(struct ip);
 417                 }
 418                 if (m->m_len < sizeof(struct tcpiphdr)) {
 419                         if ((m = m_pullup(m, sizeof(struct tcpiphdr))) == 0) {
 420                                 tcpstat.tcps_rcvshort++;
 421                                 return;
 422                         }
 423                 }
 424                 ip = mtod(m, struct ip *);
 425                 ipov = (struct ipovly *)ip;
 426                 th = (struct tcphdr *)((caddr_t)ip + off0);
 427                 tlen = ip->ip_len;
 428
 429                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
 430                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
 431                                 th->th_sum = m->m_pkthdr.csum_data;
 432                         else
 433                                 th->th_sum = in_pseudo(ip->ip_src.s_addr,
 434                                                 ip->ip_dst.s_addr,
 435                                                 htonl(m->m_pkthdr.csum_data +
 436                                                         ip->ip_len +
 437                                                         IPPROTO_TCP));
 438                         th->th_sum ^= 0xffff;
 439                 } else {
 440                         /*
 441                          * Checksum extended TCP header and data.
 442                          */
 443                         len = sizeof(struct ip) + tlen;
 444                         bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
 445                         ipov->ih_len = (u_short)tlen;
 446                         ipov->ih_len = htons(ipov->ih_len);
 447                         th->th_sum = in_cksum(m, len);
 448                 }
 449                 if (th->th_sum) {
 450                         tcpstat.tcps_rcvbadsum++;
 451                         goto drop;
 452                 }
 453 #ifdef INET6
 454                 /* Re-initialization for later version check */
 455                 ip->ip_v = IPVERSION;
 456 #endif
 457         }
 458
 459         /*
 460          * Check that TCP offset makes sense,
 461          * pull out TCP options and adjust length.              XXX
 462          */
 463         off = th->th_off << 2;
 464         if (off < sizeof(struct tcphdr) || off > tlen) {
 465                 tcpstat.tcps_rcvbadoff++;
 466                 goto drop;
 467         }
 468         tlen -= off;    /* tlen is used instead of ti->ti_len */
 469         if (off > sizeof(struct tcphdr)) {
 470                 if (isipv6) {
 471                         IP6_EXTHDR_CHECK(m, off0, off, );
 472                         ip6 = mtod(m, struct ip6_hdr *);
 473                         th = (struct tcphdr *)((caddr_t)ip6 + off0);
 474                 } else {
 475                         if (m->m_len < sizeof(struct ip) + off) {
 476                                 if ((m = m_pullup(m, sizeof(struct ip) + off))
 477                                                 == 0) {
 478                                         tcpstat.tcps_rcvshort++;
 479                                         return;
 480                                 }
 481                                 ip = mtod(m, struct ip *);
 482                                 ipov = (struct ipovly *)ip;
 483                                 th = (struct tcphdr *)((caddr_t)ip + off0);
 484                         }
 485                 }
 486                 optlen = off - sizeof(struct tcphdr);
 487                 optp = (u_char *)(th + 1);
 488         }
 489         thflags = th->th_flags;
 490
 491 #ifdef TCP_DROP_SYNFIN
 492         /*
 493          * If the drop_synfin option is enabled, drop all packets with
 494          * both the SYN and FIN bits set. This prevents e.g. nmap from
 495          * identifying the TCP/IP stack.
 496          *
 497          * This is a violation of the TCP specification.
 498          */
 499         if (drop_synfin && (thflags & (TH_SYN|TH_FIN)) == (TH_SYN|TH_FIN))
 500                 goto drop;
 501 #endif
 502
 503         /*
 504          * Convert TCP protocol specific fields to host format.
 505          */
 506         th->th_seq = ntohl(th->th_seq);
 507         th->th_ack = ntohl(th->th_ack);
 508         th->th_win = ntohs(th->th_win);
 509         th->th_urp = ntohs(th->th_urp);
 510
 511         /*
 512          * Delay droping TCP, IP headers, IPv6 ext headers, and TCP options,
 513          * until after ip6_savecontrol() is called and before other functions
 514          * which don't want those proto headers.
 515          * Because ip6_savecontrol() is going to parse the mbuf to
 516          * search for data to be passed up to user-land, it wants mbuf
 517          * parameters to be unchanged.
 518          * XXX: the call of ip6_savecontrol() has been obsoleted based on
 519          * latest version of the advanced API (20020110).
 520          */
 521         drop_hdrlen = off0 + off;
 522
 523         /*
 524          * Locate pcb for segment.
 525          */
 526 findpcb:
 527         /* IPFIREWALL_FORWARD section */
 528         if (next_hop != NULL && isipv6 == 0) {  /* IPv6 support is not yet */
 529                 /*
 530                  * Transparently forwarded. Pretend to be the destination.
 531                  * already got one like this?
 532                  */
 533                 inp = in_pcblookup_hash(&tcbinfo, ip->ip_src, th->th_sport,
 534                                         ip->ip_dst, th->th_dport,
 535                                         0, m->m_pkthdr.rcvif);
 536                 if (!inp) {
 537                         /* It's new.  Try find the ambushing socket. */
 538                         inp = in_pcblookup_hash(&tcbinfo,
 539                                                 ip->ip_src, th->th_sport,
 540                                                 next_hop->sin_addr,
 541                                                 next_hop->sin_port ?
 542                                                     ntohs(next_hop->sin_port) :
 543                                                     th->th_dport,
 544                                                 1, m->m_pkthdr.rcvif);
 545                 }
 546         } else {
 547                 if (isipv6)
 548                         inp = in6_pcblookup_hash(&tcbinfo,
 549                                                  &ip6->ip6_src, th->th_sport,
 550                                                  &ip6->ip6_dst, th->th_dport,
 551                                                  1, m->m_pkthdr.rcvif);
 552                 else
 553                         inp = in_pcblookup_hash(&tcbinfo,
 554                                                 ip->ip_src, th->th_sport,
 555                                                 ip->ip_dst, th->th_dport,
 556                                                 1, m->m_pkthdr.rcvif);
 557       }
 558
 559 #ifdef IPSEC
 560         if (isipv6) {
 561                 if (inp != NULL && ipsec6_in_reject_so(m, inp->inp_socket)) {
 562                         ipsec6stat.in_polvio++;
 563                         goto drop;
 564                 }
 565         } else {
 566                 if (inp != NULL && ipsec4_in_reject_so(m, inp->inp_socket)) {
 567                         ipsecstat.in_polvio++;
 568                         goto drop;
 569                 }
 570         }
 571 #endif
 572 #ifdef FAST_IPSEC
 573         if (isipv6) {
 574                 if (inp != NULL && ipsec6_in_reject(m, inp)) {
 575                         goto drop;
 576                 }
 577         } else {
 578                 if (inp != NULL && ipsec4_in_reject(m, inp)) {
 579                         goto drop;
 580                 }
 581         }
 582 #endif
 583
 584         /*
 585          * If the state is CLOSED (i.e., TCB does not exist) then
 586          * all data in the incoming segment is discarded.
 587          * If the TCB exists but is in CLOSED state, it is embryonic,
 588          * but should either do a listen or a connect soon.
 589          */
 590         if (inp == NULL) {
 591                 if (log_in_vain) {
 592 #ifdef INET6
 593                         char dbuf[INET6_ADDRSTRLEN+2], sbuf[INET6_ADDRSTRLEN+2];
 594 #else
 595                         char dbuf[4*sizeof "123"], sbuf[4*sizeof "123"];
 596 #endif
 597                         if (isipv6) {
 598                                 strcpy(dbuf, "[");
 599                                 strcpy(sbuf, "[");
 600                                 strcat(dbuf, ip6_sprintf(&ip6->ip6_dst));
 601                                 strcat(sbuf, ip6_sprintf(&ip6->ip6_src));
 602                                 strcat(dbuf, "]");
 603                                 strcat(sbuf, "]");
 604                         } else {
 605                                 strcpy(dbuf, inet_ntoa(ip->ip_dst));
 606                                 strcpy(sbuf, inet_ntoa(ip->ip_src));
 607                         }
 608                         switch (log_in_vain) {
 609                         case 1:
 610                                 if ((thflags & TH_SYN) == 0)
 611                                         break;
 612                         case 2:
 613                                 log(LOG_INFO,
 614                                     "Connection attempt to TCP %s:%d "
 615                                     "from %s:%d flags:0x%02x\n",
 616                                     dbuf, ntohs(th->th_dport), sbuf,
 617                                     ntohs(th->th_sport), thflags);
 618                                 break;
 619                         default:
 620                                 break;
 621                         }
 622                 }
 623                 if (blackhole) {
 624                         switch (blackhole) {
 625                         case 1:
 626                                 if (thflags & TH_SYN)
 627                                         goto drop;
 628                                 break;
 629                         case 2:
 630                                 goto drop;
 631                         default:
 632                                 goto drop;
 633                         }
 634                 }
 635                 rstreason = BANDLIM_RST_CLOSEDPORT;
 636                 goto dropwithreset;
 637         }
 638         tp = intotcpcb(inp);
 639         if (tp == NULL) {
 640                 rstreason = BANDLIM_RST_CLOSEDPORT;
 641                 goto dropwithreset;
 642         }
 643         if (tp->t_state == TCPS_CLOSED)
 644                 goto drop;
 645
 646         /* Unscale the window into a 32-bit value. */
 647         if ((thflags & TH_SYN) == 0)
 648                 tiwin = th->th_win << tp->snd_scale;
 649         else
 650                 tiwin = th->th_win;
 651
 652         so = inp->inp_socket;
 653
 654 #ifdef TCPDEBUG
 655         if (so->so_options & SO_DEBUG) {
 656                 ostate = tp->t_state;
 657                 if (isipv6)
 658                         bcopy((char *)ip6, (char *)tcp_saveipgen, sizeof(*ip6));
 659                 else
 660                         bcopy((char *)ip, (char *)tcp_saveipgen, sizeof(*ip));
 661                 tcp_savetcp = *th;
 662         }
 663 #endif
 664
 665         if (so->so_options & SO_ACCEPTCONN) {
 666                 struct in_conninfo inc;
 667
 668 #ifdef INET6
 669                 inc.inc_isipv6 = isipv6;
 670 #endif
 671                 if (isipv6) {
 672                         inc.inc6_faddr = ip6->ip6_src;
 673                         inc.inc6_laddr = ip6->ip6_dst;
 674                         inc.inc6_route.ro_rt = NULL;            /* XXX */
 675                 } else {
 676                         inc.inc_faddr = ip->ip_src;
 677                         inc.inc_laddr = ip->ip_dst;
 678                         inc.inc_route.ro_rt = NULL;             /* XXX */
 679                 }
 680                 inc.inc_fport = th->th_sport;
 681                 inc.inc_lport = th->th_dport;
 682
 683                 /*
 684                  * If the state is LISTEN then ignore segment if it contains
 685                  * a RST.  If the segment contains an ACK then it is bad and
 686                  * send a RST.  If it does not contain a SYN then it is not
 687                  * interesting; drop it.
 688                  *
 689                  * If the state is SYN_RECEIVED (syncache) and seg contains
 690                  * an ACK, but not for our SYN/ACK, send a RST.  If the seg
 691                  * contains a RST, check the sequence number to see if it
 692                  * is a valid reset segment.
 693                  */
 694                 if ((thflags & (TH_RST|TH_ACK|TH_SYN)) != TH_SYN) {
 695                         if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
 696                                 if (!syncache_expand(&inc, th, &so, m)) {
 697                                         /*
 698                                          * No syncache entry, or ACK was not
 699                                          * for our SYN/ACK.  Send a RST.
 700                                          */
 701                                         tcpstat.tcps_badsyn++;
 702                                         rstreason = BANDLIM_RST_OPENPORT;
 703                                         goto dropwithreset;
 704                                 }
 705                                 if (so == NULL)
 706                                         /*
 707                                          * Could not complete 3-way handshake,
 708                                          * connection is being closed down, and
 709                                          * syncache will free mbuf.
 710                                          */
 711                                         return;
 712                                 /*
 713                                  * Socket is created in state SYN_RECEIVED.
 714                                  * Continue processing segment.
 715                                  */
 716                                 inp = sotoinpcb(so);
 717                                 tp = intotcpcb(inp);
 718                                 /*
 719                                  * This is what would have happened in
 720                                  * tcp_output() when the SYN,ACK was sent.
 721                                  */
 722                                 tp->snd_up = tp->snd_una;
 723                                 tp->snd_max = tp->snd_nxt = tp->iss + 1;
 724                                 tp->last_ack_sent = tp->rcv_nxt;
 725 /*
 726  * XXX possible bug - it doesn't appear that tp->snd_wnd is unscaled
 727  * until the _second_ ACK is received:
 728  *    rcv SYN (set wscale opts)  --> send SYN/ACK, set snd_wnd = window.
 729  *    rcv ACK, calculate tiwin --> process SYN_RECEIVED, determine wscale,
 730  *        move to ESTAB, set snd_wnd to tiwin.
 731  */
 732                                 tp->snd_wnd = tiwin;    /* unscaled */
 733                                 goto after_listen;
 734                         }
 735                         if (thflags & TH_RST) {
 736                                 syncache_chkrst(&inc, th);
 737                                 goto drop;
 738                         }
 739                         if (thflags & TH_ACK) {
 740                                 syncache_badack(&inc);
 741                                 tcpstat.tcps_badsyn++;
 742                                 rstreason = BANDLIM_RST_OPENPORT;
 743                                 goto dropwithreset;
 744                         }
 745                         goto drop;
 746                 }
 747
 748                 /*
 749                  * Segment's flags are (SYN) or (SYN|FIN).
 750                  */
 751 #ifdef INET6
 752                 /*
 753                  * If deprecated address is forbidden,
 754                  * we do not accept SYN to deprecated interface
 755                  * address to prevent any new inbound connection from
 756                  * getting established.
 757                  * When we do not accept SYN, we send a TCP RST,
 758                  * with deprecated source address (instead of dropping
 759                  * it).  We compromise it as it is much better for peer
 760                  * to send a RST, and RST will be the final packet
 761                  * for the exchange.
 762                  *
 763                  * If we do not forbid deprecated addresses, we accept
 764                  * the SYN packet.  RFC2462 does not suggest dropping
 765                  * SYN in this case.
 766                  * If we decipher RFC2462 5.5.4, it says like this:
 767                  * 1. use of deprecated addr with existing
 768                  *    communication is okay - "SHOULD continue to be
 769                  *    used"
 770                  * 2. use of it with new communication:
 771                  *   (2a) "SHOULD NOT be used if alternate address
 772                  *        with sufficient scope is available"
 773                  *   (2b) nothing mentioned otherwise.
 774                  * Here we fall into (2b) case as we have no choice in
 775                  * our source address selection - we must obey the peer.
 776                  *
 777                  * The wording in RFC2462 is confusing, and there are
 778                  * multiple description text for deprecated address
 779                  * handling - worse, they are not exactly the same.
 780                  * I believe 5.5.4 is the best one, so we follow 5.5.4.
 781                  */
 782                 if (isipv6 && !ip6_use_deprecated) {
 783                         struct in6_ifaddr *ia6;
 784
 785                         if ((ia6 = ip6_getdstifaddr(m)) &&
 786                             (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
 787                                 tp = NULL;
 788                                 rstreason = BANDLIM_RST_OPENPORT;
 789                                 goto dropwithreset;
 790                         }
 791                 }
 792 #endif
 793                 /*
 794                  * If it is from this socket, drop it, it must be forged.
 795                  * Don't bother responding if the destination was a broadcast.
 796                  */
 797                 if (th->th_dport == th->th_sport) {
 798                         if (isipv6) {
 799                                 if (IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst,
 800                                                        &ip6->ip6_src))
 801                                         goto drop;
 802                         } else {
 803                                 if (ip->ip_dst.s_addr == ip->ip_src.s_addr)
 804                                         goto drop;
 805                         }
 806                 }
 807                 /*
 808                  * RFC1122 4.2.3.10, p. 104: discard bcast/mcast SYN
 809                  *
 810                  * Note that it is quite possible to receive unicast
 811                  * link-layer packets with a broadcast IP address. Use
 812                  * in_broadcast() to find them.
 813                  */
 814                 if (m->m_flags & (M_BCAST|M_MCAST))
 815                         goto drop;
 816                 if (isipv6) {
 817                         if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
 818                             IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
 819                                 goto drop;
 820                 } else {
 821                         if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
 822                             IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
 823                             ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
 824                             in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
 825                                 goto drop;
 826                 }
 827                 /*
 828                  * SYN appears to be valid; create compressed TCP state
 829                  * for syncache, or perform t/tcp connection.
 830                  */
 831                 if (so->so_qlen <= so->so_qlimit) {
 832                         tcp_dooptions(&to, optp, optlen, 1);
 833                         if (!syncache_add(&inc, &to, th, &so, m))
 834                                 goto drop;
 835                         if (so == NULL)
 836                                 /*
 837                                  * Entry added to syncache, mbuf used to
 838                                  * send SYN,ACK packet.
 839                                  */
 840                                 return;
 841                         /*
 842                          * Segment passed TAO tests.
 843                          */
 844                         inp = sotoinpcb(so);
 845                         tp = intotcpcb(inp);
 846                         tp->snd_wnd = tiwin;
 847                         tp->t_starttime = ticks;
 848                         tp->t_state = TCPS_ESTABLISHED;
 849
 850                         /*
 851                          * If there is a FIN, or if there is data and the
 852                          * connection is local, then delay SYN,ACK(SYN) in
 853                          * the hope of piggy-backing it on a response
 854                          * segment.  Otherwise must send ACK now in case
 855                          * the other side is slow starting.
 856                          */
 857                         if (DELAY_ACK(tp) &&
 858                             ((thflags & TH_FIN) ||
 859                              (tlen != 0 &&
 860                               ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
 861                                (!isipv6 && in_localaddr(inp->inp_faddr)))))) {
 862                                 callout_reset(tp->tt_delack, tcp_delacktime,
 863                                                 tcp_timer_delack, tp);
 864                                 tp->t_flags |= TF_NEEDSYN;
 865                         } else
 866                                 tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
 867
 868                         tcpstat.tcps_connects++;
 869                         soisconnected(so);
 870                         goto trimthenstep6;
 871                 }
 872                 goto drop;
 873         }
 874 after_listen:
 875
 876 /* XXX temp debugging */
 877         /* should not happen - syncache should pick up these connections */
 878         if (tp->t_state == TCPS_LISTEN)
 879                 panic("tcp_input: TCPS_LISTEN");
 880
 881         /*
 882          * Segment received on connection.
 883          * Reset idle time and keep-alive timer.
 884          */
 885         tp->t_rcvtime = ticks;
 886         if (TCPS_HAVEESTABLISHED(tp->t_state))
 887                 callout_reset(tp->tt_keep, tcp_keepidle, tcp_timer_keep, tp);
 888
 889         /*
 890          * Process options.
 891          * XXX this is tradtitional behavior, may need to be cleaned up.
 892          */
 893         tcp_dooptions(&to, optp, optlen, thflags & TH_SYN);
 894         if (thflags & TH_SYN) {
 895                 if (to.to_flags & TOF_SCALE) {
 896                         tp->t_flags |= TF_RCVD_SCALE;
 897                         tp->requested_s_scale = to.to_requested_s_scale;
 898                 }
 899                 if (to.to_flags & TOF_TS) {
 900                         tp->t_flags |= TF_RCVD_TSTMP;
 901                         tp->ts_recent = to.to_tsval;
 902                         tp->ts_recent_age = ticks;
 903                 }
 904                 if (to.to_flags & (TOF_CC|TOF_CCNEW))
 905                         tp->t_flags |= TF_RCVD_CC;
 906                 if (to.to_flags & TOF_MSS)
 907                         tcp_mss(tp, to.to_mss);
 908         }
 909
 910         /*
 911          * Header prediction: check for the two common cases
 912          * of a uni-directional data xfer.  If the packet has
 913          * no control flags, is in-sequence, the window didn't
 914          * change and we're not retransmitting, it's a
 915          * candidate.  If the length is zero and the ack moved
 916          * forward, we're the sender side of the xfer.  Just
 917          * free the data acked & wake any higher level process
 918          * that was blocked waiting for space.  If the length
 919          * is non-zero and the ack didn't move, we're the
 920          * receiver side.  If we're getting packets in-order
 921          * (the reassembly queue is empty), add the data to
 922          * the socket buffer and note that we need a delayed ack.
 923          * Make sure that the hidden state-flags are also off.
 924          * Since we check for TCPS_ESTABLISHED above, it can only
 925          * be TH_NEEDSYN.
 926          */
 927         if (tp->t_state == TCPS_ESTABLISHED &&
 928             (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
 929             ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
 930             ((to.to_flags & TOF_TS) == 0 ||
 931              TSTMP_GEQ(to.to_tsval, tp->ts_recent)) &&
 932             /*
 933              * Using the CC option is compulsory if once started:
 934              *   the segment is OK if no T/TCP was negotiated or
 935              *   if the segment has a CC option equal to CCrecv
 936              */
 937             ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) != (TF_REQ_CC|TF_RCVD_CC) ||
 938              ((to.to_flags & TOF_CC) != 0 && to.to_cc == tp->cc_recv)) &&
 939             th->th_seq == tp->rcv_nxt &&
 940             tiwin && tiwin == tp->snd_wnd &&
 941             tp->snd_nxt == tp->snd_max) {
 942
 943                 /*
 944                  * If last ACK falls within this segment's sequence numbers,
 945                  * record the timestamp.
 946                  * NOTE that the test is modified according to the latest
 947                  * proposal of the tcplw@cray.com list (Braden 1993/04/26).
 948                  */
 949                 if ((to.to_flags & TOF_TS) != 0 &&
 950                     SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
 951                         tp->ts_recent_age = ticks;
 952                         tp->ts_recent = to.to_tsval;
 953                 }
 954
 955                 if (tlen == 0) {
 956                         if (SEQ_GT(th->th_ack, tp->snd_una) &&
 957                             SEQ_LEQ(th->th_ack, tp->snd_max) &&
 958                             tp->snd_cwnd >= tp->snd_wnd &&
 959                             ((!tcp_do_newreno &&
 960                               tp->t_dupacks < tcprexmtthresh) ||
 961                              (tcp_do_newreno && !IN_FASTRECOVERY(tp)))) {
 962                                 /*
 963                                  * this is a pure ack for outstanding data.
 964                                  */
 965                                 ++tcpstat.tcps_predack;
 966                                 /*
 967                                  * "bad retransmit" recovery
 968                                  *
 969                                  * If Eifel detection applies, then
 970                                  * it is deterministic, so use it
 971                                  * unconditionally over the old heuristic.
 972                                  * Otherwise, fall back to the old heuristic.
 973                                  */
 974                                 if (tcp_do_eifel_detect &&
 975                                     (to.to_flags & TOF_TS) && to.to_tsecr &&
 976                                     (tp->t_flags & TF_FIRSTACCACK)) {
 977                                         /* Eifel detection applicable. */
 978                                         if (to.to_tsecr < tp->t_rexmtTS) {
 979                                                 tcp_revert_congestion_state(tp);
 980                                                 ++tcpstat.tcps_eifeldetected;
 981                                         }
 982                                 } else if (tp->t_rxtshift == 1 &&
 983                                            ticks < tp->t_badrxtwin) {
 984                                         tcp_revert_congestion_state(tp);
 985                                         ++tcpstat.tcps_rttdetected;
 986                                 }
 987                                 tp->t_flags &= ~(TF_FIRSTACCACK | TF_FASTREXMT);
 988                                 /*
 989                                  * Recalculate the retransmit timer / rtt.
 990                                  *
 991                                  * Some machines (certain windows boxes)
 992                                  * send broken timestamp replies during the
 993                                  * SYN+ACK phase, ignore timestamps of 0.
 994                                  */
 995                                 if ((to.to_flags & TOF_TS) != 0 &&
 996                                     to.to_tsecr) {
 997                                         tcp_xmit_timer(tp,
 998                                             ticks - to.to_tsecr + 1);
 999                                 } else if (tp->t_rtttime &&
1000                                             SEQ_GT(th->th_ack, tp->t_rtseq)) {
1001                                         tcp_xmit_timer(tp,
1002                                                        ticks - tp->t_rtttime);
1003                                 }
1004                                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
1005                                 acked = th->th_ack - tp->snd_una;
1006                                 tcpstat.tcps_rcvackpack++;
1007                                 tcpstat.tcps_rcvackbyte += acked;
1008                                 sbdrop(&so->so_snd, acked);
1009                                 if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
1010                                     SEQ_LEQ(th->th_ack, tp->snd_recover))
1011                                         tp->snd_recover = th->th_ack - 1;
1012                                 tp->snd_una = th->th_ack;
1013                                 tp->t_dupacks = 0;
1014                                 m_freem(m);
1015                                 ND6_HINT(tp); /* some progress has been done */
1016
1017                                 /*
1018                                  * If all outstanding data are acked, stop
1019                                  * retransmit timer, otherwise restart timer
1020                                  * using current (possibly backed-off) value.
1021                                  * If process is waiting for space,
1022                                  * wakeup/selwakeup/signal.  If data
1023                                  * are ready to send, let tcp_output
1024                                  * decide between more output or persist.
1025                                  */
1026                                 if (tp->snd_una == tp->snd_max)
1027                                         callout_stop(tp->tt_rexmt);
1028                                 else if (!callout_active(tp->tt_persist))
1029                                         callout_reset(tp->tt_rexmt,
1030                                                       tp->t_rxtcur,
1031                                                       tcp_timer_rexmt, tp);
1032
1033                                 sowwakeup(so);
1034                                 if (so->so_snd.sb_cc)
1035                                         (void) tcp_output(tp);
1036                                 return;
1037                         }
1038                 } else if (th->th_ack == tp->snd_una &&
1039                     LIST_EMPTY(&tp->t_segq) &&
1040                     tlen <= sbspace(&so->so_rcv)) {
1041                         /*
1042                          * this is a pure, in-sequence data packet
1043                          * with nothing on the reassembly queue and
1044                          * we have enough buffer space to take it.
1045                          */
1046                         ++tcpstat.tcps_preddat;
1047                         tp->rcv_nxt += tlen;
1048                         tcpstat.tcps_rcvpack++;
1049                         tcpstat.tcps_rcvbyte += tlen;
1050                         ND6_HINT(tp);   /* some progress has been done */
1051                         /*
1052                          * Add data to socket buffer.
1053                          */
1054                         if (so->so_state & SS_CANTRCVMORE) {
1055                                 m_freem(m);
1056                         } else {
1057                                 m_adj(m, drop_hdrlen);  /* delayed header drop */
1058                                 sbappend(&so->so_rcv, m);
1059                         }
1060                         sorwakeup(so);
1061                         if (DELAY_ACK(tp)) {
1062                                 callout_reset(tp->tt_delack, tcp_delacktime,
1063                                     tcp_timer_delack, tp);
1064                         } else {
1065                                 tp->t_flags |= TF_ACKNOW;
1066                                 tcp_output(tp);
1067                         }
1068                         return;
1069                 }
1070         }
1071
1072         /*
1073          * Calculate amount of space in receive window,
1074          * and then do TCP input processing.
1075          * Receive window is amount of space in rcv queue,
1076          * but not less than advertised window.
1077          */
1078         { int win;
1079
1080         win = sbspace(&so->so_rcv);
1081         if (win < 0)
1082                 win = 0;
1083         tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
1084         }
1085
1086         switch (tp->t_state) {
1087
1088         /*
1089          * If the state is SYN_RECEIVED:
1090          *      if seg contains an ACK, but not for our SYN/ACK, send a RST.
1091          */
1092         case TCPS_SYN_RECEIVED:
1093                 if ((thflags & TH_ACK) &&
1094                     (SEQ_LEQ(th->th_ack, tp->snd_una) ||
1095                      SEQ_GT(th->th_ack, tp->snd_max))) {
1096                                 rstreason = BANDLIM_RST_OPENPORT;
1097                                 goto dropwithreset;
1098                 }
1099                 break;
1100
1101         /*
1102          * If the state is SYN_SENT:
1103          *      if seg contains an ACK, but not for our SYN, drop the input.
1104          *      if seg contains a RST, then drop the connection.
1105          *      if seg does not contain SYN, then drop it.
1106          * Otherwise this is an acceptable SYN segment
1107          *      initialize tp->rcv_nxt and tp->irs
1108          *      if seg contains ack then advance tp->snd_una
1109          *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
1110          *      arrange for segment to be acked (eventually)
1111          *      continue processing rest of data/controls, beginning with URG
1112          */
1113         case TCPS_SYN_SENT:
1114                 if ((taop = tcp_gettaocache(&inp->inp_inc)) == NULL) {
1115                         taop = &tao_noncached;
1116                         bzero(taop, sizeof(*taop));
1117                 }
1118
1119                 if ((thflags & TH_ACK) &&
1120                     (SEQ_LEQ(th->th_ack, tp->iss) ||
1121                      SEQ_GT(th->th_ack, tp->snd_max))) {
1122                         /*
1123                          * If we have a cached CCsent for the remote host,
1124                          * hence we haven't just crashed and restarted,
1125                          * do not send a RST.  This may be a retransmission
1126                          * from the other side after our earlier ACK was lost.
1127                          * Our new SYN, when it arrives, will serve as the
1128                          * needed ACK.
1129                          */
1130                         if (taop->tao_ccsent != 0)
1131                                 goto drop;
1132                         else {
1133                                 rstreason = BANDLIM_UNLIMITED;
1134                                 goto dropwithreset;
1135                         }
1136                 }
1137                 if (thflags & TH_RST) {
1138                         if (thflags & TH_ACK)
1139                                 tp = tcp_drop(tp, ECONNREFUSED);
1140                         goto drop;
1141                 }
1142                 if ((thflags & TH_SYN) == 0)
1143                         goto drop;
1144                 tp->snd_wnd = th->th_win;       /* initial send window */
1145                 tp->cc_recv = to.to_cc;         /* foreign CC */
1146
1147                 tp->irs = th->th_seq;
1148                 tcp_rcvseqinit(tp);
1149                 if (thflags & TH_ACK) {
1150                         /*
1151                          * Our SYN was acked.  If segment contains CC.ECHO
1152                          * option, check it to make sure this segment really
1153                          * matches our SYN.  If not, just drop it as old
1154                          * duplicate, but send an RST if we're still playing
1155                          * by the old rules.  If no CC.ECHO option, make sure
1156                          * we don't get fooled into using T/TCP.
1157                          */
1158                         if (to.to_flags & TOF_CCECHO) {
1159                                 if (tp->cc_send != to.to_ccecho) {
1160                                         if (taop->tao_ccsent != 0)
1161                                                 goto drop;
1162                                         else {
1163                                                 rstreason = BANDLIM_UNLIMITED;
1164                                                 goto dropwithreset;
1165                                         }
1166                                 }
1167                         } else
1168                                 tp->t_flags &= ~TF_RCVD_CC;
1169                         tcpstat.tcps_connects++;
1170                         soisconnected(so);
1171                         /* Do window scaling on this connection? */
1172                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1173                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1174                                 tp->snd_scale = tp->requested_s_scale;
1175                                 tp->rcv_scale = tp->request_r_scale;
1176                         }
1177                         /* Segment is acceptable, update cache if undefined. */
1178                         if (taop->tao_ccsent == 0)
1179                                 taop->tao_ccsent = to.to_ccecho;
1180
1181                         tp->rcv_adv += tp->rcv_wnd;
1182                         tp->snd_una++;          /* SYN is acked */
1183                         /*
1184                          * If there's data, delay ACK; if there's also a FIN
1185                          * ACKNOW will be turned on later.
1186                          */
1187                         if (DELAY_ACK(tp) && tlen != 0)
1188                                 callout_reset(tp->tt_delack, tcp_delacktime,
1189                                     tcp_timer_delack, tp);
1190                         else
1191                                 tp->t_flags |= TF_ACKNOW;
1192                         /*
1193                          * Received <SYN,ACK> in SYN_SENT[*] state.
1194                          * Transitions:
1195                          *      SYN_SENT  --> ESTABLISHED
1196                          *      SYN_SENT* --> FIN_WAIT_1
1197                          */
1198                         tp->t_starttime = ticks;
1199                         if (tp->t_flags & TF_NEEDFIN) {
1200                                 tp->t_state = TCPS_FIN_WAIT_1;
1201                                 tp->t_flags &= ~TF_NEEDFIN;
1202                                 thflags &= ~TH_SYN;
1203                         } else {
1204                                 tp->t_state = TCPS_ESTABLISHED;
1205                                 callout_reset(tp->tt_keep, tcp_keepidle,
1206                                               tcp_timer_keep, tp);
1207                         }
1208                 } else {
1209                         /*
1210                          * Received initial SYN in SYN-SENT[*] state =>
1211                          * simultaneous open.  If segment contains CC option
1212                          * and there is a cached CC, apply TAO test.
1213                          * If it succeeds, connection is * half-synchronized.
1214                          * Otherwise, do 3-way handshake:
1215                          *        SYN-SENT -> SYN-RECEIVED
1216                          *        SYN-SENT* -> SYN-RECEIVED*
1217                          * If there was no CC option, clear cached CC value.
1218                          */
1219                         tp->t_flags |= TF_ACKNOW;
1220                         callout_stop(tp->tt_rexmt);
1221                         if (to.to_flags & TOF_CC) {
1222                                 if (taop->tao_cc != 0 &&
1223                                     CC_GT(to.to_cc, taop->tao_cc)) {
1224                                         /*
1225                                          * update cache and make transition:
1226                                          *        SYN-SENT -> ESTABLISHED*
1227                                          *        SYN-SENT* -> FIN-WAIT-1*
1228                                          */
1229                                         taop->tao_cc = to.to_cc;
1230                                         tp->t_starttime = ticks;
1231                                         if (tp->t_flags & TF_NEEDFIN) {
1232                                                 tp->t_state = TCPS_FIN_WAIT_1;
1233                                                 tp->t_flags &= ~TF_NEEDFIN;
1234                                         } else {
1235                                                 tp->t_state = TCPS_ESTABLISHED;
1236                                                 callout_reset(tp->tt_keep,
1237                                                               tcp_keepidle,
1238                                                               tcp_timer_keep,
1239                                                               tp);
1240                                         }
1241                                         tp->t_flags |= TF_NEEDSYN;
1242                                 } else
1243                                         tp->t_state = TCPS_SYN_RECEIVED;
1244                         } else {
1245                                 /* CC.NEW or no option => invalidate cache */
1246                                 taop->tao_cc = 0;
1247                                 tp->t_state = TCPS_SYN_RECEIVED;
1248                         }
1249                 }
1250
1251 trimthenstep6:
1252                 /*
1253                  * Advance th->th_seq to correspond to first data byte.
1254                  * If data, trim to stay within window,
1255                  * dropping FIN if necessary.
1256                  */
1257                 th->th_seq++;
1258                 if (tlen > tp->rcv_wnd) {
1259                         todrop = tlen - tp->rcv_wnd;
1260                         m_adj(m, -todrop);
1261                         tlen = tp->rcv_wnd;
1262                         thflags &= ~TH_FIN;
1263                         tcpstat.tcps_rcvpackafterwin++;
1264                         tcpstat.tcps_rcvbyteafterwin += todrop;
1265                 }
1266                 tp->snd_wl1 = th->th_seq - 1;
1267                 tp->rcv_up = th->th_seq;
1268                 /*
1269                  * Client side of transaction: already sent SYN and data.
1270                  * If the remote host used T/TCP to validate the SYN,
1271                  * our data will be ACK'd; if so, enter normal data segment
1272                  * processing in the middle of step 5, ack processing.
1273                  * Otherwise, goto step 6.
1274                  */
1275                 if (thflags & TH_ACK)
1276                         goto process_ACK;
1277
1278                 goto step6;
1279
1280         /*
1281          * If the state is LAST_ACK or CLOSING or TIME_WAIT:
1282          *      if segment contains a SYN and CC [not CC.NEW] option:
1283          *              if state == TIME_WAIT and connection duration > MSL,
1284          *                  drop packet and send RST;
1285          *
1286          *              if SEG.CC > CCrecv then is new SYN, and can implicitly
1287          *                  ack the FIN (and data) in retransmission queue.
1288          *                  Complete close and delete TCPCB.  Then reprocess
1289          *                  segment, hoping to find new TCPCB in LISTEN state;
1290          *
1291          *              else must be old SYN; drop it.
1292          *      else do normal processing.
1293          */
1294         case TCPS_LAST_ACK:
1295         case TCPS_CLOSING:
1296         case TCPS_TIME_WAIT:
1297                 if ((thflags & TH_SYN) &&
1298                     (to.to_flags & TOF_CC) && tp->cc_recv != 0) {
1299                         if (tp->t_state == TCPS_TIME_WAIT &&
1300                                         (ticks - tp->t_starttime) > tcp_msl) {
1301                                 rstreason = BANDLIM_UNLIMITED;
1302                                 goto dropwithreset;
1303                         }
1304                         if (CC_GT(to.to_cc, tp->cc_recv)) {
1305                                 tp = tcp_close(tp);
1306                                 goto findpcb;
1307                         }
1308                         else
1309                                 goto drop;
1310                 }
1311                 break;  /* continue normal processing */
1312         }
1313
1314         /*
1315          * States other than LISTEN or SYN_SENT.
1316          * First check the RST flag and sequence number since reset segments
1317          * are exempt from the timestamp and connection count tests.  This
1318          * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
1319          * below which allowed reset segments in half the sequence space
1320          * to fall though and be processed (which gives forged reset
1321          * segments with a random sequence number a 50 percent chance of
1322          * killing a connection).
1323          * Then check timestamp, if present.
1324          * Then check the connection count, if present.
1325          * Then check that at least some bytes of segment are within
1326          * receive window.  If segment begins before rcv_nxt,
1327          * drop leading data (and SYN); if nothing left, just ack.
1328          *
1329          *
1330          * If the RST bit is set, check the sequence number to see
1331          * if this is a valid reset segment.
1332          * RFC 793 page 37:
1333          *   In all states except SYN-SENT, all reset (RST) segments
1334          *   are validated by checking their SEQ-fields.  A reset is
1335          *   valid if its sequence number is in the window.
1336          * Note: this does not take into account delayed ACKs, so
1337          *   we should test against last_ack_sent instead of rcv_nxt.
1338          *   The sequence number in the reset segment is normally an
1339          *   echo of our outgoing acknowlegement numbers, but some hosts
1340          *   send a reset with the sequence number at the rightmost edge
1341          *   of our receive window, and we have to handle this case.
1342          * If we have multiple segments in flight, the intial reset
1343          * segment sequence numbers will be to the left of last_ack_sent,
1344          * but they will eventually catch up.
1345          * In any case, it never made sense to trim reset segments to
1346          * fit the receive window since RFC 1122 says:
1347          *   4.2.2.12  RST Segment: RFC-793 Section 3.4
1348          *
1349          *    A TCP SHOULD allow a received RST segment to include data.
1350          *
1351          *    DISCUSSION
1352          *         It has been suggested that a RST segment could contain
1353          *         ASCII text that encoded and explained the cause of the
1354          *         RST.  No standard has yet been established for such
1355          *         data.
1356          *
1357          * If the reset segment passes the sequence number test examine
1358          * the state:
1359          *    SYN_RECEIVED STATE:
1360          *      If passive open, return to LISTEN state.
1361          *      If active open, inform user that connection was refused.
1362          *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, CLOSE_WAIT STATES:
1363          *      Inform user that connection was reset, and close tcb.
1364          *    CLOSING, LAST_ACK STATES:
1365          *      Close the tcb.
1366          *    TIME_WAIT STATE:
1367          *      Drop the segment - see Stevens, vol. 2, p. 964 and
1368          *      RFC 1337.
1369          */
1370         if (thflags & TH_RST) {
1371                 if (SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
1372                     SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
1373                         switch (tp->t_state) {
1374
1375                         case TCPS_SYN_RECEIVED:
1376                                 so->so_error = ECONNREFUSED;
1377                                 goto close;
1378
1379                         case TCPS_ESTABLISHED:
1380                         case TCPS_FIN_WAIT_1:
1381                         case TCPS_FIN_WAIT_2:
1382                         case TCPS_CLOSE_WAIT:
1383                                 so->so_error = ECONNRESET;
1384                         close:
1385                                 tp->t_state = TCPS_CLOSED;
1386                                 tcpstat.tcps_drops++;
1387                                 tp = tcp_close(tp);
1388                                 break;
1389
1390                         case TCPS_CLOSING:
1391                         case TCPS_LAST_ACK:
1392                                 tp = tcp_close(tp);
1393                                 break;
1394
1395                         case TCPS_TIME_WAIT:
1396                                 break;
1397                         }
1398                 }
1399                 goto drop;
1400         }
1401
1402         /*
1403          * RFC 1323 PAWS: If we have a timestamp reply on this segment
1404          * and it's less than ts_recent, drop it.
1405          */
1406         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
1407             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
1408
1409                 /* Check to see if ts_recent is over 24 days old.  */
1410                 if ((int)(ticks - tp->ts_recent_age) > TCP_PAWS_IDLE) {
1411                         /*
1412                          * Invalidate ts_recent.  If this segment updates
1413                          * ts_recent, the age will be reset later and ts_recent
1414                          * will get a valid value.  If it does not, setting
1415                          * ts_recent to zero will at least satisfy the
1416                          * requirement that zero be placed in the timestamp
1417                          * echo reply when ts_recent isn't valid.  The
1418                          * age isn't reset until we get a valid ts_recent
1419                          * because we don't want out-of-order segments to be
1420                          * dropped when ts_recent is old.
1421                          */
1422                         tp->ts_recent = 0;
1423                 } else {
1424                         tcpstat.tcps_rcvduppack++;
1425                         tcpstat.tcps_rcvdupbyte += tlen;
1426                         tcpstat.tcps_pawsdrop++;
1427                         if (tlen)
1428                                 goto dropafterack;
1429                         goto drop;
1430                 }
1431         }
1432
1433         /*
1434          * T/TCP mechanism
1435          *   If T/TCP was negotiated and the segment doesn't have CC,
1436          *   or if its CC is wrong then drop the segment.
1437          *   RST segments do not have to comply with this.
1438          */
1439         if ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) == (TF_REQ_CC|TF_RCVD_CC) &&
1440             ((to.to_flags & TOF_CC) == 0 || tp->cc_recv != to.to_cc))
1441                 goto dropafterack;
1442
1443         /*
1444          * In the SYN-RECEIVED state, validate that the packet belongs to
1445          * this connection before trimming the data to fit the receive
1446          * window.  Check the sequence number versus IRS since we know
1447          * the sequence numbers haven't wrapped.  This is a partial fix
1448          * for the "LAND" DoS attack.
1449          */
1450         if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
1451                 rstreason = BANDLIM_RST_OPENPORT;
1452                 goto dropwithreset;
1453         }
1454
1455         todrop = tp->rcv_nxt - th->th_seq;
1456         if (todrop > 0) {
1457                 if (thflags & TH_SYN) {
1458                         thflags &= ~TH_SYN;
1459                         th->th_seq++;
1460                         if (th->th_urp > 1)
1461                                 th->th_urp--;
1462                         else
1463                                 thflags &= ~TH_URG;
1464                         todrop--;
1465                 }
1466                 /*
1467                  * Following if statement from Stevens, vol. 2, p. 960.
1468                  */
1469                 if (todrop > tlen
1470                     || (todrop == tlen && (thflags & TH_FIN) == 0)) {
1471                         /*
1472                          * Any valid FIN must be to the left of the window.
1473                          * At this point the FIN must be a duplicate or out
1474                          * of sequence; drop it.
1475                          */
1476                         thflags &= ~TH_FIN;
1477
1478                         /*
1479                          * Send an ACK to resynchronize and drop any data.
1480                          * But keep on processing for RST or ACK.
1481                          */
1482                         tp->t_flags |= TF_ACKNOW;
1483                         todrop = tlen;
1484                         tcpstat.tcps_rcvduppack++;
1485                         tcpstat.tcps_rcvdupbyte += todrop;
1486                 } else {
1487                         tcpstat.tcps_rcvpartduppack++;
1488                         tcpstat.tcps_rcvpartdupbyte += todrop;
1489                 }
1490                 drop_hdrlen += todrop;  /* drop from the top afterwards */
1491                 th->th_seq += todrop;
1492                 tlen -= todrop;
1493                 if (th->th_urp > todrop)
1494                         th->th_urp -= todrop;
1495                 else {
1496                         thflags &= ~TH_URG;
1497                         th->th_urp = 0;
1498                 }
1499         }
1500
1501         /*
1502          * If new data are received on a connection after the
1503          * user processes are gone, then RST the other end.
1504          */
1505         if ((so->so_state & SS_NOFDREF) &&
1506             tp->t_state > TCPS_CLOSE_WAIT && tlen) {
1507                 tp = tcp_close(tp);
1508                 tcpstat.tcps_rcvafterclose++;
1509                 rstreason = BANDLIM_UNLIMITED;
1510                 goto dropwithreset;
1511         }
1512
1513         /*
1514          * If segment ends after window, drop trailing data
1515          * (and PUSH and FIN); if nothing left, just ACK.
1516          */
1517         todrop = (th->th_seq+tlen) - (tp->rcv_nxt+tp->rcv_wnd);
1518         if (todrop > 0) {
1519                 tcpstat.tcps_rcvpackafterwin++;
1520                 if (todrop >= tlen) {
1521                         tcpstat.tcps_rcvbyteafterwin += tlen;
1522                         /*
1523                          * If a new connection request is received
1524                          * while in TIME_WAIT, drop the old connection
1525                          * and start over if the sequence numbers
1526                          * are above the previous ones.
1527                          */
1528                         if (thflags & TH_SYN &&
1529                             tp->t_state == TCPS_TIME_WAIT &&
1530                             SEQ_GT(th->th_seq, tp->rcv_nxt)) {
1531                                 tp = tcp_close(tp);
1532                                 goto findpcb;
1533                         }
1534                         /*
1535                          * If window is closed can only take segments at
1536                          * window edge, and have to drop data and PUSH from
1537                          * incoming segments.  Continue processing, but
1538                          * remember to ack.  Otherwise, drop segment
1539                          * and ack.
1540                          */
1541                         if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
1542                                 tp->t_flags |= TF_ACKNOW;
1543                                 tcpstat.tcps_rcvwinprobe++;
1544                         } else
1545                                 goto dropafterack;
1546                 } else
1547                         tcpstat.tcps_rcvbyteafterwin += todrop;
1548                 m_adj(m, -todrop);
1549                 tlen -= todrop;
1550                 thflags &= ~(TH_PUSH|TH_FIN);
1551         }
1552
1553         /*
1554          * If last ACK falls within this segment's sequence numbers,
1555          * record its timestamp.
1556          * NOTE that the test is modified according to the latest
1557          * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1558          */
1559         if ((to.to_flags & TOF_TS) != 0 &&
1560             SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
1561                 tp->ts_recent_age = ticks;
1562                 tp->ts_recent = to.to_tsval;
1563         }
1564
1565         /*
1566          * If a SYN is in the window, then this is an
1567          * error and we send an RST and drop the connection.
1568          */
1569         if (thflags & TH_SYN) {
1570                 tp = tcp_drop(tp, ECONNRESET);
1571                 rstreason = BANDLIM_UNLIMITED;
1572                 goto dropwithreset;
1573         }
1574
1575         /*
1576          * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
1577          * flag is on (half-synchronized state), then queue data for
1578          * later processing; else drop segment and return.
1579          */
1580         if ((thflags & TH_ACK) == 0) {
1581                 if (tp->t_state == TCPS_SYN_RECEIVED ||
1582                     (tp->t_flags & TF_NEEDSYN))
1583                         goto step6;
1584                 else
1585                         goto drop;
1586         }
1587
1588         /*
1589          * Ack processing.
1590          */
1591         switch (tp->t_state) {
1592
1593         /*
1594          * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
1595          * ESTABLISHED state and continue processing.
1596          * The ACK was checked above.
1597          */
1598         case TCPS_SYN_RECEIVED:
1599
1600                 tcpstat.tcps_connects++;
1601                 soisconnected(so);
1602                 /* Do window scaling? */
1603                 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1604                         (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1605                         tp->snd_scale = tp->requested_s_scale;
1606                         tp->rcv_scale = tp->request_r_scale;
1607                 }
1608                 /*
1609                  * Upon successful completion of 3-way handshake,
1610                  * update cache.CC if it was undefined, pass any queued
1611                  * data to the user, and advance state appropriately.
1612                  */
1613                 if ((taop = tcp_gettaocache(&inp->inp_inc)) != NULL &&
1614                     taop->tao_cc == 0)
1615                         taop->tao_cc = tp->cc_recv;
1616
1617                 /*
1618                  * Make transitions:
1619                  *      SYN-RECEIVED  -> ESTABLISHED
1620                  *      SYN-RECEIVED* -> FIN-WAIT-1
1621                  */
1622                 tp->t_starttime = ticks;
1623                 if (tp->t_flags & TF_NEEDFIN) {
1624                         tp->t_state = TCPS_FIN_WAIT_1;
1625                         tp->t_flags &= ~TF_NEEDFIN;
1626                 } else {
1627                         tp->t_state = TCPS_ESTABLISHED;
1628                         callout_reset(tp->tt_keep, tcp_keepidle,
1629                                       tcp_timer_keep, tp);
1630                 }
1631                 /*
1632                  * If segment contains data or ACK, will call tcp_reass()
1633                  * later; if not, do so now to pass queued data to user.
1634                  */
1635                 if (tlen == 0 && (thflags & TH_FIN) == 0)
1636                         (void) tcp_reass(tp, (struct tcphdr *)0, 0,
1637                             (struct mbuf *)0);
1638                 tp->snd_wl1 = th->th_seq - 1;
1639                 /* fall into ... */
1640
1641         /*
1642          * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
1643          * ACKs.  If the ack is in the range
1644          *      tp->snd_una < th->th_ack <= tp->snd_max
1645          * then advance tp->snd_una to th->th_ack and drop
1646          * data from the retransmission queue.  If this ACK reflects
1647          * more up to date window information we update our window information.
1648          */
1649         case TCPS_ESTABLISHED:
1650         case TCPS_FIN_WAIT_1:
1651         case TCPS_FIN_WAIT_2:
1652         case TCPS_CLOSE_WAIT:
1653         case TCPS_CLOSING:
1654         case TCPS_LAST_ACK:
1655         case TCPS_TIME_WAIT:
1656
1657                 if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
1658                         if (tlen == 0 && tiwin == tp->snd_wnd) {
1659                                 tcpstat.tcps_rcvdupack++;
1660                                 /*
1661                                  * If we have outstanding data (other than
1662                                  * a window probe), this is a completely
1663                                  * duplicate ack (ie, window info didn't
1664                                  * change), the ack is the biggest we've
1665                                  * seen and we've seen exactly our rexmt
1666                                  * threshhold of them, assume a packet
1667                                  * has been dropped and retransmit it.
1668                                  * Kludge snd_nxt & the congestion
1669                                  * window so we send only this one
1670                                  * packet.
1671                                  *
1672                                  * We know we're losing at the current
1673                                  * window size so do congestion avoidance
1674                                  * (set ssthresh to half the current window
1675                                  * and pull our congestion window back to
1676                                  * the new ssthresh).
1677                                  *
1678                                  * Dup acks mean that packets have left the
1679                                  * network (they're now cached at the receiver)
1680                                  * so bump cwnd by the amount in the receiver
1681                                  * to keep a constant cwnd packets in the
1682                                  * network.
1683                                  */
1684                                 if (!callout_active(tp->tt_rexmt) ||
1685                                     th->th_ack != tp->snd_una)
1686                                         tp->t_dupacks = 0;
1687                                 else if (++tp->t_dupacks > tcprexmtthresh ||
1688                                          (tcp_do_newreno &&
1689                                           IN_FASTRECOVERY(tp))) {
1690                                         tp->snd_cwnd += tp->t_maxseg;
1691                                         (void) tcp_output(tp);
1692                                         goto drop;
1693                                 } else if (tp->t_dupacks == tcprexmtthresh) {
1694                                         tcp_seq onxt = tp->snd_nxt;
1695                                         u_int win;
1696                                         if (tcp_do_newreno &&
1697                                             SEQ_LEQ(th->th_ack,
1698                                                     tp->snd_recover)) {
1699                                                 tp->t_dupacks = 0;
1700                                                 break;
1701                                         }
1702                                         if (tcp_do_eifel_detect &&
1703                                             (tp->t_flags & TF_RCVD_TSTMP)) {
1704                                                 tcp_save_congestion_state(tp);
1705                                                 tp->t_flags |= TF_FASTREXMT;
1706                                         }
1707                                         win = min(tp->snd_wnd, tp->snd_cwnd) /
1708                                             2 / tp->t_maxseg;
1709                                         if (win < 2)
1710                                                 win = 2;
1711                                         tp->snd_ssthresh = win * tp->t_maxseg;
1712                                         ENTER_FASTRECOVERY(tp);
1713                                         tp->snd_recover = tp->snd_max;
1714                                         callout_stop(tp->tt_rexmt);
1715                                         tp->t_rtttime = 0;
1716                                         tp->snd_nxt = th->th_ack;
1717                                         tp->snd_cwnd = tp->t_maxseg;
1718                                         (void) tcp_output(tp);
1719                                         KASSERT(tp->snd_limited <= 2,
1720                                             ("tp->snd_limited too big"));
1721                                         tp->snd_cwnd = tp->snd_ssthresh +
1722                                             (tp->t_maxseg *
1723                                              (tp->t_dupacks - tp->snd_limited));
1724                                         if (SEQ_GT(onxt, tp->snd_nxt))
1725                                                 tp->snd_nxt = onxt;
1726                                         goto drop;
1727                                 } else if (tcp_do_limitedtransmit) {
1728                                         u_long oldcwnd = tp->snd_cwnd;
1729                                         tcp_seq oldsndmax = tp->snd_max;
1730                                         u_int sent;
1731                                         KASSERT(tp->t_dupacks == 1 ||
1732                                             tp->t_dupacks == 2,
1733                                             ("dupacks not 1 or 2"));
1734                                         if (tp->t_dupacks == 1)
1735                                                 tp->snd_limited = 0;
1736                                         tp->snd_cwnd =
1737                                             (tp->snd_nxt - tp->snd_una) +
1738                                             (tp->t_dupacks - tp->snd_limited) *
1739                                             tp->t_maxseg;
1740                                         (void) tcp_output(tp);
1741                                         sent = tp->snd_max - oldsndmax;
1742                                         if (sent > tp->t_maxseg) {
1743                                                 KASSERT(tp->snd_limited == 0 &&
1744                                                     tp->t_dupacks == 2,
1745                                                     ("sent too much"));
1746                                                 tp->snd_limited = 2;
1747                                         } else if (sent > 0)
1748                                                 ++tp->snd_limited;
1749                                         tp->snd_cwnd = oldcwnd;
1750                                         goto drop;
1751                                 }
1752                         } else
1753                                 tp->t_dupacks = 0;
1754                         break;
1755                 }
1756
1757                 KASSERT(SEQ_GT(th->th_ack, tp->snd_una), ("th_ack <= snd_una"));
1758
1759                 /*
1760                  * If the congestion window was inflated to account
1761                  * for the other side's cached packets, retract it.
1762                  */
1763                 if (tcp_do_newreno) {
1764                         if (IN_FASTRECOVERY(tp)) {
1765                                 if (SEQ_LT(th->th_ack, tp->snd_recover)) {
1766                                         tcp_newreno_partial_ack(tp, th);
1767                                 } else {
1768                                         /*
1769                                          * Window inflation should have left us
1770                                          * with approximately snd_ssthresh
1771                                          * outstanding data.
1772                                          * But in case we would be inclined to
1773                                          * send a burst, better to do it via
1774                                          * the slow start mechanism.
1775                                          */
1776                                         if (SEQ_GT(th->th_ack +
1777                                                         tp->snd_ssthresh,
1778                                                    tp->snd_max))
1779                                                 tp->snd_cwnd = tp->snd_max -
1780                                                                 th->th_ack +
1781                                                                 tp->t_maxseg;
1782                                         else
1783                                                 tp->snd_cwnd = tp->snd_ssthresh;
1784                                 }
1785                         }
1786                 } else {
1787                         if (tp->t_dupacks >= tcprexmtthresh &&
1788                             tp->snd_cwnd > tp->snd_ssthresh)
1789                                 tp->snd_cwnd = tp->snd_ssthresh;
1790                 }
1791                 tp->t_dupacks = 0;
1792                 if (SEQ_GT(th->th_ack, tp->snd_max)) {
1793                         tcpstat.tcps_rcvacktoomuch++;
1794                         goto dropafterack;
1795                 }
1796                 /*
1797                  * If we reach this point, ACK is not a duplicate,
1798                  *     i.e., it ACKs something we sent.
1799                  */
1800                 if (tp->t_flags & TF_NEEDSYN) {
1801                         /*
1802                          * T/TCP: Connection was half-synchronized, and our
1803                          * SYN has been ACK'd (so connection is now fully
1804                          * synchronized).  Go to non-starred state,
1805                          * increment snd_una for ACK of SYN, and check if
1806                          * we can do window scaling.
1807                          */
1808                         tp->t_flags &= ~TF_NEEDSYN;
1809                         tp->snd_una++;
1810                         /* Do window scaling? */
1811                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1812                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1813                                 tp->snd_scale = tp->requested_s_scale;
1814                                 tp->rcv_scale = tp->request_r_scale;
1815                         }
1816                 }
1817
1818 process_ACK:
1819                 acked = th->th_ack - tp->snd_una;
1820                 tcpstat.tcps_rcvackpack++;
1821                 tcpstat.tcps_rcvackbyte += acked;
1822
1823                 /*
1824                  * If we just performed our first retransmit, and the ACK
1825                  * arrives within our recovery window, then it was a mistake
1826                  * to do the retransmit in the first place.  Recover our
1827                  * original cwnd and ssthresh, and proceed to transmit where
1828                  * we left off.
1829                  */
1830                 if (tcp_do_eifel_detect && acked &&
1831                     (to.to_flags & TOF_TS) && to.to_tsecr &&
1832                     (tp->t_flags & TF_FIRSTACCACK)) {
1833                         /* Eifel detection applicable. */
1834                         if (to.to_tsecr < tp->t_rexmtTS) {
1835                                 tcp_revert_congestion_state(tp);
1836                                 ++tcpstat.tcps_eifeldetected;
1837                         }
1838                 } else if (tp->t_rxtshift == 1 && ticks < tp->t_badrxtwin) {
1839                         tcp_revert_congestion_state(tp);
1840                         ++tcpstat.tcps_rttdetected;
1841                 }
1842
1843                 /*
1844                  * If we have a timestamp reply, update smoothed
1845                  * round trip time.  If no timestamp is present but
1846                  * transmit timer is running and timed sequence
1847                  * number was acked, update smoothed round trip time.
1848                  * Since we now have an rtt measurement, cancel the
1849                  * timer backoff (cf., Phil Karn's retransmit alg.).
1850                  * Recompute the initial retransmit timer.
1851                  *
1852                  * Some machines (certain windows boxes) send broken
1853                  * timestamp replies during the SYN+ACK phase, ignore
1854                  * timestamps of 0.
1855                  */
1856                 if ((to.to_flags & TOF_TS) != 0 &&
1857                     to.to_tsecr) {
1858                         tcp_xmit_timer(tp, ticks - to.to_tsecr + 1);
1859                 } else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
1860                         tcp_xmit_timer(tp, ticks - tp->t_rtttime);
1861                 }
1862                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
1863
1864                 /*
1865                  * If all outstanding data is acked, stop retransmit
1866                  * timer and remember to restart (more output or persist).
1867                  * If there is more data to be acked, restart retransmit
1868                  * timer, using current (possibly backed-off) value.
1869                  */
1870                 if (th->th_ack == tp->snd_max) {
1871                         callout_stop(tp->tt_rexmt);
1872                         needoutput = 1;
1873                 } else if (!callout_active(tp->tt_persist))
1874                         callout_reset(tp->tt_rexmt, tp->t_rxtcur,
1875                                       tcp_timer_rexmt, tp);
1876
1877                 /*
1878                  * If no data (only SYN) was ACK'd,
1879                  *    skip rest of ACK processing.
1880                  */
1881                 if (acked == 0)
1882                         goto step6;
1883
1884                 /* Stop looking for an acceptable ACK since one was received. */
1885                 tp->t_flags &= ~(TF_FIRSTACCACK | TF_FASTREXMT);
1886
1887                 /*
1888                  * When new data is acked, open the congestion window.
1889                  * If the window gives us less than ssthresh packets
1890                  * in flight, open exponentially (maxseg per packet).
1891                  * Otherwise open linearly: maxseg per window
1892                  * (maxseg^2 / cwnd per packet).
1893                  */
1894                 if (!tcp_do_newreno || !IN_FASTRECOVERY(tp)) {
1895                         u_int cw = tp->snd_cwnd;
1896                         u_int incr = tp->t_maxseg;
1897                         if (cw > tp->snd_ssthresh)
1898                                 incr = incr * incr / cw;
1899                         tp->snd_cwnd = min(cw+incr, TCP_MAXWIN<<tp->snd_scale);
1900                 }
1901                 if (acked > so->so_snd.sb_cc) {
1902                         tp->snd_wnd -= so->so_snd.sb_cc;
1903                         sbdrop(&so->so_snd, (int)so->so_snd.sb_cc);
1904                         ourfinisacked = 1;
1905                 } else {
1906                         sbdrop(&so->so_snd, acked);
1907                         tp->snd_wnd -= acked;
1908                         ourfinisacked = 0;
1909                 }
1910                 sowwakeup(so);
1911                 /* detect una wraparound */
1912                 if (tcp_do_newreno && !IN_FASTRECOVERY(tp) &&
1913                     SEQ_GT(tp->snd_una, tp->snd_recover) &&
1914                     SEQ_LEQ(th->th_ack, tp->snd_recover))
1915                         tp->snd_recover = th->th_ack - 1;
1916                 if (tcp_do_newreno && IN_FASTRECOVERY(tp) &&
1917                     SEQ_GEQ(th->th_ack, tp->snd_recover))
1918                         EXIT_FASTRECOVERY(tp);
1919                 tp->snd_una = th->th_ack;
1920                 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
1921                         tp->snd_nxt = tp->snd_una;
1922
1923                 switch (tp->t_state) {
1924
1925                 /*
1926                  * In FIN_WAIT_1 STATE in addition to the processing
1927                  * for the ESTABLISHED state if our FIN is now acknowledged
1928                  * then enter FIN_WAIT_2.
1929                  */
1930                 case TCPS_FIN_WAIT_1:
1931                         if (ourfinisacked) {
1932                                 /*
1933                                  * If we can't receive any more
1934                                  * data, then closing user can proceed.
1935                                  * Starting the timer is contrary to the
1936                                  * specification, but if we don't get a FIN
1937                                  * we'll hang forever.
1938                                  */
1939                                 if (so->so_state & SS_CANTRCVMORE) {
1940                                         soisdisconnected(so);
1941                                         callout_reset(tp->tt_2msl, tcp_maxidle,
1942                                                       tcp_timer_2msl, tp);
1943                                 }
1944                                 tp->t_state = TCPS_FIN_WAIT_2;
1945                         }
1946                         break;
1947
1948                 /*
1949                  * In CLOSING STATE in addition to the processing for
1950                  * the ESTABLISHED state if the ACK acknowledges our FIN
1951                  * then enter the TIME-WAIT state, otherwise ignore
1952                  * the segment.
1953                  */
1954                 case TCPS_CLOSING:
1955                         if (ourfinisacked) {
1956                                 tp->t_state = TCPS_TIME_WAIT;
1957                                 tcp_canceltimers(tp);
1958                                 /* Shorten TIME_WAIT [RFC-1644, p.28] */
1959                                 if (tp->cc_recv != 0 &&
1960                                     (ticks - tp->t_starttime) < tcp_msl)
1961                                         callout_reset(tp->tt_2msl,
1962                                                       tp->t_rxtcur *
1963                                                       TCPTV_TWTRUNC,
1964                                                       tcp_timer_2msl, tp);
1965                                 else
1966                                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
1967                                                       tcp_timer_2msl, tp);
1968                                 soisdisconnected(so);
1969                         }
1970                         break;
1971
1972                 /*
1973                  * In LAST_ACK, we may still be waiting for data to drain
1974                  * and/or to be acked, as well as for the ack of our FIN.
1975                  * If our FIN is now acknowledged, delete the TCB,
1976                  * enter the closed state and return.
1977                  */
1978                 case TCPS_LAST_ACK:
1979                         if (ourfinisacked) {
1980                                 tp = tcp_close(tp);
1981                                 goto drop;
1982                         }
1983                         break;
1984
1985                 /*
1986                  * In TIME_WAIT state the only thing that should arrive
1987                  * is a retransmission of the remote FIN.  Acknowledge
1988                  * it and restart the finack timer.
1989                  */
1990                 case TCPS_TIME_WAIT:
1991                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
1992                                       tcp_timer_2msl, tp);
1993                         goto dropafterack;
1994                 }
1995         }
1996
1997 step6:
1998         /*
1999          * Update window information.
2000          * Don't look at window if no ACK: TAC's send garbage on first SYN.
2001          */
2002         if ((thflags & TH_ACK) &&
2003             (SEQ_LT(tp->snd_wl1, th->th_seq) ||
2004             (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
2005              (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
2006                 /* keep track of pure window updates */
2007                 if (tlen == 0 &&
2008                     tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
2009                         tcpstat.tcps_rcvwinupd++;
2010                 tp->snd_wnd = tiwin;
2011                 tp->snd_wl1 = th->th_seq;
2012                 tp->snd_wl2 = th->th_ack;
2013                 if (tp->snd_wnd > tp->max_sndwnd)
2014                         tp->max_sndwnd = tp->snd_wnd;
2015                 needoutput = 1;
2016         }
2017
2018         /*
2019          * Process segments with URG.
2020          */
2021         if ((thflags & TH_URG) && th->th_urp &&
2022             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2023                 /*
2024                  * This is a kludge, but if we receive and accept
2025                  * random urgent pointers, we'll crash in
2026                  * soreceive.  It's hard to imagine someone
2027                  * actually wanting to send this much urgent data.
2028                  */
2029                 if (th->th_urp + so->so_rcv.sb_cc > sb_max) {
2030                         th->th_urp = 0;                 /* XXX */
2031                         thflags &= ~TH_URG;             /* XXX */
2032                         goto dodata;                    /* XXX */
2033                 }
2034                 /*
2035                  * If this segment advances the known urgent pointer,
2036                  * then mark the data stream.  This should not happen
2037                  * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
2038                  * a FIN has been received from the remote side.
2039                  * In these states we ignore the URG.
2040                  *
2041                  * According to RFC961 (Assigned Protocols),
2042                  * the urgent pointer points to the last octet
2043                  * of urgent data.  We continue, however,
2044                  * to consider it to indicate the first octet
2045                  * of data past the urgent section as the original
2046                  * spec states (in one of two places).
2047                  */
2048                 if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
2049                         tp->rcv_up = th->th_seq + th->th_urp;
2050                         so->so_oobmark = so->so_rcv.sb_cc +
2051                             (tp->rcv_up - tp->rcv_nxt) - 1;
2052                         if (so->so_oobmark == 0)
2053                                 so->so_state |= SS_RCVATMARK;
2054                         sohasoutofband(so);
2055                         tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
2056                 }
2057                 /*
2058                  * Remove out of band data so doesn't get presented to user.
2059                  * This can happen independent of advancing the URG pointer,
2060                  * but if two URG's are pending at once, some out-of-band
2061                  * data may creep in... ick.
2062                  */
2063                 if (th->th_urp <= (u_long)tlen
2064 #ifdef SO_OOBINLINE
2065                      && (so->so_options & SO_OOBINLINE) == 0
2066 #endif
2067                      )
2068                         tcp_pulloutofband(so, th, m,
2069                                 drop_hdrlen);   /* hdr drop is delayed */
2070         } else {
2071                 /*
2072                  * If no out of band data is expected,
2073                  * pull receive urgent pointer along
2074                  * with the receive window.
2075                  */
2076                 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
2077                         tp->rcv_up = tp->rcv_nxt;
2078         }
2079 dodata:                                                 /* XXX */
2080
2081         /*
2082          * Process the segment text, merging it into the TCP sequencing queue,
2083          * and arranging for acknowledgment of receipt if necessary.
2084          * This process logically involves adjusting tp->rcv_wnd as data
2085          * is presented to the user (this happens in tcp_usrreq.c,
2086          * case PRU_RCVD).  If a FIN has already been received on this
2087          * connection then we just ignore the text.
2088          */
2089         if ((tlen || (thflags & TH_FIN)) &&
2090             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2091                 m_adj(m, drop_hdrlen);  /* delayed header drop */
2092                 /*
2093                  * Insert segment which includes th into TCP reassembly queue
2094                  * with control block tp.  Set thflags to whether reassembly now
2095                  * includes a segment with FIN.  This handles the common case
2096                  * inline (segment is the next to be received on an established
2097                  * connection, and the queue is empty), avoiding linkage into
2098                  * and removal from the queue and repetition of various
2099                  * conversions.
2100                  * Set DELACK for segments received in order, but ack
2101                  * immediately when segments are out of order (so
2102                  * fast retransmit can work).
2103                  */
2104                 if (th->th_seq == tp->rcv_nxt &&
2105                     LIST_EMPTY(&tp->t_segq) &&
2106                     TCPS_HAVEESTABLISHED(tp->t_state)) {
2107                         if (DELAY_ACK(tp))
2108                                 callout_reset(tp->tt_delack, tcp_delacktime,
2109                                               tcp_timer_delack, tp);
2110                         else
2111                                 tp->t_flags |= TF_ACKNOW;
2112                         tp->rcv_nxt += tlen;
2113                         thflags = th->th_flags & TH_FIN;
2114                         tcpstat.tcps_rcvpack++;
2115                         tcpstat.tcps_rcvbyte += tlen;
2116                         ND6_HINT(tp);
2117                         if (so->so_state & SS_CANTRCVMORE)
2118                                 m_freem(m);
2119                         else
2120                                 sbappend(&so->so_rcv, m);
2121                         sorwakeup(so);
2122                 } else {
2123                         thflags = tcp_reass(tp, th, &tlen, m);
2124                         tp->t_flags |= TF_ACKNOW;
2125                 }
2126
2127                 /*
2128                  * Note the amount of data that peer has sent into
2129                  * our window, in order to estimate the sender's
2130                  * buffer size.
2131                  */
2132                 len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
2133         } else {
2134                 m_freem(m);
2135                 thflags &= ~TH_FIN;
2136         }
2137
2138         /*
2139          * If FIN is received ACK the FIN and let the user know
2140          * that the connection is closing.
2141          */
2142         if (thflags & TH_FIN) {
2143                 if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2144                         socantrcvmore(so);
2145                         /*
2146                          * If connection is half-synchronized
2147                          * (ie NEEDSYN flag on) then delay ACK,
2148                          * so it may be piggybacked when SYN is sent.
2149                          * Otherwise, since we received a FIN then no
2150                          * more input can be expected, send ACK now.
2151                          */
2152                         if (DELAY_ACK(tp) && (tp->t_flags & TF_NEEDSYN))
2153                                 callout_reset(tp->tt_delack, tcp_delacktime,
2154                                     tcp_timer_delack, tp);
2155                         else
2156                                 tp->t_flags |= TF_ACKNOW;
2157                         tp->rcv_nxt++;
2158                 }
2159                 switch (tp->t_state) {
2160
2161                 /*
2162                  * In SYN_RECEIVED and ESTABLISHED STATES
2163                  * enter the CLOSE_WAIT state.
2164                  */
2165                 case TCPS_SYN_RECEIVED:
2166                         tp->t_starttime = ticks;
2167                         /*FALLTHROUGH*/
2168                 case TCPS_ESTABLISHED:
2169                         tp->t_state = TCPS_CLOSE_WAIT;
2170                         break;
2171
2172                 /*
2173                  * If still in FIN_WAIT_1 STATE FIN has not been acked so
2174                  * enter the CLOSING state.
2175                  */
2176                 case TCPS_FIN_WAIT_1:
2177                         tp->t_state = TCPS_CLOSING;
2178                         break;
2179
2180                 /*
2181                  * In FIN_WAIT_2 state enter the TIME_WAIT state,
2182                  * starting the time-wait timer, turning off the other
2183                  * standard timers.
2184                  */
2185                 case TCPS_FIN_WAIT_2:
2186                         tp->t_state = TCPS_TIME_WAIT;
2187                         tcp_canceltimers(tp);
2188                         /* Shorten TIME_WAIT [RFC-1644, p.28] */
2189                         if (tp->cc_recv != 0 &&
2190                             (ticks - tp->t_starttime) < tcp_msl) {
2191                                 callout_reset(tp->tt_2msl,
2192                                               tp->t_rxtcur * TCPTV_TWTRUNC,
2193                                               tcp_timer_2msl, tp);
2194                                 /* For transaction client, force ACK now. */
2195                                 tp->t_flags |= TF_ACKNOW;
2196                         }
2197                         else
2198                                 callout_reset(tp->tt_2msl, 2 * tcp_msl,
2199                                               tcp_timer_2msl, tp);
2200                         soisdisconnected(so);
2201                         break;
2202
2203                 /*
2204                  * In TIME_WAIT state restart the 2 MSL time_wait timer.
2205                  */
2206                 case TCPS_TIME_WAIT:
2207                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
2208                                       tcp_timer_2msl, tp);
2209                         break;
2210                 }
2211         }
2212 #ifdef TCPDEBUG
2213         if (so->so_options & SO_DEBUG)
2214                 tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
2215                           &tcp_savetcp, 0);
2216 #endif
2217
2218         /*
2219          * Return any desired output.
2220          */
2221         if (needoutput || (tp->t_flags & TF_ACKNOW))
2222                 (void) tcp_output(tp);
2223         return;
2224
2225 dropafterack:
2226         /*
2227          * Generate an ACK dropping incoming segment if it occupies
2228          * sequence space, where the ACK reflects our state.
2229          *
2230          * We can now skip the test for the RST flag since all
2231          * paths to this code happen after packets containing
2232          * RST have been dropped.
2233          *
2234          * In the SYN-RECEIVED state, don't send an ACK unless the
2235          * segment we received passes the SYN-RECEIVED ACK test.
2236          * If it fails send a RST.  This breaks the loop in the
2237          * "LAND" DoS attack, and also prevents an ACK storm
2238          * between two listening ports that have been sent forged
2239          * SYN segments, each with the source address of the other.
2240          */
2241         if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
2242             (SEQ_GT(tp->snd_una, th->th_ack) ||
2243              SEQ_GT(th->th_ack, tp->snd_max)) ) {
2244                 rstreason = BANDLIM_RST_OPENPORT;
2245                 goto dropwithreset;
2246         }
2247 #ifdef TCPDEBUG
2248         if (so->so_options & SO_DEBUG)
2249                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2250                           &tcp_savetcp, 0);
2251 #endif
2252         m_freem(m);
2253         tp->t_flags |= TF_ACKNOW;
2254         (void) tcp_output(tp);
2255         return;
2256
2257 dropwithreset:
2258         /*
2259          * Generate a RST, dropping incoming segment.
2260          * Make ACK acceptable to originator of segment.
2261          * Don't bother to respond if destination was broadcast/multicast.
2262          */
2263         if ((thflags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
2264                 goto drop;
2265         if (isipv6) {
2266                 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
2267                     IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
2268                         goto drop;
2269         } else {
2270                 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
2271                     IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
2272                     ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
2273                     in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
2274                         goto drop;
2275         }
2276         /* IPv6 anycast check is done at tcp6_input() */
2277
2278         /*
2279          * Perform bandwidth limiting.
2280          */
2281 #ifdef ICMP_BANDLIM
2282         if (badport_bandlim(rstreason) < 0)
2283                 goto drop;
2284 #endif
2285
2286 #ifdef TCPDEBUG
2287         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2288                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2289                           &tcp_savetcp, 0);
2290 #endif
2291         if (thflags & TH_ACK)
2292                 /* mtod() below is safe as long as hdr dropping is delayed */
2293                 tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0, th->th_ack,
2294                             TH_RST);
2295         else {
2296                 if (thflags & TH_SYN)
2297                         tlen++;
2298                 /* mtod() below is safe as long as hdr dropping is delayed */
2299                 tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
2300                             (tcp_seq)0, TH_RST|TH_ACK);
2301         }
2302         return;
2303
2304 drop:
2305         /*
2306          * Drop space held by incoming segment and return.
2307          */
2308 #ifdef TCPDEBUG
2309         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2310                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2311                           &tcp_savetcp, 0);
2312 #endif
2313         m_freem(m);
2314         return;
2315 }
2316
2317 /*
2318  * Parse TCP options and place in tcpopt.
2319  */
2320 static void
2321 tcp_dooptions(to, cp, cnt, is_syn)
2322         struct tcpopt *to;
2323         u_char *cp;
2324         int cnt;
2325 {
2326         int opt, optlen;
2327
2328         to->to_flags = 0;
2329         for (; cnt > 0; cnt -= optlen, cp += optlen) {
2330                 opt = cp[0];
2331                 if (opt == TCPOPT_EOL)
2332                         break;
2333                 if (opt == TCPOPT_NOP)
2334                         optlen = 1;
2335                 else {
2336                         if (cnt < 2)
2337                                 break;
2338                         optlen = cp[1];
2339                         if (optlen < 2 || optlen > cnt)
2340                                 break;
2341                 }
2342                 switch (opt) {
2343                 case TCPOPT_MAXSEG:
2344                         if (optlen != TCPOLEN_MAXSEG)
2345                                 continue;
2346                         if (!is_syn)
2347                                 continue;
2348                         to->to_flags |= TOF_MSS;
2349                         bcopy((char *)cp + 2,
2350                             (char *)&to->to_mss, sizeof(to->to_mss));
2351                         to->to_mss = ntohs(to->to_mss);
2352                         break;
2353                 case TCPOPT_WINDOW:
2354                         if (optlen != TCPOLEN_WINDOW)
2355                                 continue;
2356                         if (! is_syn)
2357                                 continue;
2358                         to->to_flags |= TOF_SCALE;
2359                         to->to_requested_s_scale = min(cp[2], TCP_MAX_WINSHIFT);
2360                         break;
2361                 case TCPOPT_TIMESTAMP:
2362                         if (optlen != TCPOLEN_TIMESTAMP)
2363                                 continue;
2364                         to->to_flags |= TOF_TS;
2365                         bcopy((char *)cp + 2,
2366                             (char *)&to->to_tsval, sizeof(to->to_tsval));
2367                         to->to_tsval = ntohl(to->to_tsval);
2368                         bcopy((char *)cp + 6,
2369                             (char *)&to->to_tsecr, sizeof(to->to_tsecr));
2370                         to->to_tsecr = ntohl(to->to_tsecr);
2371                         break;
2372                 case TCPOPT_CC:
2373                         if (optlen != TCPOLEN_CC)
2374                                 continue;
2375                         to->to_flags |= TOF_CC;
2376                         bcopy((char *)cp + 2,
2377                             (char *)&to->to_cc, sizeof(to->to_cc));
2378                         to->to_cc = ntohl(to->to_cc);
2379                         break;
2380                 case TCPOPT_CCNEW:
2381                         if (optlen != TCPOLEN_CC)
2382                                 continue;
2383                         if (!is_syn)
2384                                 continue;
2385                         to->to_flags |= TOF_CCNEW;
2386                         bcopy((char *)cp + 2,
2387                             (char *)&to->to_cc, sizeof(to->to_cc));
2388                         to->to_cc = ntohl(to->to_cc);
2389                         break;
2390                 case TCPOPT_CCECHO:
2391                         if (optlen != TCPOLEN_CC)
2392                                 continue;
2393                         if (!is_syn)
2394                                 continue;
2395                         to->to_flags |= TOF_CCECHO;
2396                         bcopy((char *)cp + 2,
2397                             (char *)&to->to_ccecho, sizeof(to->to_ccecho));
2398                         to->to_ccecho = ntohl(to->to_ccecho);
2399                         break;
2400                 default:
2401                         continue;
2402                 }
2403         }
2404 }
2405
2406 /*
2407  * Pull out of band byte out of a segment so
2408  * it doesn't appear in the user's data queue.
2409  * It is still reflected in the segment length for
2410  * sequencing purposes.
2411  */
2412 static void
2413 tcp_pulloutofband(so, th, m, off)
2414         struct socket *so;
2415         struct tcphdr *th;
2416         struct mbuf *m;
2417         int off;                /* delayed to be droped hdrlen */
2418 {
2419         int cnt = off + th->th_urp - 1;
2420
2421         while (cnt >= 0) {
2422                 if (m->m_len > cnt) {
2423                         char *cp = mtod(m, caddr_t) + cnt;
2424                         struct tcpcb *tp = sototcpcb(so);
2425
2426                         tp->t_iobc = *cp;
2427                         tp->t_oobflags |= TCPOOB_HAVEDATA;
2428                         bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
2429                         m->m_len--;
2430                         if (m->m_flags & M_PKTHDR)
2431                                 m->m_pkthdr.len--;
2432                         return;
2433                 }
2434                 cnt -= m->m_len;
2435                 m = m->m_next;
2436                 if (m == 0)
2437                         break;
2438         }
2439         panic("tcp_pulloutofband");
2440 }
2441
2442 /*
2443  * Collect new round-trip time estimate
2444  * and update averages and current timeout.
2445  */
2446 static void
2447 tcp_xmit_timer(tp, rtt)
2448         struct tcpcb *tp;
2449         int rtt;
2450 {
2451         int delta;
2452
2453         tcpstat.tcps_rttupdated++;
2454         tp->t_rttupdated++;
2455         if (tp->t_srtt != 0) {
2456                 /*
2457                  * srtt is stored as fixed point with 5 bits after the
2458                  * binary point (i.e., scaled by 8).  The following magic
2459                  * is equivalent to the smoothing algorithm in rfc793 with
2460                  * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
2461                  * point).  Adjust rtt to origin 0.
2462                  */
2463                 delta = ((rtt - 1) << TCP_DELTA_SHIFT)
2464                         - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
2465
2466                 if ((tp->t_srtt += delta) <= 0)
2467                         tp->t_srtt = 1;
2468
2469                 /*
2470                  * We accumulate a smoothed rtt variance (actually, a
2471                  * smoothed mean difference), then set the retransmit
2472                  * timer to smoothed rtt + 4 times the smoothed variance.
2473                  * rttvar is stored as fixed point with 4 bits after the
2474                  * binary point (scaled by 16).  The following is
2475                  * equivalent to rfc793 smoothing with an alpha of .75
2476                  * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
2477                  * rfc793's wired-in beta.
2478                  */
2479                 if (delta < 0)
2480                         delta = -delta;
2481                 delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
2482                 if ((tp->t_rttvar += delta) <= 0)
2483                         tp->t_rttvar = 1;
2484                 if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
2485                         tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2486         } else {
2487                 /*
2488                  * No rtt measurement yet - use the unsmoothed rtt.
2489                  * Set the variance to half the rtt (so our first
2490                  * retransmit happens at 3*rtt).
2491                  */
2492                 tp->t_srtt = rtt << TCP_RTT_SHIFT;
2493                 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
2494                 tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2495         }
2496         tp->t_rtttime = 0;
2497         tp->t_rxtshift = 0;
2498
2499         /*
2500          * the retransmit should happen at rtt + 4 * rttvar.
2501          * Because of the way we do the smoothing, srtt and rttvar
2502          * will each average +1/2 tick of bias.  When we compute
2503          * the retransmit timer, we want 1/2 tick of rounding and
2504          * 1 extra tick because of +-1/2 tick uncertainty in the
2505          * firing of the timer.  The bias will give us exactly the
2506          * 1.5 tick we need.  But, because the bias is
2507          * statistical, we have to test that we don't drop below
2508          * the minimum feasible timer (which is 2 ticks).
2509          */
2510         TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
2511                       max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
2512
2513         /*
2514          * We received an ack for a packet that wasn't retransmitted;
2515          * it is probably safe to discard any error indications we've
2516          * received recently.  This isn't quite right, but close enough
2517          * for now (a route might have failed after we sent a segment,
2518          * and the return path might not be symmetrical).
2519          */
2520         tp->t_softerror = 0;
2521 }
2522
2523 /*
2524  * Determine a reasonable value for maxseg size.
2525  * If the route is known, check route for mtu.
2526  * If none, use an mss that can be handled on the outgoing
2527  * interface without forcing IP to fragment; if bigger than
2528  * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
2529  * to utilize large mbufs.  If no route is found, route has no mtu,
2530  * or the destination isn't local, use a default, hopefully conservative
2531  * size (usually 512 or the default IP max size, but no more than the mtu
2532  * of the interface), as we can't discover anything about intervening
2533  * gateways or networks.  We also initialize the congestion/slow start
2534  * window to be a single segment if the destination isn't local.
2535  * While looking at the routing entry, we also initialize other path-dependent
2536  * parameters from pre-set or cached values in the routing entry.
2537  *
2538  * Also take into account the space needed for options that we
2539  * send regularly.  Make maxseg shorter by that amount to assure
2540  * that we can send maxseg amount of data even when the options
2541  * are present.  Store the upper limit of the length of options plus
2542  * data in maxopd.
2543  *
2544  * NOTE that this routine is only called when we process an incoming
2545  * segment, for outgoing segments only tcp_mssopt is called.
2546  *
2547  * In case of T/TCP, we call this routine during implicit connection
2548  * setup as well (offer = -1), to initialize maxseg from the cached
2549  * MSS of our peer.
2550  */
2551 void
2552 tcp_mss(tp, offer)
2553         struct tcpcb *tp;
2554         int offer;
2555 {
2556         struct rtentry *rt;
2557         struct ifnet *ifp;
2558         int rtt, mss;
2559         u_long bufsize;
2560         struct inpcb *inp = tp->t_inpcb;
2561         struct socket *so;
2562         struct rmxp_tao *taop;
2563         int origoffer = offer;
2564 #ifdef INET6
2565         int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
2566         size_t min_protoh = isipv6 ?
2567                             sizeof(struct ip6_hdr) + sizeof(struct tcphdr) :
2568                             sizeof(struct tcpiphdr);
2569 #else
2570         const int isipv6 = 0;
2571         const size_t min_protoh = sizeof(struct tcpiphdr);
2572 #endif
2573
2574         if (isipv6)
2575                 rt = tcp_rtlookup6(&inp->inp_inc);
2576         else
2577                 rt = tcp_rtlookup(&inp->inp_inc);
2578         if (rt == NULL) {
2579                 tp->t_maxopd = tp->t_maxseg =
2580                                 isipv6 ? tcp_v6mssdflt : tcp_mssdflt;
2581                 return;
2582         }
2583         ifp = rt->rt_ifp;
2584         so = inp->inp_socket;
2585
2586         taop = rmx_taop(rt->rt_rmx);
2587         /*
2588          * Offer == -1 means that we didn't receive SYN yet,
2589          * use cached value in that case;
2590          */
2591         if (offer == -1)
2592                 offer = taop->tao_mssopt;
2593         /*
2594          * Offer == 0 means that there was no MSS on the SYN segment,
2595          * in this case we use tcp_mssdflt.
2596          */
2597         if (offer == 0)
2598                 offer = isipv6 ? tcp_v6mssdflt : tcp_mssdflt;
2599         else
2600                 /*
2601                  * Sanity check: make sure that maxopd will be large
2602                  * enough to allow some data on segments even is the
2603                  * all the option space is used (40bytes).  Otherwise
2604                  * funny things may happen in tcp_output.
2605                  */
2606                 offer = max(offer, 64);
2607         taop->tao_mssopt = offer;
2608
2609         /*
2610          * While we're here, check if there's an initial rtt
2611          * or rttvar.  Convert from the route-table units
2612          * to scaled multiples of the slow timeout timer.
2613          */
2614         if (tp->t_srtt == 0 && (rtt = rt->rt_rmx.rmx_rtt)) {
2615                 /*
2616                  * XXX the lock bit for RTT indicates that the value
2617                  * is also a minimum value; this is subject to time.
2618                  */
2619                 if (rt->rt_rmx.rmx_locks & RTV_RTT)
2620                         tp->t_rttmin = rtt / (RTM_RTTUNIT / hz);
2621                 tp->t_srtt = rtt / (RTM_RTTUNIT / (hz * TCP_RTT_SCALE));
2622                 tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
2623                 tcpstat.tcps_usedrtt++;
2624                 if (rt->rt_rmx.rmx_rttvar) {
2625                         tp->t_rttvar = rt->rt_rmx.rmx_rttvar /
2626                             (RTM_RTTUNIT / (hz * TCP_RTTVAR_SCALE));
2627                         tcpstat.tcps_usedrttvar++;
2628                 } else {
2629                         /* default variation is +- 1 rtt */
2630                         tp->t_rttvar =
2631                             tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
2632                 }
2633                 TCPT_RANGESET(tp->t_rxtcur,
2634                               ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
2635                               tp->t_rttmin, TCPTV_REXMTMAX);
2636         }
2637         /*
2638          * if there's an mtu associated with the route, use it
2639          * else, use the link mtu.
2640          */
2641         if (rt->rt_rmx.rmx_mtu)
2642                 mss = rt->rt_rmx.rmx_mtu - min_protoh;
2643         else {
2644                 if (isipv6) {
2645                         mss = nd_ifinfo[rt->rt_ifp->if_index].linkmtu -
2646                                 min_protoh;
2647                         if (!in6_localaddr(&inp->in6p_faddr))
2648                                 mss = min(mss, tcp_v6mssdflt);
2649                 } else {
2650                         mss = ifp->if_mtu - min_protoh;
2651                         if (!in_localaddr(inp->inp_faddr))
2652                                 mss = min(mss, tcp_mssdflt);
2653                 }
2654         }
2655         mss = min(mss, offer);
2656         /*
2657          * maxopd stores the maximum length of data AND options
2658          * in a segment; maxseg is the amount of data in a normal
2659          * segment.  We need to store this value (maxopd) apart
2660          * from maxseg, because now every segment carries options
2661          * and thus we normally have somewhat less data in segments.
2662          */
2663         tp->t_maxopd = mss;
2664
2665         /*
2666          * In case of T/TCP, origoffer==-1 indicates, that no segments
2667          * were received yet.  In this case we just guess, otherwise
2668          * we do the same as before T/TCP.
2669          */
2670         if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
2671             (origoffer == -1 ||
2672              (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
2673                 mss -= TCPOLEN_TSTAMP_APPA;
2674         if ((tp->t_flags & (TF_REQ_CC|TF_NOOPT)) == TF_REQ_CC &&
2675             (origoffer == -1 ||
2676              (tp->t_flags & TF_RCVD_CC) == TF_RCVD_CC))
2677                 mss -= TCPOLEN_CC_APPA;
2678
2679 #if     (MCLBYTES & (MCLBYTES - 1)) == 0
2680                 if (mss > MCLBYTES)
2681                         mss &= ~(MCLBYTES-1);
2682 #else
2683                 if (mss > MCLBYTES)
2684                         mss = mss / MCLBYTES * MCLBYTES;
2685 #endif
2686         /*
2687          * If there's a pipesize, change the socket buffer
2688          * to that size.  Make the socket buffers an integral
2689          * number of mss units; if the mss is larger than
2690          * the socket buffer, decrease the mss.
2691          */
2692 #ifdef RTV_SPIPE
2693         if ((bufsize = rt->rt_rmx.rmx_sendpipe) == 0)
2694 #endif
2695                 bufsize = so->so_snd.sb_hiwat;
2696         if (bufsize < mss)
2697                 mss = bufsize;
2698         else {
2699                 bufsize = roundup(bufsize, mss);
2700                 if (bufsize > sb_max)
2701                         bufsize = sb_max;
2702                 if (bufsize > so->so_snd.sb_hiwat)
2703                         (void)sbreserve(&so->so_snd, bufsize, so, NULL);
2704         }
2705         tp->t_maxseg = mss;
2706
2707 #ifdef RTV_RPIPE
2708         if ((bufsize = rt->rt_rmx.rmx_recvpipe) == 0)
2709 #endif
2710                 bufsize = so->so_rcv.sb_hiwat;
2711         if (bufsize > mss) {
2712                 bufsize = roundup(bufsize, mss);
2713                 if (bufsize > sb_max)
2714                         bufsize = sb_max;
2715                 if (bufsize > so->so_rcv.sb_hiwat)
2716                         (void)sbreserve(&so->so_rcv, bufsize, so, NULL);
2717         }
2718
2719         /*
2720          * Set the slow-start flight size depending on whether this
2721          * is a local network or not.
2722          */
2723         if (tcp_do_rfc3390)
2724                 tp->snd_cwnd = min(4 * mss, max(2 * mss, 4380));
2725         else if ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
2726                  (!isipv6 && in_localaddr(inp->inp_faddr)))
2727                 tp->snd_cwnd = mss * ss_fltsz_local;
2728         else
2729                 tp->snd_cwnd = mss * ss_fltsz;
2730
2731         if (rt->rt_rmx.rmx_ssthresh) {
2732                 /*
2733                  * There's some sort of gateway or interface
2734                  * buffer limit on the path.  Use this to set
2735                  * the slow start threshhold, but set the
2736                  * threshold to no less than 2*mss.
2737                  */
2738                 tp->snd_ssthresh = max(2 * mss, rt->rt_rmx.rmx_ssthresh);
2739                 tcpstat.tcps_usedssthresh++;
2740         }
2741 }
2742
2743 /*
2744  * Determine the MSS option to send on an outgoing SYN.
2745  */
2746 int
2747 tcp_mssopt(tp)
2748         struct tcpcb *tp;
2749 {
2750         struct rtentry *rt;
2751 #ifdef INET6
2752         int isipv6 = ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
2753         int min_protoh = isipv6 ?
2754                              sizeof(struct ip6_hdr) + sizeof(struct tcphdr) :
2755                              sizeof(struct tcpiphdr);
2756 #else
2757         const int isipv6 = 0;
2758         const size_t min_protoh = sizeof(struct tcpiphdr);
2759 #endif
2760
2761         if (isipv6)
2762                 rt = tcp_rtlookup6(&tp->t_inpcb->inp_inc);
2763         else
2764                 rt = tcp_rtlookup(&tp->t_inpcb->inp_inc);
2765         if (rt == NULL)
2766                 return (isipv6 ? tcp_v6mssdflt : tcp_mssdflt);
2767
2768         return (rt->rt_ifp->if_mtu - min_protoh);
2769 }
2770
2771
2772 /*
2773  * When a partial ack arrives, force the retransmission of the
2774  * next unacknowledged segment.  Do not clear tp->t_dupacks.
2775  * By setting snd_nxt to ti_ack, this forces retransmission timer to
2776  * be started again.
2777  */
2778 static void
2779 tcp_newreno_partial_ack(tp, th)
2780         struct tcpcb *tp;
2781         struct tcphdr *th;
2782 {
2783         tcp_seq onxt = tp->snd_nxt;
2784         u_long  ocwnd = tp->snd_cwnd;
2785
2786         callout_stop(tp->tt_rexmt);
2787         tp->t_rtttime = 0;
2788         tp->snd_nxt = th->th_ack;
2789         /*
2790          * Set snd_cwnd to one segment beyond acknowledged offset
2791          * (tp->snd_una has not yet been updated when this function is called.)
2792          */
2793         tp->snd_cwnd = tp->t_maxseg + (th->th_ack - tp->snd_una);
2794         tp->t_flags |= TF_ACKNOW;
2795         (void) tcp_output(tp);
2796         tp->snd_cwnd = ocwnd;
2797         if (SEQ_GT(onxt, tp->snd_nxt))
2798                 tp->snd_nxt = onxt;
2799         /*
2800          * Partial window deflation.  Relies on fact that tp->snd_una
2801          * not updated yet.
2802          */
2803         tp->snd_cwnd -= (th->th_ack - tp->snd_una - tp->t_maxseg);
2804 }