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 1.9 2003/08/14 23:09:33 hsu Exp $
  37  */
  38
  39 #include "opt_ipfw.h"           /* for ipfw_fwd         */
  40 #include "opt_inet6.h"
  41 #include "opt_ipsec.h"
  42 #include "opt_tcpdebug.h"
  43 #include "opt_tcp_input.h"
  44
  45 #include <sys/param.h>
  46 #include <sys/systm.h>
  47 #include <sys/kernel.h>
  48 #include <sys/sysctl.h>
  49 #include <sys/malloc.h>
  50 #include <sys/mbuf.h>
  51 #include <sys/proc.h>           /* for proc0 declaration */
  52 #include <sys/protosw.h>
  53 #include <sys/socket.h>
  54 #include <sys/socketvar.h>
  55 #include <sys/syslog.h>
  56
  57 #include <machine/cpu.h>        /* before tcp_seq.h, for tcp_random18() */
  58
  59 #include <net/if.h>
  60 #include <net/route.h>
  61
  62 #include <netinet/in.h>
  63 #include <netinet/in_systm.h>
  64 #include <netinet/ip.h>
  65 #include <netinet/ip_icmp.h>    /* for ICMP_BANDLIM             */
  66 #include <netinet/in_var.h>
  67 #include <netinet/icmp_var.h>   /* for ICMP_BANDLIM             */
  68 #include <netinet/in_pcb.h>
  69 #include <netinet/ip_var.h>
  70 #include <netinet/ip6.h>
  71 #include <netinet/icmp6.h>
  72 #include <netinet6/nd6.h>
  73 #include <netinet6/ip6_var.h>
  74 #include <netinet6/in6_pcb.h>
  75 #include <netinet/tcp.h>
  76 #include <netinet/tcp_fsm.h>
  77 #include <netinet/tcp_seq.h>
  78 #include <netinet/tcp_timer.h>
  79 #include <netinet/tcp_var.h>
  80 #include <netinet6/tcp6_var.h>
  81 #include <netinet/tcpip.h>
  82 #ifdef TCPDEBUG
  83 #include <netinet/tcp_debug.h>
  84
  85 u_char tcp_saveipgen[40]; /* the size must be of max ip header, now IPv6 */
  86 struct tcphdr tcp_savetcp;
  87 #endif /* TCPDEBUG */
  88
  89 #ifdef FAST_IPSEC
  90 #include <netipsec/ipsec.h>
  91 #include <netipsec/ipsec6.h>
  92 #endif
  93
  94 #ifdef IPSEC
  95 #include <netinet6/ipsec.h>
  96 #include <netinet6/ipsec6.h>
  97 #include <netproto/key/key.h>
  98 #endif /*IPSEC*/
  99
 100 #include <machine/in_cksum.h>
 101
 102 MALLOC_DEFINE(M_TSEGQ, "tseg_qent", "TCP segment queue entry");
 103
 104 static const int tcprexmtthresh = 3;
 105 tcp_cc  tcp_ccgen;
 106
 107 struct  tcpstat tcpstat;
 108 SYSCTL_STRUCT(_net_inet_tcp, TCPCTL_STATS, stats, CTLFLAG_RW,
 109     &tcpstat , tcpstat, "TCP statistics (struct tcpstat, netinet/tcp_var.h)");
 110
 111 static int log_in_vain = 0;
 112 SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW,
 113     &log_in_vain, 0, "Log all incoming TCP connections");
 114
 115 static int blackhole = 0;
 116 SYSCTL_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_RW,
 117     &blackhole, 0, "Do not send RST when dropping refused connections");
 118
 119 int tcp_delack_enabled = 1;
 120 SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_RW,
 121     &tcp_delack_enabled, 0,
 122     "Delay ACK to try and piggyback it onto a data packet");
 123
 124 #ifdef TCP_DROP_SYNFIN
 125 static int drop_synfin = 0;
 126 SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_RW,
 127     &drop_synfin, 0, "Drop TCP packets with SYN+FIN set");
 128 #endif
 129
 130 static int tcp_do_limitedtransmit = 1;
 131 SYSCTL_INT(_net_inet_tcp, OID_AUTO, limitedtransmit, CTLFLAG_RW,
 132     &tcp_do_limitedtransmit, 0, "Enable RFC 3042 (Limited Transmit)");
 133
 134 static int tcp_do_rfc3390 = 1;
 135 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3390, CTLFLAG_RW,
 136     &tcp_do_rfc3390, 0,
 137     "Enable RFC 3390 (Increasing TCP's Initial Congestion Window)");
 138
 139 static int tcp_do_eifel_detect = 1;
 140 SYSCTL_INT(_net_inet_tcp, OID_AUTO, eifel, CTLFLAG_RW,
 141     &tcp_do_eifel_detect, 0, "Eifel detection algorithm (RFC 3522)");
 142
 143 struct inpcbhead tcb;
 144 #define tcb6    tcb  /* for KAME src sync over BSD*'s */
 145 struct inpcbinfo tcbinfo;
 146
 147 static void      tcp_dooptions(struct tcpopt *, u_char *, int, int);
 148 static void      tcp_pulloutofband(struct socket *,
 149                      struct tcphdr *, struct mbuf *, int);
 150 static int       tcp_reass(struct tcpcb *, struct tcphdr *, int *,
 151                      struct mbuf *);
 152 static void      tcp_xmit_timer(struct tcpcb *, int);
 153 static void      tcp_newreno_partial_ack(struct tcpcb *, struct tcphdr *);
 154
 155 /* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */
 156 #ifdef INET6
 157 #define ND6_HINT(tp) \
 158 do { \
 159         if ((tp) && (tp)->t_inpcb && \
 160             ((tp)->t_inpcb->inp_vflag & INP_IPV6) != 0 && \
 161             (tp)->t_inpcb->in6p_route.ro_rt) \
 162                 nd6_nud_hint((tp)->t_inpcb->in6p_route.ro_rt, NULL, 0); \
 163 } while (0)
 164 #else
 165 #define ND6_HINT(tp)
 166 #endif
 167
 168 /*
 169  * Indicate whether this ack should be delayed.  We can delay the ack if
 170  *      - delayed acks are enabled and
 171  *      - there is no delayed ack timer in progress and
 172  *      - our last ack wasn't a 0-sized window.  We never want to delay
 173  *        the ack that opens up a 0-sized window.
 174  */
 175 #define DELAY_ACK(tp) \
 176         (tcp_delack_enabled && !callout_pending(tp->tt_delack) && \
 177         (tp->t_flags & TF_RXWIN0SENT) == 0)
 178
 179 static int
 180 tcp_reass(tp, th, tlenp, m)
 181         struct tcpcb *tp;
 182         struct tcphdr *th;
 183         int *tlenp;
 184         struct mbuf *m;
 185 {
 186         struct tseg_qent *q;
 187         struct tseg_qent *p = NULL;
 188         struct tseg_qent *nq;
 189         struct tseg_qent *te;
 190         struct socket *so = tp->t_inpcb->inp_socket;
 191         int flags;
 192
 193         /*
 194          * Call with th==0 after become established to
 195          * force pre-ESTABLISHED data up to user socket.
 196          */
 197         if (th == 0)
 198                 goto present;
 199
 200         /* Allocate a new queue entry. If we can't, just drop the pkt. XXX */
 201         MALLOC(te, struct tseg_qent *, sizeof(struct tseg_qent), M_TSEGQ,
 202                M_NOWAIT);
 203         if (te == NULL) {
 204                 tcpstat.tcps_rcvmemdrop++;
 205                 m_freem(m);
 206                 return (0);
 207         }
 208
 209         /*
 210          * Find a segment which begins after this one does.
 211          */
 212         LIST_FOREACH(q, &tp->t_segq, tqe_q) {
 213                 if (SEQ_GT(q->tqe_th->th_seq, th->th_seq))
 214                         break;
 215                 p = q;
 216         }
 217
 218         /*
 219          * If there is a preceding segment, it may provide some of
 220          * our data already.  If so, drop the data from the incoming
 221          * segment.  If it provides all of our data, drop us.
 222          */
 223         if (p != NULL) {
 224                 int i;
 225                 /* conversion to int (in i) handles seq wraparound */
 226                 i = p->tqe_th->th_seq + p->tqe_len - th->th_seq;
 227                 if (i > 0) {
 228                         if (i >= *tlenp) {
 229                                 tcpstat.tcps_rcvduppack++;
 230                                 tcpstat.tcps_rcvdupbyte += *tlenp;
 231                                 m_freem(m);
 232                                 free(te, M_TSEGQ);
 233                                 /*
 234                                  * Try to present any queued data
 235                                  * at the left window edge to the user.
 236                                  * This is needed after the 3-WHS
 237                                  * completes.
 238                                  */
 239                                 goto present;   /* ??? */
 240                         }
 241                         m_adj(m, i);
 242                         *tlenp -= i;
 243                         th->th_seq += i;
 244                 }
 245         }
 246         tcpstat.tcps_rcvoopack++;
 247         tcpstat.tcps_rcvoobyte += *tlenp;
 248
 249         /*
 250          * While we overlap succeeding segments trim them or,
 251          * if they are completely covered, dequeue them.
 252          */
 253         while (q) {
 254                 int i = (th->th_seq + *tlenp) - q->tqe_th->th_seq;
 255                 if (i <= 0)
 256                         break;
 257                 if (i < q->tqe_len) {
 258                         q->tqe_th->th_seq += i;
 259                         q->tqe_len -= i;
 260                         m_adj(q->tqe_m, i);
 261                         break;
 262                 }
 263
 264                 nq = LIST_NEXT(q, tqe_q);
 265                 LIST_REMOVE(q, tqe_q);
 266                 m_freem(q->tqe_m);
 267                 free(q, M_TSEGQ);
 268                 q = nq;
 269         }
 270
 271         /* Insert the new segment queue entry into place. */
 272         te->tqe_m = m;
 273         te->tqe_th = th;
 274         te->tqe_len = *tlenp;
 275
 276         if (p == NULL) {
 277                 LIST_INSERT_HEAD(&tp->t_segq, te, tqe_q);
 278         } else {
 279                 LIST_INSERT_AFTER(p, te, tqe_q);
 280         }
 281
 282 present:
 283         /*
 284          * Present data to user, advancing rcv_nxt through
 285          * completed sequence space.
 286          */
 287         if (!TCPS_HAVEESTABLISHED(tp->t_state))
 288                 return (0);
 289         q = LIST_FIRST(&tp->t_segq);
 290         if (!q || q->tqe_th->th_seq != tp->rcv_nxt)
 291                 return (0);
 292         do {
 293                 tp->rcv_nxt += q->tqe_len;
 294                 flags = q->tqe_th->th_flags & TH_FIN;
 295                 nq = LIST_NEXT(q, tqe_q);
 296                 LIST_REMOVE(q, tqe_q);
 297                 if (so->so_state & SS_CANTRCVMORE)
 298                         m_freem(q->tqe_m);
 299                 else
 300                         sbappend(&so->so_rcv, q->tqe_m);
 301                 free(q, M_TSEGQ);
 302                 q = nq;
 303         } while (q && q->tqe_th->th_seq == tp->rcv_nxt);
 304         ND6_HINT(tp);
 305         sorwakeup(so);
 306         return (flags);
 307 }
 308
 309 /*
 310  * TCP input routine, follows pages 65-76 of the
 311  * protocol specification dated September, 1981 very closely.
 312  */
 313 #ifdef INET6
 314 int
 315 tcp6_input(mp, offp, proto)
 316         struct mbuf **mp;
 317         int *offp, proto;
 318 {
 319         struct mbuf *m = *mp;
 320         struct in6_ifaddr *ia6;
 321
 322         IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
 323
 324         /*
 325          * draft-itojun-ipv6-tcp-to-anycast
 326          * better place to put this in?
 327          */
 328         ia6 = ip6_getdstifaddr(m);
 329         if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
 330                 struct ip6_hdr *ip6;
 331
 332                 ip6 = mtod(m, struct ip6_hdr *);
 333                 icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
 334                             (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
 335                 return IPPROTO_DONE;
 336         }
 337
 338         tcp_input(m, *offp, proto);
 339         return IPPROTO_DONE;
 340 }
 341 #endif
 342
 343 void
 344 tcp_input(m, off0, proto)
 345         struct mbuf *m;
 346         int off0, proto;
 347 {
 348         struct tcphdr *th;
 349         struct ip *ip = NULL;
 350         struct ipovly *ipov;
 351         struct inpcb *inp = NULL;
 352         u_char *optp = NULL;
 353         int optlen = 0;
 354         int len, tlen, off;
 355         int drop_hdrlen;
 356         struct tcpcb *tp = NULL;
 357         int thflags;
 358         struct socket *so = 0;
 359         int todrop, acked, ourfinisacked, needoutput = 0;
 360         u_long tiwin;
 361         struct tcpopt to;               /* options in this segment */
 362         struct rmxp_tao *taop;          /* pointer to our TAO cache entry */
 363         struct rmxp_tao tao_noncached;  /* in case there's no cached entry */
 364         struct sockaddr_in *next_hop = NULL;
 365         int rstreason; /* For badport_bandlim accounting purposes */
 366         int useTS;                      /* use timestamps in Eifel detection */
 367         struct ip6_hdr *ip6 = NULL;
 368 #ifdef INET6
 369         int isipv6;
 370 #else
 371         const int isipv6 = 0;
 372 #endif
 373 #ifdef TCPDEBUG
 374         short ostate = 0;
 375 #endif
 376
 377         /* Grab info from MT_TAG mbufs prepended to the chain. */
 378         for (;m && m->m_type == MT_TAG; m = m->m_next) {
 379                 if (m->_m_tag_id == PACKET_TAG_IPFORWARD)
 380                         next_hop = (struct sockaddr_in *)m->m_hdr.mh_data;
 381         }
 382 #ifdef INET6
 383         isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
 384 #endif
 385         bzero((char *)&to, sizeof(to));
 386
 387         tcpstat.tcps_rcvtotal++;
 388
 389         if (isipv6) {
 390                 /* IP6_EXTHDR_CHECK() is already done at tcp6_input() */
 391                 ip6 = mtod(m, struct ip6_hdr *);
 392                 tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
 393                 if (in6_cksum(m, IPPROTO_TCP, off0, tlen)) {
 394                         tcpstat.tcps_rcvbadsum++;
 395                         goto drop;
 396                 }
 397                 th = (struct tcphdr *)((caddr_t)ip6 + off0);
 398
 399                 /*
 400                  * Be proactive about unspecified IPv6 address in source.
 401                  * As we use all-zero to indicate unbounded/unconnected pcb,
 402                  * unspecified IPv6 address can be used to confuse us.
 403                  *
 404                  * Note that packets with unspecified IPv6 destination is
 405                  * already dropped in ip6_input.
 406                  */
 407                 if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
 408                         /* XXX stat */
 409                         goto drop;
 410                 }
 411         } else {
 412                 /*
 413                  * Get IP and TCP header together in first mbuf.
 414                  * Note: IP leaves IP header in first mbuf.
 415                  */
 416                 if (off0 > sizeof(struct ip)) {
 417                         ip_stripoptions(m, (struct mbuf *)0);
 418                         off0 = sizeof(struct ip);
 419                 }
 420                 if (m->m_len < sizeof(struct tcpiphdr)) {
 421                         if ((m = m_pullup(m, sizeof(struct tcpiphdr))) == 0) {
 422                                 tcpstat.tcps_rcvshort++;
 423                                 return;
 424                         }
 425                 }
 426                 ip = mtod(m, struct ip *);
 427                 ipov = (struct ipovly *)ip;
 428                 th = (struct tcphdr *)((caddr_t)ip + off0);
 429                 tlen = ip->ip_len;
 430
 431                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
 432                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
 433                                 th->th_sum = m->m_pkthdr.csum_data;
 434                         else
 435                                 th->th_sum = in_pseudo(ip->ip_src.s_addr,
 436                                                 ip->ip_dst.s_addr,
 437                                                 htonl(m->m_pkthdr.csum_data +
 438                                                         ip->ip_len +
 439                                                         IPPROTO_TCP));
 440                         th->th_sum ^= 0xffff;
 441                 } else {
 442                         /*
 443                          * Checksum extended TCP header and data.
 444                          */
 445                         len = sizeof(struct ip) + tlen;
 446                         bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
 447                         ipov->ih_len = (u_short)tlen;
 448                         ipov->ih_len = htons(ipov->ih_len);
 449                         th->th_sum = in_cksum(m, len);
 450                 }
 451                 if (th->th_sum) {
 452                         tcpstat.tcps_rcvbadsum++;
 453                         goto drop;
 454                 }
 455 #ifdef INET6
 456                 /* Re-initialization for later version check */
 457                 ip->ip_v = IPVERSION;
 458 #endif
 459         }
 460
 461         /*
 462          * Check that TCP offset makes sense,
 463          * pull out TCP options and adjust length.              XXX
 464          */
 465         off = th->th_off << 2;
 466         if (off < sizeof(struct tcphdr) || off > tlen) {
 467                 tcpstat.tcps_rcvbadoff++;
 468                 goto drop;
 469         }
 470         tlen -= off;    /* tlen is used instead of ti->ti_len */
 471         if (off > sizeof(struct tcphdr)) {
 472                 if (isipv6) {
 473                         IP6_EXTHDR_CHECK(m, off0, off, );
 474                         ip6 = mtod(m, struct ip6_hdr *);
 475                         th = (struct tcphdr *)((caddr_t)ip6 + off0);
 476                 } else {
 477                         if (m->m_len < sizeof(struct ip) + off) {
 478                                 if ((m = m_pullup(m, sizeof(struct ip) + off))
 479                                                 == 0) {
 480                                         tcpstat.tcps_rcvshort++;
 481                                         return;
 482                                 }
 483                                 ip = mtod(m, struct ip *);
 484                                 ipov = (struct ipovly *)ip;
 485                                 th = (struct tcphdr *)((caddr_t)ip + off0);
 486                         }
 487                 }
 488                 optlen = off - sizeof(struct tcphdr);
 489                 optp = (u_char *)(th + 1);
 490         }
 491         thflags = th->th_flags;
 492
 493 #ifdef TCP_DROP_SYNFIN
 494         /*
 495          * If the drop_synfin option is enabled, drop all packets with
 496          * both the SYN and FIN bits set. This prevents e.g. nmap from
 497          * identifying the TCP/IP stack.
 498          *
 499          * This is a violation of the TCP specification.
 500          */
 501         if (drop_synfin && (thflags & (TH_SYN|TH_FIN)) == (TH_SYN|TH_FIN))
 502                 goto drop;
 503 #endif
 504
 505         /*
 506          * Convert TCP protocol specific fields to host format.
 507          */
 508         th->th_seq = ntohl(th->th_seq);
 509         th->th_ack = ntohl(th->th_ack);
 510         th->th_win = ntohs(th->th_win);
 511         th->th_urp = ntohs(th->th_urp);
 512
 513         /*
 514          * Delay droping TCP, IP headers, IPv6 ext headers, and TCP options,
 515          * until after ip6_savecontrol() is called and before other functions
 516          * which don't want those proto headers.
 517          * Because ip6_savecontrol() is going to parse the mbuf to
 518          * search for data to be passed up to user-land, it wants mbuf
 519          * parameters to be unchanged.
 520          * XXX: the call of ip6_savecontrol() has been obsoleted based on
 521          * latest version of the advanced API (20020110).
 522          */
 523         drop_hdrlen = off0 + off;
 524
 525         /*
 526          * Locate pcb for segment.
 527          */
 528 findpcb:
 529         /* IPFIREWALL_FORWARD section */
 530         if (next_hop != NULL && isipv6 == 0) {  /* IPv6 support is not yet */
 531                 /*
 532                  * Transparently forwarded. Pretend to be the destination.
 533                  * already got one like this?
 534                  */
 535                 inp = in_pcblookup_hash(&tcbinfo, ip->ip_src, th->th_sport,
 536                                         ip->ip_dst, th->th_dport,
 537                                         0, m->m_pkthdr.rcvif);
 538                 if (!inp) {
 539                         /* It's new.  Try find the ambushing socket. */
 540                         inp = in_pcblookup_hash(&tcbinfo,
 541                                                 ip->ip_src, th->th_sport,
 542                                                 next_hop->sin_addr,
 543                                                 next_hop->sin_port ?
 544                                                     ntohs(next_hop->sin_port) :
 545                                                     th->th_dport,
 546                                                 1, m->m_pkthdr.rcvif);
 547                 }
 548         } else {
 549                 if (isipv6)
 550                         inp = in6_pcblookup_hash(&tcbinfo,
 551                                                  &ip6->ip6_src, th->th_sport,
 552                                                  &ip6->ip6_dst, th->th_dport,
 553                                                  1, m->m_pkthdr.rcvif);
 554                 else
 555                         inp = in_pcblookup_hash(&tcbinfo,
 556                                                 ip->ip_src, th->th_sport,
 557                                                 ip->ip_dst, th->th_dport,
 558                                                 1, m->m_pkthdr.rcvif);
 559       }
 560
 561 #ifdef IPSEC
 562         if (isipv6) {
 563                 if (inp != NULL && ipsec6_in_reject_so(m, inp->inp_socket)) {
 564                         ipsec6stat.in_polvio++;
 565                         goto drop;
 566                 }
 567         } else {
 568                 if (inp != NULL && ipsec4_in_reject_so(m, inp->inp_socket)) {
 569                         ipsecstat.in_polvio++;
 570                         goto drop;
 571                 }
 572         }
 573 #endif
 574 #ifdef FAST_IPSEC
 575         if (isipv6) {
 576                 if (inp != NULL && ipsec6_in_reject(m, inp)) {
 577                         goto drop;
 578                 }
 579         } else {
 580                 if (inp != NULL && ipsec4_in_reject(m, inp)) {
 581                         goto drop;
 582                 }
 583         }
 584 #endif
 585
 586         /*
 587          * If the state is CLOSED (i.e., TCB does not exist) then
 588          * all data in the incoming segment is discarded.
 589          * If the TCB exists but is in CLOSED state, it is embryonic,
 590          * but should either do a listen or a connect soon.
 591          */
 592         if (inp == NULL) {
 593                 if (log_in_vain) {
 594 #ifdef INET6
 595                         char dbuf[INET6_ADDRSTRLEN+2], sbuf[INET6_ADDRSTRLEN+2];
 596 #else
 597                         char dbuf[4*sizeof "123"], sbuf[4*sizeof "123"];
 598 #endif
 599                         if (isipv6) {
 600                                 strcpy(dbuf, "[");
 601                                 strcpy(sbuf, "[");
 602                                 strcat(dbuf, ip6_sprintf(&ip6->ip6_dst));
 603                                 strcat(sbuf, ip6_sprintf(&ip6->ip6_src));
 604                                 strcat(dbuf, "]");
 605                                 strcat(sbuf, "]");
 606                         } else {
 607                                 strcpy(dbuf, inet_ntoa(ip->ip_dst));
 608                                 strcpy(sbuf, inet_ntoa(ip->ip_src));
 609                         }
 610                         switch (log_in_vain) {
 611                         case 1:
 612                                 if ((thflags & TH_SYN) == 0)
 613                                         break;
 614                         case 2:
 615                                 log(LOG_INFO,
 616                                     "Connection attempt to TCP %s:%d "
 617                                     "from %s:%d flags:0x%02x\n",
 618                                     dbuf, ntohs(th->th_dport), sbuf,
 619                                     ntohs(th->th_sport), thflags);
 620                                 break;
 621                         default:
 622                                 break;
 623                         }
 624                 }
 625                 if (blackhole) {
 626                         switch (blackhole) {
 627                         case 1:
 628                                 if (thflags & TH_SYN)
 629                                         goto drop;
 630                                 break;
 631                         case 2:
 632                                 goto drop;
 633                         default:
 634                                 goto drop;
 635                         }
 636                 }
 637                 rstreason = BANDLIM_RST_CLOSEDPORT;
 638                 goto dropwithreset;
 639         }
 640         tp = intotcpcb(inp);
 641         if (tp == NULL) {
 642                 rstreason = BANDLIM_RST_CLOSEDPORT;
 643                 goto dropwithreset;
 644         }
 645         if (tp->t_state == TCPS_CLOSED)
 646                 goto drop;
 647
 648         /* Unscale the window into a 32-bit value. */
 649         if ((thflags & TH_SYN) == 0)
 650                 tiwin = th->th_win << tp->snd_scale;
 651         else
 652                 tiwin = th->th_win;
 653
 654         so = inp->inp_socket;
 655         if (so->so_options & (SO_DEBUG|SO_ACCEPTCONN)) {
 656                 struct in_conninfo inc;
 657 #ifdef TCPDEBUG
 658                 if (so->so_options & SO_DEBUG) {
 659                         ostate = tp->t_state;
 660                         if (isipv6)
 661                                 bcopy((char *)ip6, (char *)tcp_saveipgen,
 662                                     sizeof(*ip6));
 663                         else
 664                                 bcopy((char *)ip, (char *)tcp_saveipgen,
 665                                     sizeof(*ip));
 666                         tcp_savetcp = *th;
 667                 }
 668 #endif
 669                 /* skip if this isn't a listen socket */
 670                 if ((so->so_options & SO_ACCEPTCONN) == 0)
 671                         goto after_listen;
 672 #ifdef INET6
 673                 inc.inc_isipv6 = isipv6;
 674 #endif
 675                 if (isipv6) {
 676                         inc.inc6_faddr = ip6->ip6_src;
 677                         inc.inc6_laddr = ip6->ip6_dst;
 678                         inc.inc6_route.ro_rt = NULL;            /* XXX */
 679                 } else {
 680                         inc.inc_faddr = ip->ip_src;
 681                         inc.inc_laddr = ip->ip_dst;
 682                         inc.inc_route.ro_rt = NULL;             /* XXX */
 683                 }
 684                 inc.inc_fport = th->th_sport;
 685                 inc.inc_lport = th->th_dport;
 686
 687                 /*
 688                  * If the state is LISTEN then ignore segment if it contains
 689                  * a RST.  If the segment contains an ACK then it is bad and
 690                  * send a RST.  If it does not contain a SYN then it is not
 691                  * interesting; drop it.
 692                  *
 693                  * If the state is SYN_RECEIVED (syncache) and seg contains
 694                  * an ACK, but not for our SYN/ACK, send a RST.  If the seg
 695                  * contains a RST, check the sequence number to see if it
 696                  * is a valid reset segment.
 697                  */
 698                 if ((thflags & (TH_RST|TH_ACK|TH_SYN)) != TH_SYN) {
 699                         if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
 700                                 if (!syncache_expand(&inc, th, &so, m)) {
 701                                         /*
 702                                          * No syncache entry, or ACK was not
 703                                          * for our SYN/ACK.  Send a RST.
 704                                          */
 705                                         tcpstat.tcps_badsyn++;
 706                                         rstreason = BANDLIM_RST_OPENPORT;
 707                                         goto dropwithreset;
 708                                 }
 709                                 if (so == NULL)
 710                                         /*
 711                                          * Could not complete 3-way handshake,
 712                                          * connection is being closed down, and
 713                                          * syncache will free mbuf.
 714                                          */
 715                                         return;
 716                                 /*
 717                                  * Socket is created in state SYN_RECEIVED.
 718                                  * Continue processing segment.
 719                                  */
 720                                 inp = sotoinpcb(so);
 721                                 tp = intotcpcb(inp);
 722                                 /*
 723                                  * This is what would have happened in
 724                                  * tcp_output() when the SYN,ACK was sent.
 725                                  */
 726                                 tp->snd_up = tp->snd_una;
 727                                 tp->snd_max = tp->snd_nxt = tp->iss + 1;
 728                                 tp->last_ack_sent = tp->rcv_nxt;
 729 /*
 730  * XXX possible bug - it doesn't appear that tp->snd_wnd is unscaled
 731  * until the _second_ ACK is received:
 732  *    rcv SYN (set wscale opts)  --> send SYN/ACK, set snd_wnd = window.
 733  *    rcv ACK, calculate tiwin --> process SYN_RECEIVED, determine wscale,
 734  *        move to ESTAB, set snd_wnd to tiwin.
 735  */
 736                                 tp->snd_wnd = tiwin;    /* unscaled */
 737                                 goto after_listen;
 738                         }
 739                         if (thflags & TH_RST) {
 740                                 syncache_chkrst(&inc, th);
 741                                 goto drop;
 742                         }
 743                         if (thflags & TH_ACK) {
 744                                 syncache_badack(&inc);
 745                                 tcpstat.tcps_badsyn++;
 746                                 rstreason = BANDLIM_RST_OPENPORT;
 747                                 goto dropwithreset;
 748                         }
 749                         goto drop;
 750                 }
 751
 752                 /*
 753                  * Segment's flags are (SYN) or (SYN|FIN).
 754                  */
 755 #ifdef INET6
 756                 /*
 757                  * If deprecated address is forbidden,
 758                  * we do not accept SYN to deprecated interface
 759                  * address to prevent any new inbound connection from
 760                  * getting established.
 761                  * When we do not accept SYN, we send a TCP RST,
 762                  * with deprecated source address (instead of dropping
 763                  * it).  We compromise it as it is much better for peer
 764                  * to send a RST, and RST will be the final packet
 765                  * for the exchange.
 766                  *
 767                  * If we do not forbid deprecated addresses, we accept
 768                  * the SYN packet.  RFC2462 does not suggest dropping
 769                  * SYN in this case.
 770                  * If we decipher RFC2462 5.5.4, it says like this:
 771                  * 1. use of deprecated addr with existing
 772                  *    communication is okay - "SHOULD continue to be
 773                  *    used"
 774                  * 2. use of it with new communication:
 775                  *   (2a) "SHOULD NOT be used if alternate address
 776                  *        with sufficient scope is available"
 777                  *   (2b) nothing mentioned otherwise.
 778                  * Here we fall into (2b) case as we have no choice in
 779                  * our source address selection - we must obey the peer.
 780                  *
 781                  * The wording in RFC2462 is confusing, and there are
 782                  * multiple description text for deprecated address
 783                  * handling - worse, they are not exactly the same.
 784                  * I believe 5.5.4 is the best one, so we follow 5.5.4.
 785                  */
 786                 if (isipv6 && !ip6_use_deprecated) {
 787                         struct in6_ifaddr *ia6;
 788
 789                         if ((ia6 = ip6_getdstifaddr(m)) &&
 790                             (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
 791                                 tp = NULL;
 792                                 rstreason = BANDLIM_RST_OPENPORT;
 793                                 goto dropwithreset;
 794                         }
 795                 }
 796 #endif
 797                 /*
 798                  * If it is from this socket, drop it, it must be forged.
 799                  * Don't bother responding if the destination was a broadcast.
 800                  */
 801                 if (th->th_dport == th->th_sport) {
 802                         if (isipv6) {
 803                                 if (IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst,
 804                                                        &ip6->ip6_src))
 805                                         goto drop;
 806                         } else {
 807                                 if (ip->ip_dst.s_addr == ip->ip_src.s_addr)
 808                                         goto drop;
 809                         }
 810                 }
 811                 /*
 812                  * RFC1122 4.2.3.10, p. 104: discard bcast/mcast SYN
 813                  *
 814                  * Note that it is quite possible to receive unicast
 815                  * link-layer packets with a broadcast IP address. Use
 816                  * in_broadcast() to find them.
 817                  */
 818                 if (m->m_flags & (M_BCAST|M_MCAST))
 819                         goto drop;
 820                 if (isipv6) {
 821                         if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
 822                             IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
 823                                 goto drop;
 824                 } else {
 825                         if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
 826                             IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
 827                             ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
 828                             in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
 829                                 goto drop;
 830                 }
 831                 /*
 832                  * SYN appears to be valid; create compressed TCP state
 833                  * for syncache, or perform t/tcp connection.
 834                  */
 835                 if (so->so_qlen <= so->so_qlimit) {
 836                         tcp_dooptions(&to, optp, optlen, 1);
 837                         if (!syncache_add(&inc, &to, th, &so, m))
 838                                 goto drop;
 839                         if (so == NULL)
 840                                 /*
 841                                  * Entry added to syncache, mbuf used to
 842                                  * send SYN,ACK packet.
 843                                  */
 844                                 return;
 845                         /*
 846                          * Segment passed TAO tests.
 847                          */
 848                         inp = sotoinpcb(so);
 849                         tp = intotcpcb(inp);
 850                         tp->snd_wnd = tiwin;
 851                         tp->t_starttime = ticks;
 852                         tp->t_state = TCPS_ESTABLISHED;
 853
 854                         /*
 855                          * If there is a FIN, or if there is data and the
 856                          * connection is local, then delay SYN,ACK(SYN) in
 857                          * the hope of piggy-backing it on a response
 858                          * segment.  Otherwise must send ACK now in case
 859                          * the other side is slow starting.
 860                          */
 861                         if (DELAY_ACK(tp) &&
 862                             ((thflags & TH_FIN) ||
 863                              (tlen != 0 &&
 864                               ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
 865                                (!isipv6 && in_localaddr(inp->inp_faddr)))))) {
 866                                 callout_reset(tp->tt_delack, tcp_delacktime,
 867                                                 tcp_timer_delack, tp);
 868                                 tp->t_flags |= TF_NEEDSYN;
 869                         } else
 870                                 tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
 871
 872                         tcpstat.tcps_connects++;
 873                         soisconnected(so);
 874                         goto trimthenstep6;
 875                 }
 876                 goto drop;
 877         }
 878 after_listen:
 879
 880 /* XXX temp debugging */
 881         /* should not happen - syncache should pick up these connections */
 882         if (tp->t_state == TCPS_LISTEN)
 883                 panic("tcp_input: TCPS_LISTEN");
 884
 885         /*
 886          * Segment received on connection.
 887          * Reset idle time and keep-alive timer.
 888          */
 889         tp->t_rcvtime = ticks;
 890         if (TCPS_HAVEESTABLISHED(tp->t_state))
 891                 callout_reset(tp->tt_keep, tcp_keepidle, tcp_timer_keep, tp);
 892
 893         /*
 894          * Process options.
 895          * XXX this is tradtitional behavior, may need to be cleaned up.
 896          */
 897         tcp_dooptions(&to, optp, optlen, thflags & TH_SYN);
 898         if (thflags & TH_SYN) {
 899                 if (to.to_flags & TOF_SCALE) {
 900                         tp->t_flags |= TF_RCVD_SCALE;
 901                         tp->requested_s_scale = to.to_requested_s_scale;
 902                 }
 903                 if (to.to_flags & TOF_TS) {
 904                         tp->t_flags |= TF_RCVD_TSTMP;
 905                         tp->ts_recent = to.to_tsval;
 906                         tp->ts_recent_age = ticks;
 907                 }
 908                 if (to.to_flags & (TOF_CC|TOF_CCNEW))
 909                         tp->t_flags |= TF_RCVD_CC;
 910                 if (to.to_flags & TOF_MSS)
 911                         tcp_mss(tp, to.to_mss);
 912         }
 913
 914         /*
 915          * Header prediction: check for the two common cases
 916          * of a uni-directional data xfer.  If the packet has
 917          * no control flags, is in-sequence, the window didn't
 918          * change and we're not retransmitting, it's a
 919          * candidate.  If the length is zero and the ack moved
 920          * forward, we're the sender side of the xfer.  Just
 921          * free the data acked & wake any higher level process
 922          * that was blocked waiting for space.  If the length
 923          * is non-zero and the ack didn't move, we're the
 924          * receiver side.  If we're getting packets in-order
 925          * (the reassembly queue is empty), add the data to
 926          * the socket buffer and note that we need a delayed ack.
 927          * Make sure that the hidden state-flags are also off.
 928          * Since we check for TCPS_ESTABLISHED above, it can only
 929          * be TH_NEEDSYN.
 930          */
 931         if (tp->t_state == TCPS_ESTABLISHED &&
 932             (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
 933             ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
 934             ((to.to_flags & TOF_TS) == 0 ||
 935              TSTMP_GEQ(to.to_tsval, tp->ts_recent)) &&
 936             /*
 937              * Using the CC option is compulsory if once started:
 938              *   the segment is OK if no T/TCP was negotiated or
 939              *   if the segment has a CC option equal to CCrecv
 940              */
 941             ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) != (TF_REQ_CC|TF_RCVD_CC) ||
 942              ((to.to_flags & TOF_CC) != 0 && to.to_cc == tp->cc_recv)) &&
 943             th->th_seq == tp->rcv_nxt &&
 944             tiwin && tiwin == tp->snd_wnd &&
 945             tp->snd_nxt == tp->snd_max) {
 946
 947                 /*
 948                  * If last ACK falls within this segment's sequence numbers,
 949                  * record the timestamp.
 950                  * NOTE that the test is modified according to the latest
 951                  * proposal of the tcplw@cray.com list (Braden 1993/04/26).
 952                  */
 953                 if ((to.to_flags & TOF_TS) != 0 &&
 954                     SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
 955                         tp->ts_recent_age = ticks;
 956                         tp->ts_recent = to.to_tsval;
 957                 }
 958
 959                 if (tlen == 0) {
 960                         if (SEQ_GT(th->th_ack, tp->snd_una) &&
 961                             SEQ_LEQ(th->th_ack, tp->snd_max) &&
 962                             tp->snd_cwnd >= tp->snd_wnd &&
 963                             ((!tcp_do_newreno &&
 964                               tp->t_dupacks < tcprexmtthresh) ||
 965                              (tcp_do_newreno && !IN_FASTRECOVERY(tp)))) {
 966                                 /*
 967                                  * this is a pure ack for outstanding data.
 968                                  */
 969                                 ++tcpstat.tcps_predack;
 970                                 /*
 971                                  * "bad retransmit" recovery
 972                                  *
 973                                  * If Eifel detection applies, then
 974                                  * it is deterministic, so use it
 975                                  * unconditionally over the old heuristic.
 976                                  * Otherwise, fall back to the old heuristic.
 977                                  */
 978                                 if (tcp_do_eifel_detect &&
 979                                     (to.to_flags & TOF_TS) && to.to_tsecr &&
 980                                     (tp->t_flags & TF_FIRSTACCACK)) {
 981                                         /* Eifel detection applicable. */
 982                                         if (to.to_tsecr < tp->t_rexmtTS) {
 983                                                 tcp_revert_congestion_state(tp);
 984                                                 ++tcpstat.tcps_eifeldetected;
 985                                         }
 986                                 } else if (tp->t_rxtshift == 1 &&
 987                                            ticks < tp->t_badrxtwin) {
 988                                         tcp_revert_congestion_state(tp);
 989                                         ++tcpstat.tcps_rttdetected;
 990                                 }
 991                                 tp->t_flags &= ~(TF_FIRSTACCACK | TF_FASTREXMT);
 992                                 /*
 993                                  * Recalculate the retransmit timer / rtt.
 994                                  *
 995                                  * Some machines (certain windows boxes)
 996                                  * send broken timestamp replies during the
 997                                  * SYN+ACK phase, ignore timestamps of 0.
 998                                  */
 999                                 if ((to.to_flags & TOF_TS) != 0 &&
1000                                     to.to_tsecr) {
1001                                         tcp_xmit_timer(tp,
1002                                             ticks - to.to_tsecr + 1);
1003                                 } else if (tp->t_rtttime &&
1004                                             SEQ_GT(th->th_ack, tp->t_rtseq)) {
1005                                         tcp_xmit_timer(tp,
1006                                                        ticks - tp->t_rtttime);
1007                                 }
1008                                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
1009                                 acked = th->th_ack - tp->snd_una;
1010                                 tcpstat.tcps_rcvackpack++;
1011                                 tcpstat.tcps_rcvackbyte += acked;
1012                                 sbdrop(&so->so_snd, acked);
1013                                 if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
1014                                     SEQ_LEQ(th->th_ack, tp->snd_recover))
1015                                         tp->snd_recover = th->th_ack - 1;
1016                                 tp->snd_una = th->th_ack;
1017                                 tp->t_dupacks = 0;
1018                                 m_freem(m);
1019                                 ND6_HINT(tp); /* some progress has been done */
1020
1021                                 /*
1022                                  * If all outstanding data are acked, stop
1023                                  * retransmit timer, otherwise restart timer
1024                                  * using current (possibly backed-off) value.
1025                                  * If process is waiting for space,
1026                                  * wakeup/selwakeup/signal.  If data
1027                                  * are ready to send, let tcp_output
1028                                  * decide between more output or persist.
1029                                  */
1030                                 if (tp->snd_una == tp->snd_max)
1031                                         callout_stop(tp->tt_rexmt);
1032                                 else if (!callout_active(tp->tt_persist))
1033                                         callout_reset(tp->tt_rexmt,
1034                                                       tp->t_rxtcur,
1035                                                       tcp_timer_rexmt, tp);
1036
1037                                 sowwakeup(so);
1038                                 if (so->so_snd.sb_cc)
1039                                         (void) tcp_output(tp);
1040                                 return;
1041                         }
1042                 } else if (th->th_ack == tp->snd_una &&
1043                     LIST_EMPTY(&tp->t_segq) &&
1044                     tlen <= sbspace(&so->so_rcv)) {
1045                         /*
1046                          * this is a pure, in-sequence data packet
1047                          * with nothing on the reassembly queue and
1048                          * we have enough buffer space to take it.
1049                          */
1050                         ++tcpstat.tcps_preddat;
1051                         tp->rcv_nxt += tlen;
1052                         tcpstat.tcps_rcvpack++;
1053                         tcpstat.tcps_rcvbyte += tlen;
1054                         ND6_HINT(tp);   /* some progress has been done */
1055                         /*
1056                          * Add data to socket buffer.
1057                          */
1058                         if (so->so_state & SS_CANTRCVMORE) {
1059                                 m_freem(m);
1060                         } else {
1061                                 m_adj(m, drop_hdrlen);  /* delayed header drop */
1062                                 sbappend(&so->so_rcv, m);
1063                         }
1064                         sorwakeup(so);
1065                         if (DELAY_ACK(tp)) {
1066                                 callout_reset(tp->tt_delack, tcp_delacktime,
1067                                     tcp_timer_delack, tp);
1068                         } else {
1069                                 tp->t_flags |= TF_ACKNOW;
1070                                 tcp_output(tp);
1071                         }
1072                         return;
1073                 }
1074         }
1075
1076         /*
1077          * Calculate amount of space in receive window,
1078          * and then do TCP input processing.
1079          * Receive window is amount of space in rcv queue,
1080          * but not less than advertised window.
1081          */
1082         { int win;
1083
1084         win = sbspace(&so->so_rcv);
1085         if (win < 0)
1086                 win = 0;
1087         tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
1088         }
1089
1090         switch (tp->t_state) {
1091
1092         /*
1093          * If the state is SYN_RECEIVED:
1094          *      if seg contains an ACK, but not for our SYN/ACK, send a RST.
1095          */
1096         case TCPS_SYN_RECEIVED:
1097                 if ((thflags & TH_ACK) &&
1098                     (SEQ_LEQ(th->th_ack, tp->snd_una) ||
1099                      SEQ_GT(th->th_ack, tp->snd_max))) {
1100                                 rstreason = BANDLIM_RST_OPENPORT;
1101                                 goto dropwithreset;
1102                 }
1103                 break;
1104
1105         /*
1106          * If the state is SYN_SENT:
1107          *      if seg contains an ACK, but not for our SYN, drop the input.
1108          *      if seg contains a RST, then drop the connection.
1109          *      if seg does not contain SYN, then drop it.
1110          * Otherwise this is an acceptable SYN segment
1111          *      initialize tp->rcv_nxt and tp->irs
1112          *      if seg contains ack then advance tp->snd_una
1113          *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
1114          *      arrange for segment to be acked (eventually)
1115          *      continue processing rest of data/controls, beginning with URG
1116          */
1117         case TCPS_SYN_SENT:
1118                 if ((taop = tcp_gettaocache(&inp->inp_inc)) == NULL) {
1119                         taop = &tao_noncached;
1120                         bzero(taop, sizeof(*taop));
1121                 }
1122
1123                 if ((thflags & TH_ACK) &&
1124                     (SEQ_LEQ(th->th_ack, tp->iss) ||
1125                      SEQ_GT(th->th_ack, tp->snd_max))) {
1126                         /*
1127                          * If we have a cached CCsent for the remote host,
1128                          * hence we haven't just crashed and restarted,
1129                          * do not send a RST.  This may be a retransmission
1130                          * from the other side after our earlier ACK was lost.
1131                          * Our new SYN, when it arrives, will serve as the
1132                          * needed ACK.
1133                          */
1134                         if (taop->tao_ccsent != 0)
1135                                 goto drop;
1136                         else {
1137                                 rstreason = BANDLIM_UNLIMITED;
1138                                 goto dropwithreset;
1139                         }
1140                 }
1141                 if (thflags & TH_RST) {
1142                         if (thflags & TH_ACK)
1143                                 tp = tcp_drop(tp, ECONNREFUSED);
1144                         goto drop;
1145                 }
1146                 if ((thflags & TH_SYN) == 0)
1147                         goto drop;
1148                 tp->snd_wnd = th->th_win;       /* initial send window */
1149                 tp->cc_recv = to.to_cc;         /* foreign CC */
1150
1151                 tp->irs = th->th_seq;
1152                 tcp_rcvseqinit(tp);
1153                 if (thflags & TH_ACK) {
1154                         /*
1155                          * Our SYN was acked.  If segment contains CC.ECHO
1156                          * option, check it to make sure this segment really
1157                          * matches our SYN.  If not, just drop it as old
1158                          * duplicate, but send an RST if we're still playing
1159                          * by the old rules.  If no CC.ECHO option, make sure
1160                          * we don't get fooled into using T/TCP.
1161                          */
1162                         if (to.to_flags & TOF_CCECHO) {
1163                                 if (tp->cc_send != to.to_ccecho) {
1164                                         if (taop->tao_ccsent != 0)
1165                                                 goto drop;
1166                                         else {
1167                                                 rstreason = BANDLIM_UNLIMITED;
1168                                                 goto dropwithreset;
1169                                         }
1170                                 }
1171                         } else
1172                                 tp->t_flags &= ~TF_RCVD_CC;
1173                         tcpstat.tcps_connects++;
1174                         soisconnected(so);
1175                         /* Do window scaling on this connection? */
1176                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1177                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1178                                 tp->snd_scale = tp->requested_s_scale;
1179                                 tp->rcv_scale = tp->request_r_scale;
1180                         }
1181                         /* Segment is acceptable, update cache if undefined. */
1182                         if (taop->tao_ccsent == 0)
1183                                 taop->tao_ccsent = to.to_ccecho;
1184
1185                         tp->rcv_adv += tp->rcv_wnd;
1186                         tp->snd_una++;          /* SYN is acked */
1187                         /*
1188                          * If there's data, delay ACK; if there's also a FIN
1189                          * ACKNOW will be turned on later.
1190                          */
1191                         if (DELAY_ACK(tp) && tlen != 0)
1192                                 callout_reset(tp->tt_delack, tcp_delacktime,
1193                                     tcp_timer_delack, tp);
1194                         else
1195                                 tp->t_flags |= TF_ACKNOW;
1196                         /*
1197                          * Received <SYN,ACK> in SYN_SENT[*] state.
1198                          * Transitions:
1199                          *      SYN_SENT  --> ESTABLISHED
1200                          *      SYN_SENT* --> FIN_WAIT_1
1201                          */
1202                         tp->t_starttime = ticks;
1203                         if (tp->t_flags & TF_NEEDFIN) {
1204                                 tp->t_state = TCPS_FIN_WAIT_1;
1205                                 tp->t_flags &= ~TF_NEEDFIN;
1206                                 thflags &= ~TH_SYN;
1207                         } else {
1208                                 tp->t_state = TCPS_ESTABLISHED;
1209                                 callout_reset(tp->tt_keep, tcp_keepidle,
1210                                               tcp_timer_keep, tp);
1211                         }
1212                 } else {
1213                         /*
1214                          * Received initial SYN in SYN-SENT[*] state =>
1215                          * simultaneous open.  If segment contains CC option
1216                          * and there is a cached CC, apply TAO test.
1217                          * If it succeeds, connection is * half-synchronized.
1218                          * Otherwise, do 3-way handshake:
1219                          *        SYN-SENT -> SYN-RECEIVED
1220                          *        SYN-SENT* -> SYN-RECEIVED*
1221                          * If there was no CC option, clear cached CC value.
1222                          */
1223                         tp->t_flags |= TF_ACKNOW;
1224                         callout_stop(tp->tt_rexmt);
1225                         if (to.to_flags & TOF_CC) {
1226                                 if (taop->tao_cc != 0 &&
1227                                     CC_GT(to.to_cc, taop->tao_cc)) {
1228                                         /*
1229                                          * update cache and make transition:
1230                                          *        SYN-SENT -> ESTABLISHED*
1231                                          *        SYN-SENT* -> FIN-WAIT-1*
1232                                          */
1233                                         taop->tao_cc = to.to_cc;
1234                                         tp->t_starttime = ticks;
1235                                         if (tp->t_flags & TF_NEEDFIN) {
1236                                                 tp->t_state = TCPS_FIN_WAIT_1;
1237                                                 tp->t_flags &= ~TF_NEEDFIN;
1238                                         } else {
1239                                                 tp->t_state = TCPS_ESTABLISHED;
1240                                                 callout_reset(tp->tt_keep,
1241                                                               tcp_keepidle,
1242                                                               tcp_timer_keep,
1243                                                               tp);
1244                                         }
1245                                         tp->t_flags |= TF_NEEDSYN;
1246                                 } else
1247                                         tp->t_state = TCPS_SYN_RECEIVED;
1248                         } else {
1249                                 /* CC.NEW or no option => invalidate cache */
1250                                 taop->tao_cc = 0;
1251                                 tp->t_state = TCPS_SYN_RECEIVED;
1252                         }
1253                 }
1254
1255 trimthenstep6:
1256                 /*
1257                  * Advance th->th_seq to correspond to first data byte.
1258                  * If data, trim to stay within window,
1259                  * dropping FIN if necessary.
1260                  */
1261                 th->th_seq++;
1262                 if (tlen > tp->rcv_wnd) {
1263                         todrop = tlen - tp->rcv_wnd;
1264                         m_adj(m, -todrop);
1265                         tlen = tp->rcv_wnd;
1266                         thflags &= ~TH_FIN;
1267                         tcpstat.tcps_rcvpackafterwin++;
1268                         tcpstat.tcps_rcvbyteafterwin += todrop;
1269                 }
1270                 tp->snd_wl1 = th->th_seq - 1;
1271                 tp->rcv_up = th->th_seq;
1272                 /*
1273                  * Client side of transaction: already sent SYN and data.
1274                  * If the remote host used T/TCP to validate the SYN,
1275                  * our data will be ACK'd; if so, enter normal data segment
1276                  * processing in the middle of step 5, ack processing.
1277                  * Otherwise, goto step 6.
1278                  */
1279                 if (thflags & TH_ACK)
1280                         goto process_ACK;
1281
1282                 goto step6;
1283
1284         /*
1285          * If the state is LAST_ACK or CLOSING or TIME_WAIT:
1286          *      if segment contains a SYN and CC [not CC.NEW] option:
1287          *              if state == TIME_WAIT and connection duration > MSL,
1288          *                  drop packet and send RST;
1289          *
1290          *              if SEG.CC > CCrecv then is new SYN, and can implicitly
1291          *                  ack the FIN (and data) in retransmission queue.
1292          *                  Complete close and delete TCPCB.  Then reprocess
1293          *                  segment, hoping to find new TCPCB in LISTEN state;
1294          *
1295          *              else must be old SYN; drop it.
1296          *      else do normal processing.
1297          */
1298         case TCPS_LAST_ACK:
1299         case TCPS_CLOSING:
1300         case TCPS_TIME_WAIT:
1301                 if ((thflags & TH_SYN) &&
1302                     (to.to_flags & TOF_CC) && tp->cc_recv != 0) {
1303                         if (tp->t_state == TCPS_TIME_WAIT &&
1304                                         (ticks - tp->t_starttime) > tcp_msl) {
1305                                 rstreason = BANDLIM_UNLIMITED;
1306                                 goto dropwithreset;
1307                         }
1308                         if (CC_GT(to.to_cc, tp->cc_recv)) {
1309                                 tp = tcp_close(tp);
1310                                 goto findpcb;
1311                         }
1312                         else
1313                                 goto drop;
1314                 }
1315                 break;  /* continue normal processing */
1316         }
1317
1318         /*
1319          * States other than LISTEN or SYN_SENT.
1320          * First check the RST flag and sequence number since reset segments
1321          * are exempt from the timestamp and connection count tests.  This
1322          * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
1323          * below which allowed reset segments in half the sequence space
1324          * to fall though and be processed (which gives forged reset
1325          * segments with a random sequence number a 50 percent chance of
1326          * killing a connection).
1327          * Then check timestamp, if present.
1328          * Then check the connection count, if present.
1329          * Then check that at least some bytes of segment are within
1330          * receive window.  If segment begins before rcv_nxt,
1331          * drop leading data (and SYN); if nothing left, just ack.
1332          *
1333          *
1334          * If the RST bit is set, check the sequence number to see
1335          * if this is a valid reset segment.
1336          * RFC 793 page 37:
1337          *   In all states except SYN-SENT, all reset (RST) segments
1338          *   are validated by checking their SEQ-fields.  A reset is
1339          *   valid if its sequence number is in the window.
1340          * Note: this does not take into account delayed ACKs, so
1341          *   we should test against last_ack_sent instead of rcv_nxt.
1342          *   The sequence number in the reset segment is normally an
1343          *   echo of our outgoing acknowlegement numbers, but some hosts
1344          *   send a reset with the sequence number at the rightmost edge
1345          *   of our receive window, and we have to handle this case.
1346          * If we have multiple segments in flight, the intial reset
1347          * segment sequence numbers will be to the left of last_ack_sent,
1348          * but they will eventually catch up.
1349          * In any case, it never made sense to trim reset segments to
1350          * fit the receive window since RFC 1122 says:
1351          *   4.2.2.12  RST Segment: RFC-793 Section 3.4
1352          *
1353          *    A TCP SHOULD allow a received RST segment to include data.
1354          *
1355          *    DISCUSSION
1356          *         It has been suggested that a RST segment could contain
1357          *         ASCII text that encoded and explained the cause of the
1358          *         RST.  No standard has yet been established for such
1359          *         data.
1360          *
1361          * If the reset segment passes the sequence number test examine
1362          * the state:
1363          *    SYN_RECEIVED STATE:
1364          *      If passive open, return to LISTEN state.
1365          *      If active open, inform user that connection was refused.
1366          *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, CLOSE_WAIT STATES:
1367          *      Inform user that connection was reset, and close tcb.
1368          *    CLOSING, LAST_ACK STATES:
1369          *      Close the tcb.
1370          *    TIME_WAIT STATE:
1371          *      Drop the segment - see Stevens, vol. 2, p. 964 and
1372          *      RFC 1337.
1373          */
1374         if (thflags & TH_RST) {
1375                 if (SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
1376                     SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
1377                         switch (tp->t_state) {
1378
1379                         case TCPS_SYN_RECEIVED:
1380                                 so->so_error = ECONNREFUSED;
1381                                 goto close;
1382
1383                         case TCPS_ESTABLISHED:
1384                         case TCPS_FIN_WAIT_1:
1385                         case TCPS_FIN_WAIT_2:
1386                         case TCPS_CLOSE_WAIT:
1387                                 so->so_error = ECONNRESET;
1388                         close:
1389                                 tp->t_state = TCPS_CLOSED;
1390                                 tcpstat.tcps_drops++;
1391                                 tp = tcp_close(tp);
1392                                 break;
1393
1394                         case TCPS_CLOSING:
1395                         case TCPS_LAST_ACK:
1396                                 tp = tcp_close(tp);
1397                                 break;
1398
1399                         case TCPS_TIME_WAIT:
1400                                 break;
1401                         }
1402                 }
1403                 goto drop;
1404         }
1405
1406         /*
1407          * RFC 1323 PAWS: If we have a timestamp reply on this segment
1408          * and it's less than ts_recent, drop it.
1409          */
1410         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
1411             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
1412
1413                 /* Check to see if ts_recent is over 24 days old.  */
1414                 if ((int)(ticks - tp->ts_recent_age) > TCP_PAWS_IDLE) {
1415                         /*
1416                          * Invalidate ts_recent.  If this segment updates
1417                          * ts_recent, the age will be reset later and ts_recent
1418                          * will get a valid value.  If it does not, setting
1419                          * ts_recent to zero will at least satisfy the
1420                          * requirement that zero be placed in the timestamp
1421                          * echo reply when ts_recent isn't valid.  The
1422                          * age isn't reset until we get a valid ts_recent
1423                          * because we don't want out-of-order segments to be
1424                          * dropped when ts_recent is old.
1425                          */
1426                         tp->ts_recent = 0;
1427                 } else {
1428                         tcpstat.tcps_rcvduppack++;
1429                         tcpstat.tcps_rcvdupbyte += tlen;
1430                         tcpstat.tcps_pawsdrop++;
1431                         if (tlen)
1432                                 goto dropafterack;
1433                         goto drop;
1434                 }
1435         }
1436
1437         /*
1438          * T/TCP mechanism
1439          *   If T/TCP was negotiated and the segment doesn't have CC,
1440          *   or if its CC is wrong then drop the segment.
1441          *   RST segments do not have to comply with this.
1442          */
1443         if ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) == (TF_REQ_CC|TF_RCVD_CC) &&
1444             ((to.to_flags & TOF_CC) == 0 || tp->cc_recv != to.to_cc))
1445                 goto dropafterack;
1446
1447         /*
1448          * In the SYN-RECEIVED state, validate that the packet belongs to
1449          * this connection before trimming the data to fit the receive
1450          * window.  Check the sequence number versus IRS since we know
1451          * the sequence numbers haven't wrapped.  This is a partial fix
1452          * for the "LAND" DoS attack.
1453          */
1454         if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
1455                 rstreason = BANDLIM_RST_OPENPORT;
1456                 goto dropwithreset;
1457         }
1458
1459         todrop = tp->rcv_nxt - th->th_seq;
1460         if (todrop > 0) {
1461                 if (thflags & TH_SYN) {
1462                         thflags &= ~TH_SYN;
1463                         th->th_seq++;
1464                         if (th->th_urp > 1)
1465                                 th->th_urp--;
1466                         else
1467                                 thflags &= ~TH_URG;
1468                         todrop--;
1469                 }
1470                 /*
1471                  * Following if statement from Stevens, vol. 2, p. 960.
1472                  */
1473                 if (todrop > tlen
1474                     || (todrop == tlen && (thflags & TH_FIN) == 0)) {
1475                         /*
1476                          * Any valid FIN must be to the left of the window.
1477                          * At this point the FIN must be a duplicate or out
1478                          * of sequence; drop it.
1479                          */
1480                         thflags &= ~TH_FIN;
1481
1482                         /*
1483                          * Send an ACK to resynchronize and drop any data.
1484                          * But keep on processing for RST or ACK.
1485                          */
1486                         tp->t_flags |= TF_ACKNOW;
1487                         todrop = tlen;
1488                         tcpstat.tcps_rcvduppack++;
1489                         tcpstat.tcps_rcvdupbyte += todrop;
1490                 } else {
1491                         tcpstat.tcps_rcvpartduppack++;
1492                         tcpstat.tcps_rcvpartdupbyte += todrop;
1493                 }
1494                 drop_hdrlen += todrop;  /* drop from the top afterwards */
1495                 th->th_seq += todrop;
1496                 tlen -= todrop;
1497                 if (th->th_urp > todrop)
1498                         th->th_urp -= todrop;
1499                 else {
1500                         thflags &= ~TH_URG;
1501                         th->th_urp = 0;
1502                 }
1503         }
1504
1505         /*
1506          * If new data are received on a connection after the
1507          * user processes are gone, then RST the other end.
1508          */
1509         if ((so->so_state & SS_NOFDREF) &&
1510             tp->t_state > TCPS_CLOSE_WAIT && tlen) {
1511                 tp = tcp_close(tp);
1512                 tcpstat.tcps_rcvafterclose++;
1513                 rstreason = BANDLIM_UNLIMITED;
1514                 goto dropwithreset;
1515         }
1516
1517         /*
1518          * If segment ends after window, drop trailing data
1519          * (and PUSH and FIN); if nothing left, just ACK.
1520          */
1521         todrop = (th->th_seq+tlen) - (tp->rcv_nxt+tp->rcv_wnd);
1522         if (todrop > 0) {
1523                 tcpstat.tcps_rcvpackafterwin++;
1524                 if (todrop >= tlen) {
1525                         tcpstat.tcps_rcvbyteafterwin += tlen;
1526                         /*
1527                          * If a new connection request is received
1528                          * while in TIME_WAIT, drop the old connection
1529                          * and start over if the sequence numbers
1530                          * are above the previous ones.
1531                          */
1532                         if (thflags & TH_SYN &&
1533                             tp->t_state == TCPS_TIME_WAIT &&
1534                             SEQ_GT(th->th_seq, tp->rcv_nxt)) {
1535                                 tp = tcp_close(tp);
1536                                 goto findpcb;
1537                         }
1538                         /*
1539                          * If window is closed can only take segments at
1540                          * window edge, and have to drop data and PUSH from
1541                          * incoming segments.  Continue processing, but
1542                          * remember to ack.  Otherwise, drop segment
1543                          * and ack.
1544                          */
1545                         if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
1546                                 tp->t_flags |= TF_ACKNOW;
1547                                 tcpstat.tcps_rcvwinprobe++;
1548                         } else
1549                                 goto dropafterack;
1550                 } else
1551                         tcpstat.tcps_rcvbyteafterwin += todrop;
1552                 m_adj(m, -todrop);
1553                 tlen -= todrop;
1554                 thflags &= ~(TH_PUSH|TH_FIN);
1555         }
1556
1557         /*
1558          * If last ACK falls within this segment's sequence numbers,
1559          * record its timestamp.
1560          * NOTE that the test is modified according to the latest
1561          * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1562          */
1563         if ((to.to_flags & TOF_TS) != 0 &&
1564             SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
1565                 tp->ts_recent_age = ticks;
1566                 tp->ts_recent = to.to_tsval;
1567         }
1568
1569         /*
1570          * If a SYN is in the window, then this is an
1571          * error and we send an RST and drop the connection.
1572          */
1573         if (thflags & TH_SYN) {
1574                 tp = tcp_drop(tp, ECONNRESET);
1575                 rstreason = BANDLIM_UNLIMITED;
1576                 goto dropwithreset;
1577         }
1578
1579         /*
1580          * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
1581          * flag is on (half-synchronized state), then queue data for
1582          * later processing; else drop segment and return.
1583          */
1584         if ((thflags & TH_ACK) == 0) {
1585                 if (tp->t_state == TCPS_SYN_RECEIVED ||
1586                     (tp->t_flags & TF_NEEDSYN))
1587                         goto step6;
1588                 else
1589                         goto drop;
1590         }
1591
1592         /*
1593          * Ack processing.
1594          */
1595         switch (tp->t_state) {
1596
1597         /*
1598          * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
1599          * ESTABLISHED state and continue processing.
1600          * The ACK was checked above.
1601          */
1602         case TCPS_SYN_RECEIVED:
1603
1604                 tcpstat.tcps_connects++;
1605                 soisconnected(so);
1606                 /* Do window scaling? */
1607                 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1608                         (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1609                         tp->snd_scale = tp->requested_s_scale;
1610                         tp->rcv_scale = tp->request_r_scale;
1611                 }
1612                 /*
1613                  * Upon successful completion of 3-way handshake,
1614                  * update cache.CC if it was undefined, pass any queued
1615                  * data to the user, and advance state appropriately.
1616                  */
1617                 if ((taop = tcp_gettaocache(&inp->inp_inc)) != NULL &&
1618                     taop->tao_cc == 0)
1619                         taop->tao_cc = tp->cc_recv;
1620
1621                 /*
1622                  * Make transitions:
1623                  *      SYN-RECEIVED  -> ESTABLISHED
1624                  *      SYN-RECEIVED* -> FIN-WAIT-1
1625                  */
1626                 tp->t_starttime = ticks;
1627                 if (tp->t_flags & TF_NEEDFIN) {
1628                         tp->t_state = TCPS_FIN_WAIT_1;
1629                         tp->t_flags &= ~TF_NEEDFIN;
1630                 } else {
1631                         tp->t_state = TCPS_ESTABLISHED;
1632                         callout_reset(tp->tt_keep, tcp_keepidle,
1633                                       tcp_timer_keep, tp);
1634                 }
1635                 /*
1636                  * If segment contains data or ACK, will call tcp_reass()
1637                  * later; if not, do so now to pass queued data to user.
1638                  */
1639                 if (tlen == 0 && (thflags & TH_FIN) == 0)
1640                         (void) tcp_reass(tp, (struct tcphdr *)0, 0,
1641                             (struct mbuf *)0);
1642                 tp->snd_wl1 = th->th_seq - 1;
1643                 /* fall into ... */
1644
1645         /*
1646          * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
1647          * ACKs.  If the ack is in the range
1648          *      tp->snd_una < th->th_ack <= tp->snd_max
1649          * then advance tp->snd_una to th->th_ack and drop
1650          * data from the retransmission queue.  If this ACK reflects
1651          * more up to date window information we update our window information.
1652          */
1653         case TCPS_ESTABLISHED:
1654         case TCPS_FIN_WAIT_1:
1655         case TCPS_FIN_WAIT_2:
1656         case TCPS_CLOSE_WAIT:
1657         case TCPS_CLOSING:
1658         case TCPS_LAST_ACK:
1659         case TCPS_TIME_WAIT:
1660
1661                 if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
1662                         if (tlen == 0 && tiwin == tp->snd_wnd) {
1663                                 tcpstat.tcps_rcvdupack++;
1664                                 /*
1665                                  * If we have outstanding data (other than
1666                                  * a window probe), this is a completely
1667                                  * duplicate ack (ie, window info didn't
1668                                  * change), the ack is the biggest we've
1669                                  * seen and we've seen exactly our rexmt
1670                                  * threshhold of them, assume a packet
1671                                  * has been dropped and retransmit it.
1672                                  * Kludge snd_nxt & the congestion
1673                                  * window so we send only this one
1674                                  * packet.
1675                                  *
1676                                  * We know we're losing at the current
1677                                  * window size so do congestion avoidance
1678                                  * (set ssthresh to half the current window
1679                                  * and pull our congestion window back to
1680                                  * the new ssthresh).
1681                                  *
1682                                  * Dup acks mean that packets have left the
1683                                  * network (they're now cached at the receiver)
1684                                  * so bump cwnd by the amount in the receiver
1685                                  * to keep a constant cwnd packets in the
1686                                  * network.
1687                                  */
1688                                 if (!callout_active(tp->tt_rexmt) ||
1689                                     th->th_ack != tp->snd_una)
1690                                         tp->t_dupacks = 0;
1691                                 else if (++tp->t_dupacks > tcprexmtthresh ||
1692                                          (tcp_do_newreno &&
1693                                           IN_FASTRECOVERY(tp))) {
1694                                         tp->snd_cwnd += tp->t_maxseg;
1695                                         (void) tcp_output(tp);
1696                                         goto drop;
1697                                 } else if (tp->t_dupacks == tcprexmtthresh) {
1698                                         tcp_seq onxt = tp->snd_nxt;
1699                                         u_int win;
1700                                         if (tcp_do_newreno &&
1701                                             SEQ_LEQ(th->th_ack,
1702                                                     tp->snd_recover)) {
1703                                                 tp->t_dupacks = 0;
1704                                                 break;
1705                                         }
1706                                         if (tcp_do_eifel_detect &&
1707                                             (tp->t_flags & TF_RCVD_TSTMP)) {
1708                                                 tcp_save_congestion_state(tp);
1709                                                 tp->t_flags |= TF_FASTREXMT;
1710                                         }
1711                                         win = min(tp->snd_wnd, tp->snd_cwnd) /
1712                                             2 / tp->t_maxseg;
1713                                         if (win < 2)
1714                                                 win = 2;
1715                                         tp->snd_ssthresh = win * tp->t_maxseg;
1716                                         ENTER_FASTRECOVERY(tp);
1717                                         tp->snd_recover = tp->snd_max;
1718                                         callout_stop(tp->tt_rexmt);
1719                                         tp->t_rtttime = 0;
1720                                         tp->snd_nxt = th->th_ack;
1721                                         tp->snd_cwnd = tp->t_maxseg;
1722                                         (void) tcp_output(tp);
1723                                         KASSERT(tp->snd_limited <= 2,
1724                                             ("tp->snd_limited too big"));
1725                                         tp->snd_cwnd = tp->snd_ssthresh +
1726                                             (tp->t_maxseg *
1727                                              (tp->t_dupacks - tp->snd_limited));
1728                                         if (SEQ_GT(onxt, tp->snd_nxt))
1729                                                 tp->snd_nxt = onxt;
1730                                         goto drop;
1731                                 } else if (tcp_do_limitedtransmit) {
1732                                         u_long oldcwnd = tp->snd_cwnd;
1733                                         tcp_seq oldsndmax = tp->snd_max;
1734                                         u_int sent;
1735                                         KASSERT(tp->t_dupacks == 1 ||
1736                                             tp->t_dupacks == 2,
1737                                             ("dupacks not 1 or 2"));
1738                                         if (tp->t_dupacks == 1) {
1739                                                 tp->snd_limited = 0;
1740                                                 tp->snd_cwnd += tp->t_maxseg;
1741                                         } else {
1742                                                 tp->snd_cwnd +=
1743                                                     tp->t_maxseg * 2;
1744                                         }
1745                                         (void) tcp_output(tp);
1746                                         sent = tp->snd_max - oldsndmax;
1747                                         if (sent > tp->t_maxseg) {
1748                                                 KASSERT(tp->snd_limited == 0 &&
1749                                                     tp->t_dupacks == 2,
1750                                                     ("sent too much"));
1751                                                 tp->snd_limited = 2;
1752                                         } else if (sent > 0)
1753                                                 ++tp->snd_limited;
1754                                         tp->snd_cwnd = oldcwnd;
1755                                         goto drop;
1756                                 }
1757                         } else
1758                                 tp->t_dupacks = 0;
1759                         break;
1760                 }
1761
1762                 KASSERT(SEQ_GT(th->th_ack, tp->snd_una), ("th_ack <= snd_una"));
1763
1764                 /*
1765                  * If the congestion window was inflated to account
1766                  * for the other side's cached packets, retract it.
1767                  */
1768                 if (tcp_do_newreno) {
1769                         if (IN_FASTRECOVERY(tp)) {
1770                                 if (SEQ_LT(th->th_ack, tp->snd_recover)) {
1771                                         tcp_newreno_partial_ack(tp, th);
1772                                 } else {
1773                                         /*
1774                                          * Window inflation should have left us
1775                                          * with approximately snd_ssthresh
1776                                          * outstanding data.
1777                                          * But in case we would be inclined to
1778                                          * send a burst, better to do it via
1779                                          * the slow start mechanism.
1780                                          */
1781                                         if (SEQ_GT(th->th_ack +
1782                                                         tp->snd_ssthresh,
1783                                                    tp->snd_max))
1784                                                 tp->snd_cwnd = tp->snd_max -
1785                                                                 th->th_ack +
1786                                                                 tp->t_maxseg;
1787                                         else
1788                                                 tp->snd_cwnd = tp->snd_ssthresh;
1789                                 }
1790                         }
1791                 } else {
1792                         if (tp->t_dupacks >= tcprexmtthresh &&
1793                             tp->snd_cwnd > tp->snd_ssthresh)
1794                                 tp->snd_cwnd = tp->snd_ssthresh;
1795                 }
1796                 tp->t_dupacks = 0;
1797                 if (SEQ_GT(th->th_ack, tp->snd_max)) {
1798                         tcpstat.tcps_rcvacktoomuch++;
1799                         goto dropafterack;
1800                 }
1801                 /*
1802                  * If we reach this point, ACK is not a duplicate,
1803                  *     i.e., it ACKs something we sent.
1804                  */
1805                 if (tp->t_flags & TF_NEEDSYN) {
1806                         /*
1807                          * T/TCP: Connection was half-synchronized, and our
1808                          * SYN has been ACK'd (so connection is now fully
1809                          * synchronized).  Go to non-starred state,
1810                          * increment snd_una for ACK of SYN, and check if
1811                          * we can do window scaling.
1812                          */
1813                         tp->t_flags &= ~TF_NEEDSYN;
1814                         tp->snd_una++;
1815                         /* Do window scaling? */
1816                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1817                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1818                                 tp->snd_scale = tp->requested_s_scale;
1819                                 tp->rcv_scale = tp->request_r_scale;
1820                         }
1821                 }
1822
1823 process_ACK:
1824                 acked = th->th_ack - tp->snd_una;
1825                 tcpstat.tcps_rcvackpack++;
1826                 tcpstat.tcps_rcvackbyte += acked;
1827
1828                 /*
1829                  * If we just performed our first retransmit, and the ACK
1830                  * arrives within our recovery window, then it was a mistake
1831                  * to do the retransmit in the first place.  Recover our
1832                  * original cwnd and ssthresh, and proceed to transmit where
1833                  * we left off.
1834                  */
1835                 if (tcp_do_eifel_detect && acked &&
1836                     (to.to_flags & TOF_TS) && to.to_tsecr &&
1837                     (tp->t_flags & TF_FIRSTACCACK)) {
1838                         /* Eifel detection applicable. */
1839                         if (to.to_tsecr < tp->t_rexmtTS) {
1840                                 tcp_revert_congestion_state(tp);
1841                                 ++tcpstat.tcps_eifeldetected;
1842                         }
1843                 } else if (tp->t_rxtshift == 1 && ticks < tp->t_badrxtwin) {
1844                         tcp_revert_congestion_state(tp);
1845                         ++tcpstat.tcps_rttdetected;
1846                 }
1847
1848                 /*
1849                  * If we have a timestamp reply, update smoothed
1850                  * round trip time.  If no timestamp is present but
1851                  * transmit timer is running and timed sequence
1852                  * number was acked, update smoothed round trip time.
1853                  * Since we now have an rtt measurement, cancel the
1854                  * timer backoff (cf., Phil Karn's retransmit alg.).
1855                  * Recompute the initial retransmit timer.
1856                  *
1857                  * Some machines (certain windows boxes) send broken
1858                  * timestamp replies during the SYN+ACK phase, ignore
1859                  * timestamps of 0.
1860                  */
1861                 if ((to.to_flags & TOF_TS) != 0 &&
1862                     to.to_tsecr) {
1863                         tcp_xmit_timer(tp, ticks - to.to_tsecr + 1);
1864                 } else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
1865                         tcp_xmit_timer(tp, ticks - tp->t_rtttime);
1866                 }
1867                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
1868
1869                 /*
1870                  * If all outstanding data is acked, stop retransmit
1871                  * timer and remember to restart (more output or persist).
1872                  * If there is more data to be acked, restart retransmit
1873                  * timer, using current (possibly backed-off) value.
1874                  */
1875                 if (th->th_ack == tp->snd_max) {
1876                         callout_stop(tp->tt_rexmt);
1877                         needoutput = 1;
1878                 } else if (!callout_active(tp->tt_persist))
1879                         callout_reset(tp->tt_rexmt, tp->t_rxtcur,
1880                                       tcp_timer_rexmt, tp);
1881
1882                 /*
1883                  * If no data (only SYN) was ACK'd,
1884                  *    skip rest of ACK processing.
1885                  */
1886                 if (acked == 0)
1887                         goto step6;
1888
1889                 /* Stop looking for an acceptable ACK since one was received. */
1890                 tp->t_flags &= ~(TF_FIRSTACCACK | TF_FASTREXMT);
1891
1892                 /*
1893                  * When new data is acked, open the congestion window.
1894                  * If the window gives us less than ssthresh packets
1895                  * in flight, open exponentially (maxseg per packet).
1896                  * Otherwise open linearly: maxseg per window
1897                  * (maxseg^2 / cwnd per packet).
1898                  */
1899                 if (!tcp_do_newreno || !IN_FASTRECOVERY(tp)) {
1900                         u_int cw = tp->snd_cwnd;
1901                         u_int incr = tp->t_maxseg;
1902                         if (cw > tp->snd_ssthresh)
1903                                 incr = incr * incr / cw;
1904                         tp->snd_cwnd = min(cw+incr, TCP_MAXWIN<<tp->snd_scale);
1905                 }
1906                 if (acked > so->so_snd.sb_cc) {
1907                         tp->snd_wnd -= so->so_snd.sb_cc;
1908                         sbdrop(&so->so_snd, (int)so->so_snd.sb_cc);
1909                         ourfinisacked = 1;
1910                 } else {
1911                         sbdrop(&so->so_snd, acked);
1912                         tp->snd_wnd -= acked;
1913                         ourfinisacked = 0;
1914                 }
1915                 sowwakeup(so);
1916                 /* detect una wraparound */
1917                 if (tcp_do_newreno && !IN_FASTRECOVERY(tp) &&
1918                     SEQ_GT(tp->snd_una, tp->snd_recover) &&
1919                     SEQ_LEQ(th->th_ack, tp->snd_recover))
1920                         tp->snd_recover = th->th_ack - 1;
1921                 if (tcp_do_newreno && IN_FASTRECOVERY(tp) &&
1922                     SEQ_GEQ(th->th_ack, tp->snd_recover))
1923                         EXIT_FASTRECOVERY(tp);
1924                 tp->snd_una = th->th_ack;
1925                 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
1926                         tp->snd_nxt = tp->snd_una;
1927
1928                 switch (tp->t_state) {
1929
1930                 /*
1931                  * In FIN_WAIT_1 STATE in addition to the processing
1932                  * for the ESTABLISHED state if our FIN is now acknowledged
1933                  * then enter FIN_WAIT_2.
1934                  */
1935                 case TCPS_FIN_WAIT_1:
1936                         if (ourfinisacked) {
1937                                 /*
1938                                  * If we can't receive any more
1939                                  * data, then closing user can proceed.
1940                                  * Starting the timer is contrary to the
1941                                  * specification, but if we don't get a FIN
1942                                  * we'll hang forever.
1943                                  */
1944                                 if (so->so_state & SS_CANTRCVMORE) {
1945                                         soisdisconnected(so);
1946                                         callout_reset(tp->tt_2msl, tcp_maxidle,
1947                                                       tcp_timer_2msl, tp);
1948                                 }
1949                                 tp->t_state = TCPS_FIN_WAIT_2;
1950                         }
1951                         break;
1952
1953                 /*
1954                  * In CLOSING STATE in addition to the processing for
1955                  * the ESTABLISHED state if the ACK acknowledges our FIN
1956                  * then enter the TIME-WAIT state, otherwise ignore
1957                  * the segment.
1958                  */
1959                 case TCPS_CLOSING:
1960                         if (ourfinisacked) {
1961                                 tp->t_state = TCPS_TIME_WAIT;
1962                                 tcp_canceltimers(tp);
1963                                 /* Shorten TIME_WAIT [RFC-1644, p.28] */
1964                                 if (tp->cc_recv != 0 &&
1965                                     (ticks - tp->t_starttime) < tcp_msl)
1966                                         callout_reset(tp->tt_2msl,
1967                                                       tp->t_rxtcur *
1968                                                       TCPTV_TWTRUNC,
1969                                                       tcp_timer_2msl, tp);
1970                                 else
1971                                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
1972                                                       tcp_timer_2msl, tp);
1973                                 soisdisconnected(so);
1974                         }
1975                         break;
1976
1977                 /*
1978                  * In LAST_ACK, we may still be waiting for data to drain
1979                  * and/or to be acked, as well as for the ack of our FIN.
1980                  * If our FIN is now acknowledged, delete the TCB,
1981                  * enter the closed state and return.
1982                  */
1983                 case TCPS_LAST_ACK:
1984                         if (ourfinisacked) {
1985                                 tp = tcp_close(tp);
1986                                 goto drop;
1987                         }
1988                         break;
1989
1990                 /*
1991                  * In TIME_WAIT state the only thing that should arrive
1992                  * is a retransmission of the remote FIN.  Acknowledge
1993                  * it and restart the finack timer.
1994                  */
1995                 case TCPS_TIME_WAIT:
1996                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
1997                                       tcp_timer_2msl, tp);
1998                         goto dropafterack;
1999                 }
2000         }
2001
2002 step6:
2003         /*
2004          * Update window information.
2005          * Don't look at window if no ACK: TAC's send garbage on first SYN.
2006          */
2007         if ((thflags & TH_ACK) &&
2008             (SEQ_LT(tp->snd_wl1, th->th_seq) ||
2009             (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
2010              (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
2011                 /* keep track of pure window updates */
2012                 if (tlen == 0 &&
2013                     tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
2014                         tcpstat.tcps_rcvwinupd++;
2015                 tp->snd_wnd = tiwin;
2016                 tp->snd_wl1 = th->th_seq;
2017                 tp->snd_wl2 = th->th_ack;
2018                 if (tp->snd_wnd > tp->max_sndwnd)
2019                         tp->max_sndwnd = tp->snd_wnd;
2020                 needoutput = 1;
2021         }
2022
2023         /*
2024          * Process segments with URG.
2025          */
2026         if ((thflags & TH_URG) && th->th_urp &&
2027             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2028                 /*
2029                  * This is a kludge, but if we receive and accept
2030                  * random urgent pointers, we'll crash in
2031                  * soreceive.  It's hard to imagine someone
2032                  * actually wanting to send this much urgent data.
2033                  */
2034                 if (th->th_urp + so->so_rcv.sb_cc > sb_max) {
2035                         th->th_urp = 0;                 /* XXX */
2036                         thflags &= ~TH_URG;             /* XXX */
2037                         goto dodata;                    /* XXX */
2038                 }
2039                 /*
2040                  * If this segment advances the known urgent pointer,
2041                  * then mark the data stream.  This should not happen
2042                  * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
2043                  * a FIN has been received from the remote side.
2044                  * In these states we ignore the URG.
2045                  *
2046                  * According to RFC961 (Assigned Protocols),
2047                  * the urgent pointer points to the last octet
2048                  * of urgent data.  We continue, however,
2049                  * to consider it to indicate the first octet
2050                  * of data past the urgent section as the original
2051                  * spec states (in one of two places).
2052                  */
2053                 if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
2054                         tp->rcv_up = th->th_seq + th->th_urp;
2055                         so->so_oobmark = so->so_rcv.sb_cc +
2056                             (tp->rcv_up - tp->rcv_nxt) - 1;
2057                         if (so->so_oobmark == 0)
2058                                 so->so_state |= SS_RCVATMARK;
2059                         sohasoutofband(so);
2060                         tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
2061                 }
2062                 /*
2063                  * Remove out of band data so doesn't get presented to user.
2064                  * This can happen independent of advancing the URG pointer,
2065                  * but if two URG's are pending at once, some out-of-band
2066                  * data may creep in... ick.
2067                  */
2068                 if (th->th_urp <= (u_long)tlen
2069 #ifdef SO_OOBINLINE
2070                      && (so->so_options & SO_OOBINLINE) == 0
2071 #endif
2072                      )
2073                         tcp_pulloutofband(so, th, m,
2074                                 drop_hdrlen);   /* hdr drop is delayed */
2075         } else {
2076                 /*
2077                  * If no out of band data is expected,
2078                  * pull receive urgent pointer along
2079                  * with the receive window.
2080                  */
2081                 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
2082                         tp->rcv_up = tp->rcv_nxt;
2083         }
2084 dodata:                                                 /* XXX */
2085
2086         /*
2087          * Process the segment text, merging it into the TCP sequencing queue,
2088          * and arranging for acknowledgment of receipt if necessary.
2089          * This process logically involves adjusting tp->rcv_wnd as data
2090          * is presented to the user (this happens in tcp_usrreq.c,
2091          * case PRU_RCVD).  If a FIN has already been received on this
2092          * connection then we just ignore the text.
2093          */
2094         if ((tlen || (thflags & TH_FIN)) &&
2095             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2096                 m_adj(m, drop_hdrlen);  /* delayed header drop */
2097                 /*
2098                  * Insert segment which includes th into TCP reassembly queue
2099                  * with control block tp.  Set thflags to whether reassembly now
2100                  * includes a segment with FIN.  This handles the common case
2101                  * inline (segment is the next to be received on an established
2102                  * connection, and the queue is empty), avoiding linkage into
2103                  * and removal from the queue and repetition of various
2104                  * conversions.
2105                  * Set DELACK for segments received in order, but ack
2106                  * immediately when segments are out of order (so
2107                  * fast retransmit can work).
2108                  */
2109                 if (th->th_seq == tp->rcv_nxt &&
2110                     LIST_EMPTY(&tp->t_segq) &&
2111                     TCPS_HAVEESTABLISHED(tp->t_state)) {
2112                         if (DELAY_ACK(tp))
2113                                 callout_reset(tp->tt_delack, tcp_delacktime,
2114                                               tcp_timer_delack, tp);
2115                         else
2116                                 tp->t_flags |= TF_ACKNOW;
2117                         tp->rcv_nxt += tlen;
2118                         thflags = th->th_flags & TH_FIN;
2119                         tcpstat.tcps_rcvpack++;
2120                         tcpstat.tcps_rcvbyte += tlen;
2121                         ND6_HINT(tp);
2122                         if (so->so_state & SS_CANTRCVMORE)
2123                                 m_freem(m);
2124                         else
2125                                 sbappend(&so->so_rcv, m);
2126                         sorwakeup(so);
2127                 } else {
2128                         thflags = tcp_reass(tp, th, &tlen, m);
2129                         tp->t_flags |= TF_ACKNOW;
2130                 }
2131
2132                 /*
2133                  * Note the amount of data that peer has sent into
2134                  * our window, in order to estimate the sender's
2135                  * buffer size.
2136                  */
2137                 len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
2138         } else {
2139                 m_freem(m);
2140                 thflags &= ~TH_FIN;
2141         }
2142
2143         /*
2144          * If FIN is received ACK the FIN and let the user know
2145          * that the connection is closing.
2146          */
2147         if (thflags & TH_FIN) {
2148                 if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2149                         socantrcvmore(so);
2150                         /*
2151                          * If connection is half-synchronized
2152                          * (ie NEEDSYN flag on) then delay ACK,
2153                          * so it may be piggybacked when SYN is sent.
2154                          * Otherwise, since we received a FIN then no
2155                          * more input can be expected, send ACK now.
2156                          */
2157                         if (DELAY_ACK(tp) && (tp->t_flags & TF_NEEDSYN))
2158                                 callout_reset(tp->tt_delack, tcp_delacktime,
2159                                     tcp_timer_delack, tp);
2160                         else
2161                                 tp->t_flags |= TF_ACKNOW;
2162                         tp->rcv_nxt++;
2163                 }
2164                 switch (tp->t_state) {
2165
2166                 /*
2167                  * In SYN_RECEIVED and ESTABLISHED STATES
2168                  * enter the CLOSE_WAIT state.
2169                  */
2170                 case TCPS_SYN_RECEIVED:
2171                         tp->t_starttime = ticks;
2172                         /*FALLTHROUGH*/
2173                 case TCPS_ESTABLISHED:
2174                         tp->t_state = TCPS_CLOSE_WAIT;
2175                         break;
2176
2177                 /*
2178                  * If still in FIN_WAIT_1 STATE FIN has not been acked so
2179                  * enter the CLOSING state.
2180                  */
2181                 case TCPS_FIN_WAIT_1:
2182                         tp->t_state = TCPS_CLOSING;
2183                         break;
2184
2185                 /*
2186                  * In FIN_WAIT_2 state enter the TIME_WAIT state,
2187                  * starting the time-wait timer, turning off the other
2188                  * standard timers.
2189                  */
2190                 case TCPS_FIN_WAIT_2:
2191                         tp->t_state = TCPS_TIME_WAIT;
2192                         tcp_canceltimers(tp);
2193                         /* Shorten TIME_WAIT [RFC-1644, p.28] */
2194                         if (tp->cc_recv != 0 &&
2195                             (ticks - tp->t_starttime) < tcp_msl) {
2196                                 callout_reset(tp->tt_2msl,
2197                                               tp->t_rxtcur * TCPTV_TWTRUNC,
2198                                               tcp_timer_2msl, tp);
2199                                 /* For transaction client, force ACK now. */
2200                                 tp->t_flags |= TF_ACKNOW;
2201                         }
2202                         else
2203                                 callout_reset(tp->tt_2msl, 2 * tcp_msl,
2204                                               tcp_timer_2msl, tp);
2205                         soisdisconnected(so);
2206                         break;
2207
2208                 /*
2209                  * In TIME_WAIT state restart the 2 MSL time_wait timer.
2210                  */
2211                 case TCPS_TIME_WAIT:
2212                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
2213                                       tcp_timer_2msl, tp);
2214                         break;
2215                 }
2216         }
2217 #ifdef TCPDEBUG
2218         if (so->so_options & SO_DEBUG)
2219                 tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
2220                           &tcp_savetcp, 0);
2221 #endif
2222
2223         /*
2224          * Return any desired output.
2225          */
2226         if (needoutput || (tp->t_flags & TF_ACKNOW))
2227                 (void) tcp_output(tp);
2228         return;
2229
2230 dropafterack:
2231         /*
2232          * Generate an ACK dropping incoming segment if it occupies
2233          * sequence space, where the ACK reflects our state.
2234          *
2235          * We can now skip the test for the RST flag since all
2236          * paths to this code happen after packets containing
2237          * RST have been dropped.
2238          *
2239          * In the SYN-RECEIVED state, don't send an ACK unless the
2240          * segment we received passes the SYN-RECEIVED ACK test.
2241          * If it fails send a RST.  This breaks the loop in the
2242          * "LAND" DoS attack, and also prevents an ACK storm
2243          * between two listening ports that have been sent forged
2244          * SYN segments, each with the source address of the other.
2245          */
2246         if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
2247             (SEQ_GT(tp->snd_una, th->th_ack) ||
2248              SEQ_GT(th->th_ack, tp->snd_max)) ) {
2249                 rstreason = BANDLIM_RST_OPENPORT;
2250                 goto dropwithreset;
2251         }
2252 #ifdef TCPDEBUG
2253         if (so->so_options & SO_DEBUG)
2254                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2255                           &tcp_savetcp, 0);
2256 #endif
2257         m_freem(m);
2258         tp->t_flags |= TF_ACKNOW;
2259         (void) tcp_output(tp);
2260         return;
2261
2262 dropwithreset:
2263         /*
2264          * Generate a RST, dropping incoming segment.
2265          * Make ACK acceptable to originator of segment.
2266          * Don't bother to respond if destination was broadcast/multicast.
2267          */
2268         if ((thflags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
2269                 goto drop;
2270         if (isipv6) {
2271                 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
2272                     IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
2273                         goto drop;
2274         } else {
2275                 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
2276                     IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
2277                     ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
2278                     in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
2279                         goto drop;
2280         }
2281         /* IPv6 anycast check is done at tcp6_input() */
2282
2283         /*
2284          * Perform bandwidth limiting.
2285          */
2286 #ifdef ICMP_BANDLIM
2287         if (badport_bandlim(rstreason) < 0)
2288                 goto drop;
2289 #endif
2290
2291 #ifdef TCPDEBUG
2292         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2293                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2294                           &tcp_savetcp, 0);
2295 #endif
2296         if (thflags & TH_ACK)
2297                 /* mtod() below is safe as long as hdr dropping is delayed */
2298                 tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0, th->th_ack,
2299                             TH_RST);
2300         else {
2301                 if (thflags & TH_SYN)
2302                         tlen++;
2303                 /* mtod() below is safe as long as hdr dropping is delayed */
2304                 tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
2305                             (tcp_seq)0, TH_RST|TH_ACK);
2306         }
2307         return;
2308
2309 drop:
2310         /*
2311          * Drop space held by incoming segment and return.
2312          */
2313 #ifdef TCPDEBUG
2314         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2315                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2316                           &tcp_savetcp, 0);
2317 #endif
2318         m_freem(m);
2319         return;
2320 }
2321
2322 /*
2323  * Parse TCP options and place in tcpopt.
2324  */
2325 static void
2326 tcp_dooptions(to, cp, cnt, is_syn)
2327         struct tcpopt *to;
2328         u_char *cp;
2329         int cnt;
2330 {
2331         int opt, optlen;
2332
2333         to->to_flags = 0;
2334         for (; cnt > 0; cnt -= optlen, cp += optlen) {
2335                 opt = cp[0];
2336                 if (opt == TCPOPT_EOL)
2337                         break;
2338                 if (opt == TCPOPT_NOP)
2339                         optlen = 1;
2340                 else {
2341                         if (cnt < 2)
2342                                 break;
2343                         optlen = cp[1];
2344                         if (optlen < 2 || optlen > cnt)
2345                                 break;
2346                 }
2347                 switch (opt) {
2348                 case TCPOPT_MAXSEG:
2349                         if (optlen != TCPOLEN_MAXSEG)
2350                                 continue;
2351                         if (!is_syn)
2352                                 continue;
2353                         to->to_flags |= TOF_MSS;
2354                         bcopy((char *)cp + 2,
2355                             (char *)&to->to_mss, sizeof(to->to_mss));
2356                         to->to_mss = ntohs(to->to_mss);
2357                         break;
2358                 case TCPOPT_WINDOW:
2359                         if (optlen != TCPOLEN_WINDOW)
2360                                 continue;
2361                         if (! is_syn)
2362                                 continue;
2363                         to->to_flags |= TOF_SCALE;
2364                         to->to_requested_s_scale = min(cp[2], TCP_MAX_WINSHIFT);
2365                         break;
2366                 case TCPOPT_TIMESTAMP:
2367                         if (optlen != TCPOLEN_TIMESTAMP)
2368                                 continue;
2369                         to->to_flags |= TOF_TS;
2370                         bcopy((char *)cp + 2,
2371                             (char *)&to->to_tsval, sizeof(to->to_tsval));
2372                         to->to_tsval = ntohl(to->to_tsval);
2373                         bcopy((char *)cp + 6,
2374                             (char *)&to->to_tsecr, sizeof(to->to_tsecr));
2375                         to->to_tsecr = ntohl(to->to_tsecr);
2376                         break;
2377                 case TCPOPT_CC:
2378                         if (optlen != TCPOLEN_CC)
2379                                 continue;
2380                         to->to_flags |= TOF_CC;
2381                         bcopy((char *)cp + 2,
2382                             (char *)&to->to_cc, sizeof(to->to_cc));
2383                         to->to_cc = ntohl(to->to_cc);
2384                         break;
2385                 case TCPOPT_CCNEW:
2386                         if (optlen != TCPOLEN_CC)
2387                                 continue;
2388                         if (!is_syn)
2389                                 continue;
2390                         to->to_flags |= TOF_CCNEW;
2391                         bcopy((char *)cp + 2,
2392                             (char *)&to->to_cc, sizeof(to->to_cc));
2393                         to->to_cc = ntohl(to->to_cc);
2394                         break;
2395                 case TCPOPT_CCECHO:
2396                         if (optlen != TCPOLEN_CC)
2397                                 continue;
2398                         if (!is_syn)
2399                                 continue;
2400                         to->to_flags |= TOF_CCECHO;
2401                         bcopy((char *)cp + 2,
2402                             (char *)&to->to_ccecho, sizeof(to->to_ccecho));
2403                         to->to_ccecho = ntohl(to->to_ccecho);
2404                         break;
2405                 default:
2406                         continue;
2407                 }
2408         }
2409 }
2410
2411 /*
2412  * Pull out of band byte out of a segment so
2413  * it doesn't appear in the user's data queue.
2414  * It is still reflected in the segment length for
2415  * sequencing purposes.
2416  */
2417 static void
2418 tcp_pulloutofband(so, th, m, off)
2419         struct socket *so;
2420         struct tcphdr *th;
2421         struct mbuf *m;
2422         int off;                /* delayed to be droped hdrlen */
2423 {
2424         int cnt = off + th->th_urp - 1;
2425
2426         while (cnt >= 0) {
2427                 if (m->m_len > cnt) {
2428                         char *cp = mtod(m, caddr_t) + cnt;
2429                         struct tcpcb *tp = sototcpcb(so);
2430
2431                         tp->t_iobc = *cp;
2432                         tp->t_oobflags |= TCPOOB_HAVEDATA;
2433                         bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
2434                         m->m_len--;
2435                         if (m->m_flags & M_PKTHDR)
2436                                 m->m_pkthdr.len--;
2437                         return;
2438                 }
2439                 cnt -= m->m_len;
2440                 m = m->m_next;
2441                 if (m == 0)
2442                         break;
2443         }
2444         panic("tcp_pulloutofband");
2445 }
2446
2447 /*
2448  * Collect new round-trip time estimate
2449  * and update averages and current timeout.
2450  */
2451 static void
2452 tcp_xmit_timer(tp, rtt)
2453         struct tcpcb *tp;
2454         int rtt;
2455 {
2456         int delta;
2457
2458         tcpstat.tcps_rttupdated++;
2459         tp->t_rttupdated++;
2460         if (tp->t_srtt != 0) {
2461                 /*
2462                  * srtt is stored as fixed point with 5 bits after the
2463                  * binary point (i.e., scaled by 8).  The following magic
2464                  * is equivalent to the smoothing algorithm in rfc793 with
2465                  * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
2466                  * point).  Adjust rtt to origin 0.
2467                  */
2468                 delta = ((rtt - 1) << TCP_DELTA_SHIFT)
2469                         - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
2470
2471                 if ((tp->t_srtt += delta) <= 0)
2472                         tp->t_srtt = 1;
2473
2474                 /*
2475                  * We accumulate a smoothed rtt variance (actually, a
2476                  * smoothed mean difference), then set the retransmit
2477                  * timer to smoothed rtt + 4 times the smoothed variance.
2478                  * rttvar is stored as fixed point with 4 bits after the
2479                  * binary point (scaled by 16).  The following is
2480                  * equivalent to rfc793 smoothing with an alpha of .75
2481                  * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
2482                  * rfc793's wired-in beta.
2483                  */
2484                 if (delta < 0)
2485                         delta = -delta;
2486                 delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
2487                 if ((tp->t_rttvar += delta) <= 0)
2488                         tp->t_rttvar = 1;
2489                 if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
2490                         tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2491         } else {
2492                 /*
2493                  * No rtt measurement yet - use the unsmoothed rtt.
2494                  * Set the variance to half the rtt (so our first
2495                  * retransmit happens at 3*rtt).
2496                  */
2497                 tp->t_srtt = rtt << TCP_RTT_SHIFT;
2498                 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
2499                 tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2500         }
2501         tp->t_rtttime = 0;
2502         tp->t_rxtshift = 0;
2503
2504         /*
2505          * the retransmit should happen at rtt + 4 * rttvar.
2506          * Because of the way we do the smoothing, srtt and rttvar
2507          * will each average +1/2 tick of bias.  When we compute
2508          * the retransmit timer, we want 1/2 tick of rounding and
2509          * 1 extra tick because of +-1/2 tick uncertainty in the
2510          * firing of the timer.  The bias will give us exactly the
2511          * 1.5 tick we need.  But, because the bias is
2512          * statistical, we have to test that we don't drop below
2513          * the minimum feasible timer (which is 2 ticks).
2514          */
2515         TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
2516                       max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
2517
2518         /*
2519          * We received an ack for a packet that wasn't retransmitted;
2520          * it is probably safe to discard any error indications we've
2521          * received recently.  This isn't quite right, but close enough
2522          * for now (a route might have failed after we sent a segment,
2523          * and the return path might not be symmetrical).
2524          */
2525         tp->t_softerror = 0;
2526 }
2527
2528 /*
2529  * Determine a reasonable value for maxseg size.
2530  * If the route is known, check route for mtu.
2531  * If none, use an mss that can be handled on the outgoing
2532  * interface without forcing IP to fragment; if bigger than
2533  * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
2534  * to utilize large mbufs.  If no route is found, route has no mtu,
2535  * or the destination isn't local, use a default, hopefully conservative
2536  * size (usually 512 or the default IP max size, but no more than the mtu
2537  * of the interface), as we can't discover anything about intervening
2538  * gateways or networks.  We also initialize the congestion/slow start
2539  * window to be a single segment if the destination isn't local.
2540  * While looking at the routing entry, we also initialize other path-dependent
2541  * parameters from pre-set or cached values in the routing entry.
2542  *
2543  * Also take into account the space needed for options that we
2544  * send regularly.  Make maxseg shorter by that amount to assure
2545  * that we can send maxseg amount of data even when the options
2546  * are present.  Store the upper limit of the length of options plus
2547  * data in maxopd.
2548  *
2549  * NOTE that this routine is only called when we process an incoming
2550  * segment, for outgoing segments only tcp_mssopt is called.
2551  *
2552  * In case of T/TCP, we call this routine during implicit connection
2553  * setup as well (offer = -1), to initialize maxseg from the cached
2554  * MSS of our peer.
2555  */
2556 void
2557 tcp_mss(tp, offer)
2558         struct tcpcb *tp;
2559         int offer;
2560 {
2561         struct rtentry *rt;
2562         struct ifnet *ifp;
2563         int rtt, mss;
2564         u_long bufsize;
2565         struct inpcb *inp = tp->t_inpcb;
2566         struct socket *so;
2567         struct rmxp_tao *taop;
2568         int origoffer = offer;
2569 #ifdef INET6
2570         int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
2571         size_t min_protoh = isipv6 ?
2572                             sizeof(struct ip6_hdr) + sizeof(struct tcphdr) :
2573                             sizeof(struct tcpiphdr);
2574 #else
2575         const int isipv6 = 0;
2576         const size_t min_protoh = sizeof(struct tcpiphdr);
2577 #endif
2578
2579         if (isipv6)
2580                 rt = tcp_rtlookup6(&inp->inp_inc);
2581         else
2582                 rt = tcp_rtlookup(&inp->inp_inc);
2583         if (rt == NULL) {
2584                 tp->t_maxopd = tp->t_maxseg =
2585                                 isipv6 ? tcp_v6mssdflt : tcp_mssdflt;
2586                 return;
2587         }
2588         ifp = rt->rt_ifp;
2589         so = inp->inp_socket;
2590
2591         taop = rmx_taop(rt->rt_rmx);
2592         /*
2593          * Offer == -1 means that we didn't receive SYN yet,
2594          * use cached value in that case;
2595          */
2596         if (offer == -1)
2597                 offer = taop->tao_mssopt;
2598         /*
2599          * Offer == 0 means that there was no MSS on the SYN segment,
2600          * in this case we use tcp_mssdflt.
2601          */
2602         if (offer == 0)
2603                 offer = isipv6 ? tcp_v6mssdflt : tcp_mssdflt;
2604         else
2605                 /*
2606                  * Sanity check: make sure that maxopd will be large
2607                  * enough to allow some data on segments even is the
2608                  * all the option space is used (40bytes).  Otherwise
2609                  * funny things may happen in tcp_output.
2610                  */
2611                 offer = max(offer, 64);
2612         taop->tao_mssopt = offer;
2613
2614         /*
2615          * While we're here, check if there's an initial rtt
2616          * or rttvar.  Convert from the route-table units
2617          * to scaled multiples of the slow timeout timer.
2618          */
2619         if (tp->t_srtt == 0 && (rtt = rt->rt_rmx.rmx_rtt)) {
2620                 /*
2621                  * XXX the lock bit for RTT indicates that the value
2622                  * is also a minimum value; this is subject to time.
2623                  */
2624                 if (rt->rt_rmx.rmx_locks & RTV_RTT)
2625                         tp->t_rttmin = rtt / (RTM_RTTUNIT / hz);
2626                 tp->t_srtt = rtt / (RTM_RTTUNIT / (hz * TCP_RTT_SCALE));
2627                 tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
2628                 tcpstat.tcps_usedrtt++;
2629                 if (rt->rt_rmx.rmx_rttvar) {
2630                         tp->t_rttvar = rt->rt_rmx.rmx_rttvar /
2631                             (RTM_RTTUNIT / (hz * TCP_RTTVAR_SCALE));
2632                         tcpstat.tcps_usedrttvar++;
2633                 } else {
2634                         /* default variation is +- 1 rtt */
2635                         tp->t_rttvar =
2636                             tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
2637                 }
2638                 TCPT_RANGESET(tp->t_rxtcur,
2639                               ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
2640                               tp->t_rttmin, TCPTV_REXMTMAX);
2641         }
2642         /*
2643          * if there's an mtu associated with the route, use it
2644          * else, use the link mtu.
2645          */
2646         if (rt->rt_rmx.rmx_mtu)
2647                 mss = rt->rt_rmx.rmx_mtu - min_protoh;
2648         else {
2649                 if (isipv6) {
2650                         mss = nd_ifinfo[rt->rt_ifp->if_index].linkmtu -
2651                                 min_protoh;
2652                         if (!in6_localaddr(&inp->in6p_faddr))
2653                                 mss = min(mss, tcp_v6mssdflt);
2654                 } else {
2655                         mss = ifp->if_mtu - min_protoh;
2656                         if (!in_localaddr(inp->inp_faddr))
2657                                 mss = min(mss, tcp_mssdflt);
2658                 }
2659         }
2660         mss = min(mss, offer);
2661         /*
2662          * maxopd stores the maximum length of data AND options
2663          * in a segment; maxseg is the amount of data in a normal
2664          * segment.  We need to store this value (maxopd) apart
2665          * from maxseg, because now every segment carries options
2666          * and thus we normally have somewhat less data in segments.
2667          */
2668         tp->t_maxopd = mss;
2669
2670         /*
2671          * In case of T/TCP, origoffer==-1 indicates, that no segments
2672          * were received yet.  In this case we just guess, otherwise
2673          * we do the same as before T/TCP.
2674          */
2675         if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
2676             (origoffer == -1 ||
2677              (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
2678                 mss -= TCPOLEN_TSTAMP_APPA;
2679         if ((tp->t_flags & (TF_REQ_CC|TF_NOOPT)) == TF_REQ_CC &&
2680             (origoffer == -1 ||
2681              (tp->t_flags & TF_RCVD_CC) == TF_RCVD_CC))
2682                 mss -= TCPOLEN_CC_APPA;
2683
2684 #if     (MCLBYTES & (MCLBYTES - 1)) == 0
2685                 if (mss > MCLBYTES)
2686                         mss &= ~(MCLBYTES-1);
2687 #else
2688                 if (mss > MCLBYTES)
2689                         mss = mss / MCLBYTES * MCLBYTES;
2690 #endif
2691         /*
2692          * If there's a pipesize, change the socket buffer
2693          * to that size.  Make the socket buffers an integral
2694          * number of mss units; if the mss is larger than
2695          * the socket buffer, decrease the mss.
2696          */
2697 #ifdef RTV_SPIPE
2698         if ((bufsize = rt->rt_rmx.rmx_sendpipe) == 0)
2699 #endif
2700                 bufsize = so->so_snd.sb_hiwat;
2701         if (bufsize < mss)
2702                 mss = bufsize;
2703         else {
2704                 bufsize = roundup(bufsize, mss);
2705                 if (bufsize > sb_max)
2706                         bufsize = sb_max;
2707                 if (bufsize > so->so_snd.sb_hiwat)
2708                         (void)sbreserve(&so->so_snd, bufsize, so, NULL);
2709         }
2710         tp->t_maxseg = mss;
2711
2712 #ifdef RTV_RPIPE
2713         if ((bufsize = rt->rt_rmx.rmx_recvpipe) == 0)
2714 #endif
2715                 bufsize = so->so_rcv.sb_hiwat;
2716         if (bufsize > mss) {
2717                 bufsize = roundup(bufsize, mss);
2718                 if (bufsize > sb_max)
2719                         bufsize = sb_max;
2720                 if (bufsize > so->so_rcv.sb_hiwat)
2721                         (void)sbreserve(&so->so_rcv, bufsize, so, NULL);
2722         }
2723
2724         /*
2725          * Set the slow-start flight size depending on whether this
2726          * is a local network or not.
2727          */
2728         if (tcp_do_rfc3390)
2729                 tp->snd_cwnd = min(4 * mss, max(2 * mss, 4380));
2730         else if ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
2731                  (!isipv6 && in_localaddr(inp->inp_faddr)))
2732                 tp->snd_cwnd = mss * ss_fltsz_local;
2733         else
2734                 tp->snd_cwnd = mss * ss_fltsz;
2735
2736         if (rt->rt_rmx.rmx_ssthresh) {
2737                 /*
2738                  * There's some sort of gateway or interface
2739                  * buffer limit on the path.  Use this to set
2740                  * the slow start threshhold, but set the
2741                  * threshold to no less than 2*mss.
2742                  */
2743                 tp->snd_ssthresh = max(2 * mss, rt->rt_rmx.rmx_ssthresh);
2744                 tcpstat.tcps_usedssthresh++;
2745         }
2746 }
2747
2748 /*
2749  * Determine the MSS option to send on an outgoing SYN.
2750  */
2751 int
2752 tcp_mssopt(tp)
2753         struct tcpcb *tp;
2754 {
2755         struct rtentry *rt;
2756 #ifdef INET6
2757         int isipv6 = ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
2758         int min_protoh = isipv6 ?
2759                              sizeof(struct ip6_hdr) + sizeof(struct tcphdr) :
2760                              sizeof(struct tcpiphdr);
2761 #else
2762         const int isipv6 = 0;
2763         const size_t min_protoh = sizeof(struct tcpiphdr);
2764 #endif
2765
2766         if (isipv6)
2767                 rt = tcp_rtlookup6(&tp->t_inpcb->inp_inc);
2768         else
2769                 rt = tcp_rtlookup(&tp->t_inpcb->inp_inc);
2770         if (rt == NULL)
2771                 return (isipv6 ? tcp_v6mssdflt : tcp_mssdflt);
2772
2773         return (rt->rt_ifp->if_mtu - min_protoh);
2774 }
2775
2776
2777 /*
2778  * When a partial ack arrives, force the retransmission of the
2779  * next unacknowledged segment.  Do not clear tp->t_dupacks.
2780  * By setting snd_nxt to ti_ack, this forces retransmission timer to
2781  * be started again.
2782  */
2783 static void
2784 tcp_newreno_partial_ack(tp, th)
2785         struct tcpcb *tp;
2786         struct tcphdr *th;
2787 {
2788         tcp_seq onxt = tp->snd_nxt;
2789         u_long  ocwnd = tp->snd_cwnd;
2790
2791         callout_stop(tp->tt_rexmt);
2792         tp->t_rtttime = 0;
2793         tp->snd_nxt = th->th_ack;
2794         /*
2795          * Set snd_cwnd to one segment beyond acknowledged offset
2796          * (tp->snd_una has not yet been updated when this function is called.)
2797          */
2798         tp->snd_cwnd = tp->t_maxseg + (th->th_ack - tp->snd_una);
2799         tp->t_flags |= TF_ACKNOW;
2800         (void) tcp_output(tp);
2801         tp->snd_cwnd = ocwnd;
2802         if (SEQ_GT(onxt, tp->snd_nxt))
2803                 tp->snd_nxt = onxt;
2804         /*
2805          * Partial window deflation.  Relies on fact that tp->snd_una
2806          * not updated yet.
2807          */
2808         tp->snd_cwnd -= (th->th_ack - tp->snd_una - tp->t_maxseg);
2809 }