sys/netinet/tcp_input.c

   1 /*
   2  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. All advertising materials mentioning features or use of this software
  14  *    must display the following acknowledgement:
  15  *      This product includes software developed by the University of
  16  *      California, Berkeley and its contributors.
  17  * 4. Neither the name of the University nor the names of its contributors
  18  *    may be used to endorse or promote products derived from this software
  19  *    without specific prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  31  * SUCH DAMAGE.
  32  *
  33  *      @(#)tcp_input.c 8.12 (Berkeley) 5/24/95
  34  * $FreeBSD: src/sys/netinet/tcp_input.c,v 1.107.2.38 2003/05/21 04:46:41 cjc Exp $
  35  * $DragonFly: src/sys/netinet/tcp_input.c,v 1.2 2003/06/17 04:28:51 dillon Exp $
  36  */
  37
  38 #include "opt_ipfw.h"           /* for ipfw_fwd         */
  39 #include "opt_inet6.h"
  40 #include "opt_ipsec.h"
  41 #include "opt_tcpdebug.h"
  42 #include "opt_tcp_input.h"
  43
  44 #include <sys/param.h>
  45 #include <sys/systm.h>
  46 #include <sys/kernel.h>
  47 #include <sys/sysctl.h>
  48 #include <sys/malloc.h>
  49 #include <sys/mbuf.h>
  50 #include <sys/proc.h>           /* for proc0 declaration */
  51 #include <sys/protosw.h>
  52 #include <sys/socket.h>
  53 #include <sys/socketvar.h>
  54 #include <sys/syslog.h>
  55
  56 #include <machine/cpu.h>        /* before tcp_seq.h, for tcp_random18() */
  57
  58 #include <net/if.h>
  59 #include <net/route.h>
  60
  61 #include <netinet/in.h>
  62 #include <netinet/in_systm.h>
  63 #include <netinet/ip.h>
  64 #include <netinet/ip_icmp.h>    /* for ICMP_BANDLIM             */
  65 #include <netinet/in_var.h>
  66 #include <netinet/icmp_var.h>   /* for ICMP_BANDLIM             */
  67 #include <netinet/in_pcb.h>
  68 #include <netinet/ip_var.h>
  69 #include <netinet/ip6.h>
  70 #include <netinet/icmp6.h>
  71 #include <netinet6/nd6.h>
  72 #include <netinet6/ip6_var.h>
  73 #include <netinet6/in6_pcb.h>
  74 #include <netinet/tcp.h>
  75 #include <netinet/tcp_fsm.h>
  76 #include <netinet/tcp_seq.h>
  77 #include <netinet/tcp_timer.h>
  78 #include <netinet/tcp_var.h>
  79 #include <netinet6/tcp6_var.h>
  80 #include <netinet/tcpip.h>
  81 #ifdef TCPDEBUG
  82 #include <netinet/tcp_debug.h>
  83
  84 u_char tcp_saveipgen[40]; /* the size must be of max ip header, now IPv6 */
  85 struct tcphdr tcp_savetcp;
  86 #endif /* TCPDEBUG */
  87
  88 #ifdef FAST_IPSEC
  89 #include <netipsec/ipsec.h>
  90 #include <netipsec/ipsec6.h>
  91 #endif
  92
  93 #ifdef IPSEC
  94 #include <netinet6/ipsec.h>
  95 #include <netinet6/ipsec6.h>
  96 #include <netkey/key.h>
  97 #endif /*IPSEC*/
  98
  99 #include <machine/in_cksum.h>
 100
 101 MALLOC_DEFINE(M_TSEGQ, "tseg_qent", "TCP segment queue entry");
 102
 103 static const int tcprexmtthresh = 3;
 104 tcp_cc  tcp_ccgen;
 105
 106 struct  tcpstat tcpstat;
 107 SYSCTL_STRUCT(_net_inet_tcp, TCPCTL_STATS, stats, CTLFLAG_RW,
 108     &tcpstat , tcpstat, "TCP statistics (struct tcpstat, netinet/tcp_var.h)");
 109
 110 static int log_in_vain = 0;
 111 SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW,
 112     &log_in_vain, 0, "Log all incoming TCP connections");
 113
 114 static int blackhole = 0;
 115 SYSCTL_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_RW,
 116     &blackhole, 0, "Do not send RST when dropping refused connections");
 117
 118 int tcp_delack_enabled = 1;
 119 SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_RW,
 120     &tcp_delack_enabled, 0,
 121     "Delay ACK to try and piggyback it onto a data packet");
 122
 123 #ifdef TCP_DROP_SYNFIN
 124 static int drop_synfin = 0;
 125 SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_RW,
 126     &drop_synfin, 0, "Drop TCP packets with SYN+FIN set");
 127 #endif
 128
 129 struct inpcbhead tcb;
 130 #define tcb6    tcb  /* for KAME src sync over BSD*'s */
 131 struct inpcbinfo tcbinfo;
 132
 133 static void      tcp_dooptions(struct tcpopt *, u_char *, int, int);
 134 static void      tcp_pulloutofband(struct socket *,
 135                      struct tcphdr *, struct mbuf *, int);
 136 static int       tcp_reass(struct tcpcb *, struct tcphdr *, int *,
 137                      struct mbuf *);
 138 static void      tcp_xmit_timer(struct tcpcb *, int);
 139 static void      tcp_newreno_partial_ack(struct tcpcb *, struct tcphdr *);
 140
 141 /* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */
 142 #ifdef INET6
 143 #define ND6_HINT(tp) \
 144 do { \
 145         if ((tp) && (tp)->t_inpcb && \
 146             ((tp)->t_inpcb->inp_vflag & INP_IPV6) != 0 && \
 147             (tp)->t_inpcb->in6p_route.ro_rt) \
 148                 nd6_nud_hint((tp)->t_inpcb->in6p_route.ro_rt, NULL, 0); \
 149 } while (0)
 150 #else
 151 #define ND6_HINT(tp)
 152 #endif
 153
 154 /*
 155  * Indicate whether this ack should be delayed.  We can delay the ack if
 156  *      - delayed acks are enabled and
 157  *      - there is no delayed ack timer in progress and
 158  *      - our last ack wasn't a 0-sized window.  We never want to delay
 159  *        the ack that opens up a 0-sized window.
 160  */
 161 #define DELAY_ACK(tp) \
 162         (tcp_delack_enabled && !callout_pending(tp->tt_delack) && \
 163         (tp->t_flags & TF_RXWIN0SENT) == 0)
 164
 165 static int
 166 tcp_reass(tp, th, tlenp, m)
 167         register struct tcpcb *tp;
 168         register struct tcphdr *th;
 169         int *tlenp;
 170         struct mbuf *m;
 171 {
 172         struct tseg_qent *q;
 173         struct tseg_qent *p = NULL;
 174         struct tseg_qent *nq;
 175         struct tseg_qent *te;
 176         struct socket *so = tp->t_inpcb->inp_socket;
 177         int flags;
 178
 179         /*
 180          * Call with th==0 after become established to
 181          * force pre-ESTABLISHED data up to user socket.
 182          */
 183         if (th == 0)
 184                 goto present;
 185
 186         /* Allocate a new queue entry. If we can't, just drop the pkt. XXX */
 187         MALLOC(te, struct tseg_qent *, sizeof(struct tseg_qent), M_TSEGQ,
 188                M_NOWAIT);
 189         if (te == NULL) {
 190                 tcpstat.tcps_rcvmemdrop++;
 191                 m_freem(m);
 192                 return (0);
 193         }
 194
 195         /*
 196          * Find a segment which begins after this one does.
 197          */
 198         LIST_FOREACH(q, &tp->t_segq, tqe_q) {
 199                 if (SEQ_GT(q->tqe_th->th_seq, th->th_seq))
 200                         break;
 201                 p = q;
 202         }
 203
 204         /*
 205          * If there is a preceding segment, it may provide some of
 206          * our data already.  If so, drop the data from the incoming
 207          * segment.  If it provides all of our data, drop us.
 208          */
 209         if (p != NULL) {
 210                 register int i;
 211                 /* conversion to int (in i) handles seq wraparound */
 212                 i = p->tqe_th->th_seq + p->tqe_len - th->th_seq;
 213                 if (i > 0) {
 214                         if (i >= *tlenp) {
 215                                 tcpstat.tcps_rcvduppack++;
 216                                 tcpstat.tcps_rcvdupbyte += *tlenp;
 217                                 m_freem(m);
 218                                 free(te, M_TSEGQ);
 219                                 /*
 220                                  * Try to present any queued data
 221                                  * at the left window edge to the user.
 222                                  * This is needed after the 3-WHS
 223                                  * completes.
 224                                  */
 225                                 goto present;   /* ??? */
 226                         }
 227                         m_adj(m, i);
 228                         *tlenp -= i;
 229                         th->th_seq += i;
 230                 }
 231         }
 232         tcpstat.tcps_rcvoopack++;
 233         tcpstat.tcps_rcvoobyte += *tlenp;
 234
 235         /*
 236          * While we overlap succeeding segments trim them or,
 237          * if they are completely covered, dequeue them.
 238          */
 239         while (q) {
 240                 register int i = (th->th_seq + *tlenp) - q->tqe_th->th_seq;
 241                 if (i <= 0)
 242                         break;
 243                 if (i < q->tqe_len) {
 244                         q->tqe_th->th_seq += i;
 245                         q->tqe_len -= i;
 246                         m_adj(q->tqe_m, i);
 247                         break;
 248                 }
 249
 250                 nq = LIST_NEXT(q, tqe_q);
 251                 LIST_REMOVE(q, tqe_q);
 252                 m_freem(q->tqe_m);
 253                 free(q, M_TSEGQ);
 254                 q = nq;
 255         }
 256
 257         /* Insert the new segment queue entry into place. */
 258         te->tqe_m = m;
 259         te->tqe_th = th;
 260         te->tqe_len = *tlenp;
 261
 262         if (p == NULL) {
 263                 LIST_INSERT_HEAD(&tp->t_segq, te, tqe_q);
 264         } else {
 265                 LIST_INSERT_AFTER(p, te, tqe_q);
 266         }
 267
 268 present:
 269         /*
 270          * Present data to user, advancing rcv_nxt through
 271          * completed sequence space.
 272          */
 273         if (!TCPS_HAVEESTABLISHED(tp->t_state))
 274                 return (0);
 275         q = LIST_FIRST(&tp->t_segq);
 276         if (!q || q->tqe_th->th_seq != tp->rcv_nxt)
 277                 return (0);
 278         do {
 279                 tp->rcv_nxt += q->tqe_len;
 280                 flags = q->tqe_th->th_flags & TH_FIN;
 281                 nq = LIST_NEXT(q, tqe_q);
 282                 LIST_REMOVE(q, tqe_q);
 283                 if (so->so_state & SS_CANTRCVMORE)
 284                         m_freem(q->tqe_m);
 285                 else
 286                         sbappend(&so->so_rcv, q->tqe_m);
 287                 free(q, M_TSEGQ);
 288                 q = nq;
 289         } while (q && q->tqe_th->th_seq == tp->rcv_nxt);
 290         ND6_HINT(tp);
 291         sorwakeup(so);
 292         return (flags);
 293 }
 294
 295 /*
 296  * TCP input routine, follows pages 65-76 of the
 297  * protocol specification dated September, 1981 very closely.
 298  */
 299 #ifdef INET6
 300 int
 301 tcp6_input(mp, offp, proto)
 302         struct mbuf **mp;
 303         int *offp, proto;
 304 {
 305         register struct mbuf *m = *mp;
 306         struct in6_ifaddr *ia6;
 307
 308         IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
 309
 310         /*
 311          * draft-itojun-ipv6-tcp-to-anycast
 312          * better place to put this in?
 313          */
 314         ia6 = ip6_getdstifaddr(m);
 315         if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
 316                 struct ip6_hdr *ip6;
 317
 318                 ip6 = mtod(m, struct ip6_hdr *);
 319                 icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
 320                             (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
 321                 return IPPROTO_DONE;
 322         }
 323
 324         tcp_input(m, *offp, proto);
 325         return IPPROTO_DONE;
 326 }
 327 #endif
 328
 329 void
 330 tcp_input(m, off0, proto)
 331         register struct mbuf *m;
 332         int off0, proto;
 333 {
 334         register struct tcphdr *th;
 335         register struct ip *ip = NULL;
 336         register struct ipovly *ipov;
 337         register struct inpcb *inp = NULL;
 338         u_char *optp = NULL;
 339         int optlen = 0;
 340         int len, tlen, off;
 341         int drop_hdrlen;
 342         register struct tcpcb *tp = NULL;
 343         register int thflags;
 344         struct socket *so = 0;
 345         int todrop, acked, ourfinisacked, needoutput = 0;
 346         u_long tiwin;
 347         struct tcpopt to;               /* options in this segment */
 348         struct rmxp_tao *taop;          /* pointer to our TAO cache entry */
 349         struct rmxp_tao tao_noncached;  /* in case there's no cached entry */
 350         struct sockaddr_in *next_hop = NULL;
 351         int rstreason; /* For badport_bandlim accounting purposes */
 352         struct ip6_hdr *ip6 = NULL;
 353 #ifdef INET6
 354         int isipv6;
 355 #else
 356         const int isipv6 = 0;
 357 #endif
 358 #ifdef TCPDEBUG
 359         short ostate = 0;
 360 #endif
 361
 362         /* Grab info from MT_TAG mbufs prepended to the chain. */
 363         for (;m && m->m_type == MT_TAG; m = m->m_next) {
 364                 if (m->_m_tag_id == PACKET_TAG_IPFORWARD)
 365                         next_hop = (struct sockaddr_in *)m->m_hdr.mh_data;
 366         }
 367 #ifdef INET6
 368         isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
 369 #endif
 370         bzero((char *)&to, sizeof(to));
 371
 372         tcpstat.tcps_rcvtotal++;
 373
 374         if (isipv6) {
 375                 /* IP6_EXTHDR_CHECK() is already done at tcp6_input() */
 376                 ip6 = mtod(m, struct ip6_hdr *);
 377                 tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
 378                 if (in6_cksum(m, IPPROTO_TCP, off0, tlen)) {
 379                         tcpstat.tcps_rcvbadsum++;
 380                         goto drop;
 381                 }
 382                 th = (struct tcphdr *)((caddr_t)ip6 + off0);
 383
 384                 /*
 385                  * Be proactive about unspecified IPv6 address in source.
 386                  * As we use all-zero to indicate unbounded/unconnected pcb,
 387                  * unspecified IPv6 address can be used to confuse us.
 388                  *
 389                  * Note that packets with unspecified IPv6 destination is
 390                  * already dropped in ip6_input.
 391                  */
 392                 if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
 393                         /* XXX stat */
 394                         goto drop;
 395                 }
 396         } else {
 397                 /*
 398                  * Get IP and TCP header together in first mbuf.
 399                  * Note: IP leaves IP header in first mbuf.
 400                  */
 401                 if (off0 > sizeof(struct ip)) {
 402                         ip_stripoptions(m, (struct mbuf *)0);
 403                         off0 = sizeof(struct ip);
 404                 }
 405                 if (m->m_len < sizeof(struct tcpiphdr)) {
 406                         if ((m = m_pullup(m, sizeof(struct tcpiphdr))) == 0) {
 407                                 tcpstat.tcps_rcvshort++;
 408                                 return;
 409                         }
 410                 }
 411                 ip = mtod(m, struct ip *);
 412                 ipov = (struct ipovly *)ip;
 413                 th = (struct tcphdr *)((caddr_t)ip + off0);
 414                 tlen = ip->ip_len;
 415
 416                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
 417                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
 418                                 th->th_sum = m->m_pkthdr.csum_data;
 419                         else
 420                                 th->th_sum = in_pseudo(ip->ip_src.s_addr,
 421                                                 ip->ip_dst.s_addr,
 422                                                 htonl(m->m_pkthdr.csum_data +
 423                                                         ip->ip_len +
 424                                                         IPPROTO_TCP));
 425                         th->th_sum ^= 0xffff;
 426                 } else {
 427                         /*
 428                          * Checksum extended TCP header and data.
 429                          */
 430                         len = sizeof(struct ip) + tlen;
 431                         bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
 432                         ipov->ih_len = (u_short)tlen;
 433                         ipov->ih_len = htons(ipov->ih_len);
 434                         th->th_sum = in_cksum(m, len);
 435                 }
 436                 if (th->th_sum) {
 437                         tcpstat.tcps_rcvbadsum++;
 438                         goto drop;
 439                 }
 440 #ifdef INET6
 441                 /* Re-initialization for later version check */
 442                 ip->ip_v = IPVERSION;
 443 #endif
 444         }
 445
 446         /*
 447          * Check that TCP offset makes sense,
 448          * pull out TCP options and adjust length.              XXX
 449          */
 450         off = th->th_off << 2;
 451         if (off < sizeof(struct tcphdr) || off > tlen) {
 452                 tcpstat.tcps_rcvbadoff++;
 453                 goto drop;
 454         }
 455         tlen -= off;    /* tlen is used instead of ti->ti_len */
 456         if (off > sizeof(struct tcphdr)) {
 457                 if (isipv6) {
 458                         IP6_EXTHDR_CHECK(m, off0, off, );
 459                         ip6 = mtod(m, struct ip6_hdr *);
 460                         th = (struct tcphdr *)((caddr_t)ip6 + off0);
 461                 } else {
 462                         if (m->m_len < sizeof(struct ip) + off) {
 463                                 if ((m = m_pullup(m, sizeof(struct ip) + off))
 464                                                 == 0) {
 465                                         tcpstat.tcps_rcvshort++;
 466                                         return;
 467                                 }
 468                                 ip = mtod(m, struct ip *);
 469                                 ipov = (struct ipovly *)ip;
 470                                 th = (struct tcphdr *)((caddr_t)ip + off0);
 471                         }
 472                 }
 473                 optlen = off - sizeof(struct tcphdr);
 474                 optp = (u_char *)(th + 1);
 475         }
 476         thflags = th->th_flags;
 477
 478 #ifdef TCP_DROP_SYNFIN
 479         /*
 480          * If the drop_synfin option is enabled, drop all packets with
 481          * both the SYN and FIN bits set. This prevents e.g. nmap from
 482          * identifying the TCP/IP stack.
 483          *
 484          * This is a violation of the TCP specification.
 485          */
 486         if (drop_synfin && (thflags & (TH_SYN|TH_FIN)) == (TH_SYN|TH_FIN))
 487                 goto drop;
 488 #endif
 489
 490         /*
 491          * Convert TCP protocol specific fields to host format.
 492          */
 493         th->th_seq = ntohl(th->th_seq);
 494         th->th_ack = ntohl(th->th_ack);
 495         th->th_win = ntohs(th->th_win);
 496         th->th_urp = ntohs(th->th_urp);
 497
 498         /*
 499          * Delay droping TCP, IP headers, IPv6 ext headers, and TCP options,
 500          * until after ip6_savecontrol() is called and before other functions
 501          * which don't want those proto headers.
 502          * Because ip6_savecontrol() is going to parse the mbuf to
 503          * search for data to be passed up to user-land, it wants mbuf
 504          * parameters to be unchanged.
 505          * XXX: the call of ip6_savecontrol() has been obsoleted based on
 506          * latest version of the advanced API (20020110).
 507          */
 508         drop_hdrlen = off0 + off;
 509
 510         /*
 511          * Locate pcb for segment.
 512          */
 513 findpcb:
 514         /* IPFIREWALL_FORWARD section */
 515         if (next_hop != NULL && isipv6 == 0) {  /* IPv6 support is not yet */
 516                 /*
 517                  * Transparently forwarded. Pretend to be the destination.
 518                  * already got one like this?
 519                  */
 520                 inp = in_pcblookup_hash(&tcbinfo, ip->ip_src, th->th_sport,
 521                                         ip->ip_dst, th->th_dport,
 522                                         0, m->m_pkthdr.rcvif);
 523                 if (!inp) {
 524                         /* It's new.  Try find the ambushing socket. */
 525                         inp = in_pcblookup_hash(&tcbinfo,
 526                                                 ip->ip_src, th->th_sport,
 527                                                 next_hop->sin_addr,
 528                                                 next_hop->sin_port ?
 529                                                     ntohs(next_hop->sin_port) :
 530                                                     th->th_dport,
 531                                                 1, m->m_pkthdr.rcvif);
 532                 }
 533         } else {
 534                 if (isipv6)
 535                         inp = in6_pcblookup_hash(&tcbinfo,
 536                                                  &ip6->ip6_src, th->th_sport,
 537                                                  &ip6->ip6_dst, th->th_dport,
 538                                                  1, m->m_pkthdr.rcvif);
 539                 else
 540                         inp = in_pcblookup_hash(&tcbinfo,
 541                                                 ip->ip_src, th->th_sport,
 542                                                 ip->ip_dst, th->th_dport,
 543                                                 1, m->m_pkthdr.rcvif);
 544       }
 545
 546 #ifdef IPSEC
 547         if (isipv6) {
 548                 if (inp != NULL && ipsec6_in_reject_so(m, inp->inp_socket)) {
 549                         ipsec6stat.in_polvio++;
 550                         goto drop;
 551                 }
 552         } else {
 553                 if (inp != NULL && ipsec4_in_reject_so(m, inp->inp_socket)) {
 554                         ipsecstat.in_polvio++;
 555                         goto drop;
 556                 }
 557         }
 558 #endif
 559 #ifdef FAST_IPSEC
 560         if (isipv6) {
 561                 if (inp != NULL && ipsec6_in_reject(m, inp)) {
 562                         goto drop;
 563                 }
 564         } else {
 565                 if (inp != NULL && ipsec4_in_reject(m, inp)) {
 566                         goto drop;
 567                 }
 568         }
 569 #endif
 570
 571         /*
 572          * If the state is CLOSED (i.e., TCB does not exist) then
 573          * all data in the incoming segment is discarded.
 574          * If the TCB exists but is in CLOSED state, it is embryonic,
 575          * but should either do a listen or a connect soon.
 576          */
 577         if (inp == NULL) {
 578                 if (log_in_vain) {
 579 #ifdef INET6
 580                         char dbuf[INET6_ADDRSTRLEN+2], sbuf[INET6_ADDRSTRLEN+2];
 581 #else
 582                         char dbuf[4*sizeof "123"], sbuf[4*sizeof "123"];
 583 #endif
 584                         if (isipv6) {
 585                                 strcpy(dbuf, "[");
 586                                 strcpy(sbuf, "[");
 587                                 strcat(dbuf, ip6_sprintf(&ip6->ip6_dst));
 588                                 strcat(sbuf, ip6_sprintf(&ip6->ip6_src));
 589                                 strcat(dbuf, "]");
 590                                 strcat(sbuf, "]");
 591                         } else {
 592                                 strcpy(dbuf, inet_ntoa(ip->ip_dst));
 593                                 strcpy(sbuf, inet_ntoa(ip->ip_src));
 594                         }
 595                         switch (log_in_vain) {
 596                         case 1:
 597                                 if ((thflags & TH_SYN) == 0)
 598                                         break;
 599                         case 2:
 600                                 log(LOG_INFO,
 601                                     "Connection attempt to TCP %s:%d "
 602                                     "from %s:%d flags:0x%02x\n",
 603                                     dbuf, ntohs(th->th_dport), sbuf,
 604                                     ntohs(th->th_sport), thflags);
 605                                 break;
 606                         default:
 607                                 break;
 608                         }
 609                 }
 610                 if (blackhole) {
 611                         switch (blackhole) {
 612                         case 1:
 613                                 if (thflags & TH_SYN)
 614                                         goto drop;
 615                                 break;
 616                         case 2:
 617                                 goto drop;
 618                         default:
 619                                 goto drop;
 620                         }
 621                 }
 622                 rstreason = BANDLIM_RST_CLOSEDPORT;
 623                 goto dropwithreset;
 624         }
 625         tp = intotcpcb(inp);
 626         if (tp == NULL) {
 627                 rstreason = BANDLIM_RST_CLOSEDPORT;
 628                 goto dropwithreset;
 629         }
 630         if (tp->t_state == TCPS_CLOSED)
 631                 goto drop;
 632
 633         /* Unscale the window into a 32-bit value. */
 634         if ((thflags & TH_SYN) == 0)
 635                 tiwin = th->th_win << tp->snd_scale;
 636         else
 637                 tiwin = th->th_win;
 638
 639         so = inp->inp_socket;
 640         if (so->so_options & (SO_DEBUG|SO_ACCEPTCONN)) {
 641                 struct in_conninfo inc;
 642 #ifdef TCPDEBUG
 643                 if (so->so_options & SO_DEBUG) {
 644                         ostate = tp->t_state;
 645                         if (isipv6)
 646                                 bcopy((char *)ip6, (char *)tcp_saveipgen,
 647                                     sizeof(*ip6));
 648                         else
 649                                 bcopy((char *)ip, (char *)tcp_saveipgen,
 650                                     sizeof(*ip));
 651                         tcp_savetcp = *th;
 652                 }
 653 #endif
 654                 /* skip if this isn't a listen socket */
 655                 if ((so->so_options & SO_ACCEPTCONN) == 0)
 656                         goto after_listen;
 657 #ifdef INET6
 658                 inc.inc_isipv6 = isipv6;
 659 #endif
 660                 if (isipv6) {
 661                         inc.inc6_faddr = ip6->ip6_src;
 662                         inc.inc6_laddr = ip6->ip6_dst;
 663                         inc.inc6_route.ro_rt = NULL;            /* XXX */
 664                 } else {
 665                         inc.inc_faddr = ip->ip_src;
 666                         inc.inc_laddr = ip->ip_dst;
 667                         inc.inc_route.ro_rt = NULL;             /* XXX */
 668                 }
 669                 inc.inc_fport = th->th_sport;
 670                 inc.inc_lport = th->th_dport;
 671
 672                 /*
 673                  * If the state is LISTEN then ignore segment if it contains
 674                  * a RST.  If the segment contains an ACK then it is bad and
 675                  * send a RST.  If it does not contain a SYN then it is not
 676                  * interesting; drop it.
 677                  *
 678                  * If the state is SYN_RECEIVED (syncache) and seg contains
 679                  * an ACK, but not for our SYN/ACK, send a RST.  If the seg
 680                  * contains a RST, check the sequence number to see if it
 681                  * is a valid reset segment.
 682                  */
 683                 if ((thflags & (TH_RST|TH_ACK|TH_SYN)) != TH_SYN) {
 684                         if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
 685                                 if (!syncache_expand(&inc, th, &so, m)) {
 686                                         /*
 687                                          * No syncache entry, or ACK was not
 688                                          * for our SYN/ACK.  Send a RST.
 689                                          */
 690                                         tcpstat.tcps_badsyn++;
 691                                         rstreason = BANDLIM_RST_OPENPORT;
 692                                         goto dropwithreset;
 693                                 }
 694                                 if (so == NULL)
 695                                         /*
 696                                          * Could not complete 3-way handshake,
 697                                          * connection is being closed down, and
 698                                          * syncache will free mbuf.
 699                                          */
 700                                         return;
 701                                 /*
 702                                  * Socket is created in state SYN_RECEIVED.
 703                                  * Continue processing segment.
 704                                  */
 705                                 inp = sotoinpcb(so);
 706                                 tp = intotcpcb(inp);
 707                                 /*
 708                                  * This is what would have happened in
 709                                  * tcp_output() when the SYN,ACK was sent.
 710                                  */
 711                                 tp->snd_up = tp->snd_una;
 712                                 tp->snd_max = tp->snd_nxt = tp->iss + 1;
 713                                 tp->last_ack_sent = tp->rcv_nxt;
 714 /*
 715  * XXX possible bug - it doesn't appear that tp->snd_wnd is unscaled
 716  * until the _second_ ACK is received:
 717  *    rcv SYN (set wscale opts)  --> send SYN/ACK, set snd_wnd = window.
 718  *    rcv ACK, calculate tiwin --> process SYN_RECEIVED, determine wscale,
 719  *        move to ESTAB, set snd_wnd to tiwin.
 720  */
 721                                 tp->snd_wnd = tiwin;    /* unscaled */
 722                                 goto after_listen;
 723                         }
 724                         if (thflags & TH_RST) {
 725                                 syncache_chkrst(&inc, th);
 726                                 goto drop;
 727                         }
 728                         if (thflags & TH_ACK) {
 729                                 syncache_badack(&inc);
 730                                 tcpstat.tcps_badsyn++;
 731                                 rstreason = BANDLIM_RST_OPENPORT;
 732                                 goto dropwithreset;
 733                         }
 734                         goto drop;
 735                 }
 736
 737                 /*
 738                  * Segment's flags are (SYN) or (SYN|FIN).
 739                  */
 740 #ifdef INET6
 741                 /*
 742                  * If deprecated address is forbidden,
 743                  * we do not accept SYN to deprecated interface
 744                  * address to prevent any new inbound connection from
 745                  * getting established.
 746                  * When we do not accept SYN, we send a TCP RST,
 747                  * with deprecated source address (instead of dropping
 748                  * it).  We compromise it as it is much better for peer
 749                  * to send a RST, and RST will be the final packet
 750                  * for the exchange.
 751                  *
 752                  * If we do not forbid deprecated addresses, we accept
 753                  * the SYN packet.  RFC2462 does not suggest dropping
 754                  * SYN in this case.
 755                  * If we decipher RFC2462 5.5.4, it says like this:
 756                  * 1. use of deprecated addr with existing
 757                  *    communication is okay - "SHOULD continue to be
 758                  *    used"
 759                  * 2. use of it with new communication:
 760                  *   (2a) "SHOULD NOT be used if alternate address
 761                  *        with sufficient scope is available"
 762                  *   (2b) nothing mentioned otherwise.
 763                  * Here we fall into (2b) case as we have no choice in
 764                  * our source address selection - we must obey the peer.
 765                  *
 766                  * The wording in RFC2462 is confusing, and there are
 767                  * multiple description text for deprecated address
 768                  * handling - worse, they are not exactly the same.
 769                  * I believe 5.5.4 is the best one, so we follow 5.5.4.
 770                  */
 771                 if (isipv6 && !ip6_use_deprecated) {
 772                         struct in6_ifaddr *ia6;
 773
 774                         if ((ia6 = ip6_getdstifaddr(m)) &&
 775                             (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
 776                                 tp = NULL;
 777                                 rstreason = BANDLIM_RST_OPENPORT;
 778                                 goto dropwithreset;
 779                         }
 780                 }
 781 #endif
 782                 /*
 783                  * If it is from this socket, drop it, it must be forged.
 784                  * Don't bother responding if the destination was a broadcast.
 785                  */
 786                 if (th->th_dport == th->th_sport) {
 787                         if (isipv6) {
 788                                 if (IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst,
 789                                                        &ip6->ip6_src))
 790                                         goto drop;
 791                         } else {
 792                                 if (ip->ip_dst.s_addr == ip->ip_src.s_addr)
 793                                         goto drop;
 794                         }
 795                 }
 796                 /*
 797                  * RFC1122 4.2.3.10, p. 104: discard bcast/mcast SYN
 798                  *
 799                  * Note that it is quite possible to receive unicast
 800                  * link-layer packets with a broadcast IP address. Use
 801                  * in_broadcast() to find them.
 802                  */
 803                 if (m->m_flags & (M_BCAST|M_MCAST))
 804                         goto drop;
 805                 if (isipv6) {
 806                         if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
 807                             IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
 808                                 goto drop;
 809                 } else {
 810                         if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
 811                             IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
 812                             ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
 813                             in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
 814                                 goto drop;
 815                 }
 816                 /*
 817                  * SYN appears to be valid; create compressed TCP state
 818                  * for syncache, or perform t/tcp connection.
 819                  */
 820                 if (so->so_qlen <= so->so_qlimit) {
 821                         tcp_dooptions(&to, optp, optlen, 1);
 822                         if (!syncache_add(&inc, &to, th, &so, m))
 823                                 goto drop;
 824                         if (so == NULL)
 825                                 /*
 826                                  * Entry added to syncache, mbuf used to
 827                                  * send SYN,ACK packet.
 828                                  */
 829                                 return;
 830                         /*
 831                          * Segment passed TAO tests.
 832                          */
 833                         inp = sotoinpcb(so);
 834                         tp = intotcpcb(inp);
 835                         tp->snd_wnd = tiwin;
 836                         tp->t_starttime = ticks;
 837                         tp->t_state = TCPS_ESTABLISHED;
 838
 839                         /*
 840                          * If there is a FIN, or if there is data and the
 841                          * connection is local, then delay SYN,ACK(SYN) in
 842                          * the hope of piggy-backing it on a response
 843                          * segment.  Otherwise must send ACK now in case
 844                          * the other side is slow starting.
 845                          */
 846                         if (DELAY_ACK(tp) &&
 847                             ((thflags & TH_FIN) ||
 848                              (tlen != 0 &&
 849                               ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
 850                                (!isipv6 && in_localaddr(inp->inp_faddr)))))) {
 851                                 callout_reset(tp->tt_delack, tcp_delacktime,
 852                                                 tcp_timer_delack, tp);
 853                                 tp->t_flags |= TF_NEEDSYN;
 854                         } else
 855                                 tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
 856
 857                         tcpstat.tcps_connects++;
 858                         soisconnected(so);
 859                         goto trimthenstep6;
 860                 }
 861                 goto drop;
 862         }
 863 after_listen:
 864
 865 /* XXX temp debugging */
 866         /* should not happen - syncache should pick up these connections */
 867         if (tp->t_state == TCPS_LISTEN)
 868                 panic("tcp_input: TCPS_LISTEN");
 869
 870         /*
 871          * Segment received on connection.
 872          * Reset idle time and keep-alive timer.
 873          */
 874         tp->t_rcvtime = ticks;
 875         if (TCPS_HAVEESTABLISHED(tp->t_state))
 876                 callout_reset(tp->tt_keep, tcp_keepidle, tcp_timer_keep, tp);
 877
 878         /*
 879          * Process options.
 880          * XXX this is tradtitional behavior, may need to be cleaned up.
 881          */
 882         tcp_dooptions(&to, optp, optlen, thflags & TH_SYN);
 883         if (thflags & TH_SYN) {
 884                 if (to.to_flags & TOF_SCALE) {
 885                         tp->t_flags |= TF_RCVD_SCALE;
 886                         tp->requested_s_scale = to.to_requested_s_scale;
 887                 }
 888                 if (to.to_flags & TOF_TS) {
 889                         tp->t_flags |= TF_RCVD_TSTMP;
 890                         tp->ts_recent = to.to_tsval;
 891                         tp->ts_recent_age = ticks;
 892                 }
 893                 if (to.to_flags & (TOF_CC|TOF_CCNEW))
 894                         tp->t_flags |= TF_RCVD_CC;
 895                 if (to.to_flags & TOF_MSS)
 896                         tcp_mss(tp, to.to_mss);
 897         }
 898
 899         /*
 900          * Header prediction: check for the two common cases
 901          * of a uni-directional data xfer.  If the packet has
 902          * no control flags, is in-sequence, the window didn't
 903          * change and we're not retransmitting, it's a
 904          * candidate.  If the length is zero and the ack moved
 905          * forward, we're the sender side of the xfer.  Just
 906          * free the data acked & wake any higher level process
 907          * that was blocked waiting for space.  If the length
 908          * is non-zero and the ack didn't move, we're the
 909          * receiver side.  If we're getting packets in-order
 910          * (the reassembly queue is empty), add the data to
 911          * the socket buffer and note that we need a delayed ack.
 912          * Make sure that the hidden state-flags are also off.
 913          * Since we check for TCPS_ESTABLISHED above, it can only
 914          * be TH_NEEDSYN.
 915          */
 916         if (tp->t_state == TCPS_ESTABLISHED &&
 917             (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
 918             ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
 919             ((to.to_flags & TOF_TS) == 0 ||
 920              TSTMP_GEQ(to.to_tsval, tp->ts_recent)) &&
 921             /*
 922              * Using the CC option is compulsory if once started:
 923              *   the segment is OK if no T/TCP was negotiated or
 924              *   if the segment has a CC option equal to CCrecv
 925              */
 926             ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) != (TF_REQ_CC|TF_RCVD_CC) ||
 927              ((to.to_flags & TOF_CC) != 0 && to.to_cc == tp->cc_recv)) &&
 928             th->th_seq == tp->rcv_nxt &&
 929             tiwin && tiwin == tp->snd_wnd &&
 930             tp->snd_nxt == tp->snd_max) {
 931
 932                 /*
 933                  * If last ACK falls within this segment's sequence numbers,
 934                  * record the timestamp.
 935                  * NOTE that the test is modified according to the latest
 936                  * proposal of the tcplw@cray.com list (Braden 1993/04/26).
 937                  */
 938                 if ((to.to_flags & TOF_TS) != 0 &&
 939                     SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
 940                         tp->ts_recent_age = ticks;
 941                         tp->ts_recent = to.to_tsval;
 942                 }
 943
 944                 if (tlen == 0) {
 945                         if (SEQ_GT(th->th_ack, tp->snd_una) &&
 946                             SEQ_LEQ(th->th_ack, tp->snd_max) &&
 947                             tp->snd_cwnd >= tp->snd_wnd &&
 948                             ((!tcp_do_newreno &&
 949                                tp->t_dupacks < tcprexmtthresh) ||
 950                              (tcp_do_newreno &&
 951                               !SEQ_LT(tp->snd_una, tp->snd_recover)))) {
 952                                 /*
 953                                  * this is a pure ack for outstanding data.
 954                                  */
 955                                 ++tcpstat.tcps_predack;
 956                                 /*
 957                                  * "bad retransmit" recovery
 958                                  */
 959                                 if (tp->t_rxtshift == 1 &&
 960                                     ticks < tp->t_badrxtwin) {
 961                                         tp->snd_cwnd = tp->snd_cwnd_prev;
 962                                         tp->snd_ssthresh =
 963                                             tp->snd_ssthresh_prev;
 964                                         tp->snd_high = tp->snd_high_prev;
 965                                         tp->snd_nxt = tp->snd_max;
 966                                         tp->t_badrxtwin = 0;
 967                                 }
 968                                 /*
 969                                  * Recalculate the retransmit timer / rtt.
 970                                  *
 971                                  * Some machines (certain windows boxes)
 972                                  * send broken timestamp replies during the
 973                                  * SYN+ACK phase, ignore timestamps of 0.
 974                                  */
 975                                 if ((to.to_flags & TOF_TS) != 0 &&
 976                                     to.to_tsecr) {
 977                                         tcp_xmit_timer(tp,
 978                                             ticks - to.to_tsecr + 1);
 979                                 } else if (tp->t_rtttime &&
 980                                             SEQ_GT(th->th_ack, tp->t_rtseq)) {
 981                                         tcp_xmit_timer(tp,
 982                                                        ticks - tp->t_rtttime);
 983                                 }
 984                                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
 985                                 acked = th->th_ack - tp->snd_una;
 986                                 tcpstat.tcps_rcvackpack++;
 987                                 tcpstat.tcps_rcvackbyte += acked;
 988                                 sbdrop(&so->so_snd, acked);
 989                                 if (SEQ_GT(tp->snd_una, tp->snd_high) &&
 990                                     SEQ_LEQ(th->th_ack, tp->snd_high))
 991                                         tp->snd_high = th->th_ack - 1;
 992                                 tp->snd_una = tp->snd_recover = th->th_ack;
 993                                 tp->t_dupacks = 0;
 994                                 m_freem(m);
 995                                 ND6_HINT(tp); /* some progress has been done */
 996
 997                                 /*
 998                                  * If all outstanding data are acked, stop
 999                                  * retransmit timer, otherwise restart timer
1000                                  * using current (possibly backed-off) value.
1001                                  * If process is waiting for space,
1002                                  * wakeup/selwakeup/signal.  If data
1003                                  * are ready to send, let tcp_output
1004                                  * decide between more output or persist.
1005                                  */
1006                                 if (tp->snd_una == tp->snd_max)
1007                                         callout_stop(tp->tt_rexmt);
1008                                 else if (!callout_active(tp->tt_persist))
1009                                         callout_reset(tp->tt_rexmt,
1010                                                       tp->t_rxtcur,
1011                                                       tcp_timer_rexmt, tp);
1012
1013                                 sowwakeup(so);
1014                                 if (so->so_snd.sb_cc)
1015                                         (void) tcp_output(tp);
1016                                 return;
1017                         }
1018                 } else if (th->th_ack == tp->snd_una &&
1019                     LIST_EMPTY(&tp->t_segq) &&
1020                     tlen <= sbspace(&so->so_rcv)) {
1021                         /*
1022                          * this is a pure, in-sequence data packet
1023                          * with nothing on the reassembly queue and
1024                          * we have enough buffer space to take it.
1025                          */
1026                         ++tcpstat.tcps_preddat;
1027                         tp->rcv_nxt += tlen;
1028                         tcpstat.tcps_rcvpack++;
1029                         tcpstat.tcps_rcvbyte += tlen;
1030                         ND6_HINT(tp);   /* some progress has been done */
1031                         /*
1032                          * Add data to socket buffer.
1033                          */
1034                         if (so->so_state & SS_CANTRCVMORE) {
1035                                 m_freem(m);
1036                         } else {
1037                                 m_adj(m, drop_hdrlen);  /* delayed header drop */
1038                                 sbappend(&so->so_rcv, m);
1039                         }
1040                         sorwakeup(so);
1041                         if (DELAY_ACK(tp)) {
1042                                 callout_reset(tp->tt_delack, tcp_delacktime,
1043                                     tcp_timer_delack, tp);
1044                         } else {
1045                                 tp->t_flags |= TF_ACKNOW;
1046                                 tcp_output(tp);
1047                         }
1048                         return;
1049                 }
1050         }
1051
1052         /*
1053          * Calculate amount of space in receive window,
1054          * and then do TCP input processing.
1055          * Receive window is amount of space in rcv queue,
1056          * but not less than advertised window.
1057          */
1058         { int win;
1059
1060         win = sbspace(&so->so_rcv);
1061         if (win < 0)
1062                 win = 0;
1063         tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
1064         }
1065
1066         switch (tp->t_state) {
1067
1068         /*
1069          * If the state is SYN_RECEIVED:
1070          *      if seg contains an ACK, but not for our SYN/ACK, send a RST.
1071          */
1072         case TCPS_SYN_RECEIVED:
1073                 if ((thflags & TH_ACK) &&
1074                     (SEQ_LEQ(th->th_ack, tp->snd_una) ||
1075                      SEQ_GT(th->th_ack, tp->snd_max))) {
1076                                 rstreason = BANDLIM_RST_OPENPORT;
1077                                 goto dropwithreset;
1078                 }
1079                 break;
1080
1081         /*
1082          * If the state is SYN_SENT:
1083          *      if seg contains an ACK, but not for our SYN, drop the input.
1084          *      if seg contains a RST, then drop the connection.
1085          *      if seg does not contain SYN, then drop it.
1086          * Otherwise this is an acceptable SYN segment
1087          *      initialize tp->rcv_nxt and tp->irs
1088          *      if seg contains ack then advance tp->snd_una
1089          *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
1090          *      arrange for segment to be acked (eventually)
1091          *      continue processing rest of data/controls, beginning with URG
1092          */
1093         case TCPS_SYN_SENT:
1094                 if ((taop = tcp_gettaocache(&inp->inp_inc)) == NULL) {
1095                         taop = &tao_noncached;
1096                         bzero(taop, sizeof(*taop));
1097                 }
1098
1099                 if ((thflags & TH_ACK) &&
1100                     (SEQ_LEQ(th->th_ack, tp->iss) ||
1101                      SEQ_GT(th->th_ack, tp->snd_max))) {
1102                         /*
1103                          * If we have a cached CCsent for the remote host,
1104                          * hence we haven't just crashed and restarted,
1105                          * do not send a RST.  This may be a retransmission
1106                          * from the other side after our earlier ACK was lost.
1107                          * Our new SYN, when it arrives, will serve as the
1108                          * needed ACK.
1109                          */
1110                         if (taop->tao_ccsent != 0)
1111                                 goto drop;
1112                         else {
1113                                 rstreason = BANDLIM_UNLIMITED;
1114                                 goto dropwithreset;
1115                         }
1116                 }
1117                 if (thflags & TH_RST) {
1118                         if (thflags & TH_ACK)
1119                                 tp = tcp_drop(tp, ECONNREFUSED);
1120                         goto drop;
1121                 }
1122                 if ((thflags & TH_SYN) == 0)
1123                         goto drop;
1124                 tp->snd_wnd = th->th_win;       /* initial send window */
1125                 tp->cc_recv = to.to_cc;         /* foreign CC */
1126
1127                 tp->irs = th->th_seq;
1128                 tcp_rcvseqinit(tp);
1129                 if (thflags & TH_ACK) {
1130                         /*
1131                          * Our SYN was acked.  If segment contains CC.ECHO
1132                          * option, check it to make sure this segment really
1133                          * matches our SYN.  If not, just drop it as old
1134                          * duplicate, but send an RST if we're still playing
1135                          * by the old rules.  If no CC.ECHO option, make sure
1136                          * we don't get fooled into using T/TCP.
1137                          */
1138                         if (to.to_flags & TOF_CCECHO) {
1139                                 if (tp->cc_send != to.to_ccecho) {
1140                                         if (taop->tao_ccsent != 0)
1141                                                 goto drop;
1142                                         else {
1143                                                 rstreason = BANDLIM_UNLIMITED;
1144                                                 goto dropwithreset;
1145                                         }
1146                                 }
1147                         } else
1148                                 tp->t_flags &= ~TF_RCVD_CC;
1149                         tcpstat.tcps_connects++;
1150                         soisconnected(so);
1151                         /* Do window scaling on this connection? */
1152                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1153                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1154                                 tp->snd_scale = tp->requested_s_scale;
1155                                 tp->rcv_scale = tp->request_r_scale;
1156                         }
1157                         /* Segment is acceptable, update cache if undefined. */
1158                         if (taop->tao_ccsent == 0)
1159                                 taop->tao_ccsent = to.to_ccecho;
1160
1161                         tp->rcv_adv += tp->rcv_wnd;
1162                         tp->snd_una++;          /* SYN is acked */
1163                         /*
1164                          * If there's data, delay ACK; if there's also a FIN
1165                          * ACKNOW will be turned on later.
1166                          */
1167                         if (DELAY_ACK(tp) && tlen != 0)
1168                                 callout_reset(tp->tt_delack, tcp_delacktime,
1169                                     tcp_timer_delack, tp);
1170                         else
1171                                 tp->t_flags |= TF_ACKNOW;
1172                         /*
1173                          * Received <SYN,ACK> in SYN_SENT[*] state.
1174                          * Transitions:
1175                          *      SYN_SENT  --> ESTABLISHED
1176                          *      SYN_SENT* --> FIN_WAIT_1
1177                          */
1178                         tp->t_starttime = ticks;
1179                         if (tp->t_flags & TF_NEEDFIN) {
1180                                 tp->t_state = TCPS_FIN_WAIT_1;
1181                                 tp->t_flags &= ~TF_NEEDFIN;
1182                                 thflags &= ~TH_SYN;
1183                         } else {
1184                                 tp->t_state = TCPS_ESTABLISHED;
1185                                 callout_reset(tp->tt_keep, tcp_keepidle,
1186                                               tcp_timer_keep, tp);
1187                         }
1188                 } else {
1189                         /*
1190                          * Received initial SYN in SYN-SENT[*] state =>
1191                          * simultaneous open.  If segment contains CC option
1192                          * and there is a cached CC, apply TAO test.
1193                          * If it succeeds, connection is * half-synchronized.
1194                          * Otherwise, do 3-way handshake:
1195                          *        SYN-SENT -> SYN-RECEIVED
1196                          *        SYN-SENT* -> SYN-RECEIVED*
1197                          * If there was no CC option, clear cached CC value.
1198                          */
1199                         tp->t_flags |= TF_ACKNOW;
1200                         callout_stop(tp->tt_rexmt);
1201                         if (to.to_flags & TOF_CC) {
1202                                 if (taop->tao_cc != 0 &&
1203                                     CC_GT(to.to_cc, taop->tao_cc)) {
1204                                         /*
1205                                          * update cache and make transition:
1206                                          *        SYN-SENT -> ESTABLISHED*
1207                                          *        SYN-SENT* -> FIN-WAIT-1*
1208                                          */
1209                                         taop->tao_cc = to.to_cc;
1210                                         tp->t_starttime = ticks;
1211                                         if (tp->t_flags & TF_NEEDFIN) {
1212                                                 tp->t_state = TCPS_FIN_WAIT_1;
1213                                                 tp->t_flags &= ~TF_NEEDFIN;
1214                                         } else {
1215                                                 tp->t_state = TCPS_ESTABLISHED;
1216                                                 callout_reset(tp->tt_keep,
1217                                                               tcp_keepidle,
1218                                                               tcp_timer_keep,
1219                                                               tp);
1220                                         }
1221                                         tp->t_flags |= TF_NEEDSYN;
1222                                 } else
1223                                         tp->t_state = TCPS_SYN_RECEIVED;
1224                         } else {
1225                                 /* CC.NEW or no option => invalidate cache */
1226                                 taop->tao_cc = 0;
1227                                 tp->t_state = TCPS_SYN_RECEIVED;
1228                         }
1229                 }
1230
1231 trimthenstep6:
1232                 /*
1233                  * Advance th->th_seq to correspond to first data byte.
1234                  * If data, trim to stay within window,
1235                  * dropping FIN if necessary.
1236                  */
1237                 th->th_seq++;
1238                 if (tlen > tp->rcv_wnd) {
1239                         todrop = tlen - tp->rcv_wnd;
1240                         m_adj(m, -todrop);
1241                         tlen = tp->rcv_wnd;
1242                         thflags &= ~TH_FIN;
1243                         tcpstat.tcps_rcvpackafterwin++;
1244                         tcpstat.tcps_rcvbyteafterwin += todrop;
1245                 }
1246                 tp->snd_wl1 = th->th_seq - 1;
1247                 tp->rcv_up = th->th_seq;
1248                 /*
1249                  * Client side of transaction: already sent SYN and data.
1250                  * If the remote host used T/TCP to validate the SYN,
1251                  * our data will be ACK'd; if so, enter normal data segment
1252                  * processing in the middle of step 5, ack processing.
1253                  * Otherwise, goto step 6.
1254                  */
1255                 if (thflags & TH_ACK)
1256                         goto process_ACK;
1257
1258                 goto step6;
1259
1260         /*
1261          * If the state is LAST_ACK or CLOSING or TIME_WAIT:
1262          *      if segment contains a SYN and CC [not CC.NEW] option:
1263          *              if state == TIME_WAIT and connection duration > MSL,
1264          *                  drop packet and send RST;
1265          *
1266          *              if SEG.CC > CCrecv then is new SYN, and can implicitly
1267          *                  ack the FIN (and data) in retransmission queue.
1268          *                  Complete close and delete TCPCB.  Then reprocess
1269          *                  segment, hoping to find new TCPCB in LISTEN state;
1270          *
1271          *              else must be old SYN; drop it.
1272          *      else do normal processing.
1273          */
1274         case TCPS_LAST_ACK:
1275         case TCPS_CLOSING:
1276         case TCPS_TIME_WAIT:
1277                 if ((thflags & TH_SYN) &&
1278                     (to.to_flags & TOF_CC) && tp->cc_recv != 0) {
1279                         if (tp->t_state == TCPS_TIME_WAIT &&
1280                                         (ticks - tp->t_starttime) > tcp_msl) {
1281                                 rstreason = BANDLIM_UNLIMITED;
1282                                 goto dropwithreset;
1283                         }
1284                         if (CC_GT(to.to_cc, tp->cc_recv)) {
1285                                 tp = tcp_close(tp);
1286                                 goto findpcb;
1287                         }
1288                         else
1289                                 goto drop;
1290                 }
1291                 break;  /* continue normal processing */
1292         }
1293
1294         /*
1295          * States other than LISTEN or SYN_SENT.
1296          * First check the RST flag and sequence number since reset segments
1297          * are exempt from the timestamp and connection count tests.  This
1298          * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
1299          * below which allowed reset segments in half the sequence space
1300          * to fall though and be processed (which gives forged reset
1301          * segments with a random sequence number a 50 percent chance of
1302          * killing a connection).
1303          * Then check timestamp, if present.
1304          * Then check the connection count, if present.
1305          * Then check that at least some bytes of segment are within
1306          * receive window.  If segment begins before rcv_nxt,
1307          * drop leading data (and SYN); if nothing left, just ack.
1308          *
1309          *
1310          * If the RST bit is set, check the sequence number to see
1311          * if this is a valid reset segment.
1312          * RFC 793 page 37:
1313          *   In all states except SYN-SENT, all reset (RST) segments
1314          *   are validated by checking their SEQ-fields.  A reset is
1315          *   valid if its sequence number is in the window.
1316          * Note: this does not take into account delayed ACKs, so
1317          *   we should test against last_ack_sent instead of rcv_nxt.
1318          *   The sequence number in the reset segment is normally an
1319          *   echo of our outgoing acknowlegement numbers, but some hosts
1320          *   send a reset with the sequence number at the rightmost edge
1321          *   of our receive window, and we have to handle this case.
1322          * If we have multiple segments in flight, the intial reset
1323          * segment sequence numbers will be to the left of last_ack_sent,
1324          * but they will eventually catch up.
1325          * In any case, it never made sense to trim reset segments to
1326          * fit the receive window since RFC 1122 says:
1327          *   4.2.2.12  RST Segment: RFC-793 Section 3.4
1328          *
1329          *    A TCP SHOULD allow a received RST segment to include data.
1330          *
1331          *    DISCUSSION
1332          *         It has been suggested that a RST segment could contain
1333          *         ASCII text that encoded and explained the cause of the
1334          *         RST.  No standard has yet been established for such
1335          *         data.
1336          *
1337          * If the reset segment passes the sequence number test examine
1338          * the state:
1339          *    SYN_RECEIVED STATE:
1340          *      If passive open, return to LISTEN state.
1341          *      If active open, inform user that connection was refused.
1342          *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, CLOSE_WAIT STATES:
1343          *      Inform user that connection was reset, and close tcb.
1344          *    CLOSING, LAST_ACK STATES:
1345          *      Close the tcb.
1346          *    TIME_WAIT STATE:
1347          *      Drop the segment - see Stevens, vol. 2, p. 964 and
1348          *      RFC 1337.
1349          */
1350         if (thflags & TH_RST) {
1351                 if (SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
1352                     SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
1353                         switch (tp->t_state) {
1354
1355                         case TCPS_SYN_RECEIVED:
1356                                 so->so_error = ECONNREFUSED;
1357                                 goto close;
1358
1359                         case TCPS_ESTABLISHED:
1360                         case TCPS_FIN_WAIT_1:
1361                         case TCPS_FIN_WAIT_2:
1362                         case TCPS_CLOSE_WAIT:
1363                                 so->so_error = ECONNRESET;
1364                         close:
1365                                 tp->t_state = TCPS_CLOSED;
1366                                 tcpstat.tcps_drops++;
1367                                 tp = tcp_close(tp);
1368                                 break;
1369
1370                         case TCPS_CLOSING:
1371                         case TCPS_LAST_ACK:
1372                                 tp = tcp_close(tp);
1373                                 break;
1374
1375                         case TCPS_TIME_WAIT:
1376                                 break;
1377                         }
1378                 }
1379                 goto drop;
1380         }
1381
1382         /*
1383          * RFC 1323 PAWS: If we have a timestamp reply on this segment
1384          * and it's less than ts_recent, drop it.
1385          */
1386         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
1387             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
1388
1389                 /* Check to see if ts_recent is over 24 days old.  */
1390                 if ((int)(ticks - tp->ts_recent_age) > TCP_PAWS_IDLE) {
1391                         /*
1392                          * Invalidate ts_recent.  If this segment updates
1393                          * ts_recent, the age will be reset later and ts_recent
1394                          * will get a valid value.  If it does not, setting
1395                          * ts_recent to zero will at least satisfy the
1396                          * requirement that zero be placed in the timestamp
1397                          * echo reply when ts_recent isn't valid.  The
1398                          * age isn't reset until we get a valid ts_recent
1399                          * because we don't want out-of-order segments to be
1400                          * dropped when ts_recent is old.
1401                          */
1402                         tp->ts_recent = 0;
1403                 } else {
1404                         tcpstat.tcps_rcvduppack++;
1405                         tcpstat.tcps_rcvdupbyte += tlen;
1406                         tcpstat.tcps_pawsdrop++;
1407                         if (tlen)
1408                                 goto dropafterack;
1409                         goto drop;
1410                 }
1411         }
1412
1413         /*
1414          * T/TCP mechanism
1415          *   If T/TCP was negotiated and the segment doesn't have CC,
1416          *   or if its CC is wrong then drop the segment.
1417          *   RST segments do not have to comply with this.
1418          */
1419         if ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) == (TF_REQ_CC|TF_RCVD_CC) &&
1420             ((to.to_flags & TOF_CC) == 0 || tp->cc_recv != to.to_cc))
1421                 goto dropafterack;
1422
1423         /*
1424          * In the SYN-RECEIVED state, validate that the packet belongs to
1425          * this connection before trimming the data to fit the receive
1426          * window.  Check the sequence number versus IRS since we know
1427          * the sequence numbers haven't wrapped.  This is a partial fix
1428          * for the "LAND" DoS attack.
1429          */
1430         if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
1431                 rstreason = BANDLIM_RST_OPENPORT;
1432                 goto dropwithreset;
1433         }
1434
1435         todrop = tp->rcv_nxt - th->th_seq;
1436         if (todrop > 0) {
1437                 if (thflags & TH_SYN) {
1438                         thflags &= ~TH_SYN;
1439                         th->th_seq++;
1440                         if (th->th_urp > 1)
1441                                 th->th_urp--;
1442                         else
1443                                 thflags &= ~TH_URG;
1444                         todrop--;
1445                 }
1446                 /*
1447                  * Following if statement from Stevens, vol. 2, p. 960.
1448                  */
1449                 if (todrop > tlen
1450                     || (todrop == tlen && (thflags & TH_FIN) == 0)) {
1451                         /*
1452                          * Any valid FIN must be to the left of the window.
1453                          * At this point the FIN must be a duplicate or out
1454                          * of sequence; drop it.
1455                          */
1456                         thflags &= ~TH_FIN;
1457
1458                         /*
1459                          * Send an ACK to resynchronize and drop any data.
1460                          * But keep on processing for RST or ACK.
1461                          */
1462                         tp->t_flags |= TF_ACKNOW;
1463                         todrop = tlen;
1464                         tcpstat.tcps_rcvduppack++;
1465                         tcpstat.tcps_rcvdupbyte += todrop;
1466                 } else {
1467                         tcpstat.tcps_rcvpartduppack++;
1468                         tcpstat.tcps_rcvpartdupbyte += todrop;
1469                 }
1470                 drop_hdrlen += todrop;  /* drop from the top afterwards */
1471                 th->th_seq += todrop;
1472                 tlen -= todrop;
1473                 if (th->th_urp > todrop)
1474                         th->th_urp -= todrop;
1475                 else {
1476                         thflags &= ~TH_URG;
1477                         th->th_urp = 0;
1478                 }
1479         }
1480
1481         /*
1482          * If new data are received on a connection after the
1483          * user processes are gone, then RST the other end.
1484          */
1485         if ((so->so_state & SS_NOFDREF) &&
1486             tp->t_state > TCPS_CLOSE_WAIT && tlen) {
1487                 tp = tcp_close(tp);
1488                 tcpstat.tcps_rcvafterclose++;
1489                 rstreason = BANDLIM_UNLIMITED;
1490                 goto dropwithreset;
1491         }
1492
1493         /*
1494          * If segment ends after window, drop trailing data
1495          * (and PUSH and FIN); if nothing left, just ACK.
1496          */
1497         todrop = (th->th_seq+tlen) - (tp->rcv_nxt+tp->rcv_wnd);
1498         if (todrop > 0) {
1499                 tcpstat.tcps_rcvpackafterwin++;
1500                 if (todrop >= tlen) {
1501                         tcpstat.tcps_rcvbyteafterwin += tlen;
1502                         /*
1503                          * If a new connection request is received
1504                          * while in TIME_WAIT, drop the old connection
1505                          * and start over if the sequence numbers
1506                          * are above the previous ones.
1507                          */
1508                         if (thflags & TH_SYN &&
1509                             tp->t_state == TCPS_TIME_WAIT &&
1510                             SEQ_GT(th->th_seq, tp->rcv_nxt)) {
1511                                 tp = tcp_close(tp);
1512                                 goto findpcb;
1513                         }
1514                         /*
1515                          * If window is closed can only take segments at
1516                          * window edge, and have to drop data and PUSH from
1517                          * incoming segments.  Continue processing, but
1518                          * remember to ack.  Otherwise, drop segment
1519                          * and ack.
1520                          */
1521                         if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
1522                                 tp->t_flags |= TF_ACKNOW;
1523                                 tcpstat.tcps_rcvwinprobe++;
1524                         } else
1525                                 goto dropafterack;
1526                 } else
1527                         tcpstat.tcps_rcvbyteafterwin += todrop;
1528                 m_adj(m, -todrop);
1529                 tlen -= todrop;
1530                 thflags &= ~(TH_PUSH|TH_FIN);
1531         }
1532
1533         /*
1534          * If last ACK falls within this segment's sequence numbers,
1535          * record its timestamp.
1536          * NOTE that the test is modified according to the latest
1537          * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1538          */
1539         if ((to.to_flags & TOF_TS) != 0 &&
1540             SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
1541                 tp->ts_recent_age = ticks;
1542                 tp->ts_recent = to.to_tsval;
1543         }
1544
1545         /*
1546          * If a SYN is in the window, then this is an
1547          * error and we send an RST and drop the connection.
1548          */
1549         if (thflags & TH_SYN) {
1550                 tp = tcp_drop(tp, ECONNRESET);
1551                 rstreason = BANDLIM_UNLIMITED;
1552                 goto dropwithreset;
1553         }
1554
1555         /*
1556          * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
1557          * flag is on (half-synchronized state), then queue data for
1558          * later processing; else drop segment and return.
1559          */
1560         if ((thflags & TH_ACK) == 0) {
1561                 if (tp->t_state == TCPS_SYN_RECEIVED ||
1562                     (tp->t_flags & TF_NEEDSYN))
1563                         goto step6;
1564                 else
1565                         goto drop;
1566         }
1567
1568         /*
1569          * Ack processing.
1570          */
1571         switch (tp->t_state) {
1572
1573         /*
1574          * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
1575          * ESTABLISHED state and continue processing.
1576          * The ACK was checked above.
1577          */
1578         case TCPS_SYN_RECEIVED:
1579
1580                 tcpstat.tcps_connects++;
1581                 soisconnected(so);
1582                 /* Do window scaling? */
1583                 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1584                         (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1585                         tp->snd_scale = tp->requested_s_scale;
1586                         tp->rcv_scale = tp->request_r_scale;
1587                 }
1588                 /*
1589                  * Upon successful completion of 3-way handshake,
1590                  * update cache.CC if it was undefined, pass any queued
1591                  * data to the user, and advance state appropriately.
1592                  */
1593                 if ((taop = tcp_gettaocache(&inp->inp_inc)) != NULL &&
1594                     taop->tao_cc == 0)
1595                         taop->tao_cc = tp->cc_recv;
1596
1597                 /*
1598                  * Make transitions:
1599                  *      SYN-RECEIVED  -> ESTABLISHED
1600                  *      SYN-RECEIVED* -> FIN-WAIT-1
1601                  */
1602                 tp->t_starttime = ticks;
1603                 if (tp->t_flags & TF_NEEDFIN) {
1604                         tp->t_state = TCPS_FIN_WAIT_1;
1605                         tp->t_flags &= ~TF_NEEDFIN;
1606                 } else {
1607                         tp->t_state = TCPS_ESTABLISHED;
1608                         callout_reset(tp->tt_keep, tcp_keepidle,
1609                                       tcp_timer_keep, tp);
1610                 }
1611                 /*
1612                  * If segment contains data or ACK, will call tcp_reass()
1613                  * later; if not, do so now to pass queued data to user.
1614                  */
1615                 if (tlen == 0 && (thflags & TH_FIN) == 0)
1616                         (void) tcp_reass(tp, (struct tcphdr *)0, 0,
1617                             (struct mbuf *)0);
1618                 tp->snd_wl1 = th->th_seq - 1;
1619                 /* fall into ... */
1620
1621         /*
1622          * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
1623          * ACKs.  If the ack is in the range
1624          *      tp->snd_una < th->th_ack <= tp->snd_max
1625          * then advance tp->snd_una to th->th_ack and drop
1626          * data from the retransmission queue.  If this ACK reflects
1627          * more up to date window information we update our window information.
1628          */
1629         case TCPS_ESTABLISHED:
1630         case TCPS_FIN_WAIT_1:
1631         case TCPS_FIN_WAIT_2:
1632         case TCPS_CLOSE_WAIT:
1633         case TCPS_CLOSING:
1634         case TCPS_LAST_ACK:
1635         case TCPS_TIME_WAIT:
1636
1637                 if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
1638                         if (tlen == 0 && tiwin == tp->snd_wnd) {
1639                                 tcpstat.tcps_rcvdupack++;
1640                                 /*
1641                                  * If we have outstanding data (other than
1642                                  * a window probe), this is a completely
1643                                  * duplicate ack (ie, window info didn't
1644                                  * change), the ack is the biggest we've
1645                                  * seen and we've seen exactly our rexmt
1646                                  * threshhold of them, assume a packet
1647                                  * has been dropped and retransmit it.
1648                                  * Kludge snd_nxt & the congestion
1649                                  * window so we send only this one
1650                                  * packet.
1651                                  *
1652                                  * We know we're losing at the current
1653                                  * window size so do congestion avoidance
1654                                  * (set ssthresh to half the current window
1655                                  * and pull our congestion window back to
1656                                  * the new ssthresh).
1657                                  *
1658                                  * Dup acks mean that packets have left the
1659                                  * network (they're now cached at the receiver)
1660                                  * so bump cwnd by the amount in the receiver
1661                                  * to keep a constant cwnd packets in the
1662                                  * network.
1663                                  */
1664                                 if (!callout_active(tp->tt_rexmt) ||
1665                                     th->th_ack != tp->snd_una)
1666                                         tp->t_dupacks = 0;
1667                                 else if (++tp->t_dupacks > tcprexmtthresh ||
1668                                          (tcp_do_newreno &&
1669                                           SEQ_LT(tp->snd_una,
1670                                                  tp->snd_recover))) {
1671                                         tp->snd_cwnd += tp->t_maxseg;
1672                                         (void) tcp_output(tp);
1673                                         goto drop;
1674                                 } else if (tp->t_dupacks == tcprexmtthresh) {
1675                                         tcp_seq onxt = tp->snd_nxt;
1676                                         u_int win;
1677                                         if (tcp_do_newreno &&
1678                                             SEQ_LEQ(th->th_ack, tp->snd_high)) {
1679                                                 tp->t_dupacks = 0;
1680                                                 break;
1681                                         }
1682                                         win = min(tp->snd_wnd, tp->snd_cwnd) /
1683                                             2 / tp->t_maxseg;
1684                                         if (win < 2)
1685                                                 win = 2;
1686                                         tp->snd_ssthresh = win * tp->t_maxseg;
1687                                         tp->snd_recover = tp->snd_max;
1688                                         callout_stop(tp->tt_rexmt);
1689                                         tp->t_rtttime = 0;
1690                                         tp->snd_nxt = th->th_ack;
1691                                         tp->snd_cwnd = tp->t_maxseg;
1692                                         (void) tcp_output(tp);
1693                                         tp->snd_cwnd = tp->snd_ssthresh +
1694                                                 tp->t_maxseg * tp->t_dupacks;
1695                                         if (SEQ_GT(onxt, tp->snd_nxt))
1696                                                 tp->snd_nxt = onxt;
1697                                         goto drop;
1698                                 }
1699                         } else
1700                                 tp->t_dupacks = 0;
1701                         break;
1702                 }
1703
1704                 KASSERT(SEQ_GT(th->th_ack, tp->snd_una), ("th_ack <= snd_una"));
1705
1706                 /*
1707                  * If the congestion window was inflated to account
1708                  * for the other side's cached packets, retract it.
1709                  */
1710                 if (tcp_do_newreno) {
1711                         if (SEQ_LT(tp->snd_una, tp->snd_recover)) {
1712                                 if (SEQ_LT(th->th_ack, tp->snd_recover)) {
1713                                         tcp_newreno_partial_ack(tp, th);
1714                                 } else {
1715                                         /*
1716                                          * Window inflation should have left us
1717                                          * with approximately snd_ssthresh
1718                                          * outstanding data.
1719                                          * But in case we would be inclined to
1720                                          * send a burst, better to do it via
1721                                          * the slow start mechanism.
1722                                          */
1723                                         if (SEQ_GT(th->th_ack +
1724                                                         tp->snd_ssthresh,
1725                                                    tp->snd_max))
1726                                                 tp->snd_cwnd = tp->snd_max -
1727                                                                 th->th_ack +
1728                                                                 tp->t_maxseg;
1729                                         else
1730                                                 tp->snd_cwnd = tp->snd_ssthresh;
1731                                 }
1732                         }
1733                 } else {
1734                         if (tp->t_dupacks >= tcprexmtthresh &&
1735                             tp->snd_cwnd > tp->snd_ssthresh)
1736                                 tp->snd_cwnd = tp->snd_ssthresh;
1737                 }
1738                 tp->t_dupacks = 0;
1739                 if (SEQ_GT(th->th_ack, tp->snd_max)) {
1740                         tcpstat.tcps_rcvacktoomuch++;
1741                         goto dropafterack;
1742                 }
1743                 /*
1744                  * If we reach this point, ACK is not a duplicate,
1745                  *     i.e., it ACKs something we sent.
1746                  */
1747                 if (tp->t_flags & TF_NEEDSYN) {
1748                         /*
1749                          * T/TCP: Connection was half-synchronized, and our
1750                          * SYN has been ACK'd (so connection is now fully
1751                          * synchronized).  Go to non-starred state,
1752                          * increment snd_una for ACK of SYN, and check if
1753                          * we can do window scaling.
1754                          */
1755                         tp->t_flags &= ~TF_NEEDSYN;
1756                         tp->snd_una++;
1757                         /* Do window scaling? */
1758                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1759                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1760                                 tp->snd_scale = tp->requested_s_scale;
1761                                 tp->rcv_scale = tp->request_r_scale;
1762                         }
1763                 }
1764
1765 process_ACK:
1766                 acked = th->th_ack - tp->snd_una;
1767                 tcpstat.tcps_rcvackpack++;
1768                 tcpstat.tcps_rcvackbyte += acked;
1769
1770                 /*
1771                  * If we just performed our first retransmit, and the ACK
1772                  * arrives within our recovery window, then it was a mistake
1773                  * to do the retransmit in the first place.  Recover our
1774                  * original cwnd and ssthresh, and proceed to transmit where
1775                  * we left off.
1776                  */
1777                 if (tp->t_rxtshift == 1 && ticks < tp->t_badrxtwin) {
1778                         tp->snd_cwnd = tp->snd_cwnd_prev;
1779                         tp->snd_ssthresh = tp->snd_ssthresh_prev;
1780                         tp->snd_high = tp->snd_high_prev;
1781                         tp->snd_nxt = tp->snd_max;
1782                         tp->t_badrxtwin = 0;    /* XXX probably not required */
1783                 }
1784
1785                 /*
1786                  * If we have a timestamp reply, update smoothed
1787                  * round trip time.  If no timestamp is present but
1788                  * transmit timer is running and timed sequence
1789                  * number was acked, update smoothed round trip time.
1790                  * Since we now have an rtt measurement, cancel the
1791                  * timer backoff (cf., Phil Karn's retransmit alg.).
1792                  * Recompute the initial retransmit timer.
1793                  *
1794                  * Some machines (certain windows boxes) send broken
1795                  * timestamp replies during the SYN+ACK phase, ignore
1796                  * timestamps of 0.
1797                  */
1798                 if ((to.to_flags & TOF_TS) != 0 &&
1799                     to.to_tsecr) {
1800                         tcp_xmit_timer(tp, ticks - to.to_tsecr + 1);
1801                 } else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
1802                         tcp_xmit_timer(tp, ticks - tp->t_rtttime);
1803                 }
1804                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
1805
1806                 /*
1807                  * If all outstanding data is acked, stop retransmit
1808                  * timer and remember to restart (more output or persist).
1809                  * If there is more data to be acked, restart retransmit
1810                  * timer, using current (possibly backed-off) value.
1811                  */
1812                 if (th->th_ack == tp->snd_max) {
1813                         callout_stop(tp->tt_rexmt);
1814                         needoutput = 1;
1815                 } else if (!callout_active(tp->tt_persist))
1816                         callout_reset(tp->tt_rexmt, tp->t_rxtcur,
1817                                       tcp_timer_rexmt, tp);
1818
1819                 /*
1820                  * If no data (only SYN) was ACK'd,
1821                  *    skip rest of ACK processing.
1822                  */
1823                 if (acked == 0)
1824                         goto step6;
1825
1826                 /*
1827                  * When new data is acked, open the congestion window.
1828                  * If the window gives us less than ssthresh packets
1829                  * in flight, open exponentially (maxseg per packet).
1830                  * Otherwise open linearly: maxseg per window
1831                  * (maxseg^2 / cwnd per packet).
1832                  */
1833                 if (!tcp_do_newreno || SEQ_GEQ(tp->snd_una, tp->snd_recover)) {
1834                         register u_int cw = tp->snd_cwnd;
1835                         register u_int incr = tp->t_maxseg;
1836                         if (cw > tp->snd_ssthresh)
1837                                 incr = incr * incr / cw;
1838                         tp->snd_cwnd = min(cw+incr, TCP_MAXWIN<<tp->snd_scale);
1839                 }
1840                 if (acked > so->so_snd.sb_cc) {
1841                         tp->snd_wnd -= so->so_snd.sb_cc;
1842                         sbdrop(&so->so_snd, (int)so->so_snd.sb_cc);
1843                         ourfinisacked = 1;
1844                 } else {
1845                         sbdrop(&so->so_snd, acked);
1846                         tp->snd_wnd -= acked;
1847                         ourfinisacked = 0;
1848                 }
1849                 sowwakeup(so);
1850                 /* detect una wraparound */
1851                 if (SEQ_GEQ(tp->snd_una, tp->snd_recover) &&
1852                     SEQ_LT(th->th_ack, tp->snd_recover))
1853                         tp->snd_recover = th->th_ack;
1854                 if (SEQ_GT(tp->snd_una, tp->snd_high) &&
1855                     SEQ_LEQ(th->th_ack, tp->snd_high))
1856                         tp->snd_high = th->th_ack - 1;
1857                 tp->snd_una = th->th_ack;
1858                 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
1859                         tp->snd_nxt = tp->snd_una;
1860
1861                 switch (tp->t_state) {
1862
1863                 /*
1864                  * In FIN_WAIT_1 STATE in addition to the processing
1865                  * for the ESTABLISHED state if our FIN is now acknowledged
1866                  * then enter FIN_WAIT_2.
1867                  */
1868                 case TCPS_FIN_WAIT_1:
1869                         if (ourfinisacked) {
1870                                 /*
1871                                  * If we can't receive any more
1872                                  * data, then closing user can proceed.
1873                                  * Starting the timer is contrary to the
1874                                  * specification, but if we don't get a FIN
1875                                  * we'll hang forever.
1876                                  */
1877                                 if (so->so_state & SS_CANTRCVMORE) {
1878                                         soisdisconnected(so);
1879                                         callout_reset(tp->tt_2msl, tcp_maxidle,
1880                                                       tcp_timer_2msl, tp);
1881                                 }
1882                                 tp->t_state = TCPS_FIN_WAIT_2;
1883                         }
1884                         break;
1885
1886                 /*
1887                  * In CLOSING STATE in addition to the processing for
1888                  * the ESTABLISHED state if the ACK acknowledges our FIN
1889                  * then enter the TIME-WAIT state, otherwise ignore
1890                  * the segment.
1891                  */
1892                 case TCPS_CLOSING:
1893                         if (ourfinisacked) {
1894                                 tp->t_state = TCPS_TIME_WAIT;
1895                                 tcp_canceltimers(tp);
1896                                 /* Shorten TIME_WAIT [RFC-1644, p.28] */
1897                                 if (tp->cc_recv != 0 &&
1898                                     (ticks - tp->t_starttime) < tcp_msl)
1899                                         callout_reset(tp->tt_2msl,
1900                                                       tp->t_rxtcur *
1901                                                       TCPTV_TWTRUNC,
1902                                                       tcp_timer_2msl, tp);
1903                                 else
1904                                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
1905                                                       tcp_timer_2msl, tp);
1906                                 soisdisconnected(so);
1907                         }
1908                         break;
1909
1910                 /*
1911                  * In LAST_ACK, we may still be waiting for data to drain
1912                  * and/or to be acked, as well as for the ack of our FIN.
1913                  * If our FIN is now acknowledged, delete the TCB,
1914                  * enter the closed state and return.
1915                  */
1916                 case TCPS_LAST_ACK:
1917                         if (ourfinisacked) {
1918                                 tp = tcp_close(tp);
1919                                 goto drop;
1920                         }
1921                         break;
1922
1923                 /*
1924                  * In TIME_WAIT state the only thing that should arrive
1925                  * is a retransmission of the remote FIN.  Acknowledge
1926                  * it and restart the finack timer.
1927                  */
1928                 case TCPS_TIME_WAIT:
1929                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
1930                                       tcp_timer_2msl, tp);
1931                         goto dropafterack;
1932                 }
1933         }
1934
1935 step6:
1936         /*
1937          * Update window information.
1938          * Don't look at window if no ACK: TAC's send garbage on first SYN.
1939          */
1940         if ((thflags & TH_ACK) &&
1941             (SEQ_LT(tp->snd_wl1, th->th_seq) ||
1942             (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
1943              (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
1944                 /* keep track of pure window updates */
1945                 if (tlen == 0 &&
1946                     tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
1947                         tcpstat.tcps_rcvwinupd++;
1948                 tp->snd_wnd = tiwin;
1949                 tp->snd_wl1 = th->th_seq;
1950                 tp->snd_wl2 = th->th_ack;
1951                 if (tp->snd_wnd > tp->max_sndwnd)
1952                         tp->max_sndwnd = tp->snd_wnd;
1953                 needoutput = 1;
1954         }
1955
1956         /*
1957          * Process segments with URG.
1958          */
1959         if ((thflags & TH_URG) && th->th_urp &&
1960             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
1961                 /*
1962                  * This is a kludge, but if we receive and accept
1963                  * random urgent pointers, we'll crash in
1964                  * soreceive.  It's hard to imagine someone
1965                  * actually wanting to send this much urgent data.
1966                  */
1967                 if (th->th_urp + so->so_rcv.sb_cc > sb_max) {
1968                         th->th_urp = 0;                 /* XXX */
1969                         thflags &= ~TH_URG;             /* XXX */
1970                         goto dodata;                    /* XXX */
1971                 }
1972                 /*
1973                  * If this segment advances the known urgent pointer,
1974                  * then mark the data stream.  This should not happen
1975                  * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
1976                  * a FIN has been received from the remote side.
1977                  * In these states we ignore the URG.
1978                  *
1979                  * According to RFC961 (Assigned Protocols),
1980                  * the urgent pointer points to the last octet
1981                  * of urgent data.  We continue, however,
1982                  * to consider it to indicate the first octet
1983                  * of data past the urgent section as the original
1984                  * spec states (in one of two places).
1985                  */
1986                 if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
1987                         tp->rcv_up = th->th_seq + th->th_urp;
1988                         so->so_oobmark = so->so_rcv.sb_cc +
1989                             (tp->rcv_up - tp->rcv_nxt) - 1;
1990                         if (so->so_oobmark == 0)
1991                                 so->so_state |= SS_RCVATMARK;
1992                         sohasoutofband(so);
1993                         tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
1994                 }
1995                 /*
1996                  * Remove out of band data so doesn't get presented to user.
1997                  * This can happen independent of advancing the URG pointer,
1998                  * but if two URG's are pending at once, some out-of-band
1999                  * data may creep in... ick.
2000                  */
2001                 if (th->th_urp <= (u_long)tlen
2002 #ifdef SO_OOBINLINE
2003                      && (so->so_options & SO_OOBINLINE) == 0
2004 #endif
2005                      )
2006                         tcp_pulloutofband(so, th, m,
2007                                 drop_hdrlen);   /* hdr drop is delayed */
2008         } else {
2009                 /*
2010                  * If no out of band data is expected,
2011                  * pull receive urgent pointer along
2012                  * with the receive window.
2013                  */
2014                 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
2015                         tp->rcv_up = tp->rcv_nxt;
2016         }
2017 dodata:                                                 /* XXX */
2018
2019         /*
2020          * Process the segment text, merging it into the TCP sequencing queue,
2021          * and arranging for acknowledgment of receipt if necessary.
2022          * This process logically involves adjusting tp->rcv_wnd as data
2023          * is presented to the user (this happens in tcp_usrreq.c,
2024          * case PRU_RCVD).  If a FIN has already been received on this
2025          * connection then we just ignore the text.
2026          */
2027         if ((tlen || (thflags & TH_FIN)) &&
2028             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2029                 m_adj(m, drop_hdrlen);  /* delayed header drop */
2030                 /*
2031                  * Insert segment which includes th into TCP reassembly queue
2032                  * with control block tp.  Set thflags to whether reassembly now
2033                  * includes a segment with FIN.  This handles the common case
2034                  * inline (segment is the next to be received on an established
2035                  * connection, and the queue is empty), avoiding linkage into
2036                  * and removal from the queue and repetition of various
2037                  * conversions.
2038                  * Set DELACK for segments received in order, but ack
2039                  * immediately when segments are out of order (so
2040                  * fast retransmit can work).
2041                  */
2042                 if (th->th_seq == tp->rcv_nxt &&
2043                     LIST_EMPTY(&tp->t_segq) &&
2044                     TCPS_HAVEESTABLISHED(tp->t_state)) {
2045                         if (DELAY_ACK(tp))
2046                                 callout_reset(tp->tt_delack, tcp_delacktime,
2047                                               tcp_timer_delack, tp);
2048                         else
2049                                 tp->t_flags |= TF_ACKNOW;
2050                         tp->rcv_nxt += tlen;
2051                         thflags = th->th_flags & TH_FIN;
2052                         tcpstat.tcps_rcvpack++;
2053                         tcpstat.tcps_rcvbyte += tlen;
2054                         ND6_HINT(tp);
2055                         if (so->so_state & SS_CANTRCVMORE)
2056                                 m_freem(m);
2057                         else
2058                                 sbappend(&so->so_rcv, m);
2059                         sorwakeup(so);
2060                 } else {
2061                         thflags = tcp_reass(tp, th, &tlen, m);
2062                         tp->t_flags |= TF_ACKNOW;
2063                 }
2064
2065                 /*
2066                  * Note the amount of data that peer has sent into
2067                  * our window, in order to estimate the sender's
2068                  * buffer size.
2069                  */
2070                 len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
2071         } else {
2072                 m_freem(m);
2073                 thflags &= ~TH_FIN;
2074         }
2075
2076         /*
2077          * If FIN is received ACK the FIN and let the user know
2078          * that the connection is closing.
2079          */
2080         if (thflags & TH_FIN) {
2081                 if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2082                         socantrcvmore(so);
2083                         /*
2084                          * If connection is half-synchronized
2085                          * (ie NEEDSYN flag on) then delay ACK,
2086                          * so it may be piggybacked when SYN is sent.
2087                          * Otherwise, since we received a FIN then no
2088                          * more input can be expected, send ACK now.
2089                          */
2090                         if (DELAY_ACK(tp) && (tp->t_flags & TF_NEEDSYN))
2091                                 callout_reset(tp->tt_delack, tcp_delacktime,
2092                                     tcp_timer_delack, tp);
2093                         else
2094                                 tp->t_flags |= TF_ACKNOW;
2095                         tp->rcv_nxt++;
2096                 }
2097                 switch (tp->t_state) {
2098
2099                 /*
2100                  * In SYN_RECEIVED and ESTABLISHED STATES
2101                  * enter the CLOSE_WAIT state.
2102                  */
2103                 case TCPS_SYN_RECEIVED:
2104                         tp->t_starttime = ticks;
2105                         /*FALLTHROUGH*/
2106                 case TCPS_ESTABLISHED:
2107                         tp->t_state = TCPS_CLOSE_WAIT;
2108                         break;
2109
2110                 /*
2111                  * If still in FIN_WAIT_1 STATE FIN has not been acked so
2112                  * enter the CLOSING state.
2113                  */
2114                 case TCPS_FIN_WAIT_1:
2115                         tp->t_state = TCPS_CLOSING;
2116                         break;
2117
2118                 /*
2119                  * In FIN_WAIT_2 state enter the TIME_WAIT state,
2120                  * starting the time-wait timer, turning off the other
2121                  * standard timers.
2122                  */
2123                 case TCPS_FIN_WAIT_2:
2124                         tp->t_state = TCPS_TIME_WAIT;
2125                         tcp_canceltimers(tp);
2126                         /* Shorten TIME_WAIT [RFC-1644, p.28] */
2127                         if (tp->cc_recv != 0 &&
2128                             (ticks - tp->t_starttime) < tcp_msl) {
2129                                 callout_reset(tp->tt_2msl,
2130                                               tp->t_rxtcur * TCPTV_TWTRUNC,
2131                                               tcp_timer_2msl, tp);
2132                                 /* For transaction client, force ACK now. */
2133                                 tp->t_flags |= TF_ACKNOW;
2134                         }
2135                         else
2136                                 callout_reset(tp->tt_2msl, 2 * tcp_msl,
2137                                               tcp_timer_2msl, tp);
2138                         soisdisconnected(so);
2139                         break;
2140
2141                 /*
2142                  * In TIME_WAIT state restart the 2 MSL time_wait timer.
2143                  */
2144                 case TCPS_TIME_WAIT:
2145                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
2146                                       tcp_timer_2msl, tp);
2147                         break;
2148                 }
2149         }
2150 #ifdef TCPDEBUG
2151         if (so->so_options & SO_DEBUG)
2152                 tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
2153                           &tcp_savetcp, 0);
2154 #endif
2155
2156         /*
2157          * Return any desired output.
2158          */
2159         if (needoutput || (tp->t_flags & TF_ACKNOW))
2160                 (void) tcp_output(tp);
2161         return;
2162
2163 dropafterack:
2164         /*
2165          * Generate an ACK dropping incoming segment if it occupies
2166          * sequence space, where the ACK reflects our state.
2167          *
2168          * We can now skip the test for the RST flag since all
2169          * paths to this code happen after packets containing
2170          * RST have been dropped.
2171          *
2172          * In the SYN-RECEIVED state, don't send an ACK unless the
2173          * segment we received passes the SYN-RECEIVED ACK test.
2174          * If it fails send a RST.  This breaks the loop in the
2175          * "LAND" DoS attack, and also prevents an ACK storm
2176          * between two listening ports that have been sent forged
2177          * SYN segments, each with the source address of the other.
2178          */
2179         if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
2180             (SEQ_GT(tp->snd_una, th->th_ack) ||
2181              SEQ_GT(th->th_ack, tp->snd_max)) ) {
2182                 rstreason = BANDLIM_RST_OPENPORT;
2183                 goto dropwithreset;
2184         }
2185 #ifdef TCPDEBUG
2186         if (so->so_options & SO_DEBUG)
2187                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2188                           &tcp_savetcp, 0);
2189 #endif
2190         m_freem(m);
2191         tp->t_flags |= TF_ACKNOW;
2192         (void) tcp_output(tp);
2193         return;
2194
2195 dropwithreset:
2196         /*
2197          * Generate a RST, dropping incoming segment.
2198          * Make ACK acceptable to originator of segment.
2199          * Don't bother to respond if destination was broadcast/multicast.
2200          */
2201         if ((thflags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
2202                 goto drop;
2203         if (isipv6) {
2204                 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
2205                     IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
2206                         goto drop;
2207         } else {
2208                 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
2209                     IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
2210                     ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
2211                     in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
2212                         goto drop;
2213         }
2214         /* IPv6 anycast check is done at tcp6_input() */
2215
2216         /*
2217          * Perform bandwidth limiting.
2218          */
2219 #ifdef ICMP_BANDLIM
2220         if (badport_bandlim(rstreason) < 0)
2221                 goto drop;
2222 #endif
2223
2224 #ifdef TCPDEBUG
2225         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2226                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2227                           &tcp_savetcp, 0);
2228 #endif
2229         if (thflags & TH_ACK)
2230                 /* mtod() below is safe as long as hdr dropping is delayed */
2231                 tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0, th->th_ack,
2232                             TH_RST);
2233         else {
2234                 if (thflags & TH_SYN)
2235                         tlen++;
2236                 /* mtod() below is safe as long as hdr dropping is delayed */
2237                 tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
2238                             (tcp_seq)0, TH_RST|TH_ACK);
2239         }
2240         return;
2241
2242 drop:
2243         /*
2244          * Drop space held by incoming segment and return.
2245          */
2246 #ifdef TCPDEBUG
2247         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2248                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2249                           &tcp_savetcp, 0);
2250 #endif
2251         m_freem(m);
2252         return;
2253 }
2254
2255 /*
2256  * Parse TCP options and place in tcpopt.
2257  */
2258 static void
2259 tcp_dooptions(to, cp, cnt, is_syn)
2260         struct tcpopt *to;
2261         u_char *cp;
2262         int cnt;
2263 {
2264         int opt, optlen;
2265
2266         to->to_flags = 0;
2267         for (; cnt > 0; cnt -= optlen, cp += optlen) {
2268                 opt = cp[0];
2269                 if (opt == TCPOPT_EOL)
2270                         break;
2271                 if (opt == TCPOPT_NOP)
2272                         optlen = 1;
2273                 else {
2274                         if (cnt < 2)
2275                                 break;
2276                         optlen = cp[1];
2277                         if (optlen < 2 || optlen > cnt)
2278                                 break;
2279                 }
2280                 switch (opt) {
2281                 case TCPOPT_MAXSEG:
2282                         if (optlen != TCPOLEN_MAXSEG)
2283                                 continue;
2284                         if (!is_syn)
2285                                 continue;
2286                         to->to_flags |= TOF_MSS;
2287                         bcopy((char *)cp + 2,
2288                             (char *)&to->to_mss, sizeof(to->to_mss));
2289                         to->to_mss = ntohs(to->to_mss);
2290                         break;
2291                 case TCPOPT_WINDOW:
2292                         if (optlen != TCPOLEN_WINDOW)
2293                                 continue;
2294                         if (! is_syn)
2295                                 continue;
2296                         to->to_flags |= TOF_SCALE;
2297                         to->to_requested_s_scale = min(cp[2], TCP_MAX_WINSHIFT);
2298                         break;
2299                 case TCPOPT_TIMESTAMP:
2300                         if (optlen != TCPOLEN_TIMESTAMP)
2301                                 continue;
2302                         to->to_flags |= TOF_TS;
2303                         bcopy((char *)cp + 2,
2304                             (char *)&to->to_tsval, sizeof(to->to_tsval));
2305                         to->to_tsval = ntohl(to->to_tsval);
2306                         bcopy((char *)cp + 6,
2307                             (char *)&to->to_tsecr, sizeof(to->to_tsecr));
2308                         to->to_tsecr = ntohl(to->to_tsecr);
2309                         break;
2310                 case TCPOPT_CC:
2311                         if (optlen != TCPOLEN_CC)
2312                                 continue;
2313                         to->to_flags |= TOF_CC;
2314                         bcopy((char *)cp + 2,
2315                             (char *)&to->to_cc, sizeof(to->to_cc));
2316                         to->to_cc = ntohl(to->to_cc);
2317                         break;
2318                 case TCPOPT_CCNEW:
2319                         if (optlen != TCPOLEN_CC)
2320                                 continue;
2321                         if (!is_syn)
2322                                 continue;
2323                         to->to_flags |= TOF_CCNEW;
2324                         bcopy((char *)cp + 2,
2325                             (char *)&to->to_cc, sizeof(to->to_cc));
2326                         to->to_cc = ntohl(to->to_cc);
2327                         break;
2328                 case TCPOPT_CCECHO:
2329                         if (optlen != TCPOLEN_CC)
2330                                 continue;
2331                         if (!is_syn)
2332                                 continue;
2333                         to->to_flags |= TOF_CCECHO;
2334                         bcopy((char *)cp + 2,
2335                             (char *)&to->to_ccecho, sizeof(to->to_ccecho));
2336                         to->to_ccecho = ntohl(to->to_ccecho);
2337                         break;
2338                 default:
2339                         continue;
2340                 }
2341         }
2342 }
2343
2344 /*
2345  * Pull out of band byte out of a segment so
2346  * it doesn't appear in the user's data queue.
2347  * It is still reflected in the segment length for
2348  * sequencing purposes.
2349  */
2350 static void
2351 tcp_pulloutofband(so, th, m, off)
2352         struct socket *so;
2353         struct tcphdr *th;
2354         register struct mbuf *m;
2355         int off;                /* delayed to be droped hdrlen */
2356 {
2357         int cnt = off + th->th_urp - 1;
2358
2359         while (cnt >= 0) {
2360                 if (m->m_len > cnt) {
2361                         char *cp = mtod(m, caddr_t) + cnt;
2362                         struct tcpcb *tp = sototcpcb(so);
2363
2364                         tp->t_iobc = *cp;
2365                         tp->t_oobflags |= TCPOOB_HAVEDATA;
2366                         bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
2367                         m->m_len--;
2368                         if (m->m_flags & M_PKTHDR)
2369                                 m->m_pkthdr.len--;
2370                         return;
2371                 }
2372                 cnt -= m->m_len;
2373                 m = m->m_next;
2374                 if (m == 0)
2375                         break;
2376         }
2377         panic("tcp_pulloutofband");
2378 }
2379
2380 /*
2381  * Collect new round-trip time estimate
2382  * and update averages and current timeout.
2383  */
2384 static void
2385 tcp_xmit_timer(tp, rtt)
2386         register struct tcpcb *tp;
2387         int rtt;
2388 {
2389         register int delta;
2390
2391         tcpstat.tcps_rttupdated++;
2392         tp->t_rttupdated++;
2393         if (tp->t_srtt != 0) {
2394                 /*
2395                  * srtt is stored as fixed point with 5 bits after the
2396                  * binary point (i.e., scaled by 8).  The following magic
2397                  * is equivalent to the smoothing algorithm in rfc793 with
2398                  * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
2399                  * point).  Adjust rtt to origin 0.
2400                  */
2401                 delta = ((rtt - 1) << TCP_DELTA_SHIFT)
2402                         - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
2403
2404                 if ((tp->t_srtt += delta) <= 0)
2405                         tp->t_srtt = 1;
2406
2407                 /*
2408                  * We accumulate a smoothed rtt variance (actually, a
2409                  * smoothed mean difference), then set the retransmit
2410                  * timer to smoothed rtt + 4 times the smoothed variance.
2411                  * rttvar is stored as fixed point with 4 bits after the
2412                  * binary point (scaled by 16).  The following is
2413                  * equivalent to rfc793 smoothing with an alpha of .75
2414                  * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
2415                  * rfc793's wired-in beta.
2416                  */
2417                 if (delta < 0)
2418                         delta = -delta;
2419                 delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
2420                 if ((tp->t_rttvar += delta) <= 0)
2421                         tp->t_rttvar = 1;
2422                 if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
2423                         tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2424         } else {
2425                 /*
2426                  * No rtt measurement yet - use the unsmoothed rtt.
2427                  * Set the variance to half the rtt (so our first
2428                  * retransmit happens at 3*rtt).
2429                  */
2430                 tp->t_srtt = rtt << TCP_RTT_SHIFT;
2431                 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
2432                 tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2433         }
2434         tp->t_rtttime = 0;
2435         tp->t_rxtshift = 0;
2436
2437         /*
2438          * the retransmit should happen at rtt + 4 * rttvar.
2439          * Because of the way we do the smoothing, srtt and rttvar
2440          * will each average +1/2 tick of bias.  When we compute
2441          * the retransmit timer, we want 1/2 tick of rounding and
2442          * 1 extra tick because of +-1/2 tick uncertainty in the
2443          * firing of the timer.  The bias will give us exactly the
2444          * 1.5 tick we need.  But, because the bias is
2445          * statistical, we have to test that we don't drop below
2446          * the minimum feasible timer (which is 2 ticks).
2447          */
2448         TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
2449                       max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
2450
2451         /*
2452          * We received an ack for a packet that wasn't retransmitted;
2453          * it is probably safe to discard any error indications we've
2454          * received recently.  This isn't quite right, but close enough
2455          * for now (a route might have failed after we sent a segment,
2456          * and the return path might not be symmetrical).
2457          */
2458         tp->t_softerror = 0;
2459 }
2460
2461 /*
2462  * Determine a reasonable value for maxseg size.
2463  * If the route is known, check route for mtu.
2464  * If none, use an mss that can be handled on the outgoing
2465  * interface without forcing IP to fragment; if bigger than
2466  * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
2467  * to utilize large mbufs.  If no route is found, route has no mtu,
2468  * or the destination isn't local, use a default, hopefully conservative
2469  * size (usually 512 or the default IP max size, but no more than the mtu
2470  * of the interface), as we can't discover anything about intervening
2471  * gateways or networks.  We also initialize the congestion/slow start
2472  * window to be a single segment if the destination isn't local.
2473  * While looking at the routing entry, we also initialize other path-dependent
2474  * parameters from pre-set or cached values in the routing entry.
2475  *
2476  * Also take into account the space needed for options that we
2477  * send regularly.  Make maxseg shorter by that amount to assure
2478  * that we can send maxseg amount of data even when the options
2479  * are present.  Store the upper limit of the length of options plus
2480  * data in maxopd.
2481  *
2482  * NOTE that this routine is only called when we process an incoming
2483  * segment, for outgoing segments only tcp_mssopt is called.
2484  *
2485  * In case of T/TCP, we call this routine during implicit connection
2486  * setup as well (offer = -1), to initialize maxseg from the cached
2487  * MSS of our peer.
2488  */
2489 void
2490 tcp_mss(tp, offer)
2491         struct tcpcb *tp;
2492         int offer;
2493 {
2494         register struct rtentry *rt;
2495         struct ifnet *ifp;
2496         register int rtt, mss;
2497         u_long bufsize;
2498         struct inpcb *inp = tp->t_inpcb;
2499         struct socket *so;
2500         struct rmxp_tao *taop;
2501         int origoffer = offer;
2502 #ifdef INET6
2503         int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
2504         size_t min_protoh = isipv6 ?
2505                             sizeof(struct ip6_hdr) + sizeof(struct tcphdr) :
2506                             sizeof(struct tcpiphdr);
2507 #else
2508         const int isipv6 = 0;
2509         const size_t min_protoh = sizeof(struct tcpiphdr);
2510 #endif
2511
2512         if (isipv6)
2513                 rt = tcp_rtlookup6(&inp->inp_inc);
2514         else
2515                 rt = tcp_rtlookup(&inp->inp_inc);
2516         if (rt == NULL) {
2517                 tp->t_maxopd = tp->t_maxseg =
2518                                 isipv6 ? tcp_v6mssdflt : tcp_mssdflt;
2519                 return;
2520         }
2521         ifp = rt->rt_ifp;
2522         so = inp->inp_socket;
2523
2524         taop = rmx_taop(rt->rt_rmx);
2525         /*
2526          * Offer == -1 means that we didn't receive SYN yet,
2527          * use cached value in that case;
2528          */
2529         if (offer == -1)
2530                 offer = taop->tao_mssopt;
2531         /*
2532          * Offer == 0 means that there was no MSS on the SYN segment,
2533          * in this case we use tcp_mssdflt.
2534          */
2535         if (offer == 0)
2536                 offer = isipv6 ? tcp_v6mssdflt : tcp_mssdflt;
2537         else
2538                 /*
2539                  * Sanity check: make sure that maxopd will be large
2540                  * enough to allow some data on segments even is the
2541                  * all the option space is used (40bytes).  Otherwise
2542                  * funny things may happen in tcp_output.
2543                  */
2544                 offer = max(offer, 64);
2545         taop->tao_mssopt = offer;
2546
2547         /*
2548          * While we're here, check if there's an initial rtt
2549          * or rttvar.  Convert from the route-table units
2550          * to scaled multiples of the slow timeout timer.
2551          */
2552         if (tp->t_srtt == 0 && (rtt = rt->rt_rmx.rmx_rtt)) {
2553                 /*
2554                  * XXX the lock bit for RTT indicates that the value
2555                  * is also a minimum value; this is subject to time.
2556                  */
2557                 if (rt->rt_rmx.rmx_locks & RTV_RTT)
2558                         tp->t_rttmin = rtt / (RTM_RTTUNIT / hz);
2559                 tp->t_srtt = rtt / (RTM_RTTUNIT / (hz * TCP_RTT_SCALE));
2560                 tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
2561                 tcpstat.tcps_usedrtt++;
2562                 if (rt->rt_rmx.rmx_rttvar) {
2563                         tp->t_rttvar = rt->rt_rmx.rmx_rttvar /
2564                             (RTM_RTTUNIT / (hz * TCP_RTTVAR_SCALE));
2565                         tcpstat.tcps_usedrttvar++;
2566                 } else {
2567                         /* default variation is +- 1 rtt */
2568                         tp->t_rttvar =
2569                             tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
2570                 }
2571                 TCPT_RANGESET(tp->t_rxtcur,
2572                               ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
2573                               tp->t_rttmin, TCPTV_REXMTMAX);
2574         }
2575         /*
2576          * if there's an mtu associated with the route, use it
2577          * else, use the link mtu.
2578          */
2579         if (rt->rt_rmx.rmx_mtu)
2580                 mss = rt->rt_rmx.rmx_mtu - min_protoh;
2581         else {
2582                 if (isipv6) {
2583                         mss = nd_ifinfo[rt->rt_ifp->if_index].linkmtu -
2584                                 min_protoh;
2585                         if (!in6_localaddr(&inp->in6p_faddr))
2586                                 mss = min(mss, tcp_v6mssdflt);
2587                 } else {
2588                         mss = ifp->if_mtu - min_protoh;
2589                         if (!in_localaddr(inp->inp_faddr))
2590                                 mss = min(mss, tcp_mssdflt);
2591                 }
2592         }
2593         mss = min(mss, offer);
2594         /*
2595          * maxopd stores the maximum length of data AND options
2596          * in a segment; maxseg is the amount of data in a normal
2597          * segment.  We need to store this value (maxopd) apart
2598          * from maxseg, because now every segment carries options
2599          * and thus we normally have somewhat less data in segments.
2600          */
2601         tp->t_maxopd = mss;
2602
2603         /*
2604          * In case of T/TCP, origoffer==-1 indicates, that no segments
2605          * were received yet.  In this case we just guess, otherwise
2606          * we do the same as before T/TCP.
2607          */
2608         if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
2609             (origoffer == -1 ||
2610              (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
2611                 mss -= TCPOLEN_TSTAMP_APPA;
2612         if ((tp->t_flags & (TF_REQ_CC|TF_NOOPT)) == TF_REQ_CC &&
2613             (origoffer == -1 ||
2614              (tp->t_flags & TF_RCVD_CC) == TF_RCVD_CC))
2615                 mss -= TCPOLEN_CC_APPA;
2616
2617 #if     (MCLBYTES & (MCLBYTES - 1)) == 0
2618                 if (mss > MCLBYTES)
2619                         mss &= ~(MCLBYTES-1);
2620 #else
2621                 if (mss > MCLBYTES)
2622                         mss = mss / MCLBYTES * MCLBYTES;
2623 #endif
2624         /*
2625          * If there's a pipesize, change the socket buffer
2626          * to that size.  Make the socket buffers an integral
2627          * number of mss units; if the mss is larger than
2628          * the socket buffer, decrease the mss.
2629          */
2630 #ifdef RTV_SPIPE
2631         if ((bufsize = rt->rt_rmx.rmx_sendpipe) == 0)
2632 #endif
2633                 bufsize = so->so_snd.sb_hiwat;
2634         if (bufsize < mss)
2635                 mss = bufsize;
2636         else {
2637                 bufsize = roundup(bufsize, mss);
2638                 if (bufsize > sb_max)
2639                         bufsize = sb_max;
2640                 if (bufsize > so->so_snd.sb_hiwat)
2641                         (void)sbreserve(&so->so_snd, bufsize, so, NULL);
2642         }
2643         tp->t_maxseg = mss;
2644
2645 #ifdef RTV_RPIPE
2646         if ((bufsize = rt->rt_rmx.rmx_recvpipe) == 0)
2647 #endif
2648                 bufsize = so->so_rcv.sb_hiwat;
2649         if (bufsize > mss) {
2650                 bufsize = roundup(bufsize, mss);
2651                 if (bufsize > sb_max)
2652                         bufsize = sb_max;
2653                 if (bufsize > so->so_rcv.sb_hiwat)
2654                         (void)sbreserve(&so->so_rcv, bufsize, so, NULL);
2655         }
2656
2657         /*
2658          * Set the slow-start flight size depending on whether this
2659          * is a local network or not.
2660          */
2661         if ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
2662             (!isipv6 && in_localaddr(inp->inp_faddr)))
2663                 tp->snd_cwnd = mss * ss_fltsz_local;
2664         else
2665                 tp->snd_cwnd = mss * ss_fltsz;
2666
2667         if (rt->rt_rmx.rmx_ssthresh) {
2668                 /*
2669                  * There's some sort of gateway or interface
2670                  * buffer limit on the path.  Use this to set
2671                  * the slow start threshhold, but set the
2672                  * threshold to no less than 2*mss.
2673                  */
2674                 tp->snd_ssthresh = max(2 * mss, rt->rt_rmx.rmx_ssthresh);
2675                 tcpstat.tcps_usedssthresh++;
2676         }
2677 }
2678
2679 /*
2680  * Determine the MSS option to send on an outgoing SYN.
2681  */
2682 int
2683 tcp_mssopt(tp)
2684         struct tcpcb *tp;
2685 {
2686         struct rtentry *rt;
2687 #ifdef INET6
2688         int isipv6 = ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
2689         int min_protoh = isipv6 ?
2690                              sizeof(struct ip6_hdr) + sizeof(struct tcphdr) :
2691                              sizeof(struct tcpiphdr);
2692 #else
2693         const int isipv6 = 0;
2694         const size_t min_protoh = sizeof(struct tcpiphdr);
2695 #endif
2696
2697         if (isipv6)
2698                 rt = tcp_rtlookup6(&tp->t_inpcb->inp_inc);
2699         else
2700                 rt = tcp_rtlookup(&tp->t_inpcb->inp_inc);
2701         if (rt == NULL)
2702                 return (isipv6 ? tcp_v6mssdflt : tcp_mssdflt);
2703
2704         return (rt->rt_ifp->if_mtu - min_protoh);
2705 }
2706
2707
2708 /*
2709  * When a partial ack arrives, force the retransmission of the
2710  * next unacknowledged segment.  Do not clear tp->t_dupacks.
2711  * By setting snd_nxt to ti_ack, this forces retransmission timer to
2712  * be started again.
2713  */
2714 static void
2715 tcp_newreno_partial_ack(tp, th)
2716         struct tcpcb *tp;
2717         struct tcphdr *th;
2718 {
2719         tcp_seq onxt = tp->snd_nxt;
2720         u_long  ocwnd = tp->snd_cwnd;
2721
2722         callout_stop(tp->tt_rexmt);
2723         tp->t_rtttime = 0;
2724         tp->snd_nxt = th->th_ack;
2725         /*
2726          * Set snd_cwnd to one segment beyond acknowledged offset
2727          * (tp->snd_una has not yet been updated when this function is called.)
2728          */
2729         tp->snd_cwnd = tp->t_maxseg + (th->th_ack - tp->snd_una);
2730         tp->t_flags |= TF_ACKNOW;
2731         (void) tcp_output(tp);
2732         tp->snd_cwnd = ocwnd;
2733         if (SEQ_GT(onxt, tp->snd_nxt))
2734                 tp->snd_nxt = onxt;
2735         /*
2736          * Partial window deflation.  Relies on fact that tp->snd_una
2737          * not updated yet.
2738          */
2739         tp->snd_cwnd -= (th->th_ack - tp->snd_una - tp->t_maxseg);
2740 }