slirp/tcp_input.c

   1 /*
   2  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994
   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. Neither the name of the University nor the names of its contributors
  14  *    may be used to endorse or promote products derived from this software
  15  *    without specific prior written permission.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  27  * SUCH DAMAGE.
  28  *
  29  *      @(#)tcp_input.c 8.5 (Berkeley) 4/10/94
  30  * tcp_input.c,v 1.10 1994/10/13 18:36:32 wollman Exp
  31  */
  32
  33 /*
  34  * Changes and additions relating to SLiRP
  35  * Copyright (c) 1995 Danny Gasparovski.
  36  *
  37  * Please read the file COPYRIGHT for the
  38  * terms and conditions of the copyright.
  39  */
  40
  41 #include <slirp.h>
  42 #include "ip_icmp.h"
  43
  44 #define TCPREXMTTHRESH 3
  45
  46 #define TCP_PAWS_IDLE   (24 * 24 * 60 * 60 * PR_SLOWHZ)
  47
  48 /* for modulo comparisons of timestamps */
  49 #define TSTMP_LT(a,b)   ((int)((a)-(b)) < 0)
  50 #define TSTMP_GEQ(a,b)  ((int)((a)-(b)) >= 0)
  51
  52 /*
  53  * Insert segment ti into reassembly queue of tcp with
  54  * control block tp.  Return TH_FIN if reassembly now includes
  55  * a segment with FIN.  The macro form does the common case inline
  56  * (segment is the next to be received on an established connection,
  57  * and the queue is empty), avoiding linkage into and removal
  58  * from the queue and repetition of various conversions.
  59  * Set DELACK for segments received in order, but ack immediately
  60  * when segments are out of order (so fast retransmit can work).
  61  */
  62 #ifdef TCP_ACK_HACK
  63 #define TCP_REASS(tp, ti, m, so, flags) {\
  64        if ((ti)->ti_seq == (tp)->rcv_nxt && \
  65            tcpfrag_list_empty(tp) && \
  66            (tp)->t_state == TCPS_ESTABLISHED) {\
  67                if (ti->ti_flags & TH_PUSH) \
  68                        tp->t_flags |= TF_ACKNOW; \
  69                else \
  70                        tp->t_flags |= TF_DELACK; \
  71                (tp)->rcv_nxt += (ti)->ti_len; \
  72                flags = (ti)->ti_flags & TH_FIN; \
  73                if (so->so_emu) { \
  74                        if (tcp_emu((so),(m))) sbappend((so), (m)); \
  75                } else \
  76                        sbappend((so), (m)); \
  77         } else {\
  78                (flags) = tcp_reass((tp), (ti), (m)); \
  79                tp->t_flags |= TF_ACKNOW; \
  80        } \
  81 }
  82 #else
  83 #define TCP_REASS(tp, ti, m, so, flags) { \
  84         if ((ti)->ti_seq == (tp)->rcv_nxt && \
  85         tcpfrag_list_empty(tp) && \
  86             (tp)->t_state == TCPS_ESTABLISHED) { \
  87                 tp->t_flags |= TF_DELACK; \
  88                 (tp)->rcv_nxt += (ti)->ti_len; \
  89                 flags = (ti)->ti_flags & TH_FIN; \
  90                 if (so->so_emu) { \
  91                         if (tcp_emu((so),(m))) sbappend(so, (m)); \
  92                 } else \
  93                         sbappend((so), (m)); \
  94         } else { \
  95                 (flags) = tcp_reass((tp), (ti), (m)); \
  96                 tp->t_flags |= TF_ACKNOW; \
  97         } \
  98 }
  99 #endif
 100 static void tcp_dooptions(struct tcpcb *tp, u_char *cp, int cnt,
 101                           struct tcpiphdr *ti);
 102 static void tcp_xmit_timer(register struct tcpcb *tp, int rtt);
 103
 104 static int
 105 tcp_reass(register struct tcpcb *tp, register struct tcpiphdr *ti,
 106           struct mbuf *m)
 107 {
 108         register struct tcpiphdr *q;
 109         struct socket *so = tp->t_socket;
 110         int flags;
 111
 112         /*
 113          * Call with ti==NULL after become established to
 114          * force pre-ESTABLISHED data up to user socket.
 115          */
 116         if (ti == NULL)
 117                 goto present;
 118
 119         /*
 120          * Find a segment which begins after this one does.
 121          */
 122         for (q = tcpfrag_list_first(tp); !tcpfrag_list_end(q, tp);
 123             q = tcpiphdr_next(q))
 124                 if (SEQ_GT(q->ti_seq, ti->ti_seq))
 125                         break;
 126
 127         /*
 128          * If there is a preceding segment, it may provide some of
 129          * our data already.  If so, drop the data from the incoming
 130          * segment.  If it provides all of our data, drop us.
 131          */
 132         if (!tcpfrag_list_end(tcpiphdr_prev(q), tp)) {
 133                 register int i;
 134                 q = tcpiphdr_prev(q);
 135                 /* conversion to int (in i) handles seq wraparound */
 136                 i = q->ti_seq + q->ti_len - ti->ti_seq;
 137                 if (i > 0) {
 138                         if (i >= ti->ti_len) {
 139                                 m_free(m);
 140                                 /*
 141                                  * Try to present any queued data
 142                                  * at the left window edge to the user.
 143                                  * This is needed after the 3-WHS
 144                                  * completes.
 145                                  */
 146                                 goto present;   /* ??? */
 147                         }
 148                         m_adj(m, i);
 149                         ti->ti_len -= i;
 150                         ti->ti_seq += i;
 151                 }
 152                 q = tcpiphdr_next(q);
 153         }
 154         ti->ti_mbuf = m;
 155
 156         /*
 157          * While we overlap succeeding segments trim them or,
 158          * if they are completely covered, dequeue them.
 159          */
 160         while (!tcpfrag_list_end(q, tp)) {
 161                 register int i = (ti->ti_seq + ti->ti_len) - q->ti_seq;
 162                 if (i <= 0)
 163                         break;
 164                 if (i < q->ti_len) {
 165                         q->ti_seq += i;
 166                         q->ti_len -= i;
 167                         m_adj(q->ti_mbuf, i);
 168                         break;
 169                 }
 170                 q = tcpiphdr_next(q);
 171                 m = tcpiphdr_prev(q)->ti_mbuf;
 172                 remque(tcpiphdr2qlink(tcpiphdr_prev(q)));
 173                 m_free(m);
 174         }
 175
 176         /*
 177          * Stick new segment in its place.
 178          */
 179         insque(tcpiphdr2qlink(ti), tcpiphdr2qlink(tcpiphdr_prev(q)));
 180
 181 present:
 182         /*
 183          * Present data to user, advancing rcv_nxt through
 184          * completed sequence space.
 185          */
 186         if (!TCPS_HAVEESTABLISHED(tp->t_state))
 187                 return (0);
 188         ti = tcpfrag_list_first(tp);
 189         if (tcpfrag_list_end(ti, tp) || ti->ti_seq != tp->rcv_nxt)
 190                 return (0);
 191         if (tp->t_state == TCPS_SYN_RECEIVED && ti->ti_len)
 192                 return (0);
 193         do {
 194                 tp->rcv_nxt += ti->ti_len;
 195                 flags = ti->ti_flags & TH_FIN;
 196                 remque(tcpiphdr2qlink(ti));
 197                 m = ti->ti_mbuf;
 198                 ti = tcpiphdr_next(ti);
 199                 if (so->so_state & SS_FCANTSENDMORE)
 200                         m_free(m);
 201                 else {
 202                         if (so->so_emu) {
 203                                 if (tcp_emu(so,m)) sbappend(so, m);
 204                         } else
 205                                 sbappend(so, m);
 206                 }
 207         } while (ti != (struct tcpiphdr *)tp && ti->ti_seq == tp->rcv_nxt);
 208         return (flags);
 209 }
 210
 211 /*
 212  * TCP input routine, follows pages 65-76 of the
 213  * protocol specification dated September, 1981 very closely.
 214  */
 215 void
 216 tcp_input(struct mbuf *m, int iphlen, struct socket *inso)
 217 {
 218         struct ip save_ip, *ip;
 219         register struct tcpiphdr *ti;
 220         caddr_t optp = NULL;
 221         int optlen = 0;
 222         int len, tlen, off;
 223         register struct tcpcb *tp = NULL;
 224         register int tiflags;
 225         struct socket *so = NULL;
 226         int todrop, acked, ourfinisacked, needoutput = 0;
 227         int iss = 0;
 228         u_long tiwin;
 229         int ret;
 230     struct ex_list *ex_ptr;
 231     Slirp *slirp;
 232
 233         DEBUG_CALL("tcp_input");
 234         DEBUG_ARGS((dfd, " m = %8lx  iphlen = %2d  inso = %lx\n",
 235                     (long )m, iphlen, (long )inso ));
 236
 237         /*
 238          * If called with m == 0, then we're continuing the connect
 239          */
 240         if (m == NULL) {
 241                 so = inso;
 242                 slirp = so->slirp;
 243
 244                 /* Re-set a few variables */
 245                 tp = sototcpcb(so);
 246                 m = so->so_m;
 247                 so->so_m = NULL;
 248                 ti = so->so_ti;
 249                 tiwin = ti->ti_win;
 250                 tiflags = ti->ti_flags;
 251
 252                 goto cont_conn;
 253         }
 254         slirp = m->slirp;
 255
 256         /*
 257          * Get IP and TCP header together in first mbuf.
 258          * Note: IP leaves IP header in first mbuf.
 259          */
 260         ti = mtod(m, struct tcpiphdr *);
 261         if (iphlen > sizeof(struct ip )) {
 262           ip_stripoptions(m, (struct mbuf *)0);
 263           iphlen=sizeof(struct ip );
 264         }
 265         /* XXX Check if too short */
 266
 267
 268         /*
 269          * Save a copy of the IP header in case we want restore it
 270          * for sending an ICMP error message in response.
 271          */
 272         ip=mtod(m, struct ip *);
 273         save_ip = *ip;
 274         save_ip.ip_len+= iphlen;
 275
 276         /*
 277          * Checksum extended TCP header and data.
 278          */
 279         tlen = ((struct ip *)ti)->ip_len;
 280         tcpiphdr2qlink(ti)->next = tcpiphdr2qlink(ti)->prev = NULL;
 281         memset(&ti->ti_i.ih_mbuf, 0 , sizeof(struct mbuf_ptr));
 282         ti->ti_x1 = 0;
 283         ti->ti_len = htons((uint16_t)tlen);
 284         len = sizeof(struct ip ) + tlen;
 285         if(cksum(m, len)) {
 286           goto drop;
 287         }
 288
 289         /*
 290          * Check that TCP offset makes sense,
 291          * pull out TCP options and adjust length.              XXX
 292          */
 293         off = ti->ti_off << 2;
 294         if (off < sizeof (struct tcphdr) || off > tlen) {
 295           goto drop;
 296         }
 297         tlen -= off;
 298         ti->ti_len = tlen;
 299         if (off > sizeof (struct tcphdr)) {
 300           optlen = off - sizeof (struct tcphdr);
 301           optp = mtod(m, caddr_t) + sizeof (struct tcpiphdr);
 302         }
 303         tiflags = ti->ti_flags;
 304
 305         /*
 306          * Convert TCP protocol specific fields to host format.
 307          */
 308         NTOHL(ti->ti_seq);
 309         NTOHL(ti->ti_ack);
 310         NTOHS(ti->ti_win);
 311         NTOHS(ti->ti_urp);
 312
 313         /*
 314          * Drop TCP, IP headers and TCP options.
 315          */
 316         m->m_data += sizeof(struct tcpiphdr)+off-sizeof(struct tcphdr);
 317         m->m_len  -= sizeof(struct tcpiphdr)+off-sizeof(struct tcphdr);
 318
 319     if (slirp->restricted) {
 320         for (ex_ptr = slirp->exec_list; ex_ptr; ex_ptr = ex_ptr->ex_next) {
 321             if (ex_ptr->ex_fport == ti->ti_dport &&
 322                 ti->ti_dst.s_addr == ex_ptr->ex_addr.s_addr) {
 323                 break;
 324             }
 325         }
 326         if (!ex_ptr)
 327             goto drop;
 328     }
 329         /*
 330          * Locate pcb for segment.
 331          */
 332 findso:
 333         so = slirp->tcp_last_so;
 334         if (so->so_fport != ti->ti_dport ||
 335             so->so_lport != ti->ti_sport ||
 336             so->so_laddr.s_addr != ti->ti_src.s_addr ||
 337             so->so_faddr.s_addr != ti->ti_dst.s_addr) {
 338                 so = solookup(&slirp->tcb, ti->ti_src, ti->ti_sport,
 339                                ti->ti_dst, ti->ti_dport);
 340                 if (so)
 341                         slirp->tcp_last_so = so;
 342         }
 343
 344         /*
 345          * If the state is CLOSED (i.e., TCB does not exist) then
 346          * all data in the incoming segment is discarded.
 347          * If the TCB exists but is in CLOSED state, it is embryonic,
 348          * but should either do a listen or a connect soon.
 349          *
 350          * state == CLOSED means we've done socreate() but haven't
 351          * attached it to a protocol yet...
 352          *
 353          * XXX If a TCB does not exist, and the TH_SYN flag is
 354          * the only flag set, then create a session, mark it
 355          * as if it was LISTENING, and continue...
 356          */
 357         if (so == NULL) {
 358           if ((tiflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) != TH_SYN)
 359             goto dropwithreset;
 360
 361           if ((so = socreate(slirp)) == NULL)
 362             goto dropwithreset;
 363           if (tcp_attach(so) < 0) {
 364             free(so); /* Not sofree (if it failed, it's not insqued) */
 365             goto dropwithreset;
 366           }
 367
 368           sbreserve(&so->so_snd, TCP_SNDSPACE);
 369           sbreserve(&so->so_rcv, TCP_RCVSPACE);
 370
 371           so->so_laddr = ti->ti_src;
 372           so->so_lport = ti->ti_sport;
 373           so->so_faddr = ti->ti_dst;
 374           so->so_fport = ti->ti_dport;
 375
 376           if ((so->so_iptos = tcp_tos(so)) == 0)
 377             so->so_iptos = ((struct ip *)ti)->ip_tos;
 378
 379           tp = sototcpcb(so);
 380           tp->t_state = TCPS_LISTEN;
 381         }
 382
 383         /*
 384          * If this is a still-connecting socket, this probably
 385          * a retransmit of the SYN.  Whether it's a retransmit SYN
 386          * or something else, we nuke it.
 387          */
 388         if (so->so_state & SS_ISFCONNECTING)
 389                 goto drop;
 390
 391         tp = sototcpcb(so);
 392
 393         /* XXX Should never fail */
 394         if (tp == NULL)
 395                 goto dropwithreset;
 396         if (tp->t_state == TCPS_CLOSED)
 397                 goto drop;
 398
 399         tiwin = ti->ti_win;
 400
 401         /*
 402          * Segment received on connection.
 403          * Reset idle time and keep-alive timer.
 404          */
 405         tp->t_idle = 0;
 406         if (SO_OPTIONS)
 407            tp->t_timer[TCPT_KEEP] = TCPTV_KEEPINTVL;
 408         else
 409            tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_IDLE;
 410
 411         /*
 412          * Process options if not in LISTEN state,
 413          * else do it below (after getting remote address).
 414          */
 415         if (optp && tp->t_state != TCPS_LISTEN)
 416                 tcp_dooptions(tp, (u_char *)optp, optlen, ti);
 417
 418         /*
 419          * Header prediction: check for the two common cases
 420          * of a uni-directional data xfer.  If the packet has
 421          * no control flags, is in-sequence, the window didn't
 422          * change and we're not retransmitting, it's a
 423          * candidate.  If the length is zero and the ack moved
 424          * forward, we're the sender side of the xfer.  Just
 425          * free the data acked & wake any higher level process
 426          * that was blocked waiting for space.  If the length
 427          * is non-zero and the ack didn't move, we're the
 428          * receiver side.  If we're getting packets in-order
 429          * (the reassembly queue is empty), add the data to
 430          * the socket buffer and note that we need a delayed ack.
 431          *
 432          * XXX Some of these tests are not needed
 433          * eg: the tiwin == tp->snd_wnd prevents many more
 434          * predictions.. with no *real* advantage..
 435          */
 436         if (tp->t_state == TCPS_ESTABLISHED &&
 437             (tiflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
 438             ti->ti_seq == tp->rcv_nxt &&
 439             tiwin && tiwin == tp->snd_wnd &&
 440             tp->snd_nxt == tp->snd_max) {
 441                 if (ti->ti_len == 0) {
 442                         if (SEQ_GT(ti->ti_ack, tp->snd_una) &&
 443                             SEQ_LEQ(ti->ti_ack, tp->snd_max) &&
 444                             tp->snd_cwnd >= tp->snd_wnd) {
 445                                 /*
 446                                  * this is a pure ack for outstanding data.
 447                                  */
 448                                 if (tp->t_rtt &&
 449                                     SEQ_GT(ti->ti_ack, tp->t_rtseq))
 450                                         tcp_xmit_timer(tp, tp->t_rtt);
 451                                 acked = ti->ti_ack - tp->snd_una;
 452                                 sbdrop(&so->so_snd, acked);
 453                                 tp->snd_una = ti->ti_ack;
 454                                 m_free(m);
 455
 456                                 /*
 457                                  * If all outstanding data are acked, stop
 458                                  * retransmit timer, otherwise restart timer
 459                                  * using current (possibly backed-off) value.
 460                                  * If process is waiting for space,
 461                                  * wakeup/selwakeup/signal.  If data
 462                                  * are ready to send, let tcp_output
 463                                  * decide between more output or persist.
 464                                  */
 465                                 if (tp->snd_una == tp->snd_max)
 466                                         tp->t_timer[TCPT_REXMT] = 0;
 467                                 else if (tp->t_timer[TCPT_PERSIST] == 0)
 468                                         tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
 469
 470                                 /*
 471                                  * This is called because sowwakeup might have
 472                                  * put data into so_snd.  Since we don't so sowwakeup,
 473                                  * we don't need this.. XXX???
 474                                  */
 475                                 if (so->so_snd.sb_cc)
 476                                         (void) tcp_output(tp);
 477
 478                                 return;
 479                         }
 480                 } else if (ti->ti_ack == tp->snd_una &&
 481                     tcpfrag_list_empty(tp) &&
 482                     ti->ti_len <= sbspace(&so->so_rcv)) {
 483                         /*
 484                          * this is a pure, in-sequence data packet
 485                          * with nothing on the reassembly queue and
 486                          * we have enough buffer space to take it.
 487                          */
 488                         tp->rcv_nxt += ti->ti_len;
 489                         /*
 490                          * Add data to socket buffer.
 491                          */
 492                         if (so->so_emu) {
 493                                 if (tcp_emu(so,m)) sbappend(so, m);
 494                         } else
 495                                 sbappend(so, m);
 496
 497                         /*
 498                          * If this is a short packet, then ACK now - with Nagel
 499                          *      congestion avoidance sender won't send more until
 500                          *      he gets an ACK.
 501                          *
 502                          * It is better to not delay acks at all to maximize
 503                          * TCP throughput.  See RFC 2581.
 504                          */
 505                         tp->t_flags |= TF_ACKNOW;
 506                         tcp_output(tp);
 507                         return;
 508                 }
 509         } /* header prediction */
 510         /*
 511          * Calculate amount of space in receive window,
 512          * and then do TCP input processing.
 513          * Receive window is amount of space in rcv queue,
 514          * but not less than advertised window.
 515          */
 516         { int win;
 517           win = sbspace(&so->so_rcv);
 518           if (win < 0)
 519             win = 0;
 520           tp->rcv_wnd = max(win, (int)(tp->rcv_adv - tp->rcv_nxt));
 521         }
 522
 523         switch (tp->t_state) {
 524
 525         /*
 526          * If the state is LISTEN then ignore segment if it contains an RST.
 527          * If the segment contains an ACK then it is bad and send a RST.
 528          * If it does not contain a SYN then it is not interesting; drop it.
 529          * Don't bother responding if the destination was a broadcast.
 530          * Otherwise initialize tp->rcv_nxt, and tp->irs, select an initial
 531          * tp->iss, and send a segment:
 532          *     <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
 533          * Also initialize tp->snd_nxt to tp->iss+1 and tp->snd_una to tp->iss.
 534          * Fill in remote peer address fields if not previously specified.
 535          * Enter SYN_RECEIVED state, and process any other fields of this
 536          * segment in this state.
 537          */
 538         case TCPS_LISTEN: {
 539
 540           if (tiflags & TH_RST)
 541             goto drop;
 542           if (tiflags & TH_ACK)
 543             goto dropwithreset;
 544           if ((tiflags & TH_SYN) == 0)
 545             goto drop;
 546
 547           /*
 548            * This has way too many gotos...
 549            * But a bit of spaghetti code never hurt anybody :)
 550            */
 551
 552           /*
 553            * If this is destined for the control address, then flag to
 554            * tcp_ctl once connected, otherwise connect
 555            */
 556           if ((so->so_faddr.s_addr & slirp->vnetwork_mask.s_addr) ==
 557               slirp->vnetwork_addr.s_addr) {
 558             if (so->so_faddr.s_addr != slirp->vhost_addr.s_addr &&
 559                 so->so_faddr.s_addr != slirp->vnameserver_addr.s_addr) {
 560                 /* May be an add exec */
 561                 for (ex_ptr = slirp->exec_list; ex_ptr;
 562                      ex_ptr = ex_ptr->ex_next) {
 563                   if(ex_ptr->ex_fport == so->so_fport &&
 564                      so->so_faddr.s_addr == ex_ptr->ex_addr.s_addr) {
 565                     so->so_state |= SS_CTL;
 566                     break;
 567                   }
 568                 }
 569                 if (so->so_state & SS_CTL) {
 570                     goto cont_input;
 571                 }
 572             }
 573             /* CTL_ALIAS: Do nothing, tcp_fconnect will be called on it */
 574           }
 575
 576           if (so->so_emu & EMU_NOCONNECT) {
 577             so->so_emu &= ~EMU_NOCONNECT;
 578             goto cont_input;
 579           }
 580
 581           if((tcp_fconnect(so) == -1) && (errno != EINPROGRESS) && (errno != EWOULDBLOCK)) {
 582             u_char code=ICMP_UNREACH_NET;
 583             DEBUG_MISC((dfd, " tcp fconnect errno = %d-%s\n",
 584                         errno,strerror(errno)));
 585             if(errno == ECONNREFUSED) {
 586               /* ACK the SYN, send RST to refuse the connection */
 587               tcp_respond(tp, ti, m, ti->ti_seq+1, (tcp_seq)0,
 588                           TH_RST|TH_ACK);
 589             } else {
 590               if(errno == EHOSTUNREACH) code=ICMP_UNREACH_HOST;
 591               HTONL(ti->ti_seq);             /* restore tcp header */
 592               HTONL(ti->ti_ack);
 593               HTONS(ti->ti_win);
 594               HTONS(ti->ti_urp);
 595               m->m_data -= sizeof(struct tcpiphdr)+off-sizeof(struct tcphdr);
 596               m->m_len  += sizeof(struct tcpiphdr)+off-sizeof(struct tcphdr);
 597               *ip=save_ip;
 598               icmp_error(m, ICMP_UNREACH,code, 0,strerror(errno));
 599             }
 600             tcp_close(tp);
 601             m_free(m);
 602           } else {
 603             /*
 604              * Haven't connected yet, save the current mbuf
 605              * and ti, and return
 606              * XXX Some OS's don't tell us whether the connect()
 607              * succeeded or not.  So we must time it out.
 608              */
 609             so->so_m = m;
 610             so->so_ti = ti;
 611             tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_INIT;
 612             tp->t_state = TCPS_SYN_RECEIVED;
 613             tcp_template(tp);
 614           }
 615           return;
 616
 617         cont_conn:
 618           /* m==NULL
 619            * Check if the connect succeeded
 620            */
 621           if (so->so_state & SS_NOFDREF) {
 622             tp = tcp_close(tp);
 623             goto dropwithreset;
 624           }
 625         cont_input:
 626           tcp_template(tp);
 627
 628           if (optp)
 629             tcp_dooptions(tp, (u_char *)optp, optlen, ti);
 630
 631           if (iss)
 632             tp->iss = iss;
 633           else
 634             tp->iss = slirp->tcp_iss;
 635           slirp->tcp_iss += TCP_ISSINCR/2;
 636           tp->irs = ti->ti_seq;
 637           tcp_sendseqinit(tp);
 638           tcp_rcvseqinit(tp);
 639           tp->t_flags |= TF_ACKNOW;
 640           tp->t_state = TCPS_SYN_RECEIVED;
 641           tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_INIT;
 642           goto trimthenstep6;
 643         } /* case TCPS_LISTEN */
 644
 645         /*
 646          * If the state is SYN_SENT:
 647          *      if seg contains an ACK, but not for our SYN, drop the input.
 648          *      if seg contains a RST, then drop the connection.
 649          *      if seg does not contain SYN, then drop it.
 650          * Otherwise this is an acceptable SYN segment
 651          *      initialize tp->rcv_nxt and tp->irs
 652          *      if seg contains ack then advance tp->snd_una
 653          *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
 654          *      arrange for segment to be acked (eventually)
 655          *      continue processing rest of data/controls, beginning with URG
 656          */
 657         case TCPS_SYN_SENT:
 658                 if ((tiflags & TH_ACK) &&
 659                     (SEQ_LEQ(ti->ti_ack, tp->iss) ||
 660                      SEQ_GT(ti->ti_ack, tp->snd_max)))
 661                         goto dropwithreset;
 662
 663                 if (tiflags & TH_RST) {
 664                         if (tiflags & TH_ACK) {
 665                                 tcp_drop(tp, 0); /* XXX Check t_softerror! */
 666                         }
 667                         goto drop;
 668                 }
 669
 670                 if ((tiflags & TH_SYN) == 0)
 671                         goto drop;
 672                 if (tiflags & TH_ACK) {
 673                         tp->snd_una = ti->ti_ack;
 674                         if (SEQ_LT(tp->snd_nxt, tp->snd_una))
 675                                 tp->snd_nxt = tp->snd_una;
 676                 }
 677
 678                 tp->t_timer[TCPT_REXMT] = 0;
 679                 tp->irs = ti->ti_seq;
 680                 tcp_rcvseqinit(tp);
 681                 tp->t_flags |= TF_ACKNOW;
 682                 if (tiflags & TH_ACK && SEQ_GT(tp->snd_una, tp->iss)) {
 683                         soisfconnected(so);
 684                         tp->t_state = TCPS_ESTABLISHED;
 685
 686                         (void) tcp_reass(tp, (struct tcpiphdr *)0,
 687                                 (struct mbuf *)0);
 688                         /*
 689                          * if we didn't have to retransmit the SYN,
 690                          * use its rtt as our initial srtt & rtt var.
 691                          */
 692                         if (tp->t_rtt)
 693                                 tcp_xmit_timer(tp, tp->t_rtt);
 694                 } else
 695                         tp->t_state = TCPS_SYN_RECEIVED;
 696
 697 trimthenstep6:
 698                 /*
 699                  * Advance ti->ti_seq to correspond to first data byte.
 700                  * If data, trim to stay within window,
 701                  * dropping FIN if necessary.
 702                  */
 703                 ti->ti_seq++;
 704                 if (ti->ti_len > tp->rcv_wnd) {
 705                         todrop = ti->ti_len - tp->rcv_wnd;
 706                         m_adj(m, -todrop);
 707                         ti->ti_len = tp->rcv_wnd;
 708                         tiflags &= ~TH_FIN;
 709                 }
 710                 tp->snd_wl1 = ti->ti_seq - 1;
 711                 tp->rcv_up = ti->ti_seq;
 712                 goto step6;
 713         } /* switch tp->t_state */
 714         /*
 715          * States other than LISTEN or SYN_SENT.
 716          * Check that at least some bytes of segment are within
 717          * receive window.  If segment begins before rcv_nxt,
 718          * drop leading data (and SYN); if nothing left, just ack.
 719          */
 720         todrop = tp->rcv_nxt - ti->ti_seq;
 721         if (todrop > 0) {
 722                 if (tiflags & TH_SYN) {
 723                         tiflags &= ~TH_SYN;
 724                         ti->ti_seq++;
 725                         if (ti->ti_urp > 1)
 726                                 ti->ti_urp--;
 727                         else
 728                                 tiflags &= ~TH_URG;
 729                         todrop--;
 730                 }
 731                 /*
 732                  * Following if statement from Stevens, vol. 2, p. 960.
 733                  */
 734                 if (todrop > ti->ti_len
 735                     || (todrop == ti->ti_len && (tiflags & TH_FIN) == 0)) {
 736                         /*
 737                          * Any valid FIN must be to the left of the window.
 738                          * At this point the FIN must be a duplicate or out
 739                          * of sequence; drop it.
 740                          */
 741                         tiflags &= ~TH_FIN;
 742
 743                         /*
 744                          * Send an ACK to resynchronize and drop any data.
 745                          * But keep on processing for RST or ACK.
 746                          */
 747                         tp->t_flags |= TF_ACKNOW;
 748                         todrop = ti->ti_len;
 749                 }
 750                 m_adj(m, todrop);
 751                 ti->ti_seq += todrop;
 752                 ti->ti_len -= todrop;
 753                 if (ti->ti_urp > todrop)
 754                         ti->ti_urp -= todrop;
 755                 else {
 756                         tiflags &= ~TH_URG;
 757                         ti->ti_urp = 0;
 758                 }
 759         }
 760         /*
 761          * If new data are received on a connection after the
 762          * user processes are gone, then RST the other end.
 763          */
 764         if ((so->so_state & SS_NOFDREF) &&
 765             tp->t_state > TCPS_CLOSE_WAIT && ti->ti_len) {
 766                 tp = tcp_close(tp);
 767                 goto dropwithreset;
 768         }
 769
 770         /*
 771          * If segment ends after window, drop trailing data
 772          * (and PUSH and FIN); if nothing left, just ACK.
 773          */
 774         todrop = (ti->ti_seq+ti->ti_len) - (tp->rcv_nxt+tp->rcv_wnd);
 775         if (todrop > 0) {
 776                 if (todrop >= ti->ti_len) {
 777                         /*
 778                          * If a new connection request is received
 779                          * while in TIME_WAIT, drop the old connection
 780                          * and start over if the sequence numbers
 781                          * are above the previous ones.
 782                          */
 783                         if (tiflags & TH_SYN &&
 784                             tp->t_state == TCPS_TIME_WAIT &&
 785                             SEQ_GT(ti->ti_seq, tp->rcv_nxt)) {
 786                                 iss = tp->rcv_nxt + TCP_ISSINCR;
 787                                 tp = tcp_close(tp);
 788                                 goto findso;
 789                         }
 790                         /*
 791                          * If window is closed can only take segments at
 792                          * window edge, and have to drop data and PUSH from
 793                          * incoming segments.  Continue processing, but
 794                          * remember to ack.  Otherwise, drop segment
 795                          * and ack.
 796                          */
 797                         if (tp->rcv_wnd == 0 && ti->ti_seq == tp->rcv_nxt) {
 798                                 tp->t_flags |= TF_ACKNOW;
 799                         } else {
 800                                 goto dropafterack;
 801                         }
 802                 }
 803                 m_adj(m, -todrop);
 804                 ti->ti_len -= todrop;
 805                 tiflags &= ~(TH_PUSH|TH_FIN);
 806         }
 807
 808         /*
 809          * If the RST bit is set examine the state:
 810          *    SYN_RECEIVED STATE:
 811          *      If passive open, return to LISTEN state.
 812          *      If active open, inform user that connection was refused.
 813          *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT2, CLOSE_WAIT STATES:
 814          *      Inform user that connection was reset, and close tcb.
 815          *    CLOSING, LAST_ACK, TIME_WAIT STATES
 816          *      Close the tcb.
 817          */
 818         if (tiflags&TH_RST) switch (tp->t_state) {
 819
 820         case TCPS_SYN_RECEIVED:
 821         case TCPS_ESTABLISHED:
 822         case TCPS_FIN_WAIT_1:
 823         case TCPS_FIN_WAIT_2:
 824         case TCPS_CLOSE_WAIT:
 825                 tp->t_state = TCPS_CLOSED;
 826                 tcp_close(tp);
 827                 goto drop;
 828
 829         case TCPS_CLOSING:
 830         case TCPS_LAST_ACK:
 831         case TCPS_TIME_WAIT:
 832                 tcp_close(tp);
 833                 goto drop;
 834         }
 835
 836         /*
 837          * If a SYN is in the window, then this is an
 838          * error and we send an RST and drop the connection.
 839          */
 840         if (tiflags & TH_SYN) {
 841                 tp = tcp_drop(tp,0);
 842                 goto dropwithreset;
 843         }
 844
 845         /*
 846          * If the ACK bit is off we drop the segment and return.
 847          */
 848         if ((tiflags & TH_ACK) == 0) goto drop;
 849
 850         /*
 851          * Ack processing.
 852          */
 853         switch (tp->t_state) {
 854         /*
 855          * In SYN_RECEIVED state if the ack ACKs our SYN then enter
 856          * ESTABLISHED state and continue processing, otherwise
 857          * send an RST.  una<=ack<=max
 858          */
 859         case TCPS_SYN_RECEIVED:
 860
 861                 if (SEQ_GT(tp->snd_una, ti->ti_ack) ||
 862                     SEQ_GT(ti->ti_ack, tp->snd_max))
 863                         goto dropwithreset;
 864                 tp->t_state = TCPS_ESTABLISHED;
 865                 /*
 866                  * The sent SYN is ack'ed with our sequence number +1
 867                  * The first data byte already in the buffer will get
 868                  * lost if no correction is made.  This is only needed for
 869                  * SS_CTL since the buffer is empty otherwise.
 870                  * tp->snd_una++; or:
 871                  */
 872                 tp->snd_una=ti->ti_ack;
 873                 if (so->so_state & SS_CTL) {
 874                   /* So tcp_ctl reports the right state */
 875                   ret = tcp_ctl(so);
 876                   if (ret == 1) {
 877                     soisfconnected(so);
 878                     so->so_state &= ~SS_CTL;   /* success XXX */
 879                   } else if (ret == 2) {
 880                     so->so_state &= SS_PERSISTENT_MASK;
 881                     so->so_state |= SS_NOFDREF; /* CTL_CMD */
 882                   } else {
 883                     needoutput = 1;
 884                     tp->t_state = TCPS_FIN_WAIT_1;
 885                   }
 886                 } else {
 887                   soisfconnected(so);
 888                 }
 889
 890                 (void) tcp_reass(tp, (struct tcpiphdr *)0, (struct mbuf *)0);
 891                 tp->snd_wl1 = ti->ti_seq - 1;
 892                 /* Avoid ack processing; snd_una==ti_ack  =>  dup ack */
 893                 goto synrx_to_est;
 894                 /* fall into ... */
 895
 896         /*
 897          * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
 898          * ACKs.  If the ack is in the range
 899          *      tp->snd_una < ti->ti_ack <= tp->snd_max
 900          * then advance tp->snd_una to ti->ti_ack and drop
 901          * data from the retransmission queue.  If this ACK reflects
 902          * more up to date window information we update our window information.
 903          */
 904         case TCPS_ESTABLISHED:
 905         case TCPS_FIN_WAIT_1:
 906         case TCPS_FIN_WAIT_2:
 907         case TCPS_CLOSE_WAIT:
 908         case TCPS_CLOSING:
 909         case TCPS_LAST_ACK:
 910         case TCPS_TIME_WAIT:
 911
 912                 if (SEQ_LEQ(ti->ti_ack, tp->snd_una)) {
 913                         if (ti->ti_len == 0 && tiwin == tp->snd_wnd) {
 914                           DEBUG_MISC((dfd, " dup ack  m = %lx  so = %lx\n",
 915                                       (long )m, (long )so));
 916                                 /*
 917                                  * If we have outstanding data (other than
 918                                  * a window probe), this is a completely
 919                                  * duplicate ack (ie, window info didn't
 920                                  * change), the ack is the biggest we've
 921                                  * seen and we've seen exactly our rexmt
 922                                  * threshold of them, assume a packet
 923                                  * has been dropped and retransmit it.
 924                                  * Kludge snd_nxt & the congestion
 925                                  * window so we send only this one
 926                                  * packet.
 927                                  *
 928                                  * We know we're losing at the current
 929                                  * window size so do congestion avoidance
 930                                  * (set ssthresh to half the current window
 931                                  * and pull our congestion window back to
 932                                  * the new ssthresh).
 933                                  *
 934                                  * Dup acks mean that packets have left the
 935                                  * network (they're now cached at the receiver)
 936                                  * so bump cwnd by the amount in the receiver
 937                                  * to keep a constant cwnd packets in the
 938                                  * network.
 939                                  */
 940                                 if (tp->t_timer[TCPT_REXMT] == 0 ||
 941                                     ti->ti_ack != tp->snd_una)
 942                                         tp->t_dupacks = 0;
 943                                 else if (++tp->t_dupacks == TCPREXMTTHRESH) {
 944                                         tcp_seq onxt = tp->snd_nxt;
 945                                         u_int win =
 946                                             min(tp->snd_wnd, tp->snd_cwnd) / 2 /
 947                                                 tp->t_maxseg;
 948
 949                                         if (win < 2)
 950                                                 win = 2;
 951                                         tp->snd_ssthresh = win * tp->t_maxseg;
 952                                         tp->t_timer[TCPT_REXMT] = 0;
 953                                         tp->t_rtt = 0;
 954                                         tp->snd_nxt = ti->ti_ack;
 955                                         tp->snd_cwnd = tp->t_maxseg;
 956                                         (void) tcp_output(tp);
 957                                         tp->snd_cwnd = tp->snd_ssthresh +
 958                                                tp->t_maxseg * tp->t_dupacks;
 959                                         if (SEQ_GT(onxt, tp->snd_nxt))
 960                                                 tp->snd_nxt = onxt;
 961                                         goto drop;
 962                                 } else if (tp->t_dupacks > TCPREXMTTHRESH) {
 963                                         tp->snd_cwnd += tp->t_maxseg;
 964                                         (void) tcp_output(tp);
 965                                         goto drop;
 966                                 }
 967                         } else
 968                                 tp->t_dupacks = 0;
 969                         break;
 970                 }
 971         synrx_to_est:
 972                 /*
 973                  * If the congestion window was inflated to account
 974                  * for the other side's cached packets, retract it.
 975                  */
 976                 if (tp->t_dupacks > TCPREXMTTHRESH &&
 977                     tp->snd_cwnd > tp->snd_ssthresh)
 978                         tp->snd_cwnd = tp->snd_ssthresh;
 979                 tp->t_dupacks = 0;
 980                 if (SEQ_GT(ti->ti_ack, tp->snd_max)) {
 981                         goto dropafterack;
 982                 }
 983                 acked = ti->ti_ack - tp->snd_una;
 984
 985                 /*
 986                  * If transmit timer is running and timed sequence
 987                  * number was acked, update smoothed round trip time.
 988                  * Since we now have an rtt measurement, cancel the
 989                  * timer backoff (cf., Phil Karn's retransmit alg.).
 990                  * Recompute the initial retransmit timer.
 991                  */
 992                 if (tp->t_rtt && SEQ_GT(ti->ti_ack, tp->t_rtseq))
 993                         tcp_xmit_timer(tp,tp->t_rtt);
 994
 995                 /*
 996                  * If all outstanding data is acked, stop retransmit
 997                  * timer and remember to restart (more output or persist).
 998                  * If there is more data to be acked, restart retransmit
 999                  * timer, using current (possibly backed-off) value.
1000                  */
1001                 if (ti->ti_ack == tp->snd_max) {
1002                         tp->t_timer[TCPT_REXMT] = 0;
1003                         needoutput = 1;
1004                 } else if (tp->t_timer[TCPT_PERSIST] == 0)
1005                         tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
1006                 /*
1007                  * When new data is acked, open the congestion window.
1008                  * If the window gives us less than ssthresh packets
1009                  * in flight, open exponentially (maxseg per packet).
1010                  * Otherwise open linearly: maxseg per window
1011                  * (maxseg^2 / cwnd per packet).
1012                  */
1013                 {
1014                   register u_int cw = tp->snd_cwnd;
1015                   register u_int incr = tp->t_maxseg;
1016
1017                   if (cw > tp->snd_ssthresh)
1018                     incr = incr * incr / cw;
1019                   tp->snd_cwnd = min(cw + incr, TCP_MAXWIN<<tp->snd_scale);
1020                 }
1021                 if (acked > so->so_snd.sb_cc) {
1022                         tp->snd_wnd -= so->so_snd.sb_cc;
1023                         sbdrop(&so->so_snd, (int )so->so_snd.sb_cc);
1024                         ourfinisacked = 1;
1025                 } else {
1026                         sbdrop(&so->so_snd, acked);
1027                         tp->snd_wnd -= acked;
1028                         ourfinisacked = 0;
1029                 }
1030                 tp->snd_una = ti->ti_ack;
1031                 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
1032                         tp->snd_nxt = tp->snd_una;
1033
1034                 switch (tp->t_state) {
1035
1036                 /*
1037                  * In FIN_WAIT_1 STATE in addition to the processing
1038                  * for the ESTABLISHED state if our FIN is now acknowledged
1039                  * then enter FIN_WAIT_2.
1040                  */
1041                 case TCPS_FIN_WAIT_1:
1042                         if (ourfinisacked) {
1043                                 /*
1044                                  * If we can't receive any more
1045                                  * data, then closing user can proceed.
1046                                  * Starting the timer is contrary to the
1047                                  * specification, but if we don't get a FIN
1048                                  * we'll hang forever.
1049                                  */
1050                                 if (so->so_state & SS_FCANTRCVMORE) {
1051                                         tp->t_timer[TCPT_2MSL] = TCP_MAXIDLE;
1052                                 }
1053                                 tp->t_state = TCPS_FIN_WAIT_2;
1054                         }
1055                         break;
1056
1057                 /*
1058                  * In CLOSING STATE in addition to the processing for
1059                  * the ESTABLISHED state if the ACK acknowledges our FIN
1060                  * then enter the TIME-WAIT state, otherwise ignore
1061                  * the segment.
1062                  */
1063                 case TCPS_CLOSING:
1064                         if (ourfinisacked) {
1065                                 tp->t_state = TCPS_TIME_WAIT;
1066                                 tcp_canceltimers(tp);
1067                                 tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
1068                         }
1069                         break;
1070
1071                 /*
1072                  * In LAST_ACK, we may still be waiting for data to drain
1073                  * and/or to be acked, as well as for the ack of our FIN.
1074                  * If our FIN is now acknowledged, delete the TCB,
1075                  * enter the closed state and return.
1076                  */
1077                 case TCPS_LAST_ACK:
1078                         if (ourfinisacked) {
1079                                 tcp_close(tp);
1080                                 goto drop;
1081                         }
1082                         break;
1083
1084                 /*
1085                  * In TIME_WAIT state the only thing that should arrive
1086                  * is a retransmission of the remote FIN.  Acknowledge
1087                  * it and restart the finack timer.
1088                  */
1089                 case TCPS_TIME_WAIT:
1090                         tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
1091                         goto dropafterack;
1092                 }
1093         } /* switch(tp->t_state) */
1094
1095 step6:
1096         /*
1097          * Update window information.
1098          * Don't look at window if no ACK: TAC's send garbage on first SYN.
1099          */
1100         if ((tiflags & TH_ACK) &&
1101             (SEQ_LT(tp->snd_wl1, ti->ti_seq) ||
1102             (tp->snd_wl1 == ti->ti_seq && (SEQ_LT(tp->snd_wl2, ti->ti_ack) ||
1103             (tp->snd_wl2 == ti->ti_ack && tiwin > tp->snd_wnd))))) {
1104                 tp->snd_wnd = tiwin;
1105                 tp->snd_wl1 = ti->ti_seq;
1106                 tp->snd_wl2 = ti->ti_ack;
1107                 if (tp->snd_wnd > tp->max_sndwnd)
1108                         tp->max_sndwnd = tp->snd_wnd;
1109                 needoutput = 1;
1110         }
1111
1112         /*
1113          * Process segments with URG.
1114          */
1115         if ((tiflags & TH_URG) && ti->ti_urp &&
1116             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
1117                 /*
1118                  * This is a kludge, but if we receive and accept
1119                  * random urgent pointers, we'll crash in
1120                  * soreceive.  It's hard to imagine someone
1121                  * actually wanting to send this much urgent data.
1122                  */
1123                 if (ti->ti_urp + so->so_rcv.sb_cc > so->so_rcv.sb_datalen) {
1124                         ti->ti_urp = 0;
1125                         tiflags &= ~TH_URG;
1126                         goto dodata;
1127                 }
1128                 /*
1129                  * If this segment advances the known urgent pointer,
1130                  * then mark the data stream.  This should not happen
1131                  * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
1132                  * a FIN has been received from the remote side.
1133                  * In these states we ignore the URG.
1134                  *
1135                  * According to RFC961 (Assigned Protocols),
1136                  * the urgent pointer points to the last octet
1137                  * of urgent data.  We continue, however,
1138                  * to consider it to indicate the first octet
1139                  * of data past the urgent section as the original
1140                  * spec states (in one of two places).
1141                  */
1142                 if (SEQ_GT(ti->ti_seq+ti->ti_urp, tp->rcv_up)) {
1143                         tp->rcv_up = ti->ti_seq + ti->ti_urp;
1144                         so->so_urgc =  so->so_rcv.sb_cc +
1145                                 (tp->rcv_up - tp->rcv_nxt); /* -1; */
1146                         tp->rcv_up = ti->ti_seq + ti->ti_urp;
1147
1148                 }
1149         } else
1150                 /*
1151                  * If no out of band data is expected,
1152                  * pull receive urgent pointer along
1153                  * with the receive window.
1154                  */
1155                 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
1156                         tp->rcv_up = tp->rcv_nxt;
1157 dodata:
1158
1159         /*
1160          * If this is a small packet, then ACK now - with Nagel
1161          *      congestion avoidance sender won't send more until
1162          *      he gets an ACK.
1163          */
1164         if (ti->ti_len && (unsigned)ti->ti_len <= 5 &&
1165             ((struct tcpiphdr_2 *)ti)->first_char == (char)27) {
1166                 tp->t_flags |= TF_ACKNOW;
1167         }
1168
1169         /*
1170          * Process the segment text, merging it into the TCP sequencing queue,
1171          * and arranging for acknowledgment of receipt if necessary.
1172          * This process logically involves adjusting tp->rcv_wnd as data
1173          * is presented to the user (this happens in tcp_usrreq.c,
1174          * case PRU_RCVD).  If a FIN has already been received on this
1175          * connection then we just ignore the text.
1176          */
1177         if ((ti->ti_len || (tiflags&TH_FIN)) &&
1178             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
1179                 TCP_REASS(tp, ti, m, so, tiflags);
1180         } else {
1181                 m_free(m);
1182                 tiflags &= ~TH_FIN;
1183         }
1184
1185         /*
1186          * If FIN is received ACK the FIN and let the user know
1187          * that the connection is closing.
1188          */
1189         if (tiflags & TH_FIN) {
1190                 if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
1191                         /*
1192                          * If we receive a FIN we can't send more data,
1193                          * set it SS_FDRAIN
1194                          * Shutdown the socket if there is no rx data in the
1195                          * buffer.
1196                          * soread() is called on completion of shutdown() and
1197                          * will got to TCPS_LAST_ACK, and use tcp_output()
1198                          * to send the FIN.
1199                          */
1200                         sofwdrain(so);
1201
1202                         tp->t_flags |= TF_ACKNOW;
1203                         tp->rcv_nxt++;
1204                 }
1205                 switch (tp->t_state) {
1206
1207                 /*
1208                  * In SYN_RECEIVED and ESTABLISHED STATES
1209                  * enter the CLOSE_WAIT state.
1210                  */
1211                 case TCPS_SYN_RECEIVED:
1212                 case TCPS_ESTABLISHED:
1213                   if(so->so_emu == EMU_CTL)        /* no shutdown on socket */
1214                     tp->t_state = TCPS_LAST_ACK;
1215                   else
1216                     tp->t_state = TCPS_CLOSE_WAIT;
1217                   break;
1218
1219                 /*
1220                  * If still in FIN_WAIT_1 STATE FIN has not been acked so
1221                  * enter the CLOSING state.
1222                  */
1223                 case TCPS_FIN_WAIT_1:
1224                         tp->t_state = TCPS_CLOSING;
1225                         break;
1226
1227                 /*
1228                  * In FIN_WAIT_2 state enter the TIME_WAIT state,
1229                  * starting the time-wait timer, turning off the other
1230                  * standard timers.
1231                  */
1232                 case TCPS_FIN_WAIT_2:
1233                         tp->t_state = TCPS_TIME_WAIT;
1234                         tcp_canceltimers(tp);
1235                         tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
1236                         break;
1237
1238                 /*
1239                  * In TIME_WAIT state restart the 2 MSL time_wait timer.
1240                  */
1241                 case TCPS_TIME_WAIT:
1242                         tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
1243                         break;
1244                 }
1245         }
1246
1247         /*
1248          * Return any desired output.
1249          */
1250         if (needoutput || (tp->t_flags & TF_ACKNOW)) {
1251                 (void) tcp_output(tp);
1252         }
1253         return;
1254
1255 dropafterack:
1256         /*
1257          * Generate an ACK dropping incoming segment if it occupies
1258          * sequence space, where the ACK reflects our state.
1259          */
1260         if (tiflags & TH_RST)
1261                 goto drop;
1262         m_free(m);
1263         tp->t_flags |= TF_ACKNOW;
1264         (void) tcp_output(tp);
1265         return;
1266
1267 dropwithreset:
1268         /* reuses m if m!=NULL, m_free() unnecessary */
1269         if (tiflags & TH_ACK)
1270                 tcp_respond(tp, ti, m, (tcp_seq)0, ti->ti_ack, TH_RST);
1271         else {
1272                 if (tiflags & TH_SYN) ti->ti_len++;
1273                 tcp_respond(tp, ti, m, ti->ti_seq+ti->ti_len, (tcp_seq)0,
1274                     TH_RST|TH_ACK);
1275         }
1276
1277         return;
1278
1279 drop:
1280         /*
1281          * Drop space held by incoming segment and return.
1282          */
1283         m_free(m);
1284
1285         return;
1286 }
1287
1288 static void
1289 tcp_dooptions(struct tcpcb *tp, u_char *cp, int cnt, struct tcpiphdr *ti)
1290 {
1291         uint16_t mss;
1292         int opt, optlen;
1293
1294         DEBUG_CALL("tcp_dooptions");
1295         DEBUG_ARGS((dfd, " tp = %lx  cnt=%i\n", (long)tp, cnt));
1296
1297         for (; cnt > 0; cnt -= optlen, cp += optlen) {
1298                 opt = cp[0];
1299                 if (opt == TCPOPT_EOL)
1300                         break;
1301                 if (opt == TCPOPT_NOP)
1302                         optlen = 1;
1303                 else {
1304                         optlen = cp[1];
1305                         if (optlen <= 0)
1306                                 break;
1307                 }
1308                 switch (opt) {
1309
1310                 default:
1311                         continue;
1312
1313                 case TCPOPT_MAXSEG:
1314                         if (optlen != TCPOLEN_MAXSEG)
1315                                 continue;
1316                         if (!(ti->ti_flags & TH_SYN))
1317                                 continue;
1318                         memcpy((char *) &mss, (char *) cp + 2, sizeof(mss));
1319                         NTOHS(mss);
1320                         (void) tcp_mss(tp, mss);        /* sets t_maxseg */
1321                         break;
1322                 }
1323         }
1324 }
1325
1326
1327 /*
1328  * Pull out of band byte out of a segment so
1329  * it doesn't appear in the user's data queue.
1330  * It is still reflected in the segment length for
1331  * sequencing purposes.
1332  */
1333
1334 #ifdef notdef
1335
1336 void
1337 tcp_pulloutofband(so, ti, m)
1338         struct socket *so;
1339         struct tcpiphdr *ti;
1340         register struct mbuf *m;
1341 {
1342         int cnt = ti->ti_urp - 1;
1343
1344         while (cnt >= 0) {
1345                 if (m->m_len > cnt) {
1346                         char *cp = mtod(m, caddr_t) + cnt;
1347                         struct tcpcb *tp = sototcpcb(so);
1348
1349                         tp->t_iobc = *cp;
1350                         tp->t_oobflags |= TCPOOB_HAVEDATA;
1351                         memcpy(sp, cp+1, (unsigned)(m->m_len - cnt - 1));
1352                         m->m_len--;
1353                         return;
1354                 }
1355                 cnt -= m->m_len;
1356                 m = m->m_next; /* XXX WRONG! Fix it! */
1357                 if (m == 0)
1358                         break;
1359         }
1360         panic("tcp_pulloutofband");
1361 }
1362
1363 #endif /* notdef */
1364
1365 /*
1366  * Collect new round-trip time estimate
1367  * and update averages and current timeout.
1368  */
1369
1370 static void
1371 tcp_xmit_timer(register struct tcpcb *tp, int rtt)
1372 {
1373         register short delta;
1374
1375         DEBUG_CALL("tcp_xmit_timer");
1376         DEBUG_ARG("tp = %lx", (long)tp);
1377         DEBUG_ARG("rtt = %d", rtt);
1378
1379         if (tp->t_srtt != 0) {
1380                 /*
1381                  * srtt is stored as fixed point with 3 bits after the
1382                  * binary point (i.e., scaled by 8).  The following magic
1383                  * is equivalent to the smoothing algorithm in rfc793 with
1384                  * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
1385                  * point).  Adjust rtt to origin 0.
1386                  */
1387                 delta = rtt - 1 - (tp->t_srtt >> TCP_RTT_SHIFT);
1388                 if ((tp->t_srtt += delta) <= 0)
1389                         tp->t_srtt = 1;
1390                 /*
1391                  * We accumulate a smoothed rtt variance (actually, a
1392                  * smoothed mean difference), then set the retransmit
1393                  * timer to smoothed rtt + 4 times the smoothed variance.
1394                  * rttvar is stored as fixed point with 2 bits after the
1395                  * binary point (scaled by 4).  The following is
1396                  * equivalent to rfc793 smoothing with an alpha of .75
1397                  * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
1398                  * rfc793's wired-in beta.
1399                  */
1400                 if (delta < 0)
1401                         delta = -delta;
1402                 delta -= (tp->t_rttvar >> TCP_RTTVAR_SHIFT);
1403                 if ((tp->t_rttvar += delta) <= 0)
1404                         tp->t_rttvar = 1;
1405         } else {
1406                 /*
1407                  * No rtt measurement yet - use the unsmoothed rtt.
1408                  * Set the variance to half the rtt (so our first
1409                  * retransmit happens at 3*rtt).
1410                  */
1411                 tp->t_srtt = rtt << TCP_RTT_SHIFT;
1412                 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
1413         }
1414         tp->t_rtt = 0;
1415         tp->t_rxtshift = 0;
1416
1417         /*
1418          * the retransmit should happen at rtt + 4 * rttvar.
1419          * Because of the way we do the smoothing, srtt and rttvar
1420          * will each average +1/2 tick of bias.  When we compute
1421          * the retransmit timer, we want 1/2 tick of rounding and
1422          * 1 extra tick because of +-1/2 tick uncertainty in the
1423          * firing of the timer.  The bias will give us exactly the
1424          * 1.5 tick we need.  But, because the bias is
1425          * statistical, we have to test that we don't drop below
1426          * the minimum feasible timer (which is 2 ticks).
1427          */
1428         TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
1429             (short)tp->t_rttmin, TCPTV_REXMTMAX); /* XXX */
1430
1431         /*
1432          * We received an ack for a packet that wasn't retransmitted;
1433          * it is probably safe to discard any error indications we've
1434          * received recently.  This isn't quite right, but close enough
1435          * for now (a route might have failed after we sent a segment,
1436          * and the return path might not be symmetrical).
1437          */
1438         tp->t_softerror = 0;
1439 }
1440
1441 /*
1442  * Determine a reasonable value for maxseg size.
1443  * If the route is known, check route for mtu.
1444  * If none, use an mss that can be handled on the outgoing
1445  * interface without forcing IP to fragment; if bigger than
1446  * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
1447  * to utilize large mbufs.  If no route is found, route has no mtu,
1448  * or the destination isn't local, use a default, hopefully conservative
1449  * size (usually 512 or the default IP max size, but no more than the mtu
1450  * of the interface), as we can't discover anything about intervening
1451  * gateways or networks.  We also initialize the congestion/slow start
1452  * window to be a single segment if the destination isn't local.
1453  * While looking at the routing entry, we also initialize other path-dependent
1454  * parameters from pre-set or cached values in the routing entry.
1455  */
1456
1457 int
1458 tcp_mss(struct tcpcb *tp, u_int offer)
1459 {
1460         struct socket *so = tp->t_socket;
1461         int mss;
1462
1463         DEBUG_CALL("tcp_mss");
1464         DEBUG_ARG("tp = %lx", (long)tp);
1465         DEBUG_ARG("offer = %d", offer);
1466
1467         mss = min(IF_MTU, IF_MRU) - sizeof(struct tcpiphdr);
1468         if (offer)
1469                 mss = min(mss, offer);
1470         mss = max(mss, 32);
1471         if (mss < tp->t_maxseg || offer != 0)
1472            tp->t_maxseg = mss;
1473
1474         tp->snd_cwnd = mss;
1475
1476         sbreserve(&so->so_snd, TCP_SNDSPACE + ((TCP_SNDSPACE % mss) ?
1477                                                (mss - (TCP_SNDSPACE % mss)) :
1478                                                0));
1479         sbreserve(&so->so_rcv, TCP_RCVSPACE + ((TCP_RCVSPACE % mss) ?
1480                                                (mss - (TCP_RCVSPACE % mss)) :
1481                                                0));
1482
1483         DEBUG_MISC((dfd, " returning mss = %d\n", mss));
1484
1485         return mss;
1486 }