Initial import from FreeBSD RELENG_4:
[dragonfly.git] / 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  */
36
37 #include "opt_ipfw.h"           /* for ipfw_fwd         */
38 #include "opt_inet6.h"
39 #include "opt_ipsec.h"
40 #include "opt_tcpdebug.h"
41 #include "opt_tcp_input.h"
42
43 #include <sys/param.h>
44 #include <sys/systm.h>
45 #include <sys/kernel.h>
46 #include <sys/sysctl.h>
47 #include <sys/malloc.h>
48 #include <sys/mbuf.h>
49 #include <sys/proc.h>           /* for proc0 declaration */
50 #include <sys/protosw.h>
51 #include <sys/socket.h>
52 #include <sys/socketvar.h>
53 #include <sys/syslog.h>
54
55 #include <machine/cpu.h>        /* before tcp_seq.h, for tcp_random18() */
56
57 #include <net/if.h>
58 #include <net/route.h>
59
60 #include <netinet/in.h>
61 #include <netinet/in_systm.h>
62 #include <netinet/ip.h>
63 #include <netinet/ip_icmp.h>    /* for ICMP_BANDLIM             */
64 #include <netinet/in_var.h>
65 #include <netinet/icmp_var.h>   /* for ICMP_BANDLIM             */
66 #include <netinet/in_pcb.h>
67 #include <netinet/ip_var.h>
68 #include <netinet/ip6.h>
69 #include <netinet/icmp6.h>
70 #include <netinet6/nd6.h>
71 #include <netinet6/ip6_var.h>
72 #include <netinet6/in6_pcb.h>
73 #include <netinet/tcp.h>
74 #include <netinet/tcp_fsm.h>
75 #include <netinet/tcp_seq.h>
76 #include <netinet/tcp_timer.h>
77 #include <netinet/tcp_var.h>
78 #include <netinet6/tcp6_var.h>
79 #include <netinet/tcpip.h>
80 #ifdef TCPDEBUG
81 #include <netinet/tcp_debug.h>
82
83 u_char tcp_saveipgen[40]; /* the size must be of max ip header, now IPv6 */
84 struct tcphdr tcp_savetcp;
85 #endif /* TCPDEBUG */
86
87 #ifdef FAST_IPSEC
88 #include <netipsec/ipsec.h>
89 #include <netipsec/ipsec6.h>
90 #endif
91
92 #ifdef IPSEC
93 #include <netinet6/ipsec.h>
94 #include <netinet6/ipsec6.h>
95 #include <netkey/key.h>
96 #endif /*IPSEC*/
97
98 #include <machine/in_cksum.h>
99
100 MALLOC_DEFINE(M_TSEGQ, "tseg_qent", "TCP segment queue entry");
101
102 static const int tcprexmtthresh = 3;
103 tcp_cc  tcp_ccgen;
104
105 struct  tcpstat tcpstat;
106 SYSCTL_STRUCT(_net_inet_tcp, TCPCTL_STATS, stats, CTLFLAG_RW,
107     &tcpstat , tcpstat, "TCP statistics (struct tcpstat, netinet/tcp_var.h)");
108
109 static int log_in_vain = 0;
110 SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW, 
111     &log_in_vain, 0, "Log all incoming TCP connections");
112
113 static int blackhole = 0;
114 SYSCTL_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_RW,
115     &blackhole, 0, "Do not send RST when dropping refused connections");
116
117 int tcp_delack_enabled = 1;
118 SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_RW, 
119     &tcp_delack_enabled, 0, 
120     "Delay ACK to try and piggyback it onto a data packet");
121
122 #ifdef TCP_DROP_SYNFIN
123 static int drop_synfin = 0;
124 SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_RW,
125     &drop_synfin, 0, "Drop TCP packets with SYN+FIN set");
126 #endif
127
128 struct inpcbhead tcb;
129 #define tcb6    tcb  /* for KAME src sync over BSD*'s */
130 struct inpcbinfo tcbinfo;
131
132 static void      tcp_dooptions(struct tcpopt *, u_char *, int, int);
133 static void      tcp_pulloutofband(struct socket *,
134                      struct tcphdr *, struct mbuf *, int);
135 static int       tcp_reass(struct tcpcb *, struct tcphdr *, int *,
136                      struct mbuf *);
137 static void      tcp_xmit_timer(struct tcpcb *, int);
138 static void      tcp_newreno_partial_ack(struct tcpcb *, struct tcphdr *);
139
140 /* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */
141 #ifdef INET6
142 #define ND6_HINT(tp) \
143 do { \
144         if ((tp) && (tp)->t_inpcb && \
145             ((tp)->t_inpcb->inp_vflag & INP_IPV6) != 0 && \
146             (tp)->t_inpcb->in6p_route.ro_rt) \
147                 nd6_nud_hint((tp)->t_inpcb->in6p_route.ro_rt, NULL, 0); \
148 } while (0)
149 #else
150 #define ND6_HINT(tp)
151 #endif
152
153 /*
154  * Indicate whether this ack should be delayed.  We can delay the ack if
155  *      - delayed acks are enabled and
156  *      - there is no delayed ack timer in progress and
157  *      - our last ack wasn't a 0-sized window.  We never want to delay
158  *        the ack that opens up a 0-sized window.
159  */
160 #define DELAY_ACK(tp) \
161         (tcp_delack_enabled && !callout_pending(tp->tt_delack) && \
162         (tp->t_flags & TF_RXWIN0SENT) == 0)
163
164 static int
165 tcp_reass(tp, th, tlenp, m)
166         register struct tcpcb *tp;
167         register struct tcphdr *th;
168         int *tlenp;
169         struct mbuf *m;
170 {
171         struct tseg_qent *q;
172         struct tseg_qent *p = NULL;
173         struct tseg_qent *nq;
174         struct tseg_qent *te;
175         struct socket *so = tp->t_inpcb->inp_socket;
176         int flags;
177
178         /*
179          * Call with th==0 after become established to
180          * force pre-ESTABLISHED data up to user socket.
181          */
182         if (th == 0)
183                 goto present;
184
185         /* Allocate a new queue entry. If we can't, just drop the pkt. XXX */
186         MALLOC(te, struct tseg_qent *, sizeof(struct tseg_qent), M_TSEGQ,
187                M_NOWAIT);
188         if (te == NULL) {
189                 tcpstat.tcps_rcvmemdrop++;
190                 m_freem(m);
191                 return (0);
192         }
193
194         /*
195          * Find a segment which begins after this one does.
196          */
197         LIST_FOREACH(q, &tp->t_segq, tqe_q) {
198                 if (SEQ_GT(q->tqe_th->th_seq, th->th_seq))
199                         break;
200                 p = q;
201         }
202
203         /*
204          * If there is a preceding segment, it may provide some of
205          * our data already.  If so, drop the data from the incoming
206          * segment.  If it provides all of our data, drop us.
207          */
208         if (p != NULL) {
209                 register int i;
210                 /* conversion to int (in i) handles seq wraparound */
211                 i = p->tqe_th->th_seq + p->tqe_len - th->th_seq;
212                 if (i > 0) {
213                         if (i >= *tlenp) {
214                                 tcpstat.tcps_rcvduppack++;
215                                 tcpstat.tcps_rcvdupbyte += *tlenp;
216                                 m_freem(m);
217                                 free(te, M_TSEGQ);
218                                 /*
219                                  * Try to present any queued data
220                                  * at the left window edge to the user.
221                                  * This is needed after the 3-WHS
222                                  * completes.
223                                  */
224                                 goto present;   /* ??? */
225                         }
226                         m_adj(m, i);
227                         *tlenp -= i;
228                         th->th_seq += i;
229                 }
230         }
231         tcpstat.tcps_rcvoopack++;
232         tcpstat.tcps_rcvoobyte += *tlenp;
233
234         /*
235          * While we overlap succeeding segments trim them or,
236          * if they are completely covered, dequeue them.
237          */
238         while (q) {
239                 register int i = (th->th_seq + *tlenp) - q->tqe_th->th_seq;
240                 if (i <= 0)
241                         break;
242                 if (i < q->tqe_len) {
243                         q->tqe_th->th_seq += i;
244                         q->tqe_len -= i;
245                         m_adj(q->tqe_m, i);
246                         break;
247                 }
248
249                 nq = LIST_NEXT(q, tqe_q);
250                 LIST_REMOVE(q, tqe_q);
251                 m_freem(q->tqe_m);
252                 free(q, M_TSEGQ);
253                 q = nq;
254         }
255
256         /* Insert the new segment queue entry into place. */
257         te->tqe_m = m;
258         te->tqe_th = th;
259         te->tqe_len = *tlenp;
260
261         if (p == NULL) {
262                 LIST_INSERT_HEAD(&tp->t_segq, te, tqe_q);
263         } else {
264                 LIST_INSERT_AFTER(p, te, tqe_q);
265         }
266
267 present:
268         /*
269          * Present data to user, advancing rcv_nxt through
270          * completed sequence space.
271          */
272         if (!TCPS_HAVEESTABLISHED(tp->t_state))
273                 return (0);
274         q = LIST_FIRST(&tp->t_segq);
275         if (!q || q->tqe_th->th_seq != tp->rcv_nxt)
276                 return (0);
277         do {
278                 tp->rcv_nxt += q->tqe_len;
279                 flags = q->tqe_th->th_flags & TH_FIN;
280                 nq = LIST_NEXT(q, tqe_q);
281                 LIST_REMOVE(q, tqe_q);
282                 if (so->so_state & SS_CANTRCVMORE)
283                         m_freem(q->tqe_m);
284                 else
285                         sbappend(&so->so_rcv, q->tqe_m);
286                 free(q, M_TSEGQ);
287                 q = nq;
288         } while (q && q->tqe_th->th_seq == tp->rcv_nxt);
289         ND6_HINT(tp);
290         sorwakeup(so);
291         return (flags);
292 }
293
294 /*
295  * TCP input routine, follows pages 65-76 of the
296  * protocol specification dated September, 1981 very closely.
297  */
298 #ifdef INET6
299 int
300 tcp6_input(mp, offp, proto)
301         struct mbuf **mp;
302         int *offp, proto;
303 {
304         register struct mbuf *m = *mp;
305         struct in6_ifaddr *ia6;
306
307         IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
308
309         /*
310          * draft-itojun-ipv6-tcp-to-anycast
311          * better place to put this in?
312          */
313         ia6 = ip6_getdstifaddr(m);
314         if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {                
315                 struct ip6_hdr *ip6;
316
317                 ip6 = mtod(m, struct ip6_hdr *);
318                 icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
319                             (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
320                 return IPPROTO_DONE;
321         }
322
323         tcp_input(m, *offp, proto);
324         return IPPROTO_DONE;
325 }
326 #endif
327
328 void
329 tcp_input(m, off0, proto)
330         register struct mbuf *m;
331         int off0, proto;
332 {
333         register struct tcphdr *th;
334         register struct ip *ip = NULL;
335         register struct ipovly *ipov;
336         register struct inpcb *inp = NULL;
337         u_char *optp = NULL;
338         int optlen = 0;
339         int len, tlen, off;
340         int drop_hdrlen;
341         register struct tcpcb *tp = NULL;
342         register int thflags;
343         struct socket *so = 0;
344         int todrop, acked, ourfinisacked, needoutput = 0;
345         u_long tiwin;
346         struct tcpopt to;               /* options in this segment */
347         struct rmxp_tao *taop;          /* pointer to our TAO cache entry */
348         struct rmxp_tao tao_noncached;  /* in case there's no cached entry */
349         struct sockaddr_in *next_hop = NULL;
350         int rstreason; /* For badport_bandlim accounting purposes */
351         struct ip6_hdr *ip6 = NULL;
352 #ifdef INET6
353         int isipv6;
354 #else
355         const int isipv6 = 0;
356 #endif
357 #ifdef TCPDEBUG
358         short ostate = 0;
359 #endif
360
361         /* Grab info from MT_TAG mbufs prepended to the chain. */
362         for (;m && m->m_type == MT_TAG; m = m->m_next) {
363                 if (m->_m_tag_id == PACKET_TAG_IPFORWARD)
364                         next_hop = (struct sockaddr_in *)m->m_hdr.mh_data;
365         }
366 #ifdef INET6
367         isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
368 #endif
369         bzero((char *)&to, sizeof(to));
370
371         tcpstat.tcps_rcvtotal++;
372
373         if (isipv6) {
374                 /* IP6_EXTHDR_CHECK() is already done at tcp6_input() */
375                 ip6 = mtod(m, struct ip6_hdr *);
376                 tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
377                 if (in6_cksum(m, IPPROTO_TCP, off0, tlen)) {
378                         tcpstat.tcps_rcvbadsum++;
379                         goto drop;
380                 }
381                 th = (struct tcphdr *)((caddr_t)ip6 + off0);
382
383                 /*
384                  * Be proactive about unspecified IPv6 address in source.
385                  * As we use all-zero to indicate unbounded/unconnected pcb,
386                  * unspecified IPv6 address can be used to confuse us.
387                  *
388                  * Note that packets with unspecified IPv6 destination is
389                  * already dropped in ip6_input.
390                  */
391                 if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
392                         /* XXX stat */
393                         goto drop;
394                 }
395         } else {
396                 /*
397                  * Get IP and TCP header together in first mbuf.
398                  * Note: IP leaves IP header in first mbuf.
399                  */
400                 if (off0 > sizeof(struct ip)) {
401                         ip_stripoptions(m, (struct mbuf *)0);
402                         off0 = sizeof(struct ip);
403                 }
404                 if (m->m_len < sizeof(struct tcpiphdr)) {
405                         if ((m = m_pullup(m, sizeof(struct tcpiphdr))) == 0) {
406                                 tcpstat.tcps_rcvshort++;
407                                 return;
408                         }
409                 }
410                 ip = mtod(m, struct ip *);
411                 ipov = (struct ipovly *)ip;
412                 th = (struct tcphdr *)((caddr_t)ip + off0);
413                 tlen = ip->ip_len;
414
415                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
416                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
417                                 th->th_sum = m->m_pkthdr.csum_data;
418                         else
419                                 th->th_sum = in_pseudo(ip->ip_src.s_addr,
420                                                 ip->ip_dst.s_addr,
421                                                 htonl(m->m_pkthdr.csum_data +
422                                                         ip->ip_len +
423                                                         IPPROTO_TCP));
424                         th->th_sum ^= 0xffff;
425                 } else {
426                         /*
427                          * Checksum extended TCP header and data.
428                          */
429                         len = sizeof(struct ip) + tlen;
430                         bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
431                         ipov->ih_len = (u_short)tlen;
432                         ipov->ih_len = htons(ipov->ih_len);
433                         th->th_sum = in_cksum(m, len);
434                 }
435                 if (th->th_sum) {
436                         tcpstat.tcps_rcvbadsum++;
437                         goto drop;
438                 }
439 #ifdef INET6
440                 /* Re-initialization for later version check */
441                 ip->ip_v = IPVERSION;
442 #endif
443         }
444
445         /*
446          * Check that TCP offset makes sense,
447          * pull out TCP options and adjust length.              XXX
448          */
449         off = th->th_off << 2;
450         if (off < sizeof(struct tcphdr) || off > tlen) {
451                 tcpstat.tcps_rcvbadoff++;
452                 goto drop;
453         }
454         tlen -= off;    /* tlen is used instead of ti->ti_len */
455         if (off > sizeof(struct tcphdr)) {
456                 if (isipv6) {
457                         IP6_EXTHDR_CHECK(m, off0, off, );
458                         ip6 = mtod(m, struct ip6_hdr *);
459                         th = (struct tcphdr *)((caddr_t)ip6 + off0);
460                 } else {
461                         if (m->m_len < sizeof(struct ip) + off) {
462                                 if ((m = m_pullup(m, sizeof(struct ip) + off))
463                                                 == 0) {
464                                         tcpstat.tcps_rcvshort++;
465                                         return;
466                                 }
467                                 ip = mtod(m, struct ip *);
468                                 ipov = (struct ipovly *)ip;
469                                 th = (struct tcphdr *)((caddr_t)ip + off0);
470                         }
471                 }
472                 optlen = off - sizeof(struct tcphdr);
473                 optp = (u_char *)(th + 1);
474         }
475         thflags = th->th_flags;
476
477 #ifdef TCP_DROP_SYNFIN
478         /*
479          * If the drop_synfin option is enabled, drop all packets with
480          * both the SYN and FIN bits set. This prevents e.g. nmap from
481          * identifying the TCP/IP stack.
482          *
483          * This is a violation of the TCP specification.
484          */
485         if (drop_synfin && (thflags & (TH_SYN|TH_FIN)) == (TH_SYN|TH_FIN))
486                 goto drop;
487 #endif
488
489         /*
490          * Convert TCP protocol specific fields to host format.
491          */
492         th->th_seq = ntohl(th->th_seq);
493         th->th_ack = ntohl(th->th_ack);
494         th->th_win = ntohs(th->th_win);
495         th->th_urp = ntohs(th->th_urp);
496
497         /*
498          * Delay droping TCP, IP headers, IPv6 ext headers, and TCP options,
499          * until after ip6_savecontrol() is called and before other functions
500          * which don't want those proto headers.
501          * Because ip6_savecontrol() is going to parse the mbuf to
502          * search for data to be passed up to user-land, it wants mbuf
503          * parameters to be unchanged.
504          * XXX: the call of ip6_savecontrol() has been obsoleted based on
505          * latest version of the advanced API (20020110).
506          */
507         drop_hdrlen = off0 + off;
508
509         /*
510          * Locate pcb for segment.
511          */
512 findpcb:
513         /* IPFIREWALL_FORWARD section */
514         if (next_hop != NULL && isipv6 == 0) {  /* IPv6 support is not yet */
515                 /*
516                  * Transparently forwarded. Pretend to be the destination.
517                  * already got one like this? 
518                  */
519                 inp = in_pcblookup_hash(&tcbinfo, ip->ip_src, th->th_sport,
520                                         ip->ip_dst, th->th_dport,
521                                         0, m->m_pkthdr.rcvif);
522                 if (!inp) {
523                         /* It's new.  Try find the ambushing socket. */
524                         inp = in_pcblookup_hash(&tcbinfo,
525                                                 ip->ip_src, th->th_sport,
526                                                 next_hop->sin_addr,
527                                                 next_hop->sin_port ?
528                                                     ntohs(next_hop->sin_port) :
529                                                     th->th_dport,
530                                                 1, m->m_pkthdr.rcvif);
531                 }
532         } else {
533                 if (isipv6)
534                         inp = in6_pcblookup_hash(&tcbinfo,
535                                                  &ip6->ip6_src, th->th_sport,
536                                                  &ip6->ip6_dst, th->th_dport,
537                                                  1, m->m_pkthdr.rcvif);
538                 else
539                         inp = in_pcblookup_hash(&tcbinfo,
540                                                 ip->ip_src, th->th_sport,
541                                                 ip->ip_dst, th->th_dport,
542                                                 1, m->m_pkthdr.rcvif);
543       }
544
545 #ifdef IPSEC
546         if (isipv6) {
547                 if (inp != NULL && ipsec6_in_reject_so(m, inp->inp_socket)) {
548                         ipsec6stat.in_polvio++;
549                         goto drop;
550                 }
551         } else {
552                 if (inp != NULL && ipsec4_in_reject_so(m, inp->inp_socket)) {
553                         ipsecstat.in_polvio++;
554                         goto drop;
555                 }
556         }
557 #endif
558 #ifdef FAST_IPSEC
559         if (isipv6) {
560                 if (inp != NULL && ipsec6_in_reject(m, inp)) {
561                         goto drop;
562                 }
563         } else {
564                 if (inp != NULL && ipsec4_in_reject(m, inp)) {
565                         goto drop;
566                 }
567         }
568 #endif
569
570         /*
571          * If the state is CLOSED (i.e., TCB does not exist) then
572          * all data in the incoming segment is discarded.
573          * If the TCB exists but is in CLOSED state, it is embryonic,
574          * but should either do a listen or a connect soon.
575          */
576         if (inp == NULL) {
577                 if (log_in_vain) {
578 #ifdef INET6
579                         char dbuf[INET6_ADDRSTRLEN+2], sbuf[INET6_ADDRSTRLEN+2];
580 #else
581                         char dbuf[4*sizeof "123"], sbuf[4*sizeof "123"];
582 #endif
583                         if (isipv6) {
584                                 strcpy(dbuf, "[");
585                                 strcpy(sbuf, "[");
586                                 strcat(dbuf, ip6_sprintf(&ip6->ip6_dst));
587                                 strcat(sbuf, ip6_sprintf(&ip6->ip6_src));
588                                 strcat(dbuf, "]");
589                                 strcat(sbuf, "]");
590                         } else {
591                                 strcpy(dbuf, inet_ntoa(ip->ip_dst));
592                                 strcpy(sbuf, inet_ntoa(ip->ip_src));
593                         }
594                         switch (log_in_vain) {
595                         case 1:
596                                 if ((thflags & TH_SYN) == 0)
597                                         break;
598                         case 2:
599                                 log(LOG_INFO,
600                                     "Connection attempt to TCP %s:%d "
601                                     "from %s:%d flags:0x%02x\n",
602                                     dbuf, ntohs(th->th_dport), sbuf,
603                                     ntohs(th->th_sport), thflags);
604                                 break;
605                         default:
606                                 break;
607                         }
608                 }
609                 if (blackhole) { 
610                         switch (blackhole) {
611                         case 1:
612                                 if (thflags & TH_SYN)
613                                         goto drop;
614                                 break;
615                         case 2:
616                                 goto drop;
617                         default:
618                                 goto drop;
619                         }
620                 }
621                 rstreason = BANDLIM_RST_CLOSEDPORT;
622                 goto dropwithreset;
623         }
624         tp = intotcpcb(inp);
625         if (tp == NULL) {
626                 rstreason = BANDLIM_RST_CLOSEDPORT;
627                 goto dropwithreset;
628         }
629         if (tp->t_state == TCPS_CLOSED)
630                 goto drop;
631
632         /* Unscale the window into a 32-bit value. */
633         if ((thflags & TH_SYN) == 0)
634                 tiwin = th->th_win << tp->snd_scale;
635         else
636                 tiwin = th->th_win;
637
638         so = inp->inp_socket;
639         if (so->so_options & (SO_DEBUG|SO_ACCEPTCONN)) {
640                 struct in_conninfo inc;
641 #ifdef TCPDEBUG
642                 if (so->so_options & SO_DEBUG) {
643                         ostate = tp->t_state;
644                         if (isipv6)
645                                 bcopy((char *)ip6, (char *)tcp_saveipgen,
646                                     sizeof(*ip6));
647                         else
648                                 bcopy((char *)ip, (char *)tcp_saveipgen,
649                                     sizeof(*ip));
650                         tcp_savetcp = *th;
651                 }
652 #endif
653                 /* skip if this isn't a listen socket */
654                 if ((so->so_options & SO_ACCEPTCONN) == 0)
655                         goto after_listen;
656 #ifdef INET6
657                 inc.inc_isipv6 = isipv6;
658 #endif
659                 if (isipv6) {
660                         inc.inc6_faddr = ip6->ip6_src;
661                         inc.inc6_laddr = ip6->ip6_dst;
662                         inc.inc6_route.ro_rt = NULL;            /* XXX */
663                 } else {
664                         inc.inc_faddr = ip->ip_src;
665                         inc.inc_laddr = ip->ip_dst;
666                         inc.inc_route.ro_rt = NULL;             /* XXX */
667                 }
668                 inc.inc_fport = th->th_sport;
669                 inc.inc_lport = th->th_dport;
670
671                 /*
672                  * If the state is LISTEN then ignore segment if it contains
673                  * a RST.  If the segment contains an ACK then it is bad and
674                  * send a RST.  If it does not contain a SYN then it is not
675                  * interesting; drop it.
676                  *
677                  * If the state is SYN_RECEIVED (syncache) and seg contains
678                  * an ACK, but not for our SYN/ACK, send a RST.  If the seg
679                  * contains a RST, check the sequence number to see if it
680                  * is a valid reset segment.
681                  */
682                 if ((thflags & (TH_RST|TH_ACK|TH_SYN)) != TH_SYN) {
683                         if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
684                                 if (!syncache_expand(&inc, th, &so, m)) {
685                                         /*
686                                          * No syncache entry, or ACK was not
687                                          * for our SYN/ACK.  Send a RST.
688                                          */
689                                         tcpstat.tcps_badsyn++;
690                                         rstreason = BANDLIM_RST_OPENPORT;
691                                         goto dropwithreset;
692                                 }
693                                 if (so == NULL)
694                                         /*
695                                          * Could not complete 3-way handshake,
696                                          * connection is being closed down, and
697                                          * syncache will free mbuf.
698                                          */
699                                         return;
700                                 /*
701                                  * Socket is created in state SYN_RECEIVED.
702                                  * Continue processing segment.
703                                  */
704                                 inp = sotoinpcb(so);
705                                 tp = intotcpcb(inp);
706                                 /*
707                                  * This is what would have happened in
708                                  * tcp_output() when the SYN,ACK was sent.
709                                  */
710                                 tp->snd_up = tp->snd_una;
711                                 tp->snd_max = tp->snd_nxt = tp->iss + 1;
712                                 tp->last_ack_sent = tp->rcv_nxt;
713 /*
714  * XXX possible bug - it doesn't appear that tp->snd_wnd is unscaled
715  * until the _second_ ACK is received:
716  *    rcv SYN (set wscale opts)  --> send SYN/ACK, set snd_wnd = window.
717  *    rcv ACK, calculate tiwin --> process SYN_RECEIVED, determine wscale,
718  *        move to ESTAB, set snd_wnd to tiwin.
719  */        
720                                 tp->snd_wnd = tiwin;    /* unscaled */
721                                 goto after_listen;
722                         }
723                         if (thflags & TH_RST) {
724                                 syncache_chkrst(&inc, th);
725                                 goto drop;
726                         }
727                         if (thflags & TH_ACK) {
728                                 syncache_badack(&inc);
729                                 tcpstat.tcps_badsyn++;
730                                 rstreason = BANDLIM_RST_OPENPORT;
731                                 goto dropwithreset;
732                         }
733                         goto drop;
734                 }
735
736                 /*
737                  * Segment's flags are (SYN) or (SYN|FIN).
738                  */
739 #ifdef INET6
740                 /*
741                  * If deprecated address is forbidden,
742                  * we do not accept SYN to deprecated interface
743                  * address to prevent any new inbound connection from
744                  * getting established.
745                  * When we do not accept SYN, we send a TCP RST,
746                  * with deprecated source address (instead of dropping
747                  * it).  We compromise it as it is much better for peer
748                  * to send a RST, and RST will be the final packet
749                  * for the exchange.
750                  *
751                  * If we do not forbid deprecated addresses, we accept
752                  * the SYN packet.  RFC2462 does not suggest dropping
753                  * SYN in this case.
754                  * If we decipher RFC2462 5.5.4, it says like this:
755                  * 1. use of deprecated addr with existing
756                  *    communication is okay - "SHOULD continue to be
757                  *    used"
758                  * 2. use of it with new communication:
759                  *   (2a) "SHOULD NOT be used if alternate address
760                  *        with sufficient scope is available"
761                  *   (2b) nothing mentioned otherwise.
762                  * Here we fall into (2b) case as we have no choice in
763                  * our source address selection - we must obey the peer.
764                  *
765                  * The wording in RFC2462 is confusing, and there are
766                  * multiple description text for deprecated address
767                  * handling - worse, they are not exactly the same.
768                  * I believe 5.5.4 is the best one, so we follow 5.5.4.
769                  */
770                 if (isipv6 && !ip6_use_deprecated) {
771                         struct in6_ifaddr *ia6;
772
773                         if ((ia6 = ip6_getdstifaddr(m)) &&
774                             (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
775                                 tp = NULL;
776                                 rstreason = BANDLIM_RST_OPENPORT;
777                                 goto dropwithreset;
778                         }
779                 }
780 #endif
781                 /*
782                  * If it is from this socket, drop it, it must be forged.
783                  * Don't bother responding if the destination was a broadcast.
784                  */
785                 if (th->th_dport == th->th_sport) {
786                         if (isipv6) {
787                                 if (IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst,
788                                                        &ip6->ip6_src))
789                                         goto drop;
790                         } else {
791                                 if (ip->ip_dst.s_addr == ip->ip_src.s_addr)
792                                         goto drop;
793                         }
794                 }
795                 /*
796                  * RFC1122 4.2.3.10, p. 104: discard bcast/mcast SYN
797                  *
798                  * Note that it is quite possible to receive unicast
799                  * link-layer packets with a broadcast IP address. Use
800                  * in_broadcast() to find them.
801                  */
802                 if (m->m_flags & (M_BCAST|M_MCAST))
803                         goto drop;
804                 if (isipv6) {
805                         if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
806                             IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
807                                 goto drop;
808                 } else {
809                         if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
810                             IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
811                             ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
812                             in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
813                                 goto drop;
814                 }
815                 /*
816                  * SYN appears to be valid; create compressed TCP state
817                  * for syncache, or perform t/tcp connection.
818                  */
819                 if (so->so_qlen <= so->so_qlimit) {
820                         tcp_dooptions(&to, optp, optlen, 1);
821                         if (!syncache_add(&inc, &to, th, &so, m))
822                                 goto drop;
823                         if (so == NULL)
824                                 /*
825                                  * Entry added to syncache, mbuf used to
826                                  * send SYN,ACK packet.
827                                  */
828                                 return;
829                         /*
830                          * Segment passed TAO tests.
831                          */
832                         inp = sotoinpcb(so);
833                         tp = intotcpcb(inp);
834                         tp->snd_wnd = tiwin;
835                         tp->t_starttime = ticks;
836                         tp->t_state = TCPS_ESTABLISHED;
837
838                         /*
839                          * If there is a FIN, or if there is data and the
840                          * connection is local, then delay SYN,ACK(SYN) in
841                          * the hope of piggy-backing it on a response
842                          * segment.  Otherwise must send ACK now in case
843                          * the other side is slow starting.
844                          */
845                         if (DELAY_ACK(tp) &&
846                             ((thflags & TH_FIN) ||
847                              (tlen != 0 &&
848                               ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
849                                (!isipv6 && in_localaddr(inp->inp_faddr)))))) {
850                                 callout_reset(tp->tt_delack, tcp_delacktime,  
851                                                 tcp_timer_delack, tp);  
852                                 tp->t_flags |= TF_NEEDSYN;
853                         } else 
854                                 tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
855
856                         tcpstat.tcps_connects++;
857                         soisconnected(so);
858                         goto trimthenstep6;
859                 }
860                 goto drop;
861         }
862 after_listen:
863
864 /* XXX temp debugging */
865         /* should not happen - syncache should pick up these connections */
866         if (tp->t_state == TCPS_LISTEN)
867                 panic("tcp_input: TCPS_LISTEN");
868
869         /*
870          * Segment received on connection.
871          * Reset idle time and keep-alive timer.
872          */
873         tp->t_rcvtime = ticks;
874         if (TCPS_HAVEESTABLISHED(tp->t_state))
875                 callout_reset(tp->tt_keep, tcp_keepidle, tcp_timer_keep, tp);
876
877         /*
878          * Process options.
879          * XXX this is tradtitional behavior, may need to be cleaned up.
880          */
881         tcp_dooptions(&to, optp, optlen, thflags & TH_SYN);
882         if (thflags & TH_SYN) {
883                 if (to.to_flags & TOF_SCALE) {
884                         tp->t_flags |= TF_RCVD_SCALE;
885                         tp->requested_s_scale = to.to_requested_s_scale;
886                 }
887                 if (to.to_flags & TOF_TS) {
888                         tp->t_flags |= TF_RCVD_TSTMP;
889                         tp->ts_recent = to.to_tsval;
890                         tp->ts_recent_age = ticks;
891                 }
892                 if (to.to_flags & (TOF_CC|TOF_CCNEW))
893                         tp->t_flags |= TF_RCVD_CC;
894                 if (to.to_flags & TOF_MSS)
895                         tcp_mss(tp, to.to_mss);
896         }
897
898         /*
899          * Header prediction: check for the two common cases
900          * of a uni-directional data xfer.  If the packet has
901          * no control flags, is in-sequence, the window didn't
902          * change and we're not retransmitting, it's a
903          * candidate.  If the length is zero and the ack moved
904          * forward, we're the sender side of the xfer.  Just
905          * free the data acked & wake any higher level process
906          * that was blocked waiting for space.  If the length
907          * is non-zero and the ack didn't move, we're the
908          * receiver side.  If we're getting packets in-order
909          * (the reassembly queue is empty), add the data to
910          * the socket buffer and note that we need a delayed ack.
911          * Make sure that the hidden state-flags are also off.
912          * Since we check for TCPS_ESTABLISHED above, it can only
913          * be TH_NEEDSYN.
914          */
915         if (tp->t_state == TCPS_ESTABLISHED &&
916             (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
917             ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
918             ((to.to_flags & TOF_TS) == 0 ||
919              TSTMP_GEQ(to.to_tsval, tp->ts_recent)) &&
920             /*
921              * Using the CC option is compulsory if once started:
922              *   the segment is OK if no T/TCP was negotiated or
923              *   if the segment has a CC option equal to CCrecv
924              */
925             ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) != (TF_REQ_CC|TF_RCVD_CC) ||
926              ((to.to_flags & TOF_CC) != 0 && to.to_cc == tp->cc_recv)) &&
927             th->th_seq == tp->rcv_nxt &&
928             tiwin && tiwin == tp->snd_wnd &&
929             tp->snd_nxt == tp->snd_max) {
930
931                 /*
932                  * If last ACK falls within this segment's sequence numbers,
933                  * record the timestamp.
934                  * NOTE that the test is modified according to the latest
935                  * proposal of the tcplw@cray.com list (Braden 1993/04/26).
936                  */
937                 if ((to.to_flags & TOF_TS) != 0 &&
938                     SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
939                         tp->ts_recent_age = ticks;
940                         tp->ts_recent = to.to_tsval;
941                 }
942
943                 if (tlen == 0) {
944                         if (SEQ_GT(th->th_ack, tp->snd_una) &&
945                             SEQ_LEQ(th->th_ack, tp->snd_max) &&
946                             tp->snd_cwnd >= tp->snd_wnd &&
947                             ((!tcp_do_newreno &&
948                                tp->t_dupacks < tcprexmtthresh) ||
949                              (tcp_do_newreno &&
950                               !SEQ_LT(tp->snd_una, tp->snd_recover)))) {
951                                 /*
952                                  * this is a pure ack for outstanding data.
953                                  */
954                                 ++tcpstat.tcps_predack;
955                                 /*
956                                  * "bad retransmit" recovery
957                                  */
958                                 if (tp->t_rxtshift == 1 &&
959                                     ticks < tp->t_badrxtwin) {
960                                         tp->snd_cwnd = tp->snd_cwnd_prev;
961                                         tp->snd_ssthresh =
962                                             tp->snd_ssthresh_prev;
963                                         tp->snd_high = tp->snd_high_prev;
964                                         tp->snd_nxt = tp->snd_max;
965                                         tp->t_badrxtwin = 0;
966                                 }
967                                 /*
968                                  * Recalculate the retransmit timer / rtt.
969                                  *
970                                  * Some machines (certain windows boxes) 
971                                  * send broken timestamp replies during the
972                                  * SYN+ACK phase, ignore timestamps of 0.
973                                  */
974                                 if ((to.to_flags & TOF_TS) != 0 &&
975                                     to.to_tsecr) {
976                                         tcp_xmit_timer(tp,
977                                             ticks - to.to_tsecr + 1);
978                                 } else if (tp->t_rtttime &&
979                                             SEQ_GT(th->th_ack, tp->t_rtseq)) {
980                                         tcp_xmit_timer(tp,
981                                                        ticks - tp->t_rtttime);
982                                 }
983                                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
984                                 acked = th->th_ack - tp->snd_una;
985                                 tcpstat.tcps_rcvackpack++;
986                                 tcpstat.tcps_rcvackbyte += acked;
987                                 sbdrop(&so->so_snd, acked);
988                                 if (SEQ_GT(tp->snd_una, tp->snd_high) &&
989                                     SEQ_LEQ(th->th_ack, tp->snd_high))
990                                         tp->snd_high = th->th_ack - 1;
991                                 tp->snd_una = tp->snd_recover = th->th_ack;
992                                 tp->t_dupacks = 0;
993                                 m_freem(m);
994                                 ND6_HINT(tp); /* some progress has been done */
995
996                                 /*
997                                  * If all outstanding data are acked, stop
998                                  * retransmit timer, otherwise restart timer
999                                  * using current (possibly backed-off) value.
1000                                  * If process is waiting for space,
1001                                  * wakeup/selwakeup/signal.  If data
1002                                  * are ready to send, let tcp_output
1003                                  * decide between more output or persist.
1004                                  */
1005                                 if (tp->snd_una == tp->snd_max)
1006                                         callout_stop(tp->tt_rexmt);
1007                                 else if (!callout_active(tp->tt_persist))
1008                                         callout_reset(tp->tt_rexmt, 
1009                                                       tp->t_rxtcur,
1010                                                       tcp_timer_rexmt, tp);
1011
1012                                 sowwakeup(so);
1013                                 if (so->so_snd.sb_cc)
1014                                         (void) tcp_output(tp);
1015                                 return;
1016                         }
1017                 } else if (th->th_ack == tp->snd_una &&
1018                     LIST_EMPTY(&tp->t_segq) &&
1019                     tlen <= sbspace(&so->so_rcv)) {
1020                         /*
1021                          * this is a pure, in-sequence data packet
1022                          * with nothing on the reassembly queue and
1023                          * we have enough buffer space to take it.
1024                          */
1025                         ++tcpstat.tcps_preddat;
1026                         tp->rcv_nxt += tlen;
1027                         tcpstat.tcps_rcvpack++;
1028                         tcpstat.tcps_rcvbyte += tlen;
1029                         ND6_HINT(tp);   /* some progress has been done */
1030                         /*
1031                          * Add data to socket buffer.
1032                          */
1033                         if (so->so_state & SS_CANTRCVMORE) {
1034                                 m_freem(m);
1035                         } else {
1036                                 m_adj(m, drop_hdrlen);  /* delayed header drop */
1037                                 sbappend(&so->so_rcv, m);
1038                         }
1039                         sorwakeup(so);
1040                         if (DELAY_ACK(tp)) {
1041                                 callout_reset(tp->tt_delack, tcp_delacktime,
1042                                     tcp_timer_delack, tp);
1043                         } else {
1044                                 tp->t_flags |= TF_ACKNOW;
1045                                 tcp_output(tp);
1046                         }
1047                         return;
1048                 }
1049         }
1050
1051         /*
1052          * Calculate amount of space in receive window,
1053          * and then do TCP input processing.
1054          * Receive window is amount of space in rcv queue,
1055          * but not less than advertised window.
1056          */
1057         { int win;
1058
1059         win = sbspace(&so->so_rcv);
1060         if (win < 0)
1061                 win = 0;
1062         tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
1063         }
1064
1065         switch (tp->t_state) {
1066
1067         /*
1068          * If the state is SYN_RECEIVED:
1069          *      if seg contains an ACK, but not for our SYN/ACK, send a RST.
1070          */
1071         case TCPS_SYN_RECEIVED:
1072                 if ((thflags & TH_ACK) &&
1073                     (SEQ_LEQ(th->th_ack, tp->snd_una) ||
1074                      SEQ_GT(th->th_ack, tp->snd_max))) {
1075                                 rstreason = BANDLIM_RST_OPENPORT;
1076                                 goto dropwithreset;
1077                 }
1078                 break;
1079
1080         /*
1081          * If the state is SYN_SENT:
1082          *      if seg contains an ACK, but not for our SYN, drop the input.
1083          *      if seg contains a RST, then drop the connection.
1084          *      if seg does not contain SYN, then drop it.
1085          * Otherwise this is an acceptable SYN segment
1086          *      initialize tp->rcv_nxt and tp->irs
1087          *      if seg contains ack then advance tp->snd_una
1088          *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
1089          *      arrange for segment to be acked (eventually)
1090          *      continue processing rest of data/controls, beginning with URG
1091          */
1092         case TCPS_SYN_SENT:
1093                 if ((taop = tcp_gettaocache(&inp->inp_inc)) == NULL) {
1094                         taop = &tao_noncached;
1095                         bzero(taop, sizeof(*taop));
1096                 }
1097
1098                 if ((thflags & TH_ACK) &&
1099                     (SEQ_LEQ(th->th_ack, tp->iss) ||
1100                      SEQ_GT(th->th_ack, tp->snd_max))) {
1101                         /*
1102                          * If we have a cached CCsent for the remote host,
1103                          * hence we haven't just crashed and restarted,
1104                          * do not send a RST.  This may be a retransmission
1105                          * from the other side after our earlier ACK was lost.
1106                          * Our new SYN, when it arrives, will serve as the
1107                          * needed ACK.
1108                          */
1109                         if (taop->tao_ccsent != 0)
1110                                 goto drop;
1111                         else {
1112                                 rstreason = BANDLIM_UNLIMITED;
1113                                 goto dropwithreset;
1114                         }
1115                 }
1116                 if (thflags & TH_RST) {
1117                         if (thflags & TH_ACK)
1118                                 tp = tcp_drop(tp, ECONNREFUSED);
1119                         goto drop;
1120                 }
1121                 if ((thflags & TH_SYN) == 0)
1122                         goto drop;
1123                 tp->snd_wnd = th->th_win;       /* initial send window */
1124                 tp->cc_recv = to.to_cc;         /* foreign CC */
1125
1126                 tp->irs = th->th_seq;
1127                 tcp_rcvseqinit(tp);
1128                 if (thflags & TH_ACK) {
1129                         /*
1130                          * Our SYN was acked.  If segment contains CC.ECHO
1131                          * option, check it to make sure this segment really
1132                          * matches our SYN.  If not, just drop it as old
1133                          * duplicate, but send an RST if we're still playing
1134                          * by the old rules.  If no CC.ECHO option, make sure
1135                          * we don't get fooled into using T/TCP.
1136                          */
1137                         if (to.to_flags & TOF_CCECHO) {
1138                                 if (tp->cc_send != to.to_ccecho) {
1139                                         if (taop->tao_ccsent != 0)
1140                                                 goto drop;
1141                                         else {
1142                                                 rstreason = BANDLIM_UNLIMITED;
1143                                                 goto dropwithreset;
1144                                         }
1145                                 }
1146                         } else
1147                                 tp->t_flags &= ~TF_RCVD_CC;
1148                         tcpstat.tcps_connects++;
1149                         soisconnected(so);
1150                         /* Do window scaling on this connection? */
1151                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1152                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1153                                 tp->snd_scale = tp->requested_s_scale;
1154                                 tp->rcv_scale = tp->request_r_scale;
1155                         }
1156                         /* Segment is acceptable, update cache if undefined. */
1157                         if (taop->tao_ccsent == 0)
1158                                 taop->tao_ccsent = to.to_ccecho;
1159
1160                         tp->rcv_adv += tp->rcv_wnd;
1161                         tp->snd_una++;          /* SYN is acked */
1162                         /*
1163                          * If there's data, delay ACK; if there's also a FIN
1164                          * ACKNOW will be turned on later.
1165                          */
1166                         if (DELAY_ACK(tp) && tlen != 0)
1167                                 callout_reset(tp->tt_delack, tcp_delacktime,  
1168                                     tcp_timer_delack, tp);  
1169                         else
1170                                 tp->t_flags |= TF_ACKNOW;
1171                         /*
1172                          * Received <SYN,ACK> in SYN_SENT[*] state.
1173                          * Transitions:
1174                          *      SYN_SENT  --> ESTABLISHED
1175                          *      SYN_SENT* --> FIN_WAIT_1
1176                          */
1177                         tp->t_starttime = ticks;
1178                         if (tp->t_flags & TF_NEEDFIN) {
1179                                 tp->t_state = TCPS_FIN_WAIT_1;
1180                                 tp->t_flags &= ~TF_NEEDFIN;
1181                                 thflags &= ~TH_SYN;
1182                         } else {
1183                                 tp->t_state = TCPS_ESTABLISHED;
1184                                 callout_reset(tp->tt_keep, tcp_keepidle,
1185                                               tcp_timer_keep, tp);
1186                         }
1187                 } else {
1188                         /*
1189                          * Received initial SYN in SYN-SENT[*] state =>
1190                          * simultaneous open.  If segment contains CC option
1191                          * and there is a cached CC, apply TAO test.
1192                          * If it succeeds, connection is * half-synchronized.
1193                          * Otherwise, do 3-way handshake:
1194                          *        SYN-SENT -> SYN-RECEIVED
1195                          *        SYN-SENT* -> SYN-RECEIVED*
1196                          * If there was no CC option, clear cached CC value.
1197                          */
1198                         tp->t_flags |= TF_ACKNOW;
1199                         callout_stop(tp->tt_rexmt);
1200                         if (to.to_flags & TOF_CC) {
1201                                 if (taop->tao_cc != 0 &&
1202                                     CC_GT(to.to_cc, taop->tao_cc)) {
1203                                         /*
1204                                          * update cache and make transition:
1205                                          *        SYN-SENT -> ESTABLISHED*
1206                                          *        SYN-SENT* -> FIN-WAIT-1*
1207                                          */
1208                                         taop->tao_cc = to.to_cc;
1209                                         tp->t_starttime = ticks;
1210                                         if (tp->t_flags & TF_NEEDFIN) {
1211                                                 tp->t_state = TCPS_FIN_WAIT_1;
1212                                                 tp->t_flags &= ~TF_NEEDFIN;
1213                                         } else {
1214                                                 tp->t_state = TCPS_ESTABLISHED;
1215                                                 callout_reset(tp->tt_keep,
1216                                                               tcp_keepidle,
1217                                                               tcp_timer_keep,
1218                                                               tp);
1219                                         }
1220                                         tp->t_flags |= TF_NEEDSYN;
1221                                 } else
1222                                         tp->t_state = TCPS_SYN_RECEIVED;
1223                         } else {
1224                                 /* CC.NEW or no option => invalidate cache */
1225                                 taop->tao_cc = 0;
1226                                 tp->t_state = TCPS_SYN_RECEIVED;
1227                         }
1228                 }
1229
1230 trimthenstep6:
1231                 /*
1232                  * Advance th->th_seq to correspond to first data byte.
1233                  * If data, trim to stay within window,
1234                  * dropping FIN if necessary.
1235                  */
1236                 th->th_seq++;
1237                 if (tlen > tp->rcv_wnd) {
1238                         todrop = tlen - tp->rcv_wnd;
1239                         m_adj(m, -todrop);
1240                         tlen = tp->rcv_wnd;
1241                         thflags &= ~TH_FIN;
1242                         tcpstat.tcps_rcvpackafterwin++;
1243                         tcpstat.tcps_rcvbyteafterwin += todrop;
1244                 }
1245                 tp->snd_wl1 = th->th_seq - 1;
1246                 tp->rcv_up = th->th_seq;
1247                 /*
1248                  * Client side of transaction: already sent SYN and data.
1249                  * If the remote host used T/TCP to validate the SYN,
1250                  * our data will be ACK'd; if so, enter normal data segment
1251                  * processing in the middle of step 5, ack processing.
1252                  * Otherwise, goto step 6.
1253                  */
1254                 if (thflags & TH_ACK)
1255                         goto process_ACK;
1256
1257                 goto step6;
1258
1259         /*
1260          * If the state is LAST_ACK or CLOSING or TIME_WAIT:
1261          *      if segment contains a SYN and CC [not CC.NEW] option:
1262          *              if state == TIME_WAIT and connection duration > MSL,
1263          *                  drop packet and send RST;
1264          *
1265          *              if SEG.CC > CCrecv then is new SYN, and can implicitly
1266          *                  ack the FIN (and data) in retransmission queue.
1267          *                  Complete close and delete TCPCB.  Then reprocess
1268          *                  segment, hoping to find new TCPCB in LISTEN state;
1269          *
1270          *              else must be old SYN; drop it.
1271          *      else do normal processing.
1272          */
1273         case TCPS_LAST_ACK:
1274         case TCPS_CLOSING:
1275         case TCPS_TIME_WAIT:
1276                 if ((thflags & TH_SYN) &&
1277                     (to.to_flags & TOF_CC) && tp->cc_recv != 0) {
1278                         if (tp->t_state == TCPS_TIME_WAIT &&
1279                                         (ticks - tp->t_starttime) > tcp_msl) {
1280                                 rstreason = BANDLIM_UNLIMITED;
1281                                 goto dropwithreset;
1282                         }
1283                         if (CC_GT(to.to_cc, tp->cc_recv)) {
1284                                 tp = tcp_close(tp);
1285                                 goto findpcb;
1286                         }
1287                         else
1288                                 goto drop;
1289                 }
1290                 break;  /* continue normal processing */
1291         }
1292
1293         /*
1294          * States other than LISTEN or SYN_SENT.
1295          * First check the RST flag and sequence number since reset segments
1296          * are exempt from the timestamp and connection count tests.  This
1297          * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
1298          * below which allowed reset segments in half the sequence space
1299          * to fall though and be processed (which gives forged reset
1300          * segments with a random sequence number a 50 percent chance of
1301          * killing a connection).
1302          * Then check timestamp, if present.
1303          * Then check the connection count, if present.
1304          * Then check that at least some bytes of segment are within
1305          * receive window.  If segment begins before rcv_nxt,
1306          * drop leading data (and SYN); if nothing left, just ack.
1307          *
1308          *
1309          * If the RST bit is set, check the sequence number to see
1310          * if this is a valid reset segment.
1311          * RFC 793 page 37:
1312          *   In all states except SYN-SENT, all reset (RST) segments
1313          *   are validated by checking their SEQ-fields.  A reset is
1314          *   valid if its sequence number is in the window.
1315          * Note: this does not take into account delayed ACKs, so
1316          *   we should test against last_ack_sent instead of rcv_nxt.
1317          *   The sequence number in the reset segment is normally an
1318          *   echo of our outgoing acknowlegement numbers, but some hosts
1319          *   send a reset with the sequence number at the rightmost edge
1320          *   of our receive window, and we have to handle this case.
1321          * If we have multiple segments in flight, the intial reset
1322          * segment sequence numbers will be to the left of last_ack_sent,
1323          * but they will eventually catch up.
1324          * In any case, it never made sense to trim reset segments to
1325          * fit the receive window since RFC 1122 says:
1326          *   4.2.2.12  RST Segment: RFC-793 Section 3.4
1327          *
1328          *    A TCP SHOULD allow a received RST segment to include data.
1329          *
1330          *    DISCUSSION
1331          *         It has been suggested that a RST segment could contain
1332          *         ASCII text that encoded and explained the cause of the
1333          *         RST.  No standard has yet been established for such
1334          *         data.
1335          *
1336          * If the reset segment passes the sequence number test examine
1337          * the state:
1338          *    SYN_RECEIVED STATE:
1339          *      If passive open, return to LISTEN state.
1340          *      If active open, inform user that connection was refused.
1341          *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, CLOSE_WAIT STATES:
1342          *      Inform user that connection was reset, and close tcb.
1343          *    CLOSING, LAST_ACK STATES:
1344          *      Close the tcb.
1345          *    TIME_WAIT STATE:
1346          *      Drop the segment - see Stevens, vol. 2, p. 964 and
1347          *      RFC 1337.
1348          */
1349         if (thflags & TH_RST) {
1350                 if (SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
1351                     SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
1352                         switch (tp->t_state) {
1353
1354                         case TCPS_SYN_RECEIVED:
1355                                 so->so_error = ECONNREFUSED;
1356                                 goto close;
1357
1358                         case TCPS_ESTABLISHED:
1359                         case TCPS_FIN_WAIT_1:
1360                         case TCPS_FIN_WAIT_2:
1361                         case TCPS_CLOSE_WAIT:
1362                                 so->so_error = ECONNRESET;
1363                         close:
1364                                 tp->t_state = TCPS_CLOSED;
1365                                 tcpstat.tcps_drops++;
1366                                 tp = tcp_close(tp);
1367                                 break;
1368
1369                         case TCPS_CLOSING:
1370                         case TCPS_LAST_ACK:
1371                                 tp = tcp_close(tp);
1372                                 break;
1373
1374                         case TCPS_TIME_WAIT:
1375                                 break;
1376                         }
1377                 }
1378                 goto drop;
1379         }
1380
1381         /*
1382          * RFC 1323 PAWS: If we have a timestamp reply on this segment
1383          * and it's less than ts_recent, drop it.
1384          */
1385         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
1386             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
1387
1388                 /* Check to see if ts_recent is over 24 days old.  */
1389                 if ((int)(ticks - tp->ts_recent_age) > TCP_PAWS_IDLE) {
1390                         /*
1391                          * Invalidate ts_recent.  If this segment updates
1392                          * ts_recent, the age will be reset later and ts_recent
1393                          * will get a valid value.  If it does not, setting
1394                          * ts_recent to zero will at least satisfy the
1395                          * requirement that zero be placed in the timestamp
1396                          * echo reply when ts_recent isn't valid.  The
1397                          * age isn't reset until we get a valid ts_recent
1398                          * because we don't want out-of-order segments to be
1399                          * dropped when ts_recent is old.
1400                          */
1401                         tp->ts_recent = 0;
1402                 } else {
1403                         tcpstat.tcps_rcvduppack++;
1404                         tcpstat.tcps_rcvdupbyte += tlen;
1405                         tcpstat.tcps_pawsdrop++;
1406                         if (tlen)
1407                                 goto dropafterack;
1408                         goto drop;
1409                 }
1410         }
1411
1412         /*
1413          * T/TCP mechanism
1414          *   If T/TCP was negotiated and the segment doesn't have CC,
1415          *   or if its CC is wrong then drop the segment.
1416          *   RST segments do not have to comply with this.
1417          */
1418         if ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) == (TF_REQ_CC|TF_RCVD_CC) &&
1419             ((to.to_flags & TOF_CC) == 0 || tp->cc_recv != to.to_cc))
1420                 goto dropafterack;
1421
1422         /*
1423          * In the SYN-RECEIVED state, validate that the packet belongs to
1424          * this connection before trimming the data to fit the receive
1425          * window.  Check the sequence number versus IRS since we know
1426          * the sequence numbers haven't wrapped.  This is a partial fix
1427          * for the "LAND" DoS attack.
1428          */
1429         if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
1430                 rstreason = BANDLIM_RST_OPENPORT;
1431                 goto dropwithreset;
1432         }
1433
1434         todrop = tp->rcv_nxt - th->th_seq;
1435         if (todrop > 0) {
1436                 if (thflags & TH_SYN) {
1437                         thflags &= ~TH_SYN;
1438                         th->th_seq++;
1439                         if (th->th_urp > 1)
1440                                 th->th_urp--;
1441                         else
1442                                 thflags &= ~TH_URG;
1443                         todrop--;
1444                 }
1445                 /*
1446                  * Following if statement from Stevens, vol. 2, p. 960.
1447                  */
1448                 if (todrop > tlen
1449                     || (todrop == tlen && (thflags & TH_FIN) == 0)) {
1450                         /*
1451                          * Any valid FIN must be to the left of the window.
1452                          * At this point the FIN must be a duplicate or out
1453                          * of sequence; drop it.
1454                          */
1455                         thflags &= ~TH_FIN;
1456
1457                         /*
1458                          * Send an ACK to resynchronize and drop any data.
1459                          * But keep on processing for RST or ACK.
1460                          */
1461                         tp->t_flags |= TF_ACKNOW;
1462                         todrop = tlen;
1463                         tcpstat.tcps_rcvduppack++;
1464                         tcpstat.tcps_rcvdupbyte += todrop;
1465                 } else {
1466                         tcpstat.tcps_rcvpartduppack++;
1467                         tcpstat.tcps_rcvpartdupbyte += todrop;
1468                 }
1469                 drop_hdrlen += todrop;  /* drop from the top afterwards */
1470                 th->th_seq += todrop;
1471                 tlen -= todrop;
1472                 if (th->th_urp > todrop)
1473                         th->th_urp -= todrop;
1474                 else {
1475                         thflags &= ~TH_URG;
1476                         th->th_urp = 0;
1477                 }
1478         }
1479
1480         /*
1481          * If new data are received on a connection after the
1482          * user processes are gone, then RST the other end.
1483          */
1484         if ((so->so_state & SS_NOFDREF) &&
1485             tp->t_state > TCPS_CLOSE_WAIT && tlen) {
1486                 tp = tcp_close(tp);
1487                 tcpstat.tcps_rcvafterclose++;
1488                 rstreason = BANDLIM_UNLIMITED;
1489                 goto dropwithreset;
1490         }
1491
1492         /*
1493          * If segment ends after window, drop trailing data
1494          * (and PUSH and FIN); if nothing left, just ACK.
1495          */
1496         todrop = (th->th_seq+tlen) - (tp->rcv_nxt+tp->rcv_wnd);
1497         if (todrop > 0) {
1498                 tcpstat.tcps_rcvpackafterwin++;
1499                 if (todrop >= tlen) {
1500                         tcpstat.tcps_rcvbyteafterwin += tlen;
1501                         /*
1502                          * If a new connection request is received
1503                          * while in TIME_WAIT, drop the old connection
1504                          * and start over if the sequence numbers
1505                          * are above the previous ones.
1506                          */
1507                         if (thflags & TH_SYN &&
1508                             tp->t_state == TCPS_TIME_WAIT &&
1509                             SEQ_GT(th->th_seq, tp->rcv_nxt)) {
1510                                 tp = tcp_close(tp);
1511                                 goto findpcb;
1512                         }
1513                         /*
1514                          * If window is closed can only take segments at
1515                          * window edge, and have to drop data and PUSH from
1516                          * incoming segments.  Continue processing, but
1517                          * remember to ack.  Otherwise, drop segment
1518                          * and ack.
1519                          */
1520                         if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
1521                                 tp->t_flags |= TF_ACKNOW;
1522                                 tcpstat.tcps_rcvwinprobe++;
1523                         } else
1524                                 goto dropafterack;
1525                 } else
1526                         tcpstat.tcps_rcvbyteafterwin += todrop;
1527                 m_adj(m, -todrop);
1528                 tlen -= todrop;
1529                 thflags &= ~(TH_PUSH|TH_FIN);
1530         }
1531
1532         /*
1533          * If last ACK falls within this segment's sequence numbers,
1534          * record its timestamp.
1535          * NOTE that the test is modified according to the latest
1536          * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1537          */
1538         if ((to.to_flags & TOF_TS) != 0 &&
1539             SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
1540                 tp->ts_recent_age = ticks;
1541                 tp->ts_recent = to.to_tsval;
1542         }
1543
1544         /*
1545          * If a SYN is in the window, then this is an
1546          * error and we send an RST and drop the connection.
1547          */
1548         if (thflags & TH_SYN) {
1549                 tp = tcp_drop(tp, ECONNRESET);
1550                 rstreason = BANDLIM_UNLIMITED;
1551                 goto dropwithreset;
1552         }
1553
1554         /*
1555          * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
1556          * flag is on (half-synchronized state), then queue data for
1557          * later processing; else drop segment and return.
1558          */
1559         if ((thflags & TH_ACK) == 0) {
1560                 if (tp->t_state == TCPS_SYN_RECEIVED ||
1561                     (tp->t_flags & TF_NEEDSYN))
1562                         goto step6;
1563                 else
1564                         goto drop;
1565         }
1566
1567         /*
1568          * Ack processing.
1569          */
1570         switch (tp->t_state) {
1571
1572         /*
1573          * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
1574          * ESTABLISHED state and continue processing.
1575          * The ACK was checked above.
1576          */
1577         case TCPS_SYN_RECEIVED:
1578
1579                 tcpstat.tcps_connects++;
1580                 soisconnected(so);
1581                 /* Do window scaling? */
1582                 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1583                         (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1584                         tp->snd_scale = tp->requested_s_scale;
1585                         tp->rcv_scale = tp->request_r_scale;
1586                 }
1587                 /*
1588                  * Upon successful completion of 3-way handshake,
1589                  * update cache.CC if it was undefined, pass any queued
1590                  * data to the user, and advance state appropriately.
1591                  */
1592                 if ((taop = tcp_gettaocache(&inp->inp_inc)) != NULL &&
1593                     taop->tao_cc == 0)
1594                         taop->tao_cc = tp->cc_recv;
1595
1596                 /*
1597                  * Make transitions:
1598                  *      SYN-RECEIVED  -> ESTABLISHED
1599                  *      SYN-RECEIVED* -> FIN-WAIT-1
1600                  */
1601                 tp->t_starttime = ticks;
1602                 if (tp->t_flags & TF_NEEDFIN) {
1603                         tp->t_state = TCPS_FIN_WAIT_1;
1604                         tp->t_flags &= ~TF_NEEDFIN;
1605                 } else {
1606                         tp->t_state = TCPS_ESTABLISHED;
1607                         callout_reset(tp->tt_keep, tcp_keepidle, 
1608                                       tcp_timer_keep, tp);
1609                 }
1610                 /*
1611                  * If segment contains data or ACK, will call tcp_reass()
1612                  * later; if not, do so now to pass queued data to user.
1613                  */
1614                 if (tlen == 0 && (thflags & TH_FIN) == 0)
1615                         (void) tcp_reass(tp, (struct tcphdr *)0, 0,
1616                             (struct mbuf *)0);
1617                 tp->snd_wl1 = th->th_seq - 1;
1618                 /* fall into ... */
1619
1620         /*
1621          * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
1622          * ACKs.  If the ack is in the range
1623          *      tp->snd_una < th->th_ack <= tp->snd_max
1624          * then advance tp->snd_una to th->th_ack and drop
1625          * data from the retransmission queue.  If this ACK reflects
1626          * more up to date window information we update our window information.
1627          */
1628         case TCPS_ESTABLISHED:
1629         case TCPS_FIN_WAIT_1:
1630         case TCPS_FIN_WAIT_2:
1631         case TCPS_CLOSE_WAIT:
1632         case TCPS_CLOSING:
1633         case TCPS_LAST_ACK:
1634         case TCPS_TIME_WAIT:
1635
1636                 if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
1637                         if (tlen == 0 && tiwin == tp->snd_wnd) {
1638                                 tcpstat.tcps_rcvdupack++;
1639                                 /*
1640                                  * If we have outstanding data (other than
1641                                  * a window probe), this is a completely
1642                                  * duplicate ack (ie, window info didn't
1643                                  * change), the ack is the biggest we've
1644                                  * seen and we've seen exactly our rexmt
1645                                  * threshhold of them, assume a packet
1646                                  * has been dropped and retransmit it.
1647                                  * Kludge snd_nxt & the congestion
1648                                  * window so we send only this one
1649                                  * packet.
1650                                  *
1651                                  * We know we're losing at the current
1652                                  * window size so do congestion avoidance
1653                                  * (set ssthresh to half the current window
1654                                  * and pull our congestion window back to
1655                                  * the new ssthresh).
1656                                  *
1657                                  * Dup acks mean that packets have left the
1658                                  * network (they're now cached at the receiver)
1659                                  * so bump cwnd by the amount in the receiver
1660                                  * to keep a constant cwnd packets in the
1661                                  * network.
1662                                  */
1663                                 if (!callout_active(tp->tt_rexmt) ||
1664                                     th->th_ack != tp->snd_una)
1665                                         tp->t_dupacks = 0;
1666                                 else if (++tp->t_dupacks > tcprexmtthresh ||
1667                                          (tcp_do_newreno &&
1668                                           SEQ_LT(tp->snd_una,
1669                                                  tp->snd_recover))) {
1670                                         tp->snd_cwnd += tp->t_maxseg;
1671                                         (void) tcp_output(tp);
1672                                         goto drop;
1673                                 } else if (tp->t_dupacks == tcprexmtthresh) {
1674                                         tcp_seq onxt = tp->snd_nxt;
1675                                         u_int win;
1676                                         if (tcp_do_newreno &&
1677                                             SEQ_LEQ(th->th_ack, tp->snd_high)) {
1678                                                 tp->t_dupacks = 0;
1679                                                 break;
1680                                         }
1681                                         win = min(tp->snd_wnd, tp->snd_cwnd) /
1682                                             2 / tp->t_maxseg;
1683                                         if (win < 2)
1684                                                 win = 2;
1685                                         tp->snd_ssthresh = win * tp->t_maxseg;
1686                                         tp->snd_recover = tp->snd_max;
1687                                         callout_stop(tp->tt_rexmt);
1688                                         tp->t_rtttime = 0;
1689                                         tp->snd_nxt = th->th_ack;
1690                                         tp->snd_cwnd = tp->t_maxseg;
1691                                         (void) tcp_output(tp);
1692                                         tp->snd_cwnd = tp->snd_ssthresh +
1693                                                 tp->t_maxseg * tp->t_dupacks;
1694                                         if (SEQ_GT(onxt, tp->snd_nxt))
1695                                                 tp->snd_nxt = onxt;
1696                                         goto drop;
1697                                 }
1698                         } else
1699                                 tp->t_dupacks = 0;
1700                         break;
1701                 }
1702
1703                 KASSERT(SEQ_GT(th->th_ack, tp->snd_una), ("th_ack <= snd_una"));
1704
1705                 /*
1706                  * If the congestion window was inflated to account
1707                  * for the other side's cached packets, retract it.
1708                  */
1709                 if (tcp_do_newreno) {
1710                         if (SEQ_LT(tp->snd_una, tp->snd_recover)) {
1711                                 if (SEQ_LT(th->th_ack, tp->snd_recover)) {
1712                                         tcp_newreno_partial_ack(tp, th);
1713                                 } else {
1714                                         /*
1715                                          * Window inflation should have left us
1716                                          * with approximately snd_ssthresh
1717                                          * outstanding data.
1718                                          * But in case we would be inclined to
1719                                          * send a burst, better to do it via
1720                                          * the slow start mechanism.
1721                                          */
1722                                         if (SEQ_GT(th->th_ack +
1723                                                         tp->snd_ssthresh,
1724                                                    tp->snd_max))
1725                                                 tp->snd_cwnd = tp->snd_max -
1726                                                                 th->th_ack +
1727                                                                 tp->t_maxseg;
1728                                         else
1729                                                 tp->snd_cwnd = tp->snd_ssthresh;
1730                                 }
1731                         }
1732                 } else {
1733                         if (tp->t_dupacks >= tcprexmtthresh &&
1734                             tp->snd_cwnd > tp->snd_ssthresh)
1735                                 tp->snd_cwnd = tp->snd_ssthresh;
1736                 }
1737                 tp->t_dupacks = 0;
1738                 if (SEQ_GT(th->th_ack, tp->snd_max)) {
1739                         tcpstat.tcps_rcvacktoomuch++;
1740                         goto dropafterack;
1741                 }
1742                 /*
1743                  * If we reach this point, ACK is not a duplicate,
1744                  *     i.e., it ACKs something we sent.
1745                  */
1746                 if (tp->t_flags & TF_NEEDSYN) {
1747                         /*
1748                          * T/TCP: Connection was half-synchronized, and our
1749                          * SYN has been ACK'd (so connection is now fully
1750                          * synchronized).  Go to non-starred state,
1751                          * increment snd_una for ACK of SYN, and check if
1752                          * we can do window scaling.
1753                          */
1754                         tp->t_flags &= ~TF_NEEDSYN;
1755                         tp->snd_una++;
1756                         /* Do window scaling? */
1757                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1758                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1759                                 tp->snd_scale = tp->requested_s_scale;
1760                                 tp->rcv_scale = tp->request_r_scale;
1761                         }
1762                 }
1763
1764 process_ACK:
1765                 acked = th->th_ack - tp->snd_una;
1766                 tcpstat.tcps_rcvackpack++;
1767                 tcpstat.tcps_rcvackbyte += acked;
1768
1769                 /*
1770                  * If we just performed our first retransmit, and the ACK
1771                  * arrives within our recovery window, then it was a mistake
1772                  * to do the retransmit in the first place.  Recover our
1773                  * original cwnd and ssthresh, and proceed to transmit where
1774                  * we left off.
1775                  */
1776                 if (tp->t_rxtshift == 1 && ticks < tp->t_badrxtwin) {
1777                         tp->snd_cwnd = tp->snd_cwnd_prev;
1778                         tp->snd_ssthresh = tp->snd_ssthresh_prev;
1779                         tp->snd_high = tp->snd_high_prev;
1780                         tp->snd_nxt = tp->snd_max;
1781                         tp->t_badrxtwin = 0;    /* XXX probably not required */ 
1782                 }
1783
1784                 /*
1785                  * If we have a timestamp reply, update smoothed
1786                  * round trip time.  If no timestamp is present but
1787                  * transmit timer is running and timed sequence
1788                  * number was acked, update smoothed round trip time.
1789                  * Since we now have an rtt measurement, cancel the
1790                  * timer backoff (cf., Phil Karn's retransmit alg.).
1791                  * Recompute the initial retransmit timer.
1792                  *
1793                  * Some machines (certain windows boxes) send broken
1794                  * timestamp replies during the SYN+ACK phase, ignore 
1795                  * timestamps of 0.
1796                  */
1797                 if ((to.to_flags & TOF_TS) != 0 &&
1798                     to.to_tsecr) {
1799                         tcp_xmit_timer(tp, ticks - to.to_tsecr + 1);
1800                 } else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
1801                         tcp_xmit_timer(tp, ticks - tp->t_rtttime);
1802                 }
1803                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
1804
1805                 /*
1806                  * If all outstanding data is acked, stop retransmit
1807                  * timer and remember to restart (more output or persist).
1808                  * If there is more data to be acked, restart retransmit
1809                  * timer, using current (possibly backed-off) value.
1810                  */
1811                 if (th->th_ack == tp->snd_max) {
1812                         callout_stop(tp->tt_rexmt);
1813                         needoutput = 1;
1814                 } else if (!callout_active(tp->tt_persist))
1815                         callout_reset(tp->tt_rexmt, tp->t_rxtcur,
1816                                       tcp_timer_rexmt, tp);
1817
1818                 /*
1819                  * If no data (only SYN) was ACK'd,
1820                  *    skip rest of ACK processing.
1821                  */
1822                 if (acked == 0)
1823                         goto step6;
1824
1825                 /*
1826                  * When new data is acked, open the congestion window.
1827                  * If the window gives us less than ssthresh packets
1828                  * in flight, open exponentially (maxseg per packet).
1829                  * Otherwise open linearly: maxseg per window
1830                  * (maxseg^2 / cwnd per packet).
1831                  */
1832                 if (!tcp_do_newreno || SEQ_GEQ(tp->snd_una, tp->snd_recover)) {
1833                         register u_int cw = tp->snd_cwnd;
1834                         register u_int incr = tp->t_maxseg;
1835                         if (cw > tp->snd_ssthresh)
1836                                 incr = incr * incr / cw;
1837                         tp->snd_cwnd = min(cw+incr, TCP_MAXWIN<<tp->snd_scale);
1838                 }
1839                 if (acked > so->so_snd.sb_cc) {
1840                         tp->snd_wnd -= so->so_snd.sb_cc;
1841                         sbdrop(&so->so_snd, (int)so->so_snd.sb_cc);
1842                         ourfinisacked = 1;
1843                 } else {
1844                         sbdrop(&so->so_snd, acked);
1845                         tp->snd_wnd -= acked;
1846                         ourfinisacked = 0;
1847                 }
1848                 sowwakeup(so);
1849                 /* detect una wraparound */
1850                 if (SEQ_GEQ(tp->snd_una, tp->snd_recover) &&
1851                     SEQ_LT(th->th_ack, tp->snd_recover))
1852                         tp->snd_recover = th->th_ack;
1853                 if (SEQ_GT(tp->snd_una, tp->snd_high) &&
1854                     SEQ_LEQ(th->th_ack, tp->snd_high))
1855                         tp->snd_high = th->th_ack - 1;
1856                 tp->snd_una = th->th_ack;
1857                 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
1858                         tp->snd_nxt = tp->snd_una;
1859
1860                 switch (tp->t_state) {
1861
1862                 /*
1863                  * In FIN_WAIT_1 STATE in addition to the processing
1864                  * for the ESTABLISHED state if our FIN is now acknowledged
1865                  * then enter FIN_WAIT_2.
1866                  */
1867                 case TCPS_FIN_WAIT_1:
1868                         if (ourfinisacked) {
1869                                 /*
1870                                  * If we can't receive any more
1871                                  * data, then closing user can proceed.
1872                                  * Starting the timer is contrary to the
1873                                  * specification, but if we don't get a FIN
1874                                  * we'll hang forever.
1875                                  */
1876                                 if (so->so_state & SS_CANTRCVMORE) {
1877                                         soisdisconnected(so);
1878                                         callout_reset(tp->tt_2msl, tcp_maxidle,
1879                                                       tcp_timer_2msl, tp);
1880                                 }
1881                                 tp->t_state = TCPS_FIN_WAIT_2;
1882                         }
1883                         break;
1884
1885                 /*
1886                  * In CLOSING STATE in addition to the processing for
1887                  * the ESTABLISHED state if the ACK acknowledges our FIN
1888                  * then enter the TIME-WAIT state, otherwise ignore
1889                  * the segment.
1890                  */
1891                 case TCPS_CLOSING:
1892                         if (ourfinisacked) {
1893                                 tp->t_state = TCPS_TIME_WAIT;
1894                                 tcp_canceltimers(tp);
1895                                 /* Shorten TIME_WAIT [RFC-1644, p.28] */
1896                                 if (tp->cc_recv != 0 &&
1897                                     (ticks - tp->t_starttime) < tcp_msl)
1898                                         callout_reset(tp->tt_2msl,
1899                                                       tp->t_rxtcur *
1900                                                       TCPTV_TWTRUNC,
1901                                                       tcp_timer_2msl, tp);
1902                                 else
1903                                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
1904                                                       tcp_timer_2msl, tp);
1905                                 soisdisconnected(so);
1906                         }
1907                         break;
1908
1909                 /*
1910                  * In LAST_ACK, we may still be waiting for data to drain
1911                  * and/or to be acked, as well as for the ack of our FIN.
1912                  * If our FIN is now acknowledged, delete the TCB,
1913                  * enter the closed state and return.
1914                  */
1915                 case TCPS_LAST_ACK:
1916                         if (ourfinisacked) {
1917                                 tp = tcp_close(tp);
1918                                 goto drop;
1919                         }
1920                         break;
1921
1922                 /*
1923                  * In TIME_WAIT state the only thing that should arrive
1924                  * is a retransmission of the remote FIN.  Acknowledge
1925                  * it and restart the finack timer.
1926                  */
1927                 case TCPS_TIME_WAIT:
1928                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
1929                                       tcp_timer_2msl, tp);
1930                         goto dropafterack;
1931                 }
1932         }
1933
1934 step6:
1935         /*
1936          * Update window information.
1937          * Don't look at window if no ACK: TAC's send garbage on first SYN.
1938          */
1939         if ((thflags & TH_ACK) &&
1940             (SEQ_LT(tp->snd_wl1, th->th_seq) ||
1941             (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
1942              (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
1943                 /* keep track of pure window updates */
1944                 if (tlen == 0 &&
1945                     tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
1946                         tcpstat.tcps_rcvwinupd++;
1947                 tp->snd_wnd = tiwin;
1948                 tp->snd_wl1 = th->th_seq;
1949                 tp->snd_wl2 = th->th_ack;
1950                 if (tp->snd_wnd > tp->max_sndwnd)
1951                         tp->max_sndwnd = tp->snd_wnd;
1952                 needoutput = 1;
1953         }
1954
1955         /*
1956          * Process segments with URG.
1957          */
1958         if ((thflags & TH_URG) && th->th_urp &&
1959             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
1960                 /*
1961                  * This is a kludge, but if we receive and accept
1962                  * random urgent pointers, we'll crash in
1963                  * soreceive.  It's hard to imagine someone
1964                  * actually wanting to send this much urgent data.
1965                  */
1966                 if (th->th_urp + so->so_rcv.sb_cc > sb_max) {
1967                         th->th_urp = 0;                 /* XXX */
1968                         thflags &= ~TH_URG;             /* XXX */
1969                         goto dodata;                    /* XXX */
1970                 }
1971                 /*
1972                  * If this segment advances the known urgent pointer,
1973                  * then mark the data stream.  This should not happen
1974                  * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
1975                  * a FIN has been received from the remote side.
1976                  * In these states we ignore the URG.
1977                  *
1978                  * According to RFC961 (Assigned Protocols),
1979                  * the urgent pointer points to the last octet
1980                  * of urgent data.  We continue, however,
1981                  * to consider it to indicate the first octet
1982                  * of data past the urgent section as the original
1983                  * spec states (in one of two places).
1984                  */
1985                 if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
1986                         tp->rcv_up = th->th_seq + th->th_urp;
1987                         so->so_oobmark = so->so_rcv.sb_cc +
1988                             (tp->rcv_up - tp->rcv_nxt) - 1;
1989                         if (so->so_oobmark == 0)
1990                                 so->so_state |= SS_RCVATMARK;
1991                         sohasoutofband(so);
1992                         tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
1993                 }
1994                 /*
1995                  * Remove out of band data so doesn't get presented to user.
1996                  * This can happen independent of advancing the URG pointer,
1997                  * but if two URG's are pending at once, some out-of-band
1998                  * data may creep in... ick.
1999                  */
2000                 if (th->th_urp <= (u_long)tlen
2001 #ifdef SO_OOBINLINE
2002                      && (so->so_options & SO_OOBINLINE) == 0
2003 #endif
2004                      )
2005                         tcp_pulloutofband(so, th, m,
2006                                 drop_hdrlen);   /* hdr drop is delayed */
2007         } else {
2008                 /*
2009                  * If no out of band data is expected,
2010                  * pull receive urgent pointer along
2011                  * with the receive window.
2012                  */
2013                 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
2014                         tp->rcv_up = tp->rcv_nxt;
2015         }
2016 dodata:                                                 /* XXX */
2017
2018         /*
2019          * Process the segment text, merging it into the TCP sequencing queue,
2020          * and arranging for acknowledgment of receipt if necessary.
2021          * This process logically involves adjusting tp->rcv_wnd as data
2022          * is presented to the user (this happens in tcp_usrreq.c,
2023          * case PRU_RCVD).  If a FIN has already been received on this
2024          * connection then we just ignore the text.
2025          */
2026         if ((tlen || (thflags & TH_FIN)) &&
2027             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2028                 m_adj(m, drop_hdrlen);  /* delayed header drop */
2029                 /*
2030                  * Insert segment which includes th into TCP reassembly queue
2031                  * with control block tp.  Set thflags to whether reassembly now
2032                  * includes a segment with FIN.  This handles the common case
2033                  * inline (segment is the next to be received on an established
2034                  * connection, and the queue is empty), avoiding linkage into
2035                  * and removal from the queue and repetition of various
2036                  * conversions.
2037                  * Set DELACK for segments received in order, but ack
2038                  * immediately when segments are out of order (so
2039                  * fast retransmit can work).
2040                  */
2041                 if (th->th_seq == tp->rcv_nxt &&
2042                     LIST_EMPTY(&tp->t_segq) &&
2043                     TCPS_HAVEESTABLISHED(tp->t_state)) {
2044                         if (DELAY_ACK(tp))
2045                                 callout_reset(tp->tt_delack, tcp_delacktime,
2046                                               tcp_timer_delack, tp);
2047                         else
2048                                 tp->t_flags |= TF_ACKNOW;
2049                         tp->rcv_nxt += tlen;
2050                         thflags = th->th_flags & TH_FIN;
2051                         tcpstat.tcps_rcvpack++;
2052                         tcpstat.tcps_rcvbyte += tlen;
2053                         ND6_HINT(tp);
2054                         if (so->so_state & SS_CANTRCVMORE)
2055                                 m_freem(m);
2056                         else
2057                                 sbappend(&so->so_rcv, m);
2058                         sorwakeup(so);
2059                 } else {
2060                         thflags = tcp_reass(tp, th, &tlen, m);
2061                         tp->t_flags |= TF_ACKNOW;
2062                 }
2063
2064                 /*
2065                  * Note the amount of data that peer has sent into
2066                  * our window, in order to estimate the sender's
2067                  * buffer size.
2068                  */
2069                 len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
2070         } else {
2071                 m_freem(m);
2072                 thflags &= ~TH_FIN;
2073         }
2074
2075         /*
2076          * If FIN is received ACK the FIN and let the user know
2077          * that the connection is closing.
2078          */
2079         if (thflags & TH_FIN) {
2080                 if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2081                         socantrcvmore(so);
2082                         /*
2083                          * If connection is half-synchronized
2084                          * (ie NEEDSYN flag on) then delay ACK,
2085                          * so it may be piggybacked when SYN is sent.
2086                          * Otherwise, since we received a FIN then no
2087                          * more input can be expected, send ACK now.
2088                          */
2089                         if (DELAY_ACK(tp) && (tp->t_flags & TF_NEEDSYN))
2090                                 callout_reset(tp->tt_delack, tcp_delacktime,  
2091                                     tcp_timer_delack, tp);  
2092                         else
2093                                 tp->t_flags |= TF_ACKNOW;
2094                         tp->rcv_nxt++;
2095                 }
2096                 switch (tp->t_state) {
2097
2098                 /*
2099                  * In SYN_RECEIVED and ESTABLISHED STATES
2100                  * enter the CLOSE_WAIT state.
2101                  */
2102                 case TCPS_SYN_RECEIVED:
2103                         tp->t_starttime = ticks;
2104                         /*FALLTHROUGH*/
2105                 case TCPS_ESTABLISHED:
2106                         tp->t_state = TCPS_CLOSE_WAIT;
2107                         break;
2108
2109                 /*
2110                  * If still in FIN_WAIT_1 STATE FIN has not been acked so
2111                  * enter the CLOSING state.
2112                  */
2113                 case TCPS_FIN_WAIT_1:
2114                         tp->t_state = TCPS_CLOSING;
2115                         break;
2116
2117                 /*
2118                  * In FIN_WAIT_2 state enter the TIME_WAIT state,
2119                  * starting the time-wait timer, turning off the other
2120                  * standard timers.
2121                  */
2122                 case TCPS_FIN_WAIT_2:
2123                         tp->t_state = TCPS_TIME_WAIT;
2124                         tcp_canceltimers(tp);
2125                         /* Shorten TIME_WAIT [RFC-1644, p.28] */
2126                         if (tp->cc_recv != 0 &&
2127                             (ticks - tp->t_starttime) < tcp_msl) {
2128                                 callout_reset(tp->tt_2msl,
2129                                               tp->t_rxtcur * TCPTV_TWTRUNC,
2130                                               tcp_timer_2msl, tp);
2131                                 /* For transaction client, force ACK now. */
2132                                 tp->t_flags |= TF_ACKNOW;
2133                         }
2134                         else
2135                                 callout_reset(tp->tt_2msl, 2 * tcp_msl,
2136                                               tcp_timer_2msl, tp);
2137                         soisdisconnected(so);
2138                         break;
2139
2140                 /*
2141                  * In TIME_WAIT state restart the 2 MSL time_wait timer.
2142                  */
2143                 case TCPS_TIME_WAIT:
2144                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
2145                                       tcp_timer_2msl, tp);
2146                         break;
2147                 }
2148         }
2149 #ifdef TCPDEBUG
2150         if (so->so_options & SO_DEBUG)
2151                 tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
2152                           &tcp_savetcp, 0);
2153 #endif
2154
2155         /*
2156          * Return any desired output.
2157          */
2158         if (needoutput || (tp->t_flags & TF_ACKNOW))
2159                 (void) tcp_output(tp);
2160         return;
2161
2162 dropafterack:
2163         /*
2164          * Generate an ACK dropping incoming segment if it occupies
2165          * sequence space, where the ACK reflects our state.
2166          *
2167          * We can now skip the test for the RST flag since all
2168          * paths to this code happen after packets containing
2169          * RST have been dropped.
2170          *
2171          * In the SYN-RECEIVED state, don't send an ACK unless the
2172          * segment we received passes the SYN-RECEIVED ACK test.
2173          * If it fails send a RST.  This breaks the loop in the
2174          * "LAND" DoS attack, and also prevents an ACK storm
2175          * between two listening ports that have been sent forged
2176          * SYN segments, each with the source address of the other.
2177          */
2178         if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
2179             (SEQ_GT(tp->snd_una, th->th_ack) ||
2180              SEQ_GT(th->th_ack, tp->snd_max)) ) {
2181                 rstreason = BANDLIM_RST_OPENPORT;
2182                 goto dropwithreset;
2183         }
2184 #ifdef TCPDEBUG
2185         if (so->so_options & SO_DEBUG)
2186                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2187                           &tcp_savetcp, 0);
2188 #endif
2189         m_freem(m);
2190         tp->t_flags |= TF_ACKNOW;
2191         (void) tcp_output(tp);
2192         return;
2193
2194 dropwithreset:
2195         /*
2196          * Generate a RST, dropping incoming segment.
2197          * Make ACK acceptable to originator of segment.
2198          * Don't bother to respond if destination was broadcast/multicast.
2199          */
2200         if ((thflags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
2201                 goto drop;
2202         if (isipv6) {
2203                 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
2204                     IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
2205                         goto drop;
2206         } else {
2207                 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
2208                     IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
2209                     ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
2210                     in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
2211                         goto drop;
2212         }
2213         /* IPv6 anycast check is done at tcp6_input() */
2214
2215         /*
2216          * Perform bandwidth limiting.
2217          */
2218 #ifdef ICMP_BANDLIM
2219         if (badport_bandlim(rstreason) < 0)
2220                 goto drop;
2221 #endif
2222
2223 #ifdef TCPDEBUG
2224         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2225                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2226                           &tcp_savetcp, 0);
2227 #endif
2228         if (thflags & TH_ACK)
2229                 /* mtod() below is safe as long as hdr dropping is delayed */
2230                 tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0, th->th_ack,
2231                             TH_RST);
2232         else {
2233                 if (thflags & TH_SYN)
2234                         tlen++;
2235                 /* mtod() below is safe as long as hdr dropping is delayed */
2236                 tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
2237                             (tcp_seq)0, TH_RST|TH_ACK);
2238         }
2239         return;
2240
2241 drop:
2242         /*
2243          * Drop space held by incoming segment and return.
2244          */
2245 #ifdef TCPDEBUG
2246         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2247                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2248                           &tcp_savetcp, 0);
2249 #endif
2250         m_freem(m);
2251         return;
2252 }
2253
2254 /*
2255  * Parse TCP options and place in tcpopt.
2256  */
2257 static void
2258 tcp_dooptions(to, cp, cnt, is_syn)
2259         struct tcpopt *to;
2260         u_char *cp;
2261         int cnt;
2262 {
2263         int opt, optlen;
2264
2265         to->to_flags = 0;
2266         for (; cnt > 0; cnt -= optlen, cp += optlen) {
2267                 opt = cp[0];
2268                 if (opt == TCPOPT_EOL)
2269                         break;
2270                 if (opt == TCPOPT_NOP)
2271                         optlen = 1;
2272                 else {
2273                         if (cnt < 2)
2274                                 break;
2275                         optlen = cp[1];
2276                         if (optlen < 2 || optlen > cnt)
2277                                 break;
2278                 }
2279                 switch (opt) {
2280                 case TCPOPT_MAXSEG:
2281                         if (optlen != TCPOLEN_MAXSEG)
2282                                 continue;
2283                         if (!is_syn)
2284                                 continue;
2285                         to->to_flags |= TOF_MSS;
2286                         bcopy((char *)cp + 2,
2287                             (char *)&to->to_mss, sizeof(to->to_mss));
2288                         to->to_mss = ntohs(to->to_mss);
2289                         break;
2290                 case TCPOPT_WINDOW:
2291                         if (optlen != TCPOLEN_WINDOW)
2292                                 continue;
2293                         if (! is_syn)
2294                                 continue;
2295                         to->to_flags |= TOF_SCALE;
2296                         to->to_requested_s_scale = min(cp[2], TCP_MAX_WINSHIFT);
2297                         break;
2298                 case TCPOPT_TIMESTAMP:
2299                         if (optlen != TCPOLEN_TIMESTAMP)
2300                                 continue;
2301                         to->to_flags |= TOF_TS;
2302                         bcopy((char *)cp + 2,
2303                             (char *)&to->to_tsval, sizeof(to->to_tsval));
2304                         to->to_tsval = ntohl(to->to_tsval);
2305                         bcopy((char *)cp + 6,
2306                             (char *)&to->to_tsecr, sizeof(to->to_tsecr));
2307                         to->to_tsecr = ntohl(to->to_tsecr);
2308                         break;
2309                 case TCPOPT_CC:
2310                         if (optlen != TCPOLEN_CC)
2311                                 continue;
2312                         to->to_flags |= TOF_CC;
2313                         bcopy((char *)cp + 2,
2314                             (char *)&to->to_cc, sizeof(to->to_cc));
2315                         to->to_cc = ntohl(to->to_cc);
2316                         break;
2317                 case TCPOPT_CCNEW:
2318                         if (optlen != TCPOLEN_CC)
2319                                 continue;
2320                         if (!is_syn)
2321                                 continue;
2322                         to->to_flags |= TOF_CCNEW;
2323                         bcopy((char *)cp + 2,
2324                             (char *)&to->to_cc, sizeof(to->to_cc));
2325                         to->to_cc = ntohl(to->to_cc);
2326                         break;
2327                 case TCPOPT_CCECHO:
2328                         if (optlen != TCPOLEN_CC)
2329                                 continue;
2330                         if (!is_syn)
2331                                 continue;
2332                         to->to_flags |= TOF_CCECHO;
2333                         bcopy((char *)cp + 2,
2334                             (char *)&to->to_ccecho, sizeof(to->to_ccecho));
2335                         to->to_ccecho = ntohl(to->to_ccecho);
2336                         break;
2337                 default:
2338                         continue;
2339                 }
2340         }
2341 }
2342
2343 /*
2344  * Pull out of band byte out of a segment so
2345  * it doesn't appear in the user's data queue.
2346  * It is still reflected in the segment length for
2347  * sequencing purposes.
2348  */
2349 static void
2350 tcp_pulloutofband(so, th, m, off)
2351         struct socket *so;
2352         struct tcphdr *th;
2353         register struct mbuf *m;
2354         int off;                /* delayed to be droped hdrlen */
2355 {
2356         int cnt = off + th->th_urp - 1;
2357
2358         while (cnt >= 0) {
2359                 if (m->m_len > cnt) {
2360                         char *cp = mtod(m, caddr_t) + cnt;
2361                         struct tcpcb *tp = sototcpcb(so);
2362
2363                         tp->t_iobc = *cp;
2364                         tp->t_oobflags |= TCPOOB_HAVEDATA;
2365                         bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
2366                         m->m_len--;
2367                         if (m->m_flags & M_PKTHDR)
2368                                 m->m_pkthdr.len--;
2369                         return;
2370                 }
2371                 cnt -= m->m_len;
2372                 m = m->m_next;
2373                 if (m == 0)
2374                         break;
2375         }
2376         panic("tcp_pulloutofband");
2377 }
2378
2379 /*
2380  * Collect new round-trip time estimate
2381  * and update averages and current timeout.
2382  */
2383 static void
2384 tcp_xmit_timer(tp, rtt)
2385         register struct tcpcb *tp;
2386         int rtt;
2387 {
2388         register int delta;
2389
2390         tcpstat.tcps_rttupdated++;
2391         tp->t_rttupdated++;
2392         if (tp->t_srtt != 0) {
2393                 /*
2394                  * srtt is stored as fixed point with 5 bits after the
2395                  * binary point (i.e., scaled by 8).  The following magic
2396                  * is equivalent to the smoothing algorithm in rfc793 with
2397                  * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
2398                  * point).  Adjust rtt to origin 0.
2399                  */
2400                 delta = ((rtt - 1) << TCP_DELTA_SHIFT)
2401                         - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
2402
2403                 if ((tp->t_srtt += delta) <= 0)
2404                         tp->t_srtt = 1;
2405
2406                 /*
2407                  * We accumulate a smoothed rtt variance (actually, a
2408                  * smoothed mean difference), then set the retransmit
2409                  * timer to smoothed rtt + 4 times the smoothed variance.
2410                  * rttvar is stored as fixed point with 4 bits after the
2411                  * binary point (scaled by 16).  The following is
2412                  * equivalent to rfc793 smoothing with an alpha of .75
2413                  * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
2414                  * rfc793's wired-in beta.
2415                  */
2416                 if (delta < 0)
2417                         delta = -delta;
2418                 delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
2419                 if ((tp->t_rttvar += delta) <= 0)
2420                         tp->t_rttvar = 1;
2421                 if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
2422                         tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2423         } else {
2424                 /*
2425                  * No rtt measurement yet - use the unsmoothed rtt.
2426                  * Set the variance to half the rtt (so our first
2427                  * retransmit happens at 3*rtt).
2428                  */
2429                 tp->t_srtt = rtt << TCP_RTT_SHIFT;
2430                 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
2431                 tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2432         }
2433         tp->t_rtttime = 0;
2434         tp->t_rxtshift = 0;
2435
2436         /*
2437          * the retransmit should happen at rtt + 4 * rttvar.
2438          * Because of the way we do the smoothing, srtt and rttvar
2439          * will each average +1/2 tick of bias.  When we compute
2440          * the retransmit timer, we want 1/2 tick of rounding and
2441          * 1 extra tick because of +-1/2 tick uncertainty in the
2442          * firing of the timer.  The bias will give us exactly the
2443          * 1.5 tick we need.  But, because the bias is
2444          * statistical, we have to test that we don't drop below
2445          * the minimum feasible timer (which is 2 ticks).
2446          */
2447         TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
2448                       max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
2449
2450         /*
2451          * We received an ack for a packet that wasn't retransmitted;
2452          * it is probably safe to discard any error indications we've
2453          * received recently.  This isn't quite right, but close enough
2454          * for now (a route might have failed after we sent a segment,
2455          * and the return path might not be symmetrical).
2456          */
2457         tp->t_softerror = 0;
2458 }
2459
2460 /*
2461  * Determine a reasonable value for maxseg size.
2462  * If the route is known, check route for mtu.
2463  * If none, use an mss that can be handled on the outgoing
2464  * interface without forcing IP to fragment; if bigger than
2465  * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
2466  * to utilize large mbufs.  If no route is found, route has no mtu,
2467  * or the destination isn't local, use a default, hopefully conservative
2468  * size (usually 512 or the default IP max size, but no more than the mtu
2469  * of the interface), as we can't discover anything about intervening
2470  * gateways or networks.  We also initialize the congestion/slow start
2471  * window to be a single segment if the destination isn't local.
2472  * While looking at the routing entry, we also initialize other path-dependent
2473  * parameters from pre-set or cached values in the routing entry.
2474  *
2475  * Also take into account the space needed for options that we
2476  * send regularly.  Make maxseg shorter by that amount to assure
2477  * that we can send maxseg amount of data even when the options
2478  * are present.  Store the upper limit of the length of options plus
2479  * data in maxopd.
2480  *
2481  * NOTE that this routine is only called when we process an incoming
2482  * segment, for outgoing segments only tcp_mssopt is called.
2483  *
2484  * In case of T/TCP, we call this routine during implicit connection
2485  * setup as well (offer = -1), to initialize maxseg from the cached
2486  * MSS of our peer.
2487  */
2488 void
2489 tcp_mss(tp, offer)
2490         struct tcpcb *tp;
2491         int offer;
2492 {
2493         register struct rtentry *rt;
2494         struct ifnet *ifp;
2495         register int rtt, mss;
2496         u_long bufsize;
2497         struct inpcb *inp = tp->t_inpcb;
2498         struct socket *so;
2499         struct rmxp_tao *taop;
2500         int origoffer = offer;
2501 #ifdef INET6
2502         int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
2503         size_t min_protoh = isipv6 ?
2504                             sizeof(struct ip6_hdr) + sizeof(struct tcphdr) :
2505                             sizeof(struct tcpiphdr);
2506 #else
2507         const int isipv6 = 0;
2508         const size_t min_protoh = sizeof(struct tcpiphdr);
2509 #endif
2510
2511         if (isipv6)
2512                 rt = tcp_rtlookup6(&inp->inp_inc);
2513         else
2514                 rt = tcp_rtlookup(&inp->inp_inc);
2515         if (rt == NULL) {
2516                 tp->t_maxopd = tp->t_maxseg =
2517                                 isipv6 ? tcp_v6mssdflt : tcp_mssdflt;
2518                 return;
2519         }
2520         ifp = rt->rt_ifp;
2521         so = inp->inp_socket;
2522
2523         taop = rmx_taop(rt->rt_rmx);
2524         /*
2525          * Offer == -1 means that we didn't receive SYN yet,
2526          * use cached value in that case;
2527          */
2528         if (offer == -1)
2529                 offer = taop->tao_mssopt;
2530         /*
2531          * Offer == 0 means that there was no MSS on the SYN segment,
2532          * in this case we use tcp_mssdflt.
2533          */
2534         if (offer == 0)
2535                 offer = isipv6 ? tcp_v6mssdflt : tcp_mssdflt;
2536         else
2537                 /*
2538                  * Sanity check: make sure that maxopd will be large
2539                  * enough to allow some data on segments even is the
2540                  * all the option space is used (40bytes).  Otherwise
2541                  * funny things may happen in tcp_output.
2542                  */
2543                 offer = max(offer, 64);
2544         taop->tao_mssopt = offer;
2545
2546         /*
2547          * While we're here, check if there's an initial rtt
2548          * or rttvar.  Convert from the route-table units
2549          * to scaled multiples of the slow timeout timer.
2550          */
2551         if (tp->t_srtt == 0 && (rtt = rt->rt_rmx.rmx_rtt)) {
2552                 /*
2553                  * XXX the lock bit for RTT indicates that the value
2554                  * is also a minimum value; this is subject to time.
2555                  */
2556                 if (rt->rt_rmx.rmx_locks & RTV_RTT)
2557                         tp->t_rttmin = rtt / (RTM_RTTUNIT / hz);
2558                 tp->t_srtt = rtt / (RTM_RTTUNIT / (hz * TCP_RTT_SCALE));
2559                 tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
2560                 tcpstat.tcps_usedrtt++;
2561                 if (rt->rt_rmx.rmx_rttvar) {
2562                         tp->t_rttvar = rt->rt_rmx.rmx_rttvar /
2563                             (RTM_RTTUNIT / (hz * TCP_RTTVAR_SCALE));
2564                         tcpstat.tcps_usedrttvar++;
2565                 } else {
2566                         /* default variation is +- 1 rtt */
2567                         tp->t_rttvar =
2568                             tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
2569                 }
2570                 TCPT_RANGESET(tp->t_rxtcur,
2571                               ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
2572                               tp->t_rttmin, TCPTV_REXMTMAX);
2573         }
2574         /*
2575          * if there's an mtu associated with the route, use it
2576          * else, use the link mtu.
2577          */
2578         if (rt->rt_rmx.rmx_mtu)
2579                 mss = rt->rt_rmx.rmx_mtu - min_protoh;
2580         else {
2581                 if (isipv6) {
2582                         mss = nd_ifinfo[rt->rt_ifp->if_index].linkmtu -
2583                                 min_protoh;
2584                         if (!in6_localaddr(&inp->in6p_faddr))
2585                                 mss = min(mss, tcp_v6mssdflt);
2586                 } else {
2587                         mss = ifp->if_mtu - min_protoh;
2588                         if (!in_localaddr(inp->inp_faddr))
2589                                 mss = min(mss, tcp_mssdflt);
2590                 }
2591         }
2592         mss = min(mss, offer);
2593         /*
2594          * maxopd stores the maximum length of data AND options
2595          * in a segment; maxseg is the amount of data in a normal
2596          * segment.  We need to store this value (maxopd) apart
2597          * from maxseg, because now every segment carries options
2598          * and thus we normally have somewhat less data in segments.
2599          */
2600         tp->t_maxopd = mss;
2601
2602         /*
2603          * In case of T/TCP, origoffer==-1 indicates, that no segments
2604          * were received yet.  In this case we just guess, otherwise
2605          * we do the same as before T/TCP.
2606          */
2607         if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
2608             (origoffer == -1 ||
2609              (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
2610                 mss -= TCPOLEN_TSTAMP_APPA;
2611         if ((tp->t_flags & (TF_REQ_CC|TF_NOOPT)) == TF_REQ_CC &&
2612             (origoffer == -1 ||
2613              (tp->t_flags & TF_RCVD_CC) == TF_RCVD_CC))
2614                 mss -= TCPOLEN_CC_APPA;
2615
2616 #if     (MCLBYTES & (MCLBYTES - 1)) == 0
2617                 if (mss > MCLBYTES)
2618                         mss &= ~(MCLBYTES-1);
2619 #else
2620                 if (mss > MCLBYTES)
2621                         mss = mss / MCLBYTES * MCLBYTES;
2622 #endif
2623         /*
2624          * If there's a pipesize, change the socket buffer
2625          * to that size.  Make the socket buffers an integral
2626          * number of mss units; if the mss is larger than
2627          * the socket buffer, decrease the mss.
2628          */
2629 #ifdef RTV_SPIPE
2630         if ((bufsize = rt->rt_rmx.rmx_sendpipe) == 0)
2631 #endif
2632                 bufsize = so->so_snd.sb_hiwat;
2633         if (bufsize < mss)
2634                 mss = bufsize;
2635         else {
2636                 bufsize = roundup(bufsize, mss);
2637                 if (bufsize > sb_max)
2638                         bufsize = sb_max;
2639                 if (bufsize > so->so_snd.sb_hiwat)
2640                         (void)sbreserve(&so->so_snd, bufsize, so, NULL);
2641         }
2642         tp->t_maxseg = mss;
2643
2644 #ifdef RTV_RPIPE
2645         if ((bufsize = rt->rt_rmx.rmx_recvpipe) == 0)
2646 #endif
2647                 bufsize = so->so_rcv.sb_hiwat;
2648         if (bufsize > mss) {
2649                 bufsize = roundup(bufsize, mss);
2650                 if (bufsize > sb_max)
2651                         bufsize = sb_max;
2652                 if (bufsize > so->so_rcv.sb_hiwat)
2653                         (void)sbreserve(&so->so_rcv, bufsize, so, NULL);
2654         }
2655
2656         /*
2657          * Set the slow-start flight size depending on whether this
2658          * is a local network or not.
2659          */
2660         if ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
2661             (!isipv6 && in_localaddr(inp->inp_faddr)))
2662                 tp->snd_cwnd = mss * ss_fltsz_local;
2663         else 
2664                 tp->snd_cwnd = mss * ss_fltsz;
2665
2666         if (rt->rt_rmx.rmx_ssthresh) {
2667                 /*
2668                  * There's some sort of gateway or interface
2669                  * buffer limit on the path.  Use this to set
2670                  * the slow start threshhold, but set the
2671                  * threshold to no less than 2*mss.
2672                  */
2673                 tp->snd_ssthresh = max(2 * mss, rt->rt_rmx.rmx_ssthresh);
2674                 tcpstat.tcps_usedssthresh++;
2675         }
2676 }
2677
2678 /*
2679  * Determine the MSS option to send on an outgoing SYN.
2680  */
2681 int
2682 tcp_mssopt(tp)
2683         struct tcpcb *tp;
2684 {
2685         struct rtentry *rt;
2686 #ifdef INET6
2687         int isipv6 = ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
2688         int min_protoh = isipv6 ?
2689                              sizeof(struct ip6_hdr) + sizeof(struct tcphdr) :
2690                              sizeof(struct tcpiphdr);
2691 #else
2692         const int isipv6 = 0;
2693         const size_t min_protoh = sizeof(struct tcpiphdr);
2694 #endif
2695
2696         if (isipv6)
2697                 rt = tcp_rtlookup6(&tp->t_inpcb->inp_inc);
2698         else
2699                 rt = tcp_rtlookup(&tp->t_inpcb->inp_inc);
2700         if (rt == NULL)
2701                 return (isipv6 ? tcp_v6mssdflt : tcp_mssdflt);
2702
2703         return (rt->rt_ifp->if_mtu - min_protoh);
2704 }
2705
2706
2707 /*
2708  * When a partial ack arrives, force the retransmission of the
2709  * next unacknowledged segment.  Do not clear tp->t_dupacks.
2710  * By setting snd_nxt to ti_ack, this forces retransmission timer to
2711  * be started again.
2712  */
2713 static void
2714 tcp_newreno_partial_ack(tp, th)
2715         struct tcpcb *tp;
2716         struct tcphdr *th;
2717 {
2718         tcp_seq onxt = tp->snd_nxt;
2719         u_long  ocwnd = tp->snd_cwnd;
2720
2721         callout_stop(tp->tt_rexmt);
2722         tp->t_rtttime = 0;
2723         tp->snd_nxt = th->th_ack;
2724         /*
2725          * Set snd_cwnd to one segment beyond acknowledged offset
2726          * (tp->snd_una has not yet been updated when this function is called.)
2727          */
2728         tp->snd_cwnd = tp->t_maxseg + (th->th_ack - tp->snd_una);
2729         tp->t_flags |= TF_ACKNOW;
2730         (void) tcp_output(tp);
2731         tp->snd_cwnd = ocwnd;
2732         if (SEQ_GT(onxt, tp->snd_nxt))
2733                 tp->snd_nxt = onxt;
2734         /*
2735          * Partial window deflation.  Relies on fact that tp->snd_una
2736          * not updated yet.
2737          */
2738         tp->snd_cwnd -= (th->th_ack - tp->snd_una - tp->t_maxseg);
2739 }