Implement the Eifel Dectection Algorithm for TCP (RFC 3522).
[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  *
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8  * 1. Redistributions of source code must retain the above copyright
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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.
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14  *    must display the following acknowledgement:
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16  *      California, Berkeley and its contributors.
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18  *    may be used to endorse or promote products derived from this software
19  *    without specific prior written permission.
20  *
21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31  * SUCH DAMAGE.
32  *
33  *      @(#)tcp_input.c 8.12 (Berkeley) 5/24/95
34  * $FreeBSD: src/sys/netinet/tcp_input.c,v 1.107.2.38 2003/05/21 04:46:41 cjc Exp $
35  * $DragonFly: src/sys/netinet/tcp_input.c,v 1.8 2003/08/13 18:34:25 hsu Exp $
36  */
37
38 #include "opt_ipfw.h"           /* for ipfw_fwd         */
39 #include "opt_inet6.h"
40 #include "opt_ipsec.h"
41 #include "opt_tcpdebug.h"
42 #include "opt_tcp_input.h"
43
44 #include <sys/param.h>
45 #include <sys/systm.h>
46 #include <sys/kernel.h>
47 #include <sys/sysctl.h>
48 #include <sys/malloc.h>
49 #include <sys/mbuf.h>
50 #include <sys/proc.h>           /* for proc0 declaration */
51 #include <sys/protosw.h>
52 #include <sys/socket.h>
53 #include <sys/socketvar.h>
54 #include <sys/syslog.h>
55
56 #include <machine/cpu.h>        /* before tcp_seq.h, for tcp_random18() */
57
58 #include <net/if.h>
59 #include <net/route.h>
60
61 #include <netinet/in.h>
62 #include <netinet/in_systm.h>
63 #include <netinet/ip.h>
64 #include <netinet/ip_icmp.h>    /* for ICMP_BANDLIM             */
65 #include <netinet/in_var.h>
66 #include <netinet/icmp_var.h>   /* for ICMP_BANDLIM             */
67 #include <netinet/in_pcb.h>
68 #include <netinet/ip_var.h>
69 #include <netinet/ip6.h>
70 #include <netinet/icmp6.h>
71 #include <netinet6/nd6.h>
72 #include <netinet6/ip6_var.h>
73 #include <netinet6/in6_pcb.h>
74 #include <netinet/tcp.h>
75 #include <netinet/tcp_fsm.h>
76 #include <netinet/tcp_seq.h>
77 #include <netinet/tcp_timer.h>
78 #include <netinet/tcp_var.h>
79 #include <netinet6/tcp6_var.h>
80 #include <netinet/tcpip.h>
81 #ifdef TCPDEBUG
82 #include <netinet/tcp_debug.h>
83
84 u_char tcp_saveipgen[40]; /* the size must be of max ip header, now IPv6 */
85 struct tcphdr tcp_savetcp;
86 #endif /* TCPDEBUG */
87
88 #ifdef FAST_IPSEC
89 #include <netipsec/ipsec.h>
90 #include <netipsec/ipsec6.h>
91 #endif
92
93 #ifdef IPSEC
94 #include <netinet6/ipsec.h>
95 #include <netinet6/ipsec6.h>
96 #include <netproto/key/key.h>
97 #endif /*IPSEC*/
98
99 #include <machine/in_cksum.h>
100
101 MALLOC_DEFINE(M_TSEGQ, "tseg_qent", "TCP segment queue entry");
102
103 static const int tcprexmtthresh = 3;
104 tcp_cc  tcp_ccgen;
105
106 struct  tcpstat tcpstat;
107 SYSCTL_STRUCT(_net_inet_tcp, TCPCTL_STATS, stats, CTLFLAG_RW,
108     &tcpstat , tcpstat, "TCP statistics (struct tcpstat, netinet/tcp_var.h)");
109
110 static int log_in_vain = 0;
111 SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW, 
112     &log_in_vain, 0, "Log all incoming TCP connections");
113
114 static int blackhole = 0;
115 SYSCTL_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_RW,
116     &blackhole, 0, "Do not send RST when dropping refused connections");
117
118 int tcp_delack_enabled = 1;
119 SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_RW, 
120     &tcp_delack_enabled, 0, 
121     "Delay ACK to try and piggyback it onto a data packet");
122
123 #ifdef TCP_DROP_SYNFIN
124 static int drop_synfin = 0;
125 SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_RW,
126     &drop_synfin, 0, "Drop TCP packets with SYN+FIN set");
127 #endif
128
129 static int tcp_do_limitedtransmit = 1;
130 SYSCTL_INT(_net_inet_tcp, OID_AUTO, limitedtransmit, CTLFLAG_RW,
131     &tcp_do_limitedtransmit, 0, "Enable RFC 3042 (Limited Transmit)");
132
133 static int tcp_do_rfc3390 = 1;
134 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3390, CTLFLAG_RW,
135     &tcp_do_rfc3390, 0,
136     "Enable RFC 3390 (Increasing TCP's Initial Congestion Window)");
137
138 static int tcp_do_eifel_detect = 1;
139 SYSCTL_INT(_net_inet_tcp, OID_AUTO, eifel, CTLFLAG_RW,
140     &tcp_do_eifel_detect, 0, "Eifel detection algorithm (RFC 3522)");
141
142 struct inpcbhead tcb;
143 #define tcb6    tcb  /* for KAME src sync over BSD*'s */
144 struct inpcbinfo tcbinfo;
145
146 static void      tcp_dooptions(struct tcpopt *, u_char *, int, int);
147 static void      tcp_pulloutofband(struct socket *,
148                      struct tcphdr *, struct mbuf *, int);
149 static int       tcp_reass(struct tcpcb *, struct tcphdr *, int *,
150                      struct mbuf *);
151 static void      tcp_xmit_timer(struct tcpcb *, int);
152 static void      tcp_newreno_partial_ack(struct tcpcb *, struct tcphdr *);
153
154 /* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */
155 #ifdef INET6
156 #define ND6_HINT(tp) \
157 do { \
158         if ((tp) && (tp)->t_inpcb && \
159             ((tp)->t_inpcb->inp_vflag & INP_IPV6) != 0 && \
160             (tp)->t_inpcb->in6p_route.ro_rt) \
161                 nd6_nud_hint((tp)->t_inpcb->in6p_route.ro_rt, NULL, 0); \
162 } while (0)
163 #else
164 #define ND6_HINT(tp)
165 #endif
166
167 /*
168  * Indicate whether this ack should be delayed.  We can delay the ack if
169  *      - delayed acks are enabled and
170  *      - there is no delayed ack timer in progress and
171  *      - our last ack wasn't a 0-sized window.  We never want to delay
172  *        the ack that opens up a 0-sized window.
173  */
174 #define DELAY_ACK(tp) \
175         (tcp_delack_enabled && !callout_pending(tp->tt_delack) && \
176         (tp->t_flags & TF_RXWIN0SENT) == 0)
177
178 static int
179 tcp_reass(tp, th, tlenp, m)
180         struct tcpcb *tp;
181         struct tcphdr *th;
182         int *tlenp;
183         struct mbuf *m;
184 {
185         struct tseg_qent *q;
186         struct tseg_qent *p = NULL;
187         struct tseg_qent *nq;
188         struct tseg_qent *te;
189         struct socket *so = tp->t_inpcb->inp_socket;
190         int flags;
191
192         /*
193          * Call with th==0 after become established to
194          * force pre-ESTABLISHED data up to user socket.
195          */
196         if (th == 0)
197                 goto present;
198
199         /* Allocate a new queue entry. If we can't, just drop the pkt. XXX */
200         MALLOC(te, struct tseg_qent *, sizeof(struct tseg_qent), M_TSEGQ,
201                M_NOWAIT);
202         if (te == NULL) {
203                 tcpstat.tcps_rcvmemdrop++;
204                 m_freem(m);
205                 return (0);
206         }
207
208         /*
209          * Find a segment which begins after this one does.
210          */
211         LIST_FOREACH(q, &tp->t_segq, tqe_q) {
212                 if (SEQ_GT(q->tqe_th->th_seq, th->th_seq))
213                         break;
214                 p = q;
215         }
216
217         /*
218          * If there is a preceding segment, it may provide some of
219          * our data already.  If so, drop the data from the incoming
220          * segment.  If it provides all of our data, drop us.
221          */
222         if (p != NULL) {
223                 int i;
224                 /* conversion to int (in i) handles seq wraparound */
225                 i = p->tqe_th->th_seq + p->tqe_len - th->th_seq;
226                 if (i > 0) {
227                         if (i >= *tlenp) {
228                                 tcpstat.tcps_rcvduppack++;
229                                 tcpstat.tcps_rcvdupbyte += *tlenp;
230                                 m_freem(m);
231                                 free(te, M_TSEGQ);
232                                 /*
233                                  * Try to present any queued data
234                                  * at the left window edge to the user.
235                                  * This is needed after the 3-WHS
236                                  * completes.
237                                  */
238                                 goto present;   /* ??? */
239                         }
240                         m_adj(m, i);
241                         *tlenp -= i;
242                         th->th_seq += i;
243                 }
244         }
245         tcpstat.tcps_rcvoopack++;
246         tcpstat.tcps_rcvoobyte += *tlenp;
247
248         /*
249          * While we overlap succeeding segments trim them or,
250          * if they are completely covered, dequeue them.
251          */
252         while (q) {
253                 int i = (th->th_seq + *tlenp) - q->tqe_th->th_seq;
254                 if (i <= 0)
255                         break;
256                 if (i < q->tqe_len) {
257                         q->tqe_th->th_seq += i;
258                         q->tqe_len -= i;
259                         m_adj(q->tqe_m, i);
260                         break;
261                 }
262
263                 nq = LIST_NEXT(q, tqe_q);
264                 LIST_REMOVE(q, tqe_q);
265                 m_freem(q->tqe_m);
266                 free(q, M_TSEGQ);
267                 q = nq;
268         }
269
270         /* Insert the new segment queue entry into place. */
271         te->tqe_m = m;
272         te->tqe_th = th;
273         te->tqe_len = *tlenp;
274
275         if (p == NULL) {
276                 LIST_INSERT_HEAD(&tp->t_segq, te, tqe_q);
277         } else {
278                 LIST_INSERT_AFTER(p, te, tqe_q);
279         }
280
281 present:
282         /*
283          * Present data to user, advancing rcv_nxt through
284          * completed sequence space.
285          */
286         if (!TCPS_HAVEESTABLISHED(tp->t_state))
287                 return (0);
288         q = LIST_FIRST(&tp->t_segq);
289         if (!q || q->tqe_th->th_seq != tp->rcv_nxt)
290                 return (0);
291         do {
292                 tp->rcv_nxt += q->tqe_len;
293                 flags = q->tqe_th->th_flags & TH_FIN;
294                 nq = LIST_NEXT(q, tqe_q);
295                 LIST_REMOVE(q, tqe_q);
296                 if (so->so_state & SS_CANTRCVMORE)
297                         m_freem(q->tqe_m);
298                 else
299                         sbappend(&so->so_rcv, q->tqe_m);
300                 free(q, M_TSEGQ);
301                 q = nq;
302         } while (q && q->tqe_th->th_seq == tp->rcv_nxt);
303         ND6_HINT(tp);
304         sorwakeup(so);
305         return (flags);
306 }
307
308 /*
309  * TCP input routine, follows pages 65-76 of the
310  * protocol specification dated September, 1981 very closely.
311  */
312 #ifdef INET6
313 int
314 tcp6_input(mp, offp, proto)
315         struct mbuf **mp;
316         int *offp, proto;
317 {
318         struct mbuf *m = *mp;
319         struct in6_ifaddr *ia6;
320
321         IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
322
323         /*
324          * draft-itojun-ipv6-tcp-to-anycast
325          * better place to put this in?
326          */
327         ia6 = ip6_getdstifaddr(m);
328         if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {                
329                 struct ip6_hdr *ip6;
330
331                 ip6 = mtod(m, struct ip6_hdr *);
332                 icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
333                             (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
334                 return IPPROTO_DONE;
335         }
336
337         tcp_input(m, *offp, proto);
338         return IPPROTO_DONE;
339 }
340 #endif
341
342 void
343 tcp_input(m, off0, proto)
344         struct mbuf *m;
345         int off0, proto;
346 {
347         struct tcphdr *th;
348         struct ip *ip = NULL;
349         struct ipovly *ipov;
350         struct inpcb *inp = NULL;
351         u_char *optp = NULL;
352         int optlen = 0;
353         int len, tlen, off;
354         int drop_hdrlen;
355         struct tcpcb *tp = NULL;
356         int thflags;
357         struct socket *so = 0;
358         int todrop, acked, ourfinisacked, needoutput = 0;
359         u_long tiwin;
360         struct tcpopt to;               /* options in this segment */
361         struct rmxp_tao *taop;          /* pointer to our TAO cache entry */
362         struct rmxp_tao tao_noncached;  /* in case there's no cached entry */
363         struct sockaddr_in *next_hop = NULL;
364         int rstreason; /* For badport_bandlim accounting purposes */
365         int useTS;                      /* use timestamps in Eifel detection */
366         struct ip6_hdr *ip6 = NULL;
367 #ifdef INET6
368         int isipv6;
369 #else
370         const int isipv6 = 0;
371 #endif
372 #ifdef TCPDEBUG
373         short ostate = 0;
374 #endif
375
376         /* Grab info from MT_TAG mbufs prepended to the chain. */
377         for (;m && m->m_type == MT_TAG; m = m->m_next) {
378                 if (m->_m_tag_id == PACKET_TAG_IPFORWARD)
379                         next_hop = (struct sockaddr_in *)m->m_hdr.mh_data;
380         }
381 #ifdef INET6
382         isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
383 #endif
384         bzero((char *)&to, sizeof(to));
385
386         tcpstat.tcps_rcvtotal++;
387
388         if (isipv6) {
389                 /* IP6_EXTHDR_CHECK() is already done at tcp6_input() */
390                 ip6 = mtod(m, struct ip6_hdr *);
391                 tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
392                 if (in6_cksum(m, IPPROTO_TCP, off0, tlen)) {
393                         tcpstat.tcps_rcvbadsum++;
394                         goto drop;
395                 }
396                 th = (struct tcphdr *)((caddr_t)ip6 + off0);
397
398                 /*
399                  * Be proactive about unspecified IPv6 address in source.
400                  * As we use all-zero to indicate unbounded/unconnected pcb,
401                  * unspecified IPv6 address can be used to confuse us.
402                  *
403                  * Note that packets with unspecified IPv6 destination is
404                  * already dropped in ip6_input.
405                  */
406                 if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
407                         /* XXX stat */
408                         goto drop;
409                 }
410         } else {
411                 /*
412                  * Get IP and TCP header together in first mbuf.
413                  * Note: IP leaves IP header in first mbuf.
414                  */
415                 if (off0 > sizeof(struct ip)) {
416                         ip_stripoptions(m, (struct mbuf *)0);
417                         off0 = sizeof(struct ip);
418                 }
419                 if (m->m_len < sizeof(struct tcpiphdr)) {
420                         if ((m = m_pullup(m, sizeof(struct tcpiphdr))) == 0) {
421                                 tcpstat.tcps_rcvshort++;
422                                 return;
423                         }
424                 }
425                 ip = mtod(m, struct ip *);
426                 ipov = (struct ipovly *)ip;
427                 th = (struct tcphdr *)((caddr_t)ip + off0);
428                 tlen = ip->ip_len;
429
430                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
431                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
432                                 th->th_sum = m->m_pkthdr.csum_data;
433                         else
434                                 th->th_sum = in_pseudo(ip->ip_src.s_addr,
435                                                 ip->ip_dst.s_addr,
436                                                 htonl(m->m_pkthdr.csum_data +
437                                                         ip->ip_len +
438                                                         IPPROTO_TCP));
439                         th->th_sum ^= 0xffff;
440                 } else {
441                         /*
442                          * Checksum extended TCP header and data.
443                          */
444                         len = sizeof(struct ip) + tlen;
445                         bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
446                         ipov->ih_len = (u_short)tlen;
447                         ipov->ih_len = htons(ipov->ih_len);
448                         th->th_sum = in_cksum(m, len);
449                 }
450                 if (th->th_sum) {
451                         tcpstat.tcps_rcvbadsum++;
452                         goto drop;
453                 }
454 #ifdef INET6
455                 /* Re-initialization for later version check */
456                 ip->ip_v = IPVERSION;
457 #endif
458         }
459
460         /*
461          * Check that TCP offset makes sense,
462          * pull out TCP options and adjust length.              XXX
463          */
464         off = th->th_off << 2;
465         if (off < sizeof(struct tcphdr) || off > tlen) {
466                 tcpstat.tcps_rcvbadoff++;
467                 goto drop;
468         }
469         tlen -= off;    /* tlen is used instead of ti->ti_len */
470         if (off > sizeof(struct tcphdr)) {
471                 if (isipv6) {
472                         IP6_EXTHDR_CHECK(m, off0, off, );
473                         ip6 = mtod(m, struct ip6_hdr *);
474                         th = (struct tcphdr *)((caddr_t)ip6 + off0);
475                 } else {
476                         if (m->m_len < sizeof(struct ip) + off) {
477                                 if ((m = m_pullup(m, sizeof(struct ip) + off))
478                                                 == 0) {
479                                         tcpstat.tcps_rcvshort++;
480                                         return;
481                                 }
482                                 ip = mtod(m, struct ip *);
483                                 ipov = (struct ipovly *)ip;
484                                 th = (struct tcphdr *)((caddr_t)ip + off0);
485                         }
486                 }
487                 optlen = off - sizeof(struct tcphdr);
488                 optp = (u_char *)(th + 1);
489         }
490         thflags = th->th_flags;
491
492 #ifdef TCP_DROP_SYNFIN
493         /*
494          * If the drop_synfin option is enabled, drop all packets with
495          * both the SYN and FIN bits set. This prevents e.g. nmap from
496          * identifying the TCP/IP stack.
497          *
498          * This is a violation of the TCP specification.
499          */
500         if (drop_synfin && (thflags & (TH_SYN|TH_FIN)) == (TH_SYN|TH_FIN))
501                 goto drop;
502 #endif
503
504         /*
505          * Convert TCP protocol specific fields to host format.
506          */
507         th->th_seq = ntohl(th->th_seq);
508         th->th_ack = ntohl(th->th_ack);
509         th->th_win = ntohs(th->th_win);
510         th->th_urp = ntohs(th->th_urp);
511
512         /*
513          * Delay droping TCP, IP headers, IPv6 ext headers, and TCP options,
514          * until after ip6_savecontrol() is called and before other functions
515          * which don't want those proto headers.
516          * Because ip6_savecontrol() is going to parse the mbuf to
517          * search for data to be passed up to user-land, it wants mbuf
518          * parameters to be unchanged.
519          * XXX: the call of ip6_savecontrol() has been obsoleted based on
520          * latest version of the advanced API (20020110).
521          */
522         drop_hdrlen = off0 + off;
523
524         /*
525          * Locate pcb for segment.
526          */
527 findpcb:
528         /* IPFIREWALL_FORWARD section */
529         if (next_hop != NULL && isipv6 == 0) {  /* IPv6 support is not yet */
530                 /*
531                  * Transparently forwarded. Pretend to be the destination.
532                  * already got one like this? 
533                  */
534                 inp = in_pcblookup_hash(&tcbinfo, ip->ip_src, th->th_sport,
535                                         ip->ip_dst, th->th_dport,
536                                         0, m->m_pkthdr.rcvif);
537                 if (!inp) {
538                         /* It's new.  Try find the ambushing socket. */
539                         inp = in_pcblookup_hash(&tcbinfo,
540                                                 ip->ip_src, th->th_sport,
541                                                 next_hop->sin_addr,
542                                                 next_hop->sin_port ?
543                                                     ntohs(next_hop->sin_port) :
544                                                     th->th_dport,
545                                                 1, m->m_pkthdr.rcvif);
546                 }
547         } else {
548                 if (isipv6)
549                         inp = in6_pcblookup_hash(&tcbinfo,
550                                                  &ip6->ip6_src, th->th_sport,
551                                                  &ip6->ip6_dst, th->th_dport,
552                                                  1, m->m_pkthdr.rcvif);
553                 else
554                         inp = in_pcblookup_hash(&tcbinfo,
555                                                 ip->ip_src, th->th_sport,
556                                                 ip->ip_dst, th->th_dport,
557                                                 1, m->m_pkthdr.rcvif);
558       }
559
560 #ifdef IPSEC
561         if (isipv6) {
562                 if (inp != NULL && ipsec6_in_reject_so(m, inp->inp_socket)) {
563                         ipsec6stat.in_polvio++;
564                         goto drop;
565                 }
566         } else {
567                 if (inp != NULL && ipsec4_in_reject_so(m, inp->inp_socket)) {
568                         ipsecstat.in_polvio++;
569                         goto drop;
570                 }
571         }
572 #endif
573 #ifdef FAST_IPSEC
574         if (isipv6) {
575                 if (inp != NULL && ipsec6_in_reject(m, inp)) {
576                         goto drop;
577                 }
578         } else {
579                 if (inp != NULL && ipsec4_in_reject(m, inp)) {
580                         goto drop;
581                 }
582         }
583 #endif
584
585         /*
586          * If the state is CLOSED (i.e., TCB does not exist) then
587          * all data in the incoming segment is discarded.
588          * If the TCB exists but is in CLOSED state, it is embryonic,
589          * but should either do a listen or a connect soon.
590          */
591         if (inp == NULL) {
592                 if (log_in_vain) {
593 #ifdef INET6
594                         char dbuf[INET6_ADDRSTRLEN+2], sbuf[INET6_ADDRSTRLEN+2];
595 #else
596                         char dbuf[4*sizeof "123"], sbuf[4*sizeof "123"];
597 #endif
598                         if (isipv6) {
599                                 strcpy(dbuf, "[");
600                                 strcpy(sbuf, "[");
601                                 strcat(dbuf, ip6_sprintf(&ip6->ip6_dst));
602                                 strcat(sbuf, ip6_sprintf(&ip6->ip6_src));
603                                 strcat(dbuf, "]");
604                                 strcat(sbuf, "]");
605                         } else {
606                                 strcpy(dbuf, inet_ntoa(ip->ip_dst));
607                                 strcpy(sbuf, inet_ntoa(ip->ip_src));
608                         }
609                         switch (log_in_vain) {
610                         case 1:
611                                 if ((thflags & TH_SYN) == 0)
612                                         break;
613                         case 2:
614                                 log(LOG_INFO,
615                                     "Connection attempt to TCP %s:%d "
616                                     "from %s:%d flags:0x%02x\n",
617                                     dbuf, ntohs(th->th_dport), sbuf,
618                                     ntohs(th->th_sport), thflags);
619                                 break;
620                         default:
621                                 break;
622                         }
623                 }
624                 if (blackhole) { 
625                         switch (blackhole) {
626                         case 1:
627                                 if (thflags & TH_SYN)
628                                         goto drop;
629                                 break;
630                         case 2:
631                                 goto drop;
632                         default:
633                                 goto drop;
634                         }
635                 }
636                 rstreason = BANDLIM_RST_CLOSEDPORT;
637                 goto dropwithreset;
638         }
639         tp = intotcpcb(inp);
640         if (tp == NULL) {
641                 rstreason = BANDLIM_RST_CLOSEDPORT;
642                 goto dropwithreset;
643         }
644         if (tp->t_state == TCPS_CLOSED)
645                 goto drop;
646
647         /* Unscale the window into a 32-bit value. */
648         if ((thflags & TH_SYN) == 0)
649                 tiwin = th->th_win << tp->snd_scale;
650         else
651                 tiwin = th->th_win;
652
653         so = inp->inp_socket;
654         if (so->so_options & (SO_DEBUG|SO_ACCEPTCONN)) {
655                 struct in_conninfo inc;
656 #ifdef TCPDEBUG
657                 if (so->so_options & SO_DEBUG) {
658                         ostate = tp->t_state;
659                         if (isipv6)
660                                 bcopy((char *)ip6, (char *)tcp_saveipgen,
661                                     sizeof(*ip6));
662                         else
663                                 bcopy((char *)ip, (char *)tcp_saveipgen,
664                                     sizeof(*ip));
665                         tcp_savetcp = *th;
666                 }
667 #endif
668                 /* skip if this isn't a listen socket */
669                 if ((so->so_options & SO_ACCEPTCONN) == 0)
670                         goto after_listen;
671 #ifdef INET6
672                 inc.inc_isipv6 = isipv6;
673 #endif
674                 if (isipv6) {
675                         inc.inc6_faddr = ip6->ip6_src;
676                         inc.inc6_laddr = ip6->ip6_dst;
677                         inc.inc6_route.ro_rt = NULL;            /* XXX */
678                 } else {
679                         inc.inc_faddr = ip->ip_src;
680                         inc.inc_laddr = ip->ip_dst;
681                         inc.inc_route.ro_rt = NULL;             /* XXX */
682                 }
683                 inc.inc_fport = th->th_sport;
684                 inc.inc_lport = th->th_dport;
685
686                 /*
687                  * If the state is LISTEN then ignore segment if it contains
688                  * a RST.  If the segment contains an ACK then it is bad and
689                  * send a RST.  If it does not contain a SYN then it is not
690                  * interesting; drop it.
691                  *
692                  * If the state is SYN_RECEIVED (syncache) and seg contains
693                  * an ACK, but not for our SYN/ACK, send a RST.  If the seg
694                  * contains a RST, check the sequence number to see if it
695                  * is a valid reset segment.
696                  */
697                 if ((thflags & (TH_RST|TH_ACK|TH_SYN)) != TH_SYN) {
698                         if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
699                                 if (!syncache_expand(&inc, th, &so, m)) {
700                                         /*
701                                          * No syncache entry, or ACK was not
702                                          * for our SYN/ACK.  Send a RST.
703                                          */
704                                         tcpstat.tcps_badsyn++;
705                                         rstreason = BANDLIM_RST_OPENPORT;
706                                         goto dropwithreset;
707                                 }
708                                 if (so == NULL)
709                                         /*
710                                          * Could not complete 3-way handshake,
711                                          * connection is being closed down, and
712                                          * syncache will free mbuf.
713                                          */
714                                         return;
715                                 /*
716                                  * Socket is created in state SYN_RECEIVED.
717                                  * Continue processing segment.
718                                  */
719                                 inp = sotoinpcb(so);
720                                 tp = intotcpcb(inp);
721                                 /*
722                                  * This is what would have happened in
723                                  * tcp_output() when the SYN,ACK was sent.
724                                  */
725                                 tp->snd_up = tp->snd_una;
726                                 tp->snd_max = tp->snd_nxt = tp->iss + 1;
727                                 tp->last_ack_sent = tp->rcv_nxt;
728 /*
729  * XXX possible bug - it doesn't appear that tp->snd_wnd is unscaled
730  * until the _second_ ACK is received:
731  *    rcv SYN (set wscale opts)  --> send SYN/ACK, set snd_wnd = window.
732  *    rcv ACK, calculate tiwin --> process SYN_RECEIVED, determine wscale,
733  *        move to ESTAB, set snd_wnd to tiwin.
734  */        
735                                 tp->snd_wnd = tiwin;    /* unscaled */
736                                 goto after_listen;
737                         }
738                         if (thflags & TH_RST) {
739                                 syncache_chkrst(&inc, th);
740                                 goto drop;
741                         }
742                         if (thflags & TH_ACK) {
743                                 syncache_badack(&inc);
744                                 tcpstat.tcps_badsyn++;
745                                 rstreason = BANDLIM_RST_OPENPORT;
746                                 goto dropwithreset;
747                         }
748                         goto drop;
749                 }
750
751                 /*
752                  * Segment's flags are (SYN) or (SYN|FIN).
753                  */
754 #ifdef INET6
755                 /*
756                  * If deprecated address is forbidden,
757                  * we do not accept SYN to deprecated interface
758                  * address to prevent any new inbound connection from
759                  * getting established.
760                  * When we do not accept SYN, we send a TCP RST,
761                  * with deprecated source address (instead of dropping
762                  * it).  We compromise it as it is much better for peer
763                  * to send a RST, and RST will be the final packet
764                  * for the exchange.
765                  *
766                  * If we do not forbid deprecated addresses, we accept
767                  * the SYN packet.  RFC2462 does not suggest dropping
768                  * SYN in this case.
769                  * If we decipher RFC2462 5.5.4, it says like this:
770                  * 1. use of deprecated addr with existing
771                  *    communication is okay - "SHOULD continue to be
772                  *    used"
773                  * 2. use of it with new communication:
774                  *   (2a) "SHOULD NOT be used if alternate address
775                  *        with sufficient scope is available"
776                  *   (2b) nothing mentioned otherwise.
777                  * Here we fall into (2b) case as we have no choice in
778                  * our source address selection - we must obey the peer.
779                  *
780                  * The wording in RFC2462 is confusing, and there are
781                  * multiple description text for deprecated address
782                  * handling - worse, they are not exactly the same.
783                  * I believe 5.5.4 is the best one, so we follow 5.5.4.
784                  */
785                 if (isipv6 && !ip6_use_deprecated) {
786                         struct in6_ifaddr *ia6;
787
788                         if ((ia6 = ip6_getdstifaddr(m)) &&
789                             (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
790                                 tp = NULL;
791                                 rstreason = BANDLIM_RST_OPENPORT;
792                                 goto dropwithreset;
793                         }
794                 }
795 #endif
796                 /*
797                  * If it is from this socket, drop it, it must be forged.
798                  * Don't bother responding if the destination was a broadcast.
799                  */
800                 if (th->th_dport == th->th_sport) {
801                         if (isipv6) {
802                                 if (IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst,
803                                                        &ip6->ip6_src))
804                                         goto drop;
805                         } else {
806                                 if (ip->ip_dst.s_addr == ip->ip_src.s_addr)
807                                         goto drop;
808                         }
809                 }
810                 /*
811                  * RFC1122 4.2.3.10, p. 104: discard bcast/mcast SYN
812                  *
813                  * Note that it is quite possible to receive unicast
814                  * link-layer packets with a broadcast IP address. Use
815                  * in_broadcast() to find them.
816                  */
817                 if (m->m_flags & (M_BCAST|M_MCAST))
818                         goto drop;
819                 if (isipv6) {
820                         if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
821                             IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
822                                 goto drop;
823                 } else {
824                         if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
825                             IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
826                             ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
827                             in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
828                                 goto drop;
829                 }
830                 /*
831                  * SYN appears to be valid; create compressed TCP state
832                  * for syncache, or perform t/tcp connection.
833                  */
834                 if (so->so_qlen <= so->so_qlimit) {
835                         tcp_dooptions(&to, optp, optlen, 1);
836                         if (!syncache_add(&inc, &to, th, &so, m))
837                                 goto drop;
838                         if (so == NULL)
839                                 /*
840                                  * Entry added to syncache, mbuf used to
841                                  * send SYN,ACK packet.
842                                  */
843                                 return;
844                         /*
845                          * Segment passed TAO tests.
846                          */
847                         inp = sotoinpcb(so);
848                         tp = intotcpcb(inp);
849                         tp->snd_wnd = tiwin;
850                         tp->t_starttime = ticks;
851                         tp->t_state = TCPS_ESTABLISHED;
852
853                         /*
854                          * If there is a FIN, or if there is data and the
855                          * connection is local, then delay SYN,ACK(SYN) in
856                          * the hope of piggy-backing it on a response
857                          * segment.  Otherwise must send ACK now in case
858                          * the other side is slow starting.
859                          */
860                         if (DELAY_ACK(tp) &&
861                             ((thflags & TH_FIN) ||
862                              (tlen != 0 &&
863                               ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
864                                (!isipv6 && in_localaddr(inp->inp_faddr)))))) {
865                                 callout_reset(tp->tt_delack, tcp_delacktime,  
866                                                 tcp_timer_delack, tp);  
867                                 tp->t_flags |= TF_NEEDSYN;
868                         } else 
869                                 tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
870
871                         tcpstat.tcps_connects++;
872                         soisconnected(so);
873                         goto trimthenstep6;
874                 }
875                 goto drop;
876         }
877 after_listen:
878
879 /* XXX temp debugging */
880         /* should not happen - syncache should pick up these connections */
881         if (tp->t_state == TCPS_LISTEN)
882                 panic("tcp_input: TCPS_LISTEN");
883
884         /*
885          * Segment received on connection.
886          * Reset idle time and keep-alive timer.
887          */
888         tp->t_rcvtime = ticks;
889         if (TCPS_HAVEESTABLISHED(tp->t_state))
890                 callout_reset(tp->tt_keep, tcp_keepidle, tcp_timer_keep, tp);
891
892         /*
893          * Process options.
894          * XXX this is tradtitional behavior, may need to be cleaned up.
895          */
896         tcp_dooptions(&to, optp, optlen, thflags & TH_SYN);
897         if (thflags & TH_SYN) {
898                 if (to.to_flags & TOF_SCALE) {
899                         tp->t_flags |= TF_RCVD_SCALE;
900                         tp->requested_s_scale = to.to_requested_s_scale;
901                 }
902                 if (to.to_flags & TOF_TS) {
903                         tp->t_flags |= TF_RCVD_TSTMP;
904                         tp->ts_recent = to.to_tsval;
905                         tp->ts_recent_age = ticks;
906                 }
907                 if (to.to_flags & (TOF_CC|TOF_CCNEW))
908                         tp->t_flags |= TF_RCVD_CC;
909                 if (to.to_flags & TOF_MSS)
910                         tcp_mss(tp, to.to_mss);
911         }
912
913         /*
914          * Header prediction: check for the two common cases
915          * of a uni-directional data xfer.  If the packet has
916          * no control flags, is in-sequence, the window didn't
917          * change and we're not retransmitting, it's a
918          * candidate.  If the length is zero and the ack moved
919          * forward, we're the sender side of the xfer.  Just
920          * free the data acked & wake any higher level process
921          * that was blocked waiting for space.  If the length
922          * is non-zero and the ack didn't move, we're the
923          * receiver side.  If we're getting packets in-order
924          * (the reassembly queue is empty), add the data to
925          * the socket buffer and note that we need a delayed ack.
926          * Make sure that the hidden state-flags are also off.
927          * Since we check for TCPS_ESTABLISHED above, it can only
928          * be TH_NEEDSYN.
929          */
930         if (tp->t_state == TCPS_ESTABLISHED &&
931             (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
932             ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
933             ((to.to_flags & TOF_TS) == 0 ||
934              TSTMP_GEQ(to.to_tsval, tp->ts_recent)) &&
935             /*
936              * Using the CC option is compulsory if once started:
937              *   the segment is OK if no T/TCP was negotiated or
938              *   if the segment has a CC option equal to CCrecv
939              */
940             ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) != (TF_REQ_CC|TF_RCVD_CC) ||
941              ((to.to_flags & TOF_CC) != 0 && to.to_cc == tp->cc_recv)) &&
942             th->th_seq == tp->rcv_nxt &&
943             tiwin && tiwin == tp->snd_wnd &&
944             tp->snd_nxt == tp->snd_max) {
945
946                 /*
947                  * If last ACK falls within this segment's sequence numbers,
948                  * record the timestamp.
949                  * NOTE that the test is modified according to the latest
950                  * proposal of the tcplw@cray.com list (Braden 1993/04/26).
951                  */
952                 if ((to.to_flags & TOF_TS) != 0 &&
953                     SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
954                         tp->ts_recent_age = ticks;
955                         tp->ts_recent = to.to_tsval;
956                 }
957
958                 if (tlen == 0) {
959                         if (SEQ_GT(th->th_ack, tp->snd_una) &&
960                             SEQ_LEQ(th->th_ack, tp->snd_max) &&
961                             tp->snd_cwnd >= tp->snd_wnd &&
962                             ((!tcp_do_newreno &&
963                               tp->t_dupacks < tcprexmtthresh) ||
964                              (tcp_do_newreno && !IN_FASTRECOVERY(tp)))) {
965                                 /*
966                                  * this is a pure ack for outstanding data.
967                                  */
968                                 ++tcpstat.tcps_predack;
969                                 /*
970                                  * "bad retransmit" recovery
971                                  */
972                                 useTS = tcp_do_eifel_detect &&
973                                         (to.to_flags & TOF_TS) &&
974                                         to.to_tsecr;
975                                 if ((useTS &&
976                                      (tp->t_flags & TF_FIRSTACCACK) &&
977                                      (to.to_tsecr < tp->t_rexmtTS)) ||
978                                     (!useTS &&
979                                      (tp->t_rxtshift == 1 &&
980                                       ticks < tp->t_badrxtwin))) {
981                                         tp->snd_cwnd = tp->snd_cwnd_prev;
982                                         tp->snd_ssthresh =
983                                             tp->snd_ssthresh_prev;
984                                         tp->snd_recover = tp->snd_recover_prev;
985                                         if (tp->t_flags & TF_WASFRECOVERY)
986                                             ENTER_FASTRECOVERY(tp);
987                                         tp->snd_nxt = tp->snd_max;
988                                         tp->t_badrxtwin = 0;
989                                         tp->t_rxtshift = 0;
990                                         if (tp->t_flags & TF_FASTREXMT)
991                                                 ++tcpstat.tcps_sndfastrexmitbad;
992                                         else
993                                                 ++tcpstat.tcps_sndrtobad;
994                                 }
995                                 tp->t_flags &= ~(TF_FIRSTACCACK | TF_FASTREXMT);
996                                 /*
997                                  * Recalculate the retransmit timer / rtt.
998                                  *
999                                  * Some machines (certain windows boxes) 
1000                                  * send broken timestamp replies during the
1001                                  * SYN+ACK phase, ignore timestamps of 0.
1002                                  */
1003                                 if ((to.to_flags & TOF_TS) != 0 &&
1004                                     to.to_tsecr) {
1005                                         tcp_xmit_timer(tp,
1006                                             ticks - to.to_tsecr + 1);
1007                                 } else if (tp->t_rtttime &&
1008                                             SEQ_GT(th->th_ack, tp->t_rtseq)) {
1009                                         tcp_xmit_timer(tp,
1010                                                        ticks - tp->t_rtttime);
1011                                 }
1012                                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
1013                                 acked = th->th_ack - tp->snd_una;
1014                                 tcpstat.tcps_rcvackpack++;
1015                                 tcpstat.tcps_rcvackbyte += acked;
1016                                 sbdrop(&so->so_snd, acked);
1017                                 if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
1018                                     SEQ_LEQ(th->th_ack, tp->snd_recover))
1019                                         tp->snd_recover = th->th_ack - 1;
1020                                 tp->snd_una = th->th_ack;
1021                                 tp->t_dupacks = 0;
1022                                 m_freem(m);
1023                                 ND6_HINT(tp); /* some progress has been done */
1024
1025                                 /*
1026                                  * If all outstanding data are acked, stop
1027                                  * retransmit timer, otherwise restart timer
1028                                  * using current (possibly backed-off) value.
1029                                  * If process is waiting for space,
1030                                  * wakeup/selwakeup/signal.  If data
1031                                  * are ready to send, let tcp_output
1032                                  * decide between more output or persist.
1033                                  */
1034                                 if (tp->snd_una == tp->snd_max)
1035                                         callout_stop(tp->tt_rexmt);
1036                                 else if (!callout_active(tp->tt_persist))
1037                                         callout_reset(tp->tt_rexmt, 
1038                                                       tp->t_rxtcur,
1039                                                       tcp_timer_rexmt, tp);
1040
1041                                 sowwakeup(so);
1042                                 if (so->so_snd.sb_cc)
1043                                         (void) tcp_output(tp);
1044                                 return;
1045                         }
1046                 } else if (th->th_ack == tp->snd_una &&
1047                     LIST_EMPTY(&tp->t_segq) &&
1048                     tlen <= sbspace(&so->so_rcv)) {
1049                         /*
1050                          * this is a pure, in-sequence data packet
1051                          * with nothing on the reassembly queue and
1052                          * we have enough buffer space to take it.
1053                          */
1054                         ++tcpstat.tcps_preddat;
1055                         tp->rcv_nxt += tlen;
1056                         tcpstat.tcps_rcvpack++;
1057                         tcpstat.tcps_rcvbyte += tlen;
1058                         ND6_HINT(tp);   /* some progress has been done */
1059                         /*
1060                          * Add data to socket buffer.
1061                          */
1062                         if (so->so_state & SS_CANTRCVMORE) {
1063                                 m_freem(m);
1064                         } else {
1065                                 m_adj(m, drop_hdrlen);  /* delayed header drop */
1066                                 sbappend(&so->so_rcv, m);
1067                         }
1068                         sorwakeup(so);
1069                         if (DELAY_ACK(tp)) {
1070                                 callout_reset(tp->tt_delack, tcp_delacktime,
1071                                     tcp_timer_delack, tp);
1072                         } else {
1073                                 tp->t_flags |= TF_ACKNOW;
1074                                 tcp_output(tp);
1075                         }
1076                         return;
1077                 }
1078         }
1079
1080         /*
1081          * Calculate amount of space in receive window,
1082          * and then do TCP input processing.
1083          * Receive window is amount of space in rcv queue,
1084          * but not less than advertised window.
1085          */
1086         { int win;
1087
1088         win = sbspace(&so->so_rcv);
1089         if (win < 0)
1090                 win = 0;
1091         tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
1092         }
1093
1094         switch (tp->t_state) {
1095
1096         /*
1097          * If the state is SYN_RECEIVED:
1098          *      if seg contains an ACK, but not for our SYN/ACK, send a RST.
1099          */
1100         case TCPS_SYN_RECEIVED:
1101                 if ((thflags & TH_ACK) &&
1102                     (SEQ_LEQ(th->th_ack, tp->snd_una) ||
1103                      SEQ_GT(th->th_ack, tp->snd_max))) {
1104                                 rstreason = BANDLIM_RST_OPENPORT;
1105                                 goto dropwithreset;
1106                 }
1107                 break;
1108
1109         /*
1110          * If the state is SYN_SENT:
1111          *      if seg contains an ACK, but not for our SYN, drop the input.
1112          *      if seg contains a RST, then drop the connection.
1113          *      if seg does not contain SYN, then drop it.
1114          * Otherwise this is an acceptable SYN segment
1115          *      initialize tp->rcv_nxt and tp->irs
1116          *      if seg contains ack then advance tp->snd_una
1117          *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
1118          *      arrange for segment to be acked (eventually)
1119          *      continue processing rest of data/controls, beginning with URG
1120          */
1121         case TCPS_SYN_SENT:
1122                 if ((taop = tcp_gettaocache(&inp->inp_inc)) == NULL) {
1123                         taop = &tao_noncached;
1124                         bzero(taop, sizeof(*taop));
1125                 }
1126
1127                 if ((thflags & TH_ACK) &&
1128                     (SEQ_LEQ(th->th_ack, tp->iss) ||
1129                      SEQ_GT(th->th_ack, tp->snd_max))) {
1130                         /*
1131                          * If we have a cached CCsent for the remote host,
1132                          * hence we haven't just crashed and restarted,
1133                          * do not send a RST.  This may be a retransmission
1134                          * from the other side after our earlier ACK was lost.
1135                          * Our new SYN, when it arrives, will serve as the
1136                          * needed ACK.
1137                          */
1138                         if (taop->tao_ccsent != 0)
1139                                 goto drop;
1140                         else {
1141                                 rstreason = BANDLIM_UNLIMITED;
1142                                 goto dropwithreset;
1143                         }
1144                 }
1145                 if (thflags & TH_RST) {
1146                         if (thflags & TH_ACK)
1147                                 tp = tcp_drop(tp, ECONNREFUSED);
1148                         goto drop;
1149                 }
1150                 if ((thflags & TH_SYN) == 0)
1151                         goto drop;
1152                 tp->snd_wnd = th->th_win;       /* initial send window */
1153                 tp->cc_recv = to.to_cc;         /* foreign CC */
1154
1155                 tp->irs = th->th_seq;
1156                 tcp_rcvseqinit(tp);
1157                 if (thflags & TH_ACK) {
1158                         /*
1159                          * Our SYN was acked.  If segment contains CC.ECHO
1160                          * option, check it to make sure this segment really
1161                          * matches our SYN.  If not, just drop it as old
1162                          * duplicate, but send an RST if we're still playing
1163                          * by the old rules.  If no CC.ECHO option, make sure
1164                          * we don't get fooled into using T/TCP.
1165                          */
1166                         if (to.to_flags & TOF_CCECHO) {
1167                                 if (tp->cc_send != to.to_ccecho) {
1168                                         if (taop->tao_ccsent != 0)
1169                                                 goto drop;
1170                                         else {
1171                                                 rstreason = BANDLIM_UNLIMITED;
1172                                                 goto dropwithreset;
1173                                         }
1174                                 }
1175                         } else
1176                                 tp->t_flags &= ~TF_RCVD_CC;
1177                         tcpstat.tcps_connects++;
1178                         soisconnected(so);
1179                         /* Do window scaling on this connection? */
1180                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1181                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1182                                 tp->snd_scale = tp->requested_s_scale;
1183                                 tp->rcv_scale = tp->request_r_scale;
1184                         }
1185                         /* Segment is acceptable, update cache if undefined. */
1186                         if (taop->tao_ccsent == 0)
1187                                 taop->tao_ccsent = to.to_ccecho;
1188
1189                         tp->rcv_adv += tp->rcv_wnd;
1190                         tp->snd_una++;          /* SYN is acked */
1191                         /*
1192                          * If there's data, delay ACK; if there's also a FIN
1193                          * ACKNOW will be turned on later.
1194                          */
1195                         if (DELAY_ACK(tp) && tlen != 0)
1196                                 callout_reset(tp->tt_delack, tcp_delacktime,  
1197                                     tcp_timer_delack, tp);  
1198                         else
1199                                 tp->t_flags |= TF_ACKNOW;
1200                         /*
1201                          * Received <SYN,ACK> in SYN_SENT[*] state.
1202                          * Transitions:
1203                          *      SYN_SENT  --> ESTABLISHED
1204                          *      SYN_SENT* --> FIN_WAIT_1
1205                          */
1206                         tp->t_starttime = ticks;
1207                         if (tp->t_flags & TF_NEEDFIN) {
1208                                 tp->t_state = TCPS_FIN_WAIT_1;
1209                                 tp->t_flags &= ~TF_NEEDFIN;
1210                                 thflags &= ~TH_SYN;
1211                         } else {
1212                                 tp->t_state = TCPS_ESTABLISHED;
1213                                 callout_reset(tp->tt_keep, tcp_keepidle,
1214                                               tcp_timer_keep, tp);
1215                         }
1216                 } else {
1217                         /*
1218                          * Received initial SYN in SYN-SENT[*] state =>
1219                          * simultaneous open.  If segment contains CC option
1220                          * and there is a cached CC, apply TAO test.
1221                          * If it succeeds, connection is * half-synchronized.
1222                          * Otherwise, do 3-way handshake:
1223                          *        SYN-SENT -> SYN-RECEIVED
1224                          *        SYN-SENT* -> SYN-RECEIVED*
1225                          * If there was no CC option, clear cached CC value.
1226                          */
1227                         tp->t_flags |= TF_ACKNOW;
1228                         callout_stop(tp->tt_rexmt);
1229                         if (to.to_flags & TOF_CC) {
1230                                 if (taop->tao_cc != 0 &&
1231                                     CC_GT(to.to_cc, taop->tao_cc)) {
1232                                         /*
1233                                          * update cache and make transition:
1234                                          *        SYN-SENT -> ESTABLISHED*
1235                                          *        SYN-SENT* -> FIN-WAIT-1*
1236                                          */
1237                                         taop->tao_cc = to.to_cc;
1238                                         tp->t_starttime = ticks;
1239                                         if (tp->t_flags & TF_NEEDFIN) {
1240                                                 tp->t_state = TCPS_FIN_WAIT_1;
1241                                                 tp->t_flags &= ~TF_NEEDFIN;
1242                                         } else {
1243                                                 tp->t_state = TCPS_ESTABLISHED;
1244                                                 callout_reset(tp->tt_keep,
1245                                                               tcp_keepidle,
1246                                                               tcp_timer_keep,
1247                                                               tp);
1248                                         }
1249                                         tp->t_flags |= TF_NEEDSYN;
1250                                 } else
1251                                         tp->t_state = TCPS_SYN_RECEIVED;
1252                         } else {
1253                                 /* CC.NEW or no option => invalidate cache */
1254                                 taop->tao_cc = 0;
1255                                 tp->t_state = TCPS_SYN_RECEIVED;
1256                         }
1257                 }
1258
1259 trimthenstep6:
1260                 /*
1261                  * Advance th->th_seq to correspond to first data byte.
1262                  * If data, trim to stay within window,
1263                  * dropping FIN if necessary.
1264                  */
1265                 th->th_seq++;
1266                 if (tlen > tp->rcv_wnd) {
1267                         todrop = tlen - tp->rcv_wnd;
1268                         m_adj(m, -todrop);
1269                         tlen = tp->rcv_wnd;
1270                         thflags &= ~TH_FIN;
1271                         tcpstat.tcps_rcvpackafterwin++;
1272                         tcpstat.tcps_rcvbyteafterwin += todrop;
1273                 }
1274                 tp->snd_wl1 = th->th_seq - 1;
1275                 tp->rcv_up = th->th_seq;
1276                 /*
1277                  * Client side of transaction: already sent SYN and data.
1278                  * If the remote host used T/TCP to validate the SYN,
1279                  * our data will be ACK'd; if so, enter normal data segment
1280                  * processing in the middle of step 5, ack processing.
1281                  * Otherwise, goto step 6.
1282                  */
1283                 if (thflags & TH_ACK)
1284                         goto process_ACK;
1285
1286                 goto step6;
1287
1288         /*
1289          * If the state is LAST_ACK or CLOSING or TIME_WAIT:
1290          *      if segment contains a SYN and CC [not CC.NEW] option:
1291          *              if state == TIME_WAIT and connection duration > MSL,
1292          *                  drop packet and send RST;
1293          *
1294          *              if SEG.CC > CCrecv then is new SYN, and can implicitly
1295          *                  ack the FIN (and data) in retransmission queue.
1296          *                  Complete close and delete TCPCB.  Then reprocess
1297          *                  segment, hoping to find new TCPCB in LISTEN state;
1298          *
1299          *              else must be old SYN; drop it.
1300          *      else do normal processing.
1301          */
1302         case TCPS_LAST_ACK:
1303         case TCPS_CLOSING:
1304         case TCPS_TIME_WAIT:
1305                 if ((thflags & TH_SYN) &&
1306                     (to.to_flags & TOF_CC) && tp->cc_recv != 0) {
1307                         if (tp->t_state == TCPS_TIME_WAIT &&
1308                                         (ticks - tp->t_starttime) > tcp_msl) {
1309                                 rstreason = BANDLIM_UNLIMITED;
1310                                 goto dropwithreset;
1311                         }
1312                         if (CC_GT(to.to_cc, tp->cc_recv)) {
1313                                 tp = tcp_close(tp);
1314                                 goto findpcb;
1315                         }
1316                         else
1317                                 goto drop;
1318                 }
1319                 break;  /* continue normal processing */
1320         }
1321
1322         /*
1323          * States other than LISTEN or SYN_SENT.
1324          * First check the RST flag and sequence number since reset segments
1325          * are exempt from the timestamp and connection count tests.  This
1326          * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
1327          * below which allowed reset segments in half the sequence space
1328          * to fall though and be processed (which gives forged reset
1329          * segments with a random sequence number a 50 percent chance of
1330          * killing a connection).
1331          * Then check timestamp, if present.
1332          * Then check the connection count, if present.
1333          * Then check that at least some bytes of segment are within
1334          * receive window.  If segment begins before rcv_nxt,
1335          * drop leading data (and SYN); if nothing left, just ack.
1336          *
1337          *
1338          * If the RST bit is set, check the sequence number to see
1339          * if this is a valid reset segment.
1340          * RFC 793 page 37:
1341          *   In all states except SYN-SENT, all reset (RST) segments
1342          *   are validated by checking their SEQ-fields.  A reset is
1343          *   valid if its sequence number is in the window.
1344          * Note: this does not take into account delayed ACKs, so
1345          *   we should test against last_ack_sent instead of rcv_nxt.
1346          *   The sequence number in the reset segment is normally an
1347          *   echo of our outgoing acknowlegement numbers, but some hosts
1348          *   send a reset with the sequence number at the rightmost edge
1349          *   of our receive window, and we have to handle this case.
1350          * If we have multiple segments in flight, the intial reset
1351          * segment sequence numbers will be to the left of last_ack_sent,
1352          * but they will eventually catch up.
1353          * In any case, it never made sense to trim reset segments to
1354          * fit the receive window since RFC 1122 says:
1355          *   4.2.2.12  RST Segment: RFC-793 Section 3.4
1356          *
1357          *    A TCP SHOULD allow a received RST segment to include data.
1358          *
1359          *    DISCUSSION
1360          *         It has been suggested that a RST segment could contain
1361          *         ASCII text that encoded and explained the cause of the
1362          *         RST.  No standard has yet been established for such
1363          *         data.
1364          *
1365          * If the reset segment passes the sequence number test examine
1366          * the state:
1367          *    SYN_RECEIVED STATE:
1368          *      If passive open, return to LISTEN state.
1369          *      If active open, inform user that connection was refused.
1370          *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, CLOSE_WAIT STATES:
1371          *      Inform user that connection was reset, and close tcb.
1372          *    CLOSING, LAST_ACK STATES:
1373          *      Close the tcb.
1374          *    TIME_WAIT STATE:
1375          *      Drop the segment - see Stevens, vol. 2, p. 964 and
1376          *      RFC 1337.
1377          */
1378         if (thflags & TH_RST) {
1379                 if (SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
1380                     SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
1381                         switch (tp->t_state) {
1382
1383                         case TCPS_SYN_RECEIVED:
1384                                 so->so_error = ECONNREFUSED;
1385                                 goto close;
1386
1387                         case TCPS_ESTABLISHED:
1388                         case TCPS_FIN_WAIT_1:
1389                         case TCPS_FIN_WAIT_2:
1390                         case TCPS_CLOSE_WAIT:
1391                                 so->so_error = ECONNRESET;
1392                         close:
1393                                 tp->t_state = TCPS_CLOSED;
1394                                 tcpstat.tcps_drops++;
1395                                 tp = tcp_close(tp);
1396                                 break;
1397
1398                         case TCPS_CLOSING:
1399                         case TCPS_LAST_ACK:
1400                                 tp = tcp_close(tp);
1401                                 break;
1402
1403                         case TCPS_TIME_WAIT:
1404                                 break;
1405                         }
1406                 }
1407                 goto drop;
1408         }
1409
1410         /*
1411          * RFC 1323 PAWS: If we have a timestamp reply on this segment
1412          * and it's less than ts_recent, drop it.
1413          */
1414         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
1415             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
1416
1417                 /* Check to see if ts_recent is over 24 days old.  */
1418                 if ((int)(ticks - tp->ts_recent_age) > TCP_PAWS_IDLE) {
1419                         /*
1420                          * Invalidate ts_recent.  If this segment updates
1421                          * ts_recent, the age will be reset later and ts_recent
1422                          * will get a valid value.  If it does not, setting
1423                          * ts_recent to zero will at least satisfy the
1424                          * requirement that zero be placed in the timestamp
1425                          * echo reply when ts_recent isn't valid.  The
1426                          * age isn't reset until we get a valid ts_recent
1427                          * because we don't want out-of-order segments to be
1428                          * dropped when ts_recent is old.
1429                          */
1430                         tp->ts_recent = 0;
1431                 } else {
1432                         tcpstat.tcps_rcvduppack++;
1433                         tcpstat.tcps_rcvdupbyte += tlen;
1434                         tcpstat.tcps_pawsdrop++;
1435                         if (tlen)
1436                                 goto dropafterack;
1437                         goto drop;
1438                 }
1439         }
1440
1441         /*
1442          * T/TCP mechanism
1443          *   If T/TCP was negotiated and the segment doesn't have CC,
1444          *   or if its CC is wrong then drop the segment.
1445          *   RST segments do not have to comply with this.
1446          */
1447         if ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) == (TF_REQ_CC|TF_RCVD_CC) &&
1448             ((to.to_flags & TOF_CC) == 0 || tp->cc_recv != to.to_cc))
1449                 goto dropafterack;
1450
1451         /*
1452          * In the SYN-RECEIVED state, validate that the packet belongs to
1453          * this connection before trimming the data to fit the receive
1454          * window.  Check the sequence number versus IRS since we know
1455          * the sequence numbers haven't wrapped.  This is a partial fix
1456          * for the "LAND" DoS attack.
1457          */
1458         if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
1459                 rstreason = BANDLIM_RST_OPENPORT;
1460                 goto dropwithreset;
1461         }
1462
1463         todrop = tp->rcv_nxt - th->th_seq;
1464         if (todrop > 0) {
1465                 if (thflags & TH_SYN) {
1466                         thflags &= ~TH_SYN;
1467                         th->th_seq++;
1468                         if (th->th_urp > 1)
1469                                 th->th_urp--;
1470                         else
1471                                 thflags &= ~TH_URG;
1472                         todrop--;
1473                 }
1474                 /*
1475                  * Following if statement from Stevens, vol. 2, p. 960.
1476                  */
1477                 if (todrop > tlen
1478                     || (todrop == tlen && (thflags & TH_FIN) == 0)) {
1479                         /*
1480                          * Any valid FIN must be to the left of the window.
1481                          * At this point the FIN must be a duplicate or out
1482                          * of sequence; drop it.
1483                          */
1484                         thflags &= ~TH_FIN;
1485
1486                         /*
1487                          * Send an ACK to resynchronize and drop any data.
1488                          * But keep on processing for RST or ACK.
1489                          */
1490                         tp->t_flags |= TF_ACKNOW;
1491                         todrop = tlen;
1492                         tcpstat.tcps_rcvduppack++;
1493                         tcpstat.tcps_rcvdupbyte += todrop;
1494                 } else {
1495                         tcpstat.tcps_rcvpartduppack++;
1496                         tcpstat.tcps_rcvpartdupbyte += todrop;
1497                 }
1498                 drop_hdrlen += todrop;  /* drop from the top afterwards */
1499                 th->th_seq += todrop;
1500                 tlen -= todrop;
1501                 if (th->th_urp > todrop)
1502                         th->th_urp -= todrop;
1503                 else {
1504                         thflags &= ~TH_URG;
1505                         th->th_urp = 0;
1506                 }
1507         }
1508
1509         /*
1510          * If new data are received on a connection after the
1511          * user processes are gone, then RST the other end.
1512          */
1513         if ((so->so_state & SS_NOFDREF) &&
1514             tp->t_state > TCPS_CLOSE_WAIT && tlen) {
1515                 tp = tcp_close(tp);
1516                 tcpstat.tcps_rcvafterclose++;
1517                 rstreason = BANDLIM_UNLIMITED;
1518                 goto dropwithreset;
1519         }
1520
1521         /*
1522          * If segment ends after window, drop trailing data
1523          * (and PUSH and FIN); if nothing left, just ACK.
1524          */
1525         todrop = (th->th_seq+tlen) - (tp->rcv_nxt+tp->rcv_wnd);
1526         if (todrop > 0) {
1527                 tcpstat.tcps_rcvpackafterwin++;
1528                 if (todrop >= tlen) {
1529                         tcpstat.tcps_rcvbyteafterwin += tlen;
1530                         /*
1531                          * If a new connection request is received
1532                          * while in TIME_WAIT, drop the old connection
1533                          * and start over if the sequence numbers
1534                          * are above the previous ones.
1535                          */
1536                         if (thflags & TH_SYN &&
1537                             tp->t_state == TCPS_TIME_WAIT &&
1538                             SEQ_GT(th->th_seq, tp->rcv_nxt)) {
1539                                 tp = tcp_close(tp);
1540                                 goto findpcb;
1541                         }
1542                         /*
1543                          * If window is closed can only take segments at
1544                          * window edge, and have to drop data and PUSH from
1545                          * incoming segments.  Continue processing, but
1546                          * remember to ack.  Otherwise, drop segment
1547                          * and ack.
1548                          */
1549                         if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
1550                                 tp->t_flags |= TF_ACKNOW;
1551                                 tcpstat.tcps_rcvwinprobe++;
1552                         } else
1553                                 goto dropafterack;
1554                 } else
1555                         tcpstat.tcps_rcvbyteafterwin += todrop;
1556                 m_adj(m, -todrop);
1557                 tlen -= todrop;
1558                 thflags &= ~(TH_PUSH|TH_FIN);
1559         }
1560
1561         /*
1562          * If last ACK falls within this segment's sequence numbers,
1563          * record its timestamp.
1564          * NOTE that the test is modified according to the latest
1565          * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1566          */
1567         if ((to.to_flags & TOF_TS) != 0 &&
1568             SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
1569                 tp->ts_recent_age = ticks;
1570                 tp->ts_recent = to.to_tsval;
1571         }
1572
1573         /*
1574          * If a SYN is in the window, then this is an
1575          * error and we send an RST and drop the connection.
1576          */
1577         if (thflags & TH_SYN) {
1578                 tp = tcp_drop(tp, ECONNRESET);
1579                 rstreason = BANDLIM_UNLIMITED;
1580                 goto dropwithreset;
1581         }
1582
1583         /*
1584          * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
1585          * flag is on (half-synchronized state), then queue data for
1586          * later processing; else drop segment and return.
1587          */
1588         if ((thflags & TH_ACK) == 0) {
1589                 if (tp->t_state == TCPS_SYN_RECEIVED ||
1590                     (tp->t_flags & TF_NEEDSYN))
1591                         goto step6;
1592                 else
1593                         goto drop;
1594         }
1595
1596         /*
1597          * Ack processing.
1598          */
1599         switch (tp->t_state) {
1600
1601         /*
1602          * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
1603          * ESTABLISHED state and continue processing.
1604          * The ACK was checked above.
1605          */
1606         case TCPS_SYN_RECEIVED:
1607
1608                 tcpstat.tcps_connects++;
1609                 soisconnected(so);
1610                 /* Do window scaling? */
1611                 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1612                         (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1613                         tp->snd_scale = tp->requested_s_scale;
1614                         tp->rcv_scale = tp->request_r_scale;
1615                 }
1616                 /*
1617                  * Upon successful completion of 3-way handshake,
1618                  * update cache.CC if it was undefined, pass any queued
1619                  * data to the user, and advance state appropriately.
1620                  */
1621                 if ((taop = tcp_gettaocache(&inp->inp_inc)) != NULL &&
1622                     taop->tao_cc == 0)
1623                         taop->tao_cc = tp->cc_recv;
1624
1625                 /*
1626                  * Make transitions:
1627                  *      SYN-RECEIVED  -> ESTABLISHED
1628                  *      SYN-RECEIVED* -> FIN-WAIT-1
1629                  */
1630                 tp->t_starttime = ticks;
1631                 if (tp->t_flags & TF_NEEDFIN) {
1632                         tp->t_state = TCPS_FIN_WAIT_1;
1633                         tp->t_flags &= ~TF_NEEDFIN;
1634                 } else {
1635                         tp->t_state = TCPS_ESTABLISHED;
1636                         callout_reset(tp->tt_keep, tcp_keepidle, 
1637                                       tcp_timer_keep, tp);
1638                 }
1639                 /*
1640                  * If segment contains data or ACK, will call tcp_reass()
1641                  * later; if not, do so now to pass queued data to user.
1642                  */
1643                 if (tlen == 0 && (thflags & TH_FIN) == 0)
1644                         (void) tcp_reass(tp, (struct tcphdr *)0, 0,
1645                             (struct mbuf *)0);
1646                 tp->snd_wl1 = th->th_seq - 1;
1647                 /* fall into ... */
1648
1649         /*
1650          * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
1651          * ACKs.  If the ack is in the range
1652          *      tp->snd_una < th->th_ack <= tp->snd_max
1653          * then advance tp->snd_una to th->th_ack and drop
1654          * data from the retransmission queue.  If this ACK reflects
1655          * more up to date window information we update our window information.
1656          */
1657         case TCPS_ESTABLISHED:
1658         case TCPS_FIN_WAIT_1:
1659         case TCPS_FIN_WAIT_2:
1660         case TCPS_CLOSE_WAIT:
1661         case TCPS_CLOSING:
1662         case TCPS_LAST_ACK:
1663         case TCPS_TIME_WAIT:
1664
1665                 if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
1666                         if (tlen == 0 && tiwin == tp->snd_wnd) {
1667                                 tcpstat.tcps_rcvdupack++;
1668                                 /*
1669                                  * If we have outstanding data (other than
1670                                  * a window probe), this is a completely
1671                                  * duplicate ack (ie, window info didn't
1672                                  * change), the ack is the biggest we've
1673                                  * seen and we've seen exactly our rexmt
1674                                  * threshhold of them, assume a packet
1675                                  * has been dropped and retransmit it.
1676                                  * Kludge snd_nxt & the congestion
1677                                  * window so we send only this one
1678                                  * packet.
1679                                  *
1680                                  * We know we're losing at the current
1681                                  * window size so do congestion avoidance
1682                                  * (set ssthresh to half the current window
1683                                  * and pull our congestion window back to
1684                                  * the new ssthresh).
1685                                  *
1686                                  * Dup acks mean that packets have left the
1687                                  * network (they're now cached at the receiver)
1688                                  * so bump cwnd by the amount in the receiver
1689                                  * to keep a constant cwnd packets in the
1690                                  * network.
1691                                  */
1692                                 if (!callout_active(tp->tt_rexmt) ||
1693                                     th->th_ack != tp->snd_una)
1694                                         tp->t_dupacks = 0;
1695                                 else if (++tp->t_dupacks > tcprexmtthresh ||
1696                                          (tcp_do_newreno &&
1697                                           IN_FASTRECOVERY(tp))) {
1698                                         tp->snd_cwnd += tp->t_maxseg;
1699                                         (void) tcp_output(tp);
1700                                         goto drop;
1701                                 } else if (tp->t_dupacks == tcprexmtthresh) {
1702                                         tcp_seq onxt = tp->snd_nxt;
1703                                         u_int win;
1704                                         if (tcp_do_newreno &&
1705                                             SEQ_LEQ(th->th_ack,
1706                                                     tp->snd_recover)) {
1707                                                 tp->t_dupacks = 0;
1708                                                 break;
1709                                         }
1710                                         if (tcp_do_eifel_detect &&
1711                                             (tp->t_flags & TF_RCVD_TSTMP)) {
1712                                                 tcp_save_congestion_state(tp);
1713                                                 tp->t_flags |= TF_FASTREXMT;
1714                                         }
1715                                         win = min(tp->snd_wnd, tp->snd_cwnd) /
1716                                             2 / tp->t_maxseg;
1717                                         if (win < 2)
1718                                                 win = 2;
1719                                         tp->snd_ssthresh = win * tp->t_maxseg;
1720                                         ENTER_FASTRECOVERY(tp);
1721                                         tp->snd_recover = tp->snd_max;
1722                                         callout_stop(tp->tt_rexmt);
1723                                         tp->t_rtttime = 0;
1724                                         tp->snd_nxt = th->th_ack;
1725                                         tp->snd_cwnd = tp->t_maxseg;
1726                                         (void) tcp_output(tp);
1727                                         KASSERT(tp->snd_limited <= 2,
1728                                             ("tp->snd_limited too big"));
1729                                         tp->snd_cwnd = tp->snd_ssthresh +
1730                                             (tp->t_maxseg *
1731                                              (tp->t_dupacks - tp->snd_limited));
1732                                         if (SEQ_GT(onxt, tp->snd_nxt))
1733                                                 tp->snd_nxt = onxt;
1734                                         goto drop;
1735                                 } else if (tcp_do_limitedtransmit) {
1736                                         u_long oldcwnd = tp->snd_cwnd;
1737                                         tcp_seq oldsndmax = tp->snd_max;
1738                                         u_int sent;
1739                                         KASSERT(tp->t_dupacks == 1 ||
1740                                             tp->t_dupacks == 2,
1741                                             ("dupacks not 1 or 2"));
1742                                         if (tp->t_dupacks == 1) {
1743                                                 tp->snd_limited = 0;
1744                                                 tp->snd_cwnd += tp->t_maxseg;
1745                                         } else {
1746                                                 tp->snd_cwnd +=
1747                                                     tp->t_maxseg * 2;
1748                                         }
1749                                         (void) tcp_output(tp);
1750                                         sent = tp->snd_max - oldsndmax;
1751                                         if (sent > tp->t_maxseg) {
1752                                                 KASSERT(tp->snd_limited == 0 &&
1753                                                     tp->t_dupacks == 2,
1754                                                     ("sent too much"));
1755                                                 tp->snd_limited = 2;
1756                                         } else if (sent > 0)
1757                                                 ++tp->snd_limited;
1758                                         tp->snd_cwnd = oldcwnd;
1759                                         goto drop;
1760                                 }
1761                         } else
1762                                 tp->t_dupacks = 0;
1763                         break;
1764                 }
1765
1766                 KASSERT(SEQ_GT(th->th_ack, tp->snd_una), ("th_ack <= snd_una"));
1767
1768                 /*
1769                  * If the congestion window was inflated to account
1770                  * for the other side's cached packets, retract it.
1771                  */
1772                 if (tcp_do_newreno) {
1773                         if (IN_FASTRECOVERY(tp)) {
1774                                 if (SEQ_LT(th->th_ack, tp->snd_recover)) {
1775                                         tcp_newreno_partial_ack(tp, th);
1776                                 } else {
1777                                         /*
1778                                          * Window inflation should have left us
1779                                          * with approximately snd_ssthresh
1780                                          * outstanding data.
1781                                          * But in case we would be inclined to
1782                                          * send a burst, better to do it via
1783                                          * the slow start mechanism.
1784                                          */
1785                                         if (SEQ_GT(th->th_ack +
1786                                                         tp->snd_ssthresh,
1787                                                    tp->snd_max))
1788                                                 tp->snd_cwnd = tp->snd_max -
1789                                                                 th->th_ack +
1790                                                                 tp->t_maxseg;
1791                                         else
1792                                                 tp->snd_cwnd = tp->snd_ssthresh;
1793                                 }
1794                         }
1795                 } else {
1796                         if (tp->t_dupacks >= tcprexmtthresh &&
1797                             tp->snd_cwnd > tp->snd_ssthresh)
1798                                 tp->snd_cwnd = tp->snd_ssthresh;
1799                 }
1800                 tp->t_dupacks = 0;
1801                 if (SEQ_GT(th->th_ack, tp->snd_max)) {
1802                         tcpstat.tcps_rcvacktoomuch++;
1803                         goto dropafterack;
1804                 }
1805                 /*
1806                  * If we reach this point, ACK is not a duplicate,
1807                  *     i.e., it ACKs something we sent.
1808                  */
1809                 if (tp->t_flags & TF_NEEDSYN) {
1810                         /*
1811                          * T/TCP: Connection was half-synchronized, and our
1812                          * SYN has been ACK'd (so connection is now fully
1813                          * synchronized).  Go to non-starred state,
1814                          * increment snd_una for ACK of SYN, and check if
1815                          * we can do window scaling.
1816                          */
1817                         tp->t_flags &= ~TF_NEEDSYN;
1818                         tp->snd_una++;
1819                         /* Do window scaling? */
1820                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1821                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1822                                 tp->snd_scale = tp->requested_s_scale;
1823                                 tp->rcv_scale = tp->request_r_scale;
1824                         }
1825                 }
1826
1827 process_ACK:
1828                 acked = th->th_ack - tp->snd_una;
1829                 tcpstat.tcps_rcvackpack++;
1830                 tcpstat.tcps_rcvackbyte += acked;
1831
1832                 /*
1833                  * If we just performed our first retransmit, and the ACK
1834                  * arrives within our recovery window, then it was a mistake
1835                  * to do the retransmit in the first place.  Recover our
1836                  * original cwnd and ssthresh, and proceed to transmit where
1837                  * we left off.
1838                  */
1839                 useTS = tcp_do_eifel_detect && (to.to_flags & TOF_TS) &&
1840                     to.to_tsecr;
1841                 if ((useTS && (tp->t_flags & TF_FIRSTACCACK) && acked &&
1842                      (to.to_tsecr < tp->t_rexmtTS)) ||
1843                     (!useTS &&
1844                      (tp->t_rxtshift == 1 && ticks < tp->t_badrxtwin))) {
1845                         tp->snd_cwnd = tp->snd_cwnd_prev;
1846                         tp->snd_ssthresh = tp->snd_ssthresh_prev;
1847                         tp->snd_recover = tp->snd_recover_prev;
1848                         if (tp->t_flags & TF_WASFRECOVERY)
1849                                 ENTER_FASTRECOVERY(tp);
1850                         tp->snd_nxt = tp->snd_max;
1851                         tp->t_badrxtwin = 0;    /* XXX probably not required */
1852                         tp->t_rxtshift = 0;
1853                         if (tp->t_flags & TF_FASTREXMT)
1854                                 ++tcpstat.tcps_sndfastrexmitbad;
1855                         else
1856                                 ++tcpstat.tcps_sndrtobad;
1857                 }
1858
1859                 /*
1860                  * If we have a timestamp reply, update smoothed
1861                  * round trip time.  If no timestamp is present but
1862                  * transmit timer is running and timed sequence
1863                  * number was acked, update smoothed round trip time.
1864                  * Since we now have an rtt measurement, cancel the
1865                  * timer backoff (cf., Phil Karn's retransmit alg.).
1866                  * Recompute the initial retransmit timer.
1867                  *
1868                  * Some machines (certain windows boxes) send broken
1869                  * timestamp replies during the SYN+ACK phase, ignore 
1870                  * timestamps of 0.
1871                  */
1872                 if ((to.to_flags & TOF_TS) != 0 &&
1873                     to.to_tsecr) {
1874                         tcp_xmit_timer(tp, ticks - to.to_tsecr + 1);
1875                 } else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
1876                         tcp_xmit_timer(tp, ticks - tp->t_rtttime);
1877                 }
1878                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
1879
1880                 /*
1881                  * If all outstanding data is acked, stop retransmit
1882                  * timer and remember to restart (more output or persist).
1883                  * If there is more data to be acked, restart retransmit
1884                  * timer, using current (possibly backed-off) value.
1885                  */
1886                 if (th->th_ack == tp->snd_max) {
1887                         callout_stop(tp->tt_rexmt);
1888                         needoutput = 1;
1889                 } else if (!callout_active(tp->tt_persist))
1890                         callout_reset(tp->tt_rexmt, tp->t_rxtcur,
1891                                       tcp_timer_rexmt, tp);
1892
1893                 /*
1894                  * If no data (only SYN) was ACK'd,
1895                  *    skip rest of ACK processing.
1896                  */
1897                 if (acked == 0)
1898                         goto step6;
1899
1900                 /* Stop looking for an acceptable ACK since one was received. */
1901                 tp->t_flags &= ~(TF_FIRSTACCACK | TF_FASTREXMT);
1902
1903                 /*
1904                  * When new data is acked, open the congestion window.
1905                  * If the window gives us less than ssthresh packets
1906                  * in flight, open exponentially (maxseg per packet).
1907                  * Otherwise open linearly: maxseg per window
1908                  * (maxseg^2 / cwnd per packet).
1909                  */
1910                 if (!tcp_do_newreno || !IN_FASTRECOVERY(tp)) {
1911                         u_int cw = tp->snd_cwnd;
1912                         u_int incr = tp->t_maxseg;
1913                         if (cw > tp->snd_ssthresh)
1914                                 incr = incr * incr / cw;
1915                         tp->snd_cwnd = min(cw+incr, TCP_MAXWIN<<tp->snd_scale);
1916                 }
1917                 if (acked > so->so_snd.sb_cc) {
1918                         tp->snd_wnd -= so->so_snd.sb_cc;
1919                         sbdrop(&so->so_snd, (int)so->so_snd.sb_cc);
1920                         ourfinisacked = 1;
1921                 } else {
1922                         sbdrop(&so->so_snd, acked);
1923                         tp->snd_wnd -= acked;
1924                         ourfinisacked = 0;
1925                 }
1926                 sowwakeup(so);
1927                 /* detect una wraparound */
1928                 if (tcp_do_newreno && !IN_FASTRECOVERY(tp) &&
1929                     SEQ_GT(tp->snd_una, tp->snd_recover) &&
1930                     SEQ_LEQ(th->th_ack, tp->snd_recover))
1931                         tp->snd_recover = th->th_ack - 1;
1932                 if (tcp_do_newreno && IN_FASTRECOVERY(tp) &&
1933                     SEQ_GEQ(th->th_ack, tp->snd_recover))
1934                         EXIT_FASTRECOVERY(tp);
1935                 tp->snd_una = th->th_ack;
1936                 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
1937                         tp->snd_nxt = tp->snd_una;
1938
1939                 switch (tp->t_state) {
1940
1941                 /*
1942                  * In FIN_WAIT_1 STATE in addition to the processing
1943                  * for the ESTABLISHED state if our FIN is now acknowledged
1944                  * then enter FIN_WAIT_2.
1945                  */
1946                 case TCPS_FIN_WAIT_1:
1947                         if (ourfinisacked) {
1948                                 /*
1949                                  * If we can't receive any more
1950                                  * data, then closing user can proceed.
1951                                  * Starting the timer is contrary to the
1952                                  * specification, but if we don't get a FIN
1953                                  * we'll hang forever.
1954                                  */
1955                                 if (so->so_state & SS_CANTRCVMORE) {
1956                                         soisdisconnected(so);
1957                                         callout_reset(tp->tt_2msl, tcp_maxidle,
1958                                                       tcp_timer_2msl, tp);
1959                                 }
1960                                 tp->t_state = TCPS_FIN_WAIT_2;
1961                         }
1962                         break;
1963
1964                 /*
1965                  * In CLOSING STATE in addition to the processing for
1966                  * the ESTABLISHED state if the ACK acknowledges our FIN
1967                  * then enter the TIME-WAIT state, otherwise ignore
1968                  * the segment.
1969                  */
1970                 case TCPS_CLOSING:
1971                         if (ourfinisacked) {
1972                                 tp->t_state = TCPS_TIME_WAIT;
1973                                 tcp_canceltimers(tp);
1974                                 /* Shorten TIME_WAIT [RFC-1644, p.28] */
1975                                 if (tp->cc_recv != 0 &&
1976                                     (ticks - tp->t_starttime) < tcp_msl)
1977                                         callout_reset(tp->tt_2msl,
1978                                                       tp->t_rxtcur *
1979                                                       TCPTV_TWTRUNC,
1980                                                       tcp_timer_2msl, tp);
1981                                 else
1982                                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
1983                                                       tcp_timer_2msl, tp);
1984                                 soisdisconnected(so);
1985                         }
1986                         break;
1987
1988                 /*
1989                  * In LAST_ACK, we may still be waiting for data to drain
1990                  * and/or to be acked, as well as for the ack of our FIN.
1991                  * If our FIN is now acknowledged, delete the TCB,
1992                  * enter the closed state and return.
1993                  */
1994                 case TCPS_LAST_ACK:
1995                         if (ourfinisacked) {
1996                                 tp = tcp_close(tp);
1997                                 goto drop;
1998                         }
1999                         break;
2000
2001                 /*
2002                  * In TIME_WAIT state the only thing that should arrive
2003                  * is a retransmission of the remote FIN.  Acknowledge
2004                  * it and restart the finack timer.
2005                  */
2006                 case TCPS_TIME_WAIT:
2007                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
2008                                       tcp_timer_2msl, tp);
2009                         goto dropafterack;
2010                 }
2011         }
2012
2013 step6:
2014         /*
2015          * Update window information.
2016          * Don't look at window if no ACK: TAC's send garbage on first SYN.
2017          */
2018         if ((thflags & TH_ACK) &&
2019             (SEQ_LT(tp->snd_wl1, th->th_seq) ||
2020             (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
2021              (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
2022                 /* keep track of pure window updates */
2023                 if (tlen == 0 &&
2024                     tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
2025                         tcpstat.tcps_rcvwinupd++;
2026                 tp->snd_wnd = tiwin;
2027                 tp->snd_wl1 = th->th_seq;
2028                 tp->snd_wl2 = th->th_ack;
2029                 if (tp->snd_wnd > tp->max_sndwnd)
2030                         tp->max_sndwnd = tp->snd_wnd;
2031                 needoutput = 1;
2032         }
2033
2034         /*
2035          * Process segments with URG.
2036          */
2037         if ((thflags & TH_URG) && th->th_urp &&
2038             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2039                 /*
2040                  * This is a kludge, but if we receive and accept
2041                  * random urgent pointers, we'll crash in
2042                  * soreceive.  It's hard to imagine someone
2043                  * actually wanting to send this much urgent data.
2044                  */
2045                 if (th->th_urp + so->so_rcv.sb_cc > sb_max) {
2046                         th->th_urp = 0;                 /* XXX */
2047                         thflags &= ~TH_URG;             /* XXX */
2048                         goto dodata;                    /* XXX */
2049                 }
2050                 /*
2051                  * If this segment advances the known urgent pointer,
2052                  * then mark the data stream.  This should not happen
2053                  * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
2054                  * a FIN has been received from the remote side.
2055                  * In these states we ignore the URG.
2056                  *
2057                  * According to RFC961 (Assigned Protocols),
2058                  * the urgent pointer points to the last octet
2059                  * of urgent data.  We continue, however,
2060                  * to consider it to indicate the first octet
2061                  * of data past the urgent section as the original
2062                  * spec states (in one of two places).
2063                  */
2064                 if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
2065                         tp->rcv_up = th->th_seq + th->th_urp;
2066                         so->so_oobmark = so->so_rcv.sb_cc +
2067                             (tp->rcv_up - tp->rcv_nxt) - 1;
2068                         if (so->so_oobmark == 0)
2069                                 so->so_state |= SS_RCVATMARK;
2070                         sohasoutofband(so);
2071                         tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
2072                 }
2073                 /*
2074                  * Remove out of band data so doesn't get presented to user.
2075                  * This can happen independent of advancing the URG pointer,
2076                  * but if two URG's are pending at once, some out-of-band
2077                  * data may creep in... ick.
2078                  */
2079                 if (th->th_urp <= (u_long)tlen
2080 #ifdef SO_OOBINLINE
2081                      && (so->so_options & SO_OOBINLINE) == 0
2082 #endif
2083                      )
2084                         tcp_pulloutofband(so, th, m,
2085                                 drop_hdrlen);   /* hdr drop is delayed */
2086         } else {
2087                 /*
2088                  * If no out of band data is expected,
2089                  * pull receive urgent pointer along
2090                  * with the receive window.
2091                  */
2092                 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
2093                         tp->rcv_up = tp->rcv_nxt;
2094         }
2095 dodata:                                                 /* XXX */
2096
2097         /*
2098          * Process the segment text, merging it into the TCP sequencing queue,
2099          * and arranging for acknowledgment of receipt if necessary.
2100          * This process logically involves adjusting tp->rcv_wnd as data
2101          * is presented to the user (this happens in tcp_usrreq.c,
2102          * case PRU_RCVD).  If a FIN has already been received on this
2103          * connection then we just ignore the text.
2104          */
2105         if ((tlen || (thflags & TH_FIN)) &&
2106             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2107                 m_adj(m, drop_hdrlen);  /* delayed header drop */
2108                 /*
2109                  * Insert segment which includes th into TCP reassembly queue
2110                  * with control block tp.  Set thflags to whether reassembly now
2111                  * includes a segment with FIN.  This handles the common case
2112                  * inline (segment is the next to be received on an established
2113                  * connection, and the queue is empty), avoiding linkage into
2114                  * and removal from the queue and repetition of various
2115                  * conversions.
2116                  * Set DELACK for segments received in order, but ack
2117                  * immediately when segments are out of order (so
2118                  * fast retransmit can work).
2119                  */
2120                 if (th->th_seq == tp->rcv_nxt &&
2121                     LIST_EMPTY(&tp->t_segq) &&
2122                     TCPS_HAVEESTABLISHED(tp->t_state)) {
2123                         if (DELAY_ACK(tp))
2124                                 callout_reset(tp->tt_delack, tcp_delacktime,
2125                                               tcp_timer_delack, tp);
2126                         else
2127                                 tp->t_flags |= TF_ACKNOW;
2128                         tp->rcv_nxt += tlen;
2129                         thflags = th->th_flags & TH_FIN;
2130                         tcpstat.tcps_rcvpack++;
2131                         tcpstat.tcps_rcvbyte += tlen;
2132                         ND6_HINT(tp);
2133                         if (so->so_state & SS_CANTRCVMORE)
2134                                 m_freem(m);
2135                         else
2136                                 sbappend(&so->so_rcv, m);
2137                         sorwakeup(so);
2138                 } else {
2139                         thflags = tcp_reass(tp, th, &tlen, m);
2140                         tp->t_flags |= TF_ACKNOW;
2141                 }
2142
2143                 /*
2144                  * Note the amount of data that peer has sent into
2145                  * our window, in order to estimate the sender's
2146                  * buffer size.
2147                  */
2148                 len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
2149         } else {
2150                 m_freem(m);
2151                 thflags &= ~TH_FIN;
2152         }
2153
2154         /*
2155          * If FIN is received ACK the FIN and let the user know
2156          * that the connection is closing.
2157          */
2158         if (thflags & TH_FIN) {
2159                 if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2160                         socantrcvmore(so);
2161                         /*
2162                          * If connection is half-synchronized
2163                          * (ie NEEDSYN flag on) then delay ACK,
2164                          * so it may be piggybacked when SYN is sent.
2165                          * Otherwise, since we received a FIN then no
2166                          * more input can be expected, send ACK now.
2167                          */
2168                         if (DELAY_ACK(tp) && (tp->t_flags & TF_NEEDSYN))
2169                                 callout_reset(tp->tt_delack, tcp_delacktime,  
2170                                     tcp_timer_delack, tp);  
2171                         else
2172                                 tp->t_flags |= TF_ACKNOW;
2173                         tp->rcv_nxt++;
2174                 }
2175                 switch (tp->t_state) {
2176
2177                 /*
2178                  * In SYN_RECEIVED and ESTABLISHED STATES
2179                  * enter the CLOSE_WAIT state.
2180                  */
2181                 case TCPS_SYN_RECEIVED:
2182                         tp->t_starttime = ticks;
2183                         /*FALLTHROUGH*/
2184                 case TCPS_ESTABLISHED:
2185                         tp->t_state = TCPS_CLOSE_WAIT;
2186                         break;
2187
2188                 /*
2189                  * If still in FIN_WAIT_1 STATE FIN has not been acked so
2190                  * enter the CLOSING state.
2191                  */
2192                 case TCPS_FIN_WAIT_1:
2193                         tp->t_state = TCPS_CLOSING;
2194                         break;
2195
2196                 /*
2197                  * In FIN_WAIT_2 state enter the TIME_WAIT state,
2198                  * starting the time-wait timer, turning off the other
2199                  * standard timers.
2200                  */
2201                 case TCPS_FIN_WAIT_2:
2202                         tp->t_state = TCPS_TIME_WAIT;
2203                         tcp_canceltimers(tp);
2204                         /* Shorten TIME_WAIT [RFC-1644, p.28] */
2205                         if (tp->cc_recv != 0 &&
2206                             (ticks - tp->t_starttime) < tcp_msl) {
2207                                 callout_reset(tp->tt_2msl,
2208                                               tp->t_rxtcur * TCPTV_TWTRUNC,
2209                                               tcp_timer_2msl, tp);
2210                                 /* For transaction client, force ACK now. */
2211                                 tp->t_flags |= TF_ACKNOW;
2212                         }
2213                         else
2214                                 callout_reset(tp->tt_2msl, 2 * tcp_msl,
2215                                               tcp_timer_2msl, tp);
2216                         soisdisconnected(so);
2217                         break;
2218
2219                 /*
2220                  * In TIME_WAIT state restart the 2 MSL time_wait timer.
2221                  */
2222                 case TCPS_TIME_WAIT:
2223                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
2224                                       tcp_timer_2msl, tp);
2225                         break;
2226                 }
2227         }
2228 #ifdef TCPDEBUG
2229         if (so->so_options & SO_DEBUG)
2230                 tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
2231                           &tcp_savetcp, 0);
2232 #endif
2233
2234         /*
2235          * Return any desired output.
2236          */
2237         if (needoutput || (tp->t_flags & TF_ACKNOW))
2238                 (void) tcp_output(tp);
2239         return;
2240
2241 dropafterack:
2242         /*
2243          * Generate an ACK dropping incoming segment if it occupies
2244          * sequence space, where the ACK reflects our state.
2245          *
2246          * We can now skip the test for the RST flag since all
2247          * paths to this code happen after packets containing
2248          * RST have been dropped.
2249          *
2250          * In the SYN-RECEIVED state, don't send an ACK unless the
2251          * segment we received passes the SYN-RECEIVED ACK test.
2252          * If it fails send a RST.  This breaks the loop in the
2253          * "LAND" DoS attack, and also prevents an ACK storm
2254          * between two listening ports that have been sent forged
2255          * SYN segments, each with the source address of the other.
2256          */
2257         if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
2258             (SEQ_GT(tp->snd_una, th->th_ack) ||
2259              SEQ_GT(th->th_ack, tp->snd_max)) ) {
2260                 rstreason = BANDLIM_RST_OPENPORT;
2261                 goto dropwithreset;
2262         }
2263 #ifdef TCPDEBUG
2264         if (so->so_options & SO_DEBUG)
2265                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2266                           &tcp_savetcp, 0);
2267 #endif
2268         m_freem(m);
2269         tp->t_flags |= TF_ACKNOW;
2270         (void) tcp_output(tp);
2271         return;
2272
2273 dropwithreset:
2274         /*
2275          * Generate a RST, dropping incoming segment.
2276          * Make ACK acceptable to originator of segment.
2277          * Don't bother to respond if destination was broadcast/multicast.
2278          */
2279         if ((thflags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
2280                 goto drop;
2281         if (isipv6) {
2282                 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
2283                     IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
2284                         goto drop;
2285         } else {
2286                 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
2287                     IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
2288                     ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
2289                     in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
2290                         goto drop;
2291         }
2292         /* IPv6 anycast check is done at tcp6_input() */
2293
2294         /*
2295          * Perform bandwidth limiting.
2296          */
2297 #ifdef ICMP_BANDLIM
2298         if (badport_bandlim(rstreason) < 0)
2299                 goto drop;
2300 #endif
2301
2302 #ifdef TCPDEBUG
2303         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2304                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2305                           &tcp_savetcp, 0);
2306 #endif
2307         if (thflags & TH_ACK)
2308                 /* mtod() below is safe as long as hdr dropping is delayed */
2309                 tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0, th->th_ack,
2310                             TH_RST);
2311         else {
2312                 if (thflags & TH_SYN)
2313                         tlen++;
2314                 /* mtod() below is safe as long as hdr dropping is delayed */
2315                 tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
2316                             (tcp_seq)0, TH_RST|TH_ACK);
2317         }
2318         return;
2319
2320 drop:
2321         /*
2322          * Drop space held by incoming segment and return.
2323          */
2324 #ifdef TCPDEBUG
2325         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2326                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2327                           &tcp_savetcp, 0);
2328 #endif
2329         m_freem(m);
2330         return;
2331 }
2332
2333 /*
2334  * Parse TCP options and place in tcpopt.
2335  */
2336 static void
2337 tcp_dooptions(to, cp, cnt, is_syn)
2338         struct tcpopt *to;
2339         u_char *cp;
2340         int cnt;
2341 {
2342         int opt, optlen;
2343
2344         to->to_flags = 0;
2345         for (; cnt > 0; cnt -= optlen, cp += optlen) {
2346                 opt = cp[0];
2347                 if (opt == TCPOPT_EOL)
2348                         break;
2349                 if (opt == TCPOPT_NOP)
2350                         optlen = 1;
2351                 else {
2352                         if (cnt < 2)
2353                                 break;
2354                         optlen = cp[1];
2355                         if (optlen < 2 || optlen > cnt)
2356                                 break;
2357                 }
2358                 switch (opt) {
2359                 case TCPOPT_MAXSEG:
2360                         if (optlen != TCPOLEN_MAXSEG)
2361                                 continue;
2362                         if (!is_syn)
2363                                 continue;
2364                         to->to_flags |= TOF_MSS;
2365                         bcopy((char *)cp + 2,
2366                             (char *)&to->to_mss, sizeof(to->to_mss));
2367                         to->to_mss = ntohs(to->to_mss);
2368                         break;
2369                 case TCPOPT_WINDOW:
2370                         if (optlen != TCPOLEN_WINDOW)
2371                                 continue;
2372                         if (! is_syn)
2373                                 continue;
2374                         to->to_flags |= TOF_SCALE;
2375                         to->to_requested_s_scale = min(cp[2], TCP_MAX_WINSHIFT);
2376                         break;
2377                 case TCPOPT_TIMESTAMP:
2378                         if (optlen != TCPOLEN_TIMESTAMP)
2379                                 continue;
2380                         to->to_flags |= TOF_TS;
2381                         bcopy((char *)cp + 2,
2382                             (char *)&to->to_tsval, sizeof(to->to_tsval));
2383                         to->to_tsval = ntohl(to->to_tsval);
2384                         bcopy((char *)cp + 6,
2385                             (char *)&to->to_tsecr, sizeof(to->to_tsecr));
2386                         to->to_tsecr = ntohl(to->to_tsecr);
2387                         break;
2388                 case TCPOPT_CC:
2389                         if (optlen != TCPOLEN_CC)
2390                                 continue;
2391                         to->to_flags |= TOF_CC;
2392                         bcopy((char *)cp + 2,
2393                             (char *)&to->to_cc, sizeof(to->to_cc));
2394                         to->to_cc = ntohl(to->to_cc);
2395                         break;
2396                 case TCPOPT_CCNEW:
2397                         if (optlen != TCPOLEN_CC)
2398                                 continue;
2399                         if (!is_syn)
2400                                 continue;
2401                         to->to_flags |= TOF_CCNEW;
2402                         bcopy((char *)cp + 2,
2403                             (char *)&to->to_cc, sizeof(to->to_cc));
2404                         to->to_cc = ntohl(to->to_cc);
2405                         break;
2406                 case TCPOPT_CCECHO:
2407                         if (optlen != TCPOLEN_CC)
2408                                 continue;
2409                         if (!is_syn)
2410                                 continue;
2411                         to->to_flags |= TOF_CCECHO;
2412                         bcopy((char *)cp + 2,
2413                             (char *)&to->to_ccecho, sizeof(to->to_ccecho));
2414                         to->to_ccecho = ntohl(to->to_ccecho);
2415                         break;
2416                 default:
2417                         continue;
2418                 }
2419         }
2420 }
2421
2422 /*
2423  * Pull out of band byte out of a segment so
2424  * it doesn't appear in the user's data queue.
2425  * It is still reflected in the segment length for
2426  * sequencing purposes.
2427  */
2428 static void
2429 tcp_pulloutofband(so, th, m, off)
2430         struct socket *so;
2431         struct tcphdr *th;
2432         struct mbuf *m;
2433         int off;                /* delayed to be droped hdrlen */
2434 {
2435         int cnt = off + th->th_urp - 1;
2436
2437         while (cnt >= 0) {
2438                 if (m->m_len > cnt) {
2439                         char *cp = mtod(m, caddr_t) + cnt;
2440                         struct tcpcb *tp = sototcpcb(so);
2441
2442                         tp->t_iobc = *cp;
2443                         tp->t_oobflags |= TCPOOB_HAVEDATA;
2444                         bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
2445                         m->m_len--;
2446                         if (m->m_flags & M_PKTHDR)
2447                                 m->m_pkthdr.len--;
2448                         return;
2449                 }
2450                 cnt -= m->m_len;
2451                 m = m->m_next;
2452                 if (m == 0)
2453                         break;
2454         }
2455         panic("tcp_pulloutofband");
2456 }
2457
2458 /*
2459  * Collect new round-trip time estimate
2460  * and update averages and current timeout.
2461  */
2462 static void
2463 tcp_xmit_timer(tp, rtt)
2464         struct tcpcb *tp;
2465         int rtt;
2466 {
2467         int delta;
2468
2469         tcpstat.tcps_rttupdated++;
2470         tp->t_rttupdated++;
2471         if (tp->t_srtt != 0) {
2472                 /*
2473                  * srtt is stored as fixed point with 5 bits after the
2474                  * binary point (i.e., scaled by 8).  The following magic
2475                  * is equivalent to the smoothing algorithm in rfc793 with
2476                  * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
2477                  * point).  Adjust rtt to origin 0.
2478                  */
2479                 delta = ((rtt - 1) << TCP_DELTA_SHIFT)
2480                         - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
2481
2482                 if ((tp->t_srtt += delta) <= 0)
2483                         tp->t_srtt = 1;
2484
2485                 /*
2486                  * We accumulate a smoothed rtt variance (actually, a
2487                  * smoothed mean difference), then set the retransmit
2488                  * timer to smoothed rtt + 4 times the smoothed variance.
2489                  * rttvar is stored as fixed point with 4 bits after the
2490                  * binary point (scaled by 16).  The following is
2491                  * equivalent to rfc793 smoothing with an alpha of .75
2492                  * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
2493                  * rfc793's wired-in beta.
2494                  */
2495                 if (delta < 0)
2496                         delta = -delta;
2497                 delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
2498                 if ((tp->t_rttvar += delta) <= 0)
2499                         tp->t_rttvar = 1;
2500                 if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
2501                         tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2502         } else {
2503                 /*
2504                  * No rtt measurement yet - use the unsmoothed rtt.
2505                  * Set the variance to half the rtt (so our first
2506                  * retransmit happens at 3*rtt).
2507                  */
2508                 tp->t_srtt = rtt << TCP_RTT_SHIFT;
2509                 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
2510                 tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2511         }
2512         tp->t_rtttime = 0;
2513         tp->t_rxtshift = 0;
2514
2515         /*
2516          * the retransmit should happen at rtt + 4 * rttvar.
2517          * Because of the way we do the smoothing, srtt and rttvar
2518          * will each average +1/2 tick of bias.  When we compute
2519          * the retransmit timer, we want 1/2 tick of rounding and
2520          * 1 extra tick because of +-1/2 tick uncertainty in the
2521          * firing of the timer.  The bias will give us exactly the
2522          * 1.5 tick we need.  But, because the bias is
2523          * statistical, we have to test that we don't drop below
2524          * the minimum feasible timer (which is 2 ticks).
2525          */
2526         TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
2527                       max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
2528
2529         /*
2530          * We received an ack for a packet that wasn't retransmitted;
2531          * it is probably safe to discard any error indications we've
2532          * received recently.  This isn't quite right, but close enough
2533          * for now (a route might have failed after we sent a segment,
2534          * and the return path might not be symmetrical).
2535          */
2536         tp->t_softerror = 0;
2537 }
2538
2539 /*
2540  * Determine a reasonable value for maxseg size.
2541  * If the route is known, check route for mtu.
2542  * If none, use an mss that can be handled on the outgoing
2543  * interface without forcing IP to fragment; if bigger than
2544  * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
2545  * to utilize large mbufs.  If no route is found, route has no mtu,
2546  * or the destination isn't local, use a default, hopefully conservative
2547  * size (usually 512 or the default IP max size, but no more than the mtu
2548  * of the interface), as we can't discover anything about intervening
2549  * gateways or networks.  We also initialize the congestion/slow start
2550  * window to be a single segment if the destination isn't local.
2551  * While looking at the routing entry, we also initialize other path-dependent
2552  * parameters from pre-set or cached values in the routing entry.
2553  *
2554  * Also take into account the space needed for options that we
2555  * send regularly.  Make maxseg shorter by that amount to assure
2556  * that we can send maxseg amount of data even when the options
2557  * are present.  Store the upper limit of the length of options plus
2558  * data in maxopd.
2559  *
2560  * NOTE that this routine is only called when we process an incoming
2561  * segment, for outgoing segments only tcp_mssopt is called.
2562  *
2563  * In case of T/TCP, we call this routine during implicit connection
2564  * setup as well (offer = -1), to initialize maxseg from the cached
2565  * MSS of our peer.
2566  */
2567 void
2568 tcp_mss(tp, offer)
2569         struct tcpcb *tp;
2570         int offer;
2571 {
2572         struct rtentry *rt;
2573         struct ifnet *ifp;
2574         int rtt, mss;
2575         u_long bufsize;
2576         struct inpcb *inp = tp->t_inpcb;
2577         struct socket *so;
2578         struct rmxp_tao *taop;
2579         int origoffer = offer;
2580 #ifdef INET6
2581         int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
2582         size_t min_protoh = isipv6 ?
2583                             sizeof(struct ip6_hdr) + sizeof(struct tcphdr) :
2584                             sizeof(struct tcpiphdr);
2585 #else
2586         const int isipv6 = 0;
2587         const size_t min_protoh = sizeof(struct tcpiphdr);
2588 #endif
2589
2590         if (isipv6)
2591                 rt = tcp_rtlookup6(&inp->inp_inc);
2592         else
2593                 rt = tcp_rtlookup(&inp->inp_inc);
2594         if (rt == NULL) {
2595                 tp->t_maxopd = tp->t_maxseg =
2596                                 isipv6 ? tcp_v6mssdflt : tcp_mssdflt;
2597                 return;
2598         }
2599         ifp = rt->rt_ifp;
2600         so = inp->inp_socket;
2601
2602         taop = rmx_taop(rt->rt_rmx);
2603         /*
2604          * Offer == -1 means that we didn't receive SYN yet,
2605          * use cached value in that case;
2606          */
2607         if (offer == -1)
2608                 offer = taop->tao_mssopt;
2609         /*
2610          * Offer == 0 means that there was no MSS on the SYN segment,
2611          * in this case we use tcp_mssdflt.
2612          */
2613         if (offer == 0)
2614                 offer = isipv6 ? tcp_v6mssdflt : tcp_mssdflt;
2615         else
2616                 /*
2617                  * Sanity check: make sure that maxopd will be large
2618                  * enough to allow some data on segments even is the
2619                  * all the option space is used (40bytes).  Otherwise
2620                  * funny things may happen in tcp_output.
2621                  */
2622                 offer = max(offer, 64);
2623         taop->tao_mssopt = offer;
2624
2625         /*
2626          * While we're here, check if there's an initial rtt
2627          * or rttvar.  Convert from the route-table units
2628          * to scaled multiples of the slow timeout timer.
2629          */
2630         if (tp->t_srtt == 0 && (rtt = rt->rt_rmx.rmx_rtt)) {
2631                 /*
2632                  * XXX the lock bit for RTT indicates that the value
2633                  * is also a minimum value; this is subject to time.
2634                  */
2635                 if (rt->rt_rmx.rmx_locks & RTV_RTT)
2636                         tp->t_rttmin = rtt / (RTM_RTTUNIT / hz);
2637                 tp->t_srtt = rtt / (RTM_RTTUNIT / (hz * TCP_RTT_SCALE));
2638                 tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
2639                 tcpstat.tcps_usedrtt++;
2640                 if (rt->rt_rmx.rmx_rttvar) {
2641                         tp->t_rttvar = rt->rt_rmx.rmx_rttvar /
2642                             (RTM_RTTUNIT / (hz * TCP_RTTVAR_SCALE));
2643                         tcpstat.tcps_usedrttvar++;
2644                 } else {
2645                         /* default variation is +- 1 rtt */
2646                         tp->t_rttvar =
2647                             tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
2648                 }
2649                 TCPT_RANGESET(tp->t_rxtcur,
2650                               ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
2651                               tp->t_rttmin, TCPTV_REXMTMAX);
2652         }
2653         /*
2654          * if there's an mtu associated with the route, use it
2655          * else, use the link mtu.
2656          */
2657         if (rt->rt_rmx.rmx_mtu)
2658                 mss = rt->rt_rmx.rmx_mtu - min_protoh;
2659         else {
2660                 if (isipv6) {
2661                         mss = nd_ifinfo[rt->rt_ifp->if_index].linkmtu -
2662                                 min_protoh;
2663                         if (!in6_localaddr(&inp->in6p_faddr))
2664                                 mss = min(mss, tcp_v6mssdflt);
2665                 } else {
2666                         mss = ifp->if_mtu - min_protoh;
2667                         if (!in_localaddr(inp->inp_faddr))
2668                                 mss = min(mss, tcp_mssdflt);
2669                 }
2670         }
2671         mss = min(mss, offer);
2672         /*
2673          * maxopd stores the maximum length of data AND options
2674          * in a segment; maxseg is the amount of data in a normal
2675          * segment.  We need to store this value (maxopd) apart
2676          * from maxseg, because now every segment carries options
2677          * and thus we normally have somewhat less data in segments.
2678          */
2679         tp->t_maxopd = mss;
2680
2681         /*
2682          * In case of T/TCP, origoffer==-1 indicates, that no segments
2683          * were received yet.  In this case we just guess, otherwise
2684          * we do the same as before T/TCP.
2685          */
2686         if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
2687             (origoffer == -1 ||
2688              (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
2689                 mss -= TCPOLEN_TSTAMP_APPA;
2690         if ((tp->t_flags & (TF_REQ_CC|TF_NOOPT)) == TF_REQ_CC &&
2691             (origoffer == -1 ||
2692              (tp->t_flags & TF_RCVD_CC) == TF_RCVD_CC))
2693                 mss -= TCPOLEN_CC_APPA;
2694
2695 #if     (MCLBYTES & (MCLBYTES - 1)) == 0
2696                 if (mss > MCLBYTES)
2697                         mss &= ~(MCLBYTES-1);
2698 #else
2699                 if (mss > MCLBYTES)
2700                         mss = mss / MCLBYTES * MCLBYTES;
2701 #endif
2702         /*
2703          * If there's a pipesize, change the socket buffer
2704          * to that size.  Make the socket buffers an integral
2705          * number of mss units; if the mss is larger than
2706          * the socket buffer, decrease the mss.
2707          */
2708 #ifdef RTV_SPIPE
2709         if ((bufsize = rt->rt_rmx.rmx_sendpipe) == 0)
2710 #endif
2711                 bufsize = so->so_snd.sb_hiwat;
2712         if (bufsize < mss)
2713                 mss = bufsize;
2714         else {
2715                 bufsize = roundup(bufsize, mss);
2716                 if (bufsize > sb_max)
2717                         bufsize = sb_max;
2718                 if (bufsize > so->so_snd.sb_hiwat)
2719                         (void)sbreserve(&so->so_snd, bufsize, so, NULL);
2720         }
2721         tp->t_maxseg = mss;
2722
2723 #ifdef RTV_RPIPE
2724         if ((bufsize = rt->rt_rmx.rmx_recvpipe) == 0)
2725 #endif
2726                 bufsize = so->so_rcv.sb_hiwat;
2727         if (bufsize > mss) {
2728                 bufsize = roundup(bufsize, mss);
2729                 if (bufsize > sb_max)
2730                         bufsize = sb_max;
2731                 if (bufsize > so->so_rcv.sb_hiwat)
2732                         (void)sbreserve(&so->so_rcv, bufsize, so, NULL);
2733         }
2734
2735         /*
2736          * Set the slow-start flight size depending on whether this
2737          * is a local network or not.
2738          */
2739         if (tcp_do_rfc3390)
2740                 tp->snd_cwnd = min(4 * mss, max(2 * mss, 4380));
2741         else if ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
2742                  (!isipv6 && in_localaddr(inp->inp_faddr)))
2743                 tp->snd_cwnd = mss * ss_fltsz_local;
2744         else
2745                 tp->snd_cwnd = mss * ss_fltsz;
2746
2747         if (rt->rt_rmx.rmx_ssthresh) {
2748                 /*
2749                  * There's some sort of gateway or interface
2750                  * buffer limit on the path.  Use this to set
2751                  * the slow start threshhold, but set the
2752                  * threshold to no less than 2*mss.
2753                  */
2754                 tp->snd_ssthresh = max(2 * mss, rt->rt_rmx.rmx_ssthresh);
2755                 tcpstat.tcps_usedssthresh++;
2756         }
2757 }
2758
2759 /*
2760  * Determine the MSS option to send on an outgoing SYN.
2761  */
2762 int
2763 tcp_mssopt(tp)
2764         struct tcpcb *tp;
2765 {
2766         struct rtentry *rt;
2767 #ifdef INET6
2768         int isipv6 = ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
2769         int min_protoh = isipv6 ?
2770                              sizeof(struct ip6_hdr) + sizeof(struct tcphdr) :
2771                              sizeof(struct tcpiphdr);
2772 #else
2773         const int isipv6 = 0;
2774         const size_t min_protoh = sizeof(struct tcpiphdr);
2775 #endif
2776
2777         if (isipv6)
2778                 rt = tcp_rtlookup6(&tp->t_inpcb->inp_inc);
2779         else
2780                 rt = tcp_rtlookup(&tp->t_inpcb->inp_inc);
2781         if (rt == NULL)
2782                 return (isipv6 ? tcp_v6mssdflt : tcp_mssdflt);
2783
2784         return (rt->rt_ifp->if_mtu - min_protoh);
2785 }
2786
2787
2788 /*
2789  * When a partial ack arrives, force the retransmission of the
2790  * next unacknowledged segment.  Do not clear tp->t_dupacks.
2791  * By setting snd_nxt to ti_ack, this forces retransmission timer to
2792  * be started again.
2793  */
2794 static void
2795 tcp_newreno_partial_ack(tp, th)
2796         struct tcpcb *tp;
2797         struct tcphdr *th;
2798 {
2799         tcp_seq onxt = tp->snd_nxt;
2800         u_long  ocwnd = tp->snd_cwnd;
2801
2802         callout_stop(tp->tt_rexmt);
2803         tp->t_rtttime = 0;
2804         tp->snd_nxt = th->th_ack;
2805         /*
2806          * Set snd_cwnd to one segment beyond acknowledged offset
2807          * (tp->snd_una has not yet been updated when this function is called.)
2808          */
2809         tp->snd_cwnd = tp->t_maxseg + (th->th_ack - tp->snd_una);
2810         tp->t_flags |= TF_ACKNOW;
2811         (void) tcp_output(tp);
2812         tp->snd_cwnd = ocwnd;
2813         if (SEQ_GT(onxt, tp->snd_nxt))
2814                 tp->snd_nxt = onxt;
2815         /*
2816          * Partial window deflation.  Relies on fact that tp->snd_una
2817          * not updated yet.
2818          */
2819         tp->snd_cwnd -= (th->th_ack - tp->snd_una - tp->t_maxseg);
2820 }