84b20bf22d1b1487111e49a9703b3b0f0bfff267
[dragonfly.git] / sys / netinet / tcp_input.c
1 /*
2  * Copyright (c) 2002, 2003, 2004 Jeffrey M. Hsu.  All rights reserved.
3  * Copyright (c) 2002, 2003, 2004 The DragonFly Project.  All rights reserved.
4  *
5  * This code is derived from software contributed to The DragonFly Project
6  * by Jeffrey M. Hsu.
7  *
8  * Redistribution and use in source and binary forms, with or without
9  * modification, are permitted provided that the following conditions
10  * are met:
11  * 1. Redistributions of source code must retain the above copyright
12  *    notice, this list of conditions and the following disclaimer.
13  * 2. Redistributions in binary form must reproduce the above copyright
14  *    notice, this list of conditions and the following disclaimer in the
15  *    documentation and/or other materials provided with the distribution.
16  * 3. Neither the name of The DragonFly Project nor the names of its
17  *    contributors may be used to endorse or promote products derived
18  *    from this software without specific, prior written permission.
19  *
20  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
21  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
22  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
23  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
24  * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
25  * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
26  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
27  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
28  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
29  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
30  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31  * SUCH DAMAGE.
32  */
33
34 /*
35  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
36  *      The Regents of the University of California.  All rights reserved.
37  *
38  * Redistribution and use in source and binary forms, with or without
39  * modification, are permitted provided that the following conditions
40  * are met:
41  * 1. Redistributions of source code must retain the above copyright
42  *    notice, this list of conditions and the following disclaimer.
43  * 2. Redistributions in binary form must reproduce the above copyright
44  *    notice, this list of conditions and the following disclaimer in the
45  *    documentation and/or other materials provided with the distribution.
46  * 3. All advertising materials mentioning features or use of this software
47  *    must display the following acknowledgement:
48  *      This product includes software developed by the University of
49  *      California, Berkeley and its contributors.
50  * 4. Neither the name of the University nor the names of its contributors
51  *    may be used to endorse or promote products derived from this software
52  *    without specific prior written permission.
53  *
54  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
55  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
56  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
57  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
58  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
59  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
60  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
61  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
62  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
63  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
64  * SUCH DAMAGE.
65  *
66  *      @(#)tcp_input.c 8.12 (Berkeley) 5/24/95
67  * $FreeBSD: src/sys/netinet/tcp_input.c,v 1.107.2.38 2003/05/21 04:46:41 cjc Exp $
68  */
69
70 #include "opt_inet.h"
71 #include "opt_inet6.h"
72 #include "opt_ipsec.h"
73 #include "opt_tcpdebug.h"
74 #include "opt_tcp_input.h"
75
76 #include <sys/param.h>
77 #include <sys/systm.h>
78 #include <sys/kernel.h>
79 #include <sys/sysctl.h>
80 #include <sys/malloc.h>
81 #include <sys/mbuf.h>
82 #include <sys/proc.h>           /* for proc0 declaration */
83 #include <sys/protosw.h>
84 #include <sys/socket.h>
85 #include <sys/socketvar.h>
86 #include <sys/syslog.h>
87 #include <sys/in_cksum.h>
88
89 #include <sys/socketvar2.h>
90
91 #include <machine/cpu.h>        /* before tcp_seq.h, for tcp_random18() */
92 #include <machine/stdarg.h>
93
94 #include <net/if.h>
95 #include <net/route.h>
96
97 #include <netinet/in.h>
98 #include <netinet/in_systm.h>
99 #include <netinet/ip.h>
100 #include <netinet/ip_icmp.h>    /* for ICMP_BANDLIM */
101 #include <netinet/in_var.h>
102 #include <netinet/icmp_var.h>   /* for ICMP_BANDLIM */
103 #include <netinet/in_pcb.h>
104 #include <netinet/ip_var.h>
105 #include <netinet/ip6.h>
106 #include <netinet/icmp6.h>
107 #include <netinet6/nd6.h>
108 #include <netinet6/ip6_var.h>
109 #include <netinet6/in6_pcb.h>
110 #include <netinet/tcp.h>
111 #include <netinet/tcp_fsm.h>
112 #include <netinet/tcp_seq.h>
113 #include <netinet/tcp_timer.h>
114 #include <netinet/tcp_timer2.h>
115 #include <netinet/tcp_var.h>
116 #include <netinet6/tcp6_var.h>
117 #include <netinet/tcpip.h>
118
119 #ifdef TCPDEBUG
120 #include <netinet/tcp_debug.h>
121
122 u_char tcp_saveipgen[40];    /* the size must be of max ip header, now IPv6 */
123 struct tcphdr tcp_savetcp;
124 #endif
125
126 #ifdef FAST_IPSEC
127 #include <netproto/ipsec/ipsec.h>
128 #include <netproto/ipsec/ipsec6.h>
129 #endif
130
131 #ifdef IPSEC
132 #include <netinet6/ipsec.h>
133 #include <netinet6/ipsec6.h>
134 #include <netproto/key/key.h>
135 #endif
136
137 MALLOC_DEFINE(M_TSEGQ, "tseg_qent", "TCP segment queue entry");
138
139 static int log_in_vain = 0;
140 SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW,
141     &log_in_vain, 0, "Log all incoming TCP connections");
142
143 static int blackhole = 0;
144 SYSCTL_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_RW,
145     &blackhole, 0, "Do not send RST when dropping refused connections");
146
147 int tcp_delack_enabled = 1;
148 SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_RW,
149     &tcp_delack_enabled, 0,
150     "Delay ACK to try and piggyback it onto a data packet");
151
152 #ifdef TCP_DROP_SYNFIN
153 static int drop_synfin = 0;
154 SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_RW,
155     &drop_synfin, 0, "Drop TCP packets with SYN+FIN set");
156 #endif
157
158 static int tcp_do_limitedtransmit = 1;
159 SYSCTL_INT(_net_inet_tcp, OID_AUTO, limitedtransmit, CTLFLAG_RW,
160     &tcp_do_limitedtransmit, 0, "Enable RFC 3042 (Limited Transmit)");
161
162 static int tcp_do_early_retransmit = 1;
163 SYSCTL_INT(_net_inet_tcp, OID_AUTO, earlyretransmit, CTLFLAG_RW,
164     &tcp_do_early_retransmit, 0, "Early retransmit");
165
166 int tcp_aggregate_acks = 1;
167 SYSCTL_INT(_net_inet_tcp, OID_AUTO, aggregate_acks, CTLFLAG_RW,
168     &tcp_aggregate_acks, 0, "Aggregate built-up acks into one ack");
169
170 static int tcp_do_eifel_detect = 1;
171 SYSCTL_INT(_net_inet_tcp, OID_AUTO, eifel, CTLFLAG_RW,
172     &tcp_do_eifel_detect, 0, "Eifel detection algorithm (RFC 3522)");
173
174 static int tcp_do_abc = 1;
175 SYSCTL_INT(_net_inet_tcp, OID_AUTO, abc, CTLFLAG_RW,
176     &tcp_do_abc, 0,
177     "TCP Appropriate Byte Counting (RFC 3465)");
178
179 /*
180  * Define as tunable for easy testing with SACK on and off.
181  * Warning:  do not change setting in the middle of an existing active TCP flow,
182  *   else strange things might happen to that flow.
183  */
184 int tcp_do_sack = 1;
185 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sack, CTLFLAG_RW,
186     &tcp_do_sack, 0, "Enable SACK Algorithms");
187
188 int tcp_do_smartsack = 1;
189 SYSCTL_INT(_net_inet_tcp, OID_AUTO, smartsack, CTLFLAG_RW,
190     &tcp_do_smartsack, 0, "Enable Smart SACK Algorithms");
191
192 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, reass, CTLFLAG_RW, 0,
193     "TCP Segment Reassembly Queue");
194
195 int tcp_reass_maxseg = 0;
196 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, maxsegments, CTLFLAG_RD,
197     &tcp_reass_maxseg, 0,
198     "Global maximum number of TCP Segments in Reassembly Queue");
199
200 int tcp_reass_qsize = 0;
201 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, cursegments, CTLFLAG_RD,
202     &tcp_reass_qsize, 0,
203     "Global number of TCP Segments currently in Reassembly Queue");
204
205 static int tcp_reass_overflows = 0;
206 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, overflows, CTLFLAG_RD,
207     &tcp_reass_overflows, 0,
208     "Global number of TCP Segment Reassembly Queue Overflows");
209
210 int tcp_do_autorcvbuf = 1;
211 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_auto, CTLFLAG_RW,
212     &tcp_do_autorcvbuf, 0, "Enable automatic receive buffer sizing");
213
214 int tcp_autorcvbuf_inc = 16*1024;
215 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_inc, CTLFLAG_RW,
216     &tcp_autorcvbuf_inc, 0,
217     "Incrementor step size of automatic receive buffer");
218
219 int tcp_autorcvbuf_max = 2*1024*1024;
220 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_max, CTLFLAG_RW,
221     &tcp_autorcvbuf_max, 0, "Max size of automatic receive buffer");
222
223 int tcp_sosend_agglim = 2;
224 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sosend_agglim, CTLFLAG_RW,
225     &tcp_sosend_agglim, 0, "TCP sosend mbuf aggregation limit");
226
227 int tcp_sosend_async = 1;
228 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sosend_async, CTLFLAG_RW,
229     &tcp_sosend_async, 0, "TCP asynchronized pru_send");
230
231 static void      tcp_dooptions(struct tcpopt *, u_char *, int, boolean_t);
232 static void      tcp_pulloutofband(struct socket *,
233                      struct tcphdr *, struct mbuf *, int);
234 static int       tcp_reass(struct tcpcb *, struct tcphdr *, int *,
235                      struct mbuf *);
236 static void      tcp_xmit_timer(struct tcpcb *, int);
237 static void      tcp_newreno_partial_ack(struct tcpcb *, struct tcphdr *, int);
238 static void      tcp_sack_rexmt(struct tcpcb *, struct tcphdr *);
239 static int       tcp_rmx_msl(const struct tcpcb *);
240 static void      tcp_established(struct tcpcb *);
241
242 /* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */
243 #ifdef INET6
244 #define ND6_HINT(tp) \
245 do { \
246         if ((tp) && (tp)->t_inpcb && \
247             ((tp)->t_inpcb->inp_vflag & INP_IPV6) && \
248             (tp)->t_inpcb->in6p_route.ro_rt) \
249                 nd6_nud_hint((tp)->t_inpcb->in6p_route.ro_rt, NULL, 0); \
250 } while (0)
251 #else
252 #define ND6_HINT(tp)
253 #endif
254
255 /*
256  * Indicate whether this ack should be delayed.  We can delay the ack if
257  *      - delayed acks are enabled and
258  *      - there is no delayed ack timer in progress and
259  *      - our last ack wasn't a 0-sized window.  We never want to delay
260  *        the ack that opens up a 0-sized window.
261  */
262 #define DELAY_ACK(tp) \
263         (tcp_delack_enabled && !tcp_callout_pending(tp, tp->tt_delack) && \
264         !(tp->t_flags & TF_RXWIN0SENT))
265
266 #define acceptable_window_update(tp, th, tiwin)                         \
267     (SEQ_LT(tp->snd_wl1, th->th_seq) ||                                 \
268      (tp->snd_wl1 == th->th_seq &&                                      \
269       (SEQ_LT(tp->snd_wl2, th->th_ack) ||                               \
270        (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))
271
272 static int
273 tcp_reass(struct tcpcb *tp, struct tcphdr *th, int *tlenp, struct mbuf *m)
274 {
275         struct tseg_qent *q;
276         struct tseg_qent *p = NULL;
277         struct tseg_qent *te;
278         struct socket *so = tp->t_inpcb->inp_socket;
279         int flags;
280
281         /*
282          * Call with th == NULL after become established to
283          * force pre-ESTABLISHED data up to user socket.
284          */
285         if (th == NULL)
286                 goto present;
287
288         /*
289          * Limit the number of segments in the reassembly queue to prevent
290          * holding on to too many segments (and thus running out of mbufs).
291          * Make sure to let the missing segment through which caused this
292          * queue.  Always keep one global queue entry spare to be able to
293          * process the missing segment.
294          */
295         if (th->th_seq != tp->rcv_nxt &&
296             tcp_reass_qsize + 1 >= tcp_reass_maxseg) {
297                 tcp_reass_overflows++;
298                 tcpstat.tcps_rcvmemdrop++;
299                 m_freem(m);
300                 /* no SACK block to report */
301                 tp->reportblk.rblk_start = tp->reportblk.rblk_end;
302                 return (0);
303         }
304
305         /* Allocate a new queue entry. */
306         te = kmalloc(sizeof(struct tseg_qent), M_TSEGQ, M_INTWAIT | M_NULLOK);
307         if (te == NULL) {
308                 tcpstat.tcps_rcvmemdrop++;
309                 m_freem(m);
310                 /* no SACK block to report */
311                 tp->reportblk.rblk_start = tp->reportblk.rblk_end;
312                 return (0);
313         }
314         atomic_add_int(&tcp_reass_qsize, 1);
315
316         /*
317          * Find a segment which begins after this one does.
318          */
319         LIST_FOREACH(q, &tp->t_segq, tqe_q) {
320                 if (SEQ_GT(q->tqe_th->th_seq, th->th_seq))
321                         break;
322                 p = q;
323         }
324
325         /*
326          * If there is a preceding segment, it may provide some of
327          * our data already.  If so, drop the data from the incoming
328          * segment.  If it provides all of our data, drop us.
329          */
330         if (p != NULL) {
331                 tcp_seq_diff_t i;
332
333                 /* conversion to int (in i) handles seq wraparound */
334                 i = p->tqe_th->th_seq + p->tqe_len - th->th_seq;
335                 if (i > 0) {            /* overlaps preceding segment */
336                         tp->t_flags |= (TF_DUPSEG | TF_ENCLOSESEG);
337                         /* enclosing block starts w/ preceding segment */
338                         tp->encloseblk.rblk_start = p->tqe_th->th_seq;
339                         if (i >= *tlenp) {
340                                 /* preceding encloses incoming segment */
341                                 tp->encloseblk.rblk_end = TCP_SACK_BLKEND(
342                                     p->tqe_th->th_seq + p->tqe_len,
343                                     p->tqe_th->th_flags);
344                                 tcpstat.tcps_rcvduppack++;
345                                 tcpstat.tcps_rcvdupbyte += *tlenp;
346                                 m_freem(m);
347                                 kfree(te, M_TSEGQ);
348                                 atomic_add_int(&tcp_reass_qsize, -1);
349                                 /*
350                                  * Try to present any queued data
351                                  * at the left window edge to the user.
352                                  * This is needed after the 3-WHS
353                                  * completes.
354                                  */
355                                 goto present;   /* ??? */
356                         }
357                         m_adj(m, i);
358                         *tlenp -= i;
359                         th->th_seq += i;
360                         /* incoming segment end is enclosing block end */
361                         tp->encloseblk.rblk_end = TCP_SACK_BLKEND(
362                             th->th_seq + *tlenp, th->th_flags);
363                         /* trim end of reported D-SACK block */
364                         tp->reportblk.rblk_end = th->th_seq;
365                 }
366         }
367         tcpstat.tcps_rcvoopack++;
368         tcpstat.tcps_rcvoobyte += *tlenp;
369
370         /*
371          * While we overlap succeeding segments trim them or,
372          * if they are completely covered, dequeue them.
373          */
374         while (q) {
375                 tcp_seq_diff_t i = (th->th_seq + *tlenp) - q->tqe_th->th_seq;
376                 tcp_seq qend = q->tqe_th->th_seq + q->tqe_len;
377                 tcp_seq qend_sack = TCP_SACK_BLKEND(qend, q->tqe_th->th_flags);
378                 struct tseg_qent *nq;
379
380                 if (i <= 0)
381                         break;
382                 if (!(tp->t_flags & TF_DUPSEG)) {    /* first time through */
383                         tp->t_flags |= (TF_DUPSEG | TF_ENCLOSESEG);
384                         tp->encloseblk = tp->reportblk;
385                         /* report trailing duplicate D-SACK segment */
386                         tp->reportblk.rblk_start = q->tqe_th->th_seq;
387                 }
388                 if ((tp->t_flags & TF_ENCLOSESEG) &&
389                     SEQ_GT(qend_sack, tp->encloseblk.rblk_end)) {
390                         /* extend enclosing block if one exists */
391                         tp->encloseblk.rblk_end = qend_sack;
392                 }
393                 if (i < q->tqe_len) {
394                         q->tqe_th->th_seq += i;
395                         q->tqe_len -= i;
396                         m_adj(q->tqe_m, i);
397                         break;
398                 }
399
400                 nq = LIST_NEXT(q, tqe_q);
401                 LIST_REMOVE(q, tqe_q);
402                 m_freem(q->tqe_m);
403                 kfree(q, M_TSEGQ);
404                 atomic_add_int(&tcp_reass_qsize, -1);
405                 q = nq;
406         }
407
408         /* Insert the new segment queue entry into place. */
409         te->tqe_m = m;
410         te->tqe_th = th;
411         te->tqe_len = *tlenp;
412
413         /* check if can coalesce with following segment */
414         if (q != NULL && (th->th_seq + *tlenp == q->tqe_th->th_seq)) {
415                 tcp_seq tend = te->tqe_th->th_seq + te->tqe_len;
416                 tcp_seq tend_sack = TCP_SACK_BLKEND(tend, te->tqe_th->th_flags);
417
418                 te->tqe_len += q->tqe_len;
419                 if (q->tqe_th->th_flags & TH_FIN)
420                         te->tqe_th->th_flags |= TH_FIN;
421                 m_cat(te->tqe_m, q->tqe_m);
422                 tp->encloseblk.rblk_end = tend_sack;
423                 /*
424                  * When not reporting a duplicate segment, use
425                  * the larger enclosing block as the SACK block.
426                  */
427                 if (!(tp->t_flags & TF_DUPSEG))
428                         tp->reportblk.rblk_end = tend_sack;
429                 LIST_REMOVE(q, tqe_q);
430                 kfree(q, M_TSEGQ);
431                 atomic_add_int(&tcp_reass_qsize, -1);
432         }
433
434         if (p == NULL) {
435                 LIST_INSERT_HEAD(&tp->t_segq, te, tqe_q);
436         } else {
437                 /* check if can coalesce with preceding segment */
438                 if (p->tqe_th->th_seq + p->tqe_len == th->th_seq) {
439                         p->tqe_len += te->tqe_len;
440                         m_cat(p->tqe_m, te->tqe_m);
441                         tp->encloseblk.rblk_start = p->tqe_th->th_seq;
442                         /*
443                          * When not reporting a duplicate segment, use
444                          * the larger enclosing block as the SACK block.
445                          */
446                         if (!(tp->t_flags & TF_DUPSEG))
447                                 tp->reportblk.rblk_start = p->tqe_th->th_seq;
448                         kfree(te, M_TSEGQ);
449                         atomic_add_int(&tcp_reass_qsize, -1);
450                 } else {
451                         LIST_INSERT_AFTER(p, te, tqe_q);
452                 }
453         }
454
455 present:
456         /*
457          * Present data to user, advancing rcv_nxt through
458          * completed sequence space.
459          */
460         if (!TCPS_HAVEESTABLISHED(tp->t_state))
461                 return (0);
462         q = LIST_FIRST(&tp->t_segq);
463         if (q == NULL || q->tqe_th->th_seq != tp->rcv_nxt)
464                 return (0);
465         tp->rcv_nxt += q->tqe_len;
466         if (!(tp->t_flags & TF_DUPSEG)) {
467                 /* no SACK block to report since ACK advanced */
468                 tp->reportblk.rblk_start = tp->reportblk.rblk_end;
469         }
470         /* no enclosing block to report since ACK advanced */
471         tp->t_flags &= ~TF_ENCLOSESEG;
472         flags = q->tqe_th->th_flags & TH_FIN;
473         LIST_REMOVE(q, tqe_q);
474         KASSERT(LIST_EMPTY(&tp->t_segq) ||
475                 LIST_FIRST(&tp->t_segq)->tqe_th->th_seq != tp->rcv_nxt,
476                 ("segment not coalesced"));
477         if (so->so_state & SS_CANTRCVMORE) {
478                 m_freem(q->tqe_m);
479         } else {
480                 lwkt_gettoken(&so->so_rcv.ssb_token);
481                 ssb_appendstream(&so->so_rcv, q->tqe_m);
482                 lwkt_reltoken(&so->so_rcv.ssb_token);
483         }
484         kfree(q, M_TSEGQ);
485         atomic_add_int(&tcp_reass_qsize, -1);
486         ND6_HINT(tp);
487         sorwakeup(so);
488         return (flags);
489 }
490
491 /*
492  * TCP input routine, follows pages 65-76 of the
493  * protocol specification dated September, 1981 very closely.
494  */
495 #ifdef INET6
496 int
497 tcp6_input(struct mbuf **mp, int *offp, int proto)
498 {
499         struct mbuf *m = *mp;
500         struct in6_ifaddr *ia6;
501
502         IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
503
504         /*
505          * draft-itojun-ipv6-tcp-to-anycast
506          * better place to put this in?
507          */
508         ia6 = ip6_getdstifaddr(m);
509         if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
510                 struct ip6_hdr *ip6;
511
512                 ip6 = mtod(m, struct ip6_hdr *);
513                 icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
514                             offsetof(struct ip6_hdr, ip6_dst));
515                 return (IPPROTO_DONE);
516         }
517
518         tcp_input(mp, offp, proto);
519         return (IPPROTO_DONE);
520 }
521 #endif
522
523 int
524 tcp_input(struct mbuf **mp, int *offp, int proto)
525 {
526         int off0;
527         struct tcphdr *th;
528         struct ip *ip = NULL;
529         struct ipovly *ipov;
530         struct inpcb *inp = NULL;
531         u_char *optp = NULL;
532         int optlen = 0;
533         int tlen, off;
534         int len = 0;
535         int drop_hdrlen;
536         struct tcpcb *tp = NULL;
537         int thflags;
538         struct socket *so = NULL;
539         int todrop, acked;
540         boolean_t ourfinisacked, needoutput = FALSE;
541         u_long tiwin;
542         int recvwin;
543         struct tcpopt to;               /* options in this segment */
544         struct sockaddr_in *next_hop = NULL;
545         int rstreason; /* For badport_bandlim accounting purposes */
546         int cpu;
547         struct ip6_hdr *ip6 = NULL;
548         struct mbuf *m;
549 #ifdef INET6
550         boolean_t isipv6;
551 #else
552         const boolean_t isipv6 = FALSE;
553 #endif
554 #ifdef TCPDEBUG
555         short ostate = 0;
556 #endif
557
558         off0 = *offp;
559         m = *mp;
560         *mp = NULL;
561
562         tcpstat.tcps_rcvtotal++;
563
564         if (m->m_pkthdr.fw_flags & IPFORWARD_MBUF_TAGGED) {
565                 struct m_tag *mtag;
566
567                 mtag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
568                 KKASSERT(mtag != NULL);
569                 next_hop = m_tag_data(mtag);
570         }
571
572 #ifdef INET6
573         isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? TRUE : FALSE;
574 #endif
575
576         if (isipv6) {
577                 /* IP6_EXTHDR_CHECK() is already done at tcp6_input() */
578                 ip6 = mtod(m, struct ip6_hdr *);
579                 tlen = (sizeof *ip6) + ntohs(ip6->ip6_plen) - off0;
580                 if (in6_cksum(m, IPPROTO_TCP, off0, tlen)) {
581                         tcpstat.tcps_rcvbadsum++;
582                         goto drop;
583                 }
584                 th = (struct tcphdr *)((caddr_t)ip6 + off0);
585
586                 /*
587                  * Be proactive about unspecified IPv6 address in source.
588                  * As we use all-zero to indicate unbounded/unconnected pcb,
589                  * unspecified IPv6 address can be used to confuse us.
590                  *
591                  * Note that packets with unspecified IPv6 destination is
592                  * already dropped in ip6_input.
593                  */
594                 if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
595                         /* XXX stat */
596                         goto drop;
597                 }
598         } else {
599                 /*
600                  * Get IP and TCP header together in first mbuf.
601                  * Note: IP leaves IP header in first mbuf.
602                  */
603                 if (off0 > sizeof(struct ip)) {
604                         ip_stripoptions(m);
605                         off0 = sizeof(struct ip);
606                 }
607                 /* already checked and pulled up in ip_demux() */
608                 KASSERT(m->m_len >= sizeof(struct tcpiphdr),
609                     ("TCP header not in one mbuf: m->m_len %d", m->m_len));
610                 ip = mtod(m, struct ip *);
611                 ipov = (struct ipovly *)ip;
612                 th = (struct tcphdr *)((caddr_t)ip + off0);
613                 tlen = ip->ip_len;
614
615                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
616                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
617                                 th->th_sum = m->m_pkthdr.csum_data;
618                         else
619                                 th->th_sum = in_pseudo(ip->ip_src.s_addr,
620                                                 ip->ip_dst.s_addr,
621                                                 htonl(m->m_pkthdr.csum_data +
622                                                         ip->ip_len +
623                                                         IPPROTO_TCP));
624                         th->th_sum ^= 0xffff;
625                 } else {
626                         /*
627                          * Checksum extended TCP header and data.
628                          */
629                         len = sizeof(struct ip) + tlen;
630                         bzero(ipov->ih_x1, sizeof ipov->ih_x1);
631                         ipov->ih_len = (u_short)tlen;
632                         ipov->ih_len = htons(ipov->ih_len);
633                         th->th_sum = in_cksum(m, len);
634                 }
635                 if (th->th_sum) {
636                         tcpstat.tcps_rcvbadsum++;
637                         goto drop;
638                 }
639 #ifdef INET6
640                 /* Re-initialization for later version check */
641                 ip->ip_v = IPVERSION;
642 #endif
643         }
644
645         /*
646          * Check that TCP offset makes sense,
647          * pull out TCP options and adjust length.              XXX
648          */
649         off = th->th_off << 2;
650         /* already checked and pulled up in ip_demux() */
651         KASSERT(off >= sizeof(struct tcphdr) && off <= tlen,
652             ("bad TCP data offset %d (tlen %d)", off, tlen));
653         tlen -= off;    /* tlen is used instead of ti->ti_len */
654         if (off > sizeof(struct tcphdr)) {
655                 if (isipv6) {
656                         IP6_EXTHDR_CHECK(m, off0, off, IPPROTO_DONE);
657                         ip6 = mtod(m, struct ip6_hdr *);
658                         th = (struct tcphdr *)((caddr_t)ip6 + off0);
659                 } else {
660                         /* already pulled up in ip_demux() */
661                         KASSERT(m->m_len >= sizeof(struct ip) + off,
662                             ("TCP header and options not in one mbuf: "
663                              "m_len %d, off %d", m->m_len, off));
664                 }
665                 optlen = off - sizeof(struct tcphdr);
666                 optp = (u_char *)(th + 1);
667         }
668         thflags = th->th_flags;
669
670 #ifdef TCP_DROP_SYNFIN
671         /*
672          * If the drop_synfin option is enabled, drop all packets with
673          * both the SYN and FIN bits set. This prevents e.g. nmap from
674          * identifying the TCP/IP stack.
675          *
676          * This is a violation of the TCP specification.
677          */
678         if (drop_synfin && (thflags & (TH_SYN | TH_FIN)) == (TH_SYN | TH_FIN))
679                 goto drop;
680 #endif
681
682         /*
683          * Convert TCP protocol specific fields to host format.
684          */
685         th->th_seq = ntohl(th->th_seq);
686         th->th_ack = ntohl(th->th_ack);
687         th->th_win = ntohs(th->th_win);
688         th->th_urp = ntohs(th->th_urp);
689
690         /*
691          * Delay dropping TCP, IP headers, IPv6 ext headers, and TCP options,
692          * until after ip6_savecontrol() is called and before other functions
693          * which don't want those proto headers.
694          * Because ip6_savecontrol() is going to parse the mbuf to
695          * search for data to be passed up to user-land, it wants mbuf
696          * parameters to be unchanged.
697          * XXX: the call of ip6_savecontrol() has been obsoleted based on
698          * latest version of the advanced API (20020110).
699          */
700         drop_hdrlen = off0 + off;
701
702         /*
703          * Locate pcb for segment.
704          */
705 findpcb:
706         /* IPFIREWALL_FORWARD section */
707         if (next_hop != NULL && !isipv6) {  /* IPv6 support is not there yet */
708                 /*
709                  * Transparently forwarded. Pretend to be the destination.
710                  * already got one like this?
711                  */
712                 cpu = mycpu->gd_cpuid;
713                 inp = in_pcblookup_hash(&tcbinfo[cpu],
714                                         ip->ip_src, th->th_sport,
715                                         ip->ip_dst, th->th_dport,
716                                         0, m->m_pkthdr.rcvif);
717                 if (!inp) {
718                         /*
719                          * It's new.  Try to find the ambushing socket.
720                          */
721
722                         /*
723                          * The rest of the ipfw code stores the port in
724                          * host order.  XXX
725                          * (The IP address is still in network order.)
726                          */
727                         in_port_t dport = next_hop->sin_port ?
728                                                 htons(next_hop->sin_port) :
729                                                 th->th_dport;
730
731                         cpu = tcp_addrcpu(ip->ip_src.s_addr, th->th_sport,
732                                           next_hop->sin_addr.s_addr, dport);
733                         inp = in_pcblookup_hash(&tcbinfo[cpu],
734                                                 ip->ip_src, th->th_sport,
735                                                 next_hop->sin_addr, dport,
736                                                 1, m->m_pkthdr.rcvif);
737                 }
738         } else {
739                 if (isipv6) {
740                         inp = in6_pcblookup_hash(&tcbinfo[0],
741                                                  &ip6->ip6_src, th->th_sport,
742                                                  &ip6->ip6_dst, th->th_dport,
743                                                  1, m->m_pkthdr.rcvif);
744                 } else {
745                         cpu = mycpu->gd_cpuid;
746                         inp = in_pcblookup_hash(&tcbinfo[cpu],
747                                                 ip->ip_src, th->th_sport,
748                                                 ip->ip_dst, th->th_dport,
749                                                 1, m->m_pkthdr.rcvif);
750                 }
751         }
752
753         /*
754          * If the state is CLOSED (i.e., TCB does not exist) then
755          * all data in the incoming segment is discarded.
756          * If the TCB exists but is in CLOSED state, it is embryonic,
757          * but should either do a listen or a connect soon.
758          */
759         if (inp == NULL) {
760                 if (log_in_vain) {
761 #ifdef INET6
762                         char dbuf[INET6_ADDRSTRLEN+2], sbuf[INET6_ADDRSTRLEN+2];
763 #else
764                         char dbuf[sizeof "aaa.bbb.ccc.ddd"];
765                         char sbuf[sizeof "aaa.bbb.ccc.ddd"];
766 #endif
767                         if (isipv6) {
768                                 strcpy(dbuf, "[");
769                                 strcat(dbuf, ip6_sprintf(&ip6->ip6_dst));
770                                 strcat(dbuf, "]");
771                                 strcpy(sbuf, "[");
772                                 strcat(sbuf, ip6_sprintf(&ip6->ip6_src));
773                                 strcat(sbuf, "]");
774                         } else {
775                                 strcpy(dbuf, inet_ntoa(ip->ip_dst));
776                                 strcpy(sbuf, inet_ntoa(ip->ip_src));
777                         }
778                         switch (log_in_vain) {
779                         case 1:
780                                 if (!(thflags & TH_SYN))
781                                         break;
782                         case 2:
783                                 log(LOG_INFO,
784                                     "Connection attempt to TCP %s:%d "
785                                     "from %s:%d flags:0x%02x\n",
786                                     dbuf, ntohs(th->th_dport), sbuf,
787                                     ntohs(th->th_sport), thflags);
788                                 break;
789                         default:
790                                 break;
791                         }
792                 }
793                 if (blackhole) {
794                         switch (blackhole) {
795                         case 1:
796                                 if (thflags & TH_SYN)
797                                         goto drop;
798                                 break;
799                         case 2:
800                                 goto drop;
801                         default:
802                                 goto drop;
803                         }
804                 }
805                 rstreason = BANDLIM_RST_CLOSEDPORT;
806                 goto dropwithreset;
807         }
808
809 #ifdef IPSEC
810         if (isipv6) {
811                 if (ipsec6_in_reject_so(m, inp->inp_socket)) {
812                         ipsec6stat.in_polvio++;
813                         goto drop;
814                 }
815         } else {
816                 if (ipsec4_in_reject_so(m, inp->inp_socket)) {
817                         ipsecstat.in_polvio++;
818                         goto drop;
819                 }
820         }
821 #endif
822 #ifdef FAST_IPSEC
823         if (isipv6) {
824                 if (ipsec6_in_reject(m, inp))
825                         goto drop;
826         } else {
827                 if (ipsec4_in_reject(m, inp))
828                         goto drop;
829         }
830 #endif
831         /* Check the minimum TTL for socket. */
832 #ifdef INET6
833         if ((isipv6 ? ip6->ip6_hlim : ip->ip_ttl) < inp->inp_ip_minttl)
834                 goto drop;
835 #endif
836
837         tp = intotcpcb(inp);
838         if (tp == NULL) {
839                 rstreason = BANDLIM_RST_CLOSEDPORT;
840                 goto dropwithreset;
841         }
842         if (tp->t_state <= TCPS_CLOSED)
843                 goto drop;
844
845         /* Unscale the window into a 32-bit value. */
846         if (!(thflags & TH_SYN))
847                 tiwin = th->th_win << tp->snd_scale;
848         else
849                 tiwin = th->th_win;
850
851         so = inp->inp_socket;
852
853 #ifdef TCPDEBUG
854         if (so->so_options & SO_DEBUG) {
855                 ostate = tp->t_state;
856                 if (isipv6)
857                         bcopy(ip6, tcp_saveipgen, sizeof(*ip6));
858                 else
859                         bcopy(ip, tcp_saveipgen, sizeof(*ip));
860                 tcp_savetcp = *th;
861         }
862 #endif
863
864         bzero(&to, sizeof to);
865
866         if (so->so_options & SO_ACCEPTCONN) {
867                 struct in_conninfo inc;
868
869 #ifdef INET6
870                 inc.inc_isipv6 = (isipv6 == TRUE);
871 #endif
872                 if (isipv6) {
873                         inc.inc6_faddr = ip6->ip6_src;
874                         inc.inc6_laddr = ip6->ip6_dst;
875                         inc.inc6_route.ro_rt = NULL;            /* XXX */
876                 } else {
877                         inc.inc_faddr = ip->ip_src;
878                         inc.inc_laddr = ip->ip_dst;
879                         inc.inc_route.ro_rt = NULL;             /* XXX */
880                 }
881                 inc.inc_fport = th->th_sport;
882                 inc.inc_lport = th->th_dport;
883
884                 /*
885                  * If the state is LISTEN then ignore segment if it contains
886                  * a RST.  If the segment contains an ACK then it is bad and
887                  * send a RST.  If it does not contain a SYN then it is not
888                  * interesting; drop it.
889                  *
890                  * If the state is SYN_RECEIVED (syncache) and seg contains
891                  * an ACK, but not for our SYN/ACK, send a RST.  If the seg
892                  * contains a RST, check the sequence number to see if it
893                  * is a valid reset segment.
894                  */
895                 if ((thflags & (TH_RST | TH_ACK | TH_SYN)) != TH_SYN) {
896                         if ((thflags & (TH_RST | TH_ACK | TH_SYN)) == TH_ACK) {
897                                 if (!syncache_expand(&inc, th, &so, m)) {
898                                         /*
899                                          * No syncache entry, or ACK was not
900                                          * for our SYN/ACK.  Send a RST.
901                                          */
902                                         tcpstat.tcps_badsyn++;
903                                         rstreason = BANDLIM_RST_OPENPORT;
904                                         goto dropwithreset;
905                                 }
906
907                                 /*
908                                  * Could not complete 3-way handshake,
909                                  * connection is being closed down, and
910                                  * syncache will free mbuf.
911                                  */
912                                 if (so == NULL)
913                                         return(IPPROTO_DONE);
914
915                                 /*
916                                  * We must be in the correct protocol thread
917                                  * for this connection.
918                                  */
919                                 KKASSERT(so->so_port == &curthread->td_msgport);
920
921                                 /*
922                                  * Socket is created in state SYN_RECEIVED.
923                                  * Continue processing segment.
924                                  */
925                                 inp = so->so_pcb;
926                                 tp = intotcpcb(inp);
927                                 /*
928                                  * This is what would have happened in
929                                  * tcp_output() when the SYN,ACK was sent.
930                                  */
931                                 tp->snd_up = tp->snd_una;
932                                 tp->snd_max = tp->snd_nxt = tp->iss + 1;
933                                 tp->last_ack_sent = tp->rcv_nxt;
934 /*
935  * XXX possible bug - it doesn't appear that tp->snd_wnd is unscaled
936  * until the _second_ ACK is received:
937  *    rcv SYN (set wscale opts)  --> send SYN/ACK, set snd_wnd = window.
938  *    rcv ACK, calculate tiwin --> process SYN_RECEIVED, determine wscale,
939  *        move to ESTAB, set snd_wnd to tiwin.
940  */
941                                 tp->snd_wnd = tiwin;    /* unscaled */
942                                 goto after_listen;
943                         }
944                         if (thflags & TH_RST) {
945                                 syncache_chkrst(&inc, th);
946                                 goto drop;
947                         }
948                         if (thflags & TH_ACK) {
949                                 syncache_badack(&inc);
950                                 tcpstat.tcps_badsyn++;
951                                 rstreason = BANDLIM_RST_OPENPORT;
952                                 goto dropwithreset;
953                         }
954                         goto drop;
955                 }
956
957                 /*
958                  * Segment's flags are (SYN) or (SYN | FIN).
959                  */
960 #ifdef INET6
961                 /*
962                  * If deprecated address is forbidden,
963                  * we do not accept SYN to deprecated interface
964                  * address to prevent any new inbound connection from
965                  * getting established.
966                  * When we do not accept SYN, we send a TCP RST,
967                  * with deprecated source address (instead of dropping
968                  * it).  We compromise it as it is much better for peer
969                  * to send a RST, and RST will be the final packet
970                  * for the exchange.
971                  *
972                  * If we do not forbid deprecated addresses, we accept
973                  * the SYN packet.  RFC2462 does not suggest dropping
974                  * SYN in this case.
975                  * If we decipher RFC2462 5.5.4, it says like this:
976                  * 1. use of deprecated addr with existing
977                  *    communication is okay - "SHOULD continue to be
978                  *    used"
979                  * 2. use of it with new communication:
980                  *   (2a) "SHOULD NOT be used if alternate address
981                  *        with sufficient scope is available"
982                  *   (2b) nothing mentioned otherwise.
983                  * Here we fall into (2b) case as we have no choice in
984                  * our source address selection - we must obey the peer.
985                  *
986                  * The wording in RFC2462 is confusing, and there are
987                  * multiple description text for deprecated address
988                  * handling - worse, they are not exactly the same.
989                  * I believe 5.5.4 is the best one, so we follow 5.5.4.
990                  */
991                 if (isipv6 && !ip6_use_deprecated) {
992                         struct in6_ifaddr *ia6;
993
994                         if ((ia6 = ip6_getdstifaddr(m)) &&
995                             (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
996                                 tp = NULL;
997                                 rstreason = BANDLIM_RST_OPENPORT;
998                                 goto dropwithreset;
999                         }
1000                 }
1001 #endif
1002                 /*
1003                  * If it is from this socket, drop it, it must be forged.
1004                  * Don't bother responding if the destination was a broadcast.
1005                  */
1006                 if (th->th_dport == th->th_sport) {
1007                         if (isipv6) {
1008                                 if (IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst,
1009                                                        &ip6->ip6_src))
1010                                         goto drop;
1011                         } else {
1012                                 if (ip->ip_dst.s_addr == ip->ip_src.s_addr)
1013                                         goto drop;
1014                         }
1015                 }
1016                 /*
1017                  * RFC1122 4.2.3.10, p. 104: discard bcast/mcast SYN
1018                  *
1019                  * Note that it is quite possible to receive unicast
1020                  * link-layer packets with a broadcast IP address. Use
1021                  * in_broadcast() to find them.
1022                  */
1023                 if (m->m_flags & (M_BCAST | M_MCAST))
1024                         goto drop;
1025                 if (isipv6) {
1026                         if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
1027                             IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
1028                                 goto drop;
1029                 } else {
1030                         if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
1031                             IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
1032                             ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
1033                             in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
1034                                 goto drop;
1035                 }
1036                 /*
1037                  * SYN appears to be valid; create compressed TCP state
1038                  * for syncache, or perform t/tcp connection.
1039                  */
1040                 if (so->so_qlen <= so->so_qlimit) {
1041                         tcp_dooptions(&to, optp, optlen, TRUE);
1042                         if (!syncache_add(&inc, &to, th, so, m))
1043                                 goto drop;
1044
1045                         /*
1046                          * Entry added to syncache, mbuf used to
1047                          * send SYN,ACK packet.
1048                          */
1049                         return(IPPROTO_DONE);
1050                 }
1051                 goto drop;
1052         }
1053
1054 after_listen:
1055         /*
1056          * Should not happen - syncache should pick up these connections.
1057          *
1058          * Once we are past handling listen sockets we must be in the
1059          * correct protocol processing thread.
1060          */
1061         KASSERT(tp->t_state != TCPS_LISTEN, ("tcp_input: TCPS_LISTEN state"));
1062         KKASSERT(so->so_port == &curthread->td_msgport);
1063
1064         /*
1065          * This is the second part of the MSS DoS prevention code (after
1066          * minmss on the sending side) and it deals with too many too small
1067          * tcp packets in a too short timeframe (1 second).
1068          *
1069          * XXX Removed.  This code was crap.  It does not scale to network
1070          *     speed, and default values break NFS.  Gone.
1071          */
1072         /* REMOVED */
1073
1074         /*
1075          * Segment received on connection.
1076          *
1077          * Reset idle time and keep-alive timer.  Don't waste time if less
1078          * then a second has elapsed.
1079          */
1080         if ((int)(ticks - tp->t_rcvtime) > hz)
1081                 tcp_timer_keep_activity(tp, thflags);
1082
1083         /*
1084          * Process options.
1085          * XXX this is tradtitional behavior, may need to be cleaned up.
1086          */
1087         tcp_dooptions(&to, optp, optlen, (thflags & TH_SYN) != 0);
1088         if (tp->t_state == TCPS_SYN_SENT && (thflags & TH_SYN)) {
1089                 if (to.to_flags & TOF_SCALE) {
1090                         tp->t_flags |= TF_RCVD_SCALE;
1091                         tp->requested_s_scale = to.to_requested_s_scale;
1092                 }
1093                 if (to.to_flags & TOF_TS) {
1094                         tp->t_flags |= TF_RCVD_TSTMP;
1095                         tp->ts_recent = to.to_tsval;
1096                         tp->ts_recent_age = ticks;
1097                 }
1098                 if (!(to.to_flags & TOF_MSS))
1099                         to.to_mss = 0;
1100                 tcp_mss(tp, to.to_mss);
1101                 /*
1102                  * Only set the TF_SACK_PERMITTED per-connection flag
1103                  * if we got a SACK_PERMITTED option from the other side
1104                  * and the global tcp_do_sack variable is true.
1105                  */
1106                 if (tcp_do_sack && (to.to_flags & TOF_SACK_PERMITTED))
1107                         tp->t_flags |= TF_SACK_PERMITTED;
1108         }
1109
1110         /*
1111          * Header prediction: check for the two common cases
1112          * of a uni-directional data xfer.  If the packet has
1113          * no control flags, is in-sequence, the window didn't
1114          * change and we're not retransmitting, it's a
1115          * candidate.  If the length is zero and the ack moved
1116          * forward, we're the sender side of the xfer.  Just
1117          * free the data acked & wake any higher level process
1118          * that was blocked waiting for space.  If the length
1119          * is non-zero and the ack didn't move, we're the
1120          * receiver side.  If we're getting packets in-order
1121          * (the reassembly queue is empty), add the data to
1122          * the socket buffer and note that we need a delayed ack.
1123          * Make sure that the hidden state-flags are also off.
1124          * Since we check for TCPS_ESTABLISHED above, it can only
1125          * be TH_NEEDSYN.
1126          */
1127         if (tp->t_state == TCPS_ESTABLISHED &&
1128             (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
1129             !(tp->t_flags & (TF_NEEDSYN | TF_NEEDFIN)) &&
1130             (!(to.to_flags & TOF_TS) ||
1131              TSTMP_GEQ(to.to_tsval, tp->ts_recent)) &&
1132             th->th_seq == tp->rcv_nxt &&
1133             tp->snd_nxt == tp->snd_max) {
1134
1135                 /*
1136                  * If last ACK falls within this segment's sequence numbers,
1137                  * record the timestamp.
1138                  * NOTE that the test is modified according to the latest
1139                  * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1140                  */
1141                 if ((to.to_flags & TOF_TS) &&
1142                     SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
1143                         tp->ts_recent_age = ticks;
1144                         tp->ts_recent = to.to_tsval;
1145                 }
1146
1147                 if (tlen == 0) {
1148                         if (SEQ_GT(th->th_ack, tp->snd_una) &&
1149                             SEQ_LEQ(th->th_ack, tp->snd_max) &&
1150                             tp->snd_cwnd >= tp->snd_wnd &&
1151                             !IN_FASTRECOVERY(tp)) {
1152                                 /*
1153                                  * This is a pure ack for outstanding data.
1154                                  */
1155                                 ++tcpstat.tcps_predack;
1156                                 /*
1157                                  * "bad retransmit" recovery
1158                                  *
1159                                  * If Eifel detection applies, then
1160                                  * it is deterministic, so use it
1161                                  * unconditionally over the old heuristic.
1162                                  * Otherwise, fall back to the old heuristic.
1163                                  */
1164                                 if (tcp_do_eifel_detect &&
1165                                     (to.to_flags & TOF_TS) && to.to_tsecr &&
1166                                     (tp->t_flags & TF_FIRSTACCACK)) {
1167                                         /* Eifel detection applicable. */
1168                                         if (to.to_tsecr < tp->t_rexmtTS) {
1169                                                 tcp_revert_congestion_state(tp);
1170                                                 ++tcpstat.tcps_eifeldetected;
1171                                                 if (tp->t_rxtshift != 1 ||
1172                                                     ticks >= tp->t_badrxtwin)
1173                                                         ++tcpstat.tcps_rttcantdetect;
1174                                         }
1175                                 } else if (tp->t_rxtshift == 1 &&
1176                                            ticks < tp->t_badrxtwin) {
1177                                         tcp_revert_congestion_state(tp);
1178                                         ++tcpstat.tcps_rttdetected;
1179                                 }
1180                                 tp->t_flags &= ~(TF_FIRSTACCACK |
1181                                                  TF_FASTREXMT | TF_EARLYREXMT);
1182                                 /*
1183                                  * Recalculate the retransmit timer / rtt.
1184                                  *
1185                                  * Some machines (certain windows boxes)
1186                                  * send broken timestamp replies during the
1187                                  * SYN+ACK phase, ignore timestamps of 0.
1188                                  */
1189                                 if ((to.to_flags & TOF_TS) && to.to_tsecr) {
1190                                         tcp_xmit_timer(tp,
1191                                                        ticks - to.to_tsecr + 1);
1192                                 } else if (tp->t_rtttime &&
1193                                            SEQ_GT(th->th_ack, tp->t_rtseq)) {
1194                                         tcp_xmit_timer(tp,
1195                                                        ticks - tp->t_rtttime);
1196                                 }
1197                                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
1198                                 acked = th->th_ack - tp->snd_una;
1199                                 tcpstat.tcps_rcvackpack++;
1200                                 tcpstat.tcps_rcvackbyte += acked;
1201                                 sbdrop(&so->so_snd.sb, acked);
1202                                 tp->snd_recover = th->th_ack - 1;
1203                                 tp->snd_una = th->th_ack;
1204                                 tp->t_dupacks = 0;
1205                                 /*
1206                                  * Update window information.
1207                                  */
1208                                 if (tiwin != tp->snd_wnd &&
1209                                     acceptable_window_update(tp, th, tiwin)) {
1210                                         /* keep track of pure window updates */
1211                                         if (tp->snd_wl2 == th->th_ack &&
1212                                             tiwin > tp->snd_wnd)
1213                                                 tcpstat.tcps_rcvwinupd++;
1214                                         tp->snd_wnd = tiwin;
1215                                         tp->snd_wl1 = th->th_seq;
1216                                         tp->snd_wl2 = th->th_ack;
1217                                         if (tp->snd_wnd > tp->max_sndwnd)
1218                                                 tp->max_sndwnd = tp->snd_wnd;
1219                                 }
1220                                 m_freem(m);
1221                                 ND6_HINT(tp); /* some progress has been done */
1222                                 /*
1223                                  * If all outstanding data are acked, stop
1224                                  * retransmit timer, otherwise restart timer
1225                                  * using current (possibly backed-off) value.
1226                                  * If process is waiting for space,
1227                                  * wakeup/selwakeup/signal.  If data
1228                                  * are ready to send, let tcp_output
1229                                  * decide between more output or persist.
1230                                  */
1231                                 if (tp->snd_una == tp->snd_max) {
1232                                         tcp_callout_stop(tp, tp->tt_rexmt);
1233                                 } else if (!tcp_callout_active(tp,
1234                                             tp->tt_persist)) {
1235                                         tcp_callout_reset(tp, tp->tt_rexmt,
1236                                             tp->t_rxtcur, tcp_timer_rexmt);
1237                                 }
1238                                 sowwakeup(so);
1239                                 if (so->so_snd.ssb_cc > 0)
1240                                         tcp_output(tp);
1241                                 return(IPPROTO_DONE);
1242                         }
1243                 } else if (tiwin == tp->snd_wnd &&
1244                     th->th_ack == tp->snd_una &&
1245                     LIST_EMPTY(&tp->t_segq) &&
1246                     tlen <= ssb_space(&so->so_rcv)) {
1247                         u_long newsize = 0;     /* automatic sockbuf scaling */
1248                         /*
1249                          * This is a pure, in-sequence data packet
1250                          * with nothing on the reassembly queue and
1251                          * we have enough buffer space to take it.
1252                          */
1253                         ++tcpstat.tcps_preddat;
1254                         tp->rcv_nxt += tlen;
1255                         tcpstat.tcps_rcvpack++;
1256                         tcpstat.tcps_rcvbyte += tlen;
1257                         ND6_HINT(tp);   /* some progress has been done */
1258                 /*
1259                  * Automatic sizing of receive socket buffer.  Often the send
1260                  * buffer size is not optimally adjusted to the actual network
1261                  * conditions at hand (delay bandwidth product).  Setting the
1262                  * buffer size too small limits throughput on links with high
1263                  * bandwidth and high delay (eg. trans-continental/oceanic links).
1264                  *
1265                  * On the receive side the socket buffer memory is only rarely
1266                  * used to any significant extent.  This allows us to be much
1267                  * more aggressive in scaling the receive socket buffer.  For
1268                  * the case that the buffer space is actually used to a large
1269                  * extent and we run out of kernel memory we can simply drop
1270                  * the new segments; TCP on the sender will just retransmit it
1271                  * later.  Setting the buffer size too big may only consume too
1272                  * much kernel memory if the application doesn't read() from
1273                  * the socket or packet loss or reordering makes use of the
1274                  * reassembly queue.
1275                  *
1276                  * The criteria to step up the receive buffer one notch are:
1277                  *  1. the number of bytes received during the time it takes
1278                  *     one timestamp to be reflected back to us (the RTT);
1279                  *  2. received bytes per RTT is within seven eighth of the
1280                  *     current socket buffer size;
1281                  *  3. receive buffer size has not hit maximal automatic size;
1282                  *
1283                  * This algorithm does one step per RTT at most and only if
1284                  * we receive a bulk stream w/o packet losses or reorderings.
1285                  * Shrinking the buffer during idle times is not necessary as
1286                  * it doesn't consume any memory when idle.
1287                  *
1288                  * TODO: Only step up if the application is actually serving
1289                  * the buffer to better manage the socket buffer resources.
1290                  */
1291                         if (tcp_do_autorcvbuf &&
1292                             to.to_tsecr &&
1293                             (so->so_rcv.ssb_flags & SSB_AUTOSIZE)) {
1294                                 if (to.to_tsecr > tp->rfbuf_ts &&
1295                                     to.to_tsecr - tp->rfbuf_ts < hz) {
1296                                         if (tp->rfbuf_cnt >
1297                                             (so->so_rcv.ssb_hiwat / 8 * 7) &&
1298                                             so->so_rcv.ssb_hiwat <
1299                                             tcp_autorcvbuf_max) {
1300                                                 newsize =
1301                                                     ulmin(so->so_rcv.ssb_hiwat +
1302                                                           tcp_autorcvbuf_inc,
1303                                                           tcp_autorcvbuf_max);
1304                                         }
1305                                         /* Start over with next RTT. */
1306                                         tp->rfbuf_ts = 0;
1307                                         tp->rfbuf_cnt = 0;
1308                                 } else
1309                                         tp->rfbuf_cnt += tlen;  /* add up */
1310                         }
1311                         /*
1312                          * Add data to socket buffer.
1313                          */
1314                         if (so->so_state & SS_CANTRCVMORE) {
1315                                 m_freem(m);
1316                         } else {
1317                                 /*
1318                                  * Set new socket buffer size, give up when
1319                                  * limit is reached.
1320                                  *
1321                                  * Adjusting the size can mess up ACK
1322                                  * sequencing when pure window updates are
1323                                  * being avoided (which is the default),
1324                                  * so force an ack.
1325                                  */
1326                                 lwkt_gettoken(&so->so_rcv.ssb_token);
1327                                 if (newsize) {
1328                                         tp->t_flags |= TF_RXRESIZED;
1329                                         if (!ssb_reserve(&so->so_rcv, newsize,
1330                                                          so, NULL)) {
1331                                                 atomic_clear_int(&so->so_rcv.ssb_flags, SSB_AUTOSIZE);
1332                                         }
1333                                         if (newsize >=
1334                                             (TCP_MAXWIN << tp->rcv_scale)) {
1335                                                 atomic_clear_int(&so->so_rcv.ssb_flags, SSB_AUTOSIZE);
1336                                         }
1337                                 }
1338                                 m_adj(m, drop_hdrlen); /* delayed header drop */
1339                                 ssb_appendstream(&so->so_rcv, m);
1340                                 lwkt_reltoken(&so->so_rcv.ssb_token);
1341                         }
1342                         sorwakeup(so);
1343                         /*
1344                          * This code is responsible for most of the ACKs
1345                          * the TCP stack sends back after receiving a data
1346                          * packet.  Note that the DELAY_ACK check fails if
1347                          * the delack timer is already running, which results
1348                          * in an ack being sent every other packet (which is
1349                          * what we want).
1350                          *
1351                          * We then further aggregate acks by not actually
1352                          * sending one until the protocol thread has completed
1353                          * processing the current backlog of packets.  This
1354                          * does not delay the ack any further, but allows us
1355                          * to take advantage of the packet aggregation that
1356                          * high speed NICs do (usually blocks of 8-10 packets)
1357                          * to send a single ack rather then four or five acks,
1358                          * greatly reducing the ack rate, the return channel
1359                          * bandwidth, and the protocol overhead on both ends.
1360                          *
1361                          * Since this also has the effect of slowing down
1362                          * the exponential slow-start ramp-up, systems with 
1363                          * very large bandwidth-delay products might want
1364                          * to turn the feature off.
1365                          */
1366                         if (DELAY_ACK(tp)) {
1367                                 tcp_callout_reset(tp, tp->tt_delack,
1368                                     tcp_delacktime, tcp_timer_delack);
1369                         } else if (tcp_aggregate_acks) {
1370                                 tp->t_flags |= TF_ACKNOW;
1371                                 if (!(tp->t_flags & TF_ONOUTPUTQ)) {
1372                                         tp->t_flags |= TF_ONOUTPUTQ;
1373                                         tp->tt_cpu = mycpu->gd_cpuid;
1374                                         TAILQ_INSERT_TAIL(
1375                                             &tcpcbackq[tp->tt_cpu],
1376                                             tp, t_outputq);
1377                                 }
1378                         } else {
1379                                 tp->t_flags |= TF_ACKNOW;
1380                                 tcp_output(tp);
1381                         }
1382                         return(IPPROTO_DONE);
1383                 }
1384         }
1385
1386         /*
1387          * Calculate amount of space in receive window,
1388          * and then do TCP input processing.
1389          * Receive window is amount of space in rcv queue,
1390          * but not less than advertised window.
1391          */
1392         recvwin = ssb_space(&so->so_rcv);
1393         if (recvwin < 0)
1394                 recvwin = 0;
1395         tp->rcv_wnd = imax(recvwin, (int)(tp->rcv_adv - tp->rcv_nxt));
1396
1397         /* Reset receive buffer auto scaling when not in bulk receive mode. */
1398         tp->rfbuf_ts = 0;
1399         tp->rfbuf_cnt = 0;
1400
1401         switch (tp->t_state) {
1402         /*
1403          * If the state is SYN_RECEIVED:
1404          *      if seg contains an ACK, but not for our SYN/ACK, send a RST.
1405          */
1406         case TCPS_SYN_RECEIVED:
1407                 if ((thflags & TH_ACK) &&
1408                     (SEQ_LEQ(th->th_ack, tp->snd_una) ||
1409                      SEQ_GT(th->th_ack, tp->snd_max))) {
1410                                 rstreason = BANDLIM_RST_OPENPORT;
1411                                 goto dropwithreset;
1412                 }
1413                 break;
1414
1415         /*
1416          * If the state is SYN_SENT:
1417          *      if seg contains an ACK, but not for our SYN, drop the input.
1418          *      if seg contains a RST, then drop the connection.
1419          *      if seg does not contain SYN, then drop it.
1420          * Otherwise this is an acceptable SYN segment
1421          *      initialize tp->rcv_nxt and tp->irs
1422          *      if seg contains ack then advance tp->snd_una
1423          *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
1424          *      arrange for segment to be acked (eventually)
1425          *      continue processing rest of data/controls, beginning with URG
1426          */
1427         case TCPS_SYN_SENT:
1428                 if ((thflags & TH_ACK) &&
1429                     (SEQ_LEQ(th->th_ack, tp->iss) ||
1430                      SEQ_GT(th->th_ack, tp->snd_max))) {
1431                         rstreason = BANDLIM_UNLIMITED;
1432                         goto dropwithreset;
1433                 }
1434                 if (thflags & TH_RST) {
1435                         if (thflags & TH_ACK)
1436                                 tp = tcp_drop(tp, ECONNREFUSED);
1437                         goto drop;
1438                 }
1439                 if (!(thflags & TH_SYN))
1440                         goto drop;
1441                 tp->snd_wnd = th->th_win;       /* initial send window */
1442
1443                 tp->irs = th->th_seq;
1444                 tcp_rcvseqinit(tp);
1445                 if (thflags & TH_ACK) {
1446                         /* Our SYN was acked. */
1447                         tcpstat.tcps_connects++;
1448                         soisconnected(so);
1449                         /* Do window scaling on this connection? */
1450                         if ((tp->t_flags & (TF_RCVD_SCALE | TF_REQ_SCALE)) ==
1451                             (TF_RCVD_SCALE | TF_REQ_SCALE)) {
1452                                 tp->snd_scale = tp->requested_s_scale;
1453                                 tp->rcv_scale = tp->request_r_scale;
1454                         }
1455                         tp->rcv_adv += tp->rcv_wnd;
1456                         tp->snd_una++;          /* SYN is acked */
1457                         tcp_callout_stop(tp, tp->tt_rexmt);
1458                         /*
1459                          * If there's data, delay ACK; if there's also a FIN
1460                          * ACKNOW will be turned on later.
1461                          */
1462                         if (DELAY_ACK(tp) && tlen != 0) {
1463                                 tcp_callout_reset(tp, tp->tt_delack,
1464                                     tcp_delacktime, tcp_timer_delack);
1465                         } else {
1466                                 tp->t_flags |= TF_ACKNOW;
1467                         }
1468                         /*
1469                          * Received <SYN,ACK> in SYN_SENT[*] state.
1470                          * Transitions:
1471                          *      SYN_SENT  --> ESTABLISHED
1472                          *      SYN_SENT* --> FIN_WAIT_1
1473                          */
1474                         tp->t_starttime = ticks;
1475                         if (tp->t_flags & TF_NEEDFIN) {
1476                                 tp->t_state = TCPS_FIN_WAIT_1;
1477                                 tp->t_flags &= ~TF_NEEDFIN;
1478                                 thflags &= ~TH_SYN;
1479                         } else {
1480                                 tcp_established(tp);
1481                         }
1482                 } else {
1483                         /*
1484                          * Received initial SYN in SYN-SENT[*] state =>
1485                          * simultaneous open.
1486                          * Do 3-way handshake:
1487                          *        SYN-SENT -> SYN-RECEIVED
1488                          *        SYN-SENT* -> SYN-RECEIVED*
1489                          */
1490                         tp->t_flags |= TF_ACKNOW;
1491                         tcp_callout_stop(tp, tp->tt_rexmt);
1492                         tp->t_state = TCPS_SYN_RECEIVED;
1493                 }
1494
1495                 /*
1496                  * Advance th->th_seq to correspond to first data byte.
1497                  * If data, trim to stay within window,
1498                  * dropping FIN if necessary.
1499                  */
1500                 th->th_seq++;
1501                 if (tlen > tp->rcv_wnd) {
1502                         todrop = tlen - tp->rcv_wnd;
1503                         m_adj(m, -todrop);
1504                         tlen = tp->rcv_wnd;
1505                         thflags &= ~TH_FIN;
1506                         tcpstat.tcps_rcvpackafterwin++;
1507                         tcpstat.tcps_rcvbyteafterwin += todrop;
1508                 }
1509                 tp->snd_wl1 = th->th_seq - 1;
1510                 tp->rcv_up = th->th_seq;
1511                 /*
1512                  * Client side of transaction: already sent SYN and data.
1513                  * If the remote host used T/TCP to validate the SYN,
1514                  * our data will be ACK'd; if so, enter normal data segment
1515                  * processing in the middle of step 5, ack processing.
1516                  * Otherwise, goto step 6.
1517                  */
1518                 if (thflags & TH_ACK)
1519                         goto process_ACK;
1520
1521                 goto step6;
1522
1523         /*
1524          * If the state is LAST_ACK or CLOSING or TIME_WAIT:
1525          *      do normal processing (we no longer bother with T/TCP).
1526          */
1527         case TCPS_LAST_ACK:
1528         case TCPS_CLOSING:
1529         case TCPS_TIME_WAIT:
1530                 break;  /* continue normal processing */
1531         }
1532
1533         /*
1534          * States other than LISTEN or SYN_SENT.
1535          * First check the RST flag and sequence number since reset segments
1536          * are exempt from the timestamp and connection count tests.  This
1537          * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
1538          * below which allowed reset segments in half the sequence space
1539          * to fall though and be processed (which gives forged reset
1540          * segments with a random sequence number a 50 percent chance of
1541          * killing a connection).
1542          * Then check timestamp, if present.
1543          * Then check the connection count, if present.
1544          * Then check that at least some bytes of segment are within
1545          * receive window.  If segment begins before rcv_nxt,
1546          * drop leading data (and SYN); if nothing left, just ack.
1547          *
1548          *
1549          * If the RST bit is set, check the sequence number to see
1550          * if this is a valid reset segment.
1551          * RFC 793 page 37:
1552          *   In all states except SYN-SENT, all reset (RST) segments
1553          *   are validated by checking their SEQ-fields.  A reset is
1554          *   valid if its sequence number is in the window.
1555          * Note: this does not take into account delayed ACKs, so
1556          *   we should test against last_ack_sent instead of rcv_nxt.
1557          *   The sequence number in the reset segment is normally an
1558          *   echo of our outgoing acknowledgement numbers, but some hosts
1559          *   send a reset with the sequence number at the rightmost edge
1560          *   of our receive window, and we have to handle this case.
1561          * If we have multiple segments in flight, the intial reset
1562          * segment sequence numbers will be to the left of last_ack_sent,
1563          * but they will eventually catch up.
1564          * In any case, it never made sense to trim reset segments to
1565          * fit the receive window since RFC 1122 says:
1566          *   4.2.2.12  RST Segment: RFC-793 Section 3.4
1567          *
1568          *    A TCP SHOULD allow a received RST segment to include data.
1569          *
1570          *    DISCUSSION
1571          *         It has been suggested that a RST segment could contain
1572          *         ASCII text that encoded and explained the cause of the
1573          *         RST.  No standard has yet been established for such
1574          *         data.
1575          *
1576          * If the reset segment passes the sequence number test examine
1577          * the state:
1578          *    SYN_RECEIVED STATE:
1579          *      If passive open, return to LISTEN state.
1580          *      If active open, inform user that connection was refused.
1581          *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, CLOSE_WAIT STATES:
1582          *      Inform user that connection was reset, and close tcb.
1583          *    CLOSING, LAST_ACK STATES:
1584          *      Close the tcb.
1585          *    TIME_WAIT STATE:
1586          *      Drop the segment - see Stevens, vol. 2, p. 964 and
1587          *      RFC 1337.
1588          */
1589         if (thflags & TH_RST) {
1590                 if (SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
1591                     SEQ_LEQ(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
1592                         switch (tp->t_state) {
1593
1594                         case TCPS_SYN_RECEIVED:
1595                                 so->so_error = ECONNREFUSED;
1596                                 goto close;
1597
1598                         case TCPS_ESTABLISHED:
1599                         case TCPS_FIN_WAIT_1:
1600                         case TCPS_FIN_WAIT_2:
1601                         case TCPS_CLOSE_WAIT:
1602                                 so->so_error = ECONNRESET;
1603                         close:
1604                                 tp->t_state = TCPS_CLOSED;
1605                                 tcpstat.tcps_drops++;
1606                                 tp = tcp_close(tp);
1607                                 break;
1608
1609                         case TCPS_CLOSING:
1610                         case TCPS_LAST_ACK:
1611                                 tp = tcp_close(tp);
1612                                 break;
1613
1614                         case TCPS_TIME_WAIT:
1615                                 break;
1616                         }
1617                 }
1618                 goto drop;
1619         }
1620
1621         /*
1622          * RFC 1323 PAWS: If we have a timestamp reply on this segment
1623          * and it's less than ts_recent, drop it.
1624          */
1625         if ((to.to_flags & TOF_TS) && tp->ts_recent != 0 &&
1626             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
1627
1628                 /* Check to see if ts_recent is over 24 days old.  */
1629                 if ((int)(ticks - tp->ts_recent_age) > TCP_PAWS_IDLE) {
1630                         /*
1631                          * Invalidate ts_recent.  If this segment updates
1632                          * ts_recent, the age will be reset later and ts_recent
1633                          * will get a valid value.  If it does not, setting
1634                          * ts_recent to zero will at least satisfy the
1635                          * requirement that zero be placed in the timestamp
1636                          * echo reply when ts_recent isn't valid.  The
1637                          * age isn't reset until we get a valid ts_recent
1638                          * because we don't want out-of-order segments to be
1639                          * dropped when ts_recent is old.
1640                          */
1641                         tp->ts_recent = 0;
1642                 } else {
1643                         tcpstat.tcps_rcvduppack++;
1644                         tcpstat.tcps_rcvdupbyte += tlen;
1645                         tcpstat.tcps_pawsdrop++;
1646                         if (tlen)
1647                                 goto dropafterack;
1648                         goto drop;
1649                 }
1650         }
1651
1652         /*
1653          * In the SYN-RECEIVED state, validate that the packet belongs to
1654          * this connection before trimming the data to fit the receive
1655          * window.  Check the sequence number versus IRS since we know
1656          * the sequence numbers haven't wrapped.  This is a partial fix
1657          * for the "LAND" DoS attack.
1658          */
1659         if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
1660                 rstreason = BANDLIM_RST_OPENPORT;
1661                 goto dropwithreset;
1662         }
1663
1664         todrop = tp->rcv_nxt - th->th_seq;
1665         if (todrop > 0) {
1666                 if (TCP_DO_SACK(tp)) {
1667                         /* Report duplicate segment at head of packet. */
1668                         tp->reportblk.rblk_start = th->th_seq;
1669                         tp->reportblk.rblk_end = TCP_SACK_BLKEND(
1670                             th->th_seq + tlen, thflags);
1671                         if (SEQ_GT(tp->reportblk.rblk_end, tp->rcv_nxt))
1672                                 tp->reportblk.rblk_end = tp->rcv_nxt;
1673                         tp->t_flags |= (TF_DUPSEG | TF_SACKLEFT | TF_ACKNOW);
1674                 }
1675                 if (thflags & TH_SYN) {
1676                         thflags &= ~TH_SYN;
1677                         th->th_seq++;
1678                         if (th->th_urp > 1)
1679                                 th->th_urp--;
1680                         else
1681                                 thflags &= ~TH_URG;
1682                         todrop--;
1683                 }
1684                 /*
1685                  * Following if statement from Stevens, vol. 2, p. 960.
1686                  */
1687                 if (todrop > tlen ||
1688                     (todrop == tlen && !(thflags & TH_FIN))) {
1689                         /*
1690                          * Any valid FIN must be to the left of the window.
1691                          * At this point the FIN must be a duplicate or out
1692                          * of sequence; drop it.
1693                          */
1694                         thflags &= ~TH_FIN;
1695
1696                         /*
1697                          * Send an ACK to resynchronize and drop any data.
1698                          * But keep on processing for RST or ACK.
1699                          */
1700                         tp->t_flags |= TF_ACKNOW;
1701                         todrop = tlen;
1702                         tcpstat.tcps_rcvduppack++;
1703                         tcpstat.tcps_rcvdupbyte += todrop;
1704                 } else {
1705                         tcpstat.tcps_rcvpartduppack++;
1706                         tcpstat.tcps_rcvpartdupbyte += todrop;
1707                 }
1708                 drop_hdrlen += todrop;  /* drop from the top afterwards */
1709                 th->th_seq += todrop;
1710                 tlen -= todrop;
1711                 if (th->th_urp > todrop)
1712                         th->th_urp -= todrop;
1713                 else {
1714                         thflags &= ~TH_URG;
1715                         th->th_urp = 0;
1716                 }
1717         }
1718
1719         /*
1720          * If new data are received on a connection after the
1721          * user processes are gone, then RST the other end.
1722          */
1723         if ((so->so_state & SS_NOFDREF) &&
1724             tp->t_state > TCPS_CLOSE_WAIT && tlen) {
1725                 tp = tcp_close(tp);
1726                 tcpstat.tcps_rcvafterclose++;
1727                 rstreason = BANDLIM_UNLIMITED;
1728                 goto dropwithreset;
1729         }
1730
1731         /*
1732          * If segment ends after window, drop trailing data
1733          * (and PUSH and FIN); if nothing left, just ACK.
1734          */
1735         todrop = (th->th_seq + tlen) - (tp->rcv_nxt + tp->rcv_wnd);
1736         if (todrop > 0) {
1737                 tcpstat.tcps_rcvpackafterwin++;
1738                 if (todrop >= tlen) {
1739                         tcpstat.tcps_rcvbyteafterwin += tlen;
1740                         /*
1741                          * If a new connection request is received
1742                          * while in TIME_WAIT, drop the old connection
1743                          * and start over if the sequence numbers
1744                          * are above the previous ones.
1745                          */
1746                         if (thflags & TH_SYN &&
1747                             tp->t_state == TCPS_TIME_WAIT &&
1748                             SEQ_GT(th->th_seq, tp->rcv_nxt)) {
1749                                 tp = tcp_close(tp);
1750                                 goto findpcb;
1751                         }
1752                         /*
1753                          * If window is closed can only take segments at
1754                          * window edge, and have to drop data and PUSH from
1755                          * incoming segments.  Continue processing, but
1756                          * remember to ack.  Otherwise, drop segment
1757                          * and ack.
1758                          */
1759                         if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
1760                                 tp->t_flags |= TF_ACKNOW;
1761                                 tcpstat.tcps_rcvwinprobe++;
1762                         } else
1763                                 goto dropafterack;
1764                 } else
1765                         tcpstat.tcps_rcvbyteafterwin += todrop;
1766                 m_adj(m, -todrop);
1767                 tlen -= todrop;
1768                 thflags &= ~(TH_PUSH | TH_FIN);
1769         }
1770
1771         /*
1772          * If last ACK falls within this segment's sequence numbers,
1773          * record its timestamp.
1774          * NOTE:
1775          * 1) That the test incorporates suggestions from the latest
1776          *    proposal of the tcplw@cray.com list (Braden 1993/04/26).
1777          * 2) That updating only on newer timestamps interferes with
1778          *    our earlier PAWS tests, so this check should be solely
1779          *    predicated on the sequence space of this segment.
1780          * 3) That we modify the segment boundary check to be
1781          *        Last.ACK.Sent <= SEG.SEQ + SEG.LEN
1782          *    instead of RFC1323's
1783          *        Last.ACK.Sent < SEG.SEQ + SEG.LEN,
1784          *    This modified check allows us to overcome RFC1323's
1785          *    limitations as described in Stevens TCP/IP Illustrated
1786          *    Vol. 2 p.869. In such cases, we can still calculate the
1787          *    RTT correctly when RCV.NXT == Last.ACK.Sent.
1788          */
1789         if ((to.to_flags & TOF_TS) && SEQ_LEQ(th->th_seq, tp->last_ack_sent) &&
1790             SEQ_LEQ(tp->last_ack_sent, (th->th_seq + tlen
1791                                         + ((thflags & TH_SYN) != 0)
1792                                         + ((thflags & TH_FIN) != 0)))) {
1793                 tp->ts_recent_age = ticks;
1794                 tp->ts_recent = to.to_tsval;
1795         }
1796
1797         /*
1798          * If a SYN is in the window, then this is an
1799          * error and we send an RST and drop the connection.
1800          */
1801         if (thflags & TH_SYN) {
1802                 tp = tcp_drop(tp, ECONNRESET);
1803                 rstreason = BANDLIM_UNLIMITED;
1804                 goto dropwithreset;
1805         }
1806
1807         /*
1808          * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
1809          * flag is on (half-synchronized state), then queue data for
1810          * later processing; else drop segment and return.
1811          */
1812         if (!(thflags & TH_ACK)) {
1813                 if (tp->t_state == TCPS_SYN_RECEIVED ||
1814                     (tp->t_flags & TF_NEEDSYN))
1815                         goto step6;
1816                 else
1817                         goto drop;
1818         }
1819
1820         /*
1821          * Ack processing.
1822          */
1823         switch (tp->t_state) {
1824         /*
1825          * In SYN_RECEIVED state, the ACK acknowledges our SYN, so enter
1826          * ESTABLISHED state and continue processing.
1827          * The ACK was checked above.
1828          */
1829         case TCPS_SYN_RECEIVED:
1830
1831                 tcpstat.tcps_connects++;
1832                 soisconnected(so);
1833                 /* Do window scaling? */
1834                 if ((tp->t_flags & (TF_RCVD_SCALE | TF_REQ_SCALE)) ==
1835                     (TF_RCVD_SCALE | TF_REQ_SCALE)) {
1836                         tp->snd_scale = tp->requested_s_scale;
1837                         tp->rcv_scale = tp->request_r_scale;
1838                 }
1839                 /*
1840                  * Make transitions:
1841                  *      SYN-RECEIVED  -> ESTABLISHED
1842                  *      SYN-RECEIVED* -> FIN-WAIT-1
1843                  */
1844                 tp->t_starttime = ticks;
1845                 if (tp->t_flags & TF_NEEDFIN) {
1846                         tp->t_state = TCPS_FIN_WAIT_1;
1847                         tp->t_flags &= ~TF_NEEDFIN;
1848                 } else {
1849                         tcp_established(tp);
1850                 }
1851                 /*
1852                  * If segment contains data or ACK, will call tcp_reass()
1853                  * later; if not, do so now to pass queued data to user.
1854                  */
1855                 if (tlen == 0 && !(thflags & TH_FIN))
1856                         tcp_reass(tp, NULL, NULL, NULL);
1857                 /* fall into ... */
1858
1859         /*
1860          * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
1861          * ACKs.  If the ack is in the range
1862          *      tp->snd_una < th->th_ack <= tp->snd_max
1863          * then advance tp->snd_una to th->th_ack and drop
1864          * data from the retransmission queue.  If this ACK reflects
1865          * more up to date window information we update our window information.
1866          */
1867         case TCPS_ESTABLISHED:
1868         case TCPS_FIN_WAIT_1:
1869         case TCPS_FIN_WAIT_2:
1870         case TCPS_CLOSE_WAIT:
1871         case TCPS_CLOSING:
1872         case TCPS_LAST_ACK:
1873         case TCPS_TIME_WAIT:
1874
1875                 if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
1876                         if (TCP_DO_SACK(tp))
1877                                 tcp_sack_update_scoreboard(tp, &to);
1878                         if (tlen != 0 || tiwin != tp->snd_wnd) {
1879                                 tp->t_dupacks = 0;
1880                                 break;
1881                         }
1882                         tcpstat.tcps_rcvdupack++;
1883                         if (!tcp_callout_active(tp, tp->tt_rexmt) ||
1884                             th->th_ack != tp->snd_una) {
1885                                 tp->t_dupacks = 0;
1886                                 break;
1887                         }
1888                         /*
1889                          * We have outstanding data (other than
1890                          * a window probe), this is a completely
1891                          * duplicate ack (ie, window info didn't
1892                          * change), the ack is the biggest we've
1893                          * seen and we've seen exactly our rexmt
1894                          * threshhold of them, so assume a packet
1895                          * has been dropped and retransmit it.
1896                          * Kludge snd_nxt & the congestion
1897                          * window so we send only this one
1898                          * packet.
1899                          */
1900                         if (IN_FASTRECOVERY(tp)) {
1901                                 if (TCP_DO_SACK(tp)) {
1902                                         /* No artifical cwnd inflation. */
1903                                         tcp_sack_rexmt(tp, th);
1904                                 } else {
1905                                         /*
1906                                          * Dup acks mean that packets
1907                                          * have left the network
1908                                          * (they're now cached at the
1909                                          * receiver) so bump cwnd by
1910                                          * the amount in the receiver
1911                                          * to keep a constant cwnd
1912                                          * packets in the network.
1913                                          */
1914                                         tp->snd_cwnd += tp->t_maxseg;
1915                                         tcp_output(tp);
1916                                 }
1917                         } else if (SEQ_LT(th->th_ack, tp->snd_recover)) {
1918                                 tp->t_dupacks = 0;
1919                                 break;
1920                         } else if (++tp->t_dupacks == tcprexmtthresh) {
1921                                 tcp_seq old_snd_nxt;
1922                                 u_int win;
1923
1924 fastretransmit:
1925                                 if (tcp_do_eifel_detect &&
1926                                     (tp->t_flags & TF_RCVD_TSTMP)) {
1927                                         tcp_save_congestion_state(tp);
1928                                         tp->t_flags |= TF_FASTREXMT;
1929                                 }
1930                                 /*
1931                                  * We know we're losing at the current
1932                                  * window size, so do congestion avoidance:
1933                                  * set ssthresh to half the current window
1934                                  * and pull our congestion window back to the
1935                                  * new ssthresh.
1936                                  */
1937                                 win = min(tp->snd_wnd, tp->snd_cwnd) / 2 /
1938                                     tp->t_maxseg;
1939                                 if (win < 2)
1940                                         win = 2;
1941                                 tp->snd_ssthresh = win * tp->t_maxseg;
1942                                 ENTER_FASTRECOVERY(tp);
1943                                 tp->snd_recover = tp->snd_max;
1944                                 tcp_callout_stop(tp, tp->tt_rexmt);
1945                                 tp->t_rtttime = 0;
1946                                 old_snd_nxt = tp->snd_nxt;
1947                                 tp->snd_nxt = th->th_ack;
1948                                 tp->snd_cwnd = tp->t_maxseg;
1949                                 tcp_output(tp);
1950                                 ++tcpstat.tcps_sndfastrexmit;
1951                                 tp->snd_cwnd = tp->snd_ssthresh;
1952                                 tp->rexmt_high = tp->snd_nxt;
1953                                 if (SEQ_GT(old_snd_nxt, tp->snd_nxt))
1954                                         tp->snd_nxt = old_snd_nxt;
1955                                 KASSERT(tp->snd_limited <= 2,
1956                                     ("tp->snd_limited too big"));
1957                                 if (TCP_DO_SACK(tp))
1958                                         tcp_sack_rexmt(tp, th);
1959                                 else
1960                                         tp->snd_cwnd += tp->t_maxseg *
1961                                             (tp->t_dupacks - tp->snd_limited);
1962                         } else if (tcp_do_limitedtransmit) {
1963                                 u_long oldcwnd = tp->snd_cwnd;
1964                                 tcp_seq oldsndmax = tp->snd_max;
1965                                 tcp_seq oldsndnxt = tp->snd_nxt;
1966                                 /* outstanding data */
1967                                 uint32_t ownd = tp->snd_max - tp->snd_una;
1968                                 u_int sent;
1969
1970 #define iceildiv(n, d)          (((n)+(d)-1) / (d))
1971
1972                                 KASSERT(tp->t_dupacks == 1 ||
1973                                         tp->t_dupacks == 2,
1974                                     ("dupacks not 1 or 2"));
1975                                 if (tp->t_dupacks == 1)
1976                                         tp->snd_limited = 0;
1977                                 tp->snd_nxt = tp->snd_max;
1978                                 tp->snd_cwnd = ownd +
1979                                     (tp->t_dupacks - tp->snd_limited) *
1980                                     tp->t_maxseg;
1981                                 tcp_output(tp);
1982
1983                                 if (SEQ_LT(oldsndnxt, oldsndmax)) {
1984                                         KASSERT(SEQ_GEQ(oldsndnxt, tp->snd_una),
1985                                             ("snd_una moved in other threads"));
1986                                         tp->snd_nxt = oldsndnxt;
1987                                 }
1988                                 tp->snd_cwnd = oldcwnd;
1989                                 sent = tp->snd_max - oldsndmax;
1990                                 if (sent > tp->t_maxseg) {
1991                                         KASSERT((tp->t_dupacks == 2 &&
1992                                                  tp->snd_limited == 0) ||
1993                                                 (sent == tp->t_maxseg + 1 &&
1994                                                  tp->t_flags & TF_SENTFIN),
1995                                             ("sent too much"));
1996                                         KASSERT(sent <= tp->t_maxseg * 2,
1997                                             ("sent too many segments"));
1998                                         tp->snd_limited = 2;
1999                                         tcpstat.tcps_sndlimited += 2;
2000                                 } else if (sent > 0) {
2001                                         ++tp->snd_limited;
2002                                         ++tcpstat.tcps_sndlimited;
2003                                 } else if (tcp_do_early_retransmit &&
2004                                     (tcp_do_eifel_detect &&
2005                                      (tp->t_flags & TF_RCVD_TSTMP)) &&
2006                                     ownd < 4 * tp->t_maxseg &&
2007                                     tp->t_dupacks + 1 >=
2008                                       iceildiv(ownd, tp->t_maxseg) &&
2009                                     (!TCP_DO_SACK(tp) ||
2010                                      ownd <= tp->t_maxseg ||
2011                                      tcp_sack_has_sacked(&tp->scb,
2012                                                         ownd - tp->t_maxseg))) {
2013                                         ++tcpstat.tcps_sndearlyrexmit;
2014                                         tp->t_flags |= TF_EARLYREXMT;
2015                                         goto fastretransmit;
2016                                 }
2017                         }
2018                         goto drop;
2019                 }
2020
2021                 KASSERT(SEQ_GT(th->th_ack, tp->snd_una), ("th_ack <= snd_una"));
2022                 tp->t_dupacks = 0;
2023                 if (SEQ_GT(th->th_ack, tp->snd_max)) {
2024                         /*
2025                          * Detected optimistic ACK attack.
2026                          * Force slow-start to de-synchronize attack.
2027                          */
2028                         tp->snd_cwnd = tp->t_maxseg;
2029                         tp->snd_wacked = 0;
2030
2031                         tcpstat.tcps_rcvacktoomuch++;
2032                         goto dropafterack;
2033                 }
2034                 /*
2035                  * If we reach this point, ACK is not a duplicate,
2036                  *     i.e., it ACKs something we sent.
2037                  */
2038                 if (tp->t_flags & TF_NEEDSYN) {
2039                         /*
2040                          * T/TCP: Connection was half-synchronized, and our
2041                          * SYN has been ACK'd (so connection is now fully
2042                          * synchronized).  Go to non-starred state,
2043                          * increment snd_una for ACK of SYN, and check if
2044                          * we can do window scaling.
2045                          */
2046                         tp->t_flags &= ~TF_NEEDSYN;
2047                         tp->snd_una++;
2048                         /* Do window scaling? */
2049                         if ((tp->t_flags & (TF_RCVD_SCALE | TF_REQ_SCALE)) ==
2050                             (TF_RCVD_SCALE | TF_REQ_SCALE)) {
2051                                 tp->snd_scale = tp->requested_s_scale;
2052                                 tp->rcv_scale = tp->request_r_scale;
2053                         }
2054                 }
2055
2056 process_ACK:
2057                 acked = th->th_ack - tp->snd_una;
2058                 tcpstat.tcps_rcvackpack++;
2059                 tcpstat.tcps_rcvackbyte += acked;
2060
2061                 if (tcp_do_eifel_detect && acked > 0 &&
2062                     (to.to_flags & TOF_TS) && (to.to_tsecr != 0) &&
2063                     (tp->t_flags & TF_FIRSTACCACK)) {
2064                         /* Eifel detection applicable. */
2065                         if (to.to_tsecr < tp->t_rexmtTS) {
2066                                 ++tcpstat.tcps_eifeldetected;
2067                                 tcp_revert_congestion_state(tp);
2068                                 if (tp->t_rxtshift != 1 ||
2069                                     ticks >= tp->t_badrxtwin)
2070                                         ++tcpstat.tcps_rttcantdetect;
2071                         }
2072                 } else if (tp->t_rxtshift == 1 && ticks < tp->t_badrxtwin) {
2073                         /*
2074                          * If we just performed our first retransmit,
2075                          * and the ACK arrives within our recovery window,
2076                          * then it was a mistake to do the retransmit
2077                          * in the first place.  Recover our original cwnd
2078                          * and ssthresh, and proceed to transmit where we
2079                          * left off.
2080                          */
2081                         tcp_revert_congestion_state(tp);
2082                         ++tcpstat.tcps_rttdetected;
2083                 }
2084
2085                 /*
2086                  * If we have a timestamp reply, update smoothed
2087                  * round trip time.  If no timestamp is present but
2088                  * transmit timer is running and timed sequence
2089                  * number was acked, update smoothed round trip time.
2090                  * Since we now have an rtt measurement, cancel the
2091                  * timer backoff (cf., Phil Karn's retransmit alg.).
2092                  * Recompute the initial retransmit timer.
2093                  *
2094                  * Some machines (certain windows boxes) send broken
2095                  * timestamp replies during the SYN+ACK phase, ignore
2096                  * timestamps of 0.
2097                  */
2098                 if ((to.to_flags & TOF_TS) && (to.to_tsecr != 0))
2099                         tcp_xmit_timer(tp, ticks - to.to_tsecr + 1);
2100                 else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq))
2101                         tcp_xmit_timer(tp, ticks - tp->t_rtttime);
2102                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
2103
2104                 /*
2105                  * If no data (only SYN) was ACK'd,
2106                  *    skip rest of ACK processing.
2107                  */
2108                 if (acked == 0)
2109                         goto step6;
2110
2111                 /* Stop looking for an acceptable ACK since one was received. */
2112                 tp->t_flags &= ~(TF_FIRSTACCACK | TF_FASTREXMT | TF_EARLYREXMT);
2113
2114                 if (acked > so->so_snd.ssb_cc) {
2115                         tp->snd_wnd -= so->so_snd.ssb_cc;
2116                         sbdrop(&so->so_snd.sb, (int)so->so_snd.ssb_cc);
2117                         ourfinisacked = TRUE;
2118                 } else {
2119                         sbdrop(&so->so_snd.sb, acked);
2120                         tp->snd_wnd -= acked;
2121                         ourfinisacked = FALSE;
2122                 }
2123                 sowwakeup(so);
2124
2125                 /*
2126                  * Update window information.
2127                  */
2128                 if (acceptable_window_update(tp, th, tiwin)) {
2129                         /* keep track of pure window updates */
2130                         if (tlen == 0 && tp->snd_wl2 == th->th_ack &&
2131                             tiwin > tp->snd_wnd)
2132                                 tcpstat.tcps_rcvwinupd++;
2133                         tp->snd_wnd = tiwin;
2134                         tp->snd_wl1 = th->th_seq;
2135                         tp->snd_wl2 = th->th_ack;
2136                         if (tp->snd_wnd > tp->max_sndwnd)
2137                                 tp->max_sndwnd = tp->snd_wnd;
2138                         needoutput = TRUE;
2139                 }
2140
2141                 tp->snd_una = th->th_ack;
2142                 if (TCP_DO_SACK(tp))
2143                         tcp_sack_update_scoreboard(tp, &to);
2144                 if (IN_FASTRECOVERY(tp)) {
2145                         if (SEQ_GEQ(th->th_ack, tp->snd_recover)) {
2146                                 EXIT_FASTRECOVERY(tp);
2147                                 needoutput = TRUE;
2148                                 /*
2149                                  * If the congestion window was inflated
2150                                  * to account for the other side's
2151                                  * cached packets, retract it.
2152                                  */
2153                                 if (!TCP_DO_SACK(tp))
2154                                         tp->snd_cwnd = tp->snd_ssthresh;
2155
2156                                 /*
2157                                  * Window inflation should have left us
2158                                  * with approximately snd_ssthresh outstanding
2159                                  * data.  But, in case we would be inclined
2160                                  * to send a burst, better do it using
2161                                  * slow start.
2162                                  */
2163                                 if (SEQ_GT(th->th_ack + tp->snd_cwnd,
2164                                            tp->snd_max + 2 * tp->t_maxseg))
2165                                         tp->snd_cwnd =
2166                                             (tp->snd_max - tp->snd_una) +
2167                                             2 * tp->t_maxseg;
2168
2169                                 tp->snd_wacked = 0;
2170                         } else {
2171                                 if (TCP_DO_SACK(tp)) {
2172                                         tp->snd_max_rexmt = tp->snd_max;
2173                                         tcp_sack_rexmt(tp, th);
2174                                 } else {
2175                                         tcp_newreno_partial_ack(tp, th, acked);
2176                                 }
2177                                 needoutput = FALSE;
2178                         }
2179                 } else {
2180                         /*
2181                          * Open the congestion window.  When in slow-start,
2182                          * open exponentially: maxseg per packet.  Otherwise,
2183                          * open linearly: maxseg per window.
2184                          */
2185                         if (tp->snd_cwnd <= tp->snd_ssthresh) {
2186                                 u_int abc_sslimit =
2187                                     (SEQ_LT(tp->snd_nxt, tp->snd_max) ?
2188                                      tp->t_maxseg : 2 * tp->t_maxseg);
2189
2190                                 /* slow-start */
2191                                 tp->snd_cwnd += tcp_do_abc ?
2192                                     min(acked, abc_sslimit) : tp->t_maxseg;
2193                         } else {
2194                                 /* linear increase */
2195                                 tp->snd_wacked += tcp_do_abc ? acked :
2196                                     tp->t_maxseg;
2197                                 if (tp->snd_wacked >= tp->snd_cwnd) {
2198                                         tp->snd_wacked -= tp->snd_cwnd;
2199                                         tp->snd_cwnd += tp->t_maxseg;
2200                                 }
2201                         }
2202                         tp->snd_cwnd = min(tp->snd_cwnd,
2203                                            TCP_MAXWIN << tp->snd_scale);
2204                         tp->snd_recover = th->th_ack - 1;
2205                 }
2206                 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
2207                         tp->snd_nxt = tp->snd_una;
2208
2209                 /*
2210                  * If all outstanding data is acked, stop retransmit
2211                  * timer and remember to restart (more output or persist).
2212                  * If there is more data to be acked, restart retransmit
2213                  * timer, using current (possibly backed-off) value.
2214                  */
2215                 if (th->th_ack == tp->snd_max) {
2216                         tcp_callout_stop(tp, tp->tt_rexmt);
2217                         needoutput = TRUE;
2218                 } else if (!tcp_callout_active(tp, tp->tt_persist)) {
2219                         tcp_callout_reset(tp, tp->tt_rexmt, tp->t_rxtcur,
2220                             tcp_timer_rexmt);
2221                 }
2222
2223                 switch (tp->t_state) {
2224                 /*
2225                  * In FIN_WAIT_1 STATE in addition to the processing
2226                  * for the ESTABLISHED state if our FIN is now acknowledged
2227                  * then enter FIN_WAIT_2.
2228                  */
2229                 case TCPS_FIN_WAIT_1:
2230                         if (ourfinisacked) {
2231                                 /*
2232                                  * If we can't receive any more
2233                                  * data, then closing user can proceed.
2234                                  * Starting the timer is contrary to the
2235                                  * specification, but if we don't get a FIN
2236                                  * we'll hang forever.
2237                                  */
2238                                 if (so->so_state & SS_CANTRCVMORE) {
2239                                         soisdisconnected(so);
2240                                         tcp_callout_reset(tp, tp->tt_2msl,
2241                                             tp->t_maxidle, tcp_timer_2msl);
2242                                 }
2243                                 tp->t_state = TCPS_FIN_WAIT_2;
2244                         }
2245                         break;
2246
2247                 /*
2248                  * In CLOSING STATE in addition to the processing for
2249                  * the ESTABLISHED state if the ACK acknowledges our FIN
2250                  * then enter the TIME-WAIT state, otherwise ignore
2251                  * the segment.
2252                  */
2253                 case TCPS_CLOSING:
2254                         if (ourfinisacked) {
2255                                 tp->t_state = TCPS_TIME_WAIT;
2256                                 tcp_canceltimers(tp);
2257                                 tcp_callout_reset(tp, tp->tt_2msl,
2258                                             2 * tcp_rmx_msl(tp),
2259                                             tcp_timer_2msl);
2260                                 soisdisconnected(so);
2261                         }
2262                         break;
2263
2264                 /*
2265                  * In LAST_ACK, we may still be waiting for data to drain
2266                  * and/or to be acked, as well as for the ack of our FIN.
2267                  * If our FIN is now acknowledged, delete the TCB,
2268                  * enter the closed state and return.
2269                  */
2270                 case TCPS_LAST_ACK:
2271                         if (ourfinisacked) {
2272                                 tp = tcp_close(tp);
2273                                 goto drop;
2274                         }
2275                         break;
2276
2277                 /*
2278                  * In TIME_WAIT state the only thing that should arrive
2279                  * is a retransmission of the remote FIN.  Acknowledge
2280                  * it and restart the finack timer.
2281                  */
2282                 case TCPS_TIME_WAIT:
2283                         tcp_callout_reset(tp, tp->tt_2msl, 2 * tcp_rmx_msl(tp),
2284                             tcp_timer_2msl);
2285                         goto dropafterack;
2286                 }
2287         }
2288
2289 step6:
2290         /*
2291          * Update window information.
2292          * Don't look at window if no ACK: TAC's send garbage on first SYN.
2293          */
2294         if ((thflags & TH_ACK) &&
2295             acceptable_window_update(tp, th, tiwin)) {
2296                 /* keep track of pure window updates */
2297                 if (tlen == 0 && tp->snd_wl2 == th->th_ack &&
2298                     tiwin > tp->snd_wnd)
2299                         tcpstat.tcps_rcvwinupd++;
2300                 tp->snd_wnd = tiwin;
2301                 tp->snd_wl1 = th->th_seq;
2302                 tp->snd_wl2 = th->th_ack;
2303                 if (tp->snd_wnd > tp->max_sndwnd)
2304                         tp->max_sndwnd = tp->snd_wnd;
2305                 needoutput = TRUE;
2306         }
2307
2308         /*
2309          * Process segments with URG.
2310          */
2311         if ((thflags & TH_URG) && th->th_urp &&
2312             !TCPS_HAVERCVDFIN(tp->t_state)) {
2313                 /*
2314                  * This is a kludge, but if we receive and accept
2315                  * random urgent pointers, we'll crash in
2316                  * soreceive.  It's hard to imagine someone
2317                  * actually wanting to send this much urgent data.
2318                  */
2319                 if (th->th_urp + so->so_rcv.ssb_cc > sb_max) {
2320                         th->th_urp = 0;                 /* XXX */
2321                         thflags &= ~TH_URG;             /* XXX */
2322                         goto dodata;                    /* XXX */
2323                 }
2324                 /*
2325                  * If this segment advances the known urgent pointer,
2326                  * then mark the data stream.  This should not happen
2327                  * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
2328                  * a FIN has been received from the remote side.
2329                  * In these states we ignore the URG.
2330                  *
2331                  * According to RFC961 (Assigned Protocols),
2332                  * the urgent pointer points to the last octet
2333                  * of urgent data.  We continue, however,
2334                  * to consider it to indicate the first octet
2335                  * of data past the urgent section as the original
2336                  * spec states (in one of two places).
2337                  */
2338                 if (SEQ_GT(th->th_seq + th->th_urp, tp->rcv_up)) {
2339                         tp->rcv_up = th->th_seq + th->th_urp;
2340                         so->so_oobmark = so->so_rcv.ssb_cc +
2341                             (tp->rcv_up - tp->rcv_nxt) - 1;
2342                         if (so->so_oobmark == 0)
2343                                 sosetstate(so, SS_RCVATMARK);
2344                         sohasoutofband(so);
2345                         tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
2346                 }
2347                 /*
2348                  * Remove out of band data so doesn't get presented to user.
2349                  * This can happen independent of advancing the URG pointer,
2350                  * but if two URG's are pending at once, some out-of-band
2351                  * data may creep in... ick.
2352                  */
2353                 if (th->th_urp <= (u_long)tlen &&
2354                     !(so->so_options & SO_OOBINLINE)) {
2355                         /* hdr drop is delayed */
2356                         tcp_pulloutofband(so, th, m, drop_hdrlen);
2357                 }
2358         } else {
2359                 /*
2360                  * If no out of band data is expected,
2361                  * pull receive urgent pointer along
2362                  * with the receive window.
2363                  */
2364                 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
2365                         tp->rcv_up = tp->rcv_nxt;
2366         }
2367
2368 dodata:                                                 /* XXX */
2369         /*
2370          * Process the segment text, merging it into the TCP sequencing queue,
2371          * and arranging for acknowledgment of receipt if necessary.
2372          * This process logically involves adjusting tp->rcv_wnd as data
2373          * is presented to the user (this happens in tcp_usrreq.c,
2374          * case PRU_RCVD).  If a FIN has already been received on this
2375          * connection then we just ignore the text.
2376          */
2377         if ((tlen || (thflags & TH_FIN)) && !TCPS_HAVERCVDFIN(tp->t_state)) {
2378                 m_adj(m, drop_hdrlen);  /* delayed header drop */
2379                 /*
2380                  * Insert segment which includes th into TCP reassembly queue
2381                  * with control block tp.  Set thflags to whether reassembly now
2382                  * includes a segment with FIN.  This handles the common case
2383                  * inline (segment is the next to be received on an established
2384                  * connection, and the queue is empty), avoiding linkage into
2385                  * and removal from the queue and repetition of various
2386                  * conversions.
2387                  * Set DELACK for segments received in order, but ack
2388                  * immediately when segments are out of order (so
2389                  * fast retransmit can work).
2390                  */
2391                 if (th->th_seq == tp->rcv_nxt &&
2392                     LIST_EMPTY(&tp->t_segq) &&
2393                     TCPS_HAVEESTABLISHED(tp->t_state)) {
2394                         if (DELAY_ACK(tp)) {
2395                                 tcp_callout_reset(tp, tp->tt_delack,
2396                                     tcp_delacktime, tcp_timer_delack);
2397                         } else {
2398                                 tp->t_flags |= TF_ACKNOW;
2399                         }
2400                         tp->rcv_nxt += tlen;
2401                         thflags = th->th_flags & TH_FIN;
2402                         tcpstat.tcps_rcvpack++;
2403                         tcpstat.tcps_rcvbyte += tlen;
2404                         ND6_HINT(tp);
2405                         if (so->so_state & SS_CANTRCVMORE) {
2406                                 m_freem(m);
2407                         } else {
2408                                 lwkt_gettoken(&so->so_rcv.ssb_token);
2409                                 ssb_appendstream(&so->so_rcv, m);
2410                                 lwkt_reltoken(&so->so_rcv.ssb_token);
2411                         }
2412                         sorwakeup(so);
2413                 } else {
2414                         if (!(tp->t_flags & TF_DUPSEG)) {
2415                                 /* Initialize SACK report block. */
2416                                 tp->reportblk.rblk_start = th->th_seq;
2417                                 tp->reportblk.rblk_end = TCP_SACK_BLKEND(
2418                                     th->th_seq + tlen, thflags);
2419                         }
2420                         thflags = tcp_reass(tp, th, &tlen, m);
2421                         tp->t_flags |= TF_ACKNOW;
2422                 }
2423
2424                 /*
2425                  * Note the amount of data that peer has sent into
2426                  * our window, in order to estimate the sender's
2427                  * buffer size.
2428                  */
2429                 len = so->so_rcv.ssb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
2430         } else {
2431                 m_freem(m);
2432                 thflags &= ~TH_FIN;
2433         }
2434
2435         /*
2436          * If FIN is received ACK the FIN and let the user know
2437          * that the connection is closing.
2438          */
2439         if (thflags & TH_FIN) {
2440                 if (!TCPS_HAVERCVDFIN(tp->t_state)) {
2441                         socantrcvmore(so);
2442                         /*
2443                          * If connection is half-synchronized
2444                          * (ie NEEDSYN flag on) then delay ACK,
2445                          * so it may be piggybacked when SYN is sent.
2446                          * Otherwise, since we received a FIN then no
2447                          * more input can be expected, send ACK now.
2448                          */
2449                         if (DELAY_ACK(tp) && (tp->t_flags & TF_NEEDSYN)) {
2450                                 tcp_callout_reset(tp, tp->tt_delack,
2451                                     tcp_delacktime, tcp_timer_delack);
2452                         } else {
2453                                 tp->t_flags |= TF_ACKNOW;
2454                         }
2455                         tp->rcv_nxt++;
2456                 }
2457
2458                 switch (tp->t_state) {
2459                 /*
2460                  * In SYN_RECEIVED and ESTABLISHED STATES
2461                  * enter the CLOSE_WAIT state.
2462                  */
2463                 case TCPS_SYN_RECEIVED:
2464                         tp->t_starttime = ticks;
2465                         /*FALLTHROUGH*/
2466                 case TCPS_ESTABLISHED:
2467                         tp->t_state = TCPS_CLOSE_WAIT;
2468                         break;
2469
2470                 /*
2471                  * If still in FIN_WAIT_1 STATE FIN has not been acked so
2472                  * enter the CLOSING state.
2473                  */
2474                 case TCPS_FIN_WAIT_1:
2475                         tp->t_state = TCPS_CLOSING;
2476                         break;
2477
2478                 /*
2479                  * In FIN_WAIT_2 state enter the TIME_WAIT state,
2480                  * starting the time-wait timer, turning off the other
2481                  * standard timers.
2482                  */
2483                 case TCPS_FIN_WAIT_2:
2484                         tp->t_state = TCPS_TIME_WAIT;
2485                         tcp_canceltimers(tp);
2486                         tcp_callout_reset(tp, tp->tt_2msl, 2 * tcp_rmx_msl(tp),
2487                                     tcp_timer_2msl);
2488                         soisdisconnected(so);
2489                         break;
2490
2491                 /*
2492                  * In TIME_WAIT state restart the 2 MSL time_wait timer.
2493                  */
2494                 case TCPS_TIME_WAIT:
2495                         tcp_callout_reset(tp, tp->tt_2msl, 2 * tcp_rmx_msl(tp),
2496                             tcp_timer_2msl);
2497                         break;
2498                 }
2499         }
2500
2501 #ifdef TCPDEBUG
2502         if (so->so_options & SO_DEBUG)
2503                 tcp_trace(TA_INPUT, ostate, tp, tcp_saveipgen, &tcp_savetcp, 0);
2504 #endif
2505
2506         /*
2507          * Return any desired output.
2508          */
2509         if (needoutput || (tp->t_flags & TF_ACKNOW))
2510                 tcp_output(tp);
2511         tcp_sack_report_cleanup(tp);
2512         return(IPPROTO_DONE);
2513
2514 dropafterack:
2515         /*
2516          * Generate an ACK dropping incoming segment if it occupies
2517          * sequence space, where the ACK reflects our state.
2518          *
2519          * We can now skip the test for the RST flag since all
2520          * paths to this code happen after packets containing
2521          * RST have been dropped.
2522          *
2523          * In the SYN-RECEIVED state, don't send an ACK unless the
2524          * segment we received passes the SYN-RECEIVED ACK test.
2525          * If it fails send a RST.  This breaks the loop in the
2526          * "LAND" DoS attack, and also prevents an ACK storm
2527          * between two listening ports that have been sent forged
2528          * SYN segments, each with the source address of the other.
2529          */
2530         if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
2531             (SEQ_GT(tp->snd_una, th->th_ack) ||
2532              SEQ_GT(th->th_ack, tp->snd_max)) ) {
2533                 rstreason = BANDLIM_RST_OPENPORT;
2534                 goto dropwithreset;
2535         }
2536 #ifdef TCPDEBUG
2537         if (so->so_options & SO_DEBUG)
2538                 tcp_trace(TA_DROP, ostate, tp, tcp_saveipgen, &tcp_savetcp, 0);
2539 #endif
2540         m_freem(m);
2541         tp->t_flags |= TF_ACKNOW;
2542         tcp_output(tp);
2543         tcp_sack_report_cleanup(tp);
2544         return(IPPROTO_DONE);
2545
2546 dropwithreset:
2547         /*
2548          * Generate a RST, dropping incoming segment.
2549          * Make ACK acceptable to originator of segment.
2550          * Don't bother to respond if destination was broadcast/multicast.
2551          */
2552         if ((thflags & TH_RST) || m->m_flags & (M_BCAST | M_MCAST))
2553                 goto drop;
2554         if (isipv6) {
2555                 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
2556                     IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
2557                         goto drop;
2558         } else {
2559                 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
2560                     IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
2561                     ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
2562                     in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
2563                         goto drop;
2564         }
2565         /* IPv6 anycast check is done at tcp6_input() */
2566
2567         /*
2568          * Perform bandwidth limiting.
2569          */
2570 #ifdef ICMP_BANDLIM
2571         if (badport_bandlim(rstreason) < 0)
2572                 goto drop;
2573 #endif
2574
2575 #ifdef TCPDEBUG
2576         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2577                 tcp_trace(TA_DROP, ostate, tp, tcp_saveipgen, &tcp_savetcp, 0);
2578 #endif
2579         if (thflags & TH_ACK)
2580                 /* mtod() below is safe as long as hdr dropping is delayed */
2581                 tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0, th->th_ack,
2582                             TH_RST);
2583         else {
2584                 if (thflags & TH_SYN)
2585                         tlen++;
2586                 /* mtod() below is safe as long as hdr dropping is delayed */
2587                 tcp_respond(tp, mtod(m, void *), th, m, th->th_seq + tlen,
2588                             (tcp_seq)0, TH_RST | TH_ACK);
2589         }
2590         if (tp != NULL)
2591                 tcp_sack_report_cleanup(tp);
2592         return(IPPROTO_DONE);
2593
2594 drop:
2595         /*
2596          * Drop space held by incoming segment and return.
2597          */
2598 #ifdef TCPDEBUG
2599         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2600                 tcp_trace(TA_DROP, ostate, tp, tcp_saveipgen, &tcp_savetcp, 0);
2601 #endif
2602         m_freem(m);
2603         if (tp != NULL)
2604                 tcp_sack_report_cleanup(tp);
2605         return(IPPROTO_DONE);
2606 }
2607
2608 /*
2609  * Parse TCP options and place in tcpopt.
2610  */
2611 static void
2612 tcp_dooptions(struct tcpopt *to, u_char *cp, int cnt, boolean_t is_syn)
2613 {
2614         int opt, optlen, i;
2615
2616         to->to_flags = 0;
2617         for (; cnt > 0; cnt -= optlen, cp += optlen) {
2618                 opt = cp[0];
2619                 if (opt == TCPOPT_EOL)
2620                         break;
2621                 if (opt == TCPOPT_NOP)
2622                         optlen = 1;
2623                 else {
2624                         if (cnt < 2)
2625                                 break;
2626                         optlen = cp[1];
2627                         if (optlen < 2 || optlen > cnt)
2628                                 break;
2629                 }
2630                 switch (opt) {
2631                 case TCPOPT_MAXSEG:
2632                         if (optlen != TCPOLEN_MAXSEG)
2633                                 continue;
2634                         if (!is_syn)
2635                                 continue;
2636                         to->to_flags |= TOF_MSS;
2637                         bcopy(cp + 2, &to->to_mss, sizeof to->to_mss);
2638                         to->to_mss = ntohs(to->to_mss);
2639                         break;
2640                 case TCPOPT_WINDOW:
2641                         if (optlen != TCPOLEN_WINDOW)
2642                                 continue;
2643                         if (!is_syn)
2644                                 continue;
2645                         to->to_flags |= TOF_SCALE;
2646                         to->to_requested_s_scale = min(cp[2], TCP_MAX_WINSHIFT);
2647                         break;
2648                 case TCPOPT_TIMESTAMP:
2649                         if (optlen != TCPOLEN_TIMESTAMP)
2650                                 continue;
2651                         to->to_flags |= TOF_TS;
2652                         bcopy(cp + 2, &to->to_tsval, sizeof to->to_tsval);
2653                         to->to_tsval = ntohl(to->to_tsval);
2654                         bcopy(cp + 6, &to->to_tsecr, sizeof to->to_tsecr);
2655                         to->to_tsecr = ntohl(to->to_tsecr);
2656                         /*
2657                          * If echoed timestamp is later than the current time,
2658                          * fall back to non RFC1323 RTT calculation.
2659                          */
2660                         if (to->to_tsecr != 0 && TSTMP_GT(to->to_tsecr, ticks))
2661                                 to->to_tsecr = 0;
2662                         break;
2663                 case TCPOPT_SACK_PERMITTED:
2664                         if (optlen != TCPOLEN_SACK_PERMITTED)
2665                                 continue;
2666                         if (!is_syn)
2667                                 continue;
2668                         to->to_flags |= TOF_SACK_PERMITTED;
2669                         break;
2670                 case TCPOPT_SACK:
2671                         if ((optlen - 2) & 0x07)        /* not multiple of 8 */
2672                                 continue;
2673                         to->to_nsackblocks = (optlen - 2) / 8;
2674                         to->to_sackblocks = (struct raw_sackblock *) (cp + 2);
2675                         to->to_flags |= TOF_SACK;
2676                         for (i = 0; i < to->to_nsackblocks; i++) {
2677                                 struct raw_sackblock *r = &to->to_sackblocks[i];
2678
2679                                 r->rblk_start = ntohl(r->rblk_start);
2680                                 r->rblk_end = ntohl(r->rblk_end);
2681
2682                                 if (SEQ_LEQ(r->rblk_end, r->rblk_start)) {
2683                                         /*
2684                                          * Invalid SACK block; discard all
2685                                          * SACK blocks
2686                                          */
2687                                         tcpstat.tcps_rcvbadsackopt++;
2688                                         to->to_nsackblocks = 0;
2689                                         to->to_sackblocks = NULL;
2690                                         to->to_flags &= ~TOF_SACK;
2691                                         break;
2692                                 }
2693                         }
2694                         break;
2695 #ifdef TCP_SIGNATURE
2696                 /*
2697                  * XXX In order to reply to a host which has set the
2698                  * TCP_SIGNATURE option in its initial SYN, we have to
2699                  * record the fact that the option was observed here
2700                  * for the syncache code to perform the correct response.
2701                  */
2702                 case TCPOPT_SIGNATURE:
2703                         if (optlen != TCPOLEN_SIGNATURE)
2704                                 continue;
2705                         to->to_flags |= (TOF_SIGNATURE | TOF_SIGLEN);
2706                         break;
2707 #endif /* TCP_SIGNATURE */
2708                 default:
2709                         continue;
2710                 }
2711         }
2712 }
2713
2714 /*
2715  * Pull out of band byte out of a segment so
2716  * it doesn't appear in the user's data queue.
2717  * It is still reflected in the segment length for
2718  * sequencing purposes.
2719  * "off" is the delayed to be dropped hdrlen.
2720  */
2721 static void
2722 tcp_pulloutofband(struct socket *so, struct tcphdr *th, struct mbuf *m, int off)
2723 {
2724         int cnt = off + th->th_urp - 1;
2725
2726         while (cnt >= 0) {
2727                 if (m->m_len > cnt) {
2728                         char *cp = mtod(m, caddr_t) + cnt;
2729                         struct tcpcb *tp = sototcpcb(so);
2730
2731                         tp->t_iobc = *cp;
2732                         tp->t_oobflags |= TCPOOB_HAVEDATA;
2733                         bcopy(cp + 1, cp, m->m_len - cnt - 1);
2734                         m->m_len--;
2735                         if (m->m_flags & M_PKTHDR)
2736                                 m->m_pkthdr.len--;
2737                         return;
2738                 }
2739                 cnt -= m->m_len;
2740                 m = m->m_next;
2741                 if (m == NULL)
2742                         break;
2743         }
2744         panic("tcp_pulloutofband");
2745 }
2746
2747 /*
2748  * Collect new round-trip time estimate
2749  * and update averages and current timeout.
2750  */
2751 static void
2752 tcp_xmit_timer(struct tcpcb *tp, int rtt)
2753 {
2754         int delta;
2755
2756         tcpstat.tcps_rttupdated++;
2757         tp->t_rttupdated++;
2758         if (tp->t_srtt != 0) {
2759                 /*
2760                  * srtt is stored as fixed point with 5 bits after the
2761                  * binary point (i.e., scaled by 8).  The following magic
2762                  * is equivalent to the smoothing algorithm in rfc793 with
2763                  * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
2764                  * point).  Adjust rtt to origin 0.
2765                  */
2766                 delta = ((rtt - 1) << TCP_DELTA_SHIFT)
2767                         - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
2768
2769                 if ((tp->t_srtt += delta) <= 0)
2770                         tp->t_srtt = 1;
2771
2772                 /*
2773                  * We accumulate a smoothed rtt variance (actually, a
2774                  * smoothed mean difference), then set the retransmit
2775                  * timer to smoothed rtt + 4 times the smoothed variance.
2776                  * rttvar is stored as fixed point with 4 bits after the
2777                  * binary point (scaled by 16).  The following is
2778                  * equivalent to rfc793 smoothing with an alpha of .75
2779                  * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
2780                  * rfc793's wired-in beta.
2781                  */
2782                 if (delta < 0)
2783                         delta = -delta;
2784                 delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
2785                 if ((tp->t_rttvar += delta) <= 0)
2786                         tp->t_rttvar = 1;
2787                 if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
2788                         tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2789         } else {
2790                 /*
2791                  * No rtt measurement yet - use the unsmoothed rtt.
2792                  * Set the variance to half the rtt (so our first
2793                  * retransmit happens at 3*rtt).
2794                  */
2795                 tp->t_srtt = rtt << TCP_RTT_SHIFT;
2796                 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
2797                 tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2798         }
2799         tp->t_rtttime = 0;
2800         tp->t_rxtshift = 0;
2801
2802         /*
2803          * the retransmit should happen at rtt + 4 * rttvar.
2804          * Because of the way we do the smoothing, srtt and rttvar
2805          * will each average +1/2 tick of bias.  When we compute
2806          * the retransmit timer, we want 1/2 tick of rounding and
2807          * 1 extra tick because of +-1/2 tick uncertainty in the
2808          * firing of the timer.  The bias will give us exactly the
2809          * 1.5 tick we need.  But, because the bias is
2810          * statistical, we have to test that we don't drop below
2811          * the minimum feasible timer (which is 2 ticks).
2812          */
2813         TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
2814                       max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
2815
2816         /*
2817          * We received an ack for a packet that wasn't retransmitted;
2818          * it is probably safe to discard any error indications we've
2819          * received recently.  This isn't quite right, but close enough
2820          * for now (a route might have failed after we sent a segment,
2821          * and the return path might not be symmetrical).
2822          */
2823         tp->t_softerror = 0;
2824 }
2825
2826 /*
2827  * Determine a reasonable value for maxseg size.
2828  * If the route is known, check route for mtu.
2829  * If none, use an mss that can be handled on the outgoing
2830  * interface without forcing IP to fragment; if bigger than
2831  * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
2832  * to utilize large mbufs.  If no route is found, route has no mtu,
2833  * or the destination isn't local, use a default, hopefully conservative
2834  * size (usually 512 or the default IP max size, but no more than the mtu
2835  * of the interface), as we can't discover anything about intervening
2836  * gateways or networks.  We also initialize the congestion/slow start
2837  * window to be a single segment if the destination isn't local.
2838  * While looking at the routing entry, we also initialize other path-dependent
2839  * parameters from pre-set or cached values in the routing entry.
2840  *
2841  * Also take into account the space needed for options that we
2842  * send regularly.  Make maxseg shorter by that amount to assure
2843  * that we can send maxseg amount of data even when the options
2844  * are present.  Store the upper limit of the length of options plus
2845  * data in maxopd.
2846  *
2847  * NOTE that this routine is only called when we process an incoming
2848  * segment, for outgoing segments only tcp_mssopt is called.
2849  */
2850 void
2851 tcp_mss(struct tcpcb *tp, int offer)
2852 {
2853         struct rtentry *rt;
2854         struct ifnet *ifp;
2855         int rtt, mss;
2856         u_long bufsize;
2857         struct inpcb *inp = tp->t_inpcb;
2858         struct socket *so;
2859 #ifdef INET6
2860         boolean_t isipv6 = ((inp->inp_vflag & INP_IPV6) ? TRUE : FALSE);
2861         size_t min_protoh = isipv6 ?
2862                             sizeof(struct ip6_hdr) + sizeof(struct tcphdr) :
2863                             sizeof(struct tcpiphdr);
2864 #else
2865         const boolean_t isipv6 = FALSE;
2866         const size_t min_protoh = sizeof(struct tcpiphdr);
2867 #endif
2868
2869         if (isipv6)
2870                 rt = tcp_rtlookup6(&inp->inp_inc);
2871         else
2872                 rt = tcp_rtlookup(&inp->inp_inc);
2873         if (rt == NULL) {
2874                 tp->t_maxopd = tp->t_maxseg =
2875                     (isipv6 ? tcp_v6mssdflt : tcp_mssdflt);
2876                 return;
2877         }
2878         ifp = rt->rt_ifp;
2879         so = inp->inp_socket;
2880
2881         /*
2882          * Offer == 0 means that there was no MSS on the SYN segment,
2883          * in this case we use either the interface mtu or tcp_mssdflt.
2884          *
2885          * An offer which is too large will be cut down later.
2886          */
2887         if (offer == 0) {
2888                 if (isipv6) {
2889                         if (in6_localaddr(&inp->in6p_faddr)) {
2890                                 offer = ND_IFINFO(rt->rt_ifp)->linkmtu -
2891                                         min_protoh;
2892                         } else {
2893                                 offer = tcp_v6mssdflt;
2894                         }
2895                 } else {
2896                         if (in_localaddr(inp->inp_faddr))
2897                                 offer = ifp->if_mtu - min_protoh;
2898                         else
2899                                 offer = tcp_mssdflt;
2900                 }
2901         }
2902
2903         /*
2904          * Prevent DoS attack with too small MSS. Round up
2905          * to at least minmss.
2906          *
2907          * Sanity check: make sure that maxopd will be large
2908          * enough to allow some data on segments even is the
2909          * all the option space is used (40bytes).  Otherwise
2910          * funny things may happen in tcp_output.
2911          */
2912         offer = max(offer, tcp_minmss);
2913         offer = max(offer, 64);
2914
2915         rt->rt_rmx.rmx_mssopt = offer;
2916
2917         /*
2918          * While we're here, check if there's an initial rtt
2919          * or rttvar.  Convert from the route-table units
2920          * to scaled multiples of the slow timeout timer.
2921          */
2922         if (tp->t_srtt == 0 && (rtt = rt->rt_rmx.rmx_rtt)) {
2923                 /*
2924                  * XXX the lock bit for RTT indicates that the value
2925                  * is also a minimum value; this is subject to time.
2926                  */
2927                 if (rt->rt_rmx.rmx_locks & RTV_RTT)
2928                         tp->t_rttmin = rtt / (RTM_RTTUNIT / hz);
2929                 tp->t_srtt = rtt / (RTM_RTTUNIT / (hz * TCP_RTT_SCALE));
2930                 tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
2931                 tcpstat.tcps_usedrtt++;
2932                 if (rt->rt_rmx.rmx_rttvar) {
2933                         tp->t_rttvar = rt->rt_rmx.rmx_rttvar /
2934                             (RTM_RTTUNIT / (hz * TCP_RTTVAR_SCALE));
2935                         tcpstat.tcps_usedrttvar++;
2936                 } else {
2937                         /* default variation is +- 1 rtt */
2938                         tp->t_rttvar =
2939                             tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
2940                 }
2941                 TCPT_RANGESET(tp->t_rxtcur,
2942                               ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
2943                               tp->t_rttmin, TCPTV_REXMTMAX);
2944         }
2945
2946         /*
2947          * if there's an mtu associated with the route, use it
2948          * else, use the link mtu.  Take the smaller of mss or offer
2949          * as our final mss.
2950          */
2951         if (rt->rt_rmx.rmx_mtu) {
2952                 mss = rt->rt_rmx.rmx_mtu - min_protoh;
2953         } else {
2954                 if (isipv6)
2955                         mss = ND_IFINFO(rt->rt_ifp)->linkmtu - min_protoh;
2956                 else
2957                         mss = ifp->if_mtu - min_protoh;
2958         }
2959         mss = min(mss, offer);
2960
2961         /*
2962          * maxopd stores the maximum length of data AND options
2963          * in a segment; maxseg is the amount of data in a normal
2964          * segment.  We need to store this value (maxopd) apart
2965          * from maxseg, because now every segment carries options
2966          * and thus we normally have somewhat less data in segments.
2967          */
2968         tp->t_maxopd = mss;
2969
2970         if ((tp->t_flags & (TF_REQ_TSTMP | TF_NOOPT)) == TF_REQ_TSTMP &&
2971             ((tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
2972                 mss -= TCPOLEN_TSTAMP_APPA;
2973
2974 #if     (MCLBYTES & (MCLBYTES - 1)) == 0
2975                 if (mss > MCLBYTES)
2976                         mss &= ~(MCLBYTES-1);
2977 #else
2978                 if (mss > MCLBYTES)
2979                         mss = mss / MCLBYTES * MCLBYTES;
2980 #endif
2981         /*
2982          * If there's a pipesize, change the socket buffer
2983          * to that size.  Make the socket buffers an integral
2984          * number of mss units; if the mss is larger than
2985          * the socket buffer, decrease the mss.
2986          */
2987 #ifdef RTV_SPIPE
2988         if ((bufsize = rt->rt_rmx.rmx_sendpipe) == 0)
2989 #endif
2990                 bufsize = so->so_snd.ssb_hiwat;
2991         if (bufsize < mss)
2992                 mss = bufsize;
2993         else {
2994                 bufsize = roundup(bufsize, mss);
2995                 if (bufsize > sb_max)
2996                         bufsize = sb_max;
2997                 if (bufsize > so->so_snd.ssb_hiwat)
2998                         ssb_reserve(&so->so_snd, bufsize, so, NULL);
2999         }
3000         tp->t_maxseg = mss;
3001
3002 #ifdef RTV_RPIPE
3003         if ((bufsize = rt->rt_rmx.rmx_recvpipe) == 0)
3004 #endif
3005                 bufsize = so->so_rcv.ssb_hiwat;
3006         if (bufsize > mss) {
3007                 bufsize = roundup(bufsize, mss);
3008                 if (bufsize > sb_max)
3009                         bufsize = sb_max;
3010                 if (bufsize > so->so_rcv.ssb_hiwat) {
3011                         lwkt_gettoken(&so->so_rcv.ssb_token);
3012                         ssb_reserve(&so->so_rcv, bufsize, so, NULL);
3013                         lwkt_reltoken(&so->so_rcv.ssb_token);
3014                 }
3015         }
3016
3017         /*
3018          * Set the slow-start flight size
3019          *
3020          * NOTE: t_maxseg must have been configured!
3021          */
3022         tp->snd_cwnd = tcp_initial_window(tp);
3023
3024         if (rt->rt_rmx.rmx_ssthresh) {
3025                 /*
3026                  * There's some sort of gateway or interface
3027                  * buffer limit on the path.  Use this to set
3028                  * the slow start threshhold, but set the
3029                  * threshold to no less than 2*mss.
3030                  */
3031                 tp->snd_ssthresh = max(2 * mss, rt->rt_rmx.rmx_ssthresh);
3032                 tcpstat.tcps_usedssthresh++;
3033         }
3034 }
3035
3036 /*
3037  * Determine the MSS option to send on an outgoing SYN.
3038  */
3039 int
3040 tcp_mssopt(struct tcpcb *tp)
3041 {
3042         struct rtentry *rt;
3043 #ifdef INET6
3044         boolean_t isipv6 =
3045             ((tp->t_inpcb->inp_vflag & INP_IPV6) ? TRUE : FALSE);
3046         int min_protoh = isipv6 ?
3047                              sizeof(struct ip6_hdr) + sizeof(struct tcphdr) :
3048                              sizeof(struct tcpiphdr);
3049 #else
3050         const boolean_t isipv6 = FALSE;
3051         const size_t min_protoh = sizeof(struct tcpiphdr);
3052 #endif
3053
3054         if (isipv6)
3055                 rt = tcp_rtlookup6(&tp->t_inpcb->inp_inc);
3056         else
3057                 rt = tcp_rtlookup(&tp->t_inpcb->inp_inc);
3058         if (rt == NULL)
3059                 return (isipv6 ? tcp_v6mssdflt : tcp_mssdflt);
3060
3061         return (rt->rt_ifp->if_mtu - min_protoh);
3062 }
3063
3064 /*
3065  * When a partial ack arrives, force the retransmission of the
3066  * next unacknowledged segment.  Do not exit Fast Recovery.
3067  *
3068  * Implement the Slow-but-Steady variant of NewReno by restarting the
3069  * the retransmission timer.  Turn it off here so it can be restarted
3070  * later in tcp_output().
3071  */
3072 static void
3073 tcp_newreno_partial_ack(struct tcpcb *tp, struct tcphdr *th, int acked)
3074 {
3075         tcp_seq old_snd_nxt = tp->snd_nxt;
3076         u_long ocwnd = tp->snd_cwnd;
3077
3078         tcp_callout_stop(tp, tp->tt_rexmt);
3079         tp->t_rtttime = 0;
3080         tp->snd_nxt = th->th_ack;
3081         /* Set snd_cwnd to one segment beyond acknowledged offset. */
3082         tp->snd_cwnd = tp->t_maxseg;
3083         tp->t_flags |= TF_ACKNOW;
3084         tcp_output(tp);
3085         if (SEQ_GT(old_snd_nxt, tp->snd_nxt))
3086                 tp->snd_nxt = old_snd_nxt;
3087         /* partial window deflation */
3088         if (ocwnd > acked)
3089                 tp->snd_cwnd = ocwnd - acked + tp->t_maxseg;
3090         else
3091                 tp->snd_cwnd = tp->t_maxseg;
3092 }
3093
3094 /*
3095  * In contrast to the Slow-but-Steady NewReno variant,
3096  * we do not reset the retransmission timer for SACK retransmissions,
3097  * except when retransmitting snd_una.
3098  */
3099 static void
3100 tcp_sack_rexmt(struct tcpcb *tp, struct tcphdr *th)
3101 {
3102         uint32_t pipe, seglen;
3103         tcp_seq nextrexmt;
3104         boolean_t lostdup;
3105         tcp_seq old_snd_nxt = tp->snd_nxt;
3106         u_long ocwnd = tp->snd_cwnd;
3107         int nseg = 0;           /* consecutive new segments */
3108 #define MAXBURST 4              /* limit burst of new packets on partial ack */
3109
3110         tp->t_rtttime = 0;
3111         pipe = tcp_sack_compute_pipe(tp);
3112         while ((tcp_seq_diff_t)(ocwnd - pipe) >= (tcp_seq_diff_t)tp->t_maxseg &&
3113             (!tcp_do_smartsack || nseg < MAXBURST) &&
3114             tcp_sack_nextseg(tp, &nextrexmt, &seglen, &lostdup)) {
3115                 uint32_t sent;
3116                 tcp_seq old_snd_max;
3117                 int error;
3118
3119                 if (nextrexmt == tp->snd_max)
3120                         ++nseg;
3121                 tp->snd_nxt = nextrexmt;
3122                 tp->snd_cwnd = nextrexmt - tp->snd_una + seglen;
3123                 old_snd_max = tp->snd_max;
3124                 if (nextrexmt == tp->snd_una)
3125                         tcp_callout_stop(tp, tp->tt_rexmt);
3126                 error = tcp_output(tp);
3127                 if (error != 0)
3128                         break;
3129                 sent = tp->snd_nxt - nextrexmt;
3130                 if (sent <= 0)
3131                         break;
3132                 if (!lostdup)
3133                         pipe += sent;
3134                 tcpstat.tcps_sndsackpack++;
3135                 tcpstat.tcps_sndsackbyte += sent;
3136                 if (SEQ_LT(nextrexmt, old_snd_max) &&
3137                     SEQ_LT(tp->rexmt_high, tp->snd_nxt))
3138                         tp->rexmt_high = seq_min(tp->snd_nxt, old_snd_max);
3139         }
3140         if (SEQ_GT(old_snd_nxt, tp->snd_nxt))
3141                 tp->snd_nxt = old_snd_nxt;
3142         tp->snd_cwnd = ocwnd;
3143 }
3144
3145 /*
3146  * Reset idle time and keep-alive timer, typically called when a valid
3147  * tcp packet is received but may also be called when FASTKEEP is set
3148  * to prevent the previous long-timeout from calculating to a drop.
3149  *
3150  * Only update t_rcvtime for non-SYN packets.
3151  *
3152  * Handle the case where one side thinks the connection is established
3153  * but the other side has, say, rebooted without cleaning out the
3154  * connection.   The SYNs could be construed as an attack and wind
3155  * up ignored, but in case it isn't an attack we can validate the
3156  * connection by forcing a keepalive.
3157  */
3158 void
3159 tcp_timer_keep_activity(struct tcpcb *tp, int thflags)
3160 {
3161         if (TCPS_HAVEESTABLISHED(tp->t_state)) {
3162                 if ((thflags & (TH_SYN | TH_ACK)) == TH_SYN) {
3163                         tp->t_flags |= TF_KEEPALIVE;
3164                         tcp_callout_reset(tp, tp->tt_keep, hz / 2,
3165                                           tcp_timer_keep);
3166                 } else {
3167                         tp->t_rcvtime = ticks;
3168                         tp->t_flags &= ~TF_KEEPALIVE;
3169                         tcp_callout_reset(tp, tp->tt_keep,
3170                                           tcp_getkeepidle(tp),
3171                                           tcp_timer_keep);
3172                 }
3173         }
3174 }
3175
3176 static int
3177 tcp_rmx_msl(const struct tcpcb *tp)
3178 {
3179         struct rtentry *rt;
3180         struct inpcb *inp = tp->t_inpcb;
3181         int msl;
3182 #ifdef INET6
3183         boolean_t isipv6 = ((inp->inp_vflag & INP_IPV6) ? TRUE : FALSE);
3184 #else
3185         const boolean_t isipv6 = FALSE;
3186 #endif
3187
3188         if (isipv6)
3189                 rt = tcp_rtlookup6(&inp->inp_inc);
3190         else
3191                 rt = tcp_rtlookup(&inp->inp_inc);
3192         if (rt == NULL || rt->rt_rmx.rmx_msl == 0)
3193                 return tcp_msl;
3194
3195         msl = (rt->rt_rmx.rmx_msl * hz) / 1000;
3196         if (msl == 0)
3197                 msl = 1;
3198
3199         return msl;
3200 }
3201
3202 static void
3203 tcp_established(struct tcpcb *tp)
3204 {
3205         tp->t_state = TCPS_ESTABLISHED;
3206         tcp_callout_reset(tp, tp->tt_keep, tcp_getkeepidle(tp), tcp_timer_keep);
3207
3208         if (tp->t_rxtsyn > 0) {
3209                 /*
3210                  * RFC6298:
3211                  * "If the timer expires awaiting the ACK of a SYN segment
3212                  *  and the TCP implementation is using an RTO less than 3
3213                  *  seconds, the RTO MUST be re-initialized to 3 seconds
3214                  *  when data transmission begins"
3215                  */
3216                 if (tp->t_rxtcur < TCPTV_RTOBASE3)
3217                         tp->t_rxtcur = TCPTV_RTOBASE3;
3218         }
3219 }