1 /*-
2 * Copyright (c) 2001 Networks Associates Technologies, Inc.
3 * All rights reserved.
4 *
5 * This software was developed for the FreeBSD Project by Jonathan Lemon
6 * and NAI Labs, the Security Research Division of Network Associates, Inc.
7 * under DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the
8 * DARPA CHATS research program.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 * notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 * notice, this list of conditions and the following disclaimer in the
17 * documentation and/or other materials provided with the distribution.
18 * 3. The name of the author may not be used to endorse or promote
19 * products derived from this software without specific prior written
20 * permission.
21 *
22 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * SUCH DAMAGE.
33 *
34 * $FreeBSD$
35 */
36
37 #include "opt_inet.h"
38 #include "opt_inet6.h"
39 #include "opt_ipsec.h"
40 #include "opt_random_ip_id.h"
41
42 #include <sys/param.h>
43 #include <sys/systm.h>
44 #include <sys/kernel.h>
45 #include <sys/sysctl.h>
46 #include <sys/malloc.h>
47 #include <sys/mbuf.h>
48 #include <sys/md5.h>
49 #include <sys/proc.h> /* for proc0 declaration */
50 #include <sys/random.h>
51 #include <sys/socket.h>
52 #include <sys/socketvar.h>
53
54 #include <net/if.h>
55 #include <net/route.h>
56
57 #include <netinet/in.h>
58 #include <netinet/in_systm.h>
59 #include <netinet/ip.h>
60 #include <netinet/in_var.h>
61 #include <netinet/in_pcb.h>
62 #include <netinet/ip_var.h>
63 #ifdef INET6
64 #include <netinet/ip6.h>
65 #include <netinet/icmp6.h>
66 #include <netinet6/nd6.h>
67 #include <netinet6/ip6_var.h>
68 #include <netinet6/in6_pcb.h>
69 #endif
70 #include <netinet/tcp.h>
71 #include <netinet/tcp_fsm.h>
72 #include <netinet/tcp_seq.h>
73 #include <netinet/tcp_timer.h>
74 #include <netinet/tcp_var.h>
75 #ifdef INET6
76 #include <netinet6/tcp6_var.h>
77 #endif
78
79 #ifdef IPSEC
80 #include <netinet6/ipsec.h>
81 #ifdef INET6
82 #include <netinet6/ipsec6.h>
83 #endif
84 #include <netkey/key.h>
85 #endif /*IPSEC*/
86
87 #ifdef FAST_IPSEC
88 #include <netipsec/ipsec.h>
89 #ifdef INET6
90 #include <netipsec/ipsec6.h>
91 #endif
92 #include <netipsec/key.h>
93 #define IPSEC
94 #endif /*FAST_IPSEC*/
95
96 #include <machine/in_cksum.h>
97 #include <vm/vm_zone.h>
98
99 static int tcp_syncookies = 1;
100 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW,
101 &tcp_syncookies, 0,
102 "Use TCP SYN cookies if the syncache overflows");
103
104 static void syncache_drop(struct syncache *, struct syncache_head *);
105 static void syncache_free(struct syncache *);
106 static void syncache_insert(struct syncache *, struct syncache_head *);
107 struct syncache *syncache_lookup(struct in_conninfo *, struct syncache_head **);
108 static int syncache_respond(struct syncache *, struct mbuf *);
109 static struct socket *syncache_socket(struct syncache *, struct socket *);
110 static void syncache_timer(void *);
111 static u_int32_t syncookie_generate(struct syncache *, u_int32_t *);
112 static struct syncache *syncookie_lookup(struct in_conninfo *,
113 struct tcphdr *, struct socket *);
114
115 /*
116 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
117 * 3 retransmits corresponds to a timeout of (1 + 2 + 4 + 8 == 15) seconds,
118 * the odds are that the user has given up attempting to connect by then.
119 */
120 #define SYNCACHE_MAXREXMTS 3
121
122 /* Arbitrary values */
123 #define TCP_SYNCACHE_HASHSIZE 512
124 #define TCP_SYNCACHE_BUCKETLIMIT 30
125
126 struct tcp_syncache {
127 struct syncache_head *hashbase;
128 struct vm_zone *zone;
129 u_int hashsize;
130 u_int hashmask;
131 u_int bucket_limit;
132 u_int cache_count;
133 u_int cache_limit;
134 u_int rexmt_limit;
135 u_int hash_secret;
136 u_int next_reseed;
137 TAILQ_HEAD(, syncache) timerq[SYNCACHE_MAXREXMTS + 1];
138 struct callout tt_timerq[SYNCACHE_MAXREXMTS + 1];
139 };
140 static struct tcp_syncache tcp_syncache;
141
142 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, "TCP SYN cache");
143
144 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RD,
145 &tcp_syncache.bucket_limit, 0, "Per-bucket hash limit for syncache");
146
147 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RD,
148 &tcp_syncache.cache_limit, 0, "Overall entry limit for syncache");
149
150 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_RD,
151 &tcp_syncache.cache_count, 0, "Current number of entries in syncache");
152
153 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RD,
154 &tcp_syncache.hashsize, 0, "Size of TCP syncache hashtable");
155
156 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW,
157 &tcp_syncache.rexmt_limit, 0, "Limit on SYN/ACK retransmissions");
158
159 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
160
161 #define SYNCACHE_HASH(inc, mask) \
162 ((tcp_syncache.hash_secret ^ \
163 (inc)->inc_faddr.s_addr ^ \
164 ((inc)->inc_faddr.s_addr >> 16) ^ \
165 (inc)->inc_fport ^ (inc)->inc_lport) & mask)
166
167 #define SYNCACHE_HASH6(inc, mask) \
168 ((tcp_syncache.hash_secret ^ \
169 (inc)->inc6_faddr.s6_addr32[0] ^ \
170 (inc)->inc6_faddr.s6_addr32[3] ^ \
171 (inc)->inc_fport ^ (inc)->inc_lport) & mask)
172
173 #define ENDPTS_EQ(a, b) ( \
174 (a)->ie_fport == (b)->ie_fport && \
175 (a)->ie_lport == (b)->ie_lport && \
176 (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr && \
177 (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr \
178 )
179
180 #define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0)
181
182 #define SYNCACHE_TIMEOUT(sc, slot) do { \
183 sc->sc_rxtslot = slot; \
184 sc->sc_rxttime = ticks + TCPTV_RTOBASE * tcp_backoff[slot]; \
185 TAILQ_INSERT_TAIL(&tcp_syncache.timerq[slot], sc, sc_timerq); \
186 if (!callout_active(&tcp_syncache.tt_timerq[slot])) \
187 callout_reset(&tcp_syncache.tt_timerq[slot], \
188 TCPTV_RTOBASE * tcp_backoff[slot], \
189 syncache_timer, (void *)((intptr_t)slot)); \
190 } while (0)
191
192 static void
193 syncache_free(struct syncache *sc)
194 {
195 struct rtentry *rt;
196
197 if (sc->sc_ipopts)
198 (void) m_free(sc->sc_ipopts);
199 #ifdef INET6
200 if (sc->sc_inc.inc_isipv6)
201 rt = sc->sc_route6.ro_rt;
202 else
203 #endif
204 rt = sc->sc_route.ro_rt;
205 if (rt != NULL) {
206 /*
207 * If this is the only reference to a protocol cloned
208 * route, remove it immediately.
209 */
210 if (rt->rt_flags & RTF_WASCLONED &&
211 (sc->sc_flags & SCF_KEEPROUTE) == 0 &&
212 rt->rt_refcnt == 1)
213 rtrequest(RTM_DELETE, rt_key(rt),
214 rt->rt_gateway, rt_mask(rt),
215 rt->rt_flags, NULL);
216 RTFREE(rt);
217 }
218 zfree(tcp_syncache.zone, sc);
219 }
220
221 void
222 syncache_init(void)
223 {
224 int i;
225
226 tcp_syncache.cache_count = 0;
227 tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
228 tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
229 tcp_syncache.cache_limit =
230 tcp_syncache.hashsize * tcp_syncache.bucket_limit;
231 tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
232 tcp_syncache.next_reseed = 0;
233 tcp_syncache.hash_secret = arc4random();
234
235 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
236 &tcp_syncache.hashsize);
237 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
238 &tcp_syncache.cache_limit);
239 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
240 &tcp_syncache.bucket_limit);
241 if (!powerof2(tcp_syncache.hashsize)) {
242 printf("WARNING: syncache hash size is not a power of 2.\n");
243 tcp_syncache.hashsize = 512; /* safe default */
244 }
245 tcp_syncache.hashmask = tcp_syncache.hashsize - 1;
246
247 /* Allocate the hash table. */
248 MALLOC(tcp_syncache.hashbase, struct syncache_head *,
249 tcp_syncache.hashsize * sizeof(struct syncache_head),
250 M_SYNCACHE, M_WAITOK);
251
252 /* Initialize the hash buckets. */
253 for (i = 0; i < tcp_syncache.hashsize; i++) {
254 TAILQ_INIT(&tcp_syncache.hashbase[i].sch_bucket);
255 tcp_syncache.hashbase[i].sch_length = 0;
256 }
257
258 /* Initialize the timer queues. */
259 for (i = 0; i <= SYNCACHE_MAXREXMTS; i++) {
260 TAILQ_INIT(&tcp_syncache.timerq[i]);
261 callout_init(&tcp_syncache.tt_timerq[i]);
262 }
263
264 /*
265 * Allocate the syncache entries. Allow the zone to allocate one
266 * more entry than cache limit, so a new entry can bump out an
267 * older one.
268 */
269 tcp_syncache.cache_limit -= 1;
270 tcp_syncache.zone = zinit("syncache", sizeof(struct syncache),
271 tcp_syncache.cache_limit, ZONE_INTERRUPT, 0);
272 }
273
274 static void
275 syncache_insert(sc, sch)
276 struct syncache *sc;
277 struct syncache_head *sch;
278 {
279 struct syncache *sc2;
280 int s, i;
281
282 /*
283 * Make sure that we don't overflow the per-bucket
284 * limit or the total cache size limit.
285 */
286 s = splnet();
287 if (sch->sch_length >= tcp_syncache.bucket_limit) {
288 /*
289 * The bucket is full, toss the oldest element.
290 */
291 sc2 = TAILQ_FIRST(&sch->sch_bucket);
292 sc2->sc_tp->ts_recent = ticks;
293 syncache_drop(sc2, sch);
294 tcpstat.tcps_sc_bucketoverflow++;
295 } else if (tcp_syncache.cache_count >= tcp_syncache.cache_limit) {
296 /*
297 * The cache is full. Toss the oldest entry in the
298 * entire cache. This is the front entry in the
299 * first non-empty timer queue with the largest
300 * timeout value.
301 */
302 for (i = SYNCACHE_MAXREXMTS; i >= 0; i--) {
303 sc2 = TAILQ_FIRST(&tcp_syncache.timerq[i]);
304 if (sc2 != NULL)
305 break;
306 }
307 sc2->sc_tp->ts_recent = ticks;
308 syncache_drop(sc2, NULL);
309 tcpstat.tcps_sc_cacheoverflow++;
310 }
311
312 /* Initialize the entry's timer. */
313 SYNCACHE_TIMEOUT(sc, 0);
314
315 /* Put it into the bucket. */
316 TAILQ_INSERT_TAIL(&sch->sch_bucket, sc, sc_hash);
317 sch->sch_length++;
318 tcp_syncache.cache_count++;
319 tcpstat.tcps_sc_added++;
320 splx(s);
321 }
322
323 static void
324 syncache_drop(sc, sch)
325 struct syncache *sc;
326 struct syncache_head *sch;
327 {
328 int s;
329
330 if (sch == NULL) {
331 #ifdef INET6
332 if (sc->sc_inc.inc_isipv6) {
333 sch = &tcp_syncache.hashbase[
334 SYNCACHE_HASH6(&sc->sc_inc, tcp_syncache.hashmask)];
335 } else
336 #endif
337 {
338 sch = &tcp_syncache.hashbase[
339 SYNCACHE_HASH(&sc->sc_inc, tcp_syncache.hashmask)];
340 }
341 }
342
343 s = splnet();
344
345 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
346 sch->sch_length--;
347 tcp_syncache.cache_count--;
348
349 TAILQ_REMOVE(&tcp_syncache.timerq[sc->sc_rxtslot], sc, sc_timerq);
350 if (TAILQ_EMPTY(&tcp_syncache.timerq[sc->sc_rxtslot]))
351 callout_stop(&tcp_syncache.tt_timerq[sc->sc_rxtslot]);
352 splx(s);
353
354 syncache_free(sc);
355 }
356
357 /*
358 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
359 * If we have retransmitted an entry the maximum number of times, expire it.
360 */
361 static void
362 syncache_timer(xslot)
363 void *xslot;
364 {
365 intptr_t slot = (intptr_t)xslot;
366 struct syncache *sc, *nsc;
367 struct inpcb *inp;
368 int s;
369
370 s = splnet();
371 if (callout_pending(&tcp_syncache.tt_timerq[slot]) ||
372 !callout_active(&tcp_syncache.tt_timerq[slot])) {
373 splx(s);
374 return;
375 }
376 callout_deactivate(&tcp_syncache.tt_timerq[slot]);
377
378 nsc = TAILQ_FIRST(&tcp_syncache.timerq[slot]);
379 while (nsc != NULL) {
380 if (ticks < nsc->sc_rxttime)
381 break;
382 sc = nsc;
383 inp = sc->sc_tp->t_inpcb;
384 if (slot == SYNCACHE_MAXREXMTS ||
385 slot >= tcp_syncache.rexmt_limit ||
386 inp->inp_gencnt != sc->sc_inp_gencnt) {
387 nsc = TAILQ_NEXT(sc, sc_timerq);
388 syncache_drop(sc, NULL);
389 tcpstat.tcps_sc_stale++;
390 continue;
391 }
392 /*
393 * syncache_respond() may call back into the syncache to
394 * to modify another entry, so do not obtain the next
395 * entry on the timer chain until it has completed.
396 */
397 (void) syncache_respond(sc, NULL);
398 nsc = TAILQ_NEXT(sc, sc_timerq);
399 tcpstat.tcps_sc_retransmitted++;
400 TAILQ_REMOVE(&tcp_syncache.timerq[slot], sc, sc_timerq);
401 SYNCACHE_TIMEOUT(sc, slot + 1);
402 }
403 if (nsc != NULL)
404 callout_reset(&tcp_syncache.tt_timerq[slot],
405 nsc->sc_rxttime - ticks, syncache_timer, (void *)(slot));
406 splx(s);
407 }
408
409 /*
410 * Find an entry in the syncache.
411 */
412 struct syncache *
413 syncache_lookup(inc, schp)
414 struct in_conninfo *inc;
415 struct syncache_head **schp;
416 {
417 struct syncache *sc;
418 struct syncache_head *sch;
419 int s;
420
421 #ifdef INET6
422 if (inc->inc_isipv6) {
423 sch = &tcp_syncache.hashbase[
424 SYNCACHE_HASH6(inc, tcp_syncache.hashmask)];
425 *schp = sch;
426 s = splnet();
427 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
428 if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) {
429 splx(s);
430 return (sc);
431 }
432 }
433 splx(s);
434 } else
435 #endif
436 {
437 sch = &tcp_syncache.hashbase[
438 SYNCACHE_HASH(inc, tcp_syncache.hashmask)];
439 *schp = sch;
440 s = splnet();
441 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
442 #ifdef INET6
443 if (sc->sc_inc.inc_isipv6)
444 continue;
445 #endif
446 if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) {
447 splx(s);
448 return (sc);
449 }
450 }
451 splx(s);
452 }
453 return (NULL);
454 }
455
456 /*
457 * This function is called when we get a RST for a
458 * non-existent connection, so that we can see if the
459 * connection is in the syn cache. If it is, zap it.
460 */
461 void
462 syncache_chkrst(inc, th)
463 struct in_conninfo *inc;
464 struct tcphdr *th;
465 {
466 struct syncache *sc;
467 struct syncache_head *sch;
468
469 sc = syncache_lookup(inc, &sch);
470 if (sc == NULL)
471 return;
472 /*
473 * If the RST bit is set, check the sequence number to see
474 * if this is a valid reset segment.
475 * RFC 793 page 37:
476 * In all states except SYN-SENT, all reset (RST) segments
477 * are validated by checking their SEQ-fields. A reset is
478 * valid if its sequence number is in the window.
479 *
480 * The sequence number in the reset segment is normally an
481 * echo of our outgoing acknowlegement numbers, but some hosts
482 * send a reset with the sequence number at the rightmost edge
483 * of our receive window, and we have to handle this case.
484 */
485 if (SEQ_GEQ(th->th_seq, sc->sc_irs) &&
486 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
487 syncache_drop(sc, sch);
488 tcpstat.tcps_sc_reset++;
489 }
490 }
491
492 void
493 syncache_badack(inc)
494 struct in_conninfo *inc;
495 {
496 struct syncache *sc;
497 struct syncache_head *sch;
498
499 sc = syncache_lookup(inc, &sch);
500 if (sc != NULL) {
501 syncache_drop(sc, sch);
502 tcpstat.tcps_sc_badack++;
503 }
504 }
505
506 void
507 syncache_unreach(inc, th)
508 struct in_conninfo *inc;
509 struct tcphdr *th;
510 {
511 struct syncache *sc;
512 struct syncache_head *sch;
513
514 /* we are called at splnet() here */
515 sc = syncache_lookup(inc, &sch);
516 if (sc == NULL)
517 return;
518
519 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
520 if (ntohl(th->th_seq) != sc->sc_iss)
521 return;
522
523 /*
524 * If we've rertransmitted 3 times and this is our second error,
525 * we remove the entry. Otherwise, we allow it to continue on.
526 * This prevents us from incorrectly nuking an entry during a
527 * spurious network outage.
528 *
529 * See tcp_notify().
530 */
531 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxtslot < 3) {
532 sc->sc_flags |= SCF_UNREACH;
533 return;
534 }
535 syncache_drop(sc, sch);
536 tcpstat.tcps_sc_unreach++;
537 }
538
539 /*
540 * Build a new TCP socket structure from a syncache entry.
541 */
542 static struct socket *
543 syncache_socket(sc, lso)
544 struct syncache *sc;
545 struct socket *lso;
546 {
547 struct inpcb *inp = NULL;
548 struct socket *so;
549 struct tcpcb *tp;
550
551 /*
552 * Ok, create the full blown connection, and set things up
553 * as they would have been set up if we had created the
554 * connection when the SYN arrived. If we can't create
555 * the connection, abort it.
556 */
557 so = sonewconn(lso, SS_ISCONNECTED);
558 if (so == NULL) {
559 /*
560 * Drop the connection; we will send a RST if the peer
561 * retransmits the ACK,
562 */
563 tcpstat.tcps_listendrop++;
564 goto abort;
565 }
566
567 inp = sotoinpcb(so);
568
569 /*
570 * Insert new socket into hash list.
571 */
572 inp->inp_inc.inc_isipv6 = sc->sc_inc.inc_isipv6;
573 #ifdef INET6
574 if (sc->sc_inc.inc_isipv6) {
575 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
576 } else {
577 inp->inp_vflag &= ~INP_IPV6;
578 inp->inp_vflag |= INP_IPV4;
579 #endif
580 inp->inp_laddr = sc->sc_inc.inc_laddr;
581 #ifdef INET6
582 }
583 #endif
584 inp->inp_lport = sc->sc_inc.inc_lport;
585 if (in_pcbinshash(inp) != 0) {
586 /*
587 * Undo the assignments above if we failed to
588 * put the PCB on the hash lists.
589 */
590 #ifdef INET6
591 if (sc->sc_inc.inc_isipv6)
592 inp->in6p_laddr = in6addr_any;
593 else
594 #endif
595 inp->inp_laddr.s_addr = INADDR_ANY;
596 inp->inp_lport = 0;
597 goto abort;
598 }
599 #ifdef IPSEC
600 /* copy old policy into new socket's */
601 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp))
602 printf("syncache_expand: could not copy policy\n");
603 #endif
604 #ifdef INET6
605 if (sc->sc_inc.inc_isipv6) {
606 struct inpcb *oinp = sotoinpcb(lso);
607 struct in6_addr laddr6;
608 struct sockaddr_in6 *sin6;
609 /*
610 * Inherit socket options from the listening socket.
611 * Note that in6p_inputopts are not (and should not be)
612 * copied, since it stores previously received options and is
613 * used to detect if each new option is different than the
614 * previous one and hence should be passed to a user.
615 * If we copied in6p_inputopts, a user would not be able to
616 * receive options just after calling the accept system call.
617 */
618 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
619 if (oinp->in6p_outputopts)
620 inp->in6p_outputopts =
621 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
622 inp->in6p_route = sc->sc_route6;
623 sc->sc_route6.ro_rt = NULL;
624
625 MALLOC(sin6, struct sockaddr_in6 *, sizeof *sin6,
626 M_SONAME, M_NOWAIT | M_ZERO);
627 if (sin6 == NULL)
628 goto abort;
629 sin6->sin6_family = AF_INET6;
630 sin6->sin6_len = sizeof(*sin6);
631 sin6->sin6_addr = sc->sc_inc.inc6_faddr;
632 sin6->sin6_port = sc->sc_inc.inc_fport;
633 laddr6 = inp->in6p_laddr;
634 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
635 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
636 if (in6_pcbconnect(inp, (struct sockaddr *)sin6, &proc0)) {
637 inp->in6p_laddr = laddr6;
638 FREE(sin6, M_SONAME);
639 goto abort;
640 }
641 FREE(sin6, M_SONAME);
642 /* Override flowlabel from in6_pcbconnect. */
643 inp->in6p_flowinfo &= ~IPV6_FLOWLABEL_MASK;
644 inp->in6p_flowinfo |= sc->sc_flowlabel;
645 } else
646 #endif
647 {
648 struct in_addr laddr;
649 struct sockaddr_in *sin;
650
651 inp->inp_options = ip_srcroute();
652 if (inp->inp_options == NULL) {
653 inp->inp_options = sc->sc_ipopts;
654 sc->sc_ipopts = NULL;
655 }
656 inp->inp_route = sc->sc_route;
657 sc->sc_route.ro_rt = NULL;
658
659 MALLOC(sin, struct sockaddr_in *, sizeof *sin,
660 M_SONAME, M_NOWAIT | M_ZERO);
661 if (sin == NULL)
662 goto abort;
663 sin->sin_family = AF_INET;
664 sin->sin_len = sizeof(*sin);
665 sin->sin_addr = sc->sc_inc.inc_faddr;
666 sin->sin_port = sc->sc_inc.inc_fport;
667 bzero((caddr_t)sin->sin_zero, sizeof(sin->sin_zero));
668 laddr = inp->inp_laddr;
669 if (inp->inp_laddr.s_addr == INADDR_ANY)
670 inp->inp_laddr = sc->sc_inc.inc_laddr;
671 if (in_pcbconnect(inp, (struct sockaddr *)sin, &proc0)) {
672 inp->inp_laddr = laddr;
673 FREE(sin, M_SONAME);
674 goto abort;
675 }
676 FREE(sin, M_SONAME);
677 }
678
679 tp = intotcpcb(inp);
680 tp->t_state = TCPS_SYN_RECEIVED;
681 tp->iss = sc->sc_iss;
682 tp->irs = sc->sc_irs;
683 tcp_rcvseqinit(tp);
684 tcp_sendseqinit(tp);
685 tp->snd_wl1 = sc->sc_irs;
686 tp->rcv_up = sc->sc_irs + 1;
687 tp->rcv_wnd = sc->sc_wnd;
688 tp->rcv_adv += tp->rcv_wnd;
689
690 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
691 if (sc->sc_flags & SCF_NOOPT)
692 tp->t_flags |= TF_NOOPT;
693 if (sc->sc_flags & SCF_WINSCALE) {
694 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
695 tp->requested_s_scale = sc->sc_requested_s_scale;
696 tp->request_r_scale = sc->sc_request_r_scale;
697 }
698 if (sc->sc_flags & SCF_TIMESTAMP) {
699 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
700 tp->ts_recent = sc->sc_tsrecent;
701 tp->ts_recent_age = ticks;
702 }
703 if (sc->sc_flags & SCF_CC) {
704 /*
705 * Initialization of the tcpcb for transaction;
706 * set SND.WND = SEG.WND,
707 * initialize CCsend and CCrecv.
708 */
709 tp->t_flags |= TF_REQ_CC|TF_RCVD_CC;
710 tp->cc_send = sc->sc_cc_send;
711 tp->cc_recv = sc->sc_cc_recv;
712 }
713 #ifdef TCP_SIGNATURE
714 if (sc->sc_flags & SCF_SIGNATURE)
715 tp->t_flags |= TF_SIGNATURE;
716 #endif
717
718 tcp_mss(tp, sc->sc_peer_mss);
719
720 /*
721 * If the SYN,ACK was retransmitted, reset cwnd to 1 segment.
722 */
723 if (sc->sc_rxtslot != 0)
724 tp->snd_cwnd = tp->t_maxseg;
725 callout_reset(tp->tt_keep, tcp_keepinit, tcp_timer_keep, tp);
726
727 tcpstat.tcps_accepts++;
728 return (so);
729
730 abort:
731 if (so != NULL)
732 (void) soabort(so);
733 return (NULL);
734 }
735
736 /*
737 * This function gets called when we receive an ACK for a
738 * socket in the LISTEN state. We look up the connection
739 * in the syncache, and if its there, we pull it out of
740 * the cache and turn it into a full-blown connection in
741 * the SYN-RECEIVED state.
742 */
743 int
744 syncache_expand(inc, th, sop, m)
745 struct in_conninfo *inc;
746 struct tcphdr *th;
747 struct socket **sop;
748 struct mbuf *m;
749 {
750 struct syncache *sc;
751 struct syncache_head *sch;
752 struct socket *so;
753
754 sc = syncache_lookup(inc, &sch);
755 if (sc == NULL) {
756 /*
757 * There is no syncache entry, so see if this ACK is
758 * a returning syncookie. To do this, first:
759 * A. See if this socket has had a syncache entry dropped in
760 * the past. We don't want to accept a bogus syncookie
761 * if we've never received a SYN.
762 * B. check that the syncookie is valid. If it is, then
763 * cobble up a fake syncache entry, and return.
764 */
765 if (!tcp_syncookies)
766 return (0);
767 sc = syncookie_lookup(inc, th, *sop);
768 if (sc == NULL)
769 return (0);
770 sch = NULL;
771 tcpstat.tcps_sc_recvcookie++;
772 }
773
774 /*
775 * If seg contains an ACK, but not for our SYN/ACK, send a RST.
776 */
777 if (th->th_ack != sc->sc_iss + 1)
778 return (0);
779
780 so = syncache_socket(sc, *sop);
781 if (so == NULL) {
782 #if 0
783 resetandabort:
784 /* XXXjlemon check this - is this correct? */
785 (void) tcp_respond(NULL, m, m, th,
786 th->th_seq + tlen, (tcp_seq)0, TH_RST|TH_ACK);
787 #endif
788 m_freem(m); /* XXX only needed for above */
789 tcpstat.tcps_sc_aborted++;
790 } else {
791 sc->sc_flags |= SCF_KEEPROUTE;
792 tcpstat.tcps_sc_completed++;
793 }
794 if (sch == NULL)
795 syncache_free(sc);
796 else
797 syncache_drop(sc, sch);
798 *sop = so;
799 return (1);
800 }
801
802 /*
803 * Given a LISTEN socket and an inbound SYN request, add
804 * this to the syn cache, and send back a segment:
805 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
806 * to the source.
807 *
808 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
809 * Doing so would require that we hold onto the data and deliver it
810 * to the application. However, if we are the target of a SYN-flood
811 * DoS attack, an attacker could send data which would eventually
812 * consume all available buffer space if it were ACKed. By not ACKing
813 * the data, we avoid this DoS scenario.
814 */
815 int
816 syncache_add(inc, to, th, sop, m)
817 struct in_conninfo *inc;
818 struct tcpopt *to;
819 struct tcphdr *th;
820 struct socket **sop;
821 struct mbuf *m;
822 {
823 struct tcpcb *tp;
824 struct socket *so;
825 struct syncache *sc = NULL;
826 struct syncache_head *sch;
827 struct mbuf *ipopts = NULL;
828 struct rmxp_tao *taop;
829 u_int32_t flowtmp;
830 int i, s, win;
831
832 so = *sop;
833 tp = sototcpcb(so);
834
835 /*
836 * Remember the IP options, if any.
837 */
838 #ifdef INET6
839 if (!inc->inc_isipv6)
840 #endif
841 ipopts = ip_srcroute();
842
843 /*
844 * See if we already have an entry for this connection.
845 * If we do, resend the SYN,ACK, and reset the retransmit timer.
846 *
847 * XXX
848 * should the syncache be re-initialized with the contents
849 * of the new SYN here (which may have different options?)
850 */
851 sc = syncache_lookup(inc, &sch);
852 if (sc != NULL) {
853 tcpstat.tcps_sc_dupsyn++;
854 if (ipopts) {
855 /*
856 * If we were remembering a previous source route,
857 * forget it and use the new one we've been given.
858 */
859 if (sc->sc_ipopts)
860 (void) m_free(sc->sc_ipopts);
861 sc->sc_ipopts = ipopts;
862 }
863 /*
864 * Update timestamp if present.
865 */
866 if (sc->sc_flags & SCF_TIMESTAMP)
867 sc->sc_tsrecent = to->to_tsval;
868 /*
869 * PCB may have changed, pick up new values.
870 */
871 sc->sc_tp = tp;
872 sc->sc_inp_gencnt = tp->t_inpcb->inp_gencnt;
873 if (syncache_respond(sc, m) == 0) {
874 s = splnet();
875 TAILQ_REMOVE(&tcp_syncache.timerq[sc->sc_rxtslot],
876 sc, sc_timerq);
877 SYNCACHE_TIMEOUT(sc, sc->sc_rxtslot);
878 splx(s);
879 tcpstat.tcps_sndacks++;
880 tcpstat.tcps_sndtotal++;
881 }
882 *sop = NULL;
883 return (1);
884 }
885
886 sc = zalloc(tcp_syncache.zone);
887 if (sc == NULL) {
888 /*
889 * The zone allocator couldn't provide more entries.
890 * Treat this as if the cache was full; drop the oldest
891 * entry and insert the new one.
892 */
893 s = splnet();
894 for (i = SYNCACHE_MAXREXMTS; i >= 0; i--) {
895 sc = TAILQ_FIRST(&tcp_syncache.timerq[i]);
896 if (sc != NULL)
897 break;
898 }
899 sc->sc_tp->ts_recent = ticks;
900 syncache_drop(sc, NULL);
901 splx(s);
902 tcpstat.tcps_sc_zonefail++;
903 sc = zalloc(tcp_syncache.zone);
904 if (sc == NULL) {
905 if (ipopts)
906 (void) m_free(ipopts);
907 return (0);
908 }
909 }
910
911 /*
912 * Fill in the syncache values.
913 */
914 bzero(sc, sizeof(*sc));
915 sc->sc_tp = tp;
916 sc->sc_inp_gencnt = tp->t_inpcb->inp_gencnt;
917 sc->sc_ipopts = ipopts;
918 sc->sc_inc.inc_fport = inc->inc_fport;
919 sc->sc_inc.inc_lport = inc->inc_lport;
920 #ifdef INET6
921 sc->sc_inc.inc_isipv6 = inc->inc_isipv6;
922 if (inc->inc_isipv6) {
923 sc->sc_inc.inc6_faddr = inc->inc6_faddr;
924 sc->sc_inc.inc6_laddr = inc->inc6_laddr;
925 sc->sc_route6.ro_rt = NULL;
926 } else
927 #endif
928 {
929 sc->sc_inc.inc_faddr = inc->inc_faddr;
930 sc->sc_inc.inc_laddr = inc->inc_laddr;
931 sc->sc_route.ro_rt = NULL;
932 }
933 sc->sc_irs = th->th_seq;
934 sc->sc_flags = 0;
935 sc->sc_peer_mss = to->to_flags & TOF_MSS ? to->to_mss : 0;
936 sc->sc_flowlabel = 0;
937 if (tcp_syncookies) {
938 sc->sc_iss = syncookie_generate(sc, &flowtmp);
939 #ifdef INET6
940 if (inc->inc_isipv6 &&
941 (sc->sc_tp->t_inpcb->in6p_flags & IN6P_AUTOFLOWLABEL)) {
942 sc->sc_flowlabel = flowtmp & IPV6_FLOWLABEL_MASK;
943 }
944 #endif
945 } else {
946 sc->sc_iss = arc4random();
947 #ifdef INET6
948 if (inc->inc_isipv6 &&
949 (sc->sc_tp->t_inpcb->in6p_flags & IN6P_AUTOFLOWLABEL)) {
950 sc->sc_flowlabel =
951 (htonl(ip6_flow_seq++) & IPV6_FLOWLABEL_MASK);
952 }
953 #endif
954 }
955
956 /* Initial receive window: clip sbspace to [0 .. TCP_MAXWIN] */
957 win = sbspace(&so->so_rcv);
958 win = imax(win, 0);
959 win = imin(win, TCP_MAXWIN);
960 sc->sc_wnd = win;
961
962 if (tcp_do_rfc1323) {
963 /*
964 * A timestamp received in a SYN makes
965 * it ok to send timestamp requests and replies.
966 */
967 if (to->to_flags & TOF_TS) {
968 sc->sc_tsrecent = to->to_tsval;
969 sc->sc_flags |= SCF_TIMESTAMP;
970 }
971 if (to->to_flags & TOF_SCALE) {
972 int wscale = 0;
973
974 /* Compute proper scaling value from buffer space */
975 while (wscale < TCP_MAX_WINSHIFT &&
976 (TCP_MAXWIN << wscale) < so->so_rcv.sb_hiwat)
977 wscale++;
978 sc->sc_request_r_scale = wscale;
979 sc->sc_requested_s_scale = to->to_requested_s_scale;
980 sc->sc_flags |= SCF_WINSCALE;
981 }
982 }
983 if (tcp_do_rfc1644) {
984 /*
985 * A CC or CC.new option received in a SYN makes
986 * it ok to send CC in subsequent segments.
987 */
988 if (to->to_flags & (TOF_CC|TOF_CCNEW)) {
989 sc->sc_cc_recv = to->to_cc;
990 sc->sc_cc_send = CC_INC(tcp_ccgen);
991 sc->sc_flags |= SCF_CC;
992 }
993 }
994 if (tp->t_flags & TF_NOOPT)
995 sc->sc_flags = SCF_NOOPT;
996 #ifdef TCP_SIGNATURE
997 /*
998 * If listening socket requested TCP digests, and received SYN
999 * contains the option, flag this in the syncache so that
1000 * syncache_respond() will do the right thing with the SYN+ACK.
1001 * XXX Currently we always record the option by default and will
1002 * attempt to use it in syncache_respond().
1003 */
1004 if (to->to_flags & TOF_SIGNATURE)
1005 sc->sc_flags = SCF_SIGNATURE;
1006 #endif
1007
1008 /*
1009 * XXX
1010 * We have the option here of not doing TAO (even if the segment
1011 * qualifies) and instead fall back to a normal 3WHS via the syncache.
1012 * This allows us to apply synflood protection to TAO-qualifying SYNs
1013 * also. However, there should be a hueristic to determine when to
1014 * do this, and is not present at the moment.
1015 */
1016
1017 /*
1018 * Perform TAO test on incoming CC (SEG.CC) option, if any.
1019 * - compare SEG.CC against cached CC from the same host, if any.
1020 * - if SEG.CC > chached value, SYN must be new and is accepted
1021 * immediately: save new CC in the cache, mark the socket
1022 * connected, enter ESTABLISHED state, turn on flag to
1023 * send a SYN in the next segment.
1024 * A virtual advertised window is set in rcv_adv to
1025 * initialize SWS prevention. Then enter normal segment
1026 * processing: drop SYN, process data and FIN.
1027 * - otherwise do a normal 3-way handshake.
1028 */
1029 taop = tcp_gettaocache(&sc->sc_inc);
1030 if ((to->to_flags & TOF_CC) != 0) {
1031 if (((tp->t_flags & TF_NOPUSH) != 0) &&
1032 sc->sc_flags & SCF_CC &&
1033 taop != NULL && taop->tao_cc != 0 &&
1034 CC_GT(to->to_cc, taop->tao_cc)) {
1035 sc->sc_rxtslot = 0;
1036 so = syncache_socket(sc, *sop);
1037 if (so != NULL) {
1038 sc->sc_flags |= SCF_KEEPROUTE;
1039 taop->tao_cc = to->to_cc;
1040 *sop = so;
1041 }
1042 syncache_free(sc);
1043 return (so != NULL);
1044 }
1045 } else {
1046 /*
1047 * No CC option, but maybe CC.NEW: invalidate cached value.
1048 */
1049 if (taop != NULL)
1050 taop->tao_cc = 0;
1051 }
1052 /*
1053 * TAO test failed or there was no CC option,
1054 * do a standard 3-way handshake.
1055 */
1056 if (syncache_respond(sc, m) == 0) {
1057 syncache_insert(sc, sch);
1058 tcpstat.tcps_sndacks++;
1059 tcpstat.tcps_sndtotal++;
1060 } else {
1061 syncache_free(sc);
1062 tcpstat.tcps_sc_dropped++;
1063 }
1064 *sop = NULL;
1065 return (1);
1066 }
1067
1068 static int
1069 syncache_respond(sc, m)
1070 struct syncache *sc;
1071 struct mbuf *m;
1072 {
1073 u_int8_t *optp;
1074 int optlen, error;
1075 u_int16_t tlen, hlen, mssopt;
1076 struct ip *ip = NULL;
1077 struct rtentry *rt;
1078 struct tcphdr *th;
1079 #ifdef INET6
1080 struct ip6_hdr *ip6 = NULL;
1081 #endif
1082
1083 #ifdef INET6
1084 if (sc->sc_inc.inc_isipv6) {
1085 rt = tcp_rtlookup6(&sc->sc_inc);
1086 if (rt != NULL)
1087 mssopt = rt->rt_ifp->if_mtu -
1088 (sizeof(struct ip6_hdr) + sizeof(struct tcphdr));
1089 else
1090 mssopt = tcp_v6mssdflt;
1091 hlen = sizeof(struct ip6_hdr);
1092 } else
1093 #endif
1094 {
1095 rt = tcp_rtlookup(&sc->sc_inc);
1096 if (rt != NULL)
1097 mssopt = rt->rt_ifp->if_mtu -
1098 (sizeof(struct ip) + sizeof(struct tcphdr));
1099 else
1100 mssopt = tcp_mssdflt;
1101 hlen = sizeof(struct ip);
1102 }
1103
1104 /* Compute the size of the TCP options. */
1105 if (sc->sc_flags & SCF_NOOPT) {
1106 optlen = 0;
1107 } else {
1108 optlen = TCPOLEN_MAXSEG +
1109 ((sc->sc_flags & SCF_WINSCALE) ? 4 : 0) +
1110 ((sc->sc_flags & SCF_TIMESTAMP) ? TCPOLEN_TSTAMP_APPA : 0) +
1111 ((sc->sc_flags & SCF_CC) ? TCPOLEN_CC_APPA * 2 : 0);
1112 #ifdef TCP_SIGNATURE
1113 optlen += ((sc->sc_flags & SCF_SIGNATURE) ?
1114 (TCPOLEN_SIGNATURE + 2) : 0);
1115 #endif
1116 }
1117 tlen = hlen + sizeof(struct tcphdr) + optlen;
1118
1119 /*
1120 * XXX
1121 * assume that the entire packet will fit in a header mbuf
1122 */
1123 KASSERT(max_linkhdr + tlen <= MHLEN, ("syncache: mbuf too small"));
1124
1125 /*
1126 * XXX shouldn't this reuse the mbuf if possible ?
1127 * Create the IP+TCP header from scratch.
1128 */
1129 if (m)
1130 m_freem(m);
1131
1132 m = m_gethdr(M_DONTWAIT, MT_HEADER);
1133 if (m == NULL)
1134 return (ENOBUFS);
1135 m->m_data += max_linkhdr;
1136 m->m_len = tlen;
1137 m->m_pkthdr.len = tlen;
1138 m->m_pkthdr.rcvif = NULL;
1139
1140 #ifdef INET6
1141 if (sc->sc_inc.inc_isipv6) {
1142 ip6 = mtod(m, struct ip6_hdr *);
1143 ip6->ip6_vfc = IPV6_VERSION;
1144 ip6->ip6_nxt = IPPROTO_TCP;
1145 ip6->ip6_src = sc->sc_inc.inc6_laddr;
1146 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
1147 ip6->ip6_plen = htons(tlen - hlen);
1148 /* ip6_hlim is set after checksum */
1149 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK;
1150 ip6->ip6_flow |= sc->sc_flowlabel;
1151
1152 th = (struct tcphdr *)(ip6 + 1);
1153 } else
1154 #endif
1155 {
1156 ip = mtod(m, struct ip *);
1157 ip->ip_v = IPVERSION;
1158 ip->ip_hl = sizeof(struct ip) >> 2;
1159 ip->ip_len = tlen;
1160 ip->ip_id = 0;
1161 ip->ip_off = 0;
1162 ip->ip_sum = 0;
1163 ip->ip_p = IPPROTO_TCP;
1164 ip->ip_src = sc->sc_inc.inc_laddr;
1165 ip->ip_dst = sc->sc_inc.inc_faddr;
1166 ip->ip_ttl = sc->sc_tp->t_inpcb->inp_ip_ttl; /* XXX */
1167 ip->ip_tos = sc->sc_tp->t_inpcb->inp_ip_tos; /* XXX */
1168
1169 /*
1170 * See if we should do MTU discovery. Route lookups are expensive,
1171 * so we will only unset the DF bit if:
1172 *
1173 * 1) path_mtu_discovery is disabled
1174 * 2) the SCF_UNREACH flag has been set
1175 */
1176 if (path_mtu_discovery
1177 && ((sc->sc_flags & SCF_UNREACH) == 0)) {
1178 ip->ip_off |= IP_DF;
1179 }
1180
1181 th = (struct tcphdr *)(ip + 1);
1182 }
1183 th->th_sport = sc->sc_inc.inc_lport;
1184 th->th_dport = sc->sc_inc.inc_fport;
1185
1186 th->th_seq = htonl(sc->sc_iss);
1187 th->th_ack = htonl(sc->sc_irs + 1);
1188 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
1189 th->th_x2 = 0;
1190 th->th_flags = TH_SYN|TH_ACK;
1191 th->th_win = htons(sc->sc_wnd);
1192 th->th_urp = 0;
1193
1194 /* Tack on the TCP options. */
1195 if (optlen == 0)
1196 goto no_options;
1197 optp = (u_int8_t *)(th + 1);
1198 *optp++ = TCPOPT_MAXSEG;
1199 *optp++ = TCPOLEN_MAXSEG;
1200 *optp++ = (mssopt >> 8) & 0xff;
1201 *optp++ = mssopt & 0xff;
1202
1203 if (sc->sc_flags & SCF_WINSCALE) {
1204 *((u_int32_t *)optp) = htonl(TCPOPT_NOP << 24 |
1205 TCPOPT_WINDOW << 16 | TCPOLEN_WINDOW << 8 |
1206 sc->sc_request_r_scale);
1207 optp += 4;
1208 }
1209
1210 if (sc->sc_flags & SCF_TIMESTAMP) {
1211 u_int32_t *lp = (u_int32_t *)(optp);
1212
1213 /* Form timestamp option as shown in appendix A of RFC 1323. */
1214 *lp++ = htonl(TCPOPT_TSTAMP_HDR);
1215 *lp++ = htonl(ticks);
1216 *lp = htonl(sc->sc_tsrecent);
1217 optp += TCPOLEN_TSTAMP_APPA;
1218 }
1219
1220 /*
1221 * Send CC and CC.echo if we received CC from our peer.
1222 */
1223 if (sc->sc_flags & SCF_CC) {
1224 u_int32_t *lp = (u_int32_t *)(optp);
1225
1226 *lp++ = htonl(TCPOPT_CC_HDR(TCPOPT_CC));
1227 *lp++ = htonl(sc->sc_cc_send);
1228 *lp++ = htonl(TCPOPT_CC_HDR(TCPOPT_CCECHO));
1229 *lp = htonl(sc->sc_cc_recv);
1230 optp += TCPOLEN_CC_APPA * 2;
1231 }
1232 #ifdef TCP_SIGNATURE
1233 /*
1234 * Handle TCP-MD5 passive opener response.
1235 */
1236 if (sc->sc_flags & SCF_SIGNATURE) {
1237 u_int8_t *bp = optp;
1238 int i;
1239
1240 *bp++ = TCPOPT_SIGNATURE;
1241 *bp++ = TCPOLEN_SIGNATURE;
1242 for (i = 0; i < TCP_SIGLEN; i++)
1243 *bp++ = 0;
1244 tcp_signature_compute(m, sizeof(struct ip), 0, optlen,
1245 optp + 2, IPSEC_DIR_OUTBOUND);
1246 *bp++ = TCPOPT_NOP;
1247 *bp++ = TCPOPT_EOL;
1248 optp += TCPOLEN_SIGNATURE + 2;
1249 }
1250 #endif /* TCP_SIGNATURE */
1251 no_options:
1252
1253 #ifdef INET6
1254 if (sc->sc_inc.inc_isipv6) {
1255 struct route_in6 *ro6 = &sc->sc_route6;
1256
1257 th->th_sum = 0;
1258 th->th_sum = in6_cksum(m, IPPROTO_TCP, hlen, tlen - hlen);
1259 ip6->ip6_hlim = in6_selecthlim(NULL,
1260 ro6->ro_rt ? ro6->ro_rt->rt_ifp : NULL);
1261 error = ip6_output(m, NULL, ro6, 0, NULL, NULL,
1262 sc->sc_tp->t_inpcb);
1263 } else
1264 #endif
1265 {
1266 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
1267 htons(tlen - hlen + IPPROTO_TCP));
1268 m->m_pkthdr.csum_flags = CSUM_TCP;
1269 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1270 error = ip_output(m, sc->sc_ipopts, &sc->sc_route, 0, NULL,
1271 sc->sc_tp->t_inpcb);
1272 }
1273 return (error);
1274 }
1275
1276 /*
1277 * cookie layers:
1278 *
1279 * |. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .|
1280 * | peer iss |
1281 * | MD5(laddr,faddr,secret,lport,fport) |. . . . . . .|
1282 * | 0 |(A)| |
1283 * (A): peer mss index
1284 */
1285
1286 /*
1287 * The values below are chosen to minimize the size of the tcp_secret
1288 * table, as well as providing roughly a 16 second lifetime for the cookie.
1289 */
1290
1291 #define SYNCOOKIE_WNDBITS 5 /* exposed bits for window indexing */
1292 #define SYNCOOKIE_TIMESHIFT 1 /* scale ticks to window time units */
1293
1294 #define SYNCOOKIE_WNDMASK ((1 << SYNCOOKIE_WNDBITS) - 1)
1295 #define SYNCOOKIE_NSECRETS (1 << SYNCOOKIE_WNDBITS)
1296 #define SYNCOOKIE_TIMEOUT \
1297 (hz * (1 << SYNCOOKIE_WNDBITS) / (1 << SYNCOOKIE_TIMESHIFT))
1298 #define SYNCOOKIE_DATAMASK ((3 << SYNCOOKIE_WNDBITS) | SYNCOOKIE_WNDMASK)
1299
1300 static struct {
1301 u_int32_t ts_secbits[4];
1302 u_int ts_expire;
1303 } tcp_secret[SYNCOOKIE_NSECRETS];
1304
1305 static int tcp_msstab[] = { 0, 536, 1460, 8960 };
1306
1307 static MD5_CTX syn_ctx;
1308
1309 #define MD5Add(v) MD5Update(&syn_ctx, (u_char *)&v, sizeof(v))
1310
1311 struct md5_add {
1312 u_int32_t laddr, faddr;
1313 u_int32_t secbits[4];
1314 u_int16_t lport, fport;
1315 };
1316
1317 #ifdef CTASSERT
1318 CTASSERT(sizeof(struct md5_add) == 28);
1319 #endif
1320
1321 /*
1322 * Consider the problem of a recreated (and retransmitted) cookie. If the
1323 * original SYN was accepted, the connection is established. The second
1324 * SYN is inflight, and if it arrives with an ISN that falls within the
1325 * receive window, the connection is killed.
1326 *
1327 * However, since cookies have other problems, this may not be worth
1328 * worrying about.
1329 */
1330
1331 static u_int32_t
1332 syncookie_generate(struct syncache *sc, u_int32_t *flowid)
1333 {
1334 u_int32_t md5_buffer[4];
1335 u_int32_t data;
1336 int idx, i;
1337 struct md5_add add;
1338
1339 idx = ((ticks << SYNCOOKIE_TIMESHIFT) / hz) & SYNCOOKIE_WNDMASK;
1340 if (tcp_secret[idx].ts_expire < ticks) {
1341 for (i = 0; i < 4; i++)
1342 tcp_secret[idx].ts_secbits[i] = arc4random();
1343 tcp_secret[idx].ts_expire = ticks + SYNCOOKIE_TIMEOUT;
1344 }
1345 for (data = sizeof(tcp_msstab) / sizeof(int) - 1; data > 0; data--)
1346 if (tcp_msstab[data] <= sc->sc_peer_mss)
1347 break;
1348 data = (data << SYNCOOKIE_WNDBITS) | idx;
1349 data ^= sc->sc_irs; /* peer's iss */
1350 MD5Init(&syn_ctx);
1351 #ifdef INET6
1352 if (sc->sc_inc.inc_isipv6) {
1353 MD5Add(sc->sc_inc.inc6_laddr);
1354 MD5Add(sc->sc_inc.inc6_faddr);
1355 add.laddr = 0;
1356 add.faddr = 0;
1357 } else
1358 #endif
1359 {
1360 add.laddr = sc->sc_inc.inc_laddr.s_addr;
1361 add.faddr = sc->sc_inc.inc_faddr.s_addr;
1362 }
1363 add.lport = sc->sc_inc.inc_lport;
1364 add.fport = sc->sc_inc.inc_fport;
1365 add.secbits[0] = tcp_secret[idx].ts_secbits[0];
1366 add.secbits[1] = tcp_secret[idx].ts_secbits[1];
1367 add.secbits[2] = tcp_secret[idx].ts_secbits[2];
1368 add.secbits[3] = tcp_secret[idx].ts_secbits[3];
1369 MD5Add(add);
1370 MD5Final((u_char *)&md5_buffer, &syn_ctx);
1371 data ^= (md5_buffer[0] & ~SYNCOOKIE_WNDMASK);
1372 *flowid = md5_buffer[1];
1373 return (data);
1374 }
1375
1376 static struct syncache *
1377 syncookie_lookup(inc, th, so)
1378 struct in_conninfo *inc;
1379 struct tcphdr *th;
1380 struct socket *so;
1381 {
1382 u_int32_t md5_buffer[4];
1383 struct syncache *sc;
1384 u_int32_t data;
1385 int wnd, idx;
1386 struct md5_add add;
1387
1388 data = (th->th_ack - 1) ^ (th->th_seq - 1); /* remove ISS */
1389 idx = data & SYNCOOKIE_WNDMASK;
1390 if (tcp_secret[idx].ts_expire < ticks ||
1391 sototcpcb(so)->ts_recent + SYNCOOKIE_TIMEOUT < ticks)
1392 return (NULL);
1393 MD5Init(&syn_ctx);
1394 #ifdef INET6
1395 if (inc->inc_isipv6) {
1396 MD5Add(inc->inc6_laddr);
1397 MD5Add(inc->inc6_faddr);
1398 add.laddr = 0;
1399 add.faddr = 0;
1400 } else
1401 #endif
1402 {
1403 add.laddr = inc->inc_laddr.s_addr;
1404 add.faddr = inc->inc_faddr.s_addr;
1405 }
1406 add.lport = inc->inc_lport;
1407 add.fport = inc->inc_fport;
1408 add.secbits[0] = tcp_secret[idx].ts_secbits[0];
1409 add.secbits[1] = tcp_secret[idx].ts_secbits[1];
1410 add.secbits[2] = tcp_secret[idx].ts_secbits[2];
1411 add.secbits[3] = tcp_secret[idx].ts_secbits[3];
1412 MD5Add(add);
1413 MD5Final((u_char *)&md5_buffer, &syn_ctx);
1414 data ^= md5_buffer[0];
1415 if ((data & ~SYNCOOKIE_DATAMASK) != 0)
1416 return (NULL);
1417 data = data >> SYNCOOKIE_WNDBITS;
1418
1419 sc = zalloc(tcp_syncache.zone);
1420 if (sc == NULL)
1421 return (NULL);
1422 /*
1423 * Fill in the syncache values.
1424 * XXX duplicate code from syncache_add
1425 */
1426 sc->sc_ipopts = NULL;
1427 sc->sc_inc.inc_fport = inc->inc_fport;
1428 sc->sc_inc.inc_lport = inc->inc_lport;
1429 sc->sc_tp = sototcpcb(so);
1430 #ifdef INET6
1431 sc->sc_inc.inc_isipv6 = inc->inc_isipv6;
1432 if (inc->inc_isipv6) {
1433 sc->sc_inc.inc6_faddr = inc->inc6_faddr;
1434 sc->sc_inc.inc6_laddr = inc->inc6_laddr;
1435 sc->sc_route6.ro_rt = NULL;
1436 if (sc->sc_tp->t_inpcb->in6p_flags & IN6P_AUTOFLOWLABEL)
1437 sc->sc_flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK;
1438 } else
1439 #endif
1440 {
1441 sc->sc_inc.inc_faddr = inc->inc_faddr;
1442 sc->sc_inc.inc_laddr = inc->inc_laddr;
1443 sc->sc_route.ro_rt = NULL;
1444 }
1445 sc->sc_irs = th->th_seq - 1;
1446 sc->sc_iss = th->th_ack - 1;
1447 wnd = sbspace(&so->so_rcv);
1448 wnd = imax(wnd, 0);
1449 wnd = imin(wnd, TCP_MAXWIN);
1450 sc->sc_wnd = wnd;
1451 sc->sc_flags = 0;
1452 sc->sc_rxtslot = 0;
1453 sc->sc_peer_mss = tcp_msstab[data];
1454 return (sc);
1455 }
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