1 /*-
2 * Copyright (c) 2001 McAfee, Inc.
3 * Copyright (c) 2006,2013 Andre Oppermann, Internet Business Solutions AG
4 * All rights reserved.
5 *
6 * This software was developed for the FreeBSD Project by Jonathan Lemon
7 * and McAfee Research, the Security Research Division of McAfee, Inc. under
8 * DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the
9 * DARPA CHATS research program. [2001 McAfee, Inc.]
10 *
11 * Redistribution and use in source and binary forms, with or without
12 * modification, are permitted provided that the following conditions
13 * are met:
14 * 1. Redistributions of source code must retain the above copyright
15 * notice, this list of conditions and the following disclaimer.
16 * 2. Redistributions in binary form must reproduce the above copyright
17 * notice, this list of conditions and the following disclaimer in the
18 * documentation and/or other materials provided with the distribution.
19 *
20 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30 * SUCH DAMAGE.
31 */
32
33 #include <sys/cdefs.h>
34 __FBSDID("$FreeBSD$");
35
36 #include "opt_inet.h"
37 #include "opt_inet6.h"
38 #include "opt_ipsec.h"
39 #include "opt_pcbgroup.h"
40
41 #include <sys/param.h>
42 #include <sys/systm.h>
43 #include <sys/kernel.h>
44 #include <sys/sysctl.h>
45 #include <sys/limits.h>
46 #include <sys/lock.h>
47 #include <sys/mutex.h>
48 #include <sys/malloc.h>
49 #include <sys/mbuf.h>
50 #include <sys/proc.h> /* for proc0 declaration */
51 #include <sys/random.h>
52 #include <sys/socket.h>
53 #include <sys/socketvar.h>
54 #include <sys/syslog.h>
55 #include <sys/ucred.h>
56
57 #include <sys/md5.h>
58 #include <crypto/siphash/siphash.h>
59
60 #include <vm/uma.h>
61
62 #include <net/if.h>
63 #include <net/route.h>
64 #include <net/vnet.h>
65
66 #include <netinet/in.h>
67 #include <netinet/in_systm.h>
68 #include <netinet/ip.h>
69 #include <netinet/in_var.h>
70 #include <netinet/in_pcb.h>
71 #include <netinet/ip_var.h>
72 #include <netinet/ip_options.h>
73 #ifdef INET6
74 #include <netinet/ip6.h>
75 #include <netinet/icmp6.h>
76 #include <netinet6/nd6.h>
77 #include <netinet6/ip6_var.h>
78 #include <netinet6/in6_pcb.h>
79 #endif
80 #include <netinet/tcp.h>
81 #include <netinet/tcp_fsm.h>
82 #include <netinet/tcp_seq.h>
83 #include <netinet/tcp_timer.h>
84 #include <netinet/tcp_var.h>
85 #include <netinet/tcp_syncache.h>
86 #ifdef INET6
87 #include <netinet6/tcp6_var.h>
88 #endif
89 #ifdef TCP_OFFLOAD
90 #include <netinet/toecore.h>
91 #endif
92
93 #ifdef IPSEC
94 #include <netipsec/ipsec.h>
95 #ifdef INET6
96 #include <netipsec/ipsec6.h>
97 #endif
98 #include <netipsec/key.h>
99 #endif /*IPSEC*/
100
101 #include <machine/in_cksum.h>
102
103 #include <security/mac/mac_framework.h>
104
105 static VNET_DEFINE(int, tcp_syncookies) = 1;
106 #define V_tcp_syncookies VNET(tcp_syncookies)
107 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW,
108 &VNET_NAME(tcp_syncookies), 0,
109 "Use TCP SYN cookies if the syncache overflows");
110
111 static VNET_DEFINE(int, tcp_syncookiesonly) = 0;
112 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly)
113 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_RW,
114 &VNET_NAME(tcp_syncookiesonly), 0,
115 "Use only TCP SYN cookies");
116
117 #ifdef TCP_OFFLOAD
118 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL)
119 #endif
120
121 static void syncache_drop(struct syncache *, struct syncache_head *);
122 static void syncache_free(struct syncache *);
123 static void syncache_insert(struct syncache *, struct syncache_head *);
124 static int syncache_respond(struct syncache *);
125 static struct socket *syncache_socket(struct syncache *, struct socket *,
126 struct mbuf *m);
127 static int syncache_sysctl_count(SYSCTL_HANDLER_ARGS);
128 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch,
129 int docallout);
130 static void syncache_timer(void *);
131
132 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t,
133 uint8_t *, uintptr_t);
134 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *);
135 static struct syncache
136 *syncookie_lookup(struct in_conninfo *, struct syncache_head *,
137 struct syncache *, struct tcphdr *, struct tcpopt *,
138 struct socket *);
139 static void syncookie_reseed(void *);
140 #ifdef INVARIANTS
141 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
142 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
143 struct socket *lso);
144 #endif
145
146 /*
147 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
148 * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds,
149 * the odds are that the user has given up attempting to connect by then.
150 */
151 #define SYNCACHE_MAXREXMTS 3
152
153 /* Arbitrary values */
154 #define TCP_SYNCACHE_HASHSIZE 512
155 #define TCP_SYNCACHE_BUCKETLIMIT 30
156
157 static VNET_DEFINE(struct tcp_syncache, tcp_syncache);
158 #define V_tcp_syncache VNET(tcp_syncache)
159
160 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0,
161 "TCP SYN cache");
162
163 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RDTUN,
164 &VNET_NAME(tcp_syncache.bucket_limit), 0,
165 "Per-bucket hash limit for syncache");
166
167 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RDTUN,
168 &VNET_NAME(tcp_syncache.cache_limit), 0,
169 "Overall entry limit for syncache");
170
171 SYSCTL_VNET_PROC(_net_inet_tcp_syncache, OID_AUTO, count, (CTLTYPE_UINT|CTLFLAG_RD),
172 NULL, 0, &syncache_sysctl_count, "IU",
173 "Current number of entries in syncache");
174
175 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RDTUN,
176 &VNET_NAME(tcp_syncache.hashsize), 0,
177 "Size of TCP syncache hashtable");
178
179 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW,
180 &VNET_NAME(tcp_syncache.rexmt_limit), 0,
181 "Limit on SYN/ACK retransmissions");
182
183 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1;
184 SYSCTL_VNET_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail,
185 CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0,
186 "Send reset on socket allocation failure");
187
188 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
189
190 #define SYNCACHE_HASH(inc, mask) \
191 ((V_tcp_syncache.hash_secret ^ \
192 (inc)->inc_faddr.s_addr ^ \
193 ((inc)->inc_faddr.s_addr >> 16) ^ \
194 (inc)->inc_fport ^ (inc)->inc_lport) & mask)
195
196 #define SYNCACHE_HASH6(inc, mask) \
197 ((V_tcp_syncache.hash_secret ^ \
198 (inc)->inc6_faddr.s6_addr32[0] ^ \
199 (inc)->inc6_faddr.s6_addr32[3] ^ \
200 (inc)->inc_fport ^ (inc)->inc_lport) & mask)
201
202 #define ENDPTS_EQ(a, b) ( \
203 (a)->ie_fport == (b)->ie_fport && \
204 (a)->ie_lport == (b)->ie_lport && \
205 (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr && \
206 (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr \
207 )
208
209 #define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0)
210
211 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx)
212 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx)
213 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED)
214
215 /*
216 * Requires the syncache entry to be already removed from the bucket list.
217 */
218 static void
syncache_free(struct syncache * sc)219 syncache_free(struct syncache *sc)
220 {
221
222 if (sc->sc_ipopts)
223 (void) m_free(sc->sc_ipopts);
224 if (sc->sc_cred)
225 crfree(sc->sc_cred);
226 #ifdef MAC
227 mac_syncache_destroy(&sc->sc_label);
228 #endif
229
230 uma_zfree(V_tcp_syncache.zone, sc);
231 }
232
233 void
syncache_init(void)234 syncache_init(void)
235 {
236 int i;
237
238 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
239 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
240 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
241 V_tcp_syncache.hash_secret = arc4random();
242
243 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
244 &V_tcp_syncache.hashsize);
245 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
246 &V_tcp_syncache.bucket_limit);
247 if (!powerof2(V_tcp_syncache.hashsize) ||
248 V_tcp_syncache.hashsize == 0) {
249 printf("WARNING: syncache hash size is not a power of 2.\n");
250 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
251 }
252 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1;
253
254 /* Set limits. */
255 V_tcp_syncache.cache_limit =
256 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit;
257 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
258 &V_tcp_syncache.cache_limit);
259
260 /* Allocate the hash table. */
261 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize *
262 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO);
263
264 #ifdef VIMAGE
265 V_tcp_syncache.vnet = curvnet;
266 #endif
267
268 /* Initialize the hash buckets. */
269 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
270 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket);
271 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
272 NULL, MTX_DEF);
273 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer,
274 &V_tcp_syncache.hashbase[i].sch_mtx, 0);
275 V_tcp_syncache.hashbase[i].sch_length = 0;
276 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache;
277 }
278
279 /* Create the syncache entry zone. */
280 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
281 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
282 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone,
283 V_tcp_syncache.cache_limit);
284
285 /* Start the SYN cookie reseeder callout. */
286 callout_init(&V_tcp_syncache.secret.reseed, 1);
287 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0);
288 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0);
289 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz,
290 syncookie_reseed, &V_tcp_syncache);
291 }
292
293 #ifdef VIMAGE
294 void
syncache_destroy(void)295 syncache_destroy(void)
296 {
297 struct syncache_head *sch;
298 struct syncache *sc, *nsc;
299 int i;
300
301 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */
302 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
303
304 sch = &V_tcp_syncache.hashbase[i];
305 callout_drain(&sch->sch_timer);
306
307 SCH_LOCK(sch);
308 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc)
309 syncache_drop(sc, sch);
310 SCH_UNLOCK(sch);
311 KASSERT(TAILQ_EMPTY(&sch->sch_bucket),
312 ("%s: sch->sch_bucket not empty", __func__));
313 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0",
314 __func__, sch->sch_length));
315 mtx_destroy(&sch->sch_mtx);
316 }
317
318 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0,
319 ("%s: cache_count not 0", __func__));
320
321 /* Free the allocated global resources. */
322 uma_zdestroy(V_tcp_syncache.zone);
323 free(V_tcp_syncache.hashbase, M_SYNCACHE);
324
325 callout_drain(&V_tcp_syncache.secret.reseed);
326 }
327 #endif
328
329 static int
syncache_sysctl_count(SYSCTL_HANDLER_ARGS)330 syncache_sysctl_count(SYSCTL_HANDLER_ARGS)
331 {
332 int count;
333
334 count = uma_zone_get_cur(V_tcp_syncache.zone);
335 return (sysctl_handle_int(oidp, &count, 0, req));
336 }
337
338 /*
339 * Inserts a syncache entry into the specified bucket row.
340 * Locks and unlocks the syncache_head autonomously.
341 */
342 static void
syncache_insert(struct syncache * sc,struct syncache_head * sch)343 syncache_insert(struct syncache *sc, struct syncache_head *sch)
344 {
345 struct syncache *sc2;
346
347 SCH_LOCK(sch);
348
349 /*
350 * Make sure that we don't overflow the per-bucket limit.
351 * If the bucket is full, toss the oldest element.
352 */
353 if (sch->sch_length >= V_tcp_syncache.bucket_limit) {
354 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
355 ("sch->sch_length incorrect"));
356 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
357 syncache_drop(sc2, sch);
358 TCPSTAT_INC(tcps_sc_bucketoverflow);
359 }
360
361 /* Put it into the bucket. */
362 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
363 sch->sch_length++;
364
365 #ifdef TCP_OFFLOAD
366 if (ADDED_BY_TOE(sc)) {
367 struct toedev *tod = sc->sc_tod;
368
369 tod->tod_syncache_added(tod, sc->sc_todctx);
370 }
371 #endif
372
373 /* Reinitialize the bucket row's timer. */
374 if (sch->sch_length == 1)
375 sch->sch_nextc = ticks + INT_MAX;
376 syncache_timeout(sc, sch, 1);
377
378 SCH_UNLOCK(sch);
379
380 TCPSTAT_INC(tcps_sc_added);
381 }
382
383 /*
384 * Remove and free entry from syncache bucket row.
385 * Expects locked syncache head.
386 */
387 static void
syncache_drop(struct syncache * sc,struct syncache_head * sch)388 syncache_drop(struct syncache *sc, struct syncache_head *sch)
389 {
390
391 SCH_LOCK_ASSERT(sch);
392
393 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
394 sch->sch_length--;
395
396 #ifdef TCP_OFFLOAD
397 if (ADDED_BY_TOE(sc)) {
398 struct toedev *tod = sc->sc_tod;
399
400 tod->tod_syncache_removed(tod, sc->sc_todctx);
401 }
402 #endif
403
404 syncache_free(sc);
405 }
406
407 /*
408 * Engage/reengage time on bucket row.
409 */
410 static void
syncache_timeout(struct syncache * sc,struct syncache_head * sch,int docallout)411 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
412 {
413 sc->sc_rxttime = ticks +
414 TCPTV_RTOBASE * (tcp_syn_backoff[sc->sc_rxmits]);
415 sc->sc_rxmits++;
416 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
417 sch->sch_nextc = sc->sc_rxttime;
418 if (docallout)
419 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
420 syncache_timer, (void *)sch);
421 }
422 }
423
424 /*
425 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
426 * If we have retransmitted an entry the maximum number of times, expire it.
427 * One separate timer for each bucket row.
428 */
429 static void
syncache_timer(void * xsch)430 syncache_timer(void *xsch)
431 {
432 struct syncache_head *sch = (struct syncache_head *)xsch;
433 struct syncache *sc, *nsc;
434 int tick = ticks;
435 char *s;
436
437 CURVNET_SET(sch->sch_sc->vnet);
438
439 /* NB: syncache_head has already been locked by the callout. */
440 SCH_LOCK_ASSERT(sch);
441
442 /*
443 * In the following cycle we may remove some entries and/or
444 * advance some timeouts, so re-initialize the bucket timer.
445 */
446 sch->sch_nextc = tick + INT_MAX;
447
448 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
449 /*
450 * We do not check if the listen socket still exists
451 * and accept the case where the listen socket may be
452 * gone by the time we resend the SYN/ACK. We do
453 * not expect this to happens often. If it does,
454 * then the RST will be sent by the time the remote
455 * host does the SYN/ACK->ACK.
456 */
457 if (TSTMP_GT(sc->sc_rxttime, tick)) {
458 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
459 sch->sch_nextc = sc->sc_rxttime;
460 continue;
461 }
462 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
463 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
464 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
465 "giving up and removing syncache entry\n",
466 s, __func__);
467 free(s, M_TCPLOG);
468 }
469 syncache_drop(sc, sch);
470 TCPSTAT_INC(tcps_sc_stale);
471 continue;
472 }
473 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
474 log(LOG_DEBUG, "%s; %s: Response timeout, "
475 "retransmitting (%u) SYN|ACK\n",
476 s, __func__, sc->sc_rxmits);
477 free(s, M_TCPLOG);
478 }
479
480 (void) syncache_respond(sc);
481 TCPSTAT_INC(tcps_sc_retransmitted);
482 syncache_timeout(sc, sch, 0);
483 }
484 if (!TAILQ_EMPTY(&(sch)->sch_bucket))
485 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
486 syncache_timer, (void *)(sch));
487 CURVNET_RESTORE();
488 }
489
490 /*
491 * Find an entry in the syncache.
492 * Returns always with locked syncache_head plus a matching entry or NULL.
493 */
494 static struct syncache *
syncache_lookup(struct in_conninfo * inc,struct syncache_head ** schp)495 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
496 {
497 struct syncache *sc;
498 struct syncache_head *sch;
499
500 #ifdef INET6
501 if (inc->inc_flags & INC_ISIPV6) {
502 sch = &V_tcp_syncache.hashbase[
503 SYNCACHE_HASH6(inc, V_tcp_syncache.hashmask)];
504 *schp = sch;
505
506 SCH_LOCK(sch);
507
508 /* Circle through bucket row to find matching entry. */
509 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
510 if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie))
511 return (sc);
512 }
513 } else
514 #endif
515 {
516 sch = &V_tcp_syncache.hashbase[
517 SYNCACHE_HASH(inc, V_tcp_syncache.hashmask)];
518 *schp = sch;
519
520 SCH_LOCK(sch);
521
522 /* Circle through bucket row to find matching entry. */
523 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
524 #ifdef INET6
525 if (sc->sc_inc.inc_flags & INC_ISIPV6)
526 continue;
527 #endif
528 if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie))
529 return (sc);
530 }
531 }
532 SCH_LOCK_ASSERT(*schp);
533 return (NULL); /* always returns with locked sch */
534 }
535
536 /*
537 * This function is called when we get a RST for a
538 * non-existent connection, so that we can see if the
539 * connection is in the syn cache. If it is, zap it.
540 */
541 void
syncache_chkrst(struct in_conninfo * inc,struct tcphdr * th)542 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th)
543 {
544 struct syncache *sc;
545 struct syncache_head *sch;
546 char *s = NULL;
547
548 sc = syncache_lookup(inc, &sch); /* returns locked sch */
549 SCH_LOCK_ASSERT(sch);
550
551 /*
552 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags.
553 * See RFC 793 page 65, section SEGMENT ARRIVES.
554 */
555 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) {
556 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
557 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or "
558 "FIN flag set, segment ignored\n", s, __func__);
559 TCPSTAT_INC(tcps_badrst);
560 goto done;
561 }
562
563 /*
564 * No corresponding connection was found in syncache.
565 * If syncookies are enabled and possibly exclusively
566 * used, or we are under memory pressure, a valid RST
567 * may not find a syncache entry. In that case we're
568 * done and no SYN|ACK retransmissions will happen.
569 * Otherwise the RST was misdirected or spoofed.
570 */
571 if (sc == NULL) {
572 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
573 log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
574 "syncache entry (possibly syncookie only), "
575 "segment ignored\n", s, __func__);
576 TCPSTAT_INC(tcps_badrst);
577 goto done;
578 }
579
580 /*
581 * If the RST bit is set, check the sequence number to see
582 * if this is a valid reset segment.
583 * RFC 793 page 37:
584 * In all states except SYN-SENT, all reset (RST) segments
585 * are validated by checking their SEQ-fields. A reset is
586 * valid if its sequence number is in the window.
587 *
588 * The sequence number in the reset segment is normally an
589 * echo of our outgoing acknowlegement numbers, but some hosts
590 * send a reset with the sequence number at the rightmost edge
591 * of our receive window, and we have to handle this case.
592 */
593 if (SEQ_GEQ(th->th_seq, sc->sc_irs) &&
594 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
595 syncache_drop(sc, sch);
596 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
597 log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, "
598 "connection attempt aborted by remote endpoint\n",
599 s, __func__);
600 TCPSTAT_INC(tcps_sc_reset);
601 } else {
602 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
603 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
604 "IRS %u (+WND %u), segment ignored\n",
605 s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd);
606 TCPSTAT_INC(tcps_badrst);
607 }
608
609 done:
610 if (s != NULL)
611 free(s, M_TCPLOG);
612 SCH_UNLOCK(sch);
613 }
614
615 void
syncache_badack(struct in_conninfo * inc)616 syncache_badack(struct in_conninfo *inc)
617 {
618 struct syncache *sc;
619 struct syncache_head *sch;
620
621 sc = syncache_lookup(inc, &sch); /* returns locked sch */
622 SCH_LOCK_ASSERT(sch);
623 if (sc != NULL) {
624 syncache_drop(sc, sch);
625 TCPSTAT_INC(tcps_sc_badack);
626 }
627 SCH_UNLOCK(sch);
628 }
629
630 void
syncache_unreach(struct in_conninfo * inc,struct tcphdr * th)631 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th)
632 {
633 struct syncache *sc;
634 struct syncache_head *sch;
635
636 sc = syncache_lookup(inc, &sch); /* returns locked sch */
637 SCH_LOCK_ASSERT(sch);
638 if (sc == NULL)
639 goto done;
640
641 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
642 if (ntohl(th->th_seq) != sc->sc_iss)
643 goto done;
644
645 /*
646 * If we've rertransmitted 3 times and this is our second error,
647 * we remove the entry. Otherwise, we allow it to continue on.
648 * This prevents us from incorrectly nuking an entry during a
649 * spurious network outage.
650 *
651 * See tcp_notify().
652 */
653 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
654 sc->sc_flags |= SCF_UNREACH;
655 goto done;
656 }
657 syncache_drop(sc, sch);
658 TCPSTAT_INC(tcps_sc_unreach);
659 done:
660 SCH_UNLOCK(sch);
661 }
662
663 /*
664 * Build a new TCP socket structure from a syncache entry.
665 */
666 static struct socket *
syncache_socket(struct syncache * sc,struct socket * lso,struct mbuf * m)667 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
668 {
669 struct inpcb *inp = NULL;
670 struct socket *so;
671 struct tcpcb *tp;
672 int error;
673 char *s;
674
675 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
676
677 /*
678 * Ok, create the full blown connection, and set things up
679 * as they would have been set up if we had created the
680 * connection when the SYN arrived. If we can't create
681 * the connection, abort it.
682 */
683 so = sonewconn(lso, SS_ISCONNECTED);
684 if (so == NULL) {
685 /*
686 * Drop the connection; we will either send a RST or
687 * have the peer retransmit its SYN again after its
688 * RTO and try again.
689 */
690 TCPSTAT_INC(tcps_listendrop);
691 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
692 log(LOG_DEBUG, "%s; %s: Socket create failed "
693 "due to limits or memory shortage\n",
694 s, __func__);
695 free(s, M_TCPLOG);
696 }
697 goto abort2;
698 }
699 #ifdef MAC
700 mac_socketpeer_set_from_mbuf(m, so);
701 #endif
702
703 inp = sotoinpcb(so);
704 inp->inp_inc.inc_fibnum = so->so_fibnum;
705 INP_WLOCK(inp);
706 INP_HASH_WLOCK(&V_tcbinfo);
707
708 /* Insert new socket into PCB hash list. */
709 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
710 #ifdef INET6
711 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
712 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
713 } else {
714 inp->inp_vflag &= ~INP_IPV6;
715 inp->inp_vflag |= INP_IPV4;
716 #endif
717 inp->inp_laddr = sc->sc_inc.inc_laddr;
718 #ifdef INET6
719 }
720 #endif
721
722 /*
723 * If there's an mbuf and it has a flowid, then let's initialise the
724 * inp with that particular flowid.
725 */
726 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) {
727 inp->inp_flowid = m->m_pkthdr.flowid;
728 }
729
730 /*
731 * Install in the reservation hash table for now, but don't yet
732 * install a connection group since the full 4-tuple isn't yet
733 * configured.
734 */
735 inp->inp_lport = sc->sc_inc.inc_lport;
736 if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) {
737 /*
738 * Undo the assignments above if we failed to
739 * put the PCB on the hash lists.
740 */
741 #ifdef INET6
742 if (sc->sc_inc.inc_flags & INC_ISIPV6)
743 inp->in6p_laddr = in6addr_any;
744 else
745 #endif
746 inp->inp_laddr.s_addr = INADDR_ANY;
747 inp->inp_lport = 0;
748 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
749 log(LOG_DEBUG, "%s; %s: in_pcbinshash failed "
750 "with error %i\n",
751 s, __func__, error);
752 free(s, M_TCPLOG);
753 }
754 INP_HASH_WUNLOCK(&V_tcbinfo);
755 goto abort;
756 }
757 #ifdef IPSEC
758 /* Copy old policy into new socket's. */
759 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp))
760 printf("syncache_socket: could not copy policy\n");
761 #endif
762 #ifdef INET6
763 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
764 struct inpcb *oinp = sotoinpcb(lso);
765 struct in6_addr laddr6;
766 struct sockaddr_in6 sin6;
767 /*
768 * Inherit socket options from the listening socket.
769 * Note that in6p_inputopts are not (and should not be)
770 * copied, since it stores previously received options and is
771 * used to detect if each new option is different than the
772 * previous one and hence should be passed to a user.
773 * If we copied in6p_inputopts, a user would not be able to
774 * receive options just after calling the accept system call.
775 */
776 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
777 if (oinp->in6p_outputopts)
778 inp->in6p_outputopts =
779 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
780
781 sin6.sin6_family = AF_INET6;
782 sin6.sin6_len = sizeof(sin6);
783 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
784 sin6.sin6_port = sc->sc_inc.inc_fport;
785 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
786 laddr6 = inp->in6p_laddr;
787 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
788 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
789 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6,
790 thread0.td_ucred, m)) != 0) {
791 inp->in6p_laddr = laddr6;
792 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
793 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed "
794 "with error %i\n",
795 s, __func__, error);
796 free(s, M_TCPLOG);
797 }
798 INP_HASH_WUNLOCK(&V_tcbinfo);
799 goto abort;
800 }
801 /* Override flowlabel from in6_pcbconnect. */
802 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
803 inp->inp_flow |= sc->sc_flowlabel;
804 }
805 #endif /* INET6 */
806 #if defined(INET) && defined(INET6)
807 else
808 #endif
809 #ifdef INET
810 {
811 struct in_addr laddr;
812 struct sockaddr_in sin;
813
814 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
815
816 if (inp->inp_options == NULL) {
817 inp->inp_options = sc->sc_ipopts;
818 sc->sc_ipopts = NULL;
819 }
820
821 sin.sin_family = AF_INET;
822 sin.sin_len = sizeof(sin);
823 sin.sin_addr = sc->sc_inc.inc_faddr;
824 sin.sin_port = sc->sc_inc.inc_fport;
825 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
826 laddr = inp->inp_laddr;
827 if (inp->inp_laddr.s_addr == INADDR_ANY)
828 inp->inp_laddr = sc->sc_inc.inc_laddr;
829 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin,
830 thread0.td_ucred, m)) != 0) {
831 inp->inp_laddr = laddr;
832 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
833 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed "
834 "with error %i\n",
835 s, __func__, error);
836 free(s, M_TCPLOG);
837 }
838 INP_HASH_WUNLOCK(&V_tcbinfo);
839 goto abort;
840 }
841 }
842 #endif /* INET */
843 INP_HASH_WUNLOCK(&V_tcbinfo);
844 tp = intotcpcb(inp);
845 tcp_state_change(tp, TCPS_SYN_RECEIVED);
846 tp->iss = sc->sc_iss;
847 tp->irs = sc->sc_irs;
848 tcp_rcvseqinit(tp);
849 tcp_sendseqinit(tp);
850 tp->snd_wl1 = sc->sc_irs;
851 tp->snd_max = tp->iss + 1;
852 tp->snd_nxt = tp->iss + 1;
853 tp->rcv_up = sc->sc_irs + 1;
854 tp->rcv_wnd = sc->sc_wnd;
855 tp->rcv_adv += tp->rcv_wnd;
856 tp->last_ack_sent = tp->rcv_nxt;
857
858 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
859 if (sc->sc_flags & SCF_NOOPT)
860 tp->t_flags |= TF_NOOPT;
861 else {
862 if (sc->sc_flags & SCF_WINSCALE) {
863 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
864 tp->snd_scale = sc->sc_requested_s_scale;
865 tp->request_r_scale = sc->sc_requested_r_scale;
866 }
867 if (sc->sc_flags & SCF_TIMESTAMP) {
868 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
869 tp->ts_recent = sc->sc_tsreflect;
870 tp->ts_recent_age = tcp_ts_getticks();
871 tp->ts_offset = sc->sc_tsoff;
872 }
873 #ifdef TCP_SIGNATURE
874 if (sc->sc_flags & SCF_SIGNATURE)
875 tp->t_flags |= TF_SIGNATURE;
876 #endif
877 if (sc->sc_flags & SCF_SACK)
878 tp->t_flags |= TF_SACK_PERMIT;
879 }
880
881 if (sc->sc_flags & SCF_ECN)
882 tp->t_flags |= TF_ECN_PERMIT;
883
884 /*
885 * Set up MSS and get cached values from tcp_hostcache.
886 * This might overwrite some of the defaults we just set.
887 */
888 tcp_mss(tp, sc->sc_peer_mss);
889
890 /*
891 * If the SYN,ACK was retransmitted, indicate that CWND to be
892 * limited to one segment in cc_conn_init().
893 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
894 */
895 if (sc->sc_rxmits > 1)
896 tp->snd_cwnd = 1;
897
898 #ifdef TCP_OFFLOAD
899 /*
900 * Allow a TOE driver to install its hooks. Note that we hold the
901 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a
902 * new connection before the TOE driver has done its thing.
903 */
904 if (ADDED_BY_TOE(sc)) {
905 struct toedev *tod = sc->sc_tod;
906
907 tod->tod_offload_socket(tod, sc->sc_todctx, so);
908 }
909 #endif
910 /*
911 * Copy and activate timers.
912 */
913 tp->t_keepinit = sototcpcb(lso)->t_keepinit;
914 tp->t_keepidle = sototcpcb(lso)->t_keepidle;
915 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl;
916 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt;
917 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp));
918
919 INP_WUNLOCK(inp);
920
921 TCPSTAT_INC(tcps_accepts);
922 return (so);
923
924 abort:
925 INP_WUNLOCK(inp);
926 abort2:
927 if (so != NULL)
928 soabort(so);
929 return (NULL);
930 }
931
932 /*
933 * This function gets called when we receive an ACK for a
934 * socket in the LISTEN state. We look up the connection
935 * in the syncache, and if its there, we pull it out of
936 * the cache and turn it into a full-blown connection in
937 * the SYN-RECEIVED state.
938 */
939 int
syncache_expand(struct in_conninfo * inc,struct tcpopt * to,struct tcphdr * th,struct socket ** lsop,struct mbuf * m)940 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
941 struct socket **lsop, struct mbuf *m)
942 {
943 struct syncache *sc;
944 struct syncache_head *sch;
945 struct syncache scs;
946 char *s;
947
948 /*
949 * Global TCP locks are held because we manipulate the PCB lists
950 * and create a new socket.
951 */
952 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
953 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
954 ("%s: can handle only ACK", __func__));
955
956 sc = syncache_lookup(inc, &sch); /* returns locked sch */
957 SCH_LOCK_ASSERT(sch);
958
959 #ifdef INVARIANTS
960 /*
961 * Test code for syncookies comparing the syncache stored
962 * values with the reconstructed values from the cookie.
963 */
964 if (sc != NULL)
965 syncookie_cmp(inc, sch, sc, th, to, *lsop);
966 #endif
967
968 if (sc == NULL) {
969 /*
970 * There is no syncache entry, so see if this ACK is
971 * a returning syncookie. To do this, first:
972 * A. See if this socket has had a syncache entry dropped in
973 * the past. We don't want to accept a bogus syncookie
974 * if we've never received a SYN.
975 * B. check that the syncookie is valid. If it is, then
976 * cobble up a fake syncache entry, and return.
977 */
978 if (!V_tcp_syncookies) {
979 SCH_UNLOCK(sch);
980 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
981 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
982 "segment rejected (syncookies disabled)\n",
983 s, __func__);
984 goto failed;
985 }
986 bzero(&scs, sizeof(scs));
987 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop);
988 SCH_UNLOCK(sch);
989 if (sc == NULL) {
990 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
991 log(LOG_DEBUG, "%s; %s: Segment failed "
992 "SYNCOOKIE authentication, segment rejected "
993 "(probably spoofed)\n", s, __func__);
994 goto failed;
995 }
996 } else {
997 /* Pull out the entry to unlock the bucket row. */
998 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
999 sch->sch_length--;
1000 #ifdef TCP_OFFLOAD
1001 if (ADDED_BY_TOE(sc)) {
1002 struct toedev *tod = sc->sc_tod;
1003
1004 tod->tod_syncache_removed(tod, sc->sc_todctx);
1005 }
1006 #endif
1007 SCH_UNLOCK(sch);
1008 }
1009
1010 /*
1011 * Segment validation:
1012 * ACK must match our initial sequence number + 1 (the SYN|ACK).
1013 */
1014 if (th->th_ack != sc->sc_iss + 1) {
1015 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1016 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
1017 "rejected\n", s, __func__, th->th_ack, sc->sc_iss);
1018 goto failed;
1019 }
1020
1021 /*
1022 * The SEQ must fall in the window starting at the received
1023 * initial receive sequence number + 1 (the SYN).
1024 */
1025 if (SEQ_LEQ(th->th_seq, sc->sc_irs) ||
1026 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
1027 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1028 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
1029 "rejected\n", s, __func__, th->th_seq, sc->sc_irs);
1030 goto failed;
1031 }
1032
1033 /*
1034 * If timestamps were not negotiated during SYN/ACK they
1035 * must not appear on any segment during this session.
1036 */
1037 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) {
1038 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1039 log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
1040 "segment rejected\n", s, __func__);
1041 goto failed;
1042 }
1043
1044 /*
1045 * If timestamps were negotiated during SYN/ACK they should
1046 * appear on every segment during this session.
1047 * XXXAO: This is only informal as there have been unverified
1048 * reports of non-compliants stacks.
1049 */
1050 if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) {
1051 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1052 log(LOG_DEBUG, "%s; %s: Timestamp missing, "
1053 "no action\n", s, __func__);
1054 free(s, M_TCPLOG);
1055 s = NULL;
1056 }
1057 }
1058
1059 /*
1060 * If timestamps were negotiated the reflected timestamp
1061 * must be equal to what we actually sent in the SYN|ACK.
1062 */
1063 if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts) {
1064 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1065 log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, "
1066 "segment rejected\n",
1067 s, __func__, to->to_tsecr, sc->sc_ts);
1068 goto failed;
1069 }
1070
1071 *lsop = syncache_socket(sc, *lsop, m);
1072
1073 if (*lsop == NULL)
1074 TCPSTAT_INC(tcps_sc_aborted);
1075 else
1076 TCPSTAT_INC(tcps_sc_completed);
1077
1078 /* how do we find the inp for the new socket? */
1079 if (sc != &scs)
1080 syncache_free(sc);
1081 return (1);
1082 failed:
1083 if (sc != NULL && sc != &scs)
1084 syncache_free(sc);
1085 if (s != NULL)
1086 free(s, M_TCPLOG);
1087 *lsop = NULL;
1088 return (0);
1089 }
1090
1091 /*
1092 * Given a LISTEN socket and an inbound SYN request, add
1093 * this to the syn cache, and send back a segment:
1094 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
1095 * to the source.
1096 *
1097 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
1098 * Doing so would require that we hold onto the data and deliver it
1099 * to the application. However, if we are the target of a SYN-flood
1100 * DoS attack, an attacker could send data which would eventually
1101 * consume all available buffer space if it were ACKed. By not ACKing
1102 * the data, we avoid this DoS scenario.
1103 */
1104 void
syncache_add(struct in_conninfo * inc,struct tcpopt * to,struct tcphdr * th,struct inpcb * inp,struct socket ** lsop,struct mbuf * m,void * tod,void * todctx)1105 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1106 struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod,
1107 void *todctx)
1108 {
1109 struct tcpcb *tp;
1110 struct socket *so;
1111 struct syncache *sc = NULL;
1112 struct syncache_head *sch;
1113 struct mbuf *ipopts = NULL;
1114 u_int ltflags;
1115 int win, sb_hiwat, ip_ttl, ip_tos;
1116 char *s;
1117 #ifdef INET6
1118 int autoflowlabel = 0;
1119 #endif
1120 #ifdef MAC
1121 struct label *maclabel;
1122 #endif
1123 struct syncache scs;
1124 struct ucred *cred;
1125
1126 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
1127 INP_WLOCK_ASSERT(inp); /* listen socket */
1128 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
1129 ("%s: unexpected tcp flags", __func__));
1130
1131 /*
1132 * Combine all so/tp operations very early to drop the INP lock as
1133 * soon as possible.
1134 */
1135 so = *lsop;
1136 tp = sototcpcb(so);
1137 cred = crhold(so->so_cred);
1138
1139 #ifdef INET6
1140 if ((inc->inc_flags & INC_ISIPV6) &&
1141 (inp->inp_flags & IN6P_AUTOFLOWLABEL))
1142 autoflowlabel = 1;
1143 #endif
1144 ip_ttl = inp->inp_ip_ttl;
1145 ip_tos = inp->inp_ip_tos;
1146 win = sbspace(&so->so_rcv);
1147 sb_hiwat = so->so_rcv.sb_hiwat;
1148 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE));
1149
1150 /* By the time we drop the lock these should no longer be used. */
1151 so = NULL;
1152 tp = NULL;
1153
1154 #ifdef MAC
1155 if (mac_syncache_init(&maclabel) != 0) {
1156 INP_WUNLOCK(inp);
1157 INP_INFO_WUNLOCK(&V_tcbinfo);
1158 goto done;
1159 } else
1160 mac_syncache_create(maclabel, inp);
1161 #endif
1162 INP_WUNLOCK(inp);
1163 INP_INFO_WUNLOCK(&V_tcbinfo);
1164
1165 /*
1166 * Remember the IP options, if any.
1167 */
1168 #ifdef INET6
1169 if (!(inc->inc_flags & INC_ISIPV6))
1170 #endif
1171 #ifdef INET
1172 ipopts = (m) ? ip_srcroute(m) : NULL;
1173 #else
1174 ipopts = NULL;
1175 #endif
1176
1177 /*
1178 * See if we already have an entry for this connection.
1179 * If we do, resend the SYN,ACK, and reset the retransmit timer.
1180 *
1181 * XXX: should the syncache be re-initialized with the contents
1182 * of the new SYN here (which may have different options?)
1183 *
1184 * XXX: We do not check the sequence number to see if this is a
1185 * real retransmit or a new connection attempt. The question is
1186 * how to handle such a case; either ignore it as spoofed, or
1187 * drop the current entry and create a new one?
1188 */
1189 sc = syncache_lookup(inc, &sch); /* returns locked entry */
1190 SCH_LOCK_ASSERT(sch);
1191 if (sc != NULL) {
1192 TCPSTAT_INC(tcps_sc_dupsyn);
1193 if (ipopts) {
1194 /*
1195 * If we were remembering a previous source route,
1196 * forget it and use the new one we've been given.
1197 */
1198 if (sc->sc_ipopts)
1199 (void) m_free(sc->sc_ipopts);
1200 sc->sc_ipopts = ipopts;
1201 }
1202 /*
1203 * Update timestamp if present.
1204 */
1205 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
1206 sc->sc_tsreflect = to->to_tsval;
1207 else
1208 sc->sc_flags &= ~SCF_TIMESTAMP;
1209 #ifdef MAC
1210 /*
1211 * Since we have already unconditionally allocated label
1212 * storage, free it up. The syncache entry will already
1213 * have an initialized label we can use.
1214 */
1215 mac_syncache_destroy(&maclabel);
1216 #endif
1217 /* Retransmit SYN|ACK and reset retransmit count. */
1218 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
1219 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
1220 "resetting timer and retransmitting SYN|ACK\n",
1221 s, __func__);
1222 free(s, M_TCPLOG);
1223 }
1224 if (syncache_respond(sc) == 0) {
1225 sc->sc_rxmits = 0;
1226 syncache_timeout(sc, sch, 1);
1227 TCPSTAT_INC(tcps_sndacks);
1228 TCPSTAT_INC(tcps_sndtotal);
1229 }
1230 SCH_UNLOCK(sch);
1231 goto done;
1232 }
1233
1234 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1235 if (sc == NULL) {
1236 /*
1237 * The zone allocator couldn't provide more entries.
1238 * Treat this as if the cache was full; drop the oldest
1239 * entry and insert the new one.
1240 */
1241 TCPSTAT_INC(tcps_sc_zonefail);
1242 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL)
1243 syncache_drop(sc, sch);
1244 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1245 if (sc == NULL) {
1246 if (V_tcp_syncookies) {
1247 bzero(&scs, sizeof(scs));
1248 sc = &scs;
1249 } else {
1250 SCH_UNLOCK(sch);
1251 if (ipopts)
1252 (void) m_free(ipopts);
1253 goto done;
1254 }
1255 }
1256 }
1257
1258 /*
1259 * Fill in the syncache values.
1260 */
1261 #ifdef MAC
1262 sc->sc_label = maclabel;
1263 #endif
1264 sc->sc_cred = cred;
1265 cred = NULL;
1266 sc->sc_ipopts = ipopts;
1267 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1268 #ifdef INET6
1269 if (!(inc->inc_flags & INC_ISIPV6))
1270 #endif
1271 {
1272 sc->sc_ip_tos = ip_tos;
1273 sc->sc_ip_ttl = ip_ttl;
1274 }
1275 #ifdef TCP_OFFLOAD
1276 sc->sc_tod = tod;
1277 sc->sc_todctx = todctx;
1278 #endif
1279 sc->sc_irs = th->th_seq;
1280 sc->sc_iss = arc4random();
1281 sc->sc_flags = 0;
1282 sc->sc_flowlabel = 0;
1283
1284 /*
1285 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
1286 * win was derived from socket earlier in the function.
1287 */
1288 win = imax(win, 0);
1289 win = imin(win, TCP_MAXWIN);
1290 sc->sc_wnd = win;
1291
1292 if (V_tcp_do_rfc1323) {
1293 /*
1294 * A timestamp received in a SYN makes
1295 * it ok to send timestamp requests and replies.
1296 */
1297 if (to->to_flags & TOF_TS) {
1298 sc->sc_tsreflect = to->to_tsval;
1299 sc->sc_ts = tcp_ts_getticks();
1300 sc->sc_flags |= SCF_TIMESTAMP;
1301 }
1302 if (to->to_flags & TOF_SCALE) {
1303 int wscale = 0;
1304
1305 /*
1306 * Pick the smallest possible scaling factor that
1307 * will still allow us to scale up to sb_max, aka
1308 * kern.ipc.maxsockbuf.
1309 *
1310 * We do this because there are broken firewalls that
1311 * will corrupt the window scale option, leading to
1312 * the other endpoint believing that our advertised
1313 * window is unscaled. At scale factors larger than
1314 * 5 the unscaled window will drop below 1500 bytes,
1315 * leading to serious problems when traversing these
1316 * broken firewalls.
1317 *
1318 * With the default maxsockbuf of 256K, a scale factor
1319 * of 3 will be chosen by this algorithm. Those who
1320 * choose a larger maxsockbuf should watch out
1321 * for the compatiblity problems mentioned above.
1322 *
1323 * RFC1323: The Window field in a SYN (i.e., a <SYN>
1324 * or <SYN,ACK>) segment itself is never scaled.
1325 */
1326 while (wscale < TCP_MAX_WINSHIFT &&
1327 (TCP_MAXWIN << wscale) < sb_max)
1328 wscale++;
1329 sc->sc_requested_r_scale = wscale;
1330 sc->sc_requested_s_scale = to->to_wscale;
1331 sc->sc_flags |= SCF_WINSCALE;
1332 }
1333 }
1334 #ifdef TCP_SIGNATURE
1335 /*
1336 * If listening socket requested TCP digests, and received SYN
1337 * contains the option, flag this in the syncache so that
1338 * syncache_respond() will do the right thing with the SYN+ACK.
1339 * XXX: Currently we always record the option by default and will
1340 * attempt to use it in syncache_respond().
1341 */
1342 if (to->to_flags & TOF_SIGNATURE || ltflags & TF_SIGNATURE)
1343 sc->sc_flags |= SCF_SIGNATURE;
1344 #endif
1345 if (to->to_flags & TOF_SACKPERM)
1346 sc->sc_flags |= SCF_SACK;
1347 if (to->to_flags & TOF_MSS)
1348 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */
1349 if (ltflags & TF_NOOPT)
1350 sc->sc_flags |= SCF_NOOPT;
1351 if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn)
1352 sc->sc_flags |= SCF_ECN;
1353
1354 if (V_tcp_syncookies)
1355 sc->sc_iss = syncookie_generate(sch, sc);
1356 #ifdef INET6
1357 if (autoflowlabel) {
1358 if (V_tcp_syncookies)
1359 sc->sc_flowlabel = sc->sc_iss;
1360 else
1361 sc->sc_flowlabel = ip6_randomflowlabel();
1362 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK;
1363 }
1364 #endif
1365 SCH_UNLOCK(sch);
1366
1367 /*
1368 * Do a standard 3-way handshake.
1369 */
1370 if (syncache_respond(sc) == 0) {
1371 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs)
1372 syncache_free(sc);
1373 else if (sc != &scs)
1374 syncache_insert(sc, sch); /* locks and unlocks sch */
1375 TCPSTAT_INC(tcps_sndacks);
1376 TCPSTAT_INC(tcps_sndtotal);
1377 } else {
1378 if (sc != &scs)
1379 syncache_free(sc);
1380 TCPSTAT_INC(tcps_sc_dropped);
1381 }
1382
1383 done:
1384 if (cred != NULL)
1385 crfree(cred);
1386 #ifdef MAC
1387 if (sc == &scs)
1388 mac_syncache_destroy(&maclabel);
1389 #endif
1390 if (m) {
1391
1392 *lsop = NULL;
1393 m_freem(m);
1394 }
1395 }
1396
1397 static int
syncache_respond(struct syncache * sc)1398 syncache_respond(struct syncache *sc)
1399 {
1400 struct ip *ip = NULL;
1401 struct mbuf *m;
1402 struct tcphdr *th = NULL;
1403 int optlen, error = 0; /* Make compiler happy */
1404 u_int16_t hlen, tlen, mssopt;
1405 struct tcpopt to;
1406 #ifdef INET6
1407 struct ip6_hdr *ip6 = NULL;
1408 #endif
1409
1410 hlen =
1411 #ifdef INET6
1412 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
1413 #endif
1414 sizeof(struct ip);
1415 tlen = hlen + sizeof(struct tcphdr);
1416
1417 /* Determine MSS we advertize to other end of connection. */
1418 mssopt = tcp_mssopt(&sc->sc_inc);
1419 if (sc->sc_peer_mss)
1420 mssopt = max( min(sc->sc_peer_mss, mssopt), V_tcp_minmss);
1421
1422 /* XXX: Assume that the entire packet will fit in a header mbuf. */
1423 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
1424 ("syncache: mbuf too small"));
1425
1426 /* Create the IP+TCP header from scratch. */
1427 m = m_gethdr(M_NOWAIT, MT_DATA);
1428 if (m == NULL)
1429 return (ENOBUFS);
1430 #ifdef MAC
1431 mac_syncache_create_mbuf(sc->sc_label, m);
1432 #endif
1433 m->m_data += max_linkhdr;
1434 m->m_len = tlen;
1435 m->m_pkthdr.len = tlen;
1436 m->m_pkthdr.rcvif = NULL;
1437
1438 #ifdef INET6
1439 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1440 ip6 = mtod(m, struct ip6_hdr *);
1441 ip6->ip6_vfc = IPV6_VERSION;
1442 ip6->ip6_nxt = IPPROTO_TCP;
1443 ip6->ip6_src = sc->sc_inc.inc6_laddr;
1444 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
1445 ip6->ip6_plen = htons(tlen - hlen);
1446 /* ip6_hlim is set after checksum */
1447 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK;
1448 ip6->ip6_flow |= sc->sc_flowlabel;
1449
1450 th = (struct tcphdr *)(ip6 + 1);
1451 }
1452 #endif
1453 #if defined(INET6) && defined(INET)
1454 else
1455 #endif
1456 #ifdef INET
1457 {
1458 ip = mtod(m, struct ip *);
1459 ip->ip_v = IPVERSION;
1460 ip->ip_hl = sizeof(struct ip) >> 2;
1461 ip->ip_len = htons(tlen);
1462 ip->ip_id = 0;
1463 ip->ip_off = 0;
1464 ip->ip_sum = 0;
1465 ip->ip_p = IPPROTO_TCP;
1466 ip->ip_src = sc->sc_inc.inc_laddr;
1467 ip->ip_dst = sc->sc_inc.inc_faddr;
1468 ip->ip_ttl = sc->sc_ip_ttl;
1469 ip->ip_tos = sc->sc_ip_tos;
1470
1471 /*
1472 * See if we should do MTU discovery. Route lookups are
1473 * expensive, so we will only unset the DF bit if:
1474 *
1475 * 1) path_mtu_discovery is disabled
1476 * 2) the SCF_UNREACH flag has been set
1477 */
1478 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
1479 ip->ip_off |= htons(IP_DF);
1480
1481 th = (struct tcphdr *)(ip + 1);
1482 }
1483 #endif /* INET */
1484 th->th_sport = sc->sc_inc.inc_lport;
1485 th->th_dport = sc->sc_inc.inc_fport;
1486
1487 th->th_seq = htonl(sc->sc_iss);
1488 th->th_ack = htonl(sc->sc_irs + 1);
1489 th->th_off = sizeof(struct tcphdr) >> 2;
1490 th->th_x2 = 0;
1491 th->th_flags = TH_SYN|TH_ACK;
1492 th->th_win = htons(sc->sc_wnd);
1493 th->th_urp = 0;
1494
1495 if (sc->sc_flags & SCF_ECN) {
1496 th->th_flags |= TH_ECE;
1497 TCPSTAT_INC(tcps_ecn_shs);
1498 }
1499
1500 /* Tack on the TCP options. */
1501 if ((sc->sc_flags & SCF_NOOPT) == 0) {
1502 to.to_flags = 0;
1503
1504 to.to_mss = mssopt;
1505 to.to_flags = TOF_MSS;
1506 if (sc->sc_flags & SCF_WINSCALE) {
1507 to.to_wscale = sc->sc_requested_r_scale;
1508 to.to_flags |= TOF_SCALE;
1509 }
1510 if (sc->sc_flags & SCF_TIMESTAMP) {
1511 /* Virgin timestamp or TCP cookie enhanced one. */
1512 to.to_tsval = sc->sc_ts;
1513 to.to_tsecr = sc->sc_tsreflect;
1514 to.to_flags |= TOF_TS;
1515 }
1516 if (sc->sc_flags & SCF_SACK)
1517 to.to_flags |= TOF_SACKPERM;
1518 #ifdef TCP_SIGNATURE
1519 if (sc->sc_flags & SCF_SIGNATURE)
1520 to.to_flags |= TOF_SIGNATURE;
1521 #endif
1522 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
1523
1524 /* Adjust headers by option size. */
1525 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
1526 m->m_len += optlen;
1527 m->m_pkthdr.len += optlen;
1528
1529 #ifdef TCP_SIGNATURE
1530 if (sc->sc_flags & SCF_SIGNATURE)
1531 tcp_signature_compute(m, 0, 0, optlen,
1532 to.to_signature, IPSEC_DIR_OUTBOUND);
1533 #endif
1534 #ifdef INET6
1535 if (sc->sc_inc.inc_flags & INC_ISIPV6)
1536 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
1537 else
1538 #endif
1539 ip->ip_len = htons(ntohs(ip->ip_len) + optlen);
1540 } else
1541 optlen = 0;
1542
1543 M_SETFIB(m, sc->sc_inc.inc_fibnum);
1544 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1545 #ifdef INET6
1546 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1547 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
1548 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen,
1549 IPPROTO_TCP, 0);
1550 ip6->ip6_hlim = in6_selecthlim(NULL, NULL);
1551 #ifdef TCP_OFFLOAD
1552 if (ADDED_BY_TOE(sc)) {
1553 struct toedev *tod = sc->sc_tod;
1554
1555 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
1556
1557 return (error);
1558 }
1559 #endif
1560 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
1561 }
1562 #endif
1563 #if defined(INET6) && defined(INET)
1564 else
1565 #endif
1566 #ifdef INET
1567 {
1568 m->m_pkthdr.csum_flags = CSUM_TCP;
1569 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
1570 htons(tlen + optlen - hlen + IPPROTO_TCP));
1571 #ifdef TCP_OFFLOAD
1572 if (ADDED_BY_TOE(sc)) {
1573 struct toedev *tod = sc->sc_tod;
1574
1575 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
1576
1577 return (error);
1578 }
1579 #endif
1580 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
1581 }
1582 #endif
1583 return (error);
1584 }
1585
1586 /*
1587 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks
1588 * that exceed the capacity of the syncache by avoiding the storage of any
1589 * of the SYNs we receive. Syncookies defend against blind SYN flooding
1590 * attacks where the attacker does not have access to our responses.
1591 *
1592 * Syncookies encode and include all necessary information about the
1593 * connection setup within the SYN|ACK that we send back. That way we
1594 * can avoid keeping any local state until the ACK to our SYN|ACK returns
1595 * (if ever). Normally the syncache and syncookies are running in parallel
1596 * with the latter taking over when the former is exhausted. When matching
1597 * syncache entry is found the syncookie is ignored.
1598 *
1599 * The only reliable information persisting the 3WHS is our inital sequence
1600 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient
1601 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS
1602 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK
1603 * returns and signifies a legitimate connection if it matches the ACK.
1604 *
1605 * The available space of 32 bits to store the hash and to encode the SYN
1606 * option information is very tight and we should have at least 24 bits for
1607 * the MAC to keep the number of guesses by blind spoofing reasonably high.
1608 *
1609 * SYN option information we have to encode to fully restore a connection:
1610 * MSS: is imporant to chose an optimal segment size to avoid IP level
1611 * fragmentation along the path. The common MSS values can be encoded
1612 * in a 3-bit table. Uncommon values are captured by the next lower value
1613 * in the table leading to a slight increase in packetization overhead.
1614 * WSCALE: is necessary to allow large windows to be used for high delay-
1615 * bandwidth product links. Not scaling the window when it was initially
1616 * negotiated is bad for performance as lack of scaling further decreases
1617 * the apparent available send window. We only need to encode the WSCALE
1618 * we received from the remote end. Our end can be recalculated at any
1619 * time. The common WSCALE values can be encoded in a 3-bit table.
1620 * Uncommon values are captured by the next lower value in the table
1621 * making us under-estimate the available window size halving our
1622 * theoretically possible maximum throughput for that connection.
1623 * SACK: Greatly assists in packet loss recovery and requires 1 bit.
1624 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options
1625 * that are included in all segments on a connection. We enable them when
1626 * the ACK has them.
1627 *
1628 * Security of syncookies and attack vectors:
1629 *
1630 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod)
1631 * together with the gloabl secret to make it unique per connection attempt.
1632 * Thus any change of any of those parameters results in a different MAC output
1633 * in an unpredictable way unless a collision is encountered. 24 bits of the
1634 * MAC are embedded into the ISS.
1635 *
1636 * To prevent replay attacks two rotating global secrets are updated with a
1637 * new random value every 15 seconds. The life-time of a syncookie is thus
1638 * 15-30 seconds.
1639 *
1640 * Vector 1: Attacking the secret. This requires finding a weakness in the
1641 * MAC itself or the way it is used here. The attacker can do a chosen plain
1642 * text attack by varying and testing the all parameters under his control.
1643 * The strength depends on the size and randomness of the secret, and the
1644 * cryptographic security of the MAC function. Due to the constant updating
1645 * of the secret the attacker has at most 29.999 seconds to find the secret
1646 * and launch spoofed connections. After that he has to start all over again.
1647 *
1648 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC
1649 * size an average of 4,823 attempts are required for a 50% chance of success
1650 * to spoof a single syncookie (birthday collision paradox). However the
1651 * attacker is blind and doesn't know if one of his attempts succeeded unless
1652 * he has a side channel to interfere success from. A single connection setup
1653 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets.
1654 * This many attempts are required for each one blind spoofed connection. For
1655 * every additional spoofed connection he has to launch another N attempts.
1656 * Thus for a sustained rate 100 spoofed connections per second approximately
1657 * 1,800,000 packets per second would have to be sent.
1658 *
1659 * NB: The MAC function should be fast so that it doesn't become a CPU
1660 * exhaustion attack vector itself.
1661 *
1662 * References:
1663 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations
1664 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996
1665 * http://cr.yp.to/syncookies.html (overview)
1666 * http://cr.yp.to/syncookies/archive (details)
1667 *
1668 *
1669 * Schematic construction of a syncookie enabled Initial Sequence Number:
1670 * 0 1 2 3
1671 * 12345678901234567890123456789012
1672 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP|
1673 *
1674 * x 24 MAC (truncated)
1675 * W 3 Send Window Scale index
1676 * M 3 MSS index
1677 * S 1 SACK permitted
1678 * P 1 Odd/even secret
1679 */
1680
1681 /*
1682 * Distribution and probability of certain MSS values. Those in between are
1683 * rounded down to the next lower one.
1684 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011]
1685 * .2% .3% 5% 7% 7% 20% 15% 45%
1686 */
1687 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 };
1688
1689 /*
1690 * Distribution and probability of certain WSCALE values. We have to map the
1691 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3
1692 * bits based on prevalence of certain values. Where we don't have an exact
1693 * match for are rounded down to the next lower one letting us under-estimate
1694 * the true available window. At the moment this would happen only for the
1695 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer
1696 * and window size). The absence of the WSCALE option (no scaling in either
1697 * direction) is encoded with index zero.
1698 * [WSCALE values histograms, Allman, 2012]
1699 * X 10 10 35 5 6 14 10% by host
1700 * X 11 4 5 5 18 49 3% by connections
1701 */
1702 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 };
1703
1704 /*
1705 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed
1706 * and good cryptographic properties.
1707 */
1708 static uint32_t
syncookie_mac(struct in_conninfo * inc,tcp_seq irs,uint8_t flags,uint8_t * secbits,uintptr_t secmod)1709 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags,
1710 uint8_t *secbits, uintptr_t secmod)
1711 {
1712 SIPHASH_CTX ctx;
1713 uint32_t siphash[2];
1714
1715 SipHash24_Init(&ctx);
1716 SipHash_SetKey(&ctx, secbits);
1717 switch (inc->inc_flags & INC_ISIPV6) {
1718 #ifdef INET
1719 case 0:
1720 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr));
1721 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr));
1722 break;
1723 #endif
1724 #ifdef INET6
1725 case INC_ISIPV6:
1726 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr));
1727 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr));
1728 break;
1729 #endif
1730 }
1731 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport));
1732 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport));
1733 SipHash_Update(&ctx, &flags, sizeof(flags));
1734 SipHash_Update(&ctx, &secmod, sizeof(secmod));
1735 SipHash_Final((u_int8_t *)&siphash, &ctx);
1736
1737 return (siphash[0] ^ siphash[1]);
1738 }
1739
1740 static tcp_seq
syncookie_generate(struct syncache_head * sch,struct syncache * sc)1741 syncookie_generate(struct syncache_head *sch, struct syncache *sc)
1742 {
1743 u_int i, mss, secbit, wscale;
1744 uint32_t iss, hash;
1745 uint8_t *secbits;
1746 union syncookie cookie;
1747
1748 SCH_LOCK_ASSERT(sch);
1749
1750 cookie.cookie = 0;
1751
1752 /* Map our computed MSS into the 3-bit index. */
1753 mss = min(tcp_mssopt(&sc->sc_inc), max(sc->sc_peer_mss, V_tcp_minmss));
1754 for (i = sizeof(tcp_sc_msstab) / sizeof(*tcp_sc_msstab) - 1;
1755 tcp_sc_msstab[i] > mss && i > 0;
1756 i--)
1757 ;
1758 cookie.flags.mss_idx = i;
1759
1760 /*
1761 * Map the send window scale into the 3-bit index but only if
1762 * the wscale option was received.
1763 */
1764 if (sc->sc_flags & SCF_WINSCALE) {
1765 wscale = sc->sc_requested_s_scale;
1766 for (i = sizeof(tcp_sc_wstab) / sizeof(*tcp_sc_wstab) - 1;
1767 tcp_sc_wstab[i] > wscale && i > 0;
1768 i--)
1769 ;
1770 cookie.flags.wscale_idx = i;
1771 }
1772
1773 /* Can we do SACK? */
1774 if (sc->sc_flags & SCF_SACK)
1775 cookie.flags.sack_ok = 1;
1776
1777 /* Which of the two secrets to use. */
1778 secbit = sch->sch_sc->secret.oddeven & 0x1;
1779 cookie.flags.odd_even = secbit;
1780
1781 secbits = sch->sch_sc->secret.key[secbit];
1782 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits,
1783 (uintptr_t)sch);
1784
1785 /*
1786 * Put the flags into the hash and XOR them to get better ISS number
1787 * variance. This doesn't enhance the cryptographic strength and is
1788 * done to prevent the 8 cookie bits from showing up directly on the
1789 * wire.
1790 */
1791 iss = hash & ~0xff;
1792 iss |= cookie.cookie ^ (hash >> 24);
1793
1794 /* Randomize the timestamp. */
1795 if (sc->sc_flags & SCF_TIMESTAMP) {
1796 sc->sc_ts = arc4random();
1797 sc->sc_tsoff = sc->sc_ts - tcp_ts_getticks();
1798 }
1799
1800 TCPSTAT_INC(tcps_sc_sendcookie);
1801 return (iss);
1802 }
1803
1804 static struct syncache *
syncookie_lookup(struct in_conninfo * inc,struct syncache_head * sch,struct syncache * sc,struct tcphdr * th,struct tcpopt * to,struct socket * lso)1805 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch,
1806 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
1807 struct socket *lso)
1808 {
1809 uint32_t hash;
1810 uint8_t *secbits;
1811 tcp_seq ack, seq;
1812 int wnd, wscale = 0;
1813 union syncookie cookie;
1814
1815 SCH_LOCK_ASSERT(sch);
1816
1817 /*
1818 * Pull information out of SYN-ACK/ACK and revert sequence number
1819 * advances.
1820 */
1821 ack = th->th_ack - 1;
1822 seq = th->th_seq - 1;
1823
1824 /*
1825 * Unpack the flags containing enough information to restore the
1826 * connection.
1827 */
1828 cookie.cookie = (ack & 0xff) ^ (ack >> 24);
1829
1830 /* Which of the two secrets to use. */
1831 secbits = sch->sch_sc->secret.key[cookie.flags.odd_even];
1832
1833 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch);
1834
1835 /* The recomputed hash matches the ACK if this was a genuine cookie. */
1836 if ((ack & ~0xff) != (hash & ~0xff))
1837 return (NULL);
1838
1839 /* Fill in the syncache values. */
1840 sc->sc_flags = 0;
1841 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1842 sc->sc_ipopts = NULL;
1843
1844 sc->sc_irs = seq;
1845 sc->sc_iss = ack;
1846
1847 switch (inc->inc_flags & INC_ISIPV6) {
1848 #ifdef INET
1849 case 0:
1850 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl;
1851 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos;
1852 break;
1853 #endif
1854 #ifdef INET6
1855 case INC_ISIPV6:
1856 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL)
1857 sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK;
1858 break;
1859 #endif
1860 }
1861
1862 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx];
1863
1864 /* We can simply recompute receive window scale we sent earlier. */
1865 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max)
1866 wscale++;
1867
1868 /* Only use wscale if it was enabled in the orignal SYN. */
1869 if (cookie.flags.wscale_idx > 0) {
1870 sc->sc_requested_r_scale = wscale;
1871 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx];
1872 sc->sc_flags |= SCF_WINSCALE;
1873 }
1874
1875 wnd = sbspace(&lso->so_rcv);
1876 wnd = imax(wnd, 0);
1877 wnd = imin(wnd, TCP_MAXWIN);
1878 sc->sc_wnd = wnd;
1879
1880 if (cookie.flags.sack_ok)
1881 sc->sc_flags |= SCF_SACK;
1882
1883 if (to->to_flags & TOF_TS) {
1884 sc->sc_flags |= SCF_TIMESTAMP;
1885 sc->sc_tsreflect = to->to_tsval;
1886 sc->sc_ts = to->to_tsecr;
1887 sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks();
1888 }
1889
1890 if (to->to_flags & TOF_SIGNATURE)
1891 sc->sc_flags |= SCF_SIGNATURE;
1892
1893 sc->sc_rxmits = 0;
1894
1895 TCPSTAT_INC(tcps_sc_recvcookie);
1896 return (sc);
1897 }
1898
1899 #ifdef INVARIANTS
1900 static int
syncookie_cmp(struct in_conninfo * inc,struct syncache_head * sch,struct syncache * sc,struct tcphdr * th,struct tcpopt * to,struct socket * lso)1901 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
1902 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
1903 struct socket *lso)
1904 {
1905 struct syncache scs, *scx;
1906 char *s;
1907
1908 bzero(&scs, sizeof(scs));
1909 scx = syncookie_lookup(inc, sch, &scs, th, to, lso);
1910
1911 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL)
1912 return (0);
1913
1914 if (scx != NULL) {
1915 if (sc->sc_peer_mss != scx->sc_peer_mss)
1916 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n",
1917 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss);
1918
1919 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale)
1920 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n",
1921 s, __func__, sc->sc_requested_r_scale,
1922 scx->sc_requested_r_scale);
1923
1924 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale)
1925 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n",
1926 s, __func__, sc->sc_requested_s_scale,
1927 scx->sc_requested_s_scale);
1928
1929 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK))
1930 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__);
1931 }
1932
1933 if (s != NULL)
1934 free(s, M_TCPLOG);
1935 return (0);
1936 }
1937 #endif /* INVARIANTS */
1938
1939 static void
syncookie_reseed(void * arg)1940 syncookie_reseed(void *arg)
1941 {
1942 struct tcp_syncache *sc = arg;
1943 uint8_t *secbits;
1944 int secbit;
1945
1946 /*
1947 * Reseeding the secret doesn't have to be protected by a lock.
1948 * It only must be ensured that the new random values are visible
1949 * to all CPUs in a SMP environment. The atomic with release
1950 * semantics ensures that.
1951 */
1952 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1;
1953 secbits = sc->secret.key[secbit];
1954 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0);
1955 atomic_add_rel_int(&sc->secret.oddeven, 1);
1956
1957 /* Reschedule ourself. */
1958 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz);
1959 }
1960
1961 /*
1962 * Returns the current number of syncache entries. This number
1963 * will probably change before you get around to calling
1964 * syncache_pcblist.
1965 */
1966 int
syncache_pcbcount(void)1967 syncache_pcbcount(void)
1968 {
1969 struct syncache_head *sch;
1970 int count, i;
1971
1972 for (count = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
1973 /* No need to lock for a read. */
1974 sch = &V_tcp_syncache.hashbase[i];
1975 count += sch->sch_length;
1976 }
1977 return count;
1978 }
1979
1980 /*
1981 * Exports the syncache entries to userland so that netstat can display
1982 * them alongside the other sockets. This function is intended to be
1983 * called only from tcp_pcblist.
1984 *
1985 * Due to concurrency on an active system, the number of pcbs exported
1986 * may have no relation to max_pcbs. max_pcbs merely indicates the
1987 * amount of space the caller allocated for this function to use.
1988 */
1989 int
syncache_pcblist(struct sysctl_req * req,int max_pcbs,int * pcbs_exported)1990 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported)
1991 {
1992 struct xtcpcb xt;
1993 struct syncache *sc;
1994 struct syncache_head *sch;
1995 int count, error, i;
1996
1997 for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
1998 sch = &V_tcp_syncache.hashbase[i];
1999 SCH_LOCK(sch);
2000 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
2001 if (count >= max_pcbs) {
2002 SCH_UNLOCK(sch);
2003 goto exit;
2004 }
2005 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
2006 continue;
2007 bzero(&xt, sizeof(xt));
2008 xt.xt_len = sizeof(xt);
2009 if (sc->sc_inc.inc_flags & INC_ISIPV6)
2010 xt.xt_inp.inp_vflag = INP_IPV6;
2011 else
2012 xt.xt_inp.inp_vflag = INP_IPV4;
2013 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo));
2014 xt.xt_tp.t_inpcb = &xt.xt_inp;
2015 xt.xt_tp.t_state = TCPS_SYN_RECEIVED;
2016 xt.xt_socket.xso_protocol = IPPROTO_TCP;
2017 xt.xt_socket.xso_len = sizeof (struct xsocket);
2018 xt.xt_socket.so_type = SOCK_STREAM;
2019 xt.xt_socket.so_state = SS_ISCONNECTING;
2020 error = SYSCTL_OUT(req, &xt, sizeof xt);
2021 if (error) {
2022 SCH_UNLOCK(sch);
2023 goto exit;
2024 }
2025 count++;
2026 }
2027 SCH_UNLOCK(sch);
2028 }
2029 exit:
2030 *pcbs_exported = count;
2031 return error;
2032 }
2033