1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
3 *
4 * Copyright (c) 2001 McAfee, Inc.
5 * Copyright (c) 2006,2013 Andre Oppermann, Internet Business Solutions AG
6 * All rights reserved.
7 *
8 * This software was developed for the FreeBSD Project by Jonathan Lemon
9 * and McAfee Research, the Security Research Division of McAfee, Inc. under
10 * DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the
11 * DARPA CHATS research program. [2001 McAfee, Inc.]
12 *
13 * Redistribution and use in source and binary forms, with or without
14 * modification, are permitted provided that the following conditions
15 * are met:
16 * 1. Redistributions of source code must retain the above copyright
17 * notice, this list of conditions and the following disclaimer.
18 * 2. Redistributions in binary form must reproduce the above copyright
19 * notice, this list of conditions and the following disclaimer in the
20 * documentation and/or other materials provided with the distribution.
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
35 #include <sys/cdefs.h>
36 __FBSDID("$FreeBSD$");
37
38 #include "opt_inet.h"
39 #include "opt_inet6.h"
40 #include "opt_ipsec.h"
41
42 #include <sys/param.h>
43 #include <sys/systm.h>
44 #include <sys/hash.h>
45 #include <sys/refcount.h>
46 #include <sys/kernel.h>
47 #include <sys/sysctl.h>
48 #include <sys/limits.h>
49 #include <sys/lock.h>
50 #include <sys/mutex.h>
51 #include <sys/malloc.h>
52 #include <sys/mbuf.h>
53 #include <sys/proc.h> /* for proc0 declaration */
54 #include <sys/random.h>
55 #include <sys/socket.h>
56 #include <sys/socketvar.h>
57 #include <sys/syslog.h>
58 #include <sys/ucred.h>
59
60 #include <sys/md5.h>
61 #include <crypto/siphash/siphash.h>
62
63 #include <vm/uma.h>
64
65 #include <net/if.h>
66 #include <net/if_var.h>
67 #include <net/route.h>
68 #include <net/vnet.h>
69
70 #include <netinet/in.h>
71 #include <netinet/in_kdtrace.h>
72 #include <netinet/in_systm.h>
73 #include <netinet/ip.h>
74 #include <netinet/in_var.h>
75 #include <netinet/in_pcb.h>
76 #include <netinet/ip_var.h>
77 #include <netinet/ip_options.h>
78 #ifdef INET6
79 #include <netinet/ip6.h>
80 #include <netinet/icmp6.h>
81 #include <netinet6/nd6.h>
82 #include <netinet6/ip6_var.h>
83 #include <netinet6/in6_pcb.h>
84 #endif
85 #include <netinet/tcp.h>
86 #include <netinet/tcp_fastopen.h>
87 #include <netinet/tcp_fsm.h>
88 #include <netinet/tcp_seq.h>
89 #include <netinet/tcp_timer.h>
90 #include <netinet/tcp_var.h>
91 #include <netinet/tcp_syncache.h>
92 #include <netinet/tcp_ecn.h>
93 #ifdef TCP_OFFLOAD
94 #include <netinet/toecore.h>
95 #endif
96 #include <netinet/udp.h>
97
98 #include <netipsec/ipsec_support.h>
99
100 #include <machine/in_cksum.h>
101
102 #include <security/mac/mac_framework.h>
103
104 VNET_DEFINE_STATIC(int, tcp_syncookies) = 1;
105 #define V_tcp_syncookies VNET(tcp_syncookies)
106 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW,
107 &VNET_NAME(tcp_syncookies), 0,
108 "Use TCP SYN cookies if the syncache overflows");
109
110 VNET_DEFINE_STATIC(int, tcp_syncookiesonly) = 0;
111 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly)
112 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW,
113 &VNET_NAME(tcp_syncookiesonly), 0,
114 "Use only TCP SYN cookies");
115
116 VNET_DEFINE_STATIC(int, functions_inherit_listen_socket_stack) = 1;
117 #define V_functions_inherit_listen_socket_stack \
118 VNET(functions_inherit_listen_socket_stack)
119 SYSCTL_INT(_net_inet_tcp, OID_AUTO, functions_inherit_listen_socket_stack,
120 CTLFLAG_VNET | CTLFLAG_RW,
121 &VNET_NAME(functions_inherit_listen_socket_stack), 0,
122 "Inherit listen socket's stack");
123
124 #ifdef TCP_OFFLOAD
125 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL)
126 #endif
127
128 static void syncache_drop(struct syncache *, struct syncache_head *);
129 static void syncache_free(struct syncache *);
130 static void syncache_insert(struct syncache *, struct syncache_head *);
131 static int syncache_respond(struct syncache *, const struct mbuf *, int);
132 static struct socket *syncache_socket(struct syncache *, struct socket *,
133 struct mbuf *m);
134 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch,
135 int docallout);
136 static void syncache_timer(void *);
137
138 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t,
139 uint8_t *, uintptr_t);
140 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *);
141 static struct syncache
142 *syncookie_lookup(struct in_conninfo *, struct syncache_head *,
143 struct syncache *, struct tcphdr *, struct tcpopt *,
144 struct socket *, uint16_t);
145 static void syncache_pause(struct in_conninfo *);
146 static void syncache_unpause(void *);
147 static void syncookie_reseed(void *);
148 #ifdef INVARIANTS
149 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
150 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
151 struct socket *lso, uint16_t port);
152 #endif
153
154 /*
155 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
156 * 3 retransmits corresponds to a timeout with default values of
157 * tcp_rexmit_initial * ( 1 +
158 * tcp_backoff[1] +
159 * tcp_backoff[2] +
160 * tcp_backoff[3]) + 3 * tcp_rexmit_slop,
161 * 1000 ms * (1 + 2 + 4 + 8) + 3 * 200 ms = 15600 ms,
162 * the odds are that the user has given up attempting to connect by then.
163 */
164 #define SYNCACHE_MAXREXMTS 3
165
166 /* Arbitrary values */
167 #define TCP_SYNCACHE_HASHSIZE 512
168 #define TCP_SYNCACHE_BUCKETLIMIT 30
169
170 VNET_DEFINE_STATIC(struct tcp_syncache, tcp_syncache);
171 #define V_tcp_syncache VNET(tcp_syncache)
172
173 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache,
174 CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
175 "TCP SYN cache");
176
177 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
178 &VNET_NAME(tcp_syncache.bucket_limit), 0,
179 "Per-bucket hash limit for syncache");
180
181 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
182 &VNET_NAME(tcp_syncache.cache_limit), 0,
183 "Overall entry limit for syncache");
184
185 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET,
186 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache");
187
188 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN,
189 &VNET_NAME(tcp_syncache.hashsize), 0,
190 "Size of TCP syncache hashtable");
191
192 SYSCTL_BOOL(_net_inet_tcp_syncache, OID_AUTO, see_other, CTLFLAG_VNET |
193 CTLFLAG_RW, &VNET_NAME(tcp_syncache.see_other), 0,
194 "All syncache(4) entries are visible, ignoring UID/GID, jail(2) "
195 "and mac(4) checks");
196
197 static int
198 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS)
199 {
200 int error;
201 u_int new;
202
203 new = V_tcp_syncache.rexmt_limit;
204 error = sysctl_handle_int(oidp, &new, 0, req);
205 if ((error == 0) && (req->newptr != NULL)) {
206 if (new > TCP_MAXRXTSHIFT)
207 error = EINVAL;
208 else
209 V_tcp_syncache.rexmt_limit = new;
210 }
211 return (error);
212 }
213
214 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit,
215 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
216 &VNET_NAME(tcp_syncache.rexmt_limit), 0,
217 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "UI",
218 "Limit on SYN/ACK retransmissions");
219
220 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1;
221 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail,
222 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0,
223 "Send reset on socket allocation failure");
224
225 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
226
227 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx)
228 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx)
229 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED)
230
231 /*
232 * Requires the syncache entry to be already removed from the bucket list.
233 */
234 static void
235 syncache_free(struct syncache *sc)
236 {
237
238 if (sc->sc_ipopts)
239 (void) m_free(sc->sc_ipopts);
240 if (sc->sc_cred)
241 crfree(sc->sc_cred);
242 #ifdef MAC
243 mac_syncache_destroy(&sc->sc_label);
244 #endif
245
246 uma_zfree(V_tcp_syncache.zone, sc);
247 }
248
249 void
250 syncache_init(void)
251 {
252 int i;
253
254 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
255 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
256 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
257 V_tcp_syncache.hash_secret = arc4random();
258
259 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
260 &V_tcp_syncache.hashsize);
261 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
262 &V_tcp_syncache.bucket_limit);
263 if (!powerof2(V_tcp_syncache.hashsize) ||
264 V_tcp_syncache.hashsize == 0) {
265 printf("WARNING: syncache hash size is not a power of 2.\n");
266 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
267 }
268 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1;
269
270 /* Set limits. */
271 V_tcp_syncache.cache_limit =
272 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit;
273 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
274 &V_tcp_syncache.cache_limit);
275
276 /* Allocate the hash table. */
277 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize *
278 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO);
279
280 #ifdef VIMAGE
281 V_tcp_syncache.vnet = curvnet;
282 #endif
283
284 /* Initialize the hash buckets. */
285 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
286 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket);
287 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
288 NULL, MTX_DEF);
289 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer,
290 &V_tcp_syncache.hashbase[i].sch_mtx, 0);
291 V_tcp_syncache.hashbase[i].sch_length = 0;
292 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache;
293 V_tcp_syncache.hashbase[i].sch_last_overflow =
294 -(SYNCOOKIE_LIFETIME + 1);
295 }
296
297 /* Create the syncache entry zone. */
298 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
299 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
300 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone,
301 V_tcp_syncache.cache_limit);
302
303 /* Start the SYN cookie reseeder callout. */
304 callout_init(&V_tcp_syncache.secret.reseed, 1);
305 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0);
306 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0);
307 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz,
308 syncookie_reseed, &V_tcp_syncache);
309
310 /* Initialize the pause machinery. */
311 mtx_init(&V_tcp_syncache.pause_mtx, "tcp_sc_pause", NULL, MTX_DEF);
312 callout_init_mtx(&V_tcp_syncache.pause_co, &V_tcp_syncache.pause_mtx,
313 0);
314 V_tcp_syncache.pause_until = time_uptime - TCP_SYNCACHE_PAUSE_TIME;
315 V_tcp_syncache.pause_backoff = 0;
316 V_tcp_syncache.paused = false;
317 }
318
319 #ifdef VIMAGE
320 void
321 syncache_destroy(void)
322 {
323 struct syncache_head *sch;
324 struct syncache *sc, *nsc;
325 int i;
326
327 /*
328 * Stop the re-seed timer before freeing resources. No need to
329 * possibly schedule it another time.
330 */
331 callout_drain(&V_tcp_syncache.secret.reseed);
332
333 /* Stop the SYN cache pause callout. */
334 mtx_lock(&V_tcp_syncache.pause_mtx);
335 if (callout_stop(&V_tcp_syncache.pause_co) == 0) {
336 mtx_unlock(&V_tcp_syncache.pause_mtx);
337 callout_drain(&V_tcp_syncache.pause_co);
338 } else
339 mtx_unlock(&V_tcp_syncache.pause_mtx);
340
341 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */
342 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
343 sch = &V_tcp_syncache.hashbase[i];
344 callout_drain(&sch->sch_timer);
345
346 SCH_LOCK(sch);
347 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc)
348 syncache_drop(sc, sch);
349 SCH_UNLOCK(sch);
350 KASSERT(TAILQ_EMPTY(&sch->sch_bucket),
351 ("%s: sch->sch_bucket not empty", __func__));
352 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0",
353 __func__, sch->sch_length));
354 mtx_destroy(&sch->sch_mtx);
355 }
356
357 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0,
358 ("%s: cache_count not 0", __func__));
359
360 /* Free the allocated global resources. */
361 uma_zdestroy(V_tcp_syncache.zone);
362 free(V_tcp_syncache.hashbase, M_SYNCACHE);
363 mtx_destroy(&V_tcp_syncache.pause_mtx);
364 }
365 #endif
366
367 /*
368 * Inserts a syncache entry into the specified bucket row.
369 * Locks and unlocks the syncache_head autonomously.
370 */
371 static void
372 syncache_insert(struct syncache *sc, struct syncache_head *sch)
373 {
374 struct syncache *sc2;
375
376 SCH_LOCK(sch);
377
378 /*
379 * Make sure that we don't overflow the per-bucket limit.
380 * If the bucket is full, toss the oldest element.
381 */
382 if (sch->sch_length >= V_tcp_syncache.bucket_limit) {
383 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
384 ("sch->sch_length incorrect"));
385 syncache_pause(&sc->sc_inc);
386 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
387 sch->sch_last_overflow = time_uptime;
388 syncache_drop(sc2, sch);
389 }
390
391 /* Put it into the bucket. */
392 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
393 sch->sch_length++;
394
395 #ifdef TCP_OFFLOAD
396 if (ADDED_BY_TOE(sc)) {
397 struct toedev *tod = sc->sc_tod;
398
399 tod->tod_syncache_added(tod, sc->sc_todctx);
400 }
401 #endif
402
403 /* Reinitialize the bucket row's timer. */
404 if (sch->sch_length == 1)
405 sch->sch_nextc = ticks + INT_MAX;
406 syncache_timeout(sc, sch, 1);
407
408 SCH_UNLOCK(sch);
409
410 TCPSTATES_INC(TCPS_SYN_RECEIVED);
411 TCPSTAT_INC(tcps_sc_added);
412 }
413
414 /*
415 * Remove and free entry from syncache bucket row.
416 * Expects locked syncache head.
417 */
418 static void
419 syncache_drop(struct syncache *sc, struct syncache_head *sch)
420 {
421
422 SCH_LOCK_ASSERT(sch);
423
424 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
425 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
426 sch->sch_length--;
427
428 #ifdef TCP_OFFLOAD
429 if (ADDED_BY_TOE(sc)) {
430 struct toedev *tod = sc->sc_tod;
431
432 tod->tod_syncache_removed(tod, sc->sc_todctx);
433 }
434 #endif
435
436 syncache_free(sc);
437 }
438
439 /*
440 * Engage/reengage time on bucket row.
441 */
442 static void
443 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
444 {
445 int rexmt;
446
447 if (sc->sc_rxmits == 0)
448 rexmt = tcp_rexmit_initial;
449 else
450 TCPT_RANGESET(rexmt,
451 tcp_rexmit_initial * tcp_backoff[sc->sc_rxmits],
452 tcp_rexmit_min, TCPTV_REXMTMAX);
453 sc->sc_rxttime = ticks + rexmt;
454 sc->sc_rxmits++;
455 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
456 sch->sch_nextc = sc->sc_rxttime;
457 if (docallout)
458 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
459 syncache_timer, (void *)sch);
460 }
461 }
462
463 /*
464 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
465 * If we have retransmitted an entry the maximum number of times, expire it.
466 * One separate timer for each bucket row.
467 */
468 static void
469 syncache_timer(void *xsch)
470 {
471 struct syncache_head *sch = (struct syncache_head *)xsch;
472 struct syncache *sc, *nsc;
473 struct epoch_tracker et;
474 int tick = ticks;
475 char *s;
476 bool paused;
477
478 CURVNET_SET(sch->sch_sc->vnet);
479
480 /* NB: syncache_head has already been locked by the callout. */
481 SCH_LOCK_ASSERT(sch);
482
483 /*
484 * In the following cycle we may remove some entries and/or
485 * advance some timeouts, so re-initialize the bucket timer.
486 */
487 sch->sch_nextc = tick + INT_MAX;
488
489 /*
490 * If we have paused processing, unconditionally remove
491 * all syncache entries.
492 */
493 mtx_lock(&V_tcp_syncache.pause_mtx);
494 paused = V_tcp_syncache.paused;
495 mtx_unlock(&V_tcp_syncache.pause_mtx);
496
497 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
498 if (paused) {
499 syncache_drop(sc, sch);
500 continue;
501 }
502 /*
503 * We do not check if the listen socket still exists
504 * and accept the case where the listen socket may be
505 * gone by the time we resend the SYN/ACK. We do
506 * not expect this to happens often. If it does,
507 * then the RST will be sent by the time the remote
508 * host does the SYN/ACK->ACK.
509 */
510 if (TSTMP_GT(sc->sc_rxttime, tick)) {
511 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
512 sch->sch_nextc = sc->sc_rxttime;
513 continue;
514 }
515 if (sc->sc_rxmits > V_tcp_ecn_maxretries) {
516 sc->sc_flags &= ~SCF_ECN_MASK;
517 }
518 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
519 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
520 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
521 "giving up and removing syncache entry\n",
522 s, __func__);
523 free(s, M_TCPLOG);
524 }
525 syncache_drop(sc, sch);
526 TCPSTAT_INC(tcps_sc_stale);
527 continue;
528 }
529 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
530 log(LOG_DEBUG, "%s; %s: Response timeout, "
531 "retransmitting (%u) SYN|ACK\n",
532 s, __func__, sc->sc_rxmits);
533 free(s, M_TCPLOG);
534 }
535
536 NET_EPOCH_ENTER(et);
537 syncache_respond(sc, NULL, TH_SYN|TH_ACK);
538 NET_EPOCH_EXIT(et);
539 TCPSTAT_INC(tcps_sc_retransmitted);
540 syncache_timeout(sc, sch, 0);
541 }
542 if (!TAILQ_EMPTY(&(sch)->sch_bucket))
543 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
544 syncache_timer, (void *)(sch));
545 CURVNET_RESTORE();
546 }
547
548 /*
549 * Returns true if the system is only using cookies at the moment.
550 * This could be due to a sysadmin decision to only use cookies, or it
551 * could be due to the system detecting an attack.
552 */
553 static inline bool
554 syncache_cookiesonly(void)
555 {
556
557 return (V_tcp_syncookies && (V_tcp_syncache.paused ||
558 V_tcp_syncookiesonly));
559 }
560
561 /*
562 * Find the hash bucket for the given connection.
563 */
564 static struct syncache_head *
565 syncache_hashbucket(struct in_conninfo *inc)
566 {
567 uint32_t hash;
568
569 /*
570 * The hash is built on foreign port + local port + foreign address.
571 * We rely on the fact that struct in_conninfo starts with 16 bits
572 * of foreign port, then 16 bits of local port then followed by 128
573 * bits of foreign address. In case of IPv4 address, the first 3
574 * 32-bit words of the address always are zeroes.
575 */
576 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5,
577 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask;
578
579 return (&V_tcp_syncache.hashbase[hash]);
580 }
581
582 /*
583 * Find an entry in the syncache.
584 * Returns always with locked syncache_head plus a matching entry or NULL.
585 */
586 static struct syncache *
587 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
588 {
589 struct syncache *sc;
590 struct syncache_head *sch;
591
592 *schp = sch = syncache_hashbucket(inc);
593 SCH_LOCK(sch);
594
595 /* Circle through bucket row to find matching entry. */
596 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash)
597 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie,
598 sizeof(struct in_endpoints)) == 0)
599 break;
600
601 return (sc); /* Always returns with locked sch. */
602 }
603
604 /*
605 * This function is called when we get a RST for a
606 * non-existent connection, so that we can see if the
607 * connection is in the syn cache. If it is, zap it.
608 * If required send a challenge ACK.
609 */
610 void
611 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, struct mbuf *m,
612 uint16_t port)
613 {
614 struct syncache *sc;
615 struct syncache_head *sch;
616 char *s = NULL;
617
618 if (syncache_cookiesonly())
619 return;
620 sc = syncache_lookup(inc, &sch); /* returns locked sch */
621 SCH_LOCK_ASSERT(sch);
622
623 /*
624 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags.
625 * See RFC 793 page 65, section SEGMENT ARRIVES.
626 */
627 if (tcp_get_flags(th) & (TH_ACK|TH_SYN|TH_FIN)) {
628 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
629 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or "
630 "FIN flag set, segment ignored\n", s, __func__);
631 TCPSTAT_INC(tcps_badrst);
632 goto done;
633 }
634
635 /*
636 * No corresponding connection was found in syncache.
637 * If syncookies are enabled and possibly exclusively
638 * used, or we are under memory pressure, a valid RST
639 * may not find a syncache entry. In that case we're
640 * done and no SYN|ACK retransmissions will happen.
641 * Otherwise the RST was misdirected or spoofed.
642 */
643 if (sc == NULL) {
644 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
645 log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
646 "syncache entry (possibly syncookie only), "
647 "segment ignored\n", s, __func__);
648 TCPSTAT_INC(tcps_badrst);
649 goto done;
650 }
651
652 /* The remote UDP encaps port does not match. */
653 if (sc->sc_port != port) {
654 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
655 log(LOG_DEBUG, "%s; %s: Spurious RST with matching "
656 "syncache entry but non-matching UDP encaps port, "
657 "segment ignored\n", s, __func__);
658 TCPSTAT_INC(tcps_badrst);
659 goto done;
660 }
661
662 /*
663 * If the RST bit is set, check the sequence number to see
664 * if this is a valid reset segment.
665 *
666 * RFC 793 page 37:
667 * In all states except SYN-SENT, all reset (RST) segments
668 * are validated by checking their SEQ-fields. A reset is
669 * valid if its sequence number is in the window.
670 *
671 * RFC 793 page 69:
672 * There are four cases for the acceptability test for an incoming
673 * segment:
674 *
675 * Segment Receive Test
676 * Length Window
677 * ------- ------- -------------------------------------------
678 * 0 0 SEG.SEQ = RCV.NXT
679 * 0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND
680 * >0 0 not acceptable
681 * >0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND
682 * or RCV.NXT =< SEG.SEQ+SEG.LEN-1 < RCV.NXT+RCV.WND
683 *
684 * Note that when receiving a SYN segment in the LISTEN state,
685 * IRS is set to SEG.SEQ and RCV.NXT is set to SEG.SEQ+1, as
686 * described in RFC 793, page 66.
687 */
688 if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) &&
689 SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) ||
690 (sc->sc_wnd == 0 && th->th_seq == sc->sc_irs + 1)) {
691 if (V_tcp_insecure_rst ||
692 th->th_seq == sc->sc_irs + 1) {
693 syncache_drop(sc, sch);
694 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
695 log(LOG_DEBUG,
696 "%s; %s: Our SYN|ACK was rejected, "
697 "connection attempt aborted by remote "
698 "endpoint\n",
699 s, __func__);
700 TCPSTAT_INC(tcps_sc_reset);
701 } else {
702 TCPSTAT_INC(tcps_badrst);
703 /* Send challenge ACK. */
704 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
705 log(LOG_DEBUG, "%s; %s: RST with invalid "
706 " SEQ %u != NXT %u (+WND %u), "
707 "sending challenge ACK\n",
708 s, __func__,
709 th->th_seq, sc->sc_irs + 1, sc->sc_wnd);
710 syncache_respond(sc, m, TH_ACK);
711 }
712 } else {
713 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
714 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
715 "NXT %u (+WND %u), segment ignored\n",
716 s, __func__,
717 th->th_seq, sc->sc_irs + 1, sc->sc_wnd);
718 TCPSTAT_INC(tcps_badrst);
719 }
720
721 done:
722 if (s != NULL)
723 free(s, M_TCPLOG);
724 SCH_UNLOCK(sch);
725 }
726
727 void
728 syncache_badack(struct in_conninfo *inc, uint16_t port)
729 {
730 struct syncache *sc;
731 struct syncache_head *sch;
732
733 if (syncache_cookiesonly())
734 return;
735 sc = syncache_lookup(inc, &sch); /* returns locked sch */
736 SCH_LOCK_ASSERT(sch);
737 if ((sc != NULL) && (sc->sc_port == port)) {
738 syncache_drop(sc, sch);
739 TCPSTAT_INC(tcps_sc_badack);
740 }
741 SCH_UNLOCK(sch);
742 }
743
744 void
745 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq, uint16_t port)
746 {
747 struct syncache *sc;
748 struct syncache_head *sch;
749
750 if (syncache_cookiesonly())
751 return;
752 sc = syncache_lookup(inc, &sch); /* returns locked sch */
753 SCH_LOCK_ASSERT(sch);
754 if (sc == NULL)
755 goto done;
756
757 /* If the port != sc_port, then it's a bogus ICMP msg */
758 if (port != sc->sc_port)
759 goto done;
760
761 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
762 if (ntohl(th_seq) != sc->sc_iss)
763 goto done;
764
765 /*
766 * If we've rertransmitted 3 times and this is our second error,
767 * we remove the entry. Otherwise, we allow it to continue on.
768 * This prevents us from incorrectly nuking an entry during a
769 * spurious network outage.
770 *
771 * See tcp_notify().
772 */
773 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
774 sc->sc_flags |= SCF_UNREACH;
775 goto done;
776 }
777 syncache_drop(sc, sch);
778 TCPSTAT_INC(tcps_sc_unreach);
779 done:
780 SCH_UNLOCK(sch);
781 }
782
783 /*
784 * Build a new TCP socket structure from a syncache entry.
785 *
786 * On success return the newly created socket with its underlying inp locked.
787 */
788 static struct socket *
789 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
790 {
791 struct tcp_function_block *blk;
792 struct inpcb *inp = NULL;
793 struct socket *so;
794 struct tcpcb *tp;
795 int error;
796 char *s;
797
798 NET_EPOCH_ASSERT();
799
800 /*
801 * Ok, create the full blown connection, and set things up
802 * as they would have been set up if we had created the
803 * connection when the SYN arrived.
804 */
805 if ((so = solisten_clone(lso)) == NULL)
806 goto allocfail;
807 #ifdef MAC
808 mac_socketpeer_set_from_mbuf(m, so);
809 #endif
810 error = in_pcballoc(so, &V_tcbinfo);
811 if (error) {
812 sodealloc(so);
813 goto allocfail;
814 }
815 inp = sotoinpcb(so);
816 if ((tp = tcp_newtcpcb(inp)) == NULL) {
817 in_pcbdetach(inp);
818 in_pcbfree(inp);
819 sodealloc(so);
820 goto allocfail;
821 }
822 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
823 #ifdef INET6
824 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
825 inp->inp_vflag &= ~INP_IPV4;
826 inp->inp_vflag |= INP_IPV6;
827 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
828 } else {
829 inp->inp_vflag &= ~INP_IPV6;
830 inp->inp_vflag |= INP_IPV4;
831 #endif
832 inp->inp_ip_ttl = sc->sc_ip_ttl;
833 inp->inp_ip_tos = sc->sc_ip_tos;
834 inp->inp_laddr = sc->sc_inc.inc_laddr;
835 #ifdef INET6
836 }
837 #endif
838
839 /*
840 * If there's an mbuf and it has a flowid, then let's initialise the
841 * inp with that particular flowid.
842 */
843 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) {
844 inp->inp_flowid = m->m_pkthdr.flowid;
845 inp->inp_flowtype = M_HASHTYPE_GET(m);
846 #ifdef NUMA
847 inp->inp_numa_domain = m->m_pkthdr.numa_domain;
848 #endif
849 }
850
851 inp->inp_lport = sc->sc_inc.inc_lport;
852 #ifdef INET6
853 if (inp->inp_vflag & INP_IPV6PROTO) {
854 struct inpcb *oinp = sotoinpcb(lso);
855
856 /*
857 * Inherit socket options from the listening socket.
858 * Note that in6p_inputopts are not (and should not be)
859 * copied, since it stores previously received options and is
860 * used to detect if each new option is different than the
861 * previous one and hence should be passed to a user.
862 * If we copied in6p_inputopts, a user would not be able to
863 * receive options just after calling the accept system call.
864 */
865 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
866 if (oinp->in6p_outputopts)
867 inp->in6p_outputopts =
868 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
869 inp->in6p_hops = oinp->in6p_hops;
870 }
871
872 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
873 struct in6_addr laddr6;
874 struct sockaddr_in6 sin6;
875
876 sin6.sin6_family = AF_INET6;
877 sin6.sin6_len = sizeof(sin6);
878 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
879 sin6.sin6_port = sc->sc_inc.inc_fport;
880 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
881 laddr6 = inp->in6p_laddr;
882 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
883 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
884 INP_HASH_WLOCK(&V_tcbinfo);
885 error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6,
886 thread0.td_ucred, m, false);
887 INP_HASH_WUNLOCK(&V_tcbinfo);
888 if (error != 0) {
889 inp->in6p_laddr = laddr6;
890 goto abort;
891 }
892 /* Override flowlabel from in6_pcbconnect. */
893 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
894 inp->inp_flow |= sc->sc_flowlabel;
895 }
896 #endif /* INET6 */
897 #if defined(INET) && defined(INET6)
898 else
899 #endif
900 #ifdef INET
901 {
902 struct in_addr laddr;
903 struct sockaddr_in sin;
904
905 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
906
907 if (inp->inp_options == NULL) {
908 inp->inp_options = sc->sc_ipopts;
909 sc->sc_ipopts = NULL;
910 }
911
912 sin.sin_family = AF_INET;
913 sin.sin_len = sizeof(sin);
914 sin.sin_addr = sc->sc_inc.inc_faddr;
915 sin.sin_port = sc->sc_inc.inc_fport;
916 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
917 laddr = inp->inp_laddr;
918 if (inp->inp_laddr.s_addr == INADDR_ANY)
919 inp->inp_laddr = sc->sc_inc.inc_laddr;
920 INP_HASH_WLOCK(&V_tcbinfo);
921 error = in_pcbconnect(inp, (struct sockaddr *)&sin,
922 thread0.td_ucred, false);
923 INP_HASH_WUNLOCK(&V_tcbinfo);
924 if (error != 0) {
925 inp->inp_laddr = laddr;
926 goto abort;
927 }
928 }
929 #endif /* INET */
930 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
931 /* Copy old policy into new socket's. */
932 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0)
933 printf("syncache_socket: could not copy policy\n");
934 #endif
935 tp->t_state = TCPS_SYN_RECEIVED;
936 tp->iss = sc->sc_iss;
937 tp->irs = sc->sc_irs;
938 tp->t_port = sc->sc_port;
939 tcp_rcvseqinit(tp);
940 tcp_sendseqinit(tp);
941 blk = sototcpcb(lso)->t_fb;
942 if (V_functions_inherit_listen_socket_stack && blk != tp->t_fb) {
943 /*
944 * Our parents t_fb was not the default,
945 * we need to release our ref on tp->t_fb and
946 * pickup one on the new entry.
947 */
948 struct tcp_function_block *rblk;
949
950 rblk = find_and_ref_tcp_fb(blk);
951 KASSERT(rblk != NULL,
952 ("cannot find blk %p out of syncache?", blk));
953 if (tp->t_fb->tfb_tcp_fb_fini)
954 (*tp->t_fb->tfb_tcp_fb_fini)(tp, 0);
955 refcount_release(&tp->t_fb->tfb_refcnt);
956 tp->t_fb = rblk;
957 /*
958 * XXXrrs this is quite dangerous, it is possible
959 * for the new function to fail to init. We also
960 * are not asking if the handoff_is_ok though at
961 * the very start thats probalbly ok.
962 */
963 if (tp->t_fb->tfb_tcp_fb_init) {
964 (*tp->t_fb->tfb_tcp_fb_init)(tp);
965 }
966 }
967 tp->snd_wl1 = sc->sc_irs;
968 tp->snd_max = tp->iss + 1;
969 tp->snd_nxt = tp->iss + 1;
970 tp->rcv_up = sc->sc_irs + 1;
971 tp->rcv_wnd = sc->sc_wnd;
972 tp->rcv_adv += tp->rcv_wnd;
973 tp->last_ack_sent = tp->rcv_nxt;
974
975 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
976 if (sc->sc_flags & SCF_NOOPT)
977 tp->t_flags |= TF_NOOPT;
978 else {
979 if (sc->sc_flags & SCF_WINSCALE) {
980 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
981 tp->snd_scale = sc->sc_requested_s_scale;
982 tp->request_r_scale = sc->sc_requested_r_scale;
983 }
984 if (sc->sc_flags & SCF_TIMESTAMP) {
985 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
986 tp->ts_recent = sc->sc_tsreflect;
987 tp->ts_recent_age = tcp_ts_getticks();
988 tp->ts_offset = sc->sc_tsoff;
989 }
990 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
991 if (sc->sc_flags & SCF_SIGNATURE)
992 tp->t_flags |= TF_SIGNATURE;
993 #endif
994 if (sc->sc_flags & SCF_SACK)
995 tp->t_flags |= TF_SACK_PERMIT;
996 }
997
998 tcp_ecn_syncache_socket(tp, sc);
999
1000 /*
1001 * Set up MSS and get cached values from tcp_hostcache.
1002 * This might overwrite some of the defaults we just set.
1003 */
1004 tcp_mss(tp, sc->sc_peer_mss);
1005
1006 /*
1007 * If the SYN,ACK was retransmitted, indicate that CWND to be
1008 * limited to one segment in cc_conn_init().
1009 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
1010 */
1011 if (sc->sc_rxmits > 1)
1012 tp->snd_cwnd = 1;
1013
1014 #ifdef TCP_OFFLOAD
1015 /*
1016 * Allow a TOE driver to install its hooks. Note that we hold the
1017 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a
1018 * new connection before the TOE driver has done its thing.
1019 */
1020 if (ADDED_BY_TOE(sc)) {
1021 struct toedev *tod = sc->sc_tod;
1022
1023 tod->tod_offload_socket(tod, sc->sc_todctx, so);
1024 }
1025 #endif
1026 /*
1027 * Copy and activate timers.
1028 */
1029 tp->t_maxunacktime = sototcpcb(lso)->t_maxunacktime;
1030 tp->t_keepinit = sototcpcb(lso)->t_keepinit;
1031 tp->t_keepidle = sototcpcb(lso)->t_keepidle;
1032 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl;
1033 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt;
1034 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp));
1035
1036 TCPSTAT_INC(tcps_accepts);
1037 TCP_PROBE6(state__change, NULL, tp, NULL, tp, NULL, TCPS_LISTEN);
1038
1039 if (!solisten_enqueue(so, SS_ISCONNECTED))
1040 tp->t_flags |= TF_SONOTCONN;
1041
1042 return (so);
1043
1044 allocfail:
1045 /*
1046 * Drop the connection; we will either send a RST or have the peer
1047 * retransmit its SYN again after its RTO and try again.
1048 */
1049 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
1050 log(LOG_DEBUG, "%s; %s: Socket create failed "
1051 "due to limits or memory shortage\n",
1052 s, __func__);
1053 free(s, M_TCPLOG);
1054 }
1055 TCPSTAT_INC(tcps_listendrop);
1056 return (NULL);
1057
1058 abort:
1059 in_pcbdetach(inp);
1060 in_pcbfree(inp);
1061 sodealloc(so);
1062 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
1063 log(LOG_DEBUG, "%s; %s: in%s_pcbconnect failed with error %i\n",
1064 s, __func__, (sc->sc_inc.inc_flags & INC_ISIPV6) ? "6" : "",
1065 error);
1066 free(s, M_TCPLOG);
1067 }
1068 TCPSTAT_INC(tcps_listendrop);
1069 return (NULL);
1070 }
1071
1072 /*
1073 * This function gets called when we receive an ACK for a
1074 * socket in the LISTEN state. We look up the connection
1075 * in the syncache, and if its there, we pull it out of
1076 * the cache and turn it into a full-blown connection in
1077 * the SYN-RECEIVED state.
1078 *
1079 * On syncache_socket() success the newly created socket
1080 * has its underlying inp locked.
1081 */
1082 int
1083 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1084 struct socket **lsop, struct mbuf *m, uint16_t port)
1085 {
1086 struct syncache *sc;
1087 struct syncache_head *sch;
1088 struct syncache scs;
1089 char *s;
1090 bool locked;
1091
1092 NET_EPOCH_ASSERT();
1093 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
1094 ("%s: can handle only ACK", __func__));
1095
1096 if (syncache_cookiesonly()) {
1097 sc = NULL;
1098 sch = syncache_hashbucket(inc);
1099 locked = false;
1100 } else {
1101 sc = syncache_lookup(inc, &sch); /* returns locked sch */
1102 locked = true;
1103 SCH_LOCK_ASSERT(sch);
1104 }
1105
1106 #ifdef INVARIANTS
1107 /*
1108 * Test code for syncookies comparing the syncache stored
1109 * values with the reconstructed values from the cookie.
1110 */
1111 if (sc != NULL)
1112 syncookie_cmp(inc, sch, sc, th, to, *lsop, port);
1113 #endif
1114
1115 if (sc == NULL) {
1116 /*
1117 * There is no syncache entry, so see if this ACK is
1118 * a returning syncookie. To do this, first:
1119 * A. Check if syncookies are used in case of syncache
1120 * overflows
1121 * B. See if this socket has had a syncache entry dropped in
1122 * the recent past. We don't want to accept a bogus
1123 * syncookie if we've never received a SYN or accept it
1124 * twice.
1125 * C. check that the syncookie is valid. If it is, then
1126 * cobble up a fake syncache entry, and return.
1127 */
1128 if (locked && !V_tcp_syncookies) {
1129 SCH_UNLOCK(sch);
1130 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1131 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
1132 "segment rejected (syncookies disabled)\n",
1133 s, __func__);
1134 goto failed;
1135 }
1136 if (locked && !V_tcp_syncookiesonly &&
1137 sch->sch_last_overflow < time_uptime - SYNCOOKIE_LIFETIME) {
1138 SCH_UNLOCK(sch);
1139 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1140 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
1141 "segment rejected (no syncache entry)\n",
1142 s, __func__);
1143 goto failed;
1144 }
1145 bzero(&scs, sizeof(scs));
1146 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop, port);
1147 if (locked)
1148 SCH_UNLOCK(sch);
1149 if (sc == NULL) {
1150 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1151 log(LOG_DEBUG, "%s; %s: Segment failed "
1152 "SYNCOOKIE authentication, segment rejected "
1153 "(probably spoofed)\n", s, __func__);
1154 goto failed;
1155 }
1156 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1157 /* If received ACK has MD5 signature, check it. */
1158 if ((to->to_flags & TOF_SIGNATURE) != 0 &&
1159 (!TCPMD5_ENABLED() ||
1160 TCPMD5_INPUT(m, th, to->to_signature) != 0)) {
1161 /* Drop the ACK. */
1162 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1163 log(LOG_DEBUG, "%s; %s: Segment rejected, "
1164 "MD5 signature doesn't match.\n",
1165 s, __func__);
1166 free(s, M_TCPLOG);
1167 }
1168 TCPSTAT_INC(tcps_sig_err_sigopt);
1169 return (-1); /* Do not send RST */
1170 }
1171 #endif /* TCP_SIGNATURE */
1172 TCPSTATES_INC(TCPS_SYN_RECEIVED);
1173 } else {
1174 if (sc->sc_port != port) {
1175 SCH_UNLOCK(sch);
1176 return (0);
1177 }
1178 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1179 /*
1180 * If listening socket requested TCP digests, check that
1181 * received ACK has signature and it is correct.
1182 * If not, drop the ACK and leave sc entry in th cache,
1183 * because SYN was received with correct signature.
1184 */
1185 if (sc->sc_flags & SCF_SIGNATURE) {
1186 if ((to->to_flags & TOF_SIGNATURE) == 0) {
1187 /* No signature */
1188 TCPSTAT_INC(tcps_sig_err_nosigopt);
1189 SCH_UNLOCK(sch);
1190 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1191 log(LOG_DEBUG, "%s; %s: Segment "
1192 "rejected, MD5 signature wasn't "
1193 "provided.\n", s, __func__);
1194 free(s, M_TCPLOG);
1195 }
1196 return (-1); /* Do not send RST */
1197 }
1198 if (!TCPMD5_ENABLED() ||
1199 TCPMD5_INPUT(m, th, to->to_signature) != 0) {
1200 /* Doesn't match or no SA */
1201 SCH_UNLOCK(sch);
1202 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1203 log(LOG_DEBUG, "%s; %s: Segment "
1204 "rejected, MD5 signature doesn't "
1205 "match.\n", s, __func__);
1206 free(s, M_TCPLOG);
1207 }
1208 return (-1); /* Do not send RST */
1209 }
1210 }
1211 #endif /* TCP_SIGNATURE */
1212
1213 /*
1214 * RFC 7323 PAWS: If we have a timestamp on this segment and
1215 * it's less than ts_recent, drop it.
1216 * XXXMT: RFC 7323 also requires to send an ACK.
1217 * In tcp_input.c this is only done for TCP segments
1218 * with user data, so be consistent here and just drop
1219 * the segment.
1220 */
1221 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS &&
1222 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) {
1223 SCH_UNLOCK(sch);
1224 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1225 log(LOG_DEBUG,
1226 "%s; %s: SEG.TSval %u < TS.Recent %u, "
1227 "segment dropped\n", s, __func__,
1228 to->to_tsval, sc->sc_tsreflect);
1229 free(s, M_TCPLOG);
1230 }
1231 return (-1); /* Do not send RST */
1232 }
1233
1234 /*
1235 * If timestamps were not negotiated during SYN/ACK and a
1236 * segment with a timestamp is received, ignore the
1237 * timestamp and process the packet normally.
1238 * See section 3.2 of RFC 7323.
1239 */
1240 if (!(sc->sc_flags & SCF_TIMESTAMP) &&
1241 (to->to_flags & TOF_TS)) {
1242 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1243 log(LOG_DEBUG, "%s; %s: Timestamp not "
1244 "expected, segment processed normally\n",
1245 s, __func__);
1246 free(s, M_TCPLOG);
1247 s = NULL;
1248 }
1249 }
1250
1251 /*
1252 * If timestamps were negotiated during SYN/ACK and a
1253 * segment without a timestamp is received, silently drop
1254 * the segment, unless the missing timestamps are tolerated.
1255 * See section 3.2 of RFC 7323.
1256 */
1257 if ((sc->sc_flags & SCF_TIMESTAMP) &&
1258 !(to->to_flags & TOF_TS)) {
1259 if (V_tcp_tolerate_missing_ts) {
1260 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1261 log(LOG_DEBUG,
1262 "%s; %s: Timestamp missing, "
1263 "segment processed normally\n",
1264 s, __func__);
1265 free(s, M_TCPLOG);
1266 }
1267 } else {
1268 SCH_UNLOCK(sch);
1269 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1270 log(LOG_DEBUG,
1271 "%s; %s: Timestamp missing, "
1272 "segment silently dropped\n",
1273 s, __func__);
1274 free(s, M_TCPLOG);
1275 }
1276 return (-1); /* Do not send RST */
1277 }
1278 }
1279 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
1280 sch->sch_length--;
1281 #ifdef TCP_OFFLOAD
1282 if (ADDED_BY_TOE(sc)) {
1283 struct toedev *tod = sc->sc_tod;
1284
1285 tod->tod_syncache_removed(tod, sc->sc_todctx);
1286 }
1287 #endif
1288 SCH_UNLOCK(sch);
1289 }
1290
1291 /*
1292 * Segment validation:
1293 * ACK must match our initial sequence number + 1 (the SYN|ACK).
1294 */
1295 if (th->th_ack != sc->sc_iss + 1) {
1296 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1297 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
1298 "rejected\n", s, __func__, th->th_ack, sc->sc_iss);
1299 goto failed;
1300 }
1301
1302 /*
1303 * The SEQ must fall in the window starting at the received
1304 * initial receive sequence number + 1 (the SYN).
1305 */
1306 if (SEQ_LEQ(th->th_seq, sc->sc_irs) ||
1307 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
1308 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1309 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
1310 "rejected\n", s, __func__, th->th_seq, sc->sc_irs);
1311 goto failed;
1312 }
1313
1314 *lsop = syncache_socket(sc, *lsop, m);
1315
1316 if (__predict_false(*lsop == NULL)) {
1317 TCPSTAT_INC(tcps_sc_aborted);
1318 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
1319 } else
1320 TCPSTAT_INC(tcps_sc_completed);
1321
1322 /* how do we find the inp for the new socket? */
1323 if (sc != &scs)
1324 syncache_free(sc);
1325 return (1);
1326 failed:
1327 if (sc != NULL) {
1328 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
1329 if (sc != &scs)
1330 syncache_free(sc);
1331 }
1332 if (s != NULL)
1333 free(s, M_TCPLOG);
1334 *lsop = NULL;
1335 return (0);
1336 }
1337
1338 static struct socket *
1339 syncache_tfo_expand(struct syncache *sc, struct socket *lso, struct mbuf *m,
1340 uint64_t response_cookie)
1341 {
1342 struct inpcb *inp;
1343 struct tcpcb *tp;
1344 unsigned int *pending_counter;
1345 struct socket *so;
1346
1347 NET_EPOCH_ASSERT();
1348
1349 pending_counter = intotcpcb(sotoinpcb(lso))->t_tfo_pending;
1350 so = syncache_socket(sc, lso, m);
1351 if (so == NULL) {
1352 TCPSTAT_INC(tcps_sc_aborted);
1353 atomic_subtract_int(pending_counter, 1);
1354 } else {
1355 soisconnected(so);
1356 inp = sotoinpcb(so);
1357 tp = intotcpcb(inp);
1358 tp->t_flags |= TF_FASTOPEN;
1359 tp->t_tfo_cookie.server = response_cookie;
1360 tp->snd_max = tp->iss;
1361 tp->snd_nxt = tp->iss;
1362 tp->t_tfo_pending = pending_counter;
1363 TCPSTATES_INC(TCPS_SYN_RECEIVED);
1364 TCPSTAT_INC(tcps_sc_completed);
1365 }
1366
1367 return (so);
1368 }
1369
1370 /*
1371 * Given a LISTEN socket and an inbound SYN request, add
1372 * this to the syn cache, and send back a segment:
1373 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
1374 * to the source.
1375 *
1376 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
1377 * Doing so would require that we hold onto the data and deliver it
1378 * to the application. However, if we are the target of a SYN-flood
1379 * DoS attack, an attacker could send data which would eventually
1380 * consume all available buffer space if it were ACKed. By not ACKing
1381 * the data, we avoid this DoS scenario.
1382 *
1383 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO)
1384 * cookie is processed and a new socket is created. In this case, any data
1385 * accompanying the SYN will be queued to the socket by tcp_input() and will
1386 * be ACKed either when the application sends response data or the delayed
1387 * ACK timer expires, whichever comes first.
1388 */
1389 struct socket *
1390 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1391 struct inpcb *inp, struct socket *so, struct mbuf *m, void *tod,
1392 void *todctx, uint8_t iptos, uint16_t port)
1393 {
1394 struct tcpcb *tp;
1395 struct socket *rv = NULL;
1396 struct syncache *sc = NULL;
1397 struct syncache_head *sch;
1398 struct mbuf *ipopts = NULL;
1399 u_int ltflags;
1400 int win, ip_ttl, ip_tos;
1401 char *s;
1402 #ifdef INET6
1403 int autoflowlabel = 0;
1404 #endif
1405 #ifdef MAC
1406 struct label *maclabel;
1407 #endif
1408 struct syncache scs;
1409 struct ucred *cred;
1410 uint64_t tfo_response_cookie;
1411 unsigned int *tfo_pending = NULL;
1412 int tfo_cookie_valid = 0;
1413 int tfo_response_cookie_valid = 0;
1414 bool locked;
1415
1416 INP_RLOCK_ASSERT(inp); /* listen socket */
1417 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
1418 ("%s: unexpected tcp flags", __func__));
1419
1420 /*
1421 * Combine all so/tp operations very early to drop the INP lock as
1422 * soon as possible.
1423 */
1424 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so));
1425 tp = sototcpcb(so);
1426 cred = V_tcp_syncache.see_other ? NULL : crhold(so->so_cred);
1427
1428 #ifdef INET6
1429 if (inc->inc_flags & INC_ISIPV6) {
1430 if (inp->inp_flags & IN6P_AUTOFLOWLABEL) {
1431 autoflowlabel = 1;
1432 }
1433 ip_ttl = in6_selecthlim(inp, NULL);
1434 if ((inp->in6p_outputopts == NULL) ||
1435 (inp->in6p_outputopts->ip6po_tclass == -1)) {
1436 ip_tos = 0;
1437 } else {
1438 ip_tos = inp->in6p_outputopts->ip6po_tclass;
1439 }
1440 }
1441 #endif
1442 #if defined(INET6) && defined(INET)
1443 else
1444 #endif
1445 #ifdef INET
1446 {
1447 ip_ttl = inp->inp_ip_ttl;
1448 ip_tos = inp->inp_ip_tos;
1449 }
1450 #endif
1451 win = so->sol_sbrcv_hiwat;
1452 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE));
1453
1454 if (V_tcp_fastopen_server_enable && IS_FASTOPEN(tp->t_flags) &&
1455 (tp->t_tfo_pending != NULL) &&
1456 (to->to_flags & TOF_FASTOPEN)) {
1457 /*
1458 * Limit the number of pending TFO connections to
1459 * approximately half of the queue limit. This prevents TFO
1460 * SYN floods from starving the service by filling the
1461 * listen queue with bogus TFO connections.
1462 */
1463 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <=
1464 (so->sol_qlimit / 2)) {
1465 int result;
1466
1467 result = tcp_fastopen_check_cookie(inc,
1468 to->to_tfo_cookie, to->to_tfo_len,
1469 &tfo_response_cookie);
1470 tfo_cookie_valid = (result > 0);
1471 tfo_response_cookie_valid = (result >= 0);
1472 }
1473
1474 /*
1475 * Remember the TFO pending counter as it will have to be
1476 * decremented below if we don't make it to syncache_tfo_expand().
1477 */
1478 tfo_pending = tp->t_tfo_pending;
1479 }
1480
1481 #ifdef MAC
1482 if (mac_syncache_init(&maclabel) != 0) {
1483 INP_RUNLOCK(inp);
1484 goto done;
1485 } else
1486 mac_syncache_create(maclabel, inp);
1487 #endif
1488 if (!tfo_cookie_valid)
1489 INP_RUNLOCK(inp);
1490
1491 /*
1492 * Remember the IP options, if any.
1493 */
1494 #ifdef INET6
1495 if (!(inc->inc_flags & INC_ISIPV6))
1496 #endif
1497 #ifdef INET
1498 ipopts = (m) ? ip_srcroute(m) : NULL;
1499 #else
1500 ipopts = NULL;
1501 #endif
1502
1503 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1504 /*
1505 * When the socket is TCP-MD5 enabled check that,
1506 * - a signed packet is valid
1507 * - a non-signed packet does not have a security association
1508 *
1509 * If a signed packet fails validation or a non-signed packet has a
1510 * security association, the packet will be dropped.
1511 */
1512 if (ltflags & TF_SIGNATURE) {
1513 if (to->to_flags & TOF_SIGNATURE) {
1514 if (!TCPMD5_ENABLED() ||
1515 TCPMD5_INPUT(m, th, to->to_signature) != 0)
1516 goto done;
1517 } else {
1518 if (TCPMD5_ENABLED() &&
1519 TCPMD5_INPUT(m, NULL, NULL) != ENOENT)
1520 goto done;
1521 }
1522 } else if (to->to_flags & TOF_SIGNATURE)
1523 goto done;
1524 #endif /* TCP_SIGNATURE */
1525 /*
1526 * See if we already have an entry for this connection.
1527 * If we do, resend the SYN,ACK, and reset the retransmit timer.
1528 *
1529 * XXX: should the syncache be re-initialized with the contents
1530 * of the new SYN here (which may have different options?)
1531 *
1532 * XXX: We do not check the sequence number to see if this is a
1533 * real retransmit or a new connection attempt. The question is
1534 * how to handle such a case; either ignore it as spoofed, or
1535 * drop the current entry and create a new one?
1536 */
1537 if (syncache_cookiesonly()) {
1538 sc = NULL;
1539 sch = syncache_hashbucket(inc);
1540 locked = false;
1541 } else {
1542 sc = syncache_lookup(inc, &sch); /* returns locked sch */
1543 locked = true;
1544 SCH_LOCK_ASSERT(sch);
1545 }
1546 if (sc != NULL) {
1547 if (tfo_cookie_valid)
1548 INP_RUNLOCK(inp);
1549 TCPSTAT_INC(tcps_sc_dupsyn);
1550 if (ipopts) {
1551 /*
1552 * If we were remembering a previous source route,
1553 * forget it and use the new one we've been given.
1554 */
1555 if (sc->sc_ipopts)
1556 (void) m_free(sc->sc_ipopts);
1557 sc->sc_ipopts = ipopts;
1558 }
1559 /*
1560 * Update timestamp if present.
1561 */
1562 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
1563 sc->sc_tsreflect = to->to_tsval;
1564 else
1565 sc->sc_flags &= ~SCF_TIMESTAMP;
1566 /*
1567 * Adjust ECN response if needed, e.g. different
1568 * IP ECN field, or a fallback by the remote host.
1569 */
1570 if (sc->sc_flags & SCF_ECN_MASK) {
1571 sc->sc_flags &= ~SCF_ECN_MASK;
1572 sc->sc_flags = tcp_ecn_syncache_add(tcp_get_flags(th), iptos);
1573 }
1574 #ifdef MAC
1575 /*
1576 * Since we have already unconditionally allocated label
1577 * storage, free it up. The syncache entry will already
1578 * have an initialized label we can use.
1579 */
1580 mac_syncache_destroy(&maclabel);
1581 #endif
1582 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1583 /* Retransmit SYN|ACK and reset retransmit count. */
1584 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
1585 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
1586 "resetting timer and retransmitting SYN|ACK\n",
1587 s, __func__);
1588 free(s, M_TCPLOG);
1589 }
1590 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) {
1591 sc->sc_rxmits = 0;
1592 syncache_timeout(sc, sch, 1);
1593 TCPSTAT_INC(tcps_sndacks);
1594 TCPSTAT_INC(tcps_sndtotal);
1595 }
1596 SCH_UNLOCK(sch);
1597 goto donenoprobe;
1598 }
1599
1600 if (tfo_cookie_valid) {
1601 bzero(&scs, sizeof(scs));
1602 sc = &scs;
1603 goto skip_alloc;
1604 }
1605
1606 /*
1607 * Skip allocating a syncache entry if we are just going to discard
1608 * it later.
1609 */
1610 if (!locked) {
1611 bzero(&scs, sizeof(scs));
1612 sc = &scs;
1613 } else
1614 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1615 if (sc == NULL) {
1616 /*
1617 * The zone allocator couldn't provide more entries.
1618 * Treat this as if the cache was full; drop the oldest
1619 * entry and insert the new one.
1620 */
1621 TCPSTAT_INC(tcps_sc_zonefail);
1622 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) {
1623 sch->sch_last_overflow = time_uptime;
1624 syncache_drop(sc, sch);
1625 syncache_pause(inc);
1626 }
1627 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1628 if (sc == NULL) {
1629 if (V_tcp_syncookies) {
1630 bzero(&scs, sizeof(scs));
1631 sc = &scs;
1632 } else {
1633 KASSERT(locked,
1634 ("%s: bucket unexpectedly unlocked",
1635 __func__));
1636 SCH_UNLOCK(sch);
1637 if (ipopts)
1638 (void) m_free(ipopts);
1639 goto done;
1640 }
1641 }
1642 }
1643
1644 skip_alloc:
1645 if (!tfo_cookie_valid && tfo_response_cookie_valid)
1646 sc->sc_tfo_cookie = &tfo_response_cookie;
1647
1648 /*
1649 * Fill in the syncache values.
1650 */
1651 #ifdef MAC
1652 sc->sc_label = maclabel;
1653 #endif
1654 sc->sc_cred = cred;
1655 sc->sc_port = port;
1656 cred = NULL;
1657 sc->sc_ipopts = ipopts;
1658 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1659 sc->sc_ip_tos = ip_tos;
1660 sc->sc_ip_ttl = ip_ttl;
1661 #ifdef TCP_OFFLOAD
1662 sc->sc_tod = tod;
1663 sc->sc_todctx = todctx;
1664 #endif
1665 sc->sc_irs = th->th_seq;
1666 sc->sc_flags = 0;
1667 sc->sc_flowlabel = 0;
1668
1669 /*
1670 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
1671 * win was derived from socket earlier in the function.
1672 */
1673 win = imax(win, 0);
1674 win = imin(win, TCP_MAXWIN);
1675 sc->sc_wnd = win;
1676
1677 if (V_tcp_do_rfc1323 &&
1678 !(ltflags & TF_NOOPT)) {
1679 /*
1680 * A timestamp received in a SYN makes
1681 * it ok to send timestamp requests and replies.
1682 */
1683 if ((to->to_flags & TOF_TS) && (V_tcp_do_rfc1323 != 2)) {
1684 sc->sc_tsreflect = to->to_tsval;
1685 sc->sc_flags |= SCF_TIMESTAMP;
1686 sc->sc_tsoff = tcp_new_ts_offset(inc);
1687 }
1688 if ((to->to_flags & TOF_SCALE) && (V_tcp_do_rfc1323 != 3)) {
1689 int wscale = 0;
1690
1691 /*
1692 * Pick the smallest possible scaling factor that
1693 * will still allow us to scale up to sb_max, aka
1694 * kern.ipc.maxsockbuf.
1695 *
1696 * We do this because there are broken firewalls that
1697 * will corrupt the window scale option, leading to
1698 * the other endpoint believing that our advertised
1699 * window is unscaled. At scale factors larger than
1700 * 5 the unscaled window will drop below 1500 bytes,
1701 * leading to serious problems when traversing these
1702 * broken firewalls.
1703 *
1704 * With the default maxsockbuf of 256K, a scale factor
1705 * of 3 will be chosen by this algorithm. Those who
1706 * choose a larger maxsockbuf should watch out
1707 * for the compatibility problems mentioned above.
1708 *
1709 * RFC1323: The Window field in a SYN (i.e., a <SYN>
1710 * or <SYN,ACK>) segment itself is never scaled.
1711 */
1712 while (wscale < TCP_MAX_WINSHIFT &&
1713 (TCP_MAXWIN << wscale) < sb_max)
1714 wscale++;
1715 sc->sc_requested_r_scale = wscale;
1716 sc->sc_requested_s_scale = to->to_wscale;
1717 sc->sc_flags |= SCF_WINSCALE;
1718 }
1719 }
1720 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1721 /*
1722 * If incoming packet has an MD5 signature, flag this in the
1723 * syncache so that syncache_respond() will do the right thing
1724 * with the SYN+ACK.
1725 */
1726 if (to->to_flags & TOF_SIGNATURE)
1727 sc->sc_flags |= SCF_SIGNATURE;
1728 #endif /* TCP_SIGNATURE */
1729 if (to->to_flags & TOF_SACKPERM)
1730 sc->sc_flags |= SCF_SACK;
1731 if (to->to_flags & TOF_MSS)
1732 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */
1733 if (ltflags & TF_NOOPT)
1734 sc->sc_flags |= SCF_NOOPT;
1735 /* ECN Handshake */
1736 if (V_tcp_do_ecn)
1737 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos);
1738
1739 if (V_tcp_syncookies)
1740 sc->sc_iss = syncookie_generate(sch, sc);
1741 else
1742 sc->sc_iss = arc4random();
1743 #ifdef INET6
1744 if (autoflowlabel) {
1745 if (V_tcp_syncookies)
1746 sc->sc_flowlabel = sc->sc_iss;
1747 else
1748 sc->sc_flowlabel = ip6_randomflowlabel();
1749 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK;
1750 }
1751 #endif
1752 if (locked)
1753 SCH_UNLOCK(sch);
1754
1755 if (tfo_cookie_valid) {
1756 rv = syncache_tfo_expand(sc, so, m, tfo_response_cookie);
1757 /* INP_RUNLOCK(inp) will be performed by the caller */
1758 goto tfo_expanded;
1759 }
1760
1761 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1762 /*
1763 * Do a standard 3-way handshake.
1764 */
1765 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) {
1766 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs)
1767 syncache_free(sc);
1768 else if (sc != &scs)
1769 syncache_insert(sc, sch); /* locks and unlocks sch */
1770 TCPSTAT_INC(tcps_sndacks);
1771 TCPSTAT_INC(tcps_sndtotal);
1772 } else {
1773 if (sc != &scs)
1774 syncache_free(sc);
1775 TCPSTAT_INC(tcps_sc_dropped);
1776 }
1777 goto donenoprobe;
1778
1779 done:
1780 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1781 donenoprobe:
1782 if (m)
1783 m_freem(m);
1784 /*
1785 * If tfo_pending is not NULL here, then a TFO SYN that did not
1786 * result in a new socket was processed and the associated pending
1787 * counter has not yet been decremented. All such TFO processing paths
1788 * transit this point.
1789 */
1790 if (tfo_pending != NULL)
1791 tcp_fastopen_decrement_counter(tfo_pending);
1792
1793 tfo_expanded:
1794 if (cred != NULL)
1795 crfree(cred);
1796 #ifdef MAC
1797 if (sc == &scs)
1798 mac_syncache_destroy(&maclabel);
1799 #endif
1800 return (rv);
1801 }
1802
1803 /*
1804 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment,
1805 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL.
1806 */
1807 static int
1808 syncache_respond(struct syncache *sc, const struct mbuf *m0, int flags)
1809 {
1810 struct ip *ip = NULL;
1811 struct mbuf *m;
1812 struct tcphdr *th = NULL;
1813 struct udphdr *udp = NULL;
1814 int optlen, error = 0; /* Make compiler happy */
1815 u_int16_t hlen, tlen, mssopt, ulen;
1816 struct tcpopt to;
1817 #ifdef INET6
1818 struct ip6_hdr *ip6 = NULL;
1819 #endif
1820
1821 NET_EPOCH_ASSERT();
1822
1823 hlen =
1824 #ifdef INET6
1825 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
1826 #endif
1827 sizeof(struct ip);
1828 tlen = hlen + sizeof(struct tcphdr);
1829 if (sc->sc_port) {
1830 tlen += sizeof(struct udphdr);
1831 }
1832 /* Determine MSS we advertize to other end of connection. */
1833 mssopt = tcp_mssopt(&sc->sc_inc);
1834 if (sc->sc_port)
1835 mssopt -= V_tcp_udp_tunneling_overhead;
1836 mssopt = max(mssopt, V_tcp_minmss);
1837
1838 /* XXX: Assume that the entire packet will fit in a header mbuf. */
1839 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
1840 ("syncache: mbuf too small: hlen %u, sc_port %u, max_linkhdr %d + "
1841 "tlen %d + TCP_MAXOLEN %ju <= MHLEN %d", hlen, sc->sc_port,
1842 max_linkhdr, tlen, (uintmax_t)TCP_MAXOLEN, MHLEN));
1843
1844 /* Create the IP+TCP header from scratch. */
1845 m = m_gethdr(M_NOWAIT, MT_DATA);
1846 if (m == NULL)
1847 return (ENOBUFS);
1848 #ifdef MAC
1849 mac_syncache_create_mbuf(sc->sc_label, m);
1850 #endif
1851 m->m_data += max_linkhdr;
1852 m->m_len = tlen;
1853 m->m_pkthdr.len = tlen;
1854 m->m_pkthdr.rcvif = NULL;
1855
1856 #ifdef INET6
1857 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1858 ip6 = mtod(m, struct ip6_hdr *);
1859 ip6->ip6_vfc = IPV6_VERSION;
1860 ip6->ip6_src = sc->sc_inc.inc6_laddr;
1861 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
1862 ip6->ip6_plen = htons(tlen - hlen);
1863 /* ip6_hlim is set after checksum */
1864 /* Zero out traffic class and flow label. */
1865 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK;
1866 ip6->ip6_flow |= sc->sc_flowlabel;
1867 if (sc->sc_port != 0) {
1868 ip6->ip6_nxt = IPPROTO_UDP;
1869 udp = (struct udphdr *)(ip6 + 1);
1870 udp->uh_sport = htons(V_tcp_udp_tunneling_port);
1871 udp->uh_dport = sc->sc_port;
1872 ulen = (tlen - sizeof(struct ip6_hdr));
1873 th = (struct tcphdr *)(udp + 1);
1874 } else {
1875 ip6->ip6_nxt = IPPROTO_TCP;
1876 th = (struct tcphdr *)(ip6 + 1);
1877 }
1878 ip6->ip6_flow |= htonl(sc->sc_ip_tos << 20);
1879 }
1880 #endif
1881 #if defined(INET6) && defined(INET)
1882 else
1883 #endif
1884 #ifdef INET
1885 {
1886 ip = mtod(m, struct ip *);
1887 ip->ip_v = IPVERSION;
1888 ip->ip_hl = sizeof(struct ip) >> 2;
1889 ip->ip_len = htons(tlen);
1890 ip->ip_id = 0;
1891 ip->ip_off = 0;
1892 ip->ip_sum = 0;
1893 ip->ip_src = sc->sc_inc.inc_laddr;
1894 ip->ip_dst = sc->sc_inc.inc_faddr;
1895 ip->ip_ttl = sc->sc_ip_ttl;
1896 ip->ip_tos = sc->sc_ip_tos;
1897
1898 /*
1899 * See if we should do MTU discovery. Route lookups are
1900 * expensive, so we will only unset the DF bit if:
1901 *
1902 * 1) path_mtu_discovery is disabled
1903 * 2) the SCF_UNREACH flag has been set
1904 */
1905 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
1906 ip->ip_off |= htons(IP_DF);
1907 if (sc->sc_port == 0) {
1908 ip->ip_p = IPPROTO_TCP;
1909 th = (struct tcphdr *)(ip + 1);
1910 } else {
1911 ip->ip_p = IPPROTO_UDP;
1912 udp = (struct udphdr *)(ip + 1);
1913 udp->uh_sport = htons(V_tcp_udp_tunneling_port);
1914 udp->uh_dport = sc->sc_port;
1915 ulen = (tlen - sizeof(struct ip));
1916 th = (struct tcphdr *)(udp + 1);
1917 }
1918 }
1919 #endif /* INET */
1920 th->th_sport = sc->sc_inc.inc_lport;
1921 th->th_dport = sc->sc_inc.inc_fport;
1922
1923 if (flags & TH_SYN)
1924 th->th_seq = htonl(sc->sc_iss);
1925 else
1926 th->th_seq = htonl(sc->sc_iss + 1);
1927 th->th_ack = htonl(sc->sc_irs + 1);
1928 th->th_off = sizeof(struct tcphdr) >> 2;
1929 th->th_win = htons(sc->sc_wnd);
1930 th->th_urp = 0;
1931
1932 flags = tcp_ecn_syncache_respond(flags, sc);
1933 tcp_set_flags(th, flags);
1934
1935 /* Tack on the TCP options. */
1936 if ((sc->sc_flags & SCF_NOOPT) == 0) {
1937 to.to_flags = 0;
1938
1939 if (flags & TH_SYN) {
1940 to.to_mss = mssopt;
1941 to.to_flags = TOF_MSS;
1942 if (sc->sc_flags & SCF_WINSCALE) {
1943 to.to_wscale = sc->sc_requested_r_scale;
1944 to.to_flags |= TOF_SCALE;
1945 }
1946 if (sc->sc_flags & SCF_SACK)
1947 to.to_flags |= TOF_SACKPERM;
1948 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1949 if (sc->sc_flags & SCF_SIGNATURE)
1950 to.to_flags |= TOF_SIGNATURE;
1951 #endif
1952 if (sc->sc_tfo_cookie) {
1953 to.to_flags |= TOF_FASTOPEN;
1954 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
1955 to.to_tfo_cookie = sc->sc_tfo_cookie;
1956 /* don't send cookie again when retransmitting response */
1957 sc->sc_tfo_cookie = NULL;
1958 }
1959 }
1960 if (sc->sc_flags & SCF_TIMESTAMP) {
1961 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks();
1962 to.to_tsecr = sc->sc_tsreflect;
1963 to.to_flags |= TOF_TS;
1964 }
1965 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
1966
1967 /* Adjust headers by option size. */
1968 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
1969 m->m_len += optlen;
1970 m->m_pkthdr.len += optlen;
1971 #ifdef INET6
1972 if (sc->sc_inc.inc_flags & INC_ISIPV6)
1973 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
1974 else
1975 #endif
1976 ip->ip_len = htons(ntohs(ip->ip_len) + optlen);
1977 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1978 if (sc->sc_flags & SCF_SIGNATURE) {
1979 KASSERT(to.to_flags & TOF_SIGNATURE,
1980 ("tcp_addoptions() didn't set tcp_signature"));
1981
1982 /* NOTE: to.to_signature is inside of mbuf */
1983 if (!TCPMD5_ENABLED() ||
1984 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) {
1985 m_freem(m);
1986 return (EACCES);
1987 }
1988 }
1989 #endif
1990 } else
1991 optlen = 0;
1992
1993 if (udp) {
1994 ulen += optlen;
1995 udp->uh_ulen = htons(ulen);
1996 }
1997 M_SETFIB(m, sc->sc_inc.inc_fibnum);
1998 /*
1999 * If we have peer's SYN and it has a flowid, then let's assign it to
2000 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid
2001 * to SYN|ACK due to lack of inp here.
2002 */
2003 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) {
2004 m->m_pkthdr.flowid = m0->m_pkthdr.flowid;
2005 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0));
2006 }
2007 #ifdef INET6
2008 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
2009 if (sc->sc_port) {
2010 m->m_pkthdr.csum_flags = CSUM_UDP_IPV6;
2011 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
2012 udp->uh_sum = in6_cksum_pseudo(ip6, ulen,
2013 IPPROTO_UDP, 0);
2014 th->th_sum = htons(0);
2015 } else {
2016 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
2017 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
2018 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen,
2019 IPPROTO_TCP, 0);
2020 }
2021 ip6->ip6_hlim = sc->sc_ip_ttl;
2022 #ifdef TCP_OFFLOAD
2023 if (ADDED_BY_TOE(sc)) {
2024 struct toedev *tod = sc->sc_tod;
2025
2026 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
2027
2028 return (error);
2029 }
2030 #endif
2031 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th);
2032 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
2033 }
2034 #endif
2035 #if defined(INET6) && defined(INET)
2036 else
2037 #endif
2038 #ifdef INET
2039 {
2040 if (sc->sc_port) {
2041 m->m_pkthdr.csum_flags = CSUM_UDP;
2042 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
2043 udp->uh_sum = in_pseudo(ip->ip_src.s_addr,
2044 ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP));
2045 th->th_sum = htons(0);
2046 } else {
2047 m->m_pkthdr.csum_flags = CSUM_TCP;
2048 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
2049 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
2050 htons(tlen + optlen - hlen + IPPROTO_TCP));
2051 }
2052 #ifdef TCP_OFFLOAD
2053 if (ADDED_BY_TOE(sc)) {
2054 struct toedev *tod = sc->sc_tod;
2055
2056 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
2057
2058 return (error);
2059 }
2060 #endif
2061 TCP_PROBE5(send, NULL, NULL, ip, NULL, th);
2062 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
2063 }
2064 #endif
2065 return (error);
2066 }
2067
2068 /*
2069 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks
2070 * that exceed the capacity of the syncache by avoiding the storage of any
2071 * of the SYNs we receive. Syncookies defend against blind SYN flooding
2072 * attacks where the attacker does not have access to our responses.
2073 *
2074 * Syncookies encode and include all necessary information about the
2075 * connection setup within the SYN|ACK that we send back. That way we
2076 * can avoid keeping any local state until the ACK to our SYN|ACK returns
2077 * (if ever). Normally the syncache and syncookies are running in parallel
2078 * with the latter taking over when the former is exhausted. When matching
2079 * syncache entry is found the syncookie is ignored.
2080 *
2081 * The only reliable information persisting the 3WHS is our initial sequence
2082 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient
2083 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS
2084 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK
2085 * returns and signifies a legitimate connection if it matches the ACK.
2086 *
2087 * The available space of 32 bits to store the hash and to encode the SYN
2088 * option information is very tight and we should have at least 24 bits for
2089 * the MAC to keep the number of guesses by blind spoofing reasonably high.
2090 *
2091 * SYN option information we have to encode to fully restore a connection:
2092 * MSS: is imporant to chose an optimal segment size to avoid IP level
2093 * fragmentation along the path. The common MSS values can be encoded
2094 * in a 3-bit table. Uncommon values are captured by the next lower value
2095 * in the table leading to a slight increase in packetization overhead.
2096 * WSCALE: is necessary to allow large windows to be used for high delay-
2097 * bandwidth product links. Not scaling the window when it was initially
2098 * negotiated is bad for performance as lack of scaling further decreases
2099 * the apparent available send window. We only need to encode the WSCALE
2100 * we received from the remote end. Our end can be recalculated at any
2101 * time. The common WSCALE values can be encoded in a 3-bit table.
2102 * Uncommon values are captured by the next lower value in the table
2103 * making us under-estimate the available window size halving our
2104 * theoretically possible maximum throughput for that connection.
2105 * SACK: Greatly assists in packet loss recovery and requires 1 bit.
2106 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options
2107 * that are included in all segments on a connection. We enable them when
2108 * the ACK has them.
2109 *
2110 * Security of syncookies and attack vectors:
2111 *
2112 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod)
2113 * together with the gloabl secret to make it unique per connection attempt.
2114 * Thus any change of any of those parameters results in a different MAC output
2115 * in an unpredictable way unless a collision is encountered. 24 bits of the
2116 * MAC are embedded into the ISS.
2117 *
2118 * To prevent replay attacks two rotating global secrets are updated with a
2119 * new random value every 15 seconds. The life-time of a syncookie is thus
2120 * 15-30 seconds.
2121 *
2122 * Vector 1: Attacking the secret. This requires finding a weakness in the
2123 * MAC itself or the way it is used here. The attacker can do a chosen plain
2124 * text attack by varying and testing the all parameters under his control.
2125 * The strength depends on the size and randomness of the secret, and the
2126 * cryptographic security of the MAC function. Due to the constant updating
2127 * of the secret the attacker has at most 29.999 seconds to find the secret
2128 * and launch spoofed connections. After that he has to start all over again.
2129 *
2130 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC
2131 * size an average of 4,823 attempts are required for a 50% chance of success
2132 * to spoof a single syncookie (birthday collision paradox). However the
2133 * attacker is blind and doesn't know if one of his attempts succeeded unless
2134 * he has a side channel to interfere success from. A single connection setup
2135 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets.
2136 * This many attempts are required for each one blind spoofed connection. For
2137 * every additional spoofed connection he has to launch another N attempts.
2138 * Thus for a sustained rate 100 spoofed connections per second approximately
2139 * 1,800,000 packets per second would have to be sent.
2140 *
2141 * NB: The MAC function should be fast so that it doesn't become a CPU
2142 * exhaustion attack vector itself.
2143 *
2144 * References:
2145 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations
2146 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996
2147 * http://cr.yp.to/syncookies.html (overview)
2148 * http://cr.yp.to/syncookies/archive (details)
2149 *
2150 *
2151 * Schematic construction of a syncookie enabled Initial Sequence Number:
2152 * 0 1 2 3
2153 * 12345678901234567890123456789012
2154 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP|
2155 *
2156 * x 24 MAC (truncated)
2157 * W 3 Send Window Scale index
2158 * M 3 MSS index
2159 * S 1 SACK permitted
2160 * P 1 Odd/even secret
2161 */
2162
2163 /*
2164 * Distribution and probability of certain MSS values. Those in between are
2165 * rounded down to the next lower one.
2166 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011]
2167 * .2% .3% 5% 7% 7% 20% 15% 45%
2168 */
2169 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 };
2170
2171 /*
2172 * Distribution and probability of certain WSCALE values. We have to map the
2173 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3
2174 * bits based on prevalence of certain values. Where we don't have an exact
2175 * match for are rounded down to the next lower one letting us under-estimate
2176 * the true available window. At the moment this would happen only for the
2177 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer
2178 * and window size). The absence of the WSCALE option (no scaling in either
2179 * direction) is encoded with index zero.
2180 * [WSCALE values histograms, Allman, 2012]
2181 * X 10 10 35 5 6 14 10% by host
2182 * X 11 4 5 5 18 49 3% by connections
2183 */
2184 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 };
2185
2186 /*
2187 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed
2188 * and good cryptographic properties.
2189 */
2190 static uint32_t
2191 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags,
2192 uint8_t *secbits, uintptr_t secmod)
2193 {
2194 SIPHASH_CTX ctx;
2195 uint32_t siphash[2];
2196
2197 SipHash24_Init(&ctx);
2198 SipHash_SetKey(&ctx, secbits);
2199 switch (inc->inc_flags & INC_ISIPV6) {
2200 #ifdef INET
2201 case 0:
2202 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr));
2203 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr));
2204 break;
2205 #endif
2206 #ifdef INET6
2207 case INC_ISIPV6:
2208 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr));
2209 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr));
2210 break;
2211 #endif
2212 }
2213 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport));
2214 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport));
2215 SipHash_Update(&ctx, &irs, sizeof(irs));
2216 SipHash_Update(&ctx, &flags, sizeof(flags));
2217 SipHash_Update(&ctx, &secmod, sizeof(secmod));
2218 SipHash_Final((u_int8_t *)&siphash, &ctx);
2219
2220 return (siphash[0] ^ siphash[1]);
2221 }
2222
2223 static tcp_seq
2224 syncookie_generate(struct syncache_head *sch, struct syncache *sc)
2225 {
2226 u_int i, secbit, wscale;
2227 uint32_t iss, hash;
2228 uint8_t *secbits;
2229 union syncookie cookie;
2230
2231 cookie.cookie = 0;
2232
2233 /* Map our computed MSS into the 3-bit index. */
2234 for (i = nitems(tcp_sc_msstab) - 1;
2235 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0;
2236 i--)
2237 ;
2238 cookie.flags.mss_idx = i;
2239
2240 /*
2241 * Map the send window scale into the 3-bit index but only if
2242 * the wscale option was received.
2243 */
2244 if (sc->sc_flags & SCF_WINSCALE) {
2245 wscale = sc->sc_requested_s_scale;
2246 for (i = nitems(tcp_sc_wstab) - 1;
2247 tcp_sc_wstab[i] > wscale && i > 0;
2248 i--)
2249 ;
2250 cookie.flags.wscale_idx = i;
2251 }
2252
2253 /* Can we do SACK? */
2254 if (sc->sc_flags & SCF_SACK)
2255 cookie.flags.sack_ok = 1;
2256
2257 /* Which of the two secrets to use. */
2258 secbit = V_tcp_syncache.secret.oddeven & 0x1;
2259 cookie.flags.odd_even = secbit;
2260
2261 secbits = V_tcp_syncache.secret.key[secbit];
2262 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits,
2263 (uintptr_t)sch);
2264
2265 /*
2266 * Put the flags into the hash and XOR them to get better ISS number
2267 * variance. This doesn't enhance the cryptographic strength and is
2268 * done to prevent the 8 cookie bits from showing up directly on the
2269 * wire.
2270 */
2271 iss = hash & ~0xff;
2272 iss |= cookie.cookie ^ (hash >> 24);
2273
2274 TCPSTAT_INC(tcps_sc_sendcookie);
2275 return (iss);
2276 }
2277
2278 static struct syncache *
2279 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch,
2280 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
2281 struct socket *lso, uint16_t port)
2282 {
2283 uint32_t hash;
2284 uint8_t *secbits;
2285 tcp_seq ack, seq;
2286 int wnd, wscale = 0;
2287 union syncookie cookie;
2288
2289 /*
2290 * Pull information out of SYN-ACK/ACK and revert sequence number
2291 * advances.
2292 */
2293 ack = th->th_ack - 1;
2294 seq = th->th_seq - 1;
2295
2296 /*
2297 * Unpack the flags containing enough information to restore the
2298 * connection.
2299 */
2300 cookie.cookie = (ack & 0xff) ^ (ack >> 24);
2301
2302 /* Which of the two secrets to use. */
2303 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even];
2304
2305 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch);
2306
2307 /* The recomputed hash matches the ACK if this was a genuine cookie. */
2308 if ((ack & ~0xff) != (hash & ~0xff))
2309 return (NULL);
2310
2311 /* Fill in the syncache values. */
2312 sc->sc_flags = 0;
2313 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
2314 sc->sc_ipopts = NULL;
2315
2316 sc->sc_irs = seq;
2317 sc->sc_iss = ack;
2318
2319 switch (inc->inc_flags & INC_ISIPV6) {
2320 #ifdef INET
2321 case 0:
2322 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl;
2323 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos;
2324 break;
2325 #endif
2326 #ifdef INET6
2327 case INC_ISIPV6:
2328 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL)
2329 sc->sc_flowlabel =
2330 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK;
2331 break;
2332 #endif
2333 }
2334
2335 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx];
2336
2337 /* We can simply recompute receive window scale we sent earlier. */
2338 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max)
2339 wscale++;
2340
2341 /* Only use wscale if it was enabled in the orignal SYN. */
2342 if (cookie.flags.wscale_idx > 0) {
2343 sc->sc_requested_r_scale = wscale;
2344 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx];
2345 sc->sc_flags |= SCF_WINSCALE;
2346 }
2347
2348 wnd = lso->sol_sbrcv_hiwat;
2349 wnd = imax(wnd, 0);
2350 wnd = imin(wnd, TCP_MAXWIN);
2351 sc->sc_wnd = wnd;
2352
2353 if (cookie.flags.sack_ok)
2354 sc->sc_flags |= SCF_SACK;
2355
2356 if (to->to_flags & TOF_TS) {
2357 sc->sc_flags |= SCF_TIMESTAMP;
2358 sc->sc_tsreflect = to->to_tsval;
2359 sc->sc_tsoff = tcp_new_ts_offset(inc);
2360 }
2361
2362 if (to->to_flags & TOF_SIGNATURE)
2363 sc->sc_flags |= SCF_SIGNATURE;
2364
2365 sc->sc_rxmits = 0;
2366
2367 sc->sc_port = port;
2368
2369 TCPSTAT_INC(tcps_sc_recvcookie);
2370 return (sc);
2371 }
2372
2373 #ifdef INVARIANTS
2374 static int
2375 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
2376 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
2377 struct socket *lso, uint16_t port)
2378 {
2379 struct syncache scs, *scx;
2380 char *s;
2381
2382 bzero(&scs, sizeof(scs));
2383 scx = syncookie_lookup(inc, sch, &scs, th, to, lso, port);
2384
2385 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL)
2386 return (0);
2387
2388 if (scx != NULL) {
2389 if (sc->sc_peer_mss != scx->sc_peer_mss)
2390 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n",
2391 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss);
2392
2393 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale)
2394 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n",
2395 s, __func__, sc->sc_requested_r_scale,
2396 scx->sc_requested_r_scale);
2397
2398 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale)
2399 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n",
2400 s, __func__, sc->sc_requested_s_scale,
2401 scx->sc_requested_s_scale);
2402
2403 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK))
2404 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__);
2405 }
2406
2407 if (s != NULL)
2408 free(s, M_TCPLOG);
2409 return (0);
2410 }
2411 #endif /* INVARIANTS */
2412
2413 static void
2414 syncookie_reseed(void *arg)
2415 {
2416 struct tcp_syncache *sc = arg;
2417 uint8_t *secbits;
2418 int secbit;
2419
2420 /*
2421 * Reseeding the secret doesn't have to be protected by a lock.
2422 * It only must be ensured that the new random values are visible
2423 * to all CPUs in a SMP environment. The atomic with release
2424 * semantics ensures that.
2425 */
2426 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1;
2427 secbits = sc->secret.key[secbit];
2428 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0);
2429 atomic_add_rel_int(&sc->secret.oddeven, 1);
2430
2431 /* Reschedule ourself. */
2432 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz);
2433 }
2434
2435 /*
2436 * We have overflowed a bucket. Let's pause dealing with the syncache.
2437 * This function will increment the bucketoverflow statistics appropriately
2438 * (once per pause when pausing is enabled; otherwise, once per overflow).
2439 */
2440 static void
2441 syncache_pause(struct in_conninfo *inc)
2442 {
2443 time_t delta;
2444 const char *s;
2445
2446 /* XXX:
2447 * 2. Add sysctl read here so we don't get the benefit of this
2448 * change without the new sysctl.
2449 */
2450
2451 /*
2452 * Try an unlocked read. If we already know that another thread
2453 * has activated the feature, there is no need to proceed.
2454 */
2455 if (V_tcp_syncache.paused)
2456 return;
2457
2458 /* Are cookied enabled? If not, we can't pause. */
2459 if (!V_tcp_syncookies) {
2460 TCPSTAT_INC(tcps_sc_bucketoverflow);
2461 return;
2462 }
2463
2464 /*
2465 * We may be the first thread to find an overflow. Get the lock
2466 * and evaluate if we need to take action.
2467 */
2468 mtx_lock(&V_tcp_syncache.pause_mtx);
2469 if (V_tcp_syncache.paused) {
2470 mtx_unlock(&V_tcp_syncache.pause_mtx);
2471 return;
2472 }
2473
2474 /* Activate protection. */
2475 V_tcp_syncache.paused = true;
2476 TCPSTAT_INC(tcps_sc_bucketoverflow);
2477
2478 /*
2479 * Determine the last backoff time. If we are seeing a re-newed
2480 * attack within that same time after last reactivating the syncache,
2481 * consider it an extension of the same attack.
2482 */
2483 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff;
2484 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) {
2485 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) {
2486 delta <<= 1;
2487 V_tcp_syncache.pause_backoff++;
2488 }
2489 } else {
2490 delta = TCP_SYNCACHE_PAUSE_TIME;
2491 V_tcp_syncache.pause_backoff = 0;
2492 }
2493
2494 /* Log a warning, including IP addresses, if able. */
2495 if (inc != NULL)
2496 s = tcp_log_addrs(inc, NULL, NULL, NULL);
2497 else
2498 s = (const char *)NULL;
2499 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for "
2500 "the next %lld seconds%s%s%s\n", (long long)delta,
2501 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "",
2502 (s != NULL) ? ")" : "");
2503 free(__DECONST(void *, s), M_TCPLOG);
2504
2505 /* Use the calculated delta to set a new pause time. */
2506 V_tcp_syncache.pause_until = time_uptime + delta;
2507 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause,
2508 &V_tcp_syncache);
2509 mtx_unlock(&V_tcp_syncache.pause_mtx);
2510 }
2511
2512 /* Evaluate whether we need to unpause. */
2513 static void
2514 syncache_unpause(void *arg)
2515 {
2516 struct tcp_syncache *sc;
2517 time_t delta;
2518
2519 sc = arg;
2520 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED);
2521 callout_deactivate(&sc->pause_co);
2522
2523 /*
2524 * Check to make sure we are not running early. If the pause
2525 * time has expired, then deactivate the protection.
2526 */
2527 if ((delta = sc->pause_until - time_uptime) > 0)
2528 callout_schedule(&sc->pause_co, delta * hz);
2529 else
2530 sc->paused = false;
2531 }
2532
2533 /*
2534 * Exports the syncache entries to userland so that netstat can display
2535 * them alongside the other sockets. This function is intended to be
2536 * called only from tcp_pcblist.
2537 *
2538 * Due to concurrency on an active system, the number of pcbs exported
2539 * may have no relation to max_pcbs. max_pcbs merely indicates the
2540 * amount of space the caller allocated for this function to use.
2541 */
2542 int
2543 syncache_pcblist(struct sysctl_req *req)
2544 {
2545 struct xtcpcb xt;
2546 struct syncache *sc;
2547 struct syncache_head *sch;
2548 int error, i;
2549
2550 bzero(&xt, sizeof(xt));
2551 xt.xt_len = sizeof(xt);
2552 xt.t_state = TCPS_SYN_RECEIVED;
2553 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP;
2554 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket);
2555 xt.xt_inp.xi_socket.so_type = SOCK_STREAM;
2556 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING;
2557
2558 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
2559 sch = &V_tcp_syncache.hashbase[i];
2560 SCH_LOCK(sch);
2561 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
2562 if (sc->sc_cred != NULL &&
2563 cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
2564 continue;
2565 if (sc->sc_inc.inc_flags & INC_ISIPV6)
2566 xt.xt_inp.inp_vflag = INP_IPV6;
2567 else
2568 xt.xt_inp.inp_vflag = INP_IPV4;
2569 xt.xt_encaps_port = sc->sc_port;
2570 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc,
2571 sizeof (struct in_conninfo));
2572 error = SYSCTL_OUT(req, &xt, sizeof xt);
2573 if (error) {
2574 SCH_UNLOCK(sch);
2575 return (0);
2576 }
2577 }
2578 SCH_UNLOCK(sch);
2579 }
2580
2581 return (0);
2582 }
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