1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause
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 #include "opt_inet.h"
37 #include "opt_inet6.h"
38 #include "opt_ipsec.h"
39
40 #include <sys/param.h>
41 #include <sys/systm.h>
42 #include <sys/hash.h>
43 #include <sys/refcount.h>
44 #include <sys/kernel.h>
45 #include <sys/sysctl.h>
46 #include <sys/limits.h>
47 #include <sys/lock.h>
48 #include <sys/mutex.h>
49 #include <sys/malloc.h>
50 #include <sys/mbuf.h>
51 #include <sys/proc.h> /* for proc0 declaration */
52 #include <sys/random.h>
53 #include <sys/socket.h>
54 #include <sys/socketvar.h>
55 #include <sys/syslog.h>
56 #include <sys/ucred.h>
57
58 #include <sys/md5.h>
59 #include <crypto/siphash/siphash.h>
60
61 #include <vm/uma.h>
62
63 #include <net/if.h>
64 #include <net/if_var.h>
65 #include <net/route.h>
66 #include <net/vnet.h>
67
68 #include <netinet/in.h>
69 #include <netinet/in_kdtrace.h>
70 #include <netinet/in_systm.h>
71 #include <netinet/ip.h>
72 #include <netinet/in_var.h>
73 #include <netinet/in_pcb.h>
74 #include <netinet/ip_var.h>
75 #include <netinet/ip_options.h>
76 #ifdef INET6
77 #include <netinet/ip6.h>
78 #include <netinet/icmp6.h>
79 #include <netinet6/nd6.h>
80 #include <netinet6/ip6_var.h>
81 #include <netinet6/in6_pcb.h>
82 #endif
83 #include <netinet/tcp.h>
84 #include <netinet/tcp_fastopen.h>
85 #include <netinet/tcp_fsm.h>
86 #include <netinet/tcp_seq.h>
87 #include <netinet/tcp_timer.h>
88 #include <netinet/tcp_var.h>
89 #include <netinet/tcp_syncache.h>
90 #include <netinet/tcp_ecn.h>
91 #ifdef TCP_BLACKBOX
92 #include <netinet/tcp_log_buf.h>
93 #endif
94 #ifdef TCP_OFFLOAD
95 #include <netinet/toecore.h>
96 #endif
97 #include <netinet/udp.h>
98
99 #include <netipsec/ipsec_support.h>
100
101 #include <machine/in_cksum.h>
102
103 #include <security/mac/mac_framework.h>
104
105 VNET_DEFINE_STATIC(int, tcp_syncookies) = 1;
106 #define V_tcp_syncookies VNET(tcp_syncookies)
107 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW,
108 &VNET_NAME(tcp_syncookies), 0,
109 "Use TCP SYN cookies if the syncache overflows");
110
111 VNET_DEFINE_STATIC(int, tcp_syncookiesonly) = 0;
112 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly)
113 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW,
114 &VNET_NAME(tcp_syncookiesonly), 0,
115 "Use only TCP SYN cookies");
116
117 VNET_DEFINE_STATIC(int, functions_inherit_listen_socket_stack) = 1;
118 #define V_functions_inherit_listen_socket_stack \
119 VNET(functions_inherit_listen_socket_stack)
120 SYSCTL_INT(_net_inet_tcp, OID_AUTO, functions_inherit_listen_socket_stack,
121 CTLFLAG_VNET | CTLFLAG_RW,
122 &VNET_NAME(functions_inherit_listen_socket_stack), 0,
123 "Inherit listen socket's stack");
124
125 #ifdef TCP_OFFLOAD
126 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL)
127 #endif
128
129 static void syncache_drop(struct syncache *, struct syncache_head *);
130 static void syncache_free(struct syncache *);
131 static void syncache_insert(struct syncache *, struct syncache_head *);
132 static int syncache_respond(struct syncache *, const struct mbuf *, int);
133 static struct socket *syncache_socket(struct syncache *, struct socket *,
134 struct mbuf *m);
135 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch,
136 int docallout);
137 static void syncache_timer(void *);
138
139 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t,
140 uint8_t *, uintptr_t);
141 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *);
142 static struct syncache
143 *syncookie_lookup(struct in_conninfo *, struct syncache_head *,
144 struct syncache *, struct tcphdr *, struct tcpopt *,
145 struct socket *, uint16_t);
146 static void syncache_pause(struct in_conninfo *);
147 static void syncache_unpause(void *);
148 static void syncookie_reseed(void *);
149 #ifdef INVARIANTS
150 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
151 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
152 struct socket *lso, uint16_t port);
153 #endif
154
155 /*
156 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
157 * 3 retransmits corresponds to a timeout with default values of
158 * tcp_rexmit_initial * ( 1 +
159 * tcp_backoff[1] +
160 * tcp_backoff[2] +
161 * tcp_backoff[3]) + 3 * tcp_rexmit_slop,
162 * 1000 ms * (1 + 2 + 4 + 8) + 3 * 200 ms = 15600 ms,
163 * the odds are that the user has given up attempting to connect by then.
164 */
165 #define SYNCACHE_MAXREXMTS 3
166
167 /* Arbitrary values */
168 #define TCP_SYNCACHE_HASHSIZE 512
169 #define TCP_SYNCACHE_BUCKETLIMIT 30
170
171 VNET_DEFINE_STATIC(struct tcp_syncache, tcp_syncache);
172 #define V_tcp_syncache VNET(tcp_syncache)
173
174 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache,
175 CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
176 "TCP SYN cache");
177
178 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
179 &VNET_NAME(tcp_syncache.bucket_limit), 0,
180 "Per-bucket hash limit for syncache");
181
182 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
183 &VNET_NAME(tcp_syncache.cache_limit), 0,
184 "Overall entry limit for syncache");
185
186 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET,
187 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache");
188
189 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN,
190 &VNET_NAME(tcp_syncache.hashsize), 0,
191 "Size of TCP syncache hashtable");
192
193 SYSCTL_BOOL(_net_inet_tcp_syncache, OID_AUTO, see_other, CTLFLAG_VNET |
194 CTLFLAG_RW, &VNET_NAME(tcp_syncache.see_other), 0,
195 "All syncache(4) entries are visible, ignoring UID/GID, jail(2) "
196 "and mac(4) checks");
197
198 static int
sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS)199 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS)
200 {
201 int error;
202 u_int new;
203
204 new = V_tcp_syncache.rexmt_limit;
205 error = sysctl_handle_int(oidp, &new, 0, req);
206 if ((error == 0) && (req->newptr != NULL)) {
207 if (new > TCP_MAXRXTSHIFT)
208 error = EINVAL;
209 else
210 V_tcp_syncache.rexmt_limit = new;
211 }
212 return (error);
213 }
214
215 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit,
216 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
217 &VNET_NAME(tcp_syncache.rexmt_limit), 0,
218 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "IU",
219 "Limit on SYN/ACK retransmissions");
220
221 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1;
222 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail,
223 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0,
224 "Send reset on socket allocation failure");
225
226 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
227
228 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx)
229 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx)
230 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED)
231
232 /*
233 * Requires the syncache entry to be already removed from the bucket list.
234 */
235 static void
syncache_free(struct syncache * sc)236 syncache_free(struct syncache *sc)
237 {
238
239 if (sc->sc_ipopts)
240 (void)m_free(sc->sc_ipopts);
241 if (sc->sc_cred)
242 crfree(sc->sc_cred);
243 #ifdef MAC
244 mac_syncache_destroy(&sc->sc_label);
245 #endif
246
247 uma_zfree(V_tcp_syncache.zone, sc);
248 }
249
250 void
syncache_init(void)251 syncache_init(void)
252 {
253 int i;
254
255 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
256 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
257 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
258 V_tcp_syncache.hash_secret = arc4random();
259
260 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
261 &V_tcp_syncache.hashsize);
262 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
263 &V_tcp_syncache.bucket_limit);
264 if (!powerof2(V_tcp_syncache.hashsize) ||
265 V_tcp_syncache.hashsize == 0) {
266 printf("WARNING: syncache hash size is not a power of 2.\n");
267 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
268 }
269 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1;
270
271 /* Set limits. */
272 V_tcp_syncache.cache_limit =
273 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit;
274 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
275 &V_tcp_syncache.cache_limit);
276
277 /* Allocate the hash table. */
278 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize *
279 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO);
280
281 #ifdef VIMAGE
282 V_tcp_syncache.vnet = curvnet;
283 #endif
284
285 /* Initialize the hash buckets. */
286 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
287 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket);
288 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
289 NULL, MTX_DEF);
290 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer,
291 &V_tcp_syncache.hashbase[i].sch_mtx, 0);
292 V_tcp_syncache.hashbase[i].sch_length = 0;
293 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache;
294 V_tcp_syncache.hashbase[i].sch_last_overflow =
295 -(SYNCOOKIE_LIFETIME + 1);
296 }
297
298 /* Create the syncache entry zone. */
299 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
300 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
301 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone,
302 V_tcp_syncache.cache_limit);
303
304 /* Start the SYN cookie reseeder callout. */
305 callout_init(&V_tcp_syncache.secret.reseed, 1);
306 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0);
307 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0);
308 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz,
309 syncookie_reseed, &V_tcp_syncache);
310
311 /* Initialize the pause machinery. */
312 mtx_init(&V_tcp_syncache.pause_mtx, "tcp_sc_pause", NULL, MTX_DEF);
313 callout_init_mtx(&V_tcp_syncache.pause_co, &V_tcp_syncache.pause_mtx,
314 0);
315 V_tcp_syncache.pause_until = time_uptime - TCP_SYNCACHE_PAUSE_TIME;
316 V_tcp_syncache.pause_backoff = 0;
317 V_tcp_syncache.paused = false;
318 }
319
320 #ifdef VIMAGE
321 void
syncache_destroy(void)322 syncache_destroy(void)
323 {
324 struct syncache_head *sch;
325 struct syncache *sc, *nsc;
326 int i;
327
328 /*
329 * Stop the re-seed timer before freeing resources. No need to
330 * possibly schedule it another time.
331 */
332 callout_drain(&V_tcp_syncache.secret.reseed);
333
334 /* Stop the SYN cache pause callout. */
335 mtx_lock(&V_tcp_syncache.pause_mtx);
336 if (callout_stop(&V_tcp_syncache.pause_co) == 0) {
337 mtx_unlock(&V_tcp_syncache.pause_mtx);
338 callout_drain(&V_tcp_syncache.pause_co);
339 } else
340 mtx_unlock(&V_tcp_syncache.pause_mtx);
341
342 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */
343 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
344 sch = &V_tcp_syncache.hashbase[i];
345 callout_drain(&sch->sch_timer);
346
347 SCH_LOCK(sch);
348 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc)
349 syncache_drop(sc, sch);
350 SCH_UNLOCK(sch);
351 KASSERT(TAILQ_EMPTY(&sch->sch_bucket),
352 ("%s: sch->sch_bucket not empty", __func__));
353 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0",
354 __func__, sch->sch_length));
355 mtx_destroy(&sch->sch_mtx);
356 }
357
358 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0,
359 ("%s: cache_count not 0", __func__));
360
361 /* Free the allocated global resources. */
362 uma_zdestroy(V_tcp_syncache.zone);
363 free(V_tcp_syncache.hashbase, M_SYNCACHE);
364 mtx_destroy(&V_tcp_syncache.pause_mtx);
365 }
366 #endif
367
368 /*
369 * Inserts a syncache entry into the specified bucket row.
370 * Locks and unlocks the syncache_head autonomously.
371 */
372 static void
syncache_insert(struct syncache * sc,struct syncache_head * sch)373 syncache_insert(struct syncache *sc, struct syncache_head *sch)
374 {
375 struct syncache *sc2;
376
377 SCH_LOCK(sch);
378
379 /*
380 * Make sure that we don't overflow the per-bucket limit.
381 * If the bucket is full, toss the oldest element.
382 */
383 if (sch->sch_length >= V_tcp_syncache.bucket_limit) {
384 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
385 ("sch->sch_length incorrect"));
386 syncache_pause(&sc->sc_inc);
387 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
388 sch->sch_last_overflow = time_uptime;
389 syncache_drop(sc2, sch);
390 }
391
392 /* Put it into the bucket. */
393 TAILQ_INSERT_HEAD(&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_added(tod, sc->sc_todctx);
401 }
402 #endif
403
404 /* Reinitialize the bucket row's timer. */
405 if (sch->sch_length == 1)
406 sch->sch_nextc = ticks + INT_MAX;
407 syncache_timeout(sc, sch, 1);
408
409 SCH_UNLOCK(sch);
410
411 TCPSTATES_INC(TCPS_SYN_RECEIVED);
412 TCPSTAT_INC(tcps_sc_added);
413 }
414
415 /*
416 * Remove and free entry from syncache bucket row.
417 * Expects locked syncache head.
418 */
419 static void
syncache_drop(struct syncache * sc,struct syncache_head * sch)420 syncache_drop(struct syncache *sc, struct syncache_head *sch)
421 {
422
423 SCH_LOCK_ASSERT(sch);
424
425 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
426 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
427 sch->sch_length--;
428
429 #ifdef TCP_OFFLOAD
430 if (ADDED_BY_TOE(sc)) {
431 struct toedev *tod = sc->sc_tod;
432
433 tod->tod_syncache_removed(tod, sc->sc_todctx);
434 }
435 #endif
436
437 syncache_free(sc);
438 }
439
440 /*
441 * Engage/reengage time on bucket row.
442 */
443 static void
syncache_timeout(struct syncache * sc,struct syncache_head * sch,int docallout)444 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
445 {
446 int rexmt;
447
448 if (sc->sc_rxmits == 0)
449 rexmt = tcp_rexmit_initial;
450 else
451 TCPT_RANGESET(rexmt,
452 tcp_rexmit_initial * tcp_backoff[sc->sc_rxmits],
453 tcp_rexmit_min, TCPTV_REXMTMAX);
454 sc->sc_rxttime = ticks + rexmt;
455 sc->sc_rxmits++;
456 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
457 sch->sch_nextc = sc->sc_rxttime;
458 if (docallout)
459 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
460 syncache_timer, (void *)sch);
461 }
462 }
463
464 /*
465 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
466 * If we have retransmitted an entry the maximum number of times, expire it.
467 * One separate timer for each bucket row.
468 */
469 static void
syncache_timer(void * xsch)470 syncache_timer(void *xsch)
471 {
472 struct syncache_head *sch = (struct syncache_head *)xsch;
473 struct syncache *sc, *nsc;
474 struct epoch_tracker et;
475 int tick = ticks;
476 char *s;
477 bool paused;
478
479 CURVNET_SET(sch->sch_sc->vnet);
480
481 /* NB: syncache_head has already been locked by the callout. */
482 SCH_LOCK_ASSERT(sch);
483
484 /*
485 * In the following cycle we may remove some entries and/or
486 * advance some timeouts, so re-initialize the bucket timer.
487 */
488 sch->sch_nextc = tick + INT_MAX;
489
490 /*
491 * If we have paused processing, unconditionally remove
492 * all syncache entries.
493 */
494 mtx_lock(&V_tcp_syncache.pause_mtx);
495 paused = V_tcp_syncache.paused;
496 mtx_unlock(&V_tcp_syncache.pause_mtx);
497
498 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
499 if (paused) {
500 syncache_drop(sc, sch);
501 continue;
502 }
503 /*
504 * We do not check if the listen socket still exists
505 * and accept the case where the listen socket may be
506 * gone by the time we resend the SYN/ACK. We do
507 * not expect this to happens often. If it does,
508 * then the RST will be sent by the time the remote
509 * host does the SYN/ACK->ACK.
510 */
511 if (TSTMP_GT(sc->sc_rxttime, tick)) {
512 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
513 sch->sch_nextc = sc->sc_rxttime;
514 continue;
515 }
516 if (sc->sc_rxmits > V_tcp_ecn_maxretries) {
517 sc->sc_flags &= ~SCF_ECN_MASK;
518 }
519 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
520 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
521 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
522 "giving up and removing syncache entry\n",
523 s, __func__);
524 free(s, M_TCPLOG);
525 }
526 syncache_drop(sc, sch);
527 TCPSTAT_INC(tcps_sc_stale);
528 continue;
529 }
530 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
531 log(LOG_DEBUG, "%s; %s: Response timeout, "
532 "retransmitting (%u) SYN|ACK\n",
533 s, __func__, sc->sc_rxmits);
534 free(s, M_TCPLOG);
535 }
536
537 NET_EPOCH_ENTER(et);
538 if (syncache_respond(sc, NULL, TH_SYN|TH_ACK) == 0) {
539 syncache_timeout(sc, sch, 0);
540 TCPSTAT_INC(tcps_sndacks);
541 TCPSTAT_INC(tcps_sndtotal);
542 TCPSTAT_INC(tcps_sc_retransmitted);
543 } else {
544 syncache_drop(sc, sch);
545 TCPSTAT_INC(tcps_sc_dropped);
546 }
547 NET_EPOCH_EXIT(et);
548 }
549 if (!TAILQ_EMPTY(&(sch)->sch_bucket))
550 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
551 syncache_timer, (void *)(sch));
552 CURVNET_RESTORE();
553 }
554
555 /*
556 * Returns true if the system is only using cookies at the moment.
557 * This could be due to a sysadmin decision to only use cookies, or it
558 * could be due to the system detecting an attack.
559 */
560 static inline bool
syncache_cookiesonly(void)561 syncache_cookiesonly(void)
562 {
563
564 return (V_tcp_syncookies && (V_tcp_syncache.paused ||
565 V_tcp_syncookiesonly));
566 }
567
568 /*
569 * Find the hash bucket for the given connection.
570 */
571 static struct syncache_head *
syncache_hashbucket(struct in_conninfo * inc)572 syncache_hashbucket(struct in_conninfo *inc)
573 {
574 uint32_t hash;
575
576 /*
577 * The hash is built on foreign port + local port + foreign address.
578 * We rely on the fact that struct in_conninfo starts with 16 bits
579 * of foreign port, then 16 bits of local port then followed by 128
580 * bits of foreign address. In case of IPv4 address, the first 3
581 * 32-bit words of the address always are zeroes.
582 */
583 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5,
584 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask;
585
586 return (&V_tcp_syncache.hashbase[hash]);
587 }
588
589 /*
590 * Find an entry in the syncache.
591 * Returns always with locked syncache_head plus a matching entry or NULL.
592 */
593 static struct syncache *
syncache_lookup(struct in_conninfo * inc,struct syncache_head ** schp)594 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
595 {
596 struct syncache *sc;
597 struct syncache_head *sch;
598
599 *schp = sch = syncache_hashbucket(inc);
600 SCH_LOCK(sch);
601
602 /* Circle through bucket row to find matching entry. */
603 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash)
604 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie,
605 sizeof(struct in_endpoints)) == 0)
606 break;
607
608 return (sc); /* Always returns with locked sch. */
609 }
610
611 /*
612 * This function is called when we get a RST for a
613 * non-existent connection, so that we can see if the
614 * connection is in the syn cache. If it is, zap it.
615 * If required send a challenge ACK.
616 */
617 void
syncache_chkrst(struct in_conninfo * inc,struct tcphdr * th,struct mbuf * m,uint16_t port)618 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, struct mbuf *m,
619 uint16_t port)
620 {
621 struct syncache *sc;
622 struct syncache_head *sch;
623 char *s = NULL;
624
625 if (syncache_cookiesonly())
626 return;
627 sc = syncache_lookup(inc, &sch); /* returns locked sch */
628 SCH_LOCK_ASSERT(sch);
629
630 /*
631 * No corresponding connection was found in syncache.
632 * If syncookies are enabled and possibly exclusively
633 * used, or we are under memory pressure, a valid RST
634 * may not find a syncache entry. In that case we're
635 * done and no SYN|ACK retransmissions will happen.
636 * Otherwise the RST was misdirected or spoofed.
637 */
638 if (sc == NULL) {
639 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
640 log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
641 "syncache entry (possibly syncookie only), "
642 "segment ignored\n", s, __func__);
643 TCPSTAT_INC(tcps_badrst);
644 goto done;
645 }
646
647 /* The remote UDP encaps port does not match. */
648 if (sc->sc_port != port) {
649 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
650 log(LOG_DEBUG, "%s; %s: Spurious RST with matching "
651 "syncache entry but non-matching UDP encaps port, "
652 "segment ignored\n", s, __func__);
653 TCPSTAT_INC(tcps_badrst);
654 goto done;
655 }
656
657 /*
658 * If the RST bit is set, check the sequence number to see
659 * if this is a valid reset segment.
660 *
661 * RFC 793 page 37:
662 * In all states except SYN-SENT, all reset (RST) segments
663 * are validated by checking their SEQ-fields. A reset is
664 * valid if its sequence number is in the window.
665 *
666 * RFC 793 page 69:
667 * There are four cases for the acceptability test for an incoming
668 * segment:
669 *
670 * Segment Receive Test
671 * Length Window
672 * ------- ------- -------------------------------------------
673 * 0 0 SEG.SEQ = RCV.NXT
674 * 0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND
675 * >0 0 not acceptable
676 * >0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND
677 * or RCV.NXT =< SEG.SEQ+SEG.LEN-1 < RCV.NXT+RCV.WND
678 *
679 * Note that when receiving a SYN segment in the LISTEN state,
680 * IRS is set to SEG.SEQ and RCV.NXT is set to SEG.SEQ+1, as
681 * described in RFC 793, page 66.
682 */
683 if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) &&
684 SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) ||
685 (sc->sc_wnd == 0 && th->th_seq == sc->sc_irs + 1)) {
686 if (V_tcp_insecure_rst ||
687 th->th_seq == sc->sc_irs + 1) {
688 syncache_drop(sc, sch);
689 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
690 log(LOG_DEBUG,
691 "%s; %s: Our SYN|ACK was rejected, "
692 "connection attempt aborted by remote "
693 "endpoint\n",
694 s, __func__);
695 TCPSTAT_INC(tcps_sc_reset);
696 } else {
697 TCPSTAT_INC(tcps_badrst);
698 /* Send challenge ACK. */
699 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
700 log(LOG_DEBUG, "%s; %s: RST with invalid "
701 " SEQ %u != NXT %u (+WND %u), "
702 "sending challenge ACK\n",
703 s, __func__,
704 th->th_seq, sc->sc_irs + 1, sc->sc_wnd);
705 if (syncache_respond(sc, m, TH_ACK) == 0) {
706 TCPSTAT_INC(tcps_sndacks);
707 TCPSTAT_INC(tcps_sndtotal);
708 } else {
709 syncache_drop(sc, sch);
710 TCPSTAT_INC(tcps_sc_dropped);
711 }
712 }
713 } else {
714 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
715 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
716 "NXT %u (+WND %u), segment ignored\n",
717 s, __func__,
718 th->th_seq, sc->sc_irs + 1, sc->sc_wnd);
719 TCPSTAT_INC(tcps_badrst);
720 }
721
722 done:
723 if (s != NULL)
724 free(s, M_TCPLOG);
725 SCH_UNLOCK(sch);
726 }
727
728 void
syncache_badack(struct in_conninfo * inc,uint16_t port)729 syncache_badack(struct in_conninfo *inc, uint16_t port)
730 {
731 struct syncache *sc;
732 struct syncache_head *sch;
733
734 if (syncache_cookiesonly())
735 return;
736 sc = syncache_lookup(inc, &sch); /* returns locked sch */
737 SCH_LOCK_ASSERT(sch);
738 if ((sc != NULL) && (sc->sc_port == port)) {
739 syncache_drop(sc, sch);
740 TCPSTAT_INC(tcps_sc_badack);
741 }
742 SCH_UNLOCK(sch);
743 }
744
745 void
syncache_unreach(struct in_conninfo * inc,tcp_seq th_seq,uint16_t port)746 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq, uint16_t port)
747 {
748 struct syncache *sc;
749 struct syncache_head *sch;
750
751 if (syncache_cookiesonly())
752 return;
753 sc = syncache_lookup(inc, &sch); /* returns locked sch */
754 SCH_LOCK_ASSERT(sch);
755 if (sc == NULL)
756 goto done;
757
758 /* If the port != sc_port, then it's a bogus ICMP msg */
759 if (port != sc->sc_port)
760 goto done;
761
762 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
763 if (ntohl(th_seq) != sc->sc_iss)
764 goto done;
765
766 /*
767 * If we've rertransmitted 3 times and this is our second error,
768 * we remove the entry. Otherwise, we allow it to continue on.
769 * This prevents us from incorrectly nuking an entry during a
770 * spurious network outage.
771 *
772 * See tcp_notify().
773 */
774 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
775 sc->sc_flags |= SCF_UNREACH;
776 goto done;
777 }
778 syncache_drop(sc, sch);
779 TCPSTAT_INC(tcps_sc_unreach);
780 done:
781 SCH_UNLOCK(sch);
782 }
783
784 /*
785 * Build a new TCP socket structure from a syncache entry.
786 *
787 * On success return the newly created socket with its underlying inp locked.
788 */
789 static struct socket *
syncache_socket(struct syncache * sc,struct socket * lso,struct mbuf * m)790 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
791 {
792 struct tcpcb *listening_tcb;
793 struct inpcb *inp = NULL;
794 struct socket *so;
795 struct tcpcb *tp;
796 int error;
797 char *s;
798
799 NET_EPOCH_ASSERT();
800
801 /*
802 * Ok, create the full blown connection, and set things up
803 * as they would have been set up if we had created the
804 * connection when the SYN arrived.
805 */
806 if ((so = solisten_clone(lso)) == NULL)
807 goto allocfail;
808 #ifdef MAC
809 mac_socketpeer_set_from_mbuf(m, so);
810 #endif
811 error = in_pcballoc(so, &V_tcbinfo);
812 if (error) {
813 sodealloc(so);
814 goto allocfail;
815 }
816 inp = sotoinpcb(so);
817 if (V_functions_inherit_listen_socket_stack)
818 listening_tcb = sototcpcb(lso);
819 else
820 listening_tcb = NULL;
821 if ((tp = tcp_newtcpcb(inp, listening_tcb)) == NULL) {
822 in_pcbfree(inp);
823 sodealloc(so);
824 goto allocfail;
825 }
826 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
827 #ifdef INET6
828 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
829 inp->inp_vflag &= ~INP_IPV4;
830 inp->inp_vflag |= INP_IPV6;
831 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
832 } else {
833 inp->inp_vflag &= ~INP_IPV6;
834 inp->inp_vflag |= INP_IPV4;
835 #endif
836 inp->inp_ip_ttl = sc->sc_ip_ttl;
837 inp->inp_ip_tos = sc->sc_ip_tos;
838 inp->inp_laddr = sc->sc_inc.inc_laddr;
839 #ifdef INET6
840 }
841 #endif
842
843 /*
844 * If there's an mbuf and it has a flowid, then let's initialise the
845 * inp with that particular flowid.
846 */
847 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) {
848 inp->inp_flowid = m->m_pkthdr.flowid;
849 inp->inp_flowtype = M_HASHTYPE_GET(m);
850 #ifdef NUMA
851 inp->inp_numa_domain = m->m_pkthdr.numa_domain;
852 #endif
853 }
854
855 inp->inp_lport = sc->sc_inc.inc_lport;
856 #ifdef INET6
857 if (inp->inp_vflag & INP_IPV6PROTO) {
858 struct inpcb *oinp = sotoinpcb(lso);
859
860 /*
861 * Inherit socket options from the listening socket.
862 * Note that in6p_inputopts are not (and should not be)
863 * copied, since it stores previously received options and is
864 * used to detect if each new option is different than the
865 * previous one and hence should be passed to a user.
866 * If we copied in6p_inputopts, a user would not be able to
867 * receive options just after calling the accept system call.
868 */
869 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
870 if (oinp->in6p_outputopts)
871 inp->in6p_outputopts =
872 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
873 inp->in6p_hops = oinp->in6p_hops;
874 }
875
876 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
877 struct sockaddr_in6 sin6;
878
879 sin6.sin6_family = AF_INET6;
880 sin6.sin6_len = sizeof(sin6);
881 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
882 sin6.sin6_port = sc->sc_inc.inc_fport;
883 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
884 INP_HASH_WLOCK(&V_tcbinfo);
885 error = in6_pcbconnect(inp, &sin6, thread0.td_ucred, false);
886 INP_HASH_WUNLOCK(&V_tcbinfo);
887 if (error != 0)
888 goto abort;
889 /* Override flowlabel from in6_pcbconnect. */
890 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
891 inp->inp_flow |= sc->sc_flowlabel;
892 }
893 #endif /* INET6 */
894 #if defined(INET) && defined(INET6)
895 else
896 #endif
897 #ifdef INET
898 {
899 struct sockaddr_in sin;
900
901 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
902
903 if (inp->inp_options == NULL) {
904 inp->inp_options = sc->sc_ipopts;
905 sc->sc_ipopts = NULL;
906 }
907
908 sin.sin_family = AF_INET;
909 sin.sin_len = sizeof(sin);
910 sin.sin_addr = sc->sc_inc.inc_faddr;
911 sin.sin_port = sc->sc_inc.inc_fport;
912 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
913 INP_HASH_WLOCK(&V_tcbinfo);
914 error = in_pcbconnect(inp, &sin, thread0.td_ucred, false);
915 INP_HASH_WUNLOCK(&V_tcbinfo);
916 if (error != 0)
917 goto abort;
918 }
919 #endif /* INET */
920 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
921 /* Copy old policy into new socket's. */
922 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0)
923 printf("syncache_socket: could not copy policy\n");
924 #endif
925 tp->t_state = TCPS_SYN_RECEIVED;
926 tp->iss = sc->sc_iss;
927 tp->irs = sc->sc_irs;
928 tp->t_port = sc->sc_port;
929 tcp_rcvseqinit(tp);
930 tcp_sendseqinit(tp);
931 tp->snd_wl1 = sc->sc_irs;
932 tp->snd_max = tp->iss + 1;
933 tp->snd_nxt = tp->iss + 1;
934 tp->rcv_up = sc->sc_irs + 1;
935 tp->rcv_wnd = sc->sc_wnd;
936 tp->rcv_adv += tp->rcv_wnd;
937 tp->last_ack_sent = tp->rcv_nxt;
938
939 tp->t_flags = sototcpcb(lso)->t_flags &
940 (TF_LRD|TF_NOPUSH|TF_NODELAY);
941 if (sc->sc_flags & SCF_NOOPT)
942 tp->t_flags |= TF_NOOPT;
943 else {
944 if (sc->sc_flags & SCF_WINSCALE) {
945 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
946 tp->snd_scale = sc->sc_requested_s_scale;
947 tp->request_r_scale = sc->sc_requested_r_scale;
948 }
949 if (sc->sc_flags & SCF_TIMESTAMP) {
950 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
951 tp->ts_recent = sc->sc_tsreflect;
952 tp->ts_recent_age = tcp_ts_getticks();
953 tp->ts_offset = sc->sc_tsoff;
954 }
955 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
956 if (sc->sc_flags & SCF_SIGNATURE)
957 tp->t_flags |= TF_SIGNATURE;
958 #endif
959 if (sc->sc_flags & SCF_SACK)
960 tp->t_flags |= TF_SACK_PERMIT;
961 }
962
963 tcp_ecn_syncache_socket(tp, sc);
964
965 /*
966 * Set up MSS and get cached values from tcp_hostcache.
967 * This might overwrite some of the defaults we just set.
968 */
969 tcp_mss(tp, sc->sc_peer_mss);
970
971 /*
972 * If the SYN,ACK was retransmitted, indicate that CWND to be
973 * limited to one segment in cc_conn_init().
974 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
975 */
976 if (sc->sc_rxmits > 1)
977 tp->snd_cwnd = 1;
978
979 #ifdef TCP_OFFLOAD
980 /*
981 * Allow a TOE driver to install its hooks. Note that we hold the
982 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a
983 * new connection before the TOE driver has done its thing.
984 */
985 if (ADDED_BY_TOE(sc)) {
986 struct toedev *tod = sc->sc_tod;
987
988 tod->tod_offload_socket(tod, sc->sc_todctx, so);
989 }
990 #endif
991 #ifdef TCP_BLACKBOX
992 /*
993 * Inherit the log state from the listening socket, if
994 * - the log state of the listening socket is not off and
995 * - the listening socket was not auto selected from all sessions and
996 * - a log id is not set on the listening socket.
997 * This avoids inheriting a log state which was automatically set.
998 */
999 if ((tcp_get_bblog_state(sototcpcb(lso)) != TCP_LOG_STATE_OFF) &&
1000 ((sototcpcb(lso)->t_flags2 & TF2_LOG_AUTO) == 0) &&
1001 (sototcpcb(lso)->t_lib == NULL)) {
1002 tcp_log_state_change(tp, tcp_get_bblog_state(sototcpcb(lso)));
1003 }
1004 #endif
1005 /*
1006 * Copy and activate timers.
1007 */
1008 tp->t_maxunacktime = sototcpcb(lso)->t_maxunacktime;
1009 tp->t_keepinit = sototcpcb(lso)->t_keepinit;
1010 tp->t_keepidle = sototcpcb(lso)->t_keepidle;
1011 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl;
1012 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt;
1013 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp));
1014
1015 TCPSTAT_INC(tcps_accepts);
1016 TCP_PROBE6(state__change, NULL, tp, NULL, tp, NULL, TCPS_LISTEN);
1017
1018 if (!solisten_enqueue(so, SS_ISCONNECTED))
1019 tp->t_flags |= TF_SONOTCONN;
1020
1021 return (so);
1022
1023 allocfail:
1024 /*
1025 * Drop the connection; we will either send a RST or have the peer
1026 * retransmit its SYN again after its RTO and try again.
1027 */
1028 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
1029 log(LOG_DEBUG, "%s; %s: Socket create failed "
1030 "due to limits or memory shortage\n",
1031 s, __func__);
1032 free(s, M_TCPLOG);
1033 }
1034 TCPSTAT_INC(tcps_listendrop);
1035 return (NULL);
1036
1037 abort:
1038 tcp_discardcb(tp);
1039 in_pcbfree(inp);
1040 sodealloc(so);
1041 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
1042 log(LOG_DEBUG, "%s; %s: in%s_pcbconnect failed with error %i\n",
1043 s, __func__, (sc->sc_inc.inc_flags & INC_ISIPV6) ? "6" : "",
1044 error);
1045 free(s, M_TCPLOG);
1046 }
1047 TCPSTAT_INC(tcps_listendrop);
1048 return (NULL);
1049 }
1050
1051 /*
1052 * This function gets called when we receive an ACK for a
1053 * socket in the LISTEN state. We look up the connection
1054 * in the syncache, and if its there, we pull it out of
1055 * the cache and turn it into a full-blown connection in
1056 * the SYN-RECEIVED state.
1057 *
1058 * On syncache_socket() success the newly created socket
1059 * has its underlying inp locked.
1060 */
1061 int
syncache_expand(struct in_conninfo * inc,struct tcpopt * to,struct tcphdr * th,struct socket ** lsop,struct mbuf * m,uint16_t port)1062 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1063 struct socket **lsop, struct mbuf *m, uint16_t port)
1064 {
1065 struct syncache *sc;
1066 struct syncache_head *sch;
1067 struct syncache scs;
1068 char *s;
1069 bool locked;
1070
1071 NET_EPOCH_ASSERT();
1072 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
1073 ("%s: can handle only ACK", __func__));
1074
1075 if (syncache_cookiesonly()) {
1076 sc = NULL;
1077 sch = syncache_hashbucket(inc);
1078 locked = false;
1079 } else {
1080 sc = syncache_lookup(inc, &sch); /* returns locked sch */
1081 locked = true;
1082 SCH_LOCK_ASSERT(sch);
1083 }
1084
1085 #ifdef INVARIANTS
1086 /*
1087 * Test code for syncookies comparing the syncache stored
1088 * values with the reconstructed values from the cookie.
1089 */
1090 if (sc != NULL)
1091 syncookie_cmp(inc, sch, sc, th, to, *lsop, port);
1092 #endif
1093
1094 if (sc == NULL) {
1095 /*
1096 * There is no syncache entry, so see if this ACK is
1097 * a returning syncookie. To do this, first:
1098 * A. Check if syncookies are used in case of syncache
1099 * overflows
1100 * B. See if this socket has had a syncache entry dropped in
1101 * the recent past. We don't want to accept a bogus
1102 * syncookie if we've never received a SYN or accept it
1103 * twice.
1104 * C. check that the syncookie is valid. If it is, then
1105 * cobble up a fake syncache entry, and return.
1106 */
1107 if (locked && !V_tcp_syncookies) {
1108 SCH_UNLOCK(sch);
1109 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1110 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
1111 "segment rejected (syncookies disabled)\n",
1112 s, __func__);
1113 goto failed;
1114 }
1115 if (locked && !V_tcp_syncookiesonly &&
1116 sch->sch_last_overflow < time_uptime - SYNCOOKIE_LIFETIME) {
1117 SCH_UNLOCK(sch);
1118 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1119 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
1120 "segment rejected (no syncache entry)\n",
1121 s, __func__);
1122 goto failed;
1123 }
1124 bzero(&scs, sizeof(scs));
1125 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop, port);
1126 if (locked)
1127 SCH_UNLOCK(sch);
1128 if (sc == NULL) {
1129 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1130 log(LOG_DEBUG, "%s; %s: Segment failed "
1131 "SYNCOOKIE authentication, segment rejected "
1132 "(probably spoofed)\n", s, __func__);
1133 goto failed;
1134 }
1135 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1136 /* If received ACK has MD5 signature, check it. */
1137 if ((to->to_flags & TOF_SIGNATURE) != 0 &&
1138 (!TCPMD5_ENABLED() ||
1139 TCPMD5_INPUT(m, th, to->to_signature) != 0)) {
1140 /* Drop the ACK. */
1141 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1142 log(LOG_DEBUG, "%s; %s: Segment rejected, "
1143 "MD5 signature doesn't match.\n",
1144 s, __func__);
1145 free(s, M_TCPLOG);
1146 }
1147 TCPSTAT_INC(tcps_sig_err_sigopt);
1148 return (-1); /* Do not send RST */
1149 }
1150 #endif /* TCP_SIGNATURE */
1151 TCPSTATES_INC(TCPS_SYN_RECEIVED);
1152 } else {
1153 if (sc->sc_port != port) {
1154 SCH_UNLOCK(sch);
1155 return (0);
1156 }
1157 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1158 /*
1159 * If listening socket requested TCP digests, check that
1160 * received ACK has signature and it is correct.
1161 * If not, drop the ACK and leave sc entry in th cache,
1162 * because SYN was received with correct signature.
1163 */
1164 if (sc->sc_flags & SCF_SIGNATURE) {
1165 if ((to->to_flags & TOF_SIGNATURE) == 0) {
1166 /* No signature */
1167 TCPSTAT_INC(tcps_sig_err_nosigopt);
1168 SCH_UNLOCK(sch);
1169 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1170 log(LOG_DEBUG, "%s; %s: Segment "
1171 "rejected, MD5 signature wasn't "
1172 "provided.\n", s, __func__);
1173 free(s, M_TCPLOG);
1174 }
1175 return (-1); /* Do not send RST */
1176 }
1177 if (!TCPMD5_ENABLED() ||
1178 TCPMD5_INPUT(m, th, to->to_signature) != 0) {
1179 /* Doesn't match or no SA */
1180 SCH_UNLOCK(sch);
1181 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1182 log(LOG_DEBUG, "%s; %s: Segment "
1183 "rejected, MD5 signature doesn't "
1184 "match.\n", s, __func__);
1185 free(s, M_TCPLOG);
1186 }
1187 return (-1); /* Do not send RST */
1188 }
1189 }
1190 #endif /* TCP_SIGNATURE */
1191
1192 /*
1193 * RFC 7323 PAWS: If we have a timestamp on this segment and
1194 * it's less than ts_recent, drop it.
1195 * XXXMT: RFC 7323 also requires to send an ACK.
1196 * In tcp_input.c this is only done for TCP segments
1197 * with user data, so be consistent here and just drop
1198 * the segment.
1199 */
1200 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS &&
1201 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) {
1202 SCH_UNLOCK(sch);
1203 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1204 log(LOG_DEBUG,
1205 "%s; %s: SEG.TSval %u < TS.Recent %u, "
1206 "segment dropped\n", s, __func__,
1207 to->to_tsval, sc->sc_tsreflect);
1208 free(s, M_TCPLOG);
1209 }
1210 return (-1); /* Do not send RST */
1211 }
1212
1213 /*
1214 * If timestamps were not negotiated during SYN/ACK and a
1215 * segment with a timestamp is received, ignore the
1216 * timestamp and process the packet normally.
1217 * See section 3.2 of RFC 7323.
1218 */
1219 if (!(sc->sc_flags & SCF_TIMESTAMP) &&
1220 (to->to_flags & TOF_TS)) {
1221 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1222 log(LOG_DEBUG, "%s; %s: Timestamp not "
1223 "expected, segment processed normally\n",
1224 s, __func__);
1225 free(s, M_TCPLOG);
1226 s = NULL;
1227 }
1228 }
1229
1230 /*
1231 * If timestamps were negotiated during SYN/ACK and a
1232 * segment without a timestamp is received, silently drop
1233 * the segment, unless the missing timestamps are tolerated.
1234 * See section 3.2 of RFC 7323.
1235 */
1236 if ((sc->sc_flags & SCF_TIMESTAMP) &&
1237 !(to->to_flags & TOF_TS)) {
1238 if (V_tcp_tolerate_missing_ts) {
1239 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1240 log(LOG_DEBUG,
1241 "%s; %s: Timestamp missing, "
1242 "segment processed normally\n",
1243 s, __func__);
1244 free(s, M_TCPLOG);
1245 }
1246 } else {
1247 SCH_UNLOCK(sch);
1248 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1249 log(LOG_DEBUG,
1250 "%s; %s: Timestamp missing, "
1251 "segment silently dropped\n",
1252 s, __func__);
1253 free(s, M_TCPLOG);
1254 }
1255 return (-1); /* Do not send RST */
1256 }
1257 }
1258 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
1259 sch->sch_length--;
1260 #ifdef TCP_OFFLOAD
1261 if (ADDED_BY_TOE(sc)) {
1262 struct toedev *tod = sc->sc_tod;
1263
1264 tod->tod_syncache_removed(tod, sc->sc_todctx);
1265 }
1266 #endif
1267 SCH_UNLOCK(sch);
1268 }
1269
1270 /*
1271 * Segment validation:
1272 * ACK must match our initial sequence number + 1 (the SYN|ACK).
1273 */
1274 if (th->th_ack != sc->sc_iss + 1) {
1275 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1276 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
1277 "rejected\n", s, __func__, th->th_ack, sc->sc_iss);
1278 goto failed;
1279 }
1280
1281 /*
1282 * The SEQ must fall in the window starting at the received
1283 * initial receive sequence number + 1 (the SYN).
1284 */
1285 if (SEQ_LEQ(th->th_seq, sc->sc_irs) ||
1286 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
1287 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1288 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
1289 "rejected\n", s, __func__, th->th_seq, sc->sc_irs);
1290 goto failed;
1291 }
1292
1293 *lsop = syncache_socket(sc, *lsop, m);
1294
1295 if (__predict_false(*lsop == NULL)) {
1296 TCPSTAT_INC(tcps_sc_aborted);
1297 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
1298 } else
1299 TCPSTAT_INC(tcps_sc_completed);
1300
1301 /* how do we find the inp for the new socket? */
1302 if (sc != &scs)
1303 syncache_free(sc);
1304 return (1);
1305 failed:
1306 if (sc != NULL) {
1307 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
1308 if (sc != &scs)
1309 syncache_free(sc);
1310 }
1311 if (s != NULL)
1312 free(s, M_TCPLOG);
1313 *lsop = NULL;
1314 return (0);
1315 }
1316
1317 static struct socket *
syncache_tfo_expand(struct syncache * sc,struct socket * lso,struct mbuf * m,uint64_t response_cookie)1318 syncache_tfo_expand(struct syncache *sc, struct socket *lso, struct mbuf *m,
1319 uint64_t response_cookie)
1320 {
1321 struct inpcb *inp;
1322 struct tcpcb *tp;
1323 unsigned int *pending_counter;
1324 struct socket *so;
1325
1326 NET_EPOCH_ASSERT();
1327
1328 pending_counter = intotcpcb(sotoinpcb(lso))->t_tfo_pending;
1329 so = syncache_socket(sc, lso, m);
1330 if (so == NULL) {
1331 TCPSTAT_INC(tcps_sc_aborted);
1332 atomic_subtract_int(pending_counter, 1);
1333 } else {
1334 soisconnected(so);
1335 inp = sotoinpcb(so);
1336 tp = intotcpcb(inp);
1337 tp->t_flags |= TF_FASTOPEN;
1338 tp->t_tfo_cookie.server = response_cookie;
1339 tp->snd_max = tp->iss;
1340 tp->snd_nxt = tp->iss;
1341 tp->t_tfo_pending = pending_counter;
1342 TCPSTATES_INC(TCPS_SYN_RECEIVED);
1343 TCPSTAT_INC(tcps_sc_completed);
1344 }
1345
1346 return (so);
1347 }
1348
1349 /*
1350 * Given a LISTEN socket and an inbound SYN request, add
1351 * this to the syn cache, and send back a segment:
1352 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
1353 * to the source.
1354 *
1355 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
1356 * Doing so would require that we hold onto the data and deliver it
1357 * to the application. However, if we are the target of a SYN-flood
1358 * DoS attack, an attacker could send data which would eventually
1359 * consume all available buffer space if it were ACKed. By not ACKing
1360 * the data, we avoid this DoS scenario.
1361 *
1362 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO)
1363 * cookie is processed and a new socket is created. In this case, any data
1364 * accompanying the SYN will be queued to the socket by tcp_input() and will
1365 * be ACKed either when the application sends response data or the delayed
1366 * ACK timer expires, whichever comes first.
1367 */
1368 struct socket *
syncache_add(struct in_conninfo * inc,struct tcpopt * to,struct tcphdr * th,struct inpcb * inp,struct socket * so,struct mbuf * m,void * tod,void * todctx,uint8_t iptos,uint16_t port)1369 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1370 struct inpcb *inp, struct socket *so, struct mbuf *m, void *tod,
1371 void *todctx, uint8_t iptos, uint16_t port)
1372 {
1373 struct tcpcb *tp;
1374 struct socket *rv = NULL;
1375 struct syncache *sc = NULL;
1376 struct syncache_head *sch;
1377 struct mbuf *ipopts = NULL;
1378 u_int ltflags;
1379 int win, ip_ttl, ip_tos;
1380 char *s;
1381 #ifdef INET6
1382 int autoflowlabel = 0;
1383 #endif
1384 #ifdef MAC
1385 struct label *maclabel = NULL;
1386 #endif
1387 struct syncache scs;
1388 uint64_t tfo_response_cookie;
1389 unsigned int *tfo_pending = NULL;
1390 int tfo_cookie_valid = 0;
1391 int tfo_response_cookie_valid = 0;
1392 bool locked;
1393
1394 INP_RLOCK_ASSERT(inp); /* listen socket */
1395 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
1396 ("%s: unexpected tcp flags", __func__));
1397
1398 /*
1399 * Combine all so/tp operations very early to drop the INP lock as
1400 * soon as possible.
1401 */
1402 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so));
1403 tp = sototcpcb(so);
1404
1405 #ifdef INET6
1406 if (inc->inc_flags & INC_ISIPV6) {
1407 if (inp->inp_flags & IN6P_AUTOFLOWLABEL) {
1408 autoflowlabel = 1;
1409 }
1410 ip_ttl = in6_selecthlim(inp, NULL);
1411 if ((inp->in6p_outputopts == NULL) ||
1412 (inp->in6p_outputopts->ip6po_tclass == -1)) {
1413 ip_tos = 0;
1414 } else {
1415 ip_tos = inp->in6p_outputopts->ip6po_tclass;
1416 }
1417 }
1418 #endif
1419 #if defined(INET6) && defined(INET)
1420 else
1421 #endif
1422 #ifdef INET
1423 {
1424 ip_ttl = inp->inp_ip_ttl;
1425 ip_tos = inp->inp_ip_tos;
1426 }
1427 #endif
1428 win = so->sol_sbrcv_hiwat;
1429 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE));
1430
1431 if (V_tcp_fastopen_server_enable && IS_FASTOPEN(tp->t_flags) &&
1432 (tp->t_tfo_pending != NULL) &&
1433 (to->to_flags & TOF_FASTOPEN)) {
1434 /*
1435 * Limit the number of pending TFO connections to
1436 * approximately half of the queue limit. This prevents TFO
1437 * SYN floods from starving the service by filling the
1438 * listen queue with bogus TFO connections.
1439 */
1440 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <=
1441 (so->sol_qlimit / 2)) {
1442 int result;
1443
1444 result = tcp_fastopen_check_cookie(inc,
1445 to->to_tfo_cookie, to->to_tfo_len,
1446 &tfo_response_cookie);
1447 tfo_cookie_valid = (result > 0);
1448 tfo_response_cookie_valid = (result >= 0);
1449 }
1450
1451 /*
1452 * Remember the TFO pending counter as it will have to be
1453 * decremented below if we don't make it to syncache_tfo_expand().
1454 */
1455 tfo_pending = tp->t_tfo_pending;
1456 }
1457
1458 #ifdef MAC
1459 if (mac_syncache_init(&maclabel) != 0) {
1460 INP_RUNLOCK(inp);
1461 goto done;
1462 } else
1463 mac_syncache_create(maclabel, inp);
1464 #endif
1465 if (!tfo_cookie_valid)
1466 INP_RUNLOCK(inp);
1467
1468 /*
1469 * Remember the IP options, if any.
1470 */
1471 #ifdef INET6
1472 if (!(inc->inc_flags & INC_ISIPV6))
1473 #endif
1474 #ifdef INET
1475 ipopts = (m) ? ip_srcroute(m) : NULL;
1476 #else
1477 ipopts = NULL;
1478 #endif
1479
1480 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1481 /*
1482 * When the socket is TCP-MD5 enabled check that,
1483 * - a signed packet is valid
1484 * - a non-signed packet does not have a security association
1485 *
1486 * If a signed packet fails validation or a non-signed packet has a
1487 * security association, the packet will be dropped.
1488 */
1489 if (ltflags & TF_SIGNATURE) {
1490 if (to->to_flags & TOF_SIGNATURE) {
1491 if (!TCPMD5_ENABLED() ||
1492 TCPMD5_INPUT(m, th, to->to_signature) != 0)
1493 goto done;
1494 } else {
1495 if (TCPMD5_ENABLED() &&
1496 TCPMD5_INPUT(m, NULL, NULL) != ENOENT)
1497 goto done;
1498 }
1499 } else if (to->to_flags & TOF_SIGNATURE)
1500 goto done;
1501 #endif /* TCP_SIGNATURE */
1502 /*
1503 * See if we already have an entry for this connection.
1504 * If we do, resend the SYN,ACK, and reset the retransmit timer.
1505 *
1506 * XXX: should the syncache be re-initialized with the contents
1507 * of the new SYN here (which may have different options?)
1508 *
1509 * XXX: We do not check the sequence number to see if this is a
1510 * real retransmit or a new connection attempt. The question is
1511 * how to handle such a case; either ignore it as spoofed, or
1512 * drop the current entry and create a new one?
1513 */
1514 if (syncache_cookiesonly()) {
1515 sc = NULL;
1516 sch = syncache_hashbucket(inc);
1517 locked = false;
1518 } else {
1519 sc = syncache_lookup(inc, &sch); /* returns locked sch */
1520 locked = true;
1521 SCH_LOCK_ASSERT(sch);
1522 }
1523 if (sc != NULL) {
1524 if (tfo_cookie_valid)
1525 INP_RUNLOCK(inp);
1526 TCPSTAT_INC(tcps_sc_dupsyn);
1527 if (ipopts) {
1528 /*
1529 * If we were remembering a previous source route,
1530 * forget it and use the new one we've been given.
1531 */
1532 if (sc->sc_ipopts)
1533 (void)m_free(sc->sc_ipopts);
1534 sc->sc_ipopts = ipopts;
1535 }
1536 /*
1537 * Update timestamp if present.
1538 */
1539 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
1540 sc->sc_tsreflect = to->to_tsval;
1541 else
1542 sc->sc_flags &= ~SCF_TIMESTAMP;
1543 /*
1544 * Adjust ECN response if needed, e.g. different
1545 * IP ECN field, or a fallback by the remote host.
1546 */
1547 if (sc->sc_flags & SCF_ECN_MASK) {
1548 sc->sc_flags &= ~SCF_ECN_MASK;
1549 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos);
1550 }
1551 #ifdef MAC
1552 /*
1553 * Since we have already unconditionally allocated label
1554 * storage, free it up. The syncache entry will already
1555 * have an initialized label we can use.
1556 */
1557 mac_syncache_destroy(&maclabel);
1558 #endif
1559 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1560 /* Retransmit SYN|ACK and reset retransmit count. */
1561 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
1562 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
1563 "resetting timer and retransmitting SYN|ACK\n",
1564 s, __func__);
1565 free(s, M_TCPLOG);
1566 }
1567 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) {
1568 sc->sc_rxmits = 0;
1569 syncache_timeout(sc, sch, 1);
1570 TCPSTAT_INC(tcps_sndacks);
1571 TCPSTAT_INC(tcps_sndtotal);
1572 } else {
1573 syncache_drop(sc, sch);
1574 TCPSTAT_INC(tcps_sc_dropped);
1575 }
1576 SCH_UNLOCK(sch);
1577 goto donenoprobe;
1578 }
1579
1580 KASSERT(sc == NULL, ("sc(%p) != NULL", sc));
1581 /*
1582 * Skip allocating a syncache entry if we are just going to discard
1583 * it later.
1584 */
1585 if (!locked || tfo_cookie_valid) {
1586 bzero(&scs, sizeof(scs));
1587 sc = &scs;
1588 } else {
1589 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1590 if (sc == NULL) {
1591 /*
1592 * The zone allocator couldn't provide more entries.
1593 * Treat this as if the cache was full; drop the oldest
1594 * entry and insert the new one.
1595 */
1596 TCPSTAT_INC(tcps_sc_zonefail);
1597 sc = TAILQ_LAST(&sch->sch_bucket, sch_head);
1598 if (sc != NULL) {
1599 sch->sch_last_overflow = time_uptime;
1600 syncache_drop(sc, sch);
1601 syncache_pause(inc);
1602 }
1603 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1604 if (sc == NULL) {
1605 if (V_tcp_syncookies) {
1606 bzero(&scs, sizeof(scs));
1607 sc = &scs;
1608 } else {
1609 KASSERT(locked,
1610 ("%s: bucket unexpectedly unlocked",
1611 __func__));
1612 SCH_UNLOCK(sch);
1613 goto done;
1614 }
1615 }
1616 }
1617 }
1618
1619 KASSERT(sc != NULL, ("sc == NULL"));
1620 if (!tfo_cookie_valid && tfo_response_cookie_valid)
1621 sc->sc_tfo_cookie = &tfo_response_cookie;
1622
1623 /*
1624 * Fill in the syncache values.
1625 */
1626 #ifdef MAC
1627 sc->sc_label = maclabel;
1628 #endif
1629 /*
1630 * sc_cred is only used in syncache_pcblist() to list TCP endpoints in
1631 * TCPS_SYN_RECEIVED state when V_tcp_syncache.see_other is false.
1632 * Therefore, store the credentials and take a reference count only
1633 * when needed:
1634 * - sc is allocated from the zone and not using the on stack instance.
1635 * - the sysctl variable net.inet.tcp.syncache.see_other is false.
1636 * The reference count is decremented when a zone allocated sc is
1637 * freed in syncache_free().
1638 */
1639 if (sc != &scs && !V_tcp_syncache.see_other)
1640 sc->sc_cred = crhold(so->so_cred);
1641 else
1642 sc->sc_cred = NULL;
1643 sc->sc_port = port;
1644 sc->sc_ipopts = ipopts;
1645 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1646 sc->sc_ip_tos = ip_tos;
1647 sc->sc_ip_ttl = ip_ttl;
1648 #ifdef TCP_OFFLOAD
1649 sc->sc_tod = tod;
1650 sc->sc_todctx = todctx;
1651 #endif
1652 sc->sc_irs = th->th_seq;
1653 sc->sc_flags = 0;
1654 sc->sc_flowlabel = 0;
1655
1656 /*
1657 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
1658 * win was derived from socket earlier in the function.
1659 */
1660 win = imax(win, 0);
1661 win = imin(win, TCP_MAXWIN);
1662 sc->sc_wnd = win;
1663
1664 if (V_tcp_do_rfc1323 &&
1665 !(ltflags & TF_NOOPT)) {
1666 /*
1667 * A timestamp received in a SYN makes
1668 * it ok to send timestamp requests and replies.
1669 */
1670 if ((to->to_flags & TOF_TS) && (V_tcp_do_rfc1323 != 2)) {
1671 sc->sc_tsreflect = to->to_tsval;
1672 sc->sc_flags |= SCF_TIMESTAMP;
1673 sc->sc_tsoff = tcp_new_ts_offset(inc);
1674 }
1675 if ((to->to_flags & TOF_SCALE) && (V_tcp_do_rfc1323 != 3)) {
1676 int wscale = 0;
1677
1678 /*
1679 * Pick the smallest possible scaling factor that
1680 * will still allow us to scale up to sb_max, aka
1681 * kern.ipc.maxsockbuf.
1682 *
1683 * We do this because there are broken firewalls that
1684 * will corrupt the window scale option, leading to
1685 * the other endpoint believing that our advertised
1686 * window is unscaled. At scale factors larger than
1687 * 5 the unscaled window will drop below 1500 bytes,
1688 * leading to serious problems when traversing these
1689 * broken firewalls.
1690 *
1691 * With the default maxsockbuf of 256K, a scale factor
1692 * of 3 will be chosen by this algorithm. Those who
1693 * choose a larger maxsockbuf should watch out
1694 * for the compatibility problems mentioned above.
1695 *
1696 * RFC1323: The Window field in a SYN (i.e., a <SYN>
1697 * or <SYN,ACK>) segment itself is never scaled.
1698 */
1699 while (wscale < TCP_MAX_WINSHIFT &&
1700 (TCP_MAXWIN << wscale) < sb_max)
1701 wscale++;
1702 sc->sc_requested_r_scale = wscale;
1703 sc->sc_requested_s_scale = to->to_wscale;
1704 sc->sc_flags |= SCF_WINSCALE;
1705 }
1706 }
1707 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1708 /*
1709 * If incoming packet has an MD5 signature, flag this in the
1710 * syncache so that syncache_respond() will do the right thing
1711 * with the SYN+ACK.
1712 */
1713 if (to->to_flags & TOF_SIGNATURE)
1714 sc->sc_flags |= SCF_SIGNATURE;
1715 #endif /* TCP_SIGNATURE */
1716 if (to->to_flags & TOF_SACKPERM)
1717 sc->sc_flags |= SCF_SACK;
1718 if (to->to_flags & TOF_MSS)
1719 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */
1720 if (ltflags & TF_NOOPT)
1721 sc->sc_flags |= SCF_NOOPT;
1722 /* ECN Handshake */
1723 if (V_tcp_do_ecn && (tp->t_flags2 & TF2_CANNOT_DO_ECN) == 0)
1724 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos);
1725
1726 if (V_tcp_syncookies)
1727 sc->sc_iss = syncookie_generate(sch, sc);
1728 else
1729 sc->sc_iss = arc4random();
1730 #ifdef INET6
1731 if (autoflowlabel) {
1732 if (V_tcp_syncookies)
1733 sc->sc_flowlabel = sc->sc_iss;
1734 else
1735 sc->sc_flowlabel = ip6_randomflowlabel();
1736 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK;
1737 }
1738 #endif
1739 if (locked)
1740 SCH_UNLOCK(sch);
1741
1742 if (tfo_cookie_valid) {
1743 rv = syncache_tfo_expand(sc, so, m, tfo_response_cookie);
1744 /* INP_RUNLOCK(inp) will be performed by the caller */
1745 goto tfo_expanded;
1746 }
1747
1748 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1749 /*
1750 * Do a standard 3-way handshake.
1751 */
1752 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) {
1753 if (sc != &scs)
1754 syncache_insert(sc, sch); /* locks and unlocks sch */
1755 TCPSTAT_INC(tcps_sndacks);
1756 TCPSTAT_INC(tcps_sndtotal);
1757 } else {
1758 if (sc != &scs)
1759 syncache_free(sc);
1760 TCPSTAT_INC(tcps_sc_dropped);
1761 }
1762 goto donenoprobe;
1763
1764 done:
1765 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1766 donenoprobe:
1767 if (m)
1768 m_freem(m);
1769 /*
1770 * If tfo_pending is not NULL here, then a TFO SYN that did not
1771 * result in a new socket was processed and the associated pending
1772 * counter has not yet been decremented. All such TFO processing paths
1773 * transit this point.
1774 */
1775 if (tfo_pending != NULL)
1776 tcp_fastopen_decrement_counter(tfo_pending);
1777
1778 tfo_expanded:
1779 if (sc == NULL || sc == &scs) {
1780 #ifdef MAC
1781 mac_syncache_destroy(&maclabel);
1782 #endif
1783 if (ipopts)
1784 (void)m_free(ipopts);
1785 }
1786 return (rv);
1787 }
1788
1789 /*
1790 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment,
1791 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL.
1792 */
1793 static int
syncache_respond(struct syncache * sc,const struct mbuf * m0,int flags)1794 syncache_respond(struct syncache *sc, const struct mbuf *m0, int flags)
1795 {
1796 struct ip *ip = NULL;
1797 struct mbuf *m;
1798 struct tcphdr *th = NULL;
1799 struct udphdr *udp = NULL;
1800 int optlen, error = 0; /* Make compiler happy */
1801 u_int16_t hlen, tlen, mssopt, ulen;
1802 struct tcpopt to;
1803 #ifdef INET6
1804 struct ip6_hdr *ip6 = NULL;
1805 #endif
1806
1807 NET_EPOCH_ASSERT();
1808
1809 hlen =
1810 #ifdef INET6
1811 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
1812 #endif
1813 sizeof(struct ip);
1814 tlen = hlen + sizeof(struct tcphdr);
1815 if (sc->sc_port) {
1816 tlen += sizeof(struct udphdr);
1817 }
1818 /* Determine MSS we advertize to other end of connection. */
1819 mssopt = tcp_mssopt(&sc->sc_inc);
1820 if (sc->sc_port)
1821 mssopt -= V_tcp_udp_tunneling_overhead;
1822 mssopt = max(mssopt, V_tcp_minmss);
1823
1824 /* XXX: Assume that the entire packet will fit in a header mbuf. */
1825 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
1826 ("syncache: mbuf too small: hlen %u, sc_port %u, max_linkhdr %d + "
1827 "tlen %d + TCP_MAXOLEN %ju <= MHLEN %d", hlen, sc->sc_port,
1828 max_linkhdr, tlen, (uintmax_t)TCP_MAXOLEN, MHLEN));
1829
1830 /* Create the IP+TCP header from scratch. */
1831 m = m_gethdr(M_NOWAIT, MT_DATA);
1832 if (m == NULL)
1833 return (ENOBUFS);
1834 #ifdef MAC
1835 mac_syncache_create_mbuf(sc->sc_label, m);
1836 #endif
1837 m->m_data += max_linkhdr;
1838 m->m_len = tlen;
1839 m->m_pkthdr.len = tlen;
1840 m->m_pkthdr.rcvif = NULL;
1841
1842 #ifdef INET6
1843 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1844 ip6 = mtod(m, struct ip6_hdr *);
1845 ip6->ip6_vfc = IPV6_VERSION;
1846 ip6->ip6_src = sc->sc_inc.inc6_laddr;
1847 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
1848 ip6->ip6_plen = htons(tlen - hlen);
1849 /* ip6_hlim is set after checksum */
1850 /* Zero out traffic class and flow label. */
1851 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK;
1852 ip6->ip6_flow |= sc->sc_flowlabel;
1853 if (sc->sc_port != 0) {
1854 ip6->ip6_nxt = IPPROTO_UDP;
1855 udp = (struct udphdr *)(ip6 + 1);
1856 udp->uh_sport = htons(V_tcp_udp_tunneling_port);
1857 udp->uh_dport = sc->sc_port;
1858 ulen = (tlen - sizeof(struct ip6_hdr));
1859 th = (struct tcphdr *)(udp + 1);
1860 } else {
1861 ip6->ip6_nxt = IPPROTO_TCP;
1862 th = (struct tcphdr *)(ip6 + 1);
1863 }
1864 ip6->ip6_flow |= htonl(sc->sc_ip_tos << IPV6_FLOWLABEL_LEN);
1865 }
1866 #endif
1867 #if defined(INET6) && defined(INET)
1868 else
1869 #endif
1870 #ifdef INET
1871 {
1872 ip = mtod(m, struct ip *);
1873 ip->ip_v = IPVERSION;
1874 ip->ip_hl = sizeof(struct ip) >> 2;
1875 ip->ip_len = htons(tlen);
1876 ip->ip_id = 0;
1877 ip->ip_off = 0;
1878 ip->ip_sum = 0;
1879 ip->ip_src = sc->sc_inc.inc_laddr;
1880 ip->ip_dst = sc->sc_inc.inc_faddr;
1881 ip->ip_ttl = sc->sc_ip_ttl;
1882 ip->ip_tos = sc->sc_ip_tos;
1883
1884 /*
1885 * See if we should do MTU discovery. Route lookups are
1886 * expensive, so we will only unset the DF bit if:
1887 *
1888 * 1) path_mtu_discovery is disabled
1889 * 2) the SCF_UNREACH flag has been set
1890 */
1891 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
1892 ip->ip_off |= htons(IP_DF);
1893 if (sc->sc_port == 0) {
1894 ip->ip_p = IPPROTO_TCP;
1895 th = (struct tcphdr *)(ip + 1);
1896 } else {
1897 ip->ip_p = IPPROTO_UDP;
1898 udp = (struct udphdr *)(ip + 1);
1899 udp->uh_sport = htons(V_tcp_udp_tunneling_port);
1900 udp->uh_dport = sc->sc_port;
1901 ulen = (tlen - sizeof(struct ip));
1902 th = (struct tcphdr *)(udp + 1);
1903 }
1904 }
1905 #endif /* INET */
1906 th->th_sport = sc->sc_inc.inc_lport;
1907 th->th_dport = sc->sc_inc.inc_fport;
1908
1909 if (flags & TH_SYN)
1910 th->th_seq = htonl(sc->sc_iss);
1911 else
1912 th->th_seq = htonl(sc->sc_iss + 1);
1913 th->th_ack = htonl(sc->sc_irs + 1);
1914 th->th_off = sizeof(struct tcphdr) >> 2;
1915 th->th_win = htons(sc->sc_wnd);
1916 th->th_urp = 0;
1917
1918 flags = tcp_ecn_syncache_respond(flags, sc);
1919 tcp_set_flags(th, flags);
1920
1921 /* Tack on the TCP options. */
1922 if ((sc->sc_flags & SCF_NOOPT) == 0) {
1923 to.to_flags = 0;
1924
1925 if (flags & TH_SYN) {
1926 to.to_mss = mssopt;
1927 to.to_flags = TOF_MSS;
1928 if (sc->sc_flags & SCF_WINSCALE) {
1929 to.to_wscale = sc->sc_requested_r_scale;
1930 to.to_flags |= TOF_SCALE;
1931 }
1932 if (sc->sc_flags & SCF_SACK)
1933 to.to_flags |= TOF_SACKPERM;
1934 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1935 if (sc->sc_flags & SCF_SIGNATURE)
1936 to.to_flags |= TOF_SIGNATURE;
1937 #endif
1938 if (sc->sc_tfo_cookie) {
1939 to.to_flags |= TOF_FASTOPEN;
1940 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
1941 to.to_tfo_cookie = sc->sc_tfo_cookie;
1942 /* don't send cookie again when retransmitting response */
1943 sc->sc_tfo_cookie = NULL;
1944 }
1945 }
1946 if (sc->sc_flags & SCF_TIMESTAMP) {
1947 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks();
1948 to.to_tsecr = sc->sc_tsreflect;
1949 to.to_flags |= TOF_TS;
1950 }
1951 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
1952
1953 /* Adjust headers by option size. */
1954 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
1955 m->m_len += optlen;
1956 m->m_pkthdr.len += optlen;
1957 #ifdef INET6
1958 if (sc->sc_inc.inc_flags & INC_ISIPV6)
1959 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
1960 else
1961 #endif
1962 ip->ip_len = htons(ntohs(ip->ip_len) + optlen);
1963 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1964 if (sc->sc_flags & SCF_SIGNATURE) {
1965 KASSERT(to.to_flags & TOF_SIGNATURE,
1966 ("tcp_addoptions() didn't set tcp_signature"));
1967
1968 /* NOTE: to.to_signature is inside of mbuf */
1969 if (!TCPMD5_ENABLED() ||
1970 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) {
1971 m_freem(m);
1972 return (EACCES);
1973 }
1974 }
1975 #endif
1976 } else
1977 optlen = 0;
1978
1979 if (udp) {
1980 ulen += optlen;
1981 udp->uh_ulen = htons(ulen);
1982 }
1983 M_SETFIB(m, sc->sc_inc.inc_fibnum);
1984 /*
1985 * If we have peer's SYN and it has a flowid, then let's assign it to
1986 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid
1987 * to SYN|ACK due to lack of inp here.
1988 */
1989 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) {
1990 m->m_pkthdr.flowid = m0->m_pkthdr.flowid;
1991 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0));
1992 }
1993 #ifdef INET6
1994 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1995 if (sc->sc_port) {
1996 m->m_pkthdr.csum_flags = CSUM_UDP_IPV6;
1997 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
1998 udp->uh_sum = in6_cksum_pseudo(ip6, ulen,
1999 IPPROTO_UDP, 0);
2000 th->th_sum = htons(0);
2001 } else {
2002 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
2003 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
2004 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen,
2005 IPPROTO_TCP, 0);
2006 }
2007 ip6->ip6_hlim = sc->sc_ip_ttl;
2008 #ifdef TCP_OFFLOAD
2009 if (ADDED_BY_TOE(sc)) {
2010 struct toedev *tod = sc->sc_tod;
2011
2012 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
2013
2014 return (error);
2015 }
2016 #endif
2017 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th);
2018 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
2019 }
2020 #endif
2021 #if defined(INET6) && defined(INET)
2022 else
2023 #endif
2024 #ifdef INET
2025 {
2026 if (sc->sc_port) {
2027 m->m_pkthdr.csum_flags = CSUM_UDP;
2028 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
2029 udp->uh_sum = in_pseudo(ip->ip_src.s_addr,
2030 ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP));
2031 th->th_sum = htons(0);
2032 } else {
2033 m->m_pkthdr.csum_flags = CSUM_TCP;
2034 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
2035 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
2036 htons(tlen + optlen - hlen + IPPROTO_TCP));
2037 }
2038 #ifdef TCP_OFFLOAD
2039 if (ADDED_BY_TOE(sc)) {
2040 struct toedev *tod = sc->sc_tod;
2041
2042 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
2043
2044 return (error);
2045 }
2046 #endif
2047 TCP_PROBE5(send, NULL, NULL, ip, NULL, th);
2048 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
2049 }
2050 #endif
2051 return (error);
2052 }
2053
2054 /*
2055 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks
2056 * that exceed the capacity of the syncache by avoiding the storage of any
2057 * of the SYNs we receive. Syncookies defend against blind SYN flooding
2058 * attacks where the attacker does not have access to our responses.
2059 *
2060 * Syncookies encode and include all necessary information about the
2061 * connection setup within the SYN|ACK that we send back. That way we
2062 * can avoid keeping any local state until the ACK to our SYN|ACK returns
2063 * (if ever). Normally the syncache and syncookies are running in parallel
2064 * with the latter taking over when the former is exhausted. When matching
2065 * syncache entry is found the syncookie is ignored.
2066 *
2067 * The only reliable information persisting the 3WHS is our initial sequence
2068 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient
2069 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS
2070 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK
2071 * returns and signifies a legitimate connection if it matches the ACK.
2072 *
2073 * The available space of 32 bits to store the hash and to encode the SYN
2074 * option information is very tight and we should have at least 24 bits for
2075 * the MAC to keep the number of guesses by blind spoofing reasonably high.
2076 *
2077 * SYN option information we have to encode to fully restore a connection:
2078 * MSS: is imporant to chose an optimal segment size to avoid IP level
2079 * fragmentation along the path. The common MSS values can be encoded
2080 * in a 3-bit table. Uncommon values are captured by the next lower value
2081 * in the table leading to a slight increase in packetization overhead.
2082 * WSCALE: is necessary to allow large windows to be used for high delay-
2083 * bandwidth product links. Not scaling the window when it was initially
2084 * negotiated is bad for performance as lack of scaling further decreases
2085 * the apparent available send window. We only need to encode the WSCALE
2086 * we received from the remote end. Our end can be recalculated at any
2087 * time. The common WSCALE values can be encoded in a 3-bit table.
2088 * Uncommon values are captured by the next lower value in the table
2089 * making us under-estimate the available window size halving our
2090 * theoretically possible maximum throughput for that connection.
2091 * SACK: Greatly assists in packet loss recovery and requires 1 bit.
2092 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options
2093 * that are included in all segments on a connection. We enable them when
2094 * the ACK has them.
2095 *
2096 * Security of syncookies and attack vectors:
2097 *
2098 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod)
2099 * together with the gloabl secret to make it unique per connection attempt.
2100 * Thus any change of any of those parameters results in a different MAC output
2101 * in an unpredictable way unless a collision is encountered. 24 bits of the
2102 * MAC are embedded into the ISS.
2103 *
2104 * To prevent replay attacks two rotating global secrets are updated with a
2105 * new random value every 15 seconds. The life-time of a syncookie is thus
2106 * 15-30 seconds.
2107 *
2108 * Vector 1: Attacking the secret. This requires finding a weakness in the
2109 * MAC itself or the way it is used here. The attacker can do a chosen plain
2110 * text attack by varying and testing the all parameters under his control.
2111 * The strength depends on the size and randomness of the secret, and the
2112 * cryptographic security of the MAC function. Due to the constant updating
2113 * of the secret the attacker has at most 29.999 seconds to find the secret
2114 * and launch spoofed connections. After that he has to start all over again.
2115 *
2116 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC
2117 * size an average of 4,823 attempts are required for a 50% chance of success
2118 * to spoof a single syncookie (birthday collision paradox). However the
2119 * attacker is blind and doesn't know if one of his attempts succeeded unless
2120 * he has a side channel to interfere success from. A single connection setup
2121 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets.
2122 * This many attempts are required for each one blind spoofed connection. For
2123 * every additional spoofed connection he has to launch another N attempts.
2124 * Thus for a sustained rate 100 spoofed connections per second approximately
2125 * 1,800,000 packets per second would have to be sent.
2126 *
2127 * NB: The MAC function should be fast so that it doesn't become a CPU
2128 * exhaustion attack vector itself.
2129 *
2130 * References:
2131 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations
2132 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996
2133 * http://cr.yp.to/syncookies.html (overview)
2134 * http://cr.yp.to/syncookies/archive (details)
2135 *
2136 *
2137 * Schematic construction of a syncookie enabled Initial Sequence Number:
2138 * 0 1 2 3
2139 * 12345678901234567890123456789012
2140 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP|
2141 *
2142 * x 24 MAC (truncated)
2143 * W 3 Send Window Scale index
2144 * M 3 MSS index
2145 * S 1 SACK permitted
2146 * P 1 Odd/even secret
2147 */
2148
2149 /*
2150 * Distribution and probability of certain MSS values. Those in between are
2151 * rounded down to the next lower one.
2152 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011]
2153 * .2% .3% 5% 7% 7% 20% 15% 45%
2154 */
2155 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 };
2156
2157 /*
2158 * Distribution and probability of certain WSCALE values. We have to map the
2159 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3
2160 * bits based on prevalence of certain values. Where we don't have an exact
2161 * match for are rounded down to the next lower one letting us under-estimate
2162 * the true available window. At the moment this would happen only for the
2163 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer
2164 * and window size). The absence of the WSCALE option (no scaling in either
2165 * direction) is encoded with index zero.
2166 * [WSCALE values histograms, Allman, 2012]
2167 * X 10 10 35 5 6 14 10% by host
2168 * X 11 4 5 5 18 49 3% by connections
2169 */
2170 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 };
2171
2172 /*
2173 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed
2174 * and good cryptographic properties.
2175 */
2176 static uint32_t
syncookie_mac(struct in_conninfo * inc,tcp_seq irs,uint8_t flags,uint8_t * secbits,uintptr_t secmod)2177 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags,
2178 uint8_t *secbits, uintptr_t secmod)
2179 {
2180 SIPHASH_CTX ctx;
2181 uint32_t siphash[2];
2182
2183 SipHash24_Init(&ctx);
2184 SipHash_SetKey(&ctx, secbits);
2185 switch (inc->inc_flags & INC_ISIPV6) {
2186 #ifdef INET
2187 case 0:
2188 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr));
2189 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr));
2190 break;
2191 #endif
2192 #ifdef INET6
2193 case INC_ISIPV6:
2194 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr));
2195 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr));
2196 break;
2197 #endif
2198 }
2199 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport));
2200 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport));
2201 SipHash_Update(&ctx, &irs, sizeof(irs));
2202 SipHash_Update(&ctx, &flags, sizeof(flags));
2203 SipHash_Update(&ctx, &secmod, sizeof(secmod));
2204 SipHash_Final((u_int8_t *)&siphash, &ctx);
2205
2206 return (siphash[0] ^ siphash[1]);
2207 }
2208
2209 static tcp_seq
syncookie_generate(struct syncache_head * sch,struct syncache * sc)2210 syncookie_generate(struct syncache_head *sch, struct syncache *sc)
2211 {
2212 u_int i, secbit, wscale;
2213 uint32_t iss, hash;
2214 uint8_t *secbits;
2215 union syncookie cookie;
2216
2217 cookie.cookie = 0;
2218
2219 /* Map our computed MSS into the 3-bit index. */
2220 for (i = nitems(tcp_sc_msstab) - 1;
2221 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0;
2222 i--)
2223 ;
2224 cookie.flags.mss_idx = i;
2225
2226 /*
2227 * Map the send window scale into the 3-bit index but only if
2228 * the wscale option was received.
2229 */
2230 if (sc->sc_flags & SCF_WINSCALE) {
2231 wscale = sc->sc_requested_s_scale;
2232 for (i = nitems(tcp_sc_wstab) - 1;
2233 tcp_sc_wstab[i] > wscale && i > 0;
2234 i--)
2235 ;
2236 cookie.flags.wscale_idx = i;
2237 }
2238
2239 /* Can we do SACK? */
2240 if (sc->sc_flags & SCF_SACK)
2241 cookie.flags.sack_ok = 1;
2242
2243 /* Which of the two secrets to use. */
2244 secbit = V_tcp_syncache.secret.oddeven & 0x1;
2245 cookie.flags.odd_even = secbit;
2246
2247 secbits = V_tcp_syncache.secret.key[secbit];
2248 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits,
2249 (uintptr_t)sch);
2250
2251 /*
2252 * Put the flags into the hash and XOR them to get better ISS number
2253 * variance. This doesn't enhance the cryptographic strength and is
2254 * done to prevent the 8 cookie bits from showing up directly on the
2255 * wire.
2256 */
2257 iss = hash & ~0xff;
2258 iss |= cookie.cookie ^ (hash >> 24);
2259
2260 TCPSTAT_INC(tcps_sc_sendcookie);
2261 return (iss);
2262 }
2263
2264 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,uint16_t port)2265 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch,
2266 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
2267 struct socket *lso, uint16_t port)
2268 {
2269 uint32_t hash;
2270 uint8_t *secbits;
2271 tcp_seq ack, seq;
2272 int wnd, wscale = 0;
2273 union syncookie cookie;
2274
2275 /*
2276 * Pull information out of SYN-ACK/ACK and revert sequence number
2277 * advances.
2278 */
2279 ack = th->th_ack - 1;
2280 seq = th->th_seq - 1;
2281
2282 /*
2283 * Unpack the flags containing enough information to restore the
2284 * connection.
2285 */
2286 cookie.cookie = (ack & 0xff) ^ (ack >> 24);
2287
2288 /* Which of the two secrets to use. */
2289 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even];
2290
2291 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch);
2292
2293 /* The recomputed hash matches the ACK if this was a genuine cookie. */
2294 if ((ack & ~0xff) != (hash & ~0xff))
2295 return (NULL);
2296
2297 /* Fill in the syncache values. */
2298 sc->sc_flags = 0;
2299 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
2300 sc->sc_ipopts = NULL;
2301
2302 sc->sc_irs = seq;
2303 sc->sc_iss = ack;
2304
2305 switch (inc->inc_flags & INC_ISIPV6) {
2306 #ifdef INET
2307 case 0:
2308 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl;
2309 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos;
2310 break;
2311 #endif
2312 #ifdef INET6
2313 case INC_ISIPV6:
2314 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL)
2315 sc->sc_flowlabel =
2316 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK;
2317 break;
2318 #endif
2319 }
2320
2321 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx];
2322
2323 /* We can simply recompute receive window scale we sent earlier. */
2324 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max)
2325 wscale++;
2326
2327 /* Only use wscale if it was enabled in the orignal SYN. */
2328 if (cookie.flags.wscale_idx > 0) {
2329 sc->sc_requested_r_scale = wscale;
2330 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx];
2331 sc->sc_flags |= SCF_WINSCALE;
2332 }
2333
2334 wnd = lso->sol_sbrcv_hiwat;
2335 wnd = imax(wnd, 0);
2336 wnd = imin(wnd, TCP_MAXWIN);
2337 sc->sc_wnd = wnd;
2338
2339 if (cookie.flags.sack_ok)
2340 sc->sc_flags |= SCF_SACK;
2341
2342 if (to->to_flags & TOF_TS) {
2343 sc->sc_flags |= SCF_TIMESTAMP;
2344 sc->sc_tsreflect = to->to_tsval;
2345 sc->sc_tsoff = tcp_new_ts_offset(inc);
2346 }
2347
2348 if (to->to_flags & TOF_SIGNATURE)
2349 sc->sc_flags |= SCF_SIGNATURE;
2350
2351 sc->sc_rxmits = 0;
2352
2353 sc->sc_port = port;
2354
2355 TCPSTAT_INC(tcps_sc_recvcookie);
2356 return (sc);
2357 }
2358
2359 #ifdef INVARIANTS
2360 static int
syncookie_cmp(struct in_conninfo * inc,struct syncache_head * sch,struct syncache * sc,struct tcphdr * th,struct tcpopt * to,struct socket * lso,uint16_t port)2361 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
2362 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
2363 struct socket *lso, uint16_t port)
2364 {
2365 struct syncache scs, *scx;
2366 char *s;
2367
2368 bzero(&scs, sizeof(scs));
2369 scx = syncookie_lookup(inc, sch, &scs, th, to, lso, port);
2370
2371 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL)
2372 return (0);
2373
2374 if (scx != NULL) {
2375 if (sc->sc_peer_mss != scx->sc_peer_mss)
2376 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n",
2377 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss);
2378
2379 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale)
2380 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n",
2381 s, __func__, sc->sc_requested_r_scale,
2382 scx->sc_requested_r_scale);
2383
2384 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale)
2385 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n",
2386 s, __func__, sc->sc_requested_s_scale,
2387 scx->sc_requested_s_scale);
2388
2389 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK))
2390 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__);
2391 }
2392
2393 if (s != NULL)
2394 free(s, M_TCPLOG);
2395 return (0);
2396 }
2397 #endif /* INVARIANTS */
2398
2399 static void
syncookie_reseed(void * arg)2400 syncookie_reseed(void *arg)
2401 {
2402 struct tcp_syncache *sc = arg;
2403 uint8_t *secbits;
2404 int secbit;
2405
2406 /*
2407 * Reseeding the secret doesn't have to be protected by a lock.
2408 * It only must be ensured that the new random values are visible
2409 * to all CPUs in a SMP environment. The atomic with release
2410 * semantics ensures that.
2411 */
2412 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1;
2413 secbits = sc->secret.key[secbit];
2414 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0);
2415 atomic_add_rel_int(&sc->secret.oddeven, 1);
2416
2417 /* Reschedule ourself. */
2418 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz);
2419 }
2420
2421 /*
2422 * We have overflowed a bucket. Let's pause dealing with the syncache.
2423 * This function will increment the bucketoverflow statistics appropriately
2424 * (once per pause when pausing is enabled; otherwise, once per overflow).
2425 */
2426 static void
syncache_pause(struct in_conninfo * inc)2427 syncache_pause(struct in_conninfo *inc)
2428 {
2429 time_t delta;
2430 const char *s;
2431
2432 /* XXX:
2433 * 2. Add sysctl read here so we don't get the benefit of this
2434 * change without the new sysctl.
2435 */
2436
2437 /*
2438 * Try an unlocked read. If we already know that another thread
2439 * has activated the feature, there is no need to proceed.
2440 */
2441 if (V_tcp_syncache.paused)
2442 return;
2443
2444 /* Are cookied enabled? If not, we can't pause. */
2445 if (!V_tcp_syncookies) {
2446 TCPSTAT_INC(tcps_sc_bucketoverflow);
2447 return;
2448 }
2449
2450 /*
2451 * We may be the first thread to find an overflow. Get the lock
2452 * and evaluate if we need to take action.
2453 */
2454 mtx_lock(&V_tcp_syncache.pause_mtx);
2455 if (V_tcp_syncache.paused) {
2456 mtx_unlock(&V_tcp_syncache.pause_mtx);
2457 return;
2458 }
2459
2460 /* Activate protection. */
2461 V_tcp_syncache.paused = true;
2462 TCPSTAT_INC(tcps_sc_bucketoverflow);
2463
2464 /*
2465 * Determine the last backoff time. If we are seeing a re-newed
2466 * attack within that same time after last reactivating the syncache,
2467 * consider it an extension of the same attack.
2468 */
2469 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff;
2470 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) {
2471 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) {
2472 delta <<= 1;
2473 V_tcp_syncache.pause_backoff++;
2474 }
2475 } else {
2476 delta = TCP_SYNCACHE_PAUSE_TIME;
2477 V_tcp_syncache.pause_backoff = 0;
2478 }
2479
2480 /* Log a warning, including IP addresses, if able. */
2481 if (inc != NULL)
2482 s = tcp_log_addrs(inc, NULL, NULL, NULL);
2483 else
2484 s = (const char *)NULL;
2485 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for "
2486 "the next %lld seconds%s%s%s\n", (long long)delta,
2487 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "",
2488 (s != NULL) ? ")" : "");
2489 free(__DECONST(void *, s), M_TCPLOG);
2490
2491 /* Use the calculated delta to set a new pause time. */
2492 V_tcp_syncache.pause_until = time_uptime + delta;
2493 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause,
2494 &V_tcp_syncache);
2495 mtx_unlock(&V_tcp_syncache.pause_mtx);
2496 }
2497
2498 /* Evaluate whether we need to unpause. */
2499 static void
syncache_unpause(void * arg)2500 syncache_unpause(void *arg)
2501 {
2502 struct tcp_syncache *sc;
2503 time_t delta;
2504
2505 sc = arg;
2506 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED);
2507 callout_deactivate(&sc->pause_co);
2508
2509 /*
2510 * Check to make sure we are not running early. If the pause
2511 * time has expired, then deactivate the protection.
2512 */
2513 if ((delta = sc->pause_until - time_uptime) > 0)
2514 callout_schedule(&sc->pause_co, delta * hz);
2515 else
2516 sc->paused = false;
2517 }
2518
2519 /*
2520 * Exports the syncache entries to userland so that netstat can display
2521 * them alongside the other sockets. This function is intended to be
2522 * called only from tcp_pcblist.
2523 *
2524 * Due to concurrency on an active system, the number of pcbs exported
2525 * may have no relation to max_pcbs. max_pcbs merely indicates the
2526 * amount of space the caller allocated for this function to use.
2527 */
2528 int
syncache_pcblist(struct sysctl_req * req)2529 syncache_pcblist(struct sysctl_req *req)
2530 {
2531 struct xtcpcb xt;
2532 struct syncache *sc;
2533 struct syncache_head *sch;
2534 int error, i;
2535
2536 bzero(&xt, sizeof(xt));
2537 xt.xt_len = sizeof(xt);
2538 xt.t_state = TCPS_SYN_RECEIVED;
2539 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP;
2540 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket);
2541 xt.xt_inp.xi_socket.so_type = SOCK_STREAM;
2542 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING;
2543
2544 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
2545 sch = &V_tcp_syncache.hashbase[i];
2546 SCH_LOCK(sch);
2547 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
2548 if (sc->sc_cred != NULL &&
2549 cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
2550 continue;
2551 if (sc->sc_inc.inc_flags & INC_ISIPV6)
2552 xt.xt_inp.inp_vflag = INP_IPV6;
2553 else
2554 xt.xt_inp.inp_vflag = INP_IPV4;
2555 xt.xt_encaps_port = sc->sc_port;
2556 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc,
2557 sizeof (struct in_conninfo));
2558 error = SYSCTL_OUT(req, &xt, sizeof xt);
2559 if (error) {
2560 SCH_UNLOCK(sch);
2561 return (0);
2562 }
2563 }
2564 SCH_UNLOCK(sch);
2565 }
2566
2567 return (0);
2568 }
2569