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 "opt_inet.h"
36 #include "opt_inet6.h"
37 #include "opt_ipsec.h"
38 #include "opt_rss.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/in_rss.h>
75 #include <netinet/ip_var.h>
76 #include <netinet/ip_options.h>
77 #ifdef INET6
78 #include <netinet/ip6.h>
79 #include <netinet/icmp6.h>
80 #include <netinet6/nd6.h>
81 #include <netinet6/ip6_var.h>
82 #include <netinet6/in6_pcb.h>
83 #include <netinet6/in6_rss.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_BLACKBOX
94 #include <netinet/tcp_log_buf.h>
95 #endif
96 #ifdef TCP_OFFLOAD
97 #include <netinet/toecore.h>
98 #endif
99 #include <netinet/udp.h>
100
101 #include <netipsec/ipsec_support.h>
102
103 #include <machine/in_cksum.h>
104
105 #include <security/mac/mac_framework.h>
106
107 VNET_DEFINE_STATIC(bool, tcp_syncookies) = true;
108 #define V_tcp_syncookies VNET(tcp_syncookies)
109 SYSCTL_BOOL(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW,
110 &VNET_NAME(tcp_syncookies), 0,
111 "Use TCP SYN cookies if the syncache overflows");
112
113 VNET_DEFINE_STATIC(bool, tcp_syncookiesonly) = false;
114 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly)
115 SYSCTL_BOOL(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW,
116 &VNET_NAME(tcp_syncookiesonly), 0,
117 "Use only TCP SYN cookies");
118
119 #ifdef TCP_OFFLOAD
120 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL)
121 #endif
122
123 static void syncache_drop(struct syncache *, struct syncache_head *);
124 static void syncache_free(struct syncache *);
125 static void syncache_insert(struct syncache *, struct syncache_head *);
126 static int syncache_respond(struct syncache *, int);
127 static void syncache_send_challenge_ack(struct syncache *);
128 static struct socket *syncache_socket(struct syncache *, struct socket *,
129 struct mbuf *m);
130 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch,
131 int docallout);
132 static void syncache_timer(void *);
133
134 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t,
135 uint8_t *, uintptr_t);
136 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *);
137 static bool syncookie_expand(struct in_conninfo *,
138 const struct syncache_head *, struct syncache *,
139 struct tcphdr *, struct tcpopt *, struct socket *,
140 uint16_t);
141 static void syncache_pause(struct in_conninfo *);
142 static void syncache_unpause(void *);
143 static void syncookie_reseed(void *);
144 #ifdef INVARIANTS
145 static void syncookie_cmp(struct in_conninfo *,
146 const struct syncache_head *, struct syncache *,
147 struct tcphdr *, struct tcpopt *, struct socket *,
148 uint16_t);
149 #endif
150
151 /*
152 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
153 * 3 retransmits corresponds to a timeout with default values of
154 * tcp_rexmit_initial * ( 1 +
155 * tcp_backoff[1] +
156 * tcp_backoff[2] +
157 * tcp_backoff[3]) + 3 * tcp_rexmit_slop,
158 * 1000 ms * (1 + 2 + 4 + 8) + 3 * 200 ms = 15600 ms,
159 * the odds are that the user has given up attempting to connect by then.
160 */
161 #define SYNCACHE_MAXREXMTS 3
162
163 /* Arbitrary values */
164 #define TCP_SYNCACHE_HASHSIZE 512
165 #define TCP_SYNCACHE_BUCKETLIMIT 30
166
167 VNET_DEFINE_STATIC(struct tcp_syncache, tcp_syncache);
168 #define V_tcp_syncache VNET(tcp_syncache)
169
170 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache,
171 CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
172 "TCP SYN cache");
173
174 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
175 &VNET_NAME(tcp_syncache.bucket_limit), 0,
176 "Per-bucket hash limit for syncache");
177
178 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
179 &VNET_NAME(tcp_syncache.cache_limit), 0,
180 "Overall entry limit for syncache");
181
182 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET,
183 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache");
184
185 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN,
186 &VNET_NAME(tcp_syncache.hashsize), 0,
187 "Size of TCP syncache hashtable");
188
189 SYSCTL_BOOL(_net_inet_tcp_syncache, OID_AUTO, see_other, CTLFLAG_VNET |
190 CTLFLAG_RW, &VNET_NAME(tcp_syncache.see_other), 0,
191 "All syncache(4) entries are visible, ignoring UID/GID, jail(2) "
192 "and mac(4) checks");
193
194 static int
sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS)195 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS)
196 {
197 int error;
198 u_int new;
199
200 new = V_tcp_syncache.rexmt_limit;
201 error = sysctl_handle_int(oidp, &new, 0, req);
202 if ((error == 0) && (req->newptr != NULL)) {
203 if (new > TCP_MAXRXTSHIFT)
204 error = EINVAL;
205 else
206 V_tcp_syncache.rexmt_limit = new;
207 }
208 return (error);
209 }
210
211 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit,
212 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
213 &VNET_NAME(tcp_syncache.rexmt_limit), 0,
214 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "IU",
215 "Limit on SYN/ACK retransmissions");
216
217 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1;
218 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail,
219 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0,
220 "Send reset on socket allocation failure");
221
222 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
223
224 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx)
225 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx)
226 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED)
227
228 /*
229 * Requires the syncache entry to be already removed from the bucket list.
230 */
231 static void
syncache_free(struct syncache * sc)232 syncache_free(struct syncache *sc)
233 {
234
235 if (sc->sc_ipopts)
236 (void)m_free(sc->sc_ipopts);
237 if (sc->sc_cred)
238 crfree(sc->sc_cred);
239 #ifdef MAC
240 mac_syncache_destroy(&sc->sc_label);
241 #endif
242
243 uma_zfree(V_tcp_syncache.zone, sc);
244 }
245
246 void
syncache_init(void)247 syncache_init(void)
248 {
249 int i;
250
251 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
252 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
253 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
254 V_tcp_syncache.hash_secret = arc4random();
255
256 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
257 &V_tcp_syncache.hashsize);
258 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
259 &V_tcp_syncache.bucket_limit);
260 if (!powerof2(V_tcp_syncache.hashsize) ||
261 V_tcp_syncache.hashsize == 0) {
262 printf("WARNING: syncache hash size is not a power of 2.\n");
263 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
264 }
265 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1;
266
267 /* Set limits. */
268 V_tcp_syncache.cache_limit =
269 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit;
270 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
271 &V_tcp_syncache.cache_limit);
272
273 /* Allocate the hash table. */
274 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize *
275 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO);
276
277 #ifdef VIMAGE
278 V_tcp_syncache.vnet = curvnet;
279 #endif
280
281 /* Initialize the hash buckets. */
282 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
283 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket);
284 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
285 NULL, MTX_DEF);
286 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer,
287 &V_tcp_syncache.hashbase[i].sch_mtx, 0);
288 V_tcp_syncache.hashbase[i].sch_length = 0;
289 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache;
290 V_tcp_syncache.hashbase[i].sch_last_overflow =
291 -(SYNCOOKIE_LIFETIME + 1);
292 }
293
294 /* Create the syncache entry zone. */
295 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
296 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
297 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone,
298 V_tcp_syncache.cache_limit);
299
300 /* Start the SYN cookie reseeder callout. */
301 callout_init(&V_tcp_syncache.secret.reseed, 1);
302 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0);
303 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0);
304 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz,
305 syncookie_reseed, &V_tcp_syncache);
306
307 /* Initialize the pause machinery. */
308 mtx_init(&V_tcp_syncache.pause_mtx, "tcp_sc_pause", NULL, MTX_DEF);
309 callout_init_mtx(&V_tcp_syncache.pause_co, &V_tcp_syncache.pause_mtx,
310 0);
311 V_tcp_syncache.pause_until = time_uptime - TCP_SYNCACHE_PAUSE_TIME;
312 V_tcp_syncache.pause_backoff = 0;
313 V_tcp_syncache.paused = false;
314 }
315
316 #ifdef VIMAGE
317 void
syncache_destroy(void)318 syncache_destroy(void)
319 {
320 struct syncache_head *sch;
321 struct syncache *sc, *nsc;
322 int i;
323
324 /*
325 * Stop the re-seed timer before freeing resources. No need to
326 * possibly schedule it another time.
327 */
328 callout_drain(&V_tcp_syncache.secret.reseed);
329
330 /* Stop the SYN cache pause callout. */
331 mtx_lock(&V_tcp_syncache.pause_mtx);
332 if (callout_stop(&V_tcp_syncache.pause_co) == 0) {
333 mtx_unlock(&V_tcp_syncache.pause_mtx);
334 callout_drain(&V_tcp_syncache.pause_co);
335 } else
336 mtx_unlock(&V_tcp_syncache.pause_mtx);
337
338 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */
339 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
340 sch = &V_tcp_syncache.hashbase[i];
341 callout_drain(&sch->sch_timer);
342
343 SCH_LOCK(sch);
344 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc)
345 syncache_drop(sc, sch);
346 SCH_UNLOCK(sch);
347 KASSERT(TAILQ_EMPTY(&sch->sch_bucket),
348 ("%s: sch->sch_bucket not empty", __func__));
349 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0",
350 __func__, sch->sch_length));
351 mtx_destroy(&sch->sch_mtx);
352 }
353
354 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0,
355 ("%s: cache_count not 0", __func__));
356
357 /* Free the allocated global resources. */
358 uma_zdestroy(V_tcp_syncache.zone);
359 free(V_tcp_syncache.hashbase, M_SYNCACHE);
360 mtx_destroy(&V_tcp_syncache.pause_mtx);
361 }
362 #endif
363
364 /*
365 * Inserts a syncache entry into the specified bucket row.
366 * Locks and unlocks the syncache_head autonomously.
367 */
368 static void
syncache_insert(struct syncache * sc,struct syncache_head * sch)369 syncache_insert(struct syncache *sc, struct syncache_head *sch)
370 {
371 struct syncache *sc2;
372
373 SCH_LOCK(sch);
374
375 /*
376 * Make sure that we don't overflow the per-bucket limit.
377 * If the bucket is full, toss the oldest element.
378 */
379 if (sch->sch_length >= V_tcp_syncache.bucket_limit) {
380 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
381 ("sch->sch_length incorrect"));
382 syncache_pause(&sc->sc_inc);
383 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
384 sch->sch_last_overflow = time_uptime;
385 syncache_drop(sc2, sch);
386 }
387
388 /* Put it into the bucket. */
389 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
390 sch->sch_length++;
391
392 #ifdef TCP_OFFLOAD
393 if (ADDED_BY_TOE(sc)) {
394 struct toedev *tod = sc->sc_tod;
395
396 tod->tod_syncache_added(tod, sc->sc_todctx);
397 }
398 #endif
399
400 /* Reinitialize the bucket row's timer. */
401 if (sch->sch_length == 1)
402 sch->sch_nextc = ticks + INT_MAX;
403 syncache_timeout(sc, sch, 1);
404
405 SCH_UNLOCK(sch);
406
407 TCPSTATES_INC(TCPS_SYN_RECEIVED);
408 TCPSTAT_INC(tcps_sc_added);
409 }
410
411 /*
412 * Remove and free entry from syncache bucket row.
413 * Expects locked syncache head.
414 */
415 static void
syncache_drop(struct syncache * sc,struct syncache_head * sch)416 syncache_drop(struct syncache *sc, struct syncache_head *sch)
417 {
418
419 SCH_LOCK_ASSERT(sch);
420
421 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
422 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
423 sch->sch_length--;
424
425 #ifdef TCP_OFFLOAD
426 if (ADDED_BY_TOE(sc)) {
427 struct toedev *tod = sc->sc_tod;
428
429 tod->tod_syncache_removed(tod, sc->sc_todctx);
430 }
431 #endif
432
433 syncache_free(sc);
434 }
435
436 /*
437 * Engage/reengage time on bucket row.
438 */
439 static void
syncache_timeout(struct syncache * sc,struct syncache_head * sch,int docallout)440 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
441 {
442 int rexmt;
443
444 if (sc->sc_rxmits == 0)
445 rexmt = tcp_rexmit_initial;
446 else
447 TCPT_RANGESET(rexmt,
448 tcp_rexmit_initial * tcp_backoff[sc->sc_rxmits],
449 tcp_rexmit_min, tcp_rexmit_max);
450 sc->sc_rxttime = ticks + rexmt;
451 sc->sc_rxmits++;
452 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
453 sch->sch_nextc = sc->sc_rxttime;
454 if (docallout)
455 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
456 syncache_timer, (void *)sch);
457 }
458 }
459
460 /*
461 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
462 * If we have retransmitted an entry the maximum number of times, expire it.
463 * One separate timer for each bucket row.
464 */
465 static void
syncache_timer(void * xsch)466 syncache_timer(void *xsch)
467 {
468 struct syncache_head *sch = (struct syncache_head *)xsch;
469 struct syncache *sc, *nsc;
470 struct epoch_tracker et;
471 int tick = ticks;
472 char *s;
473 bool paused;
474
475 CURVNET_SET(sch->sch_sc->vnet);
476
477 /* NB: syncache_head has already been locked by the callout. */
478 SCH_LOCK_ASSERT(sch);
479
480 /*
481 * In the following cycle we may remove some entries and/or
482 * advance some timeouts, so re-initialize the bucket timer.
483 */
484 sch->sch_nextc = tick + INT_MAX;
485
486 /*
487 * If we have paused processing, unconditionally remove
488 * all syncache entries.
489 */
490 mtx_lock(&V_tcp_syncache.pause_mtx);
491 paused = V_tcp_syncache.paused;
492 mtx_unlock(&V_tcp_syncache.pause_mtx);
493
494 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
495 if (paused) {
496 syncache_drop(sc, sch);
497 continue;
498 }
499 /*
500 * We do not check if the listen socket still exists
501 * and accept the case where the listen socket may be
502 * gone by the time we resend the SYN/ACK. We do
503 * not expect this to happens often. If it does,
504 * then the RST will be sent by the time the remote
505 * host does the SYN/ACK->ACK.
506 */
507 if (TSTMP_GT(sc->sc_rxttime, tick)) {
508 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
509 sch->sch_nextc = sc->sc_rxttime;
510 continue;
511 }
512 if (sc->sc_rxmits > V_tcp_ecn_maxretries) {
513 sc->sc_flags &= ~SCF_ECN_MASK;
514 }
515 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
516 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
517 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
518 "giving up and removing syncache entry\n",
519 s, __func__);
520 free(s, M_TCPLOG);
521 }
522 syncache_drop(sc, sch);
523 TCPSTAT_INC(tcps_sc_stale);
524 continue;
525 }
526 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
527 log(LOG_DEBUG, "%s; %s: Response timeout, "
528 "retransmitting (%u) SYN|ACK\n",
529 s, __func__, sc->sc_rxmits);
530 free(s, M_TCPLOG);
531 }
532
533 NET_EPOCH_ENTER(et);
534 if (syncache_respond(sc, TH_SYN|TH_ACK) == 0) {
535 syncache_timeout(sc, sch, 0);
536 TCPSTAT_INC(tcps_sndacks);
537 TCPSTAT_INC(tcps_sndtotal);
538 TCPSTAT_INC(tcps_sc_retransmitted);
539 } else {
540 /*
541 * Most likely we are memory constrained, so free
542 * resources.
543 */
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 return ((V_tcp_syncookies && V_tcp_syncache.paused) ||
564 V_tcp_syncookiesonly);
565 }
566
567 /*
568 * Find the hash bucket for the given connection.
569 */
570 static struct syncache_head *
syncache_hashbucket(struct in_conninfo * inc)571 syncache_hashbucket(struct in_conninfo *inc)
572 {
573 uint32_t hash;
574
575 /*
576 * The hash is built on foreign port + local port + foreign address.
577 * We rely on the fact that struct in_conninfo starts with 16 bits
578 * of foreign port, then 16 bits of local port then followed by 128
579 * bits of foreign address. In case of IPv4 address, the first 3
580 * 32-bit words of the address always are zeroes.
581 */
582 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5,
583 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask;
584
585 return (&V_tcp_syncache.hashbase[hash]);
586 }
587
588 /*
589 * Find an entry in the syncache.
590 * Returns always with locked syncache_head plus a matching entry or NULL.
591 */
592 static struct syncache *
syncache_lookup(struct in_conninfo * inc,struct syncache_head ** schp)593 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
594 {
595 struct syncache *sc;
596 struct syncache_head *sch;
597
598 *schp = sch = syncache_hashbucket(inc);
599 SCH_LOCK(sch);
600
601 /* Circle through bucket row to find matching entry. */
602 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash)
603 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie,
604 sizeof(struct in_endpoints)) == 0)
605 break;
606
607 return (sc); /* Always returns with locked sch. */
608 }
609
610 /*
611 * This function is called when we get a RST for a
612 * non-existent connection, so that we can see if the
613 * connection is in the syn cache. If it is, zap it.
614 * If required send a challenge ACK.
615 */
616 void
syncache_chkrst(struct in_conninfo * inc,struct tcphdr * th,uint16_t port)617 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, uint16_t port)
618 {
619 struct syncache *sc;
620 struct syncache_head *sch;
621 char *s = NULL;
622
623 if (syncache_cookiesonly())
624 return;
625 sc = syncache_lookup(inc, &sch); /* returns locked sch */
626 SCH_LOCK_ASSERT(sch);
627
628 /*
629 * No corresponding connection was found in syncache.
630 * If syncookies are enabled and possibly exclusively
631 * used, or we are under memory pressure, a valid RST
632 * may not find a syncache entry. In that case we're
633 * done and no SYN|ACK retransmissions will happen.
634 * Otherwise the RST was misdirected or spoofed.
635 */
636 if (sc == NULL) {
637 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
638 log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
639 "syncache entry (possibly syncookie only), "
640 "segment ignored\n", s, __func__);
641 TCPSTAT_INC(tcps_badrst);
642 goto done;
643 }
644
645 /* The remote UDP encaps port does not match. */
646 if (sc->sc_port != port) {
647 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
648 log(LOG_DEBUG, "%s; %s: Spurious RST with matching "
649 "syncache entry but non-matching UDP encaps port, "
650 "segment ignored\n", s, __func__);
651 TCPSTAT_INC(tcps_badrst);
652 goto done;
653 }
654
655 /*
656 * If the RST bit is set, check the sequence number to see
657 * if this is a valid reset segment.
658 *
659 * RFC 793 page 37:
660 * In all states except SYN-SENT, all reset (RST) segments
661 * are validated by checking their SEQ-fields. A reset is
662 * valid if its sequence number is in the window.
663 *
664 * RFC 793 page 69:
665 * There are four cases for the acceptability test for an incoming
666 * segment:
667 *
668 * Segment Receive Test
669 * Length Window
670 * ------- ------- -------------------------------------------
671 * 0 0 SEG.SEQ = RCV.NXT
672 * 0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND
673 * >0 0 not acceptable
674 * >0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND
675 * or RCV.NXT =< SEG.SEQ+SEG.LEN-1 < RCV.NXT+RCV.WND
676 *
677 * Note that when receiving a SYN segment in the LISTEN state,
678 * IRS is set to SEG.SEQ and RCV.NXT is set to SEG.SEQ+1, as
679 * described in RFC 793, page 66.
680 */
681 if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) &&
682 SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) ||
683 (sc->sc_wnd == 0 && th->th_seq == sc->sc_irs + 1)) {
684 if (V_tcp_insecure_rst ||
685 th->th_seq == sc->sc_irs + 1) {
686 syncache_drop(sc, sch);
687 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
688 log(LOG_DEBUG,
689 "%s; %s: Our SYN|ACK was rejected, "
690 "connection attempt aborted by remote "
691 "endpoint\n",
692 s, __func__);
693 TCPSTAT_INC(tcps_sc_reset);
694 } else {
695 TCPSTAT_INC(tcps_badrst);
696 /* Send challenge ACK. */
697 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
698 log(LOG_DEBUG, "%s; %s: RST with invalid "
699 " SEQ %u != NXT %u (+WND %u), "
700 "sending challenge ACK\n",
701 s, __func__,
702 th->th_seq, sc->sc_irs + 1, sc->sc_wnd);
703 syncache_send_challenge_ack(sc);
704 }
705 } else {
706 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
707 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
708 "NXT %u (+WND %u), segment ignored\n",
709 s, __func__,
710 th->th_seq, sc->sc_irs + 1, sc->sc_wnd);
711 TCPSTAT_INC(tcps_badrst);
712 }
713
714 done:
715 if (s != NULL)
716 free(s, M_TCPLOG);
717 SCH_UNLOCK(sch);
718 }
719
720 void
syncache_unreach(struct in_conninfo * inc,tcp_seq th_seq,uint16_t port)721 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq, uint16_t port)
722 {
723 struct syncache *sc;
724 struct syncache_head *sch;
725
726 if (syncache_cookiesonly())
727 return;
728 sc = syncache_lookup(inc, &sch); /* returns locked sch */
729 SCH_LOCK_ASSERT(sch);
730 if (sc == NULL)
731 goto done;
732
733 /* If the port != sc_port, then it's a bogus ICMP msg */
734 if (port != sc->sc_port)
735 goto done;
736
737 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
738 if (ntohl(th_seq) != sc->sc_iss)
739 goto done;
740
741 /*
742 * If we've retransmitted 3 times and this is our second error,
743 * we remove the entry. Otherwise, we allow it to continue on.
744 * This prevents us from incorrectly nuking an entry during a
745 * spurious network outage.
746 *
747 * See tcp_notify().
748 */
749 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
750 sc->sc_flags |= SCF_UNREACH;
751 goto done;
752 }
753 syncache_drop(sc, sch);
754 TCPSTAT_INC(tcps_sc_unreach);
755 done:
756 SCH_UNLOCK(sch);
757 }
758
759 /*
760 * Build a new TCP socket structure from a syncache entry.
761 *
762 * On success return the newly created socket with its underlying inp locked.
763 */
764 static struct socket *
syncache_socket(struct syncache * sc,struct socket * lso,struct mbuf * m)765 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
766 {
767 struct inpcb *inp = NULL;
768 struct socket *so;
769 struct tcpcb *tp;
770 int error;
771 char *s;
772
773 NET_EPOCH_ASSERT();
774
775 /*
776 * Ok, create the full blown connection, and set things up
777 * as they would have been set up if we had created the
778 * connection when the SYN arrived.
779 */
780 if ((so = solisten_clone(lso)) == NULL)
781 goto allocfail;
782 #ifdef MAC
783 mac_socketpeer_set_from_mbuf(m, so);
784 #endif
785 error = in_pcballoc(so, &V_tcbinfo);
786 if (error) {
787 sodealloc(so);
788 goto allocfail;
789 }
790 inp = sotoinpcb(so);
791 if ((tp = tcp_newtcpcb(inp, sototcpcb(lso))) == NULL) {
792 in_pcbfree(inp);
793 sodealloc(so);
794 goto allocfail;
795 }
796 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
797 #ifdef INET6
798 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
799 inp->inp_vflag &= ~INP_IPV4;
800 inp->inp_vflag |= INP_IPV6;
801 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
802 } else {
803 inp->inp_vflag &= ~INP_IPV6;
804 inp->inp_vflag |= INP_IPV4;
805 #endif
806 inp->inp_ip_ttl = sc->sc_ip_ttl;
807 inp->inp_ip_tos = sc->sc_ip_tos;
808 inp->inp_laddr = sc->sc_inc.inc_laddr;
809 #ifdef INET6
810 }
811 #endif
812 inp->inp_lport = sc->sc_inc.inc_lport;
813 #ifdef INET6
814 if (inp->inp_vflag & INP_IPV6PROTO) {
815 struct inpcb *oinp = sotoinpcb(lso);
816
817 /*
818 * Inherit socket options from the listening socket.
819 * Note that in6p_inputopts are not (and should not be)
820 * copied, since it stores previously received options and is
821 * used to detect if each new option is different than the
822 * previous one and hence should be passed to a user.
823 * If we copied in6p_inputopts, a user would not be able to
824 * receive options just after calling the accept system call.
825 */
826 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
827 if (oinp->in6p_outputopts)
828 inp->in6p_outputopts =
829 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
830 inp->in6p_hops = oinp->in6p_hops;
831 }
832
833 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
834 struct sockaddr_in6 sin6;
835
836 sin6.sin6_family = AF_INET6;
837 sin6.sin6_len = sizeof(sin6);
838 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
839 sin6.sin6_port = sc->sc_inc.inc_fport;
840 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
841 INP_HASH_WLOCK(&V_tcbinfo);
842 error = in6_pcbconnect(inp, &sin6, thread0.td_ucred, false);
843 INP_HASH_WUNLOCK(&V_tcbinfo);
844 if (error != 0)
845 goto abort;
846 /* Override flowlabel from in6_pcbconnect. */
847 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
848 inp->inp_flow |= sc->sc_flowlabel;
849 }
850 #endif /* INET6 */
851 #if defined(INET) && defined(INET6)
852 else
853 #endif
854 #ifdef INET
855 {
856 struct sockaddr_in sin;
857
858 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
859
860 if (inp->inp_options == NULL) {
861 inp->inp_options = sc->sc_ipopts;
862 sc->sc_ipopts = NULL;
863 }
864
865 sin.sin_family = AF_INET;
866 sin.sin_len = sizeof(sin);
867 sin.sin_addr = sc->sc_inc.inc_faddr;
868 sin.sin_port = sc->sc_inc.inc_fport;
869 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
870 INP_HASH_WLOCK(&V_tcbinfo);
871 error = in_pcbconnect(inp, &sin, thread0.td_ucred);
872 INP_HASH_WUNLOCK(&V_tcbinfo);
873 if (error != 0)
874 goto abort;
875 }
876 #endif /* INET */
877 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
878 /* Copy old policy into new socket's. */
879 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0)
880 printf("syncache_socket: could not copy policy\n");
881 #endif
882 if (sc->sc_flowtype != M_HASHTYPE_NONE) {
883 inp->inp_flowid = sc->sc_flowid;
884 inp->inp_flowtype = sc->sc_flowtype;
885 #ifdef RSS
886 } else {
887 /* assign flowid by software RSS hash */
888 #ifdef INET6
889 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
890 rss_proto_software_hash_v6(&inp->in6p_faddr,
891 &inp->in6p_laddr,
892 inp->inp_fport,
893 inp->inp_lport,
894 IPPROTO_TCP,
895 &inp->inp_flowid,
896 &inp->inp_flowtype);
897 } else
898 #endif /* INET6 */
899 {
900 rss_proto_software_hash_v4(inp->inp_faddr,
901 inp->inp_laddr,
902 inp->inp_fport,
903 inp->inp_lport,
904 IPPROTO_TCP,
905 &inp->inp_flowid,
906 &inp->inp_flowtype);
907 }
908 #endif /* RSS */
909 }
910 #ifdef NUMA
911 inp->inp_numa_domain = sc->sc_numa_domain;
912 #endif
913
914 tp->t_state = TCPS_SYN_RECEIVED;
915 tp->iss = sc->sc_iss;
916 tp->irs = sc->sc_irs;
917 tp->t_port = sc->sc_port;
918 tcp_rcvseqinit(tp);
919 tcp_sendseqinit(tp);
920 tp->snd_wl1 = sc->sc_irs;
921 tp->snd_max = tp->iss + 1;
922 tp->snd_nxt = tp->iss + 1;
923 tp->rcv_up = sc->sc_irs + 1;
924 tp->rcv_wnd = sc->sc_wnd;
925 tp->rcv_adv += tp->rcv_wnd;
926 tp->last_ack_sent = tp->rcv_nxt;
927
928 tp->t_flags = sototcpcb(lso)->t_flags &
929 (TF_LRD|TF_NOPUSH|TF_NODELAY);
930 if (sc->sc_flags & SCF_NOOPT)
931 tp->t_flags |= TF_NOOPT;
932 else {
933 if (sc->sc_flags & SCF_WINSCALE) {
934 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
935 tp->snd_scale = sc->sc_requested_s_scale;
936 tp->request_r_scale = sc->sc_requested_r_scale;
937 }
938 if (sc->sc_flags & SCF_TIMESTAMP) {
939 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
940 tp->ts_recent = sc->sc_tsreflect;
941 tp->ts_recent_age = tcp_ts_getticks();
942 tp->ts_offset = sc->sc_tsoff;
943 }
944 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
945 if (sc->sc_flags & SCF_SIGNATURE)
946 tp->t_flags |= TF_SIGNATURE;
947 #endif
948 if (sc->sc_flags & SCF_SACK)
949 tp->t_flags |= TF_SACK_PERMIT;
950 }
951
952 tcp_ecn_syncache_socket(tp, sc);
953
954 /*
955 * Set up MSS and get cached values from tcp_hostcache.
956 * This might overwrite some of the defaults we just set.
957 */
958 tcp_mss(tp, sc->sc_peer_mss);
959
960 /*
961 * If the SYN,ACK was retransmitted, indicate that CWND to be
962 * limited to one segment in cc_conn_init().
963 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
964 */
965 if (sc->sc_rxmits > 1)
966 tp->snd_cwnd = 1;
967
968 /* Copy over the challenge ACK state. */
969 tp->t_challenge_ack_end = sc->sc_challenge_ack_end;
970 tp->t_challenge_ack_cnt = sc->sc_challenge_ack_cnt;
971
972 #ifdef TCP_OFFLOAD
973 /*
974 * Allow a TOE driver to install its hooks. Note that we hold the
975 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a
976 * new connection before the TOE driver has done its thing.
977 */
978 if (ADDED_BY_TOE(sc)) {
979 struct toedev *tod = sc->sc_tod;
980
981 tod->tod_offload_socket(tod, sc->sc_todctx, so);
982 }
983 #endif
984 #ifdef TCP_BLACKBOX
985 /*
986 * Inherit the log state from the listening socket, if
987 * - the log state of the listening socket is not off and
988 * - the listening socket was not auto selected from all sessions and
989 * - a log id is not set on the listening socket.
990 * This avoids inheriting a log state which was automatically set.
991 */
992 if ((tcp_get_bblog_state(sototcpcb(lso)) != TCP_LOG_STATE_OFF) &&
993 ((sototcpcb(lso)->t_flags2 & TF2_LOG_AUTO) == 0) &&
994 (sototcpcb(lso)->t_lib == NULL)) {
995 tcp_log_state_change(tp, tcp_get_bblog_state(sototcpcb(lso)));
996 }
997 #endif
998 /*
999 * Copy and activate timers.
1000 */
1001 tp->t_maxunacktime = sototcpcb(lso)->t_maxunacktime;
1002 tp->t_keepinit = sototcpcb(lso)->t_keepinit;
1003 tp->t_keepidle = sototcpcb(lso)->t_keepidle;
1004 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl;
1005 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt;
1006 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp));
1007
1008 TCPSTAT_INC(tcps_accepts);
1009 TCP_PROBE6(state__change, NULL, tp, NULL, tp, NULL, TCPS_LISTEN);
1010
1011 if (!solisten_enqueue(so, SS_ISCONNECTED))
1012 tp->t_flags |= TF_SONOTCONN;
1013 /* Can we inherit anything from the listener? */
1014 if (tp->t_fb->tfb_inherit != NULL) {
1015 (*tp->t_fb->tfb_inherit)(tp, sotoinpcb(lso));
1016 }
1017 return (so);
1018
1019 allocfail:
1020 /*
1021 * Drop the connection; we will either send a RST or have the peer
1022 * retransmit its SYN again after its RTO and try again.
1023 */
1024 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
1025 log(LOG_DEBUG, "%s; %s: Socket create failed "
1026 "due to limits or memory shortage\n",
1027 s, __func__);
1028 free(s, M_TCPLOG);
1029 }
1030 TCPSTAT_INC(tcps_listendrop);
1031 return (NULL);
1032
1033 abort:
1034 tcp_discardcb(tp);
1035 in_pcbfree(inp);
1036 sodealloc(so);
1037 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
1038 log(LOG_DEBUG, "%s; %s: in%s_pcbconnect failed with error %i\n",
1039 s, __func__, (sc->sc_inc.inc_flags & INC_ISIPV6) ? "6" : "",
1040 error);
1041 free(s, M_TCPLOG);
1042 }
1043 TCPSTAT_INC(tcps_listendrop);
1044 return (NULL);
1045 }
1046
1047 /*
1048 * This function gets called when we receive an ACK for a
1049 * socket in the LISTEN state. We look up the connection
1050 * in the syncache, and if its there, we pull it out of
1051 * the cache and turn it into a full-blown connection in
1052 * the SYN-RECEIVED state.
1053 *
1054 * On syncache_socket() success the newly created socket
1055 * has its underlying inp locked.
1056 *
1057 * *lsop is updated, if and only if 1 is returned.
1058 */
1059 int
syncache_expand(struct in_conninfo * inc,struct tcpopt * to,struct tcphdr * th,struct socket ** lsop,struct mbuf * m,uint16_t port)1060 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1061 struct socket **lsop, struct mbuf *m, uint16_t port)
1062 {
1063 struct syncache *sc;
1064 struct syncache_head *sch;
1065 struct syncache scs;
1066 char *s;
1067 bool locked;
1068
1069 NET_EPOCH_ASSERT();
1070 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
1071 ("%s: can handle only ACK", __func__));
1072
1073 if (syncache_cookiesonly()) {
1074 sc = NULL;
1075 sch = syncache_hashbucket(inc);
1076 locked = false;
1077 } else {
1078 sc = syncache_lookup(inc, &sch); /* returns locked sch */
1079 locked = true;
1080 SCH_LOCK_ASSERT(sch);
1081 }
1082
1083 #ifdef INVARIANTS
1084 /*
1085 * Test code for syncookies comparing the syncache stored
1086 * values with the reconstructed values from the cookie.
1087 */
1088 if (sc != NULL)
1089 syncookie_cmp(inc, sch, sc, th, to, *lsop, port);
1090 #endif
1091
1092 if (sc == NULL) {
1093 if (locked) {
1094 /*
1095 * The syncache is currently in use (neither disabled,
1096 * nor paused), but no entry was found.
1097 */
1098 if (!V_tcp_syncookies) {
1099 /*
1100 * Since no syncookies are used in case of
1101 * a bucket overflow, don't even check for
1102 * a valid syncookie.
1103 */
1104 SCH_UNLOCK(sch);
1105 TCPSTAT_INC(tcps_sc_spurcookie);
1106 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1107 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
1108 "segment rejected "
1109 "(syncookies disabled)\n",
1110 s, __func__);
1111 free(s, M_TCPLOG);
1112 }
1113 return (0);
1114 }
1115 if (sch->sch_last_overflow <
1116 time_uptime - SYNCOOKIE_LIFETIME) {
1117 /*
1118 * Since the bucket did not overflow recently,
1119 * don't even check for a valid syncookie.
1120 */
1121 SCH_UNLOCK(sch);
1122 TCPSTAT_INC(tcps_sc_spurcookie);
1123 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1124 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
1125 "segment rejected "
1126 "(no syncache entry)\n",
1127 s, __func__);
1128 free(s, M_TCPLOG);
1129 }
1130 return (0);
1131 }
1132 SCH_UNLOCK(sch);
1133 }
1134 bzero(&scs, sizeof(scs));
1135 /*
1136 * Now check, if the syncookie is valid. If it is, create an on
1137 * stack syncache entry.
1138 */
1139 if (syncookie_expand(inc, sch, &scs, th, to, *lsop, port)) {
1140 sc = &scs;
1141 TCPSTAT_INC(tcps_sc_recvcookie);
1142 } else {
1143 TCPSTAT_INC(tcps_sc_failcookie);
1144 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1145 log(LOG_DEBUG, "%s; %s: Segment failed "
1146 "SYNCOOKIE authentication, segment rejected "
1147 "(probably spoofed)\n", s, __func__);
1148 free(s, M_TCPLOG);
1149 }
1150 return (0);
1151 }
1152 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1153 /* If received ACK has MD5 signature, check it. */
1154 if ((to->to_flags & TOF_SIGNATURE) != 0 &&
1155 (!TCPMD5_ENABLED() ||
1156 TCPMD5_INPUT(m, th, to->to_signature) != 0)) {
1157 /* Drop the ACK. */
1158 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1159 log(LOG_DEBUG, "%s; %s: Segment rejected, "
1160 "MD5 signature doesn't match.\n",
1161 s, __func__);
1162 free(s, M_TCPLOG);
1163 }
1164 TCPSTAT_INC(tcps_sig_err_sigopt);
1165 return (-1); /* Do not send RST */
1166 }
1167 #endif /* TCP_SIGNATURE */
1168 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) {
1169 sc->sc_flowid = m->m_pkthdr.flowid;
1170 sc->sc_flowtype = M_HASHTYPE_GET(m);
1171 }
1172 #ifdef NUMA
1173 sc->sc_numa_domain = m ? m->m_pkthdr.numa_domain : M_NODOM;
1174 #endif
1175 TCPSTATES_INC(TCPS_SYN_RECEIVED);
1176 } else {
1177 if (sc->sc_port != port) {
1178 SCH_UNLOCK(sch);
1179 return (0);
1180 }
1181 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1182 /*
1183 * If listening socket requested TCP digests, check that
1184 * received ACK has signature and it is correct.
1185 * If not, drop the ACK and leave sc entry in the cache,
1186 * because SYN was received with correct signature.
1187 */
1188 if (sc->sc_flags & SCF_SIGNATURE) {
1189 if ((to->to_flags & TOF_SIGNATURE) == 0) {
1190 /* No signature */
1191 TCPSTAT_INC(tcps_sig_err_nosigopt);
1192 SCH_UNLOCK(sch);
1193 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1194 log(LOG_DEBUG, "%s; %s: Segment "
1195 "rejected, MD5 signature wasn't "
1196 "provided.\n", s, __func__);
1197 free(s, M_TCPLOG);
1198 }
1199 return (-1); /* Do not send RST */
1200 }
1201 if (!TCPMD5_ENABLED() ||
1202 TCPMD5_INPUT(m, th, to->to_signature) != 0) {
1203 /* Doesn't match or no SA */
1204 SCH_UNLOCK(sch);
1205 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1206 log(LOG_DEBUG, "%s; %s: Segment "
1207 "rejected, MD5 signature doesn't "
1208 "match.\n", s, __func__);
1209 free(s, M_TCPLOG);
1210 }
1211 return (-1); /* Do not send RST */
1212 }
1213 }
1214 #endif /* TCP_SIGNATURE */
1215
1216 /*
1217 * RFC 7323 PAWS: If we have a timestamp on this segment and
1218 * it's less than ts_recent, drop it.
1219 * XXXMT: RFC 7323 also requires to send an ACK.
1220 * In tcp_input.c this is only done for TCP segments
1221 * with user data, so be consistent here and just drop
1222 * the segment.
1223 */
1224 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS &&
1225 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) {
1226 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1227 log(LOG_DEBUG,
1228 "%s; %s: SEG.TSval %u < TS.Recent %u, "
1229 "segment dropped\n", s, __func__,
1230 to->to_tsval, sc->sc_tsreflect);
1231 }
1232 SCH_UNLOCK(sch);
1233 free(s, M_TCPLOG);
1234 return (-1); /* Do not send RST */
1235 }
1236
1237 /*
1238 * If timestamps were not negotiated during SYN/ACK and a
1239 * segment with a timestamp is received, ignore the
1240 * timestamp and process the packet normally.
1241 * See section 3.2 of RFC 7323.
1242 */
1243 if (!(sc->sc_flags & SCF_TIMESTAMP) &&
1244 (to->to_flags & TOF_TS)) {
1245 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1246 log(LOG_DEBUG, "%s; %s: Timestamp not "
1247 "expected, segment processed normally\n",
1248 s, __func__);
1249 free(s, M_TCPLOG);
1250 }
1251 }
1252
1253 /*
1254 * If timestamps were negotiated during SYN/ACK and a
1255 * segment without a timestamp is received, silently drop
1256 * the segment, unless the missing timestamps are tolerated.
1257 * See section 3.2 of RFC 7323.
1258 */
1259 if ((sc->sc_flags & SCF_TIMESTAMP) &&
1260 !(to->to_flags & TOF_TS)) {
1261 if (V_tcp_tolerate_missing_ts) {
1262 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1263 log(LOG_DEBUG,
1264 "%s; %s: Timestamp missing, "
1265 "segment processed normally\n",
1266 s, __func__);
1267 free(s, M_TCPLOG);
1268 }
1269 } else {
1270 SCH_UNLOCK(sch);
1271 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1272 log(LOG_DEBUG,
1273 "%s; %s: Timestamp missing, "
1274 "segment silently dropped\n",
1275 s, __func__);
1276 free(s, M_TCPLOG);
1277 }
1278 return (-1); /* Do not send RST */
1279 }
1280 }
1281
1282 /*
1283 * SEG.SEQ validation:
1284 * The SEG.SEQ must be in the window starting at our
1285 * initial receive sequence number + 1.
1286 */
1287 if (SEQ_LEQ(th->th_seq, sc->sc_irs) ||
1288 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
1289 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1290 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, "
1291 "sending challenge ACK\n",
1292 s, __func__, th->th_seq, sc->sc_irs + 1);
1293 syncache_send_challenge_ack(sc);
1294 SCH_UNLOCK(sch);
1295 free(s, M_TCPLOG);
1296 return (-1); /* Do not send RST */
1297 }
1298
1299 /*
1300 * SEG.ACK validation:
1301 * SEG.ACK must match our initial send sequence number + 1.
1302 */
1303 if (th->th_ack != sc->sc_iss + 1) {
1304 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1305 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, "
1306 "segment rejected\n",
1307 s, __func__, th->th_ack, sc->sc_iss + 1);
1308 SCH_UNLOCK(sch);
1309 free(s, M_TCPLOG);
1310 return (0); /* Do send RST, do not free sc. */
1311 }
1312
1313 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
1314 sch->sch_length--;
1315 #ifdef TCP_OFFLOAD
1316 if (ADDED_BY_TOE(sc)) {
1317 struct toedev *tod = sc->sc_tod;
1318
1319 tod->tod_syncache_removed(tod, sc->sc_todctx);
1320 }
1321 #endif
1322 SCH_UNLOCK(sch);
1323 }
1324
1325 *lsop = syncache_socket(sc, *lsop, m);
1326
1327 if (__predict_false(*lsop == NULL)) {
1328 TCPSTAT_INC(tcps_sc_aborted);
1329 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
1330 } else if (sc != &scs)
1331 TCPSTAT_INC(tcps_sc_completed);
1332
1333 if (sc != &scs)
1334 syncache_free(sc);
1335 return (1);
1336 }
1337
1338 static struct socket *
syncache_tfo_expand(struct syncache * sc,struct socket * lso,struct mbuf * m,uint64_t response_cookie)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 *
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)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 ucred *cred;
1398 struct syncache_head *sch;
1399 struct mbuf *ipopts = NULL;
1400 u_int ltflags;
1401 int win, ip_ttl, ip_tos;
1402 char *s;
1403 #ifdef INET6
1404 int autoflowlabel = 0;
1405 #endif
1406 #ifdef MAC
1407 struct label *maclabel = NULL;
1408 #endif
1409 struct syncache scs;
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 && (tp->t_flags & TF_FASTOPEN) &&
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, 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 } else {
1596 /*
1597 * Most likely we are memory constrained, so free
1598 * resources.
1599 */
1600 syncache_drop(sc, sch);
1601 TCPSTAT_INC(tcps_sc_dropped);
1602 }
1603 SCH_UNLOCK(sch);
1604 goto donenoprobe;
1605 }
1606
1607 KASSERT(sc == NULL, ("sc(%p) != NULL", sc));
1608 /*
1609 * Skip allocating a syncache entry if we are just going to discard
1610 * it later.
1611 */
1612 if (!locked || tfo_cookie_valid) {
1613 bzero(&scs, sizeof(scs));
1614 sc = &scs;
1615 } else {
1616 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1617 if (sc == NULL) {
1618 /*
1619 * The zone allocator couldn't provide more entries.
1620 * Treat this as if the cache was full; drop the oldest
1621 * entry and insert the new one.
1622 */
1623 TCPSTAT_INC(tcps_sc_zonefail);
1624 sc = TAILQ_LAST(&sch->sch_bucket, sch_head);
1625 if (sc != NULL) {
1626 sch->sch_last_overflow = time_uptime;
1627 syncache_drop(sc, sch);
1628 syncache_pause(inc);
1629 }
1630 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1631 if (sc == NULL) {
1632 if (V_tcp_syncookies) {
1633 bzero(&scs, sizeof(scs));
1634 sc = &scs;
1635 } else {
1636 KASSERT(locked,
1637 ("%s: bucket unexpectedly unlocked",
1638 __func__));
1639 SCH_UNLOCK(sch);
1640 goto done;
1641 }
1642 }
1643 }
1644 }
1645
1646 KASSERT(sc != NULL, ("sc == NULL"));
1647 if (!tfo_cookie_valid && tfo_response_cookie_valid)
1648 sc->sc_tfo_cookie = &tfo_response_cookie;
1649
1650 /*
1651 * Fill in the syncache values.
1652 */
1653 #ifdef MAC
1654 sc->sc_label = maclabel;
1655 #endif
1656 /*
1657 * sc_cred is only used in syncache_pcblist() to list TCP endpoints in
1658 * TCPS_SYN_RECEIVED state when V_tcp_syncache.see_other is false.
1659 * Therefore, store the credentials only when needed:
1660 * - sc is allocated from the zone and not using the on stack instance.
1661 * - the sysctl variable net.inet.tcp.syncache.see_other is false.
1662 * The reference count is decremented when a zone allocated sc is
1663 * freed in syncache_free().
1664 */
1665 if (sc != &scs && !V_tcp_syncache.see_other) {
1666 sc->sc_cred = cred;
1667 cred = NULL;
1668 } else
1669 sc->sc_cred = NULL;
1670 sc->sc_port = port;
1671 sc->sc_ipopts = ipopts;
1672 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1673 sc->sc_ip_tos = ip_tos;
1674 sc->sc_ip_ttl = ip_ttl;
1675 #ifdef TCP_OFFLOAD
1676 sc->sc_tod = tod;
1677 sc->sc_todctx = todctx;
1678 #endif
1679 sc->sc_irs = th->th_seq;
1680 sc->sc_flags = 0;
1681 sc->sc_flowlabel = 0;
1682
1683 /*
1684 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
1685 * win was derived from socket earlier in the function.
1686 */
1687 win = imax(win, 0);
1688 win = imin(win, TCP_MAXWIN);
1689 sc->sc_wnd = win;
1690
1691 if (V_tcp_do_rfc1323 &&
1692 !(ltflags & TF_NOOPT)) {
1693 /*
1694 * A timestamp received in a SYN makes
1695 * it ok to send timestamp requests and replies.
1696 */
1697 if ((to->to_flags & TOF_TS) && (V_tcp_do_rfc1323 != 2)) {
1698 sc->sc_tsreflect = to->to_tsval;
1699 sc->sc_flags |= SCF_TIMESTAMP;
1700 sc->sc_tsoff = tcp_new_ts_offset(inc);
1701 }
1702 if ((to->to_flags & TOF_SCALE) && (V_tcp_do_rfc1323 != 3)) {
1703 u_int wscale = 0;
1704
1705 /*
1706 * Pick the smallest possible scaling factor that
1707 * will still allow us to scale up to sb_max, aka
1708 * kern.ipc.maxsockbuf.
1709 *
1710 * We do this because there are broken firewalls that
1711 * will corrupt the window scale option, leading to
1712 * the other endpoint believing that our advertised
1713 * window is unscaled. At scale factors larger than
1714 * 5 the unscaled window will drop below 1500 bytes,
1715 * leading to serious problems when traversing these
1716 * broken firewalls.
1717 *
1718 * With the default maxsockbuf of 256K, a scale factor
1719 * of 3 will be chosen by this algorithm. Those who
1720 * choose a larger maxsockbuf should watch out
1721 * for the compatibility problems mentioned above.
1722 *
1723 * RFC1323: The Window field in a SYN (i.e., a <SYN>
1724 * or <SYN,ACK>) segment itself is never scaled.
1725 */
1726 while (wscale < TCP_MAX_WINSHIFT &&
1727 (TCP_MAXWIN << wscale) < sb_max)
1728 wscale++;
1729 sc->sc_requested_r_scale = wscale;
1730 sc->sc_requested_s_scale = to->to_wscale;
1731 sc->sc_flags |= SCF_WINSCALE;
1732 }
1733 }
1734 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1735 /*
1736 * If incoming packet has an MD5 signature, flag this in the
1737 * syncache so that syncache_respond() will do the right thing
1738 * with the SYN+ACK.
1739 */
1740 if (to->to_flags & TOF_SIGNATURE)
1741 sc->sc_flags |= SCF_SIGNATURE;
1742 #endif /* TCP_SIGNATURE */
1743 if (to->to_flags & TOF_SACKPERM)
1744 sc->sc_flags |= SCF_SACK;
1745 if (to->to_flags & TOF_MSS)
1746 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */
1747 if (ltflags & TF_NOOPT)
1748 sc->sc_flags |= SCF_NOOPT;
1749 /* ECN Handshake */
1750 if (V_tcp_do_ecn && (tp->t_flags2 & TF2_CANNOT_DO_ECN) == 0)
1751 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos);
1752
1753 if (V_tcp_syncookies || V_tcp_syncookiesonly)
1754 sc->sc_iss = syncookie_generate(sch, sc);
1755 else
1756 sc->sc_iss = arc4random();
1757 #ifdef INET6
1758 if (autoflowlabel) {
1759 if (V_tcp_syncookies || V_tcp_syncookiesonly)
1760 sc->sc_flowlabel = sc->sc_iss;
1761 else
1762 sc->sc_flowlabel = ip6_randomflowlabel();
1763 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK;
1764 }
1765 #endif
1766 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) {
1767 sc->sc_flowid = m->m_pkthdr.flowid;
1768 sc->sc_flowtype = M_HASHTYPE_GET(m);
1769 }
1770 #ifdef NUMA
1771 sc->sc_numa_domain = m ? m->m_pkthdr.numa_domain : M_NODOM;
1772 #endif
1773 if (locked)
1774 SCH_UNLOCK(sch);
1775
1776 if (tfo_cookie_valid) {
1777 rv = syncache_tfo_expand(sc, so, m, tfo_response_cookie);
1778 /* INP_RUNLOCK(inp) will be performed by the caller */
1779 goto tfo_expanded;
1780 }
1781
1782 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1783 /*
1784 * Do a standard 3-way handshake.
1785 */
1786 if (syncache_respond(sc, TH_SYN|TH_ACK) == 0) {
1787 if (sc != &scs)
1788 syncache_insert(sc, sch); /* locks and unlocks sch */
1789 TCPSTAT_INC(tcps_sndacks);
1790 TCPSTAT_INC(tcps_sndtotal);
1791 } else {
1792 /*
1793 * Most likely we are memory constrained, so free resources.
1794 */
1795 if (sc != &scs)
1796 syncache_free(sc);
1797 TCPSTAT_INC(tcps_sc_dropped);
1798 }
1799 goto donenoprobe;
1800
1801 done:
1802 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1803 donenoprobe:
1804 if (m)
1805 m_freem(m);
1806 /*
1807 * If tfo_pending is not NULL here, then a TFO SYN that did not
1808 * result in a new socket was processed and the associated pending
1809 * counter has not yet been decremented. All such TFO processing paths
1810 * transit this point.
1811 */
1812 if (tfo_pending != NULL)
1813 tcp_fastopen_decrement_counter(tfo_pending);
1814
1815 tfo_expanded:
1816 if (cred != NULL)
1817 crfree(cred);
1818 if (sc == NULL || sc == &scs) {
1819 #ifdef MAC
1820 mac_syncache_destroy(&maclabel);
1821 #endif
1822 if (ipopts)
1823 (void)m_free(ipopts);
1824 }
1825 return (rv);
1826 }
1827
1828 /*
1829 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment
1830 * or upon 3WHS ACK timeout.
1831 */
1832 static int
syncache_respond(struct syncache * sc,int flags)1833 syncache_respond(struct syncache *sc, int flags)
1834 {
1835 struct ip *ip = NULL;
1836 struct mbuf *m;
1837 struct tcphdr *th = NULL;
1838 struct udphdr *udp = NULL;
1839 int optlen, error = 0; /* Make compiler happy */
1840 u_int16_t hlen, tlen, mssopt, ulen;
1841 struct tcpopt to;
1842 #ifdef INET6
1843 struct ip6_hdr *ip6 = NULL;
1844 #endif
1845
1846 NET_EPOCH_ASSERT();
1847
1848 hlen =
1849 #ifdef INET6
1850 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
1851 #endif
1852 sizeof(struct ip);
1853 tlen = hlen + sizeof(struct tcphdr);
1854 if (sc->sc_port) {
1855 tlen += sizeof(struct udphdr);
1856 }
1857 /* Determine MSS we advertize to other end of connection. */
1858 mssopt = tcp_mssopt(&sc->sc_inc);
1859 if (sc->sc_port)
1860 mssopt -= V_tcp_udp_tunneling_overhead;
1861 mssopt = max(mssopt, V_tcp_minmss);
1862
1863 /* XXX: Assume that the entire packet will fit in a header mbuf. */
1864 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
1865 ("syncache: mbuf too small: hlen %u, sc_port %u, max_linkhdr %d + "
1866 "tlen %d + TCP_MAXOLEN %ju <= MHLEN %d", hlen, sc->sc_port,
1867 max_linkhdr, tlen, (uintmax_t)TCP_MAXOLEN, MHLEN));
1868
1869 /* Create the IP+TCP header from scratch. */
1870 m = m_gethdr(M_NOWAIT, MT_DATA);
1871 if (m == NULL)
1872 return (ENOBUFS);
1873 #ifdef MAC
1874 mac_syncache_create_mbuf(sc->sc_label, m);
1875 #endif
1876 m->m_data += max_linkhdr;
1877 m->m_len = tlen;
1878 m->m_pkthdr.len = tlen;
1879 m->m_pkthdr.rcvif = NULL;
1880
1881 #ifdef INET6
1882 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1883 ip6 = mtod(m, struct ip6_hdr *);
1884 ip6->ip6_vfc = IPV6_VERSION;
1885 ip6->ip6_src = sc->sc_inc.inc6_laddr;
1886 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
1887 ip6->ip6_plen = htons(tlen - hlen);
1888 /* ip6_hlim is set after checksum */
1889 /* Zero out traffic class and flow label. */
1890 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK;
1891 ip6->ip6_flow |= sc->sc_flowlabel;
1892 if (sc->sc_port != 0) {
1893 ip6->ip6_nxt = IPPROTO_UDP;
1894 udp = (struct udphdr *)(ip6 + 1);
1895 udp->uh_sport = htons(V_tcp_udp_tunneling_port);
1896 udp->uh_dport = sc->sc_port;
1897 ulen = (tlen - sizeof(struct ip6_hdr));
1898 th = (struct tcphdr *)(udp + 1);
1899 } else {
1900 ip6->ip6_nxt = IPPROTO_TCP;
1901 th = (struct tcphdr *)(ip6 + 1);
1902 }
1903 ip6->ip6_flow |= htonl(sc->sc_ip_tos << IPV6_FLOWLABEL_LEN);
1904 }
1905 #endif
1906 #if defined(INET6) && defined(INET)
1907 else
1908 #endif
1909 #ifdef INET
1910 {
1911 ip = mtod(m, struct ip *);
1912 ip->ip_v = IPVERSION;
1913 ip->ip_hl = sizeof(struct ip) >> 2;
1914 ip->ip_len = htons(tlen);
1915 ip->ip_id = 0;
1916 ip->ip_off = 0;
1917 ip->ip_sum = 0;
1918 ip->ip_src = sc->sc_inc.inc_laddr;
1919 ip->ip_dst = sc->sc_inc.inc_faddr;
1920 ip->ip_ttl = sc->sc_ip_ttl;
1921 ip->ip_tos = sc->sc_ip_tos;
1922
1923 /*
1924 * See if we should do MTU discovery. Route lookups are
1925 * expensive, so we will only unset the DF bit if:
1926 *
1927 * 1) path_mtu_discovery is disabled
1928 * 2) the SCF_UNREACH flag has been set
1929 */
1930 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
1931 ip->ip_off |= htons(IP_DF);
1932 if (sc->sc_port == 0) {
1933 ip->ip_p = IPPROTO_TCP;
1934 th = (struct tcphdr *)(ip + 1);
1935 } else {
1936 ip->ip_p = IPPROTO_UDP;
1937 udp = (struct udphdr *)(ip + 1);
1938 udp->uh_sport = htons(V_tcp_udp_tunneling_port);
1939 udp->uh_dport = sc->sc_port;
1940 ulen = (tlen - sizeof(struct ip));
1941 th = (struct tcphdr *)(udp + 1);
1942 }
1943 }
1944 #endif /* INET */
1945 th->th_sport = sc->sc_inc.inc_lport;
1946 th->th_dport = sc->sc_inc.inc_fport;
1947
1948 if (flags & TH_SYN)
1949 th->th_seq = htonl(sc->sc_iss);
1950 else
1951 th->th_seq = htonl(sc->sc_iss + 1);
1952 th->th_ack = htonl(sc->sc_irs + 1);
1953 th->th_off = sizeof(struct tcphdr) >> 2;
1954 th->th_win = htons(sc->sc_wnd);
1955 th->th_urp = 0;
1956
1957 flags = tcp_ecn_syncache_respond(flags, sc);
1958 tcp_set_flags(th, flags);
1959
1960 /* Tack on the TCP options. */
1961 if ((sc->sc_flags & SCF_NOOPT) == 0) {
1962 to.to_flags = 0;
1963
1964 if (flags & TH_SYN) {
1965 to.to_mss = mssopt;
1966 to.to_flags = TOF_MSS;
1967 if (sc->sc_flags & SCF_WINSCALE) {
1968 to.to_wscale = sc->sc_requested_r_scale;
1969 to.to_flags |= TOF_SCALE;
1970 }
1971 if (sc->sc_flags & SCF_SACK)
1972 to.to_flags |= TOF_SACKPERM;
1973 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1974 if (sc->sc_flags & SCF_SIGNATURE)
1975 to.to_flags |= TOF_SIGNATURE;
1976 #endif
1977 if (sc->sc_tfo_cookie) {
1978 to.to_flags |= TOF_FASTOPEN;
1979 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
1980 to.to_tfo_cookie = sc->sc_tfo_cookie;
1981 /* don't send cookie again when retransmitting response */
1982 sc->sc_tfo_cookie = NULL;
1983 }
1984 }
1985 if (sc->sc_flags & SCF_TIMESTAMP) {
1986 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks();
1987 to.to_tsecr = sc->sc_tsreflect;
1988 to.to_flags |= TOF_TS;
1989 }
1990 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
1991
1992 /* Adjust headers by option size. */
1993 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
1994 m->m_len += optlen;
1995 m->m_pkthdr.len += optlen;
1996 #ifdef INET6
1997 if (sc->sc_inc.inc_flags & INC_ISIPV6)
1998 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
1999 else
2000 #endif
2001 ip->ip_len = htons(ntohs(ip->ip_len) + optlen);
2002 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
2003 if (sc->sc_flags & SCF_SIGNATURE) {
2004 KASSERT(to.to_flags & TOF_SIGNATURE,
2005 ("tcp_addoptions() didn't set tcp_signature"));
2006
2007 /* NOTE: to.to_signature is inside of mbuf */
2008 if (!TCPMD5_ENABLED() ||
2009 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) {
2010 m_freem(m);
2011 return (EACCES);
2012 }
2013 }
2014 #endif
2015 } else
2016 optlen = 0;
2017
2018 if (udp) {
2019 ulen += optlen;
2020 udp->uh_ulen = htons(ulen);
2021 }
2022 M_SETFIB(m, sc->sc_inc.inc_fibnum);
2023 m->m_pkthdr.flowid = sc->sc_flowid;
2024 M_HASHTYPE_SET(m, sc->sc_flowtype);
2025 #ifdef NUMA
2026 m->m_pkthdr.numa_domain = sc->sc_numa_domain;
2027 #endif
2028 #ifdef INET6
2029 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
2030 if (sc->sc_port) {
2031 m->m_pkthdr.csum_flags = CSUM_UDP_IPV6;
2032 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
2033 udp->uh_sum = in6_cksum_pseudo(ip6, ulen,
2034 IPPROTO_UDP, 0);
2035 th->th_sum = htons(0);
2036 } else {
2037 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
2038 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
2039 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen,
2040 IPPROTO_TCP, 0);
2041 }
2042 ip6->ip6_hlim = sc->sc_ip_ttl;
2043 #ifdef TCP_OFFLOAD
2044 if (ADDED_BY_TOE(sc)) {
2045 struct toedev *tod = sc->sc_tod;
2046
2047 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
2048
2049 return (error);
2050 }
2051 #endif
2052 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th);
2053 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
2054 }
2055 #endif
2056 #if defined(INET6) && defined(INET)
2057 else
2058 #endif
2059 #ifdef INET
2060 {
2061 if (sc->sc_port) {
2062 m->m_pkthdr.csum_flags = CSUM_UDP;
2063 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
2064 udp->uh_sum = in_pseudo(ip->ip_src.s_addr,
2065 ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP));
2066 th->th_sum = htons(0);
2067 } else {
2068 m->m_pkthdr.csum_flags = CSUM_TCP;
2069 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
2070 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
2071 htons(tlen + optlen - hlen + IPPROTO_TCP));
2072 }
2073 #ifdef TCP_OFFLOAD
2074 if (ADDED_BY_TOE(sc)) {
2075 struct toedev *tod = sc->sc_tod;
2076
2077 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
2078
2079 return (error);
2080 }
2081 #endif
2082 TCP_PROBE5(send, NULL, NULL, ip, NULL, th);
2083 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
2084 }
2085 #endif
2086 return (error);
2087 }
2088
2089 static void
syncache_send_challenge_ack(struct syncache * sc)2090 syncache_send_challenge_ack(struct syncache *sc)
2091 {
2092 if (tcp_challenge_ack_check(&sc->sc_challenge_ack_end,
2093 &sc->sc_challenge_ack_cnt)) {
2094 if (syncache_respond(sc, TH_ACK) == 0) {
2095 TCPSTAT_INC(tcps_sndacks);
2096 TCPSTAT_INC(tcps_sndtotal);
2097 }
2098 }
2099 }
2100
2101 /*
2102 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks
2103 * that exceed the capacity of the syncache by avoiding the storage of any
2104 * of the SYNs we receive. Syncookies defend against blind SYN flooding
2105 * attacks where the attacker does not have access to our responses.
2106 *
2107 * Syncookies encode and include all necessary information about the
2108 * connection setup within the SYN|ACK that we send back. That way we
2109 * can avoid keeping any local state until the ACK to our SYN|ACK returns
2110 * (if ever). Normally the syncache and syncookies are running in parallel
2111 * with the latter taking over when the former is exhausted. When matching
2112 * syncache entry is found the syncookie is ignored.
2113 *
2114 * The only reliable information persisting the 3WHS is our initial sequence
2115 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient
2116 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS
2117 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK
2118 * returns and signifies a legitimate connection if it matches the ACK.
2119 *
2120 * The available space of 32 bits to store the hash and to encode the SYN
2121 * option information is very tight and we should have at least 24 bits for
2122 * the MAC to keep the number of guesses by blind spoofing reasonably high.
2123 *
2124 * SYN option information we have to encode to fully restore a connection:
2125 * MSS: is imporant to chose an optimal segment size to avoid IP level
2126 * fragmentation along the path. The common MSS values can be encoded
2127 * in a 3-bit table. Uncommon values are captured by the next lower value
2128 * in the table leading to a slight increase in packetization overhead.
2129 * WSCALE: is necessary to allow large windows to be used for high delay-
2130 * bandwidth product links. Not scaling the window when it was initially
2131 * negotiated is bad for performance as lack of scaling further decreases
2132 * the apparent available send window. We only need to encode the WSCALE
2133 * we received from the remote end. Our end can be recalculated at any
2134 * time. The common WSCALE values can be encoded in a 3-bit table.
2135 * Uncommon values are captured by the next lower value in the table
2136 * making us under-estimate the available window size halving our
2137 * theoretically possible maximum throughput for that connection.
2138 * SACK: Greatly assists in packet loss recovery and requires 1 bit.
2139 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options
2140 * that are included in all segments on a connection. We enable them when
2141 * the ACK has them.
2142 *
2143 * Security of syncookies and attack vectors:
2144 *
2145 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod)
2146 * together with the gloabl secret to make it unique per connection attempt.
2147 * Thus any change of any of those parameters results in a different MAC output
2148 * in an unpredictable way unless a collision is encountered. 24 bits of the
2149 * MAC are embedded into the ISS.
2150 *
2151 * To prevent replay attacks two rotating global secrets are updated with a
2152 * new random value every 15 seconds. The life-time of a syncookie is thus
2153 * 15-30 seconds.
2154 *
2155 * Vector 1: Attacking the secret. This requires finding a weakness in the
2156 * MAC itself or the way it is used here. The attacker can do a chosen plain
2157 * text attack by varying and testing the all parameters under his control.
2158 * The strength depends on the size and randomness of the secret, and the
2159 * cryptographic security of the MAC function. Due to the constant updating
2160 * of the secret the attacker has at most 29.999 seconds to find the secret
2161 * and launch spoofed connections. After that he has to start all over again.
2162 *
2163 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC
2164 * size an average of 4,823 attempts are required for a 50% chance of success
2165 * to spoof a single syncookie (birthday collision paradox). However the
2166 * attacker is blind and doesn't know if one of his attempts succeeded unless
2167 * he has a side channel to interfere success from. A single connection setup
2168 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets.
2169 * This many attempts are required for each one blind spoofed connection. For
2170 * every additional spoofed connection he has to launch another N attempts.
2171 * Thus for a sustained rate 100 spoofed connections per second approximately
2172 * 1,800,000 packets per second would have to be sent.
2173 *
2174 * NB: The MAC function should be fast so that it doesn't become a CPU
2175 * exhaustion attack vector itself.
2176 *
2177 * References:
2178 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations
2179 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996
2180 * http://cr.yp.to/syncookies.html (overview)
2181 * http://cr.yp.to/syncookies/archive (details)
2182 *
2183 *
2184 * Schematic construction of a syncookie enabled Initial Sequence Number:
2185 * 0 1 2 3
2186 * 12345678901234567890123456789012
2187 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP|
2188 *
2189 * x 24 MAC (truncated)
2190 * W 3 Send Window Scale index
2191 * M 3 MSS index
2192 * S 1 SACK permitted
2193 * P 1 Odd/even secret
2194 */
2195
2196 /*
2197 * Distribution and probability of certain MSS values. Those in between are
2198 * rounded down to the next lower one.
2199 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011]
2200 * .2% .3% 5% 7% 7% 20% 15% 45%
2201 */
2202 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 };
2203
2204 /*
2205 * Distribution and probability of certain WSCALE values. We have to map the
2206 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3
2207 * bits based on prevalence of certain values. Where we don't have an exact
2208 * match for are rounded down to the next lower one letting us under-estimate
2209 * the true available window. At the moment this would happen only for the
2210 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer
2211 * and window size). The absence of the WSCALE option (no scaling in either
2212 * direction) is encoded with index zero.
2213 * [WSCALE values histograms, Allman, 2012]
2214 * X 10 10 35 5 6 14 10% by host
2215 * X 11 4 5 5 18 49 3% by connections
2216 */
2217 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 };
2218
2219 /*
2220 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed
2221 * and good cryptographic properties.
2222 */
2223 static uint32_t
syncookie_mac(struct in_conninfo * inc,tcp_seq irs,uint8_t flags,uint8_t * secbits,uintptr_t secmod)2224 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags,
2225 uint8_t *secbits, uintptr_t secmod)
2226 {
2227 SIPHASH_CTX ctx;
2228 uint32_t siphash[2];
2229
2230 SipHash24_Init(&ctx);
2231 SipHash_SetKey(&ctx, secbits);
2232 switch (inc->inc_flags & INC_ISIPV6) {
2233 #ifdef INET
2234 case 0:
2235 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr));
2236 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr));
2237 break;
2238 #endif
2239 #ifdef INET6
2240 case INC_ISIPV6:
2241 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr));
2242 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr));
2243 break;
2244 #endif
2245 }
2246 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport));
2247 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport));
2248 SipHash_Update(&ctx, &irs, sizeof(irs));
2249 SipHash_Update(&ctx, &flags, sizeof(flags));
2250 SipHash_Update(&ctx, &secmod, sizeof(secmod));
2251 SipHash_Final((u_int8_t *)&siphash, &ctx);
2252
2253 return (siphash[0] ^ siphash[1]);
2254 }
2255
2256 static tcp_seq
syncookie_generate(struct syncache_head * sch,struct syncache * sc)2257 syncookie_generate(struct syncache_head *sch, struct syncache *sc)
2258 {
2259 u_int i, secbit, wscale;
2260 uint32_t iss, hash;
2261 uint8_t *secbits;
2262 union syncookie cookie;
2263
2264 cookie.cookie = 0;
2265
2266 /* Map our computed MSS into the 3-bit index. */
2267 for (i = nitems(tcp_sc_msstab) - 1;
2268 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0;
2269 i--)
2270 ;
2271 cookie.flags.mss_idx = i;
2272
2273 /*
2274 * Map the send window scale into the 3-bit index but only if
2275 * the wscale option was received.
2276 */
2277 if (sc->sc_flags & SCF_WINSCALE) {
2278 wscale = sc->sc_requested_s_scale;
2279 for (i = nitems(tcp_sc_wstab) - 1;
2280 tcp_sc_wstab[i] > wscale && i > 0;
2281 i--)
2282 ;
2283 cookie.flags.wscale_idx = i;
2284 }
2285
2286 /* Can we do SACK? */
2287 if (sc->sc_flags & SCF_SACK)
2288 cookie.flags.sack_ok = 1;
2289
2290 /* Which of the two secrets to use. */
2291 secbit = V_tcp_syncache.secret.oddeven & 0x1;
2292 cookie.flags.odd_even = secbit;
2293
2294 secbits = V_tcp_syncache.secret.key[secbit];
2295 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits,
2296 (uintptr_t)sch);
2297
2298 /*
2299 * Put the flags into the hash and XOR them to get better ISS number
2300 * variance. This doesn't enhance the cryptographic strength and is
2301 * done to prevent the 8 cookie bits from showing up directly on the
2302 * wire.
2303 */
2304 iss = hash & ~0xff;
2305 iss |= cookie.cookie ^ (hash >> 24);
2306
2307 TCPSTAT_INC(tcps_sc_sendcookie);
2308 return (iss);
2309 }
2310
2311 static bool
syncookie_expand(struct in_conninfo * inc,const struct syncache_head * sch,struct syncache * sc,struct tcphdr * th,struct tcpopt * to,struct socket * lso,uint16_t port)2312 syncookie_expand(struct in_conninfo *inc, const struct syncache_head *sch,
2313 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
2314 struct socket *lso, uint16_t port)
2315 {
2316 uint32_t hash;
2317 uint8_t *secbits;
2318 tcp_seq ack, seq;
2319 int wnd;
2320 union syncookie cookie;
2321
2322 /*
2323 * Pull information out of SYN-ACK/ACK and revert sequence number
2324 * advances.
2325 */
2326 ack = th->th_ack - 1;
2327 seq = th->th_seq - 1;
2328
2329 /*
2330 * Unpack the flags containing enough information to restore the
2331 * connection.
2332 */
2333 cookie.cookie = (ack & 0xff) ^ (ack >> 24);
2334
2335 /* Which of the two secrets to use. */
2336 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even];
2337
2338 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch);
2339
2340 /* The recomputed hash matches the ACK if this was a genuine cookie. */
2341 if ((ack & ~0xff) != (hash & ~0xff))
2342 return (false);
2343
2344 /* Fill in the syncache values. */
2345 sc->sc_flags = 0;
2346 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
2347 sc->sc_ipopts = NULL;
2348
2349 sc->sc_irs = seq;
2350 sc->sc_iss = ack;
2351
2352 switch (inc->inc_flags & INC_ISIPV6) {
2353 #ifdef INET
2354 case 0:
2355 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl;
2356 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos;
2357 break;
2358 #endif
2359 #ifdef INET6
2360 case INC_ISIPV6:
2361 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL)
2362 sc->sc_flowlabel =
2363 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK;
2364 break;
2365 #endif
2366 }
2367
2368 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx];
2369
2370 /* Only use wscale if it was enabled in the orignal SYN. */
2371 if (cookie.flags.wscale_idx > 0) {
2372 u_int wscale = 0;
2373
2374 /* Recompute the receive window scale that was sent earlier. */
2375 while (wscale < TCP_MAX_WINSHIFT &&
2376 (TCP_MAXWIN << wscale) < sb_max)
2377 wscale++;
2378 sc->sc_requested_r_scale = wscale;
2379 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx];
2380 sc->sc_flags |= SCF_WINSCALE;
2381 }
2382
2383 wnd = lso->sol_sbrcv_hiwat;
2384 wnd = imax(wnd, 0);
2385 wnd = imin(wnd, TCP_MAXWIN);
2386 sc->sc_wnd = wnd;
2387
2388 if (cookie.flags.sack_ok)
2389 sc->sc_flags |= SCF_SACK;
2390
2391 if (to->to_flags & TOF_TS) {
2392 sc->sc_flags |= SCF_TIMESTAMP;
2393 sc->sc_tsreflect = to->to_tsval;
2394 sc->sc_tsoff = tcp_new_ts_offset(inc);
2395 }
2396
2397 if (to->to_flags & TOF_SIGNATURE)
2398 sc->sc_flags |= SCF_SIGNATURE;
2399
2400 sc->sc_rxmits = 0;
2401
2402 sc->sc_port = port;
2403
2404 return (true);
2405 }
2406
2407 #ifdef INVARIANTS
2408 static void
syncookie_cmp(struct in_conninfo * inc,const struct syncache_head * sch,struct syncache * sc,struct tcphdr * th,struct tcpopt * to,struct socket * lso,uint16_t port)2409 syncookie_cmp(struct in_conninfo *inc, const struct syncache_head *sch,
2410 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
2411 struct socket *lso, uint16_t port)
2412 {
2413 struct syncache scs;
2414 char *s;
2415
2416 bzero(&scs, sizeof(scs));
2417 if (syncookie_expand(inc, sch, &scs, th, to, lso, port) &&
2418 (sc->sc_peer_mss != scs.sc_peer_mss ||
2419 sc->sc_requested_r_scale != scs.sc_requested_r_scale ||
2420 sc->sc_requested_s_scale != scs.sc_requested_s_scale ||
2421 (sc->sc_flags & SCF_SACK) != (scs.sc_flags & SCF_SACK))) {
2422
2423 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL)
2424 return;
2425
2426 if (sc->sc_peer_mss != scs.sc_peer_mss)
2427 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n",
2428 s, __func__, sc->sc_peer_mss, scs.sc_peer_mss);
2429
2430 if (sc->sc_requested_r_scale != scs.sc_requested_r_scale)
2431 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n",
2432 s, __func__, sc->sc_requested_r_scale,
2433 scs.sc_requested_r_scale);
2434
2435 if (sc->sc_requested_s_scale != scs.sc_requested_s_scale)
2436 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n",
2437 s, __func__, sc->sc_requested_s_scale,
2438 scs.sc_requested_s_scale);
2439
2440 if ((sc->sc_flags & SCF_SACK) != (scs.sc_flags & SCF_SACK))
2441 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__);
2442
2443 free(s, M_TCPLOG);
2444 }
2445 }
2446 #endif /* INVARIANTS */
2447
2448 static void
syncookie_reseed(void * arg)2449 syncookie_reseed(void *arg)
2450 {
2451 struct tcp_syncache *sc = arg;
2452 uint8_t *secbits;
2453 int secbit;
2454
2455 /*
2456 * Reseeding the secret doesn't have to be protected by a lock.
2457 * It only must be ensured that the new random values are visible
2458 * to all CPUs in a SMP environment. The atomic with release
2459 * semantics ensures that.
2460 */
2461 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1;
2462 secbits = sc->secret.key[secbit];
2463 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0);
2464 atomic_add_rel_int(&sc->secret.oddeven, 1);
2465
2466 /* Reschedule ourself. */
2467 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz);
2468 }
2469
2470 /*
2471 * We have overflowed a bucket. Let's pause dealing with the syncache.
2472 * This function will increment the bucketoverflow statistics appropriately
2473 * (once per pause when pausing is enabled; otherwise, once per overflow).
2474 */
2475 static void
syncache_pause(struct in_conninfo * inc)2476 syncache_pause(struct in_conninfo *inc)
2477 {
2478 time_t delta;
2479 const char *s;
2480
2481 /* XXX:
2482 * 2. Add sysctl read here so we don't get the benefit of this
2483 * change without the new sysctl.
2484 */
2485
2486 /*
2487 * Try an unlocked read. If we already know that another thread
2488 * has activated the feature, there is no need to proceed.
2489 */
2490 if (V_tcp_syncache.paused)
2491 return;
2492
2493 /* Are cookied enabled? If not, we can't pause. */
2494 if (!V_tcp_syncookies) {
2495 TCPSTAT_INC(tcps_sc_bucketoverflow);
2496 return;
2497 }
2498
2499 /*
2500 * We may be the first thread to find an overflow. Get the lock
2501 * and evaluate if we need to take action.
2502 */
2503 mtx_lock(&V_tcp_syncache.pause_mtx);
2504 if (V_tcp_syncache.paused) {
2505 mtx_unlock(&V_tcp_syncache.pause_mtx);
2506 return;
2507 }
2508
2509 /* Activate protection. */
2510 V_tcp_syncache.paused = true;
2511 TCPSTAT_INC(tcps_sc_bucketoverflow);
2512
2513 /*
2514 * Determine the last backoff time. If we are seeing a re-newed
2515 * attack within that same time after last reactivating the syncache,
2516 * consider it an extension of the same attack.
2517 */
2518 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff;
2519 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) {
2520 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) {
2521 delta <<= 1;
2522 V_tcp_syncache.pause_backoff++;
2523 }
2524 } else {
2525 delta = TCP_SYNCACHE_PAUSE_TIME;
2526 V_tcp_syncache.pause_backoff = 0;
2527 }
2528
2529 /* Log a warning, including IP addresses, if able. */
2530 if (inc != NULL)
2531 s = tcp_log_addrs(inc, NULL, NULL, NULL);
2532 else
2533 s = (const char *)NULL;
2534 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for "
2535 "the next %lld seconds%s%s%s\n", (long long)delta,
2536 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "",
2537 (s != NULL) ? ")" : "");
2538 free(__DECONST(void *, s), M_TCPLOG);
2539
2540 /* Use the calculated delta to set a new pause time. */
2541 V_tcp_syncache.pause_until = time_uptime + delta;
2542 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause,
2543 &V_tcp_syncache);
2544 mtx_unlock(&V_tcp_syncache.pause_mtx);
2545 }
2546
2547 /* Evaluate whether we need to unpause. */
2548 static void
syncache_unpause(void * arg)2549 syncache_unpause(void *arg)
2550 {
2551 struct tcp_syncache *sc;
2552 time_t delta;
2553
2554 sc = arg;
2555 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED);
2556 callout_deactivate(&sc->pause_co);
2557
2558 /*
2559 * Check to make sure we are not running early. If the pause
2560 * time has expired, then deactivate the protection.
2561 */
2562 if ((delta = sc->pause_until - time_uptime) > 0)
2563 callout_schedule(&sc->pause_co, delta * hz);
2564 else
2565 sc->paused = false;
2566 }
2567
2568 /*
2569 * Exports the syncache entries to userland so that netstat can display
2570 * them alongside the other sockets. This function is intended to be
2571 * called only from tcp_pcblist.
2572 *
2573 * Due to concurrency on an active system, the number of pcbs exported
2574 * may have no relation to max_pcbs. max_pcbs merely indicates the
2575 * amount of space the caller allocated for this function to use.
2576 */
2577 int
syncache_pcblist(struct sysctl_req * req)2578 syncache_pcblist(struct sysctl_req *req)
2579 {
2580 struct xtcpcb xt;
2581 struct syncache *sc;
2582 struct syncache_head *sch;
2583 int error, i;
2584
2585 bzero(&xt, sizeof(xt));
2586 xt.xt_len = sizeof(xt);
2587 xt.t_state = TCPS_SYN_RECEIVED;
2588 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP;
2589 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket);
2590 xt.xt_inp.xi_socket.so_type = SOCK_STREAM;
2591 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING;
2592
2593 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
2594 sch = &V_tcp_syncache.hashbase[i];
2595 SCH_LOCK(sch);
2596 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
2597 if (sc->sc_cred != NULL &&
2598 cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
2599 continue;
2600 if (sc->sc_inc.inc_flags & INC_ISIPV6)
2601 xt.xt_inp.inp_vflag = INP_IPV6;
2602 else
2603 xt.xt_inp.inp_vflag = INP_IPV4;
2604 xt.xt_encaps_port = sc->sc_port;
2605 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc,
2606 sizeof (struct in_conninfo));
2607 error = SYSCTL_OUT(req, &xt, sizeof xt);
2608 if (error) {
2609 SCH_UNLOCK(sch);
2610 return (0);
2611 }
2612 }
2613 SCH_UNLOCK(sch);
2614 }
2615
2616 return (0);
2617 }
2618