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 #ifdef TCP_OFFLOAD
118 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL)
119 #endif
120
121 static void syncache_drop(struct syncache *, struct syncache_head *);
122 static void syncache_free(struct syncache *);
123 static void syncache_insert(struct syncache *, struct syncache_head *);
124 static int syncache_respond(struct syncache *, const struct mbuf *, int);
125 static struct socket *syncache_socket(struct syncache *, struct socket *,
126 struct mbuf *m);
127 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch,
128 int docallout);
129 static void syncache_timer(void *);
130
131 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t,
132 uint8_t *, uintptr_t);
133 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *);
134 static struct syncache
135 *syncookie_lookup(struct in_conninfo *, struct syncache_head *,
136 struct syncache *, struct tcphdr *, struct tcpopt *,
137 struct socket *, uint16_t);
138 static void syncache_pause(struct in_conninfo *);
139 static void syncache_unpause(void *);
140 static void syncookie_reseed(void *);
141 #ifdef INVARIANTS
142 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
143 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
144 struct socket *lso, uint16_t port);
145 #endif
146
147 /*
148 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
149 * 3 retransmits corresponds to a timeout with default values of
150 * tcp_rexmit_initial * ( 1 +
151 * tcp_backoff[1] +
152 * tcp_backoff[2] +
153 * tcp_backoff[3]) + 3 * tcp_rexmit_slop,
154 * 1000 ms * (1 + 2 + 4 + 8) + 3 * 200 ms = 15600 ms,
155 * the odds are that the user has given up attempting to connect by then.
156 */
157 #define SYNCACHE_MAXREXMTS 3
158
159 /* Arbitrary values */
160 #define TCP_SYNCACHE_HASHSIZE 512
161 #define TCP_SYNCACHE_BUCKETLIMIT 30
162
163 VNET_DEFINE_STATIC(struct tcp_syncache, tcp_syncache);
164 #define V_tcp_syncache VNET(tcp_syncache)
165
166 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache,
167 CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
168 "TCP SYN cache");
169
170 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
171 &VNET_NAME(tcp_syncache.bucket_limit), 0,
172 "Per-bucket hash limit for syncache");
173
174 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
175 &VNET_NAME(tcp_syncache.cache_limit), 0,
176 "Overall entry limit for syncache");
177
178 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET,
179 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache");
180
181 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN,
182 &VNET_NAME(tcp_syncache.hashsize), 0,
183 "Size of TCP syncache hashtable");
184
185 SYSCTL_BOOL(_net_inet_tcp_syncache, OID_AUTO, see_other, CTLFLAG_VNET |
186 CTLFLAG_RW, &VNET_NAME(tcp_syncache.see_other), 0,
187 "All syncache(4) entries are visible, ignoring UID/GID, jail(2) "
188 "and mac(4) checks");
189
190 static int
sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS)191 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS)
192 {
193 int error;
194 u_int new;
195
196 new = V_tcp_syncache.rexmt_limit;
197 error = sysctl_handle_int(oidp, &new, 0, req);
198 if ((error == 0) && (req->newptr != NULL)) {
199 if (new > TCP_MAXRXTSHIFT)
200 error = EINVAL;
201 else
202 V_tcp_syncache.rexmt_limit = new;
203 }
204 return (error);
205 }
206
207 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit,
208 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
209 &VNET_NAME(tcp_syncache.rexmt_limit), 0,
210 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "IU",
211 "Limit on SYN/ACK retransmissions");
212
213 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1;
214 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail,
215 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0,
216 "Send reset on socket allocation failure");
217
218 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
219
220 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx)
221 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx)
222 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED)
223
224 /*
225 * Requires the syncache entry to be already removed from the bucket list.
226 */
227 static void
syncache_free(struct syncache * sc)228 syncache_free(struct syncache *sc)
229 {
230
231 if (sc->sc_ipopts)
232 (void)m_free(sc->sc_ipopts);
233 if (sc->sc_cred)
234 crfree(sc->sc_cred);
235 #ifdef MAC
236 mac_syncache_destroy(&sc->sc_label);
237 #endif
238
239 uma_zfree(V_tcp_syncache.zone, sc);
240 }
241
242 void
syncache_init(void)243 syncache_init(void)
244 {
245 int i;
246
247 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
248 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
249 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
250 V_tcp_syncache.hash_secret = arc4random();
251
252 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
253 &V_tcp_syncache.hashsize);
254 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
255 &V_tcp_syncache.bucket_limit);
256 if (!powerof2(V_tcp_syncache.hashsize) ||
257 V_tcp_syncache.hashsize == 0) {
258 printf("WARNING: syncache hash size is not a power of 2.\n");
259 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
260 }
261 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1;
262
263 /* Set limits. */
264 V_tcp_syncache.cache_limit =
265 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit;
266 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
267 &V_tcp_syncache.cache_limit);
268
269 /* Allocate the hash table. */
270 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize *
271 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO);
272
273 #ifdef VIMAGE
274 V_tcp_syncache.vnet = curvnet;
275 #endif
276
277 /* Initialize the hash buckets. */
278 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
279 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket);
280 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
281 NULL, MTX_DEF);
282 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer,
283 &V_tcp_syncache.hashbase[i].sch_mtx, 0);
284 V_tcp_syncache.hashbase[i].sch_length = 0;
285 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache;
286 V_tcp_syncache.hashbase[i].sch_last_overflow =
287 -(SYNCOOKIE_LIFETIME + 1);
288 }
289
290 /* Create the syncache entry zone. */
291 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
292 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
293 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone,
294 V_tcp_syncache.cache_limit);
295
296 /* Start the SYN cookie reseeder callout. */
297 callout_init(&V_tcp_syncache.secret.reseed, 1);
298 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0);
299 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0);
300 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz,
301 syncookie_reseed, &V_tcp_syncache);
302
303 /* Initialize the pause machinery. */
304 mtx_init(&V_tcp_syncache.pause_mtx, "tcp_sc_pause", NULL, MTX_DEF);
305 callout_init_mtx(&V_tcp_syncache.pause_co, &V_tcp_syncache.pause_mtx,
306 0);
307 V_tcp_syncache.pause_until = time_uptime - TCP_SYNCACHE_PAUSE_TIME;
308 V_tcp_syncache.pause_backoff = 0;
309 V_tcp_syncache.paused = false;
310 }
311
312 #ifdef VIMAGE
313 void
syncache_destroy(void)314 syncache_destroy(void)
315 {
316 struct syncache_head *sch;
317 struct syncache *sc, *nsc;
318 int i;
319
320 /*
321 * Stop the re-seed timer before freeing resources. No need to
322 * possibly schedule it another time.
323 */
324 callout_drain(&V_tcp_syncache.secret.reseed);
325
326 /* Stop the SYN cache pause callout. */
327 mtx_lock(&V_tcp_syncache.pause_mtx);
328 if (callout_stop(&V_tcp_syncache.pause_co) == 0) {
329 mtx_unlock(&V_tcp_syncache.pause_mtx);
330 callout_drain(&V_tcp_syncache.pause_co);
331 } else
332 mtx_unlock(&V_tcp_syncache.pause_mtx);
333
334 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */
335 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
336 sch = &V_tcp_syncache.hashbase[i];
337 callout_drain(&sch->sch_timer);
338
339 SCH_LOCK(sch);
340 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc)
341 syncache_drop(sc, sch);
342 SCH_UNLOCK(sch);
343 KASSERT(TAILQ_EMPTY(&sch->sch_bucket),
344 ("%s: sch->sch_bucket not empty", __func__));
345 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0",
346 __func__, sch->sch_length));
347 mtx_destroy(&sch->sch_mtx);
348 }
349
350 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0,
351 ("%s: cache_count not 0", __func__));
352
353 /* Free the allocated global resources. */
354 uma_zdestroy(V_tcp_syncache.zone);
355 free(V_tcp_syncache.hashbase, M_SYNCACHE);
356 mtx_destroy(&V_tcp_syncache.pause_mtx);
357 }
358 #endif
359
360 /*
361 * Inserts a syncache entry into the specified bucket row.
362 * Locks and unlocks the syncache_head autonomously.
363 */
364 static void
syncache_insert(struct syncache * sc,struct syncache_head * sch)365 syncache_insert(struct syncache *sc, struct syncache_head *sch)
366 {
367 struct syncache *sc2;
368
369 SCH_LOCK(sch);
370
371 /*
372 * Make sure that we don't overflow the per-bucket limit.
373 * If the bucket is full, toss the oldest element.
374 */
375 if (sch->sch_length >= V_tcp_syncache.bucket_limit) {
376 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
377 ("sch->sch_length incorrect"));
378 syncache_pause(&sc->sc_inc);
379 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
380 sch->sch_last_overflow = time_uptime;
381 syncache_drop(sc2, sch);
382 }
383
384 /* Put it into the bucket. */
385 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
386 sch->sch_length++;
387
388 #ifdef TCP_OFFLOAD
389 if (ADDED_BY_TOE(sc)) {
390 struct toedev *tod = sc->sc_tod;
391
392 tod->tod_syncache_added(tod, sc->sc_todctx);
393 }
394 #endif
395
396 /* Reinitialize the bucket row's timer. */
397 if (sch->sch_length == 1)
398 sch->sch_nextc = ticks + INT_MAX;
399 syncache_timeout(sc, sch, 1);
400
401 SCH_UNLOCK(sch);
402
403 TCPSTATES_INC(TCPS_SYN_RECEIVED);
404 TCPSTAT_INC(tcps_sc_added);
405 }
406
407 /*
408 * Remove and free entry from syncache bucket row.
409 * Expects locked syncache head.
410 */
411 static void
syncache_drop(struct syncache * sc,struct syncache_head * sch)412 syncache_drop(struct syncache *sc, struct syncache_head *sch)
413 {
414
415 SCH_LOCK_ASSERT(sch);
416
417 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
418 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
419 sch->sch_length--;
420
421 #ifdef TCP_OFFLOAD
422 if (ADDED_BY_TOE(sc)) {
423 struct toedev *tod = sc->sc_tod;
424
425 tod->tod_syncache_removed(tod, sc->sc_todctx);
426 }
427 #endif
428
429 syncache_free(sc);
430 }
431
432 /*
433 * Engage/reengage time on bucket row.
434 */
435 static void
syncache_timeout(struct syncache * sc,struct syncache_head * sch,int docallout)436 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
437 {
438 int rexmt;
439
440 if (sc->sc_rxmits == 0)
441 rexmt = tcp_rexmit_initial;
442 else
443 TCPT_RANGESET(rexmt,
444 tcp_rexmit_initial * tcp_backoff[sc->sc_rxmits],
445 tcp_rexmit_min, TCPTV_REXMTMAX);
446 sc->sc_rxttime = ticks + rexmt;
447 sc->sc_rxmits++;
448 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
449 sch->sch_nextc = sc->sc_rxttime;
450 if (docallout)
451 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
452 syncache_timer, (void *)sch);
453 }
454 }
455
456 /*
457 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
458 * If we have retransmitted an entry the maximum number of times, expire it.
459 * One separate timer for each bucket row.
460 */
461 static void
syncache_timer(void * xsch)462 syncache_timer(void *xsch)
463 {
464 struct syncache_head *sch = (struct syncache_head *)xsch;
465 struct syncache *sc, *nsc;
466 struct epoch_tracker et;
467 int tick = ticks;
468 char *s;
469 bool paused;
470
471 CURVNET_SET(sch->sch_sc->vnet);
472
473 /* NB: syncache_head has already been locked by the callout. */
474 SCH_LOCK_ASSERT(sch);
475
476 /*
477 * In the following cycle we may remove some entries and/or
478 * advance some timeouts, so re-initialize the bucket timer.
479 */
480 sch->sch_nextc = tick + INT_MAX;
481
482 /*
483 * If we have paused processing, unconditionally remove
484 * all syncache entries.
485 */
486 mtx_lock(&V_tcp_syncache.pause_mtx);
487 paused = V_tcp_syncache.paused;
488 mtx_unlock(&V_tcp_syncache.pause_mtx);
489
490 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
491 if (paused) {
492 syncache_drop(sc, sch);
493 continue;
494 }
495 /*
496 * We do not check if the listen socket still exists
497 * and accept the case where the listen socket may be
498 * gone by the time we resend the SYN/ACK. We do
499 * not expect this to happens often. If it does,
500 * then the RST will be sent by the time the remote
501 * host does the SYN/ACK->ACK.
502 */
503 if (TSTMP_GT(sc->sc_rxttime, tick)) {
504 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
505 sch->sch_nextc = sc->sc_rxttime;
506 continue;
507 }
508 if (sc->sc_rxmits > V_tcp_ecn_maxretries) {
509 sc->sc_flags &= ~SCF_ECN_MASK;
510 }
511 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
512 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
513 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
514 "giving up and removing syncache entry\n",
515 s, __func__);
516 free(s, M_TCPLOG);
517 }
518 syncache_drop(sc, sch);
519 TCPSTAT_INC(tcps_sc_stale);
520 continue;
521 }
522 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
523 log(LOG_DEBUG, "%s; %s: Response timeout, "
524 "retransmitting (%u) SYN|ACK\n",
525 s, __func__, sc->sc_rxmits);
526 free(s, M_TCPLOG);
527 }
528
529 NET_EPOCH_ENTER(et);
530 if (syncache_respond(sc, NULL, TH_SYN|TH_ACK) == 0) {
531 syncache_timeout(sc, sch, 0);
532 TCPSTAT_INC(tcps_sndacks);
533 TCPSTAT_INC(tcps_sndtotal);
534 TCPSTAT_INC(tcps_sc_retransmitted);
535 } else {
536 syncache_drop(sc, sch);
537 TCPSTAT_INC(tcps_sc_dropped);
538 }
539 NET_EPOCH_EXIT(et);
540 }
541 if (!TAILQ_EMPTY(&(sch)->sch_bucket))
542 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
543 syncache_timer, (void *)(sch));
544 CURVNET_RESTORE();
545 }
546
547 /*
548 * Returns true if the system is only using cookies at the moment.
549 * This could be due to a sysadmin decision to only use cookies, or it
550 * could be due to the system detecting an attack.
551 */
552 static inline bool
syncache_cookiesonly(void)553 syncache_cookiesonly(void)
554 {
555
556 return (V_tcp_syncookies && (V_tcp_syncache.paused ||
557 V_tcp_syncookiesonly));
558 }
559
560 /*
561 * Find the hash bucket for the given connection.
562 */
563 static struct syncache_head *
syncache_hashbucket(struct in_conninfo * inc)564 syncache_hashbucket(struct in_conninfo *inc)
565 {
566 uint32_t hash;
567
568 /*
569 * The hash is built on foreign port + local port + foreign address.
570 * We rely on the fact that struct in_conninfo starts with 16 bits
571 * of foreign port, then 16 bits of local port then followed by 128
572 * bits of foreign address. In case of IPv4 address, the first 3
573 * 32-bit words of the address always are zeroes.
574 */
575 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5,
576 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask;
577
578 return (&V_tcp_syncache.hashbase[hash]);
579 }
580
581 /*
582 * Find an entry in the syncache.
583 * Returns always with locked syncache_head plus a matching entry or NULL.
584 */
585 static struct syncache *
syncache_lookup(struct in_conninfo * inc,struct syncache_head ** schp)586 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
587 {
588 struct syncache *sc;
589 struct syncache_head *sch;
590
591 *schp = sch = syncache_hashbucket(inc);
592 SCH_LOCK(sch);
593
594 /* Circle through bucket row to find matching entry. */
595 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash)
596 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie,
597 sizeof(struct in_endpoints)) == 0)
598 break;
599
600 return (sc); /* Always returns with locked sch. */
601 }
602
603 /*
604 * This function is called when we get a RST for a
605 * non-existent connection, so that we can see if the
606 * connection is in the syn cache. If it is, zap it.
607 * If required send a challenge ACK.
608 */
609 void
syncache_chkrst(struct in_conninfo * inc,struct tcphdr * th,struct mbuf * m,uint16_t port)610 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, struct mbuf *m,
611 uint16_t port)
612 {
613 struct syncache *sc;
614 struct syncache_head *sch;
615 char *s = NULL;
616
617 if (syncache_cookiesonly())
618 return;
619 sc = syncache_lookup(inc, &sch); /* returns locked sch */
620 SCH_LOCK_ASSERT(sch);
621
622 /*
623 * No corresponding connection was found in syncache.
624 * If syncookies are enabled and possibly exclusively
625 * used, or we are under memory pressure, a valid RST
626 * may not find a syncache entry. In that case we're
627 * done and no SYN|ACK retransmissions will happen.
628 * Otherwise the RST was misdirected or spoofed.
629 */
630 if (sc == NULL) {
631 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
632 log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
633 "syncache entry (possibly syncookie only), "
634 "segment ignored\n", s, __func__);
635 TCPSTAT_INC(tcps_badrst);
636 goto done;
637 }
638
639 /* The remote UDP encaps port does not match. */
640 if (sc->sc_port != port) {
641 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
642 log(LOG_DEBUG, "%s; %s: Spurious RST with matching "
643 "syncache entry but non-matching UDP encaps port, "
644 "segment ignored\n", s, __func__);
645 TCPSTAT_INC(tcps_badrst);
646 goto done;
647 }
648
649 /*
650 * If the RST bit is set, check the sequence number to see
651 * if this is a valid reset segment.
652 *
653 * RFC 793 page 37:
654 * In all states except SYN-SENT, all reset (RST) segments
655 * are validated by checking their SEQ-fields. A reset is
656 * valid if its sequence number is in the window.
657 *
658 * RFC 793 page 69:
659 * There are four cases for the acceptability test for an incoming
660 * segment:
661 *
662 * Segment Receive Test
663 * Length Window
664 * ------- ------- -------------------------------------------
665 * 0 0 SEG.SEQ = RCV.NXT
666 * 0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND
667 * >0 0 not acceptable
668 * >0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND
669 * or RCV.NXT =< SEG.SEQ+SEG.LEN-1 < RCV.NXT+RCV.WND
670 *
671 * Note that when receiving a SYN segment in the LISTEN state,
672 * IRS is set to SEG.SEQ and RCV.NXT is set to SEG.SEQ+1, as
673 * described in RFC 793, page 66.
674 */
675 if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) &&
676 SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) ||
677 (sc->sc_wnd == 0 && th->th_seq == sc->sc_irs + 1)) {
678 if (V_tcp_insecure_rst ||
679 th->th_seq == sc->sc_irs + 1) {
680 syncache_drop(sc, sch);
681 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
682 log(LOG_DEBUG,
683 "%s; %s: Our SYN|ACK was rejected, "
684 "connection attempt aborted by remote "
685 "endpoint\n",
686 s, __func__);
687 TCPSTAT_INC(tcps_sc_reset);
688 } else {
689 TCPSTAT_INC(tcps_badrst);
690 /* Send challenge ACK. */
691 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
692 log(LOG_DEBUG, "%s; %s: RST with invalid "
693 " SEQ %u != NXT %u (+WND %u), "
694 "sending challenge ACK\n",
695 s, __func__,
696 th->th_seq, sc->sc_irs + 1, sc->sc_wnd);
697 if (syncache_respond(sc, m, TH_ACK) == 0) {
698 TCPSTAT_INC(tcps_sndacks);
699 TCPSTAT_INC(tcps_sndtotal);
700 } else {
701 syncache_drop(sc, sch);
702 TCPSTAT_INC(tcps_sc_dropped);
703 }
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_badack(struct in_conninfo * inc,uint16_t port)721 syncache_badack(struct in_conninfo *inc, 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) && (sc->sc_port == port)) {
731 syncache_drop(sc, sch);
732 TCPSTAT_INC(tcps_sc_badack);
733 }
734 SCH_UNLOCK(sch);
735 }
736
737 void
syncache_unreach(struct in_conninfo * inc,tcp_seq th_seq,uint16_t port)738 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq, uint16_t port)
739 {
740 struct syncache *sc;
741 struct syncache_head *sch;
742
743 if (syncache_cookiesonly())
744 return;
745 sc = syncache_lookup(inc, &sch); /* returns locked sch */
746 SCH_LOCK_ASSERT(sch);
747 if (sc == NULL)
748 goto done;
749
750 /* If the port != sc_port, then it's a bogus ICMP msg */
751 if (port != sc->sc_port)
752 goto done;
753
754 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
755 if (ntohl(th_seq) != sc->sc_iss)
756 goto done;
757
758 /*
759 * If we've rertransmitted 3 times and this is our second error,
760 * we remove the entry. Otherwise, we allow it to continue on.
761 * This prevents us from incorrectly nuking an entry during a
762 * spurious network outage.
763 *
764 * See tcp_notify().
765 */
766 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
767 sc->sc_flags |= SCF_UNREACH;
768 goto done;
769 }
770 syncache_drop(sc, sch);
771 TCPSTAT_INC(tcps_sc_unreach);
772 done:
773 SCH_UNLOCK(sch);
774 }
775
776 /*
777 * Build a new TCP socket structure from a syncache entry.
778 *
779 * On success return the newly created socket with its underlying inp locked.
780 */
781 static struct socket *
syncache_socket(struct syncache * sc,struct socket * lso,struct mbuf * m)782 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
783 {
784 struct inpcb *inp = NULL;
785 struct socket *so;
786 struct tcpcb *tp;
787 int error;
788 char *s;
789
790 NET_EPOCH_ASSERT();
791
792 /*
793 * Ok, create the full blown connection, and set things up
794 * as they would have been set up if we had created the
795 * connection when the SYN arrived.
796 */
797 if ((so = solisten_clone(lso)) == NULL)
798 goto allocfail;
799 #ifdef MAC
800 mac_socketpeer_set_from_mbuf(m, so);
801 #endif
802 error = in_pcballoc(so, &V_tcbinfo);
803 if (error) {
804 sodealloc(so);
805 goto allocfail;
806 }
807 inp = sotoinpcb(so);
808 if ((tp = tcp_newtcpcb(inp, sototcpcb(lso))) == NULL) {
809 in_pcbfree(inp);
810 sodealloc(so);
811 goto allocfail;
812 }
813 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
814 #ifdef INET6
815 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
816 inp->inp_vflag &= ~INP_IPV4;
817 inp->inp_vflag |= INP_IPV6;
818 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
819 } else {
820 inp->inp_vflag &= ~INP_IPV6;
821 inp->inp_vflag |= INP_IPV4;
822 #endif
823 inp->inp_ip_ttl = sc->sc_ip_ttl;
824 inp->inp_ip_tos = sc->sc_ip_tos;
825 inp->inp_laddr = sc->sc_inc.inc_laddr;
826 #ifdef INET6
827 }
828 #endif
829
830 /*
831 * If there's an mbuf and it has a flowid, then let's initialise the
832 * inp with that particular flowid.
833 */
834 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) {
835 inp->inp_flowid = m->m_pkthdr.flowid;
836 inp->inp_flowtype = M_HASHTYPE_GET(m);
837 #ifdef NUMA
838 inp->inp_numa_domain = m->m_pkthdr.numa_domain;
839 #endif
840 }
841
842 inp->inp_lport = sc->sc_inc.inc_lport;
843 #ifdef INET6
844 if (inp->inp_vflag & INP_IPV6PROTO) {
845 struct inpcb *oinp = sotoinpcb(lso);
846
847 /*
848 * Inherit socket options from the listening socket.
849 * Note that in6p_inputopts are not (and should not be)
850 * copied, since it stores previously received options and is
851 * used to detect if each new option is different than the
852 * previous one and hence should be passed to a user.
853 * If we copied in6p_inputopts, a user would not be able to
854 * receive options just after calling the accept system call.
855 */
856 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
857 if (oinp->in6p_outputopts)
858 inp->in6p_outputopts =
859 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
860 inp->in6p_hops = oinp->in6p_hops;
861 }
862
863 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
864 struct sockaddr_in6 sin6;
865
866 sin6.sin6_family = AF_INET6;
867 sin6.sin6_len = sizeof(sin6);
868 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
869 sin6.sin6_port = sc->sc_inc.inc_fport;
870 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
871 INP_HASH_WLOCK(&V_tcbinfo);
872 error = in6_pcbconnect(inp, &sin6, thread0.td_ucred, false);
873 INP_HASH_WUNLOCK(&V_tcbinfo);
874 if (error != 0)
875 goto abort;
876 /* Override flowlabel from in6_pcbconnect. */
877 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
878 inp->inp_flow |= sc->sc_flowlabel;
879 }
880 #endif /* INET6 */
881 #if defined(INET) && defined(INET6)
882 else
883 #endif
884 #ifdef INET
885 {
886 struct sockaddr_in sin;
887
888 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
889
890 if (inp->inp_options == NULL) {
891 inp->inp_options = sc->sc_ipopts;
892 sc->sc_ipopts = NULL;
893 }
894
895 sin.sin_family = AF_INET;
896 sin.sin_len = sizeof(sin);
897 sin.sin_addr = sc->sc_inc.inc_faddr;
898 sin.sin_port = sc->sc_inc.inc_fport;
899 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
900 INP_HASH_WLOCK(&V_tcbinfo);
901 error = in_pcbconnect(inp, &sin, thread0.td_ucred);
902 INP_HASH_WUNLOCK(&V_tcbinfo);
903 if (error != 0)
904 goto abort;
905 }
906 #endif /* INET */
907 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
908 /* Copy old policy into new socket's. */
909 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0)
910 printf("syncache_socket: could not copy policy\n");
911 #endif
912 tp->t_state = TCPS_SYN_RECEIVED;
913 tp->iss = sc->sc_iss;
914 tp->irs = sc->sc_irs;
915 tp->t_port = sc->sc_port;
916 tcp_rcvseqinit(tp);
917 tcp_sendseqinit(tp);
918 tp->snd_wl1 = sc->sc_irs;
919 tp->snd_max = tp->iss + 1;
920 tp->snd_nxt = tp->iss + 1;
921 tp->rcv_up = sc->sc_irs + 1;
922 tp->rcv_wnd = sc->sc_wnd;
923 tp->rcv_adv += tp->rcv_wnd;
924 tp->last_ack_sent = tp->rcv_nxt;
925
926 tp->t_flags = sototcpcb(lso)->t_flags &
927 (TF_LRD|TF_NOPUSH|TF_NODELAY);
928 if (sc->sc_flags & SCF_NOOPT)
929 tp->t_flags |= TF_NOOPT;
930 else {
931 if (sc->sc_flags & SCF_WINSCALE) {
932 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
933 tp->snd_scale = sc->sc_requested_s_scale;
934 tp->request_r_scale = sc->sc_requested_r_scale;
935 }
936 if (sc->sc_flags & SCF_TIMESTAMP) {
937 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
938 tp->ts_recent = sc->sc_tsreflect;
939 tp->ts_recent_age = tcp_ts_getticks();
940 tp->ts_offset = sc->sc_tsoff;
941 }
942 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
943 if (sc->sc_flags & SCF_SIGNATURE)
944 tp->t_flags |= TF_SIGNATURE;
945 #endif
946 if (sc->sc_flags & SCF_SACK)
947 tp->t_flags |= TF_SACK_PERMIT;
948 }
949
950 tcp_ecn_syncache_socket(tp, sc);
951
952 /*
953 * Set up MSS and get cached values from tcp_hostcache.
954 * This might overwrite some of the defaults we just set.
955 */
956 tcp_mss(tp, sc->sc_peer_mss);
957
958 /*
959 * If the SYN,ACK was retransmitted, indicate that CWND to be
960 * limited to one segment in cc_conn_init().
961 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
962 */
963 if (sc->sc_rxmits > 1)
964 tp->snd_cwnd = 1;
965
966 #ifdef TCP_OFFLOAD
967 /*
968 * Allow a TOE driver to install its hooks. Note that we hold the
969 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a
970 * new connection before the TOE driver has done its thing.
971 */
972 if (ADDED_BY_TOE(sc)) {
973 struct toedev *tod = sc->sc_tod;
974
975 tod->tod_offload_socket(tod, sc->sc_todctx, so);
976 }
977 #endif
978 #ifdef TCP_BLACKBOX
979 /*
980 * Inherit the log state from the listening socket, if
981 * - the log state of the listening socket is not off and
982 * - the listening socket was not auto selected from all sessions and
983 * - a log id is not set on the listening socket.
984 * This avoids inheriting a log state which was automatically set.
985 */
986 if ((tcp_get_bblog_state(sototcpcb(lso)) != TCP_LOG_STATE_OFF) &&
987 ((sototcpcb(lso)->t_flags2 & TF2_LOG_AUTO) == 0) &&
988 (sototcpcb(lso)->t_lib == NULL)) {
989 tcp_log_state_change(tp, tcp_get_bblog_state(sototcpcb(lso)));
990 }
991 #endif
992 /*
993 * Copy and activate timers.
994 */
995 tp->t_maxunacktime = sototcpcb(lso)->t_maxunacktime;
996 tp->t_keepinit = sototcpcb(lso)->t_keepinit;
997 tp->t_keepidle = sototcpcb(lso)->t_keepidle;
998 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl;
999 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt;
1000 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp));
1001
1002 TCPSTAT_INC(tcps_accepts);
1003 TCP_PROBE6(state__change, NULL, tp, NULL, tp, NULL, TCPS_LISTEN);
1004
1005 if (!solisten_enqueue(so, SS_ISCONNECTED))
1006 tp->t_flags |= TF_SONOTCONN;
1007 /* Can we inherit anything from the listener? */
1008 if (tp->t_fb->tfb_inherit != NULL) {
1009 (*tp->t_fb->tfb_inherit)(tp, sotoinpcb(lso));
1010 }
1011 return (so);
1012
1013 allocfail:
1014 /*
1015 * Drop the connection; we will either send a RST or have the peer
1016 * retransmit its SYN again after its RTO and try again.
1017 */
1018 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
1019 log(LOG_DEBUG, "%s; %s: Socket create failed "
1020 "due to limits or memory shortage\n",
1021 s, __func__);
1022 free(s, M_TCPLOG);
1023 }
1024 TCPSTAT_INC(tcps_listendrop);
1025 return (NULL);
1026
1027 abort:
1028 tcp_discardcb(tp);
1029 in_pcbfree(inp);
1030 sodealloc(so);
1031 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
1032 log(LOG_DEBUG, "%s; %s: in%s_pcbconnect failed with error %i\n",
1033 s, __func__, (sc->sc_inc.inc_flags & INC_ISIPV6) ? "6" : "",
1034 error);
1035 free(s, M_TCPLOG);
1036 }
1037 TCPSTAT_INC(tcps_listendrop);
1038 return (NULL);
1039 }
1040
1041 /*
1042 * This function gets called when we receive an ACK for a
1043 * socket in the LISTEN state. We look up the connection
1044 * in the syncache, and if its there, we pull it out of
1045 * the cache and turn it into a full-blown connection in
1046 * the SYN-RECEIVED state.
1047 *
1048 * On syncache_socket() success the newly created socket
1049 * has its underlying inp locked.
1050 */
1051 int
syncache_expand(struct in_conninfo * inc,struct tcpopt * to,struct tcphdr * th,struct socket ** lsop,struct mbuf * m,uint16_t port)1052 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1053 struct socket **lsop, struct mbuf *m, uint16_t port)
1054 {
1055 struct syncache *sc;
1056 struct syncache_head *sch;
1057 struct syncache scs;
1058 char *s;
1059 bool locked;
1060
1061 NET_EPOCH_ASSERT();
1062 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
1063 ("%s: can handle only ACK", __func__));
1064
1065 if (syncache_cookiesonly()) {
1066 sc = NULL;
1067 sch = syncache_hashbucket(inc);
1068 locked = false;
1069 } else {
1070 sc = syncache_lookup(inc, &sch); /* returns locked sch */
1071 locked = true;
1072 SCH_LOCK_ASSERT(sch);
1073 }
1074
1075 #ifdef INVARIANTS
1076 /*
1077 * Test code for syncookies comparing the syncache stored
1078 * values with the reconstructed values from the cookie.
1079 */
1080 if (sc != NULL)
1081 syncookie_cmp(inc, sch, sc, th, to, *lsop, port);
1082 #endif
1083
1084 if (sc == NULL) {
1085 /*
1086 * There is no syncache entry, so see if this ACK is
1087 * a returning syncookie. To do this, first:
1088 * A. Check if syncookies are used in case of syncache
1089 * overflows
1090 * B. See if this socket has had a syncache entry dropped in
1091 * the recent past. We don't want to accept a bogus
1092 * syncookie if we've never received a SYN or accept it
1093 * twice.
1094 * C. check that the syncookie is valid. If it is, then
1095 * cobble up a fake syncache entry, and return.
1096 */
1097 if (locked && !V_tcp_syncookies) {
1098 SCH_UNLOCK(sch);
1099 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1100 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
1101 "segment rejected (syncookies disabled)\n",
1102 s, __func__);
1103 goto failed;
1104 }
1105 if (locked && !V_tcp_syncookiesonly &&
1106 sch->sch_last_overflow < time_uptime - SYNCOOKIE_LIFETIME) {
1107 SCH_UNLOCK(sch);
1108 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1109 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
1110 "segment rejected (no syncache entry)\n",
1111 s, __func__);
1112 goto failed;
1113 }
1114 bzero(&scs, sizeof(scs));
1115 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop, port);
1116 if (locked)
1117 SCH_UNLOCK(sch);
1118 if (sc == NULL) {
1119 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1120 log(LOG_DEBUG, "%s; %s: Segment failed "
1121 "SYNCOOKIE authentication, segment rejected "
1122 "(probably spoofed)\n", s, __func__);
1123 goto failed;
1124 }
1125 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1126 /* If received ACK has MD5 signature, check it. */
1127 if ((to->to_flags & TOF_SIGNATURE) != 0 &&
1128 (!TCPMD5_ENABLED() ||
1129 TCPMD5_INPUT(m, th, to->to_signature) != 0)) {
1130 /* Drop the ACK. */
1131 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1132 log(LOG_DEBUG, "%s; %s: Segment rejected, "
1133 "MD5 signature doesn't match.\n",
1134 s, __func__);
1135 free(s, M_TCPLOG);
1136 }
1137 TCPSTAT_INC(tcps_sig_err_sigopt);
1138 return (-1); /* Do not send RST */
1139 }
1140 #endif /* TCP_SIGNATURE */
1141 TCPSTATES_INC(TCPS_SYN_RECEIVED);
1142 } else {
1143 if (sc->sc_port != port) {
1144 SCH_UNLOCK(sch);
1145 return (0);
1146 }
1147 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1148 /*
1149 * If listening socket requested TCP digests, check that
1150 * received ACK has signature and it is correct.
1151 * If not, drop the ACK and leave sc entry in th cache,
1152 * because SYN was received with correct signature.
1153 */
1154 if (sc->sc_flags & SCF_SIGNATURE) {
1155 if ((to->to_flags & TOF_SIGNATURE) == 0) {
1156 /* No signature */
1157 TCPSTAT_INC(tcps_sig_err_nosigopt);
1158 SCH_UNLOCK(sch);
1159 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1160 log(LOG_DEBUG, "%s; %s: Segment "
1161 "rejected, MD5 signature wasn't "
1162 "provided.\n", s, __func__);
1163 free(s, M_TCPLOG);
1164 }
1165 return (-1); /* Do not send RST */
1166 }
1167 if (!TCPMD5_ENABLED() ||
1168 TCPMD5_INPUT(m, th, to->to_signature) != 0) {
1169 /* Doesn't match or no SA */
1170 SCH_UNLOCK(sch);
1171 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1172 log(LOG_DEBUG, "%s; %s: Segment "
1173 "rejected, MD5 signature doesn't "
1174 "match.\n", s, __func__);
1175 free(s, M_TCPLOG);
1176 }
1177 return (-1); /* Do not send RST */
1178 }
1179 }
1180 #endif /* TCP_SIGNATURE */
1181
1182 /*
1183 * RFC 7323 PAWS: If we have a timestamp on this segment and
1184 * it's less than ts_recent, drop it.
1185 * XXXMT: RFC 7323 also requires to send an ACK.
1186 * In tcp_input.c this is only done for TCP segments
1187 * with user data, so be consistent here and just drop
1188 * the segment.
1189 */
1190 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS &&
1191 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) {
1192 SCH_UNLOCK(sch);
1193 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1194 log(LOG_DEBUG,
1195 "%s; %s: SEG.TSval %u < TS.Recent %u, "
1196 "segment dropped\n", s, __func__,
1197 to->to_tsval, sc->sc_tsreflect);
1198 free(s, M_TCPLOG);
1199 }
1200 return (-1); /* Do not send RST */
1201 }
1202
1203 /*
1204 * If timestamps were not negotiated during SYN/ACK and a
1205 * segment with a timestamp is received, ignore the
1206 * timestamp and process the packet normally.
1207 * See section 3.2 of RFC 7323.
1208 */
1209 if (!(sc->sc_flags & SCF_TIMESTAMP) &&
1210 (to->to_flags & TOF_TS)) {
1211 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1212 log(LOG_DEBUG, "%s; %s: Timestamp not "
1213 "expected, segment processed normally\n",
1214 s, __func__);
1215 free(s, M_TCPLOG);
1216 s = NULL;
1217 }
1218 }
1219
1220 /*
1221 * If timestamps were negotiated during SYN/ACK and a
1222 * segment without a timestamp is received, silently drop
1223 * the segment, unless the missing timestamps are tolerated.
1224 * See section 3.2 of RFC 7323.
1225 */
1226 if ((sc->sc_flags & SCF_TIMESTAMP) &&
1227 !(to->to_flags & TOF_TS)) {
1228 if (V_tcp_tolerate_missing_ts) {
1229 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1230 log(LOG_DEBUG,
1231 "%s; %s: Timestamp missing, "
1232 "segment processed normally\n",
1233 s, __func__);
1234 free(s, M_TCPLOG);
1235 }
1236 } else {
1237 SCH_UNLOCK(sch);
1238 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1239 log(LOG_DEBUG,
1240 "%s; %s: Timestamp missing, "
1241 "segment silently dropped\n",
1242 s, __func__);
1243 free(s, M_TCPLOG);
1244 }
1245 return (-1); /* Do not send RST */
1246 }
1247 }
1248 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
1249 sch->sch_length--;
1250 #ifdef TCP_OFFLOAD
1251 if (ADDED_BY_TOE(sc)) {
1252 struct toedev *tod = sc->sc_tod;
1253
1254 tod->tod_syncache_removed(tod, sc->sc_todctx);
1255 }
1256 #endif
1257 SCH_UNLOCK(sch);
1258 }
1259
1260 /*
1261 * Segment validation:
1262 * ACK must match our initial sequence number + 1 (the SYN|ACK).
1263 */
1264 if (th->th_ack != sc->sc_iss + 1) {
1265 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1266 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
1267 "rejected\n", s, __func__, th->th_ack, sc->sc_iss);
1268 goto failed;
1269 }
1270
1271 /*
1272 * The SEQ must fall in the window starting at the received
1273 * initial receive sequence number + 1 (the SYN).
1274 */
1275 if (SEQ_LEQ(th->th_seq, sc->sc_irs) ||
1276 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
1277 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1278 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
1279 "rejected\n", s, __func__, th->th_seq, sc->sc_irs);
1280 goto failed;
1281 }
1282
1283 *lsop = syncache_socket(sc, *lsop, m);
1284
1285 if (__predict_false(*lsop == NULL)) {
1286 TCPSTAT_INC(tcps_sc_aborted);
1287 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
1288 } else
1289 TCPSTAT_INC(tcps_sc_completed);
1290
1291 /* how do we find the inp for the new socket? */
1292 if (sc != &scs)
1293 syncache_free(sc);
1294 return (1);
1295 failed:
1296 if (sc != NULL) {
1297 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
1298 if (sc != &scs)
1299 syncache_free(sc);
1300 }
1301 if (s != NULL)
1302 free(s, M_TCPLOG);
1303 *lsop = NULL;
1304 return (0);
1305 }
1306
1307 static struct socket *
syncache_tfo_expand(struct syncache * sc,struct socket * lso,struct mbuf * m,uint64_t response_cookie)1308 syncache_tfo_expand(struct syncache *sc, struct socket *lso, struct mbuf *m,
1309 uint64_t response_cookie)
1310 {
1311 struct inpcb *inp;
1312 struct tcpcb *tp;
1313 unsigned int *pending_counter;
1314 struct socket *so;
1315
1316 NET_EPOCH_ASSERT();
1317
1318 pending_counter = intotcpcb(sotoinpcb(lso))->t_tfo_pending;
1319 so = syncache_socket(sc, lso, m);
1320 if (so == NULL) {
1321 TCPSTAT_INC(tcps_sc_aborted);
1322 atomic_subtract_int(pending_counter, 1);
1323 } else {
1324 soisconnected(so);
1325 inp = sotoinpcb(so);
1326 tp = intotcpcb(inp);
1327 tp->t_flags |= TF_FASTOPEN;
1328 tp->t_tfo_cookie.server = response_cookie;
1329 tp->snd_max = tp->iss;
1330 tp->snd_nxt = tp->iss;
1331 tp->t_tfo_pending = pending_counter;
1332 TCPSTATES_INC(TCPS_SYN_RECEIVED);
1333 TCPSTAT_INC(tcps_sc_completed);
1334 }
1335
1336 return (so);
1337 }
1338
1339 /*
1340 * Given a LISTEN socket and an inbound SYN request, add
1341 * this to the syn cache, and send back a segment:
1342 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
1343 * to the source.
1344 *
1345 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
1346 * Doing so would require that we hold onto the data and deliver it
1347 * to the application. However, if we are the target of a SYN-flood
1348 * DoS attack, an attacker could send data which would eventually
1349 * consume all available buffer space if it were ACKed. By not ACKing
1350 * the data, we avoid this DoS scenario.
1351 *
1352 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO)
1353 * cookie is processed and a new socket is created. In this case, any data
1354 * accompanying the SYN will be queued to the socket by tcp_input() and will
1355 * be ACKed either when the application sends response data or the delayed
1356 * ACK timer expires, whichever comes first.
1357 */
1358 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)1359 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1360 struct inpcb *inp, struct socket *so, struct mbuf *m, void *tod,
1361 void *todctx, uint8_t iptos, uint16_t port)
1362 {
1363 struct tcpcb *tp;
1364 struct socket *rv = NULL;
1365 struct syncache *sc = NULL;
1366 struct syncache_head *sch;
1367 struct mbuf *ipopts = NULL;
1368 u_int ltflags;
1369 int win, ip_ttl, ip_tos;
1370 char *s;
1371 #ifdef INET6
1372 int autoflowlabel = 0;
1373 #endif
1374 #ifdef MAC
1375 struct label *maclabel = NULL;
1376 #endif
1377 struct syncache scs;
1378 uint64_t tfo_response_cookie;
1379 unsigned int *tfo_pending = NULL;
1380 int tfo_cookie_valid = 0;
1381 int tfo_response_cookie_valid = 0;
1382 bool locked;
1383
1384 INP_RLOCK_ASSERT(inp); /* listen socket */
1385 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
1386 ("%s: unexpected tcp flags", __func__));
1387
1388 /*
1389 * Combine all so/tp operations very early to drop the INP lock as
1390 * soon as possible.
1391 */
1392 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so));
1393 tp = sototcpcb(so);
1394
1395 #ifdef INET6
1396 if (inc->inc_flags & INC_ISIPV6) {
1397 if (inp->inp_flags & IN6P_AUTOFLOWLABEL) {
1398 autoflowlabel = 1;
1399 }
1400 ip_ttl = in6_selecthlim(inp, NULL);
1401 if ((inp->in6p_outputopts == NULL) ||
1402 (inp->in6p_outputopts->ip6po_tclass == -1)) {
1403 ip_tos = 0;
1404 } else {
1405 ip_tos = inp->in6p_outputopts->ip6po_tclass;
1406 }
1407 }
1408 #endif
1409 #if defined(INET6) && defined(INET)
1410 else
1411 #endif
1412 #ifdef INET
1413 {
1414 ip_ttl = inp->inp_ip_ttl;
1415 ip_tos = inp->inp_ip_tos;
1416 }
1417 #endif
1418 win = so->sol_sbrcv_hiwat;
1419 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE));
1420
1421 if (V_tcp_fastopen_server_enable && (tp->t_flags & TF_FASTOPEN) &&
1422 (tp->t_tfo_pending != NULL) &&
1423 (to->to_flags & TOF_FASTOPEN)) {
1424 /*
1425 * Limit the number of pending TFO connections to
1426 * approximately half of the queue limit. This prevents TFO
1427 * SYN floods from starving the service by filling the
1428 * listen queue with bogus TFO connections.
1429 */
1430 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <=
1431 (so->sol_qlimit / 2)) {
1432 int result;
1433
1434 result = tcp_fastopen_check_cookie(inc,
1435 to->to_tfo_cookie, to->to_tfo_len,
1436 &tfo_response_cookie);
1437 tfo_cookie_valid = (result > 0);
1438 tfo_response_cookie_valid = (result >= 0);
1439 }
1440
1441 /*
1442 * Remember the TFO pending counter as it will have to be
1443 * decremented below if we don't make it to syncache_tfo_expand().
1444 */
1445 tfo_pending = tp->t_tfo_pending;
1446 }
1447
1448 #ifdef MAC
1449 if (mac_syncache_init(&maclabel) != 0) {
1450 INP_RUNLOCK(inp);
1451 goto done;
1452 } else
1453 mac_syncache_create(maclabel, inp);
1454 #endif
1455 if (!tfo_cookie_valid)
1456 INP_RUNLOCK(inp);
1457
1458 /*
1459 * Remember the IP options, if any.
1460 */
1461 #ifdef INET6
1462 if (!(inc->inc_flags & INC_ISIPV6))
1463 #endif
1464 #ifdef INET
1465 ipopts = (m) ? ip_srcroute(m) : NULL;
1466 #else
1467 ipopts = NULL;
1468 #endif
1469
1470 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1471 /*
1472 * When the socket is TCP-MD5 enabled check that,
1473 * - a signed packet is valid
1474 * - a non-signed packet does not have a security association
1475 *
1476 * If a signed packet fails validation or a non-signed packet has a
1477 * security association, the packet will be dropped.
1478 */
1479 if (ltflags & TF_SIGNATURE) {
1480 if (to->to_flags & TOF_SIGNATURE) {
1481 if (!TCPMD5_ENABLED() ||
1482 TCPMD5_INPUT(m, th, to->to_signature) != 0)
1483 goto done;
1484 } else {
1485 if (TCPMD5_ENABLED() &&
1486 TCPMD5_INPUT(m, NULL, NULL) != ENOENT)
1487 goto done;
1488 }
1489 } else if (to->to_flags & TOF_SIGNATURE)
1490 goto done;
1491 #endif /* TCP_SIGNATURE */
1492 /*
1493 * See if we already have an entry for this connection.
1494 * If we do, resend the SYN,ACK, and reset the retransmit timer.
1495 *
1496 * XXX: should the syncache be re-initialized with the contents
1497 * of the new SYN here (which may have different options?)
1498 *
1499 * XXX: We do not check the sequence number to see if this is a
1500 * real retransmit or a new connection attempt. The question is
1501 * how to handle such a case; either ignore it as spoofed, or
1502 * drop the current entry and create a new one?
1503 */
1504 if (syncache_cookiesonly()) {
1505 sc = NULL;
1506 sch = syncache_hashbucket(inc);
1507 locked = false;
1508 } else {
1509 sc = syncache_lookup(inc, &sch); /* returns locked sch */
1510 locked = true;
1511 SCH_LOCK_ASSERT(sch);
1512 }
1513 if (sc != NULL) {
1514 if (tfo_cookie_valid)
1515 INP_RUNLOCK(inp);
1516 TCPSTAT_INC(tcps_sc_dupsyn);
1517 if (ipopts) {
1518 /*
1519 * If we were remembering a previous source route,
1520 * forget it and use the new one we've been given.
1521 */
1522 if (sc->sc_ipopts)
1523 (void)m_free(sc->sc_ipopts);
1524 sc->sc_ipopts = ipopts;
1525 }
1526 /*
1527 * Update timestamp if present.
1528 */
1529 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
1530 sc->sc_tsreflect = to->to_tsval;
1531 else
1532 sc->sc_flags &= ~SCF_TIMESTAMP;
1533 /*
1534 * Adjust ECN response if needed, e.g. different
1535 * IP ECN field, or a fallback by the remote host.
1536 */
1537 if (sc->sc_flags & SCF_ECN_MASK) {
1538 sc->sc_flags &= ~SCF_ECN_MASK;
1539 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos);
1540 }
1541 #ifdef MAC
1542 /*
1543 * Since we have already unconditionally allocated label
1544 * storage, free it up. The syncache entry will already
1545 * have an initialized label we can use.
1546 */
1547 mac_syncache_destroy(&maclabel);
1548 #endif
1549 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1550 /* Retransmit SYN|ACK and reset retransmit count. */
1551 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
1552 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
1553 "resetting timer and retransmitting SYN|ACK\n",
1554 s, __func__);
1555 free(s, M_TCPLOG);
1556 }
1557 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) {
1558 sc->sc_rxmits = 0;
1559 syncache_timeout(sc, sch, 1);
1560 TCPSTAT_INC(tcps_sndacks);
1561 TCPSTAT_INC(tcps_sndtotal);
1562 } else {
1563 syncache_drop(sc, sch);
1564 TCPSTAT_INC(tcps_sc_dropped);
1565 }
1566 SCH_UNLOCK(sch);
1567 goto donenoprobe;
1568 }
1569
1570 KASSERT(sc == NULL, ("sc(%p) != NULL", sc));
1571 /*
1572 * Skip allocating a syncache entry if we are just going to discard
1573 * it later.
1574 */
1575 if (!locked || tfo_cookie_valid) {
1576 bzero(&scs, sizeof(scs));
1577 sc = &scs;
1578 } else {
1579 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1580 if (sc == NULL) {
1581 /*
1582 * The zone allocator couldn't provide more entries.
1583 * Treat this as if the cache was full; drop the oldest
1584 * entry and insert the new one.
1585 */
1586 TCPSTAT_INC(tcps_sc_zonefail);
1587 sc = TAILQ_LAST(&sch->sch_bucket, sch_head);
1588 if (sc != NULL) {
1589 sch->sch_last_overflow = time_uptime;
1590 syncache_drop(sc, sch);
1591 syncache_pause(inc);
1592 }
1593 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1594 if (sc == NULL) {
1595 if (V_tcp_syncookies) {
1596 bzero(&scs, sizeof(scs));
1597 sc = &scs;
1598 } else {
1599 KASSERT(locked,
1600 ("%s: bucket unexpectedly unlocked",
1601 __func__));
1602 SCH_UNLOCK(sch);
1603 goto done;
1604 }
1605 }
1606 }
1607 }
1608
1609 KASSERT(sc != NULL, ("sc == NULL"));
1610 if (!tfo_cookie_valid && tfo_response_cookie_valid)
1611 sc->sc_tfo_cookie = &tfo_response_cookie;
1612
1613 /*
1614 * Fill in the syncache values.
1615 */
1616 #ifdef MAC
1617 sc->sc_label = maclabel;
1618 #endif
1619 /*
1620 * sc_cred is only used in syncache_pcblist() to list TCP endpoints in
1621 * TCPS_SYN_RECEIVED state when V_tcp_syncache.see_other is false.
1622 * Therefore, store the credentials and take a reference count only
1623 * when needed:
1624 * - sc is allocated from the zone and not using the on stack instance.
1625 * - the sysctl variable net.inet.tcp.syncache.see_other is false.
1626 * The reference count is decremented when a zone allocated sc is
1627 * freed in syncache_free().
1628 */
1629 if (sc != &scs && !V_tcp_syncache.see_other)
1630 sc->sc_cred = crhold(so->so_cred);
1631 else
1632 sc->sc_cred = NULL;
1633 sc->sc_port = port;
1634 sc->sc_ipopts = ipopts;
1635 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1636 sc->sc_ip_tos = ip_tos;
1637 sc->sc_ip_ttl = ip_ttl;
1638 #ifdef TCP_OFFLOAD
1639 sc->sc_tod = tod;
1640 sc->sc_todctx = todctx;
1641 #endif
1642 sc->sc_irs = th->th_seq;
1643 sc->sc_flags = 0;
1644 sc->sc_flowlabel = 0;
1645
1646 /*
1647 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
1648 * win was derived from socket earlier in the function.
1649 */
1650 win = imax(win, 0);
1651 win = imin(win, TCP_MAXWIN);
1652 sc->sc_wnd = win;
1653
1654 if (V_tcp_do_rfc1323 &&
1655 !(ltflags & TF_NOOPT)) {
1656 /*
1657 * A timestamp received in a SYN makes
1658 * it ok to send timestamp requests and replies.
1659 */
1660 if ((to->to_flags & TOF_TS) && (V_tcp_do_rfc1323 != 2)) {
1661 sc->sc_tsreflect = to->to_tsval;
1662 sc->sc_flags |= SCF_TIMESTAMP;
1663 sc->sc_tsoff = tcp_new_ts_offset(inc);
1664 }
1665 if ((to->to_flags & TOF_SCALE) && (V_tcp_do_rfc1323 != 3)) {
1666 int wscale = 0;
1667
1668 /*
1669 * Pick the smallest possible scaling factor that
1670 * will still allow us to scale up to sb_max, aka
1671 * kern.ipc.maxsockbuf.
1672 *
1673 * We do this because there are broken firewalls that
1674 * will corrupt the window scale option, leading to
1675 * the other endpoint believing that our advertised
1676 * window is unscaled. At scale factors larger than
1677 * 5 the unscaled window will drop below 1500 bytes,
1678 * leading to serious problems when traversing these
1679 * broken firewalls.
1680 *
1681 * With the default maxsockbuf of 256K, a scale factor
1682 * of 3 will be chosen by this algorithm. Those who
1683 * choose a larger maxsockbuf should watch out
1684 * for the compatibility problems mentioned above.
1685 *
1686 * RFC1323: The Window field in a SYN (i.e., a <SYN>
1687 * or <SYN,ACK>) segment itself is never scaled.
1688 */
1689 while (wscale < TCP_MAX_WINSHIFT &&
1690 (TCP_MAXWIN << wscale) < sb_max)
1691 wscale++;
1692 sc->sc_requested_r_scale = wscale;
1693 sc->sc_requested_s_scale = to->to_wscale;
1694 sc->sc_flags |= SCF_WINSCALE;
1695 }
1696 }
1697 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1698 /*
1699 * If incoming packet has an MD5 signature, flag this in the
1700 * syncache so that syncache_respond() will do the right thing
1701 * with the SYN+ACK.
1702 */
1703 if (to->to_flags & TOF_SIGNATURE)
1704 sc->sc_flags |= SCF_SIGNATURE;
1705 #endif /* TCP_SIGNATURE */
1706 if (to->to_flags & TOF_SACKPERM)
1707 sc->sc_flags |= SCF_SACK;
1708 if (to->to_flags & TOF_MSS)
1709 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */
1710 if (ltflags & TF_NOOPT)
1711 sc->sc_flags |= SCF_NOOPT;
1712 /* ECN Handshake */
1713 if (V_tcp_do_ecn && (tp->t_flags2 & TF2_CANNOT_DO_ECN) == 0)
1714 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos);
1715
1716 if (V_tcp_syncookies)
1717 sc->sc_iss = syncookie_generate(sch, sc);
1718 else
1719 sc->sc_iss = arc4random();
1720 #ifdef INET6
1721 if (autoflowlabel) {
1722 if (V_tcp_syncookies)
1723 sc->sc_flowlabel = sc->sc_iss;
1724 else
1725 sc->sc_flowlabel = ip6_randomflowlabel();
1726 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK;
1727 }
1728 #endif
1729 if (locked)
1730 SCH_UNLOCK(sch);
1731
1732 if (tfo_cookie_valid) {
1733 rv = syncache_tfo_expand(sc, so, m, tfo_response_cookie);
1734 /* INP_RUNLOCK(inp) will be performed by the caller */
1735 goto tfo_expanded;
1736 }
1737
1738 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1739 /*
1740 * Do a standard 3-way handshake.
1741 */
1742 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) {
1743 if (sc != &scs)
1744 syncache_insert(sc, sch); /* locks and unlocks sch */
1745 TCPSTAT_INC(tcps_sndacks);
1746 TCPSTAT_INC(tcps_sndtotal);
1747 } else {
1748 if (sc != &scs)
1749 syncache_free(sc);
1750 TCPSTAT_INC(tcps_sc_dropped);
1751 }
1752 goto donenoprobe;
1753
1754 done:
1755 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1756 donenoprobe:
1757 if (m)
1758 m_freem(m);
1759 /*
1760 * If tfo_pending is not NULL here, then a TFO SYN that did not
1761 * result in a new socket was processed and the associated pending
1762 * counter has not yet been decremented. All such TFO processing paths
1763 * transit this point.
1764 */
1765 if (tfo_pending != NULL)
1766 tcp_fastopen_decrement_counter(tfo_pending);
1767
1768 tfo_expanded:
1769 if (sc == NULL || sc == &scs) {
1770 #ifdef MAC
1771 mac_syncache_destroy(&maclabel);
1772 #endif
1773 if (ipopts)
1774 (void)m_free(ipopts);
1775 }
1776 return (rv);
1777 }
1778
1779 /*
1780 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment,
1781 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL.
1782 */
1783 static int
syncache_respond(struct syncache * sc,const struct mbuf * m0,int flags)1784 syncache_respond(struct syncache *sc, const struct mbuf *m0, int flags)
1785 {
1786 struct ip *ip = NULL;
1787 struct mbuf *m;
1788 struct tcphdr *th = NULL;
1789 struct udphdr *udp = NULL;
1790 int optlen, error = 0; /* Make compiler happy */
1791 u_int16_t hlen, tlen, mssopt, ulen;
1792 struct tcpopt to;
1793 #ifdef INET6
1794 struct ip6_hdr *ip6 = NULL;
1795 #endif
1796
1797 NET_EPOCH_ASSERT();
1798
1799 hlen =
1800 #ifdef INET6
1801 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
1802 #endif
1803 sizeof(struct ip);
1804 tlen = hlen + sizeof(struct tcphdr);
1805 if (sc->sc_port) {
1806 tlen += sizeof(struct udphdr);
1807 }
1808 /* Determine MSS we advertize to other end of connection. */
1809 mssopt = tcp_mssopt(&sc->sc_inc);
1810 if (sc->sc_port)
1811 mssopt -= V_tcp_udp_tunneling_overhead;
1812 mssopt = max(mssopt, V_tcp_minmss);
1813
1814 /* XXX: Assume that the entire packet will fit in a header mbuf. */
1815 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
1816 ("syncache: mbuf too small: hlen %u, sc_port %u, max_linkhdr %d + "
1817 "tlen %d + TCP_MAXOLEN %ju <= MHLEN %d", hlen, sc->sc_port,
1818 max_linkhdr, tlen, (uintmax_t)TCP_MAXOLEN, MHLEN));
1819
1820 /* Create the IP+TCP header from scratch. */
1821 m = m_gethdr(M_NOWAIT, MT_DATA);
1822 if (m == NULL)
1823 return (ENOBUFS);
1824 #ifdef MAC
1825 mac_syncache_create_mbuf(sc->sc_label, m);
1826 #endif
1827 m->m_data += max_linkhdr;
1828 m->m_len = tlen;
1829 m->m_pkthdr.len = tlen;
1830 m->m_pkthdr.rcvif = NULL;
1831
1832 #ifdef INET6
1833 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1834 ip6 = mtod(m, struct ip6_hdr *);
1835 ip6->ip6_vfc = IPV6_VERSION;
1836 ip6->ip6_src = sc->sc_inc.inc6_laddr;
1837 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
1838 ip6->ip6_plen = htons(tlen - hlen);
1839 /* ip6_hlim is set after checksum */
1840 /* Zero out traffic class and flow label. */
1841 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK;
1842 ip6->ip6_flow |= sc->sc_flowlabel;
1843 if (sc->sc_port != 0) {
1844 ip6->ip6_nxt = IPPROTO_UDP;
1845 udp = (struct udphdr *)(ip6 + 1);
1846 udp->uh_sport = htons(V_tcp_udp_tunneling_port);
1847 udp->uh_dport = sc->sc_port;
1848 ulen = (tlen - sizeof(struct ip6_hdr));
1849 th = (struct tcphdr *)(udp + 1);
1850 } else {
1851 ip6->ip6_nxt = IPPROTO_TCP;
1852 th = (struct tcphdr *)(ip6 + 1);
1853 }
1854 ip6->ip6_flow |= htonl(sc->sc_ip_tos << IPV6_FLOWLABEL_LEN);
1855 }
1856 #endif
1857 #if defined(INET6) && defined(INET)
1858 else
1859 #endif
1860 #ifdef INET
1861 {
1862 ip = mtod(m, struct ip *);
1863 ip->ip_v = IPVERSION;
1864 ip->ip_hl = sizeof(struct ip) >> 2;
1865 ip->ip_len = htons(tlen);
1866 ip->ip_id = 0;
1867 ip->ip_off = 0;
1868 ip->ip_sum = 0;
1869 ip->ip_src = sc->sc_inc.inc_laddr;
1870 ip->ip_dst = sc->sc_inc.inc_faddr;
1871 ip->ip_ttl = sc->sc_ip_ttl;
1872 ip->ip_tos = sc->sc_ip_tos;
1873
1874 /*
1875 * See if we should do MTU discovery. Route lookups are
1876 * expensive, so we will only unset the DF bit if:
1877 *
1878 * 1) path_mtu_discovery is disabled
1879 * 2) the SCF_UNREACH flag has been set
1880 */
1881 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
1882 ip->ip_off |= htons(IP_DF);
1883 if (sc->sc_port == 0) {
1884 ip->ip_p = IPPROTO_TCP;
1885 th = (struct tcphdr *)(ip + 1);
1886 } else {
1887 ip->ip_p = IPPROTO_UDP;
1888 udp = (struct udphdr *)(ip + 1);
1889 udp->uh_sport = htons(V_tcp_udp_tunneling_port);
1890 udp->uh_dport = sc->sc_port;
1891 ulen = (tlen - sizeof(struct ip));
1892 th = (struct tcphdr *)(udp + 1);
1893 }
1894 }
1895 #endif /* INET */
1896 th->th_sport = sc->sc_inc.inc_lport;
1897 th->th_dport = sc->sc_inc.inc_fport;
1898
1899 if (flags & TH_SYN)
1900 th->th_seq = htonl(sc->sc_iss);
1901 else
1902 th->th_seq = htonl(sc->sc_iss + 1);
1903 th->th_ack = htonl(sc->sc_irs + 1);
1904 th->th_off = sizeof(struct tcphdr) >> 2;
1905 th->th_win = htons(sc->sc_wnd);
1906 th->th_urp = 0;
1907
1908 flags = tcp_ecn_syncache_respond(flags, sc);
1909 tcp_set_flags(th, flags);
1910
1911 /* Tack on the TCP options. */
1912 if ((sc->sc_flags & SCF_NOOPT) == 0) {
1913 to.to_flags = 0;
1914
1915 if (flags & TH_SYN) {
1916 to.to_mss = mssopt;
1917 to.to_flags = TOF_MSS;
1918 if (sc->sc_flags & SCF_WINSCALE) {
1919 to.to_wscale = sc->sc_requested_r_scale;
1920 to.to_flags |= TOF_SCALE;
1921 }
1922 if (sc->sc_flags & SCF_SACK)
1923 to.to_flags |= TOF_SACKPERM;
1924 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1925 if (sc->sc_flags & SCF_SIGNATURE)
1926 to.to_flags |= TOF_SIGNATURE;
1927 #endif
1928 if (sc->sc_tfo_cookie) {
1929 to.to_flags |= TOF_FASTOPEN;
1930 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
1931 to.to_tfo_cookie = sc->sc_tfo_cookie;
1932 /* don't send cookie again when retransmitting response */
1933 sc->sc_tfo_cookie = NULL;
1934 }
1935 }
1936 if (sc->sc_flags & SCF_TIMESTAMP) {
1937 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks();
1938 to.to_tsecr = sc->sc_tsreflect;
1939 to.to_flags |= TOF_TS;
1940 }
1941 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
1942
1943 /* Adjust headers by option size. */
1944 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
1945 m->m_len += optlen;
1946 m->m_pkthdr.len += optlen;
1947 #ifdef INET6
1948 if (sc->sc_inc.inc_flags & INC_ISIPV6)
1949 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
1950 else
1951 #endif
1952 ip->ip_len = htons(ntohs(ip->ip_len) + optlen);
1953 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1954 if (sc->sc_flags & SCF_SIGNATURE) {
1955 KASSERT(to.to_flags & TOF_SIGNATURE,
1956 ("tcp_addoptions() didn't set tcp_signature"));
1957
1958 /* NOTE: to.to_signature is inside of mbuf */
1959 if (!TCPMD5_ENABLED() ||
1960 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) {
1961 m_freem(m);
1962 return (EACCES);
1963 }
1964 }
1965 #endif
1966 } else
1967 optlen = 0;
1968
1969 if (udp) {
1970 ulen += optlen;
1971 udp->uh_ulen = htons(ulen);
1972 }
1973 M_SETFIB(m, sc->sc_inc.inc_fibnum);
1974 /*
1975 * If we have peer's SYN and it has a flowid, then let's assign it to
1976 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid
1977 * to SYN|ACK due to lack of inp here.
1978 */
1979 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) {
1980 m->m_pkthdr.flowid = m0->m_pkthdr.flowid;
1981 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0));
1982 }
1983 #ifdef INET6
1984 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1985 if (sc->sc_port) {
1986 m->m_pkthdr.csum_flags = CSUM_UDP_IPV6;
1987 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
1988 udp->uh_sum = in6_cksum_pseudo(ip6, ulen,
1989 IPPROTO_UDP, 0);
1990 th->th_sum = htons(0);
1991 } else {
1992 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
1993 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1994 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen,
1995 IPPROTO_TCP, 0);
1996 }
1997 ip6->ip6_hlim = sc->sc_ip_ttl;
1998 #ifdef TCP_OFFLOAD
1999 if (ADDED_BY_TOE(sc)) {
2000 struct toedev *tod = sc->sc_tod;
2001
2002 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
2003
2004 return (error);
2005 }
2006 #endif
2007 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th);
2008 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
2009 }
2010 #endif
2011 #if defined(INET6) && defined(INET)
2012 else
2013 #endif
2014 #ifdef INET
2015 {
2016 if (sc->sc_port) {
2017 m->m_pkthdr.csum_flags = CSUM_UDP;
2018 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
2019 udp->uh_sum = in_pseudo(ip->ip_src.s_addr,
2020 ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP));
2021 th->th_sum = htons(0);
2022 } else {
2023 m->m_pkthdr.csum_flags = CSUM_TCP;
2024 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
2025 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
2026 htons(tlen + optlen - hlen + IPPROTO_TCP));
2027 }
2028 #ifdef TCP_OFFLOAD
2029 if (ADDED_BY_TOE(sc)) {
2030 struct toedev *tod = sc->sc_tod;
2031
2032 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
2033
2034 return (error);
2035 }
2036 #endif
2037 TCP_PROBE5(send, NULL, NULL, ip, NULL, th);
2038 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
2039 }
2040 #endif
2041 return (error);
2042 }
2043
2044 /*
2045 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks
2046 * that exceed the capacity of the syncache by avoiding the storage of any
2047 * of the SYNs we receive. Syncookies defend against blind SYN flooding
2048 * attacks where the attacker does not have access to our responses.
2049 *
2050 * Syncookies encode and include all necessary information about the
2051 * connection setup within the SYN|ACK that we send back. That way we
2052 * can avoid keeping any local state until the ACK to our SYN|ACK returns
2053 * (if ever). Normally the syncache and syncookies are running in parallel
2054 * with the latter taking over when the former is exhausted. When matching
2055 * syncache entry is found the syncookie is ignored.
2056 *
2057 * The only reliable information persisting the 3WHS is our initial sequence
2058 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient
2059 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS
2060 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK
2061 * returns and signifies a legitimate connection if it matches the ACK.
2062 *
2063 * The available space of 32 bits to store the hash and to encode the SYN
2064 * option information is very tight and we should have at least 24 bits for
2065 * the MAC to keep the number of guesses by blind spoofing reasonably high.
2066 *
2067 * SYN option information we have to encode to fully restore a connection:
2068 * MSS: is imporant to chose an optimal segment size to avoid IP level
2069 * fragmentation along the path. The common MSS values can be encoded
2070 * in a 3-bit table. Uncommon values are captured by the next lower value
2071 * in the table leading to a slight increase in packetization overhead.
2072 * WSCALE: is necessary to allow large windows to be used for high delay-
2073 * bandwidth product links. Not scaling the window when it was initially
2074 * negotiated is bad for performance as lack of scaling further decreases
2075 * the apparent available send window. We only need to encode the WSCALE
2076 * we received from the remote end. Our end can be recalculated at any
2077 * time. The common WSCALE values can be encoded in a 3-bit table.
2078 * Uncommon values are captured by the next lower value in the table
2079 * making us under-estimate the available window size halving our
2080 * theoretically possible maximum throughput for that connection.
2081 * SACK: Greatly assists in packet loss recovery and requires 1 bit.
2082 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options
2083 * that are included in all segments on a connection. We enable them when
2084 * the ACK has them.
2085 *
2086 * Security of syncookies and attack vectors:
2087 *
2088 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod)
2089 * together with the gloabl secret to make it unique per connection attempt.
2090 * Thus any change of any of those parameters results in a different MAC output
2091 * in an unpredictable way unless a collision is encountered. 24 bits of the
2092 * MAC are embedded into the ISS.
2093 *
2094 * To prevent replay attacks two rotating global secrets are updated with a
2095 * new random value every 15 seconds. The life-time of a syncookie is thus
2096 * 15-30 seconds.
2097 *
2098 * Vector 1: Attacking the secret. This requires finding a weakness in the
2099 * MAC itself or the way it is used here. The attacker can do a chosen plain
2100 * text attack by varying and testing the all parameters under his control.
2101 * The strength depends on the size and randomness of the secret, and the
2102 * cryptographic security of the MAC function. Due to the constant updating
2103 * of the secret the attacker has at most 29.999 seconds to find the secret
2104 * and launch spoofed connections. After that he has to start all over again.
2105 *
2106 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC
2107 * size an average of 4,823 attempts are required for a 50% chance of success
2108 * to spoof a single syncookie (birthday collision paradox). However the
2109 * attacker is blind and doesn't know if one of his attempts succeeded unless
2110 * he has a side channel to interfere success from. A single connection setup
2111 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets.
2112 * This many attempts are required for each one blind spoofed connection. For
2113 * every additional spoofed connection he has to launch another N attempts.
2114 * Thus for a sustained rate 100 spoofed connections per second approximately
2115 * 1,800,000 packets per second would have to be sent.
2116 *
2117 * NB: The MAC function should be fast so that it doesn't become a CPU
2118 * exhaustion attack vector itself.
2119 *
2120 * References:
2121 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations
2122 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996
2123 * http://cr.yp.to/syncookies.html (overview)
2124 * http://cr.yp.to/syncookies/archive (details)
2125 *
2126 *
2127 * Schematic construction of a syncookie enabled Initial Sequence Number:
2128 * 0 1 2 3
2129 * 12345678901234567890123456789012
2130 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP|
2131 *
2132 * x 24 MAC (truncated)
2133 * W 3 Send Window Scale index
2134 * M 3 MSS index
2135 * S 1 SACK permitted
2136 * P 1 Odd/even secret
2137 */
2138
2139 /*
2140 * Distribution and probability of certain MSS values. Those in between are
2141 * rounded down to the next lower one.
2142 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011]
2143 * .2% .3% 5% 7% 7% 20% 15% 45%
2144 */
2145 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 };
2146
2147 /*
2148 * Distribution and probability of certain WSCALE values. We have to map the
2149 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3
2150 * bits based on prevalence of certain values. Where we don't have an exact
2151 * match for are rounded down to the next lower one letting us under-estimate
2152 * the true available window. At the moment this would happen only for the
2153 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer
2154 * and window size). The absence of the WSCALE option (no scaling in either
2155 * direction) is encoded with index zero.
2156 * [WSCALE values histograms, Allman, 2012]
2157 * X 10 10 35 5 6 14 10% by host
2158 * X 11 4 5 5 18 49 3% by connections
2159 */
2160 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 };
2161
2162 /*
2163 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed
2164 * and good cryptographic properties.
2165 */
2166 static uint32_t
syncookie_mac(struct in_conninfo * inc,tcp_seq irs,uint8_t flags,uint8_t * secbits,uintptr_t secmod)2167 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags,
2168 uint8_t *secbits, uintptr_t secmod)
2169 {
2170 SIPHASH_CTX ctx;
2171 uint32_t siphash[2];
2172
2173 SipHash24_Init(&ctx);
2174 SipHash_SetKey(&ctx, secbits);
2175 switch (inc->inc_flags & INC_ISIPV6) {
2176 #ifdef INET
2177 case 0:
2178 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr));
2179 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr));
2180 break;
2181 #endif
2182 #ifdef INET6
2183 case INC_ISIPV6:
2184 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr));
2185 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr));
2186 break;
2187 #endif
2188 }
2189 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport));
2190 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport));
2191 SipHash_Update(&ctx, &irs, sizeof(irs));
2192 SipHash_Update(&ctx, &flags, sizeof(flags));
2193 SipHash_Update(&ctx, &secmod, sizeof(secmod));
2194 SipHash_Final((u_int8_t *)&siphash, &ctx);
2195
2196 return (siphash[0] ^ siphash[1]);
2197 }
2198
2199 static tcp_seq
syncookie_generate(struct syncache_head * sch,struct syncache * sc)2200 syncookie_generate(struct syncache_head *sch, struct syncache *sc)
2201 {
2202 u_int i, secbit, wscale;
2203 uint32_t iss, hash;
2204 uint8_t *secbits;
2205 union syncookie cookie;
2206
2207 cookie.cookie = 0;
2208
2209 /* Map our computed MSS into the 3-bit index. */
2210 for (i = nitems(tcp_sc_msstab) - 1;
2211 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0;
2212 i--)
2213 ;
2214 cookie.flags.mss_idx = i;
2215
2216 /*
2217 * Map the send window scale into the 3-bit index but only if
2218 * the wscale option was received.
2219 */
2220 if (sc->sc_flags & SCF_WINSCALE) {
2221 wscale = sc->sc_requested_s_scale;
2222 for (i = nitems(tcp_sc_wstab) - 1;
2223 tcp_sc_wstab[i] > wscale && i > 0;
2224 i--)
2225 ;
2226 cookie.flags.wscale_idx = i;
2227 }
2228
2229 /* Can we do SACK? */
2230 if (sc->sc_flags & SCF_SACK)
2231 cookie.flags.sack_ok = 1;
2232
2233 /* Which of the two secrets to use. */
2234 secbit = V_tcp_syncache.secret.oddeven & 0x1;
2235 cookie.flags.odd_even = secbit;
2236
2237 secbits = V_tcp_syncache.secret.key[secbit];
2238 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits,
2239 (uintptr_t)sch);
2240
2241 /*
2242 * Put the flags into the hash and XOR them to get better ISS number
2243 * variance. This doesn't enhance the cryptographic strength and is
2244 * done to prevent the 8 cookie bits from showing up directly on the
2245 * wire.
2246 */
2247 iss = hash & ~0xff;
2248 iss |= cookie.cookie ^ (hash >> 24);
2249
2250 TCPSTAT_INC(tcps_sc_sendcookie);
2251 return (iss);
2252 }
2253
2254 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)2255 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch,
2256 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
2257 struct socket *lso, uint16_t port)
2258 {
2259 uint32_t hash;
2260 uint8_t *secbits;
2261 tcp_seq ack, seq;
2262 int wnd, wscale = 0;
2263 union syncookie cookie;
2264
2265 /*
2266 * Pull information out of SYN-ACK/ACK and revert sequence number
2267 * advances.
2268 */
2269 ack = th->th_ack - 1;
2270 seq = th->th_seq - 1;
2271
2272 /*
2273 * Unpack the flags containing enough information to restore the
2274 * connection.
2275 */
2276 cookie.cookie = (ack & 0xff) ^ (ack >> 24);
2277
2278 /* Which of the two secrets to use. */
2279 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even];
2280
2281 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch);
2282
2283 /* The recomputed hash matches the ACK if this was a genuine cookie. */
2284 if ((ack & ~0xff) != (hash & ~0xff))
2285 return (NULL);
2286
2287 /* Fill in the syncache values. */
2288 sc->sc_flags = 0;
2289 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
2290 sc->sc_ipopts = NULL;
2291
2292 sc->sc_irs = seq;
2293 sc->sc_iss = ack;
2294
2295 switch (inc->inc_flags & INC_ISIPV6) {
2296 #ifdef INET
2297 case 0:
2298 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl;
2299 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos;
2300 break;
2301 #endif
2302 #ifdef INET6
2303 case INC_ISIPV6:
2304 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL)
2305 sc->sc_flowlabel =
2306 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK;
2307 break;
2308 #endif
2309 }
2310
2311 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx];
2312
2313 /* We can simply recompute receive window scale we sent earlier. */
2314 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max)
2315 wscale++;
2316
2317 /* Only use wscale if it was enabled in the orignal SYN. */
2318 if (cookie.flags.wscale_idx > 0) {
2319 sc->sc_requested_r_scale = wscale;
2320 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx];
2321 sc->sc_flags |= SCF_WINSCALE;
2322 }
2323
2324 wnd = lso->sol_sbrcv_hiwat;
2325 wnd = imax(wnd, 0);
2326 wnd = imin(wnd, TCP_MAXWIN);
2327 sc->sc_wnd = wnd;
2328
2329 if (cookie.flags.sack_ok)
2330 sc->sc_flags |= SCF_SACK;
2331
2332 if (to->to_flags & TOF_TS) {
2333 sc->sc_flags |= SCF_TIMESTAMP;
2334 sc->sc_tsreflect = to->to_tsval;
2335 sc->sc_tsoff = tcp_new_ts_offset(inc);
2336 }
2337
2338 if (to->to_flags & TOF_SIGNATURE)
2339 sc->sc_flags |= SCF_SIGNATURE;
2340
2341 sc->sc_rxmits = 0;
2342
2343 sc->sc_port = port;
2344
2345 TCPSTAT_INC(tcps_sc_recvcookie);
2346 return (sc);
2347 }
2348
2349 #ifdef INVARIANTS
2350 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)2351 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
2352 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
2353 struct socket *lso, uint16_t port)
2354 {
2355 struct syncache scs, *scx;
2356 char *s;
2357
2358 bzero(&scs, sizeof(scs));
2359 scx = syncookie_lookup(inc, sch, &scs, th, to, lso, port);
2360
2361 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL)
2362 return (0);
2363
2364 if (scx != NULL) {
2365 if (sc->sc_peer_mss != scx->sc_peer_mss)
2366 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n",
2367 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss);
2368
2369 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale)
2370 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n",
2371 s, __func__, sc->sc_requested_r_scale,
2372 scx->sc_requested_r_scale);
2373
2374 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale)
2375 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n",
2376 s, __func__, sc->sc_requested_s_scale,
2377 scx->sc_requested_s_scale);
2378
2379 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK))
2380 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__);
2381 }
2382
2383 if (s != NULL)
2384 free(s, M_TCPLOG);
2385 return (0);
2386 }
2387 #endif /* INVARIANTS */
2388
2389 static void
syncookie_reseed(void * arg)2390 syncookie_reseed(void *arg)
2391 {
2392 struct tcp_syncache *sc = arg;
2393 uint8_t *secbits;
2394 int secbit;
2395
2396 /*
2397 * Reseeding the secret doesn't have to be protected by a lock.
2398 * It only must be ensured that the new random values are visible
2399 * to all CPUs in a SMP environment. The atomic with release
2400 * semantics ensures that.
2401 */
2402 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1;
2403 secbits = sc->secret.key[secbit];
2404 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0);
2405 atomic_add_rel_int(&sc->secret.oddeven, 1);
2406
2407 /* Reschedule ourself. */
2408 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz);
2409 }
2410
2411 /*
2412 * We have overflowed a bucket. Let's pause dealing with the syncache.
2413 * This function will increment the bucketoverflow statistics appropriately
2414 * (once per pause when pausing is enabled; otherwise, once per overflow).
2415 */
2416 static void
syncache_pause(struct in_conninfo * inc)2417 syncache_pause(struct in_conninfo *inc)
2418 {
2419 time_t delta;
2420 const char *s;
2421
2422 /* XXX:
2423 * 2. Add sysctl read here so we don't get the benefit of this
2424 * change without the new sysctl.
2425 */
2426
2427 /*
2428 * Try an unlocked read. If we already know that another thread
2429 * has activated the feature, there is no need to proceed.
2430 */
2431 if (V_tcp_syncache.paused)
2432 return;
2433
2434 /* Are cookied enabled? If not, we can't pause. */
2435 if (!V_tcp_syncookies) {
2436 TCPSTAT_INC(tcps_sc_bucketoverflow);
2437 return;
2438 }
2439
2440 /*
2441 * We may be the first thread to find an overflow. Get the lock
2442 * and evaluate if we need to take action.
2443 */
2444 mtx_lock(&V_tcp_syncache.pause_mtx);
2445 if (V_tcp_syncache.paused) {
2446 mtx_unlock(&V_tcp_syncache.pause_mtx);
2447 return;
2448 }
2449
2450 /* Activate protection. */
2451 V_tcp_syncache.paused = true;
2452 TCPSTAT_INC(tcps_sc_bucketoverflow);
2453
2454 /*
2455 * Determine the last backoff time. If we are seeing a re-newed
2456 * attack within that same time after last reactivating the syncache,
2457 * consider it an extension of the same attack.
2458 */
2459 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff;
2460 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) {
2461 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) {
2462 delta <<= 1;
2463 V_tcp_syncache.pause_backoff++;
2464 }
2465 } else {
2466 delta = TCP_SYNCACHE_PAUSE_TIME;
2467 V_tcp_syncache.pause_backoff = 0;
2468 }
2469
2470 /* Log a warning, including IP addresses, if able. */
2471 if (inc != NULL)
2472 s = tcp_log_addrs(inc, NULL, NULL, NULL);
2473 else
2474 s = (const char *)NULL;
2475 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for "
2476 "the next %lld seconds%s%s%s\n", (long long)delta,
2477 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "",
2478 (s != NULL) ? ")" : "");
2479 free(__DECONST(void *, s), M_TCPLOG);
2480
2481 /* Use the calculated delta to set a new pause time. */
2482 V_tcp_syncache.pause_until = time_uptime + delta;
2483 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause,
2484 &V_tcp_syncache);
2485 mtx_unlock(&V_tcp_syncache.pause_mtx);
2486 }
2487
2488 /* Evaluate whether we need to unpause. */
2489 static void
syncache_unpause(void * arg)2490 syncache_unpause(void *arg)
2491 {
2492 struct tcp_syncache *sc;
2493 time_t delta;
2494
2495 sc = arg;
2496 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED);
2497 callout_deactivate(&sc->pause_co);
2498
2499 /*
2500 * Check to make sure we are not running early. If the pause
2501 * time has expired, then deactivate the protection.
2502 */
2503 if ((delta = sc->pause_until - time_uptime) > 0)
2504 callout_schedule(&sc->pause_co, delta * hz);
2505 else
2506 sc->paused = false;
2507 }
2508
2509 /*
2510 * Exports the syncache entries to userland so that netstat can display
2511 * them alongside the other sockets. This function is intended to be
2512 * called only from tcp_pcblist.
2513 *
2514 * Due to concurrency on an active system, the number of pcbs exported
2515 * may have no relation to max_pcbs. max_pcbs merely indicates the
2516 * amount of space the caller allocated for this function to use.
2517 */
2518 int
syncache_pcblist(struct sysctl_req * req)2519 syncache_pcblist(struct sysctl_req *req)
2520 {
2521 struct xtcpcb xt;
2522 struct syncache *sc;
2523 struct syncache_head *sch;
2524 int error, i;
2525
2526 bzero(&xt, sizeof(xt));
2527 xt.xt_len = sizeof(xt);
2528 xt.t_state = TCPS_SYN_RECEIVED;
2529 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP;
2530 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket);
2531 xt.xt_inp.xi_socket.so_type = SOCK_STREAM;
2532 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING;
2533
2534 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
2535 sch = &V_tcp_syncache.hashbase[i];
2536 SCH_LOCK(sch);
2537 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
2538 if (sc->sc_cred != NULL &&
2539 cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
2540 continue;
2541 if (sc->sc_inc.inc_flags & INC_ISIPV6)
2542 xt.xt_inp.inp_vflag = INP_IPV6;
2543 else
2544 xt.xt_inp.inp_vflag = INP_IPV4;
2545 xt.xt_encaps_port = sc->sc_port;
2546 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc,
2547 sizeof (struct in_conninfo));
2548 error = SYSCTL_OUT(req, &xt, sizeof xt);
2549 if (error) {
2550 SCH_UNLOCK(sch);
2551 return (0);
2552 }
2553 }
2554 SCH_UNLOCK(sch);
2555 }
2556
2557 return (0);
2558 }
2559