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 bool syncookie_expand(struct in_conninfo *,
135 const struct syncache_head *, struct syncache *,
136 struct tcphdr *, struct tcpopt *, struct socket *,
137 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 void syncookie_cmp(struct in_conninfo *,
143 const struct syncache_head *, struct syncache *,
144 struct tcphdr *, struct tcpopt *, struct socket *,
145 uint16_t);
146 #endif
147
148 /*
149 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
150 * 3 retransmits corresponds to a timeout with default values of
151 * tcp_rexmit_initial * ( 1 +
152 * tcp_backoff[1] +
153 * tcp_backoff[2] +
154 * tcp_backoff[3]) + 3 * tcp_rexmit_slop,
155 * 1000 ms * (1 + 2 + 4 + 8) + 3 * 200 ms = 15600 ms,
156 * the odds are that the user has given up attempting to connect by then.
157 */
158 #define SYNCACHE_MAXREXMTS 3
159
160 /* Arbitrary values */
161 #define TCP_SYNCACHE_HASHSIZE 512
162 #define TCP_SYNCACHE_BUCKETLIMIT 30
163
164 VNET_DEFINE_STATIC(struct tcp_syncache, tcp_syncache);
165 #define V_tcp_syncache VNET(tcp_syncache)
166
167 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache,
168 CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
169 "TCP SYN cache");
170
171 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
172 &VNET_NAME(tcp_syncache.bucket_limit), 0,
173 "Per-bucket hash limit for syncache");
174
175 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
176 &VNET_NAME(tcp_syncache.cache_limit), 0,
177 "Overall entry limit for syncache");
178
179 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET,
180 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache");
181
182 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN,
183 &VNET_NAME(tcp_syncache.hashsize), 0,
184 "Size of TCP syncache hashtable");
185
186 SYSCTL_BOOL(_net_inet_tcp_syncache, OID_AUTO, see_other, CTLFLAG_VNET |
187 CTLFLAG_RW, &VNET_NAME(tcp_syncache.see_other), 0,
188 "All syncache(4) entries are visible, ignoring UID/GID, jail(2) "
189 "and mac(4) checks");
190
191 static int
sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS)192 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS)
193 {
194 int error;
195 u_int new;
196
197 new = V_tcp_syncache.rexmt_limit;
198 error = sysctl_handle_int(oidp, &new, 0, req);
199 if ((error == 0) && (req->newptr != NULL)) {
200 if (new > TCP_MAXRXTSHIFT)
201 error = EINVAL;
202 else
203 V_tcp_syncache.rexmt_limit = new;
204 }
205 return (error);
206 }
207
208 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit,
209 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
210 &VNET_NAME(tcp_syncache.rexmt_limit), 0,
211 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "IU",
212 "Limit on SYN/ACK retransmissions");
213
214 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1;
215 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail,
216 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0,
217 "Send reset on socket allocation failure");
218
219 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
220
221 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx)
222 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx)
223 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED)
224
225 /*
226 * Requires the syncache entry to be already removed from the bucket list.
227 */
228 static void
syncache_free(struct syncache * sc)229 syncache_free(struct syncache *sc)
230 {
231
232 if (sc->sc_ipopts)
233 (void)m_free(sc->sc_ipopts);
234 if (sc->sc_cred)
235 crfree(sc->sc_cred);
236 #ifdef MAC
237 mac_syncache_destroy(&sc->sc_label);
238 #endif
239
240 uma_zfree(V_tcp_syncache.zone, sc);
241 }
242
243 void
syncache_init(void)244 syncache_init(void)
245 {
246 int i;
247
248 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
249 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
250 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
251 V_tcp_syncache.hash_secret = arc4random();
252
253 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
254 &V_tcp_syncache.hashsize);
255 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
256 &V_tcp_syncache.bucket_limit);
257 if (!powerof2(V_tcp_syncache.hashsize) ||
258 V_tcp_syncache.hashsize == 0) {
259 printf("WARNING: syncache hash size is not a power of 2.\n");
260 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
261 }
262 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1;
263
264 /* Set limits. */
265 V_tcp_syncache.cache_limit =
266 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit;
267 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
268 &V_tcp_syncache.cache_limit);
269
270 /* Allocate the hash table. */
271 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize *
272 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO);
273
274 #ifdef VIMAGE
275 V_tcp_syncache.vnet = curvnet;
276 #endif
277
278 /* Initialize the hash buckets. */
279 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
280 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket);
281 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
282 NULL, MTX_DEF);
283 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer,
284 &V_tcp_syncache.hashbase[i].sch_mtx, 0);
285 V_tcp_syncache.hashbase[i].sch_length = 0;
286 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache;
287 V_tcp_syncache.hashbase[i].sch_last_overflow =
288 -(SYNCOOKIE_LIFETIME + 1);
289 }
290
291 /* Create the syncache entry zone. */
292 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
293 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
294 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone,
295 V_tcp_syncache.cache_limit);
296
297 /* Start the SYN cookie reseeder callout. */
298 callout_init(&V_tcp_syncache.secret.reseed, 1);
299 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0);
300 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0);
301 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz,
302 syncookie_reseed, &V_tcp_syncache);
303
304 /* Initialize the pause machinery. */
305 mtx_init(&V_tcp_syncache.pause_mtx, "tcp_sc_pause", NULL, MTX_DEF);
306 callout_init_mtx(&V_tcp_syncache.pause_co, &V_tcp_syncache.pause_mtx,
307 0);
308 V_tcp_syncache.pause_until = time_uptime - TCP_SYNCACHE_PAUSE_TIME;
309 V_tcp_syncache.pause_backoff = 0;
310 V_tcp_syncache.paused = false;
311 }
312
313 #ifdef VIMAGE
314 void
syncache_destroy(void)315 syncache_destroy(void)
316 {
317 struct syncache_head *sch;
318 struct syncache *sc, *nsc;
319 int i;
320
321 /*
322 * Stop the re-seed timer before freeing resources. No need to
323 * possibly schedule it another time.
324 */
325 callout_drain(&V_tcp_syncache.secret.reseed);
326
327 /* Stop the SYN cache pause callout. */
328 mtx_lock(&V_tcp_syncache.pause_mtx);
329 if (callout_stop(&V_tcp_syncache.pause_co) == 0) {
330 mtx_unlock(&V_tcp_syncache.pause_mtx);
331 callout_drain(&V_tcp_syncache.pause_co);
332 } else
333 mtx_unlock(&V_tcp_syncache.pause_mtx);
334
335 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */
336 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
337 sch = &V_tcp_syncache.hashbase[i];
338 callout_drain(&sch->sch_timer);
339
340 SCH_LOCK(sch);
341 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc)
342 syncache_drop(sc, sch);
343 SCH_UNLOCK(sch);
344 KASSERT(TAILQ_EMPTY(&sch->sch_bucket),
345 ("%s: sch->sch_bucket not empty", __func__));
346 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0",
347 __func__, sch->sch_length));
348 mtx_destroy(&sch->sch_mtx);
349 }
350
351 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0,
352 ("%s: cache_count not 0", __func__));
353
354 /* Free the allocated global resources. */
355 uma_zdestroy(V_tcp_syncache.zone);
356 free(V_tcp_syncache.hashbase, M_SYNCACHE);
357 mtx_destroy(&V_tcp_syncache.pause_mtx);
358 }
359 #endif
360
361 /*
362 * Inserts a syncache entry into the specified bucket row.
363 * Locks and unlocks the syncache_head autonomously.
364 */
365 static void
syncache_insert(struct syncache * sc,struct syncache_head * sch)366 syncache_insert(struct syncache *sc, struct syncache_head *sch)
367 {
368 struct syncache *sc2;
369
370 SCH_LOCK(sch);
371
372 /*
373 * Make sure that we don't overflow the per-bucket limit.
374 * If the bucket is full, toss the oldest element.
375 */
376 if (sch->sch_length >= V_tcp_syncache.bucket_limit) {
377 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
378 ("sch->sch_length incorrect"));
379 syncache_pause(&sc->sc_inc);
380 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
381 sch->sch_last_overflow = time_uptime;
382 syncache_drop(sc2, sch);
383 }
384
385 /* Put it into the bucket. */
386 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
387 sch->sch_length++;
388
389 #ifdef TCP_OFFLOAD
390 if (ADDED_BY_TOE(sc)) {
391 struct toedev *tod = sc->sc_tod;
392
393 tod->tod_syncache_added(tod, sc->sc_todctx);
394 }
395 #endif
396
397 /* Reinitialize the bucket row's timer. */
398 if (sch->sch_length == 1)
399 sch->sch_nextc = ticks + INT_MAX;
400 syncache_timeout(sc, sch, 1);
401
402 SCH_UNLOCK(sch);
403
404 TCPSTATES_INC(TCPS_SYN_RECEIVED);
405 TCPSTAT_INC(tcps_sc_added);
406 }
407
408 /*
409 * Remove and free entry from syncache bucket row.
410 * Expects locked syncache head.
411 */
412 static void
syncache_drop(struct syncache * sc,struct syncache_head * sch)413 syncache_drop(struct syncache *sc, struct syncache_head *sch)
414 {
415
416 SCH_LOCK_ASSERT(sch);
417
418 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
419 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
420 sch->sch_length--;
421
422 #ifdef TCP_OFFLOAD
423 if (ADDED_BY_TOE(sc)) {
424 struct toedev *tod = sc->sc_tod;
425
426 tod->tod_syncache_removed(tod, sc->sc_todctx);
427 }
428 #endif
429
430 syncache_free(sc);
431 }
432
433 /*
434 * Engage/reengage time on bucket row.
435 */
436 static void
syncache_timeout(struct syncache * sc,struct syncache_head * sch,int docallout)437 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
438 {
439 int rexmt;
440
441 if (sc->sc_rxmits == 0)
442 rexmt = tcp_rexmit_initial;
443 else
444 TCPT_RANGESET(rexmt,
445 tcp_rexmit_initial * tcp_backoff[sc->sc_rxmits],
446 tcp_rexmit_min, tcp_rexmit_max);
447 sc->sc_rxttime = ticks + rexmt;
448 sc->sc_rxmits++;
449 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
450 sch->sch_nextc = sc->sc_rxttime;
451 if (docallout)
452 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
453 syncache_timer, (void *)sch);
454 }
455 }
456
457 /*
458 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
459 * If we have retransmitted an entry the maximum number of times, expire it.
460 * One separate timer for each bucket row.
461 */
462 static void
syncache_timer(void * xsch)463 syncache_timer(void *xsch)
464 {
465 struct syncache_head *sch = (struct syncache_head *)xsch;
466 struct syncache *sc, *nsc;
467 struct epoch_tracker et;
468 int tick = ticks;
469 char *s;
470 bool paused;
471
472 CURVNET_SET(sch->sch_sc->vnet);
473
474 /* NB: syncache_head has already been locked by the callout. */
475 SCH_LOCK_ASSERT(sch);
476
477 /*
478 * In the following cycle we may remove some entries and/or
479 * advance some timeouts, so re-initialize the bucket timer.
480 */
481 sch->sch_nextc = tick + INT_MAX;
482
483 /*
484 * If we have paused processing, unconditionally remove
485 * all syncache entries.
486 */
487 mtx_lock(&V_tcp_syncache.pause_mtx);
488 paused = V_tcp_syncache.paused;
489 mtx_unlock(&V_tcp_syncache.pause_mtx);
490
491 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
492 if (paused) {
493 syncache_drop(sc, sch);
494 continue;
495 }
496 /*
497 * We do not check if the listen socket still exists
498 * and accept the case where the listen socket may be
499 * gone by the time we resend the SYN/ACK. We do
500 * not expect this to happens often. If it does,
501 * then the RST will be sent by the time the remote
502 * host does the SYN/ACK->ACK.
503 */
504 if (TSTMP_GT(sc->sc_rxttime, tick)) {
505 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
506 sch->sch_nextc = sc->sc_rxttime;
507 continue;
508 }
509 if (sc->sc_rxmits > V_tcp_ecn_maxretries) {
510 sc->sc_flags &= ~SCF_ECN_MASK;
511 }
512 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
513 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
514 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
515 "giving up and removing syncache entry\n",
516 s, __func__);
517 free(s, M_TCPLOG);
518 }
519 syncache_drop(sc, sch);
520 TCPSTAT_INC(tcps_sc_stale);
521 continue;
522 }
523 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
524 log(LOG_DEBUG, "%s; %s: Response timeout, "
525 "retransmitting (%u) SYN|ACK\n",
526 s, __func__, sc->sc_rxmits);
527 free(s, M_TCPLOG);
528 }
529
530 NET_EPOCH_ENTER(et);
531 if (syncache_respond(sc, NULL, TH_SYN|TH_ACK) == 0) {
532 syncache_timeout(sc, sch, 0);
533 TCPSTAT_INC(tcps_sndacks);
534 TCPSTAT_INC(tcps_sndtotal);
535 TCPSTAT_INC(tcps_sc_retransmitted);
536 } else {
537 syncache_drop(sc, sch);
538 TCPSTAT_INC(tcps_sc_dropped);
539 }
540 NET_EPOCH_EXIT(et);
541 }
542 if (!TAILQ_EMPTY(&(sch)->sch_bucket))
543 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
544 syncache_timer, (void *)(sch));
545 CURVNET_RESTORE();
546 }
547
548 /*
549 * Returns true if the system is only using cookies at the moment.
550 * This could be due to a sysadmin decision to only use cookies, or it
551 * could be due to the system detecting an attack.
552 */
553 static inline bool
syncache_cookiesonly(void)554 syncache_cookiesonly(void)
555 {
556
557 return (V_tcp_syncookies && (V_tcp_syncache.paused ||
558 V_tcp_syncookiesonly));
559 }
560
561 /*
562 * Find the hash bucket for the given connection.
563 */
564 static struct syncache_head *
syncache_hashbucket(struct in_conninfo * inc)565 syncache_hashbucket(struct in_conninfo *inc)
566 {
567 uint32_t hash;
568
569 /*
570 * The hash is built on foreign port + local port + foreign address.
571 * We rely on the fact that struct in_conninfo starts with 16 bits
572 * of foreign port, then 16 bits of local port then followed by 128
573 * bits of foreign address. In case of IPv4 address, the first 3
574 * 32-bit words of the address always are zeroes.
575 */
576 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5,
577 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask;
578
579 return (&V_tcp_syncache.hashbase[hash]);
580 }
581
582 /*
583 * Find an entry in the syncache.
584 * Returns always with locked syncache_head plus a matching entry or NULL.
585 */
586 static struct syncache *
syncache_lookup(struct in_conninfo * inc,struct syncache_head ** schp)587 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
588 {
589 struct syncache *sc;
590 struct syncache_head *sch;
591
592 *schp = sch = syncache_hashbucket(inc);
593 SCH_LOCK(sch);
594
595 /* Circle through bucket row to find matching entry. */
596 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash)
597 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie,
598 sizeof(struct in_endpoints)) == 0)
599 break;
600
601 return (sc); /* Always returns with locked sch. */
602 }
603
604 /*
605 * This function is called when we get a RST for a
606 * non-existent connection, so that we can see if the
607 * connection is in the syn cache. If it is, zap it.
608 * If required send a challenge ACK.
609 */
610 void
syncache_chkrst(struct in_conninfo * inc,struct tcphdr * th,struct mbuf * m,uint16_t port)611 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, struct mbuf *m,
612 uint16_t port)
613 {
614 struct syncache *sc;
615 struct syncache_head *sch;
616 char *s = NULL;
617
618 if (syncache_cookiesonly())
619 return;
620 sc = syncache_lookup(inc, &sch); /* returns locked sch */
621 SCH_LOCK_ASSERT(sch);
622
623 /*
624 * No corresponding connection was found in syncache.
625 * If syncookies are enabled and possibly exclusively
626 * used, or we are under memory pressure, a valid RST
627 * may not find a syncache entry. In that case we're
628 * done and no SYN|ACK retransmissions will happen.
629 * Otherwise the RST was misdirected or spoofed.
630 */
631 if (sc == NULL) {
632 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
633 log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
634 "syncache entry (possibly syncookie only), "
635 "segment ignored\n", s, __func__);
636 TCPSTAT_INC(tcps_badrst);
637 goto done;
638 }
639
640 /* The remote UDP encaps port does not match. */
641 if (sc->sc_port != port) {
642 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
643 log(LOG_DEBUG, "%s; %s: Spurious RST with matching "
644 "syncache entry but non-matching UDP encaps port, "
645 "segment ignored\n", s, __func__);
646 TCPSTAT_INC(tcps_badrst);
647 goto done;
648 }
649
650 /*
651 * If the RST bit is set, check the sequence number to see
652 * if this is a valid reset segment.
653 *
654 * RFC 793 page 37:
655 * In all states except SYN-SENT, all reset (RST) segments
656 * are validated by checking their SEQ-fields. A reset is
657 * valid if its sequence number is in the window.
658 *
659 * RFC 793 page 69:
660 * There are four cases for the acceptability test for an incoming
661 * segment:
662 *
663 * Segment Receive Test
664 * Length Window
665 * ------- ------- -------------------------------------------
666 * 0 0 SEG.SEQ = RCV.NXT
667 * 0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND
668 * >0 0 not acceptable
669 * >0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND
670 * or RCV.NXT =< SEG.SEQ+SEG.LEN-1 < RCV.NXT+RCV.WND
671 *
672 * Note that when receiving a SYN segment in the LISTEN state,
673 * IRS is set to SEG.SEQ and RCV.NXT is set to SEG.SEQ+1, as
674 * described in RFC 793, page 66.
675 */
676 if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) &&
677 SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) ||
678 (sc->sc_wnd == 0 && th->th_seq == sc->sc_irs + 1)) {
679 if (V_tcp_insecure_rst ||
680 th->th_seq == sc->sc_irs + 1) {
681 syncache_drop(sc, sch);
682 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
683 log(LOG_DEBUG,
684 "%s; %s: Our SYN|ACK was rejected, "
685 "connection attempt aborted by remote "
686 "endpoint\n",
687 s, __func__);
688 TCPSTAT_INC(tcps_sc_reset);
689 } else {
690 TCPSTAT_INC(tcps_badrst);
691 /* Send challenge ACK. */
692 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
693 log(LOG_DEBUG, "%s; %s: RST with invalid "
694 " SEQ %u != NXT %u (+WND %u), "
695 "sending challenge ACK\n",
696 s, __func__,
697 th->th_seq, sc->sc_irs + 1, sc->sc_wnd);
698 if (syncache_respond(sc, m, TH_ACK) == 0) {
699 TCPSTAT_INC(tcps_sndacks);
700 TCPSTAT_INC(tcps_sndtotal);
701 } else {
702 syncache_drop(sc, sch);
703 TCPSTAT_INC(tcps_sc_dropped);
704 }
705 }
706 } else {
707 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
708 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
709 "NXT %u (+WND %u), segment ignored\n",
710 s, __func__,
711 th->th_seq, sc->sc_irs + 1, sc->sc_wnd);
712 TCPSTAT_INC(tcps_badrst);
713 }
714
715 done:
716 if (s != NULL)
717 free(s, M_TCPLOG);
718 SCH_UNLOCK(sch);
719 }
720
721 void
syncache_badack(struct in_conninfo * inc,uint16_t port)722 syncache_badack(struct in_conninfo *inc, uint16_t port)
723 {
724 struct syncache *sc;
725 struct syncache_head *sch;
726
727 if (syncache_cookiesonly())
728 return;
729 sc = syncache_lookup(inc, &sch); /* returns locked sch */
730 SCH_LOCK_ASSERT(sch);
731 if ((sc != NULL) && (sc->sc_port == port)) {
732 syncache_drop(sc, sch);
733 TCPSTAT_INC(tcps_sc_badack);
734 }
735 SCH_UNLOCK(sch);
736 }
737
738 void
syncache_unreach(struct in_conninfo * inc,tcp_seq th_seq,uint16_t port)739 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq, uint16_t port)
740 {
741 struct syncache *sc;
742 struct syncache_head *sch;
743
744 if (syncache_cookiesonly())
745 return;
746 sc = syncache_lookup(inc, &sch); /* returns locked sch */
747 SCH_LOCK_ASSERT(sch);
748 if (sc == NULL)
749 goto done;
750
751 /* If the port != sc_port, then it's a bogus ICMP msg */
752 if (port != sc->sc_port)
753 goto done;
754
755 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
756 if (ntohl(th_seq) != sc->sc_iss)
757 goto done;
758
759 /*
760 * If we've rertransmitted 3 times and this is our second error,
761 * we remove the entry. Otherwise, we allow it to continue on.
762 * This prevents us from incorrectly nuking an entry during a
763 * spurious network outage.
764 *
765 * See tcp_notify().
766 */
767 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
768 sc->sc_flags |= SCF_UNREACH;
769 goto done;
770 }
771 syncache_drop(sc, sch);
772 TCPSTAT_INC(tcps_sc_unreach);
773 done:
774 SCH_UNLOCK(sch);
775 }
776
777 /*
778 * Build a new TCP socket structure from a syncache entry.
779 *
780 * On success return the newly created socket with its underlying inp locked.
781 */
782 static struct socket *
syncache_socket(struct syncache * sc,struct socket * lso,struct mbuf * m)783 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
784 {
785 struct inpcb *inp = NULL;
786 struct socket *so;
787 struct tcpcb *tp;
788 int error;
789 char *s;
790
791 NET_EPOCH_ASSERT();
792
793 /*
794 * Ok, create the full blown connection, and set things up
795 * as they would have been set up if we had created the
796 * connection when the SYN arrived.
797 */
798 if ((so = solisten_clone(lso)) == NULL)
799 goto allocfail;
800 #ifdef MAC
801 mac_socketpeer_set_from_mbuf(m, so);
802 #endif
803 error = in_pcballoc(so, &V_tcbinfo);
804 if (error) {
805 sodealloc(so);
806 goto allocfail;
807 }
808 inp = sotoinpcb(so);
809 if ((tp = tcp_newtcpcb(inp, sototcpcb(lso))) == NULL) {
810 in_pcbfree(inp);
811 sodealloc(so);
812 goto allocfail;
813 }
814 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
815 #ifdef INET6
816 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
817 inp->inp_vflag &= ~INP_IPV4;
818 inp->inp_vflag |= INP_IPV6;
819 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
820 } else {
821 inp->inp_vflag &= ~INP_IPV6;
822 inp->inp_vflag |= INP_IPV4;
823 #endif
824 inp->inp_ip_ttl = sc->sc_ip_ttl;
825 inp->inp_ip_tos = sc->sc_ip_tos;
826 inp->inp_laddr = sc->sc_inc.inc_laddr;
827 #ifdef INET6
828 }
829 #endif
830
831 /*
832 * If there's an mbuf and it has a flowid, then let's initialise the
833 * inp with that particular flowid.
834 */
835 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) {
836 inp->inp_flowid = m->m_pkthdr.flowid;
837 inp->inp_flowtype = M_HASHTYPE_GET(m);
838 #ifdef NUMA
839 inp->inp_numa_domain = m->m_pkthdr.numa_domain;
840 #endif
841 }
842
843 inp->inp_lport = sc->sc_inc.inc_lport;
844 #ifdef INET6
845 if (inp->inp_vflag & INP_IPV6PROTO) {
846 struct inpcb *oinp = sotoinpcb(lso);
847
848 /*
849 * Inherit socket options from the listening socket.
850 * Note that in6p_inputopts are not (and should not be)
851 * copied, since it stores previously received options and is
852 * used to detect if each new option is different than the
853 * previous one and hence should be passed to a user.
854 * If we copied in6p_inputopts, a user would not be able to
855 * receive options just after calling the accept system call.
856 */
857 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
858 if (oinp->in6p_outputopts)
859 inp->in6p_outputopts =
860 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
861 inp->in6p_hops = oinp->in6p_hops;
862 }
863
864 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
865 struct sockaddr_in6 sin6;
866
867 sin6.sin6_family = AF_INET6;
868 sin6.sin6_len = sizeof(sin6);
869 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
870 sin6.sin6_port = sc->sc_inc.inc_fport;
871 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
872 INP_HASH_WLOCK(&V_tcbinfo);
873 error = in6_pcbconnect(inp, &sin6, thread0.td_ucred, false);
874 INP_HASH_WUNLOCK(&V_tcbinfo);
875 if (error != 0)
876 goto abort;
877 /* Override flowlabel from in6_pcbconnect. */
878 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
879 inp->inp_flow |= sc->sc_flowlabel;
880 }
881 #endif /* INET6 */
882 #if defined(INET) && defined(INET6)
883 else
884 #endif
885 #ifdef INET
886 {
887 struct sockaddr_in sin;
888
889 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
890
891 if (inp->inp_options == NULL) {
892 inp->inp_options = sc->sc_ipopts;
893 sc->sc_ipopts = NULL;
894 }
895
896 sin.sin_family = AF_INET;
897 sin.sin_len = sizeof(sin);
898 sin.sin_addr = sc->sc_inc.inc_faddr;
899 sin.sin_port = sc->sc_inc.inc_fport;
900 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
901 INP_HASH_WLOCK(&V_tcbinfo);
902 error = in_pcbconnect(inp, &sin, thread0.td_ucred);
903 INP_HASH_WUNLOCK(&V_tcbinfo);
904 if (error != 0)
905 goto abort;
906 }
907 #endif /* INET */
908 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
909 /* Copy old policy into new socket's. */
910 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0)
911 printf("syncache_socket: could not copy policy\n");
912 #endif
913 tp->t_state = TCPS_SYN_RECEIVED;
914 tp->iss = sc->sc_iss;
915 tp->irs = sc->sc_irs;
916 tp->t_port = sc->sc_port;
917 tcp_rcvseqinit(tp);
918 tcp_sendseqinit(tp);
919 tp->snd_wl1 = sc->sc_irs;
920 tp->snd_max = tp->iss + 1;
921 tp->snd_nxt = tp->iss + 1;
922 tp->rcv_up = sc->sc_irs + 1;
923 tp->rcv_wnd = sc->sc_wnd;
924 tp->rcv_adv += tp->rcv_wnd;
925 tp->last_ack_sent = tp->rcv_nxt;
926
927 tp->t_flags = sototcpcb(lso)->t_flags &
928 (TF_LRD|TF_NOPUSH|TF_NODELAY);
929 if (sc->sc_flags & SCF_NOOPT)
930 tp->t_flags |= TF_NOOPT;
931 else {
932 if (sc->sc_flags & SCF_WINSCALE) {
933 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
934 tp->snd_scale = sc->sc_requested_s_scale;
935 tp->request_r_scale = sc->sc_requested_r_scale;
936 }
937 if (sc->sc_flags & SCF_TIMESTAMP) {
938 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
939 tp->ts_recent = sc->sc_tsreflect;
940 tp->ts_recent_age = tcp_ts_getticks();
941 tp->ts_offset = sc->sc_tsoff;
942 }
943 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
944 if (sc->sc_flags & SCF_SIGNATURE)
945 tp->t_flags |= TF_SIGNATURE;
946 #endif
947 if (sc->sc_flags & SCF_SACK)
948 tp->t_flags |= TF_SACK_PERMIT;
949 }
950
951 tcp_ecn_syncache_socket(tp, sc);
952
953 /*
954 * Set up MSS and get cached values from tcp_hostcache.
955 * This might overwrite some of the defaults we just set.
956 */
957 tcp_mss(tp, sc->sc_peer_mss);
958
959 /*
960 * If the SYN,ACK was retransmitted, indicate that CWND to be
961 * limited to one segment in cc_conn_init().
962 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
963 */
964 if (sc->sc_rxmits > 1)
965 tp->snd_cwnd = 1;
966
967 #ifdef TCP_OFFLOAD
968 /*
969 * Allow a TOE driver to install its hooks. Note that we hold the
970 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a
971 * new connection before the TOE driver has done its thing.
972 */
973 if (ADDED_BY_TOE(sc)) {
974 struct toedev *tod = sc->sc_tod;
975
976 tod->tod_offload_socket(tod, sc->sc_todctx, so);
977 }
978 #endif
979 #ifdef TCP_BLACKBOX
980 /*
981 * Inherit the log state from the listening socket, if
982 * - the log state of the listening socket is not off and
983 * - the listening socket was not auto selected from all sessions and
984 * - a log id is not set on the listening socket.
985 * This avoids inheriting a log state which was automatically set.
986 */
987 if ((tcp_get_bblog_state(sototcpcb(lso)) != TCP_LOG_STATE_OFF) &&
988 ((sototcpcb(lso)->t_flags2 & TF2_LOG_AUTO) == 0) &&
989 (sototcpcb(lso)->t_lib == NULL)) {
990 tcp_log_state_change(tp, tcp_get_bblog_state(sototcpcb(lso)));
991 }
992 #endif
993 /*
994 * Copy and activate timers.
995 */
996 tp->t_maxunacktime = sototcpcb(lso)->t_maxunacktime;
997 tp->t_keepinit = sototcpcb(lso)->t_keepinit;
998 tp->t_keepidle = sototcpcb(lso)->t_keepidle;
999 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl;
1000 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt;
1001 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp));
1002
1003 TCPSTAT_INC(tcps_accepts);
1004 TCP_PROBE6(state__change, NULL, tp, NULL, tp, NULL, TCPS_LISTEN);
1005
1006 if (!solisten_enqueue(so, SS_ISCONNECTED))
1007 tp->t_flags |= TF_SONOTCONN;
1008 /* Can we inherit anything from the listener? */
1009 if (tp->t_fb->tfb_inherit != NULL) {
1010 (*tp->t_fb->tfb_inherit)(tp, sotoinpcb(lso));
1011 }
1012 return (so);
1013
1014 allocfail:
1015 /*
1016 * Drop the connection; we will either send a RST or have the peer
1017 * retransmit its SYN again after its RTO and try again.
1018 */
1019 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
1020 log(LOG_DEBUG, "%s; %s: Socket create failed "
1021 "due to limits or memory shortage\n",
1022 s, __func__);
1023 free(s, M_TCPLOG);
1024 }
1025 TCPSTAT_INC(tcps_listendrop);
1026 return (NULL);
1027
1028 abort:
1029 tcp_discardcb(tp);
1030 in_pcbfree(inp);
1031 sodealloc(so);
1032 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
1033 log(LOG_DEBUG, "%s; %s: in%s_pcbconnect failed with error %i\n",
1034 s, __func__, (sc->sc_inc.inc_flags & INC_ISIPV6) ? "6" : "",
1035 error);
1036 free(s, M_TCPLOG);
1037 }
1038 TCPSTAT_INC(tcps_listendrop);
1039 return (NULL);
1040 }
1041
1042 /*
1043 * This function gets called when we receive an ACK for a
1044 * socket in the LISTEN state. We look up the connection
1045 * in the syncache, and if its there, we pull it out of
1046 * the cache and turn it into a full-blown connection in
1047 * the SYN-RECEIVED state.
1048 *
1049 * On syncache_socket() success the newly created socket
1050 * has its underlying inp locked.
1051 */
1052 int
syncache_expand(struct in_conninfo * inc,struct tcpopt * to,struct tcphdr * th,struct socket ** lsop,struct mbuf * m,uint16_t port)1053 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1054 struct socket **lsop, struct mbuf *m, uint16_t port)
1055 {
1056 struct syncache *sc;
1057 struct syncache_head *sch;
1058 struct syncache scs;
1059 char *s;
1060 bool locked;
1061
1062 NET_EPOCH_ASSERT();
1063 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
1064 ("%s: can handle only ACK", __func__));
1065
1066 if (syncache_cookiesonly()) {
1067 sc = NULL;
1068 sch = syncache_hashbucket(inc);
1069 locked = false;
1070 } else {
1071 sc = syncache_lookup(inc, &sch); /* returns locked sch */
1072 locked = true;
1073 SCH_LOCK_ASSERT(sch);
1074 }
1075
1076 #ifdef INVARIANTS
1077 /*
1078 * Test code for syncookies comparing the syncache stored
1079 * values with the reconstructed values from the cookie.
1080 */
1081 if (sc != NULL)
1082 syncookie_cmp(inc, sch, sc, th, to, *lsop, port);
1083 #endif
1084
1085 if (sc == NULL) {
1086 /*
1087 * There is no syncache entry, so see if this ACK is
1088 * a returning syncookie. To do this, first:
1089 * A. Check if syncookies are used in case of syncache
1090 * overflows
1091 * B. See if this socket has had a syncache entry dropped in
1092 * the recent past. We don't want to accept a bogus
1093 * syncookie if we've never received a SYN or accept it
1094 * twice.
1095 * C. check that the syncookie is valid. If it is, then
1096 * cobble up a fake syncache entry, and return.
1097 */
1098 if (locked && !V_tcp_syncookies) {
1099 SCH_UNLOCK(sch);
1100 TCPSTAT_INC(tcps_sc_spurcookie);
1101 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1102 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
1103 "segment rejected (syncookies disabled)\n",
1104 s, __func__);
1105 goto failed;
1106 }
1107 if (locked && !V_tcp_syncookiesonly &&
1108 sch->sch_last_overflow < time_uptime - SYNCOOKIE_LIFETIME) {
1109 SCH_UNLOCK(sch);
1110 TCPSTAT_INC(tcps_sc_spurcookie);
1111 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1112 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
1113 "segment rejected (no syncache entry)\n",
1114 s, __func__);
1115 goto failed;
1116 }
1117 if (locked)
1118 SCH_UNLOCK(sch);
1119 bzero(&scs, sizeof(scs));
1120 if (syncookie_expand(inc, sch, &scs, th, to, *lsop, port)) {
1121 sc = &scs;
1122 TCPSTAT_INC(tcps_sc_recvcookie);
1123 } else {
1124 TCPSTAT_INC(tcps_sc_failcookie);
1125 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1126 log(LOG_DEBUG, "%s; %s: Segment failed "
1127 "SYNCOOKIE authentication, segment rejected "
1128 "(probably spoofed)\n", s, __func__);
1129 goto failed;
1130 }
1131 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1132 /* If received ACK has MD5 signature, check it. */
1133 if ((to->to_flags & TOF_SIGNATURE) != 0 &&
1134 (!TCPMD5_ENABLED() ||
1135 TCPMD5_INPUT(m, th, to->to_signature) != 0)) {
1136 /* Drop the ACK. */
1137 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1138 log(LOG_DEBUG, "%s; %s: Segment rejected, "
1139 "MD5 signature doesn't match.\n",
1140 s, __func__);
1141 free(s, M_TCPLOG);
1142 }
1143 TCPSTAT_INC(tcps_sig_err_sigopt);
1144 return (-1); /* Do not send RST */
1145 }
1146 #endif /* TCP_SIGNATURE */
1147 TCPSTATES_INC(TCPS_SYN_RECEIVED);
1148 } else {
1149 if (sc->sc_port != port) {
1150 SCH_UNLOCK(sch);
1151 return (0);
1152 }
1153 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1154 /*
1155 * If listening socket requested TCP digests, check that
1156 * received ACK has signature and it is correct.
1157 * If not, drop the ACK and leave sc entry in th cache,
1158 * because SYN was received with correct signature.
1159 */
1160 if (sc->sc_flags & SCF_SIGNATURE) {
1161 if ((to->to_flags & TOF_SIGNATURE) == 0) {
1162 /* No signature */
1163 TCPSTAT_INC(tcps_sig_err_nosigopt);
1164 SCH_UNLOCK(sch);
1165 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1166 log(LOG_DEBUG, "%s; %s: Segment "
1167 "rejected, MD5 signature wasn't "
1168 "provided.\n", s, __func__);
1169 free(s, M_TCPLOG);
1170 }
1171 return (-1); /* Do not send RST */
1172 }
1173 if (!TCPMD5_ENABLED() ||
1174 TCPMD5_INPUT(m, th, to->to_signature) != 0) {
1175 /* Doesn't match or no SA */
1176 SCH_UNLOCK(sch);
1177 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1178 log(LOG_DEBUG, "%s; %s: Segment "
1179 "rejected, MD5 signature doesn't "
1180 "match.\n", s, __func__);
1181 free(s, M_TCPLOG);
1182 }
1183 return (-1); /* Do not send RST */
1184 }
1185 }
1186 #endif /* TCP_SIGNATURE */
1187
1188 /*
1189 * RFC 7323 PAWS: If we have a timestamp on this segment and
1190 * it's less than ts_recent, drop it.
1191 * XXXMT: RFC 7323 also requires to send an ACK.
1192 * In tcp_input.c this is only done for TCP segments
1193 * with user data, so be consistent here and just drop
1194 * the segment.
1195 */
1196 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS &&
1197 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) {
1198 SCH_UNLOCK(sch);
1199 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1200 log(LOG_DEBUG,
1201 "%s; %s: SEG.TSval %u < TS.Recent %u, "
1202 "segment dropped\n", s, __func__,
1203 to->to_tsval, sc->sc_tsreflect);
1204 free(s, M_TCPLOG);
1205 }
1206 return (-1); /* Do not send RST */
1207 }
1208
1209 /*
1210 * If timestamps were not negotiated during SYN/ACK and a
1211 * segment with a timestamp is received, ignore the
1212 * timestamp and process the packet normally.
1213 * See section 3.2 of RFC 7323.
1214 */
1215 if (!(sc->sc_flags & SCF_TIMESTAMP) &&
1216 (to->to_flags & TOF_TS)) {
1217 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1218 log(LOG_DEBUG, "%s; %s: Timestamp not "
1219 "expected, segment processed normally\n",
1220 s, __func__);
1221 free(s, M_TCPLOG);
1222 s = NULL;
1223 }
1224 }
1225
1226 /*
1227 * If timestamps were negotiated during SYN/ACK and a
1228 * segment without a timestamp is received, silently drop
1229 * the segment, unless the missing timestamps are tolerated.
1230 * See section 3.2 of RFC 7323.
1231 */
1232 if ((sc->sc_flags & SCF_TIMESTAMP) &&
1233 !(to->to_flags & TOF_TS)) {
1234 if (V_tcp_tolerate_missing_ts) {
1235 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1236 log(LOG_DEBUG,
1237 "%s; %s: Timestamp missing, "
1238 "segment processed normally\n",
1239 s, __func__);
1240 free(s, M_TCPLOG);
1241 }
1242 } else {
1243 SCH_UNLOCK(sch);
1244 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1245 log(LOG_DEBUG,
1246 "%s; %s: Timestamp missing, "
1247 "segment silently dropped\n",
1248 s, __func__);
1249 free(s, M_TCPLOG);
1250 }
1251 return (-1); /* Do not send RST */
1252 }
1253 }
1254 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
1255 sch->sch_length--;
1256 #ifdef TCP_OFFLOAD
1257 if (ADDED_BY_TOE(sc)) {
1258 struct toedev *tod = sc->sc_tod;
1259
1260 tod->tod_syncache_removed(tod, sc->sc_todctx);
1261 }
1262 #endif
1263 SCH_UNLOCK(sch);
1264 }
1265
1266 /*
1267 * Segment validation:
1268 * ACK must match our initial sequence number + 1 (the SYN|ACK).
1269 */
1270 if (th->th_ack != sc->sc_iss + 1) {
1271 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1272 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
1273 "rejected\n", s, __func__, th->th_ack, sc->sc_iss);
1274 goto failed;
1275 }
1276
1277 /*
1278 * The SEQ must fall in the window starting at the received
1279 * initial receive sequence number + 1 (the SYN).
1280 */
1281 if (SEQ_LEQ(th->th_seq, sc->sc_irs) ||
1282 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
1283 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1284 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
1285 "rejected\n", s, __func__, th->th_seq, sc->sc_irs);
1286 goto failed;
1287 }
1288
1289 *lsop = syncache_socket(sc, *lsop, m);
1290
1291 if (__predict_false(*lsop == NULL)) {
1292 TCPSTAT_INC(tcps_sc_aborted);
1293 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
1294 } else
1295 TCPSTAT_INC(tcps_sc_completed);
1296
1297 /* how do we find the inp for the new socket? */
1298 if (sc != &scs)
1299 syncache_free(sc);
1300 return (1);
1301 failed:
1302 if (sc != NULL) {
1303 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
1304 if (sc != &scs)
1305 syncache_free(sc);
1306 }
1307 if (s != NULL)
1308 free(s, M_TCPLOG);
1309 *lsop = NULL;
1310 return (0);
1311 }
1312
1313 static struct socket *
syncache_tfo_expand(struct syncache * sc,struct socket * lso,struct mbuf * m,uint64_t response_cookie)1314 syncache_tfo_expand(struct syncache *sc, struct socket *lso, struct mbuf *m,
1315 uint64_t response_cookie)
1316 {
1317 struct inpcb *inp;
1318 struct tcpcb *tp;
1319 unsigned int *pending_counter;
1320 struct socket *so;
1321
1322 NET_EPOCH_ASSERT();
1323
1324 pending_counter = intotcpcb(sotoinpcb(lso))->t_tfo_pending;
1325 so = syncache_socket(sc, lso, m);
1326 if (so == NULL) {
1327 TCPSTAT_INC(tcps_sc_aborted);
1328 atomic_subtract_int(pending_counter, 1);
1329 } else {
1330 soisconnected(so);
1331 inp = sotoinpcb(so);
1332 tp = intotcpcb(inp);
1333 tp->t_flags |= TF_FASTOPEN;
1334 tp->t_tfo_cookie.server = response_cookie;
1335 tp->snd_max = tp->iss;
1336 tp->snd_nxt = tp->iss;
1337 tp->t_tfo_pending = pending_counter;
1338 TCPSTATES_INC(TCPS_SYN_RECEIVED);
1339 TCPSTAT_INC(tcps_sc_completed);
1340 }
1341
1342 return (so);
1343 }
1344
1345 /*
1346 * Given a LISTEN socket and an inbound SYN request, add
1347 * this to the syn cache, and send back a segment:
1348 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
1349 * to the source.
1350 *
1351 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
1352 * Doing so would require that we hold onto the data and deliver it
1353 * to the application. However, if we are the target of a SYN-flood
1354 * DoS attack, an attacker could send data which would eventually
1355 * consume all available buffer space if it were ACKed. By not ACKing
1356 * the data, we avoid this DoS scenario.
1357 *
1358 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO)
1359 * cookie is processed and a new socket is created. In this case, any data
1360 * accompanying the SYN will be queued to the socket by tcp_input() and will
1361 * be ACKed either when the application sends response data or the delayed
1362 * ACK timer expires, whichever comes first.
1363 */
1364 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)1365 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1366 struct inpcb *inp, struct socket *so, struct mbuf *m, void *tod,
1367 void *todctx, uint8_t iptos, uint16_t port)
1368 {
1369 struct tcpcb *tp;
1370 struct socket *rv = NULL;
1371 struct syncache *sc = NULL;
1372 struct syncache_head *sch;
1373 struct mbuf *ipopts = NULL;
1374 u_int ltflags;
1375 int win, ip_ttl, ip_tos;
1376 char *s;
1377 #ifdef INET6
1378 int autoflowlabel = 0;
1379 #endif
1380 #ifdef MAC
1381 struct label *maclabel = NULL;
1382 #endif
1383 struct syncache scs;
1384 uint64_t tfo_response_cookie;
1385 unsigned int *tfo_pending = NULL;
1386 int tfo_cookie_valid = 0;
1387 int tfo_response_cookie_valid = 0;
1388 bool locked;
1389
1390 INP_RLOCK_ASSERT(inp); /* listen socket */
1391 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
1392 ("%s: unexpected tcp flags", __func__));
1393
1394 /*
1395 * Combine all so/tp operations very early to drop the INP lock as
1396 * soon as possible.
1397 */
1398 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so));
1399 tp = sototcpcb(so);
1400
1401 #ifdef INET6
1402 if (inc->inc_flags & INC_ISIPV6) {
1403 if (inp->inp_flags & IN6P_AUTOFLOWLABEL) {
1404 autoflowlabel = 1;
1405 }
1406 ip_ttl = in6_selecthlim(inp, NULL);
1407 if ((inp->in6p_outputopts == NULL) ||
1408 (inp->in6p_outputopts->ip6po_tclass == -1)) {
1409 ip_tos = 0;
1410 } else {
1411 ip_tos = inp->in6p_outputopts->ip6po_tclass;
1412 }
1413 }
1414 #endif
1415 #if defined(INET6) && defined(INET)
1416 else
1417 #endif
1418 #ifdef INET
1419 {
1420 ip_ttl = inp->inp_ip_ttl;
1421 ip_tos = inp->inp_ip_tos;
1422 }
1423 #endif
1424 win = so->sol_sbrcv_hiwat;
1425 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE));
1426
1427 if (V_tcp_fastopen_server_enable && (tp->t_flags & TF_FASTOPEN) &&
1428 (tp->t_tfo_pending != NULL) &&
1429 (to->to_flags & TOF_FASTOPEN)) {
1430 /*
1431 * Limit the number of pending TFO connections to
1432 * approximately half of the queue limit. This prevents TFO
1433 * SYN floods from starving the service by filling the
1434 * listen queue with bogus TFO connections.
1435 */
1436 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <=
1437 (so->sol_qlimit / 2)) {
1438 int result;
1439
1440 result = tcp_fastopen_check_cookie(inc,
1441 to->to_tfo_cookie, to->to_tfo_len,
1442 &tfo_response_cookie);
1443 tfo_cookie_valid = (result > 0);
1444 tfo_response_cookie_valid = (result >= 0);
1445 }
1446
1447 /*
1448 * Remember the TFO pending counter as it will have to be
1449 * decremented below if we don't make it to syncache_tfo_expand().
1450 */
1451 tfo_pending = tp->t_tfo_pending;
1452 }
1453
1454 #ifdef MAC
1455 if (mac_syncache_init(&maclabel) != 0) {
1456 INP_RUNLOCK(inp);
1457 goto done;
1458 } else
1459 mac_syncache_create(maclabel, inp);
1460 #endif
1461 if (!tfo_cookie_valid)
1462 INP_RUNLOCK(inp);
1463
1464 /*
1465 * Remember the IP options, if any.
1466 */
1467 #ifdef INET6
1468 if (!(inc->inc_flags & INC_ISIPV6))
1469 #endif
1470 #ifdef INET
1471 ipopts = (m) ? ip_srcroute(m) : NULL;
1472 #else
1473 ipopts = NULL;
1474 #endif
1475
1476 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1477 /*
1478 * When the socket is TCP-MD5 enabled check that,
1479 * - a signed packet is valid
1480 * - a non-signed packet does not have a security association
1481 *
1482 * If a signed packet fails validation or a non-signed packet has a
1483 * security association, the packet will be dropped.
1484 */
1485 if (ltflags & TF_SIGNATURE) {
1486 if (to->to_flags & TOF_SIGNATURE) {
1487 if (!TCPMD5_ENABLED() ||
1488 TCPMD5_INPUT(m, th, to->to_signature) != 0)
1489 goto done;
1490 } else {
1491 if (TCPMD5_ENABLED() &&
1492 TCPMD5_INPUT(m, NULL, NULL) != ENOENT)
1493 goto done;
1494 }
1495 } else if (to->to_flags & TOF_SIGNATURE)
1496 goto done;
1497 #endif /* TCP_SIGNATURE */
1498 /*
1499 * See if we already have an entry for this connection.
1500 * If we do, resend the SYN,ACK, and reset the retransmit timer.
1501 *
1502 * XXX: should the syncache be re-initialized with the contents
1503 * of the new SYN here (which may have different options?)
1504 *
1505 * XXX: We do not check the sequence number to see if this is a
1506 * real retransmit or a new connection attempt. The question is
1507 * how to handle such a case; either ignore it as spoofed, or
1508 * drop the current entry and create a new one?
1509 */
1510 if (syncache_cookiesonly()) {
1511 sc = NULL;
1512 sch = syncache_hashbucket(inc);
1513 locked = false;
1514 } else {
1515 sc = syncache_lookup(inc, &sch); /* returns locked sch */
1516 locked = true;
1517 SCH_LOCK_ASSERT(sch);
1518 }
1519 if (sc != NULL) {
1520 if (tfo_cookie_valid)
1521 INP_RUNLOCK(inp);
1522 TCPSTAT_INC(tcps_sc_dupsyn);
1523 if (ipopts) {
1524 /*
1525 * If we were remembering a previous source route,
1526 * forget it and use the new one we've been given.
1527 */
1528 if (sc->sc_ipopts)
1529 (void)m_free(sc->sc_ipopts);
1530 sc->sc_ipopts = ipopts;
1531 }
1532 /*
1533 * Update timestamp if present.
1534 */
1535 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
1536 sc->sc_tsreflect = to->to_tsval;
1537 else
1538 sc->sc_flags &= ~SCF_TIMESTAMP;
1539 /*
1540 * Adjust ECN response if needed, e.g. different
1541 * IP ECN field, or a fallback by the remote host.
1542 */
1543 if (sc->sc_flags & SCF_ECN_MASK) {
1544 sc->sc_flags &= ~SCF_ECN_MASK;
1545 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos);
1546 }
1547 #ifdef MAC
1548 /*
1549 * Since we have already unconditionally allocated label
1550 * storage, free it up. The syncache entry will already
1551 * have an initialized label we can use.
1552 */
1553 mac_syncache_destroy(&maclabel);
1554 #endif
1555 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1556 /* Retransmit SYN|ACK and reset retransmit count. */
1557 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
1558 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
1559 "resetting timer and retransmitting SYN|ACK\n",
1560 s, __func__);
1561 free(s, M_TCPLOG);
1562 }
1563 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) {
1564 sc->sc_rxmits = 0;
1565 syncache_timeout(sc, sch, 1);
1566 TCPSTAT_INC(tcps_sndacks);
1567 TCPSTAT_INC(tcps_sndtotal);
1568 } else {
1569 syncache_drop(sc, sch);
1570 TCPSTAT_INC(tcps_sc_dropped);
1571 }
1572 SCH_UNLOCK(sch);
1573 goto donenoprobe;
1574 }
1575
1576 KASSERT(sc == NULL, ("sc(%p) != NULL", sc));
1577 /*
1578 * Skip allocating a syncache entry if we are just going to discard
1579 * it later.
1580 */
1581 if (!locked || tfo_cookie_valid) {
1582 bzero(&scs, sizeof(scs));
1583 sc = &scs;
1584 } else {
1585 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1586 if (sc == NULL) {
1587 /*
1588 * The zone allocator couldn't provide more entries.
1589 * Treat this as if the cache was full; drop the oldest
1590 * entry and insert the new one.
1591 */
1592 TCPSTAT_INC(tcps_sc_zonefail);
1593 sc = TAILQ_LAST(&sch->sch_bucket, sch_head);
1594 if (sc != NULL) {
1595 sch->sch_last_overflow = time_uptime;
1596 syncache_drop(sc, sch);
1597 syncache_pause(inc);
1598 }
1599 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1600 if (sc == NULL) {
1601 if (V_tcp_syncookies) {
1602 bzero(&scs, sizeof(scs));
1603 sc = &scs;
1604 } else {
1605 KASSERT(locked,
1606 ("%s: bucket unexpectedly unlocked",
1607 __func__));
1608 SCH_UNLOCK(sch);
1609 goto done;
1610 }
1611 }
1612 }
1613 }
1614
1615 KASSERT(sc != NULL, ("sc == NULL"));
1616 if (!tfo_cookie_valid && tfo_response_cookie_valid)
1617 sc->sc_tfo_cookie = &tfo_response_cookie;
1618
1619 /*
1620 * Fill in the syncache values.
1621 */
1622 #ifdef MAC
1623 sc->sc_label = maclabel;
1624 #endif
1625 /*
1626 * sc_cred is only used in syncache_pcblist() to list TCP endpoints in
1627 * TCPS_SYN_RECEIVED state when V_tcp_syncache.see_other is false.
1628 * Therefore, store the credentials and take a reference count only
1629 * when needed:
1630 * - sc is allocated from the zone and not using the on stack instance.
1631 * - the sysctl variable net.inet.tcp.syncache.see_other is false.
1632 * The reference count is decremented when a zone allocated sc is
1633 * freed in syncache_free().
1634 */
1635 if (sc != &scs && !V_tcp_syncache.see_other)
1636 sc->sc_cred = crhold(so->so_cred);
1637 else
1638 sc->sc_cred = NULL;
1639 sc->sc_port = port;
1640 sc->sc_ipopts = ipopts;
1641 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1642 sc->sc_ip_tos = ip_tos;
1643 sc->sc_ip_ttl = ip_ttl;
1644 #ifdef TCP_OFFLOAD
1645 sc->sc_tod = tod;
1646 sc->sc_todctx = todctx;
1647 #endif
1648 sc->sc_irs = th->th_seq;
1649 sc->sc_flags = 0;
1650 sc->sc_flowlabel = 0;
1651
1652 /*
1653 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
1654 * win was derived from socket earlier in the function.
1655 */
1656 win = imax(win, 0);
1657 win = imin(win, TCP_MAXWIN);
1658 sc->sc_wnd = win;
1659
1660 if (V_tcp_do_rfc1323 &&
1661 !(ltflags & TF_NOOPT)) {
1662 /*
1663 * A timestamp received in a SYN makes
1664 * it ok to send timestamp requests and replies.
1665 */
1666 if ((to->to_flags & TOF_TS) && (V_tcp_do_rfc1323 != 2)) {
1667 sc->sc_tsreflect = to->to_tsval;
1668 sc->sc_flags |= SCF_TIMESTAMP;
1669 sc->sc_tsoff = tcp_new_ts_offset(inc);
1670 }
1671 if ((to->to_flags & TOF_SCALE) && (V_tcp_do_rfc1323 != 3)) {
1672 int wscale = 0;
1673
1674 /*
1675 * Pick the smallest possible scaling factor that
1676 * will still allow us to scale up to sb_max, aka
1677 * kern.ipc.maxsockbuf.
1678 *
1679 * We do this because there are broken firewalls that
1680 * will corrupt the window scale option, leading to
1681 * the other endpoint believing that our advertised
1682 * window is unscaled. At scale factors larger than
1683 * 5 the unscaled window will drop below 1500 bytes,
1684 * leading to serious problems when traversing these
1685 * broken firewalls.
1686 *
1687 * With the default maxsockbuf of 256K, a scale factor
1688 * of 3 will be chosen by this algorithm. Those who
1689 * choose a larger maxsockbuf should watch out
1690 * for the compatibility problems mentioned above.
1691 *
1692 * RFC1323: The Window field in a SYN (i.e., a <SYN>
1693 * or <SYN,ACK>) segment itself is never scaled.
1694 */
1695 while (wscale < TCP_MAX_WINSHIFT &&
1696 (TCP_MAXWIN << wscale) < sb_max)
1697 wscale++;
1698 sc->sc_requested_r_scale = wscale;
1699 sc->sc_requested_s_scale = to->to_wscale;
1700 sc->sc_flags |= SCF_WINSCALE;
1701 }
1702 }
1703 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1704 /*
1705 * If incoming packet has an MD5 signature, flag this in the
1706 * syncache so that syncache_respond() will do the right thing
1707 * with the SYN+ACK.
1708 */
1709 if (to->to_flags & TOF_SIGNATURE)
1710 sc->sc_flags |= SCF_SIGNATURE;
1711 #endif /* TCP_SIGNATURE */
1712 if (to->to_flags & TOF_SACKPERM)
1713 sc->sc_flags |= SCF_SACK;
1714 if (to->to_flags & TOF_MSS)
1715 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */
1716 if (ltflags & TF_NOOPT)
1717 sc->sc_flags |= SCF_NOOPT;
1718 /* ECN Handshake */
1719 if (V_tcp_do_ecn && (tp->t_flags2 & TF2_CANNOT_DO_ECN) == 0)
1720 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos);
1721
1722 if (V_tcp_syncookies)
1723 sc->sc_iss = syncookie_generate(sch, sc);
1724 else
1725 sc->sc_iss = arc4random();
1726 #ifdef INET6
1727 if (autoflowlabel) {
1728 if (V_tcp_syncookies)
1729 sc->sc_flowlabel = sc->sc_iss;
1730 else
1731 sc->sc_flowlabel = ip6_randomflowlabel();
1732 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK;
1733 }
1734 #endif
1735 if (locked)
1736 SCH_UNLOCK(sch);
1737
1738 if (tfo_cookie_valid) {
1739 rv = syncache_tfo_expand(sc, so, m, tfo_response_cookie);
1740 /* INP_RUNLOCK(inp) will be performed by the caller */
1741 goto tfo_expanded;
1742 }
1743
1744 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1745 /*
1746 * Do a standard 3-way handshake.
1747 */
1748 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) {
1749 if (sc != &scs)
1750 syncache_insert(sc, sch); /* locks and unlocks sch */
1751 TCPSTAT_INC(tcps_sndacks);
1752 TCPSTAT_INC(tcps_sndtotal);
1753 } else {
1754 if (sc != &scs)
1755 syncache_free(sc);
1756 TCPSTAT_INC(tcps_sc_dropped);
1757 }
1758 goto donenoprobe;
1759
1760 done:
1761 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1762 donenoprobe:
1763 if (m)
1764 m_freem(m);
1765 /*
1766 * If tfo_pending is not NULL here, then a TFO SYN that did not
1767 * result in a new socket was processed and the associated pending
1768 * counter has not yet been decremented. All such TFO processing paths
1769 * transit this point.
1770 */
1771 if (tfo_pending != NULL)
1772 tcp_fastopen_decrement_counter(tfo_pending);
1773
1774 tfo_expanded:
1775 if (sc == NULL || sc == &scs) {
1776 #ifdef MAC
1777 mac_syncache_destroy(&maclabel);
1778 #endif
1779 if (ipopts)
1780 (void)m_free(ipopts);
1781 }
1782 return (rv);
1783 }
1784
1785 /*
1786 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment,
1787 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL.
1788 */
1789 static int
syncache_respond(struct syncache * sc,const struct mbuf * m0,int flags)1790 syncache_respond(struct syncache *sc, const struct mbuf *m0, int flags)
1791 {
1792 struct ip *ip = NULL;
1793 struct mbuf *m;
1794 struct tcphdr *th = NULL;
1795 struct udphdr *udp = NULL;
1796 int optlen, error = 0; /* Make compiler happy */
1797 u_int16_t hlen, tlen, mssopt, ulen;
1798 struct tcpopt to;
1799 #ifdef INET6
1800 struct ip6_hdr *ip6 = NULL;
1801 #endif
1802
1803 NET_EPOCH_ASSERT();
1804
1805 hlen =
1806 #ifdef INET6
1807 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
1808 #endif
1809 sizeof(struct ip);
1810 tlen = hlen + sizeof(struct tcphdr);
1811 if (sc->sc_port) {
1812 tlen += sizeof(struct udphdr);
1813 }
1814 /* Determine MSS we advertize to other end of connection. */
1815 mssopt = tcp_mssopt(&sc->sc_inc);
1816 if (sc->sc_port)
1817 mssopt -= V_tcp_udp_tunneling_overhead;
1818 mssopt = max(mssopt, V_tcp_minmss);
1819
1820 /* XXX: Assume that the entire packet will fit in a header mbuf. */
1821 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
1822 ("syncache: mbuf too small: hlen %u, sc_port %u, max_linkhdr %d + "
1823 "tlen %d + TCP_MAXOLEN %ju <= MHLEN %d", hlen, sc->sc_port,
1824 max_linkhdr, tlen, (uintmax_t)TCP_MAXOLEN, MHLEN));
1825
1826 /* Create the IP+TCP header from scratch. */
1827 m = m_gethdr(M_NOWAIT, MT_DATA);
1828 if (m == NULL)
1829 return (ENOBUFS);
1830 #ifdef MAC
1831 mac_syncache_create_mbuf(sc->sc_label, m);
1832 #endif
1833 m->m_data += max_linkhdr;
1834 m->m_len = tlen;
1835 m->m_pkthdr.len = tlen;
1836 m->m_pkthdr.rcvif = NULL;
1837
1838 #ifdef INET6
1839 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1840 ip6 = mtod(m, struct ip6_hdr *);
1841 ip6->ip6_vfc = IPV6_VERSION;
1842 ip6->ip6_src = sc->sc_inc.inc6_laddr;
1843 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
1844 ip6->ip6_plen = htons(tlen - hlen);
1845 /* ip6_hlim is set after checksum */
1846 /* Zero out traffic class and flow label. */
1847 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK;
1848 ip6->ip6_flow |= sc->sc_flowlabel;
1849 if (sc->sc_port != 0) {
1850 ip6->ip6_nxt = IPPROTO_UDP;
1851 udp = (struct udphdr *)(ip6 + 1);
1852 udp->uh_sport = htons(V_tcp_udp_tunneling_port);
1853 udp->uh_dport = sc->sc_port;
1854 ulen = (tlen - sizeof(struct ip6_hdr));
1855 th = (struct tcphdr *)(udp + 1);
1856 } else {
1857 ip6->ip6_nxt = IPPROTO_TCP;
1858 th = (struct tcphdr *)(ip6 + 1);
1859 }
1860 ip6->ip6_flow |= htonl(sc->sc_ip_tos << IPV6_FLOWLABEL_LEN);
1861 }
1862 #endif
1863 #if defined(INET6) && defined(INET)
1864 else
1865 #endif
1866 #ifdef INET
1867 {
1868 ip = mtod(m, struct ip *);
1869 ip->ip_v = IPVERSION;
1870 ip->ip_hl = sizeof(struct ip) >> 2;
1871 ip->ip_len = htons(tlen);
1872 ip->ip_id = 0;
1873 ip->ip_off = 0;
1874 ip->ip_sum = 0;
1875 ip->ip_src = sc->sc_inc.inc_laddr;
1876 ip->ip_dst = sc->sc_inc.inc_faddr;
1877 ip->ip_ttl = sc->sc_ip_ttl;
1878 ip->ip_tos = sc->sc_ip_tos;
1879
1880 /*
1881 * See if we should do MTU discovery. Route lookups are
1882 * expensive, so we will only unset the DF bit if:
1883 *
1884 * 1) path_mtu_discovery is disabled
1885 * 2) the SCF_UNREACH flag has been set
1886 */
1887 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
1888 ip->ip_off |= htons(IP_DF);
1889 if (sc->sc_port == 0) {
1890 ip->ip_p = IPPROTO_TCP;
1891 th = (struct tcphdr *)(ip + 1);
1892 } else {
1893 ip->ip_p = IPPROTO_UDP;
1894 udp = (struct udphdr *)(ip + 1);
1895 udp->uh_sport = htons(V_tcp_udp_tunneling_port);
1896 udp->uh_dport = sc->sc_port;
1897 ulen = (tlen - sizeof(struct ip));
1898 th = (struct tcphdr *)(udp + 1);
1899 }
1900 }
1901 #endif /* INET */
1902 th->th_sport = sc->sc_inc.inc_lport;
1903 th->th_dport = sc->sc_inc.inc_fport;
1904
1905 if (flags & TH_SYN)
1906 th->th_seq = htonl(sc->sc_iss);
1907 else
1908 th->th_seq = htonl(sc->sc_iss + 1);
1909 th->th_ack = htonl(sc->sc_irs + 1);
1910 th->th_off = sizeof(struct tcphdr) >> 2;
1911 th->th_win = htons(sc->sc_wnd);
1912 th->th_urp = 0;
1913
1914 flags = tcp_ecn_syncache_respond(flags, sc);
1915 tcp_set_flags(th, flags);
1916
1917 /* Tack on the TCP options. */
1918 if ((sc->sc_flags & SCF_NOOPT) == 0) {
1919 to.to_flags = 0;
1920
1921 if (flags & TH_SYN) {
1922 to.to_mss = mssopt;
1923 to.to_flags = TOF_MSS;
1924 if (sc->sc_flags & SCF_WINSCALE) {
1925 to.to_wscale = sc->sc_requested_r_scale;
1926 to.to_flags |= TOF_SCALE;
1927 }
1928 if (sc->sc_flags & SCF_SACK)
1929 to.to_flags |= TOF_SACKPERM;
1930 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1931 if (sc->sc_flags & SCF_SIGNATURE)
1932 to.to_flags |= TOF_SIGNATURE;
1933 #endif
1934 if (sc->sc_tfo_cookie) {
1935 to.to_flags |= TOF_FASTOPEN;
1936 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
1937 to.to_tfo_cookie = sc->sc_tfo_cookie;
1938 /* don't send cookie again when retransmitting response */
1939 sc->sc_tfo_cookie = NULL;
1940 }
1941 }
1942 if (sc->sc_flags & SCF_TIMESTAMP) {
1943 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks();
1944 to.to_tsecr = sc->sc_tsreflect;
1945 to.to_flags |= TOF_TS;
1946 }
1947 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
1948
1949 /* Adjust headers by option size. */
1950 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
1951 m->m_len += optlen;
1952 m->m_pkthdr.len += optlen;
1953 #ifdef INET6
1954 if (sc->sc_inc.inc_flags & INC_ISIPV6)
1955 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
1956 else
1957 #endif
1958 ip->ip_len = htons(ntohs(ip->ip_len) + optlen);
1959 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1960 if (sc->sc_flags & SCF_SIGNATURE) {
1961 KASSERT(to.to_flags & TOF_SIGNATURE,
1962 ("tcp_addoptions() didn't set tcp_signature"));
1963
1964 /* NOTE: to.to_signature is inside of mbuf */
1965 if (!TCPMD5_ENABLED() ||
1966 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) {
1967 m_freem(m);
1968 return (EACCES);
1969 }
1970 }
1971 #endif
1972 } else
1973 optlen = 0;
1974
1975 if (udp) {
1976 ulen += optlen;
1977 udp->uh_ulen = htons(ulen);
1978 }
1979 M_SETFIB(m, sc->sc_inc.inc_fibnum);
1980 /*
1981 * If we have peer's SYN and it has a flowid, then let's assign it to
1982 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid
1983 * to SYN|ACK due to lack of inp here.
1984 */
1985 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) {
1986 m->m_pkthdr.flowid = m0->m_pkthdr.flowid;
1987 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0));
1988 }
1989 #ifdef INET6
1990 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1991 if (sc->sc_port) {
1992 m->m_pkthdr.csum_flags = CSUM_UDP_IPV6;
1993 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
1994 udp->uh_sum = in6_cksum_pseudo(ip6, ulen,
1995 IPPROTO_UDP, 0);
1996 th->th_sum = htons(0);
1997 } else {
1998 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
1999 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
2000 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen,
2001 IPPROTO_TCP, 0);
2002 }
2003 ip6->ip6_hlim = sc->sc_ip_ttl;
2004 #ifdef TCP_OFFLOAD
2005 if (ADDED_BY_TOE(sc)) {
2006 struct toedev *tod = sc->sc_tod;
2007
2008 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
2009
2010 return (error);
2011 }
2012 #endif
2013 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th);
2014 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
2015 }
2016 #endif
2017 #if defined(INET6) && defined(INET)
2018 else
2019 #endif
2020 #ifdef INET
2021 {
2022 if (sc->sc_port) {
2023 m->m_pkthdr.csum_flags = CSUM_UDP;
2024 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
2025 udp->uh_sum = in_pseudo(ip->ip_src.s_addr,
2026 ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP));
2027 th->th_sum = htons(0);
2028 } else {
2029 m->m_pkthdr.csum_flags = CSUM_TCP;
2030 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
2031 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
2032 htons(tlen + optlen - hlen + IPPROTO_TCP));
2033 }
2034 #ifdef TCP_OFFLOAD
2035 if (ADDED_BY_TOE(sc)) {
2036 struct toedev *tod = sc->sc_tod;
2037
2038 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
2039
2040 return (error);
2041 }
2042 #endif
2043 TCP_PROBE5(send, NULL, NULL, ip, NULL, th);
2044 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
2045 }
2046 #endif
2047 return (error);
2048 }
2049
2050 /*
2051 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks
2052 * that exceed the capacity of the syncache by avoiding the storage of any
2053 * of the SYNs we receive. Syncookies defend against blind SYN flooding
2054 * attacks where the attacker does not have access to our responses.
2055 *
2056 * Syncookies encode and include all necessary information about the
2057 * connection setup within the SYN|ACK that we send back. That way we
2058 * can avoid keeping any local state until the ACK to our SYN|ACK returns
2059 * (if ever). Normally the syncache and syncookies are running in parallel
2060 * with the latter taking over when the former is exhausted. When matching
2061 * syncache entry is found the syncookie is ignored.
2062 *
2063 * The only reliable information persisting the 3WHS is our initial sequence
2064 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient
2065 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS
2066 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK
2067 * returns and signifies a legitimate connection if it matches the ACK.
2068 *
2069 * The available space of 32 bits to store the hash and to encode the SYN
2070 * option information is very tight and we should have at least 24 bits for
2071 * the MAC to keep the number of guesses by blind spoofing reasonably high.
2072 *
2073 * SYN option information we have to encode to fully restore a connection:
2074 * MSS: is imporant to chose an optimal segment size to avoid IP level
2075 * fragmentation along the path. The common MSS values can be encoded
2076 * in a 3-bit table. Uncommon values are captured by the next lower value
2077 * in the table leading to a slight increase in packetization overhead.
2078 * WSCALE: is necessary to allow large windows to be used for high delay-
2079 * bandwidth product links. Not scaling the window when it was initially
2080 * negotiated is bad for performance as lack of scaling further decreases
2081 * the apparent available send window. We only need to encode the WSCALE
2082 * we received from the remote end. Our end can be recalculated at any
2083 * time. The common WSCALE values can be encoded in a 3-bit table.
2084 * Uncommon values are captured by the next lower value in the table
2085 * making us under-estimate the available window size halving our
2086 * theoretically possible maximum throughput for that connection.
2087 * SACK: Greatly assists in packet loss recovery and requires 1 bit.
2088 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options
2089 * that are included in all segments on a connection. We enable them when
2090 * the ACK has them.
2091 *
2092 * Security of syncookies and attack vectors:
2093 *
2094 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod)
2095 * together with the gloabl secret to make it unique per connection attempt.
2096 * Thus any change of any of those parameters results in a different MAC output
2097 * in an unpredictable way unless a collision is encountered. 24 bits of the
2098 * MAC are embedded into the ISS.
2099 *
2100 * To prevent replay attacks two rotating global secrets are updated with a
2101 * new random value every 15 seconds. The life-time of a syncookie is thus
2102 * 15-30 seconds.
2103 *
2104 * Vector 1: Attacking the secret. This requires finding a weakness in the
2105 * MAC itself or the way it is used here. The attacker can do a chosen plain
2106 * text attack by varying and testing the all parameters under his control.
2107 * The strength depends on the size and randomness of the secret, and the
2108 * cryptographic security of the MAC function. Due to the constant updating
2109 * of the secret the attacker has at most 29.999 seconds to find the secret
2110 * and launch spoofed connections. After that he has to start all over again.
2111 *
2112 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC
2113 * size an average of 4,823 attempts are required for a 50% chance of success
2114 * to spoof a single syncookie (birthday collision paradox). However the
2115 * attacker is blind and doesn't know if one of his attempts succeeded unless
2116 * he has a side channel to interfere success from. A single connection setup
2117 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets.
2118 * This many attempts are required for each one blind spoofed connection. For
2119 * every additional spoofed connection he has to launch another N attempts.
2120 * Thus for a sustained rate 100 spoofed connections per second approximately
2121 * 1,800,000 packets per second would have to be sent.
2122 *
2123 * NB: The MAC function should be fast so that it doesn't become a CPU
2124 * exhaustion attack vector itself.
2125 *
2126 * References:
2127 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations
2128 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996
2129 * http://cr.yp.to/syncookies.html (overview)
2130 * http://cr.yp.to/syncookies/archive (details)
2131 *
2132 *
2133 * Schematic construction of a syncookie enabled Initial Sequence Number:
2134 * 0 1 2 3
2135 * 12345678901234567890123456789012
2136 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP|
2137 *
2138 * x 24 MAC (truncated)
2139 * W 3 Send Window Scale index
2140 * M 3 MSS index
2141 * S 1 SACK permitted
2142 * P 1 Odd/even secret
2143 */
2144
2145 /*
2146 * Distribution and probability of certain MSS values. Those in between are
2147 * rounded down to the next lower one.
2148 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011]
2149 * .2% .3% 5% 7% 7% 20% 15% 45%
2150 */
2151 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 };
2152
2153 /*
2154 * Distribution and probability of certain WSCALE values. We have to map the
2155 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3
2156 * bits based on prevalence of certain values. Where we don't have an exact
2157 * match for are rounded down to the next lower one letting us under-estimate
2158 * the true available window. At the moment this would happen only for the
2159 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer
2160 * and window size). The absence of the WSCALE option (no scaling in either
2161 * direction) is encoded with index zero.
2162 * [WSCALE values histograms, Allman, 2012]
2163 * X 10 10 35 5 6 14 10% by host
2164 * X 11 4 5 5 18 49 3% by connections
2165 */
2166 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 };
2167
2168 /*
2169 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed
2170 * and good cryptographic properties.
2171 */
2172 static uint32_t
syncookie_mac(struct in_conninfo * inc,tcp_seq irs,uint8_t flags,uint8_t * secbits,uintptr_t secmod)2173 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags,
2174 uint8_t *secbits, uintptr_t secmod)
2175 {
2176 SIPHASH_CTX ctx;
2177 uint32_t siphash[2];
2178
2179 SipHash24_Init(&ctx);
2180 SipHash_SetKey(&ctx, secbits);
2181 switch (inc->inc_flags & INC_ISIPV6) {
2182 #ifdef INET
2183 case 0:
2184 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr));
2185 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr));
2186 break;
2187 #endif
2188 #ifdef INET6
2189 case INC_ISIPV6:
2190 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr));
2191 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr));
2192 break;
2193 #endif
2194 }
2195 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport));
2196 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport));
2197 SipHash_Update(&ctx, &irs, sizeof(irs));
2198 SipHash_Update(&ctx, &flags, sizeof(flags));
2199 SipHash_Update(&ctx, &secmod, sizeof(secmod));
2200 SipHash_Final((u_int8_t *)&siphash, &ctx);
2201
2202 return (siphash[0] ^ siphash[1]);
2203 }
2204
2205 static tcp_seq
syncookie_generate(struct syncache_head * sch,struct syncache * sc)2206 syncookie_generate(struct syncache_head *sch, struct syncache *sc)
2207 {
2208 u_int i, secbit, wscale;
2209 uint32_t iss, hash;
2210 uint8_t *secbits;
2211 union syncookie cookie;
2212
2213 cookie.cookie = 0;
2214
2215 /* Map our computed MSS into the 3-bit index. */
2216 for (i = nitems(tcp_sc_msstab) - 1;
2217 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0;
2218 i--)
2219 ;
2220 cookie.flags.mss_idx = i;
2221
2222 /*
2223 * Map the send window scale into the 3-bit index but only if
2224 * the wscale option was received.
2225 */
2226 if (sc->sc_flags & SCF_WINSCALE) {
2227 wscale = sc->sc_requested_s_scale;
2228 for (i = nitems(tcp_sc_wstab) - 1;
2229 tcp_sc_wstab[i] > wscale && i > 0;
2230 i--)
2231 ;
2232 cookie.flags.wscale_idx = i;
2233 }
2234
2235 /* Can we do SACK? */
2236 if (sc->sc_flags & SCF_SACK)
2237 cookie.flags.sack_ok = 1;
2238
2239 /* Which of the two secrets to use. */
2240 secbit = V_tcp_syncache.secret.oddeven & 0x1;
2241 cookie.flags.odd_even = secbit;
2242
2243 secbits = V_tcp_syncache.secret.key[secbit];
2244 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits,
2245 (uintptr_t)sch);
2246
2247 /*
2248 * Put the flags into the hash and XOR them to get better ISS number
2249 * variance. This doesn't enhance the cryptographic strength and is
2250 * done to prevent the 8 cookie bits from showing up directly on the
2251 * wire.
2252 */
2253 iss = hash & ~0xff;
2254 iss |= cookie.cookie ^ (hash >> 24);
2255
2256 TCPSTAT_INC(tcps_sc_sendcookie);
2257 return (iss);
2258 }
2259
2260 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)2261 syncookie_expand(struct in_conninfo *inc, const struct syncache_head *sch,
2262 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
2263 struct socket *lso, uint16_t port)
2264 {
2265 uint32_t hash;
2266 uint8_t *secbits;
2267 tcp_seq ack, seq;
2268 int wnd, wscale = 0;
2269 union syncookie cookie;
2270
2271 /*
2272 * Pull information out of SYN-ACK/ACK and revert sequence number
2273 * advances.
2274 */
2275 ack = th->th_ack - 1;
2276 seq = th->th_seq - 1;
2277
2278 /*
2279 * Unpack the flags containing enough information to restore the
2280 * connection.
2281 */
2282 cookie.cookie = (ack & 0xff) ^ (ack >> 24);
2283
2284 /* Which of the two secrets to use. */
2285 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even];
2286
2287 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch);
2288
2289 /* The recomputed hash matches the ACK if this was a genuine cookie. */
2290 if ((ack & ~0xff) != (hash & ~0xff))
2291 return (false);
2292
2293 /* Fill in the syncache values. */
2294 sc->sc_flags = 0;
2295 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
2296 sc->sc_ipopts = NULL;
2297
2298 sc->sc_irs = seq;
2299 sc->sc_iss = ack;
2300
2301 switch (inc->inc_flags & INC_ISIPV6) {
2302 #ifdef INET
2303 case 0:
2304 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl;
2305 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos;
2306 break;
2307 #endif
2308 #ifdef INET6
2309 case INC_ISIPV6:
2310 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL)
2311 sc->sc_flowlabel =
2312 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK;
2313 break;
2314 #endif
2315 }
2316
2317 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx];
2318
2319 /* We can simply recompute receive window scale we sent earlier. */
2320 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max)
2321 wscale++;
2322
2323 /* Only use wscale if it was enabled in the orignal SYN. */
2324 if (cookie.flags.wscale_idx > 0) {
2325 sc->sc_requested_r_scale = wscale;
2326 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx];
2327 sc->sc_flags |= SCF_WINSCALE;
2328 }
2329
2330 wnd = lso->sol_sbrcv_hiwat;
2331 wnd = imax(wnd, 0);
2332 wnd = imin(wnd, TCP_MAXWIN);
2333 sc->sc_wnd = wnd;
2334
2335 if (cookie.flags.sack_ok)
2336 sc->sc_flags |= SCF_SACK;
2337
2338 if (to->to_flags & TOF_TS) {
2339 sc->sc_flags |= SCF_TIMESTAMP;
2340 sc->sc_tsreflect = to->to_tsval;
2341 sc->sc_tsoff = tcp_new_ts_offset(inc);
2342 }
2343
2344 if (to->to_flags & TOF_SIGNATURE)
2345 sc->sc_flags |= SCF_SIGNATURE;
2346
2347 sc->sc_rxmits = 0;
2348
2349 sc->sc_port = port;
2350
2351 return (true);
2352 }
2353
2354 #ifdef INVARIANTS
2355 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)2356 syncookie_cmp(struct in_conninfo *inc, const struct syncache_head *sch,
2357 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
2358 struct socket *lso, uint16_t port)
2359 {
2360 struct syncache scs;
2361 char *s;
2362
2363 bzero(&scs, sizeof(scs));
2364 if (syncookie_expand(inc, sch, &scs, th, to, lso, port) &&
2365 (sc->sc_peer_mss != scs.sc_peer_mss ||
2366 sc->sc_requested_r_scale != scs.sc_requested_r_scale ||
2367 sc->sc_requested_s_scale != scs.sc_requested_s_scale ||
2368 (sc->sc_flags & SCF_SACK) != (scs.sc_flags & SCF_SACK))) {
2369
2370 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL)
2371 return;
2372
2373 if (sc->sc_peer_mss != scs.sc_peer_mss)
2374 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n",
2375 s, __func__, sc->sc_peer_mss, scs.sc_peer_mss);
2376
2377 if (sc->sc_requested_r_scale != scs.sc_requested_r_scale)
2378 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n",
2379 s, __func__, sc->sc_requested_r_scale,
2380 scs.sc_requested_r_scale);
2381
2382 if (sc->sc_requested_s_scale != scs.sc_requested_s_scale)
2383 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n",
2384 s, __func__, sc->sc_requested_s_scale,
2385 scs.sc_requested_s_scale);
2386
2387 if ((sc->sc_flags & SCF_SACK) != (scs.sc_flags & SCF_SACK))
2388 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__);
2389
2390 free(s, M_TCPLOG);
2391 }
2392 }
2393 #endif /* INVARIANTS */
2394
2395 static void
syncookie_reseed(void * arg)2396 syncookie_reseed(void *arg)
2397 {
2398 struct tcp_syncache *sc = arg;
2399 uint8_t *secbits;
2400 int secbit;
2401
2402 /*
2403 * Reseeding the secret doesn't have to be protected by a lock.
2404 * It only must be ensured that the new random values are visible
2405 * to all CPUs in a SMP environment. The atomic with release
2406 * semantics ensures that.
2407 */
2408 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1;
2409 secbits = sc->secret.key[secbit];
2410 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0);
2411 atomic_add_rel_int(&sc->secret.oddeven, 1);
2412
2413 /* Reschedule ourself. */
2414 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz);
2415 }
2416
2417 /*
2418 * We have overflowed a bucket. Let's pause dealing with the syncache.
2419 * This function will increment the bucketoverflow statistics appropriately
2420 * (once per pause when pausing is enabled; otherwise, once per overflow).
2421 */
2422 static void
syncache_pause(struct in_conninfo * inc)2423 syncache_pause(struct in_conninfo *inc)
2424 {
2425 time_t delta;
2426 const char *s;
2427
2428 /* XXX:
2429 * 2. Add sysctl read here so we don't get the benefit of this
2430 * change without the new sysctl.
2431 */
2432
2433 /*
2434 * Try an unlocked read. If we already know that another thread
2435 * has activated the feature, there is no need to proceed.
2436 */
2437 if (V_tcp_syncache.paused)
2438 return;
2439
2440 /* Are cookied enabled? If not, we can't pause. */
2441 if (!V_tcp_syncookies) {
2442 TCPSTAT_INC(tcps_sc_bucketoverflow);
2443 return;
2444 }
2445
2446 /*
2447 * We may be the first thread to find an overflow. Get the lock
2448 * and evaluate if we need to take action.
2449 */
2450 mtx_lock(&V_tcp_syncache.pause_mtx);
2451 if (V_tcp_syncache.paused) {
2452 mtx_unlock(&V_tcp_syncache.pause_mtx);
2453 return;
2454 }
2455
2456 /* Activate protection. */
2457 V_tcp_syncache.paused = true;
2458 TCPSTAT_INC(tcps_sc_bucketoverflow);
2459
2460 /*
2461 * Determine the last backoff time. If we are seeing a re-newed
2462 * attack within that same time after last reactivating the syncache,
2463 * consider it an extension of the same attack.
2464 */
2465 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff;
2466 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) {
2467 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) {
2468 delta <<= 1;
2469 V_tcp_syncache.pause_backoff++;
2470 }
2471 } else {
2472 delta = TCP_SYNCACHE_PAUSE_TIME;
2473 V_tcp_syncache.pause_backoff = 0;
2474 }
2475
2476 /* Log a warning, including IP addresses, if able. */
2477 if (inc != NULL)
2478 s = tcp_log_addrs(inc, NULL, NULL, NULL);
2479 else
2480 s = (const char *)NULL;
2481 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for "
2482 "the next %lld seconds%s%s%s\n", (long long)delta,
2483 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "",
2484 (s != NULL) ? ")" : "");
2485 free(__DECONST(void *, s), M_TCPLOG);
2486
2487 /* Use the calculated delta to set a new pause time. */
2488 V_tcp_syncache.pause_until = time_uptime + delta;
2489 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause,
2490 &V_tcp_syncache);
2491 mtx_unlock(&V_tcp_syncache.pause_mtx);
2492 }
2493
2494 /* Evaluate whether we need to unpause. */
2495 static void
syncache_unpause(void * arg)2496 syncache_unpause(void *arg)
2497 {
2498 struct tcp_syncache *sc;
2499 time_t delta;
2500
2501 sc = arg;
2502 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED);
2503 callout_deactivate(&sc->pause_co);
2504
2505 /*
2506 * Check to make sure we are not running early. If the pause
2507 * time has expired, then deactivate the protection.
2508 */
2509 if ((delta = sc->pause_until - time_uptime) > 0)
2510 callout_schedule(&sc->pause_co, delta * hz);
2511 else
2512 sc->paused = false;
2513 }
2514
2515 /*
2516 * Exports the syncache entries to userland so that netstat can display
2517 * them alongside the other sockets. This function is intended to be
2518 * called only from tcp_pcblist.
2519 *
2520 * Due to concurrency on an active system, the number of pcbs exported
2521 * may have no relation to max_pcbs. max_pcbs merely indicates the
2522 * amount of space the caller allocated for this function to use.
2523 */
2524 int
syncache_pcblist(struct sysctl_req * req)2525 syncache_pcblist(struct sysctl_req *req)
2526 {
2527 struct xtcpcb xt;
2528 struct syncache *sc;
2529 struct syncache_head *sch;
2530 int error, i;
2531
2532 bzero(&xt, sizeof(xt));
2533 xt.xt_len = sizeof(xt);
2534 xt.t_state = TCPS_SYN_RECEIVED;
2535 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP;
2536 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket);
2537 xt.xt_inp.xi_socket.so_type = SOCK_STREAM;
2538 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING;
2539
2540 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
2541 sch = &V_tcp_syncache.hashbase[i];
2542 SCH_LOCK(sch);
2543 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
2544 if (sc->sc_cred != NULL &&
2545 cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
2546 continue;
2547 if (sc->sc_inc.inc_flags & INC_ISIPV6)
2548 xt.xt_inp.inp_vflag = INP_IPV6;
2549 else
2550 xt.xt_inp.inp_vflag = INP_IPV4;
2551 xt.xt_encaps_port = sc->sc_port;
2552 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc,
2553 sizeof (struct in_conninfo));
2554 error = SYSCTL_OUT(req, &xt, sizeof xt);
2555 if (error) {
2556 SCH_UNLOCK(sch);
2557 return (0);
2558 }
2559 }
2560 SCH_UNLOCK(sch);
2561 }
2562
2563 return (0);
2564 }
2565