1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause
3 *
4 * Copyright (c) 2001 McAfee, Inc.
5 * Copyright (c) 2006,2013 Andre Oppermann, Internet Business Solutions AG
6 * All rights reserved.
7 *
8 * This software was developed for the FreeBSD Project by Jonathan Lemon
9 * and McAfee Research, the Security Research Division of McAfee, Inc. under
10 * DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the
11 * DARPA CHATS research program. [2001 McAfee, Inc.]
12 *
13 * Redistribution and use in source and binary forms, with or without
14 * modification, are permitted provided that the following conditions
15 * are met:
16 * 1. Redistributions of source code must retain the above copyright
17 * notice, this list of conditions and the following disclaimer.
18 * 2. Redistributions in binary form must reproduce the above copyright
19 * notice, this list of conditions and the following disclaimer in the
20 * documentation and/or other materials provided with the distribution.
21 *
22 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * SUCH DAMAGE.
33 */
34
35 #include "opt_inet.h"
36 #include "opt_inet6.h"
37 #include "opt_ipsec.h"
38
39 #include <sys/param.h>
40 #include <sys/systm.h>
41 #include <sys/hash.h>
42 #include <sys/refcount.h>
43 #include <sys/kernel.h>
44 #include <sys/sysctl.h>
45 #include <sys/limits.h>
46 #include <sys/lock.h>
47 #include <sys/mutex.h>
48 #include <sys/malloc.h>
49 #include <sys/mbuf.h>
50 #include <sys/proc.h> /* for proc0 declaration */
51 #include <sys/random.h>
52 #include <sys/socket.h>
53 #include <sys/socketvar.h>
54 #include <sys/syslog.h>
55 #include <sys/ucred.h>
56
57 #include <sys/md5.h>
58 #include <crypto/siphash/siphash.h>
59
60 #include <vm/uma.h>
61
62 #include <net/if.h>
63 #include <net/if_var.h>
64 #include <net/route.h>
65 #include <net/vnet.h>
66
67 #include <netinet/in.h>
68 #include <netinet/in_kdtrace.h>
69 #include <netinet/in_systm.h>
70 #include <netinet/ip.h>
71 #include <netinet/in_var.h>
72 #include <netinet/in_pcb.h>
73 #include <netinet/in_rss.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 #include <netinet6/in6_rss.h>
83 #endif
84 #include <netinet/tcp.h>
85 #include <netinet/tcp_fastopen.h>
86 #include <netinet/tcp_fsm.h>
87 #include <netinet/tcp_seq.h>
88 #include <netinet/tcp_timer.h>
89 #include <netinet/tcp_var.h>
90 #include <netinet/tcp_syncache.h>
91 #include <netinet/tcp_ecn.h>
92 #ifdef TCP_BLACKBOX
93 #include <netinet/tcp_log_buf.h>
94 #endif
95 #ifdef TCP_OFFLOAD
96 #include <netinet/toecore.h>
97 #endif
98 #include <netinet/udp.h>
99
100 #include <netipsec/ipsec_support.h>
101
102 #include <machine/in_cksum.h>
103
104 #include <security/mac/mac_framework.h>
105
106 VNET_DEFINE_STATIC(bool, tcp_syncookies) = true;
107 #define V_tcp_syncookies VNET(tcp_syncookies)
108 SYSCTL_BOOL(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW,
109 &VNET_NAME(tcp_syncookies), 0,
110 "Use TCP SYN cookies if the syncache overflows");
111
112 VNET_DEFINE_STATIC(bool, tcp_syncookiesonly) = false;
113 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly)
114 SYSCTL_BOOL(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW,
115 &VNET_NAME(tcp_syncookiesonly), 0,
116 "Use only TCP SYN cookies");
117
118 #ifdef TCP_OFFLOAD
119 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL)
120 #endif
121
122 static void syncache_drop(struct syncache *, struct syncache_head *);
123 static void syncache_free(struct syncache *);
124 static void syncache_insert(struct syncache *, struct syncache_head *);
125 static int syncache_respond(struct syncache *, int);
126 static void syncache_send_challenge_ack(struct syncache *);
127 static struct socket *syncache_socket(struct syncache *, struct socket *,
128 struct mbuf *m);
129 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch,
130 int docallout);
131 static void syncache_timer(void *);
132
133 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t,
134 uint8_t *, uintptr_t);
135 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *);
136 static bool syncookie_expand(struct in_conninfo *,
137 const struct syncache_head *, struct syncache *,
138 struct tcphdr *, struct tcpopt *, struct socket *,
139 uint16_t);
140 static void syncache_pause(struct in_conninfo *);
141 static void syncache_unpause(void *);
142 static void syncookie_reseed(void *);
143 #ifdef INVARIANTS
144 static void syncookie_cmp(struct in_conninfo *,
145 const struct syncache_head *, struct syncache *,
146 struct tcphdr *, struct tcpopt *, struct socket *,
147 uint16_t);
148 #endif
149
150 /*
151 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
152 * 3 retransmits corresponds to a timeout with default values of
153 * tcp_rexmit_initial * ( 1 +
154 * tcp_backoff[1] +
155 * tcp_backoff[2] +
156 * tcp_backoff[3]) + 3 * tcp_rexmit_slop,
157 * 1000 ms * (1 + 2 + 4 + 8) + 3 * 200 ms = 15600 ms,
158 * the odds are that the user has given up attempting to connect by then.
159 */
160 #define SYNCACHE_MAXREXMTS 3
161
162 /* Arbitrary values */
163 #define TCP_SYNCACHE_HASHSIZE 512
164 #define TCP_SYNCACHE_BUCKETLIMIT 30
165
166 VNET_DEFINE_STATIC(struct tcp_syncache, tcp_syncache);
167 #define V_tcp_syncache VNET(tcp_syncache)
168
169 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache,
170 CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
171 "TCP SYN cache");
172
173 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
174 &VNET_NAME(tcp_syncache.bucket_limit), 0,
175 "Per-bucket hash limit for syncache");
176
177 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
178 &VNET_NAME(tcp_syncache.cache_limit), 0,
179 "Overall entry limit for syncache");
180
181 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET,
182 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache");
183
184 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN,
185 &VNET_NAME(tcp_syncache.hashsize), 0,
186 "Size of TCP syncache hashtable");
187
188 SYSCTL_BOOL(_net_inet_tcp_syncache, OID_AUTO, see_other, CTLFLAG_VNET |
189 CTLFLAG_RW, &VNET_NAME(tcp_syncache.see_other), 0,
190 "All syncache(4) entries are visible, ignoring UID/GID, jail(2) "
191 "and mac(4) checks");
192
193 static int
sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS)194 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS)
195 {
196 int error;
197 u_int new;
198
199 new = V_tcp_syncache.rexmt_limit;
200 error = sysctl_handle_int(oidp, &new, 0, req);
201 if ((error == 0) && (req->newptr != NULL)) {
202 if (new > TCP_MAXRXTSHIFT)
203 error = EINVAL;
204 else
205 V_tcp_syncache.rexmt_limit = new;
206 }
207 return (error);
208 }
209
210 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit,
211 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
212 &VNET_NAME(tcp_syncache.rexmt_limit), 0,
213 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "IU",
214 "Limit on SYN/ACK retransmissions");
215
216 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1;
217 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail,
218 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0,
219 "Send reset on socket allocation failure");
220
221 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
222
223 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx)
224 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx)
225 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED)
226
227 static void
syncache_release(struct syncache * sc)228 syncache_release(struct syncache *sc)
229 {
230 if (sc->sc_ipopts != NULL)
231 (void)m_free(sc->sc_ipopts);
232 if (sc->sc_cred != NULL)
233 crfree(sc->sc_cred);
234 #ifdef MAC
235 mac_syncache_destroy(&sc->sc_label);
236 #endif
237 }
238
239 /*
240 * Requires the syncache entry to be already removed from the bucket list.
241 */
242 static void
syncache_free(struct syncache * sc)243 syncache_free(struct syncache *sc)
244 {
245 syncache_release(sc);
246 uma_zfree(V_tcp_syncache.zone, sc);
247 }
248
249 void
syncache_init(void)250 syncache_init(void)
251 {
252 int i;
253
254 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
255 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
256 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
257 V_tcp_syncache.hash_secret = arc4random();
258
259 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
260 &V_tcp_syncache.hashsize);
261 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
262 &V_tcp_syncache.bucket_limit);
263 if (!powerof2(V_tcp_syncache.hashsize) ||
264 V_tcp_syncache.hashsize == 0) {
265 printf("WARNING: syncache hash size is not a power of 2.\n");
266 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
267 }
268 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1;
269
270 /* Set limits. */
271 V_tcp_syncache.cache_limit =
272 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit;
273 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
274 &V_tcp_syncache.cache_limit);
275
276 /* Allocate the hash table. */
277 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize *
278 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO);
279
280 #ifdef VIMAGE
281 V_tcp_syncache.vnet = curvnet;
282 #endif
283
284 /* Initialize the hash buckets. */
285 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
286 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket);
287 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
288 NULL, MTX_DEF);
289 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer,
290 &V_tcp_syncache.hashbase[i].sch_mtx, 0);
291 V_tcp_syncache.hashbase[i].sch_length = 0;
292 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache;
293 V_tcp_syncache.hashbase[i].sch_last_overflow =
294 -(SYNCOOKIE_LIFETIME + 1);
295 }
296
297 /* Create the syncache entry zone. */
298 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
299 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
300 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone,
301 V_tcp_syncache.cache_limit);
302
303 /* Start the SYN cookie reseeder callout. */
304 callout_init(&V_tcp_syncache.secret.reseed, 1);
305 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0);
306 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0);
307 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz,
308 syncookie_reseed, &V_tcp_syncache);
309
310 /* Initialize the pause machinery. */
311 mtx_init(&V_tcp_syncache.pause_mtx, "tcp_sc_pause", NULL, MTX_DEF);
312 callout_init_mtx(&V_tcp_syncache.pause_co, &V_tcp_syncache.pause_mtx,
313 0);
314 V_tcp_syncache.pause_until = time_uptime - TCP_SYNCACHE_PAUSE_TIME;
315 V_tcp_syncache.pause_backoff = 0;
316 V_tcp_syncache.paused = false;
317 }
318
319 #ifdef VIMAGE
320 void
syncache_destroy(void)321 syncache_destroy(void)
322 {
323 struct syncache_head *sch;
324 struct syncache *sc, *nsc;
325 int i;
326
327 /*
328 * Stop the re-seed timer before freeing resources. No need to
329 * possibly schedule it another time.
330 */
331 callout_drain(&V_tcp_syncache.secret.reseed);
332
333 /* Stop the SYN cache pause callout. */
334 mtx_lock(&V_tcp_syncache.pause_mtx);
335 if (callout_stop(&V_tcp_syncache.pause_co) == 0) {
336 mtx_unlock(&V_tcp_syncache.pause_mtx);
337 callout_drain(&V_tcp_syncache.pause_co);
338 } else
339 mtx_unlock(&V_tcp_syncache.pause_mtx);
340
341 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */
342 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
343 sch = &V_tcp_syncache.hashbase[i];
344 callout_drain(&sch->sch_timer);
345
346 SCH_LOCK(sch);
347 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc)
348 syncache_drop(sc, sch);
349 SCH_UNLOCK(sch);
350 KASSERT(TAILQ_EMPTY(&sch->sch_bucket),
351 ("%s: sch->sch_bucket not empty", __func__));
352 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0",
353 __func__, sch->sch_length));
354 mtx_destroy(&sch->sch_mtx);
355 }
356
357 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0,
358 ("%s: cache_count not 0", __func__));
359
360 /* Free the allocated global resources. */
361 uma_zdestroy(V_tcp_syncache.zone);
362 free(V_tcp_syncache.hashbase, M_SYNCACHE);
363 mtx_destroy(&V_tcp_syncache.pause_mtx);
364 }
365 #endif
366
367 /*
368 * Inserts a syncache entry into the specified bucket row.
369 * Locks and unlocks the syncache_head autonomously.
370 */
371 static void
syncache_insert(struct syncache * sc,struct syncache_head * sch)372 syncache_insert(struct syncache *sc, struct syncache_head *sch)
373 {
374 struct syncache *sc2;
375
376 SCH_LOCK(sch);
377
378 /*
379 * Make sure that we don't overflow the per-bucket limit.
380 * If the bucket is full, toss the oldest element.
381 */
382 if (sch->sch_length >= V_tcp_syncache.bucket_limit) {
383 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
384 ("sch->sch_length incorrect"));
385 syncache_pause(&sc->sc_inc);
386 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
387 sch->sch_last_overflow = time_uptime;
388 syncache_drop(sc2, sch);
389 }
390
391 /* Put it into the bucket. */
392 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
393 sch->sch_length++;
394
395 #ifdef TCP_OFFLOAD
396 if (ADDED_BY_TOE(sc)) {
397 struct toedev *tod = sc->sc_tod;
398
399 tod->tod_syncache_added(tod, sc->sc_todctx);
400 }
401 #endif
402
403 /* Reinitialize the bucket row's timer. */
404 if (sch->sch_length == 1)
405 sch->sch_nextc = ticks + INT_MAX;
406 syncache_timeout(sc, sch, 1);
407
408 SCH_UNLOCK(sch);
409
410 TCPSTATES_INC(TCPS_SYN_RECEIVED);
411 TCPSTAT_INC(tcps_sc_added);
412 }
413
414 /*
415 * Remove and free entry from syncache bucket row.
416 * Expects locked syncache head.
417 */
418 static void
syncache_drop(struct syncache * sc,struct syncache_head * sch)419 syncache_drop(struct syncache *sc, struct syncache_head *sch)
420 {
421
422 SCH_LOCK_ASSERT(sch);
423
424 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
425 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
426 sch->sch_length--;
427
428 #ifdef TCP_OFFLOAD
429 if (ADDED_BY_TOE(sc)) {
430 struct toedev *tod = sc->sc_tod;
431
432 tod->tod_syncache_removed(tod, sc->sc_todctx);
433 }
434 #endif
435
436 syncache_free(sc);
437 }
438
439 /*
440 * Engage/reengage time on bucket row.
441 */
442 static void
syncache_timeout(struct syncache * sc,struct syncache_head * sch,int docallout)443 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
444 {
445 int rexmt;
446
447 if (sc->sc_rxmits == 0)
448 rexmt = tcp_rexmit_initial;
449 else
450 TCPT_RANGESET(rexmt,
451 tcp_rexmit_initial * tcp_backoff[sc->sc_rxmits],
452 tcp_rexmit_min, tcp_rexmit_max);
453 sc->sc_rxttime = ticks + rexmt;
454 sc->sc_rxmits++;
455 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
456 sch->sch_nextc = sc->sc_rxttime;
457 if (docallout)
458 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
459 syncache_timer, (void *)sch);
460 }
461 }
462
463 /*
464 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
465 * If we have retransmitted an entry the maximum number of times, expire it.
466 * One separate timer for each bucket row.
467 */
468 static void
syncache_timer(void * xsch)469 syncache_timer(void *xsch)
470 {
471 struct syncache_head *sch = (struct syncache_head *)xsch;
472 struct syncache *sc, *nsc;
473 struct epoch_tracker et;
474 int tick = ticks;
475 char *s;
476 bool paused;
477
478 CURVNET_SET(sch->sch_sc->vnet);
479
480 /* NB: syncache_head has already been locked by the callout. */
481 SCH_LOCK_ASSERT(sch);
482
483 /*
484 * In the following cycle we may remove some entries and/or
485 * advance some timeouts, so re-initialize the bucket timer.
486 */
487 sch->sch_nextc = tick + INT_MAX;
488
489 /*
490 * If we have paused processing, unconditionally remove
491 * all syncache entries.
492 */
493 mtx_lock(&V_tcp_syncache.pause_mtx);
494 paused = V_tcp_syncache.paused;
495 mtx_unlock(&V_tcp_syncache.pause_mtx);
496
497 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
498 if (paused) {
499 syncache_drop(sc, sch);
500 continue;
501 }
502 /*
503 * We do not check if the listen socket still exists
504 * and accept the case where the listen socket may be
505 * gone by the time we resend the SYN/ACK. We do
506 * not expect this to happens often. If it does,
507 * then the RST will be sent by the time the remote
508 * host does the SYN/ACK->ACK.
509 */
510 if (TSTMP_GT(sc->sc_rxttime, tick)) {
511 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
512 sch->sch_nextc = sc->sc_rxttime;
513 continue;
514 }
515 if (sc->sc_rxmits > V_tcp_ecn_maxretries) {
516 sc->sc_flags &= ~SCF_ECN_MASK;
517 }
518 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
519 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
520 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
521 "giving up and removing syncache entry\n",
522 s, __func__);
523 free(s, M_TCPLOG);
524 }
525 syncache_drop(sc, sch);
526 TCPSTAT_INC(tcps_sc_stale);
527 continue;
528 }
529 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
530 log(LOG_DEBUG, "%s; %s: Response timeout, "
531 "retransmitting (%u) SYN|ACK\n",
532 s, __func__, sc->sc_rxmits);
533 free(s, M_TCPLOG);
534 }
535
536 NET_EPOCH_ENTER(et);
537 if (syncache_respond(sc, TH_SYN|TH_ACK) == 0) {
538 syncache_timeout(sc, sch, 0);
539 TCPSTAT_INC(tcps_sndacks);
540 TCPSTAT_INC(tcps_sndtotal);
541 TCPSTAT_INC(tcps_sc_retransmitted);
542 } else {
543 /*
544 * Most likely we are memory constrained, so free
545 * resources.
546 */
547 syncache_drop(sc, sch);
548 TCPSTAT_INC(tcps_sc_dropped);
549 }
550 NET_EPOCH_EXIT(et);
551 }
552 if (!TAILQ_EMPTY(&(sch)->sch_bucket))
553 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
554 syncache_timer, (void *)(sch));
555 CURVNET_RESTORE();
556 }
557
558 /*
559 * Returns true if the system is only using cookies at the moment.
560 * This could be due to a sysadmin decision to only use cookies, or it
561 * could be due to the system detecting an attack.
562 */
563 static inline bool
syncache_cookiesonly(void)564 syncache_cookiesonly(void)
565 {
566 return ((V_tcp_syncookies && V_tcp_syncache.paused) ||
567 V_tcp_syncookiesonly);
568 }
569
570 /*
571 * Find the hash bucket for the given connection.
572 */
573 static struct syncache_head *
syncache_hashbucket(struct in_conninfo * inc)574 syncache_hashbucket(struct in_conninfo *inc)
575 {
576 uint32_t hash;
577
578 /*
579 * The hash is built on foreign port + local port + foreign address.
580 * We rely on the fact that struct in_conninfo starts with 16 bits
581 * of foreign port, then 16 bits of local port then followed by 128
582 * bits of foreign address. In case of IPv4 address, the first 3
583 * 32-bit words of the address always are zeroes.
584 */
585 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5,
586 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask;
587
588 return (&V_tcp_syncache.hashbase[hash]);
589 }
590
591 /*
592 * Find an entry in the syncache.
593 * Returns always with locked syncache_head plus a matching entry or NULL.
594 */
595 static struct syncache *
syncache_lookup(struct in_conninfo * inc,struct syncache_head ** schp)596 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
597 {
598 struct syncache *sc;
599 struct syncache_head *sch;
600
601 *schp = sch = syncache_hashbucket(inc);
602 SCH_LOCK(sch);
603
604 /* Circle through bucket row to find matching entry. */
605 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash)
606 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie,
607 sizeof(struct in_endpoints)) == 0)
608 break;
609
610 return (sc); /* Always returns with locked sch. */
611 }
612
613 /*
614 * This function is called when we get a RST for a
615 * non-existent connection, so that we can see if the
616 * connection is in the syn cache. If it is, zap it.
617 * If required send a challenge ACK.
618 */
619 void
syncache_chkrst(struct in_conninfo * inc,struct tcphdr * th,uint16_t port)620 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, uint16_t port)
621 {
622 struct syncache *sc;
623 struct syncache_head *sch;
624 char *s = NULL;
625
626 if (syncache_cookiesonly())
627 return;
628 sc = syncache_lookup(inc, &sch); /* returns locked sch */
629 SCH_LOCK_ASSERT(sch);
630
631 /*
632 * No corresponding connection was found in syncache.
633 * If syncookies are enabled and possibly exclusively
634 * used, or we are under memory pressure, a valid RST
635 * may not find a syncache entry. In that case we're
636 * done and no SYN|ACK retransmissions will happen.
637 * Otherwise the RST was misdirected or spoofed.
638 */
639 if (sc == NULL) {
640 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
641 log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
642 "syncache entry (possibly syncookie only), "
643 "segment ignored\n", s, __func__);
644 TCPSTAT_INC(tcps_badrst);
645 goto done;
646 }
647
648 /* The remote UDP encaps port does not match. */
649 if (sc->sc_port != port) {
650 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
651 log(LOG_DEBUG, "%s; %s: Spurious RST with matching "
652 "syncache entry but non-matching UDP encaps port, "
653 "segment ignored\n", s, __func__);
654 TCPSTAT_INC(tcps_badrst);
655 goto done;
656 }
657
658 /*
659 * If the RST bit is set, check the sequence number to see
660 * if this is a valid reset segment.
661 *
662 * RFC 793 page 37:
663 * In all states except SYN-SENT, all reset (RST) segments
664 * are validated by checking their SEQ-fields. A reset is
665 * valid if its sequence number is in the window.
666 *
667 * RFC 793 page 69:
668 * There are four cases for the acceptability test for an incoming
669 * segment:
670 *
671 * Segment Receive Test
672 * Length Window
673 * ------- ------- -------------------------------------------
674 * 0 0 SEG.SEQ = RCV.NXT
675 * 0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND
676 * >0 0 not acceptable
677 * >0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND
678 * or RCV.NXT =< SEG.SEQ+SEG.LEN-1 < RCV.NXT+RCV.WND
679 *
680 * Note that when receiving a SYN segment in the LISTEN state,
681 * IRS is set to SEG.SEQ and RCV.NXT is set to SEG.SEQ+1, as
682 * described in RFC 793, page 66.
683 */
684 if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) &&
685 SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) ||
686 (sc->sc_wnd == 0 && th->th_seq == sc->sc_irs + 1)) {
687 if (V_tcp_insecure_rst ||
688 th->th_seq == sc->sc_irs + 1) {
689 syncache_drop(sc, sch);
690 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
691 log(LOG_DEBUG,
692 "%s; %s: Our SYN|ACK was rejected, "
693 "connection attempt aborted by remote "
694 "endpoint\n",
695 s, __func__);
696 TCPSTAT_INC(tcps_sc_reset);
697 } else {
698 TCPSTAT_INC(tcps_badrst);
699 /* Send challenge ACK. */
700 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
701 log(LOG_DEBUG, "%s; %s: RST with invalid "
702 " SEQ %u != NXT %u (+WND %u), "
703 "sending challenge ACK\n",
704 s, __func__,
705 th->th_seq, sc->sc_irs + 1, sc->sc_wnd);
706 syncache_send_challenge_ack(sc);
707 }
708 } else {
709 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
710 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
711 "NXT %u (+WND %u), segment ignored\n",
712 s, __func__,
713 th->th_seq, sc->sc_irs + 1, sc->sc_wnd);
714 TCPSTAT_INC(tcps_badrst);
715 }
716
717 done:
718 if (s != NULL)
719 free(s, M_TCPLOG);
720 SCH_UNLOCK(sch);
721 }
722
723 void
syncache_unreach(struct in_conninfo * inc,tcp_seq th_seq,uint16_t port)724 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq, uint16_t port)
725 {
726 struct syncache *sc;
727 struct syncache_head *sch;
728
729 if (syncache_cookiesonly())
730 return;
731 sc = syncache_lookup(inc, &sch); /* returns locked sch */
732 SCH_LOCK_ASSERT(sch);
733 if (sc == NULL)
734 goto done;
735
736 /* If the port != sc_port, then it's a bogus ICMP msg */
737 if (port != sc->sc_port)
738 goto done;
739
740 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
741 if (ntohl(th_seq) != sc->sc_iss)
742 goto done;
743
744 /*
745 * If we've retransmitted 3 times and this is our second error,
746 * we remove the entry. Otherwise, we allow it to continue on.
747 * This prevents us from incorrectly nuking an entry during a
748 * spurious network outage.
749 *
750 * See tcp_notify().
751 */
752 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
753 sc->sc_flags |= SCF_UNREACH;
754 goto done;
755 }
756 syncache_drop(sc, sch);
757 TCPSTAT_INC(tcps_sc_unreach);
758 done:
759 SCH_UNLOCK(sch);
760 }
761
762 /*
763 * Build a new TCP socket structure from a syncache entry.
764 *
765 * On success return the newly created socket with its underlying inp locked.
766 */
767 static struct socket *
syncache_socket(struct syncache * sc,struct socket * lso,struct mbuf * m)768 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
769 {
770 struct inpcb *inp = NULL;
771 struct socket *so;
772 struct tcpcb *tp;
773 int error;
774 char *s;
775
776 NET_EPOCH_ASSERT();
777
778 /*
779 * Creation of a socket via solisten_clone() bypasses call to pr_attach.
780 * That's why there is some pasted code from soattach() and from
781 * tcp_usr_attach() here. This should improve once TCP is PR_SOCKBUF.
782 */
783 if ((so = solisten_clone(lso)) == NULL)
784 goto allocfail;
785 mtx_init(&so->so_snd_mtx, "so_snd", NULL, MTX_DEF);
786 mtx_init(&so->so_rcv_mtx, "so_rcv", NULL, MTX_DEF);
787 so->so_snd.sb_mtx = &so->so_snd_mtx;
788 so->so_rcv.sb_mtx = &so->so_rcv_mtx;
789 error = soreserve(so, lso->sol_sbsnd_hiwat, lso->sol_sbrcv_hiwat);
790 if (error) {
791 sodealloc(so);
792 goto allocfail;
793 }
794 #ifdef MAC
795 mac_socketpeer_set_from_mbuf(m, so);
796 #endif
797 error = in_pcballoc(so, &V_tcbinfo);
798 if (error) {
799 sodealloc(so);
800 goto allocfail;
801 }
802 inp = sotoinpcb(so);
803 if ((tp = tcp_newtcpcb(inp, sototcpcb(lso))) == NULL) {
804 in_pcbfree(inp);
805 sodealloc(so);
806 goto allocfail;
807 }
808 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
809 #ifdef INET6
810 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
811 inp->inp_vflag &= ~INP_IPV4;
812 inp->inp_vflag |= INP_IPV6;
813 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
814 } else {
815 inp->inp_vflag &= ~INP_IPV6;
816 inp->inp_vflag |= INP_IPV4;
817 #endif
818 inp->inp_ip_ttl = sc->sc_ip_ttl;
819 inp->inp_ip_tos = sc->sc_ip_tos;
820 inp->inp_laddr = sc->sc_inc.inc_laddr;
821 #ifdef INET6
822 }
823 #endif
824 inp->inp_lport = sc->sc_inc.inc_lport;
825 #ifdef INET6
826 if (inp->inp_vflag & INP_IPV6PROTO) {
827 struct inpcb *oinp = sotoinpcb(lso);
828
829 /*
830 * Inherit socket options from the listening socket.
831 * Note that in6p_inputopts are not (and should not be)
832 * copied, since it stores previously received options and is
833 * used to detect if each new option is different than the
834 * previous one and hence should be passed to a user.
835 * If we copied in6p_inputopts, a user would not be able to
836 * receive options just after calling the accept system call.
837 */
838 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
839 if (oinp->in6p_outputopts)
840 inp->in6p_outputopts =
841 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
842 inp->in6p_hops = oinp->in6p_hops;
843 }
844
845 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
846 struct sockaddr_in6 sin6;
847
848 sin6.sin6_family = AF_INET6;
849 sin6.sin6_len = sizeof(sin6);
850 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
851 sin6.sin6_port = sc->sc_inc.inc_fport;
852 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
853 error = in6_pcbconnect(inp, &sin6, thread0.td_ucred, false);
854 if (error != 0)
855 goto abort;
856 /* Override flowlabel from in6_pcbconnect. */
857 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
858 inp->inp_flow |= sc->sc_flowlabel;
859 }
860 #endif /* INET6 */
861 #if defined(INET) && defined(INET6)
862 else
863 #endif
864 #ifdef INET
865 {
866 struct sockaddr_in sin;
867
868 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
869
870 if (inp->inp_options == NULL) {
871 inp->inp_options = sc->sc_ipopts;
872 sc->sc_ipopts = NULL;
873 }
874
875 sin.sin_family = AF_INET;
876 sin.sin_len = sizeof(sin);
877 sin.sin_addr = sc->sc_inc.inc_faddr;
878 sin.sin_port = sc->sc_inc.inc_fport;
879 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
880 error = in_pcbconnect(inp, &sin, thread0.td_ucred);
881 if (error != 0)
882 goto abort;
883 }
884 #endif /* INET */
885 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
886 /* Copy old policy into new socket's. */
887 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0)
888 printf("syncache_socket: could not copy policy\n");
889 #endif
890 if (sc->sc_flowtype != M_HASHTYPE_NONE) {
891 inp->inp_flowid = sc->sc_flowid;
892 inp->inp_flowtype = sc->sc_flowtype;
893 } else {
894 /* assign flowid by software RSS hash */
895 #ifdef INET6
896 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
897 rss_proto_software_hash_v6(&inp->in6p_faddr,
898 &inp->in6p_laddr,
899 inp->inp_fport,
900 inp->inp_lport,
901 IPPROTO_TCP,
902 &inp->inp_flowid,
903 &inp->inp_flowtype);
904 } else
905 #endif /* INET6 */
906 {
907 #ifdef INET
908 rss_proto_software_hash_v4(inp->inp_faddr,
909 inp->inp_laddr,
910 inp->inp_fport,
911 inp->inp_lport,
912 IPPROTO_TCP,
913 &inp->inp_flowid,
914 &inp->inp_flowtype);
915 #endif /* INET */
916 }
917 }
918 #ifdef NUMA
919 inp->inp_numa_domain = sc->sc_numa_domain;
920 #endif
921
922 tp->t_state = TCPS_SYN_RECEIVED;
923 tp->iss = sc->sc_iss;
924 tp->irs = sc->sc_irs;
925 tp->t_port = sc->sc_port;
926 tcp_rcvseqinit(tp);
927 tcp_sendseqinit(tp);
928 tp->snd_wl1 = sc->sc_irs;
929 tp->snd_max = tp->iss + 1;
930 tp->snd_nxt = tp->iss + 1;
931 tp->rcv_up = sc->sc_irs + 1;
932 tp->rcv_wnd = sc->sc_wnd;
933 tp->rcv_adv += tp->rcv_wnd;
934 tp->last_ack_sent = tp->rcv_nxt;
935
936 tp->t_flags = sototcpcb(lso)->t_flags &
937 (TF_LRD|TF_NOPUSH|TF_NODELAY);
938 if (sc->sc_flags & SCF_NOOPT)
939 tp->t_flags |= TF_NOOPT;
940 else {
941 if (sc->sc_flags & SCF_WINSCALE) {
942 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
943 tp->snd_scale = sc->sc_requested_s_scale;
944 tp->request_r_scale = sc->sc_requested_r_scale;
945 }
946 if (sc->sc_flags & SCF_TIMESTAMP) {
947 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
948 tp->ts_recent = sc->sc_tsreflect;
949 tp->ts_recent_age = tcp_ts_getticks();
950 tp->ts_offset = sc->sc_tsoff;
951 }
952 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
953 if (sc->sc_flags & SCF_SIGNATURE)
954 tp->t_flags |= TF_SIGNATURE;
955 #endif
956 if (sc->sc_flags & SCF_SACK)
957 tp->t_flags |= TF_SACK_PERMIT;
958 }
959
960 tcp_ecn_syncache_socket(tp, sc);
961
962 /*
963 * Set up MSS and get cached values from tcp_hostcache.
964 * This might overwrite some of the defaults we just set.
965 */
966 tcp_mss(tp, sc->sc_peer_mss);
967
968 /*
969 * If the SYN,ACK was retransmitted, indicate that CWND to be
970 * limited to one segment in cc_conn_init().
971 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
972 */
973 if (sc->sc_rxmits > 1)
974 tp->snd_cwnd = 1;
975
976 /* Copy over the challenge ACK state. */
977 tp->t_challenge_ack_end = sc->sc_challenge_ack_end;
978 tp->t_challenge_ack_cnt = sc->sc_challenge_ack_cnt;
979
980 #ifdef TCP_OFFLOAD
981 /*
982 * Allow a TOE driver to install its hooks. Note that we hold the
983 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a
984 * new connection before the TOE driver has done its thing.
985 */
986 if (ADDED_BY_TOE(sc)) {
987 struct toedev *tod = sc->sc_tod;
988
989 tod->tod_offload_socket(tod, sc->sc_todctx, so);
990 }
991 #endif
992 #ifdef TCP_BLACKBOX
993 /*
994 * Inherit the log state from the listening socket, if
995 * - the log state of the listening socket is not off and
996 * - the listening socket was not auto selected from all sessions and
997 * - a log id is not set on the listening socket.
998 * This avoids inheriting a log state which was automatically set.
999 */
1000 if ((tcp_get_bblog_state(sototcpcb(lso)) != TCP_LOG_STATE_OFF) &&
1001 ((sototcpcb(lso)->t_flags2 & TF2_LOG_AUTO) == 0) &&
1002 (sototcpcb(lso)->t_lib == NULL)) {
1003 tcp_log_state_change(tp, tcp_get_bblog_state(sototcpcb(lso)));
1004 }
1005 #endif
1006 /*
1007 * Copy and activate timers.
1008 */
1009 tp->t_maxunacktime = sototcpcb(lso)->t_maxunacktime;
1010 tp->t_keepinit = sototcpcb(lso)->t_keepinit;
1011 tp->t_keepidle = sototcpcb(lso)->t_keepidle;
1012 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl;
1013 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt;
1014 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp));
1015
1016 TCPSTAT_INC(tcps_accepts);
1017 TCP_PROBE6(state__change, NULL, tp, NULL, tp, NULL, TCPS_LISTEN);
1018
1019 if (!solisten_enqueue(so, SS_ISCONNECTED))
1020 tp->t_flags |= TF_SONOTCONN;
1021 /* Can we inherit anything from the listener? */
1022 if (tp->t_fb->tfb_inherit != NULL) {
1023 (*tp->t_fb->tfb_inherit)(tp, sotoinpcb(lso));
1024 }
1025 return (so);
1026
1027 allocfail:
1028 /*
1029 * Drop the connection; we will either send a RST or have the peer
1030 * retransmit its SYN again after its RTO and try again.
1031 */
1032 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
1033 log(LOG_DEBUG, "%s; %s: Socket create failed "
1034 "due to limits or memory shortage\n",
1035 s, __func__);
1036 free(s, M_TCPLOG);
1037 }
1038 TCPSTAT_INC(tcps_listendrop);
1039 return (NULL);
1040
1041 abort:
1042 tcp_discardcb(tp);
1043 in_pcbfree(inp);
1044 sodealloc(so);
1045 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
1046 log(LOG_DEBUG, "%s; %s: in%s_pcbconnect failed with error %i\n",
1047 s, __func__, (sc->sc_inc.inc_flags & INC_ISIPV6) ? "6" : "",
1048 error);
1049 free(s, M_TCPLOG);
1050 }
1051 TCPSTAT_INC(tcps_listendrop);
1052 return (NULL);
1053 }
1054
1055 /*
1056 * This function gets called when we receive an ACK for a
1057 * socket in the LISTEN state. We look up the connection
1058 * in the syncache, and if its there, we pull it out of
1059 * the cache and turn it into a full-blown connection in
1060 * the SYN-RECEIVED state.
1061 *
1062 * On syncache_socket() success the newly created socket
1063 * has its underlying inp locked.
1064 *
1065 * *lsop is updated, if and only if 1 is returned.
1066 */
1067 int
syncache_expand(struct in_conninfo * inc,struct tcpopt * to,struct tcphdr * th,struct socket ** lsop,struct mbuf * m,uint16_t port)1068 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1069 struct socket **lsop, struct mbuf *m, uint16_t port)
1070 {
1071 struct syncache *sc;
1072 struct syncache_head *sch;
1073 struct syncache scs;
1074 char *s;
1075 bool locked;
1076
1077 NET_EPOCH_ASSERT();
1078 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
1079 ("%s: can handle only ACK", __func__));
1080
1081 if (syncache_cookiesonly()) {
1082 sc = NULL;
1083 sch = syncache_hashbucket(inc);
1084 locked = false;
1085 } else {
1086 sc = syncache_lookup(inc, &sch); /* returns locked sch */
1087 locked = true;
1088 SCH_LOCK_ASSERT(sch);
1089 }
1090
1091 #ifdef INVARIANTS
1092 /*
1093 * Test code for syncookies comparing the syncache stored
1094 * values with the reconstructed values from the cookie.
1095 */
1096 if (sc != NULL)
1097 syncookie_cmp(inc, sch, sc, th, to, *lsop, port);
1098 #endif
1099
1100 if (sc == NULL) {
1101 if (locked) {
1102 /*
1103 * The syncache is currently in use (neither disabled,
1104 * nor paused), but no entry was found.
1105 */
1106 if (!V_tcp_syncookies) {
1107 /*
1108 * Since no syncookies are used in case of
1109 * a bucket overflow, don't even check for
1110 * a valid syncookie.
1111 */
1112 SCH_UNLOCK(sch);
1113 TCPSTAT_INC(tcps_sc_spurcookie);
1114 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1115 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
1116 "segment rejected "
1117 "(syncookies disabled)\n",
1118 s, __func__);
1119 free(s, M_TCPLOG);
1120 }
1121 return (0);
1122 }
1123 if (sch->sch_last_overflow <
1124 time_uptime - SYNCOOKIE_LIFETIME) {
1125 /*
1126 * Since the bucket did not overflow recently,
1127 * don't even check for a valid syncookie.
1128 */
1129 SCH_UNLOCK(sch);
1130 TCPSTAT_INC(tcps_sc_spurcookie);
1131 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1132 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
1133 "segment rejected "
1134 "(no syncache entry)\n",
1135 s, __func__);
1136 free(s, M_TCPLOG);
1137 }
1138 return (0);
1139 }
1140 SCH_UNLOCK(sch);
1141 }
1142 bzero(&scs, sizeof(scs));
1143 /*
1144 * Now check, if the syncookie is valid. If it is, create an on
1145 * stack syncache entry.
1146 */
1147 if (syncookie_expand(inc, sch, &scs, th, to, *lsop, port)) {
1148 sc = &scs;
1149 TCPSTAT_INC(tcps_sc_recvcookie);
1150 } else {
1151 TCPSTAT_INC(tcps_sc_failcookie);
1152 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1153 log(LOG_DEBUG, "%s; %s: Segment failed "
1154 "SYNCOOKIE authentication, segment rejected "
1155 "(probably spoofed)\n", s, __func__);
1156 free(s, M_TCPLOG);
1157 }
1158 return (0);
1159 }
1160 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1161 /* If received ACK has MD5 signature, check it. */
1162 if ((to->to_flags & TOF_SIGNATURE) != 0 &&
1163 (!TCPMD5_ENABLED() ||
1164 TCPMD5_INPUT(m, th, to->to_signature) != 0)) {
1165 /* Drop the ACK. */
1166 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1167 log(LOG_DEBUG, "%s; %s: Segment rejected, "
1168 "MD5 signature doesn't match.\n",
1169 s, __func__);
1170 free(s, M_TCPLOG);
1171 }
1172 return (-1); /* Do not send RST */
1173 }
1174 #endif /* TCP_SIGNATURE */
1175 if (m != NULL && M_HASHTYPE_ISHASH_TCP(m)) {
1176 sc->sc_flowid = m->m_pkthdr.flowid;
1177 sc->sc_flowtype = M_HASHTYPE_GET(m);
1178 }
1179 #ifdef NUMA
1180 sc->sc_numa_domain = m ? m->m_pkthdr.numa_domain : M_NODOM;
1181 #endif
1182 TCPSTATES_INC(TCPS_SYN_RECEIVED);
1183 } else {
1184 if (sc->sc_port != port) {
1185 SCH_UNLOCK(sch);
1186 return (0);
1187 }
1188 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1189 /*
1190 * If listening socket requested TCP digests, check that
1191 * received ACK has signature and it is correct.
1192 * If not, drop the ACK and leave sc entry in the cache,
1193 * because SYN was received with correct signature.
1194 */
1195 if (sc->sc_flags & SCF_SIGNATURE) {
1196 if ((to->to_flags & TOF_SIGNATURE) == 0) {
1197 /* No signature */
1198 TCPSTAT_INC(tcps_sig_err_nosigopt);
1199 SCH_UNLOCK(sch);
1200 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1201 log(LOG_DEBUG, "%s; %s: Segment "
1202 "rejected, MD5 signature wasn't "
1203 "provided.\n", s, __func__);
1204 free(s, M_TCPLOG);
1205 }
1206 return (-1); /* Do not send RST */
1207 }
1208 if (!TCPMD5_ENABLED() ||
1209 TCPMD5_INPUT(m, th, to->to_signature) != 0) {
1210 /* Doesn't match or no SA */
1211 SCH_UNLOCK(sch);
1212 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1213 log(LOG_DEBUG, "%s; %s: Segment "
1214 "rejected, MD5 signature doesn't "
1215 "match.\n", s, __func__);
1216 free(s, M_TCPLOG);
1217 }
1218 return (-1); /* Do not send RST */
1219 }
1220 }
1221 #endif /* TCP_SIGNATURE */
1222
1223 /*
1224 * RFC 7323 PAWS: If we have a timestamp on this segment and
1225 * it's less than ts_recent, drop it.
1226 * XXXMT: RFC 7323 also requires to send an ACK.
1227 * In tcp_input.c this is only done for TCP segments
1228 * with user data, so be consistent here and just drop
1229 * the segment.
1230 */
1231 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS &&
1232 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) {
1233 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1234 log(LOG_DEBUG,
1235 "%s; %s: SEG.TSval %u < TS.Recent %u, "
1236 "segment dropped\n", s, __func__,
1237 to->to_tsval, sc->sc_tsreflect);
1238 }
1239 SCH_UNLOCK(sch);
1240 free(s, M_TCPLOG);
1241 return (-1); /* Do not send RST */
1242 }
1243
1244 /*
1245 * If timestamps were not negotiated during SYN/ACK and a
1246 * segment with a timestamp is received, ignore the
1247 * timestamp and process the packet normally.
1248 * See section 3.2 of RFC 7323.
1249 */
1250 if (!(sc->sc_flags & SCF_TIMESTAMP) &&
1251 (to->to_flags & TOF_TS)) {
1252 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1253 log(LOG_DEBUG, "%s; %s: Timestamp not "
1254 "expected, segment processed normally\n",
1255 s, __func__);
1256 free(s, M_TCPLOG);
1257 }
1258 }
1259
1260 /*
1261 * If timestamps were negotiated during SYN/ACK and a
1262 * segment without a timestamp is received, silently drop
1263 * the segment, unless the missing timestamps are tolerated.
1264 * See section 3.2 of RFC 7323.
1265 */
1266 if ((sc->sc_flags & SCF_TIMESTAMP) &&
1267 !(to->to_flags & TOF_TS)) {
1268 if (V_tcp_tolerate_missing_ts) {
1269 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1270 log(LOG_DEBUG,
1271 "%s; %s: Timestamp missing, "
1272 "segment processed normally\n",
1273 s, __func__);
1274 free(s, M_TCPLOG);
1275 }
1276 } else {
1277 SCH_UNLOCK(sch);
1278 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1279 log(LOG_DEBUG,
1280 "%s; %s: Timestamp missing, "
1281 "segment silently dropped\n",
1282 s, __func__);
1283 free(s, M_TCPLOG);
1284 }
1285 return (-1); /* Do not send RST */
1286 }
1287 }
1288
1289 /*
1290 * SEG.SEQ validation:
1291 * The SEG.SEQ must be in the window starting at our
1292 * initial receive sequence number + 1.
1293 */
1294 if (SEQ_LEQ(th->th_seq, sc->sc_irs) ||
1295 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
1296 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1297 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, "
1298 "sending challenge ACK\n",
1299 s, __func__, th->th_seq, sc->sc_irs + 1);
1300 syncache_send_challenge_ack(sc);
1301 SCH_UNLOCK(sch);
1302 free(s, M_TCPLOG);
1303 return (-1); /* Do not send RST */
1304 }
1305
1306 /*
1307 * SEG.ACK validation:
1308 * SEG.ACK must match our initial send sequence number + 1.
1309 */
1310 if (th->th_ack != sc->sc_iss + 1) {
1311 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1312 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, "
1313 "segment rejected\n",
1314 s, __func__, th->th_ack, sc->sc_iss + 1);
1315 SCH_UNLOCK(sch);
1316 free(s, M_TCPLOG);
1317 return (0); /* Do send RST, do not free sc. */
1318 }
1319
1320 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
1321 sch->sch_length--;
1322 #ifdef TCP_OFFLOAD
1323 if (ADDED_BY_TOE(sc)) {
1324 struct toedev *tod = sc->sc_tod;
1325
1326 tod->tod_syncache_removed(tod, sc->sc_todctx);
1327 }
1328 #endif
1329 SCH_UNLOCK(sch);
1330 }
1331
1332 *lsop = syncache_socket(sc, *lsop, m);
1333
1334 if (__predict_false(*lsop == NULL)) {
1335 TCPSTAT_INC(tcps_sc_aborted);
1336 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
1337 } else if (sc != &scs)
1338 TCPSTAT_INC(tcps_sc_completed);
1339
1340 if (sc != &scs)
1341 syncache_free(sc);
1342 return (1);
1343 }
1344
1345 static struct socket *
syncache_tfo_expand(struct syncache * sc,struct socket * lso,struct mbuf * m,uint64_t response_cookie)1346 syncache_tfo_expand(struct syncache *sc, struct socket *lso, struct mbuf *m,
1347 uint64_t response_cookie)
1348 {
1349 struct inpcb *inp;
1350 struct tcpcb *tp;
1351 unsigned int *pending_counter;
1352 struct socket *so;
1353
1354 NET_EPOCH_ASSERT();
1355
1356 pending_counter = intotcpcb(sotoinpcb(lso))->t_tfo_pending;
1357 so = syncache_socket(sc, lso, m);
1358 if (so == NULL) {
1359 TCPSTAT_INC(tcps_sc_aborted);
1360 atomic_subtract_int(pending_counter, 1);
1361 } else {
1362 soisconnected(so);
1363 inp = sotoinpcb(so);
1364 tp = intotcpcb(inp);
1365 tp->t_flags |= TF_FASTOPEN;
1366 tp->t_tfo_cookie.server = response_cookie;
1367 tp->snd_max = tp->iss;
1368 tp->snd_nxt = tp->iss;
1369 tp->t_tfo_pending = pending_counter;
1370 TCPSTATES_INC(TCPS_SYN_RECEIVED);
1371 TCPSTAT_INC(tcps_sc_completed);
1372 }
1373
1374 return (so);
1375 }
1376
1377 /*
1378 * Given a LISTEN socket and an inbound SYN request, add
1379 * this to the syn cache, and send back a segment:
1380 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
1381 * to the source.
1382 *
1383 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
1384 * Doing so would require that we hold onto the data and deliver it
1385 * to the application. However, if we are the target of a SYN-flood
1386 * DoS attack, an attacker could send data which would eventually
1387 * consume all available buffer space if it were ACKed. By not ACKing
1388 * the data, we avoid this DoS scenario.
1389 *
1390 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO)
1391 * cookie is processed and a new socket is created. In this case, any data
1392 * accompanying the SYN will be queued to the socket by tcp_input() and will
1393 * be ACKed either when the application sends response data or the delayed
1394 * ACK timer expires, whichever comes first.
1395 */
1396 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)1397 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1398 struct inpcb *inp, struct socket *so, struct mbuf *m, void *tod,
1399 void *todctx, uint8_t iptos, uint16_t port)
1400 {
1401 struct tcpcb *tp;
1402 struct socket *rv = NULL;
1403 struct syncache *sc = NULL;
1404 struct ucred *cred;
1405 struct syncache_head *sch;
1406 struct mbuf *ipopts = NULL;
1407 u_int ltflags;
1408 int win, ip_ttl, ip_tos;
1409 char *s;
1410 #ifdef INET6
1411 int autoflowlabel = 0;
1412 #endif
1413 #ifdef MAC
1414 struct label *maclabel = NULL;
1415 #endif
1416 struct syncache scs;
1417 uint64_t tfo_response_cookie;
1418 unsigned int *tfo_pending = NULL;
1419 int tfo_cookie_valid = 0;
1420 int tfo_response_cookie_valid = 0;
1421 bool locked;
1422
1423 INP_RLOCK_ASSERT(inp); /* listen socket */
1424 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
1425 ("%s: unexpected tcp flags", __func__));
1426
1427 /*
1428 * Combine all so/tp operations very early to drop the INP lock as
1429 * soon as possible.
1430 */
1431 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so));
1432 tp = sototcpcb(so);
1433 bzero(&scs, sizeof(scs));
1434 cred = V_tcp_syncache.see_other ? NULL : crhold(so->so_cred);
1435
1436 #ifdef INET6
1437 if (inc->inc_flags & INC_ISIPV6) {
1438 if (inp->inp_flags & IN6P_AUTOFLOWLABEL) {
1439 autoflowlabel = 1;
1440 }
1441 ip_ttl = in6_selecthlim(inp, NULL);
1442 if ((inp->in6p_outputopts == NULL) ||
1443 (inp->in6p_outputopts->ip6po_tclass == -1)) {
1444 ip_tos = 0;
1445 } else {
1446 ip_tos = inp->in6p_outputopts->ip6po_tclass;
1447 }
1448 }
1449 #endif
1450 #if defined(INET6) && defined(INET)
1451 else
1452 #endif
1453 #ifdef INET
1454 {
1455 ip_ttl = inp->inp_ip_ttl;
1456 ip_tos = inp->inp_ip_tos;
1457 }
1458 #endif
1459 win = so->sol_sbrcv_hiwat;
1460 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE));
1461
1462 if (V_tcp_fastopen_server_enable && (tp->t_flags & TF_FASTOPEN) &&
1463 (tp->t_tfo_pending != NULL) &&
1464 (to->to_flags & TOF_FASTOPEN)) {
1465 /*
1466 * Limit the number of pending TFO connections to
1467 * approximately half of the queue limit. This prevents TFO
1468 * SYN floods from starving the service by filling the
1469 * listen queue with bogus TFO connections.
1470 */
1471 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <=
1472 (so->sol_qlimit / 2)) {
1473 int result;
1474
1475 result = tcp_fastopen_check_cookie(inc,
1476 to->to_tfo_cookie, to->to_tfo_len,
1477 &tfo_response_cookie);
1478 tfo_cookie_valid = (result > 0);
1479 tfo_response_cookie_valid = (result >= 0);
1480 }
1481
1482 /*
1483 * Remember the TFO pending counter as it will have to be
1484 * decremented below if we don't make it to syncache_tfo_expand().
1485 */
1486 tfo_pending = tp->t_tfo_pending;
1487 }
1488
1489 #ifdef MAC
1490 if (mac_syncache_init(&maclabel) != 0) {
1491 INP_RUNLOCK(inp);
1492 goto done;
1493 } else
1494 mac_syncache_create(maclabel, inp);
1495 #endif
1496 if (!tfo_cookie_valid)
1497 INP_RUNLOCK(inp);
1498
1499 /*
1500 * Remember the IP options, if any.
1501 */
1502 #ifdef INET6
1503 if (!(inc->inc_flags & INC_ISIPV6))
1504 #endif
1505 #ifdef INET
1506 ipopts = (m) ? ip_srcroute(m) : NULL;
1507 #else
1508 ipopts = NULL;
1509 #endif
1510
1511 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1512 /*
1513 * When the socket is TCP-MD5 enabled check that,
1514 * - a signed packet is valid
1515 * - a non-signed packet does not have a security association
1516 *
1517 * If a signed packet fails validation or a non-signed packet has a
1518 * security association, the packet will be dropped.
1519 */
1520 if (ltflags & TF_SIGNATURE) {
1521 if (to->to_flags & TOF_SIGNATURE) {
1522 if (!TCPMD5_ENABLED() ||
1523 TCPMD5_INPUT(m, th, to->to_signature) != 0)
1524 goto done;
1525 } else {
1526 if (TCPMD5_ENABLED() &&
1527 TCPMD5_INPUT(m, NULL, NULL) != ENOENT)
1528 goto done;
1529 }
1530 } else if (to->to_flags & TOF_SIGNATURE) {
1531 TCPSTAT_INC(tcps_sig_err_sigopt);
1532 goto done;
1533 }
1534 #endif /* TCP_SIGNATURE */
1535 /*
1536 * See if we already have an entry for this connection.
1537 * If we do, resend the SYN,ACK, and reset the retransmit timer.
1538 *
1539 * XXX: should the syncache be re-initialized with the contents
1540 * of the new SYN here (which may have different options?)
1541 *
1542 * XXX: We do not check the sequence number to see if this is a
1543 * real retransmit or a new connection attempt. The question is
1544 * how to handle such a case; either ignore it as spoofed, or
1545 * drop the current entry and create a new one?
1546 */
1547 if (syncache_cookiesonly()) {
1548 sc = NULL;
1549 sch = syncache_hashbucket(inc);
1550 locked = false;
1551 } else {
1552 sc = syncache_lookup(inc, &sch); /* returns locked sch */
1553 locked = true;
1554 SCH_LOCK_ASSERT(sch);
1555 }
1556 if (sc != NULL) {
1557 if (tfo_cookie_valid)
1558 INP_RUNLOCK(inp);
1559 TCPSTAT_INC(tcps_sc_dupsyn);
1560 if (ipopts != NULL) {
1561 /*
1562 * If we were remembering a previous source route,
1563 * forget it and use the new one we've been given.
1564 */
1565 if (sc->sc_ipopts != NULL)
1566 (void)m_free(sc->sc_ipopts);
1567 sc->sc_ipopts = ipopts;
1568 ipopts = NULL;
1569 }
1570 /*
1571 * Update timestamp if present.
1572 */
1573 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
1574 sc->sc_tsreflect = to->to_tsval;
1575 else
1576 sc->sc_flags &= ~SCF_TIMESTAMP;
1577 /*
1578 * Adjust ECN response if needed, e.g. different
1579 * IP ECN field, or a fallback by the remote host.
1580 */
1581 if (sc->sc_flags & SCF_ECN_MASK) {
1582 sc->sc_flags &= ~SCF_ECN_MASK;
1583 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos);
1584 }
1585 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1586 /* Retransmit SYN|ACK and reset retransmit count. */
1587 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
1588 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
1589 "resetting timer and retransmitting SYN|ACK\n",
1590 s, __func__);
1591 free(s, M_TCPLOG);
1592 }
1593 if (syncache_respond(sc, TH_SYN|TH_ACK) == 0) {
1594 sc->sc_rxmits = 0;
1595 syncache_timeout(sc, sch, 1);
1596 TCPSTAT_INC(tcps_sndacks);
1597 TCPSTAT_INC(tcps_sndtotal);
1598 } else {
1599 /*
1600 * Most likely we are memory constrained, so free
1601 * resources.
1602 */
1603 syncache_drop(sc, sch);
1604 TCPSTAT_INC(tcps_sc_dropped);
1605 }
1606 SCH_UNLOCK(sch);
1607 goto donenoprobe;
1608 }
1609
1610 KASSERT(sc == NULL, ("sc(%p) != NULL", sc));
1611 /*
1612 * Skip allocating a syncache entry if we are just going to discard
1613 * it later.
1614 */
1615 if (!locked || tfo_cookie_valid)
1616 sc = &scs;
1617 else {
1618 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1619 if (sc == NULL) {
1620 /*
1621 * The zone allocator couldn't provide more entries.
1622 * Treat this as if the cache was full; drop the oldest
1623 * entry and insert the new one.
1624 */
1625 TCPSTAT_INC(tcps_sc_zonefail);
1626 sc = TAILQ_LAST(&sch->sch_bucket, sch_head);
1627 if (sc != NULL) {
1628 sch->sch_last_overflow = time_uptime;
1629 syncache_drop(sc, sch);
1630 syncache_pause(inc);
1631 }
1632 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1633 if (sc == NULL) {
1634 if (V_tcp_syncookies)
1635 sc = &scs;
1636 else {
1637 KASSERT(locked,
1638 ("%s: bucket unexpectedly unlocked",
1639 __func__));
1640 SCH_UNLOCK(sch);
1641 goto done;
1642 }
1643 }
1644 }
1645 }
1646
1647 KASSERT(sc != NULL, ("sc == NULL"));
1648 if (!tfo_cookie_valid && tfo_response_cookie_valid)
1649 sc->sc_tfo_cookie = &tfo_response_cookie;
1650
1651 /*
1652 * Fill in the syncache values.
1653 */
1654 #ifdef MAC
1655 sc->sc_label = maclabel;
1656 maclabel = NULL;
1657 #endif
1658 sc->sc_cred = cred;
1659 cred = NULL;
1660 sc->sc_ipopts = ipopts;
1661 ipopts = NULL;
1662 sc->sc_port = port;
1663 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1664 sc->sc_ip_tos = ip_tos;
1665 sc->sc_ip_ttl = ip_ttl;
1666 #ifdef TCP_OFFLOAD
1667 sc->sc_tod = tod;
1668 sc->sc_todctx = todctx;
1669 #endif
1670 sc->sc_irs = th->th_seq;
1671 sc->sc_flags = 0;
1672 sc->sc_flowlabel = 0;
1673
1674 /*
1675 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
1676 * win was derived from socket earlier in the function.
1677 */
1678 win = imax(win, 0);
1679 win = imin(win, TCP_MAXWIN);
1680 sc->sc_wnd = win;
1681
1682 if (V_tcp_do_rfc1323 &&
1683 !(ltflags & TF_NOOPT)) {
1684 /*
1685 * A timestamp received in a SYN makes
1686 * it ok to send timestamp requests and replies.
1687 */
1688 if ((to->to_flags & TOF_TS) && (V_tcp_do_rfc1323 != 2)) {
1689 sc->sc_tsreflect = to->to_tsval;
1690 sc->sc_flags |= SCF_TIMESTAMP;
1691 sc->sc_tsoff = tcp_new_ts_offset(inc);
1692 }
1693 if ((to->to_flags & TOF_SCALE) && (V_tcp_do_rfc1323 != 3)) {
1694 u_int wscale = 0;
1695
1696 /*
1697 * Pick the smallest possible scaling factor that
1698 * will still allow us to scale up to sb_max, aka
1699 * kern.ipc.maxsockbuf.
1700 *
1701 * We do this because there are broken firewalls that
1702 * will corrupt the window scale option, leading to
1703 * the other endpoint believing that our advertised
1704 * window is unscaled. At scale factors larger than
1705 * 5 the unscaled window will drop below 1500 bytes,
1706 * leading to serious problems when traversing these
1707 * broken firewalls.
1708 *
1709 * With the default maxsockbuf of 256K, a scale factor
1710 * of 3 will be chosen by this algorithm. Those who
1711 * choose a larger maxsockbuf should watch out
1712 * for the compatibility problems mentioned above.
1713 *
1714 * RFC1323: The Window field in a SYN (i.e., a <SYN>
1715 * or <SYN,ACK>) segment itself is never scaled.
1716 */
1717 while (wscale < TCP_MAX_WINSHIFT &&
1718 (TCP_MAXWIN << wscale) < sb_max)
1719 wscale++;
1720 sc->sc_requested_r_scale = wscale;
1721 sc->sc_requested_s_scale = to->to_wscale;
1722 sc->sc_flags |= SCF_WINSCALE;
1723 }
1724 }
1725 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1726 /*
1727 * If incoming packet has an MD5 signature, flag this in the
1728 * syncache so that syncache_respond() will do the right thing
1729 * with the SYN+ACK.
1730 */
1731 if (to->to_flags & TOF_SIGNATURE)
1732 sc->sc_flags |= SCF_SIGNATURE;
1733 #endif /* TCP_SIGNATURE */
1734 if (to->to_flags & TOF_SACKPERM)
1735 sc->sc_flags |= SCF_SACK;
1736 if (to->to_flags & TOF_MSS)
1737 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */
1738 if (ltflags & TF_NOOPT)
1739 sc->sc_flags |= SCF_NOOPT;
1740 /* ECN Handshake */
1741 if (V_tcp_do_ecn && (tp->t_flags2 & TF2_CANNOT_DO_ECN) == 0)
1742 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos);
1743
1744 if (V_tcp_syncookies || V_tcp_syncookiesonly)
1745 sc->sc_iss = syncookie_generate(sch, sc);
1746 else
1747 sc->sc_iss = arc4random();
1748 #ifdef INET6
1749 if (autoflowlabel) {
1750 if (V_tcp_syncookies || V_tcp_syncookiesonly)
1751 sc->sc_flowlabel = sc->sc_iss;
1752 else
1753 sc->sc_flowlabel = ip6_randomflowlabel();
1754 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK;
1755 }
1756 #endif
1757 if (m != NULL && M_HASHTYPE_ISHASH_TCP(m)) {
1758 sc->sc_flowid = m->m_pkthdr.flowid;
1759 sc->sc_flowtype = M_HASHTYPE_GET(m);
1760 }
1761 #ifdef NUMA
1762 sc->sc_numa_domain = m ? m->m_pkthdr.numa_domain : M_NODOM;
1763 #endif
1764 if (locked)
1765 SCH_UNLOCK(sch);
1766
1767 if (tfo_cookie_valid) {
1768 rv = syncache_tfo_expand(sc, so, m, tfo_response_cookie);
1769 /* INP_RUNLOCK(inp) will be performed by the caller */
1770 goto tfo_expanded;
1771 }
1772
1773 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1774 /*
1775 * Do a standard 3-way handshake.
1776 */
1777 if (syncache_respond(sc, TH_SYN|TH_ACK) == 0) {
1778 if (sc != &scs)
1779 syncache_insert(sc, sch); /* locks and unlocks sch */
1780 TCPSTAT_INC(tcps_sndacks);
1781 TCPSTAT_INC(tcps_sndtotal);
1782 } else {
1783 /*
1784 * Most likely we are memory constrained, so free resources.
1785 */
1786 if (sc != &scs)
1787 syncache_free(sc);
1788 TCPSTAT_INC(tcps_sc_dropped);
1789 }
1790 goto donenoprobe;
1791
1792 done:
1793 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1794 donenoprobe:
1795 if (m)
1796 m_freem(m);
1797 /*
1798 * If tfo_pending is not NULL here, then a TFO SYN that did not
1799 * result in a new socket was processed and the associated pending
1800 * counter has not yet been decremented. All such TFO processing paths
1801 * transit this point.
1802 */
1803 if (tfo_pending != NULL)
1804 tcp_fastopen_decrement_counter(tfo_pending);
1805
1806 tfo_expanded:
1807 if (cred != NULL)
1808 crfree(cred);
1809 #ifdef MAC
1810 if (maclabel != NULL)
1811 mac_syncache_destroy(&maclabel);
1812 #endif
1813 if (ipopts != NULL)
1814 (void)m_free(ipopts);
1815 syncache_release(&scs);
1816 return (rv);
1817 }
1818
1819 /*
1820 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment
1821 * or upon 3WHS ACK timeout.
1822 */
1823 static int
syncache_respond(struct syncache * sc,int flags)1824 syncache_respond(struct syncache *sc, int flags)
1825 {
1826 struct ip *ip = NULL;
1827 struct mbuf *m;
1828 struct tcphdr *th = NULL;
1829 struct udphdr *udp = NULL;
1830 int optlen, error = 0; /* Make compiler happy */
1831 u_int16_t hlen, tlen, mssopt, ulen;
1832 struct tcpopt to;
1833 #ifdef INET6
1834 struct ip6_hdr *ip6 = NULL;
1835 #endif
1836
1837 NET_EPOCH_ASSERT();
1838
1839 hlen =
1840 #ifdef INET6
1841 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
1842 #endif
1843 sizeof(struct ip);
1844 tlen = hlen + sizeof(struct tcphdr);
1845 if (sc->sc_port) {
1846 tlen += sizeof(struct udphdr);
1847 }
1848 /* Determine MSS we advertize to other end of connection. */
1849 mssopt = tcp_mssopt(&sc->sc_inc);
1850 if (sc->sc_port)
1851 mssopt -= V_tcp_udp_tunneling_overhead;
1852 mssopt = max(mssopt, V_tcp_minmss);
1853
1854 /* XXX: Assume that the entire packet will fit in a header mbuf. */
1855 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
1856 ("syncache: mbuf too small: hlen %u, sc_port %u, max_linkhdr %d + "
1857 "tlen %d + TCP_MAXOLEN %ju <= MHLEN %d", hlen, sc->sc_port,
1858 max_linkhdr, tlen, (uintmax_t)TCP_MAXOLEN, MHLEN));
1859
1860 /* Create the IP+TCP header from scratch. */
1861 m = m_gethdr(M_NOWAIT, MT_DATA);
1862 if (m == NULL)
1863 return (ENOBUFS);
1864 #ifdef MAC
1865 mac_syncache_create_mbuf(sc->sc_label, m);
1866 #endif
1867 m->m_data += max_linkhdr;
1868 m->m_len = tlen;
1869 m->m_pkthdr.len = tlen;
1870 m->m_pkthdr.rcvif = NULL;
1871
1872 #ifdef INET6
1873 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1874 ip6 = mtod(m, struct ip6_hdr *);
1875 ip6->ip6_vfc = IPV6_VERSION;
1876 ip6->ip6_src = sc->sc_inc.inc6_laddr;
1877 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
1878 ip6->ip6_plen = htons(tlen - hlen);
1879 /* ip6_hlim is set after checksum */
1880 /* Zero out traffic class and flow label. */
1881 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK;
1882 ip6->ip6_flow |= sc->sc_flowlabel;
1883 if (sc->sc_port != 0) {
1884 ip6->ip6_nxt = IPPROTO_UDP;
1885 udp = (struct udphdr *)(ip6 + 1);
1886 udp->uh_sport = htons(V_tcp_udp_tunneling_port);
1887 udp->uh_dport = sc->sc_port;
1888 ulen = (tlen - sizeof(struct ip6_hdr));
1889 th = (struct tcphdr *)(udp + 1);
1890 } else {
1891 ip6->ip6_nxt = IPPROTO_TCP;
1892 th = (struct tcphdr *)(ip6 + 1);
1893 }
1894 ip6->ip6_flow |= htonl(sc->sc_ip_tos << IPV6_FLOWLABEL_LEN);
1895 }
1896 #endif
1897 #if defined(INET6) && defined(INET)
1898 else
1899 #endif
1900 #ifdef INET
1901 {
1902 ip = mtod(m, struct ip *);
1903 ip->ip_v = IPVERSION;
1904 ip->ip_hl = sizeof(struct ip) >> 2;
1905 ip->ip_len = htons(tlen);
1906 ip->ip_id = 0;
1907 ip->ip_off = 0;
1908 ip->ip_sum = 0;
1909 ip->ip_src = sc->sc_inc.inc_laddr;
1910 ip->ip_dst = sc->sc_inc.inc_faddr;
1911 ip->ip_ttl = sc->sc_ip_ttl;
1912 ip->ip_tos = sc->sc_ip_tos;
1913
1914 /*
1915 * See if we should do MTU discovery. Route lookups are
1916 * expensive, so we will only unset the DF bit if:
1917 *
1918 * 1) path_mtu_discovery is disabled
1919 * 2) the SCF_UNREACH flag has been set
1920 */
1921 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
1922 ip->ip_off |= htons(IP_DF);
1923 if (sc->sc_port == 0) {
1924 ip->ip_p = IPPROTO_TCP;
1925 th = (struct tcphdr *)(ip + 1);
1926 } else {
1927 ip->ip_p = IPPROTO_UDP;
1928 udp = (struct udphdr *)(ip + 1);
1929 udp->uh_sport = htons(V_tcp_udp_tunneling_port);
1930 udp->uh_dport = sc->sc_port;
1931 ulen = (tlen - sizeof(struct ip));
1932 th = (struct tcphdr *)(udp + 1);
1933 }
1934 }
1935 #endif /* INET */
1936 th->th_sport = sc->sc_inc.inc_lport;
1937 th->th_dport = sc->sc_inc.inc_fport;
1938
1939 if (flags & TH_SYN)
1940 th->th_seq = htonl(sc->sc_iss);
1941 else
1942 th->th_seq = htonl(sc->sc_iss + 1);
1943 th->th_ack = htonl(sc->sc_irs + 1);
1944 th->th_off = sizeof(struct tcphdr) >> 2;
1945 th->th_win = htons(sc->sc_wnd);
1946 th->th_urp = 0;
1947
1948 flags = tcp_ecn_syncache_respond(flags, sc);
1949 tcp_set_flags(th, flags);
1950
1951 /* Tack on the TCP options. */
1952 if ((sc->sc_flags & SCF_NOOPT) == 0) {
1953 to.to_flags = 0;
1954
1955 if (flags & TH_SYN) {
1956 to.to_mss = mssopt;
1957 to.to_flags = TOF_MSS;
1958 if (sc->sc_flags & SCF_WINSCALE) {
1959 to.to_wscale = sc->sc_requested_r_scale;
1960 to.to_flags |= TOF_SCALE;
1961 }
1962 if (sc->sc_flags & SCF_SACK)
1963 to.to_flags |= TOF_SACKPERM;
1964 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1965 if (sc->sc_flags & SCF_SIGNATURE)
1966 to.to_flags |= TOF_SIGNATURE;
1967 #endif
1968 if (sc->sc_tfo_cookie) {
1969 to.to_flags |= TOF_FASTOPEN;
1970 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
1971 to.to_tfo_cookie = sc->sc_tfo_cookie;
1972 /* don't send cookie again when retransmitting response */
1973 sc->sc_tfo_cookie = NULL;
1974 }
1975 }
1976 if (sc->sc_flags & SCF_TIMESTAMP) {
1977 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks();
1978 to.to_tsecr = sc->sc_tsreflect;
1979 to.to_flags |= TOF_TS;
1980 }
1981 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
1982
1983 /* Adjust headers by option size. */
1984 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
1985 m->m_len += optlen;
1986 m->m_pkthdr.len += optlen;
1987 #ifdef INET6
1988 if (sc->sc_inc.inc_flags & INC_ISIPV6)
1989 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
1990 else
1991 #endif
1992 ip->ip_len = htons(ntohs(ip->ip_len) + optlen);
1993 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1994 if (sc->sc_flags & SCF_SIGNATURE) {
1995 KASSERT(to.to_flags & TOF_SIGNATURE,
1996 ("tcp_addoptions() didn't set tcp_signature"));
1997
1998 /* NOTE: to.to_signature is inside of mbuf */
1999 if (!TCPMD5_ENABLED() ||
2000 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) {
2001 m_freem(m);
2002 return (EACCES);
2003 }
2004 }
2005 #endif
2006 } else
2007 optlen = 0;
2008
2009 if (udp) {
2010 ulen += optlen;
2011 udp->uh_ulen = htons(ulen);
2012 }
2013 M_SETFIB(m, sc->sc_inc.inc_fibnum);
2014 m->m_pkthdr.flowid = sc->sc_flowid;
2015 M_HASHTYPE_SET(m, sc->sc_flowtype);
2016 #ifdef NUMA
2017 m->m_pkthdr.numa_domain = sc->sc_numa_domain;
2018 #endif
2019 #ifdef INET6
2020 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
2021 if (sc->sc_port) {
2022 m->m_pkthdr.csum_flags = CSUM_UDP_IPV6;
2023 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
2024 udp->uh_sum = in6_cksum_pseudo(ip6, ulen,
2025 IPPROTO_UDP, 0);
2026 th->th_sum = htons(0);
2027 } else {
2028 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
2029 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
2030 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen,
2031 IPPROTO_TCP, 0);
2032 }
2033 ip6->ip6_hlim = sc->sc_ip_ttl;
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, ip6, NULL, th);
2044 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
2045 }
2046 #endif
2047 #if defined(INET6) && defined(INET)
2048 else
2049 #endif
2050 #ifdef INET
2051 {
2052 if (sc->sc_port) {
2053 m->m_pkthdr.csum_flags = CSUM_UDP;
2054 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
2055 udp->uh_sum = in_pseudo(ip->ip_src.s_addr,
2056 ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP));
2057 th->th_sum = htons(0);
2058 } else {
2059 m->m_pkthdr.csum_flags = CSUM_TCP;
2060 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
2061 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
2062 htons(tlen + optlen - hlen + IPPROTO_TCP));
2063 }
2064 #ifdef TCP_OFFLOAD
2065 if (ADDED_BY_TOE(sc)) {
2066 struct toedev *tod = sc->sc_tod;
2067
2068 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
2069
2070 return (error);
2071 }
2072 #endif
2073 TCP_PROBE5(send, NULL, NULL, ip, NULL, th);
2074 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
2075 }
2076 #endif
2077 return (error);
2078 }
2079
2080 static void
syncache_send_challenge_ack(struct syncache * sc)2081 syncache_send_challenge_ack(struct syncache *sc)
2082 {
2083 if (tcp_challenge_ack_check(&sc->sc_challenge_ack_end,
2084 &sc->sc_challenge_ack_cnt)) {
2085 if (syncache_respond(sc, TH_ACK) == 0) {
2086 TCPSTAT_INC(tcps_sndacks);
2087 TCPSTAT_INC(tcps_sndtotal);
2088 }
2089 }
2090 }
2091
2092 /*
2093 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks
2094 * that exceed the capacity of the syncache by avoiding the storage of any
2095 * of the SYNs we receive. Syncookies defend against blind SYN flooding
2096 * attacks where the attacker does not have access to our responses.
2097 *
2098 * Syncookies encode and include all necessary information about the
2099 * connection setup within the SYN|ACK that we send back. That way we
2100 * can avoid keeping any local state until the ACK to our SYN|ACK returns
2101 * (if ever). Normally the syncache and syncookies are running in parallel
2102 * with the latter taking over when the former is exhausted. When matching
2103 * syncache entry is found the syncookie is ignored.
2104 *
2105 * The only reliable information persisting the 3WHS is our initial sequence
2106 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient
2107 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS
2108 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK
2109 * returns and signifies a legitimate connection if it matches the ACK.
2110 *
2111 * The available space of 32 bits to store the hash and to encode the SYN
2112 * option information is very tight and we should have at least 24 bits for
2113 * the MAC to keep the number of guesses by blind spoofing reasonably high.
2114 *
2115 * SYN option information we have to encode to fully restore a connection:
2116 * MSS: is imporant to chose an optimal segment size to avoid IP level
2117 * fragmentation along the path. The common MSS values can be encoded
2118 * in a 3-bit table. Uncommon values are captured by the next lower value
2119 * in the table leading to a slight increase in packetization overhead.
2120 * WSCALE: is necessary to allow large windows to be used for high delay-
2121 * bandwidth product links. Not scaling the window when it was initially
2122 * negotiated is bad for performance as lack of scaling further decreases
2123 * the apparent available send window. We only need to encode the WSCALE
2124 * we received from the remote end. Our end can be recalculated at any
2125 * time. The common WSCALE values can be encoded in a 3-bit table.
2126 * Uncommon values are captured by the next lower value in the table
2127 * making us under-estimate the available window size halving our
2128 * theoretically possible maximum throughput for that connection.
2129 * SACK: Greatly assists in packet loss recovery and requires 1 bit.
2130 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options
2131 * that are included in all segments on a connection. We enable them when
2132 * the ACK has them.
2133 *
2134 * Security of syncookies and attack vectors:
2135 *
2136 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod)
2137 * together with the gloabl secret to make it unique per connection attempt.
2138 * Thus any change of any of those parameters results in a different MAC output
2139 * in an unpredictable way unless a collision is encountered. 24 bits of the
2140 * MAC are embedded into the ISS.
2141 *
2142 * To prevent replay attacks two rotating global secrets are updated with a
2143 * new random value every 15 seconds. The life-time of a syncookie is thus
2144 * 15-30 seconds.
2145 *
2146 * Vector 1: Attacking the secret. This requires finding a weakness in the
2147 * MAC itself or the way it is used here. The attacker can do a chosen plain
2148 * text attack by varying and testing the all parameters under his control.
2149 * The strength depends on the size and randomness of the secret, and the
2150 * cryptographic security of the MAC function. Due to the constant updating
2151 * of the secret the attacker has at most 29.999 seconds to find the secret
2152 * and launch spoofed connections. After that he has to start all over again.
2153 *
2154 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC
2155 * size an average of 4,823 attempts are required for a 50% chance of success
2156 * to spoof a single syncookie (birthday collision paradox). However the
2157 * attacker is blind and doesn't know if one of his attempts succeeded unless
2158 * he has a side channel to interfere success from. A single connection setup
2159 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets.
2160 * This many attempts are required for each one blind spoofed connection. For
2161 * every additional spoofed connection he has to launch another N attempts.
2162 * Thus for a sustained rate 100 spoofed connections per second approximately
2163 * 1,800,000 packets per second would have to be sent.
2164 *
2165 * NB: The MAC function should be fast so that it doesn't become a CPU
2166 * exhaustion attack vector itself.
2167 *
2168 * References:
2169 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations
2170 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996
2171 * http://cr.yp.to/syncookies.html (overview)
2172 * http://cr.yp.to/syncookies/archive (details)
2173 *
2174 *
2175 * Schematic construction of a syncookie enabled Initial Sequence Number:
2176 * 0 1 2 3
2177 * 12345678901234567890123456789012
2178 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP|
2179 *
2180 * x 24 MAC (truncated)
2181 * W 3 Send Window Scale index
2182 * M 3 MSS index
2183 * S 1 SACK permitted
2184 * P 1 Odd/even secret
2185 */
2186
2187 /*
2188 * Distribution and probability of certain MSS values. Those in between are
2189 * rounded down to the next lower one.
2190 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011]
2191 * .2% .3% 5% 7% 7% 20% 15% 45%
2192 */
2193 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 };
2194
2195 /*
2196 * Distribution and probability of certain WSCALE values. We have to map the
2197 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3
2198 * bits based on prevalence of certain values. Where we don't have an exact
2199 * match for are rounded down to the next lower one letting us under-estimate
2200 * the true available window. At the moment this would happen only for the
2201 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer
2202 * and window size). The absence of the WSCALE option (no scaling in either
2203 * direction) is encoded with index zero.
2204 * [WSCALE values histograms, Allman, 2012]
2205 * X 10 10 35 5 6 14 10% by host
2206 * X 11 4 5 5 18 49 3% by connections
2207 */
2208 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 };
2209
2210 /*
2211 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed
2212 * and good cryptographic properties.
2213 */
2214 static uint32_t
syncookie_mac(struct in_conninfo * inc,tcp_seq irs,uint8_t flags,uint8_t * secbits,uintptr_t secmod)2215 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags,
2216 uint8_t *secbits, uintptr_t secmod)
2217 {
2218 SIPHASH_CTX ctx;
2219 uint32_t siphash[2];
2220
2221 SipHash24_Init(&ctx);
2222 SipHash_SetKey(&ctx, secbits);
2223 switch (inc->inc_flags & INC_ISIPV6) {
2224 #ifdef INET
2225 case 0:
2226 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr));
2227 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr));
2228 break;
2229 #endif
2230 #ifdef INET6
2231 case INC_ISIPV6:
2232 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr));
2233 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr));
2234 break;
2235 #endif
2236 }
2237 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport));
2238 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport));
2239 SipHash_Update(&ctx, &irs, sizeof(irs));
2240 SipHash_Update(&ctx, &flags, sizeof(flags));
2241 SipHash_Update(&ctx, &secmod, sizeof(secmod));
2242 SipHash_Final((u_int8_t *)&siphash, &ctx);
2243
2244 return (siphash[0] ^ siphash[1]);
2245 }
2246
2247 static tcp_seq
syncookie_generate(struct syncache_head * sch,struct syncache * sc)2248 syncookie_generate(struct syncache_head *sch, struct syncache *sc)
2249 {
2250 u_int i, secbit, wscale;
2251 uint32_t iss, hash;
2252 uint8_t *secbits;
2253 union syncookie cookie;
2254
2255 cookie.cookie = 0;
2256
2257 /* Map our computed MSS into the 3-bit index. */
2258 for (i = nitems(tcp_sc_msstab) - 1;
2259 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0;
2260 i--)
2261 ;
2262 cookie.flags.mss_idx = i;
2263
2264 /*
2265 * Map the send window scale into the 3-bit index but only if
2266 * the wscale option was received.
2267 */
2268 if (sc->sc_flags & SCF_WINSCALE) {
2269 wscale = sc->sc_requested_s_scale;
2270 for (i = nitems(tcp_sc_wstab) - 1;
2271 tcp_sc_wstab[i] > wscale && i > 0;
2272 i--)
2273 ;
2274 cookie.flags.wscale_idx = i;
2275 }
2276
2277 /* Can we do SACK? */
2278 if (sc->sc_flags & SCF_SACK)
2279 cookie.flags.sack_ok = 1;
2280
2281 /* Which of the two secrets to use. */
2282 secbit = V_tcp_syncache.secret.oddeven & 0x1;
2283 cookie.flags.odd_even = secbit;
2284
2285 secbits = V_tcp_syncache.secret.key[secbit];
2286 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits,
2287 (uintptr_t)sch);
2288
2289 /*
2290 * Put the flags into the hash and XOR them to get better ISS number
2291 * variance. This doesn't enhance the cryptographic strength and is
2292 * done to prevent the 8 cookie bits from showing up directly on the
2293 * wire.
2294 */
2295 iss = hash & ~0xff;
2296 iss |= cookie.cookie ^ (hash >> 24);
2297
2298 TCPSTAT_INC(tcps_sc_sendcookie);
2299 return (iss);
2300 }
2301
2302 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)2303 syncookie_expand(struct in_conninfo *inc, const struct syncache_head *sch,
2304 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
2305 struct socket *lso, uint16_t port)
2306 {
2307 uint32_t hash;
2308 uint8_t *secbits;
2309 tcp_seq ack, seq;
2310 int wnd;
2311 union syncookie cookie;
2312
2313 /*
2314 * Pull information out of SYN-ACK/ACK and revert sequence number
2315 * advances.
2316 */
2317 ack = th->th_ack - 1;
2318 seq = th->th_seq - 1;
2319
2320 /*
2321 * Unpack the flags containing enough information to restore the
2322 * connection.
2323 */
2324 cookie.cookie = (ack & 0xff) ^ (ack >> 24);
2325
2326 /* Which of the two secrets to use. */
2327 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even];
2328
2329 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch);
2330
2331 /* The recomputed hash matches the ACK if this was a genuine cookie. */
2332 if ((ack & ~0xff) != (hash & ~0xff))
2333 return (false);
2334
2335 /* Fill in the syncache values. */
2336 sc->sc_flags = 0;
2337 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
2338 sc->sc_ipopts = NULL;
2339
2340 sc->sc_irs = seq;
2341 sc->sc_iss = ack;
2342
2343 switch (inc->inc_flags & INC_ISIPV6) {
2344 #ifdef INET
2345 case 0:
2346 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl;
2347 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos;
2348 break;
2349 #endif
2350 #ifdef INET6
2351 case INC_ISIPV6:
2352 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL)
2353 sc->sc_flowlabel =
2354 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK;
2355 break;
2356 #endif
2357 }
2358
2359 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx];
2360
2361 /* Only use wscale if it was enabled in the orignal SYN. */
2362 if (cookie.flags.wscale_idx > 0) {
2363 u_int wscale = 0;
2364
2365 /* Recompute the receive window scale that was sent earlier. */
2366 while (wscale < TCP_MAX_WINSHIFT &&
2367 (TCP_MAXWIN << wscale) < sb_max)
2368 wscale++;
2369 sc->sc_requested_r_scale = wscale;
2370 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx];
2371 sc->sc_flags |= SCF_WINSCALE;
2372 }
2373
2374 wnd = lso->sol_sbrcv_hiwat;
2375 wnd = imax(wnd, 0);
2376 wnd = imin(wnd, TCP_MAXWIN);
2377 sc->sc_wnd = wnd;
2378
2379 if (cookie.flags.sack_ok)
2380 sc->sc_flags |= SCF_SACK;
2381
2382 if (to->to_flags & TOF_TS) {
2383 sc->sc_flags |= SCF_TIMESTAMP;
2384 sc->sc_tsreflect = to->to_tsval;
2385 sc->sc_tsoff = tcp_new_ts_offset(inc);
2386 }
2387
2388 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
2389 if (to->to_flags & TOF_SIGNATURE)
2390 sc->sc_flags |= SCF_SIGNATURE;
2391 #endif
2392
2393 sc->sc_rxmits = 0;
2394
2395 sc->sc_port = port;
2396
2397 return (true);
2398 }
2399
2400 #ifdef INVARIANTS
2401 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)2402 syncookie_cmp(struct in_conninfo *inc, const struct syncache_head *sch,
2403 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
2404 struct socket *lso, uint16_t port)
2405 {
2406 struct syncache scs;
2407 char *s;
2408
2409 bzero(&scs, sizeof(scs));
2410 if (syncookie_expand(inc, sch, &scs, th, to, lso, port) &&
2411 (sc->sc_peer_mss != scs.sc_peer_mss ||
2412 sc->sc_requested_r_scale != scs.sc_requested_r_scale ||
2413 sc->sc_requested_s_scale != scs.sc_requested_s_scale ||
2414 (sc->sc_flags & SCF_SACK) != (scs.sc_flags & SCF_SACK))) {
2415
2416 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL)
2417 return;
2418
2419 if (sc->sc_peer_mss != scs.sc_peer_mss)
2420 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n",
2421 s, __func__, sc->sc_peer_mss, scs.sc_peer_mss);
2422
2423 if (sc->sc_requested_r_scale != scs.sc_requested_r_scale)
2424 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n",
2425 s, __func__, sc->sc_requested_r_scale,
2426 scs.sc_requested_r_scale);
2427
2428 if (sc->sc_requested_s_scale != scs.sc_requested_s_scale)
2429 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n",
2430 s, __func__, sc->sc_requested_s_scale,
2431 scs.sc_requested_s_scale);
2432
2433 if ((sc->sc_flags & SCF_SACK) != (scs.sc_flags & SCF_SACK))
2434 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__);
2435
2436 free(s, M_TCPLOG);
2437 }
2438 }
2439 #endif /* INVARIANTS */
2440
2441 static void
syncookie_reseed(void * arg)2442 syncookie_reseed(void *arg)
2443 {
2444 struct tcp_syncache *sc = arg;
2445 uint8_t *secbits;
2446 int secbit;
2447
2448 /*
2449 * Reseeding the secret doesn't have to be protected by a lock.
2450 * It only must be ensured that the new random values are visible
2451 * to all CPUs in a SMP environment. The atomic with release
2452 * semantics ensures that.
2453 */
2454 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1;
2455 secbits = sc->secret.key[secbit];
2456 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0);
2457 atomic_add_rel_int(&sc->secret.oddeven, 1);
2458
2459 /* Reschedule ourself. */
2460 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz);
2461 }
2462
2463 /*
2464 * We have overflowed a bucket. Let's pause dealing with the syncache.
2465 * This function will increment the bucketoverflow statistics appropriately
2466 * (once per pause when pausing is enabled; otherwise, once per overflow).
2467 */
2468 static void
syncache_pause(struct in_conninfo * inc)2469 syncache_pause(struct in_conninfo *inc)
2470 {
2471 time_t delta;
2472 const char *s;
2473
2474 /* XXX:
2475 * 2. Add sysctl read here so we don't get the benefit of this
2476 * change without the new sysctl.
2477 */
2478
2479 /*
2480 * Try an unlocked read. If we already know that another thread
2481 * has activated the feature, there is no need to proceed.
2482 */
2483 if (V_tcp_syncache.paused)
2484 return;
2485
2486 /* Are cookied enabled? If not, we can't pause. */
2487 if (!V_tcp_syncookies) {
2488 TCPSTAT_INC(tcps_sc_bucketoverflow);
2489 return;
2490 }
2491
2492 /*
2493 * We may be the first thread to find an overflow. Get the lock
2494 * and evaluate if we need to take action.
2495 */
2496 mtx_lock(&V_tcp_syncache.pause_mtx);
2497 if (V_tcp_syncache.paused) {
2498 mtx_unlock(&V_tcp_syncache.pause_mtx);
2499 return;
2500 }
2501
2502 /* Activate protection. */
2503 V_tcp_syncache.paused = true;
2504 TCPSTAT_INC(tcps_sc_bucketoverflow);
2505
2506 /*
2507 * Determine the last backoff time. If we are seeing a re-newed
2508 * attack within that same time after last reactivating the syncache,
2509 * consider it an extension of the same attack.
2510 */
2511 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff;
2512 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) {
2513 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) {
2514 delta <<= 1;
2515 V_tcp_syncache.pause_backoff++;
2516 }
2517 } else {
2518 delta = TCP_SYNCACHE_PAUSE_TIME;
2519 V_tcp_syncache.pause_backoff = 0;
2520 }
2521
2522 /* Log a warning, including IP addresses, if able. */
2523 if (inc != NULL)
2524 s = tcp_log_addrs(inc, NULL, NULL, NULL);
2525 else
2526 s = (const char *)NULL;
2527 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for "
2528 "the next %lld seconds%s%s%s\n", (long long)delta,
2529 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "",
2530 (s != NULL) ? ")" : "");
2531 free(__DECONST(void *, s), M_TCPLOG);
2532
2533 /* Use the calculated delta to set a new pause time. */
2534 V_tcp_syncache.pause_until = time_uptime + delta;
2535 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause,
2536 &V_tcp_syncache);
2537 mtx_unlock(&V_tcp_syncache.pause_mtx);
2538 }
2539
2540 /* Evaluate whether we need to unpause. */
2541 static void
syncache_unpause(void * arg)2542 syncache_unpause(void *arg)
2543 {
2544 struct tcp_syncache *sc;
2545 time_t delta;
2546
2547 sc = arg;
2548 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED);
2549 callout_deactivate(&sc->pause_co);
2550
2551 /*
2552 * Check to make sure we are not running early. If the pause
2553 * time has expired, then deactivate the protection.
2554 */
2555 if ((delta = sc->pause_until - time_uptime) > 0)
2556 callout_schedule(&sc->pause_co, delta * hz);
2557 else
2558 sc->paused = false;
2559 }
2560
2561 /*
2562 * Exports the syncache entries to userland so that netstat can display
2563 * them alongside the other sockets. This function is intended to be
2564 * called only from tcp_pcblist.
2565 *
2566 * Due to concurrency on an active system, the number of pcbs exported
2567 * may have no relation to max_pcbs. max_pcbs merely indicates the
2568 * amount of space the caller allocated for this function to use.
2569 */
2570 int
syncache_pcblist(struct sysctl_req * req)2571 syncache_pcblist(struct sysctl_req *req)
2572 {
2573 struct xtcpcb xt;
2574 struct syncache *sc;
2575 struct syncache_head *sch;
2576 int error, i;
2577
2578 bzero(&xt, sizeof(xt));
2579 xt.xt_len = sizeof(xt);
2580 xt.t_state = TCPS_SYN_RECEIVED;
2581 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP;
2582 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket);
2583 xt.xt_inp.xi_socket.so_type = SOCK_STREAM;
2584 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING;
2585
2586 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
2587 sch = &V_tcp_syncache.hashbase[i];
2588 SCH_LOCK(sch);
2589 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
2590 if (sc->sc_cred != NULL &&
2591 cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
2592 continue;
2593 if (sc->sc_inc.inc_flags & INC_ISIPV6)
2594 xt.xt_inp.inp_vflag = INP_IPV6;
2595 else
2596 xt.xt_inp.inp_vflag = INP_IPV4;
2597 xt.xt_encaps_port = sc->sc_port;
2598 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc,
2599 sizeof (struct in_conninfo));
2600 error = SYSCTL_OUT(req, &xt, sizeof xt);
2601 if (error) {
2602 SCH_UNLOCK(sch);
2603 return (0);
2604 }
2605 }
2606 SCH_UNLOCK(sch);
2607 }
2608
2609 return (0);
2610 }
2611