1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
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 __FBSDID("$FreeBSD$");
37
38 #include "opt_inet.h"
39 #include "opt_inet6.h"
40 #include "opt_ipsec.h"
41 #include "opt_pcbgroup.h"
42
43 #include <sys/param.h>
44 #include <sys/systm.h>
45 #include <sys/hash.h>
46 #include <sys/refcount.h>
47 #include <sys/kernel.h>
48 #include <sys/sysctl.h>
49 #include <sys/limits.h>
50 #include <sys/lock.h>
51 #include <sys/mutex.h>
52 #include <sys/malloc.h>
53 #include <sys/mbuf.h>
54 #include <sys/proc.h> /* for proc0 declaration */
55 #include <sys/random.h>
56 #include <sys/socket.h>
57 #include <sys/socketvar.h>
58 #include <sys/syslog.h>
59 #include <sys/ucred.h>
60
61 #include <sys/md5.h>
62 #include <crypto/siphash/siphash.h>
63
64 #include <vm/uma.h>
65
66 #include <net/if.h>
67 #include <net/if_var.h>
68 #include <net/route.h>
69 #include <net/vnet.h>
70
71 #include <netinet/in.h>
72 #include <netinet/in_kdtrace.h>
73 #include <netinet/in_systm.h>
74 #include <netinet/ip.h>
75 #include <netinet/in_var.h>
76 #include <netinet/in_pcb.h>
77 #include <netinet/ip_var.h>
78 #include <netinet/ip_options.h>
79 #ifdef INET6
80 #include <netinet/ip6.h>
81 #include <netinet/icmp6.h>
82 #include <netinet6/nd6.h>
83 #include <netinet6/ip6_var.h>
84 #include <netinet6/in6_pcb.h>
85 #endif
86 #include <netinet/tcp.h>
87 #include <netinet/tcp_fastopen.h>
88 #include <netinet/tcp_fsm.h>
89 #include <netinet/tcp_seq.h>
90 #include <netinet/tcp_timer.h>
91 #include <netinet/tcp_var.h>
92 #include <netinet/tcp_syncache.h>
93 #ifdef INET6
94 #include <netinet6/tcp6_var.h>
95 #endif
96 #ifdef TCP_OFFLOAD
97 #include <netinet/toecore.h>
98 #endif
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(int, tcp_syncookies) = 1;
107 #define V_tcp_syncookies VNET(tcp_syncookies)
108 SYSCTL_INT(_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(int, tcp_syncookiesonly) = 0;
113 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly)
114 SYSCTL_INT(_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 VNET_DEFINE_STATIC(int, functions_inherit_listen_socket_stack) = 1;
119 #define V_functions_inherit_listen_socket_stack \
120 VNET(functions_inherit_listen_socket_stack)
121 SYSCTL_INT(_net_inet_tcp, OID_AUTO, functions_inherit_listen_socket_stack,
122 CTLFLAG_VNET | CTLFLAG_RW,
123 &VNET_NAME(functions_inherit_listen_socket_stack), 0,
124 "Inherit listen socket's stack");
125
126 #ifdef TCP_OFFLOAD
127 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL)
128 #endif
129
130 static void syncache_drop(struct syncache *, struct syncache_head *);
131 static void syncache_free(struct syncache *);
132 static void syncache_insert(struct syncache *, struct syncache_head *);
133 static int syncache_respond(struct syncache *, struct syncache_head *,
134 const struct mbuf *, int);
135 static struct socket *syncache_socket(struct syncache *, struct socket *,
136 struct mbuf *m);
137 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch,
138 int docallout);
139 static void syncache_timer(void *);
140
141 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t,
142 uint8_t *, uintptr_t);
143 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *);
144 static struct syncache
145 *syncookie_lookup(struct in_conninfo *, struct syncache_head *,
146 struct syncache *, struct tcphdr *, struct tcpopt *,
147 struct socket *);
148 static void syncookie_reseed(void *);
149 #ifdef INVARIANTS
150 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
151 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
152 struct socket *lso);
153 #endif
154
155 /*
156 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
157 * 3 retransmits corresponds to a timeout with default values of
158 * tcp_rexmit_initial * ( 1 +
159 * tcp_backoff[1] +
160 * tcp_backoff[2] +
161 * tcp_backoff[3]) + 3 * tcp_rexmit_slop,
162 * 1000 ms * (1 + 2 + 4 + 8) + 3 * 200 ms = 15600 ms,
163 * the odds are that the user has given up attempting to connect by then.
164 */
165 #define SYNCACHE_MAXREXMTS 3
166
167 /* Arbitrary values */
168 #define TCP_SYNCACHE_HASHSIZE 512
169 #define TCP_SYNCACHE_BUCKETLIMIT 30
170
171 VNET_DEFINE_STATIC(struct tcp_syncache, tcp_syncache);
172 #define V_tcp_syncache VNET(tcp_syncache)
173
174 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0,
175 "TCP SYN cache");
176
177 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
178 &VNET_NAME(tcp_syncache.bucket_limit), 0,
179 "Per-bucket hash limit for syncache");
180
181 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
182 &VNET_NAME(tcp_syncache.cache_limit), 0,
183 "Overall entry limit for syncache");
184
185 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET,
186 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache");
187
188 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN,
189 &VNET_NAME(tcp_syncache.hashsize), 0,
190 "Size of TCP syncache hashtable");
191
192 static int
sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS)193 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS)
194 {
195 int error;
196 u_int new;
197
198 new = V_tcp_syncache.rexmt_limit;
199 error = sysctl_handle_int(oidp, &new, 0, req);
200 if ((error == 0) && (req->newptr != NULL)) {
201 if (new > TCP_MAXRXTSHIFT)
202 error = EINVAL;
203 else
204 V_tcp_syncache.rexmt_limit = new;
205 }
206 return (error);
207 }
208
209 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit,
210 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW,
211 &VNET_NAME(tcp_syncache.rexmt_limit), 0,
212 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "UI",
213 "Limit on SYN/ACK retransmissions");
214
215 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1;
216 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail,
217 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0,
218 "Send reset on socket allocation failure");
219
220 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
221
222 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx)
223 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx)
224 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED)
225
226 /*
227 * Requires the syncache entry to be already removed from the bucket list.
228 */
229 static void
syncache_free(struct syncache * sc)230 syncache_free(struct syncache *sc)
231 {
232
233 if (sc->sc_ipopts)
234 (void) m_free(sc->sc_ipopts);
235 if (sc->sc_cred)
236 crfree(sc->sc_cred);
237 #ifdef MAC
238 mac_syncache_destroy(&sc->sc_label);
239 #endif
240
241 uma_zfree(V_tcp_syncache.zone, sc);
242 }
243
244 void
syncache_init(void)245 syncache_init(void)
246 {
247 int i;
248
249 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
250 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
251 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
252 V_tcp_syncache.hash_secret = arc4random();
253
254 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
255 &V_tcp_syncache.hashsize);
256 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
257 &V_tcp_syncache.bucket_limit);
258 if (!powerof2(V_tcp_syncache.hashsize) ||
259 V_tcp_syncache.hashsize == 0) {
260 printf("WARNING: syncache hash size is not a power of 2.\n");
261 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
262 }
263 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1;
264
265 /* Set limits. */
266 V_tcp_syncache.cache_limit =
267 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit;
268 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
269 &V_tcp_syncache.cache_limit);
270
271 /* Allocate the hash table. */
272 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize *
273 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO);
274
275 #ifdef VIMAGE
276 V_tcp_syncache.vnet = curvnet;
277 #endif
278
279 /* Initialize the hash buckets. */
280 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
281 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket);
282 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
283 NULL, MTX_DEF);
284 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer,
285 &V_tcp_syncache.hashbase[i].sch_mtx, 0);
286 V_tcp_syncache.hashbase[i].sch_length = 0;
287 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache;
288 V_tcp_syncache.hashbase[i].sch_last_overflow =
289 -(SYNCOOKIE_LIFETIME + 1);
290 }
291
292 /* Create the syncache entry zone. */
293 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
294 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
295 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone,
296 V_tcp_syncache.cache_limit);
297
298 /* Start the SYN cookie reseeder callout. */
299 callout_init(&V_tcp_syncache.secret.reseed, 1);
300 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0);
301 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0);
302 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz,
303 syncookie_reseed, &V_tcp_syncache);
304 }
305
306 #ifdef VIMAGE
307 void
syncache_destroy(void)308 syncache_destroy(void)
309 {
310 struct syncache_head *sch;
311 struct syncache *sc, *nsc;
312 int i;
313
314 /*
315 * Stop the re-seed timer before freeing resources. No need to
316 * possibly schedule it another time.
317 */
318 callout_drain(&V_tcp_syncache.secret.reseed);
319
320 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */
321 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
322
323 sch = &V_tcp_syncache.hashbase[i];
324 callout_drain(&sch->sch_timer);
325
326 SCH_LOCK(sch);
327 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc)
328 syncache_drop(sc, sch);
329 SCH_UNLOCK(sch);
330 KASSERT(TAILQ_EMPTY(&sch->sch_bucket),
331 ("%s: sch->sch_bucket not empty", __func__));
332 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0",
333 __func__, sch->sch_length));
334 mtx_destroy(&sch->sch_mtx);
335 }
336
337 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0,
338 ("%s: cache_count not 0", __func__));
339
340 /* Free the allocated global resources. */
341 uma_zdestroy(V_tcp_syncache.zone);
342 free(V_tcp_syncache.hashbase, M_SYNCACHE);
343 }
344 #endif
345
346 /*
347 * Inserts a syncache entry into the specified bucket row.
348 * Locks and unlocks the syncache_head autonomously.
349 */
350 static void
syncache_insert(struct syncache * sc,struct syncache_head * sch)351 syncache_insert(struct syncache *sc, struct syncache_head *sch)
352 {
353 struct syncache *sc2;
354
355 SCH_LOCK(sch);
356
357 /*
358 * Make sure that we don't overflow the per-bucket limit.
359 * If the bucket is full, toss the oldest element.
360 */
361 if (sch->sch_length >= V_tcp_syncache.bucket_limit) {
362 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
363 ("sch->sch_length incorrect"));
364 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
365 sch->sch_last_overflow = time_uptime;
366 syncache_drop(sc2, sch);
367 TCPSTAT_INC(tcps_sc_bucketoverflow);
368 }
369
370 /* Put it into the bucket. */
371 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
372 sch->sch_length++;
373
374 #ifdef TCP_OFFLOAD
375 if (ADDED_BY_TOE(sc)) {
376 struct toedev *tod = sc->sc_tod;
377
378 tod->tod_syncache_added(tod, sc->sc_todctx);
379 }
380 #endif
381
382 /* Reinitialize the bucket row's timer. */
383 if (sch->sch_length == 1)
384 sch->sch_nextc = ticks + INT_MAX;
385 syncache_timeout(sc, sch, 1);
386
387 SCH_UNLOCK(sch);
388
389 TCPSTATES_INC(TCPS_SYN_RECEIVED);
390 TCPSTAT_INC(tcps_sc_added);
391 }
392
393 /*
394 * Remove and free entry from syncache bucket row.
395 * Expects locked syncache head.
396 */
397 static void
syncache_drop(struct syncache * sc,struct syncache_head * sch)398 syncache_drop(struct syncache *sc, struct syncache_head *sch)
399 {
400
401 SCH_LOCK_ASSERT(sch);
402
403 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
404 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
405 sch->sch_length--;
406
407 #ifdef TCP_OFFLOAD
408 if (ADDED_BY_TOE(sc)) {
409 struct toedev *tod = sc->sc_tod;
410
411 tod->tod_syncache_removed(tod, sc->sc_todctx);
412 }
413 #endif
414
415 syncache_free(sc);
416 }
417
418 /*
419 * Engage/reengage time on bucket row.
420 */
421 static void
syncache_timeout(struct syncache * sc,struct syncache_head * sch,int docallout)422 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
423 {
424 int rexmt;
425
426 if (sc->sc_rxmits == 0)
427 rexmt = tcp_rexmit_initial;
428 else
429 TCPT_RANGESET(rexmt,
430 tcp_rexmit_initial * tcp_backoff[sc->sc_rxmits],
431 tcp_rexmit_min, TCPTV_REXMTMAX);
432 sc->sc_rxttime = ticks + rexmt;
433 sc->sc_rxmits++;
434 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
435 sch->sch_nextc = sc->sc_rxttime;
436 if (docallout)
437 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
438 syncache_timer, (void *)sch);
439 }
440 }
441
442 /*
443 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
444 * If we have retransmitted an entry the maximum number of times, expire it.
445 * One separate timer for each bucket row.
446 */
447 static void
syncache_timer(void * xsch)448 syncache_timer(void *xsch)
449 {
450 struct syncache_head *sch = (struct syncache_head *)xsch;
451 struct syncache *sc, *nsc;
452 int tick = ticks;
453 char *s;
454
455 CURVNET_SET(sch->sch_sc->vnet);
456
457 /* NB: syncache_head has already been locked by the callout. */
458 SCH_LOCK_ASSERT(sch);
459
460 /*
461 * In the following cycle we may remove some entries and/or
462 * advance some timeouts, so re-initialize the bucket timer.
463 */
464 sch->sch_nextc = tick + INT_MAX;
465
466 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
467 /*
468 * We do not check if the listen socket still exists
469 * and accept the case where the listen socket may be
470 * gone by the time we resend the SYN/ACK. We do
471 * not expect this to happens often. If it does,
472 * then the RST will be sent by the time the remote
473 * host does the SYN/ACK->ACK.
474 */
475 if (TSTMP_GT(sc->sc_rxttime, tick)) {
476 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
477 sch->sch_nextc = sc->sc_rxttime;
478 continue;
479 }
480 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
481 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
482 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
483 "giving up and removing syncache entry\n",
484 s, __func__);
485 free(s, M_TCPLOG);
486 }
487 syncache_drop(sc, sch);
488 TCPSTAT_INC(tcps_sc_stale);
489 continue;
490 }
491 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
492 log(LOG_DEBUG, "%s; %s: Response timeout, "
493 "retransmitting (%u) SYN|ACK\n",
494 s, __func__, sc->sc_rxmits);
495 free(s, M_TCPLOG);
496 }
497
498 syncache_respond(sc, sch, NULL, TH_SYN|TH_ACK);
499 TCPSTAT_INC(tcps_sc_retransmitted);
500 syncache_timeout(sc, sch, 0);
501 }
502 if (!TAILQ_EMPTY(&(sch)->sch_bucket))
503 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
504 syncache_timer, (void *)(sch));
505 CURVNET_RESTORE();
506 }
507
508 /*
509 * Find an entry in the syncache.
510 * Returns always with locked syncache_head plus a matching entry or NULL.
511 */
512 static struct syncache *
syncache_lookup(struct in_conninfo * inc,struct syncache_head ** schp)513 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
514 {
515 struct syncache *sc;
516 struct syncache_head *sch;
517 uint32_t hash;
518
519 /*
520 * The hash is built on foreign port + local port + foreign address.
521 * We rely on the fact that struct in_conninfo starts with 16 bits
522 * of foreign port, then 16 bits of local port then followed by 128
523 * bits of foreign address. In case of IPv4 address, the first 3
524 * 32-bit words of the address always are zeroes.
525 */
526 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5,
527 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask;
528
529 sch = &V_tcp_syncache.hashbase[hash];
530 *schp = sch;
531 SCH_LOCK(sch);
532
533 /* Circle through bucket row to find matching entry. */
534 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash)
535 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie,
536 sizeof(struct in_endpoints)) == 0)
537 break;
538
539 return (sc); /* Always returns with locked sch. */
540 }
541
542 /*
543 * This function is called when we get a RST for a
544 * non-existent connection, so that we can see if the
545 * connection is in the syn cache. If it is, zap it.
546 * If required send a challenge ACK.
547 */
548 void
syncache_chkrst(struct in_conninfo * inc,struct tcphdr * th,struct mbuf * m)549 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, struct mbuf *m)
550 {
551 struct syncache *sc;
552 struct syncache_head *sch;
553 char *s = NULL;
554
555 sc = syncache_lookup(inc, &sch); /* returns locked sch */
556 SCH_LOCK_ASSERT(sch);
557
558 /*
559 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags.
560 * See RFC 793 page 65, section SEGMENT ARRIVES.
561 */
562 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) {
563 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
564 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or "
565 "FIN flag set, segment ignored\n", s, __func__);
566 TCPSTAT_INC(tcps_badrst);
567 goto done;
568 }
569
570 /*
571 * No corresponding connection was found in syncache.
572 * If syncookies are enabled and possibly exclusively
573 * used, or we are under memory pressure, a valid RST
574 * may not find a syncache entry. In that case we're
575 * done and no SYN|ACK retransmissions will happen.
576 * Otherwise the RST was misdirected or spoofed.
577 */
578 if (sc == NULL) {
579 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
580 log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
581 "syncache entry (possibly syncookie only), "
582 "segment ignored\n", s, __func__);
583 TCPSTAT_INC(tcps_badrst);
584 goto done;
585 }
586
587 /*
588 * If the RST bit is set, check the sequence number to see
589 * if this is a valid reset segment.
590 *
591 * RFC 793 page 37:
592 * In all states except SYN-SENT, all reset (RST) segments
593 * are validated by checking their SEQ-fields. A reset is
594 * valid if its sequence number is in the window.
595 *
596 * RFC 793 page 69:
597 * There are four cases for the acceptability test for an incoming
598 * segment:
599 *
600 * Segment Receive Test
601 * Length Window
602 * ------- ------- -------------------------------------------
603 * 0 0 SEG.SEQ = RCV.NXT
604 * 0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND
605 * >0 0 not acceptable
606 * >0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND
607 * or RCV.NXT =< SEG.SEQ+SEG.LEN-1 < RCV.NXT+RCV.WND
608 *
609 * Note that when receiving a SYN segment in the LISTEN state,
610 * IRS is set to SEG.SEQ and RCV.NXT is set to SEG.SEQ+1, as
611 * described in RFC 793, page 66.
612 */
613 if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) &&
614 SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) ||
615 (sc->sc_wnd == 0 && th->th_seq == sc->sc_irs + 1)) {
616 if (V_tcp_insecure_rst ||
617 th->th_seq == sc->sc_irs + 1) {
618 syncache_drop(sc, sch);
619 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
620 log(LOG_DEBUG,
621 "%s; %s: Our SYN|ACK was rejected, "
622 "connection attempt aborted by remote "
623 "endpoint\n",
624 s, __func__);
625 TCPSTAT_INC(tcps_sc_reset);
626 } else {
627 TCPSTAT_INC(tcps_badrst);
628 /* Send challenge ACK. */
629 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
630 log(LOG_DEBUG, "%s; %s: RST with invalid "
631 " SEQ %u != NXT %u (+WND %u), "
632 "sending challenge ACK\n",
633 s, __func__,
634 th->th_seq, sc->sc_irs + 1, sc->sc_wnd);
635 syncache_respond(sc, sch, m, TH_ACK);
636 }
637 } else {
638 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
639 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
640 "NXT %u (+WND %u), segment ignored\n",
641 s, __func__,
642 th->th_seq, sc->sc_irs + 1, sc->sc_wnd);
643 TCPSTAT_INC(tcps_badrst);
644 }
645
646 done:
647 if (s != NULL)
648 free(s, M_TCPLOG);
649 SCH_UNLOCK(sch);
650 }
651
652 void
syncache_badack(struct in_conninfo * inc)653 syncache_badack(struct in_conninfo *inc)
654 {
655 struct syncache *sc;
656 struct syncache_head *sch;
657
658 sc = syncache_lookup(inc, &sch); /* returns locked sch */
659 SCH_LOCK_ASSERT(sch);
660 if (sc != NULL) {
661 syncache_drop(sc, sch);
662 TCPSTAT_INC(tcps_sc_badack);
663 }
664 SCH_UNLOCK(sch);
665 }
666
667 void
syncache_unreach(struct in_conninfo * inc,tcp_seq th_seq)668 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq)
669 {
670 struct syncache *sc;
671 struct syncache_head *sch;
672
673 sc = syncache_lookup(inc, &sch); /* returns locked sch */
674 SCH_LOCK_ASSERT(sch);
675 if (sc == NULL)
676 goto done;
677
678 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
679 if (ntohl(th_seq) != sc->sc_iss)
680 goto done;
681
682 /*
683 * If we've rertransmitted 3 times and this is our second error,
684 * we remove the entry. Otherwise, we allow it to continue on.
685 * This prevents us from incorrectly nuking an entry during a
686 * spurious network outage.
687 *
688 * See tcp_notify().
689 */
690 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
691 sc->sc_flags |= SCF_UNREACH;
692 goto done;
693 }
694 syncache_drop(sc, sch);
695 TCPSTAT_INC(tcps_sc_unreach);
696 done:
697 SCH_UNLOCK(sch);
698 }
699
700 /*
701 * Build a new TCP socket structure from a syncache entry.
702 *
703 * On success return the newly created socket with its underlying inp locked.
704 */
705 static struct socket *
syncache_socket(struct syncache * sc,struct socket * lso,struct mbuf * m)706 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
707 {
708 struct tcp_function_block *blk;
709 struct inpcb *inp = NULL;
710 struct socket *so;
711 struct tcpcb *tp;
712 int error;
713 char *s;
714
715 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
716
717 /*
718 * Ok, create the full blown connection, and set things up
719 * as they would have been set up if we had created the
720 * connection when the SYN arrived. If we can't create
721 * the connection, abort it.
722 */
723 so = sonewconn(lso, 0);
724 if (so == NULL) {
725 /*
726 * Drop the connection; we will either send a RST or
727 * have the peer retransmit its SYN again after its
728 * RTO and try again.
729 */
730 TCPSTAT_INC(tcps_listendrop);
731 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
732 log(LOG_DEBUG, "%s; %s: Socket create failed "
733 "due to limits or memory shortage\n",
734 s, __func__);
735 free(s, M_TCPLOG);
736 }
737 goto abort2;
738 }
739 #ifdef MAC
740 mac_socketpeer_set_from_mbuf(m, so);
741 #endif
742
743 inp = sotoinpcb(so);
744 inp->inp_inc.inc_fibnum = so->so_fibnum;
745 INP_WLOCK(inp);
746 /*
747 * Exclusive pcbinfo lock is not required in syncache socket case even
748 * if two inpcb locks can be acquired simultaneously:
749 * - the inpcb in LISTEN state,
750 * - the newly created inp.
751 *
752 * In this case, an inp cannot be at same time in LISTEN state and
753 * just created by an accept() call.
754 */
755 INP_HASH_WLOCK(&V_tcbinfo);
756
757 /* Insert new socket into PCB hash list. */
758 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
759 #ifdef INET6
760 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
761 inp->inp_vflag &= ~INP_IPV4;
762 inp->inp_vflag |= INP_IPV6;
763 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
764 } else {
765 inp->inp_vflag &= ~INP_IPV6;
766 inp->inp_vflag |= INP_IPV4;
767 #endif
768 inp->inp_laddr = sc->sc_inc.inc_laddr;
769 #ifdef INET6
770 }
771 #endif
772
773 /*
774 * If there's an mbuf and it has a flowid, then let's initialise the
775 * inp with that particular flowid.
776 */
777 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) {
778 inp->inp_flowid = m->m_pkthdr.flowid;
779 inp->inp_flowtype = M_HASHTYPE_GET(m);
780 }
781
782 /*
783 * Install in the reservation hash table for now, but don't yet
784 * install a connection group since the full 4-tuple isn't yet
785 * configured.
786 */
787 inp->inp_lport = sc->sc_inc.inc_lport;
788 if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) {
789 /*
790 * Undo the assignments above if we failed to
791 * put the PCB on the hash lists.
792 */
793 #ifdef INET6
794 if (sc->sc_inc.inc_flags & INC_ISIPV6)
795 inp->in6p_laddr = in6addr_any;
796 else
797 #endif
798 inp->inp_laddr.s_addr = INADDR_ANY;
799 inp->inp_lport = 0;
800 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
801 log(LOG_DEBUG, "%s; %s: in_pcbinshash failed "
802 "with error %i\n",
803 s, __func__, error);
804 free(s, M_TCPLOG);
805 }
806 INP_HASH_WUNLOCK(&V_tcbinfo);
807 goto abort;
808 }
809 #ifdef INET6
810 if (inp->inp_vflag & INP_IPV6PROTO) {
811 struct inpcb *oinp = sotoinpcb(lso);
812
813 /*
814 * Inherit socket options from the listening socket.
815 * Note that in6p_inputopts are not (and should not be)
816 * copied, since it stores previously received options and is
817 * used to detect if each new option is different than the
818 * previous one and hence should be passed to a user.
819 * If we copied in6p_inputopts, a user would not be able to
820 * receive options just after calling the accept system call.
821 */
822 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
823 if (oinp->in6p_outputopts)
824 inp->in6p_outputopts =
825 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
826 }
827
828 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
829 struct in6_addr laddr6;
830 struct sockaddr_in6 sin6;
831
832 sin6.sin6_family = AF_INET6;
833 sin6.sin6_len = sizeof(sin6);
834 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
835 sin6.sin6_port = sc->sc_inc.inc_fport;
836 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
837 laddr6 = inp->in6p_laddr;
838 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
839 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
840 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6,
841 thread0.td_ucred, m)) != 0) {
842 inp->in6p_laddr = laddr6;
843 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
844 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed "
845 "with error %i\n",
846 s, __func__, error);
847 free(s, M_TCPLOG);
848 }
849 INP_HASH_WUNLOCK(&V_tcbinfo);
850 goto abort;
851 }
852 /* Override flowlabel from in6_pcbconnect. */
853 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
854 inp->inp_flow |= sc->sc_flowlabel;
855 }
856 #endif /* INET6 */
857 #if defined(INET) && defined(INET6)
858 else
859 #endif
860 #ifdef INET
861 {
862 struct in_addr laddr;
863 struct sockaddr_in sin;
864
865 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
866
867 if (inp->inp_options == NULL) {
868 inp->inp_options = sc->sc_ipopts;
869 sc->sc_ipopts = NULL;
870 }
871
872 sin.sin_family = AF_INET;
873 sin.sin_len = sizeof(sin);
874 sin.sin_addr = sc->sc_inc.inc_faddr;
875 sin.sin_port = sc->sc_inc.inc_fport;
876 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
877 laddr = inp->inp_laddr;
878 if (inp->inp_laddr.s_addr == INADDR_ANY)
879 inp->inp_laddr = sc->sc_inc.inc_laddr;
880 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin,
881 thread0.td_ucred, m)) != 0) {
882 inp->inp_laddr = laddr;
883 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
884 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed "
885 "with error %i\n",
886 s, __func__, error);
887 free(s, M_TCPLOG);
888 }
889 INP_HASH_WUNLOCK(&V_tcbinfo);
890 goto abort;
891 }
892 }
893 #endif /* INET */
894 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
895 /* Copy old policy into new socket's. */
896 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0)
897 printf("syncache_socket: could not copy policy\n");
898 #endif
899 INP_HASH_WUNLOCK(&V_tcbinfo);
900 tp = intotcpcb(inp);
901 tcp_state_change(tp, TCPS_SYN_RECEIVED);
902 tp->iss = sc->sc_iss;
903 tp->irs = sc->sc_irs;
904 tcp_rcvseqinit(tp);
905 tcp_sendseqinit(tp);
906 blk = sototcpcb(lso)->t_fb;
907 if (V_functions_inherit_listen_socket_stack && blk != tp->t_fb) {
908 /*
909 * Our parents t_fb was not the default,
910 * we need to release our ref on tp->t_fb and
911 * pickup one on the new entry.
912 */
913 struct tcp_function_block *rblk;
914
915 rblk = find_and_ref_tcp_fb(blk);
916 KASSERT(rblk != NULL,
917 ("cannot find blk %p out of syncache?", blk));
918 if (tp->t_fb->tfb_tcp_fb_fini)
919 (*tp->t_fb->tfb_tcp_fb_fini)(tp, 0);
920 refcount_release(&tp->t_fb->tfb_refcnt);
921 tp->t_fb = rblk;
922 /*
923 * XXXrrs this is quite dangerous, it is possible
924 * for the new function to fail to init. We also
925 * are not asking if the handoff_is_ok though at
926 * the very start thats probalbly ok.
927 */
928 if (tp->t_fb->tfb_tcp_fb_init) {
929 (*tp->t_fb->tfb_tcp_fb_init)(tp);
930 }
931 }
932 tp->snd_wl1 = sc->sc_irs;
933 tp->snd_max = tp->iss + 1;
934 tp->snd_nxt = tp->iss + 1;
935 tp->rcv_up = sc->sc_irs + 1;
936 tp->rcv_wnd = sc->sc_wnd;
937 tp->rcv_adv += tp->rcv_wnd;
938 tp->last_ack_sent = tp->rcv_nxt;
939
940 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
941 if (sc->sc_flags & SCF_NOOPT)
942 tp->t_flags |= TF_NOOPT;
943 else {
944 if (sc->sc_flags & SCF_WINSCALE) {
945 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
946 tp->snd_scale = sc->sc_requested_s_scale;
947 tp->request_r_scale = sc->sc_requested_r_scale;
948 }
949 if (sc->sc_flags & SCF_TIMESTAMP) {
950 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
951 tp->ts_recent = sc->sc_tsreflect;
952 tp->ts_recent_age = tcp_ts_getticks();
953 tp->ts_offset = sc->sc_tsoff;
954 }
955 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
956 if (sc->sc_flags & SCF_SIGNATURE)
957 tp->t_flags |= TF_SIGNATURE;
958 #endif
959 if (sc->sc_flags & SCF_SACK)
960 tp->t_flags |= TF_SACK_PERMIT;
961 }
962
963 if (sc->sc_flags & SCF_ECN)
964 tp->t_flags |= TF_ECN_PERMIT;
965
966 /*
967 * Set up MSS and get cached values from tcp_hostcache.
968 * This might overwrite some of the defaults we just set.
969 */
970 tcp_mss(tp, sc->sc_peer_mss);
971
972 /*
973 * If the SYN,ACK was retransmitted, indicate that CWND to be
974 * limited to one segment in cc_conn_init().
975 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
976 */
977 if (sc->sc_rxmits > 1)
978 tp->snd_cwnd = 1;
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 /*
993 * Copy and activate timers.
994 */
995 tp->t_keepinit = sototcpcb(lso)->t_keepinit;
996 tp->t_keepidle = sototcpcb(lso)->t_keepidle;
997 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl;
998 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt;
999 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp));
1000
1001 TCPSTAT_INC(tcps_accepts);
1002 return (so);
1003
1004 abort:
1005 INP_WUNLOCK(inp);
1006 abort2:
1007 if (so != NULL)
1008 soabort(so);
1009 return (NULL);
1010 }
1011
1012 /*
1013 * This function gets called when we receive an ACK for a
1014 * socket in the LISTEN state. We look up the connection
1015 * in the syncache, and if its there, we pull it out of
1016 * the cache and turn it into a full-blown connection in
1017 * the SYN-RECEIVED state.
1018 *
1019 * On syncache_socket() success the newly created socket
1020 * has its underlying inp locked.
1021 */
1022 int
syncache_expand(struct in_conninfo * inc,struct tcpopt * to,struct tcphdr * th,struct socket ** lsop,struct mbuf * m)1023 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1024 struct socket **lsop, struct mbuf *m)
1025 {
1026 struct syncache *sc;
1027 struct syncache_head *sch;
1028 struct syncache scs;
1029 char *s;
1030
1031 /*
1032 * Global TCP locks are held because we manipulate the PCB lists
1033 * and create a new socket.
1034 */
1035 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
1036 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
1037 ("%s: can handle only ACK", __func__));
1038
1039 sc = syncache_lookup(inc, &sch); /* returns locked sch */
1040 SCH_LOCK_ASSERT(sch);
1041
1042 #ifdef INVARIANTS
1043 /*
1044 * Test code for syncookies comparing the syncache stored
1045 * values with the reconstructed values from the cookie.
1046 */
1047 if (sc != NULL)
1048 syncookie_cmp(inc, sch, sc, th, to, *lsop);
1049 #endif
1050
1051 if (sc == NULL) {
1052 /*
1053 * There is no syncache entry, so see if this ACK is
1054 * a returning syncookie. To do this, first:
1055 * A. Check if syncookies are used in case of syncache
1056 * overflows
1057 * B. See if this socket has had a syncache entry dropped in
1058 * the recent past. We don't want to accept a bogus
1059 * syncookie if we've never received a SYN or accept it
1060 * twice.
1061 * C. check that the syncookie is valid. If it is, then
1062 * cobble up a fake syncache entry, and return.
1063 */
1064 if (!V_tcp_syncookies) {
1065 SCH_UNLOCK(sch);
1066 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1067 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
1068 "segment rejected (syncookies disabled)\n",
1069 s, __func__);
1070 goto failed;
1071 }
1072 if (!V_tcp_syncookiesonly &&
1073 sch->sch_last_overflow < time_uptime - SYNCOOKIE_LIFETIME) {
1074 SCH_UNLOCK(sch);
1075 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1076 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
1077 "segment rejected (no syncache entry)\n",
1078 s, __func__);
1079 goto failed;
1080 }
1081 bzero(&scs, sizeof(scs));
1082 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop);
1083 SCH_UNLOCK(sch);
1084 if (sc == NULL) {
1085 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1086 log(LOG_DEBUG, "%s; %s: Segment failed "
1087 "SYNCOOKIE authentication, segment rejected "
1088 "(probably spoofed)\n", s, __func__);
1089 goto failed;
1090 }
1091 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1092 /* If received ACK has MD5 signature, check it. */
1093 if ((to->to_flags & TOF_SIGNATURE) != 0 &&
1094 (!TCPMD5_ENABLED() ||
1095 TCPMD5_INPUT(m, th, to->to_signature) != 0)) {
1096 /* Drop the ACK. */
1097 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1098 log(LOG_DEBUG, "%s; %s: Segment rejected, "
1099 "MD5 signature doesn't match.\n",
1100 s, __func__);
1101 free(s, M_TCPLOG);
1102 }
1103 TCPSTAT_INC(tcps_sig_err_sigopt);
1104 return (-1); /* Do not send RST */
1105 }
1106 #endif /* TCP_SIGNATURE */
1107 } else {
1108 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1109 /*
1110 * If listening socket requested TCP digests, check that
1111 * received ACK has signature and it is correct.
1112 * If not, drop the ACK and leave sc entry in th cache,
1113 * because SYN was received with correct signature.
1114 */
1115 if (sc->sc_flags & SCF_SIGNATURE) {
1116 if ((to->to_flags & TOF_SIGNATURE) == 0) {
1117 /* No signature */
1118 TCPSTAT_INC(tcps_sig_err_nosigopt);
1119 SCH_UNLOCK(sch);
1120 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1121 log(LOG_DEBUG, "%s; %s: Segment "
1122 "rejected, MD5 signature wasn't "
1123 "provided.\n", s, __func__);
1124 free(s, M_TCPLOG);
1125 }
1126 return (-1); /* Do not send RST */
1127 }
1128 if (!TCPMD5_ENABLED() ||
1129 TCPMD5_INPUT(m, th, to->to_signature) != 0) {
1130 /* Doesn't match or no SA */
1131 SCH_UNLOCK(sch);
1132 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1133 log(LOG_DEBUG, "%s; %s: Segment "
1134 "rejected, MD5 signature doesn't "
1135 "match.\n", s, __func__);
1136 free(s, M_TCPLOG);
1137 }
1138 return (-1); /* Do not send RST */
1139 }
1140 }
1141 #endif /* TCP_SIGNATURE */
1142
1143 /*
1144 * RFC 7323 PAWS: If we have a timestamp on this segment and
1145 * it's less than ts_recent, drop it.
1146 * XXXMT: RFC 7323 also requires to send an ACK.
1147 * In tcp_input.c this is only done for TCP segments
1148 * with user data, so be consistent here and just drop
1149 * the segment.
1150 */
1151 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS &&
1152 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) {
1153 SCH_UNLOCK(sch);
1154 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1155 log(LOG_DEBUG,
1156 "%s; %s: SEG.TSval %u < TS.Recent %u, "
1157 "segment dropped\n", s, __func__,
1158 to->to_tsval, sc->sc_tsreflect);
1159 free(s, M_TCPLOG);
1160 }
1161 return (-1); /* Do not send RST */
1162 }
1163
1164 /*
1165 * Pull out the entry to unlock the bucket row.
1166 *
1167 * NOTE: We must decrease TCPS_SYN_RECEIVED count here, not
1168 * tcp_state_change(). The tcpcb is not existent at this
1169 * moment. A new one will be allocated via syncache_socket->
1170 * sonewconn->tcp_usr_attach in TCPS_CLOSED state, then
1171 * syncache_socket() will change it to TCPS_SYN_RECEIVED.
1172 */
1173 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
1174 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
1175 sch->sch_length--;
1176 #ifdef TCP_OFFLOAD
1177 if (ADDED_BY_TOE(sc)) {
1178 struct toedev *tod = sc->sc_tod;
1179
1180 tod->tod_syncache_removed(tod, sc->sc_todctx);
1181 }
1182 #endif
1183 SCH_UNLOCK(sch);
1184 }
1185
1186 /*
1187 * Segment validation:
1188 * ACK must match our initial sequence number + 1 (the SYN|ACK).
1189 */
1190 if (th->th_ack != sc->sc_iss + 1) {
1191 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1192 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
1193 "rejected\n", s, __func__, th->th_ack, sc->sc_iss);
1194 goto failed;
1195 }
1196
1197 /*
1198 * The SEQ must fall in the window starting at the received
1199 * initial receive sequence number + 1 (the SYN).
1200 */
1201 if (SEQ_LEQ(th->th_seq, sc->sc_irs) ||
1202 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
1203 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1204 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
1205 "rejected\n", s, __func__, th->th_seq, sc->sc_irs);
1206 goto failed;
1207 }
1208
1209 /*
1210 * If timestamps were not negotiated during SYN/ACK they
1211 * must not appear on any segment during this session.
1212 */
1213 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) {
1214 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1215 log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
1216 "segment rejected\n", s, __func__);
1217 goto failed;
1218 }
1219
1220 /*
1221 * If timestamps were negotiated during SYN/ACK they should
1222 * appear on every segment during this session.
1223 * XXXAO: This is only informal as there have been unverified
1224 * reports of non-compliants stacks.
1225 */
1226 if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) {
1227 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1228 log(LOG_DEBUG, "%s; %s: Timestamp missing, "
1229 "no action\n", s, __func__);
1230 free(s, M_TCPLOG);
1231 s = NULL;
1232 }
1233 }
1234
1235 *lsop = syncache_socket(sc, *lsop, m);
1236
1237 if (*lsop == NULL)
1238 TCPSTAT_INC(tcps_sc_aborted);
1239 else
1240 TCPSTAT_INC(tcps_sc_completed);
1241
1242 /* how do we find the inp for the new socket? */
1243 if (sc != &scs)
1244 syncache_free(sc);
1245 return (1);
1246 failed:
1247 if (sc != NULL && sc != &scs)
1248 syncache_free(sc);
1249 if (s != NULL)
1250 free(s, M_TCPLOG);
1251 *lsop = NULL;
1252 return (0);
1253 }
1254
1255 static void
syncache_tfo_expand(struct syncache * sc,struct socket ** lsop,struct mbuf * m,uint64_t response_cookie)1256 syncache_tfo_expand(struct syncache *sc, struct socket **lsop, struct mbuf *m,
1257 uint64_t response_cookie)
1258 {
1259 struct inpcb *inp;
1260 struct tcpcb *tp;
1261 unsigned int *pending_counter;
1262
1263 /*
1264 * Global TCP locks are held because we manipulate the PCB lists
1265 * and create a new socket.
1266 */
1267 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
1268
1269 pending_counter = intotcpcb(sotoinpcb(*lsop))->t_tfo_pending;
1270 *lsop = syncache_socket(sc, *lsop, m);
1271 if (*lsop == NULL) {
1272 TCPSTAT_INC(tcps_sc_aborted);
1273 atomic_subtract_int(pending_counter, 1);
1274 } else {
1275 soisconnected(*lsop);
1276 inp = sotoinpcb(*lsop);
1277 tp = intotcpcb(inp);
1278 tp->t_flags |= TF_FASTOPEN;
1279 tp->t_tfo_cookie.server = response_cookie;
1280 tp->snd_max = tp->iss;
1281 tp->snd_nxt = tp->iss;
1282 tp->t_tfo_pending = pending_counter;
1283 TCPSTAT_INC(tcps_sc_completed);
1284 }
1285 }
1286
1287 /*
1288 * Given a LISTEN socket and an inbound SYN request, add
1289 * this to the syn cache, and send back a segment:
1290 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
1291 * to the source.
1292 *
1293 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
1294 * Doing so would require that we hold onto the data and deliver it
1295 * to the application. However, if we are the target of a SYN-flood
1296 * DoS attack, an attacker could send data which would eventually
1297 * consume all available buffer space if it were ACKed. By not ACKing
1298 * the data, we avoid this DoS scenario.
1299 *
1300 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO)
1301 * cookie is processed and a new socket is created. In this case, any data
1302 * accompanying the SYN will be queued to the socket by tcp_input() and will
1303 * be ACKed either when the application sends response data or the delayed
1304 * ACK timer expires, whichever comes first.
1305 */
1306 int
syncache_add(struct in_conninfo * inc,struct tcpopt * to,struct tcphdr * th,struct inpcb * inp,struct socket ** lsop,struct mbuf * m,void * tod,void * todctx)1307 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1308 struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod,
1309 void *todctx)
1310 {
1311 struct tcpcb *tp;
1312 struct socket *so;
1313 struct syncache *sc = NULL;
1314 struct syncache_head *sch;
1315 struct mbuf *ipopts = NULL;
1316 u_int ltflags;
1317 int win, ip_ttl, ip_tos;
1318 char *s;
1319 int rv = 0;
1320 #ifdef INET6
1321 int autoflowlabel = 0;
1322 #endif
1323 #ifdef MAC
1324 struct label *maclabel;
1325 #endif
1326 struct syncache scs;
1327 struct ucred *cred;
1328 uint64_t tfo_response_cookie;
1329 unsigned int *tfo_pending = NULL;
1330 int tfo_cookie_valid = 0;
1331 int tfo_response_cookie_valid = 0;
1332
1333 INP_WLOCK_ASSERT(inp); /* listen socket */
1334 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
1335 ("%s: unexpected tcp flags", __func__));
1336
1337 /*
1338 * Combine all so/tp operations very early to drop the INP lock as
1339 * soon as possible.
1340 */
1341 so = *lsop;
1342 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so));
1343 tp = sototcpcb(so);
1344 cred = crhold(so->so_cred);
1345
1346 #ifdef INET6
1347 if ((inc->inc_flags & INC_ISIPV6) &&
1348 (inp->inp_flags & IN6P_AUTOFLOWLABEL))
1349 autoflowlabel = 1;
1350 #endif
1351 ip_ttl = inp->inp_ip_ttl;
1352 ip_tos = inp->inp_ip_tos;
1353 win = so->sol_sbrcv_hiwat;
1354 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE));
1355
1356 if (V_tcp_fastopen_server_enable && IS_FASTOPEN(tp->t_flags) &&
1357 (tp->t_tfo_pending != NULL) &&
1358 (to->to_flags & TOF_FASTOPEN)) {
1359 /*
1360 * Limit the number of pending TFO connections to
1361 * approximately half of the queue limit. This prevents TFO
1362 * SYN floods from starving the service by filling the
1363 * listen queue with bogus TFO connections.
1364 */
1365 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <=
1366 (so->sol_qlimit / 2)) {
1367 int result;
1368
1369 result = tcp_fastopen_check_cookie(inc,
1370 to->to_tfo_cookie, to->to_tfo_len,
1371 &tfo_response_cookie);
1372 tfo_cookie_valid = (result > 0);
1373 tfo_response_cookie_valid = (result >= 0);
1374 }
1375
1376 /*
1377 * Remember the TFO pending counter as it will have to be
1378 * decremented below if we don't make it to syncache_tfo_expand().
1379 */
1380 tfo_pending = tp->t_tfo_pending;
1381 }
1382
1383 /* By the time we drop the lock these should no longer be used. */
1384 so = NULL;
1385 tp = NULL;
1386
1387 #ifdef MAC
1388 if (mac_syncache_init(&maclabel) != 0) {
1389 INP_WUNLOCK(inp);
1390 goto done;
1391 } else
1392 mac_syncache_create(maclabel, inp);
1393 #endif
1394 if (!tfo_cookie_valid)
1395 INP_WUNLOCK(inp);
1396
1397 /*
1398 * Remember the IP options, if any.
1399 */
1400 #ifdef INET6
1401 if (!(inc->inc_flags & INC_ISIPV6))
1402 #endif
1403 #ifdef INET
1404 ipopts = (m) ? ip_srcroute(m) : NULL;
1405 #else
1406 ipopts = NULL;
1407 #endif
1408
1409 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1410 /*
1411 * If listening socket requested TCP digests, check that received
1412 * SYN has signature and it is correct. If signature doesn't match
1413 * or TCP_SIGNATURE support isn't enabled, drop the packet.
1414 */
1415 if (ltflags & TF_SIGNATURE) {
1416 if ((to->to_flags & TOF_SIGNATURE) == 0) {
1417 TCPSTAT_INC(tcps_sig_err_nosigopt);
1418 goto done;
1419 }
1420 if (!TCPMD5_ENABLED() ||
1421 TCPMD5_INPUT(m, th, to->to_signature) != 0)
1422 goto done;
1423 }
1424 #endif /* TCP_SIGNATURE */
1425 /*
1426 * See if we already have an entry for this connection.
1427 * If we do, resend the SYN,ACK, and reset the retransmit timer.
1428 *
1429 * XXX: should the syncache be re-initialized with the contents
1430 * of the new SYN here (which may have different options?)
1431 *
1432 * XXX: We do not check the sequence number to see if this is a
1433 * real retransmit or a new connection attempt. The question is
1434 * how to handle such a case; either ignore it as spoofed, or
1435 * drop the current entry and create a new one?
1436 */
1437 sc = syncache_lookup(inc, &sch); /* returns locked entry */
1438 SCH_LOCK_ASSERT(sch);
1439 if (sc != NULL) {
1440 if (tfo_cookie_valid)
1441 INP_WUNLOCK(inp);
1442 TCPSTAT_INC(tcps_sc_dupsyn);
1443 if (ipopts) {
1444 /*
1445 * If we were remembering a previous source route,
1446 * forget it and use the new one we've been given.
1447 */
1448 if (sc->sc_ipopts)
1449 (void) m_free(sc->sc_ipopts);
1450 sc->sc_ipopts = ipopts;
1451 }
1452 /*
1453 * Update timestamp if present.
1454 */
1455 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
1456 sc->sc_tsreflect = to->to_tsval;
1457 else
1458 sc->sc_flags &= ~SCF_TIMESTAMP;
1459 #ifdef MAC
1460 /*
1461 * Since we have already unconditionally allocated label
1462 * storage, free it up. The syncache entry will already
1463 * have an initialized label we can use.
1464 */
1465 mac_syncache_destroy(&maclabel);
1466 #endif
1467 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1468 /* Retransmit SYN|ACK and reset retransmit count. */
1469 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
1470 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
1471 "resetting timer and retransmitting SYN|ACK\n",
1472 s, __func__);
1473 free(s, M_TCPLOG);
1474 }
1475 if (syncache_respond(sc, sch, m, TH_SYN|TH_ACK) == 0) {
1476 sc->sc_rxmits = 0;
1477 syncache_timeout(sc, sch, 1);
1478 TCPSTAT_INC(tcps_sndacks);
1479 TCPSTAT_INC(tcps_sndtotal);
1480 }
1481 SCH_UNLOCK(sch);
1482 goto donenoprobe;
1483 }
1484
1485 if (tfo_cookie_valid) {
1486 bzero(&scs, sizeof(scs));
1487 sc = &scs;
1488 goto skip_alloc;
1489 }
1490
1491 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1492 if (sc == NULL) {
1493 /*
1494 * The zone allocator couldn't provide more entries.
1495 * Treat this as if the cache was full; drop the oldest
1496 * entry and insert the new one.
1497 */
1498 TCPSTAT_INC(tcps_sc_zonefail);
1499 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) {
1500 sch->sch_last_overflow = time_uptime;
1501 syncache_drop(sc, sch);
1502 }
1503 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1504 if (sc == NULL) {
1505 if (V_tcp_syncookies) {
1506 bzero(&scs, sizeof(scs));
1507 sc = &scs;
1508 } else {
1509 SCH_UNLOCK(sch);
1510 if (ipopts)
1511 (void) m_free(ipopts);
1512 goto done;
1513 }
1514 }
1515 }
1516
1517 skip_alloc:
1518 if (!tfo_cookie_valid && tfo_response_cookie_valid)
1519 sc->sc_tfo_cookie = &tfo_response_cookie;
1520
1521 /*
1522 * Fill in the syncache values.
1523 */
1524 #ifdef MAC
1525 sc->sc_label = maclabel;
1526 #endif
1527 sc->sc_cred = cred;
1528 cred = NULL;
1529 sc->sc_ipopts = ipopts;
1530 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1531 #ifdef INET6
1532 if (!(inc->inc_flags & INC_ISIPV6))
1533 #endif
1534 {
1535 sc->sc_ip_tos = ip_tos;
1536 sc->sc_ip_ttl = ip_ttl;
1537 }
1538 #ifdef TCP_OFFLOAD
1539 sc->sc_tod = tod;
1540 sc->sc_todctx = todctx;
1541 #endif
1542 sc->sc_irs = th->th_seq;
1543 sc->sc_iss = arc4random();
1544 sc->sc_flags = 0;
1545 sc->sc_flowlabel = 0;
1546
1547 /*
1548 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
1549 * win was derived from socket earlier in the function.
1550 */
1551 win = imax(win, 0);
1552 win = imin(win, TCP_MAXWIN);
1553 sc->sc_wnd = win;
1554
1555 if (V_tcp_do_rfc1323) {
1556 /*
1557 * A timestamp received in a SYN makes
1558 * it ok to send timestamp requests and replies.
1559 */
1560 if (to->to_flags & TOF_TS) {
1561 sc->sc_tsreflect = to->to_tsval;
1562 sc->sc_flags |= SCF_TIMESTAMP;
1563 sc->sc_tsoff = tcp_new_ts_offset(inc);
1564 }
1565 if (to->to_flags & TOF_SCALE) {
1566 int wscale = 0;
1567
1568 /*
1569 * Pick the smallest possible scaling factor that
1570 * will still allow us to scale up to sb_max, aka
1571 * kern.ipc.maxsockbuf.
1572 *
1573 * We do this because there are broken firewalls that
1574 * will corrupt the window scale option, leading to
1575 * the other endpoint believing that our advertised
1576 * window is unscaled. At scale factors larger than
1577 * 5 the unscaled window will drop below 1500 bytes,
1578 * leading to serious problems when traversing these
1579 * broken firewalls.
1580 *
1581 * With the default maxsockbuf of 256K, a scale factor
1582 * of 3 will be chosen by this algorithm. Those who
1583 * choose a larger maxsockbuf should watch out
1584 * for the compatibility problems mentioned above.
1585 *
1586 * RFC1323: The Window field in a SYN (i.e., a <SYN>
1587 * or <SYN,ACK>) segment itself is never scaled.
1588 */
1589 while (wscale < TCP_MAX_WINSHIFT &&
1590 (TCP_MAXWIN << wscale) < sb_max)
1591 wscale++;
1592 sc->sc_requested_r_scale = wscale;
1593 sc->sc_requested_s_scale = to->to_wscale;
1594 sc->sc_flags |= SCF_WINSCALE;
1595 }
1596 }
1597 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1598 /*
1599 * If listening socket requested TCP digests, flag this in the
1600 * syncache so that syncache_respond() will do the right thing
1601 * with the SYN+ACK.
1602 */
1603 if (ltflags & TF_SIGNATURE)
1604 sc->sc_flags |= SCF_SIGNATURE;
1605 #endif /* TCP_SIGNATURE */
1606 if (to->to_flags & TOF_SACKPERM)
1607 sc->sc_flags |= SCF_SACK;
1608 if (to->to_flags & TOF_MSS)
1609 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */
1610 if (ltflags & TF_NOOPT)
1611 sc->sc_flags |= SCF_NOOPT;
1612 if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn)
1613 sc->sc_flags |= SCF_ECN;
1614
1615 if (V_tcp_syncookies)
1616 sc->sc_iss = syncookie_generate(sch, sc);
1617 #ifdef INET6
1618 if (autoflowlabel) {
1619 if (V_tcp_syncookies)
1620 sc->sc_flowlabel = sc->sc_iss;
1621 else
1622 sc->sc_flowlabel = ip6_randomflowlabel();
1623 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK;
1624 }
1625 #endif
1626 SCH_UNLOCK(sch);
1627
1628 if (tfo_cookie_valid) {
1629 syncache_tfo_expand(sc, lsop, m, tfo_response_cookie);
1630 /* INP_WUNLOCK(inp) will be performed by the caller */
1631 rv = 1;
1632 goto tfo_expanded;
1633 }
1634
1635 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1636 /*
1637 * Do a standard 3-way handshake.
1638 */
1639 if (syncache_respond(sc, sch, m, TH_SYN|TH_ACK) == 0) {
1640 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs)
1641 syncache_free(sc);
1642 else if (sc != &scs)
1643 syncache_insert(sc, sch); /* locks and unlocks sch */
1644 TCPSTAT_INC(tcps_sndacks);
1645 TCPSTAT_INC(tcps_sndtotal);
1646 } else {
1647 if (sc != &scs)
1648 syncache_free(sc);
1649 TCPSTAT_INC(tcps_sc_dropped);
1650 }
1651 goto donenoprobe;
1652
1653 done:
1654 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1655 donenoprobe:
1656 if (m) {
1657 *lsop = NULL;
1658 m_freem(m);
1659 }
1660 /*
1661 * If tfo_pending is not NULL here, then a TFO SYN that did not
1662 * result in a new socket was processed and the associated pending
1663 * counter has not yet been decremented. All such TFO processing paths
1664 * transit this point.
1665 */
1666 if (tfo_pending != NULL)
1667 tcp_fastopen_decrement_counter(tfo_pending);
1668
1669 tfo_expanded:
1670 if (cred != NULL)
1671 crfree(cred);
1672 #ifdef MAC
1673 if (sc == &scs)
1674 mac_syncache_destroy(&maclabel);
1675 #endif
1676 return (rv);
1677 }
1678
1679 /*
1680 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment,
1681 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL.
1682 */
1683 static int
syncache_respond(struct syncache * sc,struct syncache_head * sch,const struct mbuf * m0,int flags)1684 syncache_respond(struct syncache *sc, struct syncache_head *sch,
1685 const struct mbuf *m0, int flags)
1686 {
1687 struct ip *ip = NULL;
1688 struct mbuf *m;
1689 struct tcphdr *th = NULL;
1690 int optlen, error = 0; /* Make compiler happy */
1691 u_int16_t hlen, tlen, mssopt;
1692 struct tcpopt to;
1693 #ifdef INET6
1694 struct ip6_hdr *ip6 = NULL;
1695 #endif
1696 hlen =
1697 #ifdef INET6
1698 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
1699 #endif
1700 sizeof(struct ip);
1701 tlen = hlen + sizeof(struct tcphdr);
1702
1703 /* Determine MSS we advertize to other end of connection. */
1704 mssopt = max(tcp_mssopt(&sc->sc_inc), V_tcp_minmss);
1705
1706 /* XXX: Assume that the entire packet will fit in a header mbuf. */
1707 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
1708 ("syncache: mbuf too small"));
1709
1710 /* Create the IP+TCP header from scratch. */
1711 m = m_gethdr(M_NOWAIT, MT_DATA);
1712 if (m == NULL)
1713 return (ENOBUFS);
1714 #ifdef MAC
1715 mac_syncache_create_mbuf(sc->sc_label, m);
1716 #endif
1717 m->m_data += max_linkhdr;
1718 m->m_len = tlen;
1719 m->m_pkthdr.len = tlen;
1720 m->m_pkthdr.rcvif = NULL;
1721
1722 #ifdef INET6
1723 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1724 ip6 = mtod(m, struct ip6_hdr *);
1725 ip6->ip6_vfc = IPV6_VERSION;
1726 ip6->ip6_nxt = IPPROTO_TCP;
1727 ip6->ip6_src = sc->sc_inc.inc6_laddr;
1728 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
1729 ip6->ip6_plen = htons(tlen - hlen);
1730 /* ip6_hlim is set after checksum */
1731 /* Zero out traffic class and flow label. */
1732 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK;
1733 ip6->ip6_flow |= sc->sc_flowlabel;
1734
1735 th = (struct tcphdr *)(ip6 + 1);
1736 }
1737 #endif
1738 #if defined(INET6) && defined(INET)
1739 else
1740 #endif
1741 #ifdef INET
1742 {
1743 ip = mtod(m, struct ip *);
1744 ip->ip_v = IPVERSION;
1745 ip->ip_hl = sizeof(struct ip) >> 2;
1746 ip->ip_len = htons(tlen);
1747 ip->ip_id = 0;
1748 ip->ip_off = 0;
1749 ip->ip_sum = 0;
1750 ip->ip_p = IPPROTO_TCP;
1751 ip->ip_src = sc->sc_inc.inc_laddr;
1752 ip->ip_dst = sc->sc_inc.inc_faddr;
1753 ip->ip_ttl = sc->sc_ip_ttl;
1754 ip->ip_tos = sc->sc_ip_tos;
1755
1756 /*
1757 * See if we should do MTU discovery. Route lookups are
1758 * expensive, so we will only unset the DF bit if:
1759 *
1760 * 1) path_mtu_discovery is disabled
1761 * 2) the SCF_UNREACH flag has been set
1762 */
1763 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
1764 ip->ip_off |= htons(IP_DF);
1765
1766 th = (struct tcphdr *)(ip + 1);
1767 }
1768 #endif /* INET */
1769 th->th_sport = sc->sc_inc.inc_lport;
1770 th->th_dport = sc->sc_inc.inc_fport;
1771
1772 if (flags & TH_SYN)
1773 th->th_seq = htonl(sc->sc_iss);
1774 else
1775 th->th_seq = htonl(sc->sc_iss + 1);
1776 th->th_ack = htonl(sc->sc_irs + 1);
1777 th->th_off = sizeof(struct tcphdr) >> 2;
1778 th->th_x2 = 0;
1779 th->th_flags = flags;
1780 th->th_win = htons(sc->sc_wnd);
1781 th->th_urp = 0;
1782
1783 if ((flags & TH_SYN) && (sc->sc_flags & SCF_ECN)) {
1784 th->th_flags |= TH_ECE;
1785 TCPSTAT_INC(tcps_ecn_shs);
1786 }
1787
1788 /* Tack on the TCP options. */
1789 if ((sc->sc_flags & SCF_NOOPT) == 0) {
1790 to.to_flags = 0;
1791
1792 if (flags & TH_SYN) {
1793 to.to_mss = mssopt;
1794 to.to_flags = TOF_MSS;
1795 if (sc->sc_flags & SCF_WINSCALE) {
1796 to.to_wscale = sc->sc_requested_r_scale;
1797 to.to_flags |= TOF_SCALE;
1798 }
1799 if (sc->sc_flags & SCF_SACK)
1800 to.to_flags |= TOF_SACKPERM;
1801 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1802 if (sc->sc_flags & SCF_SIGNATURE)
1803 to.to_flags |= TOF_SIGNATURE;
1804 #endif
1805 if (sc->sc_tfo_cookie) {
1806 to.to_flags |= TOF_FASTOPEN;
1807 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
1808 to.to_tfo_cookie = sc->sc_tfo_cookie;
1809 /* don't send cookie again when retransmitting response */
1810 sc->sc_tfo_cookie = NULL;
1811 }
1812 }
1813 if (sc->sc_flags & SCF_TIMESTAMP) {
1814 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks();
1815 to.to_tsecr = sc->sc_tsreflect;
1816 to.to_flags |= TOF_TS;
1817 }
1818 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
1819
1820 /* Adjust headers by option size. */
1821 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
1822 m->m_len += optlen;
1823 m->m_pkthdr.len += optlen;
1824 #ifdef INET6
1825 if (sc->sc_inc.inc_flags & INC_ISIPV6)
1826 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
1827 else
1828 #endif
1829 ip->ip_len = htons(ntohs(ip->ip_len) + optlen);
1830 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1831 if (sc->sc_flags & SCF_SIGNATURE) {
1832 KASSERT(to.to_flags & TOF_SIGNATURE,
1833 ("tcp_addoptions() didn't set tcp_signature"));
1834
1835 /* NOTE: to.to_signature is inside of mbuf */
1836 if (!TCPMD5_ENABLED() ||
1837 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) {
1838 m_freem(m);
1839 return (EACCES);
1840 }
1841 }
1842 #endif
1843 } else
1844 optlen = 0;
1845
1846 M_SETFIB(m, sc->sc_inc.inc_fibnum);
1847 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1848 /*
1849 * If we have peer's SYN and it has a flowid, then let's assign it to
1850 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid
1851 * to SYN|ACK due to lack of inp here.
1852 */
1853 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) {
1854 m->m_pkthdr.flowid = m0->m_pkthdr.flowid;
1855 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0));
1856 }
1857 #ifdef INET6
1858 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1859 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
1860 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen,
1861 IPPROTO_TCP, 0);
1862 ip6->ip6_hlim = in6_selecthlim(NULL, NULL);
1863 #ifdef TCP_OFFLOAD
1864 if (ADDED_BY_TOE(sc)) {
1865 struct toedev *tod = sc->sc_tod;
1866
1867 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
1868
1869 return (error);
1870 }
1871 #endif
1872 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th);
1873 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
1874 }
1875 #endif
1876 #if defined(INET6) && defined(INET)
1877 else
1878 #endif
1879 #ifdef INET
1880 {
1881 m->m_pkthdr.csum_flags = CSUM_TCP;
1882 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
1883 htons(tlen + optlen - hlen + IPPROTO_TCP));
1884 #ifdef TCP_OFFLOAD
1885 if (ADDED_BY_TOE(sc)) {
1886 struct toedev *tod = sc->sc_tod;
1887
1888 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
1889
1890 return (error);
1891 }
1892 #endif
1893 TCP_PROBE5(send, NULL, NULL, ip, NULL, th);
1894 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
1895 }
1896 #endif
1897 return (error);
1898 }
1899
1900 /*
1901 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks
1902 * that exceed the capacity of the syncache by avoiding the storage of any
1903 * of the SYNs we receive. Syncookies defend against blind SYN flooding
1904 * attacks where the attacker does not have access to our responses.
1905 *
1906 * Syncookies encode and include all necessary information about the
1907 * connection setup within the SYN|ACK that we send back. That way we
1908 * can avoid keeping any local state until the ACK to our SYN|ACK returns
1909 * (if ever). Normally the syncache and syncookies are running in parallel
1910 * with the latter taking over when the former is exhausted. When matching
1911 * syncache entry is found the syncookie is ignored.
1912 *
1913 * The only reliable information persisting the 3WHS is our initial sequence
1914 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient
1915 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS
1916 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK
1917 * returns and signifies a legitimate connection if it matches the ACK.
1918 *
1919 * The available space of 32 bits to store the hash and to encode the SYN
1920 * option information is very tight and we should have at least 24 bits for
1921 * the MAC to keep the number of guesses by blind spoofing reasonably high.
1922 *
1923 * SYN option information we have to encode to fully restore a connection:
1924 * MSS: is imporant to chose an optimal segment size to avoid IP level
1925 * fragmentation along the path. The common MSS values can be encoded
1926 * in a 3-bit table. Uncommon values are captured by the next lower value
1927 * in the table leading to a slight increase in packetization overhead.
1928 * WSCALE: is necessary to allow large windows to be used for high delay-
1929 * bandwidth product links. Not scaling the window when it was initially
1930 * negotiated is bad for performance as lack of scaling further decreases
1931 * the apparent available send window. We only need to encode the WSCALE
1932 * we received from the remote end. Our end can be recalculated at any
1933 * time. The common WSCALE values can be encoded in a 3-bit table.
1934 * Uncommon values are captured by the next lower value in the table
1935 * making us under-estimate the available window size halving our
1936 * theoretically possible maximum throughput for that connection.
1937 * SACK: Greatly assists in packet loss recovery and requires 1 bit.
1938 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options
1939 * that are included in all segments on a connection. We enable them when
1940 * the ACK has them.
1941 *
1942 * Security of syncookies and attack vectors:
1943 *
1944 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod)
1945 * together with the gloabl secret to make it unique per connection attempt.
1946 * Thus any change of any of those parameters results in a different MAC output
1947 * in an unpredictable way unless a collision is encountered. 24 bits of the
1948 * MAC are embedded into the ISS.
1949 *
1950 * To prevent replay attacks two rotating global secrets are updated with a
1951 * new random value every 15 seconds. The life-time of a syncookie is thus
1952 * 15-30 seconds.
1953 *
1954 * Vector 1: Attacking the secret. This requires finding a weakness in the
1955 * MAC itself or the way it is used here. The attacker can do a chosen plain
1956 * text attack by varying and testing the all parameters under his control.
1957 * The strength depends on the size and randomness of the secret, and the
1958 * cryptographic security of the MAC function. Due to the constant updating
1959 * of the secret the attacker has at most 29.999 seconds to find the secret
1960 * and launch spoofed connections. After that he has to start all over again.
1961 *
1962 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC
1963 * size an average of 4,823 attempts are required for a 50% chance of success
1964 * to spoof a single syncookie (birthday collision paradox). However the
1965 * attacker is blind and doesn't know if one of his attempts succeeded unless
1966 * he has a side channel to interfere success from. A single connection setup
1967 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets.
1968 * This many attempts are required for each one blind spoofed connection. For
1969 * every additional spoofed connection he has to launch another N attempts.
1970 * Thus for a sustained rate 100 spoofed connections per second approximately
1971 * 1,800,000 packets per second would have to be sent.
1972 *
1973 * NB: The MAC function should be fast so that it doesn't become a CPU
1974 * exhaustion attack vector itself.
1975 *
1976 * References:
1977 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations
1978 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996
1979 * http://cr.yp.to/syncookies.html (overview)
1980 * http://cr.yp.to/syncookies/archive (details)
1981 *
1982 *
1983 * Schematic construction of a syncookie enabled Initial Sequence Number:
1984 * 0 1 2 3
1985 * 12345678901234567890123456789012
1986 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP|
1987 *
1988 * x 24 MAC (truncated)
1989 * W 3 Send Window Scale index
1990 * M 3 MSS index
1991 * S 1 SACK permitted
1992 * P 1 Odd/even secret
1993 */
1994
1995 /*
1996 * Distribution and probability of certain MSS values. Those in between are
1997 * rounded down to the next lower one.
1998 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011]
1999 * .2% .3% 5% 7% 7% 20% 15% 45%
2000 */
2001 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 };
2002
2003 /*
2004 * Distribution and probability of certain WSCALE values. We have to map the
2005 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3
2006 * bits based on prevalence of certain values. Where we don't have an exact
2007 * match for are rounded down to the next lower one letting us under-estimate
2008 * the true available window. At the moment this would happen only for the
2009 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer
2010 * and window size). The absence of the WSCALE option (no scaling in either
2011 * direction) is encoded with index zero.
2012 * [WSCALE values histograms, Allman, 2012]
2013 * X 10 10 35 5 6 14 10% by host
2014 * X 11 4 5 5 18 49 3% by connections
2015 */
2016 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 };
2017
2018 /*
2019 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed
2020 * and good cryptographic properties.
2021 */
2022 static uint32_t
syncookie_mac(struct in_conninfo * inc,tcp_seq irs,uint8_t flags,uint8_t * secbits,uintptr_t secmod)2023 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags,
2024 uint8_t *secbits, uintptr_t secmod)
2025 {
2026 SIPHASH_CTX ctx;
2027 uint32_t siphash[2];
2028
2029 SipHash24_Init(&ctx);
2030 SipHash_SetKey(&ctx, secbits);
2031 switch (inc->inc_flags & INC_ISIPV6) {
2032 #ifdef INET
2033 case 0:
2034 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr));
2035 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr));
2036 break;
2037 #endif
2038 #ifdef INET6
2039 case INC_ISIPV6:
2040 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr));
2041 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr));
2042 break;
2043 #endif
2044 }
2045 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport));
2046 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport));
2047 SipHash_Update(&ctx, &irs, sizeof(irs));
2048 SipHash_Update(&ctx, &flags, sizeof(flags));
2049 SipHash_Update(&ctx, &secmod, sizeof(secmod));
2050 SipHash_Final((u_int8_t *)&siphash, &ctx);
2051
2052 return (siphash[0] ^ siphash[1]);
2053 }
2054
2055 static tcp_seq
syncookie_generate(struct syncache_head * sch,struct syncache * sc)2056 syncookie_generate(struct syncache_head *sch, struct syncache *sc)
2057 {
2058 u_int i, secbit, wscale;
2059 uint32_t iss, hash;
2060 uint8_t *secbits;
2061 union syncookie cookie;
2062
2063 SCH_LOCK_ASSERT(sch);
2064
2065 cookie.cookie = 0;
2066
2067 /* Map our computed MSS into the 3-bit index. */
2068 for (i = nitems(tcp_sc_msstab) - 1;
2069 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0;
2070 i--)
2071 ;
2072 cookie.flags.mss_idx = i;
2073
2074 /*
2075 * Map the send window scale into the 3-bit index but only if
2076 * the wscale option was received.
2077 */
2078 if (sc->sc_flags & SCF_WINSCALE) {
2079 wscale = sc->sc_requested_s_scale;
2080 for (i = nitems(tcp_sc_wstab) - 1;
2081 tcp_sc_wstab[i] > wscale && i > 0;
2082 i--)
2083 ;
2084 cookie.flags.wscale_idx = i;
2085 }
2086
2087 /* Can we do SACK? */
2088 if (sc->sc_flags & SCF_SACK)
2089 cookie.flags.sack_ok = 1;
2090
2091 /* Which of the two secrets to use. */
2092 secbit = sch->sch_sc->secret.oddeven & 0x1;
2093 cookie.flags.odd_even = secbit;
2094
2095 secbits = sch->sch_sc->secret.key[secbit];
2096 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits,
2097 (uintptr_t)sch);
2098
2099 /*
2100 * Put the flags into the hash and XOR them to get better ISS number
2101 * variance. This doesn't enhance the cryptographic strength and is
2102 * done to prevent the 8 cookie bits from showing up directly on the
2103 * wire.
2104 */
2105 iss = hash & ~0xff;
2106 iss |= cookie.cookie ^ (hash >> 24);
2107
2108 TCPSTAT_INC(tcps_sc_sendcookie);
2109 return (iss);
2110 }
2111
2112 static struct syncache *
syncookie_lookup(struct in_conninfo * inc,struct syncache_head * sch,struct syncache * sc,struct tcphdr * th,struct tcpopt * to,struct socket * lso)2113 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch,
2114 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
2115 struct socket *lso)
2116 {
2117 uint32_t hash;
2118 uint8_t *secbits;
2119 tcp_seq ack, seq;
2120 int wnd, wscale = 0;
2121 union syncookie cookie;
2122
2123 SCH_LOCK_ASSERT(sch);
2124
2125 /*
2126 * Pull information out of SYN-ACK/ACK and revert sequence number
2127 * advances.
2128 */
2129 ack = th->th_ack - 1;
2130 seq = th->th_seq - 1;
2131
2132 /*
2133 * Unpack the flags containing enough information to restore the
2134 * connection.
2135 */
2136 cookie.cookie = (ack & 0xff) ^ (ack >> 24);
2137
2138 /* Which of the two secrets to use. */
2139 secbits = sch->sch_sc->secret.key[cookie.flags.odd_even];
2140
2141 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch);
2142
2143 /* The recomputed hash matches the ACK if this was a genuine cookie. */
2144 if ((ack & ~0xff) != (hash & ~0xff))
2145 return (NULL);
2146
2147 /* Fill in the syncache values. */
2148 sc->sc_flags = 0;
2149 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
2150 sc->sc_ipopts = NULL;
2151
2152 sc->sc_irs = seq;
2153 sc->sc_iss = ack;
2154
2155 switch (inc->inc_flags & INC_ISIPV6) {
2156 #ifdef INET
2157 case 0:
2158 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl;
2159 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos;
2160 break;
2161 #endif
2162 #ifdef INET6
2163 case INC_ISIPV6:
2164 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL)
2165 sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK;
2166 break;
2167 #endif
2168 }
2169
2170 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx];
2171
2172 /* We can simply recompute receive window scale we sent earlier. */
2173 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max)
2174 wscale++;
2175
2176 /* Only use wscale if it was enabled in the orignal SYN. */
2177 if (cookie.flags.wscale_idx > 0) {
2178 sc->sc_requested_r_scale = wscale;
2179 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx];
2180 sc->sc_flags |= SCF_WINSCALE;
2181 }
2182
2183 wnd = lso->sol_sbrcv_hiwat;
2184 wnd = imax(wnd, 0);
2185 wnd = imin(wnd, TCP_MAXWIN);
2186 sc->sc_wnd = wnd;
2187
2188 if (cookie.flags.sack_ok)
2189 sc->sc_flags |= SCF_SACK;
2190
2191 if (to->to_flags & TOF_TS) {
2192 sc->sc_flags |= SCF_TIMESTAMP;
2193 sc->sc_tsreflect = to->to_tsval;
2194 sc->sc_tsoff = tcp_new_ts_offset(inc);
2195 }
2196
2197 if (to->to_flags & TOF_SIGNATURE)
2198 sc->sc_flags |= SCF_SIGNATURE;
2199
2200 sc->sc_rxmits = 0;
2201
2202 TCPSTAT_INC(tcps_sc_recvcookie);
2203 return (sc);
2204 }
2205
2206 #ifdef INVARIANTS
2207 static int
syncookie_cmp(struct in_conninfo * inc,struct syncache_head * sch,struct syncache * sc,struct tcphdr * th,struct tcpopt * to,struct socket * lso)2208 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
2209 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
2210 struct socket *lso)
2211 {
2212 struct syncache scs, *scx;
2213 char *s;
2214
2215 bzero(&scs, sizeof(scs));
2216 scx = syncookie_lookup(inc, sch, &scs, th, to, lso);
2217
2218 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL)
2219 return (0);
2220
2221 if (scx != NULL) {
2222 if (sc->sc_peer_mss != scx->sc_peer_mss)
2223 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n",
2224 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss);
2225
2226 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale)
2227 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n",
2228 s, __func__, sc->sc_requested_r_scale,
2229 scx->sc_requested_r_scale);
2230
2231 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale)
2232 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n",
2233 s, __func__, sc->sc_requested_s_scale,
2234 scx->sc_requested_s_scale);
2235
2236 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK))
2237 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__);
2238 }
2239
2240 if (s != NULL)
2241 free(s, M_TCPLOG);
2242 return (0);
2243 }
2244 #endif /* INVARIANTS */
2245
2246 static void
syncookie_reseed(void * arg)2247 syncookie_reseed(void *arg)
2248 {
2249 struct tcp_syncache *sc = arg;
2250 uint8_t *secbits;
2251 int secbit;
2252
2253 /*
2254 * Reseeding the secret doesn't have to be protected by a lock.
2255 * It only must be ensured that the new random values are visible
2256 * to all CPUs in a SMP environment. The atomic with release
2257 * semantics ensures that.
2258 */
2259 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1;
2260 secbits = sc->secret.key[secbit];
2261 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0);
2262 atomic_add_rel_int(&sc->secret.oddeven, 1);
2263
2264 /* Reschedule ourself. */
2265 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz);
2266 }
2267
2268 /*
2269 * Exports the syncache entries to userland so that netstat can display
2270 * them alongside the other sockets. This function is intended to be
2271 * called only from tcp_pcblist.
2272 *
2273 * Due to concurrency on an active system, the number of pcbs exported
2274 * may have no relation to max_pcbs. max_pcbs merely indicates the
2275 * amount of space the caller allocated for this function to use.
2276 */
2277 int
syncache_pcblist(struct sysctl_req * req,int max_pcbs,int * pcbs_exported)2278 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported)
2279 {
2280 struct xtcpcb xt;
2281 struct syncache *sc;
2282 struct syncache_head *sch;
2283 int count, error, i;
2284
2285 for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
2286 sch = &V_tcp_syncache.hashbase[i];
2287 SCH_LOCK(sch);
2288 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
2289 if (count >= max_pcbs) {
2290 SCH_UNLOCK(sch);
2291 goto exit;
2292 }
2293 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
2294 continue;
2295 bzero(&xt, sizeof(xt));
2296 xt.xt_len = sizeof(xt);
2297 if (sc->sc_inc.inc_flags & INC_ISIPV6)
2298 xt.xt_inp.inp_vflag = INP_IPV6;
2299 else
2300 xt.xt_inp.inp_vflag = INP_IPV4;
2301 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc,
2302 sizeof (struct in_conninfo));
2303 xt.t_state = TCPS_SYN_RECEIVED;
2304 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP;
2305 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket);
2306 xt.xt_inp.xi_socket.so_type = SOCK_STREAM;
2307 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING;
2308 error = SYSCTL_OUT(req, &xt, sizeof xt);
2309 if (error) {
2310 SCH_UNLOCK(sch);
2311 goto exit;
2312 }
2313 count++;
2314 }
2315 SCH_UNLOCK(sch);
2316 }
2317 exit:
2318 *pcbs_exported = count;
2319 return error;
2320 }
2321