2 * SPDX-License-Identifier: BSD-2-Clause
4 * Copyright (c) 2001 McAfee, Inc.
5 * Copyright (c) 2006,2013 Andre Oppermann, Internet Business Solutions AG
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.]
13 * Redistribution and use in source and binary forms, with or without
14 * modification, are permitted provided that the following conditions
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.
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
35 #include <sys/cdefs.h>
36 __FBSDID("$FreeBSD$");
39 #include "opt_inet6.h"
40 #include "opt_ipsec.h"
42 #include <sys/param.h>
43 #include <sys/systm.h>
45 #include <sys/refcount.h>
46 #include <sys/kernel.h>
47 #include <sys/sysctl.h>
48 #include <sys/limits.h>
50 #include <sys/mutex.h>
51 #include <sys/malloc.h>
53 #include <sys/proc.h> /* for proc0 declaration */
54 #include <sys/random.h>
55 #include <sys/socket.h>
56 #include <sys/socketvar.h>
57 #include <sys/syslog.h>
58 #include <sys/ucred.h>
61 #include <crypto/siphash/siphash.h>
66 #include <net/if_var.h>
67 #include <net/route.h>
70 #include <netinet/in.h>
71 #include <netinet/in_kdtrace.h>
72 #include <netinet/in_systm.h>
73 #include <netinet/ip.h>
74 #include <netinet/in_var.h>
75 #include <netinet/in_pcb.h>
76 #include <netinet/ip_var.h>
77 #include <netinet/ip_options.h>
79 #include <netinet/ip6.h>
80 #include <netinet/icmp6.h>
81 #include <netinet6/nd6.h>
82 #include <netinet6/ip6_var.h>
83 #include <netinet6/in6_pcb.h>
85 #include <netinet/tcp.h>
86 #include <netinet/tcp_fastopen.h>
87 #include <netinet/tcp_fsm.h>
88 #include <netinet/tcp_seq.h>
89 #include <netinet/tcp_timer.h>
90 #include <netinet/tcp_var.h>
91 #include <netinet/tcp_syncache.h>
92 #include <netinet/tcp_ecn.h>
94 #include <netinet/tcp_log_buf.h>
97 #include <netinet/toecore.h>
99 #include <netinet/udp.h>
101 #include <netipsec/ipsec_support.h>
103 #include <machine/in_cksum.h>
105 #include <security/mac/mac_framework.h>
107 VNET_DEFINE_STATIC(int, tcp_syncookies) = 1;
108 #define V_tcp_syncookies VNET(tcp_syncookies)
109 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW,
110 &VNET_NAME(tcp_syncookies), 0,
111 "Use TCP SYN cookies if the syncache overflows");
113 VNET_DEFINE_STATIC(int, tcp_syncookiesonly) = 0;
114 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly)
115 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW,
116 &VNET_NAME(tcp_syncookiesonly), 0,
117 "Use only TCP SYN cookies");
119 VNET_DEFINE_STATIC(int, functions_inherit_listen_socket_stack) = 1;
120 #define V_functions_inherit_listen_socket_stack \
121 VNET(functions_inherit_listen_socket_stack)
122 SYSCTL_INT(_net_inet_tcp, OID_AUTO, functions_inherit_listen_socket_stack,
123 CTLFLAG_VNET | CTLFLAG_RW,
124 &VNET_NAME(functions_inherit_listen_socket_stack), 0,
125 "Inherit listen socket's stack");
128 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL)
131 static void syncache_drop(struct syncache *, struct syncache_head *);
132 static void syncache_free(struct syncache *);
133 static void syncache_insert(struct syncache *, struct syncache_head *);
134 static int syncache_respond(struct syncache *, const struct mbuf *, int);
135 static struct socket *syncache_socket(struct syncache *, struct socket *,
137 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch,
139 static void syncache_timer(void *);
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 *, uint16_t);
148 static void syncache_pause(struct in_conninfo *);
149 static void syncache_unpause(void *);
150 static void syncookie_reseed(void *);
152 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
153 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
154 struct socket *lso, uint16_t port);
158 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
159 * 3 retransmits corresponds to a timeout with default values of
160 * tcp_rexmit_initial * ( 1 +
163 * tcp_backoff[3]) + 3 * tcp_rexmit_slop,
164 * 1000 ms * (1 + 2 + 4 + 8) + 3 * 200 ms = 15600 ms,
165 * the odds are that the user has given up attempting to connect by then.
167 #define SYNCACHE_MAXREXMTS 3
169 /* Arbitrary values */
170 #define TCP_SYNCACHE_HASHSIZE 512
171 #define TCP_SYNCACHE_BUCKETLIMIT 30
173 VNET_DEFINE_STATIC(struct tcp_syncache, tcp_syncache);
174 #define V_tcp_syncache VNET(tcp_syncache)
176 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache,
177 CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
180 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
181 &VNET_NAME(tcp_syncache.bucket_limit), 0,
182 "Per-bucket hash limit for syncache");
184 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
185 &VNET_NAME(tcp_syncache.cache_limit), 0,
186 "Overall entry limit for syncache");
188 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET,
189 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache");
191 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN,
192 &VNET_NAME(tcp_syncache.hashsize), 0,
193 "Size of TCP syncache hashtable");
195 SYSCTL_BOOL(_net_inet_tcp_syncache, OID_AUTO, see_other, CTLFLAG_VNET |
196 CTLFLAG_RW, &VNET_NAME(tcp_syncache.see_other), 0,
197 "All syncache(4) entries are visible, ignoring UID/GID, jail(2) "
198 "and mac(4) checks");
201 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS)
206 new = V_tcp_syncache.rexmt_limit;
207 error = sysctl_handle_int(oidp, &new, 0, req);
208 if ((error == 0) && (req->newptr != NULL)) {
209 if (new > TCP_MAXRXTSHIFT)
212 V_tcp_syncache.rexmt_limit = new;
217 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit,
218 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
219 &VNET_NAME(tcp_syncache.rexmt_limit), 0,
220 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "UI",
221 "Limit on SYN/ACK retransmissions");
223 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1;
224 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail,
225 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0,
226 "Send reset on socket allocation failure");
228 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
230 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx)
231 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx)
232 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED)
235 * Requires the syncache entry to be already removed from the bucket list.
238 syncache_free(struct syncache *sc)
242 (void) m_free(sc->sc_ipopts);
246 mac_syncache_destroy(&sc->sc_label);
249 uma_zfree(V_tcp_syncache.zone, sc);
257 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
258 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
259 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
260 V_tcp_syncache.hash_secret = arc4random();
262 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
263 &V_tcp_syncache.hashsize);
264 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
265 &V_tcp_syncache.bucket_limit);
266 if (!powerof2(V_tcp_syncache.hashsize) ||
267 V_tcp_syncache.hashsize == 0) {
268 printf("WARNING: syncache hash size is not a power of 2.\n");
269 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
271 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1;
274 V_tcp_syncache.cache_limit =
275 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit;
276 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
277 &V_tcp_syncache.cache_limit);
279 /* Allocate the hash table. */
280 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize *
281 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO);
284 V_tcp_syncache.vnet = curvnet;
287 /* Initialize the hash buckets. */
288 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
289 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket);
290 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
292 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer,
293 &V_tcp_syncache.hashbase[i].sch_mtx, 0);
294 V_tcp_syncache.hashbase[i].sch_length = 0;
295 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache;
296 V_tcp_syncache.hashbase[i].sch_last_overflow =
297 -(SYNCOOKIE_LIFETIME + 1);
300 /* Create the syncache entry zone. */
301 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
302 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
303 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone,
304 V_tcp_syncache.cache_limit);
306 /* Start the SYN cookie reseeder callout. */
307 callout_init(&V_tcp_syncache.secret.reseed, 1);
308 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0);
309 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0);
310 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz,
311 syncookie_reseed, &V_tcp_syncache);
313 /* Initialize the pause machinery. */
314 mtx_init(&V_tcp_syncache.pause_mtx, "tcp_sc_pause", NULL, MTX_DEF);
315 callout_init_mtx(&V_tcp_syncache.pause_co, &V_tcp_syncache.pause_mtx,
317 V_tcp_syncache.pause_until = time_uptime - TCP_SYNCACHE_PAUSE_TIME;
318 V_tcp_syncache.pause_backoff = 0;
319 V_tcp_syncache.paused = false;
324 syncache_destroy(void)
326 struct syncache_head *sch;
327 struct syncache *sc, *nsc;
331 * Stop the re-seed timer before freeing resources. No need to
332 * possibly schedule it another time.
334 callout_drain(&V_tcp_syncache.secret.reseed);
336 /* Stop the SYN cache pause callout. */
337 mtx_lock(&V_tcp_syncache.pause_mtx);
338 if (callout_stop(&V_tcp_syncache.pause_co) == 0) {
339 mtx_unlock(&V_tcp_syncache.pause_mtx);
340 callout_drain(&V_tcp_syncache.pause_co);
342 mtx_unlock(&V_tcp_syncache.pause_mtx);
344 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */
345 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
346 sch = &V_tcp_syncache.hashbase[i];
347 callout_drain(&sch->sch_timer);
350 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc)
351 syncache_drop(sc, sch);
353 KASSERT(TAILQ_EMPTY(&sch->sch_bucket),
354 ("%s: sch->sch_bucket not empty", __func__));
355 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0",
356 __func__, sch->sch_length));
357 mtx_destroy(&sch->sch_mtx);
360 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0,
361 ("%s: cache_count not 0", __func__));
363 /* Free the allocated global resources. */
364 uma_zdestroy(V_tcp_syncache.zone);
365 free(V_tcp_syncache.hashbase, M_SYNCACHE);
366 mtx_destroy(&V_tcp_syncache.pause_mtx);
371 * Inserts a syncache entry into the specified bucket row.
372 * Locks and unlocks the syncache_head autonomously.
375 syncache_insert(struct syncache *sc, struct syncache_head *sch)
377 struct syncache *sc2;
382 * Make sure that we don't overflow the per-bucket limit.
383 * If the bucket is full, toss the oldest element.
385 if (sch->sch_length >= V_tcp_syncache.bucket_limit) {
386 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
387 ("sch->sch_length incorrect"));
388 syncache_pause(&sc->sc_inc);
389 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
390 sch->sch_last_overflow = time_uptime;
391 syncache_drop(sc2, sch);
394 /* Put it into the bucket. */
395 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
399 if (ADDED_BY_TOE(sc)) {
400 struct toedev *tod = sc->sc_tod;
402 tod->tod_syncache_added(tod, sc->sc_todctx);
406 /* Reinitialize the bucket row's timer. */
407 if (sch->sch_length == 1)
408 sch->sch_nextc = ticks + INT_MAX;
409 syncache_timeout(sc, sch, 1);
413 TCPSTATES_INC(TCPS_SYN_RECEIVED);
414 TCPSTAT_INC(tcps_sc_added);
418 * Remove and free entry from syncache bucket row.
419 * Expects locked syncache head.
422 syncache_drop(struct syncache *sc, struct syncache_head *sch)
425 SCH_LOCK_ASSERT(sch);
427 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
428 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
432 if (ADDED_BY_TOE(sc)) {
433 struct toedev *tod = sc->sc_tod;
435 tod->tod_syncache_removed(tod, sc->sc_todctx);
443 * Engage/reengage time on bucket row.
446 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
450 if (sc->sc_rxmits == 0)
451 rexmt = tcp_rexmit_initial;
454 tcp_rexmit_initial * tcp_backoff[sc->sc_rxmits],
455 tcp_rexmit_min, TCPTV_REXMTMAX);
456 sc->sc_rxttime = ticks + rexmt;
458 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
459 sch->sch_nextc = sc->sc_rxttime;
461 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
462 syncache_timer, (void *)sch);
467 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
468 * If we have retransmitted an entry the maximum number of times, expire it.
469 * One separate timer for each bucket row.
472 syncache_timer(void *xsch)
474 struct syncache_head *sch = (struct syncache_head *)xsch;
475 struct syncache *sc, *nsc;
476 struct epoch_tracker et;
481 CURVNET_SET(sch->sch_sc->vnet);
483 /* NB: syncache_head has already been locked by the callout. */
484 SCH_LOCK_ASSERT(sch);
487 * In the following cycle we may remove some entries and/or
488 * advance some timeouts, so re-initialize the bucket timer.
490 sch->sch_nextc = tick + INT_MAX;
493 * If we have paused processing, unconditionally remove
494 * all syncache entries.
496 mtx_lock(&V_tcp_syncache.pause_mtx);
497 paused = V_tcp_syncache.paused;
498 mtx_unlock(&V_tcp_syncache.pause_mtx);
500 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
502 syncache_drop(sc, sch);
506 * We do not check if the listen socket still exists
507 * and accept the case where the listen socket may be
508 * gone by the time we resend the SYN/ACK. We do
509 * not expect this to happens often. If it does,
510 * then the RST will be sent by the time the remote
511 * host does the SYN/ACK->ACK.
513 if (TSTMP_GT(sc->sc_rxttime, tick)) {
514 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
515 sch->sch_nextc = sc->sc_rxttime;
518 if (sc->sc_rxmits > V_tcp_ecn_maxretries) {
519 sc->sc_flags &= ~SCF_ECN_MASK;
521 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
522 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
523 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
524 "giving up and removing syncache entry\n",
528 syncache_drop(sc, sch);
529 TCPSTAT_INC(tcps_sc_stale);
532 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
533 log(LOG_DEBUG, "%s; %s: Response timeout, "
534 "retransmitting (%u) SYN|ACK\n",
535 s, __func__, sc->sc_rxmits);
540 syncache_respond(sc, NULL, TH_SYN|TH_ACK);
542 TCPSTAT_INC(tcps_sc_retransmitted);
543 syncache_timeout(sc, sch, 0);
545 if (!TAILQ_EMPTY(&(sch)->sch_bucket))
546 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
547 syncache_timer, (void *)(sch));
552 * Returns true if the system is only using cookies at the moment.
553 * This could be due to a sysadmin decision to only use cookies, or it
554 * could be due to the system detecting an attack.
557 syncache_cookiesonly(void)
560 return (V_tcp_syncookies && (V_tcp_syncache.paused ||
561 V_tcp_syncookiesonly));
565 * Find the hash bucket for the given connection.
567 static struct syncache_head *
568 syncache_hashbucket(struct in_conninfo *inc)
573 * The hash is built on foreign port + local port + foreign address.
574 * We rely on the fact that struct in_conninfo starts with 16 bits
575 * of foreign port, then 16 bits of local port then followed by 128
576 * bits of foreign address. In case of IPv4 address, the first 3
577 * 32-bit words of the address always are zeroes.
579 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5,
580 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask;
582 return (&V_tcp_syncache.hashbase[hash]);
586 * Find an entry in the syncache.
587 * Returns always with locked syncache_head plus a matching entry or NULL.
589 static struct syncache *
590 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
593 struct syncache_head *sch;
595 *schp = sch = syncache_hashbucket(inc);
598 /* Circle through bucket row to find matching entry. */
599 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash)
600 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie,
601 sizeof(struct in_endpoints)) == 0)
604 return (sc); /* Always returns with locked sch. */
608 * This function is called when we get a RST for a
609 * non-existent connection, so that we can see if the
610 * connection is in the syn cache. If it is, zap it.
611 * If required send a challenge ACK.
614 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, struct mbuf *m,
618 struct syncache_head *sch;
621 if (syncache_cookiesonly())
623 sc = syncache_lookup(inc, &sch); /* returns locked sch */
624 SCH_LOCK_ASSERT(sch);
627 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags.
628 * See RFC 793 page 65, section SEGMENT ARRIVES.
630 if (tcp_get_flags(th) & (TH_ACK|TH_SYN|TH_FIN)) {
631 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
632 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or "
633 "FIN flag set, segment ignored\n", s, __func__);
634 TCPSTAT_INC(tcps_badrst);
639 * No corresponding connection was found in syncache.
640 * If syncookies are enabled and possibly exclusively
641 * used, or we are under memory pressure, a valid RST
642 * may not find a syncache entry. In that case we're
643 * done and no SYN|ACK retransmissions will happen.
644 * Otherwise the RST was misdirected or spoofed.
647 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
648 log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
649 "syncache entry (possibly syncookie only), "
650 "segment ignored\n", s, __func__);
651 TCPSTAT_INC(tcps_badrst);
655 /* The remote UDP encaps port does not match. */
656 if (sc->sc_port != port) {
657 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
658 log(LOG_DEBUG, "%s; %s: Spurious RST with matching "
659 "syncache entry but non-matching UDP encaps port, "
660 "segment ignored\n", s, __func__);
661 TCPSTAT_INC(tcps_badrst);
666 * If the RST bit is set, check the sequence number to see
667 * if this is a valid reset segment.
670 * In all states except SYN-SENT, all reset (RST) segments
671 * are validated by checking their SEQ-fields. A reset is
672 * valid if its sequence number is in the window.
675 * There are four cases for the acceptability test for an incoming
678 * Segment Receive Test
680 * ------- ------- -------------------------------------------
681 * 0 0 SEG.SEQ = RCV.NXT
682 * 0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND
683 * >0 0 not acceptable
684 * >0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND
685 * or RCV.NXT =< SEG.SEQ+SEG.LEN-1 < RCV.NXT+RCV.WND
687 * Note that when receiving a SYN segment in the LISTEN state,
688 * IRS is set to SEG.SEQ and RCV.NXT is set to SEG.SEQ+1, as
689 * described in RFC 793, page 66.
691 if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) &&
692 SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) ||
693 (sc->sc_wnd == 0 && th->th_seq == sc->sc_irs + 1)) {
694 if (V_tcp_insecure_rst ||
695 th->th_seq == sc->sc_irs + 1) {
696 syncache_drop(sc, sch);
697 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
699 "%s; %s: Our SYN|ACK was rejected, "
700 "connection attempt aborted by remote "
703 TCPSTAT_INC(tcps_sc_reset);
705 TCPSTAT_INC(tcps_badrst);
706 /* Send challenge ACK. */
707 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
708 log(LOG_DEBUG, "%s; %s: RST with invalid "
709 " SEQ %u != NXT %u (+WND %u), "
710 "sending challenge ACK\n",
712 th->th_seq, sc->sc_irs + 1, sc->sc_wnd);
713 syncache_respond(sc, m, TH_ACK);
716 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
717 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
718 "NXT %u (+WND %u), segment ignored\n",
720 th->th_seq, sc->sc_irs + 1, sc->sc_wnd);
721 TCPSTAT_INC(tcps_badrst);
731 syncache_badack(struct in_conninfo *inc, uint16_t port)
734 struct syncache_head *sch;
736 if (syncache_cookiesonly())
738 sc = syncache_lookup(inc, &sch); /* returns locked sch */
739 SCH_LOCK_ASSERT(sch);
740 if ((sc != NULL) && (sc->sc_port == port)) {
741 syncache_drop(sc, sch);
742 TCPSTAT_INC(tcps_sc_badack);
748 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq, uint16_t port)
751 struct syncache_head *sch;
753 if (syncache_cookiesonly())
755 sc = syncache_lookup(inc, &sch); /* returns locked sch */
756 SCH_LOCK_ASSERT(sch);
760 /* If the port != sc_port, then it's a bogus ICMP msg */
761 if (port != sc->sc_port)
764 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
765 if (ntohl(th_seq) != sc->sc_iss)
769 * If we've rertransmitted 3 times and this is our second error,
770 * we remove the entry. Otherwise, we allow it to continue on.
771 * This prevents us from incorrectly nuking an entry during a
772 * spurious network outage.
776 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
777 sc->sc_flags |= SCF_UNREACH;
780 syncache_drop(sc, sch);
781 TCPSTAT_INC(tcps_sc_unreach);
787 * Build a new TCP socket structure from a syncache entry.
789 * On success return the newly created socket with its underlying inp locked.
791 static struct socket *
792 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
794 struct tcp_function_block *blk;
795 struct inpcb *inp = NULL;
804 * Ok, create the full blown connection, and set things up
805 * as they would have been set up if we had created the
806 * connection when the SYN arrived.
808 if ((so = solisten_clone(lso)) == NULL)
811 mac_socketpeer_set_from_mbuf(m, so);
813 error = in_pcballoc(so, &V_tcbinfo);
819 if ((tp = tcp_newtcpcb(inp)) == NULL) {
825 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
827 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
828 inp->inp_vflag &= ~INP_IPV4;
829 inp->inp_vflag |= INP_IPV6;
830 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
832 inp->inp_vflag &= ~INP_IPV6;
833 inp->inp_vflag |= INP_IPV4;
835 inp->inp_ip_ttl = sc->sc_ip_ttl;
836 inp->inp_ip_tos = sc->sc_ip_tos;
837 inp->inp_laddr = sc->sc_inc.inc_laddr;
843 * If there's an mbuf and it has a flowid, then let's initialise the
844 * inp with that particular flowid.
846 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) {
847 inp->inp_flowid = m->m_pkthdr.flowid;
848 inp->inp_flowtype = M_HASHTYPE_GET(m);
850 inp->inp_numa_domain = m->m_pkthdr.numa_domain;
854 inp->inp_lport = sc->sc_inc.inc_lport;
856 if (inp->inp_vflag & INP_IPV6PROTO) {
857 struct inpcb *oinp = sotoinpcb(lso);
860 * Inherit socket options from the listening socket.
861 * Note that in6p_inputopts are not (and should not be)
862 * copied, since it stores previously received options and is
863 * used to detect if each new option is different than the
864 * previous one and hence should be passed to a user.
865 * If we copied in6p_inputopts, a user would not be able to
866 * receive options just after calling the accept system call.
868 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
869 if (oinp->in6p_outputopts)
870 inp->in6p_outputopts =
871 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
872 inp->in6p_hops = oinp->in6p_hops;
875 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
876 struct sockaddr_in6 sin6;
878 sin6.sin6_family = AF_INET6;
879 sin6.sin6_len = sizeof(sin6);
880 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
881 sin6.sin6_port = sc->sc_inc.inc_fport;
882 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
883 INP_HASH_WLOCK(&V_tcbinfo);
884 error = in6_pcbconnect(inp, &sin6, thread0.td_ucred, false);
885 INP_HASH_WUNLOCK(&V_tcbinfo);
888 /* Override flowlabel from in6_pcbconnect. */
889 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
890 inp->inp_flow |= sc->sc_flowlabel;
893 #if defined(INET) && defined(INET6)
898 struct sockaddr_in sin;
900 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
902 if (inp->inp_options == NULL) {
903 inp->inp_options = sc->sc_ipopts;
904 sc->sc_ipopts = NULL;
907 sin.sin_family = AF_INET;
908 sin.sin_len = sizeof(sin);
909 sin.sin_addr = sc->sc_inc.inc_faddr;
910 sin.sin_port = sc->sc_inc.inc_fport;
911 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
912 INP_HASH_WLOCK(&V_tcbinfo);
913 error = in_pcbconnect(inp, &sin, thread0.td_ucred, false);
914 INP_HASH_WUNLOCK(&V_tcbinfo);
919 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
920 /* Copy old policy into new socket's. */
921 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0)
922 printf("syncache_socket: could not copy policy\n");
924 tp->t_state = TCPS_SYN_RECEIVED;
925 tp->iss = sc->sc_iss;
926 tp->irs = sc->sc_irs;
927 tp->t_port = sc->sc_port;
930 blk = sototcpcb(lso)->t_fb;
931 if (V_functions_inherit_listen_socket_stack && blk != tp->t_fb) {
933 * Our parents t_fb was not the default,
934 * we need to release our ref on tp->t_fb and
935 * pickup one on the new entry.
937 struct tcp_function_block *rblk;
940 rblk = find_and_ref_tcp_fb(blk);
941 KASSERT(rblk != NULL,
942 ("cannot find blk %p out of syncache?", blk));
944 if (rblk->tfb_tcp_fb_init == NULL ||
945 (*rblk->tfb_tcp_fb_init)(tp, &ptr) == 0) {
946 /* Release the old stack */
947 if (tp->t_fb->tfb_tcp_fb_fini != NULL)
948 (*tp->t_fb->tfb_tcp_fb_fini)(tp, 0);
949 refcount_release(&tp->t_fb->tfb_refcnt);
950 /* Now set in all the pointers */
955 * Initialization failed. Release the reference count on
956 * the looked up default stack.
958 refcount_release(&rblk->tfb_refcnt);
961 tp->snd_wl1 = sc->sc_irs;
962 tp->snd_max = tp->iss + 1;
963 tp->snd_nxt = tp->iss + 1;
964 tp->rcv_up = sc->sc_irs + 1;
965 tp->rcv_wnd = sc->sc_wnd;
966 tp->rcv_adv += tp->rcv_wnd;
967 tp->last_ack_sent = tp->rcv_nxt;
969 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
970 if (sc->sc_flags & SCF_NOOPT)
971 tp->t_flags |= TF_NOOPT;
973 if (sc->sc_flags & SCF_WINSCALE) {
974 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
975 tp->snd_scale = sc->sc_requested_s_scale;
976 tp->request_r_scale = sc->sc_requested_r_scale;
978 if (sc->sc_flags & SCF_TIMESTAMP) {
979 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
980 tp->ts_recent = sc->sc_tsreflect;
981 tp->ts_recent_age = tcp_ts_getticks();
982 tp->ts_offset = sc->sc_tsoff;
984 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
985 if (sc->sc_flags & SCF_SIGNATURE)
986 tp->t_flags |= TF_SIGNATURE;
988 if (sc->sc_flags & SCF_SACK)
989 tp->t_flags |= TF_SACK_PERMIT;
992 tcp_ecn_syncache_socket(tp, sc);
995 * Set up MSS and get cached values from tcp_hostcache.
996 * This might overwrite some of the defaults we just set.
998 tcp_mss(tp, sc->sc_peer_mss);
1001 * If the SYN,ACK was retransmitted, indicate that CWND to be
1002 * limited to one segment in cc_conn_init().
1003 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
1005 if (sc->sc_rxmits > 1)
1010 * Allow a TOE driver to install its hooks. Note that we hold the
1011 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a
1012 * new connection before the TOE driver has done its thing.
1014 if (ADDED_BY_TOE(sc)) {
1015 struct toedev *tod = sc->sc_tod;
1017 tod->tod_offload_socket(tod, sc->sc_todctx, so);
1022 * Inherit the log state from the listening socket, if
1023 * - the log state of the listening socket is not off and
1024 * - the listening socket was not auto selected from all sessions and
1025 * - a log id is not set on the listening socket.
1026 * This avoids inheriting a log state which was automatically set.
1028 if ((tcp_get_bblog_state(sototcpcb(lso)) != TCP_LOG_STATE_OFF) &&
1029 ((sototcpcb(lso)->t_flags2 & TF2_LOG_AUTO) == 0) &&
1030 (sototcpcb(lso)->t_lib == NULL)) {
1031 tcp_log_state_change(tp, tcp_get_bblog_state(sototcpcb(lso)));
1035 * Copy and activate timers.
1037 tp->t_maxunacktime = sototcpcb(lso)->t_maxunacktime;
1038 tp->t_keepinit = sototcpcb(lso)->t_keepinit;
1039 tp->t_keepidle = sototcpcb(lso)->t_keepidle;
1040 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl;
1041 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt;
1042 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp));
1044 TCPSTAT_INC(tcps_accepts);
1045 TCP_PROBE6(state__change, NULL, tp, NULL, tp, NULL, TCPS_LISTEN);
1047 if (!solisten_enqueue(so, SS_ISCONNECTED))
1048 tp->t_flags |= TF_SONOTCONN;
1054 * Drop the connection; we will either send a RST or have the peer
1055 * retransmit its SYN again after its RTO and try again.
1057 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
1058 log(LOG_DEBUG, "%s; %s: Socket create failed "
1059 "due to limits or memory shortage\n",
1063 TCPSTAT_INC(tcps_listendrop);
1070 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
1071 log(LOG_DEBUG, "%s; %s: in%s_pcbconnect failed with error %i\n",
1072 s, __func__, (sc->sc_inc.inc_flags & INC_ISIPV6) ? "6" : "",
1076 TCPSTAT_INC(tcps_listendrop);
1081 * This function gets called when we receive an ACK for a
1082 * socket in the LISTEN state. We look up the connection
1083 * in the syncache, and if its there, we pull it out of
1084 * the cache and turn it into a full-blown connection in
1085 * the SYN-RECEIVED state.
1087 * On syncache_socket() success the newly created socket
1088 * has its underlying inp locked.
1091 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1092 struct socket **lsop, struct mbuf *m, uint16_t port)
1094 struct syncache *sc;
1095 struct syncache_head *sch;
1096 struct syncache scs;
1101 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
1102 ("%s: can handle only ACK", __func__));
1104 if (syncache_cookiesonly()) {
1106 sch = syncache_hashbucket(inc);
1109 sc = syncache_lookup(inc, &sch); /* returns locked sch */
1111 SCH_LOCK_ASSERT(sch);
1116 * Test code for syncookies comparing the syncache stored
1117 * values with the reconstructed values from the cookie.
1120 syncookie_cmp(inc, sch, sc, th, to, *lsop, port);
1125 * There is no syncache entry, so see if this ACK is
1126 * a returning syncookie. To do this, first:
1127 * A. Check if syncookies are used in case of syncache
1129 * B. See if this socket has had a syncache entry dropped in
1130 * the recent past. We don't want to accept a bogus
1131 * syncookie if we've never received a SYN or accept it
1133 * C. check that the syncookie is valid. If it is, then
1134 * cobble up a fake syncache entry, and return.
1136 if (locked && !V_tcp_syncookies) {
1138 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1139 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
1140 "segment rejected (syncookies disabled)\n",
1144 if (locked && !V_tcp_syncookiesonly &&
1145 sch->sch_last_overflow < time_uptime - SYNCOOKIE_LIFETIME) {
1147 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1148 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
1149 "segment rejected (no syncache entry)\n",
1153 bzero(&scs, sizeof(scs));
1154 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop, port);
1158 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1159 log(LOG_DEBUG, "%s; %s: Segment failed "
1160 "SYNCOOKIE authentication, segment rejected "
1161 "(probably spoofed)\n", s, __func__);
1164 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1165 /* If received ACK has MD5 signature, check it. */
1166 if ((to->to_flags & TOF_SIGNATURE) != 0 &&
1167 (!TCPMD5_ENABLED() ||
1168 TCPMD5_INPUT(m, th, to->to_signature) != 0)) {
1170 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1171 log(LOG_DEBUG, "%s; %s: Segment rejected, "
1172 "MD5 signature doesn't match.\n",
1176 TCPSTAT_INC(tcps_sig_err_sigopt);
1177 return (-1); /* Do not send RST */
1179 #endif /* TCP_SIGNATURE */
1180 TCPSTATES_INC(TCPS_SYN_RECEIVED);
1182 if (sc->sc_port != port) {
1186 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1188 * If listening socket requested TCP digests, check that
1189 * received ACK has signature and it is correct.
1190 * If not, drop the ACK and leave sc entry in th cache,
1191 * because SYN was received with correct signature.
1193 if (sc->sc_flags & SCF_SIGNATURE) {
1194 if ((to->to_flags & TOF_SIGNATURE) == 0) {
1196 TCPSTAT_INC(tcps_sig_err_nosigopt);
1198 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1199 log(LOG_DEBUG, "%s; %s: Segment "
1200 "rejected, MD5 signature wasn't "
1201 "provided.\n", s, __func__);
1204 return (-1); /* Do not send RST */
1206 if (!TCPMD5_ENABLED() ||
1207 TCPMD5_INPUT(m, th, to->to_signature) != 0) {
1208 /* Doesn't match or no SA */
1210 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1211 log(LOG_DEBUG, "%s; %s: Segment "
1212 "rejected, MD5 signature doesn't "
1213 "match.\n", s, __func__);
1216 return (-1); /* Do not send RST */
1219 #endif /* TCP_SIGNATURE */
1222 * RFC 7323 PAWS: If we have a timestamp on this segment and
1223 * it's less than ts_recent, drop it.
1224 * XXXMT: RFC 7323 also requires to send an ACK.
1225 * In tcp_input.c this is only done for TCP segments
1226 * with user data, so be consistent here and just drop
1229 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS &&
1230 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) {
1232 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1234 "%s; %s: SEG.TSval %u < TS.Recent %u, "
1235 "segment dropped\n", s, __func__,
1236 to->to_tsval, sc->sc_tsreflect);
1239 return (-1); /* Do not send RST */
1243 * If timestamps were not negotiated during SYN/ACK and a
1244 * segment with a timestamp is received, ignore the
1245 * timestamp and process the packet normally.
1246 * See section 3.2 of RFC 7323.
1248 if (!(sc->sc_flags & SCF_TIMESTAMP) &&
1249 (to->to_flags & TOF_TS)) {
1250 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1251 log(LOG_DEBUG, "%s; %s: Timestamp not "
1252 "expected, segment processed normally\n",
1260 * If timestamps were negotiated during SYN/ACK and a
1261 * segment without a timestamp is received, silently drop
1262 * the segment, unless the missing timestamps are tolerated.
1263 * See section 3.2 of RFC 7323.
1265 if ((sc->sc_flags & SCF_TIMESTAMP) &&
1266 !(to->to_flags & TOF_TS)) {
1267 if (V_tcp_tolerate_missing_ts) {
1268 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1270 "%s; %s: Timestamp missing, "
1271 "segment processed normally\n",
1277 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1279 "%s; %s: Timestamp missing, "
1280 "segment silently dropped\n",
1284 return (-1); /* Do not send RST */
1287 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
1290 if (ADDED_BY_TOE(sc)) {
1291 struct toedev *tod = sc->sc_tod;
1293 tod->tod_syncache_removed(tod, sc->sc_todctx);
1300 * Segment validation:
1301 * ACK must match our initial sequence number + 1 (the SYN|ACK).
1303 if (th->th_ack != sc->sc_iss + 1) {
1304 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1305 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
1306 "rejected\n", s, __func__, th->th_ack, sc->sc_iss);
1311 * The SEQ must fall in the window starting at the received
1312 * initial receive sequence number + 1 (the SYN).
1314 if (SEQ_LEQ(th->th_seq, sc->sc_irs) ||
1315 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
1316 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1317 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
1318 "rejected\n", s, __func__, th->th_seq, sc->sc_irs);
1322 *lsop = syncache_socket(sc, *lsop, m);
1324 if (__predict_false(*lsop == NULL)) {
1325 TCPSTAT_INC(tcps_sc_aborted);
1326 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
1328 TCPSTAT_INC(tcps_sc_completed);
1330 /* how do we find the inp for the new socket? */
1336 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
1346 static struct socket *
1347 syncache_tfo_expand(struct syncache *sc, struct socket *lso, struct mbuf *m,
1348 uint64_t response_cookie)
1352 unsigned int *pending_counter;
1357 pending_counter = intotcpcb(sotoinpcb(lso))->t_tfo_pending;
1358 so = syncache_socket(sc, lso, m);
1360 TCPSTAT_INC(tcps_sc_aborted);
1361 atomic_subtract_int(pending_counter, 1);
1364 inp = sotoinpcb(so);
1365 tp = intotcpcb(inp);
1366 tp->t_flags |= TF_FASTOPEN;
1367 tp->t_tfo_cookie.server = response_cookie;
1368 tp->snd_max = tp->iss;
1369 tp->snd_nxt = tp->iss;
1370 tp->t_tfo_pending = pending_counter;
1371 TCPSTATES_INC(TCPS_SYN_RECEIVED);
1372 TCPSTAT_INC(tcps_sc_completed);
1379 * Given a LISTEN socket and an inbound SYN request, add
1380 * this to the syn cache, and send back a segment:
1381 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
1384 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
1385 * Doing so would require that we hold onto the data and deliver it
1386 * to the application. However, if we are the target of a SYN-flood
1387 * DoS attack, an attacker could send data which would eventually
1388 * consume all available buffer space if it were ACKed. By not ACKing
1389 * the data, we avoid this DoS scenario.
1391 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO)
1392 * cookie is processed and a new socket is created. In this case, any data
1393 * accompanying the SYN will be queued to the socket by tcp_input() and will
1394 * be ACKed either when the application sends response data or the delayed
1395 * ACK timer expires, whichever comes first.
1398 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1399 struct inpcb *inp, struct socket *so, struct mbuf *m, void *tod,
1400 void *todctx, uint8_t iptos, uint16_t port)
1403 struct socket *rv = NULL;
1404 struct syncache *sc = NULL;
1405 struct syncache_head *sch;
1406 struct mbuf *ipopts = NULL;
1408 int win, ip_ttl, ip_tos;
1411 int autoflowlabel = 0;
1414 struct label *maclabel;
1416 struct syncache scs;
1418 uint64_t tfo_response_cookie;
1419 unsigned int *tfo_pending = NULL;
1420 int tfo_cookie_valid = 0;
1421 int tfo_response_cookie_valid = 0;
1424 INP_RLOCK_ASSERT(inp); /* listen socket */
1425 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
1426 ("%s: unexpected tcp flags", __func__));
1429 * Combine all so/tp operations very early to drop the INP lock as
1432 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so));
1434 cred = V_tcp_syncache.see_other ? NULL : crhold(so->so_cred);
1437 if (inc->inc_flags & INC_ISIPV6) {
1438 if (inp->inp_flags & IN6P_AUTOFLOWLABEL) {
1441 ip_ttl = in6_selecthlim(inp, NULL);
1442 if ((inp->in6p_outputopts == NULL) ||
1443 (inp->in6p_outputopts->ip6po_tclass == -1)) {
1446 ip_tos = inp->in6p_outputopts->ip6po_tclass;
1450 #if defined(INET6) && defined(INET)
1455 ip_ttl = inp->inp_ip_ttl;
1456 ip_tos = inp->inp_ip_tos;
1459 win = so->sol_sbrcv_hiwat;
1460 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE));
1462 if (V_tcp_fastopen_server_enable && IS_FASTOPEN(tp->t_flags) &&
1463 (tp->t_tfo_pending != NULL) &&
1464 (to->to_flags & TOF_FASTOPEN)) {
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.
1471 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <=
1472 (so->sol_qlimit / 2)) {
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);
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().
1486 tfo_pending = tp->t_tfo_pending;
1490 if (mac_syncache_init(&maclabel) != 0) {
1494 mac_syncache_create(maclabel, inp);
1496 if (!tfo_cookie_valid)
1500 * Remember the IP options, if any.
1503 if (!(inc->inc_flags & INC_ISIPV6))
1506 ipopts = (m) ? ip_srcroute(m) : NULL;
1511 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
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
1517 * If a signed packet fails validation or a non-signed packet has a
1518 * security association, the packet will be dropped.
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)
1526 if (TCPMD5_ENABLED() &&
1527 TCPMD5_INPUT(m, NULL, NULL) != ENOENT)
1530 } else if (to->to_flags & TOF_SIGNATURE)
1532 #endif /* TCP_SIGNATURE */
1534 * See if we already have an entry for this connection.
1535 * If we do, resend the SYN,ACK, and reset the retransmit timer.
1537 * XXX: should the syncache be re-initialized with the contents
1538 * of the new SYN here (which may have different options?)
1540 * XXX: We do not check the sequence number to see if this is a
1541 * real retransmit or a new connection attempt. The question is
1542 * how to handle such a case; either ignore it as spoofed, or
1543 * drop the current entry and create a new one?
1545 if (syncache_cookiesonly()) {
1547 sch = syncache_hashbucket(inc);
1550 sc = syncache_lookup(inc, &sch); /* returns locked sch */
1552 SCH_LOCK_ASSERT(sch);
1555 if (tfo_cookie_valid)
1557 TCPSTAT_INC(tcps_sc_dupsyn);
1560 * If we were remembering a previous source route,
1561 * forget it and use the new one we've been given.
1564 (void) m_free(sc->sc_ipopts);
1565 sc->sc_ipopts = ipopts;
1568 * Update timestamp if present.
1570 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
1571 sc->sc_tsreflect = to->to_tsval;
1573 sc->sc_flags &= ~SCF_TIMESTAMP;
1575 * Adjust ECN response if needed, e.g. different
1576 * IP ECN field, or a fallback by the remote host.
1578 if (sc->sc_flags & SCF_ECN_MASK) {
1579 sc->sc_flags &= ~SCF_ECN_MASK;
1580 sc->sc_flags = tcp_ecn_syncache_add(tcp_get_flags(th), iptos);
1584 * Since we have already unconditionally allocated label
1585 * storage, free it up. The syncache entry will already
1586 * have an initialized label we can use.
1588 mac_syncache_destroy(&maclabel);
1590 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1591 /* Retransmit SYN|ACK and reset retransmit count. */
1592 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
1593 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
1594 "resetting timer and retransmitting SYN|ACK\n",
1598 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) {
1600 syncache_timeout(sc, sch, 1);
1601 TCPSTAT_INC(tcps_sndacks);
1602 TCPSTAT_INC(tcps_sndtotal);
1608 if (tfo_cookie_valid) {
1609 bzero(&scs, sizeof(scs));
1615 * Skip allocating a syncache entry if we are just going to discard
1619 bzero(&scs, sizeof(scs));
1622 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1625 * The zone allocator couldn't provide more entries.
1626 * Treat this as if the cache was full; drop the oldest
1627 * entry and insert the new one.
1629 TCPSTAT_INC(tcps_sc_zonefail);
1630 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) {
1631 sch->sch_last_overflow = time_uptime;
1632 syncache_drop(sc, sch);
1633 syncache_pause(inc);
1635 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1637 if (V_tcp_syncookies) {
1638 bzero(&scs, sizeof(scs));
1642 ("%s: bucket unexpectedly unlocked",
1646 (void) m_free(ipopts);
1653 if (!tfo_cookie_valid && tfo_response_cookie_valid)
1654 sc->sc_tfo_cookie = &tfo_response_cookie;
1657 * Fill in the syncache values.
1660 sc->sc_label = maclabel;
1665 sc->sc_ipopts = ipopts;
1666 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1667 sc->sc_ip_tos = ip_tos;
1668 sc->sc_ip_ttl = ip_ttl;
1671 sc->sc_todctx = todctx;
1673 sc->sc_irs = th->th_seq;
1675 sc->sc_flowlabel = 0;
1678 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
1679 * win was derived from socket earlier in the function.
1682 win = imin(win, TCP_MAXWIN);
1685 if (V_tcp_do_rfc1323 &&
1686 !(ltflags & TF_NOOPT)) {
1688 * A timestamp received in a SYN makes
1689 * it ok to send timestamp requests and replies.
1691 if ((to->to_flags & TOF_TS) && (V_tcp_do_rfc1323 != 2)) {
1692 sc->sc_tsreflect = to->to_tsval;
1693 sc->sc_flags |= SCF_TIMESTAMP;
1694 sc->sc_tsoff = tcp_new_ts_offset(inc);
1696 if ((to->to_flags & TOF_SCALE) && (V_tcp_do_rfc1323 != 3)) {
1700 * Pick the smallest possible scaling factor that
1701 * will still allow us to scale up to sb_max, aka
1702 * kern.ipc.maxsockbuf.
1704 * We do this because there are broken firewalls that
1705 * will corrupt the window scale option, leading to
1706 * the other endpoint believing that our advertised
1707 * window is unscaled. At scale factors larger than
1708 * 5 the unscaled window will drop below 1500 bytes,
1709 * leading to serious problems when traversing these
1712 * With the default maxsockbuf of 256K, a scale factor
1713 * of 3 will be chosen by this algorithm. Those who
1714 * choose a larger maxsockbuf should watch out
1715 * for the compatibility problems mentioned above.
1717 * RFC1323: The Window field in a SYN (i.e., a <SYN>
1718 * or <SYN,ACK>) segment itself is never scaled.
1720 while (wscale < TCP_MAX_WINSHIFT &&
1721 (TCP_MAXWIN << wscale) < sb_max)
1723 sc->sc_requested_r_scale = wscale;
1724 sc->sc_requested_s_scale = to->to_wscale;
1725 sc->sc_flags |= SCF_WINSCALE;
1728 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1730 * If incoming packet has an MD5 signature, flag this in the
1731 * syncache so that syncache_respond() will do the right thing
1734 if (to->to_flags & TOF_SIGNATURE)
1735 sc->sc_flags |= SCF_SIGNATURE;
1736 #endif /* TCP_SIGNATURE */
1737 if (to->to_flags & TOF_SACKPERM)
1738 sc->sc_flags |= SCF_SACK;
1739 if (to->to_flags & TOF_MSS)
1740 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */
1741 if (ltflags & TF_NOOPT)
1742 sc->sc_flags |= SCF_NOOPT;
1744 if (V_tcp_do_ecn && (tp->t_flags2 & TF2_CANNOT_DO_ECN) == 0)
1745 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos);
1747 if (V_tcp_syncookies)
1748 sc->sc_iss = syncookie_generate(sch, sc);
1750 sc->sc_iss = arc4random();
1752 if (autoflowlabel) {
1753 if (V_tcp_syncookies)
1754 sc->sc_flowlabel = sc->sc_iss;
1756 sc->sc_flowlabel = ip6_randomflowlabel();
1757 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK;
1763 if (tfo_cookie_valid) {
1764 rv = syncache_tfo_expand(sc, so, m, tfo_response_cookie);
1765 /* INP_RUNLOCK(inp) will be performed by the caller */
1769 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1771 * Do a standard 3-way handshake.
1773 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) {
1774 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs)
1776 else if (sc != &scs)
1777 syncache_insert(sc, sch); /* locks and unlocks sch */
1778 TCPSTAT_INC(tcps_sndacks);
1779 TCPSTAT_INC(tcps_sndtotal);
1783 TCPSTAT_INC(tcps_sc_dropped);
1788 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1793 * If tfo_pending is not NULL here, then a TFO SYN that did not
1794 * result in a new socket was processed and the associated pending
1795 * counter has not yet been decremented. All such TFO processing paths
1796 * transit this point.
1798 if (tfo_pending != NULL)
1799 tcp_fastopen_decrement_counter(tfo_pending);
1806 mac_syncache_destroy(&maclabel);
1812 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment,
1813 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL.
1816 syncache_respond(struct syncache *sc, const struct mbuf *m0, int flags)
1818 struct ip *ip = NULL;
1820 struct tcphdr *th = NULL;
1821 struct udphdr *udp = NULL;
1822 int optlen, error = 0; /* Make compiler happy */
1823 u_int16_t hlen, tlen, mssopt, ulen;
1826 struct ip6_hdr *ip6 = NULL;
1833 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
1836 tlen = hlen + sizeof(struct tcphdr);
1838 tlen += sizeof(struct udphdr);
1840 /* Determine MSS we advertize to other end of connection. */
1841 mssopt = tcp_mssopt(&sc->sc_inc);
1843 mssopt -= V_tcp_udp_tunneling_overhead;
1844 mssopt = max(mssopt, V_tcp_minmss);
1846 /* XXX: Assume that the entire packet will fit in a header mbuf. */
1847 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
1848 ("syncache: mbuf too small: hlen %u, sc_port %u, max_linkhdr %d + "
1849 "tlen %d + TCP_MAXOLEN %ju <= MHLEN %d", hlen, sc->sc_port,
1850 max_linkhdr, tlen, (uintmax_t)TCP_MAXOLEN, MHLEN));
1852 /* Create the IP+TCP header from scratch. */
1853 m = m_gethdr(M_NOWAIT, MT_DATA);
1857 mac_syncache_create_mbuf(sc->sc_label, m);
1859 m->m_data += max_linkhdr;
1861 m->m_pkthdr.len = tlen;
1862 m->m_pkthdr.rcvif = NULL;
1865 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1866 ip6 = mtod(m, struct ip6_hdr *);
1867 ip6->ip6_vfc = IPV6_VERSION;
1868 ip6->ip6_src = sc->sc_inc.inc6_laddr;
1869 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
1870 ip6->ip6_plen = htons(tlen - hlen);
1871 /* ip6_hlim is set after checksum */
1872 /* Zero out traffic class and flow label. */
1873 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK;
1874 ip6->ip6_flow |= sc->sc_flowlabel;
1875 if (sc->sc_port != 0) {
1876 ip6->ip6_nxt = IPPROTO_UDP;
1877 udp = (struct udphdr *)(ip6 + 1);
1878 udp->uh_sport = htons(V_tcp_udp_tunneling_port);
1879 udp->uh_dport = sc->sc_port;
1880 ulen = (tlen - sizeof(struct ip6_hdr));
1881 th = (struct tcphdr *)(udp + 1);
1883 ip6->ip6_nxt = IPPROTO_TCP;
1884 th = (struct tcphdr *)(ip6 + 1);
1886 ip6->ip6_flow |= htonl(sc->sc_ip_tos << IPV6_FLOWLABEL_LEN);
1889 #if defined(INET6) && defined(INET)
1894 ip = mtod(m, struct ip *);
1895 ip->ip_v = IPVERSION;
1896 ip->ip_hl = sizeof(struct ip) >> 2;
1897 ip->ip_len = htons(tlen);
1901 ip->ip_src = sc->sc_inc.inc_laddr;
1902 ip->ip_dst = sc->sc_inc.inc_faddr;
1903 ip->ip_ttl = sc->sc_ip_ttl;
1904 ip->ip_tos = sc->sc_ip_tos;
1907 * See if we should do MTU discovery. Route lookups are
1908 * expensive, so we will only unset the DF bit if:
1910 * 1) path_mtu_discovery is disabled
1911 * 2) the SCF_UNREACH flag has been set
1913 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
1914 ip->ip_off |= htons(IP_DF);
1915 if (sc->sc_port == 0) {
1916 ip->ip_p = IPPROTO_TCP;
1917 th = (struct tcphdr *)(ip + 1);
1919 ip->ip_p = IPPROTO_UDP;
1920 udp = (struct udphdr *)(ip + 1);
1921 udp->uh_sport = htons(V_tcp_udp_tunneling_port);
1922 udp->uh_dport = sc->sc_port;
1923 ulen = (tlen - sizeof(struct ip));
1924 th = (struct tcphdr *)(udp + 1);
1928 th->th_sport = sc->sc_inc.inc_lport;
1929 th->th_dport = sc->sc_inc.inc_fport;
1932 th->th_seq = htonl(sc->sc_iss);
1934 th->th_seq = htonl(sc->sc_iss + 1);
1935 th->th_ack = htonl(sc->sc_irs + 1);
1936 th->th_off = sizeof(struct tcphdr) >> 2;
1937 th->th_win = htons(sc->sc_wnd);
1940 flags = tcp_ecn_syncache_respond(flags, sc);
1941 tcp_set_flags(th, flags);
1943 /* Tack on the TCP options. */
1944 if ((sc->sc_flags & SCF_NOOPT) == 0) {
1947 if (flags & TH_SYN) {
1949 to.to_flags = TOF_MSS;
1950 if (sc->sc_flags & SCF_WINSCALE) {
1951 to.to_wscale = sc->sc_requested_r_scale;
1952 to.to_flags |= TOF_SCALE;
1954 if (sc->sc_flags & SCF_SACK)
1955 to.to_flags |= TOF_SACKPERM;
1956 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1957 if (sc->sc_flags & SCF_SIGNATURE)
1958 to.to_flags |= TOF_SIGNATURE;
1960 if (sc->sc_tfo_cookie) {
1961 to.to_flags |= TOF_FASTOPEN;
1962 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
1963 to.to_tfo_cookie = sc->sc_tfo_cookie;
1964 /* don't send cookie again when retransmitting response */
1965 sc->sc_tfo_cookie = NULL;
1968 if (sc->sc_flags & SCF_TIMESTAMP) {
1969 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks();
1970 to.to_tsecr = sc->sc_tsreflect;
1971 to.to_flags |= TOF_TS;
1973 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
1975 /* Adjust headers by option size. */
1976 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
1978 m->m_pkthdr.len += optlen;
1980 if (sc->sc_inc.inc_flags & INC_ISIPV6)
1981 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
1984 ip->ip_len = htons(ntohs(ip->ip_len) + optlen);
1985 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1986 if (sc->sc_flags & SCF_SIGNATURE) {
1987 KASSERT(to.to_flags & TOF_SIGNATURE,
1988 ("tcp_addoptions() didn't set tcp_signature"));
1990 /* NOTE: to.to_signature is inside of mbuf */
1991 if (!TCPMD5_ENABLED() ||
1992 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) {
2003 udp->uh_ulen = htons(ulen);
2005 M_SETFIB(m, sc->sc_inc.inc_fibnum);
2007 * If we have peer's SYN and it has a flowid, then let's assign it to
2008 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid
2009 * to SYN|ACK due to lack of inp here.
2011 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) {
2012 m->m_pkthdr.flowid = m0->m_pkthdr.flowid;
2013 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0));
2016 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
2018 m->m_pkthdr.csum_flags = CSUM_UDP_IPV6;
2019 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
2020 udp->uh_sum = in6_cksum_pseudo(ip6, ulen,
2022 th->th_sum = htons(0);
2024 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
2025 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
2026 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen,
2029 ip6->ip6_hlim = sc->sc_ip_ttl;
2031 if (ADDED_BY_TOE(sc)) {
2032 struct toedev *tod = sc->sc_tod;
2034 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
2039 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th);
2040 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
2043 #if defined(INET6) && defined(INET)
2049 m->m_pkthdr.csum_flags = CSUM_UDP;
2050 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
2051 udp->uh_sum = in_pseudo(ip->ip_src.s_addr,
2052 ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP));
2053 th->th_sum = htons(0);
2055 m->m_pkthdr.csum_flags = CSUM_TCP;
2056 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
2057 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
2058 htons(tlen + optlen - hlen + IPPROTO_TCP));
2061 if (ADDED_BY_TOE(sc)) {
2062 struct toedev *tod = sc->sc_tod;
2064 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
2069 TCP_PROBE5(send, NULL, NULL, ip, NULL, th);
2070 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
2077 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks
2078 * that exceed the capacity of the syncache by avoiding the storage of any
2079 * of the SYNs we receive. Syncookies defend against blind SYN flooding
2080 * attacks where the attacker does not have access to our responses.
2082 * Syncookies encode and include all necessary information about the
2083 * connection setup within the SYN|ACK that we send back. That way we
2084 * can avoid keeping any local state until the ACK to our SYN|ACK returns
2085 * (if ever). Normally the syncache and syncookies are running in parallel
2086 * with the latter taking over when the former is exhausted. When matching
2087 * syncache entry is found the syncookie is ignored.
2089 * The only reliable information persisting the 3WHS is our initial sequence
2090 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient
2091 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS
2092 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK
2093 * returns and signifies a legitimate connection if it matches the ACK.
2095 * The available space of 32 bits to store the hash and to encode the SYN
2096 * option information is very tight and we should have at least 24 bits for
2097 * the MAC to keep the number of guesses by blind spoofing reasonably high.
2099 * SYN option information we have to encode to fully restore a connection:
2100 * MSS: is imporant to chose an optimal segment size to avoid IP level
2101 * fragmentation along the path. The common MSS values can be encoded
2102 * in a 3-bit table. Uncommon values are captured by the next lower value
2103 * in the table leading to a slight increase in packetization overhead.
2104 * WSCALE: is necessary to allow large windows to be used for high delay-
2105 * bandwidth product links. Not scaling the window when it was initially
2106 * negotiated is bad for performance as lack of scaling further decreases
2107 * the apparent available send window. We only need to encode the WSCALE
2108 * we received from the remote end. Our end can be recalculated at any
2109 * time. The common WSCALE values can be encoded in a 3-bit table.
2110 * Uncommon values are captured by the next lower value in the table
2111 * making us under-estimate the available window size halving our
2112 * theoretically possible maximum throughput for that connection.
2113 * SACK: Greatly assists in packet loss recovery and requires 1 bit.
2114 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options
2115 * that are included in all segments on a connection. We enable them when
2118 * Security of syncookies and attack vectors:
2120 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod)
2121 * together with the gloabl secret to make it unique per connection attempt.
2122 * Thus any change of any of those parameters results in a different MAC output
2123 * in an unpredictable way unless a collision is encountered. 24 bits of the
2124 * MAC are embedded into the ISS.
2126 * To prevent replay attacks two rotating global secrets are updated with a
2127 * new random value every 15 seconds. The life-time of a syncookie is thus
2130 * Vector 1: Attacking the secret. This requires finding a weakness in the
2131 * MAC itself or the way it is used here. The attacker can do a chosen plain
2132 * text attack by varying and testing the all parameters under his control.
2133 * The strength depends on the size and randomness of the secret, and the
2134 * cryptographic security of the MAC function. Due to the constant updating
2135 * of the secret the attacker has at most 29.999 seconds to find the secret
2136 * and launch spoofed connections. After that he has to start all over again.
2138 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC
2139 * size an average of 4,823 attempts are required for a 50% chance of success
2140 * to spoof a single syncookie (birthday collision paradox). However the
2141 * attacker is blind and doesn't know if one of his attempts succeeded unless
2142 * he has a side channel to interfere success from. A single connection setup
2143 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets.
2144 * This many attempts are required for each one blind spoofed connection. For
2145 * every additional spoofed connection he has to launch another N attempts.
2146 * Thus for a sustained rate 100 spoofed connections per second approximately
2147 * 1,800,000 packets per second would have to be sent.
2149 * NB: The MAC function should be fast so that it doesn't become a CPU
2150 * exhaustion attack vector itself.
2153 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations
2154 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996
2155 * http://cr.yp.to/syncookies.html (overview)
2156 * http://cr.yp.to/syncookies/archive (details)
2159 * Schematic construction of a syncookie enabled Initial Sequence Number:
2161 * 12345678901234567890123456789012
2162 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP|
2164 * x 24 MAC (truncated)
2165 * W 3 Send Window Scale index
2167 * S 1 SACK permitted
2168 * P 1 Odd/even secret
2172 * Distribution and probability of certain MSS values. Those in between are
2173 * rounded down to the next lower one.
2174 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011]
2175 * .2% .3% 5% 7% 7% 20% 15% 45%
2177 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 };
2180 * Distribution and probability of certain WSCALE values. We have to map the
2181 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3
2182 * bits based on prevalence of certain values. Where we don't have an exact
2183 * match for are rounded down to the next lower one letting us under-estimate
2184 * the true available window. At the moment this would happen only for the
2185 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer
2186 * and window size). The absence of the WSCALE option (no scaling in either
2187 * direction) is encoded with index zero.
2188 * [WSCALE values histograms, Allman, 2012]
2189 * X 10 10 35 5 6 14 10% by host
2190 * X 11 4 5 5 18 49 3% by connections
2192 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 };
2195 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed
2196 * and good cryptographic properties.
2199 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags,
2200 uint8_t *secbits, uintptr_t secmod)
2203 uint32_t siphash[2];
2205 SipHash24_Init(&ctx);
2206 SipHash_SetKey(&ctx, secbits);
2207 switch (inc->inc_flags & INC_ISIPV6) {
2210 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr));
2211 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr));
2216 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr));
2217 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr));
2221 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport));
2222 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport));
2223 SipHash_Update(&ctx, &irs, sizeof(irs));
2224 SipHash_Update(&ctx, &flags, sizeof(flags));
2225 SipHash_Update(&ctx, &secmod, sizeof(secmod));
2226 SipHash_Final((u_int8_t *)&siphash, &ctx);
2228 return (siphash[0] ^ siphash[1]);
2232 syncookie_generate(struct syncache_head *sch, struct syncache *sc)
2234 u_int i, secbit, wscale;
2237 union syncookie cookie;
2241 /* Map our computed MSS into the 3-bit index. */
2242 for (i = nitems(tcp_sc_msstab) - 1;
2243 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0;
2246 cookie.flags.mss_idx = i;
2249 * Map the send window scale into the 3-bit index but only if
2250 * the wscale option was received.
2252 if (sc->sc_flags & SCF_WINSCALE) {
2253 wscale = sc->sc_requested_s_scale;
2254 for (i = nitems(tcp_sc_wstab) - 1;
2255 tcp_sc_wstab[i] > wscale && i > 0;
2258 cookie.flags.wscale_idx = i;
2261 /* Can we do SACK? */
2262 if (sc->sc_flags & SCF_SACK)
2263 cookie.flags.sack_ok = 1;
2265 /* Which of the two secrets to use. */
2266 secbit = V_tcp_syncache.secret.oddeven & 0x1;
2267 cookie.flags.odd_even = secbit;
2269 secbits = V_tcp_syncache.secret.key[secbit];
2270 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits,
2274 * Put the flags into the hash and XOR them to get better ISS number
2275 * variance. This doesn't enhance the cryptographic strength and is
2276 * done to prevent the 8 cookie bits from showing up directly on the
2280 iss |= cookie.cookie ^ (hash >> 24);
2282 TCPSTAT_INC(tcps_sc_sendcookie);
2286 static struct syncache *
2287 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch,
2288 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
2289 struct socket *lso, uint16_t port)
2294 int wnd, wscale = 0;
2295 union syncookie cookie;
2298 * Pull information out of SYN-ACK/ACK and revert sequence number
2301 ack = th->th_ack - 1;
2302 seq = th->th_seq - 1;
2305 * Unpack the flags containing enough information to restore the
2308 cookie.cookie = (ack & 0xff) ^ (ack >> 24);
2310 /* Which of the two secrets to use. */
2311 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even];
2313 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch);
2315 /* The recomputed hash matches the ACK if this was a genuine cookie. */
2316 if ((ack & ~0xff) != (hash & ~0xff))
2319 /* Fill in the syncache values. */
2321 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
2322 sc->sc_ipopts = NULL;
2327 switch (inc->inc_flags & INC_ISIPV6) {
2330 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl;
2331 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos;
2336 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL)
2338 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK;
2343 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx];
2345 /* We can simply recompute receive window scale we sent earlier. */
2346 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max)
2349 /* Only use wscale if it was enabled in the orignal SYN. */
2350 if (cookie.flags.wscale_idx > 0) {
2351 sc->sc_requested_r_scale = wscale;
2352 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx];
2353 sc->sc_flags |= SCF_WINSCALE;
2356 wnd = lso->sol_sbrcv_hiwat;
2358 wnd = imin(wnd, TCP_MAXWIN);
2361 if (cookie.flags.sack_ok)
2362 sc->sc_flags |= SCF_SACK;
2364 if (to->to_flags & TOF_TS) {
2365 sc->sc_flags |= SCF_TIMESTAMP;
2366 sc->sc_tsreflect = to->to_tsval;
2367 sc->sc_tsoff = tcp_new_ts_offset(inc);
2370 if (to->to_flags & TOF_SIGNATURE)
2371 sc->sc_flags |= SCF_SIGNATURE;
2377 TCPSTAT_INC(tcps_sc_recvcookie);
2383 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
2384 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
2385 struct socket *lso, uint16_t port)
2387 struct syncache scs, *scx;
2390 bzero(&scs, sizeof(scs));
2391 scx = syncookie_lookup(inc, sch, &scs, th, to, lso, port);
2393 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL)
2397 if (sc->sc_peer_mss != scx->sc_peer_mss)
2398 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n",
2399 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss);
2401 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale)
2402 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n",
2403 s, __func__, sc->sc_requested_r_scale,
2404 scx->sc_requested_r_scale);
2406 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale)
2407 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n",
2408 s, __func__, sc->sc_requested_s_scale,
2409 scx->sc_requested_s_scale);
2411 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK))
2412 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__);
2419 #endif /* INVARIANTS */
2422 syncookie_reseed(void *arg)
2424 struct tcp_syncache *sc = arg;
2429 * Reseeding the secret doesn't have to be protected by a lock.
2430 * It only must be ensured that the new random values are visible
2431 * to all CPUs in a SMP environment. The atomic with release
2432 * semantics ensures that.
2434 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1;
2435 secbits = sc->secret.key[secbit];
2436 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0);
2437 atomic_add_rel_int(&sc->secret.oddeven, 1);
2439 /* Reschedule ourself. */
2440 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz);
2444 * We have overflowed a bucket. Let's pause dealing with the syncache.
2445 * This function will increment the bucketoverflow statistics appropriately
2446 * (once per pause when pausing is enabled; otherwise, once per overflow).
2449 syncache_pause(struct in_conninfo *inc)
2455 * 2. Add sysctl read here so we don't get the benefit of this
2456 * change without the new sysctl.
2460 * Try an unlocked read. If we already know that another thread
2461 * has activated the feature, there is no need to proceed.
2463 if (V_tcp_syncache.paused)
2466 /* Are cookied enabled? If not, we can't pause. */
2467 if (!V_tcp_syncookies) {
2468 TCPSTAT_INC(tcps_sc_bucketoverflow);
2473 * We may be the first thread to find an overflow. Get the lock
2474 * and evaluate if we need to take action.
2476 mtx_lock(&V_tcp_syncache.pause_mtx);
2477 if (V_tcp_syncache.paused) {
2478 mtx_unlock(&V_tcp_syncache.pause_mtx);
2482 /* Activate protection. */
2483 V_tcp_syncache.paused = true;
2484 TCPSTAT_INC(tcps_sc_bucketoverflow);
2487 * Determine the last backoff time. If we are seeing a re-newed
2488 * attack within that same time after last reactivating the syncache,
2489 * consider it an extension of the same attack.
2491 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff;
2492 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) {
2493 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) {
2495 V_tcp_syncache.pause_backoff++;
2498 delta = TCP_SYNCACHE_PAUSE_TIME;
2499 V_tcp_syncache.pause_backoff = 0;
2502 /* Log a warning, including IP addresses, if able. */
2504 s = tcp_log_addrs(inc, NULL, NULL, NULL);
2506 s = (const char *)NULL;
2507 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for "
2508 "the next %lld seconds%s%s%s\n", (long long)delta,
2509 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "",
2510 (s != NULL) ? ")" : "");
2511 free(__DECONST(void *, s), M_TCPLOG);
2513 /* Use the calculated delta to set a new pause time. */
2514 V_tcp_syncache.pause_until = time_uptime + delta;
2515 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause,
2517 mtx_unlock(&V_tcp_syncache.pause_mtx);
2520 /* Evaluate whether we need to unpause. */
2522 syncache_unpause(void *arg)
2524 struct tcp_syncache *sc;
2528 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED);
2529 callout_deactivate(&sc->pause_co);
2532 * Check to make sure we are not running early. If the pause
2533 * time has expired, then deactivate the protection.
2535 if ((delta = sc->pause_until - time_uptime) > 0)
2536 callout_schedule(&sc->pause_co, delta * hz);
2542 * Exports the syncache entries to userland so that netstat can display
2543 * them alongside the other sockets. This function is intended to be
2544 * called only from tcp_pcblist.
2546 * Due to concurrency on an active system, the number of pcbs exported
2547 * may have no relation to max_pcbs. max_pcbs merely indicates the
2548 * amount of space the caller allocated for this function to use.
2551 syncache_pcblist(struct sysctl_req *req)
2554 struct syncache *sc;
2555 struct syncache_head *sch;
2558 bzero(&xt, sizeof(xt));
2559 xt.xt_len = sizeof(xt);
2560 xt.t_state = TCPS_SYN_RECEIVED;
2561 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP;
2562 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket);
2563 xt.xt_inp.xi_socket.so_type = SOCK_STREAM;
2564 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING;
2566 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
2567 sch = &V_tcp_syncache.hashbase[i];
2569 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
2570 if (sc->sc_cred != NULL &&
2571 cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
2573 if (sc->sc_inc.inc_flags & INC_ISIPV6)
2574 xt.xt_inp.inp_vflag = INP_IPV6;
2576 xt.xt_inp.inp_vflag = INP_IPV4;
2577 xt.xt_encaps_port = sc->sc_port;
2578 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc,
2579 sizeof (struct in_conninfo));
2580 error = SYSCTL_OUT(req, &xt, sizeof xt);