2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
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"
41 #include "opt_pcbgroup.h"
43 #include <sys/param.h>
44 #include <sys/systm.h>
46 #include <sys/refcount.h>
47 #include <sys/kernel.h>
48 #include <sys/sysctl.h>
49 #include <sys/limits.h>
51 #include <sys/mutex.h>
52 #include <sys/malloc.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>
62 #include <crypto/siphash/siphash.h>
67 #include <net/if_var.h>
68 #include <net/route.h>
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>
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>
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>
94 #include <netinet6/tcp6_var.h>
97 #include <netinet/toecore.h>
100 #include <netipsec/ipsec_support.h>
102 #include <machine/in_cksum.h>
104 #include <security/mac/mac_framework.h>
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");
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");
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");
127 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL)
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 *, const struct mbuf *, int);
134 static struct socket *syncache_socket(struct syncache *, struct socket *,
136 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch,
138 static void syncache_timer(void *);
140 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t,
141 uint8_t *, uintptr_t);
142 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *);
143 static struct syncache
144 *syncookie_lookup(struct in_conninfo *, struct syncache_head *,
145 struct syncache *, struct tcphdr *, struct tcpopt *,
147 static void syncache_pause(struct in_conninfo *);
148 static void syncache_unpause(void *);
149 static void syncookie_reseed(void *);
151 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
152 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
157 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
158 * 3 retransmits corresponds to a timeout with default values of
159 * tcp_rexmit_initial * ( 1 +
162 * tcp_backoff[3]) + 3 * tcp_rexmit_slop,
163 * 1000 ms * (1 + 2 + 4 + 8) + 3 * 200 ms = 15600 ms,
164 * the odds are that the user has given up attempting to connect by then.
166 #define SYNCACHE_MAXREXMTS 3
168 /* Arbitrary values */
169 #define TCP_SYNCACHE_HASHSIZE 512
170 #define TCP_SYNCACHE_BUCKETLIMIT 30
172 VNET_DEFINE_STATIC(struct tcp_syncache, tcp_syncache);
173 #define V_tcp_syncache VNET(tcp_syncache)
175 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache,
176 CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
179 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
180 &VNET_NAME(tcp_syncache.bucket_limit), 0,
181 "Per-bucket hash limit for syncache");
183 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
184 &VNET_NAME(tcp_syncache.cache_limit), 0,
185 "Overall entry limit for syncache");
187 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET,
188 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache");
190 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN,
191 &VNET_NAME(tcp_syncache.hashsize), 0,
192 "Size of TCP syncache hashtable");
195 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS)
200 new = V_tcp_syncache.rexmt_limit;
201 error = sysctl_handle_int(oidp, &new, 0, req);
202 if ((error == 0) && (req->newptr != NULL)) {
203 if (new > TCP_MAXRXTSHIFT)
206 V_tcp_syncache.rexmt_limit = new;
211 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit,
212 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
213 &VNET_NAME(tcp_syncache.rexmt_limit), 0,
214 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "UI",
215 "Limit on SYN/ACK retransmissions");
217 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1;
218 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail,
219 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0,
220 "Send reset on socket allocation failure");
222 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
224 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx)
225 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx)
226 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED)
229 * Requires the syncache entry to be already removed from the bucket list.
232 syncache_free(struct syncache *sc)
236 (void) m_free(sc->sc_ipopts);
240 mac_syncache_destroy(&sc->sc_label);
243 uma_zfree(V_tcp_syncache.zone, sc);
251 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
252 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
253 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
254 V_tcp_syncache.hash_secret = arc4random();
256 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
257 &V_tcp_syncache.hashsize);
258 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
259 &V_tcp_syncache.bucket_limit);
260 if (!powerof2(V_tcp_syncache.hashsize) ||
261 V_tcp_syncache.hashsize == 0) {
262 printf("WARNING: syncache hash size is not a power of 2.\n");
263 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
265 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1;
268 V_tcp_syncache.cache_limit =
269 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit;
270 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
271 &V_tcp_syncache.cache_limit);
273 /* Allocate the hash table. */
274 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize *
275 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO);
278 V_tcp_syncache.vnet = curvnet;
281 /* Initialize the hash buckets. */
282 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
283 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket);
284 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
286 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer,
287 &V_tcp_syncache.hashbase[i].sch_mtx, 0);
288 V_tcp_syncache.hashbase[i].sch_length = 0;
289 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache;
290 V_tcp_syncache.hashbase[i].sch_last_overflow =
291 -(SYNCOOKIE_LIFETIME + 1);
294 /* Create the syncache entry zone. */
295 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
296 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
297 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone,
298 V_tcp_syncache.cache_limit);
300 /* Start the SYN cookie reseeder callout. */
301 callout_init(&V_tcp_syncache.secret.reseed, 1);
302 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0);
303 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0);
304 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz,
305 syncookie_reseed, &V_tcp_syncache);
307 /* Initialize the pause machinery. */
308 mtx_init(&V_tcp_syncache.pause_mtx, "tcp_sc_pause", NULL, MTX_DEF);
309 callout_init_mtx(&V_tcp_syncache.pause_co, &V_tcp_syncache.pause_mtx,
311 V_tcp_syncache.pause_until = time_uptime - TCP_SYNCACHE_PAUSE_TIME;
312 V_tcp_syncache.pause_backoff = 0;
313 V_tcp_syncache.paused = false;
318 syncache_destroy(void)
320 struct syncache_head *sch;
321 struct syncache *sc, *nsc;
325 * Stop the re-seed timer before freeing resources. No need to
326 * possibly schedule it another time.
328 callout_drain(&V_tcp_syncache.secret.reseed);
330 /* Stop the SYN cache pause callout. */
331 mtx_lock(&V_tcp_syncache.pause_mtx);
332 if (callout_stop(&V_tcp_syncache.pause_co) == 0) {
333 mtx_unlock(&V_tcp_syncache.pause_mtx);
334 callout_drain(&V_tcp_syncache.pause_co);
336 mtx_unlock(&V_tcp_syncache.pause_mtx);
338 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */
339 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
340 sch = &V_tcp_syncache.hashbase[i];
341 callout_drain(&sch->sch_timer);
344 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc)
345 syncache_drop(sc, sch);
347 KASSERT(TAILQ_EMPTY(&sch->sch_bucket),
348 ("%s: sch->sch_bucket not empty", __func__));
349 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0",
350 __func__, sch->sch_length));
351 mtx_destroy(&sch->sch_mtx);
354 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0,
355 ("%s: cache_count not 0", __func__));
357 /* Free the allocated global resources. */
358 uma_zdestroy(V_tcp_syncache.zone);
359 free(V_tcp_syncache.hashbase, M_SYNCACHE);
360 mtx_destroy(&V_tcp_syncache.pause_mtx);
365 * Inserts a syncache entry into the specified bucket row.
366 * Locks and unlocks the syncache_head autonomously.
369 syncache_insert(struct syncache *sc, struct syncache_head *sch)
371 struct syncache *sc2;
376 * Make sure that we don't overflow the per-bucket limit.
377 * If the bucket is full, toss the oldest element.
379 if (sch->sch_length >= V_tcp_syncache.bucket_limit) {
380 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
381 ("sch->sch_length incorrect"));
382 syncache_pause(&sc->sc_inc);
383 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
384 sch->sch_last_overflow = time_uptime;
385 syncache_drop(sc2, sch);
388 /* Put it into the bucket. */
389 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
393 if (ADDED_BY_TOE(sc)) {
394 struct toedev *tod = sc->sc_tod;
396 tod->tod_syncache_added(tod, sc->sc_todctx);
400 /* Reinitialize the bucket row's timer. */
401 if (sch->sch_length == 1)
402 sch->sch_nextc = ticks + INT_MAX;
403 syncache_timeout(sc, sch, 1);
407 TCPSTATES_INC(TCPS_SYN_RECEIVED);
408 TCPSTAT_INC(tcps_sc_added);
412 * Remove and free entry from syncache bucket row.
413 * Expects locked syncache head.
416 syncache_drop(struct syncache *sc, struct syncache_head *sch)
419 SCH_LOCK_ASSERT(sch);
421 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
422 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
426 if (ADDED_BY_TOE(sc)) {
427 struct toedev *tod = sc->sc_tod;
429 tod->tod_syncache_removed(tod, sc->sc_todctx);
437 * Engage/reengage time on bucket row.
440 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
444 if (sc->sc_rxmits == 0)
445 rexmt = tcp_rexmit_initial;
448 tcp_rexmit_initial * tcp_backoff[sc->sc_rxmits],
449 tcp_rexmit_min, TCPTV_REXMTMAX);
450 sc->sc_rxttime = ticks + rexmt;
452 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
453 sch->sch_nextc = sc->sc_rxttime;
455 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
456 syncache_timer, (void *)sch);
461 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
462 * If we have retransmitted an entry the maximum number of times, expire it.
463 * One separate timer for each bucket row.
466 syncache_timer(void *xsch)
468 struct syncache_head *sch = (struct syncache_head *)xsch;
469 struct syncache *sc, *nsc;
470 struct epoch_tracker et;
475 CURVNET_SET(sch->sch_sc->vnet);
477 /* NB: syncache_head has already been locked by the callout. */
478 SCH_LOCK_ASSERT(sch);
481 * In the following cycle we may remove some entries and/or
482 * advance some timeouts, so re-initialize the bucket timer.
484 sch->sch_nextc = tick + INT_MAX;
487 * If we have paused processing, unconditionally remove
488 * all syncache entries.
490 mtx_lock(&V_tcp_syncache.pause_mtx);
491 paused = V_tcp_syncache.paused;
492 mtx_unlock(&V_tcp_syncache.pause_mtx);
494 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
496 syncache_drop(sc, sch);
500 * We do not check if the listen socket still exists
501 * and accept the case where the listen socket may be
502 * gone by the time we resend the SYN/ACK. We do
503 * not expect this to happens often. If it does,
504 * then the RST will be sent by the time the remote
505 * host does the SYN/ACK->ACK.
507 if (TSTMP_GT(sc->sc_rxttime, tick)) {
508 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
509 sch->sch_nextc = sc->sc_rxttime;
512 if (sc->sc_rxmits > V_tcp_ecn_maxretries) {
513 sc->sc_flags &= ~SCF_ECN;
515 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
516 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
517 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
518 "giving up and removing syncache entry\n",
522 syncache_drop(sc, sch);
523 TCPSTAT_INC(tcps_sc_stale);
526 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
527 log(LOG_DEBUG, "%s; %s: Response timeout, "
528 "retransmitting (%u) SYN|ACK\n",
529 s, __func__, sc->sc_rxmits);
534 syncache_respond(sc, NULL, TH_SYN|TH_ACK);
536 TCPSTAT_INC(tcps_sc_retransmitted);
537 syncache_timeout(sc, sch, 0);
539 if (!TAILQ_EMPTY(&(sch)->sch_bucket))
540 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
541 syncache_timer, (void *)(sch));
546 * Returns true if the system is only using cookies at the moment.
547 * This could be due to a sysadmin decision to only use cookies, or it
548 * could be due to the system detecting an attack.
551 syncache_cookiesonly(void)
554 return (V_tcp_syncookies && (V_tcp_syncache.paused ||
555 V_tcp_syncookiesonly));
559 * Find the hash bucket for the given connection.
561 static struct syncache_head *
562 syncache_hashbucket(struct in_conninfo *inc)
567 * The hash is built on foreign port + local port + foreign address.
568 * We rely on the fact that struct in_conninfo starts with 16 bits
569 * of foreign port, then 16 bits of local port then followed by 128
570 * bits of foreign address. In case of IPv4 address, the first 3
571 * 32-bit words of the address always are zeroes.
573 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5,
574 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask;
576 return (&V_tcp_syncache.hashbase[hash]);
580 * Find an entry in the syncache.
581 * Returns always with locked syncache_head plus a matching entry or NULL.
583 static struct syncache *
584 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
587 struct syncache_head *sch;
589 *schp = sch = syncache_hashbucket(inc);
592 /* Circle through bucket row to find matching entry. */
593 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash)
594 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie,
595 sizeof(struct in_endpoints)) == 0)
598 return (sc); /* Always returns with locked sch. */
602 * This function is called when we get a RST for a
603 * non-existent connection, so that we can see if the
604 * connection is in the syn cache. If it is, zap it.
605 * If required send a challenge ACK.
608 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, struct mbuf *m)
611 struct syncache_head *sch;
614 if (syncache_cookiesonly())
616 sc = syncache_lookup(inc, &sch); /* returns locked sch */
617 SCH_LOCK_ASSERT(sch);
620 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags.
621 * See RFC 793 page 65, section SEGMENT ARRIVES.
623 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) {
624 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
625 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or "
626 "FIN flag set, segment ignored\n", s, __func__);
627 TCPSTAT_INC(tcps_badrst);
632 * No corresponding connection was found in syncache.
633 * If syncookies are enabled and possibly exclusively
634 * used, or we are under memory pressure, a valid RST
635 * may not find a syncache entry. In that case we're
636 * done and no SYN|ACK retransmissions will happen.
637 * Otherwise the RST was misdirected or spoofed.
640 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
641 log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
642 "syncache entry (possibly syncookie only), "
643 "segment ignored\n", s, __func__);
644 TCPSTAT_INC(tcps_badrst);
649 * If the RST bit is set, check the sequence number to see
650 * if this is a valid reset segment.
653 * In all states except SYN-SENT, all reset (RST) segments
654 * are validated by checking their SEQ-fields. A reset is
655 * valid if its sequence number is in the window.
658 * There are four cases for the acceptability test for an incoming
661 * Segment Receive Test
663 * ------- ------- -------------------------------------------
664 * 0 0 SEG.SEQ = RCV.NXT
665 * 0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND
666 * >0 0 not acceptable
667 * >0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND
668 * or RCV.NXT =< SEG.SEQ+SEG.LEN-1 < RCV.NXT+RCV.WND
670 * Note that when receiving a SYN segment in the LISTEN state,
671 * IRS is set to SEG.SEQ and RCV.NXT is set to SEG.SEQ+1, as
672 * described in RFC 793, page 66.
674 if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) &&
675 SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) ||
676 (sc->sc_wnd == 0 && th->th_seq == sc->sc_irs + 1)) {
677 if (V_tcp_insecure_rst ||
678 th->th_seq == sc->sc_irs + 1) {
679 syncache_drop(sc, sch);
680 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
682 "%s; %s: Our SYN|ACK was rejected, "
683 "connection attempt aborted by remote "
686 TCPSTAT_INC(tcps_sc_reset);
688 TCPSTAT_INC(tcps_badrst);
689 /* Send challenge ACK. */
690 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
691 log(LOG_DEBUG, "%s; %s: RST with invalid "
692 " SEQ %u != NXT %u (+WND %u), "
693 "sending challenge ACK\n",
695 th->th_seq, sc->sc_irs + 1, sc->sc_wnd);
696 syncache_respond(sc, m, TH_ACK);
699 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
700 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
701 "NXT %u (+WND %u), segment ignored\n",
703 th->th_seq, sc->sc_irs + 1, sc->sc_wnd);
704 TCPSTAT_INC(tcps_badrst);
714 syncache_badack(struct in_conninfo *inc)
717 struct syncache_head *sch;
719 if (syncache_cookiesonly())
721 sc = syncache_lookup(inc, &sch); /* returns locked sch */
722 SCH_LOCK_ASSERT(sch);
724 syncache_drop(sc, sch);
725 TCPSTAT_INC(tcps_sc_badack);
731 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq)
734 struct syncache_head *sch;
736 if (syncache_cookiesonly())
738 sc = syncache_lookup(inc, &sch); /* returns locked sch */
739 SCH_LOCK_ASSERT(sch);
743 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
744 if (ntohl(th_seq) != sc->sc_iss)
748 * If we've rertransmitted 3 times and this is our second error,
749 * we remove the entry. Otherwise, we allow it to continue on.
750 * This prevents us from incorrectly nuking an entry during a
751 * spurious network outage.
755 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
756 sc->sc_flags |= SCF_UNREACH;
759 syncache_drop(sc, sch);
760 TCPSTAT_INC(tcps_sc_unreach);
766 * Build a new TCP socket structure from a syncache entry.
768 * On success return the newly created socket with its underlying inp locked.
770 static struct socket *
771 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
773 struct tcp_function_block *blk;
774 struct inpcb *inp = NULL;
783 * Ok, create the full blown connection, and set things up
784 * as they would have been set up if we had created the
785 * connection when the SYN arrived. If we can't create
786 * the connection, abort it.
788 so = sonewconn(lso, 0);
791 * Drop the connection; we will either send a RST or
792 * have the peer retransmit its SYN again after its
795 TCPSTAT_INC(tcps_listendrop);
796 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
797 log(LOG_DEBUG, "%s; %s: Socket create failed "
798 "due to limits or memory shortage\n",
805 mac_socketpeer_set_from_mbuf(m, so);
809 inp->inp_inc.inc_fibnum = so->so_fibnum;
812 * Exclusive pcbinfo lock is not required in syncache socket case even
813 * if two inpcb locks can be acquired simultaneously:
814 * - the inpcb in LISTEN state,
815 * - the newly created inp.
817 * In this case, an inp cannot be at same time in LISTEN state and
818 * just created by an accept() call.
820 INP_HASH_WLOCK(&V_tcbinfo);
822 /* Insert new socket into PCB hash list. */
823 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
825 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
826 inp->inp_vflag &= ~INP_IPV4;
827 inp->inp_vflag |= INP_IPV6;
828 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
830 inp->inp_vflag &= ~INP_IPV6;
831 inp->inp_vflag |= INP_IPV4;
833 inp->inp_ip_ttl = sc->sc_ip_ttl;
834 inp->inp_ip_tos = sc->sc_ip_tos;
835 inp->inp_laddr = sc->sc_inc.inc_laddr;
841 * If there's an mbuf and it has a flowid, then let's initialise the
842 * inp with that particular flowid.
844 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) {
845 inp->inp_flowid = m->m_pkthdr.flowid;
846 inp->inp_flowtype = M_HASHTYPE_GET(m);
848 inp->inp_numa_domain = m->m_pkthdr.numa_domain;
852 inp->inp_lport = sc->sc_inc.inc_lport;
854 if (inp->inp_vflag & INP_IPV6PROTO) {
855 struct inpcb *oinp = sotoinpcb(lso);
858 * Inherit socket options from the listening socket.
859 * Note that in6p_inputopts are not (and should not be)
860 * copied, since it stores previously received options and is
861 * used to detect if each new option is different than the
862 * previous one and hence should be passed to a user.
863 * If we copied in6p_inputopts, a user would not be able to
864 * receive options just after calling the accept system call.
866 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
867 if (oinp->in6p_outputopts)
868 inp->in6p_outputopts =
869 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
870 inp->in6p_hops = oinp->in6p_hops;
873 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
874 struct in6_addr laddr6;
875 struct sockaddr_in6 sin6;
877 sin6.sin6_family = AF_INET6;
878 sin6.sin6_len = sizeof(sin6);
879 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
880 sin6.sin6_port = sc->sc_inc.inc_fport;
881 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
882 laddr6 = inp->in6p_laddr;
883 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
884 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
885 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6,
886 thread0.td_ucred, m, false)) != 0) {
887 inp->in6p_laddr = laddr6;
888 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
889 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed "
894 INP_HASH_WUNLOCK(&V_tcbinfo);
897 /* Override flowlabel from in6_pcbconnect. */
898 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
899 inp->inp_flow |= sc->sc_flowlabel;
902 #if defined(INET) && defined(INET6)
907 struct in_addr laddr;
908 struct sockaddr_in sin;
910 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
912 if (inp->inp_options == NULL) {
913 inp->inp_options = sc->sc_ipopts;
914 sc->sc_ipopts = NULL;
917 sin.sin_family = AF_INET;
918 sin.sin_len = sizeof(sin);
919 sin.sin_addr = sc->sc_inc.inc_faddr;
920 sin.sin_port = sc->sc_inc.inc_fport;
921 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
922 laddr = inp->inp_laddr;
923 if (inp->inp_laddr.s_addr == INADDR_ANY)
924 inp->inp_laddr = sc->sc_inc.inc_laddr;
925 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin,
926 thread0.td_ucred, m, false)) != 0) {
927 inp->inp_laddr = laddr;
928 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
929 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed "
934 INP_HASH_WUNLOCK(&V_tcbinfo);
939 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
940 /* Copy old policy into new socket's. */
941 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0)
942 printf("syncache_socket: could not copy policy\n");
944 INP_HASH_WUNLOCK(&V_tcbinfo);
946 tcp_state_change(tp, TCPS_SYN_RECEIVED);
947 tp->iss = sc->sc_iss;
948 tp->irs = sc->sc_irs;
951 blk = sototcpcb(lso)->t_fb;
952 if (V_functions_inherit_listen_socket_stack && blk != tp->t_fb) {
954 * Our parents t_fb was not the default,
955 * we need to release our ref on tp->t_fb and
956 * pickup one on the new entry.
958 struct tcp_function_block *rblk;
960 rblk = find_and_ref_tcp_fb(blk);
961 KASSERT(rblk != NULL,
962 ("cannot find blk %p out of syncache?", blk));
963 if (tp->t_fb->tfb_tcp_fb_fini)
964 (*tp->t_fb->tfb_tcp_fb_fini)(tp, 0);
965 refcount_release(&tp->t_fb->tfb_refcnt);
968 * XXXrrs this is quite dangerous, it is possible
969 * for the new function to fail to init. We also
970 * are not asking if the handoff_is_ok though at
971 * the very start thats probalbly ok.
973 if (tp->t_fb->tfb_tcp_fb_init) {
974 (*tp->t_fb->tfb_tcp_fb_init)(tp);
977 tp->snd_wl1 = sc->sc_irs;
978 tp->snd_max = tp->iss + 1;
979 tp->snd_nxt = tp->iss + 1;
980 tp->rcv_up = sc->sc_irs + 1;
981 tp->rcv_wnd = sc->sc_wnd;
982 tp->rcv_adv += tp->rcv_wnd;
983 tp->last_ack_sent = tp->rcv_nxt;
985 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
986 if (sc->sc_flags & SCF_NOOPT)
987 tp->t_flags |= TF_NOOPT;
989 if (sc->sc_flags & SCF_WINSCALE) {
990 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
991 tp->snd_scale = sc->sc_requested_s_scale;
992 tp->request_r_scale = sc->sc_requested_r_scale;
994 if (sc->sc_flags & SCF_TIMESTAMP) {
995 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
996 tp->ts_recent = sc->sc_tsreflect;
997 tp->ts_recent_age = tcp_ts_getticks();
998 tp->ts_offset = sc->sc_tsoff;
1000 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1001 if (sc->sc_flags & SCF_SIGNATURE)
1002 tp->t_flags |= TF_SIGNATURE;
1004 if (sc->sc_flags & SCF_SACK)
1005 tp->t_flags |= TF_SACK_PERMIT;
1008 if (sc->sc_flags & SCF_ECN)
1009 tp->t_flags2 |= TF2_ECN_PERMIT;
1012 * Set up MSS and get cached values from tcp_hostcache.
1013 * This might overwrite some of the defaults we just set.
1015 tcp_mss(tp, sc->sc_peer_mss);
1018 * If the SYN,ACK was retransmitted, indicate that CWND to be
1019 * limited to one segment in cc_conn_init().
1020 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
1022 if (sc->sc_rxmits > 1)
1027 * Allow a TOE driver to install its hooks. Note that we hold the
1028 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a
1029 * new connection before the TOE driver has done its thing.
1031 if (ADDED_BY_TOE(sc)) {
1032 struct toedev *tod = sc->sc_tod;
1034 tod->tod_offload_socket(tod, sc->sc_todctx, so);
1038 * Copy and activate timers.
1040 tp->t_keepinit = sototcpcb(lso)->t_keepinit;
1041 tp->t_keepidle = sototcpcb(lso)->t_keepidle;
1042 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl;
1043 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt;
1044 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp));
1046 TCPSTAT_INC(tcps_accepts);
1058 * This function gets called when we receive an ACK for a
1059 * socket in the LISTEN state. We look up the connection
1060 * in the syncache, and if its there, we pull it out of
1061 * the cache and turn it into a full-blown connection in
1062 * the SYN-RECEIVED state.
1064 * On syncache_socket() success the newly created socket
1065 * has its underlying inp locked.
1068 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1069 struct socket **lsop, struct mbuf *m)
1071 struct syncache *sc;
1072 struct syncache_head *sch;
1073 struct syncache scs;
1078 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
1079 ("%s: can handle only ACK", __func__));
1081 if (syncache_cookiesonly()) {
1083 sch = syncache_hashbucket(inc);
1086 sc = syncache_lookup(inc, &sch); /* returns locked sch */
1088 SCH_LOCK_ASSERT(sch);
1093 * Test code for syncookies comparing the syncache stored
1094 * values with the reconstructed values from the cookie.
1097 syncookie_cmp(inc, sch, sc, th, to, *lsop);
1102 * There is no syncache entry, so see if this ACK is
1103 * a returning syncookie. To do this, first:
1104 * A. Check if syncookies are used in case of syncache
1106 * B. See if this socket has had a syncache entry dropped in
1107 * the recent past. We don't want to accept a bogus
1108 * syncookie if we've never received a SYN or accept it
1110 * C. check that the syncookie is valid. If it is, then
1111 * cobble up a fake syncache entry, and return.
1113 if (locked && !V_tcp_syncookies) {
1115 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1116 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
1117 "segment rejected (syncookies disabled)\n",
1121 if (locked && !V_tcp_syncookiesonly &&
1122 sch->sch_last_overflow < time_uptime - SYNCOOKIE_LIFETIME) {
1124 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1125 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
1126 "segment rejected (no syncache entry)\n",
1130 bzero(&scs, sizeof(scs));
1131 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop);
1135 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1136 log(LOG_DEBUG, "%s; %s: Segment failed "
1137 "SYNCOOKIE authentication, segment rejected "
1138 "(probably spoofed)\n", s, __func__);
1141 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1142 /* If received ACK has MD5 signature, check it. */
1143 if ((to->to_flags & TOF_SIGNATURE) != 0 &&
1144 (!TCPMD5_ENABLED() ||
1145 TCPMD5_INPUT(m, th, to->to_signature) != 0)) {
1147 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1148 log(LOG_DEBUG, "%s; %s: Segment rejected, "
1149 "MD5 signature doesn't match.\n",
1153 TCPSTAT_INC(tcps_sig_err_sigopt);
1154 return (-1); /* Do not send RST */
1156 #endif /* TCP_SIGNATURE */
1158 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1160 * If listening socket requested TCP digests, check that
1161 * received ACK has signature and it is correct.
1162 * If not, drop the ACK and leave sc entry in th cache,
1163 * because SYN was received with correct signature.
1165 if (sc->sc_flags & SCF_SIGNATURE) {
1166 if ((to->to_flags & TOF_SIGNATURE) == 0) {
1168 TCPSTAT_INC(tcps_sig_err_nosigopt);
1170 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1171 log(LOG_DEBUG, "%s; %s: Segment "
1172 "rejected, MD5 signature wasn't "
1173 "provided.\n", s, __func__);
1176 return (-1); /* Do not send RST */
1178 if (!TCPMD5_ENABLED() ||
1179 TCPMD5_INPUT(m, th, to->to_signature) != 0) {
1180 /* Doesn't match or no SA */
1182 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1183 log(LOG_DEBUG, "%s; %s: Segment "
1184 "rejected, MD5 signature doesn't "
1185 "match.\n", s, __func__);
1188 return (-1); /* Do not send RST */
1191 #endif /* TCP_SIGNATURE */
1194 * RFC 7323 PAWS: If we have a timestamp on this segment and
1195 * it's less than ts_recent, drop it.
1196 * XXXMT: RFC 7323 also requires to send an ACK.
1197 * In tcp_input.c this is only done for TCP segments
1198 * with user data, so be consistent here and just drop
1201 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS &&
1202 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) {
1204 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1206 "%s; %s: SEG.TSval %u < TS.Recent %u, "
1207 "segment dropped\n", s, __func__,
1208 to->to_tsval, sc->sc_tsreflect);
1211 return (-1); /* Do not send RST */
1215 * If timestamps were not negotiated during SYN/ACK and a
1216 * segment with a timestamp is received, ignore the
1217 * timestamp and process the packet normally.
1218 * See section 3.2 of RFC 7323.
1220 if (!(sc->sc_flags & SCF_TIMESTAMP) &&
1221 (to->to_flags & TOF_TS)) {
1222 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1223 log(LOG_DEBUG, "%s; %s: Timestamp not "
1224 "expected, segment processed normally\n",
1232 * If timestamps were negotiated during SYN/ACK and a
1233 * segment without a timestamp is received, silently drop
1235 * See section 3.2 of RFC 7323.
1237 if ((sc->sc_flags & SCF_TIMESTAMP) &&
1238 !(to->to_flags & TOF_TS)) {
1240 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1241 log(LOG_DEBUG, "%s; %s: Timestamp missing, "
1242 "segment silently dropped\n", s, __func__);
1245 return (-1); /* Do not send RST */
1249 * Pull out the entry to unlock the bucket row.
1251 * NOTE: We must decrease TCPS_SYN_RECEIVED count here, not
1252 * tcp_state_change(). The tcpcb is not existent at this
1253 * moment. A new one will be allocated via syncache_socket->
1254 * sonewconn->tcp_usr_attach in TCPS_CLOSED state, then
1255 * syncache_socket() will change it to TCPS_SYN_RECEIVED.
1257 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
1258 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
1261 if (ADDED_BY_TOE(sc)) {
1262 struct toedev *tod = sc->sc_tod;
1264 tod->tod_syncache_removed(tod, sc->sc_todctx);
1271 * Segment validation:
1272 * ACK must match our initial sequence number + 1 (the SYN|ACK).
1274 if (th->th_ack != sc->sc_iss + 1) {
1275 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1276 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
1277 "rejected\n", s, __func__, th->th_ack, sc->sc_iss);
1282 * The SEQ must fall in the window starting at the received
1283 * initial receive sequence number + 1 (the SYN).
1285 if (SEQ_LEQ(th->th_seq, sc->sc_irs) ||
1286 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
1287 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1288 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
1289 "rejected\n", s, __func__, th->th_seq, sc->sc_irs);
1293 *lsop = syncache_socket(sc, *lsop, m);
1296 TCPSTAT_INC(tcps_sc_aborted);
1298 TCPSTAT_INC(tcps_sc_completed);
1300 /* how do we find the inp for the new socket? */
1305 if (sc != NULL && sc != &scs)
1314 syncache_tfo_expand(struct syncache *sc, struct socket **lsop, struct mbuf *m,
1315 uint64_t response_cookie)
1319 unsigned int *pending_counter;
1323 pending_counter = intotcpcb(sotoinpcb(*lsop))->t_tfo_pending;
1324 *lsop = syncache_socket(sc, *lsop, m);
1325 if (*lsop == NULL) {
1326 TCPSTAT_INC(tcps_sc_aborted);
1327 atomic_subtract_int(pending_counter, 1);
1329 soisconnected(*lsop);
1330 inp = sotoinpcb(*lsop);
1331 tp = intotcpcb(inp);
1332 tp->t_flags |= TF_FASTOPEN;
1333 tp->t_tfo_cookie.server = response_cookie;
1334 tp->snd_max = tp->iss;
1335 tp->snd_nxt = tp->iss;
1336 tp->t_tfo_pending = pending_counter;
1337 TCPSTAT_INC(tcps_sc_completed);
1342 * Given a LISTEN socket and an inbound SYN request, add
1343 * this to the syn cache, and send back a segment:
1344 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
1347 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
1348 * Doing so would require that we hold onto the data and deliver it
1349 * to the application. However, if we are the target of a SYN-flood
1350 * DoS attack, an attacker could send data which would eventually
1351 * consume all available buffer space if it were ACKed. By not ACKing
1352 * the data, we avoid this DoS scenario.
1354 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO)
1355 * cookie is processed and a new socket is created. In this case, any data
1356 * accompanying the SYN will be queued to the socket by tcp_input() and will
1357 * be ACKed either when the application sends response data or the delayed
1358 * ACK timer expires, whichever comes first.
1361 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1362 struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod,
1363 void *todctx, uint8_t iptos)
1367 struct syncache *sc = NULL;
1368 struct syncache_head *sch;
1369 struct mbuf *ipopts = NULL;
1371 int win, ip_ttl, ip_tos;
1375 int autoflowlabel = 0;
1378 struct label *maclabel;
1380 struct syncache scs;
1382 uint64_t tfo_response_cookie;
1383 unsigned int *tfo_pending = NULL;
1384 int tfo_cookie_valid = 0;
1385 int tfo_response_cookie_valid = 0;
1388 INP_WLOCK_ASSERT(inp); /* listen socket */
1389 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
1390 ("%s: unexpected tcp flags", __func__));
1393 * Combine all so/tp operations very early to drop the INP lock as
1397 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so));
1399 cred = crhold(so->so_cred);
1402 if (inc->inc_flags & INC_ISIPV6) {
1403 if (inp->inp_flags & IN6P_AUTOFLOWLABEL) {
1406 ip_ttl = in6_selecthlim(inp, NULL);
1407 if ((inp->in6p_outputopts == NULL) ||
1408 (inp->in6p_outputopts->ip6po_tclass == -1)) {
1411 ip_tos = inp->in6p_outputopts->ip6po_tclass;
1415 #if defined(INET6) && defined(INET)
1420 ip_ttl = inp->inp_ip_ttl;
1421 ip_tos = inp->inp_ip_tos;
1424 win = so->sol_sbrcv_hiwat;
1425 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE));
1427 if (V_tcp_fastopen_server_enable && IS_FASTOPEN(tp->t_flags) &&
1428 (tp->t_tfo_pending != NULL) &&
1429 (to->to_flags & TOF_FASTOPEN)) {
1431 * Limit the number of pending TFO connections to
1432 * approximately half of the queue limit. This prevents TFO
1433 * SYN floods from starving the service by filling the
1434 * listen queue with bogus TFO connections.
1436 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <=
1437 (so->sol_qlimit / 2)) {
1440 result = tcp_fastopen_check_cookie(inc,
1441 to->to_tfo_cookie, to->to_tfo_len,
1442 &tfo_response_cookie);
1443 tfo_cookie_valid = (result > 0);
1444 tfo_response_cookie_valid = (result >= 0);
1448 * Remember the TFO pending counter as it will have to be
1449 * decremented below if we don't make it to syncache_tfo_expand().
1451 tfo_pending = tp->t_tfo_pending;
1454 /* By the time we drop the lock these should no longer be used. */
1459 if (mac_syncache_init(&maclabel) != 0) {
1463 mac_syncache_create(maclabel, inp);
1465 if (!tfo_cookie_valid)
1469 * Remember the IP options, if any.
1472 if (!(inc->inc_flags & INC_ISIPV6))
1475 ipopts = (m) ? ip_srcroute(m) : NULL;
1480 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1482 * If listening socket requested TCP digests, check that received
1483 * SYN has signature and it is correct. If signature doesn't match
1484 * or TCP_SIGNATURE support isn't enabled, drop the packet.
1486 if (ltflags & TF_SIGNATURE) {
1487 if ((to->to_flags & TOF_SIGNATURE) == 0) {
1488 TCPSTAT_INC(tcps_sig_err_nosigopt);
1491 if (!TCPMD5_ENABLED() ||
1492 TCPMD5_INPUT(m, th, to->to_signature) != 0)
1495 #endif /* TCP_SIGNATURE */
1497 * See if we already have an entry for this connection.
1498 * If we do, resend the SYN,ACK, and reset the retransmit timer.
1500 * XXX: should the syncache be re-initialized with the contents
1501 * of the new SYN here (which may have different options?)
1503 * XXX: We do not check the sequence number to see if this is a
1504 * real retransmit or a new connection attempt. The question is
1505 * how to handle such a case; either ignore it as spoofed, or
1506 * drop the current entry and create a new one?
1508 if (syncache_cookiesonly()) {
1510 sch = syncache_hashbucket(inc);
1513 sc = syncache_lookup(inc, &sch); /* returns locked sch */
1515 SCH_LOCK_ASSERT(sch);
1518 if (tfo_cookie_valid)
1520 TCPSTAT_INC(tcps_sc_dupsyn);
1523 * If we were remembering a previous source route,
1524 * forget it and use the new one we've been given.
1527 (void) m_free(sc->sc_ipopts);
1528 sc->sc_ipopts = ipopts;
1531 * Update timestamp if present.
1533 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
1534 sc->sc_tsreflect = to->to_tsval;
1536 sc->sc_flags &= ~SCF_TIMESTAMP;
1538 * Disable ECN if needed.
1540 if ((sc->sc_flags & SCF_ECN) &&
1541 ((th->th_flags & (TH_ECE|TH_CWR)) != (TH_ECE|TH_CWR))) {
1542 sc->sc_flags &= ~SCF_ECN;
1546 * Since we have already unconditionally allocated label
1547 * storage, free it up. The syncache entry will already
1548 * have an initialized label we can use.
1550 mac_syncache_destroy(&maclabel);
1552 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1553 /* Retransmit SYN|ACK and reset retransmit count. */
1554 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
1555 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
1556 "resetting timer and retransmitting SYN|ACK\n",
1560 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) {
1562 syncache_timeout(sc, sch, 1);
1563 TCPSTAT_INC(tcps_sndacks);
1564 TCPSTAT_INC(tcps_sndtotal);
1570 if (tfo_cookie_valid) {
1571 bzero(&scs, sizeof(scs));
1577 * Skip allocating a syncache entry if we are just going to discard
1581 bzero(&scs, sizeof(scs));
1584 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1587 * The zone allocator couldn't provide more entries.
1588 * Treat this as if the cache was full; drop the oldest
1589 * entry and insert the new one.
1591 TCPSTAT_INC(tcps_sc_zonefail);
1592 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) {
1593 sch->sch_last_overflow = time_uptime;
1594 syncache_drop(sc, sch);
1595 syncache_pause(inc);
1597 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1599 if (V_tcp_syncookies) {
1600 bzero(&scs, sizeof(scs));
1604 ("%s: bucket unexpectedly unlocked",
1608 (void) m_free(ipopts);
1615 if (!tfo_cookie_valid && tfo_response_cookie_valid)
1616 sc->sc_tfo_cookie = &tfo_response_cookie;
1619 * Fill in the syncache values.
1622 sc->sc_label = maclabel;
1626 sc->sc_ipopts = ipopts;
1627 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1628 sc->sc_ip_tos = ip_tos;
1629 sc->sc_ip_ttl = ip_ttl;
1632 sc->sc_todctx = todctx;
1634 sc->sc_irs = th->th_seq;
1636 sc->sc_flowlabel = 0;
1639 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
1640 * win was derived from socket earlier in the function.
1643 win = imin(win, TCP_MAXWIN);
1646 if (V_tcp_do_rfc1323) {
1648 * A timestamp received in a SYN makes
1649 * it ok to send timestamp requests and replies.
1651 if (to->to_flags & TOF_TS) {
1652 sc->sc_tsreflect = to->to_tsval;
1653 sc->sc_flags |= SCF_TIMESTAMP;
1654 sc->sc_tsoff = tcp_new_ts_offset(inc);
1656 if (to->to_flags & TOF_SCALE) {
1660 * Pick the smallest possible scaling factor that
1661 * will still allow us to scale up to sb_max, aka
1662 * kern.ipc.maxsockbuf.
1664 * We do this because there are broken firewalls that
1665 * will corrupt the window scale option, leading to
1666 * the other endpoint believing that our advertised
1667 * window is unscaled. At scale factors larger than
1668 * 5 the unscaled window will drop below 1500 bytes,
1669 * leading to serious problems when traversing these
1672 * With the default maxsockbuf of 256K, a scale factor
1673 * of 3 will be chosen by this algorithm. Those who
1674 * choose a larger maxsockbuf should watch out
1675 * for the compatibility problems mentioned above.
1677 * RFC1323: The Window field in a SYN (i.e., a <SYN>
1678 * or <SYN,ACK>) segment itself is never scaled.
1680 while (wscale < TCP_MAX_WINSHIFT &&
1681 (TCP_MAXWIN << wscale) < sb_max)
1683 sc->sc_requested_r_scale = wscale;
1684 sc->sc_requested_s_scale = to->to_wscale;
1685 sc->sc_flags |= SCF_WINSCALE;
1688 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1690 * If listening socket requested TCP digests, flag this in the
1691 * syncache so that syncache_respond() will do the right thing
1694 if (ltflags & TF_SIGNATURE)
1695 sc->sc_flags |= SCF_SIGNATURE;
1696 #endif /* TCP_SIGNATURE */
1697 if (to->to_flags & TOF_SACKPERM)
1698 sc->sc_flags |= SCF_SACK;
1699 if (to->to_flags & TOF_MSS)
1700 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */
1701 if (ltflags & TF_NOOPT)
1702 sc->sc_flags |= SCF_NOOPT;
1703 if (((th->th_flags & (TH_ECE|TH_CWR)) == (TH_ECE|TH_CWR)) &&
1705 sc->sc_flags |= SCF_ECN;
1707 if (V_tcp_syncookies)
1708 sc->sc_iss = syncookie_generate(sch, sc);
1710 sc->sc_iss = arc4random();
1712 if (autoflowlabel) {
1713 if (V_tcp_syncookies)
1714 sc->sc_flowlabel = sc->sc_iss;
1716 sc->sc_flowlabel = ip6_randomflowlabel();
1717 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK;
1723 if (tfo_cookie_valid) {
1724 syncache_tfo_expand(sc, lsop, m, tfo_response_cookie);
1725 /* INP_WUNLOCK(inp) will be performed by the caller */
1730 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1732 * Do a standard 3-way handshake.
1734 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) {
1735 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs)
1737 else if (sc != &scs)
1738 syncache_insert(sc, sch); /* locks and unlocks sch */
1739 TCPSTAT_INC(tcps_sndacks);
1740 TCPSTAT_INC(tcps_sndtotal);
1744 TCPSTAT_INC(tcps_sc_dropped);
1749 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1756 * If tfo_pending is not NULL here, then a TFO SYN that did not
1757 * result in a new socket was processed and the associated pending
1758 * counter has not yet been decremented. All such TFO processing paths
1759 * transit this point.
1761 if (tfo_pending != NULL)
1762 tcp_fastopen_decrement_counter(tfo_pending);
1769 mac_syncache_destroy(&maclabel);
1775 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment,
1776 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL.
1779 syncache_respond(struct syncache *sc, const struct mbuf *m0, int flags)
1781 struct ip *ip = NULL;
1783 struct tcphdr *th = NULL;
1784 int optlen, error = 0; /* Make compiler happy */
1785 u_int16_t hlen, tlen, mssopt;
1788 struct ip6_hdr *ip6 = NULL;
1795 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
1798 tlen = hlen + sizeof(struct tcphdr);
1800 /* Determine MSS we advertize to other end of connection. */
1801 mssopt = max(tcp_mssopt(&sc->sc_inc), V_tcp_minmss);
1803 /* XXX: Assume that the entire packet will fit in a header mbuf. */
1804 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
1805 ("syncache: mbuf too small"));
1807 /* Create the IP+TCP header from scratch. */
1808 m = m_gethdr(M_NOWAIT, MT_DATA);
1812 mac_syncache_create_mbuf(sc->sc_label, m);
1814 m->m_data += max_linkhdr;
1816 m->m_pkthdr.len = tlen;
1817 m->m_pkthdr.rcvif = NULL;
1820 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1821 ip6 = mtod(m, struct ip6_hdr *);
1822 ip6->ip6_vfc = IPV6_VERSION;
1823 ip6->ip6_nxt = IPPROTO_TCP;
1824 ip6->ip6_src = sc->sc_inc.inc6_laddr;
1825 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
1826 ip6->ip6_plen = htons(tlen - hlen);
1827 /* ip6_hlim is set after checksum */
1828 /* Zero out traffic class and flow label. */
1829 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK;
1830 ip6->ip6_flow |= sc->sc_flowlabel;
1831 ip6->ip6_flow |= htonl(sc->sc_ip_tos << 20);
1833 th = (struct tcphdr *)(ip6 + 1);
1836 #if defined(INET6) && defined(INET)
1841 ip = mtod(m, struct ip *);
1842 ip->ip_v = IPVERSION;
1843 ip->ip_hl = sizeof(struct ip) >> 2;
1844 ip->ip_len = htons(tlen);
1848 ip->ip_p = IPPROTO_TCP;
1849 ip->ip_src = sc->sc_inc.inc_laddr;
1850 ip->ip_dst = sc->sc_inc.inc_faddr;
1851 ip->ip_ttl = sc->sc_ip_ttl;
1852 ip->ip_tos = sc->sc_ip_tos;
1855 * See if we should do MTU discovery. Route lookups are
1856 * expensive, so we will only unset the DF bit if:
1858 * 1) path_mtu_discovery is disabled
1859 * 2) the SCF_UNREACH flag has been set
1861 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
1862 ip->ip_off |= htons(IP_DF);
1864 th = (struct tcphdr *)(ip + 1);
1867 th->th_sport = sc->sc_inc.inc_lport;
1868 th->th_dport = sc->sc_inc.inc_fport;
1871 th->th_seq = htonl(sc->sc_iss);
1873 th->th_seq = htonl(sc->sc_iss + 1);
1874 th->th_ack = htonl(sc->sc_irs + 1);
1875 th->th_off = sizeof(struct tcphdr) >> 2;
1877 th->th_flags = flags;
1878 th->th_win = htons(sc->sc_wnd);
1881 if ((flags & TH_SYN) && (sc->sc_flags & SCF_ECN)) {
1882 th->th_flags |= TH_ECE;
1883 TCPSTAT_INC(tcps_ecn_shs);
1886 /* Tack on the TCP options. */
1887 if ((sc->sc_flags & SCF_NOOPT) == 0) {
1890 if (flags & TH_SYN) {
1892 to.to_flags = TOF_MSS;
1893 if (sc->sc_flags & SCF_WINSCALE) {
1894 to.to_wscale = sc->sc_requested_r_scale;
1895 to.to_flags |= TOF_SCALE;
1897 if (sc->sc_flags & SCF_SACK)
1898 to.to_flags |= TOF_SACKPERM;
1899 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1900 if (sc->sc_flags & SCF_SIGNATURE)
1901 to.to_flags |= TOF_SIGNATURE;
1903 if (sc->sc_tfo_cookie) {
1904 to.to_flags |= TOF_FASTOPEN;
1905 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
1906 to.to_tfo_cookie = sc->sc_tfo_cookie;
1907 /* don't send cookie again when retransmitting response */
1908 sc->sc_tfo_cookie = NULL;
1911 if (sc->sc_flags & SCF_TIMESTAMP) {
1912 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks();
1913 to.to_tsecr = sc->sc_tsreflect;
1914 to.to_flags |= TOF_TS;
1916 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
1918 /* Adjust headers by option size. */
1919 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
1921 m->m_pkthdr.len += optlen;
1923 if (sc->sc_inc.inc_flags & INC_ISIPV6)
1924 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
1927 ip->ip_len = htons(ntohs(ip->ip_len) + optlen);
1928 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1929 if (sc->sc_flags & SCF_SIGNATURE) {
1930 KASSERT(to.to_flags & TOF_SIGNATURE,
1931 ("tcp_addoptions() didn't set tcp_signature"));
1933 /* NOTE: to.to_signature is inside of mbuf */
1934 if (!TCPMD5_ENABLED() ||
1935 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) {
1944 M_SETFIB(m, sc->sc_inc.inc_fibnum);
1945 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1947 * If we have peer's SYN and it has a flowid, then let's assign it to
1948 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid
1949 * to SYN|ACK due to lack of inp here.
1951 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) {
1952 m->m_pkthdr.flowid = m0->m_pkthdr.flowid;
1953 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0));
1956 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1957 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
1958 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen,
1960 ip6->ip6_hlim = sc->sc_ip_ttl;
1962 if (ADDED_BY_TOE(sc)) {
1963 struct toedev *tod = sc->sc_tod;
1965 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
1970 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th);
1971 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
1974 #if defined(INET6) && defined(INET)
1979 m->m_pkthdr.csum_flags = CSUM_TCP;
1980 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
1981 htons(tlen + optlen - hlen + IPPROTO_TCP));
1983 if (ADDED_BY_TOE(sc)) {
1984 struct toedev *tod = sc->sc_tod;
1986 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
1991 TCP_PROBE5(send, NULL, NULL, ip, NULL, th);
1992 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
1999 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks
2000 * that exceed the capacity of the syncache by avoiding the storage of any
2001 * of the SYNs we receive. Syncookies defend against blind SYN flooding
2002 * attacks where the attacker does not have access to our responses.
2004 * Syncookies encode and include all necessary information about the
2005 * connection setup within the SYN|ACK that we send back. That way we
2006 * can avoid keeping any local state until the ACK to our SYN|ACK returns
2007 * (if ever). Normally the syncache and syncookies are running in parallel
2008 * with the latter taking over when the former is exhausted. When matching
2009 * syncache entry is found the syncookie is ignored.
2011 * The only reliable information persisting the 3WHS is our initial sequence
2012 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient
2013 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS
2014 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK
2015 * returns and signifies a legitimate connection if it matches the ACK.
2017 * The available space of 32 bits to store the hash and to encode the SYN
2018 * option information is very tight and we should have at least 24 bits for
2019 * the MAC to keep the number of guesses by blind spoofing reasonably high.
2021 * SYN option information we have to encode to fully restore a connection:
2022 * MSS: is imporant to chose an optimal segment size to avoid IP level
2023 * fragmentation along the path. The common MSS values can be encoded
2024 * in a 3-bit table. Uncommon values are captured by the next lower value
2025 * in the table leading to a slight increase in packetization overhead.
2026 * WSCALE: is necessary to allow large windows to be used for high delay-
2027 * bandwidth product links. Not scaling the window when it was initially
2028 * negotiated is bad for performance as lack of scaling further decreases
2029 * the apparent available send window. We only need to encode the WSCALE
2030 * we received from the remote end. Our end can be recalculated at any
2031 * time. The common WSCALE values can be encoded in a 3-bit table.
2032 * Uncommon values are captured by the next lower value in the table
2033 * making us under-estimate the available window size halving our
2034 * theoretically possible maximum throughput for that connection.
2035 * SACK: Greatly assists in packet loss recovery and requires 1 bit.
2036 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options
2037 * that are included in all segments on a connection. We enable them when
2040 * Security of syncookies and attack vectors:
2042 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod)
2043 * together with the gloabl secret to make it unique per connection attempt.
2044 * Thus any change of any of those parameters results in a different MAC output
2045 * in an unpredictable way unless a collision is encountered. 24 bits of the
2046 * MAC are embedded into the ISS.
2048 * To prevent replay attacks two rotating global secrets are updated with a
2049 * new random value every 15 seconds. The life-time of a syncookie is thus
2052 * Vector 1: Attacking the secret. This requires finding a weakness in the
2053 * MAC itself or the way it is used here. The attacker can do a chosen plain
2054 * text attack by varying and testing the all parameters under his control.
2055 * The strength depends on the size and randomness of the secret, and the
2056 * cryptographic security of the MAC function. Due to the constant updating
2057 * of the secret the attacker has at most 29.999 seconds to find the secret
2058 * and launch spoofed connections. After that he has to start all over again.
2060 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC
2061 * size an average of 4,823 attempts are required for a 50% chance of success
2062 * to spoof a single syncookie (birthday collision paradox). However the
2063 * attacker is blind and doesn't know if one of his attempts succeeded unless
2064 * he has a side channel to interfere success from. A single connection setup
2065 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets.
2066 * This many attempts are required for each one blind spoofed connection. For
2067 * every additional spoofed connection he has to launch another N attempts.
2068 * Thus for a sustained rate 100 spoofed connections per second approximately
2069 * 1,800,000 packets per second would have to be sent.
2071 * NB: The MAC function should be fast so that it doesn't become a CPU
2072 * exhaustion attack vector itself.
2075 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations
2076 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996
2077 * http://cr.yp.to/syncookies.html (overview)
2078 * http://cr.yp.to/syncookies/archive (details)
2081 * Schematic construction of a syncookie enabled Initial Sequence Number:
2083 * 12345678901234567890123456789012
2084 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP|
2086 * x 24 MAC (truncated)
2087 * W 3 Send Window Scale index
2089 * S 1 SACK permitted
2090 * P 1 Odd/even secret
2094 * Distribution and probability of certain MSS values. Those in between are
2095 * rounded down to the next lower one.
2096 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011]
2097 * .2% .3% 5% 7% 7% 20% 15% 45%
2099 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 };
2102 * Distribution and probability of certain WSCALE values. We have to map the
2103 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3
2104 * bits based on prevalence of certain values. Where we don't have an exact
2105 * match for are rounded down to the next lower one letting us under-estimate
2106 * the true available window. At the moment this would happen only for the
2107 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer
2108 * and window size). The absence of the WSCALE option (no scaling in either
2109 * direction) is encoded with index zero.
2110 * [WSCALE values histograms, Allman, 2012]
2111 * X 10 10 35 5 6 14 10% by host
2112 * X 11 4 5 5 18 49 3% by connections
2114 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 };
2117 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed
2118 * and good cryptographic properties.
2121 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags,
2122 uint8_t *secbits, uintptr_t secmod)
2125 uint32_t siphash[2];
2127 SipHash24_Init(&ctx);
2128 SipHash_SetKey(&ctx, secbits);
2129 switch (inc->inc_flags & INC_ISIPV6) {
2132 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr));
2133 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr));
2138 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr));
2139 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr));
2143 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport));
2144 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport));
2145 SipHash_Update(&ctx, &irs, sizeof(irs));
2146 SipHash_Update(&ctx, &flags, sizeof(flags));
2147 SipHash_Update(&ctx, &secmod, sizeof(secmod));
2148 SipHash_Final((u_int8_t *)&siphash, &ctx);
2150 return (siphash[0] ^ siphash[1]);
2154 syncookie_generate(struct syncache_head *sch, struct syncache *sc)
2156 u_int i, secbit, wscale;
2159 union syncookie cookie;
2163 /* Map our computed MSS into the 3-bit index. */
2164 for (i = nitems(tcp_sc_msstab) - 1;
2165 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0;
2168 cookie.flags.mss_idx = i;
2171 * Map the send window scale into the 3-bit index but only if
2172 * the wscale option was received.
2174 if (sc->sc_flags & SCF_WINSCALE) {
2175 wscale = sc->sc_requested_s_scale;
2176 for (i = nitems(tcp_sc_wstab) - 1;
2177 tcp_sc_wstab[i] > wscale && i > 0;
2180 cookie.flags.wscale_idx = i;
2183 /* Can we do SACK? */
2184 if (sc->sc_flags & SCF_SACK)
2185 cookie.flags.sack_ok = 1;
2187 /* Which of the two secrets to use. */
2188 secbit = V_tcp_syncache.secret.oddeven & 0x1;
2189 cookie.flags.odd_even = secbit;
2191 secbits = V_tcp_syncache.secret.key[secbit];
2192 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits,
2196 * Put the flags into the hash and XOR them to get better ISS number
2197 * variance. This doesn't enhance the cryptographic strength and is
2198 * done to prevent the 8 cookie bits from showing up directly on the
2202 iss |= cookie.cookie ^ (hash >> 24);
2204 TCPSTAT_INC(tcps_sc_sendcookie);
2208 static struct syncache *
2209 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch,
2210 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
2216 int wnd, wscale = 0;
2217 union syncookie cookie;
2220 * Pull information out of SYN-ACK/ACK and revert sequence number
2223 ack = th->th_ack - 1;
2224 seq = th->th_seq - 1;
2227 * Unpack the flags containing enough information to restore the
2230 cookie.cookie = (ack & 0xff) ^ (ack >> 24);
2232 /* Which of the two secrets to use. */
2233 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even];
2235 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch);
2237 /* The recomputed hash matches the ACK if this was a genuine cookie. */
2238 if ((ack & ~0xff) != (hash & ~0xff))
2241 /* Fill in the syncache values. */
2243 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
2244 sc->sc_ipopts = NULL;
2249 switch (inc->inc_flags & INC_ISIPV6) {
2252 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl;
2253 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos;
2258 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL)
2260 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK;
2265 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx];
2267 /* We can simply recompute receive window scale we sent earlier. */
2268 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max)
2271 /* Only use wscale if it was enabled in the orignal SYN. */
2272 if (cookie.flags.wscale_idx > 0) {
2273 sc->sc_requested_r_scale = wscale;
2274 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx];
2275 sc->sc_flags |= SCF_WINSCALE;
2278 wnd = lso->sol_sbrcv_hiwat;
2280 wnd = imin(wnd, TCP_MAXWIN);
2283 if (cookie.flags.sack_ok)
2284 sc->sc_flags |= SCF_SACK;
2286 if (to->to_flags & TOF_TS) {
2287 sc->sc_flags |= SCF_TIMESTAMP;
2288 sc->sc_tsreflect = to->to_tsval;
2289 sc->sc_tsoff = tcp_new_ts_offset(inc);
2292 if (to->to_flags & TOF_SIGNATURE)
2293 sc->sc_flags |= SCF_SIGNATURE;
2297 TCPSTAT_INC(tcps_sc_recvcookie);
2303 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
2304 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
2307 struct syncache scs, *scx;
2310 bzero(&scs, sizeof(scs));
2311 scx = syncookie_lookup(inc, sch, &scs, th, to, lso);
2313 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL)
2317 if (sc->sc_peer_mss != scx->sc_peer_mss)
2318 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n",
2319 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss);
2321 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale)
2322 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n",
2323 s, __func__, sc->sc_requested_r_scale,
2324 scx->sc_requested_r_scale);
2326 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale)
2327 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n",
2328 s, __func__, sc->sc_requested_s_scale,
2329 scx->sc_requested_s_scale);
2331 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK))
2332 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__);
2339 #endif /* INVARIANTS */
2342 syncookie_reseed(void *arg)
2344 struct tcp_syncache *sc = arg;
2349 * Reseeding the secret doesn't have to be protected by a lock.
2350 * It only must be ensured that the new random values are visible
2351 * to all CPUs in a SMP environment. The atomic with release
2352 * semantics ensures that.
2354 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1;
2355 secbits = sc->secret.key[secbit];
2356 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0);
2357 atomic_add_rel_int(&sc->secret.oddeven, 1);
2359 /* Reschedule ourself. */
2360 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz);
2364 * We have overflowed a bucket. Let's pause dealing with the syncache.
2365 * This function will increment the bucketoverflow statistics appropriately
2366 * (once per pause when pausing is enabled; otherwise, once per overflow).
2369 syncache_pause(struct in_conninfo *inc)
2375 * 2. Add sysctl read here so we don't get the benefit of this
2376 * change without the new sysctl.
2380 * Try an unlocked read. If we already know that another thread
2381 * has activated the feature, there is no need to proceed.
2383 if (V_tcp_syncache.paused)
2386 /* Are cookied enabled? If not, we can't pause. */
2387 if (!V_tcp_syncookies) {
2388 TCPSTAT_INC(tcps_sc_bucketoverflow);
2393 * We may be the first thread to find an overflow. Get the lock
2394 * and evaluate if we need to take action.
2396 mtx_lock(&V_tcp_syncache.pause_mtx);
2397 if (V_tcp_syncache.paused) {
2398 mtx_unlock(&V_tcp_syncache.pause_mtx);
2402 /* Activate protection. */
2403 V_tcp_syncache.paused = true;
2404 TCPSTAT_INC(tcps_sc_bucketoverflow);
2407 * Determine the last backoff time. If we are seeing a re-newed
2408 * attack within that same time after last reactivating the syncache,
2409 * consider it an extension of the same attack.
2411 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff;
2412 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) {
2413 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) {
2415 V_tcp_syncache.pause_backoff++;
2418 delta = TCP_SYNCACHE_PAUSE_TIME;
2419 V_tcp_syncache.pause_backoff = 0;
2422 /* Log a warning, including IP addresses, if able. */
2424 s = tcp_log_addrs(inc, NULL, NULL, NULL);
2426 s = (const char *)NULL;
2427 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for "
2428 "the next %lld seconds%s%s%s\n", (long long)delta,
2429 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "",
2430 (s != NULL) ? ")" : "");
2431 free(__DECONST(void *, s), M_TCPLOG);
2433 /* Use the calculated delta to set a new pause time. */
2434 V_tcp_syncache.pause_until = time_uptime + delta;
2435 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause,
2437 mtx_unlock(&V_tcp_syncache.pause_mtx);
2440 /* Evaluate whether we need to unpause. */
2442 syncache_unpause(void *arg)
2444 struct tcp_syncache *sc;
2448 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED);
2449 callout_deactivate(&sc->pause_co);
2452 * Check to make sure we are not running early. If the pause
2453 * time has expired, then deactivate the protection.
2455 if ((delta = sc->pause_until - time_uptime) > 0)
2456 callout_schedule(&sc->pause_co, delta * hz);
2462 * Exports the syncache entries to userland so that netstat can display
2463 * them alongside the other sockets. This function is intended to be
2464 * called only from tcp_pcblist.
2466 * Due to concurrency on an active system, the number of pcbs exported
2467 * may have no relation to max_pcbs. max_pcbs merely indicates the
2468 * amount of space the caller allocated for this function to use.
2471 syncache_pcblist(struct sysctl_req *req)
2474 struct syncache *sc;
2475 struct syncache_head *sch;
2478 bzero(&xt, sizeof(xt));
2479 xt.xt_len = sizeof(xt);
2480 xt.t_state = TCPS_SYN_RECEIVED;
2481 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP;
2482 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket);
2483 xt.xt_inp.xi_socket.so_type = SOCK_STREAM;
2484 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING;
2486 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
2487 sch = &V_tcp_syncache.hashbase[i];
2489 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
2490 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
2492 if (sc->sc_inc.inc_flags & INC_ISIPV6)
2493 xt.xt_inp.inp_vflag = INP_IPV6;
2495 xt.xt_inp.inp_vflag = INP_IPV4;
2496 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc,
2497 sizeof (struct in_conninfo));
2498 error = SYSCTL_OUT(req, &xt, sizeof xt);