2 * Copyright (c) 2001 McAfee, Inc.
3 * Copyright (c) 2006,2013 Andre Oppermann, Internet Business Solutions AG
6 * This software was developed for the FreeBSD Project by Jonathan Lemon
7 * and McAfee Research, the Security Research Division of McAfee, Inc. under
8 * DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the
9 * DARPA CHATS research program. [2001 McAfee, Inc.]
11 * Redistribution and use in source and binary forms, with or without
12 * modification, are permitted provided that the following conditions
14 * 1. Redistributions of source code must retain the above copyright
15 * notice, this list of conditions and the following disclaimer.
16 * 2. Redistributions in binary form must reproduce the above copyright
17 * notice, this list of conditions and the following disclaimer in the
18 * documentation and/or other materials provided with the distribution.
20 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
33 #include <sys/cdefs.h>
34 __FBSDID("$FreeBSD$");
37 #include "opt_inet6.h"
38 #include "opt_ipsec.h"
39 #include "opt_pcbgroup.h"
41 #include <sys/param.h>
42 #include <sys/systm.h>
44 #include <sys/kernel.h>
45 #include <sys/sysctl.h>
46 #include <sys/limits.h>
48 #include <sys/mutex.h>
49 #include <sys/malloc.h>
51 #include <sys/proc.h> /* for proc0 declaration */
52 #include <sys/random.h>
53 #include <sys/socket.h>
54 #include <sys/socketvar.h>
55 #include <sys/syslog.h>
56 #include <sys/ucred.h>
59 #include <crypto/siphash/siphash.h>
64 #include <net/if_var.h>
65 #include <net/route.h>
68 #include <netinet/in.h>
69 #include <netinet/in_systm.h>
70 #include <netinet/ip.h>
71 #include <netinet/in_var.h>
72 #include <netinet/in_pcb.h>
73 #include <netinet/ip_var.h>
74 #include <netinet/ip_options.h>
76 #include <netinet/ip6.h>
77 #include <netinet/icmp6.h>
78 #include <netinet6/nd6.h>
79 #include <netinet6/ip6_var.h>
80 #include <netinet6/in6_pcb.h>
82 #include <netinet/tcp.h>
83 #include <netinet/tcp_fsm.h>
84 #include <netinet/tcp_seq.h>
85 #include <netinet/tcp_timer.h>
86 #include <netinet/tcp_var.h>
87 #include <netinet/tcp_syncache.h>
89 #include <netinet6/tcp6_var.h>
92 #include <netinet/toecore.h>
96 #include <netipsec/ipsec.h>
98 #include <netipsec/ipsec6.h>
100 #include <netipsec/key.h>
103 #include <machine/in_cksum.h>
105 #include <security/mac/mac_framework.h>
107 static VNET_DEFINE(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 static VNET_DEFINE(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");
120 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL)
123 static void syncache_drop(struct syncache *, struct syncache_head *);
124 static void syncache_free(struct syncache *);
125 static void syncache_insert(struct syncache *, struct syncache_head *);
126 static int syncache_respond(struct syncache *, struct syncache_head *, int);
127 static struct socket *syncache_socket(struct syncache *, struct socket *,
129 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch,
131 static void syncache_timer(void *);
133 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t,
134 uint8_t *, uintptr_t);
135 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *);
136 static struct syncache
137 *syncookie_lookup(struct in_conninfo *, struct syncache_head *,
138 struct syncache *, struct tcphdr *, struct tcpopt *,
140 static void syncookie_reseed(void *);
142 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
143 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
148 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
149 * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds,
150 * the odds are that the user has given up attempting to connect by then.
152 #define SYNCACHE_MAXREXMTS 3
154 /* Arbitrary values */
155 #define TCP_SYNCACHE_HASHSIZE 512
156 #define TCP_SYNCACHE_BUCKETLIMIT 30
158 static VNET_DEFINE(struct tcp_syncache, tcp_syncache);
159 #define V_tcp_syncache VNET(tcp_syncache)
161 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0,
164 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
165 &VNET_NAME(tcp_syncache.bucket_limit), 0,
166 "Per-bucket hash limit for syncache");
168 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
169 &VNET_NAME(tcp_syncache.cache_limit), 0,
170 "Overall entry limit for syncache");
172 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET,
173 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache");
175 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN,
176 &VNET_NAME(tcp_syncache.hashsize), 0,
177 "Size of TCP syncache hashtable");
179 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_VNET | CTLFLAG_RW,
180 &VNET_NAME(tcp_syncache.rexmt_limit), 0,
181 "Limit on SYN/ACK retransmissions");
183 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1;
184 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail,
185 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0,
186 "Send reset on socket allocation failure");
188 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
190 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx)
191 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx)
192 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED)
195 * Requires the syncache entry to be already removed from the bucket list.
198 syncache_free(struct syncache *sc)
202 (void) m_free(sc->sc_ipopts);
206 mac_syncache_destroy(&sc->sc_label);
209 uma_zfree(V_tcp_syncache.zone, sc);
217 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
218 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
219 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
220 V_tcp_syncache.hash_secret = arc4random();
222 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
223 &V_tcp_syncache.hashsize);
224 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
225 &V_tcp_syncache.bucket_limit);
226 if (!powerof2(V_tcp_syncache.hashsize) ||
227 V_tcp_syncache.hashsize == 0) {
228 printf("WARNING: syncache hash size is not a power of 2.\n");
229 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
231 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1;
234 V_tcp_syncache.cache_limit =
235 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit;
236 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
237 &V_tcp_syncache.cache_limit);
239 /* Allocate the hash table. */
240 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize *
241 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO);
244 V_tcp_syncache.vnet = curvnet;
247 /* Initialize the hash buckets. */
248 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
249 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket);
250 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
252 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer,
253 &V_tcp_syncache.hashbase[i].sch_mtx, 0);
254 V_tcp_syncache.hashbase[i].sch_length = 0;
255 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache;
258 /* Create the syncache entry zone. */
259 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
260 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
261 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone,
262 V_tcp_syncache.cache_limit);
264 /* Start the SYN cookie reseeder callout. */
265 callout_init(&V_tcp_syncache.secret.reseed, 1);
266 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0);
267 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0);
268 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz,
269 syncookie_reseed, &V_tcp_syncache);
274 syncache_destroy(void)
276 struct syncache_head *sch;
277 struct syncache *sc, *nsc;
280 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */
281 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
283 sch = &V_tcp_syncache.hashbase[i];
284 callout_drain(&sch->sch_timer);
287 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc)
288 syncache_drop(sc, sch);
290 KASSERT(TAILQ_EMPTY(&sch->sch_bucket),
291 ("%s: sch->sch_bucket not empty", __func__));
292 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0",
293 __func__, sch->sch_length));
294 mtx_destroy(&sch->sch_mtx);
297 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0,
298 ("%s: cache_count not 0", __func__));
300 /* Free the allocated global resources. */
301 uma_zdestroy(V_tcp_syncache.zone);
302 free(V_tcp_syncache.hashbase, M_SYNCACHE);
304 callout_drain(&V_tcp_syncache.secret.reseed);
309 * Inserts a syncache entry into the specified bucket row.
310 * Locks and unlocks the syncache_head autonomously.
313 syncache_insert(struct syncache *sc, struct syncache_head *sch)
315 struct syncache *sc2;
320 * Make sure that we don't overflow the per-bucket limit.
321 * If the bucket is full, toss the oldest element.
323 if (sch->sch_length >= V_tcp_syncache.bucket_limit) {
324 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
325 ("sch->sch_length incorrect"));
326 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
327 syncache_drop(sc2, sch);
328 TCPSTAT_INC(tcps_sc_bucketoverflow);
331 /* Put it into the bucket. */
332 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
336 if (ADDED_BY_TOE(sc)) {
337 struct toedev *tod = sc->sc_tod;
339 tod->tod_syncache_added(tod, sc->sc_todctx);
343 /* Reinitialize the bucket row's timer. */
344 if (sch->sch_length == 1)
345 sch->sch_nextc = ticks + INT_MAX;
346 syncache_timeout(sc, sch, 1);
350 TCPSTAT_INC(tcps_sc_added);
354 * Remove and free entry from syncache bucket row.
355 * Expects locked syncache head.
358 syncache_drop(struct syncache *sc, struct syncache_head *sch)
361 SCH_LOCK_ASSERT(sch);
363 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
367 if (ADDED_BY_TOE(sc)) {
368 struct toedev *tod = sc->sc_tod;
370 tod->tod_syncache_removed(tod, sc->sc_todctx);
378 * Engage/reengage time on bucket row.
381 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
383 sc->sc_rxttime = ticks +
384 TCPTV_RTOBASE * (tcp_syn_backoff[sc->sc_rxmits]);
386 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
387 sch->sch_nextc = sc->sc_rxttime;
389 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
390 syncache_timer, (void *)sch);
395 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
396 * If we have retransmitted an entry the maximum number of times, expire it.
397 * One separate timer for each bucket row.
400 syncache_timer(void *xsch)
402 struct syncache_head *sch = (struct syncache_head *)xsch;
403 struct syncache *sc, *nsc;
407 CURVNET_SET(sch->sch_sc->vnet);
409 /* NB: syncache_head has already been locked by the callout. */
410 SCH_LOCK_ASSERT(sch);
413 * In the following cycle we may remove some entries and/or
414 * advance some timeouts, so re-initialize the bucket timer.
416 sch->sch_nextc = tick + INT_MAX;
418 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
420 * We do not check if the listen socket still exists
421 * and accept the case where the listen socket may be
422 * gone by the time we resend the SYN/ACK. We do
423 * not expect this to happens often. If it does,
424 * then the RST will be sent by the time the remote
425 * host does the SYN/ACK->ACK.
427 if (TSTMP_GT(sc->sc_rxttime, tick)) {
428 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
429 sch->sch_nextc = sc->sc_rxttime;
432 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
433 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
434 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
435 "giving up and removing syncache entry\n",
439 syncache_drop(sc, sch);
440 TCPSTAT_INC(tcps_sc_stale);
443 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
444 log(LOG_DEBUG, "%s; %s: Response timeout, "
445 "retransmitting (%u) SYN|ACK\n",
446 s, __func__, sc->sc_rxmits);
450 syncache_respond(sc, sch, 1);
451 TCPSTAT_INC(tcps_sc_retransmitted);
452 syncache_timeout(sc, sch, 0);
454 if (!TAILQ_EMPTY(&(sch)->sch_bucket))
455 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
456 syncache_timer, (void *)(sch));
461 * Find an entry in the syncache.
462 * Returns always with locked syncache_head plus a matching entry or NULL.
464 static struct syncache *
465 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
468 struct syncache_head *sch;
472 * The hash is built on foreign port + local port + foreign address.
473 * We rely on the fact that struct in_conninfo starts with 16 bits
474 * of foreign port, then 16 bits of local port then followed by 128
475 * bits of foreign address. In case of IPv4 address, the first 3
476 * 32-bit words of the address always are zeroes.
478 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5,
479 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask;
481 sch = &V_tcp_syncache.hashbase[hash];
485 /* Circle through bucket row to find matching entry. */
486 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash)
487 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie,
488 sizeof(struct in_endpoints)) == 0)
491 return (sc); /* Always returns with locked sch. */
495 * This function is called when we get a RST for a
496 * non-existent connection, so that we can see if the
497 * connection is in the syn cache. If it is, zap it.
500 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th)
503 struct syncache_head *sch;
506 sc = syncache_lookup(inc, &sch); /* returns locked sch */
507 SCH_LOCK_ASSERT(sch);
510 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags.
511 * See RFC 793 page 65, section SEGMENT ARRIVES.
513 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) {
514 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
515 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or "
516 "FIN flag set, segment ignored\n", s, __func__);
517 TCPSTAT_INC(tcps_badrst);
522 * No corresponding connection was found in syncache.
523 * If syncookies are enabled and possibly exclusively
524 * used, or we are under memory pressure, a valid RST
525 * may not find a syncache entry. In that case we're
526 * done and no SYN|ACK retransmissions will happen.
527 * Otherwise the RST was misdirected or spoofed.
530 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
531 log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
532 "syncache entry (possibly syncookie only), "
533 "segment ignored\n", s, __func__);
534 TCPSTAT_INC(tcps_badrst);
539 * If the RST bit is set, check the sequence number to see
540 * if this is a valid reset segment.
542 * In all states except SYN-SENT, all reset (RST) segments
543 * are validated by checking their SEQ-fields. A reset is
544 * valid if its sequence number is in the window.
546 * The sequence number in the reset segment is normally an
547 * echo of our outgoing acknowlegement numbers, but some hosts
548 * send a reset with the sequence number at the rightmost edge
549 * of our receive window, and we have to handle this case.
551 if (SEQ_GEQ(th->th_seq, sc->sc_irs) &&
552 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
553 syncache_drop(sc, sch);
554 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
555 log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, "
556 "connection attempt aborted by remote endpoint\n",
558 TCPSTAT_INC(tcps_sc_reset);
560 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
561 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
562 "IRS %u (+WND %u), segment ignored\n",
563 s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd);
564 TCPSTAT_INC(tcps_badrst);
574 syncache_badack(struct in_conninfo *inc)
577 struct syncache_head *sch;
579 sc = syncache_lookup(inc, &sch); /* returns locked sch */
580 SCH_LOCK_ASSERT(sch);
582 syncache_drop(sc, sch);
583 TCPSTAT_INC(tcps_sc_badack);
589 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th)
592 struct syncache_head *sch;
594 sc = syncache_lookup(inc, &sch); /* returns locked sch */
595 SCH_LOCK_ASSERT(sch);
599 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
600 if (ntohl(th->th_seq) != sc->sc_iss)
604 * If we've rertransmitted 3 times and this is our second error,
605 * we remove the entry. Otherwise, we allow it to continue on.
606 * This prevents us from incorrectly nuking an entry during a
607 * spurious network outage.
611 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
612 sc->sc_flags |= SCF_UNREACH;
615 syncache_drop(sc, sch);
616 TCPSTAT_INC(tcps_sc_unreach);
622 * Build a new TCP socket structure from a syncache entry.
624 * On success return the newly created socket with its underlying inp locked.
626 static struct socket *
627 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
629 struct inpcb *inp = NULL;
635 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
638 * Ok, create the full blown connection, and set things up
639 * as they would have been set up if we had created the
640 * connection when the SYN arrived. If we can't create
641 * the connection, abort it.
643 so = sonewconn(lso, 0);
646 * Drop the connection; we will either send a RST or
647 * have the peer retransmit its SYN again after its
650 TCPSTAT_INC(tcps_listendrop);
651 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
652 log(LOG_DEBUG, "%s; %s: Socket create failed "
653 "due to limits or memory shortage\n",
660 mac_socketpeer_set_from_mbuf(m, so);
664 inp->inp_inc.inc_fibnum = so->so_fibnum;
667 * Exclusive pcbinfo lock is not required in syncache socket case even
668 * if two inpcb locks can be acquired simultaneously:
669 * - the inpcb in LISTEN state,
670 * - the newly created inp.
672 * In this case, an inp cannot be at same time in LISTEN state and
673 * just created by an accept() call.
675 INP_HASH_WLOCK(&V_tcbinfo);
677 /* Insert new socket into PCB hash list. */
678 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
680 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
681 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
683 inp->inp_vflag &= ~INP_IPV6;
684 inp->inp_vflag |= INP_IPV4;
686 inp->inp_laddr = sc->sc_inc.inc_laddr;
692 * If there's an mbuf and it has a flowid, then let's initialise the
693 * inp with that particular flowid.
695 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) {
696 inp->inp_flowid = m->m_pkthdr.flowid;
697 inp->inp_flowtype = M_HASHTYPE_GET(m);
701 * Install in the reservation hash table for now, but don't yet
702 * install a connection group since the full 4-tuple isn't yet
705 inp->inp_lport = sc->sc_inc.inc_lport;
706 if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) {
708 * Undo the assignments above if we failed to
709 * put the PCB on the hash lists.
712 if (sc->sc_inc.inc_flags & INC_ISIPV6)
713 inp->in6p_laddr = in6addr_any;
716 inp->inp_laddr.s_addr = INADDR_ANY;
718 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
719 log(LOG_DEBUG, "%s; %s: in_pcbinshash failed "
724 INP_HASH_WUNLOCK(&V_tcbinfo);
728 /* Copy old policy into new socket's. */
729 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp))
730 printf("syncache_socket: could not copy policy\n");
733 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
734 struct inpcb *oinp = sotoinpcb(lso);
735 struct in6_addr laddr6;
736 struct sockaddr_in6 sin6;
738 * Inherit socket options from the listening socket.
739 * Note that in6p_inputopts are not (and should not be)
740 * copied, since it stores previously received options and is
741 * used to detect if each new option is different than the
742 * previous one and hence should be passed to a user.
743 * If we copied in6p_inputopts, a user would not be able to
744 * receive options just after calling the accept system call.
746 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
747 if (oinp->in6p_outputopts)
748 inp->in6p_outputopts =
749 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
751 sin6.sin6_family = AF_INET6;
752 sin6.sin6_len = sizeof(sin6);
753 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
754 sin6.sin6_port = sc->sc_inc.inc_fport;
755 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
756 laddr6 = inp->in6p_laddr;
757 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
758 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
759 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6,
760 thread0.td_ucred, m)) != 0) {
761 inp->in6p_laddr = laddr6;
762 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
763 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed "
768 INP_HASH_WUNLOCK(&V_tcbinfo);
771 /* Override flowlabel from in6_pcbconnect. */
772 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
773 inp->inp_flow |= sc->sc_flowlabel;
776 #if defined(INET) && defined(INET6)
781 struct in_addr laddr;
782 struct sockaddr_in sin;
784 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
786 if (inp->inp_options == NULL) {
787 inp->inp_options = sc->sc_ipopts;
788 sc->sc_ipopts = NULL;
791 sin.sin_family = AF_INET;
792 sin.sin_len = sizeof(sin);
793 sin.sin_addr = sc->sc_inc.inc_faddr;
794 sin.sin_port = sc->sc_inc.inc_fport;
795 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
796 laddr = inp->inp_laddr;
797 if (inp->inp_laddr.s_addr == INADDR_ANY)
798 inp->inp_laddr = sc->sc_inc.inc_laddr;
799 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin,
800 thread0.td_ucred, m)) != 0) {
801 inp->inp_laddr = laddr;
802 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
803 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed "
808 INP_HASH_WUNLOCK(&V_tcbinfo);
813 INP_HASH_WUNLOCK(&V_tcbinfo);
815 tcp_state_change(tp, TCPS_SYN_RECEIVED);
816 tp->iss = sc->sc_iss;
817 tp->irs = sc->sc_irs;
820 tp->snd_wl1 = sc->sc_irs;
821 tp->snd_max = tp->iss + 1;
822 tp->snd_nxt = tp->iss + 1;
823 tp->rcv_up = sc->sc_irs + 1;
824 tp->rcv_wnd = sc->sc_wnd;
825 tp->rcv_adv += tp->rcv_wnd;
826 tp->last_ack_sent = tp->rcv_nxt;
828 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
829 if (sc->sc_flags & SCF_NOOPT)
830 tp->t_flags |= TF_NOOPT;
832 if (sc->sc_flags & SCF_WINSCALE) {
833 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
834 tp->snd_scale = sc->sc_requested_s_scale;
835 tp->request_r_scale = sc->sc_requested_r_scale;
837 if (sc->sc_flags & SCF_TIMESTAMP) {
838 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
839 tp->ts_recent = sc->sc_tsreflect;
840 tp->ts_recent_age = tcp_ts_getticks();
841 tp->ts_offset = sc->sc_tsoff;
844 if (sc->sc_flags & SCF_SIGNATURE)
845 tp->t_flags |= TF_SIGNATURE;
847 if (sc->sc_flags & SCF_SACK)
848 tp->t_flags |= TF_SACK_PERMIT;
851 if (sc->sc_flags & SCF_ECN)
852 tp->t_flags |= TF_ECN_PERMIT;
855 * Set up MSS and get cached values from tcp_hostcache.
856 * This might overwrite some of the defaults we just set.
858 tcp_mss(tp, sc->sc_peer_mss);
861 * If the SYN,ACK was retransmitted, indicate that CWND to be
862 * limited to one segment in cc_conn_init().
863 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
865 if (sc->sc_rxmits > 1)
870 * Allow a TOE driver to install its hooks. Note that we hold the
871 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a
872 * new connection before the TOE driver has done its thing.
874 if (ADDED_BY_TOE(sc)) {
875 struct toedev *tod = sc->sc_tod;
877 tod->tod_offload_socket(tod, sc->sc_todctx, so);
881 * Copy and activate timers.
883 tp->t_keepinit = sototcpcb(lso)->t_keepinit;
884 tp->t_keepidle = sototcpcb(lso)->t_keepidle;
885 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl;
886 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt;
887 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp));
891 TCPSTAT_INC(tcps_accepts);
903 * This function gets called when we receive an ACK for a
904 * socket in the LISTEN state. We look up the connection
905 * in the syncache, and if its there, we pull it out of
906 * the cache and turn it into a full-blown connection in
907 * the SYN-RECEIVED state.
909 * On syncache_socket() success the newly created socket
910 * has its underlying inp locked.
913 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
914 struct socket **lsop, struct mbuf *m)
917 struct syncache_head *sch;
922 * Global TCP locks are held because we manipulate the PCB lists
923 * and create a new socket.
925 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
926 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
927 ("%s: can handle only ACK", __func__));
929 sc = syncache_lookup(inc, &sch); /* returns locked sch */
930 SCH_LOCK_ASSERT(sch);
934 * Test code for syncookies comparing the syncache stored
935 * values with the reconstructed values from the cookie.
938 syncookie_cmp(inc, sch, sc, th, to, *lsop);
943 * There is no syncache entry, so see if this ACK is
944 * a returning syncookie. To do this, first:
945 * A. See if this socket has had a syncache entry dropped in
946 * the past. We don't want to accept a bogus syncookie
947 * if we've never received a SYN.
948 * B. check that the syncookie is valid. If it is, then
949 * cobble up a fake syncache entry, and return.
951 if (!V_tcp_syncookies) {
953 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
954 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
955 "segment rejected (syncookies disabled)\n",
959 bzero(&scs, sizeof(scs));
960 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop);
963 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
964 log(LOG_DEBUG, "%s; %s: Segment failed "
965 "SYNCOOKIE authentication, segment rejected "
966 "(probably spoofed)\n", s, __func__);
970 /* Pull out the entry to unlock the bucket row. */
971 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
974 if (ADDED_BY_TOE(sc)) {
975 struct toedev *tod = sc->sc_tod;
977 tod->tod_syncache_removed(tod, sc->sc_todctx);
984 * Segment validation:
985 * ACK must match our initial sequence number + 1 (the SYN|ACK).
987 if (th->th_ack != sc->sc_iss + 1) {
988 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
989 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
990 "rejected\n", s, __func__, th->th_ack, sc->sc_iss);
995 * The SEQ must fall in the window starting at the received
996 * initial receive sequence number + 1 (the SYN).
998 if (SEQ_LEQ(th->th_seq, sc->sc_irs) ||
999 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
1000 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1001 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
1002 "rejected\n", s, __func__, th->th_seq, sc->sc_irs);
1007 * If timestamps were not negotiated during SYN/ACK they
1008 * must not appear on any segment during this session.
1010 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) {
1011 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1012 log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
1013 "segment rejected\n", s, __func__);
1018 * If timestamps were negotiated during SYN/ACK they should
1019 * appear on every segment during this session.
1020 * XXXAO: This is only informal as there have been unverified
1021 * reports of non-compliants stacks.
1023 if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) {
1024 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1025 log(LOG_DEBUG, "%s; %s: Timestamp missing, "
1026 "no action\n", s, __func__);
1033 * If timestamps were negotiated the reflected timestamp
1034 * must be equal to what we actually sent in the SYN|ACK.
1036 if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts) {
1037 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1038 log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, "
1039 "segment rejected\n",
1040 s, __func__, to->to_tsecr, sc->sc_ts);
1044 *lsop = syncache_socket(sc, *lsop, m);
1047 TCPSTAT_INC(tcps_sc_aborted);
1049 TCPSTAT_INC(tcps_sc_completed);
1051 /* how do we find the inp for the new socket? */
1056 if (sc != NULL && sc != &scs)
1065 * Given a LISTEN socket and an inbound SYN request, add
1066 * this to the syn cache, and send back a segment:
1067 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
1070 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
1071 * Doing so would require that we hold onto the data and deliver it
1072 * to the application. However, if we are the target of a SYN-flood
1073 * DoS attack, an attacker could send data which would eventually
1074 * consume all available buffer space if it were ACKed. By not ACKing
1075 * the data, we avoid this DoS scenario.
1078 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1079 struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod,
1084 struct syncache *sc = NULL;
1085 struct syncache_head *sch;
1086 struct mbuf *ipopts = NULL;
1088 int win, sb_hiwat, ip_ttl, ip_tos;
1091 int autoflowlabel = 0;
1094 struct label *maclabel;
1096 struct syncache scs;
1099 INP_WLOCK_ASSERT(inp); /* listen socket */
1100 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
1101 ("%s: unexpected tcp flags", __func__));
1104 * Combine all so/tp operations very early to drop the INP lock as
1109 cred = crhold(so->so_cred);
1112 if ((inc->inc_flags & INC_ISIPV6) &&
1113 (inp->inp_flags & IN6P_AUTOFLOWLABEL))
1116 ip_ttl = inp->inp_ip_ttl;
1117 ip_tos = inp->inp_ip_tos;
1118 win = sbspace(&so->so_rcv);
1119 sb_hiwat = so->so_rcv.sb_hiwat;
1120 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE));
1122 /* By the time we drop the lock these should no longer be used. */
1127 if (mac_syncache_init(&maclabel) != 0) {
1131 mac_syncache_create(maclabel, inp);
1136 * Remember the IP options, if any.
1139 if (!(inc->inc_flags & INC_ISIPV6))
1142 ipopts = (m) ? ip_srcroute(m) : NULL;
1148 * See if we already have an entry for this connection.
1149 * If we do, resend the SYN,ACK, and reset the retransmit timer.
1151 * XXX: should the syncache be re-initialized with the contents
1152 * of the new SYN here (which may have different options?)
1154 * XXX: We do not check the sequence number to see if this is a
1155 * real retransmit or a new connection attempt. The question is
1156 * how to handle such a case; either ignore it as spoofed, or
1157 * drop the current entry and create a new one?
1159 sc = syncache_lookup(inc, &sch); /* returns locked entry */
1160 SCH_LOCK_ASSERT(sch);
1162 TCPSTAT_INC(tcps_sc_dupsyn);
1165 * If we were remembering a previous source route,
1166 * forget it and use the new one we've been given.
1169 (void) m_free(sc->sc_ipopts);
1170 sc->sc_ipopts = ipopts;
1173 * Update timestamp if present.
1175 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
1176 sc->sc_tsreflect = to->to_tsval;
1178 sc->sc_flags &= ~SCF_TIMESTAMP;
1181 * Since we have already unconditionally allocated label
1182 * storage, free it up. The syncache entry will already
1183 * have an initialized label we can use.
1185 mac_syncache_destroy(&maclabel);
1187 /* Retransmit SYN|ACK and reset retransmit count. */
1188 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
1189 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
1190 "resetting timer and retransmitting SYN|ACK\n",
1194 if (syncache_respond(sc, sch, 1) == 0) {
1196 syncache_timeout(sc, sch, 1);
1197 TCPSTAT_INC(tcps_sndacks);
1198 TCPSTAT_INC(tcps_sndtotal);
1204 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1207 * The zone allocator couldn't provide more entries.
1208 * Treat this as if the cache was full; drop the oldest
1209 * entry and insert the new one.
1211 TCPSTAT_INC(tcps_sc_zonefail);
1212 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL)
1213 syncache_drop(sc, sch);
1214 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1216 if (V_tcp_syncookies) {
1217 bzero(&scs, sizeof(scs));
1222 (void) m_free(ipopts);
1229 * Fill in the syncache values.
1232 sc->sc_label = maclabel;
1236 sc->sc_ipopts = ipopts;
1237 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1239 if (!(inc->inc_flags & INC_ISIPV6))
1242 sc->sc_ip_tos = ip_tos;
1243 sc->sc_ip_ttl = ip_ttl;
1247 sc->sc_todctx = todctx;
1249 sc->sc_irs = th->th_seq;
1250 sc->sc_iss = arc4random();
1252 sc->sc_flowlabel = 0;
1255 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
1256 * win was derived from socket earlier in the function.
1259 win = imin(win, TCP_MAXWIN);
1262 if (V_tcp_do_rfc1323) {
1264 * A timestamp received in a SYN makes
1265 * it ok to send timestamp requests and replies.
1267 if (to->to_flags & TOF_TS) {
1268 sc->sc_tsreflect = to->to_tsval;
1269 sc->sc_ts = tcp_ts_getticks();
1270 sc->sc_flags |= SCF_TIMESTAMP;
1272 if (to->to_flags & TOF_SCALE) {
1276 * Pick the smallest possible scaling factor that
1277 * will still allow us to scale up to sb_max, aka
1278 * kern.ipc.maxsockbuf.
1280 * We do this because there are broken firewalls that
1281 * will corrupt the window scale option, leading to
1282 * the other endpoint believing that our advertised
1283 * window is unscaled. At scale factors larger than
1284 * 5 the unscaled window will drop below 1500 bytes,
1285 * leading to serious problems when traversing these
1288 * With the default maxsockbuf of 256K, a scale factor
1289 * of 3 will be chosen by this algorithm. Those who
1290 * choose a larger maxsockbuf should watch out
1291 * for the compatiblity problems mentioned above.
1293 * RFC1323: The Window field in a SYN (i.e., a <SYN>
1294 * or <SYN,ACK>) segment itself is never scaled.
1296 while (wscale < TCP_MAX_WINSHIFT &&
1297 (TCP_MAXWIN << wscale) < sb_max)
1299 sc->sc_requested_r_scale = wscale;
1300 sc->sc_requested_s_scale = to->to_wscale;
1301 sc->sc_flags |= SCF_WINSCALE;
1304 #ifdef TCP_SIGNATURE
1306 * If listening socket requested TCP digests, OR received SYN
1307 * contains the option, flag this in the syncache so that
1308 * syncache_respond() will do the right thing with the SYN+ACK.
1310 if (to->to_flags & TOF_SIGNATURE || ltflags & TF_SIGNATURE)
1311 sc->sc_flags |= SCF_SIGNATURE;
1313 if (to->to_flags & TOF_SACKPERM)
1314 sc->sc_flags |= SCF_SACK;
1315 if (to->to_flags & TOF_MSS)
1316 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */
1317 if (ltflags & TF_NOOPT)
1318 sc->sc_flags |= SCF_NOOPT;
1319 if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn)
1320 sc->sc_flags |= SCF_ECN;
1322 if (V_tcp_syncookies)
1323 sc->sc_iss = syncookie_generate(sch, sc);
1325 if (autoflowlabel) {
1326 if (V_tcp_syncookies)
1327 sc->sc_flowlabel = sc->sc_iss;
1329 sc->sc_flowlabel = ip6_randomflowlabel();
1330 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK;
1336 * Do a standard 3-way handshake.
1338 if (syncache_respond(sc, sch, 0) == 0) {
1339 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs)
1341 else if (sc != &scs)
1342 syncache_insert(sc, sch); /* locks and unlocks sch */
1343 TCPSTAT_INC(tcps_sndacks);
1344 TCPSTAT_INC(tcps_sndtotal);
1348 TCPSTAT_INC(tcps_sc_dropped);
1356 mac_syncache_destroy(&maclabel);
1366 syncache_respond(struct syncache *sc, struct syncache_head *sch, int locked)
1368 struct ip *ip = NULL;
1370 struct tcphdr *th = NULL;
1371 int optlen, error = 0; /* Make compiler happy */
1372 u_int16_t hlen, tlen, mssopt;
1375 struct ip6_hdr *ip6 = NULL;
1377 #ifdef TCP_SIGNATURE
1378 struct secasvar *sav;
1383 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
1386 tlen = hlen + sizeof(struct tcphdr);
1388 /* Determine MSS we advertize to other end of connection. */
1389 mssopt = tcp_mssopt(&sc->sc_inc);
1390 if (sc->sc_peer_mss)
1391 mssopt = max( min(sc->sc_peer_mss, mssopt), V_tcp_minmss);
1393 /* XXX: Assume that the entire packet will fit in a header mbuf. */
1394 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
1395 ("syncache: mbuf too small"));
1397 /* Create the IP+TCP header from scratch. */
1398 m = m_gethdr(M_NOWAIT, MT_DATA);
1402 mac_syncache_create_mbuf(sc->sc_label, m);
1404 m->m_data += max_linkhdr;
1406 m->m_pkthdr.len = tlen;
1407 m->m_pkthdr.rcvif = NULL;
1410 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1411 ip6 = mtod(m, struct ip6_hdr *);
1412 ip6->ip6_vfc = IPV6_VERSION;
1413 ip6->ip6_nxt = IPPROTO_TCP;
1414 ip6->ip6_src = sc->sc_inc.inc6_laddr;
1415 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
1416 ip6->ip6_plen = htons(tlen - hlen);
1417 /* ip6_hlim is set after checksum */
1418 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK;
1419 ip6->ip6_flow |= sc->sc_flowlabel;
1421 th = (struct tcphdr *)(ip6 + 1);
1424 #if defined(INET6) && defined(INET)
1429 ip = mtod(m, struct ip *);
1430 ip->ip_v = IPVERSION;
1431 ip->ip_hl = sizeof(struct ip) >> 2;
1432 ip->ip_len = htons(tlen);
1436 ip->ip_p = IPPROTO_TCP;
1437 ip->ip_src = sc->sc_inc.inc_laddr;
1438 ip->ip_dst = sc->sc_inc.inc_faddr;
1439 ip->ip_ttl = sc->sc_ip_ttl;
1440 ip->ip_tos = sc->sc_ip_tos;
1443 * See if we should do MTU discovery. Route lookups are
1444 * expensive, so we will only unset the DF bit if:
1446 * 1) path_mtu_discovery is disabled
1447 * 2) the SCF_UNREACH flag has been set
1449 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
1450 ip->ip_off |= htons(IP_DF);
1452 th = (struct tcphdr *)(ip + 1);
1455 th->th_sport = sc->sc_inc.inc_lport;
1456 th->th_dport = sc->sc_inc.inc_fport;
1458 th->th_seq = htonl(sc->sc_iss);
1459 th->th_ack = htonl(sc->sc_irs + 1);
1460 th->th_off = sizeof(struct tcphdr) >> 2;
1462 th->th_flags = TH_SYN|TH_ACK;
1463 th->th_win = htons(sc->sc_wnd);
1466 if (sc->sc_flags & SCF_ECN) {
1467 th->th_flags |= TH_ECE;
1468 TCPSTAT_INC(tcps_ecn_shs);
1471 /* Tack on the TCP options. */
1472 if ((sc->sc_flags & SCF_NOOPT) == 0) {
1476 to.to_flags = TOF_MSS;
1477 if (sc->sc_flags & SCF_WINSCALE) {
1478 to.to_wscale = sc->sc_requested_r_scale;
1479 to.to_flags |= TOF_SCALE;
1481 if (sc->sc_flags & SCF_TIMESTAMP) {
1482 /* Virgin timestamp or TCP cookie enhanced one. */
1483 to.to_tsval = sc->sc_ts;
1484 to.to_tsecr = sc->sc_tsreflect;
1485 to.to_flags |= TOF_TS;
1487 if (sc->sc_flags & SCF_SACK)
1488 to.to_flags |= TOF_SACKPERM;
1489 #ifdef TCP_SIGNATURE
1491 if (sc->sc_flags & SCF_SIGNATURE) {
1492 sav = tcp_get_sav(m, IPSEC_DIR_OUTBOUND);
1494 to.to_flags |= TOF_SIGNATURE;
1498 * We've got SCF_SIGNATURE flag
1499 * inherited from listening socket,
1500 * but no SADB key for given source
1501 * address. Assume signature is not
1502 * required and remove signature flag
1503 * instead of silently dropping
1508 sc->sc_flags &= ~SCF_SIGNATURE;
1514 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
1516 /* Adjust headers by option size. */
1517 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
1519 m->m_pkthdr.len += optlen;
1521 #ifdef TCP_SIGNATURE
1522 if (sc->sc_flags & SCF_SIGNATURE)
1523 tcp_signature_do_compute(m, 0, optlen,
1524 to.to_signature, sav);
1527 if (sc->sc_inc.inc_flags & INC_ISIPV6)
1528 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
1531 ip->ip_len = htons(ntohs(ip->ip_len) + optlen);
1535 M_SETFIB(m, sc->sc_inc.inc_fibnum);
1536 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1538 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1539 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
1540 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen,
1542 ip6->ip6_hlim = in6_selecthlim(NULL, NULL);
1544 if (ADDED_BY_TOE(sc)) {
1545 struct toedev *tod = sc->sc_tod;
1547 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
1552 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
1555 #if defined(INET6) && defined(INET)
1560 m->m_pkthdr.csum_flags = CSUM_TCP;
1561 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
1562 htons(tlen + optlen - hlen + IPPROTO_TCP));
1564 if (ADDED_BY_TOE(sc)) {
1565 struct toedev *tod = sc->sc_tod;
1567 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
1572 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
1579 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks
1580 * that exceed the capacity of the syncache by avoiding the storage of any
1581 * of the SYNs we receive. Syncookies defend against blind SYN flooding
1582 * attacks where the attacker does not have access to our responses.
1584 * Syncookies encode and include all necessary information about the
1585 * connection setup within the SYN|ACK that we send back. That way we
1586 * can avoid keeping any local state until the ACK to our SYN|ACK returns
1587 * (if ever). Normally the syncache and syncookies are running in parallel
1588 * with the latter taking over when the former is exhausted. When matching
1589 * syncache entry is found the syncookie is ignored.
1591 * The only reliable information persisting the 3WHS is our inital sequence
1592 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient
1593 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS
1594 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK
1595 * returns and signifies a legitimate connection if it matches the ACK.
1597 * The available space of 32 bits to store the hash and to encode the SYN
1598 * option information is very tight and we should have at least 24 bits for
1599 * the MAC to keep the number of guesses by blind spoofing reasonably high.
1601 * SYN option information we have to encode to fully restore a connection:
1602 * MSS: is imporant to chose an optimal segment size to avoid IP level
1603 * fragmentation along the path. The common MSS values can be encoded
1604 * in a 3-bit table. Uncommon values are captured by the next lower value
1605 * in the table leading to a slight increase in packetization overhead.
1606 * WSCALE: is necessary to allow large windows to be used for high delay-
1607 * bandwidth product links. Not scaling the window when it was initially
1608 * negotiated is bad for performance as lack of scaling further decreases
1609 * the apparent available send window. We only need to encode the WSCALE
1610 * we received from the remote end. Our end can be recalculated at any
1611 * time. The common WSCALE values can be encoded in a 3-bit table.
1612 * Uncommon values are captured by the next lower value in the table
1613 * making us under-estimate the available window size halving our
1614 * theoretically possible maximum throughput for that connection.
1615 * SACK: Greatly assists in packet loss recovery and requires 1 bit.
1616 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options
1617 * that are included in all segments on a connection. We enable them when
1620 * Security of syncookies and attack vectors:
1622 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod)
1623 * together with the gloabl secret to make it unique per connection attempt.
1624 * Thus any change of any of those parameters results in a different MAC output
1625 * in an unpredictable way unless a collision is encountered. 24 bits of the
1626 * MAC are embedded into the ISS.
1628 * To prevent replay attacks two rotating global secrets are updated with a
1629 * new random value every 15 seconds. The life-time of a syncookie is thus
1632 * Vector 1: Attacking the secret. This requires finding a weakness in the
1633 * MAC itself or the way it is used here. The attacker can do a chosen plain
1634 * text attack by varying and testing the all parameters under his control.
1635 * The strength depends on the size and randomness of the secret, and the
1636 * cryptographic security of the MAC function. Due to the constant updating
1637 * of the secret the attacker has at most 29.999 seconds to find the secret
1638 * and launch spoofed connections. After that he has to start all over again.
1640 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC
1641 * size an average of 4,823 attempts are required for a 50% chance of success
1642 * to spoof a single syncookie (birthday collision paradox). However the
1643 * attacker is blind and doesn't know if one of his attempts succeeded unless
1644 * he has a side channel to interfere success from. A single connection setup
1645 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets.
1646 * This many attempts are required for each one blind spoofed connection. For
1647 * every additional spoofed connection he has to launch another N attempts.
1648 * Thus for a sustained rate 100 spoofed connections per second approximately
1649 * 1,800,000 packets per second would have to be sent.
1651 * NB: The MAC function should be fast so that it doesn't become a CPU
1652 * exhaustion attack vector itself.
1655 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations
1656 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996
1657 * http://cr.yp.to/syncookies.html (overview)
1658 * http://cr.yp.to/syncookies/archive (details)
1661 * Schematic construction of a syncookie enabled Initial Sequence Number:
1663 * 12345678901234567890123456789012
1664 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP|
1666 * x 24 MAC (truncated)
1667 * W 3 Send Window Scale index
1669 * S 1 SACK permitted
1670 * P 1 Odd/even secret
1674 * Distribution and probability of certain MSS values. Those in between are
1675 * rounded down to the next lower one.
1676 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011]
1677 * .2% .3% 5% 7% 7% 20% 15% 45%
1679 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 };
1682 * Distribution and probability of certain WSCALE values. We have to map the
1683 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3
1684 * bits based on prevalence of certain values. Where we don't have an exact
1685 * match for are rounded down to the next lower one letting us under-estimate
1686 * the true available window. At the moment this would happen only for the
1687 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer
1688 * and window size). The absence of the WSCALE option (no scaling in either
1689 * direction) is encoded with index zero.
1690 * [WSCALE values histograms, Allman, 2012]
1691 * X 10 10 35 5 6 14 10% by host
1692 * X 11 4 5 5 18 49 3% by connections
1694 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 };
1697 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed
1698 * and good cryptographic properties.
1701 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags,
1702 uint8_t *secbits, uintptr_t secmod)
1705 uint32_t siphash[2];
1707 SipHash24_Init(&ctx);
1708 SipHash_SetKey(&ctx, secbits);
1709 switch (inc->inc_flags & INC_ISIPV6) {
1712 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr));
1713 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr));
1718 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr));
1719 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr));
1723 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport));
1724 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport));
1725 SipHash_Update(&ctx, &irs, sizeof(irs));
1726 SipHash_Update(&ctx, &flags, sizeof(flags));
1727 SipHash_Update(&ctx, &secmod, sizeof(secmod));
1728 SipHash_Final((u_int8_t *)&siphash, &ctx);
1730 return (siphash[0] ^ siphash[1]);
1734 syncookie_generate(struct syncache_head *sch, struct syncache *sc)
1736 u_int i, mss, secbit, wscale;
1739 union syncookie cookie;
1741 SCH_LOCK_ASSERT(sch);
1745 /* Map our computed MSS into the 3-bit index. */
1746 mss = min(tcp_mssopt(&sc->sc_inc), max(sc->sc_peer_mss, V_tcp_minmss));
1747 for (i = sizeof(tcp_sc_msstab) / sizeof(*tcp_sc_msstab) - 1;
1748 tcp_sc_msstab[i] > mss && i > 0;
1751 cookie.flags.mss_idx = i;
1754 * Map the send window scale into the 3-bit index but only if
1755 * the wscale option was received.
1757 if (sc->sc_flags & SCF_WINSCALE) {
1758 wscale = sc->sc_requested_s_scale;
1759 for (i = sizeof(tcp_sc_wstab) / sizeof(*tcp_sc_wstab) - 1;
1760 tcp_sc_wstab[i] > wscale && i > 0;
1763 cookie.flags.wscale_idx = i;
1766 /* Can we do SACK? */
1767 if (sc->sc_flags & SCF_SACK)
1768 cookie.flags.sack_ok = 1;
1770 /* Which of the two secrets to use. */
1771 secbit = sch->sch_sc->secret.oddeven & 0x1;
1772 cookie.flags.odd_even = secbit;
1774 secbits = sch->sch_sc->secret.key[secbit];
1775 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits,
1779 * Put the flags into the hash and XOR them to get better ISS number
1780 * variance. This doesn't enhance the cryptographic strength and is
1781 * done to prevent the 8 cookie bits from showing up directly on the
1785 iss |= cookie.cookie ^ (hash >> 24);
1787 /* Randomize the timestamp. */
1788 if (sc->sc_flags & SCF_TIMESTAMP) {
1789 sc->sc_ts = arc4random();
1790 sc->sc_tsoff = sc->sc_ts - tcp_ts_getticks();
1793 TCPSTAT_INC(tcps_sc_sendcookie);
1797 static struct syncache *
1798 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch,
1799 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
1805 int wnd, wscale = 0;
1806 union syncookie cookie;
1808 SCH_LOCK_ASSERT(sch);
1811 * Pull information out of SYN-ACK/ACK and revert sequence number
1814 ack = th->th_ack - 1;
1815 seq = th->th_seq - 1;
1818 * Unpack the flags containing enough information to restore the
1821 cookie.cookie = (ack & 0xff) ^ (ack >> 24);
1823 /* Which of the two secrets to use. */
1824 secbits = sch->sch_sc->secret.key[cookie.flags.odd_even];
1826 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch);
1828 /* The recomputed hash matches the ACK if this was a genuine cookie. */
1829 if ((ack & ~0xff) != (hash & ~0xff))
1832 /* Fill in the syncache values. */
1834 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1835 sc->sc_ipopts = NULL;
1840 switch (inc->inc_flags & INC_ISIPV6) {
1843 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl;
1844 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos;
1849 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL)
1850 sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK;
1855 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx];
1857 /* We can simply recompute receive window scale we sent earlier. */
1858 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max)
1861 /* Only use wscale if it was enabled in the orignal SYN. */
1862 if (cookie.flags.wscale_idx > 0) {
1863 sc->sc_requested_r_scale = wscale;
1864 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx];
1865 sc->sc_flags |= SCF_WINSCALE;
1868 wnd = sbspace(&lso->so_rcv);
1870 wnd = imin(wnd, TCP_MAXWIN);
1873 if (cookie.flags.sack_ok)
1874 sc->sc_flags |= SCF_SACK;
1876 if (to->to_flags & TOF_TS) {
1877 sc->sc_flags |= SCF_TIMESTAMP;
1878 sc->sc_tsreflect = to->to_tsval;
1879 sc->sc_ts = to->to_tsecr;
1880 sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks();
1883 if (to->to_flags & TOF_SIGNATURE)
1884 sc->sc_flags |= SCF_SIGNATURE;
1888 TCPSTAT_INC(tcps_sc_recvcookie);
1894 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
1895 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
1898 struct syncache scs, *scx;
1901 bzero(&scs, sizeof(scs));
1902 scx = syncookie_lookup(inc, sch, &scs, th, to, lso);
1904 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL)
1908 if (sc->sc_peer_mss != scx->sc_peer_mss)
1909 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n",
1910 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss);
1912 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale)
1913 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n",
1914 s, __func__, sc->sc_requested_r_scale,
1915 scx->sc_requested_r_scale);
1917 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale)
1918 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n",
1919 s, __func__, sc->sc_requested_s_scale,
1920 scx->sc_requested_s_scale);
1922 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK))
1923 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__);
1930 #endif /* INVARIANTS */
1933 syncookie_reseed(void *arg)
1935 struct tcp_syncache *sc = arg;
1940 * Reseeding the secret doesn't have to be protected by a lock.
1941 * It only must be ensured that the new random values are visible
1942 * to all CPUs in a SMP environment. The atomic with release
1943 * semantics ensures that.
1945 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1;
1946 secbits = sc->secret.key[secbit];
1947 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0);
1948 atomic_add_rel_int(&sc->secret.oddeven, 1);
1950 /* Reschedule ourself. */
1951 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz);
1955 * Returns the current number of syncache entries. This number
1956 * will probably change before you get around to calling
1960 syncache_pcbcount(void)
1962 struct syncache_head *sch;
1965 for (count = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
1966 /* No need to lock for a read. */
1967 sch = &V_tcp_syncache.hashbase[i];
1968 count += sch->sch_length;
1974 * Exports the syncache entries to userland so that netstat can display
1975 * them alongside the other sockets. This function is intended to be
1976 * called only from tcp_pcblist.
1978 * Due to concurrency on an active system, the number of pcbs exported
1979 * may have no relation to max_pcbs. max_pcbs merely indicates the
1980 * amount of space the caller allocated for this function to use.
1983 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported)
1986 struct syncache *sc;
1987 struct syncache_head *sch;
1988 int count, error, i;
1990 for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
1991 sch = &V_tcp_syncache.hashbase[i];
1993 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
1994 if (count >= max_pcbs) {
1998 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
2000 bzero(&xt, sizeof(xt));
2001 xt.xt_len = sizeof(xt);
2002 if (sc->sc_inc.inc_flags & INC_ISIPV6)
2003 xt.xt_inp.inp_vflag = INP_IPV6;
2005 xt.xt_inp.inp_vflag = INP_IPV4;
2006 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo));
2007 xt.xt_tp.t_inpcb = &xt.xt_inp;
2008 xt.xt_tp.t_state = TCPS_SYN_RECEIVED;
2009 xt.xt_socket.xso_protocol = IPPROTO_TCP;
2010 xt.xt_socket.xso_len = sizeof (struct xsocket);
2011 xt.xt_socket.so_type = SOCK_STREAM;
2012 xt.xt_socket.so_state = SS_ISCONNECTING;
2013 error = SYSCTL_OUT(req, &xt, sizeof xt);
2023 *pcbs_exported = count;