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>
43 #include <sys/kernel.h>
44 #include <sys/sysctl.h>
45 #include <sys/limits.h>
47 #include <sys/mutex.h>
48 #include <sys/malloc.h>
50 #include <sys/proc.h> /* for proc0 declaration */
51 #include <sys/random.h>
52 #include <sys/socket.h>
53 #include <sys/socketvar.h>
54 #include <sys/syslog.h>
55 #include <sys/ucred.h>
58 #include <crypto/siphash/siphash.h>
63 #include <net/if_var.h>
64 #include <net/route.h>
67 #include <netinet/in.h>
68 #include <netinet/in_systm.h>
69 #include <netinet/ip.h>
70 #include <netinet/in_var.h>
71 #include <netinet/in_pcb.h>
72 #include <netinet/ip_var.h>
73 #include <netinet/ip_options.h>
75 #include <netinet/ip6.h>
76 #include <netinet/icmp6.h>
77 #include <netinet6/nd6.h>
78 #include <netinet6/ip6_var.h>
79 #include <netinet6/in6_pcb.h>
81 #include <netinet/tcp.h>
82 #include <netinet/tcp_fsm.h>
83 #include <netinet/tcp_seq.h>
84 #include <netinet/tcp_timer.h>
85 #include <netinet/tcp_var.h>
86 #include <netinet/tcp_syncache.h>
88 #include <netinet6/tcp6_var.h>
91 #include <netinet/toecore.h>
95 #include <netipsec/ipsec.h>
97 #include <netipsec/ipsec6.h>
99 #include <netipsec/key.h>
102 #include <machine/in_cksum.h>
104 #include <security/mac/mac_framework.h>
106 static VNET_DEFINE(int, tcp_syncookies) = 1;
107 #define V_tcp_syncookies VNET(tcp_syncookies)
108 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW,
109 &VNET_NAME(tcp_syncookies), 0,
110 "Use TCP SYN cookies if the syncache overflows");
112 static VNET_DEFINE(int, tcp_syncookiesonly) = 0;
113 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly)
114 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_RW,
115 &VNET_NAME(tcp_syncookiesonly), 0,
116 "Use only TCP SYN cookies");
119 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL)
122 static void syncache_drop(struct syncache *, struct syncache_head *);
123 static void syncache_free(struct syncache *);
124 static void syncache_insert(struct syncache *, struct syncache_head *);
125 struct syncache *syncache_lookup(struct in_conninfo *, struct syncache_head **);
126 static int syncache_respond(struct syncache *);
127 static struct socket *syncache_socket(struct syncache *, struct socket *,
129 static int syncache_sysctl_count(SYSCTL_HANDLER_ARGS);
130 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch,
132 static void syncache_timer(void *);
134 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t,
135 uint8_t *, uintptr_t);
136 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *);
137 static struct syncache
138 *syncookie_lookup(struct in_conninfo *, struct syncache_head *,
139 struct syncache *, struct tcphdr *, struct tcpopt *,
141 static void syncookie_reseed(void *);
143 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
144 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
149 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
150 * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds,
151 * the odds are that the user has given up attempting to connect by then.
153 #define SYNCACHE_MAXREXMTS 3
155 /* Arbitrary values */
156 #define TCP_SYNCACHE_HASHSIZE 512
157 #define TCP_SYNCACHE_BUCKETLIMIT 30
159 static VNET_DEFINE(struct tcp_syncache, tcp_syncache);
160 #define V_tcp_syncache VNET(tcp_syncache)
162 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0,
165 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RDTUN,
166 &VNET_NAME(tcp_syncache.bucket_limit), 0,
167 "Per-bucket hash limit for syncache");
169 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RDTUN,
170 &VNET_NAME(tcp_syncache.cache_limit), 0,
171 "Overall entry limit for syncache");
173 SYSCTL_VNET_PROC(_net_inet_tcp_syncache, OID_AUTO, count, (CTLTYPE_UINT|CTLFLAG_RD),
174 NULL, 0, &syncache_sysctl_count, "IU",
175 "Current number of entries in syncache");
177 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RDTUN,
178 &VNET_NAME(tcp_syncache.hashsize), 0,
179 "Size of TCP syncache hashtable");
181 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW,
182 &VNET_NAME(tcp_syncache.rexmt_limit), 0,
183 "Limit on SYN/ACK retransmissions");
185 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1;
186 SYSCTL_VNET_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail,
187 CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0,
188 "Send reset on socket allocation failure");
190 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
192 #define SYNCACHE_HASH(inc, mask) \
193 ((V_tcp_syncache.hash_secret ^ \
194 (inc)->inc_faddr.s_addr ^ \
195 ((inc)->inc_faddr.s_addr >> 16) ^ \
196 (inc)->inc_fport ^ (inc)->inc_lport) & mask)
198 #define SYNCACHE_HASH6(inc, mask) \
199 ((V_tcp_syncache.hash_secret ^ \
200 (inc)->inc6_faddr.s6_addr32[0] ^ \
201 (inc)->inc6_faddr.s6_addr32[3] ^ \
202 (inc)->inc_fport ^ (inc)->inc_lport) & mask)
204 #define ENDPTS_EQ(a, b) ( \
205 (a)->ie_fport == (b)->ie_fport && \
206 (a)->ie_lport == (b)->ie_lport && \
207 (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr && \
208 (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr \
211 #define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0)
213 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx)
214 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx)
215 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED)
218 * Requires the syncache entry to be already removed from the bucket list.
221 syncache_free(struct syncache *sc)
225 (void) m_free(sc->sc_ipopts);
229 mac_syncache_destroy(&sc->sc_label);
232 uma_zfree(V_tcp_syncache.zone, sc);
240 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
241 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
242 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
243 V_tcp_syncache.hash_secret = arc4random();
245 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
246 &V_tcp_syncache.hashsize);
247 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
248 &V_tcp_syncache.bucket_limit);
249 if (!powerof2(V_tcp_syncache.hashsize) ||
250 V_tcp_syncache.hashsize == 0) {
251 printf("WARNING: syncache hash size is not a power of 2.\n");
252 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
254 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1;
257 V_tcp_syncache.cache_limit =
258 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit;
259 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
260 &V_tcp_syncache.cache_limit);
262 /* Allocate the hash table. */
263 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize *
264 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO);
267 V_tcp_syncache.vnet = curvnet;
270 /* Initialize the hash buckets. */
271 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
272 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket);
273 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
275 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer,
276 &V_tcp_syncache.hashbase[i].sch_mtx, 0);
277 V_tcp_syncache.hashbase[i].sch_length = 0;
278 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache;
281 /* Create the syncache entry zone. */
282 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
283 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
284 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone,
285 V_tcp_syncache.cache_limit);
287 /* Start the SYN cookie reseeder callout. */
288 callout_init(&V_tcp_syncache.secret.reseed, 1);
289 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0);
290 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0);
291 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz,
292 syncookie_reseed, &V_tcp_syncache);
297 syncache_destroy(void)
299 struct syncache_head *sch;
300 struct syncache *sc, *nsc;
303 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */
304 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
306 sch = &V_tcp_syncache.hashbase[i];
307 callout_drain(&sch->sch_timer);
310 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc)
311 syncache_drop(sc, sch);
313 KASSERT(TAILQ_EMPTY(&sch->sch_bucket),
314 ("%s: sch->sch_bucket not empty", __func__));
315 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0",
316 __func__, sch->sch_length));
317 mtx_destroy(&sch->sch_mtx);
320 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0,
321 ("%s: cache_count not 0", __func__));
323 /* Free the allocated global resources. */
324 uma_zdestroy(V_tcp_syncache.zone);
325 free(V_tcp_syncache.hashbase, M_SYNCACHE);
327 callout_drain(&V_tcp_syncache.secret.reseed);
332 syncache_sysctl_count(SYSCTL_HANDLER_ARGS)
336 count = uma_zone_get_cur(V_tcp_syncache.zone);
337 return (sysctl_handle_int(oidp, &count, 0, req));
341 * Inserts a syncache entry into the specified bucket row.
342 * Locks and unlocks the syncache_head autonomously.
345 syncache_insert(struct syncache *sc, struct syncache_head *sch)
347 struct syncache *sc2;
352 * Make sure that we don't overflow the per-bucket limit.
353 * If the bucket is full, toss the oldest element.
355 if (sch->sch_length >= V_tcp_syncache.bucket_limit) {
356 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
357 ("sch->sch_length incorrect"));
358 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
359 syncache_drop(sc2, sch);
360 TCPSTAT_INC(tcps_sc_bucketoverflow);
363 /* Put it into the bucket. */
364 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
368 if (ADDED_BY_TOE(sc)) {
369 struct toedev *tod = sc->sc_tod;
371 tod->tod_syncache_added(tod, sc->sc_todctx);
375 /* Reinitialize the bucket row's timer. */
376 if (sch->sch_length == 1)
377 sch->sch_nextc = ticks + INT_MAX;
378 syncache_timeout(sc, sch, 1);
382 TCPSTAT_INC(tcps_sc_added);
386 * Remove and free entry from syncache bucket row.
387 * Expects locked syncache head.
390 syncache_drop(struct syncache *sc, struct syncache_head *sch)
393 SCH_LOCK_ASSERT(sch);
395 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
399 if (ADDED_BY_TOE(sc)) {
400 struct toedev *tod = sc->sc_tod;
402 tod->tod_syncache_removed(tod, sc->sc_todctx);
410 * Engage/reengage time on bucket row.
413 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
415 sc->sc_rxttime = ticks +
416 TCPTV_RTOBASE * (tcp_syn_backoff[sc->sc_rxmits]);
418 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
419 sch->sch_nextc = sc->sc_rxttime;
421 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
422 syncache_timer, (void *)sch);
427 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
428 * If we have retransmitted an entry the maximum number of times, expire it.
429 * One separate timer for each bucket row.
432 syncache_timer(void *xsch)
434 struct syncache_head *sch = (struct syncache_head *)xsch;
435 struct syncache *sc, *nsc;
439 CURVNET_SET(sch->sch_sc->vnet);
441 /* NB: syncache_head has already been locked by the callout. */
442 SCH_LOCK_ASSERT(sch);
445 * In the following cycle we may remove some entries and/or
446 * advance some timeouts, so re-initialize the bucket timer.
448 sch->sch_nextc = tick + INT_MAX;
450 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
452 * We do not check if the listen socket still exists
453 * and accept the case where the listen socket may be
454 * gone by the time we resend the SYN/ACK. We do
455 * not expect this to happens often. If it does,
456 * then the RST will be sent by the time the remote
457 * host does the SYN/ACK->ACK.
459 if (TSTMP_GT(sc->sc_rxttime, tick)) {
460 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
461 sch->sch_nextc = sc->sc_rxttime;
464 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
465 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
466 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
467 "giving up and removing syncache entry\n",
471 syncache_drop(sc, sch);
472 TCPSTAT_INC(tcps_sc_stale);
475 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
476 log(LOG_DEBUG, "%s; %s: Response timeout, "
477 "retransmitting (%u) SYN|ACK\n",
478 s, __func__, sc->sc_rxmits);
482 (void) syncache_respond(sc);
483 TCPSTAT_INC(tcps_sc_retransmitted);
484 syncache_timeout(sc, sch, 0);
486 if (!TAILQ_EMPTY(&(sch)->sch_bucket))
487 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
488 syncache_timer, (void *)(sch));
493 * Find an entry in the syncache.
494 * Returns always with locked syncache_head plus a matching entry or NULL.
497 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
500 struct syncache_head *sch;
503 if (inc->inc_flags & INC_ISIPV6) {
504 sch = &V_tcp_syncache.hashbase[
505 SYNCACHE_HASH6(inc, V_tcp_syncache.hashmask)];
510 /* Circle through bucket row to find matching entry. */
511 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
512 if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie))
518 sch = &V_tcp_syncache.hashbase[
519 SYNCACHE_HASH(inc, V_tcp_syncache.hashmask)];
524 /* Circle through bucket row to find matching entry. */
525 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
527 if (sc->sc_inc.inc_flags & INC_ISIPV6)
530 if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie))
534 SCH_LOCK_ASSERT(*schp);
535 return (NULL); /* always returns with locked sch */
539 * This function is called when we get a RST for a
540 * non-existent connection, so that we can see if the
541 * connection is in the syn cache. If it is, zap it.
544 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th)
547 struct syncache_head *sch;
550 sc = syncache_lookup(inc, &sch); /* returns locked sch */
551 SCH_LOCK_ASSERT(sch);
554 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags.
555 * See RFC 793 page 65, section SEGMENT ARRIVES.
557 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) {
558 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
559 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or "
560 "FIN flag set, segment ignored\n", s, __func__);
561 TCPSTAT_INC(tcps_badrst);
566 * No corresponding connection was found in syncache.
567 * If syncookies are enabled and possibly exclusively
568 * used, or we are under memory pressure, a valid RST
569 * may not find a syncache entry. In that case we're
570 * done and no SYN|ACK retransmissions will happen.
571 * Otherwise the RST was misdirected or spoofed.
574 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
575 log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
576 "syncache entry (possibly syncookie only), "
577 "segment ignored\n", s, __func__);
578 TCPSTAT_INC(tcps_badrst);
583 * If the RST bit is set, check the sequence number to see
584 * if this is a valid reset segment.
586 * In all states except SYN-SENT, all reset (RST) segments
587 * are validated by checking their SEQ-fields. A reset is
588 * valid if its sequence number is in the window.
590 * The sequence number in the reset segment is normally an
591 * echo of our outgoing acknowlegement numbers, but some hosts
592 * send a reset with the sequence number at the rightmost edge
593 * of our receive window, and we have to handle this case.
595 if (SEQ_GEQ(th->th_seq, sc->sc_irs) &&
596 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
597 syncache_drop(sc, sch);
598 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
599 log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, "
600 "connection attempt aborted by remote endpoint\n",
602 TCPSTAT_INC(tcps_sc_reset);
604 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
605 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
606 "IRS %u (+WND %u), segment ignored\n",
607 s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd);
608 TCPSTAT_INC(tcps_badrst);
618 syncache_badack(struct in_conninfo *inc)
621 struct syncache_head *sch;
623 sc = syncache_lookup(inc, &sch); /* returns locked sch */
624 SCH_LOCK_ASSERT(sch);
626 syncache_drop(sc, sch);
627 TCPSTAT_INC(tcps_sc_badack);
633 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th)
636 struct syncache_head *sch;
638 sc = syncache_lookup(inc, &sch); /* returns locked sch */
639 SCH_LOCK_ASSERT(sch);
643 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
644 if (ntohl(th->th_seq) != sc->sc_iss)
648 * If we've rertransmitted 3 times and this is our second error,
649 * we remove the entry. Otherwise, we allow it to continue on.
650 * This prevents us from incorrectly nuking an entry during a
651 * spurious network outage.
655 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
656 sc->sc_flags |= SCF_UNREACH;
659 syncache_drop(sc, sch);
660 TCPSTAT_INC(tcps_sc_unreach);
666 * Build a new TCP socket structure from a syncache entry.
668 static struct socket *
669 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
671 struct inpcb *inp = NULL;
677 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
680 * Ok, create the full blown connection, and set things up
681 * as they would have been set up if we had created the
682 * connection when the SYN arrived. If we can't create
683 * the connection, abort it.
685 so = sonewconn(lso, SS_ISCONNECTED);
688 * Drop the connection; we will either send a RST or
689 * have the peer retransmit its SYN again after its
692 TCPSTAT_INC(tcps_listendrop);
693 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
694 log(LOG_DEBUG, "%s; %s: Socket create failed "
695 "due to limits or memory shortage\n",
702 mac_socketpeer_set_from_mbuf(m, so);
706 inp->inp_inc.inc_fibnum = so->so_fibnum;
708 INP_HASH_WLOCK(&V_tcbinfo);
710 /* Insert new socket into PCB hash list. */
711 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
713 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
714 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
716 inp->inp_vflag &= ~INP_IPV6;
717 inp->inp_vflag |= INP_IPV4;
719 inp->inp_laddr = sc->sc_inc.inc_laddr;
725 * Install in the reservation hash table for now, but don't yet
726 * install a connection group since the full 4-tuple isn't yet
729 inp->inp_lport = sc->sc_inc.inc_lport;
730 if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) {
732 * Undo the assignments above if we failed to
733 * put the PCB on the hash lists.
736 if (sc->sc_inc.inc_flags & INC_ISIPV6)
737 inp->in6p_laddr = in6addr_any;
740 inp->inp_laddr.s_addr = INADDR_ANY;
742 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
743 log(LOG_DEBUG, "%s; %s: in_pcbinshash failed "
748 INP_HASH_WUNLOCK(&V_tcbinfo);
752 /* Copy old policy into new socket's. */
753 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp))
754 printf("syncache_socket: could not copy policy\n");
757 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
758 struct inpcb *oinp = sotoinpcb(lso);
759 struct in6_addr laddr6;
760 struct sockaddr_in6 sin6;
762 * Inherit socket options from the listening socket.
763 * Note that in6p_inputopts are not (and should not be)
764 * copied, since it stores previously received options and is
765 * used to detect if each new option is different than the
766 * previous one and hence should be passed to a user.
767 * If we copied in6p_inputopts, a user would not be able to
768 * receive options just after calling the accept system call.
770 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
771 if (oinp->in6p_outputopts)
772 inp->in6p_outputopts =
773 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
775 sin6.sin6_family = AF_INET6;
776 sin6.sin6_len = sizeof(sin6);
777 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
778 sin6.sin6_port = sc->sc_inc.inc_fport;
779 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
780 laddr6 = inp->in6p_laddr;
781 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
782 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
783 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6,
784 thread0.td_ucred, m)) != 0) {
785 inp->in6p_laddr = laddr6;
786 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
787 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed "
792 INP_HASH_WUNLOCK(&V_tcbinfo);
795 /* Override flowlabel from in6_pcbconnect. */
796 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
797 inp->inp_flow |= sc->sc_flowlabel;
800 #if defined(INET) && defined(INET6)
805 struct in_addr laddr;
806 struct sockaddr_in sin;
808 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
810 if (inp->inp_options == NULL) {
811 inp->inp_options = sc->sc_ipopts;
812 sc->sc_ipopts = NULL;
815 sin.sin_family = AF_INET;
816 sin.sin_len = sizeof(sin);
817 sin.sin_addr = sc->sc_inc.inc_faddr;
818 sin.sin_port = sc->sc_inc.inc_fport;
819 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
820 laddr = inp->inp_laddr;
821 if (inp->inp_laddr.s_addr == INADDR_ANY)
822 inp->inp_laddr = sc->sc_inc.inc_laddr;
823 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin,
824 thread0.td_ucred, m)) != 0) {
825 inp->inp_laddr = laddr;
826 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
827 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed "
832 INP_HASH_WUNLOCK(&V_tcbinfo);
837 INP_HASH_WUNLOCK(&V_tcbinfo);
839 tcp_state_change(tp, TCPS_SYN_RECEIVED);
840 tp->iss = sc->sc_iss;
841 tp->irs = sc->sc_irs;
844 tp->snd_wl1 = sc->sc_irs;
845 tp->snd_max = tp->iss + 1;
846 tp->snd_nxt = tp->iss + 1;
847 tp->rcv_up = sc->sc_irs + 1;
848 tp->rcv_wnd = sc->sc_wnd;
849 tp->rcv_adv += tp->rcv_wnd;
850 tp->last_ack_sent = tp->rcv_nxt;
852 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
853 if (sc->sc_flags & SCF_NOOPT)
854 tp->t_flags |= TF_NOOPT;
856 if (sc->sc_flags & SCF_WINSCALE) {
857 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
858 tp->snd_scale = sc->sc_requested_s_scale;
859 tp->request_r_scale = sc->sc_requested_r_scale;
861 if (sc->sc_flags & SCF_TIMESTAMP) {
862 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
863 tp->ts_recent = sc->sc_tsreflect;
864 tp->ts_recent_age = tcp_ts_getticks();
865 tp->ts_offset = sc->sc_tsoff;
868 if (sc->sc_flags & SCF_SIGNATURE)
869 tp->t_flags |= TF_SIGNATURE;
871 if (sc->sc_flags & SCF_SACK)
872 tp->t_flags |= TF_SACK_PERMIT;
875 if (sc->sc_flags & SCF_ECN)
876 tp->t_flags |= TF_ECN_PERMIT;
879 * Set up MSS and get cached values from tcp_hostcache.
880 * This might overwrite some of the defaults we just set.
882 tcp_mss(tp, sc->sc_peer_mss);
885 * If the SYN,ACK was retransmitted, indicate that CWND to be
886 * limited to one segment in cc_conn_init().
887 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
889 if (sc->sc_rxmits > 1)
894 * Allow a TOE driver to install its hooks. Note that we hold the
895 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a
896 * new connection before the TOE driver has done its thing.
898 if (ADDED_BY_TOE(sc)) {
899 struct toedev *tod = sc->sc_tod;
901 tod->tod_offload_socket(tod, sc->sc_todctx, so);
905 * Copy and activate timers.
907 tp->t_keepinit = sototcpcb(lso)->t_keepinit;
908 tp->t_keepidle = sototcpcb(lso)->t_keepidle;
909 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl;
910 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt;
911 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp));
915 TCPSTAT_INC(tcps_accepts);
927 * This function gets called when we receive an ACK for a
928 * socket in the LISTEN state. We look up the connection
929 * in the syncache, and if its there, we pull it out of
930 * the cache and turn it into a full-blown connection in
931 * the SYN-RECEIVED state.
934 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
935 struct socket **lsop, struct mbuf *m)
938 struct syncache_head *sch;
943 * Global TCP locks are held because we manipulate the PCB lists
944 * and create a new socket.
946 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
947 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
948 ("%s: can handle only ACK", __func__));
950 sc = syncache_lookup(inc, &sch); /* returns locked sch */
951 SCH_LOCK_ASSERT(sch);
955 * Test code for syncookies comparing the syncache stored
956 * values with the reconstructed values from the cookie.
959 syncookie_cmp(inc, sch, sc, th, to, *lsop);
964 * There is no syncache entry, so see if this ACK is
965 * a returning syncookie. To do this, first:
966 * A. See if this socket has had a syncache entry dropped in
967 * the past. We don't want to accept a bogus syncookie
968 * if we've never received a SYN.
969 * B. check that the syncookie is valid. If it is, then
970 * cobble up a fake syncache entry, and return.
972 if (!V_tcp_syncookies) {
974 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
975 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
976 "segment rejected (syncookies disabled)\n",
980 bzero(&scs, sizeof(scs));
981 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop);
984 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
985 log(LOG_DEBUG, "%s; %s: Segment failed "
986 "SYNCOOKIE authentication, segment rejected "
987 "(probably spoofed)\n", s, __func__);
991 /* Pull out the entry to unlock the bucket row. */
992 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
995 if (ADDED_BY_TOE(sc)) {
996 struct toedev *tod = sc->sc_tod;
998 tod->tod_syncache_removed(tod, sc->sc_todctx);
1005 * Segment validation:
1006 * ACK must match our initial sequence number + 1 (the SYN|ACK).
1008 if (th->th_ack != sc->sc_iss + 1) {
1009 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1010 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
1011 "rejected\n", s, __func__, th->th_ack, sc->sc_iss);
1016 * The SEQ must fall in the window starting at the received
1017 * initial receive sequence number + 1 (the SYN).
1019 if (SEQ_LEQ(th->th_seq, sc->sc_irs) ||
1020 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
1021 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1022 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
1023 "rejected\n", s, __func__, th->th_seq, sc->sc_irs);
1028 * If timestamps were not negotiated during SYN/ACK they
1029 * must not appear on any segment during this session.
1031 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) {
1032 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1033 log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
1034 "segment rejected\n", s, __func__);
1039 * If timestamps were negotiated during SYN/ACK they should
1040 * appear on every segment during this session.
1041 * XXXAO: This is only informal as there have been unverified
1042 * reports of non-compliants stacks.
1044 if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) {
1045 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1046 log(LOG_DEBUG, "%s; %s: Timestamp missing, "
1047 "no action\n", s, __func__);
1054 * If timestamps were negotiated the reflected timestamp
1055 * must be equal to what we actually sent in the SYN|ACK.
1057 if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts) {
1058 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1059 log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, "
1060 "segment rejected\n",
1061 s, __func__, to->to_tsecr, sc->sc_ts);
1065 *lsop = syncache_socket(sc, *lsop, m);
1068 TCPSTAT_INC(tcps_sc_aborted);
1070 TCPSTAT_INC(tcps_sc_completed);
1072 /* how do we find the inp for the new socket? */
1077 if (sc != NULL && sc != &scs)
1086 * Given a LISTEN socket and an inbound SYN request, add
1087 * this to the syn cache, and send back a segment:
1088 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
1091 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
1092 * Doing so would require that we hold onto the data and deliver it
1093 * to the application. However, if we are the target of a SYN-flood
1094 * DoS attack, an attacker could send data which would eventually
1095 * consume all available buffer space if it were ACKed. By not ACKing
1096 * the data, we avoid this DoS scenario.
1099 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1100 struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod,
1105 struct syncache *sc = NULL;
1106 struct syncache_head *sch;
1107 struct mbuf *ipopts = NULL;
1109 int win, sb_hiwat, ip_ttl, ip_tos;
1112 int autoflowlabel = 0;
1115 struct label *maclabel;
1117 struct syncache scs;
1120 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
1121 INP_WLOCK_ASSERT(inp); /* listen socket */
1122 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
1123 ("%s: unexpected tcp flags", __func__));
1126 * Combine all so/tp operations very early to drop the INP lock as
1131 cred = crhold(so->so_cred);
1134 if ((inc->inc_flags & INC_ISIPV6) &&
1135 (inp->inp_flags & IN6P_AUTOFLOWLABEL))
1138 ip_ttl = inp->inp_ip_ttl;
1139 ip_tos = inp->inp_ip_tos;
1140 win = sbspace(&so->so_rcv);
1141 sb_hiwat = so->so_rcv.sb_hiwat;
1142 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE));
1144 /* By the time we drop the lock these should no longer be used. */
1149 if (mac_syncache_init(&maclabel) != 0) {
1151 INP_INFO_WUNLOCK(&V_tcbinfo);
1154 mac_syncache_create(maclabel, inp);
1157 INP_INFO_WUNLOCK(&V_tcbinfo);
1160 * Remember the IP options, if any.
1163 if (!(inc->inc_flags & INC_ISIPV6))
1166 ipopts = (m) ? ip_srcroute(m) : NULL;
1172 * See if we already have an entry for this connection.
1173 * If we do, resend the SYN,ACK, and reset the retransmit timer.
1175 * XXX: should the syncache be re-initialized with the contents
1176 * of the new SYN here (which may have different options?)
1178 * XXX: We do not check the sequence number to see if this is a
1179 * real retransmit or a new connection attempt. The question is
1180 * how to handle such a case; either ignore it as spoofed, or
1181 * drop the current entry and create a new one?
1183 sc = syncache_lookup(inc, &sch); /* returns locked entry */
1184 SCH_LOCK_ASSERT(sch);
1186 TCPSTAT_INC(tcps_sc_dupsyn);
1189 * If we were remembering a previous source route,
1190 * forget it and use the new one we've been given.
1193 (void) m_free(sc->sc_ipopts);
1194 sc->sc_ipopts = ipopts;
1197 * Update timestamp if present.
1199 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
1200 sc->sc_tsreflect = to->to_tsval;
1202 sc->sc_flags &= ~SCF_TIMESTAMP;
1205 * Since we have already unconditionally allocated label
1206 * storage, free it up. The syncache entry will already
1207 * have an initialized label we can use.
1209 mac_syncache_destroy(&maclabel);
1211 /* Retransmit SYN|ACK and reset retransmit count. */
1212 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
1213 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
1214 "resetting timer and retransmitting SYN|ACK\n",
1218 if (syncache_respond(sc) == 0) {
1220 syncache_timeout(sc, sch, 1);
1221 TCPSTAT_INC(tcps_sndacks);
1222 TCPSTAT_INC(tcps_sndtotal);
1228 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1231 * The zone allocator couldn't provide more entries.
1232 * Treat this as if the cache was full; drop the oldest
1233 * entry and insert the new one.
1235 TCPSTAT_INC(tcps_sc_zonefail);
1236 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL)
1237 syncache_drop(sc, sch);
1238 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1240 if (V_tcp_syncookies) {
1241 bzero(&scs, sizeof(scs));
1246 (void) m_free(ipopts);
1253 * Fill in the syncache values.
1256 sc->sc_label = maclabel;
1260 sc->sc_ipopts = ipopts;
1261 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1263 if (!(inc->inc_flags & INC_ISIPV6))
1266 sc->sc_ip_tos = ip_tos;
1267 sc->sc_ip_ttl = ip_ttl;
1271 sc->sc_todctx = todctx;
1273 sc->sc_irs = th->th_seq;
1274 sc->sc_iss = arc4random();
1276 sc->sc_flowlabel = 0;
1279 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
1280 * win was derived from socket earlier in the function.
1283 win = imin(win, TCP_MAXWIN);
1286 if (V_tcp_do_rfc1323) {
1288 * A timestamp received in a SYN makes
1289 * it ok to send timestamp requests and replies.
1291 if (to->to_flags & TOF_TS) {
1292 sc->sc_tsreflect = to->to_tsval;
1293 sc->sc_ts = tcp_ts_getticks();
1294 sc->sc_flags |= SCF_TIMESTAMP;
1296 if (to->to_flags & TOF_SCALE) {
1300 * Pick the smallest possible scaling factor that
1301 * will still allow us to scale up to sb_max, aka
1302 * kern.ipc.maxsockbuf.
1304 * We do this because there are broken firewalls that
1305 * will corrupt the window scale option, leading to
1306 * the other endpoint believing that our advertised
1307 * window is unscaled. At scale factors larger than
1308 * 5 the unscaled window will drop below 1500 bytes,
1309 * leading to serious problems when traversing these
1312 * With the default maxsockbuf of 256K, a scale factor
1313 * of 3 will be chosen by this algorithm. Those who
1314 * choose a larger maxsockbuf should watch out
1315 * for the compatiblity problems mentioned above.
1317 * RFC1323: The Window field in a SYN (i.e., a <SYN>
1318 * or <SYN,ACK>) segment itself is never scaled.
1320 while (wscale < TCP_MAX_WINSHIFT &&
1321 (TCP_MAXWIN << wscale) < sb_max)
1323 sc->sc_requested_r_scale = wscale;
1324 sc->sc_requested_s_scale = to->to_wscale;
1325 sc->sc_flags |= SCF_WINSCALE;
1328 #ifdef TCP_SIGNATURE
1330 * If listening socket requested TCP digests, and received SYN
1331 * contains the option, flag this in the syncache so that
1332 * syncache_respond() will do the right thing with the SYN+ACK.
1333 * XXX: Currently we always record the option by default and will
1334 * attempt to use it in syncache_respond().
1336 if (to->to_flags & TOF_SIGNATURE || ltflags & TF_SIGNATURE)
1337 sc->sc_flags |= SCF_SIGNATURE;
1339 if (to->to_flags & TOF_SACKPERM)
1340 sc->sc_flags |= SCF_SACK;
1341 if (to->to_flags & TOF_MSS)
1342 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */
1343 if (ltflags & TF_NOOPT)
1344 sc->sc_flags |= SCF_NOOPT;
1345 if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn)
1346 sc->sc_flags |= SCF_ECN;
1348 if (V_tcp_syncookies)
1349 sc->sc_iss = syncookie_generate(sch, sc);
1351 if (autoflowlabel) {
1352 if (V_tcp_syncookies)
1353 sc->sc_flowlabel = sc->sc_iss;
1355 sc->sc_flowlabel = ip6_randomflowlabel();
1356 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK;
1362 * Do a standard 3-way handshake.
1364 if (syncache_respond(sc) == 0) {
1365 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs)
1367 else if (sc != &scs)
1368 syncache_insert(sc, sch); /* locks and unlocks sch */
1369 TCPSTAT_INC(tcps_sndacks);
1370 TCPSTAT_INC(tcps_sndtotal);
1374 TCPSTAT_INC(tcps_sc_dropped);
1382 mac_syncache_destroy(&maclabel);
1392 syncache_respond(struct syncache *sc)
1394 struct ip *ip = NULL;
1396 struct tcphdr *th = NULL;
1397 int optlen, error = 0; /* Make compiler happy */
1398 u_int16_t hlen, tlen, mssopt;
1401 struct ip6_hdr *ip6 = NULL;
1406 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
1409 tlen = hlen + sizeof(struct tcphdr);
1411 /* Determine MSS we advertize to other end of connection. */
1412 mssopt = tcp_mssopt(&sc->sc_inc);
1413 if (sc->sc_peer_mss)
1414 mssopt = max( min(sc->sc_peer_mss, mssopt), V_tcp_minmss);
1416 /* XXX: Assume that the entire packet will fit in a header mbuf. */
1417 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
1418 ("syncache: mbuf too small"));
1420 /* Create the IP+TCP header from scratch. */
1421 m = m_gethdr(M_NOWAIT, MT_DATA);
1425 mac_syncache_create_mbuf(sc->sc_label, m);
1427 m->m_data += max_linkhdr;
1429 m->m_pkthdr.len = tlen;
1430 m->m_pkthdr.rcvif = NULL;
1433 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1434 ip6 = mtod(m, struct ip6_hdr *);
1435 ip6->ip6_vfc = IPV6_VERSION;
1436 ip6->ip6_nxt = IPPROTO_TCP;
1437 ip6->ip6_src = sc->sc_inc.inc6_laddr;
1438 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
1439 ip6->ip6_plen = htons(tlen - hlen);
1440 /* ip6_hlim is set after checksum */
1441 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK;
1442 ip6->ip6_flow |= sc->sc_flowlabel;
1444 th = (struct tcphdr *)(ip6 + 1);
1447 #if defined(INET6) && defined(INET)
1452 ip = mtod(m, struct ip *);
1453 ip->ip_v = IPVERSION;
1454 ip->ip_hl = sizeof(struct ip) >> 2;
1455 ip->ip_len = htons(tlen);
1459 ip->ip_p = IPPROTO_TCP;
1460 ip->ip_src = sc->sc_inc.inc_laddr;
1461 ip->ip_dst = sc->sc_inc.inc_faddr;
1462 ip->ip_ttl = sc->sc_ip_ttl;
1463 ip->ip_tos = sc->sc_ip_tos;
1466 * See if we should do MTU discovery. Route lookups are
1467 * expensive, so we will only unset the DF bit if:
1469 * 1) path_mtu_discovery is disabled
1470 * 2) the SCF_UNREACH flag has been set
1472 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
1473 ip->ip_off |= htons(IP_DF);
1475 th = (struct tcphdr *)(ip + 1);
1478 th->th_sport = sc->sc_inc.inc_lport;
1479 th->th_dport = sc->sc_inc.inc_fport;
1481 th->th_seq = htonl(sc->sc_iss);
1482 th->th_ack = htonl(sc->sc_irs + 1);
1483 th->th_off = sizeof(struct tcphdr) >> 2;
1485 th->th_flags = TH_SYN|TH_ACK;
1486 th->th_win = htons(sc->sc_wnd);
1489 if (sc->sc_flags & SCF_ECN) {
1490 th->th_flags |= TH_ECE;
1491 TCPSTAT_INC(tcps_ecn_shs);
1494 /* Tack on the TCP options. */
1495 if ((sc->sc_flags & SCF_NOOPT) == 0) {
1499 to.to_flags = TOF_MSS;
1500 if (sc->sc_flags & SCF_WINSCALE) {
1501 to.to_wscale = sc->sc_requested_r_scale;
1502 to.to_flags |= TOF_SCALE;
1504 if (sc->sc_flags & SCF_TIMESTAMP) {
1505 /* Virgin timestamp or TCP cookie enhanced one. */
1506 to.to_tsval = sc->sc_ts;
1507 to.to_tsecr = sc->sc_tsreflect;
1508 to.to_flags |= TOF_TS;
1510 if (sc->sc_flags & SCF_SACK)
1511 to.to_flags |= TOF_SACKPERM;
1512 #ifdef TCP_SIGNATURE
1513 if (sc->sc_flags & SCF_SIGNATURE)
1514 to.to_flags |= TOF_SIGNATURE;
1516 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
1518 /* Adjust headers by option size. */
1519 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
1521 m->m_pkthdr.len += optlen;
1523 #ifdef TCP_SIGNATURE
1524 if (sc->sc_flags & SCF_SIGNATURE)
1525 tcp_signature_compute(m, 0, 0, optlen,
1526 to.to_signature, IPSEC_DIR_OUTBOUND);
1529 if (sc->sc_inc.inc_flags & INC_ISIPV6)
1530 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
1533 ip->ip_len = htons(ntohs(ip->ip_len) + optlen);
1537 M_SETFIB(m, sc->sc_inc.inc_fibnum);
1538 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1540 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1541 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
1542 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen,
1544 ip6->ip6_hlim = in6_selecthlim(NULL, NULL);
1546 if (ADDED_BY_TOE(sc)) {
1547 struct toedev *tod = sc->sc_tod;
1549 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
1554 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
1557 #if defined(INET6) && defined(INET)
1562 m->m_pkthdr.csum_flags = CSUM_TCP;
1563 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
1564 htons(tlen + optlen - hlen + IPPROTO_TCP));
1566 if (ADDED_BY_TOE(sc)) {
1567 struct toedev *tod = sc->sc_tod;
1569 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
1574 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
1581 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks
1582 * that exceed the capacity of the syncache by avoiding the storage of any
1583 * of the SYNs we receive. Syncookies defend against blind SYN flooding
1584 * attacks where the attacker does not have access to our responses.
1586 * Syncookies encode and include all necessary information about the
1587 * connection setup within the SYN|ACK that we send back. That way we
1588 * can avoid keeping any local state until the ACK to our SYN|ACK returns
1589 * (if ever). Normally the syncache and syncookies are running in parallel
1590 * with the latter taking over when the former is exhausted. When matching
1591 * syncache entry is found the syncookie is ignored.
1593 * The only reliable information persisting the 3WHS is our inital sequence
1594 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient
1595 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS
1596 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK
1597 * returns and signifies a legitimate connection if it matches the ACK.
1599 * The available space of 32 bits to store the hash and to encode the SYN
1600 * option information is very tight and we should have at least 24 bits for
1601 * the MAC to keep the number of guesses by blind spoofing reasonably high.
1603 * SYN option information we have to encode to fully restore a connection:
1604 * MSS: is imporant to chose an optimal segment size to avoid IP level
1605 * fragmentation along the path. The common MSS values can be encoded
1606 * in a 3-bit table. Uncommon values are captured by the next lower value
1607 * in the table leading to a slight increase in packetization overhead.
1608 * WSCALE: is necessary to allow large windows to be used for high delay-
1609 * bandwidth product links. Not scaling the window when it was initially
1610 * negotiated is bad for performance as lack of scaling further decreases
1611 * the apparent available send window. We only need to encode the WSCALE
1612 * we received from the remote end. Our end can be recalculated at any
1613 * time. The common WSCALE values can be encoded in a 3-bit table.
1614 * Uncommon values are captured by the next lower value in the table
1615 * making us under-estimate the available window size halving our
1616 * theoretically possible maximum throughput for that connection.
1617 * SACK: Greatly assists in packet loss recovery and requires 1 bit.
1618 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options
1619 * that are included in all segments on a connection. We enable them when
1622 * Security of syncookies and attack vectors:
1624 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod)
1625 * together with the gloabl secret to make it unique per connection attempt.
1626 * Thus any change of any of those parameters results in a different MAC output
1627 * in an unpredictable way unless a collision is encountered. 24 bits of the
1628 * MAC are embedded into the ISS.
1630 * To prevent replay attacks two rotating global secrets are updated with a
1631 * new random value every 15 seconds. The life-time of a syncookie is thus
1634 * Vector 1: Attacking the secret. This requires finding a weakness in the
1635 * MAC itself or the way it is used here. The attacker can do a chosen plain
1636 * text attack by varying and testing the all parameters under his control.
1637 * The strength depends on the size and randomness of the secret, and the
1638 * cryptographic security of the MAC function. Due to the constant updating
1639 * of the secret the attacker has at most 29.999 seconds to find the secret
1640 * and launch spoofed connections. After that he has to start all over again.
1642 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC
1643 * size an average of 4,823 attempts are required for a 50% chance of success
1644 * to spoof a single syncookie (birthday collision paradox). However the
1645 * attacker is blind and doesn't know if one of his attempts succeeded unless
1646 * he has a side channel to interfere success from. A single connection setup
1647 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets.
1648 * This many attempts are required for each one blind spoofed connection. For
1649 * every additional spoofed connection he has to launch another N attempts.
1650 * Thus for a sustained rate 100 spoofed connections per second approximately
1651 * 1,800,000 packets per second would have to be sent.
1653 * NB: The MAC function should be fast so that it doesn't become a CPU
1654 * exhaustion attack vector itself.
1657 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations
1658 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996
1659 * http://cr.yp.to/syncookies.html (overview)
1660 * http://cr.yp.to/syncookies/archive (details)
1663 * Schematic construction of a syncookie enabled Initial Sequence Number:
1665 * 12345678901234567890123456789012
1666 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP|
1668 * x 24 MAC (truncated)
1669 * W 3 Send Window Scale index
1671 * S 1 SACK permitted
1672 * P 1 Odd/even secret
1676 * Distribution and probability of certain MSS values. Those in between are
1677 * rounded down to the next lower one.
1678 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011]
1679 * .2% .3% 5% 7% 7% 20% 15% 45%
1681 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 };
1684 * Distribution and probability of certain WSCALE values. We have to map the
1685 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3
1686 * bits based on prevalence of certain values. Where we don't have an exact
1687 * match for are rounded down to the next lower one letting us under-estimate
1688 * the true available window. At the moment this would happen only for the
1689 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer
1690 * and window size). The absence of the WSCALE option (no scaling in either
1691 * direction) is encoded with index zero.
1692 * [WSCALE values histograms, Allman, 2012]
1693 * X 10 10 35 5 6 14 10% by host
1694 * X 11 4 5 5 18 49 3% by connections
1696 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 };
1699 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed
1700 * and good cryptographic properties.
1703 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags,
1704 uint8_t *secbits, uintptr_t secmod)
1707 uint32_t siphash[2];
1709 SipHash24_Init(&ctx);
1710 SipHash_SetKey(&ctx, secbits);
1711 switch (inc->inc_flags & INC_ISIPV6) {
1714 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr));
1715 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr));
1720 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr));
1721 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr));
1725 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport));
1726 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport));
1727 SipHash_Update(&ctx, &flags, sizeof(flags));
1728 SipHash_Update(&ctx, &secmod, sizeof(secmod));
1729 SipHash_Final((u_int8_t *)&siphash, &ctx);
1731 return (siphash[0] ^ siphash[1]);
1735 syncookie_generate(struct syncache_head *sch, struct syncache *sc)
1737 u_int i, mss, secbit, wscale;
1740 union syncookie cookie;
1742 SCH_LOCK_ASSERT(sch);
1746 /* Map our computed MSS into the 3-bit index. */
1747 mss = min(tcp_mssopt(&sc->sc_inc), max(sc->sc_peer_mss, V_tcp_minmss));
1748 for (i = sizeof(tcp_sc_msstab) / sizeof(*tcp_sc_msstab) - 1;
1749 tcp_sc_msstab[i] > mss && i > 0;
1752 cookie.flags.mss_idx = i;
1755 * Map the send window scale into the 3-bit index but only if
1756 * the wscale option was received.
1758 if (sc->sc_flags & SCF_WINSCALE) {
1759 wscale = sc->sc_requested_s_scale;
1760 for (i = sizeof(tcp_sc_wstab) / sizeof(*tcp_sc_wstab) - 1;
1761 tcp_sc_wstab[i] > wscale && i > 0;
1764 cookie.flags.wscale_idx = i;
1767 /* Can we do SACK? */
1768 if (sc->sc_flags & SCF_SACK)
1769 cookie.flags.sack_ok = 1;
1771 /* Which of the two secrets to use. */
1772 secbit = sch->sch_sc->secret.oddeven & 0x1;
1773 cookie.flags.odd_even = secbit;
1775 secbits = sch->sch_sc->secret.key[secbit];
1776 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits,
1780 * Put the flags into the hash and XOR them to get better ISS number
1781 * variance. This doesn't enhance the cryptographic strength and is
1782 * done to prevent the 8 cookie bits from showing up directly on the
1786 iss |= cookie.cookie ^ (hash >> 24);
1788 /* Randomize the timestamp. */
1789 if (sc->sc_flags & SCF_TIMESTAMP) {
1790 sc->sc_ts = arc4random();
1791 sc->sc_tsoff = sc->sc_ts - tcp_ts_getticks();
1794 TCPSTAT_INC(tcps_sc_sendcookie);
1798 static struct syncache *
1799 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch,
1800 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
1806 int wnd, wscale = 0;
1807 union syncookie cookie;
1809 SCH_LOCK_ASSERT(sch);
1812 * Pull information out of SYN-ACK/ACK and revert sequence number
1815 ack = th->th_ack - 1;
1816 seq = th->th_seq - 1;
1819 * Unpack the flags containing enough information to restore the
1822 cookie.cookie = (ack & 0xff) ^ (ack >> 24);
1824 /* Which of the two secrets to use. */
1825 secbits = sch->sch_sc->secret.key[cookie.flags.odd_even];
1827 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch);
1829 /* The recomputed hash matches the ACK if this was a genuine cookie. */
1830 if ((ack & ~0xff) != (hash & ~0xff))
1833 /* Fill in the syncache values. */
1835 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1836 sc->sc_ipopts = NULL;
1841 switch (inc->inc_flags & INC_ISIPV6) {
1844 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl;
1845 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos;
1850 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL)
1851 sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK;
1856 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx];
1858 /* We can simply recompute receive window scale we sent earlier. */
1859 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max)
1862 /* Only use wscale if it was enabled in the orignal SYN. */
1863 if (cookie.flags.wscale_idx > 0) {
1864 sc->sc_requested_r_scale = wscale;
1865 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx];
1866 sc->sc_flags |= SCF_WINSCALE;
1869 wnd = sbspace(&lso->so_rcv);
1871 wnd = imin(wnd, TCP_MAXWIN);
1874 if (cookie.flags.sack_ok)
1875 sc->sc_flags |= SCF_SACK;
1877 if (to->to_flags & TOF_TS) {
1878 sc->sc_flags |= SCF_TIMESTAMP;
1879 sc->sc_tsreflect = to->to_tsval;
1880 sc->sc_ts = to->to_tsecr;
1881 sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks();
1884 if (to->to_flags & TOF_SIGNATURE)
1885 sc->sc_flags |= SCF_SIGNATURE;
1889 TCPSTAT_INC(tcps_sc_recvcookie);
1895 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
1896 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
1899 struct syncache scs, *scx;
1902 bzero(&scs, sizeof(scs));
1903 scx = syncookie_lookup(inc, sch, &scs, th, to, lso);
1905 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL)
1909 if (sc->sc_peer_mss != scx->sc_peer_mss)
1910 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n",
1911 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss);
1913 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale)
1914 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n",
1915 s, __func__, sc->sc_requested_r_scale,
1916 scx->sc_requested_r_scale);
1918 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale)
1919 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n",
1920 s, __func__, sc->sc_requested_s_scale,
1921 scx->sc_requested_s_scale);
1923 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK))
1924 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__);
1931 #endif /* INVARIANTS */
1934 syncookie_reseed(void *arg)
1936 struct tcp_syncache *sc = arg;
1941 * Reseeding the secret doesn't have to be protected by a lock.
1942 * It only must be ensured that the new random values are visible
1943 * to all CPUs in a SMP environment. The atomic with release
1944 * semantics ensures that.
1946 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1;
1947 secbits = sc->secret.key[secbit];
1948 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0);
1949 atomic_add_rel_int(&sc->secret.oddeven, 1);
1951 /* Reschedule ourself. */
1952 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz);
1956 * Returns the current number of syncache entries. This number
1957 * will probably change before you get around to calling
1961 syncache_pcbcount(void)
1963 struct syncache_head *sch;
1966 for (count = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
1967 /* No need to lock for a read. */
1968 sch = &V_tcp_syncache.hashbase[i];
1969 count += sch->sch_length;
1975 * Exports the syncache entries to userland so that netstat can display
1976 * them alongside the other sockets. This function is intended to be
1977 * called only from tcp_pcblist.
1979 * Due to concurrency on an active system, the number of pcbs exported
1980 * may have no relation to max_pcbs. max_pcbs merely indicates the
1981 * amount of space the caller allocated for this function to use.
1984 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported)
1987 struct syncache *sc;
1988 struct syncache_head *sch;
1989 int count, error, i;
1991 for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
1992 sch = &V_tcp_syncache.hashbase[i];
1994 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
1995 if (count >= max_pcbs) {
1999 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
2001 bzero(&xt, sizeof(xt));
2002 xt.xt_len = sizeof(xt);
2003 if (sc->sc_inc.inc_flags & INC_ISIPV6)
2004 xt.xt_inp.inp_vflag = INP_IPV6;
2006 xt.xt_inp.inp_vflag = INP_IPV4;
2007 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo));
2008 xt.xt_tp.t_inpcb = &xt.xt_inp;
2009 xt.xt_tp.t_state = TCPS_SYN_RECEIVED;
2010 xt.xt_socket.xso_protocol = IPPROTO_TCP;
2011 xt.xt_socket.xso_len = sizeof (struct xsocket);
2012 xt.xt_socket.so_type = SOCK_STREAM;
2013 xt.xt_socket.so_state = SS_ISCONNECTING;
2014 error = SYSCTL_OUT(req, &xt, sizeof xt);
2024 *pcbs_exported = count;