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/refcount.h>
45 #include <sys/kernel.h>
46 #include <sys/sysctl.h>
47 #include <sys/limits.h>
49 #include <sys/mutex.h>
50 #include <sys/malloc.h>
52 #include <sys/proc.h> /* for proc0 declaration */
53 #include <sys/random.h>
54 #include <sys/socket.h>
55 #include <sys/socketvar.h>
56 #include <sys/syslog.h>
57 #include <sys/ucred.h>
60 #include <crypto/siphash/siphash.h>
65 #include <net/if_var.h>
66 #include <net/route.h>
69 #include <netinet/in.h>
70 #include <netinet/in_systm.h>
71 #include <netinet/ip.h>
72 #include <netinet/in_var.h>
73 #include <netinet/in_pcb.h>
74 #include <netinet/ip_var.h>
75 #include <netinet/ip_options.h>
77 #include <netinet/ip6.h>
78 #include <netinet/icmp6.h>
79 #include <netinet6/nd6.h>
80 #include <netinet6/ip6_var.h>
81 #include <netinet6/in6_pcb.h>
83 #include <netinet/tcp.h>
85 #include <netinet/tcp_fastopen.h>
87 #include <netinet/tcp_fsm.h>
88 #include <netinet/tcp_seq.h>
89 #include <netinet/tcp_timer.h>
90 #include <netinet/tcp_var.h>
91 #include <netinet/tcp_syncache.h>
93 #include <netinet6/tcp6_var.h>
96 #include <netinet/toecore.h>
100 #include <netipsec/ipsec.h>
102 #include <netipsec/ipsec6.h>
104 #include <netipsec/key.h>
107 #include <machine/in_cksum.h>
109 #include <security/mac/mac_framework.h>
111 static VNET_DEFINE(int, tcp_syncookies) = 1;
112 #define V_tcp_syncookies VNET(tcp_syncookies)
113 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW,
114 &VNET_NAME(tcp_syncookies), 0,
115 "Use TCP SYN cookies if the syncache overflows");
117 static VNET_DEFINE(int, tcp_syncookiesonly) = 0;
118 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly)
119 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW,
120 &VNET_NAME(tcp_syncookiesonly), 0,
121 "Use only TCP SYN cookies");
123 static VNET_DEFINE(int, functions_inherit_listen_socket_stack) = 1;
124 #define V_functions_inherit_listen_socket_stack \
125 VNET(functions_inherit_listen_socket_stack)
126 SYSCTL_INT(_net_inet_tcp, OID_AUTO, functions_inherit_listen_socket_stack,
127 CTLFLAG_VNET | CTLFLAG_RW,
128 &VNET_NAME(functions_inherit_listen_socket_stack), 0,
129 "Inherit listen socket's stack");
132 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL)
135 static void syncache_drop(struct syncache *, struct syncache_head *);
136 static void syncache_free(struct syncache *);
137 static void syncache_insert(struct syncache *, struct syncache_head *);
138 static int syncache_respond(struct syncache *, struct syncache_head *, int,
139 const struct mbuf *);
140 static struct socket *syncache_socket(struct syncache *, struct socket *,
142 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch,
144 static void syncache_timer(void *);
146 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t,
147 uint8_t *, uintptr_t);
148 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *);
149 static struct syncache
150 *syncookie_lookup(struct in_conninfo *, struct syncache_head *,
151 struct syncache *, struct tcphdr *, struct tcpopt *,
153 static void syncookie_reseed(void *);
155 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
156 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
161 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
162 * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds,
163 * the odds are that the user has given up attempting to connect by then.
165 #define SYNCACHE_MAXREXMTS 3
167 /* Arbitrary values */
168 #define TCP_SYNCACHE_HASHSIZE 512
169 #define TCP_SYNCACHE_BUCKETLIMIT 30
171 static VNET_DEFINE(struct tcp_syncache, tcp_syncache);
172 #define V_tcp_syncache VNET(tcp_syncache)
174 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0,
177 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
178 &VNET_NAME(tcp_syncache.bucket_limit), 0,
179 "Per-bucket hash limit for syncache");
181 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
182 &VNET_NAME(tcp_syncache.cache_limit), 0,
183 "Overall entry limit for syncache");
185 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET,
186 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache");
188 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN,
189 &VNET_NAME(tcp_syncache.hashsize), 0,
190 "Size of TCP syncache hashtable");
192 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_VNET | CTLFLAG_RW,
193 &VNET_NAME(tcp_syncache.rexmt_limit), 0,
194 "Limit on SYN/ACK retransmissions");
196 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1;
197 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail,
198 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0,
199 "Send reset on socket allocation failure");
201 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
203 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx)
204 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx)
205 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED)
208 * Requires the syncache entry to be already removed from the bucket list.
211 syncache_free(struct syncache *sc)
215 (void) m_free(sc->sc_ipopts);
219 mac_syncache_destroy(&sc->sc_label);
222 uma_zfree(V_tcp_syncache.zone, sc);
230 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
231 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
232 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
233 V_tcp_syncache.hash_secret = arc4random();
235 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
236 &V_tcp_syncache.hashsize);
237 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
238 &V_tcp_syncache.bucket_limit);
239 if (!powerof2(V_tcp_syncache.hashsize) ||
240 V_tcp_syncache.hashsize == 0) {
241 printf("WARNING: syncache hash size is not a power of 2.\n");
242 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
244 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1;
247 V_tcp_syncache.cache_limit =
248 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit;
249 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
250 &V_tcp_syncache.cache_limit);
252 /* Allocate the hash table. */
253 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize *
254 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO);
257 V_tcp_syncache.vnet = curvnet;
260 /* Initialize the hash buckets. */
261 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
262 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket);
263 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
265 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer,
266 &V_tcp_syncache.hashbase[i].sch_mtx, 0);
267 V_tcp_syncache.hashbase[i].sch_length = 0;
268 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache;
271 /* Create the syncache entry zone. */
272 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
273 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
274 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone,
275 V_tcp_syncache.cache_limit);
277 /* Start the SYN cookie reseeder callout. */
278 callout_init(&V_tcp_syncache.secret.reseed, 1);
279 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0);
280 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0);
281 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz,
282 syncookie_reseed, &V_tcp_syncache);
287 syncache_destroy(void)
289 struct syncache_head *sch;
290 struct syncache *sc, *nsc;
294 * Stop the re-seed timer before freeing resources. No need to
295 * possibly schedule it another time.
297 callout_drain(&V_tcp_syncache.secret.reseed);
299 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */
300 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
302 sch = &V_tcp_syncache.hashbase[i];
303 callout_drain(&sch->sch_timer);
306 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc)
307 syncache_drop(sc, sch);
309 KASSERT(TAILQ_EMPTY(&sch->sch_bucket),
310 ("%s: sch->sch_bucket not empty", __func__));
311 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0",
312 __func__, sch->sch_length));
313 mtx_destroy(&sch->sch_mtx);
316 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0,
317 ("%s: cache_count not 0", __func__));
319 /* Free the allocated global resources. */
320 uma_zdestroy(V_tcp_syncache.zone);
321 free(V_tcp_syncache.hashbase, M_SYNCACHE);
326 * Inserts a syncache entry into the specified bucket row.
327 * Locks and unlocks the syncache_head autonomously.
330 syncache_insert(struct syncache *sc, struct syncache_head *sch)
332 struct syncache *sc2;
337 * Make sure that we don't overflow the per-bucket limit.
338 * If the bucket is full, toss the oldest element.
340 if (sch->sch_length >= V_tcp_syncache.bucket_limit) {
341 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
342 ("sch->sch_length incorrect"));
343 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
344 syncache_drop(sc2, sch);
345 TCPSTAT_INC(tcps_sc_bucketoverflow);
348 /* Put it into the bucket. */
349 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
353 if (ADDED_BY_TOE(sc)) {
354 struct toedev *tod = sc->sc_tod;
356 tod->tod_syncache_added(tod, sc->sc_todctx);
360 /* Reinitialize the bucket row's timer. */
361 if (sch->sch_length == 1)
362 sch->sch_nextc = ticks + INT_MAX;
363 syncache_timeout(sc, sch, 1);
367 TCPSTATES_INC(TCPS_SYN_RECEIVED);
368 TCPSTAT_INC(tcps_sc_added);
372 * Remove and free entry from syncache bucket row.
373 * Expects locked syncache head.
376 syncache_drop(struct syncache *sc, struct syncache_head *sch)
379 SCH_LOCK_ASSERT(sch);
381 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
382 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
386 if (ADDED_BY_TOE(sc)) {
387 struct toedev *tod = sc->sc_tod;
389 tod->tod_syncache_removed(tod, sc->sc_todctx);
397 * Engage/reengage time on bucket row.
400 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
402 sc->sc_rxttime = ticks +
403 TCPTV_RTOBASE * (tcp_syn_backoff[sc->sc_rxmits]);
405 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
406 sch->sch_nextc = sc->sc_rxttime;
408 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
409 syncache_timer, (void *)sch);
414 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
415 * If we have retransmitted an entry the maximum number of times, expire it.
416 * One separate timer for each bucket row.
419 syncache_timer(void *xsch)
421 struct syncache_head *sch = (struct syncache_head *)xsch;
422 struct syncache *sc, *nsc;
426 CURVNET_SET(sch->sch_sc->vnet);
428 /* NB: syncache_head has already been locked by the callout. */
429 SCH_LOCK_ASSERT(sch);
432 * In the following cycle we may remove some entries and/or
433 * advance some timeouts, so re-initialize the bucket timer.
435 sch->sch_nextc = tick + INT_MAX;
437 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
439 * We do not check if the listen socket still exists
440 * and accept the case where the listen socket may be
441 * gone by the time we resend the SYN/ACK. We do
442 * not expect this to happens often. If it does,
443 * then the RST will be sent by the time the remote
444 * host does the SYN/ACK->ACK.
446 if (TSTMP_GT(sc->sc_rxttime, tick)) {
447 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
448 sch->sch_nextc = sc->sc_rxttime;
451 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
452 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
453 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
454 "giving up and removing syncache entry\n",
458 syncache_drop(sc, sch);
459 TCPSTAT_INC(tcps_sc_stale);
462 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
463 log(LOG_DEBUG, "%s; %s: Response timeout, "
464 "retransmitting (%u) SYN|ACK\n",
465 s, __func__, sc->sc_rxmits);
469 syncache_respond(sc, sch, 1, NULL);
470 TCPSTAT_INC(tcps_sc_retransmitted);
471 syncache_timeout(sc, sch, 0);
473 if (!TAILQ_EMPTY(&(sch)->sch_bucket))
474 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
475 syncache_timer, (void *)(sch));
480 * Find an entry in the syncache.
481 * Returns always with locked syncache_head plus a matching entry or NULL.
483 static struct syncache *
484 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
487 struct syncache_head *sch;
491 * The hash is built on foreign port + local port + foreign address.
492 * We rely on the fact that struct in_conninfo starts with 16 bits
493 * of foreign port, then 16 bits of local port then followed by 128
494 * bits of foreign address. In case of IPv4 address, the first 3
495 * 32-bit words of the address always are zeroes.
497 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5,
498 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask;
500 sch = &V_tcp_syncache.hashbase[hash];
504 /* Circle through bucket row to find matching entry. */
505 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash)
506 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie,
507 sizeof(struct in_endpoints)) == 0)
510 return (sc); /* Always returns with locked sch. */
514 * This function is called when we get a RST for a
515 * non-existent connection, so that we can see if the
516 * connection is in the syn cache. If it is, zap it.
519 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th)
522 struct syncache_head *sch;
525 sc = syncache_lookup(inc, &sch); /* returns locked sch */
526 SCH_LOCK_ASSERT(sch);
529 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags.
530 * See RFC 793 page 65, section SEGMENT ARRIVES.
532 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) {
533 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
534 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or "
535 "FIN flag set, segment ignored\n", s, __func__);
536 TCPSTAT_INC(tcps_badrst);
541 * No corresponding connection was found in syncache.
542 * If syncookies are enabled and possibly exclusively
543 * used, or we are under memory pressure, a valid RST
544 * may not find a syncache entry. In that case we're
545 * done and no SYN|ACK retransmissions will happen.
546 * Otherwise the RST was misdirected or spoofed.
549 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
550 log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
551 "syncache entry (possibly syncookie only), "
552 "segment ignored\n", s, __func__);
553 TCPSTAT_INC(tcps_badrst);
558 * If the RST bit is set, check the sequence number to see
559 * if this is a valid reset segment.
561 * In all states except SYN-SENT, all reset (RST) segments
562 * are validated by checking their SEQ-fields. A reset is
563 * valid if its sequence number is in the window.
565 * The sequence number in the reset segment is normally an
566 * echo of our outgoing acknowlegement numbers, but some hosts
567 * send a reset with the sequence number at the rightmost edge
568 * of our receive window, and we have to handle this case.
570 if (SEQ_GEQ(th->th_seq, sc->sc_irs) &&
571 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
572 syncache_drop(sc, sch);
573 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
574 log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, "
575 "connection attempt aborted by remote endpoint\n",
577 TCPSTAT_INC(tcps_sc_reset);
579 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
580 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
581 "IRS %u (+WND %u), segment ignored\n",
582 s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd);
583 TCPSTAT_INC(tcps_badrst);
593 syncache_badack(struct in_conninfo *inc)
596 struct syncache_head *sch;
598 sc = syncache_lookup(inc, &sch); /* returns locked sch */
599 SCH_LOCK_ASSERT(sch);
601 syncache_drop(sc, sch);
602 TCPSTAT_INC(tcps_sc_badack);
608 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th)
611 struct syncache_head *sch;
613 sc = syncache_lookup(inc, &sch); /* returns locked sch */
614 SCH_LOCK_ASSERT(sch);
618 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
619 if (ntohl(th->th_seq) != sc->sc_iss)
623 * If we've rertransmitted 3 times and this is our second error,
624 * we remove the entry. Otherwise, we allow it to continue on.
625 * This prevents us from incorrectly nuking an entry during a
626 * spurious network outage.
630 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
631 sc->sc_flags |= SCF_UNREACH;
634 syncache_drop(sc, sch);
635 TCPSTAT_INC(tcps_sc_unreach);
641 * Build a new TCP socket structure from a syncache entry.
643 * On success return the newly created socket with its underlying inp locked.
645 static struct socket *
646 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
648 struct tcp_function_block *blk;
649 struct inpcb *inp = NULL;
655 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
658 * Ok, create the full blown connection, and set things up
659 * as they would have been set up if we had created the
660 * connection when the SYN arrived. If we can't create
661 * the connection, abort it.
663 so = sonewconn(lso, 0);
666 * Drop the connection; we will either send a RST or
667 * have the peer retransmit its SYN again after its
670 TCPSTAT_INC(tcps_listendrop);
671 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
672 log(LOG_DEBUG, "%s; %s: Socket create failed "
673 "due to limits or memory shortage\n",
680 mac_socketpeer_set_from_mbuf(m, so);
684 inp->inp_inc.inc_fibnum = so->so_fibnum;
687 * Exclusive pcbinfo lock is not required in syncache socket case even
688 * if two inpcb locks can be acquired simultaneously:
689 * - the inpcb in LISTEN state,
690 * - the newly created inp.
692 * In this case, an inp cannot be at same time in LISTEN state and
693 * just created by an accept() call.
695 INP_HASH_WLOCK(&V_tcbinfo);
697 /* Insert new socket into PCB hash list. */
698 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
700 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
701 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
703 inp->inp_vflag &= ~INP_IPV6;
704 inp->inp_vflag |= INP_IPV4;
706 inp->inp_laddr = sc->sc_inc.inc_laddr;
712 * If there's an mbuf and it has a flowid, then let's initialise the
713 * inp with that particular flowid.
715 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) {
716 inp->inp_flowid = m->m_pkthdr.flowid;
717 inp->inp_flowtype = M_HASHTYPE_GET(m);
721 * Install in the reservation hash table for now, but don't yet
722 * install a connection group since the full 4-tuple isn't yet
725 inp->inp_lport = sc->sc_inc.inc_lport;
726 if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) {
728 * Undo the assignments above if we failed to
729 * put the PCB on the hash lists.
732 if (sc->sc_inc.inc_flags & INC_ISIPV6)
733 inp->in6p_laddr = in6addr_any;
736 inp->inp_laddr.s_addr = INADDR_ANY;
738 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
739 log(LOG_DEBUG, "%s; %s: in_pcbinshash failed "
744 INP_HASH_WUNLOCK(&V_tcbinfo);
748 /* Copy old policy into new socket's. */
749 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp))
750 printf("syncache_socket: could not copy policy\n");
753 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
754 struct inpcb *oinp = sotoinpcb(lso);
755 struct in6_addr laddr6;
756 struct sockaddr_in6 sin6;
758 * Inherit socket options from the listening socket.
759 * Note that in6p_inputopts are not (and should not be)
760 * copied, since it stores previously received options and is
761 * used to detect if each new option is different than the
762 * previous one and hence should be passed to a user.
763 * If we copied in6p_inputopts, a user would not be able to
764 * receive options just after calling the accept system call.
766 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
767 if (oinp->in6p_outputopts)
768 inp->in6p_outputopts =
769 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
771 sin6.sin6_family = AF_INET6;
772 sin6.sin6_len = sizeof(sin6);
773 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
774 sin6.sin6_port = sc->sc_inc.inc_fport;
775 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
776 laddr6 = inp->in6p_laddr;
777 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
778 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
779 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6,
780 thread0.td_ucred, m)) != 0) {
781 inp->in6p_laddr = laddr6;
782 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
783 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed "
788 INP_HASH_WUNLOCK(&V_tcbinfo);
791 /* Override flowlabel from in6_pcbconnect. */
792 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
793 inp->inp_flow |= sc->sc_flowlabel;
796 #if defined(INET) && defined(INET6)
801 struct in_addr laddr;
802 struct sockaddr_in sin;
804 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
806 if (inp->inp_options == NULL) {
807 inp->inp_options = sc->sc_ipopts;
808 sc->sc_ipopts = NULL;
811 sin.sin_family = AF_INET;
812 sin.sin_len = sizeof(sin);
813 sin.sin_addr = sc->sc_inc.inc_faddr;
814 sin.sin_port = sc->sc_inc.inc_fport;
815 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
816 laddr = inp->inp_laddr;
817 if (inp->inp_laddr.s_addr == INADDR_ANY)
818 inp->inp_laddr = sc->sc_inc.inc_laddr;
819 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin,
820 thread0.td_ucred, m)) != 0) {
821 inp->inp_laddr = laddr;
822 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
823 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed "
828 INP_HASH_WUNLOCK(&V_tcbinfo);
833 INP_HASH_WUNLOCK(&V_tcbinfo);
835 tcp_state_change(tp, TCPS_SYN_RECEIVED);
836 tp->iss = sc->sc_iss;
837 tp->irs = sc->sc_irs;
840 blk = sototcpcb(lso)->t_fb;
841 if (V_functions_inherit_listen_socket_stack && blk != tp->t_fb) {
843 * Our parents t_fb was not the default,
844 * we need to release our ref on tp->t_fb and
845 * pickup one on the new entry.
847 struct tcp_function_block *rblk;
849 rblk = find_and_ref_tcp_fb(blk);
850 KASSERT(rblk != NULL,
851 ("cannot find blk %p out of syncache?", blk));
852 if (tp->t_fb->tfb_tcp_fb_fini)
853 (*tp->t_fb->tfb_tcp_fb_fini)(tp, 0);
854 refcount_release(&tp->t_fb->tfb_refcnt);
856 if (tp->t_fb->tfb_tcp_fb_init) {
857 (*tp->t_fb->tfb_tcp_fb_init)(tp);
860 tp->snd_wl1 = sc->sc_irs;
861 tp->snd_max = tp->iss + 1;
862 tp->snd_nxt = tp->iss + 1;
863 tp->rcv_up = sc->sc_irs + 1;
864 tp->rcv_wnd = sc->sc_wnd;
865 tp->rcv_adv += tp->rcv_wnd;
866 tp->last_ack_sent = tp->rcv_nxt;
868 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
869 if (sc->sc_flags & SCF_NOOPT)
870 tp->t_flags |= TF_NOOPT;
872 if (sc->sc_flags & SCF_WINSCALE) {
873 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
874 tp->snd_scale = sc->sc_requested_s_scale;
875 tp->request_r_scale = sc->sc_requested_r_scale;
877 if (sc->sc_flags & SCF_TIMESTAMP) {
878 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
879 tp->ts_recent = sc->sc_tsreflect;
880 tp->ts_recent_age = tcp_ts_getticks();
881 tp->ts_offset = sc->sc_tsoff;
884 if (sc->sc_flags & SCF_SIGNATURE)
885 tp->t_flags |= TF_SIGNATURE;
887 if (sc->sc_flags & SCF_SACK)
888 tp->t_flags |= TF_SACK_PERMIT;
891 if (sc->sc_flags & SCF_ECN)
892 tp->t_flags |= TF_ECN_PERMIT;
895 * Set up MSS and get cached values from tcp_hostcache.
896 * This might overwrite some of the defaults we just set.
898 tcp_mss(tp, sc->sc_peer_mss);
901 * If the SYN,ACK was retransmitted, indicate that CWND to be
902 * limited to one segment in cc_conn_init().
903 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
905 if (sc->sc_rxmits > 1)
910 * Allow a TOE driver to install its hooks. Note that we hold the
911 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a
912 * new connection before the TOE driver has done its thing.
914 if (ADDED_BY_TOE(sc)) {
915 struct toedev *tod = sc->sc_tod;
917 tod->tod_offload_socket(tod, sc->sc_todctx, so);
921 * Copy and activate timers.
923 tp->t_keepinit = sototcpcb(lso)->t_keepinit;
924 tp->t_keepidle = sototcpcb(lso)->t_keepidle;
925 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl;
926 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt;
927 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp));
929 TCPSTAT_INC(tcps_accepts);
941 * This function gets called when we receive an ACK for a
942 * socket in the LISTEN state. We look up the connection
943 * in the syncache, and if its there, we pull it out of
944 * the cache and turn it into a full-blown connection in
945 * the SYN-RECEIVED state.
947 * On syncache_socket() success the newly created socket
948 * has its underlying inp locked.
951 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
952 struct socket **lsop, struct mbuf *m)
955 struct syncache_head *sch;
960 * Global TCP locks are held because we manipulate the PCB lists
961 * and create a new socket.
963 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
964 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
965 ("%s: can handle only ACK", __func__));
967 sc = syncache_lookup(inc, &sch); /* returns locked sch */
968 SCH_LOCK_ASSERT(sch);
972 * Test code for syncookies comparing the syncache stored
973 * values with the reconstructed values from the cookie.
976 syncookie_cmp(inc, sch, sc, th, to, *lsop);
981 * There is no syncache entry, so see if this ACK is
982 * a returning syncookie. To do this, first:
983 * A. See if this socket has had a syncache entry dropped in
984 * the past. We don't want to accept a bogus syncookie
985 * if we've never received a SYN.
986 * B. check that the syncookie is valid. If it is, then
987 * cobble up a fake syncache entry, and return.
989 if (!V_tcp_syncookies) {
991 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
992 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
993 "segment rejected (syncookies disabled)\n",
997 bzero(&scs, sizeof(scs));
998 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop);
1001 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1002 log(LOG_DEBUG, "%s; %s: Segment failed "
1003 "SYNCOOKIE authentication, segment rejected "
1004 "(probably spoofed)\n", s, __func__);
1009 * Pull out the entry to unlock the bucket row.
1011 * NOTE: We must decrease TCPS_SYN_RECEIVED count here, not
1012 * tcp_state_change(). The tcpcb is not existent at this
1013 * moment. A new one will be allocated via syncache_socket->
1014 * sonewconn->tcp_usr_attach in TCPS_CLOSED state, then
1015 * syncache_socket() will change it to TCPS_SYN_RECEIVED.
1017 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
1018 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
1021 if (ADDED_BY_TOE(sc)) {
1022 struct toedev *tod = sc->sc_tod;
1024 tod->tod_syncache_removed(tod, sc->sc_todctx);
1031 * Segment validation:
1032 * ACK must match our initial sequence number + 1 (the SYN|ACK).
1034 if (th->th_ack != sc->sc_iss + 1) {
1035 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1036 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
1037 "rejected\n", s, __func__, th->th_ack, sc->sc_iss);
1042 * The SEQ must fall in the window starting at the received
1043 * initial receive sequence number + 1 (the SYN).
1045 if (SEQ_LEQ(th->th_seq, sc->sc_irs) ||
1046 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
1047 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1048 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
1049 "rejected\n", s, __func__, th->th_seq, sc->sc_irs);
1054 * If timestamps were not negotiated during SYN/ACK they
1055 * must not appear on any segment during this session.
1057 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) {
1058 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1059 log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
1060 "segment rejected\n", s, __func__);
1065 * If timestamps were negotiated during SYN/ACK they should
1066 * appear on every segment during this session.
1067 * XXXAO: This is only informal as there have been unverified
1068 * reports of non-compliants stacks.
1070 if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) {
1071 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1072 log(LOG_DEBUG, "%s; %s: Timestamp missing, "
1073 "no action\n", s, __func__);
1080 * If timestamps were negotiated, the reflected timestamp
1081 * must be equal to what we actually sent in the SYN|ACK
1082 * except in the case of 0. Some boxes are known for sending
1083 * broken timestamp replies during the 3whs (and potentially
1084 * during the connection also).
1086 * Accept the final ACK of 3whs with reflected timestamp of 0
1087 * instead of sending a RST and deleting the syncache entry.
1089 if ((to->to_flags & TOF_TS) && to->to_tsecr &&
1090 to->to_tsecr != sc->sc_ts) {
1091 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1092 log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, "
1093 "segment rejected\n",
1094 s, __func__, to->to_tsecr, sc->sc_ts);
1098 *lsop = syncache_socket(sc, *lsop, m);
1101 TCPSTAT_INC(tcps_sc_aborted);
1103 TCPSTAT_INC(tcps_sc_completed);
1105 /* how do we find the inp for the new socket? */
1110 if (sc != NULL && sc != &scs)
1120 syncache_tfo_expand(struct syncache *sc, struct socket **lsop, struct mbuf *m,
1121 uint64_t response_cookie)
1125 unsigned int *pending_counter;
1128 * Global TCP locks are held because we manipulate the PCB lists
1129 * and create a new socket.
1131 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
1133 pending_counter = intotcpcb(sotoinpcb(*lsop))->t_tfo_pending;
1134 *lsop = syncache_socket(sc, *lsop, m);
1135 if (*lsop == NULL) {
1136 TCPSTAT_INC(tcps_sc_aborted);
1137 atomic_subtract_int(pending_counter, 1);
1139 inp = sotoinpcb(*lsop);
1140 tp = intotcpcb(inp);
1141 tp->t_flags |= TF_FASTOPEN;
1142 tp->t_tfo_cookie = response_cookie;
1143 tp->snd_max = tp->iss;
1144 tp->snd_nxt = tp->iss;
1145 tp->t_tfo_pending = pending_counter;
1146 TCPSTAT_INC(tcps_sc_completed);
1149 #endif /* TCP_RFC7413 */
1152 * Given a LISTEN socket and an inbound SYN request, add
1153 * this to the syn cache, and send back a segment:
1154 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
1157 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
1158 * Doing so would require that we hold onto the data and deliver it
1159 * to the application. However, if we are the target of a SYN-flood
1160 * DoS attack, an attacker could send data which would eventually
1161 * consume all available buffer space if it were ACKed. By not ACKing
1162 * the data, we avoid this DoS scenario.
1164 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO)
1165 * cookie is processed and a new socket is created. In this case, any data
1166 * accompanying the SYN will be queued to the socket by tcp_input() and will
1167 * be ACKed either when the application sends response data or the delayed
1168 * ACK timer expires, whichever comes first.
1171 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1172 struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod,
1177 struct syncache *sc = NULL;
1178 struct syncache_head *sch;
1179 struct mbuf *ipopts = NULL;
1181 int win, ip_ttl, ip_tos;
1185 int autoflowlabel = 0;
1188 struct label *maclabel;
1190 struct syncache scs;
1193 uint64_t tfo_response_cookie;
1194 unsigned int *tfo_pending = NULL;
1195 int tfo_cookie_valid = 0;
1196 int tfo_response_cookie_valid = 0;
1199 INP_WLOCK_ASSERT(inp); /* listen socket */
1200 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
1201 ("%s: unexpected tcp flags", __func__));
1204 * Combine all so/tp operations very early to drop the INP lock as
1209 cred = crhold(so->so_cred);
1212 if ((inc->inc_flags & INC_ISIPV6) &&
1213 (inp->inp_flags & IN6P_AUTOFLOWLABEL))
1216 ip_ttl = inp->inp_ip_ttl;
1217 ip_tos = inp->inp_ip_tos;
1218 win = sbspace(&so->so_rcv);
1219 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE));
1222 if (V_tcp_fastopen_enabled && IS_FASTOPEN(tp->t_flags) &&
1223 (tp->t_tfo_pending != NULL) && (to->to_flags & TOF_FASTOPEN)) {
1225 * Limit the number of pending TFO connections to
1226 * approximately half of the queue limit. This prevents TFO
1227 * SYN floods from starving the service by filling the
1228 * listen queue with bogus TFO connections.
1230 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <=
1231 (so->so_qlimit / 2)) {
1234 result = tcp_fastopen_check_cookie(inc,
1235 to->to_tfo_cookie, to->to_tfo_len,
1236 &tfo_response_cookie);
1237 tfo_cookie_valid = (result > 0);
1238 tfo_response_cookie_valid = (result >= 0);
1242 * Remember the TFO pending counter as it will have to be
1243 * decremented below if we don't make it to syncache_tfo_expand().
1245 tfo_pending = tp->t_tfo_pending;
1249 /* By the time we drop the lock these should no longer be used. */
1254 if (mac_syncache_init(&maclabel) != 0) {
1258 mac_syncache_create(maclabel, inp);
1261 if (!tfo_cookie_valid)
1266 * Remember the IP options, if any.
1269 if (!(inc->inc_flags & INC_ISIPV6))
1272 ipopts = (m) ? ip_srcroute(m) : NULL;
1278 * See if we already have an entry for this connection.
1279 * If we do, resend the SYN,ACK, and reset the retransmit timer.
1281 * XXX: should the syncache be re-initialized with the contents
1282 * of the new SYN here (which may have different options?)
1284 * XXX: We do not check the sequence number to see if this is a
1285 * real retransmit or a new connection attempt. The question is
1286 * how to handle such a case; either ignore it as spoofed, or
1287 * drop the current entry and create a new one?
1289 sc = syncache_lookup(inc, &sch); /* returns locked entry */
1290 SCH_LOCK_ASSERT(sch);
1293 if (tfo_cookie_valid)
1296 TCPSTAT_INC(tcps_sc_dupsyn);
1299 * If we were remembering a previous source route,
1300 * forget it and use the new one we've been given.
1303 (void) m_free(sc->sc_ipopts);
1304 sc->sc_ipopts = ipopts;
1307 * Update timestamp if present.
1309 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
1310 sc->sc_tsreflect = to->to_tsval;
1312 sc->sc_flags &= ~SCF_TIMESTAMP;
1315 * Since we have already unconditionally allocated label
1316 * storage, free it up. The syncache entry will already
1317 * have an initialized label we can use.
1319 mac_syncache_destroy(&maclabel);
1321 /* Retransmit SYN|ACK and reset retransmit count. */
1322 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
1323 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
1324 "resetting timer and retransmitting SYN|ACK\n",
1328 if (syncache_respond(sc, sch, 1, m) == 0) {
1330 syncache_timeout(sc, sch, 1);
1331 TCPSTAT_INC(tcps_sndacks);
1332 TCPSTAT_INC(tcps_sndtotal);
1339 if (tfo_cookie_valid) {
1340 bzero(&scs, sizeof(scs));
1346 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1349 * The zone allocator couldn't provide more entries.
1350 * Treat this as if the cache was full; drop the oldest
1351 * entry and insert the new one.
1353 TCPSTAT_INC(tcps_sc_zonefail);
1354 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL)
1355 syncache_drop(sc, sch);
1356 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1358 if (V_tcp_syncookies) {
1359 bzero(&scs, sizeof(scs));
1364 (void) m_free(ipopts);
1372 if (!tfo_cookie_valid && tfo_response_cookie_valid)
1373 sc->sc_tfo_cookie = &tfo_response_cookie;
1377 * Fill in the syncache values.
1380 sc->sc_label = maclabel;
1384 sc->sc_ipopts = ipopts;
1385 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1387 if (!(inc->inc_flags & INC_ISIPV6))
1390 sc->sc_ip_tos = ip_tos;
1391 sc->sc_ip_ttl = ip_ttl;
1395 sc->sc_todctx = todctx;
1397 sc->sc_irs = th->th_seq;
1398 sc->sc_iss = arc4random();
1400 sc->sc_flowlabel = 0;
1403 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
1404 * win was derived from socket earlier in the function.
1407 win = imin(win, TCP_MAXWIN);
1410 if (V_tcp_do_rfc1323) {
1412 * A timestamp received in a SYN makes
1413 * it ok to send timestamp requests and replies.
1415 if (to->to_flags & TOF_TS) {
1416 sc->sc_tsreflect = to->to_tsval;
1417 sc->sc_ts = tcp_ts_getticks();
1418 sc->sc_flags |= SCF_TIMESTAMP;
1420 if (to->to_flags & TOF_SCALE) {
1424 * Pick the smallest possible scaling factor that
1425 * will still allow us to scale up to sb_max, aka
1426 * kern.ipc.maxsockbuf.
1428 * We do this because there are broken firewalls that
1429 * will corrupt the window scale option, leading to
1430 * the other endpoint believing that our advertised
1431 * window is unscaled. At scale factors larger than
1432 * 5 the unscaled window will drop below 1500 bytes,
1433 * leading to serious problems when traversing these
1436 * With the default maxsockbuf of 256K, a scale factor
1437 * of 3 will be chosen by this algorithm. Those who
1438 * choose a larger maxsockbuf should watch out
1439 * for the compatibility problems mentioned above.
1441 * RFC1323: The Window field in a SYN (i.e., a <SYN>
1442 * or <SYN,ACK>) segment itself is never scaled.
1444 while (wscale < TCP_MAX_WINSHIFT &&
1445 (TCP_MAXWIN << wscale) < sb_max)
1447 sc->sc_requested_r_scale = wscale;
1448 sc->sc_requested_s_scale = to->to_wscale;
1449 sc->sc_flags |= SCF_WINSCALE;
1452 #ifdef TCP_SIGNATURE
1454 * If listening socket requested TCP digests, OR received SYN
1455 * contains the option, flag this in the syncache so that
1456 * syncache_respond() will do the right thing with the SYN+ACK.
1458 if (to->to_flags & TOF_SIGNATURE || ltflags & TF_SIGNATURE)
1459 sc->sc_flags |= SCF_SIGNATURE;
1461 if (to->to_flags & TOF_SACKPERM)
1462 sc->sc_flags |= SCF_SACK;
1463 if (to->to_flags & TOF_MSS)
1464 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */
1465 if (ltflags & TF_NOOPT)
1466 sc->sc_flags |= SCF_NOOPT;
1467 if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn)
1468 sc->sc_flags |= SCF_ECN;
1470 if (V_tcp_syncookies)
1471 sc->sc_iss = syncookie_generate(sch, sc);
1473 if (autoflowlabel) {
1474 if (V_tcp_syncookies)
1475 sc->sc_flowlabel = sc->sc_iss;
1477 sc->sc_flowlabel = ip6_randomflowlabel();
1478 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK;
1484 if (tfo_cookie_valid) {
1485 syncache_tfo_expand(sc, lsop, m, tfo_response_cookie);
1486 /* INP_WUNLOCK(inp) will be performed by the caller */
1493 * Do a standard 3-way handshake.
1495 if (syncache_respond(sc, sch, 0, m) == 0) {
1496 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs)
1498 else if (sc != &scs)
1499 syncache_insert(sc, sch); /* locks and unlocks sch */
1500 TCPSTAT_INC(tcps_sndacks);
1501 TCPSTAT_INC(tcps_sndtotal);
1505 TCPSTAT_INC(tcps_sc_dropped);
1515 * If tfo_pending is not NULL here, then a TFO SYN that did not
1516 * result in a new socket was processed and the associated pending
1517 * counter has not yet been decremented. All such TFO processing paths
1518 * transit this point.
1520 if (tfo_pending != NULL)
1521 tcp_fastopen_decrement_counter(tfo_pending);
1529 mac_syncache_destroy(&maclabel);
1535 * Send SYN|ACK to the peer. Either in response to the peer's SYN,
1536 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL.
1539 syncache_respond(struct syncache *sc, struct syncache_head *sch, int locked,
1540 const struct mbuf *m0)
1542 struct ip *ip = NULL;
1544 struct tcphdr *th = NULL;
1545 int optlen, error = 0; /* Make compiler happy */
1546 u_int16_t hlen, tlen, mssopt;
1549 struct ip6_hdr *ip6 = NULL;
1551 #ifdef TCP_SIGNATURE
1552 struct secasvar *sav;
1557 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
1560 tlen = hlen + sizeof(struct tcphdr);
1562 /* Determine MSS we advertize to other end of connection. */
1563 mssopt = tcp_mssopt(&sc->sc_inc);
1564 if (sc->sc_peer_mss)
1565 mssopt = max( min(sc->sc_peer_mss, mssopt), V_tcp_minmss);
1567 /* XXX: Assume that the entire packet will fit in a header mbuf. */
1568 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
1569 ("syncache: mbuf too small"));
1571 /* Create the IP+TCP header from scratch. */
1572 m = m_gethdr(M_NOWAIT, MT_DATA);
1576 mac_syncache_create_mbuf(sc->sc_label, m);
1578 m->m_data += max_linkhdr;
1580 m->m_pkthdr.len = tlen;
1581 m->m_pkthdr.rcvif = NULL;
1584 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1585 ip6 = mtod(m, struct ip6_hdr *);
1586 ip6->ip6_vfc = IPV6_VERSION;
1587 ip6->ip6_nxt = IPPROTO_TCP;
1588 ip6->ip6_src = sc->sc_inc.inc6_laddr;
1589 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
1590 ip6->ip6_plen = htons(tlen - hlen);
1591 /* ip6_hlim is set after checksum */
1592 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK;
1593 ip6->ip6_flow |= sc->sc_flowlabel;
1595 th = (struct tcphdr *)(ip6 + 1);
1598 #if defined(INET6) && defined(INET)
1603 ip = mtod(m, struct ip *);
1604 ip->ip_v = IPVERSION;
1605 ip->ip_hl = sizeof(struct ip) >> 2;
1606 ip->ip_len = htons(tlen);
1610 ip->ip_p = IPPROTO_TCP;
1611 ip->ip_src = sc->sc_inc.inc_laddr;
1612 ip->ip_dst = sc->sc_inc.inc_faddr;
1613 ip->ip_ttl = sc->sc_ip_ttl;
1614 ip->ip_tos = sc->sc_ip_tos;
1617 * See if we should do MTU discovery. Route lookups are
1618 * expensive, so we will only unset the DF bit if:
1620 * 1) path_mtu_discovery is disabled
1621 * 2) the SCF_UNREACH flag has been set
1623 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
1624 ip->ip_off |= htons(IP_DF);
1626 th = (struct tcphdr *)(ip + 1);
1629 th->th_sport = sc->sc_inc.inc_lport;
1630 th->th_dport = sc->sc_inc.inc_fport;
1632 th->th_seq = htonl(sc->sc_iss);
1633 th->th_ack = htonl(sc->sc_irs + 1);
1634 th->th_off = sizeof(struct tcphdr) >> 2;
1636 th->th_flags = TH_SYN|TH_ACK;
1637 th->th_win = htons(sc->sc_wnd);
1640 if (sc->sc_flags & SCF_ECN) {
1641 th->th_flags |= TH_ECE;
1642 TCPSTAT_INC(tcps_ecn_shs);
1645 /* Tack on the TCP options. */
1646 if ((sc->sc_flags & SCF_NOOPT) == 0) {
1650 to.to_flags = TOF_MSS;
1651 if (sc->sc_flags & SCF_WINSCALE) {
1652 to.to_wscale = sc->sc_requested_r_scale;
1653 to.to_flags |= TOF_SCALE;
1655 if (sc->sc_flags & SCF_TIMESTAMP) {
1656 /* Virgin timestamp or TCP cookie enhanced one. */
1657 to.to_tsval = sc->sc_ts;
1658 to.to_tsecr = sc->sc_tsreflect;
1659 to.to_flags |= TOF_TS;
1661 if (sc->sc_flags & SCF_SACK)
1662 to.to_flags |= TOF_SACKPERM;
1663 #ifdef TCP_SIGNATURE
1665 if (sc->sc_flags & SCF_SIGNATURE) {
1666 sav = tcp_get_sav(m, IPSEC_DIR_OUTBOUND);
1668 to.to_flags |= TOF_SIGNATURE;
1672 * We've got SCF_SIGNATURE flag
1673 * inherited from listening socket,
1674 * but no SADB key for given source
1675 * address. Assume signature is not
1676 * required and remove signature flag
1677 * instead of silently dropping
1682 sc->sc_flags &= ~SCF_SIGNATURE;
1690 if (sc->sc_tfo_cookie) {
1691 to.to_flags |= TOF_FASTOPEN;
1692 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
1693 to.to_tfo_cookie = sc->sc_tfo_cookie;
1694 /* don't send cookie again when retransmitting response */
1695 sc->sc_tfo_cookie = NULL;
1698 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
1700 /* Adjust headers by option size. */
1701 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
1703 m->m_pkthdr.len += optlen;
1705 #ifdef TCP_SIGNATURE
1706 if (sc->sc_flags & SCF_SIGNATURE)
1707 tcp_signature_do_compute(m, 0, optlen,
1708 to.to_signature, sav);
1711 if (sc->sc_inc.inc_flags & INC_ISIPV6)
1712 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
1715 ip->ip_len = htons(ntohs(ip->ip_len) + optlen);
1719 M_SETFIB(m, sc->sc_inc.inc_fibnum);
1720 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1722 * If we have peer's SYN and it has a flowid, then let's assign it to
1723 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid
1724 * to SYN|ACK due to lack of inp here.
1726 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) {
1727 m->m_pkthdr.flowid = m0->m_pkthdr.flowid;
1728 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0));
1731 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1732 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
1733 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen,
1735 ip6->ip6_hlim = in6_selecthlim(NULL, NULL);
1737 if (ADDED_BY_TOE(sc)) {
1738 struct toedev *tod = sc->sc_tod;
1740 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
1745 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
1748 #if defined(INET6) && defined(INET)
1753 m->m_pkthdr.csum_flags = CSUM_TCP;
1754 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
1755 htons(tlen + optlen - hlen + IPPROTO_TCP));
1757 if (ADDED_BY_TOE(sc)) {
1758 struct toedev *tod = sc->sc_tod;
1760 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
1765 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
1772 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks
1773 * that exceed the capacity of the syncache by avoiding the storage of any
1774 * of the SYNs we receive. Syncookies defend against blind SYN flooding
1775 * attacks where the attacker does not have access to our responses.
1777 * Syncookies encode and include all necessary information about the
1778 * connection setup within the SYN|ACK that we send back. That way we
1779 * can avoid keeping any local state until the ACK to our SYN|ACK returns
1780 * (if ever). Normally the syncache and syncookies are running in parallel
1781 * with the latter taking over when the former is exhausted. When matching
1782 * syncache entry is found the syncookie is ignored.
1784 * The only reliable information persisting the 3WHS is our initial sequence
1785 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient
1786 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS
1787 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK
1788 * returns and signifies a legitimate connection if it matches the ACK.
1790 * The available space of 32 bits to store the hash and to encode the SYN
1791 * option information is very tight and we should have at least 24 bits for
1792 * the MAC to keep the number of guesses by blind spoofing reasonably high.
1794 * SYN option information we have to encode to fully restore a connection:
1795 * MSS: is imporant to chose an optimal segment size to avoid IP level
1796 * fragmentation along the path. The common MSS values can be encoded
1797 * in a 3-bit table. Uncommon values are captured by the next lower value
1798 * in the table leading to a slight increase in packetization overhead.
1799 * WSCALE: is necessary to allow large windows to be used for high delay-
1800 * bandwidth product links. Not scaling the window when it was initially
1801 * negotiated is bad for performance as lack of scaling further decreases
1802 * the apparent available send window. We only need to encode the WSCALE
1803 * we received from the remote end. Our end can be recalculated at any
1804 * time. The common WSCALE values can be encoded in a 3-bit table.
1805 * Uncommon values are captured by the next lower value in the table
1806 * making us under-estimate the available window size halving our
1807 * theoretically possible maximum throughput for that connection.
1808 * SACK: Greatly assists in packet loss recovery and requires 1 bit.
1809 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options
1810 * that are included in all segments on a connection. We enable them when
1813 * Security of syncookies and attack vectors:
1815 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod)
1816 * together with the gloabl secret to make it unique per connection attempt.
1817 * Thus any change of any of those parameters results in a different MAC output
1818 * in an unpredictable way unless a collision is encountered. 24 bits of the
1819 * MAC are embedded into the ISS.
1821 * To prevent replay attacks two rotating global secrets are updated with a
1822 * new random value every 15 seconds. The life-time of a syncookie is thus
1825 * Vector 1: Attacking the secret. This requires finding a weakness in the
1826 * MAC itself or the way it is used here. The attacker can do a chosen plain
1827 * text attack by varying and testing the all parameters under his control.
1828 * The strength depends on the size and randomness of the secret, and the
1829 * cryptographic security of the MAC function. Due to the constant updating
1830 * of the secret the attacker has at most 29.999 seconds to find the secret
1831 * and launch spoofed connections. After that he has to start all over again.
1833 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC
1834 * size an average of 4,823 attempts are required for a 50% chance of success
1835 * to spoof a single syncookie (birthday collision paradox). However the
1836 * attacker is blind and doesn't know if one of his attempts succeeded unless
1837 * he has a side channel to interfere success from. A single connection setup
1838 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets.
1839 * This many attempts are required for each one blind spoofed connection. For
1840 * every additional spoofed connection he has to launch another N attempts.
1841 * Thus for a sustained rate 100 spoofed connections per second approximately
1842 * 1,800,000 packets per second would have to be sent.
1844 * NB: The MAC function should be fast so that it doesn't become a CPU
1845 * exhaustion attack vector itself.
1848 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations
1849 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996
1850 * http://cr.yp.to/syncookies.html (overview)
1851 * http://cr.yp.to/syncookies/archive (details)
1854 * Schematic construction of a syncookie enabled Initial Sequence Number:
1856 * 12345678901234567890123456789012
1857 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP|
1859 * x 24 MAC (truncated)
1860 * W 3 Send Window Scale index
1862 * S 1 SACK permitted
1863 * P 1 Odd/even secret
1867 * Distribution and probability of certain MSS values. Those in between are
1868 * rounded down to the next lower one.
1869 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011]
1870 * .2% .3% 5% 7% 7% 20% 15% 45%
1872 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 };
1875 * Distribution and probability of certain WSCALE values. We have to map the
1876 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3
1877 * bits based on prevalence of certain values. Where we don't have an exact
1878 * match for are rounded down to the next lower one letting us under-estimate
1879 * the true available window. At the moment this would happen only for the
1880 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer
1881 * and window size). The absence of the WSCALE option (no scaling in either
1882 * direction) is encoded with index zero.
1883 * [WSCALE values histograms, Allman, 2012]
1884 * X 10 10 35 5 6 14 10% by host
1885 * X 11 4 5 5 18 49 3% by connections
1887 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 };
1890 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed
1891 * and good cryptographic properties.
1894 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags,
1895 uint8_t *secbits, uintptr_t secmod)
1898 uint32_t siphash[2];
1900 SipHash24_Init(&ctx);
1901 SipHash_SetKey(&ctx, secbits);
1902 switch (inc->inc_flags & INC_ISIPV6) {
1905 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr));
1906 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr));
1911 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr));
1912 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr));
1916 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport));
1917 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport));
1918 SipHash_Update(&ctx, &irs, sizeof(irs));
1919 SipHash_Update(&ctx, &flags, sizeof(flags));
1920 SipHash_Update(&ctx, &secmod, sizeof(secmod));
1921 SipHash_Final((u_int8_t *)&siphash, &ctx);
1923 return (siphash[0] ^ siphash[1]);
1927 syncookie_generate(struct syncache_head *sch, struct syncache *sc)
1929 u_int i, mss, secbit, wscale;
1932 union syncookie cookie;
1934 SCH_LOCK_ASSERT(sch);
1938 /* Map our computed MSS into the 3-bit index. */
1939 mss = min(tcp_mssopt(&sc->sc_inc), max(sc->sc_peer_mss, V_tcp_minmss));
1940 for (i = nitems(tcp_sc_msstab) - 1; tcp_sc_msstab[i] > mss && i > 0;
1943 cookie.flags.mss_idx = i;
1946 * Map the send window scale into the 3-bit index but only if
1947 * the wscale option was received.
1949 if (sc->sc_flags & SCF_WINSCALE) {
1950 wscale = sc->sc_requested_s_scale;
1951 for (i = nitems(tcp_sc_wstab) - 1;
1952 tcp_sc_wstab[i] > wscale && i > 0;
1955 cookie.flags.wscale_idx = i;
1958 /* Can we do SACK? */
1959 if (sc->sc_flags & SCF_SACK)
1960 cookie.flags.sack_ok = 1;
1962 /* Which of the two secrets to use. */
1963 secbit = sch->sch_sc->secret.oddeven & 0x1;
1964 cookie.flags.odd_even = secbit;
1966 secbits = sch->sch_sc->secret.key[secbit];
1967 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits,
1971 * Put the flags into the hash and XOR them to get better ISS number
1972 * variance. This doesn't enhance the cryptographic strength and is
1973 * done to prevent the 8 cookie bits from showing up directly on the
1977 iss |= cookie.cookie ^ (hash >> 24);
1979 /* Randomize the timestamp. */
1980 if (sc->sc_flags & SCF_TIMESTAMP) {
1981 sc->sc_ts = arc4random();
1982 sc->sc_tsoff = sc->sc_ts - tcp_ts_getticks();
1985 TCPSTAT_INC(tcps_sc_sendcookie);
1989 static struct syncache *
1990 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch,
1991 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
1997 int wnd, wscale = 0;
1998 union syncookie cookie;
2000 SCH_LOCK_ASSERT(sch);
2003 * Pull information out of SYN-ACK/ACK and revert sequence number
2006 ack = th->th_ack - 1;
2007 seq = th->th_seq - 1;
2010 * Unpack the flags containing enough information to restore the
2013 cookie.cookie = (ack & 0xff) ^ (ack >> 24);
2015 /* Which of the two secrets to use. */
2016 secbits = sch->sch_sc->secret.key[cookie.flags.odd_even];
2018 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch);
2020 /* The recomputed hash matches the ACK if this was a genuine cookie. */
2021 if ((ack & ~0xff) != (hash & ~0xff))
2024 /* Fill in the syncache values. */
2026 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
2027 sc->sc_ipopts = NULL;
2032 switch (inc->inc_flags & INC_ISIPV6) {
2035 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl;
2036 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos;
2041 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL)
2042 sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK;
2047 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx];
2049 /* We can simply recompute receive window scale we sent earlier. */
2050 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max)
2053 /* Only use wscale if it was enabled in the orignal SYN. */
2054 if (cookie.flags.wscale_idx > 0) {
2055 sc->sc_requested_r_scale = wscale;
2056 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx];
2057 sc->sc_flags |= SCF_WINSCALE;
2060 wnd = sbspace(&lso->so_rcv);
2062 wnd = imin(wnd, TCP_MAXWIN);
2065 if (cookie.flags.sack_ok)
2066 sc->sc_flags |= SCF_SACK;
2068 if (to->to_flags & TOF_TS) {
2069 sc->sc_flags |= SCF_TIMESTAMP;
2070 sc->sc_tsreflect = to->to_tsval;
2071 sc->sc_ts = to->to_tsecr;
2072 sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks();
2075 if (to->to_flags & TOF_SIGNATURE)
2076 sc->sc_flags |= SCF_SIGNATURE;
2080 TCPSTAT_INC(tcps_sc_recvcookie);
2086 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
2087 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
2090 struct syncache scs, *scx;
2093 bzero(&scs, sizeof(scs));
2094 scx = syncookie_lookup(inc, sch, &scs, th, to, lso);
2096 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL)
2100 if (sc->sc_peer_mss != scx->sc_peer_mss)
2101 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n",
2102 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss);
2104 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale)
2105 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n",
2106 s, __func__, sc->sc_requested_r_scale,
2107 scx->sc_requested_r_scale);
2109 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale)
2110 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n",
2111 s, __func__, sc->sc_requested_s_scale,
2112 scx->sc_requested_s_scale);
2114 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK))
2115 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__);
2122 #endif /* INVARIANTS */
2125 syncookie_reseed(void *arg)
2127 struct tcp_syncache *sc = arg;
2132 * Reseeding the secret doesn't have to be protected by a lock.
2133 * It only must be ensured that the new random values are visible
2134 * to all CPUs in a SMP environment. The atomic with release
2135 * semantics ensures that.
2137 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1;
2138 secbits = sc->secret.key[secbit];
2139 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0);
2140 atomic_add_rel_int(&sc->secret.oddeven, 1);
2142 /* Reschedule ourself. */
2143 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz);
2147 * Exports the syncache entries to userland so that netstat can display
2148 * them alongside the other sockets. This function is intended to be
2149 * called only from tcp_pcblist.
2151 * Due to concurrency on an active system, the number of pcbs exported
2152 * may have no relation to max_pcbs. max_pcbs merely indicates the
2153 * amount of space the caller allocated for this function to use.
2156 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported)
2159 struct syncache *sc;
2160 struct syncache_head *sch;
2161 int count, error, i;
2163 for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
2164 sch = &V_tcp_syncache.hashbase[i];
2166 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
2167 if (count >= max_pcbs) {
2171 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
2173 bzero(&xt, sizeof(xt));
2174 xt.xt_len = sizeof(xt);
2175 if (sc->sc_inc.inc_flags & INC_ISIPV6)
2176 xt.xt_inp.inp_vflag = INP_IPV6;
2178 xt.xt_inp.inp_vflag = INP_IPV4;
2179 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo));
2180 xt.xt_tp.t_inpcb = &xt.xt_inp;
2181 xt.xt_tp.t_state = TCPS_SYN_RECEIVED;
2182 xt.xt_socket.xso_protocol = IPPROTO_TCP;
2183 xt.xt_socket.xso_len = sizeof (struct xsocket);
2184 xt.xt_socket.so_type = SOCK_STREAM;
2185 xt.xt_socket.so_state = SS_ISCONNECTING;
2186 error = SYSCTL_OUT(req, &xt, sizeof xt);
2196 *pcbs_exported = count;