2 * Copyright (c) 2001 McAfee, Inc.
3 * Copyright (c) 2006 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.
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"
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>
51 #include <sys/proc.h> /* for proc0 declaration */
52 #include <sys/random.h>
53 #include <sys/socket.h>
54 #include <sys/socketvar.h>
55 #include <sys/syslog.h>
60 #include <net/route.h>
62 #include <netinet/in.h>
63 #include <netinet/in_systm.h>
64 #include <netinet/ip.h>
65 #include <netinet/in_var.h>
66 #include <netinet/in_pcb.h>
67 #include <netinet/ip_var.h>
68 #include <netinet/ip_options.h>
70 #include <netinet/ip6.h>
71 #include <netinet/icmp6.h>
72 #include <netinet6/nd6.h>
73 #include <netinet6/ip6_var.h>
74 #include <netinet6/in6_pcb.h>
76 #include <netinet/tcp.h>
77 #include <netinet/tcp_fsm.h>
78 #include <netinet/tcp_seq.h>
79 #include <netinet/tcp_timer.h>
80 #include <netinet/tcp_var.h>
81 #include <netinet/tcp_syncache.h>
82 #include <netinet/tcp_offload.h>
84 #include <netinet6/tcp6_var.h>
88 #include <netipsec/ipsec.h>
90 #include <netipsec/ipsec6.h>
92 #include <netipsec/key.h>
95 #include <machine/in_cksum.h>
97 #include <security/mac/mac_framework.h>
99 static int tcp_syncookies = 1;
100 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW,
102 "Use TCP SYN cookies if the syncache overflows");
104 static int tcp_syncookiesonly = 0;
105 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_RW,
106 &tcp_syncookiesonly, 0,
107 "Use only TCP SYN cookies");
109 #define SYNCOOKIE_SECRET_SIZE 8 /* dwords */
110 #define SYNCOOKIE_LIFETIME 16 /* seconds */
113 TAILQ_ENTRY(syncache) sc_hash;
114 struct in_conninfo sc_inc; /* addresses */
115 int sc_rxttime; /* retransmit time */
116 u_int16_t sc_rxmits; /* retransmit counter */
118 u_int32_t sc_tsreflect; /* timestamp to reflect */
119 u_int32_t sc_ts; /* our timestamp to send */
120 u_int32_t sc_tsoff; /* ts offset w/ syncookies */
121 u_int32_t sc_flowlabel; /* IPv6 flowlabel */
122 tcp_seq sc_irs; /* seq from peer */
123 tcp_seq sc_iss; /* our ISS */
124 struct mbuf *sc_ipopts; /* source route */
126 u_int16_t sc_peer_mss; /* peer's MSS */
127 u_int16_t sc_wnd; /* advertised window */
128 u_int8_t sc_ip_ttl; /* IPv4 TTL */
129 u_int8_t sc_ip_tos; /* IPv4 TOS */
130 u_int8_t sc_requested_s_scale:4,
131 sc_requested_r_scale:4;
133 #define SCF_NOOPT 0x01 /* no TCP options */
134 #define SCF_WINSCALE 0x02 /* negotiated window scaling */
135 #define SCF_TIMESTAMP 0x04 /* negotiated timestamps */
136 /* MSS is implicit */
137 #define SCF_UNREACH 0x10 /* icmp unreachable received */
138 #define SCF_SIGNATURE 0x20 /* send MD5 digests */
139 #define SCF_SACK 0x80 /* send SACK option */
140 #ifndef TCP_OFFLOAD_DISABLE
141 struct toe_usrreqs *sc_tu; /* TOE operations */
142 void *sc_toepcb; /* TOE protocol block */
145 struct label *sc_label; /* MAC label reference */
149 #ifdef TCP_OFFLOAD_DISABLE
150 #define TOEPCB_ISSET(sc) (0)
152 #define TOEPCB_ISSET(sc) ((sc)->sc_toepcb != NULL)
156 struct syncache_head {
158 TAILQ_HEAD(sch_head, syncache) sch_bucket;
159 struct callout sch_timer;
163 u_int32_t sch_secbits_odd[SYNCOOKIE_SECRET_SIZE];
164 u_int32_t sch_secbits_even[SYNCOOKIE_SECRET_SIZE];
165 u_int sch_reseed; /* time_uptime, seconds */
168 static void syncache_drop(struct syncache *, struct syncache_head *);
169 static void syncache_free(struct syncache *);
170 static void syncache_insert(struct syncache *, struct syncache_head *);
171 struct syncache *syncache_lookup(struct in_conninfo *, struct syncache_head **);
172 static int syncache_respond(struct syncache *);
173 static struct socket *syncache_socket(struct syncache *, struct socket *,
175 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch,
177 static void syncache_timer(void *);
178 static void syncookie_generate(struct syncache_head *, struct syncache *,
180 static struct syncache
181 *syncookie_lookup(struct in_conninfo *, struct syncache_head *,
182 struct syncache *, struct tcpopt *, struct tcphdr *,
186 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
187 * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds,
188 * the odds are that the user has given up attempting to connect by then.
190 #define SYNCACHE_MAXREXMTS 3
192 /* Arbitrary values */
193 #define TCP_SYNCACHE_HASHSIZE 512
194 #define TCP_SYNCACHE_BUCKETLIMIT 30
196 struct tcp_syncache {
197 struct syncache_head *hashbase;
202 u_int cache_count; /* XXX: unprotected */
207 static struct tcp_syncache tcp_syncache;
209 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, "TCP SYN cache");
211 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RDTUN,
212 &tcp_syncache.bucket_limit, 0, "Per-bucket hash limit for syncache");
214 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RDTUN,
215 &tcp_syncache.cache_limit, 0, "Overall entry limit for syncache");
217 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_RD,
218 &tcp_syncache.cache_count, 0, "Current number of entries in syncache");
220 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RDTUN,
221 &tcp_syncache.hashsize, 0, "Size of TCP syncache hashtable");
223 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW,
224 &tcp_syncache.rexmt_limit, 0, "Limit on SYN/ACK retransmissions");
226 int tcp_sc_rst_sock_fail = 1;
227 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, CTLFLAG_RW,
228 &tcp_sc_rst_sock_fail, 0, "Send reset on socket allocation failure");
230 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
232 #define SYNCACHE_HASH(inc, mask) \
233 ((tcp_syncache.hash_secret ^ \
234 (inc)->inc_faddr.s_addr ^ \
235 ((inc)->inc_faddr.s_addr >> 16) ^ \
236 (inc)->inc_fport ^ (inc)->inc_lport) & mask)
238 #define SYNCACHE_HASH6(inc, mask) \
239 ((tcp_syncache.hash_secret ^ \
240 (inc)->inc6_faddr.s6_addr32[0] ^ \
241 (inc)->inc6_faddr.s6_addr32[3] ^ \
242 (inc)->inc_fport ^ (inc)->inc_lport) & mask)
244 #define ENDPTS_EQ(a, b) ( \
245 (a)->ie_fport == (b)->ie_fport && \
246 (a)->ie_lport == (b)->ie_lport && \
247 (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr && \
248 (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr \
251 #define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0)
253 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx)
254 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx)
255 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED)
258 * Requires the syncache entry to be already removed from the bucket list.
261 syncache_free(struct syncache *sc)
264 (void) m_free(sc->sc_ipopts);
266 mac_syncache_destroy(&sc->sc_label);
269 uma_zfree(tcp_syncache.zone, sc);
277 tcp_syncache.cache_count = 0;
278 tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
279 tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
280 tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
281 tcp_syncache.hash_secret = arc4random();
283 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
284 &tcp_syncache.hashsize);
285 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
286 &tcp_syncache.bucket_limit);
287 if (!powerof2(tcp_syncache.hashsize) || tcp_syncache.hashsize == 0) {
288 printf("WARNING: syncache hash size is not a power of 2.\n");
289 tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
291 tcp_syncache.hashmask = tcp_syncache.hashsize - 1;
294 tcp_syncache.cache_limit =
295 tcp_syncache.hashsize * tcp_syncache.bucket_limit;
296 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
297 &tcp_syncache.cache_limit);
299 /* Allocate the hash table. */
300 MALLOC(tcp_syncache.hashbase, struct syncache_head *,
301 tcp_syncache.hashsize * sizeof(struct syncache_head),
302 M_SYNCACHE, M_WAITOK | M_ZERO);
304 /* Initialize the hash buckets. */
305 for (i = 0; i < tcp_syncache.hashsize; i++) {
306 TAILQ_INIT(&tcp_syncache.hashbase[i].sch_bucket);
307 mtx_init(&tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
309 callout_init_mtx(&tcp_syncache.hashbase[i].sch_timer,
310 &tcp_syncache.hashbase[i].sch_mtx, 0);
311 tcp_syncache.hashbase[i].sch_length = 0;
314 /* Create the syncache entry zone. */
315 tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
316 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
317 uma_zone_set_max(tcp_syncache.zone, tcp_syncache.cache_limit);
321 * Inserts a syncache entry into the specified bucket row.
322 * Locks and unlocks the syncache_head autonomously.
325 syncache_insert(struct syncache *sc, struct syncache_head *sch)
327 struct syncache *sc2;
332 * Make sure that we don't overflow the per-bucket limit.
333 * If the bucket is full, toss the oldest element.
335 if (sch->sch_length >= tcp_syncache.bucket_limit) {
336 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
337 ("sch->sch_length incorrect"));
338 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
339 syncache_drop(sc2, sch);
340 tcpstat.tcps_sc_bucketoverflow++;
343 /* Put it into the bucket. */
344 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
347 /* Reinitialize the bucket row's timer. */
348 if (sch->sch_length == 1)
349 sch->sch_nextc = ticks + INT_MAX;
350 syncache_timeout(sc, sch, 1);
354 tcp_syncache.cache_count++;
355 tcpstat.tcps_sc_added++;
359 * Remove and free entry from syncache bucket row.
360 * Expects locked syncache head.
363 syncache_drop(struct syncache *sc, struct syncache_head *sch)
366 SCH_LOCK_ASSERT(sch);
368 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
371 #ifndef TCP_OFFLOAD_DISABLE
373 sc->sc_tu->tu_syncache_event(TOE_SC_DROP, sc->sc_toepcb);
376 tcp_syncache.cache_count--;
380 * Engage/reengage time on bucket row.
383 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
385 sc->sc_rxttime = ticks +
386 TCPTV_RTOBASE * (tcp_backoff[sc->sc_rxmits]);
388 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
389 sch->sch_nextc = sc->sc_rxttime;
391 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
392 syncache_timer, (void *)sch);
397 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
398 * If we have retransmitted an entry the maximum number of times, expire it.
399 * One separate timer for each bucket row.
402 syncache_timer(void *xsch)
404 struct syncache_head *sch = (struct syncache_head *)xsch;
405 struct syncache *sc, *nsc;
409 /* NB: syncache_head has already been locked by the callout. */
410 SCH_LOCK_ASSERT(sch);
413 * In the following cycle we may remove some entries and/or
414 * advance some timeouts, so re-initialize the bucket timer.
416 sch->sch_nextc = tick + INT_MAX;
418 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
420 * We do not check if the listen socket still exists
421 * and accept the case where the listen socket may be
422 * gone by the time we resend the SYN/ACK. We do
423 * not expect this to happens often. If it does,
424 * then the RST will be sent by the time the remote
425 * host does the SYN/ACK->ACK.
427 if (TSTMP_GT(sc->sc_rxttime, tick)) {
428 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
429 sch->sch_nextc = sc->sc_rxttime;
432 if (sc->sc_rxmits > tcp_syncache.rexmt_limit) {
433 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
434 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
435 "giving up and removing syncache entry\n",
439 syncache_drop(sc, sch);
440 tcpstat.tcps_sc_stale++;
443 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
444 log(LOG_DEBUG, "%s; %s: Response timeout, "
445 "retransmitting (%u) SYN|ACK\n",
446 s, __func__, sc->sc_rxmits);
450 (void) syncache_respond(sc);
451 tcpstat.tcps_sc_retransmitted++;
452 syncache_timeout(sc, sch, 0);
454 if (!TAILQ_EMPTY(&(sch)->sch_bucket))
455 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
456 syncache_timer, (void *)(sch));
460 * Find an entry in the syncache.
461 * Returns always with locked syncache_head plus a matching entry or NULL.
464 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
467 struct syncache_head *sch;
470 if (inc->inc_isipv6) {
471 sch = &tcp_syncache.hashbase[
472 SYNCACHE_HASH6(inc, tcp_syncache.hashmask)];
477 /* Circle through bucket row to find matching entry. */
478 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
479 if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie))
485 sch = &tcp_syncache.hashbase[
486 SYNCACHE_HASH(inc, tcp_syncache.hashmask)];
491 /* Circle through bucket row to find matching entry. */
492 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
494 if (sc->sc_inc.inc_isipv6)
497 if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie))
501 SCH_LOCK_ASSERT(*schp);
502 return (NULL); /* always returns with locked sch */
506 * This function is called when we get a RST for a
507 * non-existent connection, so that we can see if the
508 * connection is in the syn cache. If it is, zap it.
511 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th)
514 struct syncache_head *sch;
517 sc = syncache_lookup(inc, &sch); /* returns locked sch */
518 SCH_LOCK_ASSERT(sch);
521 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags.
522 * See RFC 793 page 65, section SEGMENT ARRIVES.
524 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) {
525 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
526 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or "
527 "FIN flag set, segment ignored\n", s, __func__);
528 tcpstat.tcps_badrst++;
533 * No corresponding connection was found in syncache.
534 * If syncookies are enabled and possibly exclusively
535 * used, or we are under memory pressure, a valid RST
536 * may not find a syncache entry. In that case we're
537 * done and no SYN|ACK retransmissions will happen.
538 * Otherwise the the RST was misdirected or spoofed.
541 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
542 log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
543 "syncache entry (possibly syncookie only), "
544 "segment ignored\n", s, __func__);
545 tcpstat.tcps_badrst++;
550 * If the RST bit is set, check the sequence number to see
551 * if this is a valid reset segment.
553 * In all states except SYN-SENT, all reset (RST) segments
554 * are validated by checking their SEQ-fields. A reset is
555 * valid if its sequence number is in the window.
557 * The sequence number in the reset segment is normally an
558 * echo of our outgoing acknowlegement numbers, but some hosts
559 * send a reset with the sequence number at the rightmost edge
560 * of our receive window, and we have to handle this case.
562 if (SEQ_GEQ(th->th_seq, sc->sc_irs) &&
563 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
564 syncache_drop(sc, sch);
565 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
566 log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, "
567 "connection attempt aborted by remote endpoint\n",
569 tcpstat.tcps_sc_reset++;
571 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
572 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
573 "IRS %u (+WND %u), segment ignored\n",
574 s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd);
575 tcpstat.tcps_badrst++;
585 syncache_badack(struct in_conninfo *inc)
588 struct syncache_head *sch;
590 sc = syncache_lookup(inc, &sch); /* returns locked sch */
591 SCH_LOCK_ASSERT(sch);
593 syncache_drop(sc, sch);
594 tcpstat.tcps_sc_badack++;
600 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th)
603 struct syncache_head *sch;
605 sc = syncache_lookup(inc, &sch); /* returns locked sch */
606 SCH_LOCK_ASSERT(sch);
610 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
611 if (ntohl(th->th_seq) != sc->sc_iss)
615 * If we've rertransmitted 3 times and this is our second error,
616 * we remove the entry. Otherwise, we allow it to continue on.
617 * This prevents us from incorrectly nuking an entry during a
618 * spurious network outage.
622 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
623 sc->sc_flags |= SCF_UNREACH;
626 syncache_drop(sc, sch);
627 tcpstat.tcps_sc_unreach++;
633 * Build a new TCP socket structure from a syncache entry.
635 static struct socket *
636 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
638 struct inpcb *inp = NULL;
643 INP_INFO_WLOCK_ASSERT(&tcbinfo);
646 * Ok, create the full blown connection, and set things up
647 * as they would have been set up if we had created the
648 * connection when the SYN arrived. If we can't create
649 * the connection, abort it.
651 so = sonewconn(lso, SS_ISCONNECTED);
654 * Drop the connection; we will either send a RST or
655 * have the peer retransmit its SYN again after its
658 tcpstat.tcps_listendrop++;
659 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
660 log(LOG_DEBUG, "%s; %s: Socket create failed "
661 "due to limits or memory shortage\n",
669 mac_socketpeer_set_from_mbuf(m, so);
674 inp->inp_inc.inc_fibnum = sc->sc_inc.inc_fibnum;
675 so->so_fibnum = sc->sc_inc.inc_fibnum;
678 /* Insert new socket into PCB hash list. */
679 inp->inp_inc.inc_isipv6 = sc->sc_inc.inc_isipv6;
681 if (sc->sc_inc.inc_isipv6) {
682 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
684 inp->inp_vflag &= ~INP_IPV6;
685 inp->inp_vflag |= INP_IPV4;
687 inp->inp_laddr = sc->sc_inc.inc_laddr;
691 inp->inp_lport = sc->sc_inc.inc_lport;
692 if (in_pcbinshash(inp) != 0) {
694 * Undo the assignments above if we failed to
695 * put the PCB on the hash lists.
698 if (sc->sc_inc.inc_isipv6)
699 inp->in6p_laddr = in6addr_any;
702 inp->inp_laddr.s_addr = INADDR_ANY;
707 /* Copy old policy into new socket's. */
708 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp))
709 printf("syncache_socket: could not copy policy\n");
712 if (sc->sc_inc.inc_isipv6) {
713 struct inpcb *oinp = sotoinpcb(lso);
714 struct in6_addr laddr6;
715 struct sockaddr_in6 sin6;
717 * Inherit socket options from the listening socket.
718 * Note that in6p_inputopts are not (and should not be)
719 * copied, since it stores previously received options and is
720 * used to detect if each new option is different than the
721 * previous one and hence should be passed to a user.
722 * If we copied in6p_inputopts, a user would not be able to
723 * receive options just after calling the accept system call.
725 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
726 if (oinp->in6p_outputopts)
727 inp->in6p_outputopts =
728 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
730 sin6.sin6_family = AF_INET6;
731 sin6.sin6_len = sizeof(sin6);
732 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
733 sin6.sin6_port = sc->sc_inc.inc_fport;
734 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
735 laddr6 = inp->in6p_laddr;
736 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
737 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
738 if (in6_pcbconnect(inp, (struct sockaddr *)&sin6,
740 inp->in6p_laddr = laddr6;
743 /* Override flowlabel from in6_pcbconnect. */
744 inp->in6p_flowinfo &= ~IPV6_FLOWLABEL_MASK;
745 inp->in6p_flowinfo |= sc->sc_flowlabel;
749 struct in_addr laddr;
750 struct sockaddr_in sin;
752 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
754 if (inp->inp_options == NULL) {
755 inp->inp_options = sc->sc_ipopts;
756 sc->sc_ipopts = NULL;
759 sin.sin_family = AF_INET;
760 sin.sin_len = sizeof(sin);
761 sin.sin_addr = sc->sc_inc.inc_faddr;
762 sin.sin_port = sc->sc_inc.inc_fport;
763 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
764 laddr = inp->inp_laddr;
765 if (inp->inp_laddr.s_addr == INADDR_ANY)
766 inp->inp_laddr = sc->sc_inc.inc_laddr;
767 if (in_pcbconnect(inp, (struct sockaddr *)&sin,
769 inp->inp_laddr = laddr;
774 tp->t_state = TCPS_SYN_RECEIVED;
775 tp->iss = sc->sc_iss;
776 tp->irs = sc->sc_irs;
779 tp->snd_wl1 = sc->sc_irs;
780 tp->snd_max = tp->iss + 1;
781 tp->snd_nxt = tp->iss + 1;
782 tp->rcv_up = sc->sc_irs + 1;
783 tp->rcv_wnd = sc->sc_wnd;
784 tp->rcv_adv += tp->rcv_wnd;
785 tp->last_ack_sent = tp->rcv_nxt;
787 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
788 if (sc->sc_flags & SCF_NOOPT)
789 tp->t_flags |= TF_NOOPT;
791 if (sc->sc_flags & SCF_WINSCALE) {
792 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
793 tp->snd_scale = sc->sc_requested_s_scale;
794 tp->request_r_scale = sc->sc_requested_r_scale;
796 if (sc->sc_flags & SCF_TIMESTAMP) {
797 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
798 tp->ts_recent = sc->sc_tsreflect;
799 tp->ts_recent_age = ticks;
800 tp->ts_offset = sc->sc_tsoff;
803 if (sc->sc_flags & SCF_SIGNATURE)
804 tp->t_flags |= TF_SIGNATURE;
806 if (sc->sc_flags & SCF_SACK)
807 tp->t_flags |= TF_SACK_PERMIT;
811 * Set up MSS and get cached values from tcp_hostcache.
812 * This might overwrite some of the defaults we just set.
814 tcp_mss(tp, sc->sc_peer_mss);
817 * If the SYN,ACK was retransmitted, reset cwnd to 1 segment.
820 tp->snd_cwnd = tp->t_maxseg;
821 tcp_timer_activate(tp, TT_KEEP, tcp_keepinit);
825 tcpstat.tcps_accepts++;
837 * This function gets called when we receive an ACK for a
838 * socket in the LISTEN state. We look up the connection
839 * in the syncache, and if its there, we pull it out of
840 * the cache and turn it into a full-blown connection in
841 * the SYN-RECEIVED state.
844 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
845 struct socket **lsop, struct mbuf *m)
848 struct syncache_head *sch;
853 * Global TCP locks are held because we manipulate the PCB lists
854 * and create a new socket.
856 INP_INFO_WLOCK_ASSERT(&tcbinfo);
857 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
858 ("%s: can handle only ACK", __func__));
860 sc = syncache_lookup(inc, &sch); /* returns locked sch */
861 SCH_LOCK_ASSERT(sch);
864 * There is no syncache entry, so see if this ACK is
865 * a returning syncookie. To do this, first:
866 * A. See if this socket has had a syncache entry dropped in
867 * the past. We don't want to accept a bogus syncookie
868 * if we've never received a SYN.
869 * B. check that the syncookie is valid. If it is, then
870 * cobble up a fake syncache entry, and return.
872 if (!tcp_syncookies) {
874 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
875 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
876 "segment rejected (syncookies disabled)\n",
880 bzero(&scs, sizeof(scs));
881 sc = syncookie_lookup(inc, sch, &scs, to, th, *lsop);
884 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
885 log(LOG_DEBUG, "%s; %s: Segment failed "
886 "SYNCOOKIE authentication, segment rejected "
887 "(probably spoofed)\n", s, __func__);
891 /* Pull out the entry to unlock the bucket row. */
892 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
894 tcp_syncache.cache_count--;
899 * Segment validation:
900 * ACK must match our initial sequence number + 1 (the SYN|ACK).
902 if (th->th_ack != sc->sc_iss + 1 && !TOEPCB_ISSET(sc)) {
903 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
904 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
905 "rejected\n", s, __func__, th->th_ack, sc->sc_iss);
909 * The SEQ must fall in the window starting a the received initial receive
910 * sequence number + 1 (the SYN).
913 if ((SEQ_LEQ(th->th_seq, sc->sc_irs) ||
914 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd )) &&
917 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
918 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
919 "rejected\n", s, __func__, th->th_seq, sc->sc_irs);
923 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) {
924 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
925 log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
926 "segment rejected\n", s, __func__);
930 * If timestamps were negotiated the reflected timestamp
931 * must be equal to what we actually sent in the SYN|ACK.
933 if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts &&
935 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
936 log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, "
937 "segment rejected\n",
938 s, __func__, to->to_tsecr, sc->sc_ts);
942 *lsop = syncache_socket(sc, *lsop, m);
945 tcpstat.tcps_sc_aborted++;
947 tcpstat.tcps_sc_completed++;
949 /* how do we find the inp for the new socket? */
954 if (sc != NULL && sc != &scs)
963 * Given a LISTEN socket and an inbound SYN request, add
964 * this to the syn cache, and send back a segment:
965 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
968 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
969 * Doing so would require that we hold onto the data and deliver it
970 * to the application. However, if we are the target of a SYN-flood
971 * DoS attack, an attacker could send data which would eventually
972 * consume all available buffer space if it were ACKed. By not ACKing
973 * the data, we avoid this DoS scenario.
976 _syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
977 struct inpcb *inp, struct socket **lsop, struct mbuf *m,
978 struct toe_usrreqs *tu, void *toepcb)
982 struct syncache *sc = NULL;
983 struct syncache_head *sch;
984 struct mbuf *ipopts = NULL;
986 int win, sb_hiwat, ip_ttl, ip_tos, noopt;
989 int autoflowlabel = 0;
992 struct label *maclabel;
996 INP_INFO_WLOCK_ASSERT(&tcbinfo);
997 INP_WLOCK_ASSERT(inp); /* listen socket */
998 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
999 ("%s: unexpected tcp flags", __func__));
1002 * Combine all so/tp operations very early to drop the INP lock as
1009 if (inc->inc_isipv6 &&
1010 (inp->in6p_flags & IN6P_AUTOFLOWLABEL))
1013 ip_ttl = inp->inp_ip_ttl;
1014 ip_tos = inp->inp_ip_tos;
1015 win = sbspace(&so->so_rcv);
1016 sb_hiwat = so->so_rcv.sb_hiwat;
1017 noopt = (tp->t_flags & TF_NOOPT);
1023 if (mac_syncache_init(&maclabel) != 0) {
1025 INP_INFO_WUNLOCK(&tcbinfo);
1028 mac_syncache_create(maclabel, inp);
1031 INP_INFO_WUNLOCK(&tcbinfo);
1034 * Remember the IP options, if any.
1037 if (!inc->inc_isipv6)
1039 ipopts = (m) ? ip_srcroute(m) : NULL;
1042 * See if we already have an entry for this connection.
1043 * If we do, resend the SYN,ACK, and reset the retransmit timer.
1045 * XXX: should the syncache be re-initialized with the contents
1046 * of the new SYN here (which may have different options?)
1048 * XXX: We do not check the sequence number to see if this is a
1049 * real retransmit or a new connection attempt. The question is
1050 * how to handle such a case; either ignore it as spoofed, or
1051 * drop the current entry and create a new one?
1053 sc = syncache_lookup(inc, &sch); /* returns locked entry */
1054 SCH_LOCK_ASSERT(sch);
1056 #ifndef TCP_OFFLOAD_DISABLE
1058 sc->sc_tu->tu_syncache_event(TOE_SC_ENTRY_PRESENT,
1061 tcpstat.tcps_sc_dupsyn++;
1064 * If we were remembering a previous source route,
1065 * forget it and use the new one we've been given.
1068 (void) m_free(sc->sc_ipopts);
1069 sc->sc_ipopts = ipopts;
1072 * Update timestamp if present.
1074 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
1075 sc->sc_tsreflect = to->to_tsval;
1077 sc->sc_flags &= ~SCF_TIMESTAMP;
1080 * Since we have already unconditionally allocated label
1081 * storage, free it up. The syncache entry will already
1082 * have an initialized label we can use.
1084 mac_syncache_destroy(&maclabel);
1085 KASSERT(sc->sc_label != NULL,
1086 ("%s: label not initialized", __func__));
1088 /* Retransmit SYN|ACK and reset retransmit count. */
1089 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
1090 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
1091 "resetting timer and retransmitting SYN|ACK\n",
1095 if (!TOEPCB_ISSET(sc) && syncache_respond(sc) == 0) {
1097 syncache_timeout(sc, sch, 1);
1098 tcpstat.tcps_sndacks++;
1099 tcpstat.tcps_sndtotal++;
1105 sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT | M_ZERO);
1108 * The zone allocator couldn't provide more entries.
1109 * Treat this as if the cache was full; drop the oldest
1110 * entry and insert the new one.
1112 tcpstat.tcps_sc_zonefail++;
1113 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL)
1114 syncache_drop(sc, sch);
1115 sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT | M_ZERO);
1117 if (tcp_syncookies) {
1118 bzero(&scs, sizeof(scs));
1123 (void) m_free(ipopts);
1130 * Fill in the syncache values.
1133 sc->sc_label = maclabel;
1135 sc->sc_ipopts = ipopts;
1136 sc->sc_inc.inc_fibnum = inp->inp_inc.inc_fibnum;
1137 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1139 if (!inc->inc_isipv6)
1142 sc->sc_ip_tos = ip_tos;
1143 sc->sc_ip_ttl = ip_ttl;
1145 #ifndef TCP_OFFLOAD_DISABLE
1147 sc->sc_toepcb = toepcb;
1149 sc->sc_irs = th->th_seq;
1150 sc->sc_iss = arc4random();
1152 sc->sc_flowlabel = 0;
1155 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
1156 * win was derived from socket earlier in the function.
1159 win = imin(win, TCP_MAXWIN);
1162 if (tcp_do_rfc1323) {
1164 * A timestamp received in a SYN makes
1165 * it ok to send timestamp requests and replies.
1167 if (to->to_flags & TOF_TS) {
1168 sc->sc_tsreflect = to->to_tsval;
1170 sc->sc_flags |= SCF_TIMESTAMP;
1172 if (to->to_flags & TOF_SCALE) {
1176 * Pick the smallest possible scaling factor that
1177 * will still allow us to scale up to sb_max, aka
1178 * kern.ipc.maxsockbuf.
1180 * We do this because there are broken firewalls that
1181 * will corrupt the window scale option, leading to
1182 * the other endpoint believing that our advertised
1183 * window is unscaled. At scale factors larger than
1184 * 5 the unscaled window will drop below 1500 bytes,
1185 * leading to serious problems when traversing these
1188 * With the default maxsockbuf of 256K, a scale factor
1189 * of 3 will be chosen by this algorithm. Those who
1190 * choose a larger maxsockbuf should watch out
1191 * for the compatiblity problems mentioned above.
1193 * RFC1323: The Window field in a SYN (i.e., a <SYN>
1194 * or <SYN,ACK>) segment itself is never scaled.
1196 while (wscale < TCP_MAX_WINSHIFT &&
1197 (TCP_MAXWIN << wscale) < sb_max)
1199 sc->sc_requested_r_scale = wscale;
1200 sc->sc_requested_s_scale = to->to_wscale;
1201 sc->sc_flags |= SCF_WINSCALE;
1204 #ifdef TCP_SIGNATURE
1206 * If listening socket requested TCP digests, and received SYN
1207 * contains the option, flag this in the syncache so that
1208 * syncache_respond() will do the right thing with the SYN+ACK.
1209 * XXX: Currently we always record the option by default and will
1210 * attempt to use it in syncache_respond().
1212 if (to->to_flags & TOF_SIGNATURE)
1213 sc->sc_flags |= SCF_SIGNATURE;
1215 if (to->to_flags & TOF_SACKPERM)
1216 sc->sc_flags |= SCF_SACK;
1217 if (to->to_flags & TOF_MSS)
1218 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */
1220 sc->sc_flags |= SCF_NOOPT;
1222 if (tcp_syncookies) {
1223 syncookie_generate(sch, sc, &flowtmp);
1226 sc->sc_flowlabel = flowtmp;
1232 (htonl(ip6_randomflowlabel()) & IPV6_FLOWLABEL_MASK);
1238 * Do a standard 3-way handshake.
1240 if (TOEPCB_ISSET(sc) || syncache_respond(sc) == 0) {
1241 if (tcp_syncookies && tcp_syncookiesonly && sc != &scs)
1243 else if (sc != &scs)
1244 syncache_insert(sc, sch); /* locks and unlocks sch */
1245 tcpstat.tcps_sndacks++;
1246 tcpstat.tcps_sndtotal++;
1250 tcpstat.tcps_sc_dropped++;
1256 mac_syncache_destroy(&maclabel);
1267 syncache_respond(struct syncache *sc)
1269 struct ip *ip = NULL;
1273 u_int16_t hlen, tlen, mssopt;
1276 struct ip6_hdr *ip6 = NULL;
1281 (sc->sc_inc.inc_isipv6) ? sizeof(struct ip6_hdr) :
1284 tlen = hlen + sizeof(struct tcphdr);
1286 /* Determine MSS we advertize to other end of connection. */
1287 mssopt = tcp_mssopt(&sc->sc_inc);
1288 if (sc->sc_peer_mss)
1289 mssopt = max( min(sc->sc_peer_mss, mssopt), tcp_minmss);
1291 /* XXX: Assume that the entire packet will fit in a header mbuf. */
1292 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
1293 ("syncache: mbuf too small"));
1295 /* Create the IP+TCP header from scratch. */
1296 m = m_gethdr(M_DONTWAIT, MT_DATA);
1300 mac_syncache_create_mbuf(sc->sc_label, m);
1302 m->m_data += max_linkhdr;
1304 m->m_pkthdr.len = tlen;
1305 m->m_pkthdr.rcvif = NULL;
1308 if (sc->sc_inc.inc_isipv6) {
1309 ip6 = mtod(m, struct ip6_hdr *);
1310 ip6->ip6_vfc = IPV6_VERSION;
1311 ip6->ip6_nxt = IPPROTO_TCP;
1312 ip6->ip6_src = sc->sc_inc.inc6_laddr;
1313 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
1314 ip6->ip6_plen = htons(tlen - hlen);
1315 /* ip6_hlim is set after checksum */
1316 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK;
1317 ip6->ip6_flow |= sc->sc_flowlabel;
1319 th = (struct tcphdr *)(ip6 + 1);
1323 ip = mtod(m, struct ip *);
1324 ip->ip_v = IPVERSION;
1325 ip->ip_hl = sizeof(struct ip) >> 2;
1330 ip->ip_p = IPPROTO_TCP;
1331 ip->ip_src = sc->sc_inc.inc_laddr;
1332 ip->ip_dst = sc->sc_inc.inc_faddr;
1333 ip->ip_ttl = sc->sc_ip_ttl;
1334 ip->ip_tos = sc->sc_ip_tos;
1337 * See if we should do MTU discovery. Route lookups are
1338 * expensive, so we will only unset the DF bit if:
1340 * 1) path_mtu_discovery is disabled
1341 * 2) the SCF_UNREACH flag has been set
1343 if (path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
1344 ip->ip_off |= IP_DF;
1346 th = (struct tcphdr *)(ip + 1);
1348 th->th_sport = sc->sc_inc.inc_lport;
1349 th->th_dport = sc->sc_inc.inc_fport;
1351 th->th_seq = htonl(sc->sc_iss);
1352 th->th_ack = htonl(sc->sc_irs + 1);
1353 th->th_off = sizeof(struct tcphdr) >> 2;
1355 th->th_flags = TH_SYN|TH_ACK;
1356 th->th_win = htons(sc->sc_wnd);
1359 /* Tack on the TCP options. */
1360 if ((sc->sc_flags & SCF_NOOPT) == 0) {
1364 to.to_flags = TOF_MSS;
1365 if (sc->sc_flags & SCF_WINSCALE) {
1366 to.to_wscale = sc->sc_requested_r_scale;
1367 to.to_flags |= TOF_SCALE;
1369 if (sc->sc_flags & SCF_TIMESTAMP) {
1370 /* Virgin timestamp or TCP cookie enhanced one. */
1371 to.to_tsval = sc->sc_ts;
1372 to.to_tsecr = sc->sc_tsreflect;
1373 to.to_flags |= TOF_TS;
1375 if (sc->sc_flags & SCF_SACK)
1376 to.to_flags |= TOF_SACKPERM;
1377 #ifdef TCP_SIGNATURE
1378 if (sc->sc_flags & SCF_SIGNATURE)
1379 to.to_flags |= TOF_SIGNATURE;
1381 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
1383 /* Adjust headers by option size. */
1384 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
1386 m->m_pkthdr.len += optlen;
1388 #ifdef TCP_SIGNATURE
1389 if (sc->sc_flags & SCF_SIGNATURE)
1390 tcp_signature_compute(m, sizeof(struct ip), 0, optlen,
1391 to.to_signature, IPSEC_DIR_OUTBOUND);
1394 if (sc->sc_inc.inc_isipv6)
1395 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
1398 ip->ip_len += optlen;
1403 if (sc->sc_inc.inc_isipv6) {
1405 th->th_sum = in6_cksum(m, IPPROTO_TCP, hlen,
1406 tlen + optlen - hlen);
1407 ip6->ip6_hlim = in6_selecthlim(NULL, NULL);
1408 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
1412 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
1413 htons(tlen + optlen - hlen + IPPROTO_TCP));
1414 m->m_pkthdr.csum_flags = CSUM_TCP;
1415 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1416 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
1422 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1423 struct inpcb *inp, struct socket **lsop, struct mbuf *m)
1425 _syncache_add(inc, to, th, inp, lsop, m, NULL, NULL);
1429 syncache_offload_add(struct in_conninfo *inc, struct tcpopt *to,
1430 struct tcphdr *th, struct inpcb *inp, struct socket **lsop,
1431 struct toe_usrreqs *tu, void *toepcb)
1434 INP_INFO_WLOCK(&tcbinfo);
1436 _syncache_add(inc, to, th, inp, lsop, NULL, tu, toepcb);
1440 * The purpose of SYN cookies is to avoid keeping track of all SYN's we
1441 * receive and to be able to handle SYN floods from bogus source addresses
1442 * (where we will never receive any reply). SYN floods try to exhaust all
1443 * our memory and available slots in the SYN cache table to cause a denial
1444 * of service to legitimate users of the local host.
1446 * The idea of SYN cookies is to encode and include all necessary information
1447 * about the connection setup state within the SYN-ACK we send back and thus
1448 * to get along without keeping any local state until the ACK to the SYN-ACK
1449 * arrives (if ever). Everything we need to know should be available from
1450 * the information we encoded in the SYN-ACK.
1452 * More information about the theory behind SYN cookies and its first
1453 * discussion and specification can be found at:
1454 * http://cr.yp.to/syncookies.html (overview)
1455 * http://cr.yp.to/syncookies/archive (gory details)
1457 * This implementation extends the orginal idea and first implementation
1458 * of FreeBSD by using not only the initial sequence number field to store
1459 * information but also the timestamp field if present. This way we can
1460 * keep track of the entire state we need to know to recreate the session in
1461 * its original form. Almost all TCP speakers implement RFC1323 timestamps
1462 * these days. For those that do not we still have to live with the known
1463 * shortcomings of the ISN only SYN cookies.
1467 * Initial sequence number we send:
1468 * 31|................................|0
1469 * DDDDDDDDDDDDDDDDDDDDDDDDDMMMRRRP
1470 * D = MD5 Digest (first dword)
1472 * R = Rotation of secret
1473 * P = Odd or Even secret
1475 * The MD5 Digest is computed with over following parameters:
1476 * a) randomly rotated secret
1477 * b) struct in_conninfo containing the remote/local ip/port (IPv4&IPv6)
1478 * c) the received initial sequence number from remote host
1479 * d) the rotation offset and odd/even bit
1481 * Timestamp we send:
1482 * 31|................................|0
1483 * DDDDDDDDDDDDDDDDDDDDDDSSSSRRRRA5
1484 * D = MD5 Digest (third dword) (only as filler)
1485 * S = Requested send window scale
1486 * R = Requested receive window scale
1488 * 5 = TCP-MD5 enabled (not implemented yet)
1489 * XORed with MD5 Digest (forth dword)
1491 * The timestamp isn't cryptographically secure and doesn't need to be.
1492 * The double use of the MD5 digest dwords ties it to a specific remote/
1493 * local host/port, remote initial sequence number and our local time
1494 * limited secret. A received timestamp is reverted (XORed) and then
1495 * the contained MD5 dword is compared to the computed one to ensure the
1496 * timestamp belongs to the SYN-ACK we sent. The other parameters may
1497 * have been tampered with but this isn't different from supplying bogus
1498 * values in the SYN in the first place.
1500 * Some problems with SYN cookies remain however:
1501 * Consider the problem of a recreated (and retransmitted) cookie. If the
1502 * original SYN was accepted, the connection is established. The second
1503 * SYN is inflight, and if it arrives with an ISN that falls within the
1504 * receive window, the connection is killed.
1507 * A heuristic to determine when to accept syn cookies is not necessary.
1508 * An ACK flood would cause the syncookie verification to be attempted,
1509 * but a SYN flood causes syncookies to be generated. Both are of equal
1510 * cost, so there's no point in trying to optimize the ACK flood case.
1511 * Also, if you don't process certain ACKs for some reason, then all someone
1512 * would have to do is launch a SYN and ACK flood at the same time, which
1513 * would stop cookie verification and defeat the entire purpose of syncookies.
1515 static int tcp_sc_msstab[] = { 0, 256, 468, 536, 996, 1452, 1460, 8960 };
1518 syncookie_generate(struct syncache_head *sch, struct syncache *sc,
1519 u_int32_t *flowlabel)
1522 u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)];
1525 u_int off, pmss, mss;
1528 SCH_LOCK_ASSERT(sch);
1530 /* Which of the two secrets to use. */
1531 secbits = sch->sch_oddeven ?
1532 sch->sch_secbits_odd : sch->sch_secbits_even;
1534 /* Reseed secret if too old. */
1535 if (sch->sch_reseed < time_uptime) {
1536 sch->sch_oddeven = sch->sch_oddeven ? 0 : 1; /* toggle */
1537 secbits = sch->sch_oddeven ?
1538 sch->sch_secbits_odd : sch->sch_secbits_even;
1539 for (i = 0; i < SYNCOOKIE_SECRET_SIZE; i++)
1540 secbits[i] = arc4random();
1541 sch->sch_reseed = time_uptime + SYNCOOKIE_LIFETIME;
1544 /* Secret rotation offset. */
1545 off = sc->sc_iss & 0x7; /* iss was randomized before */
1547 /* Maximum segment size calculation. */
1548 pmss = max( min(sc->sc_peer_mss, tcp_mssopt(&sc->sc_inc)), tcp_minmss);
1549 for (mss = sizeof(tcp_sc_msstab) / sizeof(int) - 1; mss > 0; mss--)
1550 if (tcp_sc_msstab[mss] <= pmss)
1553 /* Fold parameters and MD5 digest into the ISN we will send. */
1554 data = sch->sch_oddeven;/* odd or even secret, 1 bit */
1555 data |= off << 1; /* secret offset, derived from iss, 3 bits */
1556 data |= mss << 4; /* mss, 3 bits */
1559 MD5Update(&ctx, ((u_int8_t *)secbits) + off,
1560 SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off);
1561 MD5Update(&ctx, secbits, off);
1562 MD5Update(&ctx, &sc->sc_inc, sizeof(sc->sc_inc));
1563 MD5Update(&ctx, &sc->sc_irs, sizeof(sc->sc_irs));
1564 MD5Update(&ctx, &data, sizeof(data));
1565 MD5Final((u_int8_t *)&md5_buffer, &ctx);
1567 data |= (md5_buffer[0] << 7);
1571 *flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK;
1574 /* Additional parameters are stored in the timestamp if present. */
1575 if (sc->sc_flags & SCF_TIMESTAMP) {
1576 data = ((sc->sc_flags & SCF_SIGNATURE) ? 1 : 0); /* TCP-MD5, 1 bit */
1577 data |= ((sc->sc_flags & SCF_SACK) ? 1 : 0) << 1; /* SACK, 1 bit */
1578 data |= sc->sc_requested_s_scale << 2; /* SWIN scale, 4 bits */
1579 data |= sc->sc_requested_r_scale << 6; /* RWIN scale, 4 bits */
1580 data |= md5_buffer[2] << 10; /* more digest bits */
1581 data ^= md5_buffer[3];
1583 sc->sc_tsoff = data - ticks; /* after XOR */
1586 tcpstat.tcps_sc_sendcookie++;
1590 static struct syncache *
1591 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch,
1592 struct syncache *sc, struct tcpopt *to, struct tcphdr *th,
1596 u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)];
1600 int off, mss, wnd, flags;
1602 SCH_LOCK_ASSERT(sch);
1605 * Pull information out of SYN-ACK/ACK and
1606 * revert sequence number advances.
1608 ack = th->th_ack - 1;
1609 seq = th->th_seq - 1;
1610 off = (ack >> 1) & 0x7;
1611 mss = (ack >> 4) & 0x7;
1614 /* Which of the two secrets to use. */
1615 secbits = (flags & 0x1) ? sch->sch_secbits_odd : sch->sch_secbits_even;
1618 * The secret wasn't updated for the lifetime of a syncookie,
1619 * so this SYN-ACK/ACK is either too old (replay) or totally bogus.
1621 if (sch->sch_reseed + SYNCOOKIE_LIFETIME < time_uptime) {
1625 /* Recompute the digest so we can compare it. */
1627 MD5Update(&ctx, ((u_int8_t *)secbits) + off,
1628 SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off);
1629 MD5Update(&ctx, secbits, off);
1630 MD5Update(&ctx, inc, sizeof(*inc));
1631 MD5Update(&ctx, &seq, sizeof(seq));
1632 MD5Update(&ctx, &flags, sizeof(flags));
1633 MD5Final((u_int8_t *)&md5_buffer, &ctx);
1635 /* Does the digest part of or ACK'ed ISS match? */
1636 if ((ack & (~0x7f)) != (md5_buffer[0] << 7))
1639 /* Does the digest part of our reflected timestamp match? */
1640 if (to->to_flags & TOF_TS) {
1641 data = md5_buffer[3] ^ to->to_tsecr;
1642 if ((data & (~0x3ff)) != (md5_buffer[2] << 10))
1646 /* Fill in the syncache values. */
1647 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1648 sc->sc_ipopts = NULL;
1654 if (inc->inc_isipv6) {
1655 if (sotoinpcb(so)->in6p_flags & IN6P_AUTOFLOWLABEL)
1656 sc->sc_flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK;
1660 sc->sc_ip_ttl = sotoinpcb(so)->inp_ip_ttl;
1661 sc->sc_ip_tos = sotoinpcb(so)->inp_ip_tos;
1664 /* Additional parameters that were encoded in the timestamp. */
1666 sc->sc_flags |= SCF_TIMESTAMP;
1667 sc->sc_tsreflect = to->to_tsval;
1668 sc->sc_ts = to->to_tsecr;
1669 sc->sc_tsoff = to->to_tsecr - ticks;
1670 sc->sc_flags |= (data & 0x1) ? SCF_SIGNATURE : 0;
1671 sc->sc_flags |= ((data >> 1) & 0x1) ? SCF_SACK : 0;
1672 sc->sc_requested_s_scale = min((data >> 2) & 0xf,
1674 sc->sc_requested_r_scale = min((data >> 6) & 0xf,
1676 if (sc->sc_requested_s_scale || sc->sc_requested_r_scale)
1677 sc->sc_flags |= SCF_WINSCALE;
1679 sc->sc_flags |= SCF_NOOPT;
1681 wnd = sbspace(&so->so_rcv);
1683 wnd = imin(wnd, TCP_MAXWIN);
1687 sc->sc_peer_mss = tcp_sc_msstab[mss];
1689 tcpstat.tcps_sc_recvcookie++;
1694 * Returns the current number of syncache entries. This number
1695 * will probably change before you get around to calling
1700 syncache_pcbcount(void)
1702 struct syncache_head *sch;
1705 for (count = 0, i = 0; i < tcp_syncache.hashsize; i++) {
1706 /* No need to lock for a read. */
1707 sch = &tcp_syncache.hashbase[i];
1708 count += sch->sch_length;
1714 * Exports the syncache entries to userland so that netstat can display
1715 * them alongside the other sockets. This function is intended to be
1716 * called only from tcp_pcblist.
1718 * Due to concurrency on an active system, the number of pcbs exported
1719 * may have no relation to max_pcbs. max_pcbs merely indicates the
1720 * amount of space the caller allocated for this function to use.
1723 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported)
1726 struct syncache *sc;
1727 struct syncache_head *sch;
1728 int count, error, i;
1730 for (count = 0, error = 0, i = 0; i < tcp_syncache.hashsize; i++) {
1731 sch = &tcp_syncache.hashbase[i];
1733 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
1734 if (count >= max_pcbs) {
1738 bzero(&xt, sizeof(xt));
1739 xt.xt_len = sizeof(xt);
1740 if (sc->sc_inc.inc_isipv6)
1741 xt.xt_inp.inp_vflag = INP_IPV6;
1743 xt.xt_inp.inp_vflag = INP_IPV4;
1744 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo));
1745 xt.xt_tp.t_inpcb = &xt.xt_inp;
1746 xt.xt_tp.t_state = TCPS_SYN_RECEIVED;
1747 xt.xt_socket.xso_protocol = IPPROTO_TCP;
1748 xt.xt_socket.xso_len = sizeof (struct xsocket);
1749 xt.xt_socket.so_type = SOCK_STREAM;
1750 xt.xt_socket.so_state = SS_ISCONNECTING;
1751 error = SYSCTL_OUT(req, &xt, sizeof xt);
1761 *pcbs_exported = count;