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sys/netinet/tcp_syncache.c
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1 /*- 2 * Copyright (c) 2001 McAfee, Inc. 3 * Copyright (c) 2006 Andre Oppermann, Internet Business Solutions AG 4 * All rights reserved. 5 * 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. 10 * 11 * Redistribution and use in source and binary forms, with or without 12 * modification, are permitted provided that the following conditions 13 * are met: 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. 19 * 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 30 * SUCH DAMAGE. 31 */ 32 33 #include <sys/cdefs.h> 34 __FBSDID("$FreeBSD$"); 35 36 #include "opt_inet.h" 37 #include "opt_inet6.h" 38 #include "opt_ipsec.h" 39 #include "opt_mac.h" 40 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> 46 #include <sys/lock.h> 47 #include <sys/mutex.h> 48 #include <sys/malloc.h> 49 #include <sys/mbuf.h> 50 #include <sys/md5.h> 51 #include <sys/proc.h> /* for proc0 declaration */ 52 #include <sys/random.h> 53 #include <sys/socket.h> 54 #include <sys/socketvar.h> 55 #include <sys/syslog.h> 56 57 #include <vm/uma.h> 58 59 #include <net/if.h> 60 #include <net/route.h> 61 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> 69 #ifdef INET6 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> 75 #endif 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 #ifdef INET6 83 #include <netinet6/tcp6_var.h> 84 #endif 85 86 #ifdef IPSEC 87 #include <netipsec/ipsec.h> 88 #ifdef INET6 89 #include <netipsec/ipsec6.h> 90 #endif 91 #include <netipsec/key.h> 92 #endif /*IPSEC*/ 93 94 #include <machine/in_cksum.h> 95 96 #include <security/mac/mac_framework.h> 97 98 static int tcp_syncookies = 1; 99 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW, 100 &tcp_syncookies, 0, 101 "Use TCP SYN cookies if the syncache overflows"); 102 103 static int tcp_syncookiesonly = 0; 104 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_RW, 105 &tcp_syncookiesonly, 0, 106 "Use only TCP SYN cookies"); 107 108 #define SYNCOOKIE_SECRET_SIZE 8 /* dwords */ 109 #define SYNCOOKIE_LIFETIME 16 /* seconds */ 110 111 struct syncache { 112 TAILQ_ENTRY(syncache) sc_hash; 113 struct in_conninfo sc_inc; /* addresses */ 114 int sc_rxttime; /* retransmit time */ 115 u_int16_t sc_rxmits; /* retransmit counter */ 116 117 u_int32_t sc_tsreflect; /* timestamp to reflect */ 118 u_int32_t sc_ts; /* our timestamp to send */ 119 u_int32_t sc_tsoff; /* ts offset w/ syncookies */ 120 u_int32_t sc_flowlabel; /* IPv6 flowlabel */ 121 tcp_seq sc_irs; /* seq from peer */ 122 tcp_seq sc_iss; /* our ISS */ 123 struct mbuf *sc_ipopts; /* source route */ 124 125 u_int16_t sc_peer_mss; /* peer's MSS */ 126 u_int16_t sc_wnd; /* advertised window */ 127 u_int8_t sc_ip_ttl; /* IPv4 TTL */ 128 u_int8_t sc_ip_tos; /* IPv4 TOS */ 129 u_int8_t sc_requested_s_scale:4, 130 sc_requested_r_scale:4; 131 u_int8_t sc_flags; 132 #define SCF_NOOPT 0x01 /* no TCP options */ 133 #define SCF_WINSCALE 0x02 /* negotiated window scaling */ 134 #define SCF_TIMESTAMP 0x04 /* negotiated timestamps */ 135 /* MSS is implicit */ 136 #define SCF_UNREACH 0x10 /* icmp unreachable received */ 137 #define SCF_SIGNATURE 0x20 /* send MD5 digests */ 138 #define SCF_SACK 0x80 /* send SACK option */ 139 #ifndef DISABLE_TCP_OFFLOAD 140 void *sc_pspare[2]; /* toepcb / toe_usrreqs */ 141 #endif 142 #ifdef MAC 143 struct label *sc_label; /* MAC label reference */ 144 #endif 145 }; 146 147 struct syncache_head { 148 struct mtx sch_mtx; 149 TAILQ_HEAD(sch_head, syncache) sch_bucket; 150 struct callout sch_timer; 151 int sch_nextc; 152 u_int sch_length; 153 u_int sch_oddeven; 154 u_int32_t sch_secbits_odd[SYNCOOKIE_SECRET_SIZE]; 155 u_int32_t sch_secbits_even[SYNCOOKIE_SECRET_SIZE]; 156 u_int sch_reseed; /* time_uptime, seconds */ 157 }; 158 159 static void syncache_drop(struct syncache *, struct syncache_head *); 160 static void syncache_free(struct syncache *); 161 static void syncache_insert(struct syncache *, struct syncache_head *); 162 struct syncache *syncache_lookup(struct in_conninfo *, struct syncache_head **); 163 static int syncache_respond(struct syncache *); 164 static struct socket *syncache_socket(struct syncache *, struct socket *, 165 struct mbuf *m); 166 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 167 int docallout); 168 static void syncache_timer(void *); 169 static void syncookie_generate(struct syncache_head *, struct syncache *, 170 u_int32_t *); 171 static struct syncache 172 *syncookie_lookup(struct in_conninfo *, struct syncache_head *, 173 struct syncache *, struct tcpopt *, struct tcphdr *, 174 struct socket *); 175 176 /* 177 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 178 * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds, 179 * the odds are that the user has given up attempting to connect by then. 180 */ 181 #define SYNCACHE_MAXREXMTS 3 182 183 /* Arbitrary values */ 184 #define TCP_SYNCACHE_HASHSIZE 512 185 #define TCP_SYNCACHE_BUCKETLIMIT 30 186 187 struct tcp_syncache { 188 struct syncache_head *hashbase; 189 uma_zone_t zone; 190 u_int hashsize; 191 u_int hashmask; 192 u_int bucket_limit; 193 u_int cache_count; /* XXX: unprotected */ 194 u_int cache_limit; 195 u_int rexmt_limit; 196 u_int hash_secret; 197 }; 198 static struct tcp_syncache tcp_syncache; 199 200 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, "TCP SYN cache"); 201 202 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RDTUN, 203 &tcp_syncache.bucket_limit, 0, "Per-bucket hash limit for syncache"); 204 205 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RDTUN, 206 &tcp_syncache.cache_limit, 0, "Overall entry limit for syncache"); 207 208 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_RD, 209 &tcp_syncache.cache_count, 0, "Current number of entries in syncache"); 210 211 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RDTUN, 212 &tcp_syncache.hashsize, 0, "Size of TCP syncache hashtable"); 213 214 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW, 215 &tcp_syncache.rexmt_limit, 0, "Limit on SYN/ACK retransmissions"); 216 217 int tcp_sc_rst_sock_fail = 1; 218 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, CTLFLAG_RW, 219 &tcp_sc_rst_sock_fail, 0, "Send reset on socket allocation failure"); 220 221 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 222 223 #define SYNCACHE_HASH(inc, mask) \ 224 ((tcp_syncache.hash_secret ^ \ 225 (inc)->inc_faddr.s_addr ^ \ 226 ((inc)->inc_faddr.s_addr >> 16) ^ \ 227 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 228 229 #define SYNCACHE_HASH6(inc, mask) \ 230 ((tcp_syncache.hash_secret ^ \ 231 (inc)->inc6_faddr.s6_addr32[0] ^ \ 232 (inc)->inc6_faddr.s6_addr32[3] ^ \ 233 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 234 235 #define ENDPTS_EQ(a, b) ( \ 236 (a)->ie_fport == (b)->ie_fport && \ 237 (a)->ie_lport == (b)->ie_lport && \ 238 (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr && \ 239 (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr \ 240 ) 241 242 #define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0) 243 244 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 245 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 246 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 247 248 /* 249 * Requires the syncache entry to be already removed from the bucket list. 250 */ 251 static void 252 syncache_free(struct syncache *sc) 253 { 254 if (sc->sc_ipopts) 255 (void) m_free(sc->sc_ipopts); 256 #ifdef MAC 257 mac_destroy_syncache(&sc->sc_label); 258 #endif 259 260 uma_zfree(tcp_syncache.zone, sc); 261 } 262 263 void 264 syncache_init(void) 265 { 266 int i; 267 268 tcp_syncache.cache_count = 0; 269 tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 270 tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 271 tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 272 tcp_syncache.hash_secret = arc4random(); 273 274 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 275 &tcp_syncache.hashsize); 276 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 277 &tcp_syncache.bucket_limit); 278 if (!powerof2(tcp_syncache.hashsize) || tcp_syncache.hashsize == 0) { 279 printf("WARNING: syncache hash size is not a power of 2.\n"); 280 tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 281 } 282 tcp_syncache.hashmask = tcp_syncache.hashsize - 1; 283 284 /* Set limits. */ 285 tcp_syncache.cache_limit = 286 tcp_syncache.hashsize * tcp_syncache.bucket_limit; 287 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 288 &tcp_syncache.cache_limit); 289 290 /* Allocate the hash table. */ 291 MALLOC(tcp_syncache.hashbase, struct syncache_head *, 292 tcp_syncache.hashsize * sizeof(struct syncache_head), 293 M_SYNCACHE, M_WAITOK | M_ZERO); 294 295 /* Initialize the hash buckets. */ 296 for (i = 0; i < tcp_syncache.hashsize; i++) { 297 TAILQ_INIT(&tcp_syncache.hashbase[i].sch_bucket); 298 mtx_init(&tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 299 NULL, MTX_DEF); 300 callout_init_mtx(&tcp_syncache.hashbase[i].sch_timer, 301 &tcp_syncache.hashbase[i].sch_mtx, 0); 302 tcp_syncache.hashbase[i].sch_length = 0; 303 } 304 305 /* Create the syncache entry zone. */ 306 tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 307 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 308 uma_zone_set_max(tcp_syncache.zone, tcp_syncache.cache_limit); 309 } 310 311 /* 312 * Inserts a syncache entry into the specified bucket row. 313 * Locks and unlocks the syncache_head autonomously. 314 */ 315 static void 316 syncache_insert(struct syncache *sc, struct syncache_head *sch) 317 { 318 struct syncache *sc2; 319 320 SCH_LOCK(sch); 321 322 /* 323 * Make sure that we don't overflow the per-bucket limit. 324 * If the bucket is full, toss the oldest element. 325 */ 326 if (sch->sch_length >= tcp_syncache.bucket_limit) { 327 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 328 ("sch->sch_length incorrect")); 329 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 330 syncache_drop(sc2, sch); 331 tcpstat.tcps_sc_bucketoverflow++; 332 } 333 334 /* Put it into the bucket. */ 335 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 336 sch->sch_length++; 337 338 /* Reinitialize the bucket row's timer. */ 339 if (sch->sch_length == 1) 340 sch->sch_nextc = ticks + INT_MAX; 341 syncache_timeout(sc, sch, 1); 342 343 SCH_UNLOCK(sch); 344 345 tcp_syncache.cache_count++; 346 tcpstat.tcps_sc_added++; 347 } 348 349 /* 350 * Remove and free entry from syncache bucket row. 351 * Expects locked syncache head. 352 */ 353 static void 354 syncache_drop(struct syncache *sc, struct syncache_head *sch) 355 { 356 357 SCH_LOCK_ASSERT(sch); 358 359 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 360 sch->sch_length--; 361 362 syncache_free(sc); 363 tcp_syncache.cache_count--; 364 } 365 366 /* 367 * Engage/reengage time on bucket row. 368 */ 369 static void 370 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 371 { 372 sc->sc_rxttime = ticks + 373 TCPTV_RTOBASE * (tcp_backoff[sc->sc_rxmits]); 374 sc->sc_rxmits++; 375 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 376 sch->sch_nextc = sc->sc_rxttime; 377 if (docallout) 378 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 379 syncache_timer, (void *)sch); 380 } 381 } 382 383 /* 384 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 385 * If we have retransmitted an entry the maximum number of times, expire it. 386 * One separate timer for each bucket row. 387 */ 388 static void 389 syncache_timer(void *xsch) 390 { 391 struct syncache_head *sch = (struct syncache_head *)xsch; 392 struct syncache *sc, *nsc; 393 int tick = ticks; 394 char *s; 395 396 /* NB: syncache_head has already been locked by the callout. */ 397 SCH_LOCK_ASSERT(sch); 398 399 /* 400 * In the following cycle we may remove some entries and/or 401 * advance some timeouts, so re-initialize the bucket timer. 402 */ 403 sch->sch_nextc = tick + INT_MAX; 404 405 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 406 /* 407 * We do not check if the listen socket still exists 408 * and accept the case where the listen socket may be 409 * gone by the time we resend the SYN/ACK. We do 410 * not expect this to happens often. If it does, 411 * then the RST will be sent by the time the remote 412 * host does the SYN/ACK->ACK. 413 */ 414 if (TSTMP_GT(sc->sc_rxttime, tick)) { 415 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 416 sch->sch_nextc = sc->sc_rxttime; 417 continue; 418 } 419 420 if (sc->sc_rxmits > tcp_syncache.rexmt_limit) { 421 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 422 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 423 "giving up and removing syncache entry\n", 424 s, __func__); 425 free(s, M_TCPLOG); 426 } 427 syncache_drop(sc, sch); 428 tcpstat.tcps_sc_stale++; 429 continue; 430 } 431 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 432 log(LOG_DEBUG, "%s; %s: Response timeout, " 433 "retransmitting (%u) SYN|ACK\n", 434 s, __func__, sc->sc_rxmits); 435 free(s, M_TCPLOG); 436 } 437 438 (void) syncache_respond(sc); 439 tcpstat.tcps_sc_retransmitted++; 440 syncache_timeout(sc, sch, 0); 441 } 442 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 443 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 444 syncache_timer, (void *)(sch)); 445 } 446 447 /* 448 * Find an entry in the syncache. 449 * Returns always with locked syncache_head plus a matching entry or NULL. 450 */ 451 struct syncache * 452 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 453 { 454 struct syncache *sc; 455 struct syncache_head *sch; 456 457 #ifdef INET6 458 if (inc->inc_isipv6) { 459 sch = &tcp_syncache.hashbase[ 460 SYNCACHE_HASH6(inc, tcp_syncache.hashmask)]; 461 *schp = sch; 462 463 SCH_LOCK(sch); 464 465 /* Circle through bucket row to find matching entry. */ 466 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 467 if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) 468 return (sc); 469 } 470 } else 471 #endif 472 { 473 sch = &tcp_syncache.hashbase[ 474 SYNCACHE_HASH(inc, tcp_syncache.hashmask)]; 475 *schp = sch; 476 477 SCH_LOCK(sch); 478 479 /* Circle through bucket row to find matching entry. */ 480 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 481 #ifdef INET6 482 if (sc->sc_inc.inc_isipv6) 483 continue; 484 #endif 485 if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) 486 return (sc); 487 } 488 } 489 SCH_LOCK_ASSERT(*schp); 490 return (NULL); /* always returns with locked sch */ 491 } 492 493 /* 494 * This function is called when we get a RST for a 495 * non-existent connection, so that we can see if the 496 * connection is in the syn cache. If it is, zap it. 497 */ 498 void 499 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th) 500 { 501 struct syncache *sc; 502 struct syncache_head *sch; 503 char *s = NULL; 504 505 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 506 SCH_LOCK_ASSERT(sch); 507 508 /* 509 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags. 510 * See RFC 793 page 65, section SEGMENT ARRIVES. 511 */ 512 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) { 513 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 514 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or " 515 "FIN flag set, segment ignored\n", s, __func__); 516 tcpstat.tcps_badrst++; 517 goto done; 518 } 519 520 /* 521 * No corresponding connection was found in syncache. 522 * If syncookies are enabled and possibly exclusively 523 * used, or we are under memory pressure, a valid RST 524 * may not find a syncache entry. In that case we're 525 * done and no SYN|ACK retransmissions will happen. 526 * Otherwise the the RST was misdirected or spoofed. 527 */ 528 if (sc == NULL) { 529 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 530 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 531 "syncache entry (possibly syncookie only), " 532 "segment ignored\n", s, __func__); 533 tcpstat.tcps_badrst++; 534 goto done; 535 } 536 537 /* 538 * If the RST bit is set, check the sequence number to see 539 * if this is a valid reset segment. 540 * RFC 793 page 37: 541 * In all states except SYN-SENT, all reset (RST) segments 542 * are validated by checking their SEQ-fields. A reset is 543 * valid if its sequence number is in the window. 544 * 545 * The sequence number in the reset segment is normally an 546 * echo of our outgoing acknowlegement numbers, but some hosts 547 * send a reset with the sequence number at the rightmost edge 548 * of our receive window, and we have to handle this case. 549 */ 550 if (SEQ_GEQ(th->th_seq, sc->sc_irs) && 551 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 552 syncache_drop(sc, sch); 553 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 554 log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, " 555 "connection attempt aborted by remote endpoint\n", 556 s, __func__); 557 tcpstat.tcps_sc_reset++; 558 } else if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 559 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != IRS %u " 560 "(+WND %u), segment ignored\n", 561 s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd); 562 tcpstat.tcps_badrst++; 563 } 564 565 done: 566 if (s != NULL) 567 free(s, M_TCPLOG); 568 SCH_UNLOCK(sch); 569 } 570 571 void 572 syncache_badack(struct in_conninfo *inc) 573 { 574 struct syncache *sc; 575 struct syncache_head *sch; 576 577 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 578 SCH_LOCK_ASSERT(sch); 579 if (sc != NULL) { 580 syncache_drop(sc, sch); 581 tcpstat.tcps_sc_badack++; 582 } 583 SCH_UNLOCK(sch); 584 } 585 586 void 587 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th) 588 { 589 struct syncache *sc; 590 struct syncache_head *sch; 591 592 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 593 SCH_LOCK_ASSERT(sch); 594 if (sc == NULL) 595 goto done; 596 597 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 598 if (ntohl(th->th_seq) != sc->sc_iss) 599 goto done; 600 601 /* 602 * If we've rertransmitted 3 times and this is our second error, 603 * we remove the entry. Otherwise, we allow it to continue on. 604 * This prevents us from incorrectly nuking an entry during a 605 * spurious network outage. 606 * 607 * See tcp_notify(). 608 */ 609 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 610 sc->sc_flags |= SCF_UNREACH; 611 goto done; 612 } 613 syncache_drop(sc, sch); 614 tcpstat.tcps_sc_unreach++; 615 done: 616 SCH_UNLOCK(sch); 617 } 618 619 /* 620 * Build a new TCP socket structure from a syncache entry. 621 */ 622 static struct socket * 623 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 624 { 625 struct inpcb *inp = NULL; 626 struct socket *so; 627 struct tcpcb *tp; 628 char *s; 629 630 INP_INFO_WLOCK_ASSERT(&tcbinfo); 631 632 /* 633 * Ok, create the full blown connection, and set things up 634 * as they would have been set up if we had created the 635 * connection when the SYN arrived. If we can't create 636 * the connection, abort it. 637 */ 638 so = sonewconn(lso, SS_ISCONNECTED); 639 if (so == NULL) { 640 /* 641 * Drop the connection; we will either send a RST or 642 * have the peer retransmit its SYN again after its 643 * RTO and try again. 644 */ 645 tcpstat.tcps_listendrop++; 646 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 647 log(LOG_DEBUG, "%s; %s: Socket create failed " 648 "due to limits or memory shortage\n", 649 s, __func__); 650 free(s, M_TCPLOG); 651 } 652 goto abort2; 653 } 654 #ifdef MAC 655 SOCK_LOCK(so); 656 mac_set_socket_peer_from_mbuf(m, so); 657 SOCK_UNLOCK(so); 658 #endif 659 660 inp = sotoinpcb(so); 661 INP_LOCK(inp); 662 663 /* Insert new socket into PCB hash list. */ 664 inp->inp_inc.inc_isipv6 = sc->sc_inc.inc_isipv6; 665 #ifdef INET6 666 if (sc->sc_inc.inc_isipv6) { 667 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 668 } else { 669 inp->inp_vflag &= ~INP_IPV6; 670 inp->inp_vflag |= INP_IPV4; 671 #endif 672 inp->inp_laddr = sc->sc_inc.inc_laddr; 673 #ifdef INET6 674 } 675 #endif 676 inp->inp_lport = sc->sc_inc.inc_lport; 677 if (in_pcbinshash(inp) != 0) { 678 /* 679 * Undo the assignments above if we failed to 680 * put the PCB on the hash lists. 681 */ 682 #ifdef INET6 683 if (sc->sc_inc.inc_isipv6) 684 inp->in6p_laddr = in6addr_any; 685 else 686 #endif 687 inp->inp_laddr.s_addr = INADDR_ANY; 688 inp->inp_lport = 0; 689 goto abort; 690 } 691 #ifdef IPSEC 692 /* Copy old policy into new socket's. */ 693 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp)) 694 printf("syncache_socket: could not copy policy\n"); 695 #endif 696 #ifdef INET6 697 if (sc->sc_inc.inc_isipv6) { 698 struct inpcb *oinp = sotoinpcb(lso); 699 struct in6_addr laddr6; 700 struct sockaddr_in6 sin6; 701 /* 702 * Inherit socket options from the listening socket. 703 * Note that in6p_inputopts are not (and should not be) 704 * copied, since it stores previously received options and is 705 * used to detect if each new option is different than the 706 * previous one and hence should be passed to a user. 707 * If we copied in6p_inputopts, a user would not be able to 708 * receive options just after calling the accept system call. 709 */ 710 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 711 if (oinp->in6p_outputopts) 712 inp->in6p_outputopts = 713 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 714 715 sin6.sin6_family = AF_INET6; 716 sin6.sin6_len = sizeof(sin6); 717 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 718 sin6.sin6_port = sc->sc_inc.inc_fport; 719 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 720 laddr6 = inp->in6p_laddr; 721 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 722 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 723 if (in6_pcbconnect(inp, (struct sockaddr *)&sin6, 724 thread0.td_ucred)) { 725 inp->in6p_laddr = laddr6; 726 goto abort; 727 } 728 /* Override flowlabel from in6_pcbconnect. */ 729 inp->in6p_flowinfo &= ~IPV6_FLOWLABEL_MASK; 730 inp->in6p_flowinfo |= sc->sc_flowlabel; 731 } else 732 #endif 733 { 734 struct in_addr laddr; 735 struct sockaddr_in sin; 736 737 inp->inp_options = ip_srcroute(m); 738 if (inp->inp_options == NULL) { 739 inp->inp_options = sc->sc_ipopts; 740 sc->sc_ipopts = NULL; 741 } 742 743 sin.sin_family = AF_INET; 744 sin.sin_len = sizeof(sin); 745 sin.sin_addr = sc->sc_inc.inc_faddr; 746 sin.sin_port = sc->sc_inc.inc_fport; 747 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 748 laddr = inp->inp_laddr; 749 if (inp->inp_laddr.s_addr == INADDR_ANY) 750 inp->inp_laddr = sc->sc_inc.inc_laddr; 751 if (in_pcbconnect(inp, (struct sockaddr *)&sin, 752 thread0.td_ucred)) { 753 inp->inp_laddr = laddr; 754 goto abort; 755 } 756 } 757 tp = intotcpcb(inp); 758 tp->t_state = TCPS_SYN_RECEIVED; 759 tp->iss = sc->sc_iss; 760 tp->irs = sc->sc_irs; 761 tcp_rcvseqinit(tp); 762 tcp_sendseqinit(tp); 763 tp->snd_wl1 = sc->sc_irs; 764 tp->snd_max = tp->iss + 1; 765 tp->snd_nxt = tp->iss + 1; 766 tp->rcv_up = sc->sc_irs + 1; 767 tp->rcv_wnd = sc->sc_wnd; 768 tp->rcv_adv += tp->rcv_wnd; 769 tp->last_ack_sent = tp->rcv_nxt; 770 771 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 772 if (sc->sc_flags & SCF_NOOPT) 773 tp->t_flags |= TF_NOOPT; 774 else { 775 if (sc->sc_flags & SCF_WINSCALE) { 776 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 777 tp->snd_scale = sc->sc_requested_s_scale; 778 tp->request_r_scale = sc->sc_requested_r_scale; 779 } 780 if (sc->sc_flags & SCF_TIMESTAMP) { 781 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 782 tp->ts_recent = sc->sc_tsreflect; 783 tp->ts_recent_age = ticks; 784 tp->ts_offset = sc->sc_tsoff; 785 } 786 #ifdef TCP_SIGNATURE 787 if (sc->sc_flags & SCF_SIGNATURE) 788 tp->t_flags |= TF_SIGNATURE; 789 #endif 790 if (sc->sc_flags & SCF_SACK) 791 tp->t_flags |= TF_SACK_PERMIT; 792 } 793 794 /* 795 * Set up MSS and get cached values from tcp_hostcache. 796 * This might overwrite some of the defaults we just set. 797 */ 798 tcp_mss(tp, sc->sc_peer_mss); 799 800 /* 801 * If the SYN,ACK was retransmitted, reset cwnd to 1 segment. 802 */ 803 if (sc->sc_rxmits) 804 tp->snd_cwnd = tp->t_maxseg; 805 tcp_timer_activate(tp, TT_KEEP, tcp_keepinit); 806 807 INP_UNLOCK(inp); 808 809 tcpstat.tcps_accepts++; 810 return (so); 811 812 abort: 813 INP_UNLOCK(inp); 814 abort2: 815 if (so != NULL) 816 soabort(so); 817 return (NULL); 818 } 819 820 /* 821 * This function gets called when we receive an ACK for a 822 * socket in the LISTEN state. We look up the connection 823 * in the syncache, and if its there, we pull it out of 824 * the cache and turn it into a full-blown connection in 825 * the SYN-RECEIVED state. 826 */ 827 int 828 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 829 struct socket **lsop, struct mbuf *m) 830 { 831 struct syncache *sc; 832 struct syncache_head *sch; 833 struct syncache scs; 834 char *s; 835 836 /* 837 * Global TCP locks are held because we manipulate the PCB lists 838 * and create a new socket. 839 */ 840 INP_INFO_WLOCK_ASSERT(&tcbinfo); 841 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 842 ("%s: can handle only ACK", __func__)); 843 844 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 845 SCH_LOCK_ASSERT(sch); 846 if (sc == NULL) { 847 /* 848 * There is no syncache entry, so see if this ACK is 849 * a returning syncookie. To do this, first: 850 * A. See if this socket has had a syncache entry dropped in 851 * the past. We don't want to accept a bogus syncookie 852 * if we've never received a SYN. 853 * B. check that the syncookie is valid. If it is, then 854 * cobble up a fake syncache entry, and return. 855 */ 856 if (!tcp_syncookies) { 857 SCH_UNLOCK(sch); 858 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 859 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 860 "segment rejected (syncookies disabled)\n", 861 s, __func__); 862 goto failed; 863 } 864 bzero(&scs, sizeof(scs)); 865 sc = syncookie_lookup(inc, sch, &scs, to, th, *lsop); 866 SCH_UNLOCK(sch); 867 if (sc == NULL) { 868 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 869 log(LOG_DEBUG, "%s; %s: Segment failed " 870 "SYNCOOKIE authentication, segment rejected " 871 "(probably spoofed)\n", s, __func__); 872 goto failed; 873 } 874 } else { 875 /* Pull out the entry to unlock the bucket row. */ 876 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 877 sch->sch_length--; 878 tcp_syncache.cache_count--; 879 SCH_UNLOCK(sch); 880 } 881 882 /* 883 * Segment validation: 884 * ACK must match our initial sequence number + 1 (the SYN|ACK). 885 */ 886 if (th->th_ack != sc->sc_iss + 1) { 887 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 888 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 889 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 890 goto failed; 891 } 892 /* 893 * The SEQ must match the received initial receive sequence 894 * number + 1 (the SYN) because we didn't ACK any data that 895 * may have come with the SYN. 896 */ 897 if (th->th_seq != sc->sc_irs + 1) { 898 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 899 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 900 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 901 goto failed; 902 } 903 #if 0 904 /* 905 * If timestamps were present in the SYN and we accepted 906 * them in our SYN|ACK we require them to be present from 907 * now on. And vice versa. 908 * 909 * Unfortunately, during testing of 7.0 some users found 910 * network devices that violate this constraint, so it must 911 * be disabled. 912 */ 913 if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) { 914 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 915 log(LOG_DEBUG, "%s; %s: Timestamp missing, " 916 "segment rejected\n", s, __func__); 917 goto failed; 918 } 919 #endif 920 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) { 921 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 922 log(LOG_DEBUG, "%s; %s: Timestamp not expected, " 923 "segment rejected\n", s, __func__); 924 goto failed; 925 } 926 /* 927 * If timestamps were negotiated the reflected timestamp 928 * must be equal to what we actually sent in the SYN|ACK. 929 */ 930 if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts) { 931 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 932 log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, " 933 "segment rejected\n", 934 s, __func__, to->to_tsecr, sc->sc_ts); 935 goto failed; 936 } 937 938 *lsop = syncache_socket(sc, *lsop, m); 939 940 if (*lsop == NULL) 941 tcpstat.tcps_sc_aborted++; 942 else 943 tcpstat.tcps_sc_completed++; 944 945 if (sc != &scs) 946 syncache_free(sc); 947 return (1); 948 failed: 949 if (sc != NULL && sc != &scs) 950 syncache_free(sc); 951 if (s != NULL) 952 free(s, M_TCPLOG); 953 *lsop = NULL; 954 return (0); 955 } 956 957 /* 958 * Given a LISTEN socket and an inbound SYN request, add 959 * this to the syn cache, and send back a segment: 960 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 961 * to the source. 962 * 963 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 964 * Doing so would require that we hold onto the data and deliver it 965 * to the application. However, if we are the target of a SYN-flood 966 * DoS attack, an attacker could send data which would eventually 967 * consume all available buffer space if it were ACKed. By not ACKing 968 * the data, we avoid this DoS scenario. 969 */ 970 void 971 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 972 struct inpcb *inp, struct socket **lsop, struct mbuf *m) 973 { 974 struct tcpcb *tp; 975 struct socket *so; 976 struct syncache *sc = NULL; 977 struct syncache_head *sch; 978 struct mbuf *ipopts = NULL; 979 u_int32_t flowtmp; 980 int win, sb_hiwat, ip_ttl, ip_tos, noopt; 981 char *s; 982 #ifdef INET6 983 int autoflowlabel = 0; 984 #endif 985 #ifdef MAC 986 struct label *maclabel; 987 #endif 988 struct syncache scs; 989 990 INP_INFO_WLOCK_ASSERT(&tcbinfo); 991 INP_LOCK_ASSERT(inp); /* listen socket */ 992 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 993 ("%s: unexpected tcp flags", __func__)); 994 995 /* 996 * Combine all so/tp operations very early to drop the INP lock as 997 * soon as possible. 998 */ 999 so = *lsop; 1000 tp = sototcpcb(so); 1001 1002 #ifdef INET6 1003 if (inc->inc_isipv6 && 1004 (inp->in6p_flags & IN6P_AUTOFLOWLABEL)) 1005 autoflowlabel = 1; 1006 #endif 1007 ip_ttl = inp->inp_ip_ttl; 1008 ip_tos = inp->inp_ip_tos; 1009 win = sbspace(&so->so_rcv); 1010 sb_hiwat = so->so_rcv.sb_hiwat; 1011 noopt = (tp->t_flags & TF_NOOPT); 1012 1013 so = NULL; 1014 tp = NULL; 1015 1016 #ifdef MAC 1017 if (mac_init_syncache(&maclabel) != 0) { 1018 INP_UNLOCK(inp); 1019 INP_INFO_WUNLOCK(&tcbinfo); 1020 goto done; 1021 } else 1022 mac_init_syncache_from_inpcb(maclabel, inp); 1023 #endif 1024 INP_UNLOCK(inp); 1025 INP_INFO_WUNLOCK(&tcbinfo); 1026 1027 /* 1028 * Remember the IP options, if any. 1029 */ 1030 #ifdef INET6 1031 if (!inc->inc_isipv6) 1032 #endif 1033 ipopts = ip_srcroute(m); 1034 1035 /* 1036 * See if we already have an entry for this connection. 1037 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1038 * 1039 * XXX: should the syncache be re-initialized with the contents 1040 * of the new SYN here (which may have different options?) 1041 * 1042 * XXX: We do not check the sequence number to see if this is a 1043 * real retransmit or a new connection attempt. The question is 1044 * how to handle such a case; either ignore it as spoofed, or 1045 * drop the current entry and create a new one? 1046 */ 1047 sc = syncache_lookup(inc, &sch); /* returns locked entry */ 1048 SCH_LOCK_ASSERT(sch); 1049 if (sc != NULL) { 1050 tcpstat.tcps_sc_dupsyn++; 1051 if (ipopts) { 1052 /* 1053 * If we were remembering a previous source route, 1054 * forget it and use the new one we've been given. 1055 */ 1056 if (sc->sc_ipopts) 1057 (void) m_free(sc->sc_ipopts); 1058 sc->sc_ipopts = ipopts; 1059 } 1060 /* 1061 * Update timestamp if present. 1062 */ 1063 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1064 sc->sc_tsreflect = to->to_tsval; 1065 else 1066 sc->sc_flags &= ~SCF_TIMESTAMP; 1067 #ifdef MAC 1068 /* 1069 * Since we have already unconditionally allocated label 1070 * storage, free it up. The syncache entry will already 1071 * have an initialized label we can use. 1072 */ 1073 mac_destroy_syncache(&maclabel); 1074 KASSERT(sc->sc_label != NULL, 1075 ("%s: label not initialized", __func__)); 1076 #endif 1077 /* Retransmit SYN|ACK and reset retransmit count. */ 1078 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1079 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1080 "resetting timer and retransmitting SYN|ACK\n", 1081 s, __func__); 1082 free(s, M_TCPLOG); 1083 } 1084 if (syncache_respond(sc) == 0) { 1085 sc->sc_rxmits = 0; 1086 syncache_timeout(sc, sch, 1); 1087 tcpstat.tcps_sndacks++; 1088 tcpstat.tcps_sndtotal++; 1089 } 1090 SCH_UNLOCK(sch); 1091 goto done; 1092 } 1093 1094 sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT | M_ZERO); 1095 if (sc == NULL) { 1096 /* 1097 * The zone allocator couldn't provide more entries. 1098 * Treat this as if the cache was full; drop the oldest 1099 * entry and insert the new one. 1100 */ 1101 tcpstat.tcps_sc_zonefail++; 1102 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) 1103 syncache_drop(sc, sch); 1104 sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT | M_ZERO); 1105 if (sc == NULL) { 1106 if (tcp_syncookies) { 1107 bzero(&scs, sizeof(scs)); 1108 sc = &scs; 1109 } else { 1110 SCH_UNLOCK(sch); 1111 if (ipopts) 1112 (void) m_free(ipopts); 1113 goto done; 1114 } 1115 } 1116 } 1117 1118 /* 1119 * Fill in the syncache values. 1120 */ 1121 #ifdef MAC 1122 sc->sc_label = maclabel; 1123 #endif 1124 sc->sc_ipopts = ipopts; 1125 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1126 #ifdef INET6 1127 if (!inc->inc_isipv6) 1128 #endif 1129 { 1130 sc->sc_ip_tos = ip_tos; 1131 sc->sc_ip_ttl = ip_ttl; 1132 } 1133 1134 sc->sc_irs = th->th_seq; 1135 sc->sc_iss = arc4random(); 1136 sc->sc_flags = 0; 1137 sc->sc_flowlabel = 0; 1138 1139 /* 1140 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1141 * win was derived from socket earlier in the function. 1142 */ 1143 win = imax(win, 0); 1144 win = imin(win, TCP_MAXWIN); 1145 sc->sc_wnd = win; 1146 1147 if (tcp_do_rfc1323) { 1148 /* 1149 * A timestamp received in a SYN makes 1150 * it ok to send timestamp requests and replies. 1151 */ 1152 if (to->to_flags & TOF_TS) { 1153 sc->sc_tsreflect = to->to_tsval; 1154 sc->sc_ts = ticks; 1155 sc->sc_flags |= SCF_TIMESTAMP; 1156 } 1157 if (to->to_flags & TOF_SCALE) { 1158 int wscale = 0; 1159 1160 /* 1161 * Pick the smallest possible scaling factor that 1162 * will still allow us to scale up to sb_max, aka 1163 * kern.ipc.maxsockbuf. 1164 * 1165 * We do this because there are broken firewalls that 1166 * will corrupt the window scale option, leading to 1167 * the other endpoint believing that our advertised 1168 * window is unscaled. At scale factors larger than 1169 * 5 the unscaled window will drop below 1500 bytes, 1170 * leading to serious problems when traversing these 1171 * broken firewalls. 1172 * 1173 * With the default maxsockbuf of 256K, a scale factor 1174 * of 3 will be chosen by this algorithm. Those who 1175 * choose a larger maxsockbuf should watch out 1176 * for the compatiblity problems mentioned above. 1177 * 1178 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1179 * or <SYN,ACK>) segment itself is never scaled. 1180 */ 1181 while (wscale < TCP_MAX_WINSHIFT && 1182 (TCP_MAXWIN << wscale) < sb_max) 1183 wscale++; 1184 sc->sc_requested_r_scale = wscale; 1185 sc->sc_requested_s_scale = to->to_wscale; 1186 sc->sc_flags |= SCF_WINSCALE; 1187 } 1188 } 1189 #ifdef TCP_SIGNATURE 1190 /* 1191 * If listening socket requested TCP digests, and received SYN 1192 * contains the option, flag this in the syncache so that 1193 * syncache_respond() will do the right thing with the SYN+ACK. 1194 * XXX: Currently we always record the option by default and will 1195 * attempt to use it in syncache_respond(). 1196 */ 1197 if (to->to_flags & TOF_SIGNATURE) 1198 sc->sc_flags |= SCF_SIGNATURE; 1199 #endif 1200 if (to->to_flags & TOF_SACKPERM) 1201 sc->sc_flags |= SCF_SACK; 1202 if (to->to_flags & TOF_MSS) 1203 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1204 if (noopt) 1205 sc->sc_flags |= SCF_NOOPT; 1206 1207 if (tcp_syncookies) { 1208 syncookie_generate(sch, sc, &flowtmp); 1209 #ifdef INET6 1210 if (autoflowlabel) 1211 sc->sc_flowlabel = flowtmp; 1212 #endif 1213 } else { 1214 #ifdef INET6 1215 if (autoflowlabel) 1216 sc->sc_flowlabel = 1217 (htonl(ip6_randomflowlabel()) & IPV6_FLOWLABEL_MASK); 1218 #endif 1219 } 1220 SCH_UNLOCK(sch); 1221 1222 /* 1223 * Do a standard 3-way handshake. 1224 */ 1225 if (syncache_respond(sc) == 0) { 1226 if (tcp_syncookies && tcp_syncookiesonly && sc != &scs) 1227 syncache_free(sc); 1228 else if (sc != &scs) 1229 syncache_insert(sc, sch); /* locks and unlocks sch */ 1230 tcpstat.tcps_sndacks++; 1231 tcpstat.tcps_sndtotal++; 1232 } else { 1233 if (sc != &scs) 1234 syncache_free(sc); 1235 tcpstat.tcps_sc_dropped++; 1236 } 1237 1238 done: 1239 #ifdef MAC 1240 if (sc == &scs) 1241 mac_destroy_syncache(&maclabel); 1242 #endif 1243 *lsop = NULL; 1244 m_freem(m); 1245 return; 1246 } 1247 1248 static int 1249 syncache_respond(struct syncache *sc) 1250 { 1251 struct ip *ip = NULL; 1252 struct mbuf *m; 1253 struct tcphdr *th; 1254 int optlen, error; 1255 u_int16_t hlen, tlen, mssopt; 1256 struct tcpopt to; 1257 #ifdef INET6 1258 struct ip6_hdr *ip6 = NULL; 1259 #endif 1260 1261 hlen = 1262 #ifdef INET6 1263 (sc->sc_inc.inc_isipv6) ? sizeof(struct ip6_hdr) : 1264 #endif 1265 sizeof(struct ip); 1266 tlen = hlen + sizeof(struct tcphdr); 1267 1268 /* Determine MSS we advertize to other end of connection. */ 1269 mssopt = tcp_mssopt(&sc->sc_inc); 1270 if (sc->sc_peer_mss) 1271 mssopt = max( min(sc->sc_peer_mss, mssopt), tcp_minmss); 1272 1273 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1274 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1275 ("syncache: mbuf too small")); 1276 1277 /* Create the IP+TCP header from scratch. */ 1278 m = m_gethdr(M_DONTWAIT, MT_DATA); 1279 if (m == NULL) 1280 return (ENOBUFS); 1281 #ifdef MAC 1282 mac_create_mbuf_from_syncache(sc->sc_label, m); 1283 #endif 1284 m->m_data += max_linkhdr; 1285 m->m_len = tlen; 1286 m->m_pkthdr.len = tlen; 1287 m->m_pkthdr.rcvif = NULL; 1288 1289 #ifdef INET6 1290 if (sc->sc_inc.inc_isipv6) { 1291 ip6 = mtod(m, struct ip6_hdr *); 1292 ip6->ip6_vfc = IPV6_VERSION; 1293 ip6->ip6_nxt = IPPROTO_TCP; 1294 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1295 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1296 ip6->ip6_plen = htons(tlen - hlen); 1297 /* ip6_hlim is set after checksum */ 1298 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK; 1299 ip6->ip6_flow |= sc->sc_flowlabel; 1300 1301 th = (struct tcphdr *)(ip6 + 1); 1302 } else 1303 #endif 1304 { 1305 ip = mtod(m, struct ip *); 1306 ip->ip_v = IPVERSION; 1307 ip->ip_hl = sizeof(struct ip) >> 2; 1308 ip->ip_len = tlen; 1309 ip->ip_id = 0; 1310 ip->ip_off = 0; 1311 ip->ip_sum = 0; 1312 ip->ip_p = IPPROTO_TCP; 1313 ip->ip_src = sc->sc_inc.inc_laddr; 1314 ip->ip_dst = sc->sc_inc.inc_faddr; 1315 ip->ip_ttl = sc->sc_ip_ttl; 1316 ip->ip_tos = sc->sc_ip_tos; 1317 1318 /* 1319 * See if we should do MTU discovery. Route lookups are 1320 * expensive, so we will only unset the DF bit if: 1321 * 1322 * 1) path_mtu_discovery is disabled 1323 * 2) the SCF_UNREACH flag has been set 1324 */ 1325 if (path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1326 ip->ip_off |= IP_DF; 1327 1328 th = (struct tcphdr *)(ip + 1); 1329 } 1330 th->th_sport = sc->sc_inc.inc_lport; 1331 th->th_dport = sc->sc_inc.inc_fport; 1332 1333 th->th_seq = htonl(sc->sc_iss); 1334 th->th_ack = htonl(sc->sc_irs + 1); 1335 th->th_off = sizeof(struct tcphdr) >> 2; 1336 th->th_x2 = 0; 1337 th->th_flags = TH_SYN|TH_ACK; 1338 th->th_win = htons(sc->sc_wnd); 1339 th->th_urp = 0; 1340 1341 /* Tack on the TCP options. */ 1342 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1343 to.to_flags = 0; 1344 1345 to.to_mss = mssopt; 1346 to.to_flags = TOF_MSS; 1347 if (sc->sc_flags & SCF_WINSCALE) { 1348 to.to_wscale = sc->sc_requested_r_scale; 1349 to.to_flags |= TOF_SCALE; 1350 } 1351 if (sc->sc_flags & SCF_TIMESTAMP) { 1352 /* Virgin timestamp or TCP cookie enhanced one. */ 1353 to.to_tsval = sc->sc_ts; 1354 to.to_tsecr = sc->sc_tsreflect; 1355 to.to_flags |= TOF_TS; 1356 } 1357 if (sc->sc_flags & SCF_SACK) 1358 to.to_flags |= TOF_SACKPERM; 1359 #ifdef TCP_SIGNATURE 1360 if (sc->sc_flags & SCF_SIGNATURE) 1361 to.to_flags |= TOF_SIGNATURE; 1362 #endif 1363 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1364 1365 /* Adjust headers by option size. */ 1366 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1367 m->m_len += optlen; 1368 m->m_pkthdr.len += optlen; 1369 1370 #ifdef TCP_SIGNATURE 1371 if (sc->sc_flags & SCF_SIGNATURE) 1372 tcp_signature_compute(m, sizeof(struct ip), 0, optlen, 1373 to.to_signature, IPSEC_DIR_OUTBOUND); 1374 #endif 1375 #ifdef INET6 1376 if (sc->sc_inc.inc_isipv6) 1377 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1378 else 1379 #endif 1380 ip->ip_len += optlen; 1381 } else 1382 optlen = 0; 1383 1384 #ifdef INET6 1385 if (sc->sc_inc.inc_isipv6) { 1386 th->th_sum = 0; 1387 th->th_sum = in6_cksum(m, IPPROTO_TCP, hlen, 1388 tlen + optlen - hlen); 1389 ip6->ip6_hlim = in6_selecthlim(NULL, NULL); 1390 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 1391 } else 1392 #endif 1393 { 1394 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1395 htons(tlen + optlen - hlen + IPPROTO_TCP)); 1396 m->m_pkthdr.csum_flags = CSUM_TCP; 1397 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1398 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 1399 } 1400 return (error); 1401 } 1402 1403 /* 1404 * The purpose of SYN cookies is to avoid keeping track of all SYN's we 1405 * receive and to be able to handle SYN floods from bogus source addresses 1406 * (where we will never receive any reply). SYN floods try to exhaust all 1407 * our memory and available slots in the SYN cache table to cause a denial 1408 * of service to legitimate users of the local host. 1409 * 1410 * The idea of SYN cookies is to encode and include all necessary information 1411 * about the connection setup state within the SYN-ACK we send back and thus 1412 * to get along without keeping any local state until the ACK to the SYN-ACK 1413 * arrives (if ever). Everything we need to know should be available from 1414 * the information we encoded in the SYN-ACK. 1415 * 1416 * More information about the theory behind SYN cookies and its first 1417 * discussion and specification can be found at: 1418 * http://cr.yp.to/syncookies.html (overview) 1419 * http://cr.yp.to/syncookies/archive (gory details) 1420 * 1421 * This implementation extends the orginal idea and first implementation 1422 * of FreeBSD by using not only the initial sequence number field to store 1423 * information but also the timestamp field if present. This way we can 1424 * keep track of the entire state we need to know to recreate the session in 1425 * its original form. Almost all TCP speakers implement RFC1323 timestamps 1426 * these days. For those that do not we still have to live with the known 1427 * shortcomings of the ISN only SYN cookies. 1428 * 1429 * Cookie layers: 1430 * 1431 * Initial sequence number we send: 1432 * 31|................................|0 1433 * DDDDDDDDDDDDDDDDDDDDDDDDDMMMRRRP 1434 * D = MD5 Digest (first dword) 1435 * M = MSS index 1436 * R = Rotation of secret 1437 * P = Odd or Even secret 1438 * 1439 * The MD5 Digest is computed with over following parameters: 1440 * a) randomly rotated secret 1441 * b) struct in_conninfo containing the remote/local ip/port (IPv4&IPv6) 1442 * c) the received initial sequence number from remote host 1443 * d) the rotation offset and odd/even bit 1444 * 1445 * Timestamp we send: 1446 * 31|................................|0 1447 * DDDDDDDDDDDDDDDDDDDDDDSSSSRRRRA5 1448 * D = MD5 Digest (third dword) (only as filler) 1449 * S = Requested send window scale 1450 * R = Requested receive window scale 1451 * A = SACK allowed 1452 * 5 = TCP-MD5 enabled (not implemented yet) 1453 * XORed with MD5 Digest (forth dword) 1454 * 1455 * The timestamp isn't cryptographically secure and doesn't need to be. 1456 * The double use of the MD5 digest dwords ties it to a specific remote/ 1457 * local host/port, remote initial sequence number and our local time 1458 * limited secret. A received timestamp is reverted (XORed) and then 1459 * the contained MD5 dword is compared to the computed one to ensure the 1460 * timestamp belongs to the SYN-ACK we sent. The other parameters may 1461 * have been tampered with but this isn't different from supplying bogus 1462 * values in the SYN in the first place. 1463 * 1464 * Some problems with SYN cookies remain however: 1465 * Consider the problem of a recreated (and retransmitted) cookie. If the 1466 * original SYN was accepted, the connection is established. The second 1467 * SYN is inflight, and if it arrives with an ISN that falls within the 1468 * receive window, the connection is killed. 1469 * 1470 * Notes: 1471 * A heuristic to determine when to accept syn cookies is not necessary. 1472 * An ACK flood would cause the syncookie verification to be attempted, 1473 * but a SYN flood causes syncookies to be generated. Both are of equal 1474 * cost, so there's no point in trying to optimize the ACK flood case. 1475 * Also, if you don't process certain ACKs for some reason, then all someone 1476 * would have to do is launch a SYN and ACK flood at the same time, which 1477 * would stop cookie verification and defeat the entire purpose of syncookies. 1478 */ 1479 static int tcp_sc_msstab[] = { 0, 256, 468, 536, 996, 1452, 1460, 8960 }; 1480 1481 static void 1482 syncookie_generate(struct syncache_head *sch, struct syncache *sc, 1483 u_int32_t *flowlabel) 1484 { 1485 MD5_CTX ctx; 1486 u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)]; 1487 u_int32_t data; 1488 u_int32_t *secbits; 1489 u_int off, pmss, mss; 1490 int i; 1491 1492 SCH_LOCK_ASSERT(sch); 1493 1494 /* Which of the two secrets to use. */ 1495 secbits = sch->sch_oddeven ? 1496 sch->sch_secbits_odd : sch->sch_secbits_even; 1497 1498 /* Reseed secret if too old. */ 1499 if (sch->sch_reseed < time_uptime) { 1500 sch->sch_oddeven = sch->sch_oddeven ? 0 : 1; /* toggle */ 1501 secbits = sch->sch_oddeven ? 1502 sch->sch_secbits_odd : sch->sch_secbits_even; 1503 for (i = 0; i < SYNCOOKIE_SECRET_SIZE; i++) 1504 secbits[i] = arc4random(); 1505 sch->sch_reseed = time_uptime + SYNCOOKIE_LIFETIME; 1506 } 1507 1508 /* Secret rotation offset. */ 1509 off = sc->sc_iss & 0x7; /* iss was randomized before */ 1510 1511 /* Maximum segment size calculation. */ 1512 pmss = max( min(sc->sc_peer_mss, tcp_mssopt(&sc->sc_inc)), tcp_minmss); 1513 for (mss = sizeof(tcp_sc_msstab) / sizeof(int) - 1; mss > 0; mss--) 1514 if (tcp_sc_msstab[mss] <= pmss) 1515 break; 1516 1517 /* Fold parameters and MD5 digest into the ISN we will send. */ 1518 data = sch->sch_oddeven;/* odd or even secret, 1 bit */ 1519 data |= off << 1; /* secret offset, derived from iss, 3 bits */ 1520 data |= mss << 4; /* mss, 3 bits */ 1521 1522 MD5Init(&ctx); 1523 MD5Update(&ctx, ((u_int8_t *)secbits) + off, 1524 SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off); 1525 MD5Update(&ctx, secbits, off); 1526 MD5Update(&ctx, &sc->sc_inc, sizeof(sc->sc_inc)); 1527 MD5Update(&ctx, &sc->sc_irs, sizeof(sc->sc_irs)); 1528 MD5Update(&ctx, &data, sizeof(data)); 1529 MD5Final((u_int8_t *)&md5_buffer, &ctx); 1530 1531 data |= (md5_buffer[0] << 7); 1532 sc->sc_iss = data; 1533 1534 #ifdef INET6 1535 *flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK; 1536 #endif 1537 1538 /* Additional parameters are stored in the timestamp if present. */ 1539 if (sc->sc_flags & SCF_TIMESTAMP) { 1540 data = ((sc->sc_flags & SCF_SIGNATURE) ? 1 : 0); /* TCP-MD5, 1 bit */ 1541 data |= ((sc->sc_flags & SCF_SACK) ? 1 : 0) << 1; /* SACK, 1 bit */ 1542 data |= sc->sc_requested_s_scale << 2; /* SWIN scale, 4 bits */ 1543 data |= sc->sc_requested_r_scale << 6; /* RWIN scale, 4 bits */ 1544 data |= md5_buffer[2] << 10; /* more digest bits */ 1545 data ^= md5_buffer[3]; 1546 sc->sc_ts = data; 1547 sc->sc_tsoff = data - ticks; /* after XOR */ 1548 } 1549 1550 tcpstat.tcps_sc_sendcookie++; 1551 return; 1552 } 1553 1554 static struct syncache * 1555 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 1556 struct syncache *sc, struct tcpopt *to, struct tcphdr *th, 1557 struct socket *so) 1558 { 1559 MD5_CTX ctx; 1560 u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)]; 1561 u_int32_t data = 0; 1562 u_int32_t *secbits; 1563 tcp_seq ack, seq; 1564 int off, mss, wnd, flags; 1565 1566 SCH_LOCK_ASSERT(sch); 1567 1568 /* 1569 * Pull information out of SYN-ACK/ACK and 1570 * revert sequence number advances. 1571 */ 1572 ack = th->th_ack - 1; 1573 seq = th->th_seq - 1; 1574 off = (ack >> 1) & 0x7; 1575 mss = (ack >> 4) & 0x7; 1576 flags = ack & 0x7f; 1577 1578 /* Which of the two secrets to use. */ 1579 secbits = (flags & 0x1) ? sch->sch_secbits_odd : sch->sch_secbits_even; 1580 1581 /* 1582 * The secret wasn't updated for the lifetime of a syncookie, 1583 * so this SYN-ACK/ACK is either too old (replay) or totally bogus. 1584 */ 1585 if (sch->sch_reseed < time_uptime) { 1586 return (NULL); 1587 } 1588 1589 /* Recompute the digest so we can compare it. */ 1590 MD5Init(&ctx); 1591 MD5Update(&ctx, ((u_int8_t *)secbits) + off, 1592 SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off); 1593 MD5Update(&ctx, secbits, off); 1594 MD5Update(&ctx, inc, sizeof(*inc)); 1595 MD5Update(&ctx, &seq, sizeof(seq)); 1596 MD5Update(&ctx, &flags, sizeof(flags)); 1597 MD5Final((u_int8_t *)&md5_buffer, &ctx); 1598 1599 /* Does the digest part of or ACK'ed ISS match? */ 1600 if ((ack & (~0x7f)) != (md5_buffer[0] << 7)) 1601 return (NULL); 1602 1603 /* Does the digest part of our reflected timestamp match? */ 1604 if (to->to_flags & TOF_TS) { 1605 data = md5_buffer[3] ^ to->to_tsecr; 1606 if ((data & (~0x3ff)) != (md5_buffer[2] << 10)) 1607 return (NULL); 1608 } 1609 1610 /* Fill in the syncache values. */ 1611 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1612 sc->sc_ipopts = NULL; 1613 1614 sc->sc_irs = seq; 1615 sc->sc_iss = ack; 1616 1617 #ifdef INET6 1618 if (inc->inc_isipv6) { 1619 if (sotoinpcb(so)->in6p_flags & IN6P_AUTOFLOWLABEL) 1620 sc->sc_flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK; 1621 } else 1622 #endif 1623 { 1624 sc->sc_ip_ttl = sotoinpcb(so)->inp_ip_ttl; 1625 sc->sc_ip_tos = sotoinpcb(so)->inp_ip_tos; 1626 } 1627 1628 /* Additional parameters that were encoded in the timestamp. */ 1629 if (data) { 1630 sc->sc_flags |= SCF_TIMESTAMP; 1631 sc->sc_tsreflect = to->to_tsval; 1632 sc->sc_ts = to->to_tsecr; 1633 sc->sc_tsoff = to->to_tsecr - ticks; 1634 sc->sc_flags |= (data & 0x1) ? SCF_SIGNATURE : 0; 1635 sc->sc_flags |= ((data >> 1) & 0x1) ? SCF_SACK : 0; 1636 sc->sc_requested_s_scale = min((data >> 2) & 0xf, 1637 TCP_MAX_WINSHIFT); 1638 sc->sc_requested_r_scale = min((data >> 6) & 0xf, 1639 TCP_MAX_WINSHIFT); 1640 if (sc->sc_requested_s_scale || sc->sc_requested_r_scale) 1641 sc->sc_flags |= SCF_WINSCALE; 1642 } else 1643 sc->sc_flags |= SCF_NOOPT; 1644 1645 wnd = sbspace(&so->so_rcv); 1646 wnd = imax(wnd, 0); 1647 wnd = imin(wnd, TCP_MAXWIN); 1648 sc->sc_wnd = wnd; 1649 1650 sc->sc_rxmits = 0; 1651 sc->sc_peer_mss = tcp_sc_msstab[mss]; 1652 1653 tcpstat.tcps_sc_recvcookie++; 1654 return (sc); 1655 } 1656 1657 /* 1658 * Returns the current number of syncache entries. This number 1659 * will probably change before you get around to calling 1660 * syncache_pcblist. 1661 */ 1662 1663 int 1664 syncache_pcbcount(void) 1665 { 1666 struct syncache_head *sch; 1667 int count, i; 1668 1669 for (count = 0, i = 0; i < tcp_syncache.hashsize; i++) { 1670 /* No need to lock for a read. */ 1671 sch = &tcp_syncache.hashbase[i]; 1672 count += sch->sch_length; 1673 } 1674 return count; 1675 } 1676 1677 /* 1678 * Exports the syncache entries to userland so that netstat can display 1679 * them alongside the other sockets. This function is intended to be 1680 * called only from tcp_pcblist. 1681 * 1682 * Due to concurrency on an active system, the number of pcbs exported 1683 * may have no relation to max_pcbs. max_pcbs merely indicates the 1684 * amount of space the caller allocated for this function to use. 1685 */ 1686 int 1687 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported) 1688 { 1689 struct xtcpcb xt; 1690 struct syncache *sc; 1691 struct syncache_head *sch; 1692 int count, error, i; 1693 1694 for (count = 0, error = 0, i = 0; i < tcp_syncache.hashsize; i++) { 1695 sch = &tcp_syncache.hashbase[i]; 1696 SCH_LOCK(sch); 1697 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 1698 if (count >= max_pcbs) { 1699 SCH_UNLOCK(sch); 1700 goto exit; 1701 } 1702 bzero(&xt, sizeof(xt)); 1703 xt.xt_len = sizeof(xt); 1704 if (sc->sc_inc.inc_isipv6) 1705 xt.xt_inp.inp_vflag = INP_IPV6; 1706 else 1707 xt.xt_inp.inp_vflag = INP_IPV4; 1708 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo)); 1709 xt.xt_tp.t_inpcb = &xt.xt_inp; 1710 xt.xt_tp.t_state = TCPS_SYN_RECEIVED; 1711 xt.xt_socket.xso_protocol = IPPROTO_TCP; 1712 xt.xt_socket.xso_len = sizeof (struct xsocket); 1713 xt.xt_socket.so_type = SOCK_STREAM; 1714 xt.xt_socket.so_state = SS_ISCONNECTING; 1715 error = SYSCTL_OUT(req, &xt, sizeof xt); 1716 if (error) { 1717 SCH_UNLOCK(sch); 1718 goto exit; 1719 } 1720 count++; 1721 } 1722 SCH_UNLOCK(sch); 1723 } 1724 exit: 1725 *pcbs_exported = count; 1726 return error; 1727 } 1728
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