1 /*- 2 * Copyright (c) 2001 McAfee, Inc. 3 * Copyright (c) 2006,2013 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. [2001 McAfee, Inc.] 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_pcbgroup.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/proc.h> /* for proc0 declaration */ 51 #include <sys/random.h> 52 #include <sys/socket.h> 53 #include <sys/socketvar.h> 54 #include <sys/syslog.h> 55 #include <sys/ucred.h> 56 57 #include <sys/md5.h> 58 #include <crypto/siphash/siphash.h> 59 60 #include <vm/uma.h> 61 62 #include <net/if.h> 63 #include <net/if_var.h> 64 #include <net/route.h> 65 #include <net/vnet.h> 66 67 #include <netinet/in.h> 68 #include <netinet/in_systm.h> 69 #include <netinet/ip.h> 70 #include <netinet/in_var.h> 71 #include <netinet/in_pcb.h> 72 #include <netinet/ip_var.h> 73 #include <netinet/ip_options.h> 74 #ifdef INET6 75 #include <netinet/ip6.h> 76 #include <netinet/icmp6.h> 77 #include <netinet6/nd6.h> 78 #include <netinet6/ip6_var.h> 79 #include <netinet6/in6_pcb.h> 80 #endif 81 #include <netinet/tcp.h> 82 #include <netinet/tcp_fsm.h> 83 #include <netinet/tcp_seq.h> 84 #include <netinet/tcp_timer.h> 85 #include <netinet/tcp_var.h> 86 #include <netinet/tcp_syncache.h> 87 #ifdef INET6 88 #include <netinet6/tcp6_var.h> 89 #endif 90 #ifdef TCP_OFFLOAD 91 #include <netinet/toecore.h> 92 #endif 93 94 #ifdef IPSEC 95 #include <netipsec/ipsec.h> 96 #ifdef INET6 97 #include <netipsec/ipsec6.h> 98 #endif 99 #include <netipsec/key.h> 100 #endif /*IPSEC*/ 101 102 #include <machine/in_cksum.h> 103 104 #include <security/mac/mac_framework.h> 105 106 static VNET_DEFINE(int, tcp_syncookies) = 1; 107 #define V_tcp_syncookies VNET(tcp_syncookies) 108 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW, 109 &VNET_NAME(tcp_syncookies), 0, 110 "Use TCP SYN cookies if the syncache overflows"); 111 112 static VNET_DEFINE(int, tcp_syncookiesonly) = 0; 113 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly) 114 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_RW, 115 &VNET_NAME(tcp_syncookiesonly), 0, 116 "Use only TCP SYN cookies"); 117 118 #ifdef TCP_OFFLOAD 119 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL) 120 #endif 121 122 static void syncache_drop(struct syncache *, struct syncache_head *); 123 static void syncache_free(struct syncache *); 124 static void syncache_insert(struct syncache *, struct syncache_head *); 125 struct syncache *syncache_lookup(struct in_conninfo *, struct syncache_head **); 126 static int syncache_respond(struct syncache *); 127 static struct socket *syncache_socket(struct syncache *, struct socket *, 128 struct mbuf *m); 129 static int syncache_sysctl_count(SYSCTL_HANDLER_ARGS); 130 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 131 int docallout); 132 static void syncache_timer(void *); 133 134 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t, 135 uint8_t *, uintptr_t); 136 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *); 137 static struct syncache 138 *syncookie_lookup(struct in_conninfo *, struct syncache_head *, 139 struct syncache *, struct tcphdr *, struct tcpopt *, 140 struct socket *); 141 static void syncookie_reseed(void *); 142 #ifdef INVARIANTS 143 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 144 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 145 struct socket *lso); 146 #endif 147 148 /* 149 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 150 * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds, 151 * the odds are that the user has given up attempting to connect by then. 152 */ 153 #define SYNCACHE_MAXREXMTS 3 154 155 /* Arbitrary values */ 156 #define TCP_SYNCACHE_HASHSIZE 512 157 #define TCP_SYNCACHE_BUCKETLIMIT 30 158 159 static VNET_DEFINE(struct tcp_syncache, tcp_syncache); 160 #define V_tcp_syncache VNET(tcp_syncache) 161 162 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, 163 "TCP SYN cache"); 164 165 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RDTUN, 166 &VNET_NAME(tcp_syncache.bucket_limit), 0, 167 "Per-bucket hash limit for syncache"); 168 169 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RDTUN, 170 &VNET_NAME(tcp_syncache.cache_limit), 0, 171 "Overall entry limit for syncache"); 172 173 SYSCTL_VNET_PROC(_net_inet_tcp_syncache, OID_AUTO, count, (CTLTYPE_UINT|CTLFLAG_RD), 174 NULL, 0, &syncache_sysctl_count, "IU", 175 "Current number of entries in syncache"); 176 177 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RDTUN, 178 &VNET_NAME(tcp_syncache.hashsize), 0, 179 "Size of TCP syncache hashtable"); 180 181 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW, 182 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 183 "Limit on SYN/ACK retransmissions"); 184 185 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 186 SYSCTL_VNET_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 187 CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 188 "Send reset on socket allocation failure"); 189 190 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 191 192 #define SYNCACHE_HASH(inc, mask) \ 193 ((V_tcp_syncache.hash_secret ^ \ 194 (inc)->inc_faddr.s_addr ^ \ 195 ((inc)->inc_faddr.s_addr >> 16) ^ \ 196 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 197 198 #define SYNCACHE_HASH6(inc, mask) \ 199 ((V_tcp_syncache.hash_secret ^ \ 200 (inc)->inc6_faddr.s6_addr32[0] ^ \ 201 (inc)->inc6_faddr.s6_addr32[3] ^ \ 202 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 203 204 #define ENDPTS_EQ(a, b) ( \ 205 (a)->ie_fport == (b)->ie_fport && \ 206 (a)->ie_lport == (b)->ie_lport && \ 207 (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr && \ 208 (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr \ 209 ) 210 211 #define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0) 212 213 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 214 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 215 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 216 217 /* 218 * Requires the syncache entry to be already removed from the bucket list. 219 */ 220 static void 221 syncache_free(struct syncache *sc) 222 { 223 224 if (sc->sc_ipopts) 225 (void) m_free(sc->sc_ipopts); 226 if (sc->sc_cred) 227 crfree(sc->sc_cred); 228 #ifdef MAC 229 mac_syncache_destroy(&sc->sc_label); 230 #endif 231 232 uma_zfree(V_tcp_syncache.zone, sc); 233 } 234 235 void 236 syncache_init(void) 237 { 238 int i; 239 240 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 241 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 242 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 243 V_tcp_syncache.hash_secret = arc4random(); 244 245 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 246 &V_tcp_syncache.hashsize); 247 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 248 &V_tcp_syncache.bucket_limit); 249 if (!powerof2(V_tcp_syncache.hashsize) || 250 V_tcp_syncache.hashsize == 0) { 251 printf("WARNING: syncache hash size is not a power of 2.\n"); 252 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 253 } 254 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 255 256 /* Set limits. */ 257 V_tcp_syncache.cache_limit = 258 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 259 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 260 &V_tcp_syncache.cache_limit); 261 262 /* Allocate the hash table. */ 263 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 264 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 265 266 #ifdef VIMAGE 267 V_tcp_syncache.vnet = curvnet; 268 #endif 269 270 /* Initialize the hash buckets. */ 271 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 272 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 273 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 274 NULL, MTX_DEF); 275 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 276 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 277 V_tcp_syncache.hashbase[i].sch_length = 0; 278 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 279 } 280 281 /* Create the syncache entry zone. */ 282 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 283 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 284 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 285 V_tcp_syncache.cache_limit); 286 287 /* Start the SYN cookie reseeder callout. */ 288 callout_init(&V_tcp_syncache.secret.reseed, 1); 289 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 290 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 291 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 292 syncookie_reseed, &V_tcp_syncache); 293 } 294 295 #ifdef VIMAGE 296 void 297 syncache_destroy(void) 298 { 299 struct syncache_head *sch; 300 struct syncache *sc, *nsc; 301 int i; 302 303 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 304 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 305 306 sch = &V_tcp_syncache.hashbase[i]; 307 callout_drain(&sch->sch_timer); 308 309 SCH_LOCK(sch); 310 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 311 syncache_drop(sc, sch); 312 SCH_UNLOCK(sch); 313 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 314 ("%s: sch->sch_bucket not empty", __func__)); 315 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 316 __func__, sch->sch_length)); 317 mtx_destroy(&sch->sch_mtx); 318 } 319 320 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 321 ("%s: cache_count not 0", __func__)); 322 323 /* Free the allocated global resources. */ 324 uma_zdestroy(V_tcp_syncache.zone); 325 free(V_tcp_syncache.hashbase, M_SYNCACHE); 326 327 callout_drain(&V_tcp_syncache.secret.reseed); 328 } 329 #endif 330 331 static int 332 syncache_sysctl_count(SYSCTL_HANDLER_ARGS) 333 { 334 int count; 335 336 count = uma_zone_get_cur(V_tcp_syncache.zone); 337 return (sysctl_handle_int(oidp, &count, 0, req)); 338 } 339 340 /* 341 * Inserts a syncache entry into the specified bucket row. 342 * Locks and unlocks the syncache_head autonomously. 343 */ 344 static void 345 syncache_insert(struct syncache *sc, struct syncache_head *sch) 346 { 347 struct syncache *sc2; 348 349 SCH_LOCK(sch); 350 351 /* 352 * Make sure that we don't overflow the per-bucket limit. 353 * If the bucket is full, toss the oldest element. 354 */ 355 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 356 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 357 ("sch->sch_length incorrect")); 358 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 359 syncache_drop(sc2, sch); 360 TCPSTAT_INC(tcps_sc_bucketoverflow); 361 } 362 363 /* Put it into the bucket. */ 364 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 365 sch->sch_length++; 366 367 #ifdef TCP_OFFLOAD 368 if (ADDED_BY_TOE(sc)) { 369 struct toedev *tod = sc->sc_tod; 370 371 tod->tod_syncache_added(tod, sc->sc_todctx); 372 } 373 #endif 374 375 /* Reinitialize the bucket row's timer. */ 376 if (sch->sch_length == 1) 377 sch->sch_nextc = ticks + INT_MAX; 378 syncache_timeout(sc, sch, 1); 379 380 SCH_UNLOCK(sch); 381 382 TCPSTAT_INC(tcps_sc_added); 383 } 384 385 /* 386 * Remove and free entry from syncache bucket row. 387 * Expects locked syncache head. 388 */ 389 static void 390 syncache_drop(struct syncache *sc, struct syncache_head *sch) 391 { 392 393 SCH_LOCK_ASSERT(sch); 394 395 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 396 sch->sch_length--; 397 398 #ifdef TCP_OFFLOAD 399 if (ADDED_BY_TOE(sc)) { 400 struct toedev *tod = sc->sc_tod; 401 402 tod->tod_syncache_removed(tod, sc->sc_todctx); 403 } 404 #endif 405 406 syncache_free(sc); 407 } 408 409 /* 410 * Engage/reengage time on bucket row. 411 */ 412 static void 413 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 414 { 415 sc->sc_rxttime = ticks + 416 TCPTV_RTOBASE * (tcp_syn_backoff[sc->sc_rxmits]); 417 sc->sc_rxmits++; 418 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 419 sch->sch_nextc = sc->sc_rxttime; 420 if (docallout) 421 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 422 syncache_timer, (void *)sch); 423 } 424 } 425 426 /* 427 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 428 * If we have retransmitted an entry the maximum number of times, expire it. 429 * One separate timer for each bucket row. 430 */ 431 static void 432 syncache_timer(void *xsch) 433 { 434 struct syncache_head *sch = (struct syncache_head *)xsch; 435 struct syncache *sc, *nsc; 436 int tick = ticks; 437 char *s; 438 439 CURVNET_SET(sch->sch_sc->vnet); 440 441 /* NB: syncache_head has already been locked by the callout. */ 442 SCH_LOCK_ASSERT(sch); 443 444 /* 445 * In the following cycle we may remove some entries and/or 446 * advance some timeouts, so re-initialize the bucket timer. 447 */ 448 sch->sch_nextc = tick + INT_MAX; 449 450 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 451 /* 452 * We do not check if the listen socket still exists 453 * and accept the case where the listen socket may be 454 * gone by the time we resend the SYN/ACK. We do 455 * not expect this to happens often. If it does, 456 * then the RST will be sent by the time the remote 457 * host does the SYN/ACK->ACK. 458 */ 459 if (TSTMP_GT(sc->sc_rxttime, tick)) { 460 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 461 sch->sch_nextc = sc->sc_rxttime; 462 continue; 463 } 464 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 465 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 466 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 467 "giving up and removing syncache entry\n", 468 s, __func__); 469 free(s, M_TCPLOG); 470 } 471 syncache_drop(sc, sch); 472 TCPSTAT_INC(tcps_sc_stale); 473 continue; 474 } 475 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 476 log(LOG_DEBUG, "%s; %s: Response timeout, " 477 "retransmitting (%u) SYN|ACK\n", 478 s, __func__, sc->sc_rxmits); 479 free(s, M_TCPLOG); 480 } 481 482 (void) syncache_respond(sc); 483 TCPSTAT_INC(tcps_sc_retransmitted); 484 syncache_timeout(sc, sch, 0); 485 } 486 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 487 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 488 syncache_timer, (void *)(sch)); 489 CURVNET_RESTORE(); 490 } 491 492 /* 493 * Find an entry in the syncache. 494 * Returns always with locked syncache_head plus a matching entry or NULL. 495 */ 496 struct syncache * 497 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 498 { 499 struct syncache *sc; 500 struct syncache_head *sch; 501 502 #ifdef INET6 503 if (inc->inc_flags & INC_ISIPV6) { 504 sch = &V_tcp_syncache.hashbase[ 505 SYNCACHE_HASH6(inc, V_tcp_syncache.hashmask)]; 506 *schp = sch; 507 508 SCH_LOCK(sch); 509 510 /* Circle through bucket row to find matching entry. */ 511 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 512 if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) 513 return (sc); 514 } 515 } else 516 #endif 517 { 518 sch = &V_tcp_syncache.hashbase[ 519 SYNCACHE_HASH(inc, V_tcp_syncache.hashmask)]; 520 *schp = sch; 521 522 SCH_LOCK(sch); 523 524 /* Circle through bucket row to find matching entry. */ 525 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 526 #ifdef INET6 527 if (sc->sc_inc.inc_flags & INC_ISIPV6) 528 continue; 529 #endif 530 if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) 531 return (sc); 532 } 533 } 534 SCH_LOCK_ASSERT(*schp); 535 return (NULL); /* always returns with locked sch */ 536 } 537 538 /* 539 * This function is called when we get a RST for a 540 * non-existent connection, so that we can see if the 541 * connection is in the syn cache. If it is, zap it. 542 */ 543 void 544 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th) 545 { 546 struct syncache *sc; 547 struct syncache_head *sch; 548 char *s = NULL; 549 550 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 551 SCH_LOCK_ASSERT(sch); 552 553 /* 554 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags. 555 * See RFC 793 page 65, section SEGMENT ARRIVES. 556 */ 557 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) { 558 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 559 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or " 560 "FIN flag set, segment ignored\n", s, __func__); 561 TCPSTAT_INC(tcps_badrst); 562 goto done; 563 } 564 565 /* 566 * No corresponding connection was found in syncache. 567 * If syncookies are enabled and possibly exclusively 568 * used, or we are under memory pressure, a valid RST 569 * may not find a syncache entry. In that case we're 570 * done and no SYN|ACK retransmissions will happen. 571 * Otherwise the RST was misdirected or spoofed. 572 */ 573 if (sc == NULL) { 574 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 575 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 576 "syncache entry (possibly syncookie only), " 577 "segment ignored\n", s, __func__); 578 TCPSTAT_INC(tcps_badrst); 579 goto done; 580 } 581 582 /* 583 * If the RST bit is set, check the sequence number to see 584 * if this is a valid reset segment. 585 * RFC 793 page 37: 586 * In all states except SYN-SENT, all reset (RST) segments 587 * are validated by checking their SEQ-fields. A reset is 588 * valid if its sequence number is in the window. 589 * 590 * The sequence number in the reset segment is normally an 591 * echo of our outgoing acknowlegement numbers, but some hosts 592 * send a reset with the sequence number at the rightmost edge 593 * of our receive window, and we have to handle this case. 594 */ 595 if (SEQ_GEQ(th->th_seq, sc->sc_irs) && 596 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 597 syncache_drop(sc, sch); 598 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 599 log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, " 600 "connection attempt aborted by remote endpoint\n", 601 s, __func__); 602 TCPSTAT_INC(tcps_sc_reset); 603 } else { 604 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 605 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 606 "IRS %u (+WND %u), segment ignored\n", 607 s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd); 608 TCPSTAT_INC(tcps_badrst); 609 } 610 611 done: 612 if (s != NULL) 613 free(s, M_TCPLOG); 614 SCH_UNLOCK(sch); 615 } 616 617 void 618 syncache_badack(struct in_conninfo *inc) 619 { 620 struct syncache *sc; 621 struct syncache_head *sch; 622 623 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 624 SCH_LOCK_ASSERT(sch); 625 if (sc != NULL) { 626 syncache_drop(sc, sch); 627 TCPSTAT_INC(tcps_sc_badack); 628 } 629 SCH_UNLOCK(sch); 630 } 631 632 void 633 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th) 634 { 635 struct syncache *sc; 636 struct syncache_head *sch; 637 638 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 639 SCH_LOCK_ASSERT(sch); 640 if (sc == NULL) 641 goto done; 642 643 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 644 if (ntohl(th->th_seq) != sc->sc_iss) 645 goto done; 646 647 /* 648 * If we've rertransmitted 3 times and this is our second error, 649 * we remove the entry. Otherwise, we allow it to continue on. 650 * This prevents us from incorrectly nuking an entry during a 651 * spurious network outage. 652 * 653 * See tcp_notify(). 654 */ 655 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 656 sc->sc_flags |= SCF_UNREACH; 657 goto done; 658 } 659 syncache_drop(sc, sch); 660 TCPSTAT_INC(tcps_sc_unreach); 661 done: 662 SCH_UNLOCK(sch); 663 } 664 665 /* 666 * Build a new TCP socket structure from a syncache entry. 667 */ 668 static struct socket * 669 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 670 { 671 struct inpcb *inp = NULL; 672 struct socket *so; 673 struct tcpcb *tp; 674 int error; 675 char *s; 676 677 INP_INFO_WLOCK_ASSERT(&V_tcbinfo); 678 679 /* 680 * Ok, create the full blown connection, and set things up 681 * as they would have been set up if we had created the 682 * connection when the SYN arrived. If we can't create 683 * the connection, abort it. 684 */ 685 so = sonewconn(lso, SS_ISCONNECTED); 686 if (so == NULL) { 687 /* 688 * Drop the connection; we will either send a RST or 689 * have the peer retransmit its SYN again after its 690 * RTO and try again. 691 */ 692 TCPSTAT_INC(tcps_listendrop); 693 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 694 log(LOG_DEBUG, "%s; %s: Socket create failed " 695 "due to limits or memory shortage\n", 696 s, __func__); 697 free(s, M_TCPLOG); 698 } 699 goto abort2; 700 } 701 #ifdef MAC 702 mac_socketpeer_set_from_mbuf(m, so); 703 #endif 704 705 inp = sotoinpcb(so); 706 inp->inp_inc.inc_fibnum = so->so_fibnum; 707 INP_WLOCK(inp); 708 INP_HASH_WLOCK(&V_tcbinfo); 709 710 /* Insert new socket into PCB hash list. */ 711 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 712 #ifdef INET6 713 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 714 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 715 } else { 716 inp->inp_vflag &= ~INP_IPV6; 717 inp->inp_vflag |= INP_IPV4; 718 #endif 719 inp->inp_laddr = sc->sc_inc.inc_laddr; 720 #ifdef INET6 721 } 722 #endif 723 724 /* 725 * Install in the reservation hash table for now, but don't yet 726 * install a connection group since the full 4-tuple isn't yet 727 * configured. 728 */ 729 inp->inp_lport = sc->sc_inc.inc_lport; 730 if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) { 731 /* 732 * Undo the assignments above if we failed to 733 * put the PCB on the hash lists. 734 */ 735 #ifdef INET6 736 if (sc->sc_inc.inc_flags & INC_ISIPV6) 737 inp->in6p_laddr = in6addr_any; 738 else 739 #endif 740 inp->inp_laddr.s_addr = INADDR_ANY; 741 inp->inp_lport = 0; 742 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 743 log(LOG_DEBUG, "%s; %s: in_pcbinshash failed " 744 "with error %i\n", 745 s, __func__, error); 746 free(s, M_TCPLOG); 747 } 748 INP_HASH_WUNLOCK(&V_tcbinfo); 749 goto abort; 750 } 751 #ifdef IPSEC 752 /* Copy old policy into new socket's. */ 753 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp)) 754 printf("syncache_socket: could not copy policy\n"); 755 #endif 756 #ifdef INET6 757 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 758 struct inpcb *oinp = sotoinpcb(lso); 759 struct in6_addr laddr6; 760 struct sockaddr_in6 sin6; 761 /* 762 * Inherit socket options from the listening socket. 763 * Note that in6p_inputopts are not (and should not be) 764 * copied, since it stores previously received options and is 765 * used to detect if each new option is different than the 766 * previous one and hence should be passed to a user. 767 * If we copied in6p_inputopts, a user would not be able to 768 * receive options just after calling the accept system call. 769 */ 770 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 771 if (oinp->in6p_outputopts) 772 inp->in6p_outputopts = 773 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 774 775 sin6.sin6_family = AF_INET6; 776 sin6.sin6_len = sizeof(sin6); 777 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 778 sin6.sin6_port = sc->sc_inc.inc_fport; 779 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 780 laddr6 = inp->in6p_laddr; 781 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 782 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 783 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6, 784 thread0.td_ucred, m)) != 0) { 785 inp->in6p_laddr = laddr6; 786 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 787 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed " 788 "with error %i\n", 789 s, __func__, error); 790 free(s, M_TCPLOG); 791 } 792 INP_HASH_WUNLOCK(&V_tcbinfo); 793 goto abort; 794 } 795 /* Override flowlabel from in6_pcbconnect. */ 796 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 797 inp->inp_flow |= sc->sc_flowlabel; 798 } 799 #endif /* INET6 */ 800 #if defined(INET) && defined(INET6) 801 else 802 #endif 803 #ifdef INET 804 { 805 struct in_addr laddr; 806 struct sockaddr_in sin; 807 808 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 809 810 if (inp->inp_options == NULL) { 811 inp->inp_options = sc->sc_ipopts; 812 sc->sc_ipopts = NULL; 813 } 814 815 sin.sin_family = AF_INET; 816 sin.sin_len = sizeof(sin); 817 sin.sin_addr = sc->sc_inc.inc_faddr; 818 sin.sin_port = sc->sc_inc.inc_fport; 819 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 820 laddr = inp->inp_laddr; 821 if (inp->inp_laddr.s_addr == INADDR_ANY) 822 inp->inp_laddr = sc->sc_inc.inc_laddr; 823 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin, 824 thread0.td_ucred, m)) != 0) { 825 inp->inp_laddr = laddr; 826 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 827 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed " 828 "with error %i\n", 829 s, __func__, error); 830 free(s, M_TCPLOG); 831 } 832 INP_HASH_WUNLOCK(&V_tcbinfo); 833 goto abort; 834 } 835 } 836 #endif /* INET */ 837 INP_HASH_WUNLOCK(&V_tcbinfo); 838 tp = intotcpcb(inp); 839 tcp_state_change(tp, TCPS_SYN_RECEIVED); 840 tp->iss = sc->sc_iss; 841 tp->irs = sc->sc_irs; 842 tcp_rcvseqinit(tp); 843 tcp_sendseqinit(tp); 844 tp->snd_wl1 = sc->sc_irs; 845 tp->snd_max = tp->iss + 1; 846 tp->snd_nxt = tp->iss + 1; 847 tp->rcv_up = sc->sc_irs + 1; 848 tp->rcv_wnd = sc->sc_wnd; 849 tp->rcv_adv += tp->rcv_wnd; 850 tp->last_ack_sent = tp->rcv_nxt; 851 852 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 853 if (sc->sc_flags & SCF_NOOPT) 854 tp->t_flags |= TF_NOOPT; 855 else { 856 if (sc->sc_flags & SCF_WINSCALE) { 857 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 858 tp->snd_scale = sc->sc_requested_s_scale; 859 tp->request_r_scale = sc->sc_requested_r_scale; 860 } 861 if (sc->sc_flags & SCF_TIMESTAMP) { 862 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 863 tp->ts_recent = sc->sc_tsreflect; 864 tp->ts_recent_age = tcp_ts_getticks(); 865 tp->ts_offset = sc->sc_tsoff; 866 } 867 #ifdef TCP_SIGNATURE 868 if (sc->sc_flags & SCF_SIGNATURE) 869 tp->t_flags |= TF_SIGNATURE; 870 #endif 871 if (sc->sc_flags & SCF_SACK) 872 tp->t_flags |= TF_SACK_PERMIT; 873 } 874 875 if (sc->sc_flags & SCF_ECN) 876 tp->t_flags |= TF_ECN_PERMIT; 877 878 /* 879 * Set up MSS and get cached values from tcp_hostcache. 880 * This might overwrite some of the defaults we just set. 881 */ 882 tcp_mss(tp, sc->sc_peer_mss); 883 884 /* 885 * If the SYN,ACK was retransmitted, indicate that CWND to be 886 * limited to one segment in cc_conn_init(). 887 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 888 */ 889 if (sc->sc_rxmits > 1) 890 tp->snd_cwnd = 1; 891 892 #ifdef TCP_OFFLOAD 893 /* 894 * Allow a TOE driver to install its hooks. Note that we hold the 895 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 896 * new connection before the TOE driver has done its thing. 897 */ 898 if (ADDED_BY_TOE(sc)) { 899 struct toedev *tod = sc->sc_tod; 900 901 tod->tod_offload_socket(tod, sc->sc_todctx, so); 902 } 903 #endif 904 /* 905 * Copy and activate timers. 906 */ 907 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 908 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 909 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 910 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 911 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 912 913 INP_WUNLOCK(inp); 914 915 TCPSTAT_INC(tcps_accepts); 916 return (so); 917 918 abort: 919 INP_WUNLOCK(inp); 920 abort2: 921 if (so != NULL) 922 soabort(so); 923 return (NULL); 924 } 925 926 /* 927 * This function gets called when we receive an ACK for a 928 * socket in the LISTEN state. We look up the connection 929 * in the syncache, and if its there, we pull it out of 930 * the cache and turn it into a full-blown connection in 931 * the SYN-RECEIVED state. 932 */ 933 int 934 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 935 struct socket **lsop, struct mbuf *m) 936 { 937 struct syncache *sc; 938 struct syncache_head *sch; 939 struct syncache scs; 940 char *s; 941 942 /* 943 * Global TCP locks are held because we manipulate the PCB lists 944 * and create a new socket. 945 */ 946 INP_INFO_WLOCK_ASSERT(&V_tcbinfo); 947 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 948 ("%s: can handle only ACK", __func__)); 949 950 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 951 SCH_LOCK_ASSERT(sch); 952 953 #ifdef INVARIANTS 954 /* 955 * Test code for syncookies comparing the syncache stored 956 * values with the reconstructed values from the cookie. 957 */ 958 if (sc != NULL) 959 syncookie_cmp(inc, sch, sc, th, to, *lsop); 960 #endif 961 962 if (sc == NULL) { 963 /* 964 * There is no syncache entry, so see if this ACK is 965 * a returning syncookie. To do this, first: 966 * A. See if this socket has had a syncache entry dropped in 967 * the past. We don't want to accept a bogus syncookie 968 * if we've never received a SYN. 969 * B. check that the syncookie is valid. If it is, then 970 * cobble up a fake syncache entry, and return. 971 */ 972 if (!V_tcp_syncookies) { 973 SCH_UNLOCK(sch); 974 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 975 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 976 "segment rejected (syncookies disabled)\n", 977 s, __func__); 978 goto failed; 979 } 980 bzero(&scs, sizeof(scs)); 981 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop); 982 SCH_UNLOCK(sch); 983 if (sc == NULL) { 984 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 985 log(LOG_DEBUG, "%s; %s: Segment failed " 986 "SYNCOOKIE authentication, segment rejected " 987 "(probably spoofed)\n", s, __func__); 988 goto failed; 989 } 990 } else { 991 /* Pull out the entry to unlock the bucket row. */ 992 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 993 sch->sch_length--; 994 #ifdef TCP_OFFLOAD 995 if (ADDED_BY_TOE(sc)) { 996 struct toedev *tod = sc->sc_tod; 997 998 tod->tod_syncache_removed(tod, sc->sc_todctx); 999 } 1000 #endif 1001 SCH_UNLOCK(sch); 1002 } 1003 1004 /* 1005 * Segment validation: 1006 * ACK must match our initial sequence number + 1 (the SYN|ACK). 1007 */ 1008 if (th->th_ack != sc->sc_iss + 1) { 1009 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1010 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 1011 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 1012 goto failed; 1013 } 1014 1015 /* 1016 * The SEQ must fall in the window starting at the received 1017 * initial receive sequence number + 1 (the SYN). 1018 */ 1019 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1020 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1021 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1022 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 1023 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 1024 goto failed; 1025 } 1026 1027 /* 1028 * If timestamps were not negotiated during SYN/ACK they 1029 * must not appear on any segment during this session. 1030 */ 1031 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) { 1032 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1033 log(LOG_DEBUG, "%s; %s: Timestamp not expected, " 1034 "segment rejected\n", s, __func__); 1035 goto failed; 1036 } 1037 1038 /* 1039 * If timestamps were negotiated during SYN/ACK they should 1040 * appear on every segment during this session. 1041 * XXXAO: This is only informal as there have been unverified 1042 * reports of non-compliants stacks. 1043 */ 1044 if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) { 1045 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1046 log(LOG_DEBUG, "%s; %s: Timestamp missing, " 1047 "no action\n", s, __func__); 1048 free(s, M_TCPLOG); 1049 s = NULL; 1050 } 1051 } 1052 1053 /* 1054 * If timestamps were negotiated the reflected timestamp 1055 * must be equal to what we actually sent in the SYN|ACK. 1056 */ 1057 if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts) { 1058 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1059 log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, " 1060 "segment rejected\n", 1061 s, __func__, to->to_tsecr, sc->sc_ts); 1062 goto failed; 1063 } 1064 1065 *lsop = syncache_socket(sc, *lsop, m); 1066 1067 if (*lsop == NULL) 1068 TCPSTAT_INC(tcps_sc_aborted); 1069 else 1070 TCPSTAT_INC(tcps_sc_completed); 1071 1072 /* how do we find the inp for the new socket? */ 1073 if (sc != &scs) 1074 syncache_free(sc); 1075 return (1); 1076 failed: 1077 if (sc != NULL && sc != &scs) 1078 syncache_free(sc); 1079 if (s != NULL) 1080 free(s, M_TCPLOG); 1081 *lsop = NULL; 1082 return (0); 1083 } 1084 1085 /* 1086 * Given a LISTEN socket and an inbound SYN request, add 1087 * this to the syn cache, and send back a segment: 1088 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1089 * to the source. 1090 * 1091 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1092 * Doing so would require that we hold onto the data and deliver it 1093 * to the application. However, if we are the target of a SYN-flood 1094 * DoS attack, an attacker could send data which would eventually 1095 * consume all available buffer space if it were ACKed. By not ACKing 1096 * the data, we avoid this DoS scenario. 1097 */ 1098 void 1099 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1100 struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod, 1101 void *todctx) 1102 { 1103 struct tcpcb *tp; 1104 struct socket *so; 1105 struct syncache *sc = NULL; 1106 struct syncache_head *sch; 1107 struct mbuf *ipopts = NULL; 1108 u_int ltflags; 1109 int win, sb_hiwat, ip_ttl, ip_tos; 1110 char *s; 1111 #ifdef INET6 1112 int autoflowlabel = 0; 1113 #endif 1114 #ifdef MAC 1115 struct label *maclabel; 1116 #endif 1117 struct syncache scs; 1118 struct ucred *cred; 1119 1120 INP_INFO_WLOCK_ASSERT(&V_tcbinfo); 1121 INP_WLOCK_ASSERT(inp); /* listen socket */ 1122 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1123 ("%s: unexpected tcp flags", __func__)); 1124 1125 /* 1126 * Combine all so/tp operations very early to drop the INP lock as 1127 * soon as possible. 1128 */ 1129 so = *lsop; 1130 tp = sototcpcb(so); 1131 cred = crhold(so->so_cred); 1132 1133 #ifdef INET6 1134 if ((inc->inc_flags & INC_ISIPV6) && 1135 (inp->inp_flags & IN6P_AUTOFLOWLABEL)) 1136 autoflowlabel = 1; 1137 #endif 1138 ip_ttl = inp->inp_ip_ttl; 1139 ip_tos = inp->inp_ip_tos; 1140 win = sbspace(&so->so_rcv); 1141 sb_hiwat = so->so_rcv.sb_hiwat; 1142 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1143 1144 /* By the time we drop the lock these should no longer be used. */ 1145 so = NULL; 1146 tp = NULL; 1147 1148 #ifdef MAC 1149 if (mac_syncache_init(&maclabel) != 0) { 1150 INP_WUNLOCK(inp); 1151 INP_INFO_WUNLOCK(&V_tcbinfo); 1152 goto done; 1153 } else 1154 mac_syncache_create(maclabel, inp); 1155 #endif 1156 INP_WUNLOCK(inp); 1157 INP_INFO_WUNLOCK(&V_tcbinfo); 1158 1159 /* 1160 * Remember the IP options, if any. 1161 */ 1162 #ifdef INET6 1163 if (!(inc->inc_flags & INC_ISIPV6)) 1164 #endif 1165 #ifdef INET 1166 ipopts = (m) ? ip_srcroute(m) : NULL; 1167 #else 1168 ipopts = NULL; 1169 #endif 1170 1171 /* 1172 * See if we already have an entry for this connection. 1173 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1174 * 1175 * XXX: should the syncache be re-initialized with the contents 1176 * of the new SYN here (which may have different options?) 1177 * 1178 * XXX: We do not check the sequence number to see if this is a 1179 * real retransmit or a new connection attempt. The question is 1180 * how to handle such a case; either ignore it as spoofed, or 1181 * drop the current entry and create a new one? 1182 */ 1183 sc = syncache_lookup(inc, &sch); /* returns locked entry */ 1184 SCH_LOCK_ASSERT(sch); 1185 if (sc != NULL) { 1186 TCPSTAT_INC(tcps_sc_dupsyn); 1187 if (ipopts) { 1188 /* 1189 * If we were remembering a previous source route, 1190 * forget it and use the new one we've been given. 1191 */ 1192 if (sc->sc_ipopts) 1193 (void) m_free(sc->sc_ipopts); 1194 sc->sc_ipopts = ipopts; 1195 } 1196 /* 1197 * Update timestamp if present. 1198 */ 1199 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1200 sc->sc_tsreflect = to->to_tsval; 1201 else 1202 sc->sc_flags &= ~SCF_TIMESTAMP; 1203 #ifdef MAC 1204 /* 1205 * Since we have already unconditionally allocated label 1206 * storage, free it up. The syncache entry will already 1207 * have an initialized label we can use. 1208 */ 1209 mac_syncache_destroy(&maclabel); 1210 #endif 1211 /* Retransmit SYN|ACK and reset retransmit count. */ 1212 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1213 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1214 "resetting timer and retransmitting SYN|ACK\n", 1215 s, __func__); 1216 free(s, M_TCPLOG); 1217 } 1218 if (syncache_respond(sc) == 0) { 1219 sc->sc_rxmits = 0; 1220 syncache_timeout(sc, sch, 1); 1221 TCPSTAT_INC(tcps_sndacks); 1222 TCPSTAT_INC(tcps_sndtotal); 1223 } 1224 SCH_UNLOCK(sch); 1225 goto done; 1226 } 1227 1228 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1229 if (sc == NULL) { 1230 /* 1231 * The zone allocator couldn't provide more entries. 1232 * Treat this as if the cache was full; drop the oldest 1233 * entry and insert the new one. 1234 */ 1235 TCPSTAT_INC(tcps_sc_zonefail); 1236 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) 1237 syncache_drop(sc, sch); 1238 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1239 if (sc == NULL) { 1240 if (V_tcp_syncookies) { 1241 bzero(&scs, sizeof(scs)); 1242 sc = &scs; 1243 } else { 1244 SCH_UNLOCK(sch); 1245 if (ipopts) 1246 (void) m_free(ipopts); 1247 goto done; 1248 } 1249 } 1250 } 1251 1252 /* 1253 * Fill in the syncache values. 1254 */ 1255 #ifdef MAC 1256 sc->sc_label = maclabel; 1257 #endif 1258 sc->sc_cred = cred; 1259 cred = NULL; 1260 sc->sc_ipopts = ipopts; 1261 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1262 #ifdef INET6 1263 if (!(inc->inc_flags & INC_ISIPV6)) 1264 #endif 1265 { 1266 sc->sc_ip_tos = ip_tos; 1267 sc->sc_ip_ttl = ip_ttl; 1268 } 1269 #ifdef TCP_OFFLOAD 1270 sc->sc_tod = tod; 1271 sc->sc_todctx = todctx; 1272 #endif 1273 sc->sc_irs = th->th_seq; 1274 sc->sc_iss = arc4random(); 1275 sc->sc_flags = 0; 1276 sc->sc_flowlabel = 0; 1277 1278 /* 1279 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1280 * win was derived from socket earlier in the function. 1281 */ 1282 win = imax(win, 0); 1283 win = imin(win, TCP_MAXWIN); 1284 sc->sc_wnd = win; 1285 1286 if (V_tcp_do_rfc1323) { 1287 /* 1288 * A timestamp received in a SYN makes 1289 * it ok to send timestamp requests and replies. 1290 */ 1291 if (to->to_flags & TOF_TS) { 1292 sc->sc_tsreflect = to->to_tsval; 1293 sc->sc_ts = tcp_ts_getticks(); 1294 sc->sc_flags |= SCF_TIMESTAMP; 1295 } 1296 if (to->to_flags & TOF_SCALE) { 1297 int wscale = 0; 1298 1299 /* 1300 * Pick the smallest possible scaling factor that 1301 * will still allow us to scale up to sb_max, aka 1302 * kern.ipc.maxsockbuf. 1303 * 1304 * We do this because there are broken firewalls that 1305 * will corrupt the window scale option, leading to 1306 * the other endpoint believing that our advertised 1307 * window is unscaled. At scale factors larger than 1308 * 5 the unscaled window will drop below 1500 bytes, 1309 * leading to serious problems when traversing these 1310 * broken firewalls. 1311 * 1312 * With the default maxsockbuf of 256K, a scale factor 1313 * of 3 will be chosen by this algorithm. Those who 1314 * choose a larger maxsockbuf should watch out 1315 * for the compatiblity problems mentioned above. 1316 * 1317 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1318 * or <SYN,ACK>) segment itself is never scaled. 1319 */ 1320 while (wscale < TCP_MAX_WINSHIFT && 1321 (TCP_MAXWIN << wscale) < sb_max) 1322 wscale++; 1323 sc->sc_requested_r_scale = wscale; 1324 sc->sc_requested_s_scale = to->to_wscale; 1325 sc->sc_flags |= SCF_WINSCALE; 1326 } 1327 } 1328 #ifdef TCP_SIGNATURE 1329 /* 1330 * If listening socket requested TCP digests, and received SYN 1331 * contains the option, flag this in the syncache so that 1332 * syncache_respond() will do the right thing with the SYN+ACK. 1333 * XXX: Currently we always record the option by default and will 1334 * attempt to use it in syncache_respond(). 1335 */ 1336 if (to->to_flags & TOF_SIGNATURE || ltflags & TF_SIGNATURE) 1337 sc->sc_flags |= SCF_SIGNATURE; 1338 #endif 1339 if (to->to_flags & TOF_SACKPERM) 1340 sc->sc_flags |= SCF_SACK; 1341 if (to->to_flags & TOF_MSS) 1342 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1343 if (ltflags & TF_NOOPT) 1344 sc->sc_flags |= SCF_NOOPT; 1345 if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn) 1346 sc->sc_flags |= SCF_ECN; 1347 1348 if (V_tcp_syncookies) 1349 sc->sc_iss = syncookie_generate(sch, sc); 1350 #ifdef INET6 1351 if (autoflowlabel) { 1352 if (V_tcp_syncookies) 1353 sc->sc_flowlabel = sc->sc_iss; 1354 else 1355 sc->sc_flowlabel = ip6_randomflowlabel(); 1356 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1357 } 1358 #endif 1359 SCH_UNLOCK(sch); 1360 1361 /* 1362 * Do a standard 3-way handshake. 1363 */ 1364 if (syncache_respond(sc) == 0) { 1365 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs) 1366 syncache_free(sc); 1367 else if (sc != &scs) 1368 syncache_insert(sc, sch); /* locks and unlocks sch */ 1369 TCPSTAT_INC(tcps_sndacks); 1370 TCPSTAT_INC(tcps_sndtotal); 1371 } else { 1372 if (sc != &scs) 1373 syncache_free(sc); 1374 TCPSTAT_INC(tcps_sc_dropped); 1375 } 1376 1377 done: 1378 if (cred != NULL) 1379 crfree(cred); 1380 #ifdef MAC 1381 if (sc == &scs) 1382 mac_syncache_destroy(&maclabel); 1383 #endif 1384 if (m) { 1385 1386 *lsop = NULL; 1387 m_freem(m); 1388 } 1389 } 1390 1391 static int 1392 syncache_respond(struct syncache *sc) 1393 { 1394 struct ip *ip = NULL; 1395 struct mbuf *m; 1396 struct tcphdr *th = NULL; 1397 int optlen, error = 0; /* Make compiler happy */ 1398 u_int16_t hlen, tlen, mssopt; 1399 struct tcpopt to; 1400 #ifdef INET6 1401 struct ip6_hdr *ip6 = NULL; 1402 #endif 1403 1404 hlen = 1405 #ifdef INET6 1406 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1407 #endif 1408 sizeof(struct ip); 1409 tlen = hlen + sizeof(struct tcphdr); 1410 1411 /* Determine MSS we advertize to other end of connection. */ 1412 mssopt = tcp_mssopt(&sc->sc_inc); 1413 if (sc->sc_peer_mss) 1414 mssopt = max( min(sc->sc_peer_mss, mssopt), V_tcp_minmss); 1415 1416 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1417 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1418 ("syncache: mbuf too small")); 1419 1420 /* Create the IP+TCP header from scratch. */ 1421 m = m_gethdr(M_NOWAIT, MT_DATA); 1422 if (m == NULL) 1423 return (ENOBUFS); 1424 #ifdef MAC 1425 mac_syncache_create_mbuf(sc->sc_label, m); 1426 #endif 1427 m->m_data += max_linkhdr; 1428 m->m_len = tlen; 1429 m->m_pkthdr.len = tlen; 1430 m->m_pkthdr.rcvif = NULL; 1431 1432 #ifdef INET6 1433 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1434 ip6 = mtod(m, struct ip6_hdr *); 1435 ip6->ip6_vfc = IPV6_VERSION; 1436 ip6->ip6_nxt = IPPROTO_TCP; 1437 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1438 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1439 ip6->ip6_plen = htons(tlen - hlen); 1440 /* ip6_hlim is set after checksum */ 1441 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK; 1442 ip6->ip6_flow |= sc->sc_flowlabel; 1443 1444 th = (struct tcphdr *)(ip6 + 1); 1445 } 1446 #endif 1447 #if defined(INET6) && defined(INET) 1448 else 1449 #endif 1450 #ifdef INET 1451 { 1452 ip = mtod(m, struct ip *); 1453 ip->ip_v = IPVERSION; 1454 ip->ip_hl = sizeof(struct ip) >> 2; 1455 ip->ip_len = htons(tlen); 1456 ip->ip_id = 0; 1457 ip->ip_off = 0; 1458 ip->ip_sum = 0; 1459 ip->ip_p = IPPROTO_TCP; 1460 ip->ip_src = sc->sc_inc.inc_laddr; 1461 ip->ip_dst = sc->sc_inc.inc_faddr; 1462 ip->ip_ttl = sc->sc_ip_ttl; 1463 ip->ip_tos = sc->sc_ip_tos; 1464 1465 /* 1466 * See if we should do MTU discovery. Route lookups are 1467 * expensive, so we will only unset the DF bit if: 1468 * 1469 * 1) path_mtu_discovery is disabled 1470 * 2) the SCF_UNREACH flag has been set 1471 */ 1472 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1473 ip->ip_off |= htons(IP_DF); 1474 1475 th = (struct tcphdr *)(ip + 1); 1476 } 1477 #endif /* INET */ 1478 th->th_sport = sc->sc_inc.inc_lport; 1479 th->th_dport = sc->sc_inc.inc_fport; 1480 1481 th->th_seq = htonl(sc->sc_iss); 1482 th->th_ack = htonl(sc->sc_irs + 1); 1483 th->th_off = sizeof(struct tcphdr) >> 2; 1484 th->th_x2 = 0; 1485 th->th_flags = TH_SYN|TH_ACK; 1486 th->th_win = htons(sc->sc_wnd); 1487 th->th_urp = 0; 1488 1489 if (sc->sc_flags & SCF_ECN) { 1490 th->th_flags |= TH_ECE; 1491 TCPSTAT_INC(tcps_ecn_shs); 1492 } 1493 1494 /* Tack on the TCP options. */ 1495 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1496 to.to_flags = 0; 1497 1498 to.to_mss = mssopt; 1499 to.to_flags = TOF_MSS; 1500 if (sc->sc_flags & SCF_WINSCALE) { 1501 to.to_wscale = sc->sc_requested_r_scale; 1502 to.to_flags |= TOF_SCALE; 1503 } 1504 if (sc->sc_flags & SCF_TIMESTAMP) { 1505 /* Virgin timestamp or TCP cookie enhanced one. */ 1506 to.to_tsval = sc->sc_ts; 1507 to.to_tsecr = sc->sc_tsreflect; 1508 to.to_flags |= TOF_TS; 1509 } 1510 if (sc->sc_flags & SCF_SACK) 1511 to.to_flags |= TOF_SACKPERM; 1512 #ifdef TCP_SIGNATURE 1513 if (sc->sc_flags & SCF_SIGNATURE) 1514 to.to_flags |= TOF_SIGNATURE; 1515 #endif 1516 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1517 1518 /* Adjust headers by option size. */ 1519 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1520 m->m_len += optlen; 1521 m->m_pkthdr.len += optlen; 1522 1523 #ifdef TCP_SIGNATURE 1524 if (sc->sc_flags & SCF_SIGNATURE) 1525 tcp_signature_compute(m, 0, 0, optlen, 1526 to.to_signature, IPSEC_DIR_OUTBOUND); 1527 #endif 1528 #ifdef INET6 1529 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1530 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1531 else 1532 #endif 1533 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1534 } else 1535 optlen = 0; 1536 1537 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1538 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1539 #ifdef INET6 1540 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1541 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 1542 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 1543 IPPROTO_TCP, 0); 1544 ip6->ip6_hlim = in6_selecthlim(NULL, NULL); 1545 #ifdef TCP_OFFLOAD 1546 if (ADDED_BY_TOE(sc)) { 1547 struct toedev *tod = sc->sc_tod; 1548 1549 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1550 1551 return (error); 1552 } 1553 #endif 1554 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 1555 } 1556 #endif 1557 #if defined(INET6) && defined(INET) 1558 else 1559 #endif 1560 #ifdef INET 1561 { 1562 m->m_pkthdr.csum_flags = CSUM_TCP; 1563 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1564 htons(tlen + optlen - hlen + IPPROTO_TCP)); 1565 #ifdef TCP_OFFLOAD 1566 if (ADDED_BY_TOE(sc)) { 1567 struct toedev *tod = sc->sc_tod; 1568 1569 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1570 1571 return (error); 1572 } 1573 #endif 1574 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 1575 } 1576 #endif 1577 return (error); 1578 } 1579 1580 /* 1581 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 1582 * that exceed the capacity of the syncache by avoiding the storage of any 1583 * of the SYNs we receive. Syncookies defend against blind SYN flooding 1584 * attacks where the attacker does not have access to our responses. 1585 * 1586 * Syncookies encode and include all necessary information about the 1587 * connection setup within the SYN|ACK that we send back. That way we 1588 * can avoid keeping any local state until the ACK to our SYN|ACK returns 1589 * (if ever). Normally the syncache and syncookies are running in parallel 1590 * with the latter taking over when the former is exhausted. When matching 1591 * syncache entry is found the syncookie is ignored. 1592 * 1593 * The only reliable information persisting the 3WHS is our inital sequence 1594 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 1595 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 1596 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 1597 * returns and signifies a legitimate connection if it matches the ACK. 1598 * 1599 * The available space of 32 bits to store the hash and to encode the SYN 1600 * option information is very tight and we should have at least 24 bits for 1601 * the MAC to keep the number of guesses by blind spoofing reasonably high. 1602 * 1603 * SYN option information we have to encode to fully restore a connection: 1604 * MSS: is imporant to chose an optimal segment size to avoid IP level 1605 * fragmentation along the path. The common MSS values can be encoded 1606 * in a 3-bit table. Uncommon values are captured by the next lower value 1607 * in the table leading to a slight increase in packetization overhead. 1608 * WSCALE: is necessary to allow large windows to be used for high delay- 1609 * bandwidth product links. Not scaling the window when it was initially 1610 * negotiated is bad for performance as lack of scaling further decreases 1611 * the apparent available send window. We only need to encode the WSCALE 1612 * we received from the remote end. Our end can be recalculated at any 1613 * time. The common WSCALE values can be encoded in a 3-bit table. 1614 * Uncommon values are captured by the next lower value in the table 1615 * making us under-estimate the available window size halving our 1616 * theoretically possible maximum throughput for that connection. 1617 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 1618 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 1619 * that are included in all segments on a connection. We enable them when 1620 * the ACK has them. 1621 * 1622 * Security of syncookies and attack vectors: 1623 * 1624 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 1625 * together with the gloabl secret to make it unique per connection attempt. 1626 * Thus any change of any of those parameters results in a different MAC output 1627 * in an unpredictable way unless a collision is encountered. 24 bits of the 1628 * MAC are embedded into the ISS. 1629 * 1630 * To prevent replay attacks two rotating global secrets are updated with a 1631 * new random value every 15 seconds. The life-time of a syncookie is thus 1632 * 15-30 seconds. 1633 * 1634 * Vector 1: Attacking the secret. This requires finding a weakness in the 1635 * MAC itself or the way it is used here. The attacker can do a chosen plain 1636 * text attack by varying and testing the all parameters under his control. 1637 * The strength depends on the size and randomness of the secret, and the 1638 * cryptographic security of the MAC function. Due to the constant updating 1639 * of the secret the attacker has at most 29.999 seconds to find the secret 1640 * and launch spoofed connections. After that he has to start all over again. 1641 * 1642 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 1643 * size an average of 4,823 attempts are required for a 50% chance of success 1644 * to spoof a single syncookie (birthday collision paradox). However the 1645 * attacker is blind and doesn't know if one of his attempts succeeded unless 1646 * he has a side channel to interfere success from. A single connection setup 1647 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 1648 * This many attempts are required for each one blind spoofed connection. For 1649 * every additional spoofed connection he has to launch another N attempts. 1650 * Thus for a sustained rate 100 spoofed connections per second approximately 1651 * 1,800,000 packets per second would have to be sent. 1652 * 1653 * NB: The MAC function should be fast so that it doesn't become a CPU 1654 * exhaustion attack vector itself. 1655 * 1656 * References: 1657 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 1658 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 1659 * http://cr.yp.to/syncookies.html (overview) 1660 * http://cr.yp.to/syncookies/archive (details) 1661 * 1662 * 1663 * Schematic construction of a syncookie enabled Initial Sequence Number: 1664 * 0 1 2 3 1665 * 12345678901234567890123456789012 1666 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 1667 * 1668 * x 24 MAC (truncated) 1669 * W 3 Send Window Scale index 1670 * M 3 MSS index 1671 * S 1 SACK permitted 1672 * P 1 Odd/even secret 1673 */ 1674 1675 /* 1676 * Distribution and probability of certain MSS values. Those in between are 1677 * rounded down to the next lower one. 1678 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 1679 * .2% .3% 5% 7% 7% 20% 15% 45% 1680 */ 1681 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 1682 1683 /* 1684 * Distribution and probability of certain WSCALE values. We have to map the 1685 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 1686 * bits based on prevalence of certain values. Where we don't have an exact 1687 * match for are rounded down to the next lower one letting us under-estimate 1688 * the true available window. At the moment this would happen only for the 1689 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 1690 * and window size). The absence of the WSCALE option (no scaling in either 1691 * direction) is encoded with index zero. 1692 * [WSCALE values histograms, Allman, 2012] 1693 * X 10 10 35 5 6 14 10% by host 1694 * X 11 4 5 5 18 49 3% by connections 1695 */ 1696 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 1697 1698 /* 1699 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 1700 * and good cryptographic properties. 1701 */ 1702 static uint32_t 1703 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 1704 uint8_t *secbits, uintptr_t secmod) 1705 { 1706 SIPHASH_CTX ctx; 1707 uint32_t siphash[2]; 1708 1709 SipHash24_Init(&ctx); 1710 SipHash_SetKey(&ctx, secbits); 1711 switch (inc->inc_flags & INC_ISIPV6) { 1712 #ifdef INET 1713 case 0: 1714 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 1715 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 1716 break; 1717 #endif 1718 #ifdef INET6 1719 case INC_ISIPV6: 1720 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 1721 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 1722 break; 1723 #endif 1724 } 1725 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 1726 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 1727 SipHash_Update(&ctx, &flags, sizeof(flags)); 1728 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 1729 SipHash_Final((u_int8_t *)&siphash, &ctx); 1730 1731 return (siphash[0] ^ siphash[1]); 1732 } 1733 1734 static tcp_seq 1735 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 1736 { 1737 u_int i, mss, secbit, wscale; 1738 uint32_t iss, hash; 1739 uint8_t *secbits; 1740 union syncookie cookie; 1741 1742 SCH_LOCK_ASSERT(sch); 1743 1744 cookie.cookie = 0; 1745 1746 /* Map our computed MSS into the 3-bit index. */ 1747 mss = min(tcp_mssopt(&sc->sc_inc), max(sc->sc_peer_mss, V_tcp_minmss)); 1748 for (i = sizeof(tcp_sc_msstab) / sizeof(*tcp_sc_msstab) - 1; 1749 tcp_sc_msstab[i] > mss && i > 0; 1750 i--) 1751 ; 1752 cookie.flags.mss_idx = i; 1753 1754 /* 1755 * Map the send window scale into the 3-bit index but only if 1756 * the wscale option was received. 1757 */ 1758 if (sc->sc_flags & SCF_WINSCALE) { 1759 wscale = sc->sc_requested_s_scale; 1760 for (i = sizeof(tcp_sc_wstab) / sizeof(*tcp_sc_wstab) - 1; 1761 tcp_sc_wstab[i] > wscale && i > 0; 1762 i--) 1763 ; 1764 cookie.flags.wscale_idx = i; 1765 } 1766 1767 /* Can we do SACK? */ 1768 if (sc->sc_flags & SCF_SACK) 1769 cookie.flags.sack_ok = 1; 1770 1771 /* Which of the two secrets to use. */ 1772 secbit = sch->sch_sc->secret.oddeven & 0x1; 1773 cookie.flags.odd_even = secbit; 1774 1775 secbits = sch->sch_sc->secret.key[secbit]; 1776 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 1777 (uintptr_t)sch); 1778 1779 /* 1780 * Put the flags into the hash and XOR them to get better ISS number 1781 * variance. This doesn't enhance the cryptographic strength and is 1782 * done to prevent the 8 cookie bits from showing up directly on the 1783 * wire. 1784 */ 1785 iss = hash & ~0xff; 1786 iss |= cookie.cookie ^ (hash >> 24); 1787 1788 /* Randomize the timestamp. */ 1789 if (sc->sc_flags & SCF_TIMESTAMP) { 1790 sc->sc_ts = arc4random(); 1791 sc->sc_tsoff = sc->sc_ts - tcp_ts_getticks(); 1792 } 1793 1794 TCPSTAT_INC(tcps_sc_sendcookie); 1795 return (iss); 1796 } 1797 1798 static struct syncache * 1799 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 1800 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 1801 struct socket *lso) 1802 { 1803 uint32_t hash; 1804 uint8_t *secbits; 1805 tcp_seq ack, seq; 1806 int wnd, wscale = 0; 1807 union syncookie cookie; 1808 1809 SCH_LOCK_ASSERT(sch); 1810 1811 /* 1812 * Pull information out of SYN-ACK/ACK and revert sequence number 1813 * advances. 1814 */ 1815 ack = th->th_ack - 1; 1816 seq = th->th_seq - 1; 1817 1818 /* 1819 * Unpack the flags containing enough information to restore the 1820 * connection. 1821 */ 1822 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 1823 1824 /* Which of the two secrets to use. */ 1825 secbits = sch->sch_sc->secret.key[cookie.flags.odd_even]; 1826 1827 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 1828 1829 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 1830 if ((ack & ~0xff) != (hash & ~0xff)) 1831 return (NULL); 1832 1833 /* Fill in the syncache values. */ 1834 sc->sc_flags = 0; 1835 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1836 sc->sc_ipopts = NULL; 1837 1838 sc->sc_irs = seq; 1839 sc->sc_iss = ack; 1840 1841 switch (inc->inc_flags & INC_ISIPV6) { 1842 #ifdef INET 1843 case 0: 1844 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 1845 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 1846 break; 1847 #endif 1848 #ifdef INET6 1849 case INC_ISIPV6: 1850 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 1851 sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK; 1852 break; 1853 #endif 1854 } 1855 1856 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 1857 1858 /* We can simply recompute receive window scale we sent earlier. */ 1859 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) 1860 wscale++; 1861 1862 /* Only use wscale if it was enabled in the orignal SYN. */ 1863 if (cookie.flags.wscale_idx > 0) { 1864 sc->sc_requested_r_scale = wscale; 1865 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 1866 sc->sc_flags |= SCF_WINSCALE; 1867 } 1868 1869 wnd = sbspace(&lso->so_rcv); 1870 wnd = imax(wnd, 0); 1871 wnd = imin(wnd, TCP_MAXWIN); 1872 sc->sc_wnd = wnd; 1873 1874 if (cookie.flags.sack_ok) 1875 sc->sc_flags |= SCF_SACK; 1876 1877 if (to->to_flags & TOF_TS) { 1878 sc->sc_flags |= SCF_TIMESTAMP; 1879 sc->sc_tsreflect = to->to_tsval; 1880 sc->sc_ts = to->to_tsecr; 1881 sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks(); 1882 } 1883 1884 if (to->to_flags & TOF_SIGNATURE) 1885 sc->sc_flags |= SCF_SIGNATURE; 1886 1887 sc->sc_rxmits = 0; 1888 1889 TCPSTAT_INC(tcps_sc_recvcookie); 1890 return (sc); 1891 } 1892 1893 #ifdef INVARIANTS 1894 static int 1895 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 1896 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 1897 struct socket *lso) 1898 { 1899 struct syncache scs, *scx; 1900 char *s; 1901 1902 bzero(&scs, sizeof(scs)); 1903 scx = syncookie_lookup(inc, sch, &scs, th, to, lso); 1904 1905 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 1906 return (0); 1907 1908 if (scx != NULL) { 1909 if (sc->sc_peer_mss != scx->sc_peer_mss) 1910 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 1911 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss); 1912 1913 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale) 1914 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 1915 s, __func__, sc->sc_requested_r_scale, 1916 scx->sc_requested_r_scale); 1917 1918 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale) 1919 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 1920 s, __func__, sc->sc_requested_s_scale, 1921 scx->sc_requested_s_scale); 1922 1923 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK)) 1924 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 1925 } 1926 1927 if (s != NULL) 1928 free(s, M_TCPLOG); 1929 return (0); 1930 } 1931 #endif /* INVARIANTS */ 1932 1933 static void 1934 syncookie_reseed(void *arg) 1935 { 1936 struct tcp_syncache *sc = arg; 1937 uint8_t *secbits; 1938 int secbit; 1939 1940 /* 1941 * Reseeding the secret doesn't have to be protected by a lock. 1942 * It only must be ensured that the new random values are visible 1943 * to all CPUs in a SMP environment. The atomic with release 1944 * semantics ensures that. 1945 */ 1946 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 1947 secbits = sc->secret.key[secbit]; 1948 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 1949 atomic_add_rel_int(&sc->secret.oddeven, 1); 1950 1951 /* Reschedule ourself. */ 1952 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 1953 } 1954 1955 /* 1956 * Returns the current number of syncache entries. This number 1957 * will probably change before you get around to calling 1958 * syncache_pcblist. 1959 */ 1960 int 1961 syncache_pcbcount(void) 1962 { 1963 struct syncache_head *sch; 1964 int count, i; 1965 1966 for (count = 0, i = 0; i < V_tcp_syncache.hashsize; i++) { 1967 /* No need to lock for a read. */ 1968 sch = &V_tcp_syncache.hashbase[i]; 1969 count += sch->sch_length; 1970 } 1971 return count; 1972 } 1973 1974 /* 1975 * Exports the syncache entries to userland so that netstat can display 1976 * them alongside the other sockets. This function is intended to be 1977 * called only from tcp_pcblist. 1978 * 1979 * Due to concurrency on an active system, the number of pcbs exported 1980 * may have no relation to max_pcbs. max_pcbs merely indicates the 1981 * amount of space the caller allocated for this function to use. 1982 */ 1983 int 1984 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported) 1985 { 1986 struct xtcpcb xt; 1987 struct syncache *sc; 1988 struct syncache_head *sch; 1989 int count, error, i; 1990 1991 for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) { 1992 sch = &V_tcp_syncache.hashbase[i]; 1993 SCH_LOCK(sch); 1994 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 1995 if (count >= max_pcbs) { 1996 SCH_UNLOCK(sch); 1997 goto exit; 1998 } 1999 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2000 continue; 2001 bzero(&xt, sizeof(xt)); 2002 xt.xt_len = sizeof(xt); 2003 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2004 xt.xt_inp.inp_vflag = INP_IPV6; 2005 else 2006 xt.xt_inp.inp_vflag = INP_IPV4; 2007 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo)); 2008 xt.xt_tp.t_inpcb = &xt.xt_inp; 2009 xt.xt_tp.t_state = TCPS_SYN_RECEIVED; 2010 xt.xt_socket.xso_protocol = IPPROTO_TCP; 2011 xt.xt_socket.xso_len = sizeof (struct xsocket); 2012 xt.xt_socket.so_type = SOCK_STREAM; 2013 xt.xt_socket.so_state = SS_ISCONNECTING; 2014 error = SYSCTL_OUT(req, &xt, sizeof xt); 2015 if (error) { 2016 SCH_UNLOCK(sch); 2017 goto exit; 2018 } 2019 count++; 2020 } 2021 SCH_UNLOCK(sch); 2022 } 2023 exit: 2024 *pcbs_exported = count; 2025 return error; 2026 } 2027