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sys/netinet/tcp_syncache.c
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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: releng/10.0/sys/netinet/tcp_syncache.c 254889 2013-08-25 21:54:41Z markj $"); 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/route.h> 64 #include <net/vnet.h> 65 66 #include <netinet/in.h> 67 #include <netinet/in_systm.h> 68 #include <netinet/ip.h> 69 #include <netinet/in_var.h> 70 #include <netinet/in_pcb.h> 71 #include <netinet/ip_var.h> 72 #include <netinet/ip_options.h> 73 #ifdef INET6 74 #include <netinet/ip6.h> 75 #include <netinet/icmp6.h> 76 #include <netinet6/nd6.h> 77 #include <netinet6/ip6_var.h> 78 #include <netinet6/in6_pcb.h> 79 #endif 80 #include <netinet/tcp.h> 81 #include <netinet/tcp_fsm.h> 82 #include <netinet/tcp_seq.h> 83 #include <netinet/tcp_timer.h> 84 #include <netinet/tcp_var.h> 85 #include <netinet/tcp_syncache.h> 86 #ifdef INET6 87 #include <netinet6/tcp6_var.h> 88 #endif 89 #ifdef TCP_OFFLOAD 90 #include <netinet/toecore.h> 91 #endif 92 93 #ifdef IPSEC 94 #include <netipsec/ipsec.h> 95 #ifdef INET6 96 #include <netipsec/ipsec6.h> 97 #endif 98 #include <netipsec/key.h> 99 #endif /*IPSEC*/ 100 101 #include <machine/in_cksum.h> 102 103 #include <security/mac/mac_framework.h> 104 105 static VNET_DEFINE(int, tcp_syncookies) = 1; 106 #define V_tcp_syncookies VNET(tcp_syncookies) 107 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW, 108 &VNET_NAME(tcp_syncookies), 0, 109 "Use TCP SYN cookies if the syncache overflows"); 110 111 static VNET_DEFINE(int, tcp_syncookiesonly) = 0; 112 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly) 113 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_RW, 114 &VNET_NAME(tcp_syncookiesonly), 0, 115 "Use only TCP SYN cookies"); 116 117 #ifdef TCP_OFFLOAD 118 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL) 119 #endif 120 121 static void syncache_drop(struct syncache *, struct syncache_head *); 122 static void syncache_free(struct syncache *); 123 static void syncache_insert(struct syncache *, struct syncache_head *); 124 struct syncache *syncache_lookup(struct in_conninfo *, struct syncache_head **); 125 static int syncache_respond(struct syncache *); 126 static struct socket *syncache_socket(struct syncache *, struct socket *, 127 struct mbuf *m); 128 static int syncache_sysctl_count(SYSCTL_HANDLER_ARGS); 129 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 130 int docallout); 131 static void syncache_timer(void *); 132 133 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t, 134 uint8_t *, uintptr_t); 135 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *); 136 static struct syncache 137 *syncookie_lookup(struct in_conninfo *, struct syncache_head *, 138 struct syncache *, struct tcphdr *, struct tcpopt *, 139 struct socket *); 140 static void syncookie_reseed(void *); 141 #ifdef INVARIANTS 142 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 143 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 144 struct socket *lso); 145 #endif 146 147 /* 148 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 149 * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds, 150 * the odds are that the user has given up attempting to connect by then. 151 */ 152 #define SYNCACHE_MAXREXMTS 3 153 154 /* Arbitrary values */ 155 #define TCP_SYNCACHE_HASHSIZE 512 156 #define TCP_SYNCACHE_BUCKETLIMIT 30 157 158 static VNET_DEFINE(struct tcp_syncache, tcp_syncache); 159 #define V_tcp_syncache VNET(tcp_syncache) 160 161 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, 162 "TCP SYN cache"); 163 164 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RDTUN, 165 &VNET_NAME(tcp_syncache.bucket_limit), 0, 166 "Per-bucket hash limit for syncache"); 167 168 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RDTUN, 169 &VNET_NAME(tcp_syncache.cache_limit), 0, 170 "Overall entry limit for syncache"); 171 172 SYSCTL_VNET_PROC(_net_inet_tcp_syncache, OID_AUTO, count, (CTLTYPE_UINT|CTLFLAG_RD), 173 NULL, 0, &syncache_sysctl_count, "IU", 174 "Current number of entries in syncache"); 175 176 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RDTUN, 177 &VNET_NAME(tcp_syncache.hashsize), 0, 178 "Size of TCP syncache hashtable"); 179 180 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW, 181 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 182 "Limit on SYN/ACK retransmissions"); 183 184 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 185 SYSCTL_VNET_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 186 CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 187 "Send reset on socket allocation failure"); 188 189 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 190 191 #define SYNCACHE_HASH(inc, mask) \ 192 ((V_tcp_syncache.hash_secret ^ \ 193 (inc)->inc_faddr.s_addr ^ \ 194 ((inc)->inc_faddr.s_addr >> 16) ^ \ 195 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 196 197 #define SYNCACHE_HASH6(inc, mask) \ 198 ((V_tcp_syncache.hash_secret ^ \ 199 (inc)->inc6_faddr.s6_addr32[0] ^ \ 200 (inc)->inc6_faddr.s6_addr32[3] ^ \ 201 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 202 203 #define ENDPTS_EQ(a, b) ( \ 204 (a)->ie_fport == (b)->ie_fport && \ 205 (a)->ie_lport == (b)->ie_lport && \ 206 (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr && \ 207 (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr \ 208 ) 209 210 #define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0) 211 212 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 213 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 214 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 215 216 /* 217 * Requires the syncache entry to be already removed from the bucket list. 218 */ 219 static void 220 syncache_free(struct syncache *sc) 221 { 222 223 if (sc->sc_ipopts) 224 (void) m_free(sc->sc_ipopts); 225 if (sc->sc_cred) 226 crfree(sc->sc_cred); 227 #ifdef MAC 228 mac_syncache_destroy(&sc->sc_label); 229 #endif 230 231 uma_zfree(V_tcp_syncache.zone, sc); 232 } 233 234 void 235 syncache_init(void) 236 { 237 int i; 238 239 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 240 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 241 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 242 V_tcp_syncache.hash_secret = arc4random(); 243 244 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 245 &V_tcp_syncache.hashsize); 246 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 247 &V_tcp_syncache.bucket_limit); 248 if (!powerof2(V_tcp_syncache.hashsize) || 249 V_tcp_syncache.hashsize == 0) { 250 printf("WARNING: syncache hash size is not a power of 2.\n"); 251 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 252 } 253 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 254 255 /* Set limits. */ 256 V_tcp_syncache.cache_limit = 257 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 258 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 259 &V_tcp_syncache.cache_limit); 260 261 /* Allocate the hash table. */ 262 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 263 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 264 265 #ifdef VIMAGE 266 V_tcp_syncache.vnet = curvnet; 267 #endif 268 269 /* Initialize the hash buckets. */ 270 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 271 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 272 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 273 NULL, MTX_DEF); 274 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 275 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 276 V_tcp_syncache.hashbase[i].sch_length = 0; 277 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 278 } 279 280 /* Create the syncache entry zone. */ 281 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 282 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 283 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 284 V_tcp_syncache.cache_limit); 285 286 /* Start the SYN cookie reseeder callout. */ 287 callout_init(&V_tcp_syncache.secret.reseed, 1); 288 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 289 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 290 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 291 syncookie_reseed, &V_tcp_syncache); 292 } 293 294 #ifdef VIMAGE 295 void 296 syncache_destroy(void) 297 { 298 struct syncache_head *sch; 299 struct syncache *sc, *nsc; 300 int i; 301 302 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 303 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 304 305 sch = &V_tcp_syncache.hashbase[i]; 306 callout_drain(&sch->sch_timer); 307 308 SCH_LOCK(sch); 309 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 310 syncache_drop(sc, sch); 311 SCH_UNLOCK(sch); 312 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 313 ("%s: sch->sch_bucket not empty", __func__)); 314 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 315 __func__, sch->sch_length)); 316 mtx_destroy(&sch->sch_mtx); 317 } 318 319 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 320 ("%s: cache_count not 0", __func__)); 321 322 /* Free the allocated global resources. */ 323 uma_zdestroy(V_tcp_syncache.zone); 324 free(V_tcp_syncache.hashbase, M_SYNCACHE); 325 326 callout_drain(&V_tcp_syncache.secret.reseed); 327 } 328 #endif 329 330 static int 331 syncache_sysctl_count(SYSCTL_HANDLER_ARGS) 332 { 333 int count; 334 335 count = uma_zone_get_cur(V_tcp_syncache.zone); 336 return (sysctl_handle_int(oidp, &count, 0, req)); 337 } 338 339 /* 340 * Inserts a syncache entry into the specified bucket row. 341 * Locks and unlocks the syncache_head autonomously. 342 */ 343 static void 344 syncache_insert(struct syncache *sc, struct syncache_head *sch) 345 { 346 struct syncache *sc2; 347 348 SCH_LOCK(sch); 349 350 /* 351 * Make sure that we don't overflow the per-bucket limit. 352 * If the bucket is full, toss the oldest element. 353 */ 354 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 355 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 356 ("sch->sch_length incorrect")); 357 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 358 syncache_drop(sc2, sch); 359 TCPSTAT_INC(tcps_sc_bucketoverflow); 360 } 361 362 /* Put it into the bucket. */ 363 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 364 sch->sch_length++; 365 366 #ifdef TCP_OFFLOAD 367 if (ADDED_BY_TOE(sc)) { 368 struct toedev *tod = sc->sc_tod; 369 370 tod->tod_syncache_added(tod, sc->sc_todctx); 371 } 372 #endif 373 374 /* Reinitialize the bucket row's timer. */ 375 if (sch->sch_length == 1) 376 sch->sch_nextc = ticks + INT_MAX; 377 syncache_timeout(sc, sch, 1); 378 379 SCH_UNLOCK(sch); 380 381 TCPSTAT_INC(tcps_sc_added); 382 } 383 384 /* 385 * Remove and free entry from syncache bucket row. 386 * Expects locked syncache head. 387 */ 388 static void 389 syncache_drop(struct syncache *sc, struct syncache_head *sch) 390 { 391 392 SCH_LOCK_ASSERT(sch); 393 394 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 395 sch->sch_length--; 396 397 #ifdef TCP_OFFLOAD 398 if (ADDED_BY_TOE(sc)) { 399 struct toedev *tod = sc->sc_tod; 400 401 tod->tod_syncache_removed(tod, sc->sc_todctx); 402 } 403 #endif 404 405 syncache_free(sc); 406 } 407 408 /* 409 * Engage/reengage time on bucket row. 410 */ 411 static void 412 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 413 { 414 sc->sc_rxttime = ticks + 415 TCPTV_RTOBASE * (tcp_syn_backoff[sc->sc_rxmits]); 416 sc->sc_rxmits++; 417 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 418 sch->sch_nextc = sc->sc_rxttime; 419 if (docallout) 420 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 421 syncache_timer, (void *)sch); 422 } 423 } 424 425 /* 426 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 427 * If we have retransmitted an entry the maximum number of times, expire it. 428 * One separate timer for each bucket row. 429 */ 430 static void 431 syncache_timer(void *xsch) 432 { 433 struct syncache_head *sch = (struct syncache_head *)xsch; 434 struct syncache *sc, *nsc; 435 int tick = ticks; 436 char *s; 437 438 CURVNET_SET(sch->sch_sc->vnet); 439 440 /* NB: syncache_head has already been locked by the callout. */ 441 SCH_LOCK_ASSERT(sch); 442 443 /* 444 * In the following cycle we may remove some entries and/or 445 * advance some timeouts, so re-initialize the bucket timer. 446 */ 447 sch->sch_nextc = tick + INT_MAX; 448 449 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 450 /* 451 * We do not check if the listen socket still exists 452 * and accept the case where the listen socket may be 453 * gone by the time we resend the SYN/ACK. We do 454 * not expect this to happens often. If it does, 455 * then the RST will be sent by the time the remote 456 * host does the SYN/ACK->ACK. 457 */ 458 if (TSTMP_GT(sc->sc_rxttime, tick)) { 459 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 460 sch->sch_nextc = sc->sc_rxttime; 461 continue; 462 } 463 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 464 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 465 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 466 "giving up and removing syncache entry\n", 467 s, __func__); 468 free(s, M_TCPLOG); 469 } 470 syncache_drop(sc, sch); 471 TCPSTAT_INC(tcps_sc_stale); 472 continue; 473 } 474 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 475 log(LOG_DEBUG, "%s; %s: Response timeout, " 476 "retransmitting (%u) SYN|ACK\n", 477 s, __func__, sc->sc_rxmits); 478 free(s, M_TCPLOG); 479 } 480 481 (void) syncache_respond(sc); 482 TCPSTAT_INC(tcps_sc_retransmitted); 483 syncache_timeout(sc, sch, 0); 484 } 485 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 486 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 487 syncache_timer, (void *)(sch)); 488 CURVNET_RESTORE(); 489 } 490 491 /* 492 * Find an entry in the syncache. 493 * Returns always with locked syncache_head plus a matching entry or NULL. 494 */ 495 struct syncache * 496 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 497 { 498 struct syncache *sc; 499 struct syncache_head *sch; 500 501 #ifdef INET6 502 if (inc->inc_flags & INC_ISIPV6) { 503 sch = &V_tcp_syncache.hashbase[ 504 SYNCACHE_HASH6(inc, V_tcp_syncache.hashmask)]; 505 *schp = sch; 506 507 SCH_LOCK(sch); 508 509 /* Circle through bucket row to find matching entry. */ 510 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 511 if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) 512 return (sc); 513 } 514 } else 515 #endif 516 { 517 sch = &V_tcp_syncache.hashbase[ 518 SYNCACHE_HASH(inc, V_tcp_syncache.hashmask)]; 519 *schp = sch; 520 521 SCH_LOCK(sch); 522 523 /* Circle through bucket row to find matching entry. */ 524 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 525 #ifdef INET6 526 if (sc->sc_inc.inc_flags & INC_ISIPV6) 527 continue; 528 #endif 529 if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) 530 return (sc); 531 } 532 } 533 SCH_LOCK_ASSERT(*schp); 534 return (NULL); /* always returns with locked sch */ 535 } 536 537 /* 538 * This function is called when we get a RST for a 539 * non-existent connection, so that we can see if the 540 * connection is in the syn cache. If it is, zap it. 541 */ 542 void 543 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th) 544 { 545 struct syncache *sc; 546 struct syncache_head *sch; 547 char *s = NULL; 548 549 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 550 SCH_LOCK_ASSERT(sch); 551 552 /* 553 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags. 554 * See RFC 793 page 65, section SEGMENT ARRIVES. 555 */ 556 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) { 557 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 558 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or " 559 "FIN flag set, segment ignored\n", s, __func__); 560 TCPSTAT_INC(tcps_badrst); 561 goto done; 562 } 563 564 /* 565 * No corresponding connection was found in syncache. 566 * If syncookies are enabled and possibly exclusively 567 * used, or we are under memory pressure, a valid RST 568 * may not find a syncache entry. In that case we're 569 * done and no SYN|ACK retransmissions will happen. 570 * Otherwise the RST was misdirected or spoofed. 571 */ 572 if (sc == NULL) { 573 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 574 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 575 "syncache entry (possibly syncookie only), " 576 "segment ignored\n", s, __func__); 577 TCPSTAT_INC(tcps_badrst); 578 goto done; 579 } 580 581 /* 582 * If the RST bit is set, check the sequence number to see 583 * if this is a valid reset segment. 584 * RFC 793 page 37: 585 * In all states except SYN-SENT, all reset (RST) segments 586 * are validated by checking their SEQ-fields. A reset is 587 * valid if its sequence number is in the window. 588 * 589 * The sequence number in the reset segment is normally an 590 * echo of our outgoing acknowlegement numbers, but some hosts 591 * send a reset with the sequence number at the rightmost edge 592 * of our receive window, and we have to handle this case. 593 */ 594 if (SEQ_GEQ(th->th_seq, sc->sc_irs) && 595 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 596 syncache_drop(sc, sch); 597 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 598 log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, " 599 "connection attempt aborted by remote endpoint\n", 600 s, __func__); 601 TCPSTAT_INC(tcps_sc_reset); 602 } else { 603 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 604 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 605 "IRS %u (+WND %u), segment ignored\n", 606 s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd); 607 TCPSTAT_INC(tcps_badrst); 608 } 609 610 done: 611 if (s != NULL) 612 free(s, M_TCPLOG); 613 SCH_UNLOCK(sch); 614 } 615 616 void 617 syncache_badack(struct in_conninfo *inc) 618 { 619 struct syncache *sc; 620 struct syncache_head *sch; 621 622 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 623 SCH_LOCK_ASSERT(sch); 624 if (sc != NULL) { 625 syncache_drop(sc, sch); 626 TCPSTAT_INC(tcps_sc_badack); 627 } 628 SCH_UNLOCK(sch); 629 } 630 631 void 632 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th) 633 { 634 struct syncache *sc; 635 struct syncache_head *sch; 636 637 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 638 SCH_LOCK_ASSERT(sch); 639 if (sc == NULL) 640 goto done; 641 642 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 643 if (ntohl(th->th_seq) != sc->sc_iss) 644 goto done; 645 646 /* 647 * If we've rertransmitted 3 times and this is our second error, 648 * we remove the entry. Otherwise, we allow it to continue on. 649 * This prevents us from incorrectly nuking an entry during a 650 * spurious network outage. 651 * 652 * See tcp_notify(). 653 */ 654 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 655 sc->sc_flags |= SCF_UNREACH; 656 goto done; 657 } 658 syncache_drop(sc, sch); 659 TCPSTAT_INC(tcps_sc_unreach); 660 done: 661 SCH_UNLOCK(sch); 662 } 663 664 /* 665 * Build a new TCP socket structure from a syncache entry. 666 */ 667 static struct socket * 668 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 669 { 670 struct inpcb *inp = NULL; 671 struct socket *so; 672 struct tcpcb *tp; 673 int error; 674 char *s; 675 676 INP_INFO_WLOCK_ASSERT(&V_tcbinfo); 677 678 /* 679 * Ok, create the full blown connection, and set things up 680 * as they would have been set up if we had created the 681 * connection when the SYN arrived. If we can't create 682 * the connection, abort it. 683 */ 684 so = sonewconn(lso, SS_ISCONNECTED); 685 if (so == NULL) { 686 /* 687 * Drop the connection; we will either send a RST or 688 * have the peer retransmit its SYN again after its 689 * RTO and try again. 690 */ 691 TCPSTAT_INC(tcps_listendrop); 692 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 693 log(LOG_DEBUG, "%s; %s: Socket create failed " 694 "due to limits or memory shortage\n", 695 s, __func__); 696 free(s, M_TCPLOG); 697 } 698 goto abort2; 699 } 700 #ifdef MAC 701 mac_socketpeer_set_from_mbuf(m, so); 702 #endif 703 704 inp = sotoinpcb(so); 705 inp->inp_inc.inc_fibnum = so->so_fibnum; 706 INP_WLOCK(inp); 707 INP_HASH_WLOCK(&V_tcbinfo); 708 709 /* Insert new socket into PCB hash list. */ 710 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 711 #ifdef INET6 712 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 713 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 714 } else { 715 inp->inp_vflag &= ~INP_IPV6; 716 inp->inp_vflag |= INP_IPV4; 717 #endif 718 inp->inp_laddr = sc->sc_inc.inc_laddr; 719 #ifdef INET6 720 } 721 #endif 722 723 /* 724 * Install in the reservation hash table for now, but don't yet 725 * install a connection group since the full 4-tuple isn't yet 726 * configured. 727 */ 728 inp->inp_lport = sc->sc_inc.inc_lport; 729 if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) { 730 /* 731 * Undo the assignments above if we failed to 732 * put the PCB on the hash lists. 733 */ 734 #ifdef INET6 735 if (sc->sc_inc.inc_flags & INC_ISIPV6) 736 inp->in6p_laddr = in6addr_any; 737 else 738 #endif 739 inp->inp_laddr.s_addr = INADDR_ANY; 740 inp->inp_lport = 0; 741 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 742 log(LOG_DEBUG, "%s; %s: in_pcbinshash failed " 743 "with error %i\n", 744 s, __func__, error); 745 free(s, M_TCPLOG); 746 } 747 INP_HASH_WUNLOCK(&V_tcbinfo); 748 goto abort; 749 } 750 #ifdef IPSEC 751 /* Copy old policy into new socket's. */ 752 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp)) 753 printf("syncache_socket: could not copy policy\n"); 754 #endif 755 #ifdef INET6 756 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 757 struct inpcb *oinp = sotoinpcb(lso); 758 struct in6_addr laddr6; 759 struct sockaddr_in6 sin6; 760 /* 761 * Inherit socket options from the listening socket. 762 * Note that in6p_inputopts are not (and should not be) 763 * copied, since it stores previously received options and is 764 * used to detect if each new option is different than the 765 * previous one and hence should be passed to a user. 766 * If we copied in6p_inputopts, a user would not be able to 767 * receive options just after calling the accept system call. 768 */ 769 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 770 if (oinp->in6p_outputopts) 771 inp->in6p_outputopts = 772 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 773 774 sin6.sin6_family = AF_INET6; 775 sin6.sin6_len = sizeof(sin6); 776 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 777 sin6.sin6_port = sc->sc_inc.inc_fport; 778 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 779 laddr6 = inp->in6p_laddr; 780 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 781 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 782 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6, 783 thread0.td_ucred, m)) != 0) { 784 inp->in6p_laddr = laddr6; 785 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 786 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed " 787 "with error %i\n", 788 s, __func__, error); 789 free(s, M_TCPLOG); 790 } 791 INP_HASH_WUNLOCK(&V_tcbinfo); 792 goto abort; 793 } 794 /* Override flowlabel from in6_pcbconnect. */ 795 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 796 inp->inp_flow |= sc->sc_flowlabel; 797 } 798 #endif /* INET6 */ 799 #if defined(INET) && defined(INET6) 800 else 801 #endif 802 #ifdef INET 803 { 804 struct in_addr laddr; 805 struct sockaddr_in sin; 806 807 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 808 809 if (inp->inp_options == NULL) { 810 inp->inp_options = sc->sc_ipopts; 811 sc->sc_ipopts = NULL; 812 } 813 814 sin.sin_family = AF_INET; 815 sin.sin_len = sizeof(sin); 816 sin.sin_addr = sc->sc_inc.inc_faddr; 817 sin.sin_port = sc->sc_inc.inc_fport; 818 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 819 laddr = inp->inp_laddr; 820 if (inp->inp_laddr.s_addr == INADDR_ANY) 821 inp->inp_laddr = sc->sc_inc.inc_laddr; 822 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin, 823 thread0.td_ucred, m)) != 0) { 824 inp->inp_laddr = laddr; 825 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 826 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed " 827 "with error %i\n", 828 s, __func__, error); 829 free(s, M_TCPLOG); 830 } 831 INP_HASH_WUNLOCK(&V_tcbinfo); 832 goto abort; 833 } 834 } 835 #endif /* INET */ 836 INP_HASH_WUNLOCK(&V_tcbinfo); 837 tp = intotcpcb(inp); 838 tcp_state_change(tp, TCPS_SYN_RECEIVED); 839 tp->iss = sc->sc_iss; 840 tp->irs = sc->sc_irs; 841 tcp_rcvseqinit(tp); 842 tcp_sendseqinit(tp); 843 tp->snd_wl1 = sc->sc_irs; 844 tp->snd_max = tp->iss + 1; 845 tp->snd_nxt = tp->iss + 1; 846 tp->rcv_up = sc->sc_irs + 1; 847 tp->rcv_wnd = sc->sc_wnd; 848 tp->rcv_adv += tp->rcv_wnd; 849 tp->last_ack_sent = tp->rcv_nxt; 850 851 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 852 if (sc->sc_flags & SCF_NOOPT) 853 tp->t_flags |= TF_NOOPT; 854 else { 855 if (sc->sc_flags & SCF_WINSCALE) { 856 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 857 tp->snd_scale = sc->sc_requested_s_scale; 858 tp->request_r_scale = sc->sc_requested_r_scale; 859 } 860 if (sc->sc_flags & SCF_TIMESTAMP) { 861 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 862 tp->ts_recent = sc->sc_tsreflect; 863 tp->ts_recent_age = tcp_ts_getticks(); 864 tp->ts_offset = sc->sc_tsoff; 865 } 866 #ifdef TCP_SIGNATURE 867 if (sc->sc_flags & SCF_SIGNATURE) 868 tp->t_flags |= TF_SIGNATURE; 869 #endif 870 if (sc->sc_flags & SCF_SACK) 871 tp->t_flags |= TF_SACK_PERMIT; 872 } 873 874 if (sc->sc_flags & SCF_ECN) 875 tp->t_flags |= TF_ECN_PERMIT; 876 877 /* 878 * Set up MSS and get cached values from tcp_hostcache. 879 * This might overwrite some of the defaults we just set. 880 */ 881 tcp_mss(tp, sc->sc_peer_mss); 882 883 /* 884 * If the SYN,ACK was retransmitted, indicate that CWND to be 885 * limited to one segment in cc_conn_init(). 886 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 887 */ 888 if (sc->sc_rxmits > 1) 889 tp->snd_cwnd = 1; 890 891 #ifdef TCP_OFFLOAD 892 /* 893 * Allow a TOE driver to install its hooks. Note that we hold the 894 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 895 * new connection before the TOE driver has done its thing. 896 */ 897 if (ADDED_BY_TOE(sc)) { 898 struct toedev *tod = sc->sc_tod; 899 900 tod->tod_offload_socket(tod, sc->sc_todctx, so); 901 } 902 #endif 903 /* 904 * Copy and activate timers. 905 */ 906 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 907 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 908 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 909 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 910 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 911 912 INP_WUNLOCK(inp); 913 914 TCPSTAT_INC(tcps_accepts); 915 return (so); 916 917 abort: 918 INP_WUNLOCK(inp); 919 abort2: 920 if (so != NULL) 921 soabort(so); 922 return (NULL); 923 } 924 925 /* 926 * This function gets called when we receive an ACK for a 927 * socket in the LISTEN state. We look up the connection 928 * in the syncache, and if its there, we pull it out of 929 * the cache and turn it into a full-blown connection in 930 * the SYN-RECEIVED state. 931 */ 932 int 933 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 934 struct socket **lsop, struct mbuf *m) 935 { 936 struct syncache *sc; 937 struct syncache_head *sch; 938 struct syncache scs; 939 char *s; 940 941 /* 942 * Global TCP locks are held because we manipulate the PCB lists 943 * and create a new socket. 944 */ 945 INP_INFO_WLOCK_ASSERT(&V_tcbinfo); 946 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 947 ("%s: can handle only ACK", __func__)); 948 949 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 950 SCH_LOCK_ASSERT(sch); 951 952 #ifdef INVARIANTS 953 /* 954 * Test code for syncookies comparing the syncache stored 955 * values with the reconstructed values from the cookie. 956 */ 957 if (sc != NULL) 958 syncookie_cmp(inc, sch, sc, th, to, *lsop); 959 #endif 960 961 if (sc == NULL) { 962 /* 963 * There is no syncache entry, so see if this ACK is 964 * a returning syncookie. To do this, first: 965 * A. See if this socket has had a syncache entry dropped in 966 * the past. We don't want to accept a bogus syncookie 967 * if we've never received a SYN. 968 * B. check that the syncookie is valid. If it is, then 969 * cobble up a fake syncache entry, and return. 970 */ 971 if (!V_tcp_syncookies) { 972 SCH_UNLOCK(sch); 973 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 974 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 975 "segment rejected (syncookies disabled)\n", 976 s, __func__); 977 goto failed; 978 } 979 bzero(&scs, sizeof(scs)); 980 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop); 981 SCH_UNLOCK(sch); 982 if (sc == NULL) { 983 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 984 log(LOG_DEBUG, "%s; %s: Segment failed " 985 "SYNCOOKIE authentication, segment rejected " 986 "(probably spoofed)\n", s, __func__); 987 goto failed; 988 } 989 } else { 990 /* Pull out the entry to unlock the bucket row. */ 991 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 992 sch->sch_length--; 993 #ifdef TCP_OFFLOAD 994 if (ADDED_BY_TOE(sc)) { 995 struct toedev *tod = sc->sc_tod; 996 997 tod->tod_syncache_removed(tod, sc->sc_todctx); 998 } 999 #endif 1000 SCH_UNLOCK(sch); 1001 } 1002 1003 /* 1004 * Segment validation: 1005 * ACK must match our initial sequence number + 1 (the SYN|ACK). 1006 */ 1007 if (th->th_ack != sc->sc_iss + 1) { 1008 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1009 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 1010 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 1011 goto failed; 1012 } 1013 1014 /* 1015 * The SEQ must fall in the window starting at the received 1016 * initial receive sequence number + 1 (the SYN). 1017 */ 1018 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1019 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1020 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1021 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 1022 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 1023 goto failed; 1024 } 1025 1026 /* 1027 * If timestamps were not negotiated during SYN/ACK they 1028 * must not appear on any segment during this session. 1029 */ 1030 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) { 1031 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1032 log(LOG_DEBUG, "%s; %s: Timestamp not expected, " 1033 "segment rejected\n", s, __func__); 1034 goto failed; 1035 } 1036 1037 /* 1038 * If timestamps were negotiated during SYN/ACK they should 1039 * appear on every segment during this session. 1040 * XXXAO: This is only informal as there have been unverified 1041 * reports of non-compliants stacks. 1042 */ 1043 if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) { 1044 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1045 log(LOG_DEBUG, "%s; %s: Timestamp missing, " 1046 "no action\n", s, __func__); 1047 free(s, M_TCPLOG); 1048 s = NULL; 1049 } 1050 } 1051 1052 /* 1053 * If timestamps were negotiated the reflected timestamp 1054 * must be equal to what we actually sent in the SYN|ACK. 1055 */ 1056 if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts) { 1057 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1058 log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, " 1059 "segment rejected\n", 1060 s, __func__, to->to_tsecr, sc->sc_ts); 1061 goto failed; 1062 } 1063 1064 *lsop = syncache_socket(sc, *lsop, m); 1065 1066 if (*lsop == NULL) 1067 TCPSTAT_INC(tcps_sc_aborted); 1068 else 1069 TCPSTAT_INC(tcps_sc_completed); 1070 1071 /* how do we find the inp for the new socket? */ 1072 if (sc != &scs) 1073 syncache_free(sc); 1074 return (1); 1075 failed: 1076 if (sc != NULL && sc != &scs) 1077 syncache_free(sc); 1078 if (s != NULL) 1079 free(s, M_TCPLOG); 1080 *lsop = NULL; 1081 return (0); 1082 } 1083 1084 /* 1085 * Given a LISTEN socket and an inbound SYN request, add 1086 * this to the syn cache, and send back a segment: 1087 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1088 * to the source. 1089 * 1090 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1091 * Doing so would require that we hold onto the data and deliver it 1092 * to the application. However, if we are the target of a SYN-flood 1093 * DoS attack, an attacker could send data which would eventually 1094 * consume all available buffer space if it were ACKed. By not ACKing 1095 * the data, we avoid this DoS scenario. 1096 */ 1097 void 1098 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1099 struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod, 1100 void *todctx) 1101 { 1102 struct tcpcb *tp; 1103 struct socket *so; 1104 struct syncache *sc = NULL; 1105 struct syncache_head *sch; 1106 struct mbuf *ipopts = NULL; 1107 u_int ltflags; 1108 int win, sb_hiwat, ip_ttl, ip_tos; 1109 char *s; 1110 #ifdef INET6 1111 int autoflowlabel = 0; 1112 #endif 1113 #ifdef MAC 1114 struct label *maclabel; 1115 #endif 1116 struct syncache scs; 1117 struct ucred *cred; 1118 1119 INP_INFO_WLOCK_ASSERT(&V_tcbinfo); 1120 INP_WLOCK_ASSERT(inp); /* listen socket */ 1121 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1122 ("%s: unexpected tcp flags", __func__)); 1123 1124 /* 1125 * Combine all so/tp operations very early to drop the INP lock as 1126 * soon as possible. 1127 */ 1128 so = *lsop; 1129 tp = sototcpcb(so); 1130 cred = crhold(so->so_cred); 1131 1132 #ifdef INET6 1133 if ((inc->inc_flags & INC_ISIPV6) && 1134 (inp->inp_flags & IN6P_AUTOFLOWLABEL)) 1135 autoflowlabel = 1; 1136 #endif 1137 ip_ttl = inp->inp_ip_ttl; 1138 ip_tos = inp->inp_ip_tos; 1139 win = sbspace(&so->so_rcv); 1140 sb_hiwat = so->so_rcv.sb_hiwat; 1141 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1142 1143 /* By the time we drop the lock these should no longer be used. */ 1144 so = NULL; 1145 tp = NULL; 1146 1147 #ifdef MAC 1148 if (mac_syncache_init(&maclabel) != 0) { 1149 INP_WUNLOCK(inp); 1150 INP_INFO_WUNLOCK(&V_tcbinfo); 1151 goto done; 1152 } else 1153 mac_syncache_create(maclabel, inp); 1154 #endif 1155 INP_WUNLOCK(inp); 1156 INP_INFO_WUNLOCK(&V_tcbinfo); 1157 1158 /* 1159 * Remember the IP options, if any. 1160 */ 1161 #ifdef INET6 1162 if (!(inc->inc_flags & INC_ISIPV6)) 1163 #endif 1164 #ifdef INET 1165 ipopts = (m) ? ip_srcroute(m) : NULL; 1166 #else 1167 ipopts = NULL; 1168 #endif 1169 1170 /* 1171 * See if we already have an entry for this connection. 1172 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1173 * 1174 * XXX: should the syncache be re-initialized with the contents 1175 * of the new SYN here (which may have different options?) 1176 * 1177 * XXX: We do not check the sequence number to see if this is a 1178 * real retransmit or a new connection attempt. The question is 1179 * how to handle such a case; either ignore it as spoofed, or 1180 * drop the current entry and create a new one? 1181 */ 1182 sc = syncache_lookup(inc, &sch); /* returns locked entry */ 1183 SCH_LOCK_ASSERT(sch); 1184 if (sc != NULL) { 1185 TCPSTAT_INC(tcps_sc_dupsyn); 1186 if (ipopts) { 1187 /* 1188 * If we were remembering a previous source route, 1189 * forget it and use the new one we've been given. 1190 */ 1191 if (sc->sc_ipopts) 1192 (void) m_free(sc->sc_ipopts); 1193 sc->sc_ipopts = ipopts; 1194 } 1195 /* 1196 * Update timestamp if present. 1197 */ 1198 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1199 sc->sc_tsreflect = to->to_tsval; 1200 else 1201 sc->sc_flags &= ~SCF_TIMESTAMP; 1202 #ifdef MAC 1203 /* 1204 * Since we have already unconditionally allocated label 1205 * storage, free it up. The syncache entry will already 1206 * have an initialized label we can use. 1207 */ 1208 mac_syncache_destroy(&maclabel); 1209 #endif 1210 /* Retransmit SYN|ACK and reset retransmit count. */ 1211 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1212 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1213 "resetting timer and retransmitting SYN|ACK\n", 1214 s, __func__); 1215 free(s, M_TCPLOG); 1216 } 1217 if (syncache_respond(sc) == 0) { 1218 sc->sc_rxmits = 0; 1219 syncache_timeout(sc, sch, 1); 1220 TCPSTAT_INC(tcps_sndacks); 1221 TCPSTAT_INC(tcps_sndtotal); 1222 } 1223 SCH_UNLOCK(sch); 1224 goto done; 1225 } 1226 1227 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1228 if (sc == NULL) { 1229 /* 1230 * The zone allocator couldn't provide more entries. 1231 * Treat this as if the cache was full; drop the oldest 1232 * entry and insert the new one. 1233 */ 1234 TCPSTAT_INC(tcps_sc_zonefail); 1235 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) 1236 syncache_drop(sc, sch); 1237 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1238 if (sc == NULL) { 1239 if (V_tcp_syncookies) { 1240 bzero(&scs, sizeof(scs)); 1241 sc = &scs; 1242 } else { 1243 SCH_UNLOCK(sch); 1244 if (ipopts) 1245 (void) m_free(ipopts); 1246 goto done; 1247 } 1248 } 1249 } 1250 1251 /* 1252 * Fill in the syncache values. 1253 */ 1254 #ifdef MAC 1255 sc->sc_label = maclabel; 1256 #endif 1257 sc->sc_cred = cred; 1258 cred = NULL; 1259 sc->sc_ipopts = ipopts; 1260 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1261 #ifdef INET6 1262 if (!(inc->inc_flags & INC_ISIPV6)) 1263 #endif 1264 { 1265 sc->sc_ip_tos = ip_tos; 1266 sc->sc_ip_ttl = ip_ttl; 1267 } 1268 #ifdef TCP_OFFLOAD 1269 sc->sc_tod = tod; 1270 sc->sc_todctx = todctx; 1271 #endif 1272 sc->sc_irs = th->th_seq; 1273 sc->sc_iss = arc4random(); 1274 sc->sc_flags = 0; 1275 sc->sc_flowlabel = 0; 1276 1277 /* 1278 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1279 * win was derived from socket earlier in the function. 1280 */ 1281 win = imax(win, 0); 1282 win = imin(win, TCP_MAXWIN); 1283 sc->sc_wnd = win; 1284 1285 if (V_tcp_do_rfc1323) { 1286 /* 1287 * A timestamp received in a SYN makes 1288 * it ok to send timestamp requests and replies. 1289 */ 1290 if (to->to_flags & TOF_TS) { 1291 sc->sc_tsreflect = to->to_tsval; 1292 sc->sc_ts = tcp_ts_getticks(); 1293 sc->sc_flags |= SCF_TIMESTAMP; 1294 } 1295 if (to->to_flags & TOF_SCALE) { 1296 int wscale = 0; 1297 1298 /* 1299 * Pick the smallest possible scaling factor that 1300 * will still allow us to scale up to sb_max, aka 1301 * kern.ipc.maxsockbuf. 1302 * 1303 * We do this because there are broken firewalls that 1304 * will corrupt the window scale option, leading to 1305 * the other endpoint believing that our advertised 1306 * window is unscaled. At scale factors larger than 1307 * 5 the unscaled window will drop below 1500 bytes, 1308 * leading to serious problems when traversing these 1309 * broken firewalls. 1310 * 1311 * With the default maxsockbuf of 256K, a scale factor 1312 * of 3 will be chosen by this algorithm. Those who 1313 * choose a larger maxsockbuf should watch out 1314 * for the compatiblity problems mentioned above. 1315 * 1316 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1317 * or <SYN,ACK>) segment itself is never scaled. 1318 */ 1319 while (wscale < TCP_MAX_WINSHIFT && 1320 (TCP_MAXWIN << wscale) < sb_max) 1321 wscale++; 1322 sc->sc_requested_r_scale = wscale; 1323 sc->sc_requested_s_scale = to->to_wscale; 1324 sc->sc_flags |= SCF_WINSCALE; 1325 } 1326 } 1327 #ifdef TCP_SIGNATURE 1328 /* 1329 * If listening socket requested TCP digests, and received SYN 1330 * contains the option, flag this in the syncache so that 1331 * syncache_respond() will do the right thing with the SYN+ACK. 1332 * XXX: Currently we always record the option by default and will 1333 * attempt to use it in syncache_respond(). 1334 */ 1335 if (to->to_flags & TOF_SIGNATURE || ltflags & TF_SIGNATURE) 1336 sc->sc_flags |= SCF_SIGNATURE; 1337 #endif 1338 if (to->to_flags & TOF_SACKPERM) 1339 sc->sc_flags |= SCF_SACK; 1340 if (to->to_flags & TOF_MSS) 1341 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1342 if (ltflags & TF_NOOPT) 1343 sc->sc_flags |= SCF_NOOPT; 1344 if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn) 1345 sc->sc_flags |= SCF_ECN; 1346 1347 if (V_tcp_syncookies) 1348 sc->sc_iss = syncookie_generate(sch, sc); 1349 #ifdef INET6 1350 if (autoflowlabel) { 1351 if (V_tcp_syncookies) 1352 sc->sc_flowlabel = sc->sc_iss; 1353 else 1354 sc->sc_flowlabel = ip6_randomflowlabel(); 1355 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1356 } 1357 #endif 1358 SCH_UNLOCK(sch); 1359 1360 /* 1361 * Do a standard 3-way handshake. 1362 */ 1363 if (syncache_respond(sc) == 0) { 1364 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs) 1365 syncache_free(sc); 1366 else if (sc != &scs) 1367 syncache_insert(sc, sch); /* locks and unlocks sch */ 1368 TCPSTAT_INC(tcps_sndacks); 1369 TCPSTAT_INC(tcps_sndtotal); 1370 } else { 1371 if (sc != &scs) 1372 syncache_free(sc); 1373 TCPSTAT_INC(tcps_sc_dropped); 1374 } 1375 1376 done: 1377 if (cred != NULL) 1378 crfree(cred); 1379 #ifdef MAC 1380 if (sc == &scs) 1381 mac_syncache_destroy(&maclabel); 1382 #endif 1383 if (m) { 1384 1385 *lsop = NULL; 1386 m_freem(m); 1387 } 1388 } 1389 1390 static int 1391 syncache_respond(struct syncache *sc) 1392 { 1393 struct ip *ip = NULL; 1394 struct mbuf *m; 1395 struct tcphdr *th = NULL; 1396 int optlen, error = 0; /* Make compiler happy */ 1397 u_int16_t hlen, tlen, mssopt; 1398 struct tcpopt to; 1399 #ifdef INET6 1400 struct ip6_hdr *ip6 = NULL; 1401 #endif 1402 1403 hlen = 1404 #ifdef INET6 1405 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1406 #endif 1407 sizeof(struct ip); 1408 tlen = hlen + sizeof(struct tcphdr); 1409 1410 /* Determine MSS we advertize to other end of connection. */ 1411 mssopt = tcp_mssopt(&sc->sc_inc); 1412 if (sc->sc_peer_mss) 1413 mssopt = max( min(sc->sc_peer_mss, mssopt), V_tcp_minmss); 1414 1415 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1416 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1417 ("syncache: mbuf too small")); 1418 1419 /* Create the IP+TCP header from scratch. */ 1420 m = m_gethdr(M_NOWAIT, MT_DATA); 1421 if (m == NULL) 1422 return (ENOBUFS); 1423 #ifdef MAC 1424 mac_syncache_create_mbuf(sc->sc_label, m); 1425 #endif 1426 m->m_data += max_linkhdr; 1427 m->m_len = tlen; 1428 m->m_pkthdr.len = tlen; 1429 m->m_pkthdr.rcvif = NULL; 1430 1431 #ifdef INET6 1432 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1433 ip6 = mtod(m, struct ip6_hdr *); 1434 ip6->ip6_vfc = IPV6_VERSION; 1435 ip6->ip6_nxt = IPPROTO_TCP; 1436 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1437 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1438 ip6->ip6_plen = htons(tlen - hlen); 1439 /* ip6_hlim is set after checksum */ 1440 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK; 1441 ip6->ip6_flow |= sc->sc_flowlabel; 1442 1443 th = (struct tcphdr *)(ip6 + 1); 1444 } 1445 #endif 1446 #if defined(INET6) && defined(INET) 1447 else 1448 #endif 1449 #ifdef INET 1450 { 1451 ip = mtod(m, struct ip *); 1452 ip->ip_v = IPVERSION; 1453 ip->ip_hl = sizeof(struct ip) >> 2; 1454 ip->ip_len = htons(tlen); 1455 ip->ip_id = 0; 1456 ip->ip_off = 0; 1457 ip->ip_sum = 0; 1458 ip->ip_p = IPPROTO_TCP; 1459 ip->ip_src = sc->sc_inc.inc_laddr; 1460 ip->ip_dst = sc->sc_inc.inc_faddr; 1461 ip->ip_ttl = sc->sc_ip_ttl; 1462 ip->ip_tos = sc->sc_ip_tos; 1463 1464 /* 1465 * See if we should do MTU discovery. Route lookups are 1466 * expensive, so we will only unset the DF bit if: 1467 * 1468 * 1) path_mtu_discovery is disabled 1469 * 2) the SCF_UNREACH flag has been set 1470 */ 1471 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1472 ip->ip_off |= htons(IP_DF); 1473 1474 th = (struct tcphdr *)(ip + 1); 1475 } 1476 #endif /* INET */ 1477 th->th_sport = sc->sc_inc.inc_lport; 1478 th->th_dport = sc->sc_inc.inc_fport; 1479 1480 th->th_seq = htonl(sc->sc_iss); 1481 th->th_ack = htonl(sc->sc_irs + 1); 1482 th->th_off = sizeof(struct tcphdr) >> 2; 1483 th->th_x2 = 0; 1484 th->th_flags = TH_SYN|TH_ACK; 1485 th->th_win = htons(sc->sc_wnd); 1486 th->th_urp = 0; 1487 1488 if (sc->sc_flags & SCF_ECN) { 1489 th->th_flags |= TH_ECE; 1490 TCPSTAT_INC(tcps_ecn_shs); 1491 } 1492 1493 /* Tack on the TCP options. */ 1494 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1495 to.to_flags = 0; 1496 1497 to.to_mss = mssopt; 1498 to.to_flags = TOF_MSS; 1499 if (sc->sc_flags & SCF_WINSCALE) { 1500 to.to_wscale = sc->sc_requested_r_scale; 1501 to.to_flags |= TOF_SCALE; 1502 } 1503 if (sc->sc_flags & SCF_TIMESTAMP) { 1504 /* Virgin timestamp or TCP cookie enhanced one. */ 1505 to.to_tsval = sc->sc_ts; 1506 to.to_tsecr = sc->sc_tsreflect; 1507 to.to_flags |= TOF_TS; 1508 } 1509 if (sc->sc_flags & SCF_SACK) 1510 to.to_flags |= TOF_SACKPERM; 1511 #ifdef TCP_SIGNATURE 1512 if (sc->sc_flags & SCF_SIGNATURE) 1513 to.to_flags |= TOF_SIGNATURE; 1514 #endif 1515 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1516 1517 /* Adjust headers by option size. */ 1518 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1519 m->m_len += optlen; 1520 m->m_pkthdr.len += optlen; 1521 1522 #ifdef TCP_SIGNATURE 1523 if (sc->sc_flags & SCF_SIGNATURE) 1524 tcp_signature_compute(m, 0, 0, optlen, 1525 to.to_signature, IPSEC_DIR_OUTBOUND); 1526 #endif 1527 #ifdef INET6 1528 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1529 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1530 else 1531 #endif 1532 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1533 } else 1534 optlen = 0; 1535 1536 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1537 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1538 #ifdef INET6 1539 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1540 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 1541 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 1542 IPPROTO_TCP, 0); 1543 ip6->ip6_hlim = in6_selecthlim(NULL, NULL); 1544 #ifdef TCP_OFFLOAD 1545 if (ADDED_BY_TOE(sc)) { 1546 struct toedev *tod = sc->sc_tod; 1547 1548 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1549 1550 return (error); 1551 } 1552 #endif 1553 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 1554 } 1555 #endif 1556 #if defined(INET6) && defined(INET) 1557 else 1558 #endif 1559 #ifdef INET 1560 { 1561 m->m_pkthdr.csum_flags = CSUM_TCP; 1562 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1563 htons(tlen + optlen - hlen + IPPROTO_TCP)); 1564 #ifdef TCP_OFFLOAD 1565 if (ADDED_BY_TOE(sc)) { 1566 struct toedev *tod = sc->sc_tod; 1567 1568 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1569 1570 return (error); 1571 } 1572 #endif 1573 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 1574 } 1575 #endif 1576 return (error); 1577 } 1578 1579 /* 1580 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 1581 * that exceed the capacity of the syncache by avoiding the storage of any 1582 * of the SYNs we receive. Syncookies defend against blind SYN flooding 1583 * attacks where the attacker does not have access to our responses. 1584 * 1585 * Syncookies encode and include all necessary information about the 1586 * connection setup within the SYN|ACK that we send back. That way we 1587 * can avoid keeping any local state until the ACK to our SYN|ACK returns 1588 * (if ever). Normally the syncache and syncookies are running in parallel 1589 * with the latter taking over when the former is exhausted. When matching 1590 * syncache entry is found the syncookie is ignored. 1591 * 1592 * The only reliable information persisting the 3WHS is our inital sequence 1593 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 1594 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 1595 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 1596 * returns and signifies a legitimate connection if it matches the ACK. 1597 * 1598 * The available space of 32 bits to store the hash and to encode the SYN 1599 * option information is very tight and we should have at least 24 bits for 1600 * the MAC to keep the number of guesses by blind spoofing reasonably high. 1601 * 1602 * SYN option information we have to encode to fully restore a connection: 1603 * MSS: is imporant to chose an optimal segment size to avoid IP level 1604 * fragmentation along the path. The common MSS values can be encoded 1605 * in a 3-bit table. Uncommon values are captured by the next lower value 1606 * in the table leading to a slight increase in packetization overhead. 1607 * WSCALE: is necessary to allow large windows to be used for high delay- 1608 * bandwidth product links. Not scaling the window when it was initially 1609 * negotiated is bad for performance as lack of scaling further decreases 1610 * the apparent available send window. We only need to encode the WSCALE 1611 * we received from the remote end. Our end can be recalculated at any 1612 * time. The common WSCALE values can be encoded in a 3-bit table. 1613 * Uncommon values are captured by the next lower value in the table 1614 * making us under-estimate the available window size halving our 1615 * theoretically possible maximum throughput for that connection. 1616 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 1617 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 1618 * that are included in all segments on a connection. We enable them when 1619 * the ACK has them. 1620 * 1621 * Security of syncookies and attack vectors: 1622 * 1623 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 1624 * together with the gloabl secret to make it unique per connection attempt. 1625 * Thus any change of any of those parameters results in a different MAC output 1626 * in an unpredictable way unless a collision is encountered. 24 bits of the 1627 * MAC are embedded into the ISS. 1628 * 1629 * To prevent replay attacks two rotating global secrets are updated with a 1630 * new random value every 15 seconds. The life-time of a syncookie is thus 1631 * 15-30 seconds. 1632 * 1633 * Vector 1: Attacking the secret. This requires finding a weakness in the 1634 * MAC itself or the way it is used here. The attacker can do a chosen plain 1635 * text attack by varying and testing the all parameters under his control. 1636 * The strength depends on the size and randomness of the secret, and the 1637 * cryptographic security of the MAC function. Due to the constant updating 1638 * of the secret the attacker has at most 29.999 seconds to find the secret 1639 * and launch spoofed connections. After that he has to start all over again. 1640 * 1641 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 1642 * size an average of 4,823 attempts are required for a 50% chance of success 1643 * to spoof a single syncookie (birthday collision paradox). However the 1644 * attacker is blind and doesn't know if one of his attempts succeeded unless 1645 * he has a side channel to interfere success from. A single connection setup 1646 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 1647 * This many attempts are required for each one blind spoofed connection. For 1648 * every additional spoofed connection he has to launch another N attempts. 1649 * Thus for a sustained rate 100 spoofed connections per second approximately 1650 * 1,800,000 packets per second would have to be sent. 1651 * 1652 * NB: The MAC function should be fast so that it doesn't become a CPU 1653 * exhaustion attack vector itself. 1654 * 1655 * References: 1656 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 1657 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 1658 * http://cr.yp.to/syncookies.html (overview) 1659 * http://cr.yp.to/syncookies/archive (details) 1660 * 1661 * 1662 * Schematic construction of a syncookie enabled Initial Sequence Number: 1663 * 0 1 2 3 1664 * 12345678901234567890123456789012 1665 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 1666 * 1667 * x 24 MAC (truncated) 1668 * W 3 Send Window Scale index 1669 * M 3 MSS index 1670 * S 1 SACK permitted 1671 * P 1 Odd/even secret 1672 */ 1673 1674 /* 1675 * Distribution and probability of certain MSS values. Those in between are 1676 * rounded down to the next lower one. 1677 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 1678 * .2% .3% 5% 7% 7% 20% 15% 45% 1679 */ 1680 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 1681 1682 /* 1683 * Distribution and probability of certain WSCALE values. We have to map the 1684 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 1685 * bits based on prevalence of certain values. Where we don't have an exact 1686 * match for are rounded down to the next lower one letting us under-estimate 1687 * the true available window. At the moment this would happen only for the 1688 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 1689 * and window size). The absence of the WSCALE option (no scaling in either 1690 * direction) is encoded with index zero. 1691 * [WSCALE values histograms, Allman, 2012] 1692 * X 10 10 35 5 6 14 10% by host 1693 * X 11 4 5 5 18 49 3% by connections 1694 */ 1695 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 1696 1697 /* 1698 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 1699 * and good cryptographic properties. 1700 */ 1701 static uint32_t 1702 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 1703 uint8_t *secbits, uintptr_t secmod) 1704 { 1705 SIPHASH_CTX ctx; 1706 uint32_t siphash[2]; 1707 1708 SipHash24_Init(&ctx); 1709 SipHash_SetKey(&ctx, secbits); 1710 switch (inc->inc_flags & INC_ISIPV6) { 1711 #ifdef INET 1712 case 0: 1713 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 1714 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 1715 break; 1716 #endif 1717 #ifdef INET6 1718 case INC_ISIPV6: 1719 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 1720 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 1721 break; 1722 #endif 1723 } 1724 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 1725 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 1726 SipHash_Update(&ctx, &flags, sizeof(flags)); 1727 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 1728 SipHash_Final((u_int8_t *)&siphash, &ctx); 1729 1730 return (siphash[0] ^ siphash[1]); 1731 } 1732 1733 static tcp_seq 1734 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 1735 { 1736 u_int i, mss, secbit, wscale; 1737 uint32_t iss, hash; 1738 uint8_t *secbits; 1739 union syncookie cookie; 1740 1741 SCH_LOCK_ASSERT(sch); 1742 1743 cookie.cookie = 0; 1744 1745 /* Map our computed MSS into the 3-bit index. */ 1746 mss = min(tcp_mssopt(&sc->sc_inc), max(sc->sc_peer_mss, V_tcp_minmss)); 1747 for (i = sizeof(tcp_sc_msstab) / sizeof(*tcp_sc_msstab) - 1; 1748 tcp_sc_msstab[i] > mss && i > 0; 1749 i--) 1750 ; 1751 cookie.flags.mss_idx = i; 1752 1753 /* 1754 * Map the send window scale into the 3-bit index but only if 1755 * the wscale option was received. 1756 */ 1757 if (sc->sc_flags & SCF_WINSCALE) { 1758 wscale = sc->sc_requested_s_scale; 1759 for (i = sizeof(tcp_sc_wstab) / sizeof(*tcp_sc_wstab) - 1; 1760 tcp_sc_wstab[i] > wscale && i > 0; 1761 i--) 1762 ; 1763 cookie.flags.wscale_idx = i; 1764 } 1765 1766 /* Can we do SACK? */ 1767 if (sc->sc_flags & SCF_SACK) 1768 cookie.flags.sack_ok = 1; 1769 1770 /* Which of the two secrets to use. */ 1771 secbit = sch->sch_sc->secret.oddeven & 0x1; 1772 cookie.flags.odd_even = secbit; 1773 1774 secbits = sch->sch_sc->secret.key[secbit]; 1775 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 1776 (uintptr_t)sch); 1777 1778 /* 1779 * Put the flags into the hash and XOR them to get better ISS number 1780 * variance. This doesn't enhance the cryptographic strength and is 1781 * done to prevent the 8 cookie bits from showing up directly on the 1782 * wire. 1783 */ 1784 iss = hash & ~0xff; 1785 iss |= cookie.cookie ^ (hash >> 24); 1786 1787 /* Randomize the timestamp. */ 1788 if (sc->sc_flags & SCF_TIMESTAMP) { 1789 sc->sc_ts = arc4random(); 1790 sc->sc_tsoff = sc->sc_ts - tcp_ts_getticks(); 1791 } 1792 1793 TCPSTAT_INC(tcps_sc_sendcookie); 1794 return (iss); 1795 } 1796 1797 static struct syncache * 1798 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 1799 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 1800 struct socket *lso) 1801 { 1802 uint32_t hash; 1803 uint8_t *secbits; 1804 tcp_seq ack, seq; 1805 int wnd, wscale = 0; 1806 union syncookie cookie; 1807 1808 SCH_LOCK_ASSERT(sch); 1809 1810 /* 1811 * Pull information out of SYN-ACK/ACK and revert sequence number 1812 * advances. 1813 */ 1814 ack = th->th_ack - 1; 1815 seq = th->th_seq - 1; 1816 1817 /* 1818 * Unpack the flags containing enough information to restore the 1819 * connection. 1820 */ 1821 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 1822 1823 /* Which of the two secrets to use. */ 1824 secbits = sch->sch_sc->secret.key[cookie.flags.odd_even]; 1825 1826 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 1827 1828 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 1829 if ((ack & ~0xff) != (hash & ~0xff)) 1830 return (NULL); 1831 1832 /* Fill in the syncache values. */ 1833 sc->sc_flags = 0; 1834 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1835 sc->sc_ipopts = NULL; 1836 1837 sc->sc_irs = seq; 1838 sc->sc_iss = ack; 1839 1840 switch (inc->inc_flags & INC_ISIPV6) { 1841 #ifdef INET 1842 case 0: 1843 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 1844 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 1845 break; 1846 #endif 1847 #ifdef INET6 1848 case INC_ISIPV6: 1849 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 1850 sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK; 1851 break; 1852 #endif 1853 } 1854 1855 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 1856 1857 /* We can simply recompute receive window scale we sent earlier. */ 1858 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) 1859 wscale++; 1860 1861 /* Only use wscale if it was enabled in the orignal SYN. */ 1862 if (cookie.flags.wscale_idx > 0) { 1863 sc->sc_requested_r_scale = wscale; 1864 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 1865 sc->sc_flags |= SCF_WINSCALE; 1866 } 1867 1868 wnd = sbspace(&lso->so_rcv); 1869 wnd = imax(wnd, 0); 1870 wnd = imin(wnd, TCP_MAXWIN); 1871 sc->sc_wnd = wnd; 1872 1873 if (cookie.flags.sack_ok) 1874 sc->sc_flags |= SCF_SACK; 1875 1876 if (to->to_flags & TOF_TS) { 1877 sc->sc_flags |= SCF_TIMESTAMP; 1878 sc->sc_tsreflect = to->to_tsval; 1879 sc->sc_ts = to->to_tsecr; 1880 sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks(); 1881 } 1882 1883 if (to->to_flags & TOF_SIGNATURE) 1884 sc->sc_flags |= SCF_SIGNATURE; 1885 1886 sc->sc_rxmits = 0; 1887 1888 TCPSTAT_INC(tcps_sc_recvcookie); 1889 return (sc); 1890 } 1891 1892 #ifdef INVARIANTS 1893 static int 1894 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 1895 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 1896 struct socket *lso) 1897 { 1898 struct syncache scs, *scx; 1899 char *s; 1900 1901 bzero(&scs, sizeof(scs)); 1902 scx = syncookie_lookup(inc, sch, &scs, th, to, lso); 1903 1904 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 1905 return (0); 1906 1907 if (scx != NULL) { 1908 if (sc->sc_peer_mss != scx->sc_peer_mss) 1909 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 1910 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss); 1911 1912 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale) 1913 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 1914 s, __func__, sc->sc_requested_r_scale, 1915 scx->sc_requested_r_scale); 1916 1917 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale) 1918 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 1919 s, __func__, sc->sc_requested_s_scale, 1920 scx->sc_requested_s_scale); 1921 1922 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK)) 1923 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 1924 } 1925 1926 if (s != NULL) 1927 free(s, M_TCPLOG); 1928 return (0); 1929 } 1930 #endif /* INVARIANTS */ 1931 1932 static void 1933 syncookie_reseed(void *arg) 1934 { 1935 struct tcp_syncache *sc = arg; 1936 uint8_t *secbits; 1937 int secbit; 1938 1939 /* 1940 * Reseeding the secret doesn't have to be protected by a lock. 1941 * It only must be ensured that the new random values are visible 1942 * to all CPUs in a SMP environment. The atomic with release 1943 * semantics ensures that. 1944 */ 1945 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 1946 secbits = sc->secret.key[secbit]; 1947 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 1948 atomic_add_rel_int(&sc->secret.oddeven, 1); 1949 1950 /* Reschedule ourself. */ 1951 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 1952 } 1953 1954 /* 1955 * Returns the current number of syncache entries. This number 1956 * will probably change before you get around to calling 1957 * syncache_pcblist. 1958 */ 1959 int 1960 syncache_pcbcount(void) 1961 { 1962 struct syncache_head *sch; 1963 int count, i; 1964 1965 for (count = 0, i = 0; i < V_tcp_syncache.hashsize; i++) { 1966 /* No need to lock for a read. */ 1967 sch = &V_tcp_syncache.hashbase[i]; 1968 count += sch->sch_length; 1969 } 1970 return count; 1971 } 1972 1973 /* 1974 * Exports the syncache entries to userland so that netstat can display 1975 * them alongside the other sockets. This function is intended to be 1976 * called only from tcp_pcblist. 1977 * 1978 * Due to concurrency on an active system, the number of pcbs exported 1979 * may have no relation to max_pcbs. max_pcbs merely indicates the 1980 * amount of space the caller allocated for this function to use. 1981 */ 1982 int 1983 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported) 1984 { 1985 struct xtcpcb xt; 1986 struct syncache *sc; 1987 struct syncache_head *sch; 1988 int count, error, i; 1989 1990 for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) { 1991 sch = &V_tcp_syncache.hashbase[i]; 1992 SCH_LOCK(sch); 1993 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 1994 if (count >= max_pcbs) { 1995 SCH_UNLOCK(sch); 1996 goto exit; 1997 } 1998 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 1999 continue; 2000 bzero(&xt, sizeof(xt)); 2001 xt.xt_len = sizeof(xt); 2002 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2003 xt.xt_inp.inp_vflag = INP_IPV6; 2004 else 2005 xt.xt_inp.inp_vflag = INP_IPV4; 2006 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo)); 2007 xt.xt_tp.t_inpcb = &xt.xt_inp; 2008 xt.xt_tp.t_state = TCPS_SYN_RECEIVED; 2009 xt.xt_socket.xso_protocol = IPPROTO_TCP; 2010 xt.xt_socket.xso_len = sizeof (struct xsocket); 2011 xt.xt_socket.so_type = SOCK_STREAM; 2012 xt.xt_socket.so_state = SS_ISCONNECTING; 2013 error = SYSCTL_OUT(req, &xt, sizeof xt); 2014 if (error) { 2015 SCH_UNLOCK(sch); 2016 goto exit; 2017 } 2018 count++; 2019 } 2020 SCH_UNLOCK(sch); 2021 } 2022 exit: 2023 *pcbs_exported = count; 2024 return error; 2025 }
Cache object: ddaf5ef28ded2bd329c92053e4530f3c
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