1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause 3 * 4 * Copyright (c) 2001 McAfee, Inc. 5 * Copyright (c) 2006,2013 Andre Oppermann, Internet Business Solutions AG 6 * All rights reserved. 7 * 8 * This software was developed for the FreeBSD Project by Jonathan Lemon 9 * and McAfee Research, the Security Research Division of McAfee, Inc. under 10 * DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the 11 * DARPA CHATS research program. [2001 McAfee, Inc.] 12 * 13 * Redistribution and use in source and binary forms, with or without 14 * modification, are permitted provided that the following conditions 15 * are met: 16 * 1. Redistributions of source code must retain the above copyright 17 * notice, this list of conditions and the following disclaimer. 18 * 2. Redistributions in binary form must reproduce the above copyright 19 * notice, this list of conditions and the following disclaimer in the 20 * documentation and/or other materials provided with the distribution. 21 * 22 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32 * SUCH DAMAGE. 33 */ 34 35 #include "opt_inet.h" 36 #include "opt_inet6.h" 37 #include "opt_ipsec.h" 38 39 #include <sys/param.h> 40 #include <sys/systm.h> 41 #include <sys/hash.h> 42 #include <sys/refcount.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_kdtrace.h> 69 #include <netinet/in_systm.h> 70 #include <netinet/ip.h> 71 #include <netinet/in_var.h> 72 #include <netinet/in_pcb.h> 73 #include <netinet/in_rss.h> 74 #include <netinet/ip_var.h> 75 #include <netinet/ip_options.h> 76 #ifdef INET6 77 #include <netinet/ip6.h> 78 #include <netinet/icmp6.h> 79 #include <netinet6/nd6.h> 80 #include <netinet6/ip6_var.h> 81 #include <netinet6/in6_pcb.h> 82 #include <netinet6/in6_rss.h> 83 #endif 84 #include <netinet/tcp.h> 85 #include <netinet/tcp_fastopen.h> 86 #include <netinet/tcp_fsm.h> 87 #include <netinet/tcp_seq.h> 88 #include <netinet/tcp_timer.h> 89 #include <netinet/tcp_var.h> 90 #include <netinet/tcp_syncache.h> 91 #include <netinet/tcp_ecn.h> 92 #ifdef TCP_BLACKBOX 93 #include <netinet/tcp_log_buf.h> 94 #endif 95 #ifdef TCP_OFFLOAD 96 #include <netinet/toecore.h> 97 #endif 98 #include <netinet/udp.h> 99 100 #include <netipsec/ipsec_support.h> 101 102 #include <machine/in_cksum.h> 103 104 #include <security/mac/mac_framework.h> 105 106 VNET_DEFINE_STATIC(bool, tcp_syncookies) = true; 107 #define V_tcp_syncookies VNET(tcp_syncookies) 108 SYSCTL_BOOL(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW, 109 &VNET_NAME(tcp_syncookies), 0, 110 "Use TCP SYN cookies if the syncache overflows"); 111 112 VNET_DEFINE_STATIC(bool, tcp_syncookiesonly) = false; 113 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly) 114 SYSCTL_BOOL(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | 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 static int syncache_respond(struct syncache *, int); 126 static void syncache_send_challenge_ack(struct syncache *); 127 static struct socket *syncache_socket(struct syncache *, struct socket *, 128 struct mbuf *m); 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 bool syncookie_expand(struct in_conninfo *, 137 const struct syncache_head *, struct syncache *, 138 struct tcphdr *, struct tcpopt *, struct socket *, 139 uint16_t); 140 static void syncache_pause(struct in_conninfo *); 141 static void syncache_unpause(void *); 142 static void syncookie_reseed(void *); 143 #ifdef INVARIANTS 144 static void syncookie_cmp(struct in_conninfo *, 145 const struct syncache_head *, struct syncache *, 146 struct tcphdr *, struct tcpopt *, struct socket *, 147 uint16_t); 148 #endif 149 150 /* 151 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 152 * 3 retransmits corresponds to a timeout with default values of 153 * tcp_rexmit_initial * ( 1 + 154 * tcp_backoff[1] + 155 * tcp_backoff[2] + 156 * tcp_backoff[3]) + 3 * tcp_rexmit_slop, 157 * 1000 ms * (1 + 2 + 4 + 8) + 3 * 200 ms = 15600 ms, 158 * the odds are that the user has given up attempting to connect by then. 159 */ 160 #define SYNCACHE_MAXREXMTS 3 161 162 /* Arbitrary values */ 163 #define TCP_SYNCACHE_HASHSIZE 512 164 #define TCP_SYNCACHE_BUCKETLIMIT 30 165 166 VNET_DEFINE_STATIC(struct tcp_syncache, tcp_syncache); 167 #define V_tcp_syncache VNET(tcp_syncache) 168 169 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, 170 CTLFLAG_RW | CTLFLAG_MPSAFE, 0, 171 "TCP SYN cache"); 172 173 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 174 &VNET_NAME(tcp_syncache.bucket_limit), 0, 175 "Per-bucket hash limit for syncache"); 176 177 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 178 &VNET_NAME(tcp_syncache.cache_limit), 0, 179 "Overall entry limit for syncache"); 180 181 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET, 182 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache"); 183 184 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN, 185 &VNET_NAME(tcp_syncache.hashsize), 0, 186 "Size of TCP syncache hashtable"); 187 188 SYSCTL_BOOL(_net_inet_tcp_syncache, OID_AUTO, see_other, CTLFLAG_VNET | 189 CTLFLAG_RW, &VNET_NAME(tcp_syncache.see_other), 0, 190 "All syncache(4) entries are visible, ignoring UID/GID, jail(2) " 191 "and mac(4) checks"); 192 193 static int 194 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS) 195 { 196 int error; 197 u_int new; 198 199 new = V_tcp_syncache.rexmt_limit; 200 error = sysctl_handle_int(oidp, &new, 0, req); 201 if ((error == 0) && (req->newptr != NULL)) { 202 if (new > TCP_MAXRXTSHIFT) 203 error = EINVAL; 204 else 205 V_tcp_syncache.rexmt_limit = new; 206 } 207 return (error); 208 } 209 210 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, 211 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT, 212 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 213 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "IU", 214 "Limit on SYN/ACK retransmissions"); 215 216 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 217 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 218 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 219 "Send reset on socket allocation failure"); 220 221 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 222 223 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 224 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 225 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 226 227 /* 228 * Requires the syncache entry to be already removed from the bucket list. 229 */ 230 static void 231 syncache_free(struct syncache *sc) 232 { 233 234 if (sc->sc_ipopts) 235 (void)m_free(sc->sc_ipopts); 236 if (sc->sc_cred) 237 crfree(sc->sc_cred); 238 #ifdef MAC 239 mac_syncache_destroy(&sc->sc_label); 240 #endif 241 242 uma_zfree(V_tcp_syncache.zone, sc); 243 } 244 245 void 246 syncache_init(void) 247 { 248 int i; 249 250 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 251 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 252 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 253 V_tcp_syncache.hash_secret = arc4random(); 254 255 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 256 &V_tcp_syncache.hashsize); 257 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 258 &V_tcp_syncache.bucket_limit); 259 if (!powerof2(V_tcp_syncache.hashsize) || 260 V_tcp_syncache.hashsize == 0) { 261 printf("WARNING: syncache hash size is not a power of 2.\n"); 262 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 263 } 264 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 265 266 /* Set limits. */ 267 V_tcp_syncache.cache_limit = 268 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 269 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 270 &V_tcp_syncache.cache_limit); 271 272 /* Allocate the hash table. */ 273 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 274 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 275 276 #ifdef VIMAGE 277 V_tcp_syncache.vnet = curvnet; 278 #endif 279 280 /* Initialize the hash buckets. */ 281 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 282 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 283 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 284 NULL, MTX_DEF); 285 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 286 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 287 V_tcp_syncache.hashbase[i].sch_length = 0; 288 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 289 V_tcp_syncache.hashbase[i].sch_last_overflow = 290 -(SYNCOOKIE_LIFETIME + 1); 291 } 292 293 /* Create the syncache entry zone. */ 294 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 295 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 296 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 297 V_tcp_syncache.cache_limit); 298 299 /* Start the SYN cookie reseeder callout. */ 300 callout_init(&V_tcp_syncache.secret.reseed, 1); 301 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 302 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 303 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 304 syncookie_reseed, &V_tcp_syncache); 305 306 /* Initialize the pause machinery. */ 307 mtx_init(&V_tcp_syncache.pause_mtx, "tcp_sc_pause", NULL, MTX_DEF); 308 callout_init_mtx(&V_tcp_syncache.pause_co, &V_tcp_syncache.pause_mtx, 309 0); 310 V_tcp_syncache.pause_until = time_uptime - TCP_SYNCACHE_PAUSE_TIME; 311 V_tcp_syncache.pause_backoff = 0; 312 V_tcp_syncache.paused = false; 313 } 314 315 #ifdef VIMAGE 316 void 317 syncache_destroy(void) 318 { 319 struct syncache_head *sch; 320 struct syncache *sc, *nsc; 321 int i; 322 323 /* 324 * Stop the re-seed timer before freeing resources. No need to 325 * possibly schedule it another time. 326 */ 327 callout_drain(&V_tcp_syncache.secret.reseed); 328 329 /* Stop the SYN cache pause callout. */ 330 mtx_lock(&V_tcp_syncache.pause_mtx); 331 if (callout_stop(&V_tcp_syncache.pause_co) == 0) { 332 mtx_unlock(&V_tcp_syncache.pause_mtx); 333 callout_drain(&V_tcp_syncache.pause_co); 334 } else 335 mtx_unlock(&V_tcp_syncache.pause_mtx); 336 337 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 338 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 339 sch = &V_tcp_syncache.hashbase[i]; 340 callout_drain(&sch->sch_timer); 341 342 SCH_LOCK(sch); 343 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 344 syncache_drop(sc, sch); 345 SCH_UNLOCK(sch); 346 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 347 ("%s: sch->sch_bucket not empty", __func__)); 348 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 349 __func__, sch->sch_length)); 350 mtx_destroy(&sch->sch_mtx); 351 } 352 353 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 354 ("%s: cache_count not 0", __func__)); 355 356 /* Free the allocated global resources. */ 357 uma_zdestroy(V_tcp_syncache.zone); 358 free(V_tcp_syncache.hashbase, M_SYNCACHE); 359 mtx_destroy(&V_tcp_syncache.pause_mtx); 360 } 361 #endif 362 363 /* 364 * Inserts a syncache entry into the specified bucket row. 365 * Locks and unlocks the syncache_head autonomously. 366 */ 367 static void 368 syncache_insert(struct syncache *sc, struct syncache_head *sch) 369 { 370 struct syncache *sc2; 371 372 SCH_LOCK(sch); 373 374 /* 375 * Make sure that we don't overflow the per-bucket limit. 376 * If the bucket is full, toss the oldest element. 377 */ 378 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 379 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 380 ("sch->sch_length incorrect")); 381 syncache_pause(&sc->sc_inc); 382 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 383 sch->sch_last_overflow = time_uptime; 384 syncache_drop(sc2, sch); 385 } 386 387 /* Put it into the bucket. */ 388 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 389 sch->sch_length++; 390 391 #ifdef TCP_OFFLOAD 392 if (ADDED_BY_TOE(sc)) { 393 struct toedev *tod = sc->sc_tod; 394 395 tod->tod_syncache_added(tod, sc->sc_todctx); 396 } 397 #endif 398 399 /* Reinitialize the bucket row's timer. */ 400 if (sch->sch_length == 1) 401 sch->sch_nextc = ticks + INT_MAX; 402 syncache_timeout(sc, sch, 1); 403 404 SCH_UNLOCK(sch); 405 406 TCPSTATES_INC(TCPS_SYN_RECEIVED); 407 TCPSTAT_INC(tcps_sc_added); 408 } 409 410 /* 411 * Remove and free entry from syncache bucket row. 412 * Expects locked syncache head. 413 */ 414 static void 415 syncache_drop(struct syncache *sc, struct syncache_head *sch) 416 { 417 418 SCH_LOCK_ASSERT(sch); 419 420 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 421 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 422 sch->sch_length--; 423 424 #ifdef TCP_OFFLOAD 425 if (ADDED_BY_TOE(sc)) { 426 struct toedev *tod = sc->sc_tod; 427 428 tod->tod_syncache_removed(tod, sc->sc_todctx); 429 } 430 #endif 431 432 syncache_free(sc); 433 } 434 435 /* 436 * Engage/reengage time on bucket row. 437 */ 438 static void 439 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 440 { 441 int rexmt; 442 443 if (sc->sc_rxmits == 0) 444 rexmt = tcp_rexmit_initial; 445 else 446 TCPT_RANGESET(rexmt, 447 tcp_rexmit_initial * tcp_backoff[sc->sc_rxmits], 448 tcp_rexmit_min, tcp_rexmit_max); 449 sc->sc_rxttime = ticks + rexmt; 450 sc->sc_rxmits++; 451 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 452 sch->sch_nextc = sc->sc_rxttime; 453 if (docallout) 454 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 455 syncache_timer, (void *)sch); 456 } 457 } 458 459 /* 460 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 461 * If we have retransmitted an entry the maximum number of times, expire it. 462 * One separate timer for each bucket row. 463 */ 464 static void 465 syncache_timer(void *xsch) 466 { 467 struct syncache_head *sch = (struct syncache_head *)xsch; 468 struct syncache *sc, *nsc; 469 struct epoch_tracker et; 470 int tick = ticks; 471 char *s; 472 bool paused; 473 474 CURVNET_SET(sch->sch_sc->vnet); 475 476 /* NB: syncache_head has already been locked by the callout. */ 477 SCH_LOCK_ASSERT(sch); 478 479 /* 480 * In the following cycle we may remove some entries and/or 481 * advance some timeouts, so re-initialize the bucket timer. 482 */ 483 sch->sch_nextc = tick + INT_MAX; 484 485 /* 486 * If we have paused processing, unconditionally remove 487 * all syncache entries. 488 */ 489 mtx_lock(&V_tcp_syncache.pause_mtx); 490 paused = V_tcp_syncache.paused; 491 mtx_unlock(&V_tcp_syncache.pause_mtx); 492 493 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 494 if (paused) { 495 syncache_drop(sc, sch); 496 continue; 497 } 498 /* 499 * We do not check if the listen socket still exists 500 * and accept the case where the listen socket may be 501 * gone by the time we resend the SYN/ACK. We do 502 * not expect this to happens often. If it does, 503 * then the RST will be sent by the time the remote 504 * host does the SYN/ACK->ACK. 505 */ 506 if (TSTMP_GT(sc->sc_rxttime, tick)) { 507 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 508 sch->sch_nextc = sc->sc_rxttime; 509 continue; 510 } 511 if (sc->sc_rxmits > V_tcp_ecn_maxretries) { 512 sc->sc_flags &= ~SCF_ECN_MASK; 513 } 514 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 515 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 516 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 517 "giving up and removing syncache entry\n", 518 s, __func__); 519 free(s, M_TCPLOG); 520 } 521 syncache_drop(sc, sch); 522 TCPSTAT_INC(tcps_sc_stale); 523 continue; 524 } 525 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 526 log(LOG_DEBUG, "%s; %s: Response timeout, " 527 "retransmitting (%u) SYN|ACK\n", 528 s, __func__, sc->sc_rxmits); 529 free(s, M_TCPLOG); 530 } 531 532 NET_EPOCH_ENTER(et); 533 if (syncache_respond(sc, TH_SYN|TH_ACK) == 0) { 534 syncache_timeout(sc, sch, 0); 535 TCPSTAT_INC(tcps_sndacks); 536 TCPSTAT_INC(tcps_sndtotal); 537 TCPSTAT_INC(tcps_sc_retransmitted); 538 } else { 539 /* 540 * Most likely we are memory constrained, so free 541 * resources. 542 */ 543 syncache_drop(sc, sch); 544 TCPSTAT_INC(tcps_sc_dropped); 545 } 546 NET_EPOCH_EXIT(et); 547 } 548 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 549 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 550 syncache_timer, (void *)(sch)); 551 CURVNET_RESTORE(); 552 } 553 554 /* 555 * Returns true if the system is only using cookies at the moment. 556 * This could be due to a sysadmin decision to only use cookies, or it 557 * could be due to the system detecting an attack. 558 */ 559 static inline bool 560 syncache_cookiesonly(void) 561 { 562 return ((V_tcp_syncookies && V_tcp_syncache.paused) || 563 V_tcp_syncookiesonly); 564 } 565 566 /* 567 * Find the hash bucket for the given connection. 568 */ 569 static struct syncache_head * 570 syncache_hashbucket(struct in_conninfo *inc) 571 { 572 uint32_t hash; 573 574 /* 575 * The hash is built on foreign port + local port + foreign address. 576 * We rely on the fact that struct in_conninfo starts with 16 bits 577 * of foreign port, then 16 bits of local port then followed by 128 578 * bits of foreign address. In case of IPv4 address, the first 3 579 * 32-bit words of the address always are zeroes. 580 */ 581 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5, 582 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask; 583 584 return (&V_tcp_syncache.hashbase[hash]); 585 } 586 587 /* 588 * Find an entry in the syncache. 589 * Returns always with locked syncache_head plus a matching entry or NULL. 590 */ 591 static struct syncache * 592 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 593 { 594 struct syncache *sc; 595 struct syncache_head *sch; 596 597 *schp = sch = syncache_hashbucket(inc); 598 SCH_LOCK(sch); 599 600 /* Circle through bucket row to find matching entry. */ 601 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) 602 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie, 603 sizeof(struct in_endpoints)) == 0) 604 break; 605 606 return (sc); /* Always returns with locked sch. */ 607 } 608 609 /* 610 * This function is called when we get a RST for a 611 * non-existent connection, so that we can see if the 612 * connection is in the syn cache. If it is, zap it. 613 * If required send a challenge ACK. 614 */ 615 void 616 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, uint16_t port) 617 { 618 struct syncache *sc; 619 struct syncache_head *sch; 620 char *s = NULL; 621 622 if (syncache_cookiesonly()) 623 return; 624 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 625 SCH_LOCK_ASSERT(sch); 626 627 /* 628 * No corresponding connection was found in syncache. 629 * If syncookies are enabled and possibly exclusively 630 * used, or we are under memory pressure, a valid RST 631 * may not find a syncache entry. In that case we're 632 * done and no SYN|ACK retransmissions will happen. 633 * Otherwise the RST was misdirected or spoofed. 634 */ 635 if (sc == NULL) { 636 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 637 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 638 "syncache entry (possibly syncookie only), " 639 "segment ignored\n", s, __func__); 640 TCPSTAT_INC(tcps_badrst); 641 goto done; 642 } 643 644 /* The remote UDP encaps port does not match. */ 645 if (sc->sc_port != port) { 646 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 647 log(LOG_DEBUG, "%s; %s: Spurious RST with matching " 648 "syncache entry but non-matching UDP encaps port, " 649 "segment ignored\n", s, __func__); 650 TCPSTAT_INC(tcps_badrst); 651 goto done; 652 } 653 654 /* 655 * If the RST bit is set, check the sequence number to see 656 * if this is a valid reset segment. 657 * 658 * RFC 793 page 37: 659 * In all states except SYN-SENT, all reset (RST) segments 660 * are validated by checking their SEQ-fields. A reset is 661 * valid if its sequence number is in the window. 662 * 663 * RFC 793 page 69: 664 * There are four cases for the acceptability test for an incoming 665 * segment: 666 * 667 * Segment Receive Test 668 * Length Window 669 * ------- ------- ------------------------------------------- 670 * 0 0 SEG.SEQ = RCV.NXT 671 * 0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 672 * >0 0 not acceptable 673 * >0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 674 * or RCV.NXT =< SEG.SEQ+SEG.LEN-1 < RCV.NXT+RCV.WND 675 * 676 * Note that when receiving a SYN segment in the LISTEN state, 677 * IRS is set to SEG.SEQ and RCV.NXT is set to SEG.SEQ+1, as 678 * described in RFC 793, page 66. 679 */ 680 if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) && 681 SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) || 682 (sc->sc_wnd == 0 && th->th_seq == sc->sc_irs + 1)) { 683 if (V_tcp_insecure_rst || 684 th->th_seq == sc->sc_irs + 1) { 685 syncache_drop(sc, sch); 686 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 687 log(LOG_DEBUG, 688 "%s; %s: Our SYN|ACK was rejected, " 689 "connection attempt aborted by remote " 690 "endpoint\n", 691 s, __func__); 692 TCPSTAT_INC(tcps_sc_reset); 693 } else { 694 TCPSTAT_INC(tcps_badrst); 695 /* Send challenge ACK. */ 696 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 697 log(LOG_DEBUG, "%s; %s: RST with invalid " 698 " SEQ %u != NXT %u (+WND %u), " 699 "sending challenge ACK\n", 700 s, __func__, 701 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 702 syncache_send_challenge_ack(sc); 703 } 704 } else { 705 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 706 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 707 "NXT %u (+WND %u), segment ignored\n", 708 s, __func__, 709 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 710 TCPSTAT_INC(tcps_badrst); 711 } 712 713 done: 714 if (s != NULL) 715 free(s, M_TCPLOG); 716 SCH_UNLOCK(sch); 717 } 718 719 void 720 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq, uint16_t port) 721 { 722 struct syncache *sc; 723 struct syncache_head *sch; 724 725 if (syncache_cookiesonly()) 726 return; 727 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 728 SCH_LOCK_ASSERT(sch); 729 if (sc == NULL) 730 goto done; 731 732 /* If the port != sc_port, then it's a bogus ICMP msg */ 733 if (port != sc->sc_port) 734 goto done; 735 736 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 737 if (ntohl(th_seq) != sc->sc_iss) 738 goto done; 739 740 /* 741 * If we've retransmitted 3 times and this is our second error, 742 * we remove the entry. Otherwise, we allow it to continue on. 743 * This prevents us from incorrectly nuking an entry during a 744 * spurious network outage. 745 * 746 * See tcp_notify(). 747 */ 748 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 749 sc->sc_flags |= SCF_UNREACH; 750 goto done; 751 } 752 syncache_drop(sc, sch); 753 TCPSTAT_INC(tcps_sc_unreach); 754 done: 755 SCH_UNLOCK(sch); 756 } 757 758 /* 759 * Build a new TCP socket structure from a syncache entry. 760 * 761 * On success return the newly created socket with its underlying inp locked. 762 */ 763 static struct socket * 764 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 765 { 766 struct inpcb *inp = NULL; 767 struct socket *so; 768 struct tcpcb *tp; 769 int error; 770 char *s; 771 772 NET_EPOCH_ASSERT(); 773 774 /* 775 * Creation of a socket via solisten_clone() bypasses call to pr_attach. 776 * That's why there is some pasted code from soattach() and from 777 * tcp_usr_attach() here. This should improve once TCP is PR_SOCKBUF. 778 */ 779 if ((so = solisten_clone(lso)) == NULL) 780 goto allocfail; 781 mtx_init(&so->so_snd_mtx, "so_snd", NULL, MTX_DEF); 782 mtx_init(&so->so_rcv_mtx, "so_rcv", NULL, MTX_DEF); 783 so->so_snd.sb_mtx = &so->so_snd_mtx; 784 so->so_rcv.sb_mtx = &so->so_rcv_mtx; 785 error = soreserve(so, lso->sol_sbsnd_hiwat, lso->sol_sbrcv_hiwat); 786 if (error) { 787 sodealloc(so); 788 goto allocfail; 789 } 790 #ifdef MAC 791 mac_socketpeer_set_from_mbuf(m, so); 792 #endif 793 error = in_pcballoc(so, &V_tcbinfo); 794 if (error) { 795 sodealloc(so); 796 goto allocfail; 797 } 798 inp = sotoinpcb(so); 799 if ((tp = tcp_newtcpcb(inp, sototcpcb(lso))) == NULL) { 800 in_pcbfree(inp); 801 sodealloc(so); 802 goto allocfail; 803 } 804 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 805 #ifdef INET6 806 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 807 inp->inp_vflag &= ~INP_IPV4; 808 inp->inp_vflag |= INP_IPV6; 809 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 810 } else { 811 inp->inp_vflag &= ~INP_IPV6; 812 inp->inp_vflag |= INP_IPV4; 813 #endif 814 inp->inp_ip_ttl = sc->sc_ip_ttl; 815 inp->inp_ip_tos = sc->sc_ip_tos; 816 inp->inp_laddr = sc->sc_inc.inc_laddr; 817 #ifdef INET6 818 } 819 #endif 820 inp->inp_lport = sc->sc_inc.inc_lport; 821 #ifdef INET6 822 if (inp->inp_vflag & INP_IPV6PROTO) { 823 struct inpcb *oinp = sotoinpcb(lso); 824 825 /* 826 * Inherit socket options from the listening socket. 827 * Note that in6p_inputopts are not (and should not be) 828 * copied, since it stores previously received options and is 829 * used to detect if each new option is different than the 830 * previous one and hence should be passed to a user. 831 * If we copied in6p_inputopts, a user would not be able to 832 * receive options just after calling the accept system call. 833 */ 834 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 835 if (oinp->in6p_outputopts) 836 inp->in6p_outputopts = 837 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 838 inp->in6p_hops = oinp->in6p_hops; 839 } 840 841 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 842 struct sockaddr_in6 sin6; 843 844 sin6.sin6_family = AF_INET6; 845 sin6.sin6_len = sizeof(sin6); 846 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 847 sin6.sin6_port = sc->sc_inc.inc_fport; 848 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 849 error = in6_pcbconnect(inp, &sin6, thread0.td_ucred, false); 850 if (error != 0) 851 goto abort; 852 /* Override flowlabel from in6_pcbconnect. */ 853 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 854 inp->inp_flow |= sc->sc_flowlabel; 855 } 856 #endif /* INET6 */ 857 #if defined(INET) && defined(INET6) 858 else 859 #endif 860 #ifdef INET 861 { 862 struct sockaddr_in sin; 863 864 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 865 866 if (inp->inp_options == NULL) { 867 inp->inp_options = sc->sc_ipopts; 868 sc->sc_ipopts = NULL; 869 } 870 871 sin.sin_family = AF_INET; 872 sin.sin_len = sizeof(sin); 873 sin.sin_addr = sc->sc_inc.inc_faddr; 874 sin.sin_port = sc->sc_inc.inc_fport; 875 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 876 error = in_pcbconnect(inp, &sin, thread0.td_ucred); 877 if (error != 0) 878 goto abort; 879 } 880 #endif /* INET */ 881 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 882 /* Copy old policy into new socket's. */ 883 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0) 884 printf("syncache_socket: could not copy policy\n"); 885 #endif 886 if (sc->sc_flowtype != M_HASHTYPE_NONE) { 887 inp->inp_flowid = sc->sc_flowid; 888 inp->inp_flowtype = sc->sc_flowtype; 889 } else { 890 /* assign flowid by software RSS hash */ 891 #ifdef INET6 892 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 893 rss_proto_software_hash_v6(&inp->in6p_faddr, 894 &inp->in6p_laddr, 895 inp->inp_fport, 896 inp->inp_lport, 897 IPPROTO_TCP, 898 &inp->inp_flowid, 899 &inp->inp_flowtype); 900 } else 901 #endif /* INET6 */ 902 { 903 #ifdef INET 904 rss_proto_software_hash_v4(inp->inp_faddr, 905 inp->inp_laddr, 906 inp->inp_fport, 907 inp->inp_lport, 908 IPPROTO_TCP, 909 &inp->inp_flowid, 910 &inp->inp_flowtype); 911 #endif /* INET */ 912 } 913 } 914 #ifdef NUMA 915 inp->inp_numa_domain = sc->sc_numa_domain; 916 #endif 917 918 tp->t_state = TCPS_SYN_RECEIVED; 919 tp->iss = sc->sc_iss; 920 tp->irs = sc->sc_irs; 921 tp->t_port = sc->sc_port; 922 tcp_rcvseqinit(tp); 923 tcp_sendseqinit(tp); 924 tp->snd_wl1 = sc->sc_irs; 925 tp->snd_max = tp->iss + 1; 926 tp->snd_nxt = tp->iss + 1; 927 tp->rcv_up = sc->sc_irs + 1; 928 tp->rcv_wnd = sc->sc_wnd; 929 tp->rcv_adv += tp->rcv_wnd; 930 tp->last_ack_sent = tp->rcv_nxt; 931 932 tp->t_flags = sototcpcb(lso)->t_flags & 933 (TF_LRD|TF_NOPUSH|TF_NODELAY); 934 if (sc->sc_flags & SCF_NOOPT) 935 tp->t_flags |= TF_NOOPT; 936 else { 937 if (sc->sc_flags & SCF_WINSCALE) { 938 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 939 tp->snd_scale = sc->sc_requested_s_scale; 940 tp->request_r_scale = sc->sc_requested_r_scale; 941 } 942 if (sc->sc_flags & SCF_TIMESTAMP) { 943 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 944 tp->ts_recent = sc->sc_tsreflect; 945 tp->ts_recent_age = tcp_ts_getticks(); 946 tp->ts_offset = sc->sc_tsoff; 947 } 948 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 949 if (sc->sc_flags & SCF_SIGNATURE) 950 tp->t_flags |= TF_SIGNATURE; 951 #endif 952 if (sc->sc_flags & SCF_SACK) 953 tp->t_flags |= TF_SACK_PERMIT; 954 } 955 956 tcp_ecn_syncache_socket(tp, sc); 957 958 /* 959 * Set up MSS and get cached values from tcp_hostcache. 960 * This might overwrite some of the defaults we just set. 961 */ 962 tcp_mss(tp, sc->sc_peer_mss); 963 964 /* 965 * If the SYN,ACK was retransmitted, indicate that CWND to be 966 * limited to one segment in cc_conn_init(). 967 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 968 */ 969 if (sc->sc_rxmits > 1) 970 tp->snd_cwnd = 1; 971 972 /* Copy over the challenge ACK state. */ 973 tp->t_challenge_ack_end = sc->sc_challenge_ack_end; 974 tp->t_challenge_ack_cnt = sc->sc_challenge_ack_cnt; 975 976 #ifdef TCP_OFFLOAD 977 /* 978 * Allow a TOE driver to install its hooks. Note that we hold the 979 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 980 * new connection before the TOE driver has done its thing. 981 */ 982 if (ADDED_BY_TOE(sc)) { 983 struct toedev *tod = sc->sc_tod; 984 985 tod->tod_offload_socket(tod, sc->sc_todctx, so); 986 } 987 #endif 988 #ifdef TCP_BLACKBOX 989 /* 990 * Inherit the log state from the listening socket, if 991 * - the log state of the listening socket is not off and 992 * - the listening socket was not auto selected from all sessions and 993 * - a log id is not set on the listening socket. 994 * This avoids inheriting a log state which was automatically set. 995 */ 996 if ((tcp_get_bblog_state(sototcpcb(lso)) != TCP_LOG_STATE_OFF) && 997 ((sototcpcb(lso)->t_flags2 & TF2_LOG_AUTO) == 0) && 998 (sototcpcb(lso)->t_lib == NULL)) { 999 tcp_log_state_change(tp, tcp_get_bblog_state(sototcpcb(lso))); 1000 } 1001 #endif 1002 /* 1003 * Copy and activate timers. 1004 */ 1005 tp->t_maxunacktime = sototcpcb(lso)->t_maxunacktime; 1006 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 1007 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 1008 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 1009 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 1010 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 1011 1012 TCPSTAT_INC(tcps_accepts); 1013 TCP_PROBE6(state__change, NULL, tp, NULL, tp, NULL, TCPS_LISTEN); 1014 1015 if (!solisten_enqueue(so, SS_ISCONNECTED)) 1016 tp->t_flags |= TF_SONOTCONN; 1017 /* Can we inherit anything from the listener? */ 1018 if (tp->t_fb->tfb_inherit != NULL) { 1019 (*tp->t_fb->tfb_inherit)(tp, sotoinpcb(lso)); 1020 } 1021 return (so); 1022 1023 allocfail: 1024 /* 1025 * Drop the connection; we will either send a RST or have the peer 1026 * retransmit its SYN again after its RTO and try again. 1027 */ 1028 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 1029 log(LOG_DEBUG, "%s; %s: Socket create failed " 1030 "due to limits or memory shortage\n", 1031 s, __func__); 1032 free(s, M_TCPLOG); 1033 } 1034 TCPSTAT_INC(tcps_listendrop); 1035 return (NULL); 1036 1037 abort: 1038 tcp_discardcb(tp); 1039 in_pcbfree(inp); 1040 sodealloc(so); 1041 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 1042 log(LOG_DEBUG, "%s; %s: in%s_pcbconnect failed with error %i\n", 1043 s, __func__, (sc->sc_inc.inc_flags & INC_ISIPV6) ? "6" : "", 1044 error); 1045 free(s, M_TCPLOG); 1046 } 1047 TCPSTAT_INC(tcps_listendrop); 1048 return (NULL); 1049 } 1050 1051 /* 1052 * This function gets called when we receive an ACK for a 1053 * socket in the LISTEN state. We look up the connection 1054 * in the syncache, and if its there, we pull it out of 1055 * the cache and turn it into a full-blown connection in 1056 * the SYN-RECEIVED state. 1057 * 1058 * On syncache_socket() success the newly created socket 1059 * has its underlying inp locked. 1060 * 1061 * *lsop is updated, if and only if 1 is returned. 1062 */ 1063 int 1064 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1065 struct socket **lsop, struct mbuf *m, uint16_t port) 1066 { 1067 struct syncache *sc; 1068 struct syncache_head *sch; 1069 struct syncache scs; 1070 char *s; 1071 bool locked; 1072 1073 NET_EPOCH_ASSERT(); 1074 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 1075 ("%s: can handle only ACK", __func__)); 1076 1077 if (syncache_cookiesonly()) { 1078 sc = NULL; 1079 sch = syncache_hashbucket(inc); 1080 locked = false; 1081 } else { 1082 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1083 locked = true; 1084 SCH_LOCK_ASSERT(sch); 1085 } 1086 1087 #ifdef INVARIANTS 1088 /* 1089 * Test code for syncookies comparing the syncache stored 1090 * values with the reconstructed values from the cookie. 1091 */ 1092 if (sc != NULL) 1093 syncookie_cmp(inc, sch, sc, th, to, *lsop, port); 1094 #endif 1095 1096 if (sc == NULL) { 1097 if (locked) { 1098 /* 1099 * The syncache is currently in use (neither disabled, 1100 * nor paused), but no entry was found. 1101 */ 1102 if (!V_tcp_syncookies) { 1103 /* 1104 * Since no syncookies are used in case of 1105 * a bucket overflow, don't even check for 1106 * a valid syncookie. 1107 */ 1108 SCH_UNLOCK(sch); 1109 TCPSTAT_INC(tcps_sc_spurcookie); 1110 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1111 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1112 "segment rejected " 1113 "(syncookies disabled)\n", 1114 s, __func__); 1115 free(s, M_TCPLOG); 1116 } 1117 return (0); 1118 } 1119 if (sch->sch_last_overflow < 1120 time_uptime - SYNCOOKIE_LIFETIME) { 1121 /* 1122 * Since the bucket did not overflow recently, 1123 * don't even check for a valid syncookie. 1124 */ 1125 SCH_UNLOCK(sch); 1126 TCPSTAT_INC(tcps_sc_spurcookie); 1127 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1128 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1129 "segment rejected " 1130 "(no syncache entry)\n", 1131 s, __func__); 1132 free(s, M_TCPLOG); 1133 } 1134 return (0); 1135 } 1136 SCH_UNLOCK(sch); 1137 } 1138 bzero(&scs, sizeof(scs)); 1139 /* 1140 * Now check, if the syncookie is valid. If it is, create an on 1141 * stack syncache entry. 1142 */ 1143 if (syncookie_expand(inc, sch, &scs, th, to, *lsop, port)) { 1144 sc = &scs; 1145 TCPSTAT_INC(tcps_sc_recvcookie); 1146 } else { 1147 TCPSTAT_INC(tcps_sc_failcookie); 1148 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1149 log(LOG_DEBUG, "%s; %s: Segment failed " 1150 "SYNCOOKIE authentication, segment rejected " 1151 "(probably spoofed)\n", s, __func__); 1152 free(s, M_TCPLOG); 1153 } 1154 return (0); 1155 } 1156 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1157 /* If received ACK has MD5 signature, check it. */ 1158 if ((to->to_flags & TOF_SIGNATURE) != 0 && 1159 (!TCPMD5_ENABLED() || 1160 TCPMD5_INPUT(m, th, to->to_signature) != 0)) { 1161 /* Drop the ACK. */ 1162 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1163 log(LOG_DEBUG, "%s; %s: Segment rejected, " 1164 "MD5 signature doesn't match.\n", 1165 s, __func__); 1166 free(s, M_TCPLOG); 1167 } 1168 TCPSTAT_INC(tcps_sig_err_sigopt); 1169 return (-1); /* Do not send RST */ 1170 } 1171 #endif /* TCP_SIGNATURE */ 1172 if (m != NULL && M_HASHTYPE_ISHASH_TCP(m)) { 1173 sc->sc_flowid = m->m_pkthdr.flowid; 1174 sc->sc_flowtype = M_HASHTYPE_GET(m); 1175 } 1176 #ifdef NUMA 1177 sc->sc_numa_domain = m ? m->m_pkthdr.numa_domain : M_NODOM; 1178 #endif 1179 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1180 } else { 1181 if (sc->sc_port != port) { 1182 SCH_UNLOCK(sch); 1183 return (0); 1184 } 1185 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1186 /* 1187 * If listening socket requested TCP digests, check that 1188 * received ACK has signature and it is correct. 1189 * If not, drop the ACK and leave sc entry in the cache, 1190 * because SYN was received with correct signature. 1191 */ 1192 if (sc->sc_flags & SCF_SIGNATURE) { 1193 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1194 /* No signature */ 1195 TCPSTAT_INC(tcps_sig_err_nosigopt); 1196 SCH_UNLOCK(sch); 1197 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1198 log(LOG_DEBUG, "%s; %s: Segment " 1199 "rejected, MD5 signature wasn't " 1200 "provided.\n", s, __func__); 1201 free(s, M_TCPLOG); 1202 } 1203 return (-1); /* Do not send RST */ 1204 } 1205 if (!TCPMD5_ENABLED() || 1206 TCPMD5_INPUT(m, th, to->to_signature) != 0) { 1207 /* Doesn't match or no SA */ 1208 SCH_UNLOCK(sch); 1209 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1210 log(LOG_DEBUG, "%s; %s: Segment " 1211 "rejected, MD5 signature doesn't " 1212 "match.\n", s, __func__); 1213 free(s, M_TCPLOG); 1214 } 1215 return (-1); /* Do not send RST */ 1216 } 1217 } 1218 #endif /* TCP_SIGNATURE */ 1219 1220 /* 1221 * RFC 7323 PAWS: If we have a timestamp on this segment and 1222 * it's less than ts_recent, drop it. 1223 * XXXMT: RFC 7323 also requires to send an ACK. 1224 * In tcp_input.c this is only done for TCP segments 1225 * with user data, so be consistent here and just drop 1226 * the segment. 1227 */ 1228 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS && 1229 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) { 1230 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1231 log(LOG_DEBUG, 1232 "%s; %s: SEG.TSval %u < TS.Recent %u, " 1233 "segment dropped\n", s, __func__, 1234 to->to_tsval, sc->sc_tsreflect); 1235 } 1236 SCH_UNLOCK(sch); 1237 free(s, M_TCPLOG); 1238 return (-1); /* Do not send RST */ 1239 } 1240 1241 /* 1242 * If timestamps were not negotiated during SYN/ACK and a 1243 * segment with a timestamp is received, ignore the 1244 * timestamp and process the packet normally. 1245 * See section 3.2 of RFC 7323. 1246 */ 1247 if (!(sc->sc_flags & SCF_TIMESTAMP) && 1248 (to->to_flags & TOF_TS)) { 1249 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1250 log(LOG_DEBUG, "%s; %s: Timestamp not " 1251 "expected, segment processed normally\n", 1252 s, __func__); 1253 free(s, M_TCPLOG); 1254 } 1255 } 1256 1257 /* 1258 * If timestamps were negotiated during SYN/ACK and a 1259 * segment without a timestamp is received, silently drop 1260 * the segment, unless the missing timestamps are tolerated. 1261 * See section 3.2 of RFC 7323. 1262 */ 1263 if ((sc->sc_flags & SCF_TIMESTAMP) && 1264 !(to->to_flags & TOF_TS)) { 1265 if (V_tcp_tolerate_missing_ts) { 1266 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1267 log(LOG_DEBUG, 1268 "%s; %s: Timestamp missing, " 1269 "segment processed normally\n", 1270 s, __func__); 1271 free(s, M_TCPLOG); 1272 } 1273 } else { 1274 SCH_UNLOCK(sch); 1275 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1276 log(LOG_DEBUG, 1277 "%s; %s: Timestamp missing, " 1278 "segment silently dropped\n", 1279 s, __func__); 1280 free(s, M_TCPLOG); 1281 } 1282 return (-1); /* Do not send RST */ 1283 } 1284 } 1285 1286 /* 1287 * SEG.SEQ validation: 1288 * The SEG.SEQ must be in the window starting at our 1289 * initial receive sequence number + 1. 1290 */ 1291 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1292 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1293 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1294 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, " 1295 "sending challenge ACK\n", 1296 s, __func__, th->th_seq, sc->sc_irs + 1); 1297 syncache_send_challenge_ack(sc); 1298 SCH_UNLOCK(sch); 1299 free(s, M_TCPLOG); 1300 return (-1); /* Do not send RST */ 1301 } 1302 1303 /* 1304 * SEG.ACK validation: 1305 * SEG.ACK must match our initial send sequence number + 1. 1306 */ 1307 if (th->th_ack != sc->sc_iss + 1) { 1308 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1309 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, " 1310 "segment rejected\n", 1311 s, __func__, th->th_ack, sc->sc_iss + 1); 1312 SCH_UNLOCK(sch); 1313 free(s, M_TCPLOG); 1314 return (0); /* Do send RST, do not free sc. */ 1315 } 1316 1317 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 1318 sch->sch_length--; 1319 #ifdef TCP_OFFLOAD 1320 if (ADDED_BY_TOE(sc)) { 1321 struct toedev *tod = sc->sc_tod; 1322 1323 tod->tod_syncache_removed(tod, sc->sc_todctx); 1324 } 1325 #endif 1326 SCH_UNLOCK(sch); 1327 } 1328 1329 *lsop = syncache_socket(sc, *lsop, m); 1330 1331 if (__predict_false(*lsop == NULL)) { 1332 TCPSTAT_INC(tcps_sc_aborted); 1333 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1334 } else if (sc != &scs) 1335 TCPSTAT_INC(tcps_sc_completed); 1336 1337 if (sc != &scs) 1338 syncache_free(sc); 1339 return (1); 1340 } 1341 1342 static struct socket * 1343 syncache_tfo_expand(struct syncache *sc, struct socket *lso, struct mbuf *m, 1344 uint64_t response_cookie) 1345 { 1346 struct inpcb *inp; 1347 struct tcpcb *tp; 1348 unsigned int *pending_counter; 1349 struct socket *so; 1350 1351 NET_EPOCH_ASSERT(); 1352 1353 pending_counter = intotcpcb(sotoinpcb(lso))->t_tfo_pending; 1354 so = syncache_socket(sc, lso, m); 1355 if (so == NULL) { 1356 TCPSTAT_INC(tcps_sc_aborted); 1357 atomic_subtract_int(pending_counter, 1); 1358 } else { 1359 soisconnected(so); 1360 inp = sotoinpcb(so); 1361 tp = intotcpcb(inp); 1362 tp->t_flags |= TF_FASTOPEN; 1363 tp->t_tfo_cookie.server = response_cookie; 1364 tp->snd_max = tp->iss; 1365 tp->snd_nxt = tp->iss; 1366 tp->t_tfo_pending = pending_counter; 1367 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1368 TCPSTAT_INC(tcps_sc_completed); 1369 } 1370 1371 return (so); 1372 } 1373 1374 /* 1375 * Given a LISTEN socket and an inbound SYN request, add 1376 * this to the syn cache, and send back a segment: 1377 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1378 * to the source. 1379 * 1380 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1381 * Doing so would require that we hold onto the data and deliver it 1382 * to the application. However, if we are the target of a SYN-flood 1383 * DoS attack, an attacker could send data which would eventually 1384 * consume all available buffer space if it were ACKed. By not ACKing 1385 * the data, we avoid this DoS scenario. 1386 * 1387 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO) 1388 * cookie is processed and a new socket is created. In this case, any data 1389 * accompanying the SYN will be queued to the socket by tcp_input() and will 1390 * be ACKed either when the application sends response data or the delayed 1391 * ACK timer expires, whichever comes first. 1392 */ 1393 struct socket * 1394 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1395 struct inpcb *inp, struct socket *so, struct mbuf *m, void *tod, 1396 void *todctx, uint8_t iptos, uint16_t port) 1397 { 1398 struct tcpcb *tp; 1399 struct socket *rv = NULL; 1400 struct syncache *sc = NULL; 1401 struct ucred *cred; 1402 struct syncache_head *sch; 1403 struct mbuf *ipopts = NULL; 1404 u_int ltflags; 1405 int win, ip_ttl, ip_tos; 1406 char *s; 1407 #ifdef INET6 1408 int autoflowlabel = 0; 1409 #endif 1410 #ifdef MAC 1411 struct label *maclabel = NULL; 1412 #endif 1413 struct syncache scs; 1414 uint64_t tfo_response_cookie; 1415 unsigned int *tfo_pending = NULL; 1416 int tfo_cookie_valid = 0; 1417 int tfo_response_cookie_valid = 0; 1418 bool locked; 1419 1420 INP_RLOCK_ASSERT(inp); /* listen socket */ 1421 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1422 ("%s: unexpected tcp flags", __func__)); 1423 1424 /* 1425 * Combine all so/tp operations very early to drop the INP lock as 1426 * soon as possible. 1427 */ 1428 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so)); 1429 tp = sototcpcb(so); 1430 cred = V_tcp_syncache.see_other ? NULL : crhold(so->so_cred); 1431 1432 #ifdef INET6 1433 if (inc->inc_flags & INC_ISIPV6) { 1434 if (inp->inp_flags & IN6P_AUTOFLOWLABEL) { 1435 autoflowlabel = 1; 1436 } 1437 ip_ttl = in6_selecthlim(inp, NULL); 1438 if ((inp->in6p_outputopts == NULL) || 1439 (inp->in6p_outputopts->ip6po_tclass == -1)) { 1440 ip_tos = 0; 1441 } else { 1442 ip_tos = inp->in6p_outputopts->ip6po_tclass; 1443 } 1444 } 1445 #endif 1446 #if defined(INET6) && defined(INET) 1447 else 1448 #endif 1449 #ifdef INET 1450 { 1451 ip_ttl = inp->inp_ip_ttl; 1452 ip_tos = inp->inp_ip_tos; 1453 } 1454 #endif 1455 win = so->sol_sbrcv_hiwat; 1456 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1457 1458 if (V_tcp_fastopen_server_enable && (tp->t_flags & TF_FASTOPEN) && 1459 (tp->t_tfo_pending != NULL) && 1460 (to->to_flags & TOF_FASTOPEN)) { 1461 /* 1462 * Limit the number of pending TFO connections to 1463 * approximately half of the queue limit. This prevents TFO 1464 * SYN floods from starving the service by filling the 1465 * listen queue with bogus TFO connections. 1466 */ 1467 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <= 1468 (so->sol_qlimit / 2)) { 1469 int result; 1470 1471 result = tcp_fastopen_check_cookie(inc, 1472 to->to_tfo_cookie, to->to_tfo_len, 1473 &tfo_response_cookie); 1474 tfo_cookie_valid = (result > 0); 1475 tfo_response_cookie_valid = (result >= 0); 1476 } 1477 1478 /* 1479 * Remember the TFO pending counter as it will have to be 1480 * decremented below if we don't make it to syncache_tfo_expand(). 1481 */ 1482 tfo_pending = tp->t_tfo_pending; 1483 } 1484 1485 #ifdef MAC 1486 if (mac_syncache_init(&maclabel) != 0) { 1487 INP_RUNLOCK(inp); 1488 goto done; 1489 } else 1490 mac_syncache_create(maclabel, inp); 1491 #endif 1492 if (!tfo_cookie_valid) 1493 INP_RUNLOCK(inp); 1494 1495 /* 1496 * Remember the IP options, if any. 1497 */ 1498 #ifdef INET6 1499 if (!(inc->inc_flags & INC_ISIPV6)) 1500 #endif 1501 #ifdef INET 1502 ipopts = (m) ? ip_srcroute(m) : NULL; 1503 #else 1504 ipopts = NULL; 1505 #endif 1506 1507 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1508 /* 1509 * When the socket is TCP-MD5 enabled check that, 1510 * - a signed packet is valid 1511 * - a non-signed packet does not have a security association 1512 * 1513 * If a signed packet fails validation or a non-signed packet has a 1514 * security association, the packet will be dropped. 1515 */ 1516 if (ltflags & TF_SIGNATURE) { 1517 if (to->to_flags & TOF_SIGNATURE) { 1518 if (!TCPMD5_ENABLED() || 1519 TCPMD5_INPUT(m, th, to->to_signature) != 0) 1520 goto done; 1521 } else { 1522 if (TCPMD5_ENABLED() && 1523 TCPMD5_INPUT(m, NULL, NULL) != ENOENT) 1524 goto done; 1525 } 1526 } else if (to->to_flags & TOF_SIGNATURE) 1527 goto done; 1528 #endif /* TCP_SIGNATURE */ 1529 /* 1530 * See if we already have an entry for this connection. 1531 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1532 * 1533 * XXX: should the syncache be re-initialized with the contents 1534 * of the new SYN here (which may have different options?) 1535 * 1536 * XXX: We do not check the sequence number to see if this is a 1537 * real retransmit or a new connection attempt. The question is 1538 * how to handle such a case; either ignore it as spoofed, or 1539 * drop the current entry and create a new one? 1540 */ 1541 if (syncache_cookiesonly()) { 1542 sc = NULL; 1543 sch = syncache_hashbucket(inc); 1544 locked = false; 1545 } else { 1546 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1547 locked = true; 1548 SCH_LOCK_ASSERT(sch); 1549 } 1550 if (sc != NULL) { 1551 if (tfo_cookie_valid) 1552 INP_RUNLOCK(inp); 1553 TCPSTAT_INC(tcps_sc_dupsyn); 1554 if (ipopts) { 1555 /* 1556 * If we were remembering a previous source route, 1557 * forget it and use the new one we've been given. 1558 */ 1559 if (sc->sc_ipopts) 1560 (void)m_free(sc->sc_ipopts); 1561 sc->sc_ipopts = ipopts; 1562 } 1563 /* 1564 * Update timestamp if present. 1565 */ 1566 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1567 sc->sc_tsreflect = to->to_tsval; 1568 else 1569 sc->sc_flags &= ~SCF_TIMESTAMP; 1570 /* 1571 * Adjust ECN response if needed, e.g. different 1572 * IP ECN field, or a fallback by the remote host. 1573 */ 1574 if (sc->sc_flags & SCF_ECN_MASK) { 1575 sc->sc_flags &= ~SCF_ECN_MASK; 1576 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos); 1577 } 1578 #ifdef MAC 1579 /* 1580 * Since we have already unconditionally allocated label 1581 * storage, free it up. The syncache entry will already 1582 * have an initialized label we can use. 1583 */ 1584 mac_syncache_destroy(&maclabel); 1585 #endif 1586 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1587 /* Retransmit SYN|ACK and reset retransmit count. */ 1588 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1589 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1590 "resetting timer and retransmitting SYN|ACK\n", 1591 s, __func__); 1592 free(s, M_TCPLOG); 1593 } 1594 if (syncache_respond(sc, TH_SYN|TH_ACK) == 0) { 1595 sc->sc_rxmits = 0; 1596 syncache_timeout(sc, sch, 1); 1597 TCPSTAT_INC(tcps_sndacks); 1598 TCPSTAT_INC(tcps_sndtotal); 1599 } else { 1600 /* 1601 * Most likely we are memory constrained, so free 1602 * resources. 1603 */ 1604 syncache_drop(sc, sch); 1605 TCPSTAT_INC(tcps_sc_dropped); 1606 } 1607 SCH_UNLOCK(sch); 1608 goto donenoprobe; 1609 } 1610 1611 KASSERT(sc == NULL, ("sc(%p) != NULL", sc)); 1612 /* 1613 * Skip allocating a syncache entry if we are just going to discard 1614 * it later. 1615 */ 1616 if (!locked || tfo_cookie_valid) { 1617 bzero(&scs, sizeof(scs)); 1618 sc = &scs; 1619 } else { 1620 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1621 if (sc == NULL) { 1622 /* 1623 * The zone allocator couldn't provide more entries. 1624 * Treat this as if the cache was full; drop the oldest 1625 * entry and insert the new one. 1626 */ 1627 TCPSTAT_INC(tcps_sc_zonefail); 1628 sc = TAILQ_LAST(&sch->sch_bucket, sch_head); 1629 if (sc != NULL) { 1630 sch->sch_last_overflow = time_uptime; 1631 syncache_drop(sc, sch); 1632 syncache_pause(inc); 1633 } 1634 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1635 if (sc == NULL) { 1636 if (V_tcp_syncookies) { 1637 bzero(&scs, sizeof(scs)); 1638 sc = &scs; 1639 } else { 1640 KASSERT(locked, 1641 ("%s: bucket unexpectedly unlocked", 1642 __func__)); 1643 SCH_UNLOCK(sch); 1644 goto done; 1645 } 1646 } 1647 } 1648 } 1649 1650 KASSERT(sc != NULL, ("sc == NULL")); 1651 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1652 sc->sc_tfo_cookie = &tfo_response_cookie; 1653 1654 /* 1655 * Fill in the syncache values. 1656 */ 1657 #ifdef MAC 1658 sc->sc_label = maclabel; 1659 #endif 1660 /* 1661 * sc_cred is only used in syncache_pcblist() to list TCP endpoints in 1662 * TCPS_SYN_RECEIVED state when V_tcp_syncache.see_other is false. 1663 * Therefore, store the credentials only when needed: 1664 * - sc is allocated from the zone and not using the on stack instance. 1665 * - the sysctl variable net.inet.tcp.syncache.see_other is false. 1666 * The reference count is decremented when a zone allocated sc is 1667 * freed in syncache_free(). 1668 */ 1669 if (sc != &scs && !V_tcp_syncache.see_other) { 1670 sc->sc_cred = cred; 1671 cred = NULL; 1672 } else 1673 sc->sc_cred = NULL; 1674 sc->sc_port = port; 1675 sc->sc_ipopts = ipopts; 1676 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1677 sc->sc_ip_tos = ip_tos; 1678 sc->sc_ip_ttl = ip_ttl; 1679 #ifdef TCP_OFFLOAD 1680 sc->sc_tod = tod; 1681 sc->sc_todctx = todctx; 1682 #endif 1683 sc->sc_irs = th->th_seq; 1684 sc->sc_flags = 0; 1685 sc->sc_flowlabel = 0; 1686 1687 /* 1688 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1689 * win was derived from socket earlier in the function. 1690 */ 1691 win = imax(win, 0); 1692 win = imin(win, TCP_MAXWIN); 1693 sc->sc_wnd = win; 1694 1695 if (V_tcp_do_rfc1323 && 1696 !(ltflags & TF_NOOPT)) { 1697 /* 1698 * A timestamp received in a SYN makes 1699 * it ok to send timestamp requests and replies. 1700 */ 1701 if ((to->to_flags & TOF_TS) && (V_tcp_do_rfc1323 != 2)) { 1702 sc->sc_tsreflect = to->to_tsval; 1703 sc->sc_flags |= SCF_TIMESTAMP; 1704 sc->sc_tsoff = tcp_new_ts_offset(inc); 1705 } 1706 if ((to->to_flags & TOF_SCALE) && (V_tcp_do_rfc1323 != 3)) { 1707 u_int wscale = 0; 1708 1709 /* 1710 * Pick the smallest possible scaling factor that 1711 * will still allow us to scale up to sb_max, aka 1712 * kern.ipc.maxsockbuf. 1713 * 1714 * We do this because there are broken firewalls that 1715 * will corrupt the window scale option, leading to 1716 * the other endpoint believing that our advertised 1717 * window is unscaled. At scale factors larger than 1718 * 5 the unscaled window will drop below 1500 bytes, 1719 * leading to serious problems when traversing these 1720 * broken firewalls. 1721 * 1722 * With the default maxsockbuf of 256K, a scale factor 1723 * of 3 will be chosen by this algorithm. Those who 1724 * choose a larger maxsockbuf should watch out 1725 * for the compatibility problems mentioned above. 1726 * 1727 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1728 * or <SYN,ACK>) segment itself is never scaled. 1729 */ 1730 while (wscale < TCP_MAX_WINSHIFT && 1731 (TCP_MAXWIN << wscale) < sb_max) 1732 wscale++; 1733 sc->sc_requested_r_scale = wscale; 1734 sc->sc_requested_s_scale = to->to_wscale; 1735 sc->sc_flags |= SCF_WINSCALE; 1736 } 1737 } 1738 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1739 /* 1740 * If incoming packet has an MD5 signature, flag this in the 1741 * syncache so that syncache_respond() will do the right thing 1742 * with the SYN+ACK. 1743 */ 1744 if (to->to_flags & TOF_SIGNATURE) 1745 sc->sc_flags |= SCF_SIGNATURE; 1746 #endif /* TCP_SIGNATURE */ 1747 if (to->to_flags & TOF_SACKPERM) 1748 sc->sc_flags |= SCF_SACK; 1749 if (to->to_flags & TOF_MSS) 1750 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1751 if (ltflags & TF_NOOPT) 1752 sc->sc_flags |= SCF_NOOPT; 1753 /* ECN Handshake */ 1754 if (V_tcp_do_ecn && (tp->t_flags2 & TF2_CANNOT_DO_ECN) == 0) 1755 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos); 1756 1757 if (V_tcp_syncookies || V_tcp_syncookiesonly) 1758 sc->sc_iss = syncookie_generate(sch, sc); 1759 else 1760 sc->sc_iss = arc4random(); 1761 #ifdef INET6 1762 if (autoflowlabel) { 1763 if (V_tcp_syncookies || V_tcp_syncookiesonly) 1764 sc->sc_flowlabel = sc->sc_iss; 1765 else 1766 sc->sc_flowlabel = ip6_randomflowlabel(); 1767 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1768 } 1769 #endif 1770 if (m != NULL && M_HASHTYPE_ISHASH_TCP(m)) { 1771 sc->sc_flowid = m->m_pkthdr.flowid; 1772 sc->sc_flowtype = M_HASHTYPE_GET(m); 1773 } 1774 #ifdef NUMA 1775 sc->sc_numa_domain = m ? m->m_pkthdr.numa_domain : M_NODOM; 1776 #endif 1777 if (locked) 1778 SCH_UNLOCK(sch); 1779 1780 if (tfo_cookie_valid) { 1781 rv = syncache_tfo_expand(sc, so, m, tfo_response_cookie); 1782 /* INP_RUNLOCK(inp) will be performed by the caller */ 1783 goto tfo_expanded; 1784 } 1785 1786 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1787 /* 1788 * Do a standard 3-way handshake. 1789 */ 1790 if (syncache_respond(sc, TH_SYN|TH_ACK) == 0) { 1791 if (sc != &scs) 1792 syncache_insert(sc, sch); /* locks and unlocks sch */ 1793 TCPSTAT_INC(tcps_sndacks); 1794 TCPSTAT_INC(tcps_sndtotal); 1795 } else { 1796 /* 1797 * Most likely we are memory constrained, so free resources. 1798 */ 1799 if (sc != &scs) 1800 syncache_free(sc); 1801 TCPSTAT_INC(tcps_sc_dropped); 1802 } 1803 goto donenoprobe; 1804 1805 done: 1806 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1807 donenoprobe: 1808 if (m) 1809 m_freem(m); 1810 /* 1811 * If tfo_pending is not NULL here, then a TFO SYN that did not 1812 * result in a new socket was processed and the associated pending 1813 * counter has not yet been decremented. All such TFO processing paths 1814 * transit this point. 1815 */ 1816 if (tfo_pending != NULL) 1817 tcp_fastopen_decrement_counter(tfo_pending); 1818 1819 tfo_expanded: 1820 if (cred != NULL) 1821 crfree(cred); 1822 if (sc == NULL || sc == &scs) { 1823 #ifdef MAC 1824 mac_syncache_destroy(&maclabel); 1825 #endif 1826 if (ipopts) 1827 (void)m_free(ipopts); 1828 } 1829 return (rv); 1830 } 1831 1832 /* 1833 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment 1834 * or upon 3WHS ACK timeout. 1835 */ 1836 static int 1837 syncache_respond(struct syncache *sc, int flags) 1838 { 1839 struct ip *ip = NULL; 1840 struct mbuf *m; 1841 struct tcphdr *th = NULL; 1842 struct udphdr *udp = NULL; 1843 int optlen, error = 0; /* Make compiler happy */ 1844 u_int16_t hlen, tlen, mssopt, ulen; 1845 struct tcpopt to; 1846 #ifdef INET6 1847 struct ip6_hdr *ip6 = NULL; 1848 #endif 1849 1850 NET_EPOCH_ASSERT(); 1851 1852 hlen = 1853 #ifdef INET6 1854 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1855 #endif 1856 sizeof(struct ip); 1857 tlen = hlen + sizeof(struct tcphdr); 1858 if (sc->sc_port) { 1859 tlen += sizeof(struct udphdr); 1860 } 1861 /* Determine MSS we advertize to other end of connection. */ 1862 mssopt = tcp_mssopt(&sc->sc_inc); 1863 if (sc->sc_port) 1864 mssopt -= V_tcp_udp_tunneling_overhead; 1865 mssopt = max(mssopt, V_tcp_minmss); 1866 1867 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1868 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1869 ("syncache: mbuf too small: hlen %u, sc_port %u, max_linkhdr %d + " 1870 "tlen %d + TCP_MAXOLEN %ju <= MHLEN %d", hlen, sc->sc_port, 1871 max_linkhdr, tlen, (uintmax_t)TCP_MAXOLEN, MHLEN)); 1872 1873 /* Create the IP+TCP header from scratch. */ 1874 m = m_gethdr(M_NOWAIT, MT_DATA); 1875 if (m == NULL) 1876 return (ENOBUFS); 1877 #ifdef MAC 1878 mac_syncache_create_mbuf(sc->sc_label, m); 1879 #endif 1880 m->m_data += max_linkhdr; 1881 m->m_len = tlen; 1882 m->m_pkthdr.len = tlen; 1883 m->m_pkthdr.rcvif = NULL; 1884 1885 #ifdef INET6 1886 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1887 ip6 = mtod(m, struct ip6_hdr *); 1888 ip6->ip6_vfc = IPV6_VERSION; 1889 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1890 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1891 ip6->ip6_plen = htons(tlen - hlen); 1892 /* ip6_hlim is set after checksum */ 1893 /* Zero out traffic class and flow label. */ 1894 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK; 1895 ip6->ip6_flow |= sc->sc_flowlabel; 1896 if (sc->sc_port != 0) { 1897 ip6->ip6_nxt = IPPROTO_UDP; 1898 udp = (struct udphdr *)(ip6 + 1); 1899 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1900 udp->uh_dport = sc->sc_port; 1901 ulen = (tlen - sizeof(struct ip6_hdr)); 1902 th = (struct tcphdr *)(udp + 1); 1903 } else { 1904 ip6->ip6_nxt = IPPROTO_TCP; 1905 th = (struct tcphdr *)(ip6 + 1); 1906 } 1907 ip6->ip6_flow |= htonl(sc->sc_ip_tos << IPV6_FLOWLABEL_LEN); 1908 } 1909 #endif 1910 #if defined(INET6) && defined(INET) 1911 else 1912 #endif 1913 #ifdef INET 1914 { 1915 ip = mtod(m, struct ip *); 1916 ip->ip_v = IPVERSION; 1917 ip->ip_hl = sizeof(struct ip) >> 2; 1918 ip->ip_len = htons(tlen); 1919 ip->ip_id = 0; 1920 ip->ip_off = 0; 1921 ip->ip_sum = 0; 1922 ip->ip_src = sc->sc_inc.inc_laddr; 1923 ip->ip_dst = sc->sc_inc.inc_faddr; 1924 ip->ip_ttl = sc->sc_ip_ttl; 1925 ip->ip_tos = sc->sc_ip_tos; 1926 1927 /* 1928 * See if we should do MTU discovery. Route lookups are 1929 * expensive, so we will only unset the DF bit if: 1930 * 1931 * 1) path_mtu_discovery is disabled 1932 * 2) the SCF_UNREACH flag has been set 1933 */ 1934 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1935 ip->ip_off |= htons(IP_DF); 1936 if (sc->sc_port == 0) { 1937 ip->ip_p = IPPROTO_TCP; 1938 th = (struct tcphdr *)(ip + 1); 1939 } else { 1940 ip->ip_p = IPPROTO_UDP; 1941 udp = (struct udphdr *)(ip + 1); 1942 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1943 udp->uh_dport = sc->sc_port; 1944 ulen = (tlen - sizeof(struct ip)); 1945 th = (struct tcphdr *)(udp + 1); 1946 } 1947 } 1948 #endif /* INET */ 1949 th->th_sport = sc->sc_inc.inc_lport; 1950 th->th_dport = sc->sc_inc.inc_fport; 1951 1952 if (flags & TH_SYN) 1953 th->th_seq = htonl(sc->sc_iss); 1954 else 1955 th->th_seq = htonl(sc->sc_iss + 1); 1956 th->th_ack = htonl(sc->sc_irs + 1); 1957 th->th_off = sizeof(struct tcphdr) >> 2; 1958 th->th_win = htons(sc->sc_wnd); 1959 th->th_urp = 0; 1960 1961 flags = tcp_ecn_syncache_respond(flags, sc); 1962 tcp_set_flags(th, flags); 1963 1964 /* Tack on the TCP options. */ 1965 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1966 to.to_flags = 0; 1967 1968 if (flags & TH_SYN) { 1969 to.to_mss = mssopt; 1970 to.to_flags = TOF_MSS; 1971 if (sc->sc_flags & SCF_WINSCALE) { 1972 to.to_wscale = sc->sc_requested_r_scale; 1973 to.to_flags |= TOF_SCALE; 1974 } 1975 if (sc->sc_flags & SCF_SACK) 1976 to.to_flags |= TOF_SACKPERM; 1977 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1978 if (sc->sc_flags & SCF_SIGNATURE) 1979 to.to_flags |= TOF_SIGNATURE; 1980 #endif 1981 if (sc->sc_tfo_cookie) { 1982 to.to_flags |= TOF_FASTOPEN; 1983 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1984 to.to_tfo_cookie = sc->sc_tfo_cookie; 1985 /* don't send cookie again when retransmitting response */ 1986 sc->sc_tfo_cookie = NULL; 1987 } 1988 } 1989 if (sc->sc_flags & SCF_TIMESTAMP) { 1990 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks(); 1991 to.to_tsecr = sc->sc_tsreflect; 1992 to.to_flags |= TOF_TS; 1993 } 1994 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1995 1996 /* Adjust headers by option size. */ 1997 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1998 m->m_len += optlen; 1999 m->m_pkthdr.len += optlen; 2000 #ifdef INET6 2001 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2002 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 2003 else 2004 #endif 2005 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 2006 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 2007 if (sc->sc_flags & SCF_SIGNATURE) { 2008 KASSERT(to.to_flags & TOF_SIGNATURE, 2009 ("tcp_addoptions() didn't set tcp_signature")); 2010 2011 /* NOTE: to.to_signature is inside of mbuf */ 2012 if (!TCPMD5_ENABLED() || 2013 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) { 2014 m_freem(m); 2015 return (EACCES); 2016 } 2017 } 2018 #endif 2019 } else 2020 optlen = 0; 2021 2022 if (udp) { 2023 ulen += optlen; 2024 udp->uh_ulen = htons(ulen); 2025 } 2026 M_SETFIB(m, sc->sc_inc.inc_fibnum); 2027 m->m_pkthdr.flowid = sc->sc_flowid; 2028 M_HASHTYPE_SET(m, sc->sc_flowtype); 2029 #ifdef NUMA 2030 m->m_pkthdr.numa_domain = sc->sc_numa_domain; 2031 #endif 2032 #ifdef INET6 2033 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 2034 if (sc->sc_port) { 2035 m->m_pkthdr.csum_flags = CSUM_UDP_IPV6; 2036 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2037 udp->uh_sum = in6_cksum_pseudo(ip6, ulen, 2038 IPPROTO_UDP, 0); 2039 th->th_sum = htons(0); 2040 } else { 2041 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 2042 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2043 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 2044 IPPROTO_TCP, 0); 2045 } 2046 ip6->ip6_hlim = sc->sc_ip_ttl; 2047 #ifdef TCP_OFFLOAD 2048 if (ADDED_BY_TOE(sc)) { 2049 struct toedev *tod = sc->sc_tod; 2050 2051 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2052 2053 return (error); 2054 } 2055 #endif 2056 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th); 2057 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 2058 } 2059 #endif 2060 #if defined(INET6) && defined(INET) 2061 else 2062 #endif 2063 #ifdef INET 2064 { 2065 if (sc->sc_port) { 2066 m->m_pkthdr.csum_flags = CSUM_UDP; 2067 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2068 udp->uh_sum = in_pseudo(ip->ip_src.s_addr, 2069 ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP)); 2070 th->th_sum = htons(0); 2071 } else { 2072 m->m_pkthdr.csum_flags = CSUM_TCP; 2073 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2074 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 2075 htons(tlen + optlen - hlen + IPPROTO_TCP)); 2076 } 2077 #ifdef TCP_OFFLOAD 2078 if (ADDED_BY_TOE(sc)) { 2079 struct toedev *tod = sc->sc_tod; 2080 2081 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2082 2083 return (error); 2084 } 2085 #endif 2086 TCP_PROBE5(send, NULL, NULL, ip, NULL, th); 2087 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 2088 } 2089 #endif 2090 return (error); 2091 } 2092 2093 static void 2094 syncache_send_challenge_ack(struct syncache *sc) 2095 { 2096 if (tcp_challenge_ack_check(&sc->sc_challenge_ack_end, 2097 &sc->sc_challenge_ack_cnt)) { 2098 if (syncache_respond(sc, TH_ACK) == 0) { 2099 TCPSTAT_INC(tcps_sndacks); 2100 TCPSTAT_INC(tcps_sndtotal); 2101 } 2102 } 2103 } 2104 2105 /* 2106 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 2107 * that exceed the capacity of the syncache by avoiding the storage of any 2108 * of the SYNs we receive. Syncookies defend against blind SYN flooding 2109 * attacks where the attacker does not have access to our responses. 2110 * 2111 * Syncookies encode and include all necessary information about the 2112 * connection setup within the SYN|ACK that we send back. That way we 2113 * can avoid keeping any local state until the ACK to our SYN|ACK returns 2114 * (if ever). Normally the syncache and syncookies are running in parallel 2115 * with the latter taking over when the former is exhausted. When matching 2116 * syncache entry is found the syncookie is ignored. 2117 * 2118 * The only reliable information persisting the 3WHS is our initial sequence 2119 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 2120 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 2121 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 2122 * returns and signifies a legitimate connection if it matches the ACK. 2123 * 2124 * The available space of 32 bits to store the hash and to encode the SYN 2125 * option information is very tight and we should have at least 24 bits for 2126 * the MAC to keep the number of guesses by blind spoofing reasonably high. 2127 * 2128 * SYN option information we have to encode to fully restore a connection: 2129 * MSS: is imporant to chose an optimal segment size to avoid IP level 2130 * fragmentation along the path. The common MSS values can be encoded 2131 * in a 3-bit table. Uncommon values are captured by the next lower value 2132 * in the table leading to a slight increase in packetization overhead. 2133 * WSCALE: is necessary to allow large windows to be used for high delay- 2134 * bandwidth product links. Not scaling the window when it was initially 2135 * negotiated is bad for performance as lack of scaling further decreases 2136 * the apparent available send window. We only need to encode the WSCALE 2137 * we received from the remote end. Our end can be recalculated at any 2138 * time. The common WSCALE values can be encoded in a 3-bit table. 2139 * Uncommon values are captured by the next lower value in the table 2140 * making us under-estimate the available window size halving our 2141 * theoretically possible maximum throughput for that connection. 2142 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 2143 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 2144 * that are included in all segments on a connection. We enable them when 2145 * the ACK has them. 2146 * 2147 * Security of syncookies and attack vectors: 2148 * 2149 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 2150 * together with the gloabl secret to make it unique per connection attempt. 2151 * Thus any change of any of those parameters results in a different MAC output 2152 * in an unpredictable way unless a collision is encountered. 24 bits of the 2153 * MAC are embedded into the ISS. 2154 * 2155 * To prevent replay attacks two rotating global secrets are updated with a 2156 * new random value every 15 seconds. The life-time of a syncookie is thus 2157 * 15-30 seconds. 2158 * 2159 * Vector 1: Attacking the secret. This requires finding a weakness in the 2160 * MAC itself or the way it is used here. The attacker can do a chosen plain 2161 * text attack by varying and testing the all parameters under his control. 2162 * The strength depends on the size and randomness of the secret, and the 2163 * cryptographic security of the MAC function. Due to the constant updating 2164 * of the secret the attacker has at most 29.999 seconds to find the secret 2165 * and launch spoofed connections. After that he has to start all over again. 2166 * 2167 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 2168 * size an average of 4,823 attempts are required for a 50% chance of success 2169 * to spoof a single syncookie (birthday collision paradox). However the 2170 * attacker is blind and doesn't know if one of his attempts succeeded unless 2171 * he has a side channel to interfere success from. A single connection setup 2172 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 2173 * This many attempts are required for each one blind spoofed connection. For 2174 * every additional spoofed connection he has to launch another N attempts. 2175 * Thus for a sustained rate 100 spoofed connections per second approximately 2176 * 1,800,000 packets per second would have to be sent. 2177 * 2178 * NB: The MAC function should be fast so that it doesn't become a CPU 2179 * exhaustion attack vector itself. 2180 * 2181 * References: 2182 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 2183 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 2184 * http://cr.yp.to/syncookies.html (overview) 2185 * http://cr.yp.to/syncookies/archive (details) 2186 * 2187 * 2188 * Schematic construction of a syncookie enabled Initial Sequence Number: 2189 * 0 1 2 3 2190 * 12345678901234567890123456789012 2191 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 2192 * 2193 * x 24 MAC (truncated) 2194 * W 3 Send Window Scale index 2195 * M 3 MSS index 2196 * S 1 SACK permitted 2197 * P 1 Odd/even secret 2198 */ 2199 2200 /* 2201 * Distribution and probability of certain MSS values. Those in between are 2202 * rounded down to the next lower one. 2203 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 2204 * .2% .3% 5% 7% 7% 20% 15% 45% 2205 */ 2206 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 2207 2208 /* 2209 * Distribution and probability of certain WSCALE values. We have to map the 2210 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 2211 * bits based on prevalence of certain values. Where we don't have an exact 2212 * match for are rounded down to the next lower one letting us under-estimate 2213 * the true available window. At the moment this would happen only for the 2214 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 2215 * and window size). The absence of the WSCALE option (no scaling in either 2216 * direction) is encoded with index zero. 2217 * [WSCALE values histograms, Allman, 2012] 2218 * X 10 10 35 5 6 14 10% by host 2219 * X 11 4 5 5 18 49 3% by connections 2220 */ 2221 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 2222 2223 /* 2224 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 2225 * and good cryptographic properties. 2226 */ 2227 static uint32_t 2228 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 2229 uint8_t *secbits, uintptr_t secmod) 2230 { 2231 SIPHASH_CTX ctx; 2232 uint32_t siphash[2]; 2233 2234 SipHash24_Init(&ctx); 2235 SipHash_SetKey(&ctx, secbits); 2236 switch (inc->inc_flags & INC_ISIPV6) { 2237 #ifdef INET 2238 case 0: 2239 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 2240 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 2241 break; 2242 #endif 2243 #ifdef INET6 2244 case INC_ISIPV6: 2245 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 2246 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 2247 break; 2248 #endif 2249 } 2250 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 2251 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 2252 SipHash_Update(&ctx, &irs, sizeof(irs)); 2253 SipHash_Update(&ctx, &flags, sizeof(flags)); 2254 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 2255 SipHash_Final((u_int8_t *)&siphash, &ctx); 2256 2257 return (siphash[0] ^ siphash[1]); 2258 } 2259 2260 static tcp_seq 2261 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 2262 { 2263 u_int i, secbit, wscale; 2264 uint32_t iss, hash; 2265 uint8_t *secbits; 2266 union syncookie cookie; 2267 2268 cookie.cookie = 0; 2269 2270 /* Map our computed MSS into the 3-bit index. */ 2271 for (i = nitems(tcp_sc_msstab) - 1; 2272 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0; 2273 i--) 2274 ; 2275 cookie.flags.mss_idx = i; 2276 2277 /* 2278 * Map the send window scale into the 3-bit index but only if 2279 * the wscale option was received. 2280 */ 2281 if (sc->sc_flags & SCF_WINSCALE) { 2282 wscale = sc->sc_requested_s_scale; 2283 for (i = nitems(tcp_sc_wstab) - 1; 2284 tcp_sc_wstab[i] > wscale && i > 0; 2285 i--) 2286 ; 2287 cookie.flags.wscale_idx = i; 2288 } 2289 2290 /* Can we do SACK? */ 2291 if (sc->sc_flags & SCF_SACK) 2292 cookie.flags.sack_ok = 1; 2293 2294 /* Which of the two secrets to use. */ 2295 secbit = V_tcp_syncache.secret.oddeven & 0x1; 2296 cookie.flags.odd_even = secbit; 2297 2298 secbits = V_tcp_syncache.secret.key[secbit]; 2299 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 2300 (uintptr_t)sch); 2301 2302 /* 2303 * Put the flags into the hash and XOR them to get better ISS number 2304 * variance. This doesn't enhance the cryptographic strength and is 2305 * done to prevent the 8 cookie bits from showing up directly on the 2306 * wire. 2307 */ 2308 iss = hash & ~0xff; 2309 iss |= cookie.cookie ^ (hash >> 24); 2310 2311 TCPSTAT_INC(tcps_sc_sendcookie); 2312 return (iss); 2313 } 2314 2315 static bool 2316 syncookie_expand(struct in_conninfo *inc, const struct syncache_head *sch, 2317 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2318 struct socket *lso, uint16_t port) 2319 { 2320 uint32_t hash; 2321 uint8_t *secbits; 2322 tcp_seq ack, seq; 2323 int wnd; 2324 union syncookie cookie; 2325 2326 /* 2327 * Pull information out of SYN-ACK/ACK and revert sequence number 2328 * advances. 2329 */ 2330 ack = th->th_ack - 1; 2331 seq = th->th_seq - 1; 2332 2333 /* 2334 * Unpack the flags containing enough information to restore the 2335 * connection. 2336 */ 2337 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 2338 2339 /* Which of the two secrets to use. */ 2340 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even]; 2341 2342 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 2343 2344 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 2345 if ((ack & ~0xff) != (hash & ~0xff)) 2346 return (false); 2347 2348 /* Fill in the syncache values. */ 2349 sc->sc_flags = 0; 2350 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 2351 sc->sc_ipopts = NULL; 2352 2353 sc->sc_irs = seq; 2354 sc->sc_iss = ack; 2355 2356 switch (inc->inc_flags & INC_ISIPV6) { 2357 #ifdef INET 2358 case 0: 2359 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 2360 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 2361 break; 2362 #endif 2363 #ifdef INET6 2364 case INC_ISIPV6: 2365 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 2366 sc->sc_flowlabel = 2367 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK; 2368 break; 2369 #endif 2370 } 2371 2372 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 2373 2374 /* Only use wscale if it was enabled in the orignal SYN. */ 2375 if (cookie.flags.wscale_idx > 0) { 2376 u_int wscale = 0; 2377 2378 /* Recompute the receive window scale that was sent earlier. */ 2379 while (wscale < TCP_MAX_WINSHIFT && 2380 (TCP_MAXWIN << wscale) < sb_max) 2381 wscale++; 2382 sc->sc_requested_r_scale = wscale; 2383 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 2384 sc->sc_flags |= SCF_WINSCALE; 2385 } 2386 2387 wnd = lso->sol_sbrcv_hiwat; 2388 wnd = imax(wnd, 0); 2389 wnd = imin(wnd, TCP_MAXWIN); 2390 sc->sc_wnd = wnd; 2391 2392 if (cookie.flags.sack_ok) 2393 sc->sc_flags |= SCF_SACK; 2394 2395 if (to->to_flags & TOF_TS) { 2396 sc->sc_flags |= SCF_TIMESTAMP; 2397 sc->sc_tsreflect = to->to_tsval; 2398 sc->sc_tsoff = tcp_new_ts_offset(inc); 2399 } 2400 2401 if (to->to_flags & TOF_SIGNATURE) 2402 sc->sc_flags |= SCF_SIGNATURE; 2403 2404 sc->sc_rxmits = 0; 2405 2406 sc->sc_port = port; 2407 2408 return (true); 2409 } 2410 2411 #ifdef INVARIANTS 2412 static void 2413 syncookie_cmp(struct in_conninfo *inc, const struct syncache_head *sch, 2414 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2415 struct socket *lso, uint16_t port) 2416 { 2417 struct syncache scs; 2418 char *s; 2419 2420 bzero(&scs, sizeof(scs)); 2421 if (syncookie_expand(inc, sch, &scs, th, to, lso, port) && 2422 (sc->sc_peer_mss != scs.sc_peer_mss || 2423 sc->sc_requested_r_scale != scs.sc_requested_r_scale || 2424 sc->sc_requested_s_scale != scs.sc_requested_s_scale || 2425 (sc->sc_flags & SCF_SACK) != (scs.sc_flags & SCF_SACK))) { 2426 2427 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2428 return; 2429 2430 if (sc->sc_peer_mss != scs.sc_peer_mss) 2431 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2432 s, __func__, sc->sc_peer_mss, scs.sc_peer_mss); 2433 2434 if (sc->sc_requested_r_scale != scs.sc_requested_r_scale) 2435 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2436 s, __func__, sc->sc_requested_r_scale, 2437 scs.sc_requested_r_scale); 2438 2439 if (sc->sc_requested_s_scale != scs.sc_requested_s_scale) 2440 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2441 s, __func__, sc->sc_requested_s_scale, 2442 scs.sc_requested_s_scale); 2443 2444 if ((sc->sc_flags & SCF_SACK) != (scs.sc_flags & SCF_SACK)) 2445 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2446 2447 free(s, M_TCPLOG); 2448 } 2449 } 2450 #endif /* INVARIANTS */ 2451 2452 static void 2453 syncookie_reseed(void *arg) 2454 { 2455 struct tcp_syncache *sc = arg; 2456 uint8_t *secbits; 2457 int secbit; 2458 2459 /* 2460 * Reseeding the secret doesn't have to be protected by a lock. 2461 * It only must be ensured that the new random values are visible 2462 * to all CPUs in a SMP environment. The atomic with release 2463 * semantics ensures that. 2464 */ 2465 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2466 secbits = sc->secret.key[secbit]; 2467 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2468 atomic_add_rel_int(&sc->secret.oddeven, 1); 2469 2470 /* Reschedule ourself. */ 2471 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2472 } 2473 2474 /* 2475 * We have overflowed a bucket. Let's pause dealing with the syncache. 2476 * This function will increment the bucketoverflow statistics appropriately 2477 * (once per pause when pausing is enabled; otherwise, once per overflow). 2478 */ 2479 static void 2480 syncache_pause(struct in_conninfo *inc) 2481 { 2482 time_t delta; 2483 const char *s; 2484 2485 /* XXX: 2486 * 2. Add sysctl read here so we don't get the benefit of this 2487 * change without the new sysctl. 2488 */ 2489 2490 /* 2491 * Try an unlocked read. If we already know that another thread 2492 * has activated the feature, there is no need to proceed. 2493 */ 2494 if (V_tcp_syncache.paused) 2495 return; 2496 2497 /* Are cookied enabled? If not, we can't pause. */ 2498 if (!V_tcp_syncookies) { 2499 TCPSTAT_INC(tcps_sc_bucketoverflow); 2500 return; 2501 } 2502 2503 /* 2504 * We may be the first thread to find an overflow. Get the lock 2505 * and evaluate if we need to take action. 2506 */ 2507 mtx_lock(&V_tcp_syncache.pause_mtx); 2508 if (V_tcp_syncache.paused) { 2509 mtx_unlock(&V_tcp_syncache.pause_mtx); 2510 return; 2511 } 2512 2513 /* Activate protection. */ 2514 V_tcp_syncache.paused = true; 2515 TCPSTAT_INC(tcps_sc_bucketoverflow); 2516 2517 /* 2518 * Determine the last backoff time. If we are seeing a re-newed 2519 * attack within that same time after last reactivating the syncache, 2520 * consider it an extension of the same attack. 2521 */ 2522 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff; 2523 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) { 2524 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) { 2525 delta <<= 1; 2526 V_tcp_syncache.pause_backoff++; 2527 } 2528 } else { 2529 delta = TCP_SYNCACHE_PAUSE_TIME; 2530 V_tcp_syncache.pause_backoff = 0; 2531 } 2532 2533 /* Log a warning, including IP addresses, if able. */ 2534 if (inc != NULL) 2535 s = tcp_log_addrs(inc, NULL, NULL, NULL); 2536 else 2537 s = (const char *)NULL; 2538 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for " 2539 "the next %lld seconds%s%s%s\n", (long long)delta, 2540 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "", 2541 (s != NULL) ? ")" : ""); 2542 free(__DECONST(void *, s), M_TCPLOG); 2543 2544 /* Use the calculated delta to set a new pause time. */ 2545 V_tcp_syncache.pause_until = time_uptime + delta; 2546 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause, 2547 &V_tcp_syncache); 2548 mtx_unlock(&V_tcp_syncache.pause_mtx); 2549 } 2550 2551 /* Evaluate whether we need to unpause. */ 2552 static void 2553 syncache_unpause(void *arg) 2554 { 2555 struct tcp_syncache *sc; 2556 time_t delta; 2557 2558 sc = arg; 2559 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED); 2560 callout_deactivate(&sc->pause_co); 2561 2562 /* 2563 * Check to make sure we are not running early. If the pause 2564 * time has expired, then deactivate the protection. 2565 */ 2566 if ((delta = sc->pause_until - time_uptime) > 0) 2567 callout_schedule(&sc->pause_co, delta * hz); 2568 else 2569 sc->paused = false; 2570 } 2571 2572 /* 2573 * Exports the syncache entries to userland so that netstat can display 2574 * them alongside the other sockets. This function is intended to be 2575 * called only from tcp_pcblist. 2576 * 2577 * Due to concurrency on an active system, the number of pcbs exported 2578 * may have no relation to max_pcbs. max_pcbs merely indicates the 2579 * amount of space the caller allocated for this function to use. 2580 */ 2581 int 2582 syncache_pcblist(struct sysctl_req *req) 2583 { 2584 struct xtcpcb xt; 2585 struct syncache *sc; 2586 struct syncache_head *sch; 2587 int error, i; 2588 2589 bzero(&xt, sizeof(xt)); 2590 xt.xt_len = sizeof(xt); 2591 xt.t_state = TCPS_SYN_RECEIVED; 2592 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP; 2593 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket); 2594 xt.xt_inp.xi_socket.so_type = SOCK_STREAM; 2595 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING; 2596 2597 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 2598 sch = &V_tcp_syncache.hashbase[i]; 2599 SCH_LOCK(sch); 2600 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2601 if (sc->sc_cred != NULL && 2602 cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2603 continue; 2604 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2605 xt.xt_inp.inp_vflag = INP_IPV6; 2606 else 2607 xt.xt_inp.inp_vflag = INP_IPV4; 2608 xt.xt_encaps_port = sc->sc_port; 2609 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, 2610 sizeof (struct in_conninfo)); 2611 error = SYSCTL_OUT(req, &xt, sizeof xt); 2612 if (error) { 2613 SCH_UNLOCK(sch); 2614 return (0); 2615 } 2616 } 2617 SCH_UNLOCK(sch); 2618 } 2619 2620 return (0); 2621 } 2622