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 <sys/cdefs.h> 36 #include "opt_inet.h" 37 #include "opt_inet6.h" 38 #include "opt_ipsec.h" 39 40 #include <sys/param.h> 41 #include <sys/systm.h> 42 #include <sys/hash.h> 43 #include <sys/refcount.h> 44 #include <sys/kernel.h> 45 #include <sys/sysctl.h> 46 #include <sys/limits.h> 47 #include <sys/lock.h> 48 #include <sys/mutex.h> 49 #include <sys/malloc.h> 50 #include <sys/mbuf.h> 51 #include <sys/proc.h> /* for proc0 declaration */ 52 #include <sys/random.h> 53 #include <sys/socket.h> 54 #include <sys/socketvar.h> 55 #include <sys/syslog.h> 56 #include <sys/ucred.h> 57 58 #include <sys/md5.h> 59 #include <crypto/siphash/siphash.h> 60 61 #include <vm/uma.h> 62 63 #include <net/if.h> 64 #include <net/if_var.h> 65 #include <net/route.h> 66 #include <net/vnet.h> 67 68 #include <netinet/in.h> 69 #include <netinet/in_kdtrace.h> 70 #include <netinet/in_systm.h> 71 #include <netinet/ip.h> 72 #include <netinet/in_var.h> 73 #include <netinet/in_pcb.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 #endif 83 #include <netinet/tcp.h> 84 #include <netinet/tcp_fastopen.h> 85 #include <netinet/tcp_fsm.h> 86 #include <netinet/tcp_seq.h> 87 #include <netinet/tcp_timer.h> 88 #include <netinet/tcp_var.h> 89 #include <netinet/tcp_syncache.h> 90 #include <netinet/tcp_ecn.h> 91 #ifdef TCP_BLACKBOX 92 #include <netinet/tcp_log_buf.h> 93 #endif 94 #ifdef TCP_OFFLOAD 95 #include <netinet/toecore.h> 96 #endif 97 #include <netinet/udp.h> 98 99 #include <netipsec/ipsec_support.h> 100 101 #include <machine/in_cksum.h> 102 103 #include <security/mac/mac_framework.h> 104 105 VNET_DEFINE_STATIC(bool, tcp_syncookies) = true; 106 #define V_tcp_syncookies VNET(tcp_syncookies) 107 SYSCTL_BOOL(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW, 108 &VNET_NAME(tcp_syncookies), 0, 109 "Use TCP SYN cookies if the syncache overflows"); 110 111 VNET_DEFINE_STATIC(bool, tcp_syncookiesonly) = false; 112 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly) 113 SYSCTL_BOOL(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | 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 static int syncache_respond(struct syncache *, const struct mbuf *, int); 125 static struct socket *syncache_socket(struct syncache *, struct socket *, 126 struct mbuf *m); 127 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 128 int docallout); 129 static void syncache_timer(void *); 130 131 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t, 132 uint8_t *, uintptr_t); 133 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *); 134 static bool syncookie_expand(struct in_conninfo *, 135 const struct syncache_head *, struct syncache *, 136 struct tcphdr *, struct tcpopt *, struct socket *, 137 uint16_t); 138 static void syncache_pause(struct in_conninfo *); 139 static void syncache_unpause(void *); 140 static void syncookie_reseed(void *); 141 #ifdef INVARIANTS 142 static void syncookie_cmp(struct in_conninfo *, 143 const struct syncache_head *, struct syncache *, 144 struct tcphdr *, struct tcpopt *, struct socket *, 145 uint16_t); 146 #endif 147 148 /* 149 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 150 * 3 retransmits corresponds to a timeout with default values of 151 * tcp_rexmit_initial * ( 1 + 152 * tcp_backoff[1] + 153 * tcp_backoff[2] + 154 * tcp_backoff[3]) + 3 * tcp_rexmit_slop, 155 * 1000 ms * (1 + 2 + 4 + 8) + 3 * 200 ms = 15600 ms, 156 * the odds are that the user has given up attempting to connect by then. 157 */ 158 #define SYNCACHE_MAXREXMTS 3 159 160 /* Arbitrary values */ 161 #define TCP_SYNCACHE_HASHSIZE 512 162 #define TCP_SYNCACHE_BUCKETLIMIT 30 163 164 VNET_DEFINE_STATIC(struct tcp_syncache, tcp_syncache); 165 #define V_tcp_syncache VNET(tcp_syncache) 166 167 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, 168 CTLFLAG_RW | CTLFLAG_MPSAFE, 0, 169 "TCP SYN cache"); 170 171 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 172 &VNET_NAME(tcp_syncache.bucket_limit), 0, 173 "Per-bucket hash limit for syncache"); 174 175 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 176 &VNET_NAME(tcp_syncache.cache_limit), 0, 177 "Overall entry limit for syncache"); 178 179 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET, 180 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache"); 181 182 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN, 183 &VNET_NAME(tcp_syncache.hashsize), 0, 184 "Size of TCP syncache hashtable"); 185 186 SYSCTL_BOOL(_net_inet_tcp_syncache, OID_AUTO, see_other, CTLFLAG_VNET | 187 CTLFLAG_RW, &VNET_NAME(tcp_syncache.see_other), 0, 188 "All syncache(4) entries are visible, ignoring UID/GID, jail(2) " 189 "and mac(4) checks"); 190 191 static int 192 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS) 193 { 194 int error; 195 u_int new; 196 197 new = V_tcp_syncache.rexmt_limit; 198 error = sysctl_handle_int(oidp, &new, 0, req); 199 if ((error == 0) && (req->newptr != NULL)) { 200 if (new > TCP_MAXRXTSHIFT) 201 error = EINVAL; 202 else 203 V_tcp_syncache.rexmt_limit = new; 204 } 205 return (error); 206 } 207 208 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, 209 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT, 210 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 211 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "IU", 212 "Limit on SYN/ACK retransmissions"); 213 214 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 215 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 216 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 217 "Send reset on socket allocation failure"); 218 219 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 220 221 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 222 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 223 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 224 225 /* 226 * Requires the syncache entry to be already removed from the bucket list. 227 */ 228 static void 229 syncache_free(struct syncache *sc) 230 { 231 232 if (sc->sc_ipopts) 233 (void)m_free(sc->sc_ipopts); 234 if (sc->sc_cred) 235 crfree(sc->sc_cred); 236 #ifdef MAC 237 mac_syncache_destroy(&sc->sc_label); 238 #endif 239 240 uma_zfree(V_tcp_syncache.zone, sc); 241 } 242 243 void 244 syncache_init(void) 245 { 246 int i; 247 248 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 249 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 250 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 251 V_tcp_syncache.hash_secret = arc4random(); 252 253 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 254 &V_tcp_syncache.hashsize); 255 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 256 &V_tcp_syncache.bucket_limit); 257 if (!powerof2(V_tcp_syncache.hashsize) || 258 V_tcp_syncache.hashsize == 0) { 259 printf("WARNING: syncache hash size is not a power of 2.\n"); 260 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 261 } 262 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 263 264 /* Set limits. */ 265 V_tcp_syncache.cache_limit = 266 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 267 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 268 &V_tcp_syncache.cache_limit); 269 270 /* Allocate the hash table. */ 271 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 272 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 273 274 #ifdef VIMAGE 275 V_tcp_syncache.vnet = curvnet; 276 #endif 277 278 /* Initialize the hash buckets. */ 279 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 280 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 281 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 282 NULL, MTX_DEF); 283 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 284 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 285 V_tcp_syncache.hashbase[i].sch_length = 0; 286 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 287 V_tcp_syncache.hashbase[i].sch_last_overflow = 288 -(SYNCOOKIE_LIFETIME + 1); 289 } 290 291 /* Create the syncache entry zone. */ 292 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 293 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 294 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 295 V_tcp_syncache.cache_limit); 296 297 /* Start the SYN cookie reseeder callout. */ 298 callout_init(&V_tcp_syncache.secret.reseed, 1); 299 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 300 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 301 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 302 syncookie_reseed, &V_tcp_syncache); 303 304 /* Initialize the pause machinery. */ 305 mtx_init(&V_tcp_syncache.pause_mtx, "tcp_sc_pause", NULL, MTX_DEF); 306 callout_init_mtx(&V_tcp_syncache.pause_co, &V_tcp_syncache.pause_mtx, 307 0); 308 V_tcp_syncache.pause_until = time_uptime - TCP_SYNCACHE_PAUSE_TIME; 309 V_tcp_syncache.pause_backoff = 0; 310 V_tcp_syncache.paused = false; 311 } 312 313 #ifdef VIMAGE 314 void 315 syncache_destroy(void) 316 { 317 struct syncache_head *sch; 318 struct syncache *sc, *nsc; 319 int i; 320 321 /* 322 * Stop the re-seed timer before freeing resources. No need to 323 * possibly schedule it another time. 324 */ 325 callout_drain(&V_tcp_syncache.secret.reseed); 326 327 /* Stop the SYN cache pause callout. */ 328 mtx_lock(&V_tcp_syncache.pause_mtx); 329 if (callout_stop(&V_tcp_syncache.pause_co) == 0) { 330 mtx_unlock(&V_tcp_syncache.pause_mtx); 331 callout_drain(&V_tcp_syncache.pause_co); 332 } else 333 mtx_unlock(&V_tcp_syncache.pause_mtx); 334 335 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 336 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 337 sch = &V_tcp_syncache.hashbase[i]; 338 callout_drain(&sch->sch_timer); 339 340 SCH_LOCK(sch); 341 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 342 syncache_drop(sc, sch); 343 SCH_UNLOCK(sch); 344 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 345 ("%s: sch->sch_bucket not empty", __func__)); 346 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 347 __func__, sch->sch_length)); 348 mtx_destroy(&sch->sch_mtx); 349 } 350 351 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 352 ("%s: cache_count not 0", __func__)); 353 354 /* Free the allocated global resources. */ 355 uma_zdestroy(V_tcp_syncache.zone); 356 free(V_tcp_syncache.hashbase, M_SYNCACHE); 357 mtx_destroy(&V_tcp_syncache.pause_mtx); 358 } 359 #endif 360 361 /* 362 * Inserts a syncache entry into the specified bucket row. 363 * Locks and unlocks the syncache_head autonomously. 364 */ 365 static void 366 syncache_insert(struct syncache *sc, struct syncache_head *sch) 367 { 368 struct syncache *sc2; 369 370 SCH_LOCK(sch); 371 372 /* 373 * Make sure that we don't overflow the per-bucket limit. 374 * If the bucket is full, toss the oldest element. 375 */ 376 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 377 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 378 ("sch->sch_length incorrect")); 379 syncache_pause(&sc->sc_inc); 380 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 381 sch->sch_last_overflow = time_uptime; 382 syncache_drop(sc2, sch); 383 } 384 385 /* Put it into the bucket. */ 386 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 387 sch->sch_length++; 388 389 #ifdef TCP_OFFLOAD 390 if (ADDED_BY_TOE(sc)) { 391 struct toedev *tod = sc->sc_tod; 392 393 tod->tod_syncache_added(tod, sc->sc_todctx); 394 } 395 #endif 396 397 /* Reinitialize the bucket row's timer. */ 398 if (sch->sch_length == 1) 399 sch->sch_nextc = ticks + INT_MAX; 400 syncache_timeout(sc, sch, 1); 401 402 SCH_UNLOCK(sch); 403 404 TCPSTATES_INC(TCPS_SYN_RECEIVED); 405 TCPSTAT_INC(tcps_sc_added); 406 } 407 408 /* 409 * Remove and free entry from syncache bucket row. 410 * Expects locked syncache head. 411 */ 412 static void 413 syncache_drop(struct syncache *sc, struct syncache_head *sch) 414 { 415 416 SCH_LOCK_ASSERT(sch); 417 418 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 419 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 420 sch->sch_length--; 421 422 #ifdef TCP_OFFLOAD 423 if (ADDED_BY_TOE(sc)) { 424 struct toedev *tod = sc->sc_tod; 425 426 tod->tod_syncache_removed(tod, sc->sc_todctx); 427 } 428 #endif 429 430 syncache_free(sc); 431 } 432 433 /* 434 * Engage/reengage time on bucket row. 435 */ 436 static void 437 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 438 { 439 int rexmt; 440 441 if (sc->sc_rxmits == 0) 442 rexmt = tcp_rexmit_initial; 443 else 444 TCPT_RANGESET(rexmt, 445 tcp_rexmit_initial * tcp_backoff[sc->sc_rxmits], 446 tcp_rexmit_min, tcp_rexmit_max); 447 sc->sc_rxttime = ticks + rexmt; 448 sc->sc_rxmits++; 449 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 450 sch->sch_nextc = sc->sc_rxttime; 451 if (docallout) 452 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 453 syncache_timer, (void *)sch); 454 } 455 } 456 457 /* 458 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 459 * If we have retransmitted an entry the maximum number of times, expire it. 460 * One separate timer for each bucket row. 461 */ 462 static void 463 syncache_timer(void *xsch) 464 { 465 struct syncache_head *sch = (struct syncache_head *)xsch; 466 struct syncache *sc, *nsc; 467 struct epoch_tracker et; 468 int tick = ticks; 469 char *s; 470 bool paused; 471 472 CURVNET_SET(sch->sch_sc->vnet); 473 474 /* NB: syncache_head has already been locked by the callout. */ 475 SCH_LOCK_ASSERT(sch); 476 477 /* 478 * In the following cycle we may remove some entries and/or 479 * advance some timeouts, so re-initialize the bucket timer. 480 */ 481 sch->sch_nextc = tick + INT_MAX; 482 483 /* 484 * If we have paused processing, unconditionally remove 485 * all syncache entries. 486 */ 487 mtx_lock(&V_tcp_syncache.pause_mtx); 488 paused = V_tcp_syncache.paused; 489 mtx_unlock(&V_tcp_syncache.pause_mtx); 490 491 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 492 if (paused) { 493 syncache_drop(sc, sch); 494 continue; 495 } 496 /* 497 * We do not check if the listen socket still exists 498 * and accept the case where the listen socket may be 499 * gone by the time we resend the SYN/ACK. We do 500 * not expect this to happens often. If it does, 501 * then the RST will be sent by the time the remote 502 * host does the SYN/ACK->ACK. 503 */ 504 if (TSTMP_GT(sc->sc_rxttime, tick)) { 505 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 506 sch->sch_nextc = sc->sc_rxttime; 507 continue; 508 } 509 if (sc->sc_rxmits > V_tcp_ecn_maxretries) { 510 sc->sc_flags &= ~SCF_ECN_MASK; 511 } 512 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 513 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 514 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 515 "giving up and removing syncache entry\n", 516 s, __func__); 517 free(s, M_TCPLOG); 518 } 519 syncache_drop(sc, sch); 520 TCPSTAT_INC(tcps_sc_stale); 521 continue; 522 } 523 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 524 log(LOG_DEBUG, "%s; %s: Response timeout, " 525 "retransmitting (%u) SYN|ACK\n", 526 s, __func__, sc->sc_rxmits); 527 free(s, M_TCPLOG); 528 } 529 530 NET_EPOCH_ENTER(et); 531 if (syncache_respond(sc, NULL, TH_SYN|TH_ACK) == 0) { 532 syncache_timeout(sc, sch, 0); 533 TCPSTAT_INC(tcps_sndacks); 534 TCPSTAT_INC(tcps_sndtotal); 535 TCPSTAT_INC(tcps_sc_retransmitted); 536 } else { 537 syncache_drop(sc, sch); 538 TCPSTAT_INC(tcps_sc_dropped); 539 } 540 NET_EPOCH_EXIT(et); 541 } 542 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 543 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 544 syncache_timer, (void *)(sch)); 545 CURVNET_RESTORE(); 546 } 547 548 /* 549 * Returns true if the system is only using cookies at the moment. 550 * This could be due to a sysadmin decision to only use cookies, or it 551 * could be due to the system detecting an attack. 552 */ 553 static inline bool 554 syncache_cookiesonly(void) 555 { 556 return ((V_tcp_syncookies && V_tcp_syncache.paused) || 557 V_tcp_syncookiesonly); 558 } 559 560 /* 561 * Find the hash bucket for the given connection. 562 */ 563 static struct syncache_head * 564 syncache_hashbucket(struct in_conninfo *inc) 565 { 566 uint32_t hash; 567 568 /* 569 * The hash is built on foreign port + local port + foreign address. 570 * We rely on the fact that struct in_conninfo starts with 16 bits 571 * of foreign port, then 16 bits of local port then followed by 128 572 * bits of foreign address. In case of IPv4 address, the first 3 573 * 32-bit words of the address always are zeroes. 574 */ 575 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5, 576 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask; 577 578 return (&V_tcp_syncache.hashbase[hash]); 579 } 580 581 /* 582 * Find an entry in the syncache. 583 * Returns always with locked syncache_head plus a matching entry or NULL. 584 */ 585 static struct syncache * 586 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 587 { 588 struct syncache *sc; 589 struct syncache_head *sch; 590 591 *schp = sch = syncache_hashbucket(inc); 592 SCH_LOCK(sch); 593 594 /* Circle through bucket row to find matching entry. */ 595 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) 596 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie, 597 sizeof(struct in_endpoints)) == 0) 598 break; 599 600 return (sc); /* Always returns with locked sch. */ 601 } 602 603 /* 604 * This function is called when we get a RST for a 605 * non-existent connection, so that we can see if the 606 * connection is in the syn cache. If it is, zap it. 607 * If required send a challenge ACK. 608 */ 609 void 610 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, struct mbuf *m, 611 uint16_t port) 612 { 613 struct syncache *sc; 614 struct syncache_head *sch; 615 char *s = NULL; 616 617 if (syncache_cookiesonly()) 618 return; 619 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 620 SCH_LOCK_ASSERT(sch); 621 622 /* 623 * No corresponding connection was found in syncache. 624 * If syncookies are enabled and possibly exclusively 625 * used, or we are under memory pressure, a valid RST 626 * may not find a syncache entry. In that case we're 627 * done and no SYN|ACK retransmissions will happen. 628 * Otherwise the RST was misdirected or spoofed. 629 */ 630 if (sc == NULL) { 631 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 632 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 633 "syncache entry (possibly syncookie only), " 634 "segment ignored\n", s, __func__); 635 TCPSTAT_INC(tcps_badrst); 636 goto done; 637 } 638 639 /* The remote UDP encaps port does not match. */ 640 if (sc->sc_port != port) { 641 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 642 log(LOG_DEBUG, "%s; %s: Spurious RST with matching " 643 "syncache entry but non-matching UDP encaps port, " 644 "segment ignored\n", s, __func__); 645 TCPSTAT_INC(tcps_badrst); 646 goto done; 647 } 648 649 /* 650 * If the RST bit is set, check the sequence number to see 651 * if this is a valid reset segment. 652 * 653 * RFC 793 page 37: 654 * In all states except SYN-SENT, all reset (RST) segments 655 * are validated by checking their SEQ-fields. A reset is 656 * valid if its sequence number is in the window. 657 * 658 * RFC 793 page 69: 659 * There are four cases for the acceptability test for an incoming 660 * segment: 661 * 662 * Segment Receive Test 663 * Length Window 664 * ------- ------- ------------------------------------------- 665 * 0 0 SEG.SEQ = RCV.NXT 666 * 0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 667 * >0 0 not acceptable 668 * >0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 669 * or RCV.NXT =< SEG.SEQ+SEG.LEN-1 < RCV.NXT+RCV.WND 670 * 671 * Note that when receiving a SYN segment in the LISTEN state, 672 * IRS is set to SEG.SEQ and RCV.NXT is set to SEG.SEQ+1, as 673 * described in RFC 793, page 66. 674 */ 675 if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) && 676 SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) || 677 (sc->sc_wnd == 0 && th->th_seq == sc->sc_irs + 1)) { 678 if (V_tcp_insecure_rst || 679 th->th_seq == sc->sc_irs + 1) { 680 syncache_drop(sc, sch); 681 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 682 log(LOG_DEBUG, 683 "%s; %s: Our SYN|ACK was rejected, " 684 "connection attempt aborted by remote " 685 "endpoint\n", 686 s, __func__); 687 TCPSTAT_INC(tcps_sc_reset); 688 } else { 689 TCPSTAT_INC(tcps_badrst); 690 /* Send challenge ACK. */ 691 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 692 log(LOG_DEBUG, "%s; %s: RST with invalid " 693 " SEQ %u != NXT %u (+WND %u), " 694 "sending challenge ACK\n", 695 s, __func__, 696 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 697 if (syncache_respond(sc, m, TH_ACK) == 0) { 698 TCPSTAT_INC(tcps_sndacks); 699 TCPSTAT_INC(tcps_sndtotal); 700 } else { 701 syncache_drop(sc, sch); 702 TCPSTAT_INC(tcps_sc_dropped); 703 } 704 } 705 } else { 706 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 707 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 708 "NXT %u (+WND %u), segment ignored\n", 709 s, __func__, 710 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 711 TCPSTAT_INC(tcps_badrst); 712 } 713 714 done: 715 if (s != NULL) 716 free(s, M_TCPLOG); 717 SCH_UNLOCK(sch); 718 } 719 720 void 721 syncache_badack(struct in_conninfo *inc, uint16_t port) 722 { 723 struct syncache *sc; 724 struct syncache_head *sch; 725 726 if (syncache_cookiesonly()) 727 return; 728 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 729 SCH_LOCK_ASSERT(sch); 730 if ((sc != NULL) && (sc->sc_port == port)) { 731 syncache_drop(sc, sch); 732 TCPSTAT_INC(tcps_sc_badack); 733 } 734 SCH_UNLOCK(sch); 735 } 736 737 void 738 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq, uint16_t port) 739 { 740 struct syncache *sc; 741 struct syncache_head *sch; 742 743 if (syncache_cookiesonly()) 744 return; 745 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 746 SCH_LOCK_ASSERT(sch); 747 if (sc == NULL) 748 goto done; 749 750 /* If the port != sc_port, then it's a bogus ICMP msg */ 751 if (port != sc->sc_port) 752 goto done; 753 754 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 755 if (ntohl(th_seq) != sc->sc_iss) 756 goto done; 757 758 /* 759 * If we've rertransmitted 3 times and this is our second error, 760 * we remove the entry. Otherwise, we allow it to continue on. 761 * This prevents us from incorrectly nuking an entry during a 762 * spurious network outage. 763 * 764 * See tcp_notify(). 765 */ 766 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 767 sc->sc_flags |= SCF_UNREACH; 768 goto done; 769 } 770 syncache_drop(sc, sch); 771 TCPSTAT_INC(tcps_sc_unreach); 772 done: 773 SCH_UNLOCK(sch); 774 } 775 776 /* 777 * Build a new TCP socket structure from a syncache entry. 778 * 779 * On success return the newly created socket with its underlying inp locked. 780 */ 781 static struct socket * 782 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 783 { 784 struct inpcb *inp = NULL; 785 struct socket *so; 786 struct tcpcb *tp; 787 int error; 788 char *s; 789 790 NET_EPOCH_ASSERT(); 791 792 /* 793 * Ok, create the full blown connection, and set things up 794 * as they would have been set up if we had created the 795 * connection when the SYN arrived. 796 */ 797 if ((so = solisten_clone(lso)) == NULL) 798 goto allocfail; 799 #ifdef MAC 800 mac_socketpeer_set_from_mbuf(m, so); 801 #endif 802 error = in_pcballoc(so, &V_tcbinfo); 803 if (error) { 804 sodealloc(so); 805 goto allocfail; 806 } 807 inp = sotoinpcb(so); 808 if ((tp = tcp_newtcpcb(inp, sototcpcb(lso))) == NULL) { 809 in_pcbfree(inp); 810 sodealloc(so); 811 goto allocfail; 812 } 813 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 814 #ifdef INET6 815 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 816 inp->inp_vflag &= ~INP_IPV4; 817 inp->inp_vflag |= INP_IPV6; 818 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 819 } else { 820 inp->inp_vflag &= ~INP_IPV6; 821 inp->inp_vflag |= INP_IPV4; 822 #endif 823 inp->inp_ip_ttl = sc->sc_ip_ttl; 824 inp->inp_ip_tos = sc->sc_ip_tos; 825 inp->inp_laddr = sc->sc_inc.inc_laddr; 826 #ifdef INET6 827 } 828 #endif 829 830 /* 831 * If there's an mbuf and it has a flowid, then let's initialise the 832 * inp with that particular flowid. 833 */ 834 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 835 inp->inp_flowid = m->m_pkthdr.flowid; 836 inp->inp_flowtype = M_HASHTYPE_GET(m); 837 #ifdef NUMA 838 inp->inp_numa_domain = m->m_pkthdr.numa_domain; 839 #endif 840 } 841 842 inp->inp_lport = sc->sc_inc.inc_lport; 843 #ifdef INET6 844 if (inp->inp_vflag & INP_IPV6PROTO) { 845 struct inpcb *oinp = sotoinpcb(lso); 846 847 /* 848 * Inherit socket options from the listening socket. 849 * Note that in6p_inputopts are not (and should not be) 850 * copied, since it stores previously received options and is 851 * used to detect if each new option is different than the 852 * previous one and hence should be passed to a user. 853 * If we copied in6p_inputopts, a user would not be able to 854 * receive options just after calling the accept system call. 855 */ 856 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 857 if (oinp->in6p_outputopts) 858 inp->in6p_outputopts = 859 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 860 inp->in6p_hops = oinp->in6p_hops; 861 } 862 863 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 864 struct sockaddr_in6 sin6; 865 866 sin6.sin6_family = AF_INET6; 867 sin6.sin6_len = sizeof(sin6); 868 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 869 sin6.sin6_port = sc->sc_inc.inc_fport; 870 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 871 INP_HASH_WLOCK(&V_tcbinfo); 872 error = in6_pcbconnect(inp, &sin6, thread0.td_ucred, false); 873 INP_HASH_WUNLOCK(&V_tcbinfo); 874 if (error != 0) 875 goto abort; 876 /* Override flowlabel from in6_pcbconnect. */ 877 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 878 inp->inp_flow |= sc->sc_flowlabel; 879 } 880 #endif /* INET6 */ 881 #if defined(INET) && defined(INET6) 882 else 883 #endif 884 #ifdef INET 885 { 886 struct sockaddr_in sin; 887 888 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 889 890 if (inp->inp_options == NULL) { 891 inp->inp_options = sc->sc_ipopts; 892 sc->sc_ipopts = NULL; 893 } 894 895 sin.sin_family = AF_INET; 896 sin.sin_len = sizeof(sin); 897 sin.sin_addr = sc->sc_inc.inc_faddr; 898 sin.sin_port = sc->sc_inc.inc_fport; 899 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 900 INP_HASH_WLOCK(&V_tcbinfo); 901 error = in_pcbconnect(inp, &sin, thread0.td_ucred); 902 INP_HASH_WUNLOCK(&V_tcbinfo); 903 if (error != 0) 904 goto abort; 905 } 906 #endif /* INET */ 907 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 908 /* Copy old policy into new socket's. */ 909 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0) 910 printf("syncache_socket: could not copy policy\n"); 911 #endif 912 tp->t_state = TCPS_SYN_RECEIVED; 913 tp->iss = sc->sc_iss; 914 tp->irs = sc->sc_irs; 915 tp->t_port = sc->sc_port; 916 tcp_rcvseqinit(tp); 917 tcp_sendseqinit(tp); 918 tp->snd_wl1 = sc->sc_irs; 919 tp->snd_max = tp->iss + 1; 920 tp->snd_nxt = tp->iss + 1; 921 tp->rcv_up = sc->sc_irs + 1; 922 tp->rcv_wnd = sc->sc_wnd; 923 tp->rcv_adv += tp->rcv_wnd; 924 tp->last_ack_sent = tp->rcv_nxt; 925 926 tp->t_flags = sototcpcb(lso)->t_flags & 927 (TF_LRD|TF_NOPUSH|TF_NODELAY); 928 if (sc->sc_flags & SCF_NOOPT) 929 tp->t_flags |= TF_NOOPT; 930 else { 931 if (sc->sc_flags & SCF_WINSCALE) { 932 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 933 tp->snd_scale = sc->sc_requested_s_scale; 934 tp->request_r_scale = sc->sc_requested_r_scale; 935 } 936 if (sc->sc_flags & SCF_TIMESTAMP) { 937 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 938 tp->ts_recent = sc->sc_tsreflect; 939 tp->ts_recent_age = tcp_ts_getticks(); 940 tp->ts_offset = sc->sc_tsoff; 941 } 942 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 943 if (sc->sc_flags & SCF_SIGNATURE) 944 tp->t_flags |= TF_SIGNATURE; 945 #endif 946 if (sc->sc_flags & SCF_SACK) 947 tp->t_flags |= TF_SACK_PERMIT; 948 } 949 950 tcp_ecn_syncache_socket(tp, sc); 951 952 /* 953 * Set up MSS and get cached values from tcp_hostcache. 954 * This might overwrite some of the defaults we just set. 955 */ 956 tcp_mss(tp, sc->sc_peer_mss); 957 958 /* 959 * If the SYN,ACK was retransmitted, indicate that CWND to be 960 * limited to one segment in cc_conn_init(). 961 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 962 */ 963 if (sc->sc_rxmits > 1) 964 tp->snd_cwnd = 1; 965 966 #ifdef TCP_OFFLOAD 967 /* 968 * Allow a TOE driver to install its hooks. Note that we hold the 969 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 970 * new connection before the TOE driver has done its thing. 971 */ 972 if (ADDED_BY_TOE(sc)) { 973 struct toedev *tod = sc->sc_tod; 974 975 tod->tod_offload_socket(tod, sc->sc_todctx, so); 976 } 977 #endif 978 #ifdef TCP_BLACKBOX 979 /* 980 * Inherit the log state from the listening socket, if 981 * - the log state of the listening socket is not off and 982 * - the listening socket was not auto selected from all sessions and 983 * - a log id is not set on the listening socket. 984 * This avoids inheriting a log state which was automatically set. 985 */ 986 if ((tcp_get_bblog_state(sototcpcb(lso)) != TCP_LOG_STATE_OFF) && 987 ((sototcpcb(lso)->t_flags2 & TF2_LOG_AUTO) == 0) && 988 (sototcpcb(lso)->t_lib == NULL)) { 989 tcp_log_state_change(tp, tcp_get_bblog_state(sototcpcb(lso))); 990 } 991 #endif 992 /* 993 * Copy and activate timers. 994 */ 995 tp->t_maxunacktime = sototcpcb(lso)->t_maxunacktime; 996 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 997 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 998 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 999 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 1000 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 1001 1002 TCPSTAT_INC(tcps_accepts); 1003 TCP_PROBE6(state__change, NULL, tp, NULL, tp, NULL, TCPS_LISTEN); 1004 1005 if (!solisten_enqueue(so, SS_ISCONNECTED)) 1006 tp->t_flags |= TF_SONOTCONN; 1007 /* Can we inherit anything from the listener? */ 1008 if (tp->t_fb->tfb_inherit != NULL) { 1009 (*tp->t_fb->tfb_inherit)(tp, sotoinpcb(lso)); 1010 } 1011 return (so); 1012 1013 allocfail: 1014 /* 1015 * Drop the connection; we will either send a RST or have the peer 1016 * retransmit its SYN again after its RTO and try again. 1017 */ 1018 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 1019 log(LOG_DEBUG, "%s; %s: Socket create failed " 1020 "due to limits or memory shortage\n", 1021 s, __func__); 1022 free(s, M_TCPLOG); 1023 } 1024 TCPSTAT_INC(tcps_listendrop); 1025 return (NULL); 1026 1027 abort: 1028 tcp_discardcb(tp); 1029 in_pcbfree(inp); 1030 sodealloc(so); 1031 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 1032 log(LOG_DEBUG, "%s; %s: in%s_pcbconnect failed with error %i\n", 1033 s, __func__, (sc->sc_inc.inc_flags & INC_ISIPV6) ? "6" : "", 1034 error); 1035 free(s, M_TCPLOG); 1036 } 1037 TCPSTAT_INC(tcps_listendrop); 1038 return (NULL); 1039 } 1040 1041 /* 1042 * This function gets called when we receive an ACK for a 1043 * socket in the LISTEN state. We look up the connection 1044 * in the syncache, and if its there, we pull it out of 1045 * the cache and turn it into a full-blown connection in 1046 * the SYN-RECEIVED state. 1047 * 1048 * On syncache_socket() success the newly created socket 1049 * has its underlying inp locked. 1050 */ 1051 int 1052 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1053 struct socket **lsop, struct mbuf *m, uint16_t port) 1054 { 1055 struct syncache *sc; 1056 struct syncache_head *sch; 1057 struct syncache scs; 1058 char *s; 1059 bool locked; 1060 1061 NET_EPOCH_ASSERT(); 1062 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 1063 ("%s: can handle only ACK", __func__)); 1064 1065 if (syncache_cookiesonly()) { 1066 sc = NULL; 1067 sch = syncache_hashbucket(inc); 1068 locked = false; 1069 } else { 1070 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1071 locked = true; 1072 SCH_LOCK_ASSERT(sch); 1073 } 1074 1075 #ifdef INVARIANTS 1076 /* 1077 * Test code for syncookies comparing the syncache stored 1078 * values with the reconstructed values from the cookie. 1079 */ 1080 if (sc != NULL) 1081 syncookie_cmp(inc, sch, sc, th, to, *lsop, port); 1082 #endif 1083 1084 if (sc == NULL) { 1085 if (locked) { 1086 /* 1087 * The syncache is currently in use (neither disabled, 1088 * nor paused), but no entry was found. 1089 */ 1090 if (!V_tcp_syncookies) { 1091 /* 1092 * Since no syncookies are used in case of 1093 * a bucket overflow, don't even check for 1094 * a valid syncookie. 1095 */ 1096 SCH_UNLOCK(sch); 1097 TCPSTAT_INC(tcps_sc_spurcookie); 1098 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1099 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1100 "segment rejected " 1101 "(syncookies disabled)\n", 1102 s, __func__); 1103 goto failed; 1104 } 1105 if (sch->sch_last_overflow < 1106 time_uptime - SYNCOOKIE_LIFETIME) { 1107 /* 1108 * Since the bucket did not overflow recently, 1109 * don't even check for a valid syncookie. 1110 */ 1111 SCH_UNLOCK(sch); 1112 TCPSTAT_INC(tcps_sc_spurcookie); 1113 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1114 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1115 "segment rejected " 1116 "(no syncache entry)\n", 1117 s, __func__); 1118 goto failed; 1119 } 1120 SCH_UNLOCK(sch); 1121 } 1122 bzero(&scs, sizeof(scs)); 1123 /* 1124 * Now check, if the syncookie is valid. If it is, create an on 1125 * stack syncache entry. 1126 */ 1127 if (syncookie_expand(inc, sch, &scs, th, to, *lsop, port)) { 1128 sc = &scs; 1129 TCPSTAT_INC(tcps_sc_recvcookie); 1130 } else { 1131 TCPSTAT_INC(tcps_sc_failcookie); 1132 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1133 log(LOG_DEBUG, "%s; %s: Segment failed " 1134 "SYNCOOKIE authentication, segment rejected " 1135 "(probably spoofed)\n", s, __func__); 1136 goto failed; 1137 } 1138 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1139 /* If received ACK has MD5 signature, check it. */ 1140 if ((to->to_flags & TOF_SIGNATURE) != 0 && 1141 (!TCPMD5_ENABLED() || 1142 TCPMD5_INPUT(m, th, to->to_signature) != 0)) { 1143 /* Drop the ACK. */ 1144 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1145 log(LOG_DEBUG, "%s; %s: Segment rejected, " 1146 "MD5 signature doesn't match.\n", 1147 s, __func__); 1148 free(s, M_TCPLOG); 1149 } 1150 TCPSTAT_INC(tcps_sig_err_sigopt); 1151 return (-1); /* Do not send RST */ 1152 } 1153 #endif /* TCP_SIGNATURE */ 1154 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1155 } else { 1156 if (sc->sc_port != port) { 1157 SCH_UNLOCK(sch); 1158 return (0); 1159 } 1160 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1161 /* 1162 * If listening socket requested TCP digests, check that 1163 * received ACK has signature and it is correct. 1164 * If not, drop the ACK and leave sc entry in th cache, 1165 * because SYN was received with correct signature. 1166 */ 1167 if (sc->sc_flags & SCF_SIGNATURE) { 1168 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1169 /* No signature */ 1170 TCPSTAT_INC(tcps_sig_err_nosigopt); 1171 SCH_UNLOCK(sch); 1172 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1173 log(LOG_DEBUG, "%s; %s: Segment " 1174 "rejected, MD5 signature wasn't " 1175 "provided.\n", s, __func__); 1176 free(s, M_TCPLOG); 1177 } 1178 return (-1); /* Do not send RST */ 1179 } 1180 if (!TCPMD5_ENABLED() || 1181 TCPMD5_INPUT(m, th, to->to_signature) != 0) { 1182 /* Doesn't match or no SA */ 1183 SCH_UNLOCK(sch); 1184 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1185 log(LOG_DEBUG, "%s; %s: Segment " 1186 "rejected, MD5 signature doesn't " 1187 "match.\n", s, __func__); 1188 free(s, M_TCPLOG); 1189 } 1190 return (-1); /* Do not send RST */ 1191 } 1192 } 1193 #endif /* TCP_SIGNATURE */ 1194 1195 /* 1196 * RFC 7323 PAWS: If we have a timestamp on this segment and 1197 * it's less than ts_recent, drop it. 1198 * XXXMT: RFC 7323 also requires to send an ACK. 1199 * In tcp_input.c this is only done for TCP segments 1200 * with user data, so be consistent here and just drop 1201 * the segment. 1202 */ 1203 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS && 1204 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) { 1205 SCH_UNLOCK(sch); 1206 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1207 log(LOG_DEBUG, 1208 "%s; %s: SEG.TSval %u < TS.Recent %u, " 1209 "segment dropped\n", s, __func__, 1210 to->to_tsval, sc->sc_tsreflect); 1211 free(s, M_TCPLOG); 1212 } 1213 return (-1); /* Do not send RST */ 1214 } 1215 1216 /* 1217 * If timestamps were not negotiated during SYN/ACK and a 1218 * segment with a timestamp is received, ignore the 1219 * timestamp and process the packet normally. 1220 * See section 3.2 of RFC 7323. 1221 */ 1222 if (!(sc->sc_flags & SCF_TIMESTAMP) && 1223 (to->to_flags & TOF_TS)) { 1224 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1225 log(LOG_DEBUG, "%s; %s: Timestamp not " 1226 "expected, segment processed normally\n", 1227 s, __func__); 1228 free(s, M_TCPLOG); 1229 s = NULL; 1230 } 1231 } 1232 1233 /* 1234 * If timestamps were negotiated during SYN/ACK and a 1235 * segment without a timestamp is received, silently drop 1236 * the segment, unless the missing timestamps are tolerated. 1237 * See section 3.2 of RFC 7323. 1238 */ 1239 if ((sc->sc_flags & SCF_TIMESTAMP) && 1240 !(to->to_flags & TOF_TS)) { 1241 if (V_tcp_tolerate_missing_ts) { 1242 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1243 log(LOG_DEBUG, 1244 "%s; %s: Timestamp missing, " 1245 "segment processed normally\n", 1246 s, __func__); 1247 free(s, M_TCPLOG); 1248 } 1249 } else { 1250 SCH_UNLOCK(sch); 1251 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1252 log(LOG_DEBUG, 1253 "%s; %s: Timestamp missing, " 1254 "segment silently dropped\n", 1255 s, __func__); 1256 free(s, M_TCPLOG); 1257 } 1258 return (-1); /* Do not send RST */ 1259 } 1260 } 1261 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 1262 sch->sch_length--; 1263 #ifdef TCP_OFFLOAD 1264 if (ADDED_BY_TOE(sc)) { 1265 struct toedev *tod = sc->sc_tod; 1266 1267 tod->tod_syncache_removed(tod, sc->sc_todctx); 1268 } 1269 #endif 1270 SCH_UNLOCK(sch); 1271 } 1272 1273 /* 1274 * Segment validation: 1275 * ACK must match our initial sequence number + 1 (the SYN|ACK). 1276 */ 1277 if (th->th_ack != sc->sc_iss + 1) { 1278 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1279 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 1280 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 1281 goto failed; 1282 } 1283 1284 /* 1285 * The SEQ must fall in the window starting at the received 1286 * initial receive sequence number + 1 (the SYN). 1287 */ 1288 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1289 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1290 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1291 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 1292 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 1293 goto failed; 1294 } 1295 1296 *lsop = syncache_socket(sc, *lsop, m); 1297 1298 if (__predict_false(*lsop == NULL)) { 1299 TCPSTAT_INC(tcps_sc_aborted); 1300 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1301 } else if (sc != &scs) 1302 TCPSTAT_INC(tcps_sc_completed); 1303 1304 if (sc != &scs) 1305 syncache_free(sc); 1306 return (1); 1307 failed: 1308 if (sc != NULL) { 1309 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1310 if (sc != &scs) 1311 syncache_free(sc); 1312 } 1313 if (s != NULL) 1314 free(s, M_TCPLOG); 1315 *lsop = NULL; 1316 return (0); 1317 } 1318 1319 static struct socket * 1320 syncache_tfo_expand(struct syncache *sc, struct socket *lso, struct mbuf *m, 1321 uint64_t response_cookie) 1322 { 1323 struct inpcb *inp; 1324 struct tcpcb *tp; 1325 unsigned int *pending_counter; 1326 struct socket *so; 1327 1328 NET_EPOCH_ASSERT(); 1329 1330 pending_counter = intotcpcb(sotoinpcb(lso))->t_tfo_pending; 1331 so = syncache_socket(sc, lso, m); 1332 if (so == NULL) { 1333 TCPSTAT_INC(tcps_sc_aborted); 1334 atomic_subtract_int(pending_counter, 1); 1335 } else { 1336 soisconnected(so); 1337 inp = sotoinpcb(so); 1338 tp = intotcpcb(inp); 1339 tp->t_flags |= TF_FASTOPEN; 1340 tp->t_tfo_cookie.server = response_cookie; 1341 tp->snd_max = tp->iss; 1342 tp->snd_nxt = tp->iss; 1343 tp->t_tfo_pending = pending_counter; 1344 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1345 TCPSTAT_INC(tcps_sc_completed); 1346 } 1347 1348 return (so); 1349 } 1350 1351 /* 1352 * Given a LISTEN socket and an inbound SYN request, add 1353 * this to the syn cache, and send back a segment: 1354 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1355 * to the source. 1356 * 1357 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1358 * Doing so would require that we hold onto the data and deliver it 1359 * to the application. However, if we are the target of a SYN-flood 1360 * DoS attack, an attacker could send data which would eventually 1361 * consume all available buffer space if it were ACKed. By not ACKing 1362 * the data, we avoid this DoS scenario. 1363 * 1364 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO) 1365 * cookie is processed and a new socket is created. In this case, any data 1366 * accompanying the SYN will be queued to the socket by tcp_input() and will 1367 * be ACKed either when the application sends response data or the delayed 1368 * ACK timer expires, whichever comes first. 1369 */ 1370 struct socket * 1371 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1372 struct inpcb *inp, struct socket *so, struct mbuf *m, void *tod, 1373 void *todctx, uint8_t iptos, uint16_t port) 1374 { 1375 struct tcpcb *tp; 1376 struct socket *rv = NULL; 1377 struct syncache *sc = NULL; 1378 struct syncache_head *sch; 1379 struct mbuf *ipopts = NULL; 1380 u_int ltflags; 1381 int win, ip_ttl, ip_tos; 1382 char *s; 1383 #ifdef INET6 1384 int autoflowlabel = 0; 1385 #endif 1386 #ifdef MAC 1387 struct label *maclabel = NULL; 1388 #endif 1389 struct syncache scs; 1390 uint64_t tfo_response_cookie; 1391 unsigned int *tfo_pending = NULL; 1392 int tfo_cookie_valid = 0; 1393 int tfo_response_cookie_valid = 0; 1394 bool locked; 1395 1396 INP_RLOCK_ASSERT(inp); /* listen socket */ 1397 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1398 ("%s: unexpected tcp flags", __func__)); 1399 1400 /* 1401 * Combine all so/tp operations very early to drop the INP lock as 1402 * soon as possible. 1403 */ 1404 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so)); 1405 tp = sototcpcb(so); 1406 1407 #ifdef INET6 1408 if (inc->inc_flags & INC_ISIPV6) { 1409 if (inp->inp_flags & IN6P_AUTOFLOWLABEL) { 1410 autoflowlabel = 1; 1411 } 1412 ip_ttl = in6_selecthlim(inp, NULL); 1413 if ((inp->in6p_outputopts == NULL) || 1414 (inp->in6p_outputopts->ip6po_tclass == -1)) { 1415 ip_tos = 0; 1416 } else { 1417 ip_tos = inp->in6p_outputopts->ip6po_tclass; 1418 } 1419 } 1420 #endif 1421 #if defined(INET6) && defined(INET) 1422 else 1423 #endif 1424 #ifdef INET 1425 { 1426 ip_ttl = inp->inp_ip_ttl; 1427 ip_tos = inp->inp_ip_tos; 1428 } 1429 #endif 1430 win = so->sol_sbrcv_hiwat; 1431 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1432 1433 if (V_tcp_fastopen_server_enable && (tp->t_flags & TF_FASTOPEN) && 1434 (tp->t_tfo_pending != NULL) && 1435 (to->to_flags & TOF_FASTOPEN)) { 1436 /* 1437 * Limit the number of pending TFO connections to 1438 * approximately half of the queue limit. This prevents TFO 1439 * SYN floods from starving the service by filling the 1440 * listen queue with bogus TFO connections. 1441 */ 1442 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <= 1443 (so->sol_qlimit / 2)) { 1444 int result; 1445 1446 result = tcp_fastopen_check_cookie(inc, 1447 to->to_tfo_cookie, to->to_tfo_len, 1448 &tfo_response_cookie); 1449 tfo_cookie_valid = (result > 0); 1450 tfo_response_cookie_valid = (result >= 0); 1451 } 1452 1453 /* 1454 * Remember the TFO pending counter as it will have to be 1455 * decremented below if we don't make it to syncache_tfo_expand(). 1456 */ 1457 tfo_pending = tp->t_tfo_pending; 1458 } 1459 1460 #ifdef MAC 1461 if (mac_syncache_init(&maclabel) != 0) { 1462 INP_RUNLOCK(inp); 1463 goto done; 1464 } else 1465 mac_syncache_create(maclabel, inp); 1466 #endif 1467 if (!tfo_cookie_valid) 1468 INP_RUNLOCK(inp); 1469 1470 /* 1471 * Remember the IP options, if any. 1472 */ 1473 #ifdef INET6 1474 if (!(inc->inc_flags & INC_ISIPV6)) 1475 #endif 1476 #ifdef INET 1477 ipopts = (m) ? ip_srcroute(m) : NULL; 1478 #else 1479 ipopts = NULL; 1480 #endif 1481 1482 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1483 /* 1484 * When the socket is TCP-MD5 enabled check that, 1485 * - a signed packet is valid 1486 * - a non-signed packet does not have a security association 1487 * 1488 * If a signed packet fails validation or a non-signed packet has a 1489 * security association, the packet will be dropped. 1490 */ 1491 if (ltflags & TF_SIGNATURE) { 1492 if (to->to_flags & TOF_SIGNATURE) { 1493 if (!TCPMD5_ENABLED() || 1494 TCPMD5_INPUT(m, th, to->to_signature) != 0) 1495 goto done; 1496 } else { 1497 if (TCPMD5_ENABLED() && 1498 TCPMD5_INPUT(m, NULL, NULL) != ENOENT) 1499 goto done; 1500 } 1501 } else if (to->to_flags & TOF_SIGNATURE) 1502 goto done; 1503 #endif /* TCP_SIGNATURE */ 1504 /* 1505 * See if we already have an entry for this connection. 1506 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1507 * 1508 * XXX: should the syncache be re-initialized with the contents 1509 * of the new SYN here (which may have different options?) 1510 * 1511 * XXX: We do not check the sequence number to see if this is a 1512 * real retransmit or a new connection attempt. The question is 1513 * how to handle such a case; either ignore it as spoofed, or 1514 * drop the current entry and create a new one? 1515 */ 1516 if (syncache_cookiesonly()) { 1517 sc = NULL; 1518 sch = syncache_hashbucket(inc); 1519 locked = false; 1520 } else { 1521 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1522 locked = true; 1523 SCH_LOCK_ASSERT(sch); 1524 } 1525 if (sc != NULL) { 1526 if (tfo_cookie_valid) 1527 INP_RUNLOCK(inp); 1528 TCPSTAT_INC(tcps_sc_dupsyn); 1529 if (ipopts) { 1530 /* 1531 * If we were remembering a previous source route, 1532 * forget it and use the new one we've been given. 1533 */ 1534 if (sc->sc_ipopts) 1535 (void)m_free(sc->sc_ipopts); 1536 sc->sc_ipopts = ipopts; 1537 } 1538 /* 1539 * Update timestamp if present. 1540 */ 1541 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1542 sc->sc_tsreflect = to->to_tsval; 1543 else 1544 sc->sc_flags &= ~SCF_TIMESTAMP; 1545 /* 1546 * Adjust ECN response if needed, e.g. different 1547 * IP ECN field, or a fallback by the remote host. 1548 */ 1549 if (sc->sc_flags & SCF_ECN_MASK) { 1550 sc->sc_flags &= ~SCF_ECN_MASK; 1551 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos); 1552 } 1553 #ifdef MAC 1554 /* 1555 * Since we have already unconditionally allocated label 1556 * storage, free it up. The syncache entry will already 1557 * have an initialized label we can use. 1558 */ 1559 mac_syncache_destroy(&maclabel); 1560 #endif 1561 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1562 /* Retransmit SYN|ACK and reset retransmit count. */ 1563 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1564 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1565 "resetting timer and retransmitting SYN|ACK\n", 1566 s, __func__); 1567 free(s, M_TCPLOG); 1568 } 1569 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1570 sc->sc_rxmits = 0; 1571 syncache_timeout(sc, sch, 1); 1572 TCPSTAT_INC(tcps_sndacks); 1573 TCPSTAT_INC(tcps_sndtotal); 1574 } else { 1575 syncache_drop(sc, sch); 1576 TCPSTAT_INC(tcps_sc_dropped); 1577 } 1578 SCH_UNLOCK(sch); 1579 goto donenoprobe; 1580 } 1581 1582 KASSERT(sc == NULL, ("sc(%p) != NULL", sc)); 1583 /* 1584 * Skip allocating a syncache entry if we are just going to discard 1585 * it later. 1586 */ 1587 if (!locked || tfo_cookie_valid) { 1588 bzero(&scs, sizeof(scs)); 1589 sc = &scs; 1590 } else { 1591 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1592 if (sc == NULL) { 1593 /* 1594 * The zone allocator couldn't provide more entries. 1595 * Treat this as if the cache was full; drop the oldest 1596 * entry and insert the new one. 1597 */ 1598 TCPSTAT_INC(tcps_sc_zonefail); 1599 sc = TAILQ_LAST(&sch->sch_bucket, sch_head); 1600 if (sc != NULL) { 1601 sch->sch_last_overflow = time_uptime; 1602 syncache_drop(sc, sch); 1603 syncache_pause(inc); 1604 } 1605 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1606 if (sc == NULL) { 1607 if (V_tcp_syncookies) { 1608 bzero(&scs, sizeof(scs)); 1609 sc = &scs; 1610 } else { 1611 KASSERT(locked, 1612 ("%s: bucket unexpectedly unlocked", 1613 __func__)); 1614 SCH_UNLOCK(sch); 1615 goto done; 1616 } 1617 } 1618 } 1619 } 1620 1621 KASSERT(sc != NULL, ("sc == NULL")); 1622 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1623 sc->sc_tfo_cookie = &tfo_response_cookie; 1624 1625 /* 1626 * Fill in the syncache values. 1627 */ 1628 #ifdef MAC 1629 sc->sc_label = maclabel; 1630 #endif 1631 /* 1632 * sc_cred is only used in syncache_pcblist() to list TCP endpoints in 1633 * TCPS_SYN_RECEIVED state when V_tcp_syncache.see_other is false. 1634 * Therefore, store the credentials and take a reference count only 1635 * when needed: 1636 * - sc is allocated from the zone and not using the on stack instance. 1637 * - the sysctl variable net.inet.tcp.syncache.see_other is false. 1638 * The reference count is decremented when a zone allocated sc is 1639 * freed in syncache_free(). 1640 */ 1641 if (sc != &scs && !V_tcp_syncache.see_other) 1642 sc->sc_cred = crhold(so->so_cred); 1643 else 1644 sc->sc_cred = NULL; 1645 sc->sc_port = port; 1646 sc->sc_ipopts = ipopts; 1647 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1648 sc->sc_ip_tos = ip_tos; 1649 sc->sc_ip_ttl = ip_ttl; 1650 #ifdef TCP_OFFLOAD 1651 sc->sc_tod = tod; 1652 sc->sc_todctx = todctx; 1653 #endif 1654 sc->sc_irs = th->th_seq; 1655 sc->sc_flags = 0; 1656 sc->sc_flowlabel = 0; 1657 1658 /* 1659 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1660 * win was derived from socket earlier in the function. 1661 */ 1662 win = imax(win, 0); 1663 win = imin(win, TCP_MAXWIN); 1664 sc->sc_wnd = win; 1665 1666 if (V_tcp_do_rfc1323 && 1667 !(ltflags & TF_NOOPT)) { 1668 /* 1669 * A timestamp received in a SYN makes 1670 * it ok to send timestamp requests and replies. 1671 */ 1672 if ((to->to_flags & TOF_TS) && (V_tcp_do_rfc1323 != 2)) { 1673 sc->sc_tsreflect = to->to_tsval; 1674 sc->sc_flags |= SCF_TIMESTAMP; 1675 sc->sc_tsoff = tcp_new_ts_offset(inc); 1676 } 1677 if ((to->to_flags & TOF_SCALE) && (V_tcp_do_rfc1323 != 3)) { 1678 u_int wscale = 0; 1679 1680 /* 1681 * Pick the smallest possible scaling factor that 1682 * will still allow us to scale up to sb_max, aka 1683 * kern.ipc.maxsockbuf. 1684 * 1685 * We do this because there are broken firewalls that 1686 * will corrupt the window scale option, leading to 1687 * the other endpoint believing that our advertised 1688 * window is unscaled. At scale factors larger than 1689 * 5 the unscaled window will drop below 1500 bytes, 1690 * leading to serious problems when traversing these 1691 * broken firewalls. 1692 * 1693 * With the default maxsockbuf of 256K, a scale factor 1694 * of 3 will be chosen by this algorithm. Those who 1695 * choose a larger maxsockbuf should watch out 1696 * for the compatibility problems mentioned above. 1697 * 1698 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1699 * or <SYN,ACK>) segment itself is never scaled. 1700 */ 1701 while (wscale < TCP_MAX_WINSHIFT && 1702 (TCP_MAXWIN << wscale) < sb_max) 1703 wscale++; 1704 sc->sc_requested_r_scale = wscale; 1705 sc->sc_requested_s_scale = to->to_wscale; 1706 sc->sc_flags |= SCF_WINSCALE; 1707 } 1708 } 1709 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1710 /* 1711 * If incoming packet has an MD5 signature, flag this in the 1712 * syncache so that syncache_respond() will do the right thing 1713 * with the SYN+ACK. 1714 */ 1715 if (to->to_flags & TOF_SIGNATURE) 1716 sc->sc_flags |= SCF_SIGNATURE; 1717 #endif /* TCP_SIGNATURE */ 1718 if (to->to_flags & TOF_SACKPERM) 1719 sc->sc_flags |= SCF_SACK; 1720 if (to->to_flags & TOF_MSS) 1721 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1722 if (ltflags & TF_NOOPT) 1723 sc->sc_flags |= SCF_NOOPT; 1724 /* ECN Handshake */ 1725 if (V_tcp_do_ecn && (tp->t_flags2 & TF2_CANNOT_DO_ECN) == 0) 1726 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos); 1727 1728 if (V_tcp_syncookies || V_tcp_syncookiesonly) 1729 sc->sc_iss = syncookie_generate(sch, sc); 1730 else 1731 sc->sc_iss = arc4random(); 1732 #ifdef INET6 1733 if (autoflowlabel) { 1734 if (V_tcp_syncookies || V_tcp_syncookiesonly) 1735 sc->sc_flowlabel = sc->sc_iss; 1736 else 1737 sc->sc_flowlabel = ip6_randomflowlabel(); 1738 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1739 } 1740 #endif 1741 if (locked) 1742 SCH_UNLOCK(sch); 1743 1744 if (tfo_cookie_valid) { 1745 rv = syncache_tfo_expand(sc, so, m, tfo_response_cookie); 1746 /* INP_RUNLOCK(inp) will be performed by the caller */ 1747 goto tfo_expanded; 1748 } 1749 1750 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1751 /* 1752 * Do a standard 3-way handshake. 1753 */ 1754 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1755 if (sc != &scs) 1756 syncache_insert(sc, sch); /* locks and unlocks sch */ 1757 TCPSTAT_INC(tcps_sndacks); 1758 TCPSTAT_INC(tcps_sndtotal); 1759 } else { 1760 if (sc != &scs) 1761 syncache_free(sc); 1762 TCPSTAT_INC(tcps_sc_dropped); 1763 } 1764 goto donenoprobe; 1765 1766 done: 1767 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1768 donenoprobe: 1769 if (m) 1770 m_freem(m); 1771 /* 1772 * If tfo_pending is not NULL here, then a TFO SYN that did not 1773 * result in a new socket was processed and the associated pending 1774 * counter has not yet been decremented. All such TFO processing paths 1775 * transit this point. 1776 */ 1777 if (tfo_pending != NULL) 1778 tcp_fastopen_decrement_counter(tfo_pending); 1779 1780 tfo_expanded: 1781 if (sc == NULL || sc == &scs) { 1782 #ifdef MAC 1783 mac_syncache_destroy(&maclabel); 1784 #endif 1785 if (ipopts) 1786 (void)m_free(ipopts); 1787 } 1788 return (rv); 1789 } 1790 1791 /* 1792 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment, 1793 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL. 1794 */ 1795 static int 1796 syncache_respond(struct syncache *sc, const struct mbuf *m0, int flags) 1797 { 1798 struct ip *ip = NULL; 1799 struct mbuf *m; 1800 struct tcphdr *th = NULL; 1801 struct udphdr *udp = NULL; 1802 int optlen, error = 0; /* Make compiler happy */ 1803 u_int16_t hlen, tlen, mssopt, ulen; 1804 struct tcpopt to; 1805 #ifdef INET6 1806 struct ip6_hdr *ip6 = NULL; 1807 #endif 1808 1809 NET_EPOCH_ASSERT(); 1810 1811 hlen = 1812 #ifdef INET6 1813 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1814 #endif 1815 sizeof(struct ip); 1816 tlen = hlen + sizeof(struct tcphdr); 1817 if (sc->sc_port) { 1818 tlen += sizeof(struct udphdr); 1819 } 1820 /* Determine MSS we advertize to other end of connection. */ 1821 mssopt = tcp_mssopt(&sc->sc_inc); 1822 if (sc->sc_port) 1823 mssopt -= V_tcp_udp_tunneling_overhead; 1824 mssopt = max(mssopt, V_tcp_minmss); 1825 1826 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1827 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1828 ("syncache: mbuf too small: hlen %u, sc_port %u, max_linkhdr %d + " 1829 "tlen %d + TCP_MAXOLEN %ju <= MHLEN %d", hlen, sc->sc_port, 1830 max_linkhdr, tlen, (uintmax_t)TCP_MAXOLEN, MHLEN)); 1831 1832 /* Create the IP+TCP header from scratch. */ 1833 m = m_gethdr(M_NOWAIT, MT_DATA); 1834 if (m == NULL) 1835 return (ENOBUFS); 1836 #ifdef MAC 1837 mac_syncache_create_mbuf(sc->sc_label, m); 1838 #endif 1839 m->m_data += max_linkhdr; 1840 m->m_len = tlen; 1841 m->m_pkthdr.len = tlen; 1842 m->m_pkthdr.rcvif = NULL; 1843 1844 #ifdef INET6 1845 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1846 ip6 = mtod(m, struct ip6_hdr *); 1847 ip6->ip6_vfc = IPV6_VERSION; 1848 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1849 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1850 ip6->ip6_plen = htons(tlen - hlen); 1851 /* ip6_hlim is set after checksum */ 1852 /* Zero out traffic class and flow label. */ 1853 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK; 1854 ip6->ip6_flow |= sc->sc_flowlabel; 1855 if (sc->sc_port != 0) { 1856 ip6->ip6_nxt = IPPROTO_UDP; 1857 udp = (struct udphdr *)(ip6 + 1); 1858 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1859 udp->uh_dport = sc->sc_port; 1860 ulen = (tlen - sizeof(struct ip6_hdr)); 1861 th = (struct tcphdr *)(udp + 1); 1862 } else { 1863 ip6->ip6_nxt = IPPROTO_TCP; 1864 th = (struct tcphdr *)(ip6 + 1); 1865 } 1866 ip6->ip6_flow |= htonl(sc->sc_ip_tos << IPV6_FLOWLABEL_LEN); 1867 } 1868 #endif 1869 #if defined(INET6) && defined(INET) 1870 else 1871 #endif 1872 #ifdef INET 1873 { 1874 ip = mtod(m, struct ip *); 1875 ip->ip_v = IPVERSION; 1876 ip->ip_hl = sizeof(struct ip) >> 2; 1877 ip->ip_len = htons(tlen); 1878 ip->ip_id = 0; 1879 ip->ip_off = 0; 1880 ip->ip_sum = 0; 1881 ip->ip_src = sc->sc_inc.inc_laddr; 1882 ip->ip_dst = sc->sc_inc.inc_faddr; 1883 ip->ip_ttl = sc->sc_ip_ttl; 1884 ip->ip_tos = sc->sc_ip_tos; 1885 1886 /* 1887 * See if we should do MTU discovery. Route lookups are 1888 * expensive, so we will only unset the DF bit if: 1889 * 1890 * 1) path_mtu_discovery is disabled 1891 * 2) the SCF_UNREACH flag has been set 1892 */ 1893 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1894 ip->ip_off |= htons(IP_DF); 1895 if (sc->sc_port == 0) { 1896 ip->ip_p = IPPROTO_TCP; 1897 th = (struct tcphdr *)(ip + 1); 1898 } else { 1899 ip->ip_p = IPPROTO_UDP; 1900 udp = (struct udphdr *)(ip + 1); 1901 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1902 udp->uh_dport = sc->sc_port; 1903 ulen = (tlen - sizeof(struct ip)); 1904 th = (struct tcphdr *)(udp + 1); 1905 } 1906 } 1907 #endif /* INET */ 1908 th->th_sport = sc->sc_inc.inc_lport; 1909 th->th_dport = sc->sc_inc.inc_fport; 1910 1911 if (flags & TH_SYN) 1912 th->th_seq = htonl(sc->sc_iss); 1913 else 1914 th->th_seq = htonl(sc->sc_iss + 1); 1915 th->th_ack = htonl(sc->sc_irs + 1); 1916 th->th_off = sizeof(struct tcphdr) >> 2; 1917 th->th_win = htons(sc->sc_wnd); 1918 th->th_urp = 0; 1919 1920 flags = tcp_ecn_syncache_respond(flags, sc); 1921 tcp_set_flags(th, flags); 1922 1923 /* Tack on the TCP options. */ 1924 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1925 to.to_flags = 0; 1926 1927 if (flags & TH_SYN) { 1928 to.to_mss = mssopt; 1929 to.to_flags = TOF_MSS; 1930 if (sc->sc_flags & SCF_WINSCALE) { 1931 to.to_wscale = sc->sc_requested_r_scale; 1932 to.to_flags |= TOF_SCALE; 1933 } 1934 if (sc->sc_flags & SCF_SACK) 1935 to.to_flags |= TOF_SACKPERM; 1936 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1937 if (sc->sc_flags & SCF_SIGNATURE) 1938 to.to_flags |= TOF_SIGNATURE; 1939 #endif 1940 if (sc->sc_tfo_cookie) { 1941 to.to_flags |= TOF_FASTOPEN; 1942 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1943 to.to_tfo_cookie = sc->sc_tfo_cookie; 1944 /* don't send cookie again when retransmitting response */ 1945 sc->sc_tfo_cookie = NULL; 1946 } 1947 } 1948 if (sc->sc_flags & SCF_TIMESTAMP) { 1949 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks(); 1950 to.to_tsecr = sc->sc_tsreflect; 1951 to.to_flags |= TOF_TS; 1952 } 1953 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1954 1955 /* Adjust headers by option size. */ 1956 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1957 m->m_len += optlen; 1958 m->m_pkthdr.len += optlen; 1959 #ifdef INET6 1960 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1961 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1962 else 1963 #endif 1964 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1965 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1966 if (sc->sc_flags & SCF_SIGNATURE) { 1967 KASSERT(to.to_flags & TOF_SIGNATURE, 1968 ("tcp_addoptions() didn't set tcp_signature")); 1969 1970 /* NOTE: to.to_signature is inside of mbuf */ 1971 if (!TCPMD5_ENABLED() || 1972 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) { 1973 m_freem(m); 1974 return (EACCES); 1975 } 1976 } 1977 #endif 1978 } else 1979 optlen = 0; 1980 1981 if (udp) { 1982 ulen += optlen; 1983 udp->uh_ulen = htons(ulen); 1984 } 1985 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1986 /* 1987 * If we have peer's SYN and it has a flowid, then let's assign it to 1988 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid 1989 * to SYN|ACK due to lack of inp here. 1990 */ 1991 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) { 1992 m->m_pkthdr.flowid = m0->m_pkthdr.flowid; 1993 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0)); 1994 } 1995 #ifdef INET6 1996 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1997 if (sc->sc_port) { 1998 m->m_pkthdr.csum_flags = CSUM_UDP_IPV6; 1999 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2000 udp->uh_sum = in6_cksum_pseudo(ip6, ulen, 2001 IPPROTO_UDP, 0); 2002 th->th_sum = htons(0); 2003 } else { 2004 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 2005 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2006 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 2007 IPPROTO_TCP, 0); 2008 } 2009 ip6->ip6_hlim = sc->sc_ip_ttl; 2010 #ifdef TCP_OFFLOAD 2011 if (ADDED_BY_TOE(sc)) { 2012 struct toedev *tod = sc->sc_tod; 2013 2014 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2015 2016 return (error); 2017 } 2018 #endif 2019 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th); 2020 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 2021 } 2022 #endif 2023 #if defined(INET6) && defined(INET) 2024 else 2025 #endif 2026 #ifdef INET 2027 { 2028 if (sc->sc_port) { 2029 m->m_pkthdr.csum_flags = CSUM_UDP; 2030 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2031 udp->uh_sum = in_pseudo(ip->ip_src.s_addr, 2032 ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP)); 2033 th->th_sum = htons(0); 2034 } else { 2035 m->m_pkthdr.csum_flags = CSUM_TCP; 2036 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2037 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 2038 htons(tlen + optlen - hlen + IPPROTO_TCP)); 2039 } 2040 #ifdef TCP_OFFLOAD 2041 if (ADDED_BY_TOE(sc)) { 2042 struct toedev *tod = sc->sc_tod; 2043 2044 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2045 2046 return (error); 2047 } 2048 #endif 2049 TCP_PROBE5(send, NULL, NULL, ip, NULL, th); 2050 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 2051 } 2052 #endif 2053 return (error); 2054 } 2055 2056 /* 2057 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 2058 * that exceed the capacity of the syncache by avoiding the storage of any 2059 * of the SYNs we receive. Syncookies defend against blind SYN flooding 2060 * attacks where the attacker does not have access to our responses. 2061 * 2062 * Syncookies encode and include all necessary information about the 2063 * connection setup within the SYN|ACK that we send back. That way we 2064 * can avoid keeping any local state until the ACK to our SYN|ACK returns 2065 * (if ever). Normally the syncache and syncookies are running in parallel 2066 * with the latter taking over when the former is exhausted. When matching 2067 * syncache entry is found the syncookie is ignored. 2068 * 2069 * The only reliable information persisting the 3WHS is our initial sequence 2070 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 2071 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 2072 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 2073 * returns and signifies a legitimate connection if it matches the ACK. 2074 * 2075 * The available space of 32 bits to store the hash and to encode the SYN 2076 * option information is very tight and we should have at least 24 bits for 2077 * the MAC to keep the number of guesses by blind spoofing reasonably high. 2078 * 2079 * SYN option information we have to encode to fully restore a connection: 2080 * MSS: is imporant to chose an optimal segment size to avoid IP level 2081 * fragmentation along the path. The common MSS values can be encoded 2082 * in a 3-bit table. Uncommon values are captured by the next lower value 2083 * in the table leading to a slight increase in packetization overhead. 2084 * WSCALE: is necessary to allow large windows to be used for high delay- 2085 * bandwidth product links. Not scaling the window when it was initially 2086 * negotiated is bad for performance as lack of scaling further decreases 2087 * the apparent available send window. We only need to encode the WSCALE 2088 * we received from the remote end. Our end can be recalculated at any 2089 * time. The common WSCALE values can be encoded in a 3-bit table. 2090 * Uncommon values are captured by the next lower value in the table 2091 * making us under-estimate the available window size halving our 2092 * theoretically possible maximum throughput for that connection. 2093 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 2094 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 2095 * that are included in all segments on a connection. We enable them when 2096 * the ACK has them. 2097 * 2098 * Security of syncookies and attack vectors: 2099 * 2100 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 2101 * together with the gloabl secret to make it unique per connection attempt. 2102 * Thus any change of any of those parameters results in a different MAC output 2103 * in an unpredictable way unless a collision is encountered. 24 bits of the 2104 * MAC are embedded into the ISS. 2105 * 2106 * To prevent replay attacks two rotating global secrets are updated with a 2107 * new random value every 15 seconds. The life-time of a syncookie is thus 2108 * 15-30 seconds. 2109 * 2110 * Vector 1: Attacking the secret. This requires finding a weakness in the 2111 * MAC itself or the way it is used here. The attacker can do a chosen plain 2112 * text attack by varying and testing the all parameters under his control. 2113 * The strength depends on the size and randomness of the secret, and the 2114 * cryptographic security of the MAC function. Due to the constant updating 2115 * of the secret the attacker has at most 29.999 seconds to find the secret 2116 * and launch spoofed connections. After that he has to start all over again. 2117 * 2118 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 2119 * size an average of 4,823 attempts are required for a 50% chance of success 2120 * to spoof a single syncookie (birthday collision paradox). However the 2121 * attacker is blind and doesn't know if one of his attempts succeeded unless 2122 * he has a side channel to interfere success from. A single connection setup 2123 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 2124 * This many attempts are required for each one blind spoofed connection. For 2125 * every additional spoofed connection he has to launch another N attempts. 2126 * Thus for a sustained rate 100 spoofed connections per second approximately 2127 * 1,800,000 packets per second would have to be sent. 2128 * 2129 * NB: The MAC function should be fast so that it doesn't become a CPU 2130 * exhaustion attack vector itself. 2131 * 2132 * References: 2133 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 2134 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 2135 * http://cr.yp.to/syncookies.html (overview) 2136 * http://cr.yp.to/syncookies/archive (details) 2137 * 2138 * 2139 * Schematic construction of a syncookie enabled Initial Sequence Number: 2140 * 0 1 2 3 2141 * 12345678901234567890123456789012 2142 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 2143 * 2144 * x 24 MAC (truncated) 2145 * W 3 Send Window Scale index 2146 * M 3 MSS index 2147 * S 1 SACK permitted 2148 * P 1 Odd/even secret 2149 */ 2150 2151 /* 2152 * Distribution and probability of certain MSS values. Those in between are 2153 * rounded down to the next lower one. 2154 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 2155 * .2% .3% 5% 7% 7% 20% 15% 45% 2156 */ 2157 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 2158 2159 /* 2160 * Distribution and probability of certain WSCALE values. We have to map the 2161 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 2162 * bits based on prevalence of certain values. Where we don't have an exact 2163 * match for are rounded down to the next lower one letting us under-estimate 2164 * the true available window. At the moment this would happen only for the 2165 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 2166 * and window size). The absence of the WSCALE option (no scaling in either 2167 * direction) is encoded with index zero. 2168 * [WSCALE values histograms, Allman, 2012] 2169 * X 10 10 35 5 6 14 10% by host 2170 * X 11 4 5 5 18 49 3% by connections 2171 */ 2172 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 2173 2174 /* 2175 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 2176 * and good cryptographic properties. 2177 */ 2178 static uint32_t 2179 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 2180 uint8_t *secbits, uintptr_t secmod) 2181 { 2182 SIPHASH_CTX ctx; 2183 uint32_t siphash[2]; 2184 2185 SipHash24_Init(&ctx); 2186 SipHash_SetKey(&ctx, secbits); 2187 switch (inc->inc_flags & INC_ISIPV6) { 2188 #ifdef INET 2189 case 0: 2190 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 2191 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 2192 break; 2193 #endif 2194 #ifdef INET6 2195 case INC_ISIPV6: 2196 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 2197 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 2198 break; 2199 #endif 2200 } 2201 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 2202 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 2203 SipHash_Update(&ctx, &irs, sizeof(irs)); 2204 SipHash_Update(&ctx, &flags, sizeof(flags)); 2205 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 2206 SipHash_Final((u_int8_t *)&siphash, &ctx); 2207 2208 return (siphash[0] ^ siphash[1]); 2209 } 2210 2211 static tcp_seq 2212 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 2213 { 2214 u_int i, secbit, wscale; 2215 uint32_t iss, hash; 2216 uint8_t *secbits; 2217 union syncookie cookie; 2218 2219 cookie.cookie = 0; 2220 2221 /* Map our computed MSS into the 3-bit index. */ 2222 for (i = nitems(tcp_sc_msstab) - 1; 2223 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0; 2224 i--) 2225 ; 2226 cookie.flags.mss_idx = i; 2227 2228 /* 2229 * Map the send window scale into the 3-bit index but only if 2230 * the wscale option was received. 2231 */ 2232 if (sc->sc_flags & SCF_WINSCALE) { 2233 wscale = sc->sc_requested_s_scale; 2234 for (i = nitems(tcp_sc_wstab) - 1; 2235 tcp_sc_wstab[i] > wscale && i > 0; 2236 i--) 2237 ; 2238 cookie.flags.wscale_idx = i; 2239 } 2240 2241 /* Can we do SACK? */ 2242 if (sc->sc_flags & SCF_SACK) 2243 cookie.flags.sack_ok = 1; 2244 2245 /* Which of the two secrets to use. */ 2246 secbit = V_tcp_syncache.secret.oddeven & 0x1; 2247 cookie.flags.odd_even = secbit; 2248 2249 secbits = V_tcp_syncache.secret.key[secbit]; 2250 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 2251 (uintptr_t)sch); 2252 2253 /* 2254 * Put the flags into the hash and XOR them to get better ISS number 2255 * variance. This doesn't enhance the cryptographic strength and is 2256 * done to prevent the 8 cookie bits from showing up directly on the 2257 * wire. 2258 */ 2259 iss = hash & ~0xff; 2260 iss |= cookie.cookie ^ (hash >> 24); 2261 2262 TCPSTAT_INC(tcps_sc_sendcookie); 2263 return (iss); 2264 } 2265 2266 static bool 2267 syncookie_expand(struct in_conninfo *inc, const struct syncache_head *sch, 2268 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2269 struct socket *lso, uint16_t port) 2270 { 2271 uint32_t hash; 2272 uint8_t *secbits; 2273 tcp_seq ack, seq; 2274 int wnd; 2275 union syncookie cookie; 2276 2277 /* 2278 * Pull information out of SYN-ACK/ACK and revert sequence number 2279 * advances. 2280 */ 2281 ack = th->th_ack - 1; 2282 seq = th->th_seq - 1; 2283 2284 /* 2285 * Unpack the flags containing enough information to restore the 2286 * connection. 2287 */ 2288 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 2289 2290 /* Which of the two secrets to use. */ 2291 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even]; 2292 2293 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 2294 2295 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 2296 if ((ack & ~0xff) != (hash & ~0xff)) 2297 return (false); 2298 2299 /* Fill in the syncache values. */ 2300 sc->sc_flags = 0; 2301 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 2302 sc->sc_ipopts = NULL; 2303 2304 sc->sc_irs = seq; 2305 sc->sc_iss = ack; 2306 2307 switch (inc->inc_flags & INC_ISIPV6) { 2308 #ifdef INET 2309 case 0: 2310 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 2311 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 2312 break; 2313 #endif 2314 #ifdef INET6 2315 case INC_ISIPV6: 2316 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 2317 sc->sc_flowlabel = 2318 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK; 2319 break; 2320 #endif 2321 } 2322 2323 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 2324 2325 /* Only use wscale if it was enabled in the orignal SYN. */ 2326 if (cookie.flags.wscale_idx > 0) { 2327 u_int wscale = 0; 2328 2329 /* Recompute the receive window scale that was sent earlier. */ 2330 while (wscale < TCP_MAX_WINSHIFT && 2331 (TCP_MAXWIN << wscale) < sb_max) 2332 wscale++; 2333 sc->sc_requested_r_scale = wscale; 2334 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 2335 sc->sc_flags |= SCF_WINSCALE; 2336 } 2337 2338 wnd = lso->sol_sbrcv_hiwat; 2339 wnd = imax(wnd, 0); 2340 wnd = imin(wnd, TCP_MAXWIN); 2341 sc->sc_wnd = wnd; 2342 2343 if (cookie.flags.sack_ok) 2344 sc->sc_flags |= SCF_SACK; 2345 2346 if (to->to_flags & TOF_TS) { 2347 sc->sc_flags |= SCF_TIMESTAMP; 2348 sc->sc_tsreflect = to->to_tsval; 2349 sc->sc_tsoff = tcp_new_ts_offset(inc); 2350 } 2351 2352 if (to->to_flags & TOF_SIGNATURE) 2353 sc->sc_flags |= SCF_SIGNATURE; 2354 2355 sc->sc_rxmits = 0; 2356 2357 sc->sc_port = port; 2358 2359 return (true); 2360 } 2361 2362 #ifdef INVARIANTS 2363 static void 2364 syncookie_cmp(struct in_conninfo *inc, const struct syncache_head *sch, 2365 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2366 struct socket *lso, uint16_t port) 2367 { 2368 struct syncache scs; 2369 char *s; 2370 2371 bzero(&scs, sizeof(scs)); 2372 if (syncookie_expand(inc, sch, &scs, th, to, lso, port) && 2373 (sc->sc_peer_mss != scs.sc_peer_mss || 2374 sc->sc_requested_r_scale != scs.sc_requested_r_scale || 2375 sc->sc_requested_s_scale != scs.sc_requested_s_scale || 2376 (sc->sc_flags & SCF_SACK) != (scs.sc_flags & SCF_SACK))) { 2377 2378 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2379 return; 2380 2381 if (sc->sc_peer_mss != scs.sc_peer_mss) 2382 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2383 s, __func__, sc->sc_peer_mss, scs.sc_peer_mss); 2384 2385 if (sc->sc_requested_r_scale != scs.sc_requested_r_scale) 2386 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2387 s, __func__, sc->sc_requested_r_scale, 2388 scs.sc_requested_r_scale); 2389 2390 if (sc->sc_requested_s_scale != scs.sc_requested_s_scale) 2391 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2392 s, __func__, sc->sc_requested_s_scale, 2393 scs.sc_requested_s_scale); 2394 2395 if ((sc->sc_flags & SCF_SACK) != (scs.sc_flags & SCF_SACK)) 2396 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2397 2398 free(s, M_TCPLOG); 2399 } 2400 } 2401 #endif /* INVARIANTS */ 2402 2403 static void 2404 syncookie_reseed(void *arg) 2405 { 2406 struct tcp_syncache *sc = arg; 2407 uint8_t *secbits; 2408 int secbit; 2409 2410 /* 2411 * Reseeding the secret doesn't have to be protected by a lock. 2412 * It only must be ensured that the new random values are visible 2413 * to all CPUs in a SMP environment. The atomic with release 2414 * semantics ensures that. 2415 */ 2416 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2417 secbits = sc->secret.key[secbit]; 2418 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2419 atomic_add_rel_int(&sc->secret.oddeven, 1); 2420 2421 /* Reschedule ourself. */ 2422 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2423 } 2424 2425 /* 2426 * We have overflowed a bucket. Let's pause dealing with the syncache. 2427 * This function will increment the bucketoverflow statistics appropriately 2428 * (once per pause when pausing is enabled; otherwise, once per overflow). 2429 */ 2430 static void 2431 syncache_pause(struct in_conninfo *inc) 2432 { 2433 time_t delta; 2434 const char *s; 2435 2436 /* XXX: 2437 * 2. Add sysctl read here so we don't get the benefit of this 2438 * change without the new sysctl. 2439 */ 2440 2441 /* 2442 * Try an unlocked read. If we already know that another thread 2443 * has activated the feature, there is no need to proceed. 2444 */ 2445 if (V_tcp_syncache.paused) 2446 return; 2447 2448 /* Are cookied enabled? If not, we can't pause. */ 2449 if (!V_tcp_syncookies) { 2450 TCPSTAT_INC(tcps_sc_bucketoverflow); 2451 return; 2452 } 2453 2454 /* 2455 * We may be the first thread to find an overflow. Get the lock 2456 * and evaluate if we need to take action. 2457 */ 2458 mtx_lock(&V_tcp_syncache.pause_mtx); 2459 if (V_tcp_syncache.paused) { 2460 mtx_unlock(&V_tcp_syncache.pause_mtx); 2461 return; 2462 } 2463 2464 /* Activate protection. */ 2465 V_tcp_syncache.paused = true; 2466 TCPSTAT_INC(tcps_sc_bucketoverflow); 2467 2468 /* 2469 * Determine the last backoff time. If we are seeing a re-newed 2470 * attack within that same time after last reactivating the syncache, 2471 * consider it an extension of the same attack. 2472 */ 2473 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff; 2474 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) { 2475 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) { 2476 delta <<= 1; 2477 V_tcp_syncache.pause_backoff++; 2478 } 2479 } else { 2480 delta = TCP_SYNCACHE_PAUSE_TIME; 2481 V_tcp_syncache.pause_backoff = 0; 2482 } 2483 2484 /* Log a warning, including IP addresses, if able. */ 2485 if (inc != NULL) 2486 s = tcp_log_addrs(inc, NULL, NULL, NULL); 2487 else 2488 s = (const char *)NULL; 2489 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for " 2490 "the next %lld seconds%s%s%s\n", (long long)delta, 2491 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "", 2492 (s != NULL) ? ")" : ""); 2493 free(__DECONST(void *, s), M_TCPLOG); 2494 2495 /* Use the calculated delta to set a new pause time. */ 2496 V_tcp_syncache.pause_until = time_uptime + delta; 2497 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause, 2498 &V_tcp_syncache); 2499 mtx_unlock(&V_tcp_syncache.pause_mtx); 2500 } 2501 2502 /* Evaluate whether we need to unpause. */ 2503 static void 2504 syncache_unpause(void *arg) 2505 { 2506 struct tcp_syncache *sc; 2507 time_t delta; 2508 2509 sc = arg; 2510 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED); 2511 callout_deactivate(&sc->pause_co); 2512 2513 /* 2514 * Check to make sure we are not running early. If the pause 2515 * time has expired, then deactivate the protection. 2516 */ 2517 if ((delta = sc->pause_until - time_uptime) > 0) 2518 callout_schedule(&sc->pause_co, delta * hz); 2519 else 2520 sc->paused = false; 2521 } 2522 2523 /* 2524 * Exports the syncache entries to userland so that netstat can display 2525 * them alongside the other sockets. This function is intended to be 2526 * called only from tcp_pcblist. 2527 * 2528 * Due to concurrency on an active system, the number of pcbs exported 2529 * may have no relation to max_pcbs. max_pcbs merely indicates the 2530 * amount of space the caller allocated for this function to use. 2531 */ 2532 int 2533 syncache_pcblist(struct sysctl_req *req) 2534 { 2535 struct xtcpcb xt; 2536 struct syncache *sc; 2537 struct syncache_head *sch; 2538 int error, i; 2539 2540 bzero(&xt, sizeof(xt)); 2541 xt.xt_len = sizeof(xt); 2542 xt.t_state = TCPS_SYN_RECEIVED; 2543 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP; 2544 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket); 2545 xt.xt_inp.xi_socket.so_type = SOCK_STREAM; 2546 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING; 2547 2548 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 2549 sch = &V_tcp_syncache.hashbase[i]; 2550 SCH_LOCK(sch); 2551 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2552 if (sc->sc_cred != NULL && 2553 cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2554 continue; 2555 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2556 xt.xt_inp.inp_vflag = INP_IPV6; 2557 else 2558 xt.xt_inp.inp_vflag = INP_IPV4; 2559 xt.xt_encaps_port = sc->sc_port; 2560 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, 2561 sizeof (struct in_conninfo)); 2562 error = SYSCTL_OUT(req, &xt, sizeof xt); 2563 if (error) { 2564 SCH_UNLOCK(sch); 2565 return (0); 2566 } 2567 } 2568 SCH_UNLOCK(sch); 2569 } 2570 2571 return (0); 2572 } 2573