1 /*- 2 * Copyright (c) 2001 Networks Associates Technology, Inc. 3 * All rights reserved. 4 * 5 * This software was developed for the FreeBSD Project by Jonathan Lemon 6 * and NAI Labs, the Security Research Division of Network Associates, Inc. 7 * under DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the 8 * DARPA CHATS research program. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 3. The name of the author may not be used to endorse or promote 19 * products derived from this software without specific prior written 20 * permission. 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 * $FreeBSD$ 35 */ 36 37 #include "opt_inet6.h" 38 #include "opt_ipsec.h" 39 #include "opt_mac.h" 40 41 #include <sys/param.h> 42 #include <sys/systm.h> 43 #include <sys/kernel.h> 44 #include <sys/sysctl.h> 45 #include <sys/malloc.h> 46 #include <sys/mac.h> 47 #include <sys/mbuf.h> 48 #include <sys/md5.h> 49 #include <sys/proc.h> /* for proc0 declaration */ 50 #include <sys/random.h> 51 #include <sys/socket.h> 52 #include <sys/socketvar.h> 53 54 #include <net/if.h> 55 #include <net/route.h> 56 57 #include <netinet/in.h> 58 #include <netinet/in_systm.h> 59 #include <netinet/ip.h> 60 #include <netinet/in_var.h> 61 #include <netinet/in_pcb.h> 62 #include <netinet/ip_var.h> 63 #ifdef INET6 64 #include <netinet/ip6.h> 65 #include <netinet/icmp6.h> 66 #include <netinet6/nd6.h> 67 #include <netinet6/ip6_var.h> 68 #include <netinet6/in6_pcb.h> 69 #endif 70 #include <netinet/tcp.h> 71 #include <netinet/tcp_fsm.h> 72 #include <netinet/tcp_seq.h> 73 #include <netinet/tcp_timer.h> 74 #include <netinet/tcp_var.h> 75 #ifdef INET6 76 #include <netinet6/tcp6_var.h> 77 #endif 78 79 #ifdef IPSEC 80 #include <netinet6/ipsec.h> 81 #ifdef INET6 82 #include <netinet6/ipsec6.h> 83 #endif 84 #include <netkey/key.h> 85 #endif /*IPSEC*/ 86 87 #include <machine/in_cksum.h> 88 #include <vm/uma.h> 89 90 static int tcp_syncookies = 1; 91 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW, 92 &tcp_syncookies, 0, 93 "Use TCP SYN cookies if the syncache overflows"); 94 95 static void syncache_drop(struct syncache *, struct syncache_head *); 96 static void syncache_free(struct syncache *); 97 static void syncache_insert(struct syncache *, struct syncache_head *); 98 struct syncache *syncache_lookup(struct in_conninfo *, struct syncache_head **); 99 static int syncache_respond(struct syncache *, struct mbuf *); 100 static struct socket *syncache_socket(struct syncache *, struct socket *, 101 struct mbuf *m); 102 static void syncache_timer(void *); 103 static u_int32_t syncookie_generate(struct syncache *); 104 static struct syncache *syncookie_lookup(struct in_conninfo *, 105 struct tcphdr *, struct socket *); 106 107 /* 108 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 109 * 3 retransmits corresponds to a timeout of (1 + 2 + 4 + 8 == 15) seconds, 110 * the odds are that the user has given up attempting to connect by then. 111 */ 112 #define SYNCACHE_MAXREXMTS 3 113 114 /* Arbitrary values */ 115 #define TCP_SYNCACHE_HASHSIZE 512 116 #define TCP_SYNCACHE_BUCKETLIMIT 30 117 118 struct tcp_syncache { 119 struct syncache_head *hashbase; 120 uma_zone_t zone; 121 u_int hashsize; 122 u_int hashmask; 123 u_int bucket_limit; 124 u_int cache_count; 125 u_int cache_limit; 126 u_int rexmt_limit; 127 u_int hash_secret; 128 u_int next_reseed; 129 TAILQ_HEAD(, syncache) timerq[SYNCACHE_MAXREXMTS + 1]; 130 struct callout tt_timerq[SYNCACHE_MAXREXMTS + 1]; 131 }; 132 static struct tcp_syncache tcp_syncache; 133 134 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, "TCP SYN cache"); 135 136 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RD, 137 &tcp_syncache.bucket_limit, 0, "Per-bucket hash limit for syncache"); 138 139 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RD, 140 &tcp_syncache.cache_limit, 0, "Overall entry limit for syncache"); 141 142 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_RD, 143 &tcp_syncache.cache_count, 0, "Current number of entries in syncache"); 144 145 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RD, 146 &tcp_syncache.hashsize, 0, "Size of TCP syncache hashtable"); 147 148 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW, 149 &tcp_syncache.rexmt_limit, 0, "Limit on SYN/ACK retransmissions"); 150 151 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 152 153 #define SYNCACHE_HASH(inc, mask) \ 154 ((tcp_syncache.hash_secret ^ \ 155 (inc)->inc_faddr.s_addr ^ \ 156 ((inc)->inc_faddr.s_addr >> 16) ^ \ 157 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 158 159 #define SYNCACHE_HASH6(inc, mask) \ 160 ((tcp_syncache.hash_secret ^ \ 161 (inc)->inc6_faddr.s6_addr32[0] ^ \ 162 (inc)->inc6_faddr.s6_addr32[3] ^ \ 163 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 164 165 #define ENDPTS_EQ(a, b) ( \ 166 (a)->ie_fport == (b)->ie_fport && \ 167 (a)->ie_lport == (b)->ie_lport && \ 168 (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr && \ 169 (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr \ 170 ) 171 172 #define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0) 173 174 #define SYNCACHE_TIMEOUT(sc, slot) do { \ 175 sc->sc_rxtslot = slot; \ 176 sc->sc_rxttime = ticks + TCPTV_RTOBASE * tcp_backoff[slot]; \ 177 TAILQ_INSERT_TAIL(&tcp_syncache.timerq[slot], sc, sc_timerq); \ 178 if (!callout_active(&tcp_syncache.tt_timerq[slot])) \ 179 callout_reset(&tcp_syncache.tt_timerq[slot], \ 180 TCPTV_RTOBASE * tcp_backoff[slot], \ 181 syncache_timer, (void *)((intptr_t)slot)); \ 182 } while (0) 183 184 static void 185 syncache_free(struct syncache *sc) 186 { 187 struct rtentry *rt; 188 189 if (sc->sc_ipopts) 190 (void) m_free(sc->sc_ipopts); 191 #ifdef INET6 192 if (sc->sc_inc.inc_isipv6) 193 rt = sc->sc_route6.ro_rt; 194 else 195 #endif 196 rt = sc->sc_route.ro_rt; 197 if (rt != NULL) { 198 /* 199 * If this is the only reference to a protocol cloned 200 * route, remove it immediately. 201 */ 202 if (rt->rt_flags & RTF_WASCLONED && 203 (sc->sc_flags & SCF_KEEPROUTE) == 0 && 204 rt->rt_refcnt == 1) 205 rtrequest(RTM_DELETE, rt_key(rt), 206 rt->rt_gateway, rt_mask(rt), 207 rt->rt_flags, NULL); 208 RTFREE(rt); 209 } 210 uma_zfree(tcp_syncache.zone, sc); 211 } 212 213 void 214 syncache_init(void) 215 { 216 int i; 217 218 tcp_syncache.cache_count = 0; 219 tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 220 tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 221 tcp_syncache.cache_limit = 222 tcp_syncache.hashsize * tcp_syncache.bucket_limit; 223 tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 224 tcp_syncache.next_reseed = 0; 225 tcp_syncache.hash_secret = arc4random(); 226 227 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 228 &tcp_syncache.hashsize); 229 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 230 &tcp_syncache.cache_limit); 231 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 232 &tcp_syncache.bucket_limit); 233 if (!powerof2(tcp_syncache.hashsize)) { 234 printf("WARNING: syncache hash size is not a power of 2.\n"); 235 tcp_syncache.hashsize = 512; /* safe default */ 236 } 237 tcp_syncache.hashmask = tcp_syncache.hashsize - 1; 238 239 /* Allocate the hash table. */ 240 MALLOC(tcp_syncache.hashbase, struct syncache_head *, 241 tcp_syncache.hashsize * sizeof(struct syncache_head), 242 M_SYNCACHE, M_WAITOK); 243 244 /* Initialize the hash buckets. */ 245 for (i = 0; i < tcp_syncache.hashsize; i++) { 246 TAILQ_INIT(&tcp_syncache.hashbase[i].sch_bucket); 247 tcp_syncache.hashbase[i].sch_length = 0; 248 } 249 250 /* Initialize the timer queues. */ 251 for (i = 0; i <= SYNCACHE_MAXREXMTS; i++) { 252 TAILQ_INIT(&tcp_syncache.timerq[i]); 253 callout_init(&tcp_syncache.tt_timerq[i], 0); 254 } 255 256 /* 257 * Allocate the syncache entries. Allow the zone to allocate one 258 * more entry than cache limit, so a new entry can bump out an 259 * older one. 260 */ 261 tcp_syncache.cache_limit -= 1; 262 tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 263 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE); 264 uma_zone_set_max(tcp_syncache.zone, tcp_syncache.cache_limit); 265 } 266 267 static void 268 syncache_insert(sc, sch) 269 struct syncache *sc; 270 struct syncache_head *sch; 271 { 272 struct syncache *sc2; 273 int s, i; 274 275 /* 276 * Make sure that we don't overflow the per-bucket 277 * limit or the total cache size limit. 278 */ 279 s = splnet(); 280 if (sch->sch_length >= tcp_syncache.bucket_limit) { 281 /* 282 * The bucket is full, toss the oldest element. 283 */ 284 sc2 = TAILQ_FIRST(&sch->sch_bucket); 285 sc2->sc_tp->ts_recent = ticks; 286 syncache_drop(sc2, sch); 287 tcpstat.tcps_sc_bucketoverflow++; 288 } else if (tcp_syncache.cache_count >= tcp_syncache.cache_limit) { 289 /* 290 * The cache is full. Toss the oldest entry in the 291 * entire cache. This is the front entry in the 292 * first non-empty timer queue with the largest 293 * timeout value. 294 */ 295 for (i = SYNCACHE_MAXREXMTS; i >= 0; i--) { 296 sc2 = TAILQ_FIRST(&tcp_syncache.timerq[i]); 297 if (sc2 != NULL) 298 break; 299 } 300 sc2->sc_tp->ts_recent = ticks; 301 syncache_drop(sc2, NULL); 302 tcpstat.tcps_sc_cacheoverflow++; 303 } 304 305 /* Initialize the entry's timer. */ 306 SYNCACHE_TIMEOUT(sc, 0); 307 308 /* Put it into the bucket. */ 309 TAILQ_INSERT_TAIL(&sch->sch_bucket, sc, sc_hash); 310 sch->sch_length++; 311 tcp_syncache.cache_count++; 312 tcpstat.tcps_sc_added++; 313 splx(s); 314 } 315 316 static void 317 syncache_drop(sc, sch) 318 struct syncache *sc; 319 struct syncache_head *sch; 320 { 321 int s; 322 323 if (sch == NULL) { 324 #ifdef INET6 325 if (sc->sc_inc.inc_isipv6) { 326 sch = &tcp_syncache.hashbase[ 327 SYNCACHE_HASH6(&sc->sc_inc, tcp_syncache.hashmask)]; 328 } else 329 #endif 330 { 331 sch = &tcp_syncache.hashbase[ 332 SYNCACHE_HASH(&sc->sc_inc, tcp_syncache.hashmask)]; 333 } 334 } 335 336 s = splnet(); 337 338 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 339 sch->sch_length--; 340 tcp_syncache.cache_count--; 341 342 TAILQ_REMOVE(&tcp_syncache.timerq[sc->sc_rxtslot], sc, sc_timerq); 343 if (TAILQ_EMPTY(&tcp_syncache.timerq[sc->sc_rxtslot])) 344 callout_stop(&tcp_syncache.tt_timerq[sc->sc_rxtslot]); 345 splx(s); 346 347 syncache_free(sc); 348 } 349 350 /* 351 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 352 * If we have retransmitted an entry the maximum number of times, expire it. 353 */ 354 static void 355 syncache_timer(xslot) 356 void *xslot; 357 { 358 intptr_t slot = (intptr_t)xslot; 359 struct syncache *sc, *nsc; 360 struct inpcb *inp; 361 int s; 362 363 s = splnet(); 364 if (callout_pending(&tcp_syncache.tt_timerq[slot]) || 365 !callout_active(&tcp_syncache.tt_timerq[slot])) { 366 splx(s); 367 return; 368 } 369 callout_deactivate(&tcp_syncache.tt_timerq[slot]); 370 371 nsc = TAILQ_FIRST(&tcp_syncache.timerq[slot]); 372 INP_INFO_RLOCK(&tcbinfo); 373 while (nsc != NULL) { 374 if (ticks < nsc->sc_rxttime) 375 break; 376 sc = nsc; 377 inp = sc->sc_tp->t_inpcb; 378 INP_LOCK(inp); 379 if (slot == SYNCACHE_MAXREXMTS || 380 slot >= tcp_syncache.rexmt_limit || 381 inp->inp_gencnt != sc->sc_inp_gencnt) { 382 nsc = TAILQ_NEXT(sc, sc_timerq); 383 syncache_drop(sc, NULL); 384 tcpstat.tcps_sc_stale++; 385 INP_UNLOCK(inp); 386 continue; 387 } 388 /* 389 * syncache_respond() may call back into the syncache to 390 * to modify another entry, so do not obtain the next 391 * entry on the timer chain until it has completed. 392 */ 393 (void) syncache_respond(sc, NULL); 394 INP_UNLOCK(inp); 395 nsc = TAILQ_NEXT(sc, sc_timerq); 396 tcpstat.tcps_sc_retransmitted++; 397 TAILQ_REMOVE(&tcp_syncache.timerq[slot], sc, sc_timerq); 398 SYNCACHE_TIMEOUT(sc, slot + 1); 399 } 400 INP_INFO_RUNLOCK(&tcbinfo); 401 if (nsc != NULL) 402 callout_reset(&tcp_syncache.tt_timerq[slot], 403 nsc->sc_rxttime - ticks, syncache_timer, (void *)(slot)); 404 splx(s); 405 } 406 407 /* 408 * Find an entry in the syncache. 409 */ 410 struct syncache * 411 syncache_lookup(inc, schp) 412 struct in_conninfo *inc; 413 struct syncache_head **schp; 414 { 415 struct syncache *sc; 416 struct syncache_head *sch; 417 int s; 418 419 #ifdef INET6 420 if (inc->inc_isipv6) { 421 sch = &tcp_syncache.hashbase[ 422 SYNCACHE_HASH6(inc, tcp_syncache.hashmask)]; 423 *schp = sch; 424 s = splnet(); 425 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 426 if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) { 427 splx(s); 428 return (sc); 429 } 430 } 431 splx(s); 432 } else 433 #endif 434 { 435 sch = &tcp_syncache.hashbase[ 436 SYNCACHE_HASH(inc, tcp_syncache.hashmask)]; 437 *schp = sch; 438 s = splnet(); 439 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 440 #ifdef INET6 441 if (sc->sc_inc.inc_isipv6) 442 continue; 443 #endif 444 if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) { 445 splx(s); 446 return (sc); 447 } 448 } 449 splx(s); 450 } 451 return (NULL); 452 } 453 454 /* 455 * This function is called when we get a RST for a 456 * non-existent connection, so that we can see if the 457 * connection is in the syn cache. If it is, zap it. 458 */ 459 void 460 syncache_chkrst(inc, th) 461 struct in_conninfo *inc; 462 struct tcphdr *th; 463 { 464 struct syncache *sc; 465 struct syncache_head *sch; 466 467 sc = syncache_lookup(inc, &sch); 468 if (sc == NULL) 469 return; 470 /* 471 * If the RST bit is set, check the sequence number to see 472 * if this is a valid reset segment. 473 * RFC 793 page 37: 474 * In all states except SYN-SENT, all reset (RST) segments 475 * are validated by checking their SEQ-fields. A reset is 476 * valid if its sequence number is in the window. 477 * 478 * The sequence number in the reset segment is normally an 479 * echo of our outgoing acknowlegement numbers, but some hosts 480 * send a reset with the sequence number at the rightmost edge 481 * of our receive window, and we have to handle this case. 482 */ 483 if (SEQ_GEQ(th->th_seq, sc->sc_irs) && 484 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 485 syncache_drop(sc, sch); 486 tcpstat.tcps_sc_reset++; 487 } 488 } 489 490 void 491 syncache_badack(inc) 492 struct in_conninfo *inc; 493 { 494 struct syncache *sc; 495 struct syncache_head *sch; 496 497 sc = syncache_lookup(inc, &sch); 498 if (sc != NULL) { 499 syncache_drop(sc, sch); 500 tcpstat.tcps_sc_badack++; 501 } 502 } 503 504 void 505 syncache_unreach(inc, th) 506 struct in_conninfo *inc; 507 struct tcphdr *th; 508 { 509 struct syncache *sc; 510 struct syncache_head *sch; 511 512 /* we are called at splnet() here */ 513 sc = syncache_lookup(inc, &sch); 514 if (sc == NULL) 515 return; 516 517 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 518 if (ntohl(th->th_seq) != sc->sc_iss) 519 return; 520 521 /* 522 * If we've rertransmitted 3 times and this is our second error, 523 * we remove the entry. Otherwise, we allow it to continue on. 524 * This prevents us from incorrectly nuking an entry during a 525 * spurious network outage. 526 * 527 * See tcp_notify(). 528 */ 529 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxtslot < 3) { 530 sc->sc_flags |= SCF_UNREACH; 531 return; 532 } 533 syncache_drop(sc, sch); 534 tcpstat.tcps_sc_unreach++; 535 } 536 537 /* 538 * Build a new TCP socket structure from a syncache entry. 539 */ 540 static struct socket * 541 syncache_socket(sc, lso, m) 542 struct syncache *sc; 543 struct socket *lso; 544 struct mbuf *m; 545 { 546 struct inpcb *inp = NULL; 547 struct socket *so; 548 struct tcpcb *tp; 549 550 /* 551 * Ok, create the full blown connection, and set things up 552 * as they would have been set up if we had created the 553 * connection when the SYN arrived. If we can't create 554 * the connection, abort it. 555 */ 556 so = sonewconn(lso, SS_ISCONNECTED); 557 if (so == NULL) { 558 /* 559 * Drop the connection; we will send a RST if the peer 560 * retransmits the ACK, 561 */ 562 tcpstat.tcps_listendrop++; 563 goto abort; 564 } 565 #ifdef MAC 566 mac_set_socket_peer_from_mbuf(m, so); 567 #endif 568 569 inp = sotoinpcb(so); 570 571 /* 572 * Insert new socket into hash list. 573 */ 574 inp->inp_inc.inc_isipv6 = sc->sc_inc.inc_isipv6; 575 #ifdef INET6 576 if (sc->sc_inc.inc_isipv6) { 577 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 578 } else { 579 inp->inp_vflag &= ~INP_IPV6; 580 inp->inp_vflag |= INP_IPV4; 581 #endif 582 inp->inp_laddr = sc->sc_inc.inc_laddr; 583 #ifdef INET6 584 } 585 #endif 586 inp->inp_lport = sc->sc_inc.inc_lport; 587 if (in_pcbinshash(inp) != 0) { 588 /* 589 * Undo the assignments above if we failed to 590 * put the PCB on the hash lists. 591 */ 592 #ifdef INET6 593 if (sc->sc_inc.inc_isipv6) 594 inp->in6p_laddr = in6addr_any; 595 else 596 #endif 597 inp->inp_laddr.s_addr = INADDR_ANY; 598 inp->inp_lport = 0; 599 goto abort; 600 } 601 #ifdef IPSEC 602 /* copy old policy into new socket's */ 603 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp)) 604 printf("syncache_expand: could not copy policy\n"); 605 #endif 606 #ifdef INET6 607 if (sc->sc_inc.inc_isipv6) { 608 struct inpcb *oinp = sotoinpcb(lso); 609 struct in6_addr laddr6; 610 struct sockaddr_in6 *sin6; 611 /* 612 * Inherit socket options from the listening socket. 613 * Note that in6p_inputopts are not (and should not be) 614 * copied, since it stores previously received options and is 615 * used to detect if each new option is different than the 616 * previous one and hence should be passed to a user. 617 * If we copied in6p_inputopts, a user would not be able to 618 * receive options just after calling the accept system call. 619 */ 620 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 621 if (oinp->in6p_outputopts) 622 inp->in6p_outputopts = 623 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 624 inp->in6p_route = sc->sc_route6; 625 sc->sc_route6.ro_rt = NULL; 626 627 MALLOC(sin6, struct sockaddr_in6 *, sizeof *sin6, 628 M_SONAME, M_NOWAIT | M_ZERO); 629 if (sin6 == NULL) 630 goto abort; 631 sin6->sin6_family = AF_INET6; 632 sin6->sin6_len = sizeof(*sin6); 633 sin6->sin6_addr = sc->sc_inc.inc6_faddr; 634 sin6->sin6_port = sc->sc_inc.inc_fport; 635 laddr6 = inp->in6p_laddr; 636 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 637 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 638 if (in6_pcbconnect(inp, (struct sockaddr *)sin6, &thread0)) { 639 inp->in6p_laddr = laddr6; 640 FREE(sin6, M_SONAME); 641 goto abort; 642 } 643 FREE(sin6, M_SONAME); 644 } else 645 #endif 646 { 647 struct in_addr laddr; 648 struct sockaddr_in *sin; 649 650 inp->inp_options = ip_srcroute(); 651 if (inp->inp_options == NULL) { 652 inp->inp_options = sc->sc_ipopts; 653 sc->sc_ipopts = NULL; 654 } 655 inp->inp_route = sc->sc_route; 656 sc->sc_route.ro_rt = NULL; 657 658 MALLOC(sin, struct sockaddr_in *, sizeof *sin, 659 M_SONAME, M_NOWAIT | M_ZERO); 660 if (sin == NULL) 661 goto abort; 662 sin->sin_family = AF_INET; 663 sin->sin_len = sizeof(*sin); 664 sin->sin_addr = sc->sc_inc.inc_faddr; 665 sin->sin_port = sc->sc_inc.inc_fport; 666 bzero((caddr_t)sin->sin_zero, sizeof(sin->sin_zero)); 667 laddr = inp->inp_laddr; 668 if (inp->inp_laddr.s_addr == INADDR_ANY) 669 inp->inp_laddr = sc->sc_inc.inc_laddr; 670 if (in_pcbconnect(inp, (struct sockaddr *)sin, &thread0)) { 671 inp->inp_laddr = laddr; 672 FREE(sin, M_SONAME); 673 goto abort; 674 } 675 FREE(sin, M_SONAME); 676 } 677 678 tp = intotcpcb(inp); 679 tp->t_state = TCPS_SYN_RECEIVED; 680 tp->iss = sc->sc_iss; 681 tp->irs = sc->sc_irs; 682 tcp_rcvseqinit(tp); 683 tcp_sendseqinit(tp); 684 tp->snd_wl1 = sc->sc_irs; 685 tp->rcv_up = sc->sc_irs + 1; 686 tp->rcv_wnd = sc->sc_wnd; 687 tp->rcv_adv += tp->rcv_wnd; 688 689 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 690 if (sc->sc_flags & SCF_NOOPT) 691 tp->t_flags |= TF_NOOPT; 692 if (sc->sc_flags & SCF_WINSCALE) { 693 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 694 tp->requested_s_scale = sc->sc_requested_s_scale; 695 tp->request_r_scale = sc->sc_request_r_scale; 696 } 697 if (sc->sc_flags & SCF_TIMESTAMP) { 698 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 699 tp->ts_recent = sc->sc_tsrecent; 700 tp->ts_recent_age = ticks; 701 } 702 if (sc->sc_flags & SCF_CC) { 703 /* 704 * Initialization of the tcpcb for transaction; 705 * set SND.WND = SEG.WND, 706 * initialize CCsend and CCrecv. 707 */ 708 tp->t_flags |= TF_REQ_CC|TF_RCVD_CC; 709 tp->cc_send = sc->sc_cc_send; 710 tp->cc_recv = sc->sc_cc_recv; 711 } 712 713 tcp_mss(tp, sc->sc_peer_mss); 714 715 /* 716 * If the SYN,ACK was retransmitted, reset cwnd to 1 segment. 717 */ 718 if (sc->sc_rxtslot != 0) 719 tp->snd_cwnd = tp->t_maxseg; 720 callout_reset(tp->tt_keep, tcp_keepinit, tcp_timer_keep, tp); 721 722 tcpstat.tcps_accepts++; 723 return (so); 724 725 abort: 726 if (so != NULL) 727 (void) soabort(so); 728 return (NULL); 729 } 730 731 /* 732 * This function gets called when we receive an ACK for a 733 * socket in the LISTEN state. We look up the connection 734 * in the syncache, and if its there, we pull it out of 735 * the cache and turn it into a full-blown connection in 736 * the SYN-RECEIVED state. 737 */ 738 int 739 syncache_expand(inc, th, sop, m) 740 struct in_conninfo *inc; 741 struct tcphdr *th; 742 struct socket **sop; 743 struct mbuf *m; 744 { 745 struct syncache *sc; 746 struct syncache_head *sch; 747 struct socket *so; 748 749 sc = syncache_lookup(inc, &sch); 750 if (sc == NULL) { 751 /* 752 * There is no syncache entry, so see if this ACK is 753 * a returning syncookie. To do this, first: 754 * A. See if this socket has had a syncache entry dropped in 755 * the past. We don't want to accept a bogus syncookie 756 * if we've never received a SYN. 757 * B. check that the syncookie is valid. If it is, then 758 * cobble up a fake syncache entry, and return. 759 */ 760 if (!tcp_syncookies) 761 return (0); 762 sc = syncookie_lookup(inc, th, *sop); 763 if (sc == NULL) 764 return (0); 765 sch = NULL; 766 tcpstat.tcps_sc_recvcookie++; 767 } 768 769 /* 770 * If seg contains an ACK, but not for our SYN/ACK, send a RST. 771 */ 772 if (th->th_ack != sc->sc_iss + 1) 773 return (0); 774 775 so = syncache_socket(sc, *sop, m); 776 if (so == NULL) { 777 #if 0 778 resetandabort: 779 /* XXXjlemon check this - is this correct? */ 780 (void) tcp_respond(NULL, m, m, th, 781 th->th_seq + tlen, (tcp_seq)0, TH_RST|TH_ACK); 782 #endif 783 m_freem(m); /* XXX only needed for above */ 784 tcpstat.tcps_sc_aborted++; 785 } else { 786 sc->sc_flags |= SCF_KEEPROUTE; 787 tcpstat.tcps_sc_completed++; 788 } 789 if (sch == NULL) 790 syncache_free(sc); 791 else 792 syncache_drop(sc, sch); 793 *sop = so; 794 return (1); 795 } 796 797 /* 798 * Given a LISTEN socket and an inbound SYN request, add 799 * this to the syn cache, and send back a segment: 800 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 801 * to the source. 802 * 803 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 804 * Doing so would require that we hold onto the data and deliver it 805 * to the application. However, if we are the target of a SYN-flood 806 * DoS attack, an attacker could send data which would eventually 807 * consume all available buffer space if it were ACKed. By not ACKing 808 * the data, we avoid this DoS scenario. 809 */ 810 int 811 syncache_add(inc, to, th, sop, m) 812 struct in_conninfo *inc; 813 struct tcpopt *to; 814 struct tcphdr *th; 815 struct socket **sop; 816 struct mbuf *m; 817 { 818 struct tcpcb *tp; 819 struct socket *so; 820 struct syncache *sc = NULL; 821 struct syncache_head *sch; 822 struct mbuf *ipopts = NULL; 823 struct rmxp_tao *taop; 824 int i, s, win; 825 826 so = *sop; 827 tp = sototcpcb(so); 828 829 /* 830 * Remember the IP options, if any. 831 */ 832 #ifdef INET6 833 if (!inc->inc_isipv6) 834 #endif 835 ipopts = ip_srcroute(); 836 837 /* 838 * See if we already have an entry for this connection. 839 * If we do, resend the SYN,ACK, and reset the retransmit timer. 840 * 841 * XXX 842 * should the syncache be re-initialized with the contents 843 * of the new SYN here (which may have different options?) 844 */ 845 sc = syncache_lookup(inc, &sch); 846 if (sc != NULL) { 847 tcpstat.tcps_sc_dupsyn++; 848 if (ipopts) { 849 /* 850 * If we were remembering a previous source route, 851 * forget it and use the new one we've been given. 852 */ 853 if (sc->sc_ipopts) 854 (void) m_free(sc->sc_ipopts); 855 sc->sc_ipopts = ipopts; 856 } 857 /* 858 * Update timestamp if present. 859 */ 860 if (sc->sc_flags & SCF_TIMESTAMP) 861 sc->sc_tsrecent = to->to_tsval; 862 /* 863 * PCB may have changed, pick up new values. 864 */ 865 sc->sc_tp = tp; 866 sc->sc_inp_gencnt = tp->t_inpcb->inp_gencnt; 867 if (syncache_respond(sc, m) == 0) { 868 s = splnet(); 869 TAILQ_REMOVE(&tcp_syncache.timerq[sc->sc_rxtslot], 870 sc, sc_timerq); 871 SYNCACHE_TIMEOUT(sc, sc->sc_rxtslot); 872 splx(s); 873 tcpstat.tcps_sndacks++; 874 tcpstat.tcps_sndtotal++; 875 } 876 *sop = NULL; 877 return (1); 878 } 879 880 sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT); 881 if (sc == NULL) { 882 /* 883 * The zone allocator couldn't provide more entries. 884 * Treat this as if the cache was full; drop the oldest 885 * entry and insert the new one. 886 */ 887 s = splnet(); 888 for (i = SYNCACHE_MAXREXMTS; i >= 0; i--) { 889 sc = TAILQ_FIRST(&tcp_syncache.timerq[i]); 890 if (sc != NULL) 891 break; 892 } 893 sc->sc_tp->ts_recent = ticks; 894 syncache_drop(sc, NULL); 895 splx(s); 896 tcpstat.tcps_sc_zonefail++; 897 sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT); 898 if (sc == NULL) { 899 if (ipopts) 900 (void) m_free(ipopts); 901 return (0); 902 } 903 } 904 905 /* 906 * Fill in the syncache values. 907 */ 908 bzero(sc, sizeof(*sc)); 909 sc->sc_tp = tp; 910 sc->sc_inp_gencnt = tp->t_inpcb->inp_gencnt; 911 sc->sc_ipopts = ipopts; 912 sc->sc_inc.inc_fport = inc->inc_fport; 913 sc->sc_inc.inc_lport = inc->inc_lport; 914 #ifdef INET6 915 sc->sc_inc.inc_isipv6 = inc->inc_isipv6; 916 if (inc->inc_isipv6) { 917 sc->sc_inc.inc6_faddr = inc->inc6_faddr; 918 sc->sc_inc.inc6_laddr = inc->inc6_laddr; 919 sc->sc_route6.ro_rt = NULL; 920 } else 921 #endif 922 { 923 sc->sc_inc.inc_faddr = inc->inc_faddr; 924 sc->sc_inc.inc_laddr = inc->inc_laddr; 925 sc->sc_route.ro_rt = NULL; 926 } 927 sc->sc_irs = th->th_seq; 928 if (tcp_syncookies) 929 sc->sc_iss = syncookie_generate(sc); 930 else 931 sc->sc_iss = arc4random(); 932 933 /* Initial receive window: clip sbspace to [0 .. TCP_MAXWIN] */ 934 win = sbspace(&so->so_rcv); 935 win = imax(win, 0); 936 win = imin(win, TCP_MAXWIN); 937 sc->sc_wnd = win; 938 939 sc->sc_flags = 0; 940 sc->sc_peer_mss = to->to_flags & TOF_MSS ? to->to_mss : 0; 941 if (tcp_do_rfc1323) { 942 /* 943 * A timestamp received in a SYN makes 944 * it ok to send timestamp requests and replies. 945 */ 946 if (to->to_flags & TOF_TS) { 947 sc->sc_tsrecent = to->to_tsval; 948 sc->sc_flags |= SCF_TIMESTAMP; 949 } 950 if (to->to_flags & TOF_SCALE) { 951 int wscale = 0; 952 953 /* Compute proper scaling value from buffer space */ 954 while (wscale < TCP_MAX_WINSHIFT && 955 (TCP_MAXWIN << wscale) < so->so_rcv.sb_hiwat) 956 wscale++; 957 sc->sc_request_r_scale = wscale; 958 sc->sc_requested_s_scale = to->to_requested_s_scale; 959 sc->sc_flags |= SCF_WINSCALE; 960 } 961 } 962 if (tcp_do_rfc1644) { 963 /* 964 * A CC or CC.new option received in a SYN makes 965 * it ok to send CC in subsequent segments. 966 */ 967 if (to->to_flags & (TOF_CC|TOF_CCNEW)) { 968 sc->sc_cc_recv = to->to_cc; 969 sc->sc_cc_send = CC_INC(tcp_ccgen); 970 sc->sc_flags |= SCF_CC; 971 } 972 } 973 if (tp->t_flags & TF_NOOPT) 974 sc->sc_flags = SCF_NOOPT; 975 976 /* 977 * XXX 978 * We have the option here of not doing TAO (even if the segment 979 * qualifies) and instead fall back to a normal 3WHS via the syncache. 980 * This allows us to apply synflood protection to TAO-qualifying SYNs 981 * also. However, there should be a hueristic to determine when to 982 * do this, and is not present at the moment. 983 */ 984 985 /* 986 * Perform TAO test on incoming CC (SEG.CC) option, if any. 987 * - compare SEG.CC against cached CC from the same host, if any. 988 * - if SEG.CC > chached value, SYN must be new and is accepted 989 * immediately: save new CC in the cache, mark the socket 990 * connected, enter ESTABLISHED state, turn on flag to 991 * send a SYN in the next segment. 992 * A virtual advertised window is set in rcv_adv to 993 * initialize SWS prevention. Then enter normal segment 994 * processing: drop SYN, process data and FIN. 995 * - otherwise do a normal 3-way handshake. 996 */ 997 taop = tcp_gettaocache(&sc->sc_inc); 998 if ((to->to_flags & TOF_CC) != 0) { 999 if (((tp->t_flags & TF_NOPUSH) != 0) && 1000 sc->sc_flags & SCF_CC && 1001 taop != NULL && taop->tao_cc != 0 && 1002 CC_GT(to->to_cc, taop->tao_cc)) { 1003 sc->sc_rxtslot = 0; 1004 so = syncache_socket(sc, *sop, m); 1005 if (so != NULL) { 1006 sc->sc_flags |= SCF_KEEPROUTE; 1007 taop->tao_cc = to->to_cc; 1008 *sop = so; 1009 } 1010 syncache_free(sc); 1011 return (so != NULL); 1012 } 1013 } else { 1014 /* 1015 * No CC option, but maybe CC.NEW: invalidate cached value. 1016 */ 1017 if (taop != NULL) 1018 taop->tao_cc = 0; 1019 } 1020 /* 1021 * TAO test failed or there was no CC option, 1022 * do a standard 3-way handshake. 1023 */ 1024 if (syncache_respond(sc, m) == 0) { 1025 syncache_insert(sc, sch); 1026 tcpstat.tcps_sndacks++; 1027 tcpstat.tcps_sndtotal++; 1028 } else { 1029 syncache_free(sc); 1030 tcpstat.tcps_sc_dropped++; 1031 } 1032 *sop = NULL; 1033 return (1); 1034 } 1035 1036 static int 1037 syncache_respond(sc, m) 1038 struct syncache *sc; 1039 struct mbuf *m; 1040 { 1041 u_int8_t *optp; 1042 int optlen, error; 1043 u_int16_t tlen, hlen, mssopt; 1044 struct ip *ip = NULL; 1045 struct rtentry *rt; 1046 struct tcphdr *th; 1047 #ifdef INET6 1048 struct ip6_hdr *ip6 = NULL; 1049 #endif 1050 1051 #ifdef INET6 1052 if (sc->sc_inc.inc_isipv6) { 1053 rt = tcp_rtlookup6(&sc->sc_inc); 1054 if (rt != NULL) 1055 mssopt = rt->rt_ifp->if_mtu - 1056 (sizeof(struct ip6_hdr) + sizeof(struct tcphdr)); 1057 else 1058 mssopt = tcp_v6mssdflt; 1059 hlen = sizeof(struct ip6_hdr); 1060 } else 1061 #endif 1062 { 1063 rt = tcp_rtlookup(&sc->sc_inc); 1064 if (rt != NULL) 1065 mssopt = rt->rt_ifp->if_mtu - 1066 (sizeof(struct ip) + sizeof(struct tcphdr)); 1067 else 1068 mssopt = tcp_mssdflt; 1069 hlen = sizeof(struct ip); 1070 } 1071 1072 /* Compute the size of the TCP options. */ 1073 if (sc->sc_flags & SCF_NOOPT) { 1074 optlen = 0; 1075 } else { 1076 optlen = TCPOLEN_MAXSEG + 1077 ((sc->sc_flags & SCF_WINSCALE) ? 4 : 0) + 1078 ((sc->sc_flags & SCF_TIMESTAMP) ? TCPOLEN_TSTAMP_APPA : 0) + 1079 ((sc->sc_flags & SCF_CC) ? TCPOLEN_CC_APPA * 2 : 0); 1080 } 1081 tlen = hlen + sizeof(struct tcphdr) + optlen; 1082 1083 /* 1084 * XXX 1085 * assume that the entire packet will fit in a header mbuf 1086 */ 1087 KASSERT(max_linkhdr + tlen <= MHLEN, ("syncache: mbuf too small")); 1088 1089 /* 1090 * XXX shouldn't this reuse the mbuf if possible ? 1091 * Create the IP+TCP header from scratch. 1092 */ 1093 if (m) 1094 m_freem(m); 1095 1096 m = m_gethdr(M_DONTWAIT, MT_HEADER); 1097 if (m == NULL) 1098 return (ENOBUFS); 1099 m->m_data += max_linkhdr; 1100 m->m_len = tlen; 1101 m->m_pkthdr.len = tlen; 1102 m->m_pkthdr.rcvif = NULL; 1103 #ifdef MAC 1104 mac_create_mbuf_from_socket(sc->sc_tp->t_inpcb->inp_socket, m); 1105 #endif 1106 1107 #ifdef IPSEC 1108 /* use IPsec policy on listening socket to send SYN,ACK */ 1109 if (ipsec_setsocket(m, sc->sc_tp->t_inpcb->inp_socket) != 0) { 1110 m_freem(m); 1111 return (ENOBUFS); 1112 } 1113 #endif 1114 1115 #ifdef INET6 1116 if (sc->sc_inc.inc_isipv6) { 1117 ip6 = mtod(m, struct ip6_hdr *); 1118 ip6->ip6_vfc = IPV6_VERSION; 1119 ip6->ip6_nxt = IPPROTO_TCP; 1120 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1121 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1122 ip6->ip6_plen = htons(tlen - hlen); 1123 /* ip6_hlim is set after checksum */ 1124 /* ip6_flow = ??? */ 1125 1126 th = (struct tcphdr *)(ip6 + 1); 1127 } else 1128 #endif 1129 { 1130 ip = mtod(m, struct ip *); 1131 ip->ip_v = IPVERSION; 1132 ip->ip_hl = sizeof(struct ip) >> 2; 1133 ip->ip_len = tlen; 1134 ip->ip_id = 0; 1135 ip->ip_off = 0; 1136 ip->ip_sum = 0; 1137 ip->ip_p = IPPROTO_TCP; 1138 ip->ip_src = sc->sc_inc.inc_laddr; 1139 ip->ip_dst = sc->sc_inc.inc_faddr; 1140 ip->ip_ttl = sc->sc_tp->t_inpcb->inp_ip_ttl; /* XXX */ 1141 ip->ip_tos = sc->sc_tp->t_inpcb->inp_ip_tos; /* XXX */ 1142 1143 /* 1144 * See if we should do MTU discovery. Route lookups are expensive, 1145 * so we will only unset the DF bit if: 1146 * 1147 * 1) path_mtu_discovery is disabled 1148 * 2) the SCF_UNREACH flag has been set 1149 */ 1150 if (path_mtu_discovery 1151 && ((sc->sc_flags & SCF_UNREACH) == 0)) { 1152 ip->ip_off |= IP_DF; 1153 } 1154 1155 th = (struct tcphdr *)(ip + 1); 1156 } 1157 th->th_sport = sc->sc_inc.inc_lport; 1158 th->th_dport = sc->sc_inc.inc_fport; 1159 1160 th->th_seq = htonl(sc->sc_iss); 1161 th->th_ack = htonl(sc->sc_irs + 1); 1162 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1163 th->th_x2 = 0; 1164 th->th_flags = TH_SYN|TH_ACK; 1165 th->th_win = htons(sc->sc_wnd); 1166 th->th_urp = 0; 1167 1168 /* Tack on the TCP options. */ 1169 if (optlen == 0) 1170 goto no_options; 1171 optp = (u_int8_t *)(th + 1); 1172 *optp++ = TCPOPT_MAXSEG; 1173 *optp++ = TCPOLEN_MAXSEG; 1174 *optp++ = (mssopt >> 8) & 0xff; 1175 *optp++ = mssopt & 0xff; 1176 1177 if (sc->sc_flags & SCF_WINSCALE) { 1178 *((u_int32_t *)optp) = htonl(TCPOPT_NOP << 24 | 1179 TCPOPT_WINDOW << 16 | TCPOLEN_WINDOW << 8 | 1180 sc->sc_request_r_scale); 1181 optp += 4; 1182 } 1183 1184 if (sc->sc_flags & SCF_TIMESTAMP) { 1185 u_int32_t *lp = (u_int32_t *)(optp); 1186 1187 /* Form timestamp option as shown in appendix A of RFC 1323. */ 1188 *lp++ = htonl(TCPOPT_TSTAMP_HDR); 1189 *lp++ = htonl(ticks); 1190 *lp = htonl(sc->sc_tsrecent); 1191 optp += TCPOLEN_TSTAMP_APPA; 1192 } 1193 1194 /* 1195 * Send CC and CC.echo if we received CC from our peer. 1196 */ 1197 if (sc->sc_flags & SCF_CC) { 1198 u_int32_t *lp = (u_int32_t *)(optp); 1199 1200 *lp++ = htonl(TCPOPT_CC_HDR(TCPOPT_CC)); 1201 *lp++ = htonl(sc->sc_cc_send); 1202 *lp++ = htonl(TCPOPT_CC_HDR(TCPOPT_CCECHO)); 1203 *lp = htonl(sc->sc_cc_recv); 1204 optp += TCPOLEN_CC_APPA * 2; 1205 } 1206 no_options: 1207 1208 #ifdef INET6 1209 if (sc->sc_inc.inc_isipv6) { 1210 struct route_in6 *ro6 = &sc->sc_route6; 1211 1212 th->th_sum = 0; 1213 th->th_sum = in6_cksum(m, IPPROTO_TCP, hlen, tlen - hlen); 1214 ip6->ip6_hlim = in6_selecthlim(NULL, 1215 ro6->ro_rt ? ro6->ro_rt->rt_ifp : NULL); 1216 error = ip6_output(m, NULL, ro6, 0, NULL, NULL); 1217 } else 1218 #endif 1219 { 1220 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1221 htons(tlen - hlen + IPPROTO_TCP)); 1222 m->m_pkthdr.csum_flags = CSUM_TCP; 1223 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1224 error = ip_output(m, sc->sc_ipopts, &sc->sc_route, 0, NULL); 1225 } 1226 return (error); 1227 } 1228 1229 /* 1230 * cookie layers: 1231 * 1232 * |. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .| 1233 * | peer iss | 1234 * | MD5(laddr,faddr,lport,fport,secret) |. . . . . . .| 1235 * | 0 |(A)| | 1236 * (A): peer mss index 1237 */ 1238 1239 /* 1240 * The values below are chosen to minimize the size of the tcp_secret 1241 * table, as well as providing roughly a 4 second lifetime for the cookie. 1242 */ 1243 1244 #define SYNCOOKIE_HASHSHIFT 2 /* log2(# of 32bit words from hash) */ 1245 #define SYNCOOKIE_WNDBITS 7 /* exposed bits for window indexing */ 1246 #define SYNCOOKIE_TIMESHIFT 5 /* scale ticks to window time units */ 1247 1248 #define SYNCOOKIE_HASHMASK ((1 << SYNCOOKIE_HASHSHIFT) - 1) 1249 #define SYNCOOKIE_WNDMASK ((1 << SYNCOOKIE_WNDBITS) - 1) 1250 #define SYNCOOKIE_NSECRETS (1 << (SYNCOOKIE_WNDBITS - SYNCOOKIE_HASHSHIFT)) 1251 #define SYNCOOKIE_TIMEOUT \ 1252 (hz * (1 << SYNCOOKIE_WNDBITS) / (1 << SYNCOOKIE_TIMESHIFT)) 1253 #define SYNCOOKIE_DATAMASK ((3 << SYNCOOKIE_WNDBITS) | SYNCOOKIE_WNDMASK) 1254 1255 static struct { 1256 u_int32_t ts_secbits; 1257 u_int ts_expire; 1258 } tcp_secret[SYNCOOKIE_NSECRETS]; 1259 1260 static int tcp_msstab[] = { 0, 536, 1460, 8960 }; 1261 1262 static MD5_CTX syn_ctx; 1263 1264 #define MD5Add(v) MD5Update(&syn_ctx, (u_char *)&v, sizeof(v)) 1265 1266 /* 1267 * Consider the problem of a recreated (and retransmitted) cookie. If the 1268 * original SYN was accepted, the connection is established. The second 1269 * SYN is inflight, and if it arrives with an ISN that falls within the 1270 * receive window, the connection is killed. 1271 * 1272 * However, since cookies have other problems, this may not be worth 1273 * worrying about. 1274 */ 1275 1276 static u_int32_t 1277 syncookie_generate(struct syncache *sc) 1278 { 1279 u_int32_t md5_buffer[4]; 1280 u_int32_t data; 1281 int wnd, idx; 1282 1283 wnd = ((ticks << SYNCOOKIE_TIMESHIFT) / hz) & SYNCOOKIE_WNDMASK; 1284 idx = wnd >> SYNCOOKIE_HASHSHIFT; 1285 if (tcp_secret[idx].ts_expire < ticks) { 1286 tcp_secret[idx].ts_secbits = arc4random(); 1287 tcp_secret[idx].ts_expire = ticks + SYNCOOKIE_TIMEOUT; 1288 } 1289 for (data = sizeof(tcp_msstab) / sizeof(int) - 1; data > 0; data--) 1290 if (tcp_msstab[data] <= sc->sc_peer_mss) 1291 break; 1292 data = (data << SYNCOOKIE_WNDBITS) | wnd; 1293 data ^= sc->sc_irs; /* peer's iss */ 1294 MD5Init(&syn_ctx); 1295 #ifdef INET6 1296 if (sc->sc_inc.inc_isipv6) { 1297 MD5Add(sc->sc_inc.inc6_laddr); 1298 MD5Add(sc->sc_inc.inc6_faddr); 1299 } else 1300 #endif 1301 { 1302 MD5Add(sc->sc_inc.inc_laddr); 1303 MD5Add(sc->sc_inc.inc_faddr); 1304 } 1305 MD5Add(sc->sc_inc.inc_lport); 1306 MD5Add(sc->sc_inc.inc_fport); 1307 MD5Add(tcp_secret[idx].ts_secbits); 1308 MD5Final((u_char *)&md5_buffer, &syn_ctx); 1309 data ^= (md5_buffer[wnd & SYNCOOKIE_HASHMASK] & ~SYNCOOKIE_WNDMASK); 1310 return (data); 1311 } 1312 1313 static struct syncache * 1314 syncookie_lookup(inc, th, so) 1315 struct in_conninfo *inc; 1316 struct tcphdr *th; 1317 struct socket *so; 1318 { 1319 u_int32_t md5_buffer[4]; 1320 struct syncache *sc; 1321 u_int32_t data; 1322 int wnd, idx; 1323 1324 data = (th->th_ack - 1) ^ (th->th_seq - 1); /* remove ISS */ 1325 wnd = data & SYNCOOKIE_WNDMASK; 1326 idx = wnd >> SYNCOOKIE_HASHSHIFT; 1327 if (tcp_secret[idx].ts_expire < ticks || 1328 sototcpcb(so)->ts_recent + SYNCOOKIE_TIMEOUT < ticks) 1329 return (NULL); 1330 MD5Init(&syn_ctx); 1331 #ifdef INET6 1332 if (inc->inc_isipv6) { 1333 MD5Add(inc->inc6_laddr); 1334 MD5Add(inc->inc6_faddr); 1335 } else 1336 #endif 1337 { 1338 MD5Add(inc->inc_laddr); 1339 MD5Add(inc->inc_faddr); 1340 } 1341 MD5Add(inc->inc_lport); 1342 MD5Add(inc->inc_fport); 1343 MD5Add(tcp_secret[idx].ts_secbits); 1344 MD5Final((u_char *)&md5_buffer, &syn_ctx); 1345 data ^= md5_buffer[wnd & SYNCOOKIE_HASHMASK]; 1346 if ((data & ~SYNCOOKIE_DATAMASK) != 0) 1347 return (NULL); 1348 data = data >> SYNCOOKIE_WNDBITS; 1349 1350 sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT); 1351 if (sc == NULL) 1352 return (NULL); 1353 /* 1354 * Fill in the syncache values. 1355 * XXX duplicate code from syncache_add 1356 */ 1357 sc->sc_ipopts = NULL; 1358 sc->sc_inc.inc_fport = inc->inc_fport; 1359 sc->sc_inc.inc_lport = inc->inc_lport; 1360 #ifdef INET6 1361 sc->sc_inc.inc_isipv6 = inc->inc_isipv6; 1362 if (inc->inc_isipv6) { 1363 sc->sc_inc.inc6_faddr = inc->inc6_faddr; 1364 sc->sc_inc.inc6_laddr = inc->inc6_laddr; 1365 sc->sc_route6.ro_rt = NULL; 1366 } else 1367 #endif 1368 { 1369 sc->sc_inc.inc_faddr = inc->inc_faddr; 1370 sc->sc_inc.inc_laddr = inc->inc_laddr; 1371 sc->sc_route.ro_rt = NULL; 1372 } 1373 sc->sc_irs = th->th_seq - 1; 1374 sc->sc_iss = th->th_ack - 1; 1375 wnd = sbspace(&so->so_rcv); 1376 wnd = imax(wnd, 0); 1377 wnd = imin(wnd, TCP_MAXWIN); 1378 sc->sc_wnd = wnd; 1379 sc->sc_flags = 0; 1380 sc->sc_rxtslot = 0; 1381 sc->sc_peer_mss = tcp_msstab[data]; 1382 return (sc); 1383 } 1384