1 /*- 2 * SPDX-License-Identifier: BSD-3-Clause 3 * 4 * Copyright (c) 2003 Andre Oppermann, Internet Business Solutions AG 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 3. The name of the author may not be used to endorse or promote 16 * products derived from this software without specific prior written 17 * permission. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29 * SUCH DAMAGE. 30 */ 31 32 /* 33 * ip_fastforward gets its speed from processing the forwarded packet to 34 * completion (if_output on the other side) without any queues or netisr's. 35 * The receiving interface DMAs the packet into memory, the upper half of 36 * driver calls ip_fastforward, we do our routing table lookup and directly 37 * send it off to the outgoing interface, which DMAs the packet to the 38 * network card. The only part of the packet we touch with the CPU is the 39 * IP header (unless there are complex firewall rules touching other parts 40 * of the packet, but that is up to you). We are essentially limited by bus 41 * bandwidth and how fast the network card/driver can set up receives and 42 * transmits. 43 * 44 * We handle basic errors, IP header errors, checksum errors, 45 * destination unreachable, fragmentation and fragmentation needed and 46 * report them via ICMP to the sender. 47 * 48 * Else if something is not pure IPv4 unicast forwarding we fall back to 49 * the normal ip_input processing path. We should only be called from 50 * interfaces connected to the outside world. 51 * 52 * Firewalling is fully supported including divert, ipfw fwd and ipfilter 53 * ipnat and address rewrite. 54 * 55 * IPSEC is not supported if this host is a tunnel broker. IPSEC is 56 * supported for connections to/from local host. 57 * 58 * We try to do the least expensive (in CPU ops) checks and operations 59 * first to catch junk with as little overhead as possible. 60 * 61 * We take full advantage of hardware support for IP checksum and 62 * fragmentation offloading. 63 */ 64 65 /* 66 * Many thanks to Matt Thomas of NetBSD for basic structure of ip_flow.c which 67 * is being followed here. 68 */ 69 70 #include "opt_ipstealth.h" 71 #include "opt_sctp.h" 72 73 #include <sys/param.h> 74 #include <sys/systm.h> 75 #include <sys/kernel.h> 76 #include <sys/malloc.h> 77 #include <sys/mbuf.h> 78 #include <sys/protosw.h> 79 #include <sys/sdt.h> 80 #include <sys/socket.h> 81 #include <sys/sysctl.h> 82 83 #include <net/if.h> 84 #include <net/if_types.h> 85 #include <net/if_var.h> 86 #include <net/if_dl.h> 87 #include <net/if_private.h> 88 #include <net/pfil.h> 89 #include <net/route.h> 90 #include <net/route/nhop.h> 91 #include <net/vnet.h> 92 93 #include <netinet/in.h> 94 #include <netinet/in_fib.h> 95 #include <netinet/in_kdtrace.h> 96 #include <netinet/in_systm.h> 97 #include <netinet/in_var.h> 98 #include <netinet/ip.h> 99 #include <netinet/ip_var.h> 100 #include <netinet/ip_icmp.h> 101 #include <netinet/ip_options.h> 102 103 #include <machine/in_cksum.h> 104 105 #if defined(SCTP) || defined(SCTP_SUPPORT) 106 #include <netinet/sctp_crc32.h> 107 #endif 108 109 #define V_ipsendredirects VNET(ipsendredirects) 110 111 static struct mbuf * 112 ip_redir_alloc(struct mbuf *m, struct nhop_object *nh, u_short ip_len, 113 struct in_addr *osrc, struct in_addr *newgw) 114 { 115 struct in_ifaddr *nh_ia; 116 struct mbuf *mcopy; 117 118 KASSERT(nh != NULL, ("%s: m %p nh is NULL\n", __func__, m)); 119 120 /* 121 * Only send a redirect if: 122 * - Redirects are not disabled (must be checked by caller), 123 * - We have not applied NAT (must be checked by caller as possible), 124 * - Neither a MCAST or BCAST packet (must be checked by caller) 125 * [RFC1009 Appendix A.2]. 126 * - The packet does not do IP source routing or having any other 127 * IP options (this case was handled already by ip_input() calling 128 * ip_dooptions() [RFC792, p13], 129 * - The packet is being forwarded out the same physical interface 130 * that it was received from [RFC1812, 5.2.7.2]. 131 */ 132 133 /* 134 * - The forwarding route was not created by a redirect 135 * [RFC1812, 5.2.7.2], or 136 * if it was to follow a default route (see below). 137 * - The next-hop is reachable by us [RFC1009 Appendix A.2]. 138 */ 139 if ((nh->nh_flags & (NHF_DEFAULT | NHF_REDIRECT | 140 NHF_BLACKHOLE | NHF_REJECT)) != 0) 141 return (NULL); 142 143 /* Get the new gateway. */ 144 if ((nh->nh_flags & NHF_GATEWAY) == 0 || nh->gw_sa.sa_family != AF_INET) 145 return (NULL); 146 newgw->s_addr = nh->gw4_sa.sin_addr.s_addr; 147 148 /* 149 * - The resulting forwarding destination is not "This host on this 150 * network" [RFC1122, Section 3.2.1.3] (default route check above). 151 */ 152 if (newgw->s_addr == 0) 153 return (NULL); 154 155 /* 156 * - We know how to reach the sender and the source address is 157 * directly connected to us [RFC792, p13]. 158 * + The new gateway address and the source address are on the same 159 * subnet [RFC1009 Appendix A.2, RFC1122 3.2.2.2, RFC1812, 5.2.7.2]. 160 * NB: if you think multiple logical subnets on the same wire should 161 * receive redirects read [RFC1812, APPENDIX C (14->15)]. 162 */ 163 nh_ia = (struct in_ifaddr *)nh->nh_ifa; 164 if ((ntohl(osrc->s_addr) & nh_ia->ia_subnetmask) != nh_ia->ia_subnet) 165 return (NULL); 166 167 /* Prepare for sending the redirect. */ 168 169 /* 170 * Make a copy of as much as we need of the packet as the original 171 * one will be forwarded but we need (a portion) for icmp_error(). 172 */ 173 mcopy = m_gethdr(M_NOWAIT, m->m_type); 174 if (mcopy == NULL) 175 return (NULL); 176 177 if (m_dup_pkthdr(mcopy, m, M_NOWAIT) == 0) { 178 /* 179 * It's probably ok if the pkthdr dup fails (because 180 * the deep copy of the tag chain failed), but for now 181 * be conservative and just discard the copy since 182 * code below may some day want the tags. 183 */ 184 m_free(mcopy); 185 return (NULL); 186 } 187 mcopy->m_len = min(ip_len, M_TRAILINGSPACE(mcopy)); 188 mcopy->m_pkthdr.len = mcopy->m_len; 189 m_copydata(m, 0, mcopy->m_len, mtod(mcopy, caddr_t)); 190 191 return (mcopy); 192 } 193 194 195 static int 196 ip_findroute(struct nhop_object **pnh, struct in_addr dest, struct mbuf *m) 197 { 198 struct nhop_object *nh; 199 200 nh = fib4_lookup(M_GETFIB(m), dest, 0, NHR_NONE, 201 m->m_pkthdr.flowid); 202 if (nh == NULL) { 203 IPSTAT_INC(ips_noroute); 204 IPSTAT_INC(ips_cantforward); 205 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0); 206 return (EHOSTUNREACH); 207 } 208 /* 209 * Drop blackholed traffic and directed broadcasts. 210 */ 211 if ((nh->nh_flags & (NHF_BLACKHOLE | NHF_BROADCAST)) != 0) { 212 IPSTAT_INC(ips_cantforward); 213 m_freem(m); 214 return (EHOSTUNREACH); 215 } 216 217 if (nh->nh_flags & NHF_REJECT) { 218 IPSTAT_INC(ips_cantforward); 219 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0); 220 return (EHOSTUNREACH); 221 } 222 223 *pnh = nh; 224 225 return (0); 226 } 227 228 /* 229 * Try to forward a packet based on the destination address. 230 * This is a fast path optimized for the plain forwarding case. 231 * If the packet is handled (and consumed) here then we return NULL; 232 * otherwise mbuf is returned and the packet should be delivered 233 * to ip_input for full processing. 234 */ 235 struct mbuf * 236 ip_tryforward(struct mbuf *m) 237 { 238 struct ip *ip; 239 struct mbuf *m0 = NULL; 240 struct nhop_object *nh = NULL; 241 struct route ro; 242 struct sockaddr_in *dst; 243 const struct sockaddr *gw; 244 struct in_addr dest, odest, rtdest, osrc; 245 uint16_t ip_len, ip_off; 246 int error = 0; 247 struct m_tag *fwd_tag = NULL; 248 struct mbuf *mcopy = NULL; 249 struct in_addr redest; 250 /* 251 * Are we active and forwarding packets? 252 */ 253 254 M_ASSERTVALID(m); 255 M_ASSERTPKTHDR(m); 256 257 /* 258 * Only IP packets without options 259 */ 260 ip = mtod(m, struct ip *); 261 262 if (ip->ip_hl != (sizeof(struct ip) >> 2)) { 263 if (V_ip_doopts == 1) 264 return m; 265 else if (V_ip_doopts == 2) { 266 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_FILTER_PROHIB, 267 0, 0); 268 return NULL; /* mbuf already free'd */ 269 } 270 /* else ignore IP options and continue */ 271 } 272 273 /* 274 * Only unicast IP, not from loopback, no L2 or IP broadcast, 275 * no multicast, no INADDR_ANY 276 * 277 * XXX: Probably some of these checks could be direct drop 278 * conditions. However it is not clear whether there are some 279 * hacks or obscure behaviours which make it necessary to 280 * let ip_input handle it. We play safe here and let ip_input 281 * deal with it until it is proven that we can directly drop it. 282 */ 283 if ((m->m_flags & (M_BCAST|M_MCAST)) || 284 (m->m_pkthdr.rcvif->if_flags & IFF_LOOPBACK) || 285 in_broadcast(ip->ip_src) || 286 in_broadcast(ip->ip_dst) || 287 IN_MULTICAST(ntohl(ip->ip_src.s_addr)) || 288 IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) || 289 IN_LINKLOCAL(ntohl(ip->ip_src.s_addr)) || 290 IN_LINKLOCAL(ntohl(ip->ip_dst.s_addr)) ) 291 return m; 292 293 /* 294 * Is it for a local address on this host? 295 */ 296 if (in_localip(ip->ip_dst)) 297 return m; 298 299 IPSTAT_INC(ips_total); 300 301 /* 302 * Step 3: incoming packet firewall processing 303 */ 304 305 odest.s_addr = dest.s_addr = ip->ip_dst.s_addr; 306 osrc.s_addr = ip->ip_src.s_addr; 307 308 /* 309 * Run through list of ipfilter hooks for input packets 310 */ 311 if (!PFIL_HOOKED_IN(V_inet_pfil_head)) 312 goto passin; 313 314 if (pfil_mbuf_in(V_inet_pfil_head, &m, m->m_pkthdr.rcvif, 315 NULL) != PFIL_PASS) 316 goto drop; 317 318 M_ASSERTVALID(m); 319 M_ASSERTPKTHDR(m); 320 321 ip = mtod(m, struct ip *); /* m may have changed by pfil hook */ 322 dest.s_addr = ip->ip_dst.s_addr; 323 324 /* 325 * Destination address changed? 326 */ 327 if (odest.s_addr != dest.s_addr) { 328 /* 329 * Is it now for a local address on this host? 330 */ 331 if (in_localip(dest)) 332 goto forwardlocal; 333 /* 334 * Go on with new destination address 335 */ 336 } 337 338 if (m->m_flags & M_FASTFWD_OURS) { 339 /* 340 * ipfw changed it for a local address on this host. 341 */ 342 goto forwardlocal; 343 } 344 345 passin: 346 /* 347 * Step 4: decrement TTL and look up route 348 */ 349 350 /* 351 * Check TTL 352 */ 353 #ifdef IPSTEALTH 354 if (!V_ipstealth) { 355 #endif 356 if (ip->ip_ttl <= IPTTLDEC) { 357 icmp_error(m, ICMP_TIMXCEED, ICMP_TIMXCEED_INTRANS, 0, 0); 358 return NULL; /* mbuf already free'd */ 359 } 360 361 /* 362 * Decrement the TTL. 363 * If the IP header checksum field contains a valid value, incrementally 364 * change this value. Don't use hw checksum offloading, which would 365 * recompute the checksum. It's faster to just change it here 366 * according to the decremented TTL. 367 * If the checksum still needs to be computed, don't touch it. 368 */ 369 ip->ip_ttl -= IPTTLDEC; 370 if (__predict_true((m->m_pkthdr.csum_flags & CSUM_IP) == 0)) { 371 if (ip->ip_sum >= (u_int16_t) ~htons(IPTTLDEC << 8)) 372 ip->ip_sum -= ~htons(IPTTLDEC << 8); 373 else 374 ip->ip_sum += htons(IPTTLDEC << 8); 375 } 376 #ifdef IPSTEALTH 377 } 378 #endif 379 380 /* 381 * Next hop forced by pfil(9) hook? 382 */ 383 if ((m->m_flags & M_IP_NEXTHOP) && 384 ((fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL)) != NULL)) { 385 /* 386 * Now we will find route to forced destination. 387 */ 388 dest.s_addr = ((struct sockaddr_in *) 389 (fwd_tag + 1))->sin_addr.s_addr; 390 m_tag_delete(m, fwd_tag); 391 m->m_flags &= ~M_IP_NEXTHOP; 392 } 393 394 /* 395 * Find route to destination. 396 */ 397 if (ip_findroute(&nh, dest, m) != 0) 398 return (NULL); /* icmp unreach already sent */ 399 400 /* 401 * Avoid second route lookup by caching destination. 402 */ 403 rtdest.s_addr = dest.s_addr; 404 405 /* 406 * Step 5: outgoing firewall packet processing 407 */ 408 if (!PFIL_HOOKED_OUT(V_inet_pfil_head)) 409 goto passout; 410 411 if (pfil_mbuf_fwd(V_inet_pfil_head, &m, nh->nh_ifp, 412 NULL) != PFIL_PASS) 413 goto drop; 414 415 M_ASSERTVALID(m); 416 M_ASSERTPKTHDR(m); 417 418 ip = mtod(m, struct ip *); 419 dest.s_addr = ip->ip_dst.s_addr; 420 421 /* 422 * Destination address changed? 423 */ 424 if (m->m_flags & M_IP_NEXTHOP) 425 fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL); 426 else 427 fwd_tag = NULL; 428 if (odest.s_addr != dest.s_addr || fwd_tag != NULL) { 429 /* 430 * Is it now for a local address on this host? 431 */ 432 if (m->m_flags & M_FASTFWD_OURS || in_localip(dest)) { 433 forwardlocal: 434 /* 435 * Return packet for processing by ip_input(). 436 */ 437 m->m_flags |= M_FASTFWD_OURS; 438 return (m); 439 } 440 /* 441 * Redo route lookup with new destination address 442 */ 443 if (fwd_tag) { 444 dest.s_addr = ((struct sockaddr_in *) 445 (fwd_tag + 1))->sin_addr.s_addr; 446 m_tag_delete(m, fwd_tag); 447 m->m_flags &= ~M_IP_NEXTHOP; 448 } 449 if (dest.s_addr != rtdest.s_addr && 450 ip_findroute(&nh, dest, m) != 0) 451 return (NULL); /* icmp unreach already sent */ 452 } 453 454 passout: 455 /* 456 * Step 6: send off the packet 457 */ 458 ip_len = ntohs(ip->ip_len); 459 ip_off = ntohs(ip->ip_off); 460 461 bzero(&ro, sizeof(ro)); 462 dst = (struct sockaddr_in *)&ro.ro_dst; 463 dst->sin_family = AF_INET; 464 dst->sin_len = sizeof(*dst); 465 dst->sin_addr = dest; 466 if (nh->nh_flags & NHF_GATEWAY) { 467 gw = &nh->gw_sa; 468 ro.ro_flags |= RT_HAS_GW; 469 } else 470 gw = (const struct sockaddr *)dst; 471 472 /* 473 * If the IP/SCTP/TCP/UDP header still needs a valid checksum and the 474 * interface will not calculate it for us, do it here. 475 * Note that if we defer checksum calculation, we might send an ICMP 476 * message later that reflects this packet, which still has an 477 * invalid checksum. 478 */ 479 if (__predict_false(m->m_pkthdr.csum_flags & CSUM_IP & 480 ~nh->nh_ifp->if_hwassist)) { 481 ip->ip_sum = 0; 482 ip->ip_sum = in_cksum(m, (ip->ip_hl << 2)); 483 m->m_pkthdr.csum_flags &= ~CSUM_IP; 484 } 485 if (__predict_false(m->m_pkthdr.csum_flags & CSUM_DELAY_DATA & 486 ~nh->nh_ifp->if_hwassist)) { 487 in_delayed_cksum(m); 488 m->m_pkthdr.csum_flags &= ~CSUM_DELAY_DATA; 489 } 490 #if defined(SCTP) || defined(SCTP_SUPPORT) 491 if (__predict_false(m->m_pkthdr.csum_flags & CSUM_IP_SCTP & 492 ~nh->nh_ifp->if_hwassist)) { 493 sctp_delayed_cksum(m, (uint32_t)(ip->ip_hl << 2)); 494 m->m_pkthdr.csum_flags &= ~CSUM_IP_SCTP; 495 } 496 #endif 497 498 /* Handle redirect case. */ 499 redest.s_addr = 0; 500 if (V_ipsendredirects && osrc.s_addr == ip->ip_src.s_addr && 501 nh->nh_ifp == m->m_pkthdr.rcvif) 502 mcopy = ip_redir_alloc(m, nh, ip_len, &osrc, &redest); 503 504 /* 505 * Check if packet fits MTU or if hardware will fragment for us 506 */ 507 if (ip_len <= nh->nh_mtu) { 508 /* 509 * Avoid confusing lower layers. 510 */ 511 m_clrprotoflags(m); 512 /* 513 * Send off the packet via outgoing interface 514 */ 515 IP_PROBE(send, NULL, NULL, ip, nh->nh_ifp, ip, NULL); 516 error = (*nh->nh_ifp->if_output)(nh->nh_ifp, m, gw, &ro); 517 } else { 518 /* 519 * Handle EMSGSIZE with icmp reply needfrag for TCP MTU discovery 520 */ 521 if (ip_off & IP_DF) { 522 IPSTAT_INC(ips_cantfrag); 523 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_NEEDFRAG, 524 0, nh->nh_mtu); 525 goto consumed; 526 } else { 527 /* 528 * We have to fragment the packet 529 */ 530 m->m_pkthdr.csum_flags |= CSUM_IP; 531 if (ip_fragment(ip, &m, nh->nh_mtu, 532 nh->nh_ifp->if_hwassist) != 0) 533 goto drop; 534 KASSERT(m != NULL, ("null mbuf and no error")); 535 /* 536 * Send off the fragments via outgoing interface 537 */ 538 error = 0; 539 do { 540 m0 = m->m_nextpkt; 541 m->m_nextpkt = NULL; 542 /* 543 * Avoid confusing lower layers. 544 */ 545 m_clrprotoflags(m); 546 547 IP_PROBE(send, NULL, NULL, 548 mtod(m, struct ip *), nh->nh_ifp, 549 mtod(m, struct ip *), NULL); 550 error = (*nh->nh_ifp->if_output)(nh->nh_ifp, m, 551 gw, &ro); 552 if (error) 553 break; 554 } while ((m = m0) != NULL); 555 if (error) { 556 /* Reclaim remaining fragments */ 557 for (m = m0; m; m = m0) { 558 m0 = m->m_nextpkt; 559 m_freem(m); 560 } 561 } else 562 IPSTAT_INC(ips_fragmented); 563 } 564 } 565 566 if (error != 0) 567 IPSTAT_INC(ips_odropped); 568 else { 569 IPSTAT_INC(ips_forward); 570 IPSTAT_INC(ips_fastforward); 571 } 572 573 /* Send required redirect */ 574 if (mcopy != NULL) { 575 icmp_error(mcopy, ICMP_REDIRECT, ICMP_REDIRECT_HOST, redest.s_addr, 0); 576 mcopy = NULL; /* Was consumed by callee. */ 577 } 578 579 consumed: 580 if (mcopy != NULL) 581 m_freem(mcopy); 582 return NULL; 583 drop: 584 if (m) 585 m_freem(m); 586 return NULL; 587 } 588