1 /* 2 * Copyright (c) 2003 Andre Oppermann, Internet Business Solutions AG 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 3. The name of the author may not be used to endorse or promote 14 * products derived from this software without specific prior written 15 * permission. 16 * 17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 20 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 27 * SUCH DAMAGE. 28 * 29 * $FreeBSD$ 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 * We don't do ICMP redirect in the fast forwarding path. I have had my own 65 * cases where two core routers with Zebra routing suite would send millions 66 * ICMP redirects to connected hosts if the router to dest was not the default 67 * gateway. In one case it was filling the routing table of a host with close 68 * 300'000 cloned redirect entries until it ran out of kernel memory. However 69 * the networking code proved very robust and it didn't crash or went ill 70 * otherwise. 71 */ 72 73 /* 74 * Many thanks to Matt Thomas of NetBSD for basic structure of ip_flow.c which 75 * is being followed here. 76 */ 77 78 #include "opt_ipfw.h" 79 #include "opt_ipstealth.h" 80 81 #include <sys/param.h> 82 #include <sys/systm.h> 83 #include <sys/kernel.h> 84 #include <sys/malloc.h> 85 #include <sys/mbuf.h> 86 #include <sys/protosw.h> 87 #include <sys/socket.h> 88 #include <sys/sysctl.h> 89 90 #include <net/pfil.h> 91 #include <net/if.h> 92 #include <net/if_types.h> 93 #include <net/if_var.h> 94 #include <net/if_dl.h> 95 #include <net/route.h> 96 97 #include <netinet/in.h> 98 #include <netinet/in_systm.h> 99 #include <netinet/in_var.h> 100 #include <netinet/ip.h> 101 #include <netinet/ip_var.h> 102 #include <netinet/ip_icmp.h> 103 104 #include <machine/in_cksum.h> 105 106 static int ipfastforward_active = 0; 107 SYSCTL_INT(_net_inet_ip, OID_AUTO, fastforwarding, CTLFLAG_RW, 108 &ipfastforward_active, 0, "Enable fast IP forwarding"); 109 110 static struct sockaddr_in * 111 ip_findroute(struct route *ro, struct in_addr dest, struct mbuf *m) 112 { 113 struct sockaddr_in *dst; 114 struct rtentry *rt; 115 116 /* 117 * Find route to destination. 118 */ 119 bzero(ro, sizeof(*ro)); 120 dst = (struct sockaddr_in *)&ro->ro_dst; 121 dst->sin_family = AF_INET; 122 dst->sin_len = sizeof(*dst); 123 dst->sin_addr.s_addr = dest.s_addr; 124 rtalloc_ign(ro, RTF_CLONING); 125 126 /* 127 * Route there and interface still up? 128 */ 129 rt = ro->ro_rt; 130 if (rt && (rt->rt_flags & RTF_UP) && 131 (rt->rt_ifp->if_flags & IFF_UP) && 132 (rt->rt_ifp->if_flags & IFF_RUNNING)) { 133 if (rt->rt_flags & RTF_GATEWAY) 134 dst = (struct sockaddr_in *)rt->rt_gateway; 135 } else { 136 ipstat.ips_noroute++; 137 ipstat.ips_cantforward++; 138 if (rt) 139 RTFREE(rt); 140 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, NULL); 141 return NULL; 142 } 143 return dst; 144 } 145 146 /* 147 * Try to forward a packet based on the destination address. 148 * This is a fast path optimized for the plain forwarding case. 149 * If the packet is handled (and consumed) here then we return 1; 150 * otherwise 0 is returned and the packet should be delivered 151 * to ip_input for full processing. 152 */ 153 int 154 ip_fastforward(struct mbuf *m) 155 { 156 struct ip *ip; 157 struct mbuf *m0 = NULL; 158 struct route ro; 159 struct sockaddr_in *dst = NULL; 160 struct in_ifaddr *ia = NULL; 161 struct ifaddr *ifa = NULL; 162 struct ifnet *ifp; 163 struct in_addr odest, dest; 164 u_short sum, ip_len; 165 int error = 0; 166 int hlen, mtu; 167 #ifdef IPFIREWALL_FORWARD 168 struct m_tag *fwd_tag; 169 #endif 170 171 /* 172 * Are we active and forwarding packets? 173 */ 174 if (!ipfastforward_active || !ipforwarding) 175 return 0; 176 177 M_ASSERTVALID(m); 178 M_ASSERTPKTHDR(m); 179 180 ro.ro_rt = NULL; 181 182 /* 183 * Step 1: check for packet drop conditions (and sanity checks) 184 */ 185 186 /* 187 * Is entire packet big enough? 188 */ 189 if (m->m_pkthdr.len < sizeof(struct ip)) { 190 ipstat.ips_tooshort++; 191 goto drop; 192 } 193 194 /* 195 * Is first mbuf large enough for ip header and is header present? 196 */ 197 if (m->m_len < sizeof (struct ip) && 198 (m = m_pullup(m, sizeof (struct ip))) == 0) { 199 ipstat.ips_toosmall++; 200 goto drop; 201 } 202 203 ip = mtod(m, struct ip *); 204 205 /* 206 * Is it IPv4? 207 */ 208 if (ip->ip_v != IPVERSION) { 209 ipstat.ips_badvers++; 210 goto drop; 211 } 212 213 /* 214 * Is IP header length correct and is it in first mbuf? 215 */ 216 hlen = ip->ip_hl << 2; 217 if (hlen < sizeof(struct ip)) { /* minimum header length */ 218 ipstat.ips_badlen++; 219 goto drop; 220 } 221 if (hlen > m->m_len) { 222 if ((m = m_pullup(m, hlen)) == 0) { 223 ipstat.ips_badhlen++; 224 goto drop; 225 } 226 ip = mtod(m, struct ip *); 227 } 228 229 /* 230 * Checksum correct? 231 */ 232 if (m->m_pkthdr.csum_flags & CSUM_IP_CHECKED) 233 sum = !(m->m_pkthdr.csum_flags & CSUM_IP_VALID); 234 else { 235 if (hlen == sizeof(struct ip)) 236 sum = in_cksum_hdr(ip); 237 else 238 sum = in_cksum(m, hlen); 239 } 240 if (sum) { 241 ipstat.ips_badsum++; 242 goto drop; 243 } 244 m->m_pkthdr.csum_flags |= (CSUM_IP_CHECKED | CSUM_IP_VALID); 245 246 ip_len = ntohs(ip->ip_len); 247 248 /* 249 * Is IP length longer than packet we have got? 250 */ 251 if (m->m_pkthdr.len < ip_len) { 252 ipstat.ips_tooshort++; 253 goto drop; 254 } 255 256 /* 257 * Is packet longer than IP header tells us? If yes, truncate packet. 258 */ 259 if (m->m_pkthdr.len > ip_len) { 260 if (m->m_len == m->m_pkthdr.len) { 261 m->m_len = ip_len; 262 m->m_pkthdr.len = ip_len; 263 } else 264 m_adj(m, ip_len - m->m_pkthdr.len); 265 } 266 267 /* 268 * Is packet from or to 127/8? 269 */ 270 if ((ntohl(ip->ip_dst.s_addr) >> IN_CLASSA_NSHIFT) == IN_LOOPBACKNET || 271 (ntohl(ip->ip_src.s_addr) >> IN_CLASSA_NSHIFT) == IN_LOOPBACKNET) { 272 ipstat.ips_badaddr++; 273 goto drop; 274 } 275 276 #ifdef ALTQ 277 /* 278 * Is packet dropped by traffic conditioner? 279 */ 280 if (altq_input != NULL && (*altq_input)(m, AF_INET) == 0) 281 return 1; 282 #endif 283 284 /* 285 * Step 2: fallback conditions to normal ip_input path processing 286 */ 287 288 /* 289 * Only IP packets without options 290 */ 291 if (ip->ip_hl != (sizeof(struct ip) >> 2)) { 292 if (ip_doopts == 1) 293 return 0; 294 else if (ip_doopts == 2) { 295 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_FILTER_PROHIB, 296 0, NULL); 297 return 1; 298 } 299 /* else ignore IP options and continue */ 300 } 301 302 /* 303 * Only unicast IP, not from loopback, no L2 or IP broadcast, 304 * no multicast, no INADDR_ANY 305 * 306 * XXX: Probably some of these checks could be direct drop 307 * conditions. However it is not clear whether there are some 308 * hacks or obscure behaviours which make it neccessary to 309 * let ip_input handle it. We play safe here and let ip_input 310 * deal with it until it is proven that we can directly drop it. 311 */ 312 if ((m->m_pkthdr.rcvif->if_flags & IFF_LOOPBACK) || 313 ntohl(ip->ip_src.s_addr) == (u_long)INADDR_BROADCAST || 314 ntohl(ip->ip_dst.s_addr) == (u_long)INADDR_BROADCAST || 315 IN_MULTICAST(ntohl(ip->ip_src.s_addr)) || 316 IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) || 317 ip->ip_dst.s_addr == INADDR_ANY ) 318 return 0; 319 320 /* 321 * Is it for a local address on this host? 322 */ 323 if (in_localip(ip->ip_dst)) 324 return 0; 325 326 /* 327 * Or is it for a local IP broadcast address on this host? 328 */ 329 if ((m->m_flags & M_BCAST) && 330 (m->m_pkthdr.rcvif->if_flags & IFF_BROADCAST)) { 331 TAILQ_FOREACH(ifa, &m->m_pkthdr.rcvif->if_addrhead, ifa_link) { 332 if (ifa->ifa_addr->sa_family != AF_INET) 333 continue; 334 ia = ifatoia(ifa); 335 if (ia->ia_netbroadcast.s_addr == ip->ip_dst.s_addr) 336 return 0; 337 if (satosin(&ia->ia_broadaddr)->sin_addr.s_addr == 338 ip->ip_dst.s_addr) 339 return 0; 340 } 341 } 342 ipstat.ips_total++; 343 344 /* 345 * Step 3: incoming packet firewall processing 346 */ 347 348 /* 349 * Convert to host representation 350 */ 351 ip->ip_len = ntohs(ip->ip_len); 352 ip->ip_off = ntohs(ip->ip_off); 353 354 odest.s_addr = dest.s_addr = ip->ip_dst.s_addr; 355 356 /* 357 * Run through list of ipfilter hooks for input packets 358 */ 359 if (inet_pfil_hook.ph_busy_count == -1) 360 goto passin; 361 362 if (pfil_run_hooks(&inet_pfil_hook, &m, m->m_pkthdr.rcvif, PFIL_IN) || 363 m == NULL) 364 return 1; 365 366 M_ASSERTVALID(m); 367 M_ASSERTPKTHDR(m); 368 369 ip = mtod(m, struct ip *); /* m may have changed by pfil hook */ 370 dest.s_addr = ip->ip_dst.s_addr; 371 372 /* 373 * Destination address changed? 374 */ 375 if (odest.s_addr != dest.s_addr) { 376 /* 377 * Is it now for a local address on this host? 378 */ 379 if (in_localip(dest)) 380 goto forwardlocal; 381 /* 382 * Go on with new destination address 383 */ 384 } 385 #ifdef IPFIREWALL_FORWARD 386 if (m->m_flags & M_FASTFWD_OURS) { 387 /* 388 * ipfw changed it for a local address on this host. 389 */ 390 goto forwardlocal; 391 } 392 #endif /* IPFIREWALL_FORWARD */ 393 394 passin: 395 /* 396 * Step 4: decrement TTL and look up route 397 */ 398 399 /* 400 * Check TTL 401 */ 402 #ifdef IPSTEALTH 403 if (!ipstealth) { 404 #endif 405 if (ip->ip_ttl <= IPTTLDEC) { 406 icmp_error(m, ICMP_TIMXCEED, ICMP_TIMXCEED_INTRANS, 0, NULL); 407 return 1; 408 } 409 410 /* 411 * Decrement the TTL and incrementally change the checksum. 412 * Don't bother doing this with hw checksum offloading. 413 */ 414 ip->ip_ttl -= IPTTLDEC; 415 if (ip->ip_sum >= (u_int16_t) ~htons(IPTTLDEC << 8)) 416 ip->ip_sum -= ~htons(IPTTLDEC << 8); 417 else 418 ip->ip_sum += htons(IPTTLDEC << 8); 419 #ifdef IPSTEALTH 420 } 421 #endif 422 423 /* 424 * Find route to destination. 425 */ 426 if ((dst = ip_findroute(&ro, dest, m)) == NULL) 427 return 1; /* icmp unreach already sent */ 428 ifp = ro.ro_rt->rt_ifp; 429 430 /* 431 * Step 5: outgoing firewall packet processing 432 */ 433 434 /* 435 * Run through list of hooks for output packets. 436 */ 437 if (inet_pfil_hook.ph_busy_count == -1) 438 goto passout; 439 440 if (pfil_run_hooks(&inet_pfil_hook, &m, ifp, PFIL_OUT) || m == NULL) { 441 goto consumed; 442 } 443 444 M_ASSERTVALID(m); 445 M_ASSERTPKTHDR(m); 446 447 ip = mtod(m, struct ip *); 448 dest.s_addr = ip->ip_dst.s_addr; 449 450 /* 451 * Destination address changed? 452 */ 453 #ifndef IPFIREWALL_FORWARD 454 if (odest.s_addr != dest.s_addr) { 455 #else 456 fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL); 457 if (odest.s_addr != dest.s_addr || fwd_tag != NULL) { 458 #endif /* IPFIREWALL_FORWARD */ 459 /* 460 * Is it now for a local address on this host? 461 */ 462 #ifndef IPFIREWALL_FORWARD 463 if (in_localip(dest)) { 464 #else 465 if (in_localip(dest) || m->m_flags & M_FASTFWD_OURS) { 466 #endif /* IPFIREWALL_FORWARD */ 467 forwardlocal: 468 /* for ip_input */ 469 m->m_flags |= M_FASTFWD_OURS; 470 ip->ip_len = htons(ip->ip_len); 471 ip->ip_off = htons(ip->ip_off); 472 473 /* 474 * Return packet for processing by ip_input() 475 */ 476 if (ro.ro_rt) 477 RTFREE(ro.ro_rt); 478 return 0; 479 } 480 /* 481 * Redo route lookup with new destination address 482 */ 483 #ifdef IPFIREWALL_FORWARD 484 if (fwd_tag) { 485 if (!in_localip(ip->ip_src) && !in_localaddr(ip->ip_dst)) 486 dest.s_addr = ((struct sockaddr_in *)(fwd_tag+1))->sin_addr.s_addr; 487 m_tag_delete(m, fwd_tag); 488 } 489 #endif /* IPFIREWALL_FORWARD */ 490 RTFREE(ro.ro_rt); 491 if ((dst = ip_findroute(&ro, dest, m)) == NULL) 492 return 1; /* icmp unreach already sent */ 493 ifp = ro.ro_rt->rt_ifp; 494 } 495 496 passout: 497 /* 498 * Step 6: send off the packet 499 */ 500 501 /* 502 * Check if route is dampned (when ARP is unable to resolve) 503 */ 504 if ((ro.ro_rt->rt_flags & RTF_REJECT) && 505 ro.ro_rt->rt_rmx.rmx_expire >= time_second) { 506 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, NULL); 507 goto consumed; 508 } 509 510 #ifndef ALTQ 511 /* 512 * Check if there is enough space in the interface queue 513 */ 514 if ((ifp->if_snd.ifq_len + ip->ip_len / ifp->if_mtu + 1) >= 515 ifp->if_snd.ifq_maxlen) { 516 ipstat.ips_odropped++; 517 /* would send source quench here but that is depreciated */ 518 goto drop; 519 } 520 #endif 521 522 /* 523 * Check if media link state of interface is not down 524 */ 525 if (ifp->if_link_state == LINK_STATE_DOWN) { 526 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, NULL); 527 goto consumed; 528 } 529 530 /* 531 * Check if packet fits MTU or if hardware will fragement for us 532 */ 533 if (ro.ro_rt->rt_rmx.rmx_mtu) 534 mtu = min(ro.ro_rt->rt_rmx.rmx_mtu, ifp->if_mtu); 535 else 536 mtu = ifp->if_mtu; 537 538 if (ip->ip_len <= mtu || 539 (ifp->if_hwassist & CSUM_FRAGMENT && (ip->ip_off & IP_DF) == 0)) { 540 /* 541 * Restore packet header fields to original values 542 */ 543 ip->ip_len = htons(ip->ip_len); 544 ip->ip_off = htons(ip->ip_off); 545 /* 546 * Send off the packet via outgoing interface 547 */ 548 error = (*ifp->if_output)(ifp, m, 549 (struct sockaddr *)dst, ro.ro_rt); 550 } else { 551 /* 552 * Handle EMSGSIZE with icmp reply needfrag for TCP MTU discovery 553 */ 554 if (ip->ip_off & IP_DF) { 555 ipstat.ips_cantfrag++; 556 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_NEEDFRAG, 557 0, ifp); 558 goto consumed; 559 } else { 560 /* 561 * We have to fragement the packet 562 */ 563 m->m_pkthdr.csum_flags |= CSUM_IP; 564 /* 565 * ip_fragment expects ip_len and ip_off in host byte 566 * order but returns all packets in network byte order 567 */ 568 if (ip_fragment(ip, &m, mtu, ifp->if_hwassist, 569 (~ifp->if_hwassist & CSUM_DELAY_IP))) { 570 goto drop; 571 } 572 KASSERT(m != NULL, ("null mbuf and no error")); 573 /* 574 * Send off the fragments via outgoing interface 575 */ 576 error = 0; 577 do { 578 m0 = m->m_nextpkt; 579 m->m_nextpkt = NULL; 580 581 error = (*ifp->if_output)(ifp, m, 582 (struct sockaddr *)dst, ro.ro_rt); 583 if (error) 584 break; 585 } while ((m = m0) != NULL); 586 if (error) { 587 /* Reclaim remaining fragments */ 588 for (; m; m = m0) { 589 m0 = m->m_nextpkt; 590 m->m_nextpkt = NULL; 591 m_freem(m); 592 } 593 } else 594 ipstat.ips_fragmented++; 595 } 596 } 597 598 if (error != 0) 599 ipstat.ips_odropped++; 600 else { 601 ro.ro_rt->rt_rmx.rmx_pksent++; 602 ipstat.ips_forward++; 603 ipstat.ips_fastforward++; 604 } 605 consumed: 606 RTFREE(ro.ro_rt); 607 return 1; 608 drop: 609 if (m) 610 m_freem(m); 611 if (ro.ro_rt) 612 RTFREE(ro.ro_rt); 613 return 1; 614 } 615