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 * 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 destination router was not the
67 * default gateway. In one case it was filling the routing table of a host
68 * with approximately 300.000 cloned redirect entries until it ran out of
69 * kernel memory. However the networking code proved very robust and it didn't
70 * crash or fail in other ways.
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 <sys/cdefs.h>
79 __FBSDID("$FreeBSD$");
80
81 #include "opt_ipstealth.h"
82
83 #include <sys/param.h>
84 #include <sys/systm.h>
85 #include <sys/kernel.h>
86 #include <sys/malloc.h>
87 #include <sys/mbuf.h>
88 #include <sys/protosw.h>
89 #include <sys/sdt.h>
90 #include <sys/socket.h>
91 #include <sys/sysctl.h>
92
93 #include <net/if.h>
94 #include <net/if_types.h>
95 #include <net/if_var.h>
96 #include <net/if_dl.h>
97 #include <net/pfil.h>
98 #include <net/route.h>
99 #include <net/route/nhop.h>
100 #include <net/vnet.h>
101
102 #include <netinet/in.h>
103 #include <netinet/in_fib.h>
104 #include <netinet/in_kdtrace.h>
105 #include <netinet/in_systm.h>
106 #include <netinet/in_var.h>
107 #include <netinet/ip.h>
108 #include <netinet/ip_var.h>
109 #include <netinet/ip_icmp.h>
110 #include <netinet/ip_options.h>
111
112 #include <machine/in_cksum.h>
113
114 #define V_ipsendredirects VNET(ipsendredirects)
115
116 static struct mbuf *
ip_redir_alloc(struct mbuf * m,struct nhop_object * nh,struct ip * ip,in_addr_t * addr)117 ip_redir_alloc(struct mbuf *m, struct nhop_object *nh,
118 struct ip *ip, in_addr_t *addr)
119 {
120 struct mbuf *mcopy = m_gethdr(M_NOWAIT, m->m_type);
121
122 if (mcopy == NULL)
123 return (NULL);
124
125 if (m_dup_pkthdr(mcopy, m, M_NOWAIT) == 0) {
126 /*
127 * It's probably ok if the pkthdr dup fails (because
128 * the deep copy of the tag chain failed), but for now
129 * be conservative and just discard the copy since
130 * code below may some day want the tags.
131 */
132 m_free(mcopy);
133 return (NULL);
134 }
135 mcopy->m_len = min(ntohs(ip->ip_len), M_TRAILINGSPACE(mcopy));
136 mcopy->m_pkthdr.len = mcopy->m_len;
137 m_copydata(m, 0, mcopy->m_len, mtod(mcopy, caddr_t));
138
139 if (nh != NULL &&
140 ((nh->nh_flags & (NHF_REDIRECT|NHF_DEFAULT)) == 0)) {
141 struct in_ifaddr *nh_ia = (struct in_ifaddr *)(nh->nh_ifa);
142 u_long src = ntohl(ip->ip_src.s_addr);
143
144 if (nh_ia != NULL &&
145 (src & nh_ia->ia_subnetmask) == nh_ia->ia_subnet) {
146 if (nh->nh_flags & NHF_GATEWAY)
147 *addr = nh->gw4_sa.sin_addr.s_addr;
148 else
149 *addr = ip->ip_dst.s_addr;
150 }
151 }
152 return (mcopy);
153 }
154
155
156 static int
ip_findroute(struct nhop_object ** pnh,struct in_addr dest,struct mbuf * m)157 ip_findroute(struct nhop_object **pnh, struct in_addr dest, struct mbuf *m)
158 {
159 struct nhop_object *nh;
160
161 nh = fib4_lookup(M_GETFIB(m), dest, 0, NHR_NONE,
162 m->m_pkthdr.flowid);
163 if (nh == NULL) {
164 IPSTAT_INC(ips_noroute);
165 IPSTAT_INC(ips_cantforward);
166 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0);
167 return (EHOSTUNREACH);
168 }
169 /*
170 * Drop blackholed traffic and directed broadcasts.
171 */
172 if ((nh->nh_flags & (NHF_BLACKHOLE | NHF_BROADCAST)) != 0) {
173 IPSTAT_INC(ips_cantforward);
174 m_freem(m);
175 return (EHOSTUNREACH);
176 }
177
178 if (nh->nh_flags & NHF_REJECT) {
179 IPSTAT_INC(ips_cantforward);
180 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0);
181 return (EHOSTUNREACH);
182 }
183
184 *pnh = nh;
185
186 return (0);
187 }
188
189 /*
190 * Try to forward a packet based on the destination address.
191 * This is a fast path optimized for the plain forwarding case.
192 * If the packet is handled (and consumed) here then we return NULL;
193 * otherwise mbuf is returned and the packet should be delivered
194 * to ip_input for full processing.
195 */
196 struct mbuf *
ip_tryforward(struct mbuf * m)197 ip_tryforward(struct mbuf *m)
198 {
199 struct ip *ip;
200 struct mbuf *m0 = NULL;
201 struct nhop_object *nh = NULL;
202 struct sockaddr_in dst;
203 struct in_addr dest, odest, rtdest;
204 uint16_t ip_len, ip_off;
205 int error = 0;
206 struct m_tag *fwd_tag = NULL;
207 struct mbuf *mcopy = NULL;
208 struct in_addr redest;
209 /*
210 * Are we active and forwarding packets?
211 */
212
213 M_ASSERTVALID(m);
214 M_ASSERTPKTHDR(m);
215
216 #ifdef ALTQ
217 /*
218 * Is packet dropped by traffic conditioner?
219 */
220 if (altq_input != NULL && (*altq_input)(m, AF_INET) == 0)
221 goto drop;
222 #endif
223
224 /*
225 * Only IP packets without options
226 */
227 ip = mtod(m, struct ip *);
228
229 if (ip->ip_hl != (sizeof(struct ip) >> 2)) {
230 if (V_ip_doopts == 1)
231 return m;
232 else if (V_ip_doopts == 2) {
233 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_FILTER_PROHIB,
234 0, 0);
235 return NULL; /* mbuf already free'd */
236 }
237 /* else ignore IP options and continue */
238 }
239
240 /*
241 * Only unicast IP, not from loopback, no L2 or IP broadcast,
242 * no multicast, no INADDR_ANY
243 *
244 * XXX: Probably some of these checks could be direct drop
245 * conditions. However it is not clear whether there are some
246 * hacks or obscure behaviours which make it necessary to
247 * let ip_input handle it. We play safe here and let ip_input
248 * deal with it until it is proven that we can directly drop it.
249 */
250 if ((m->m_flags & (M_BCAST|M_MCAST)) ||
251 (m->m_pkthdr.rcvif->if_flags & IFF_LOOPBACK) ||
252 ntohl(ip->ip_src.s_addr) == (u_long)INADDR_BROADCAST ||
253 ntohl(ip->ip_dst.s_addr) == (u_long)INADDR_BROADCAST ||
254 IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
255 IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
256 IN_LINKLOCAL(ntohl(ip->ip_src.s_addr)) ||
257 IN_LINKLOCAL(ntohl(ip->ip_dst.s_addr)) ||
258 ip->ip_src.s_addr == INADDR_ANY ||
259 ip->ip_dst.s_addr == INADDR_ANY )
260 return m;
261
262 /*
263 * Is it for a local address on this host?
264 */
265 if (in_localip(ip->ip_dst))
266 return m;
267
268 IPSTAT_INC(ips_total);
269
270 /*
271 * Step 3: incoming packet firewall processing
272 */
273
274 odest.s_addr = dest.s_addr = ip->ip_dst.s_addr;
275
276 /*
277 * Run through list of ipfilter hooks for input packets
278 */
279 if (!PFIL_HOOKED_IN(V_inet_pfil_head))
280 goto passin;
281
282 if (pfil_run_hooks(V_inet_pfil_head, &m, m->m_pkthdr.rcvif, PFIL_IN,
283 NULL) != PFIL_PASS)
284 goto drop;
285
286 M_ASSERTVALID(m);
287 M_ASSERTPKTHDR(m);
288
289 ip = mtod(m, struct ip *); /* m may have changed by pfil hook */
290 dest.s_addr = ip->ip_dst.s_addr;
291
292 /*
293 * Destination address changed?
294 */
295 if (odest.s_addr != dest.s_addr) {
296 /*
297 * Is it now for a local address on this host?
298 */
299 if (in_localip(dest))
300 goto forwardlocal;
301 /*
302 * Go on with new destination address
303 */
304 }
305
306 if (m->m_flags & M_FASTFWD_OURS) {
307 /*
308 * ipfw changed it for a local address on this host.
309 */
310 goto forwardlocal;
311 }
312
313 passin:
314 /*
315 * Step 4: decrement TTL and look up route
316 */
317
318 /*
319 * Check TTL
320 */
321 #ifdef IPSTEALTH
322 if (!V_ipstealth) {
323 #endif
324 if (ip->ip_ttl <= IPTTLDEC) {
325 icmp_error(m, ICMP_TIMXCEED, ICMP_TIMXCEED_INTRANS, 0, 0);
326 return NULL; /* mbuf already free'd */
327 }
328
329 /*
330 * Decrement the TTL and incrementally change the IP header checksum.
331 * Don't bother doing this with hw checksum offloading, it's faster
332 * doing it right here.
333 */
334 ip->ip_ttl -= IPTTLDEC;
335 if (ip->ip_sum >= (u_int16_t) ~htons(IPTTLDEC << 8))
336 ip->ip_sum -= ~htons(IPTTLDEC << 8);
337 else
338 ip->ip_sum += htons(IPTTLDEC << 8);
339 #ifdef IPSTEALTH
340 }
341 #endif
342
343 /*
344 * Next hop forced by pfil(9) hook?
345 */
346 if ((m->m_flags & M_IP_NEXTHOP) &&
347 ((fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL)) != NULL)) {
348 /*
349 * Now we will find route to forced destination.
350 */
351 dest.s_addr = ((struct sockaddr_in *)
352 (fwd_tag + 1))->sin_addr.s_addr;
353 m_tag_delete(m, fwd_tag);
354 m->m_flags &= ~M_IP_NEXTHOP;
355 }
356
357 /*
358 * Find route to destination.
359 */
360 if (ip_findroute(&nh, dest, m) != 0)
361 return (NULL); /* icmp unreach already sent */
362
363 /*
364 * Avoid second route lookup by caching destination.
365 */
366 rtdest.s_addr = dest.s_addr;
367
368 /*
369 * Step 5: outgoing firewall packet processing
370 */
371 if (!PFIL_HOOKED_OUT(V_inet_pfil_head))
372 goto passout;
373
374 if (pfil_run_hooks(V_inet_pfil_head, &m, nh->nh_ifp,
375 PFIL_OUT | PFIL_FWD, NULL) != PFIL_PASS)
376 goto drop;
377
378 M_ASSERTVALID(m);
379 M_ASSERTPKTHDR(m);
380
381 ip = mtod(m, struct ip *);
382 dest.s_addr = ip->ip_dst.s_addr;
383
384 /*
385 * Destination address changed?
386 */
387 if (m->m_flags & M_IP_NEXTHOP)
388 fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
389 else
390 fwd_tag = NULL;
391 if (odest.s_addr != dest.s_addr || fwd_tag != NULL) {
392 /*
393 * Is it now for a local address on this host?
394 */
395 if (m->m_flags & M_FASTFWD_OURS || in_localip(dest)) {
396 forwardlocal:
397 /*
398 * Return packet for processing by ip_input().
399 */
400 m->m_flags |= M_FASTFWD_OURS;
401 return (m);
402 }
403 /*
404 * Redo route lookup with new destination address
405 */
406 if (fwd_tag) {
407 dest.s_addr = ((struct sockaddr_in *)
408 (fwd_tag + 1))->sin_addr.s_addr;
409 m_tag_delete(m, fwd_tag);
410 m->m_flags &= ~M_IP_NEXTHOP;
411 }
412 if (dest.s_addr != rtdest.s_addr &&
413 ip_findroute(&nh, dest, m) != 0)
414 return (NULL); /* icmp unreach already sent */
415 }
416
417 passout:
418 /*
419 * Step 6: send off the packet
420 */
421 ip_len = ntohs(ip->ip_len);
422 ip_off = ntohs(ip->ip_off);
423
424 bzero(&dst, sizeof(dst));
425 dst.sin_family = AF_INET;
426 dst.sin_len = sizeof(dst);
427 if (nh->nh_flags & NHF_GATEWAY)
428 dst.sin_addr = nh->gw4_sa.sin_addr;
429 else
430 dst.sin_addr = dest;
431
432 /*
433 * Handle redirect case.
434 */
435 redest.s_addr = 0;
436 if (V_ipsendredirects && (nh->nh_ifp == m->m_pkthdr.rcvif))
437 mcopy = ip_redir_alloc(m, nh, ip, &redest.s_addr);
438
439 /*
440 * Check if packet fits MTU or if hardware will fragment for us
441 */
442 if (ip_len <= nh->nh_mtu) {
443 /*
444 * Avoid confusing lower layers.
445 */
446 m_clrprotoflags(m);
447 /*
448 * Send off the packet via outgoing interface
449 */
450 IP_PROBE(send, NULL, NULL, ip, nh->nh_ifp, ip, NULL);
451 error = (*nh->nh_ifp->if_output)(nh->nh_ifp, m,
452 (struct sockaddr *)&dst, NULL);
453 } else {
454 /*
455 * Handle EMSGSIZE with icmp reply needfrag for TCP MTU discovery
456 */
457 if (ip_off & IP_DF) {
458 IPSTAT_INC(ips_cantfrag);
459 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_NEEDFRAG,
460 0, nh->nh_mtu);
461 goto consumed;
462 } else {
463 /*
464 * We have to fragment the packet
465 */
466 m->m_pkthdr.csum_flags |= CSUM_IP;
467 if (ip_fragment(ip, &m, nh->nh_mtu,
468 nh->nh_ifp->if_hwassist) != 0)
469 goto drop;
470 KASSERT(m != NULL, ("null mbuf and no error"));
471 /*
472 * Send off the fragments via outgoing interface
473 */
474 error = 0;
475 do {
476 m0 = m->m_nextpkt;
477 m->m_nextpkt = NULL;
478 /*
479 * Avoid confusing lower layers.
480 */
481 m_clrprotoflags(m);
482
483 IP_PROBE(send, NULL, NULL,
484 mtod(m, struct ip *), nh->nh_ifp,
485 mtod(m, struct ip *), NULL);
486 error = (*nh->nh_ifp->if_output)(nh->nh_ifp, m,
487 (struct sockaddr *)&dst, NULL);
488 if (error)
489 break;
490 } while ((m = m0) != NULL);
491 if (error) {
492 /* Reclaim remaining fragments */
493 for (m = m0; m; m = m0) {
494 m0 = m->m_nextpkt;
495 m_freem(m);
496 }
497 } else
498 IPSTAT_INC(ips_fragmented);
499 }
500 }
501
502 if (error != 0)
503 IPSTAT_INC(ips_odropped);
504 else {
505 IPSTAT_INC(ips_forward);
506 IPSTAT_INC(ips_fastforward);
507 }
508
509 /* Send required redirect */
510 if (mcopy != NULL) {
511 icmp_error(mcopy, ICMP_REDIRECT, ICMP_REDIRECT_HOST, redest.s_addr, 0);
512 mcopy = NULL; /* Freed by caller */
513 }
514
515 consumed:
516 if (mcopy != NULL)
517 m_freem(mcopy);
518 return NULL;
519 drop:
520 if (m)
521 m_freem(m);
522 return NULL;
523 }
524