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
30 /*
31 * ip_fastforward gets its speed from processing the forwarded packet to
32 * completion (if_output on the other side) without any queues or netisr's.
33 * The receiving interface DMAs the packet into memory, the upper half of
34 * driver calls ip_fastforward, we do our routing table lookup and directly
35 * send it off to the outgoing interface, which DMAs the packet to the
36 * network card. The only part of the packet we touch with the CPU is the
37 * IP header (unless there are complex firewall rules touching other parts
38 * of the packet, but that is up to you). We are essentially limited by bus
39 * bandwidth and how fast the network card/driver can set up receives and
40 * transmits.
41 *
42 * We handle basic errors, IP header errors, checksum errors,
43 * destination unreachable, fragmentation and fragmentation needed and
44 * report them via ICMP to the sender.
45 *
46 * Else if something is not pure IPv4 unicast forwarding we fall back to
47 * the normal ip_input processing path. We should only be called from
48 * interfaces connected to the outside world.
49 *
50 * Firewalling is fully supported including divert, ipfw fwd and ipfilter
51 * ipnat and address rewrite.
52 *
53 * IPSEC is not supported if this host is a tunnel broker. IPSEC is
54 * supported for connections to/from local host.
55 *
56 * We try to do the least expensive (in CPU ops) checks and operations
57 * first to catch junk with as little overhead as possible.
58 *
59 * We take full advantage of hardware support for IP checksum and
60 * fragmentation offloading.
61 *
62 * We don't do ICMP redirect in the fast forwarding path. I have had my own
63 * cases where two core routers with Zebra routing suite would send millions
64 * ICMP redirects to connected hosts if the destination router was not the
65 * default gateway. In one case it was filling the routing table of a host
66 * with approximately 300.000 cloned redirect entries until it ran out of
67 * kernel memory. However the networking code proved very robust and it didn't
68 * crash or fail in other ways.
69 */
70
71 /*
72 * Many thanks to Matt Thomas of NetBSD for basic structure of ip_flow.c which
73 * is being followed here.
74 */
75
76 #include <sys/cdefs.h>
77 __FBSDID("$FreeBSD$");
78
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/sdt.h>
88 #include <sys/socket.h>
89 #include <sys/sysctl.h>
90
91 #include <net/pfil.h>
92 #include <net/if.h>
93 #include <net/if_types.h>
94 #include <net/if_var.h>
95 #include <net/if_dl.h>
96 #include <net/route.h>
97 #include <net/vnet.h>
98
99 #include <netinet/in.h>
100 #include <netinet/in_fib.h>
101 #include <netinet/in_kdtrace.h>
102 #include <netinet/in_systm.h>
103 #include <netinet/in_var.h>
104 #include <netinet/ip.h>
105 #include <netinet/ip_var.h>
106 #include <netinet/ip_icmp.h>
107 #include <netinet/ip_options.h>
108
109 #include <machine/in_cksum.h>
110
111 static int
112 ip_findroute(struct nhop4_basic *pnh, struct in_addr dest, struct mbuf *m)
113 {
114
115 bzero(pnh, sizeof(*pnh));
116 if (fib4_lookup_nh_basic(M_GETFIB(m), dest, 0, 0, pnh) != 0) {
117 IPSTAT_INC(ips_noroute);
118 IPSTAT_INC(ips_cantforward);
119 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0);
120 return (EHOSTUNREACH);
121 }
122 /*
123 * Drop blackholed traffic and directed broadcasts.
124 */
125 if ((pnh->nh_flags & (NHF_BLACKHOLE | NHF_BROADCAST)) != 0) {
126 IPSTAT_INC(ips_cantforward);
127 m_freem(m);
128 return (EHOSTUNREACH);
129 }
130
131 if (pnh->nh_flags & NHF_REJECT) {
132 IPSTAT_INC(ips_cantforward);
133 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0);
134 return (EHOSTUNREACH);
135 }
136
137 return (0);
138 }
139
140 /*
141 * Try to forward a packet based on the destination address.
142 * This is a fast path optimized for the plain forwarding case.
143 * If the packet is handled (and consumed) here then we return NULL;
144 * otherwise mbuf is returned and the packet should be delivered
145 * to ip_input for full processing.
146 */
147 struct mbuf *
148 ip_tryforward(struct mbuf *m)
149 {
150 struct ip *ip;
151 struct mbuf *m0 = NULL;
152 struct nhop4_basic nh;
153 struct sockaddr_in dst;
154 struct in_addr dest, odest, rtdest;
155 uint16_t ip_len, ip_off;
156 int error = 0;
157 struct m_tag *fwd_tag = NULL;
158
159 /*
160 * Are we active and forwarding packets?
161 */
162
163 M_ASSERTVALID(m);
164 M_ASSERTPKTHDR(m);
165
166 #ifdef ALTQ
167 /*
168 * Is packet dropped by traffic conditioner?
169 */
170 if (altq_input != NULL && (*altq_input)(m, AF_INET) == 0)
171 goto drop;
172 #endif
173
174 /*
175 * Only IP packets without options
176 */
177 ip = mtod(m, struct ip *);
178
179 if (ip->ip_hl != (sizeof(struct ip) >> 2)) {
180 if (V_ip_doopts == 1)
181 return m;
182 else if (V_ip_doopts == 2) {
183 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_FILTER_PROHIB,
184 0, 0);
185 return NULL; /* mbuf already free'd */
186 }
187 /* else ignore IP options and continue */
188 }
189
190 /*
191 * Only unicast IP, not from loopback, no L2 or IP broadcast,
192 * no multicast, no INADDR_ANY
193 *
194 * XXX: Probably some of these checks could be direct drop
195 * conditions. However it is not clear whether there are some
196 * hacks or obscure behaviours which make it necessary to
197 * let ip_input handle it. We play safe here and let ip_input
198 * deal with it until it is proven that we can directly drop it.
199 */
200 if ((m->m_flags & (M_BCAST|M_MCAST)) ||
201 (m->m_pkthdr.rcvif->if_flags & IFF_LOOPBACK) ||
202 ntohl(ip->ip_src.s_addr) == (u_long)INADDR_BROADCAST ||
203 ntohl(ip->ip_dst.s_addr) == (u_long)INADDR_BROADCAST ||
204 IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
205 IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
206 IN_LINKLOCAL(ntohl(ip->ip_src.s_addr)) ||
207 IN_LINKLOCAL(ntohl(ip->ip_dst.s_addr)) ||
208 ip->ip_src.s_addr == INADDR_ANY ||
209 ip->ip_dst.s_addr == INADDR_ANY )
210 return m;
211
212 /*
213 * Is it for a local address on this host?
214 */
215 if (in_localip(ip->ip_dst))
216 return m;
217
218 IPSTAT_INC(ips_total);
219
220 /*
221 * Step 3: incoming packet firewall processing
222 */
223
224 odest.s_addr = dest.s_addr = ip->ip_dst.s_addr;
225
226 /*
227 * Run through list of ipfilter hooks for input packets
228 */
229 if (!PFIL_HOOKED(&V_inet_pfil_hook))
230 goto passin;
231
232 if (pfil_run_hooks(
233 &V_inet_pfil_hook, &m, m->m_pkthdr.rcvif, PFIL_IN, 0, NULL) ||
234 m == NULL)
235 goto drop;
236
237 M_ASSERTVALID(m);
238 M_ASSERTPKTHDR(m);
239
240 ip = mtod(m, struct ip *); /* m may have changed by pfil hook */
241 dest.s_addr = ip->ip_dst.s_addr;
242
243 /*
244 * Destination address changed?
245 */
246 if (odest.s_addr != dest.s_addr) {
247 /*
248 * Is it now for a local address on this host?
249 */
250 if (in_localip(dest))
251 goto forwardlocal;
252 /*
253 * Go on with new destination address
254 */
255 }
256
257 if (m->m_flags & M_FASTFWD_OURS) {
258 /*
259 * ipfw changed it for a local address on this host.
260 */
261 goto forwardlocal;
262 }
263
264 passin:
265 /*
266 * Step 4: decrement TTL and look up route
267 */
268
269 /*
270 * Check TTL
271 */
272 #ifdef IPSTEALTH
273 if (!V_ipstealth) {
274 #endif
275 if (ip->ip_ttl <= IPTTLDEC) {
276 icmp_error(m, ICMP_TIMXCEED, ICMP_TIMXCEED_INTRANS, 0, 0);
277 return NULL; /* mbuf already free'd */
278 }
279
280 /*
281 * Decrement the TTL and incrementally change the IP header checksum.
282 * Don't bother doing this with hw checksum offloading, it's faster
283 * doing it right here.
284 */
285 ip->ip_ttl -= IPTTLDEC;
286 if (ip->ip_sum >= (u_int16_t) ~htons(IPTTLDEC << 8))
287 ip->ip_sum -= ~htons(IPTTLDEC << 8);
288 else
289 ip->ip_sum += htons(IPTTLDEC << 8);
290 #ifdef IPSTEALTH
291 }
292 #endif
293
294 /*
295 * Next hop forced by pfil(9) hook?
296 */
297 if ((m->m_flags & M_IP_NEXTHOP) &&
298 ((fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL)) != NULL)) {
299 /*
300 * Now we will find route to forced destination.
301 */
302 dest.s_addr = ((struct sockaddr_in *)
303 (fwd_tag + 1))->sin_addr.s_addr;
304 m_tag_delete(m, fwd_tag);
305 m->m_flags &= ~M_IP_NEXTHOP;
306 }
307
308 /*
309 * Find route to destination.
310 */
311 if (ip_findroute(&nh, dest, m) != 0)
312 return (NULL); /* icmp unreach already sent */
313
314 /*
315 * Avoid second route lookup by caching destination.
316 */
317 rtdest.s_addr = dest.s_addr;
318
319 /*
320 * Step 5: outgoing firewall packet processing
321 */
322 if (!PFIL_HOOKED(&V_inet_pfil_hook))
323 goto passout;
324
325 if (pfil_run_hooks(&V_inet_pfil_hook, &m, nh.nh_ifp, PFIL_OUT, PFIL_FWD,
326 NULL) || m == NULL) {
327 goto drop;
328 }
329
330 M_ASSERTVALID(m);
331 M_ASSERTPKTHDR(m);
332
333 ip = mtod(m, struct ip *);
334 dest.s_addr = ip->ip_dst.s_addr;
335
336 /*
337 * Destination address changed?
338 */
339 if (m->m_flags & M_IP_NEXTHOP)
340 fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
341 else
342 fwd_tag = NULL;
343 if (odest.s_addr != dest.s_addr || fwd_tag != NULL) {
344 /*
345 * Is it now for a local address on this host?
346 */
347 if (m->m_flags & M_FASTFWD_OURS || in_localip(dest)) {
348 forwardlocal:
349 /*
350 * Return packet for processing by ip_input().
351 */
352 m->m_flags |= M_FASTFWD_OURS;
353 return (m);
354 }
355 /*
356 * Redo route lookup with new destination address
357 */
358 if (fwd_tag) {
359 dest.s_addr = ((struct sockaddr_in *)
360 (fwd_tag + 1))->sin_addr.s_addr;
361 m_tag_delete(m, fwd_tag);
362 m->m_flags &= ~M_IP_NEXTHOP;
363 }
364 if (dest.s_addr != rtdest.s_addr &&
365 ip_findroute(&nh, dest, m) != 0)
366 return (NULL); /* icmp unreach already sent */
367 }
368
369 passout:
370 /*
371 * Step 6: send off the packet
372 */
373 ip_len = ntohs(ip->ip_len);
374 ip_off = ntohs(ip->ip_off);
375
376 bzero(&dst, sizeof(dst));
377 dst.sin_family = AF_INET;
378 dst.sin_len = sizeof(dst);
379 dst.sin_addr = nh.nh_addr;
380
381 /*
382 * Check if packet fits MTU or if hardware will fragment for us
383 */
384 if (ip_len <= nh.nh_mtu) {
385 /*
386 * Avoid confusing lower layers.
387 */
388 m_clrprotoflags(m);
389 /*
390 * Send off the packet via outgoing interface
391 */
392 IP_PROBE(send, NULL, NULL, ip, nh.nh_ifp, ip, NULL);
393 error = (*nh.nh_ifp->if_output)(nh.nh_ifp, m,
394 (struct sockaddr *)&dst, NULL);
395 } else {
396 /*
397 * Handle EMSGSIZE with icmp reply needfrag for TCP MTU discovery
398 */
399 if (ip_off & IP_DF) {
400 IPSTAT_INC(ips_cantfrag);
401 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_NEEDFRAG,
402 0, nh.nh_mtu);
403 goto consumed;
404 } else {
405 /*
406 * We have to fragment the packet
407 */
408 m->m_pkthdr.csum_flags |= CSUM_IP;
409 if (ip_fragment(ip, &m, nh.nh_mtu,
410 nh.nh_ifp->if_hwassist) != 0)
411 goto drop;
412 KASSERT(m != NULL, ("null mbuf and no error"));
413 /*
414 * Send off the fragments via outgoing interface
415 */
416 error = 0;
417 do {
418 m0 = m->m_nextpkt;
419 m->m_nextpkt = NULL;
420 /*
421 * Avoid confusing lower layers.
422 */
423 m_clrprotoflags(m);
424
425 IP_PROBE(send, NULL, NULL,
426 mtod(m, struct ip *), nh.nh_ifp,
427 mtod(m, struct ip *), NULL);
428 /* XXX: we can use cached route here */
429 error = (*nh.nh_ifp->if_output)(nh.nh_ifp, m,
430 (struct sockaddr *)&dst, NULL);
431 if (error)
432 break;
433 } while ((m = m0) != NULL);
434 if (error) {
435 /* Reclaim remaining fragments */
436 for (m = m0; m; m = m0) {
437 m0 = m->m_nextpkt;
438 m_freem(m);
439 }
440 } else
441 IPSTAT_INC(ips_fragmented);
442 }
443 }
444
445 if (error != 0)
446 IPSTAT_INC(ips_odropped);
447 else {
448 IPSTAT_INC(ips_forward);
449 IPSTAT_INC(ips_fastforward);
450 }
451 consumed:
452 return NULL;
453 drop:
454 if (m)
455 m_freem(m);
456 return NULL;
457 }
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