1 /* $OpenBSD: bpf.c,v 1.3 2019/03/18 00:00:59 dlg Exp $ */
2
3 /* BPF socket interface code, originally contributed by Archie Cobbs. */
4
5 /*
6 * Copyright (c) 1995, 1996, 1998, 1999
7 * The Internet Software Consortium. All rights reserved.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 *
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. Neither the name of The Internet Software Consortium nor the names
19 * of its contributors may be used to endorse or promote products derived
20 * from this software without specific prior written permission.
21 *
22 * THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND
23 * CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
24 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
25 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
26 * DISCLAIMED. IN NO EVENT SHALL THE INTERNET SOFTWARE CONSORTIUM OR
27 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
28 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
29 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
30 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
31 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
32 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
33 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
34 * SUCH DAMAGE.
35 *
36 * This software has been written for the Internet Software Consortium
37 * by Ted Lemon <mellon@fugue.com> in cooperation with Vixie
38 * Enterprises. To learn more about the Internet Software Consortium,
39 * see ``http://www.vix.com/isc''. To learn more about Vixie
40 * Enterprises, see ``http://www.vix.com''.
41 */
42
43 #include <sys/types.h>
44 #include <sys/ioctl.h>
45 #include <sys/socket.h>
46
47 #include <net/bpf.h>
48 #include <net/if.h>
49
50 #include <netinet/in.h>
51 #include <netinet/if_ether.h>
52
53 #include <errno.h>
54 #include <fcntl.h>
55 #include <stdio.h>
56 #include <stdlib.h>
57 #include <string.h>
58 #include <unistd.h>
59
60 #include "dhcp.h"
61 #include "dhcpd.h"
62 #include "log.h"
63
64 ssize_t send_packet_layer3(struct interface_info *,
65 void *, size_t, struct packet_ctx *);
66
67 /*
68 * Called by get_interface_list for each interface that's discovered.
69 * Opens a packet filter for each interface and adds it to the select
70 * mask.
71 */
72 int
if_register_bpf(struct interface_info * info)73 if_register_bpf(struct interface_info *info)
74 {
75 int sock;
76
77 /* Open the BPF device */
78 if ((sock = open("/dev/bpf", O_RDWR)) == -1)
79 fatal("Can't open bpf device");
80
81 /* Set the BPF device to point at this interface. */
82 if (ioctl(sock, BIOCSETIF, &info->ifr) == -1)
83 fatal("Can't attach interface %s to bpf device", info->name);
84
85 return (sock);
86 }
87
88 void
if_register_send(struct interface_info * info)89 if_register_send(struct interface_info *info)
90 {
91 /*
92 * If we're using the bpf API for sending and receiving, we
93 * don't need to register this interface twice.
94 */
95 info->wfdesc = info->rfdesc;
96 }
97
98 /* DHCPv6 BPF filters. */
99
100 /*
101 * Packet filter program: 'ip6 and udp and dst port DHCP6_SERVER_PORT'
102 */
103 struct bpf_insn dhcp6_bpf_sfilter[] = {
104 /* Make sure this is an IP packet... */
105 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
106 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IPV6, 0, 5),
107
108 /* Make sure this is an UDP packet. */
109 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 20),
110 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 3),
111
112 /* Make sure it is the right port. */
113 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 56),
114 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, DHCP6_SERVER_PORT, 0, 1),
115
116 /* If we passed all the tests, ask for the whole packet. */
117 BPF_STMT(BPF_RET + BPF_K, (u_int)-1),
118
119 /* Otherwise, drop it. */
120 BPF_STMT(BPF_RET + BPF_K, 0),
121 };
122
123 int dhcp6_bpf_sfilter_len = sizeof(dhcp6_bpf_sfilter) / sizeof(struct bpf_insn);
124
125 /*
126 * Packet filter program: 'ip6 and udp'
127 */
128 struct bpf_insn dhcp6_bpf_wfilter[] = {
129 /* Make sure this is an IP packet... */
130 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
131 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IPV6, 0, 3),
132
133 /* Make sure this is an UDP packet. */
134 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 20),
135 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 1),
136
137 /* If we passed all the tests, ask for the whole packet. */
138 BPF_STMT(BPF_RET + BPF_K, (u_int)-1),
139
140 /* Otherwise, drop it. */
141 BPF_STMT(BPF_RET + BPF_K, 0),
142 };
143
144 int dhcp6_bpf_wfilter_len = sizeof(dhcp6_bpf_wfilter) / sizeof(struct bpf_insn);
145
146
147 void
if_register_receive(struct interface_info * info)148 if_register_receive(struct interface_info *info)
149 {
150 struct bpf_version v;
151 struct bpf_program p;
152 int flag = 1, sz, cmplt = 0;
153
154 /* Open a BPF device and hang it on this interface... */
155 info->rfdesc = if_register_bpf(info);
156
157 /* Make sure the BPF version is in range... */
158 if (ioctl(info->rfdesc, BIOCVERSION, &v) == -1)
159 fatal("Can't get BPF version");
160
161 if (v.bv_major != BPF_MAJOR_VERSION ||
162 v.bv_minor < BPF_MINOR_VERSION)
163 fatalx("Kernel BPF version out of range - recompile dhcpd!");
164
165 /*
166 * Set immediate mode so that reads return as soon as a packet
167 * comes in, rather than waiting for the input buffer to fill
168 * with packets.
169 */
170 if (ioctl(info->rfdesc, BIOCIMMEDIATE, &flag) == -1)
171 fatal("Can't set immediate mode on bpf device");
172
173 /* make sure kernel fills in the source ethernet address */
174 if (ioctl(info->rfdesc, BIOCSHDRCMPLT, &cmplt) == -1)
175 fatal("Can't set header complete flag on bpf device");
176
177 /* Get the required BPF buffer length from the kernel. */
178 if (ioctl(info->rfdesc, BIOCGBLEN, &sz) == -1)
179 fatal("Can't get bpf buffer length");
180 info->rbuf_max = sz;
181 info->rbuf = malloc(info->rbuf_max);
182 if (!info->rbuf)
183 fatalx("Can't allocate %lu bytes for bpf input buffer.",
184 (unsigned long)info->rbuf_max);
185 info->rbuf_offset = 0;
186 info->rbuf_len = 0;
187
188 /* Set up the bpf filter program structure. */
189 p.bf_len = dhcp6_bpf_sfilter_len;
190 p.bf_insns = dhcp6_bpf_sfilter;
191 if (ioctl(info->rfdesc, BIOCSETF, &p) == -1)
192 fatal("Can't install packet filter program");
193
194 /* Set up the bpf write filter program structure. */
195 p.bf_len = dhcp6_bpf_wfilter_len;
196 p.bf_insns = dhcp6_bpf_wfilter;
197 if (ioctl(info->rfdesc, BIOCSETWF, &p) == -1)
198 fatal("Can't install write filter program");
199
200 /* Only get input packets. */
201 flag = BPF_DIRECTION_OUT;
202 if (ioctl(info->rfdesc, BIOCSDIRFILT , &flag) == -1)
203 fatal("Can't set BPF direction capture");
204
205 /* Drop them so they don't go up in the network stack. */
206 flag = BPF_FILDROP_CAPTURE;
207 if (ioctl(info->rfdesc, BIOCSFILDROP, &flag) == -1)
208 fatal("Can't set BPF filter drop");
209
210 /* make sure these settings cannot be changed after dropping privs */
211 if (ioctl(info->rfdesc, BIOCLOCK) == -1)
212 fatal("Failed to lock bpf descriptor");
213 }
214
215 ssize_t
send_packet_layer3(struct interface_info * intf,void * raw,size_t len,struct packet_ctx * pc)216 send_packet_layer3(struct interface_info *intf, void *raw, size_t len,
217 struct packet_ctx *pc)
218 {
219 struct cmsghdr *cmsg;
220 ssize_t sendlen;
221 struct msghdr msg;
222 struct in6_pktinfo *ipi6;
223 struct sockaddr_storage ss;
224 struct iovec iov[2];
225 uint8_t cmsgbuf[
226 CMSG_SPACE(sizeof(struct in6_pktinfo))
227 ];
228
229 log_debug(" sending %ld bytes to %s:%d via %s",
230 len, v6addr2str(&ss2sin6(&pc->pc_dst)->sin6_addr),
231 ntohs(ss2sin6(&pc->pc_dst)->sin6_port), intf->name);
232
233 memset(&msg, 0, sizeof(msg));
234 iov[0].iov_base = raw;
235 iov[0].iov_len = len;
236 msg.msg_iov = iov;
237 msg.msg_iovlen = 1;
238
239 ss = pc->pc_dst;
240 ss2sin6(&ss)->sin6_scope_id = intf->index;
241 msg.msg_name = &ss;
242 msg.msg_namelen = ss.ss_len;
243
244 /* If binded to multicast we should select an interface. */
245 if (IN6_IS_ADDR_MULTICAST(&ss2sin6(&ss)->sin6_addr)) {
246 memset(cmsgbuf, 0, sizeof(cmsgbuf));
247 msg.msg_control = cmsgbuf;
248 msg.msg_controllen = sizeof(cmsgbuf);
249
250 /* Use the IPV6_PKTINFO to select the interface. */
251 cmsg = (struct cmsghdr *)CMSG_FIRSTHDR(&msg);
252 cmsg->cmsg_len = CMSG_LEN(sizeof(*ipi6));
253 cmsg->cmsg_level = IPPROTO_IPV6;
254 cmsg->cmsg_type = IPV6_PKTINFO;
255
256 ipi6 = (struct in6_pktinfo *)CMSG_DATA(cmsg);
257 ipi6->ipi6_ifindex = intf->index;
258 }
259
260 if ((sendlen = sendmsg(pc->pc_sd, &msg, 0)) == -1) {
261 log_warn(" failed to send message");
262 return -1;
263 }
264 if (sendlen < (ssize_t)len)
265 log_warnx(" sent less bytes than expected (%ld < %ld)",
266 sendlen, len);
267
268 return sendlen;
269 }
270
271 ssize_t
send_packet(struct interface_info * interface,void * raw,size_t len,struct packet_ctx * pc)272 send_packet(struct interface_info *interface,
273 void *raw, size_t len, struct packet_ctx *pc)
274 {
275 unsigned char buf[256];
276 struct iovec iov[2];
277 int result, bufp = 0;
278
279 if (pc->pc_sd != 0)
280 return send_packet_layer3(interface, raw, len, pc);
281
282 /* Assemble the headers... */
283 assemble_hw_header(buf, &bufp, pc);
284 assemble_udp_ip6_header(buf, &bufp, pc, raw, len);
285
286 /* Fire it off */
287 iov[0].iov_base = (char *)buf;
288 iov[0].iov_len = bufp;
289 iov[1].iov_base = (char *)raw;
290 iov[1].iov_len = len;
291
292 result = writev(interface->wfdesc, iov, 2);
293 if (result == -1)
294 log_warn("send_packet");
295
296 return (result);
297 }
298
299 ssize_t
receive_packet(struct interface_info * interface,unsigned char * buf,size_t len,struct packet_ctx * pc)300 receive_packet(struct interface_info *interface, unsigned char *buf,
301 size_t len, struct packet_ctx *pc)
302 {
303 int length = 0, offset = 0;
304 struct bpf_hdr hdr;
305
306 /*
307 * All this complexity is because BPF doesn't guarantee that
308 * only one packet will be returned at a time. We're getting
309 * what we deserve, though - this is a terrible abuse of the BPF
310 * interface. Sigh.
311 */
312
313 /* Process packets until we get one we can return or until we've
314 * done a read and gotten nothing we can return...
315 */
316 do {
317 /* If the buffer is empty, fill it. */
318 if (interface->rbuf_offset == interface->rbuf_len) {
319 length = read(interface->rfdesc, interface->rbuf,
320 interface->rbuf_max);
321 if (length <= 0)
322 return (length);
323 interface->rbuf_offset = 0;
324 interface->rbuf_len = length;
325 }
326
327 /*
328 * If there isn't room for a whole bpf header, something
329 * went wrong, but we'll ignore it and hope it goes
330 * away... XXX
331 */
332 if (interface->rbuf_len - interface->rbuf_offset <
333 sizeof(hdr)) {
334 interface->rbuf_offset = interface->rbuf_len;
335 continue;
336 }
337
338 /* Copy out a bpf header... */
339 memcpy(&hdr, &interface->rbuf[interface->rbuf_offset],
340 sizeof(hdr));
341
342 /*
343 * If the bpf header plus data doesn't fit in what's
344 * left of the buffer, stick head in sand yet again...
345 */
346 if (interface->rbuf_offset + hdr.bh_hdrlen + hdr.bh_caplen >
347 interface->rbuf_len) {
348 interface->rbuf_offset = interface->rbuf_len;
349 continue;
350 }
351
352 /*
353 * If the captured data wasn't the whole packet, or if
354 * the packet won't fit in the input buffer, all we can
355 * do is drop it.
356 */
357 if (hdr.bh_caplen != hdr.bh_datalen) {
358 interface->rbuf_offset += hdr.bh_hdrlen =
359 hdr.bh_caplen;
360 continue;
361 }
362
363 /* Skip over the BPF header... */
364 interface->rbuf_offset += hdr.bh_hdrlen;
365
366 /* Decode the physical header... */
367 offset = decode_hw_header(interface->rbuf,
368 interface->rbuf_offset, pc);
369
370 /*
371 * If a physical layer checksum failed (dunno of any
372 * physical layer that supports this, but WTH), skip
373 * this packet.
374 */
375 if (offset < 0) {
376 interface->rbuf_offset += hdr.bh_caplen;
377 continue;
378 }
379 interface->rbuf_offset += offset;
380 hdr.bh_caplen -= offset;
381
382 /* Decode the IP and UDP headers... */
383 offset = decode_udp_ip6_header(interface->rbuf,
384 interface->rbuf_offset, pc, hdr.bh_caplen);
385
386 /* If the IP or UDP checksum was bad, skip the packet... */
387 if (offset < 0) {
388 interface->rbuf_offset += hdr.bh_caplen;
389 continue;
390 }
391 interface->rbuf_offset += offset;
392 hdr.bh_caplen -= offset;
393
394 /*
395 * If there's not enough room to stash the packet data,
396 * we have to skip it (this shouldn't happen in real
397 * life, though).
398 */
399 if (hdr.bh_caplen > len) {
400 interface->rbuf_offset += hdr.bh_caplen;
401 continue;
402 }
403
404 /* Copy out the data in the packet... */
405 memcpy(buf, interface->rbuf + interface->rbuf_offset,
406 hdr.bh_caplen);
407 interface->rbuf_offset += hdr.bh_caplen;
408 return (hdr.bh_caplen);
409 } while (!length);
410 return (0);
411 }
412