1 /* $OpenBSD: bpf.c,v 1.13 2004/05/05 14:28:58 deraadt Exp $ */
3 /* BPF socket interface code, originally contributed by Archie Cobbs. */
6 * SPDX-License-Identifier: BSD-3-Clause
8 * Copyright (c) 1995, 1996, 1998, 1999
9 * The Internet Software Consortium. All rights reserved.
11 * Redistribution and use in source and binary forms, with or without
12 * modification, are permitted provided that the following conditions
15 * 1. Redistributions of source code must retain the above copyright
16 * notice, this list of conditions and the following disclaimer.
17 * 2. Redistributions in binary form must reproduce the above copyright
18 * notice, this list of conditions and the following disclaimer in the
19 * documentation and/or other materials provided with the distribution.
20 * 3. Neither the name of The Internet Software Consortium nor the names
21 * of its contributors may be used to endorse or promote products derived
22 * from this software without specific prior written permission.
24 * THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND
25 * CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
26 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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29 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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33 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
34 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
35 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
38 * This software has been written for the Internet Software Consortium
39 * by Ted Lemon <mellon@fugue.com> in cooperation with Vixie
40 * Enterprises. To learn more about the Internet Software Consortium,
41 * see ``http://www.vix.com/isc''. To learn more about Vixie
42 * Enterprises, see ``http://www.vix.com''.
45 #include <sys/cdefs.h>
46 __FBSDID("$FreeBSD$");
50 #include <sys/capsicum.h>
51 #include <sys/ioctl.h>
55 #include <netinet/in_systm.h>
56 #include <netinet/ip.h>
57 #include <netinet/udp.h>
58 #include <netinet/if_ether.h>
60 #include <capsicum_helpers.h>
62 #define BPF_FORMAT "/dev/bpf%d"
65 * Called by get_interface_list for each interface that's discovered.
66 * Opens a packet filter for each interface and adds it to the select
70 if_register_bpf(struct interface_info *info, int flags)
75 /* Open a BPF device */
77 snprintf(filename, sizeof(filename), BPF_FORMAT, b);
78 sock = open(filename, flags);
83 error("Can't find free bpf: %m");
88 /* Set the BPF device to point at this interface. */
89 if (ioctl(sock, BIOCSETIF, info->ifp) < 0)
90 error("Can't attach interface %s to bpf device %s: %m",
91 info->name, filename);
97 * Packet write filter program:
98 * 'ip and udp and src port bootps and dst port (bootps or bootpc)'
100 static struct bpf_insn dhcp_bpf_wfilter[] = {
101 BPF_STMT(BPF_LD + BPF_B + BPF_IND, 14),
102 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, (IPVERSION << 4) + 5, 0, 12),
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_IP, 0, 10),
108 /* Make sure it's a UDP packet... */
109 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23),
110 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 8),
112 /* Make sure this isn't a fragment... */
113 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
114 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 6, 0), /* patched */
116 /* Get the IP header length... */
117 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
119 /* Make sure it's from the right port... */
120 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 14),
121 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 68, 0, 3),
123 /* Make sure it is to the right ports ... */
124 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16),
125 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 67, 0, 1),
127 /* If we passed all the tests, ask for the whole packet. */
128 BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
130 /* Otherwise, drop it. */
131 BPF_STMT(BPF_RET+BPF_K, 0),
134 static int dhcp_bpf_wfilter_len = nitems(dhcp_bpf_wfilter);
137 if_register_send(struct interface_info *info)
140 struct bpf_version v;
141 struct bpf_program p;
144 /* Open a BPF device and hang it on this interface... */
145 info->wfdesc = if_register_bpf(info, O_WRONLY);
147 /* Make sure the BPF version is in range... */
148 if (ioctl(info->wfdesc, BIOCVERSION, &v) < 0)
149 error("Can't get BPF version: %m");
151 if (v.bv_major != BPF_MAJOR_VERSION ||
152 v.bv_minor < BPF_MINOR_VERSION)
153 error("Kernel BPF version out of range - recompile dhcpd!");
155 /* Set up the bpf write filter program structure. */
156 p.bf_len = dhcp_bpf_wfilter_len;
157 p.bf_insns = dhcp_bpf_wfilter;
159 if (dhcp_bpf_wfilter[7].k == 0x1fff)
160 dhcp_bpf_wfilter[7].k = htons(IP_MF|IP_OFFMASK);
162 if (ioctl(info->wfdesc, BIOCSETWF, &p) < 0)
163 error("Can't install write filter program: %m");
165 if (ioctl(info->wfdesc, BIOCLOCK, NULL) < 0)
166 error("Cannot lock bpf");
168 cap_rights_init(&rights, CAP_WRITE);
169 if (caph_rights_limit(info->wfdesc, &rights) < 0)
170 error("Can't limit bpf descriptor: %m");
173 * Use raw socket for unicast send.
175 if ((sock = socket(AF_INET, SOCK_RAW, IPPROTO_UDP)) == -1)
176 error("socket(SOCK_RAW): %m");
177 if (setsockopt(sock, IPPROTO_IP, IP_HDRINCL, &on,
179 error("setsockopt(IP_HDRINCL): %m");
184 * Packet filter program...
186 * XXX: Changes to the filter program may require changes to the
187 * constant offsets used in if_register_send to patch the BPF program!
189 static struct bpf_insn dhcp_bpf_filter[] = {
190 /* Make sure this is an IP packet... */
191 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
192 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 8),
194 /* Make sure it's a UDP packet... */
195 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23),
196 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6),
198 /* Make sure this isn't a fragment... */
199 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
200 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0),
202 /* Get the IP header length... */
203 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
205 /* Make sure it's to the right port... */
206 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16),
207 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 67, 0, 1), /* patch */
209 /* If we passed all the tests, ask for the whole packet. */
210 BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
212 /* Otherwise, drop it. */
213 BPF_STMT(BPF_RET+BPF_K, 0),
216 static int dhcp_bpf_filter_len = nitems(dhcp_bpf_filter);
219 if_register_receive(struct interface_info *info)
221 static const unsigned long cmds[2] = { SIOCGIFFLAGS, SIOCGIFMEDIA };
223 struct bpf_version v;
224 struct bpf_program p;
227 /* Open a BPF device and hang it on this interface... */
228 info->rfdesc = if_register_bpf(info, O_RDONLY);
230 /* Make sure the BPF version is in range... */
231 if (ioctl(info->rfdesc, BIOCVERSION, &v) < 0)
232 error("Can't get BPF version: %m");
234 if (v.bv_major != BPF_MAJOR_VERSION ||
235 v.bv_minor < BPF_MINOR_VERSION)
236 error("Kernel BPF version out of range - recompile dhcpd!");
239 * Set immediate mode so that reads return as soon as a packet
240 * comes in, rather than waiting for the input buffer to fill
243 if (ioctl(info->rfdesc, BIOCIMMEDIATE, &flag) < 0)
244 error("Can't set immediate mode on bpf device: %m");
246 /* Get the required BPF buffer length from the kernel. */
247 if (ioctl(info->rfdesc, BIOCGBLEN, &sz) < 0)
248 error("Can't get bpf buffer length: %m");
250 info->rbuf = malloc(info->rbuf_max);
252 error("Can't allocate %lu bytes for bpf input buffer.",
253 (unsigned long)info->rbuf_max);
254 info->rbuf_offset = 0;
257 /* Set up the bpf filter program structure. */
258 p.bf_len = dhcp_bpf_filter_len;
259 p.bf_insns = dhcp_bpf_filter;
261 /* Patch the server port into the BPF program...
263 * XXX: changes to filter program may require changes to the
264 * insn number(s) used below!
266 dhcp_bpf_filter[8].k = LOCAL_PORT;
268 if (ioctl(info->rfdesc, BIOCSETF, &p) < 0)
269 error("Can't install packet filter program: %m");
271 if (ioctl(info->rfdesc, BIOCLOCK, NULL) < 0)
272 error("Cannot lock bpf");
274 cap_rights_init(&rights, CAP_IOCTL, CAP_EVENT, CAP_READ);
275 if (caph_rights_limit(info->rfdesc, &rights) < 0)
276 error("Can't limit bpf descriptor: %m");
277 if (caph_ioctls_limit(info->rfdesc, cmds, 2) < 0)
278 error("Can't limit ioctls for bpf descriptor: %m");
282 send_packet_unpriv(int privfd, struct dhcp_packet *raw, size_t len,
283 struct in_addr from, struct in_addr to)
289 hdr.code = IMSG_SEND_PACKET;
290 hdr.len = sizeof(hdr) +
291 sizeof(size_t) + len +
292 sizeof(from) + sizeof(to);
294 if ((buf = buf_open(hdr.len)) == NULL)
295 error("buf_open: %m");
298 errs += buf_add(buf, &hdr, sizeof(hdr));
299 errs += buf_add(buf, &len, sizeof(len));
300 errs += buf_add(buf, raw, len);
301 errs += buf_add(buf, &from, sizeof(from));
302 errs += buf_add(buf, &to, sizeof(to));
304 error("buf_add: %m");
306 if (buf_close(privfd, buf) == -1)
307 error("buf_close: %m");
311 send_packet_priv(struct interface_info *interface, struct imsg_hdr *hdr, int fd)
313 unsigned char buf[256];
316 struct dhcp_packet raw;
318 struct in_addr from, to;
319 int result, bufp = 0;
321 if (hdr->len < sizeof(*hdr) + sizeof(size_t))
322 error("corrupted message received");
323 buf_read(fd, &len, sizeof(len));
324 if (hdr->len != sizeof(*hdr) + sizeof(size_t) + len +
325 sizeof(from) + sizeof(to)) {
326 error("corrupted message received");
328 if (len > sizeof(raw))
329 error("corrupted message received");
330 buf_read(fd, &raw, len);
331 buf_read(fd, &from, sizeof(from));
332 buf_read(fd, &to, sizeof(to));
334 /* Assemble the headers... */
335 if (to.s_addr == INADDR_BROADCAST)
336 assemble_hw_header(interface, buf, &bufp);
337 assemble_udp_ip_header(buf, &bufp, from.s_addr, to.s_addr,
338 htons(REMOTE_PORT), (unsigned char *)&raw, len);
340 iov[0].iov_base = buf;
341 iov[0].iov_len = bufp;
342 iov[1].iov_base = &raw;
343 iov[1].iov_len = len;
346 if (to.s_addr == INADDR_BROADCAST)
347 result = writev(interface->wfdesc, iov, 2);
349 struct sockaddr_in sato;
352 sato.sin_port = htons(REMOTE_PORT);
353 sato.sin_family = AF_INET;
354 sato.sin_len = sizeof(sato);
356 memset(&msg, 0, sizeof(msg));
357 msg.msg_name = (struct sockaddr *)&sato;
358 msg.msg_namelen = sizeof(sato);
361 result = sendmsg(interface->ufdesc, &msg, 0);
365 warning("send_packet: %m");
369 receive_packet(struct interface_info *interface, unsigned char *buf,
370 size_t len, struct sockaddr_in *from, struct hardware *hfrom)
372 int length = 0, offset = 0;
376 * All this complexity is because BPF doesn't guarantee that
377 * only one packet will be returned at a time. We're getting
378 * what we deserve, though - this is a terrible abuse of the BPF
382 /* Process packets until we get one we can return or until we've
383 * done a read and gotten nothing we can return...
386 /* If the buffer is empty, fill it. */
387 if (interface->rbuf_offset >= interface->rbuf_len) {
388 length = read(interface->rfdesc, interface->rbuf,
389 interface->rbuf_max);
392 interface->rbuf_offset = 0;
393 interface->rbuf_len = length;
397 * If there isn't room for a whole bpf header, something
398 * went wrong, but we'll ignore it and hope it goes
401 if (interface->rbuf_len - interface->rbuf_offset <
403 interface->rbuf_offset = interface->rbuf_len;
407 /* Copy out a bpf header... */
408 memcpy(&hdr, &interface->rbuf[interface->rbuf_offset],
412 * If the bpf header plus data doesn't fit in what's
413 * left of the buffer, stick head in sand yet again...
415 if (interface->rbuf_offset + hdr.bh_hdrlen + hdr.bh_caplen >
416 interface->rbuf_len) {
417 interface->rbuf_offset = interface->rbuf_len;
421 /* Skip over the BPF header... */
422 interface->rbuf_offset += hdr.bh_hdrlen;
425 * If the captured data wasn't the whole packet, or if
426 * the packet won't fit in the input buffer, all we can
429 if (hdr.bh_caplen != hdr.bh_datalen) {
430 interface->rbuf_offset =
431 BPF_WORDALIGN(interface->rbuf_offset +
436 /* Decode the physical header... */
437 offset = decode_hw_header(interface->rbuf,
438 interface->rbuf_offset, hfrom);
441 * If a physical layer checksum failed (dunno of any
442 * physical layer that supports this, but WTH), skip
446 interface->rbuf_offset =
447 BPF_WORDALIGN(interface->rbuf_offset +
451 interface->rbuf_offset += offset;
452 hdr.bh_caplen -= offset;
454 /* Decode the IP and UDP headers... */
455 offset = decode_udp_ip_header(interface->rbuf,
456 interface->rbuf_offset, from, NULL, hdr.bh_caplen);
458 /* If the IP or UDP checksum was bad, skip the packet... */
460 interface->rbuf_offset =
461 BPF_WORDALIGN(interface->rbuf_offset +
465 interface->rbuf_offset += offset;
466 hdr.bh_caplen -= offset;
469 * If there's not enough room to stash the packet data,
470 * we have to skip it (this shouldn't happen in real
473 if (hdr.bh_caplen > len) {
474 interface->rbuf_offset =
475 BPF_WORDALIGN(interface->rbuf_offset +
480 /* Copy out the data in the packet... */
481 memcpy(buf, interface->rbuf + interface->rbuf_offset,
483 interface->rbuf_offset =
484 BPF_WORDALIGN(interface->rbuf_offset +
486 return (hdr.bh_caplen);