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 * Copyright (c) 1995, 1996, 1998, 1999
7 * The Internet Software Consortium. All rights reserved.
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22 * THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND
23 * CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
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33 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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''.
43 #include <sys/cdefs.h>
44 __FBSDID("$FreeBSD$");
47 #include <sys/ioctl.h>
51 #include <netinet/in_systm.h>
52 #include <netinet/ip.h>
53 #include <netinet/udp.h>
54 #include <netinet/if_ether.h>
56 #define BPF_FORMAT "/dev/bpf%d"
59 * Called by get_interface_list for each interface that's discovered.
60 * Opens a packet filter for each interface and adds it to the select
64 if_register_bpf(struct interface_info *info)
69 /* Open a BPF device */
71 snprintf(filename, sizeof(filename), BPF_FORMAT, b);
72 sock = open(filename, O_RDWR, 0);
77 error("Can't find free bpf: %m");
82 /* Set the BPF device to point at this interface. */
83 if (ioctl(sock, BIOCSETIF, info->ifp) < 0)
84 error("Can't attach interface %s to bpf device %s: %m",
85 info->name, filename);
91 if_register_send(struct interface_info *info)
96 * If we're using the bpf API for sending and receiving, we
97 * don't need to register this interface twice.
99 info->wfdesc = info->rfdesc;
102 * Use raw socket for unicast send.
104 if ((sock = socket(AF_INET, SOCK_RAW, IPPROTO_UDP)) == -1)
105 error("socket(SOCK_RAW): %m");
106 if (setsockopt(sock, IPPROTO_IP, IP_HDRINCL, &on,
108 error("setsockopt(IP_HDRINCL): %m");
113 * Packet filter program...
115 * XXX: Changes to the filter program may require changes to the
116 * constant offsets used in if_register_send to patch the BPF program!
118 struct bpf_insn dhcp_bpf_filter[] = {
119 /* Make sure this is an IP packet... */
120 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
121 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 8),
123 /* Make sure it's a UDP packet... */
124 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23),
125 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6),
127 /* Make sure this isn't a fragment... */
128 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
129 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0),
131 /* Get the IP header length... */
132 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
134 /* Make sure it's to the right port... */
135 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16),
136 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 67, 0, 1), /* patch */
138 /* If we passed all the tests, ask for the whole packet. */
139 BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
141 /* Otherwise, drop it. */
142 BPF_STMT(BPF_RET+BPF_K, 0),
145 int dhcp_bpf_filter_len = sizeof(dhcp_bpf_filter) / sizeof(struct bpf_insn);
148 * Packet write filter program:
149 * 'ip and udp and src port bootps and dst port (bootps or bootpc)'
151 struct bpf_insn dhcp_bpf_wfilter[] = {
152 BPF_STMT(BPF_LD + BPF_B + BPF_IND, 14),
153 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, (IPVERSION << 4) + 5, 0, 12),
155 /* Make sure this is an IP packet... */
156 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
157 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 10),
159 /* Make sure it's a UDP packet... */
160 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23),
161 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 8),
163 /* Make sure this isn't a fragment... */
164 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
165 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 6, 0), /* patched */
167 /* Get the IP header length... */
168 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
170 /* Make sure it's from the right port... */
171 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 14),
172 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 68, 0, 3),
174 /* Make sure it is to the right ports ... */
175 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16),
176 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 67, 0, 1),
178 /* If we passed all the tests, ask for the whole packet. */
179 BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
181 /* Otherwise, drop it. */
182 BPF_STMT(BPF_RET+BPF_K, 0),
185 int dhcp_bpf_wfilter_len = sizeof(dhcp_bpf_wfilter) / sizeof(struct bpf_insn);
188 if_register_receive(struct interface_info *info)
190 struct bpf_version v;
191 struct bpf_program p;
194 /* Open a BPF device and hang it on this interface... */
195 info->rfdesc = if_register_bpf(info);
197 /* Make sure the BPF version is in range... */
198 if (ioctl(info->rfdesc, BIOCVERSION, &v) < 0)
199 error("Can't get BPF version: %m");
201 if (v.bv_major != BPF_MAJOR_VERSION ||
202 v.bv_minor < BPF_MINOR_VERSION)
203 error("Kernel BPF version out of range - recompile dhcpd!");
206 * Set immediate mode so that reads return as soon as a packet
207 * comes in, rather than waiting for the input buffer to fill
210 if (ioctl(info->rfdesc, BIOCIMMEDIATE, &flag) < 0)
211 error("Can't set immediate mode on bpf device: %m");
213 /* Get the required BPF buffer length from the kernel. */
214 if (ioctl(info->rfdesc, BIOCGBLEN, &sz) < 0)
215 error("Can't get bpf buffer length: %m");
217 info->rbuf = malloc(info->rbuf_max);
219 error("Can't allocate %lu bytes for bpf input buffer.",
220 (unsigned long)info->rbuf_max);
221 info->rbuf_offset = 0;
224 /* Set up the bpf filter program structure. */
225 p.bf_len = dhcp_bpf_filter_len;
226 p.bf_insns = dhcp_bpf_filter;
228 /* Patch the server port into the BPF program...
230 * XXX: changes to filter program may require changes to the
231 * insn number(s) used below!
233 dhcp_bpf_filter[8].k = LOCAL_PORT;
235 if (ioctl(info->rfdesc, BIOCSETF, &p) < 0)
236 error("Can't install packet filter program: %m");
238 /* Set up the bpf write filter program structure. */
239 p.bf_len = dhcp_bpf_wfilter_len;
240 p.bf_insns = dhcp_bpf_wfilter;
242 if (dhcp_bpf_wfilter[7].k == 0x1fff)
243 dhcp_bpf_wfilter[7].k = htons(IP_MF|IP_OFFMASK);
245 if (ioctl(info->rfdesc, BIOCSETWF, &p) < 0)
246 error("Can't install write filter program: %m");
248 if (ioctl(info->rfdesc, BIOCLOCK, NULL) < 0)
249 error("Cannot lock bpf");
253 send_packet(struct interface_info *interface, struct dhcp_packet *raw,
254 size_t len, struct in_addr from, struct sockaddr_in *to,
255 struct hardware *hto)
257 unsigned char buf[256];
260 int result, bufp = 0;
262 /* Assemble the headers... */
263 if (to->sin_addr.s_addr == INADDR_BROADCAST)
264 assemble_hw_header(interface, buf, &bufp, hto);
265 assemble_udp_ip_header(buf, &bufp, from.s_addr,
266 to->sin_addr.s_addr, to->sin_port, (unsigned char *)raw, len);
268 iov[0].iov_base = (char *)buf;
269 iov[0].iov_len = bufp;
270 iov[1].iov_base = (char *)raw;
271 iov[1].iov_len = len;
274 if (to->sin_addr.s_addr == INADDR_BROADCAST)
275 result = writev(interface->wfdesc, iov, 2);
277 memset(&msg, 0, sizeof(msg));
278 msg.msg_name = (struct sockaddr *)to;
279 msg.msg_namelen = sizeof(*to);
282 result = sendmsg(interface->ufdesc, &msg, 0);
286 warning("send_packet: %m");
291 receive_packet(struct interface_info *interface, unsigned char *buf,
292 size_t len, struct sockaddr_in *from, struct hardware *hfrom)
294 int length = 0, offset = 0;
298 * All this complexity is because BPF doesn't guarantee that
299 * only one packet will be returned at a time. We're getting
300 * what we deserve, though - this is a terrible abuse of the BPF
304 /* Process packets until we get one we can return or until we've
305 * done a read and gotten nothing we can return...
308 /* If the buffer is empty, fill it. */
309 if (interface->rbuf_offset >= interface->rbuf_len) {
310 length = read(interface->rfdesc, interface->rbuf,
311 interface->rbuf_max);
314 interface->rbuf_offset = 0;
315 interface->rbuf_len = length;
319 * If there isn't room for a whole bpf header, something
320 * went wrong, but we'll ignore it and hope it goes
323 if (interface->rbuf_len - interface->rbuf_offset <
325 interface->rbuf_offset = interface->rbuf_len;
329 /* Copy out a bpf header... */
330 memcpy(&hdr, &interface->rbuf[interface->rbuf_offset],
334 * If the bpf header plus data doesn't fit in what's
335 * left of the buffer, stick head in sand yet again...
337 if (interface->rbuf_offset + hdr.bh_hdrlen + hdr.bh_caplen >
338 interface->rbuf_len) {
339 interface->rbuf_offset = interface->rbuf_len;
343 /* Skip over the BPF header... */
344 interface->rbuf_offset += hdr.bh_hdrlen;
347 * If the captured data wasn't the whole packet, or if
348 * the packet won't fit in the input buffer, all we can
351 if (hdr.bh_caplen != hdr.bh_datalen) {
352 interface->rbuf_offset =
353 BPF_WORDALIGN(interface->rbuf_offset +
358 /* Decode the physical header... */
359 offset = decode_hw_header(interface->rbuf,
360 interface->rbuf_offset, hfrom);
363 * If a physical layer checksum failed (dunno of any
364 * physical layer that supports this, but WTH), skip
368 interface->rbuf_offset =
369 BPF_WORDALIGN(interface->rbuf_offset +
373 interface->rbuf_offset += offset;
374 hdr.bh_caplen -= offset;
376 /* Decode the IP and UDP headers... */
377 offset = decode_udp_ip_header(interface->rbuf,
378 interface->rbuf_offset, from, NULL, hdr.bh_caplen);
380 /* If the IP or UDP checksum was bad, skip the packet... */
382 interface->rbuf_offset =
383 BPF_WORDALIGN(interface->rbuf_offset +
387 interface->rbuf_offset += offset;
388 hdr.bh_caplen -= offset;
391 * If there's not enough room to stash the packet data,
392 * we have to skip it (this shouldn't happen in real
395 if (hdr.bh_caplen > len) {
396 interface->rbuf_offset =
397 BPF_WORDALIGN(interface->rbuf_offset +
402 /* Copy out the data in the packet... */
403 memcpy(buf, interface->rbuf + interface->rbuf_offset,
405 interface->rbuf_offset =
406 BPF_WORDALIGN(interface->rbuf_offset +
408 return (hdr.bh_caplen);