1 /* $OpenBSD: bpf.c,v 1.11 2016/05/28 07:00:18 natano 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 63 /* 64 * Called by get_interface_list for each interface that's discovered. 65 * Opens a packet filter for each interface and adds it to the select 66 * mask. 67 */ 68 int 69 if_register_bpf(struct interface_info *info) 70 { 71 int sock; 72 73 /* Open the BPF device */ 74 if ((sock = open("/dev/bpf0", O_RDWR)) == -1) 75 error("Can't open bpf device: %m"); 76 77 /* Set the BPF device to point at this interface. */ 78 if (ioctl(sock, BIOCSETIF, info->ifp) == -1) 79 error("Can't attach interface %s to bpf device: %m", 80 info->name); 81 82 return (sock); 83 } 84 85 void 86 if_register_send(struct interface_info *info) 87 { 88 /* 89 * If we're using the bpf API for sending and receiving, we 90 * don't need to register this interface twice. 91 */ 92 info->wfdesc = info->rfdesc; 93 } 94 95 /* 96 * Packet filter program: 'ip and udp and dst port SERVER_PORT' 97 */ 98 struct bpf_insn dhcp_bpf_filter[] = { 99 /* Make sure this is an IP packet... */ 100 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12), 101 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 8), 102 103 /* Make sure it's a UDP packet... */ 104 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23), 105 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6), 106 107 /* Make sure this isn't a fragment... */ 108 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20), 109 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0), 110 111 /* Get the IP header length... */ 112 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14), 113 114 /* Make sure it's to the right port... */ 115 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16), 116 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, SERVER_PORT, 0, 1), 117 118 /* If we passed all the tests, ask for the whole packet. */ 119 BPF_STMT(BPF_RET+BPF_K, (u_int)-1), 120 121 /* Otherwise, drop it. */ 122 BPF_STMT(BPF_RET+BPF_K, 0), 123 }; 124 125 int dhcp_bpf_filter_len = sizeof(dhcp_bpf_filter) / sizeof(struct bpf_insn); 126 127 /* 128 * Packet filter program: encapsulated 'ip and udp and dst port SERVER_PORT' 129 */ 130 struct bpf_insn dhcp_bpf_efilter[] = { 131 /* Make sure this is an encapsulated AF_INET packet... */ 132 BPF_STMT(BPF_LD + BPF_W + BPF_ABS, 0), 133 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, AF_INET << 24, 0, 10), 134 135 /* Make sure it's an IPIP packet... */ 136 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 21), 137 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_IPIP, 0, 8), 138 139 /* Make sure it's an encapsulated UDP packet... */ 140 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 41), 141 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6), 142 143 /* Make sure this isn't a fragment... */ 144 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 38), 145 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0), 146 147 /* Get the IP header length... */ 148 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 32), 149 150 /* Make sure it's to the right port... */ 151 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 34), 152 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, SERVER_PORT, 0, 1), 153 154 /* If we passed all the tests, ask for the whole packet. */ 155 BPF_STMT(BPF_RET+BPF_K, (u_int)-1), 156 157 /* Otherwise, drop it. */ 158 BPF_STMT(BPF_RET+BPF_K, 0), 159 }; 160 161 int dhcp_bpf_efilter_len = sizeof(dhcp_bpf_efilter) / sizeof(struct bpf_insn); 162 163 /* 164 * Packet write filter program: 'ip and udp and src port SERVER_PORT' 165 */ 166 struct bpf_insn dhcp_bpf_wfilter[] = { 167 /* Make sure this is an IP packet... */ 168 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12), 169 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 8), 170 171 /* Make sure it's a UDP packet... */ 172 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23), 173 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6), 174 175 /* Make sure this isn't a fragment... */ 176 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20), 177 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0), 178 179 /* Get the IP header length... */ 180 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14), 181 182 /* Make sure it's from the right port... */ 183 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 14), 184 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, SERVER_PORT, 0, 1), 185 186 /* If we passed all the tests, ask for the whole packet. */ 187 BPF_STMT(BPF_RET+BPF_K, (u_int)-1), 188 189 /* Otherwise, drop it. */ 190 BPF_STMT(BPF_RET+BPF_K, 0), 191 }; 192 193 int dhcp_bpf_wfilter_len = sizeof(dhcp_bpf_wfilter) / sizeof(struct bpf_insn); 194 195 void 196 if_register_receive(struct interface_info *info) 197 { 198 struct bpf_version v; 199 struct bpf_program p; 200 int flag = 1, sz, cmplt = 0; 201 202 /* Open a BPF device and hang it on this interface... */ 203 info->rfdesc = if_register_bpf(info); 204 205 /* Make sure the BPF version is in range... */ 206 if (ioctl(info->rfdesc, BIOCVERSION, &v) == -1) 207 error("Can't get BPF version: %m"); 208 209 if (v.bv_major != BPF_MAJOR_VERSION || 210 v.bv_minor < BPF_MINOR_VERSION) 211 error("Kernel BPF version out of range - recompile dhcpd!"); 212 213 /* 214 * Set immediate mode so that reads return as soon as a packet 215 * comes in, rather than waiting for the input buffer to fill 216 * with packets. 217 */ 218 if (ioctl(info->rfdesc, BIOCIMMEDIATE, &flag) == -1) 219 error("Can't set immediate mode on bpf device: %m"); 220 221 /* make sure kernel fills in the source ethernet address */ 222 if (ioctl(info->rfdesc, BIOCSHDRCMPLT, &cmplt) == -1) 223 error("Can't set header complete flag on bpf device: %m"); 224 225 /* Get the required BPF buffer length from the kernel. */ 226 if (ioctl(info->rfdesc, BIOCGBLEN, &sz) == -1) 227 error("Can't get bpf buffer length: %m"); 228 info->rbuf_max = sz; 229 info->rbuf = malloc(info->rbuf_max); 230 if (!info->rbuf) 231 error("Can't allocate %lu bytes for bpf input buffer.", 232 (unsigned long)info->rbuf_max); 233 info->rbuf_offset = 0; 234 info->rbuf_len = 0; 235 236 /* Set up the bpf filter program structure. */ 237 if (info->hw_address.htype == HTYPE_IPSEC_TUNNEL) { 238 p.bf_len = dhcp_bpf_efilter_len; 239 p.bf_insns = dhcp_bpf_efilter; 240 } else { 241 p.bf_len = dhcp_bpf_filter_len; 242 p.bf_insns = dhcp_bpf_filter; 243 } 244 if (ioctl(info->rfdesc, BIOCSETF, &p) == -1) 245 error("Can't install packet filter program: %m"); 246 247 /* Set up the bpf write filter program structure. */ 248 p.bf_len = dhcp_bpf_wfilter_len; 249 p.bf_insns = dhcp_bpf_wfilter; 250 251 if (ioctl(info->rfdesc, BIOCSETWF, &p) == -1) 252 error("Can't install write filter program: %m"); 253 254 /* make sure these settings cannot be changed after dropping privs */ 255 if (ioctl(info->rfdesc, BIOCLOCK) == -1) 256 error("Failed to lock bpf descriptor: %m"); 257 } 258 259 ssize_t 260 send_packet(struct interface_info *interface, 261 struct dhcp_packet *raw, size_t len, struct in_addr from, 262 struct sockaddr_in *to, struct hardware *hto) 263 { 264 unsigned char buf[256]; 265 struct iovec iov[2]; 266 int result, bufp = 0; 267 268 if (interface->hw_address.htype == HTYPE_IPSEC_TUNNEL) { 269 socklen_t slen = sizeof(*to); 270 result = sendto(server_fd, raw, len, 0, 271 (struct sockaddr *)to, slen); 272 goto done; 273 } 274 275 /* Assemble the headers... */ 276 assemble_hw_header(interface, buf, &bufp, hto); 277 assemble_udp_ip_header(interface, buf, &bufp, from.s_addr, 278 to->sin_addr.s_addr, to->sin_port, (unsigned char *)raw, len); 279 280 /* Fire it off */ 281 iov[0].iov_base = (char *)buf; 282 iov[0].iov_len = bufp; 283 iov[1].iov_base = (char *)raw; 284 iov[1].iov_len = len; 285 286 result = writev(interface->wfdesc, iov, 2); 287 done: 288 if (result == -1) 289 warning("send_packet: %m"); 290 return (result); 291 } 292 293 ssize_t 294 receive_packet(struct interface_info *interface, unsigned char *buf, 295 size_t len, struct sockaddr_in *from, struct hardware *hfrom) 296 { 297 int length = 0, offset = 0; 298 struct bpf_hdr hdr; 299 300 /* 301 * All this complexity is because BPF doesn't guarantee that 302 * only one packet will be returned at a time. We're getting 303 * what we deserve, though - this is a terrible abuse of the BPF 304 * interface. Sigh. 305 */ 306 307 /* Process packets until we get one we can return or until we've 308 * done a read and gotten nothing we can return... 309 */ 310 do { 311 /* If the buffer is empty, fill it. */ 312 if (interface->rbuf_offset == interface->rbuf_len) { 313 length = read(interface->rfdesc, interface->rbuf, 314 interface->rbuf_max); 315 if (length <= 0) 316 return (length); 317 interface->rbuf_offset = 0; 318 interface->rbuf_len = length; 319 } 320 321 /* 322 * If there isn't room for a whole bpf header, something 323 * went wrong, but we'll ignore it and hope it goes 324 * away... XXX 325 */ 326 if (interface->rbuf_len - interface->rbuf_offset < 327 sizeof(hdr)) { 328 interface->rbuf_offset = interface->rbuf_len; 329 continue; 330 } 331 332 /* Copy out a bpf header... */ 333 memcpy(&hdr, &interface->rbuf[interface->rbuf_offset], 334 sizeof(hdr)); 335 336 /* 337 * If the bpf header plus data doesn't fit in what's 338 * left of the buffer, stick head in sand yet again... 339 */ 340 if (interface->rbuf_offset + hdr.bh_hdrlen + hdr.bh_caplen > 341 interface->rbuf_len) { 342 interface->rbuf_offset = interface->rbuf_len; 343 continue; 344 } 345 346 /* 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 349 * do is drop it. 350 */ 351 if (hdr.bh_caplen != hdr.bh_datalen) { 352 interface->rbuf_offset += hdr.bh_hdrlen = hdr.bh_caplen; 353 continue; 354 } 355 356 /* Skip over the BPF header... */ 357 interface->rbuf_offset += hdr.bh_hdrlen; 358 359 /* Decode the physical header... */ 360 offset = decode_hw_header(interface, 361 interface->rbuf, interface->rbuf_offset, hfrom); 362 363 /* 364 * If a physical layer checksum failed (dunno of any 365 * physical layer that supports this, but WTH), skip 366 * this packet. 367 */ 368 if (offset < 0) { 369 interface->rbuf_offset += hdr.bh_caplen; 370 continue; 371 } 372 interface->rbuf_offset += offset; 373 hdr.bh_caplen -= offset; 374 375 /* Decode the IP and UDP headers... */ 376 offset = decode_udp_ip_header(interface, interface->rbuf, 377 interface->rbuf_offset, from, hdr.bh_caplen); 378 379 /* If the IP or UDP checksum was bad, skip the packet... */ 380 if (offset < 0) { 381 interface->rbuf_offset += hdr.bh_caplen; 382 continue; 383 } 384 interface->rbuf_offset += offset; 385 hdr.bh_caplen -= offset; 386 387 /* 388 * If there's not enough room to stash the packet data, 389 * we have to skip it (this shouldn't happen in real 390 * life, though). 391 */ 392 if (hdr.bh_caplen > len) { 393 interface->rbuf_offset += hdr.bh_caplen; 394 continue; 395 } 396 397 /* Copy out the data in the packet... */ 398 memcpy(buf, interface->rbuf + interface->rbuf_offset, 399 hdr.bh_caplen); 400 interface->rbuf_offset += hdr.bh_caplen; 401 return (hdr.bh_caplen); 402 } while (!length); 403 return (0); 404 } 405