Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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FreeBSD/Linux Kernel Cross Reference
sys/net/bpf_filter.c
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1 /* 2 * Copyright (c) 1990, 1991, 1993 3 * The Regents of the University of California. All rights reserved. 4 * 5 * This code is derived from the Stanford/CMU enet packet filter, 6 * (net/enet.c) distributed as part of 4.3BSD, and code contributed 7 * to Berkeley by Steven McCanne and Van Jacobson both of Lawrence 8 * Berkeley Laboratory. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 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. All advertising materials mentioning features or use of this software 19 * must display the following acknowledgement: 20 * This product includes software developed by the University of 21 * California, Berkeley and its contributors. 22 * 4. Neither the name of the University nor the names of its contributors 23 * may be used to endorse or promote products derived from this software 24 * without specific prior written permission. 25 * 26 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 27 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 28 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 29 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 30 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 31 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 32 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 33 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 34 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 35 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 36 * SUCH DAMAGE. 37 * 38 * @(#)bpf_filter.c 8.1 (Berkeley) 6/10/93 39 * 40 * $FreeBSD: src/sys/net/bpf_filter.c,v 1.6.4.1 1999/09/05 08:17:28 peter Exp $ 41 */ 42 43 #include <sys/param.h> 44 #include <sys/types.h> 45 #include <sys/time.h> 46 47 #ifdef sun 48 #include <netinet/in.h> 49 #endif 50 51 #if defined(sparc) || defined(mips) || defined(ibm032) 52 #define BPF_ALIGN 53 #endif 54 55 #ifndef BPF_ALIGN 56 #define EXTRACT_SHORT(p) ((u_short)ntohs(*(u_short *)p)) 57 #define EXTRACT_LONG(p) (ntohl(*(u_long *)p)) 58 #else 59 #define EXTRACT_SHORT(p)\ 60 ((u_short)\ 61 ((u_short)*((u_char *)p+0)<<8|\ 62 (u_short)*((u_char *)p+1)<<0)) 63 #define EXTRACT_LONG(p)\ 64 ((u_long)*((u_char *)p+0)<<24|\ 65 (u_long)*((u_char *)p+1)<<16|\ 66 (u_long)*((u_char *)p+2)<<8|\ 67 (u_long)*((u_char *)p+3)<<0) 68 #endif 69 70 #ifdef KERNEL 71 #include <sys/mbuf.h> 72 #define MINDEX(m, k) \ 73 { \ 74 register int len = m->m_len; \ 75 \ 76 while (k >= len) { \ 77 k -= len; \ 78 m = m->m_next; \ 79 if (m == 0) \ 80 return 0; \ 81 len = m->m_len; \ 82 } \ 83 } 84 85 static int m_xhalf __P((struct mbuf *m, int k, int *err)); 86 static int m_xword __P((struct mbuf *m, int k, int *err)); 87 88 static int 89 m_xword(m, k, err) 90 register struct mbuf *m; 91 register int k, *err; 92 { 93 register int len; 94 register u_char *cp, *np; 95 register struct mbuf *m0; 96 97 len = m->m_len; 98 while (k >= len) { 99 k -= len; 100 m = m->m_next; 101 if (m == 0) 102 goto bad; 103 len = m->m_len; 104 } 105 cp = mtod(m, u_char *) + k; 106 if (len - k >= 4) { 107 *err = 0; 108 return EXTRACT_LONG(cp); 109 } 110 m0 = m->m_next; 111 if (m0 == 0 || m0->m_len + len - k < 4) 112 goto bad; 113 *err = 0; 114 np = mtod(m0, u_char *); 115 switch (len - k) { 116 117 case 1: 118 return (cp[0] << 24) | (np[0] << 16) | (np[1] << 8) | np[2]; 119 120 case 2: 121 return (cp[0] << 24) | (cp[1] << 16) | (np[0] << 8) | 122 np[1]; 123 124 default: 125 return (cp[0] << 24) | (cp[1] << 16) | (cp[2] << 8) | 126 np[0]; 127 } 128 bad: 129 *err = 1; 130 return 0; 131 } 132 133 static int 134 m_xhalf(m, k, err) 135 register struct mbuf *m; 136 register int k, *err; 137 { 138 register int len; 139 register u_char *cp; 140 register struct mbuf *m0; 141 142 len = m->m_len; 143 while (k >= len) { 144 k -= len; 145 m = m->m_next; 146 if (m == 0) 147 goto bad; 148 len = m->m_len; 149 } 150 cp = mtod(m, u_char *) + k; 151 if (len - k >= 2) { 152 *err = 0; 153 return EXTRACT_SHORT(cp); 154 } 155 m0 = m->m_next; 156 if (m0 == 0) 157 goto bad; 158 *err = 0; 159 return (cp[0] << 8) | mtod(m0, u_char *)[0]; 160 bad: 161 *err = 1; 162 return 0; 163 } 164 #endif 165 166 #include <net/bpf.h> 167 /* 168 * Execute the filter program starting at pc on the packet p 169 * wirelen is the length of the original packet 170 * buflen is the amount of data present 171 */ 172 u_int 173 bpf_filter(pc, p, wirelen, buflen) 174 register struct bpf_insn *pc; 175 register u_char *p; 176 u_int wirelen; 177 register u_int buflen; 178 { 179 register u_long A = 0, X = 0; 180 register int k; 181 long mem[BPF_MEMWORDS]; 182 183 if (pc == 0) 184 /* 185 * No filter means accept all. 186 */ 187 return (u_int)-1; 188 189 --pc; 190 while (1) { 191 ++pc; 192 switch (pc->code) { 193 194 default: 195 #ifdef KERNEL 196 return 0; 197 #else 198 abort(); 199 #endif 200 case BPF_RET|BPF_K: 201 return (u_int)pc->k; 202 203 case BPF_RET|BPF_A: 204 return (u_int)A; 205 206 case BPF_LD|BPF_W|BPF_ABS: 207 k = pc->k; 208 if (k + sizeof(long) > buflen) { 209 #ifdef KERNEL 210 int merr; 211 212 if (buflen != 0) 213 return 0; 214 A = m_xword((struct mbuf *)p, k, &merr); 215 if (merr != 0) 216 return 0; 217 continue; 218 #else 219 return 0; 220 #endif 221 } 222 #ifdef BPF_ALIGN 223 if (((int)(p + k) & 3) != 0) 224 A = EXTRACT_LONG(&p[k]); 225 else 226 #endif 227 A = ntohl(*(long *)(p + k)); 228 continue; 229 230 case BPF_LD|BPF_H|BPF_ABS: 231 k = pc->k; 232 if (k + sizeof(short) > buflen) { 233 #ifdef KERNEL 234 int merr; 235 236 if (buflen != 0) 237 return 0; 238 A = m_xhalf((struct mbuf *)p, k, &merr); 239 continue; 240 #else 241 return 0; 242 #endif 243 } 244 A = EXTRACT_SHORT(&p[k]); 245 continue; 246 247 case BPF_LD|BPF_B|BPF_ABS: 248 k = pc->k; 249 if (k >= buflen) { 250 #ifdef KERNEL 251 register struct mbuf *m; 252 253 if (buflen != 0) 254 return 0; 255 m = (struct mbuf *)p; 256 MINDEX(m, k); 257 A = mtod(m, u_char *)[k]; 258 continue; 259 #else 260 return 0; 261 #endif 262 } 263 A = p[k]; 264 continue; 265 266 case BPF_LD|BPF_W|BPF_LEN: 267 A = wirelen; 268 continue; 269 270 case BPF_LDX|BPF_W|BPF_LEN: 271 X = wirelen; 272 continue; 273 274 case BPF_LD|BPF_W|BPF_IND: 275 k = X + pc->k; 276 if (k + sizeof(long) > buflen) { 277 #ifdef KERNEL 278 int merr; 279 280 if (buflen != 0) 281 return 0; 282 A = m_xword((struct mbuf *)p, k, &merr); 283 if (merr != 0) 284 return 0; 285 continue; 286 #else 287 return 0; 288 #endif 289 } 290 #ifdef BPF_ALIGN 291 if (((int)(p + k) & 3) != 0) 292 A = EXTRACT_LONG(&p[k]); 293 else 294 #endif 295 A = ntohl(*(long *)(p + k)); 296 continue; 297 298 case BPF_LD|BPF_H|BPF_IND: 299 k = X + pc->k; 300 if (k + sizeof(short) > buflen) { 301 #ifdef KERNEL 302 int merr; 303 304 if (buflen != 0) 305 return 0; 306 A = m_xhalf((struct mbuf *)p, k, &merr); 307 if (merr != 0) 308 return 0; 309 continue; 310 #else 311 return 0; 312 #endif 313 } 314 A = EXTRACT_SHORT(&p[k]); 315 continue; 316 317 case BPF_LD|BPF_B|BPF_IND: 318 k = X + pc->k; 319 if (k >= buflen) { 320 #ifdef KERNEL 321 register struct mbuf *m; 322 323 if (buflen != 0) 324 return 0; 325 m = (struct mbuf *)p; 326 MINDEX(m, k); 327 A = mtod(m, char *)[k]; 328 continue; 329 #else 330 return 0; 331 #endif 332 } 333 A = p[k]; 334 continue; 335 336 case BPF_LDX|BPF_MSH|BPF_B: 337 k = pc->k; 338 if (k >= buflen) { 339 #ifdef KERNEL 340 register struct mbuf *m; 341 342 if (buflen != 0) 343 return 0; 344 m = (struct mbuf *)p; 345 MINDEX(m, k); 346 X = (mtod(m, char *)[k] & 0xf) << 2; 347 continue; 348 #else 349 return 0; 350 #endif 351 } 352 X = (p[pc->k] & 0xf) << 2; 353 continue; 354 355 case BPF_LD|BPF_IMM: 356 A = pc->k; 357 continue; 358 359 case BPF_LDX|BPF_IMM: 360 X = pc->k; 361 continue; 362 363 case BPF_LD|BPF_MEM: 364 A = mem[pc->k]; 365 continue; 366 367 case BPF_LDX|BPF_MEM: 368 X = mem[pc->k]; 369 continue; 370 371 case BPF_ST: 372 mem[pc->k] = A; 373 continue; 374 375 case BPF_STX: 376 mem[pc->k] = X; 377 continue; 378 379 case BPF_JMP|BPF_JA: 380 pc += pc->k; 381 continue; 382 383 case BPF_JMP|BPF_JGT|BPF_K: 384 pc += (A > pc->k) ? pc->jt : pc->jf; 385 continue; 386 387 case BPF_JMP|BPF_JGE|BPF_K: 388 pc += (A >= pc->k) ? pc->jt : pc->jf; 389 continue; 390 391 case BPF_JMP|BPF_JEQ|BPF_K: 392 pc += (A == pc->k) ? pc->jt : pc->jf; 393 continue; 394 395 case BPF_JMP|BPF_JSET|BPF_K: 396 pc += (A & pc->k) ? pc->jt : pc->jf; 397 continue; 398 399 case BPF_JMP|BPF_JGT|BPF_X: 400 pc += (A > X) ? pc->jt : pc->jf; 401 continue; 402 403 case BPF_JMP|BPF_JGE|BPF_X: 404 pc += (A >= X) ? pc->jt : pc->jf; 405 continue; 406 407 case BPF_JMP|BPF_JEQ|BPF_X: 408 pc += (A == X) ? pc->jt : pc->jf; 409 continue; 410 411 case BPF_JMP|BPF_JSET|BPF_X: 412 pc += (A & X) ? pc->jt : pc->jf; 413 continue; 414 415 case BPF_ALU|BPF_ADD|BPF_X: 416 A += X; 417 continue; 418 419 case BPF_ALU|BPF_SUB|BPF_X: 420 A -= X; 421 continue; 422 423 case BPF_ALU|BPF_MUL|BPF_X: 424 A *= X; 425 continue; 426 427 case BPF_ALU|BPF_DIV|BPF_X: 428 if (X == 0) 429 return 0; 430 A /= X; 431 continue; 432 433 case BPF_ALU|BPF_AND|BPF_X: 434 A &= X; 435 continue; 436 437 case BPF_ALU|BPF_OR|BPF_X: 438 A |= X; 439 continue; 440 441 case BPF_ALU|BPF_LSH|BPF_X: 442 A <<= X; 443 continue; 444 445 case BPF_ALU|BPF_RSH|BPF_X: 446 A >>= X; 447 continue; 448 449 case BPF_ALU|BPF_ADD|BPF_K: 450 A += pc->k; 451 continue; 452 453 case BPF_ALU|BPF_SUB|BPF_K: 454 A -= pc->k; 455 continue; 456 457 case BPF_ALU|BPF_MUL|BPF_K: 458 A *= pc->k; 459 continue; 460 461 case BPF_ALU|BPF_DIV|BPF_K: 462 A /= pc->k; 463 continue; 464 465 case BPF_ALU|BPF_AND|BPF_K: 466 A &= pc->k; 467 continue; 468 469 case BPF_ALU|BPF_OR|BPF_K: 470 A |= pc->k; 471 continue; 472 473 case BPF_ALU|BPF_LSH|BPF_K: 474 A <<= pc->k; 475 continue; 476 477 case BPF_ALU|BPF_RSH|BPF_K: 478 A >>= pc->k; 479 continue; 480 481 case BPF_ALU|BPF_NEG: 482 A = -A; 483 continue; 484 485 case BPF_MISC|BPF_TAX: 486 X = A; 487 continue; 488 489 case BPF_MISC|BPF_TXA: 490 A = X; 491 continue; 492 } 493 } 494 } 495 496 #ifdef KERNEL 497 /* 498 * Return true if the 'fcode' is a valid filter program. 499 * The constraints are that each jump be forward and to a valid 500 * code. The code must terminate with either an accept or reject. 501 * 'valid' is an array for use by the routine (it must be at least 502 * 'len' bytes long). 503 * 504 * The kernel needs to be able to verify an application's filter code. 505 * Otherwise, a bogus program could easily crash the system. 506 */ 507 int 508 bpf_validate(f, len) 509 struct bpf_insn *f; 510 int len; 511 { 512 register int i; 513 register struct bpf_insn *p; 514 515 for (i = 0; i < len; ++i) { 516 /* 517 * Check that that jumps are forward, and within 518 * the code block. 519 */ 520 p = &f[i]; 521 if (BPF_CLASS(p->code) == BPF_JMP) { 522 register int from = i + 1; 523 524 if (BPF_OP(p->code) == BPF_JA) { 525 if (from + p->k >= len) 526 return 0; 527 } 528 else if (from + p->jt >= len || from + p->jf >= len) 529 return 0; 530 } 531 /* 532 * Check that memory operations use valid addresses. 533 */ 534 if ((BPF_CLASS(p->code) == BPF_ST || 535 (BPF_CLASS(p->code) == BPF_LD && 536 (p->code & 0xe0) == BPF_MEM)) && 537 (p->k >= BPF_MEMWORDS || p->k < 0)) 538 return 0; 539 /* 540 * Check for constant division by 0. 541 */ 542 if (p->code == (BPF_ALU|BPF_DIV|BPF_K) && p->k == 0) 543 return 0; 544 } 545 return BPF_CLASS(f[len - 1].code) == BPF_RET; 546 } 547 #endif
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