bpf_filter.c revision 1.28.2.2
1 /* $NetBSD: bpf_filter.c,v 1.28.2.2 2006/03/01 09:28:47 yamt Exp $ */ 2 3 /*- 4 * Copyright (c) 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997 5 * The Regents of the University of California. All rights reserved. 6 * 7 * This code is derived from the Stanford/CMU enet packet filter, 8 * (net/enet.c) distributed as part of 4.3BSD, and code contributed 9 * to Berkeley by Steven McCanne and Van Jacobson both of Lawrence 10 * Berkeley Laboratory. 11 * 12 * Redistribution and use in source and binary forms, with or without 13 * modification, are permitted provided that the following conditions 14 * are met: 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 University nor the names of its contributors 21 * may be used to endorse or promote products derived from this software 22 * without specific prior written permission. 23 * 24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 27 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 34 * SUCH DAMAGE. 35 * 36 * @(#)bpf_filter.c 8.1 (Berkeley) 6/10/93 37 */ 38 39 #include <sys/cdefs.h> 40 __KERNEL_RCSID(0, "$NetBSD: bpf_filter.c,v 1.28.2.2 2006/03/01 09:28:47 yamt Exp $"); 41 42 #if 0 43 #if !(defined(lint) || defined(KERNEL)) 44 static const char rcsid[] = 45 "@(#) Header: bpf_filter.c,v 1.33 97/04/26 13:37:18 leres Exp (LBL)"; 46 #endif 47 #endif 48 49 #include <sys/param.h> 50 #include <sys/time.h> 51 52 #if !defined(UNALIGNED_ACCESS) 53 #define BPF_ALIGN 54 #endif 55 56 #ifndef BPF_ALIGN 57 #define EXTRACT_SHORT(p) ((uint16_t)ntohs(*(uint16_t *)p)) 58 #define EXTRACT_LONG(p) (ntohl(*(uint32_t *)p)) 59 #else 60 #define EXTRACT_SHORT(p) \ 61 ((uint16_t) \ 62 ((uint16_t)*((u_char *)p+0)<<8| \ 63 (uint16_t)*((u_char *)p+1)<<0)) 64 #define EXTRACT_LONG(p) \ 65 ((uint32_t)*((u_char *)p+0)<<24|\ 66 (uint32_t)*((u_char *)p+1)<<16|\ 67 (uint32_t)*((u_char *)p+2)<<8| \ 68 (uint32_t)*((u_char *)p+3)<<0) 69 #endif 70 71 #ifdef _KERNEL 72 #include <sys/mbuf.h> 73 #define MINDEX(len, m, k) \ 74 { \ 75 len = m->m_len; \ 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_xword (struct mbuf *, uint32_t, int *); 86 static int m_xhalf (struct mbuf *, uint32_t, int *); 87 88 static int 89 m_xword(struct mbuf *m, uint32_t k, int *err) 90 { 91 int len; 92 u_char *cp, *np; 93 struct mbuf *m0; 94 95 MINDEX(len, m, k); 96 cp = mtod(m, u_char *) + k; 97 if (len >= k + 4) { 98 *err = 0; 99 return EXTRACT_LONG(cp); 100 } 101 m0 = m->m_next; 102 if (m0 == 0 || m0->m_len + len - k < 4) 103 goto bad; 104 *err = 0; 105 np = mtod(m0, u_char *); 106 switch (len - k) { 107 108 case 1: 109 return (cp[0] << 24) | (np[0] << 16) | (np[1] << 8) | np[2]; 110 111 case 2: 112 return (cp[0] << 24) | (cp[1] << 16) | (np[0] << 8) | np[1]; 113 114 default: 115 return (cp[0] << 24) | (cp[1] << 16) | (cp[2] << 8) | np[0]; 116 } 117 bad: 118 *err = 1; 119 120 return 0; 121 } 122 123 static int 124 m_xhalf(struct mbuf *m, uint32_t k, int *err) 125 { 126 int len; 127 u_char *cp; 128 struct mbuf *m0; 129 130 MINDEX(len, m, k); 131 cp = mtod(m, u_char *) + k; 132 if (len >= k + 2) { 133 *err = 0; 134 return EXTRACT_SHORT(cp); 135 } 136 m0 = m->m_next; 137 if (m0 == 0) 138 goto bad; 139 *err = 0; 140 return (cp[0] << 8) | mtod(m0, u_char *)[0]; 141 bad: 142 *err = 1; 143 144 return 0; 145 } 146 #else /* _KERNEL */ 147 #include <stdlib.h> 148 #endif /* !_KERNEL */ 149 150 #include <net/bpf.h> 151 152 /* 153 * Execute the filter program starting at pc on the packet p 154 * wirelen is the length of the original packet 155 * buflen is the amount of data present 156 */ 157 u_int 158 bpf_filter(struct bpf_insn *pc, u_char *p, u_int wirelen, u_int buflen) 159 { 160 uint32_t A, X, k; 161 int32_t mem[BPF_MEMWORDS]; 162 163 if (pc == 0) 164 /* 165 * No filter means accept all. 166 */ 167 return (u_int)-1; 168 A = 0; 169 X = 0; 170 --pc; 171 /* CONSTCOND */ 172 while (1) { 173 ++pc; 174 switch (pc->code) { 175 176 default: 177 #ifdef _KERNEL 178 return 0; 179 #else 180 abort(); 181 #endif 182 case BPF_RET|BPF_K: 183 return (u_int)pc->k; 184 185 case BPF_RET|BPF_A: 186 return (u_int)A; 187 188 case BPF_LD|BPF_W|BPF_ABS: 189 k = pc->k; 190 if (k + sizeof(int32_t) > buflen) { 191 #ifdef _KERNEL 192 int merr; 193 194 if (buflen != 0) 195 return 0; 196 A = m_xword((struct mbuf *)p, k, &merr); 197 if (merr != 0) 198 return 0; 199 continue; 200 #else 201 return 0; 202 #endif 203 } 204 A = EXTRACT_LONG(&p[k]); 205 continue; 206 207 case BPF_LD|BPF_H|BPF_ABS: 208 k = pc->k; 209 if (k + sizeof(int16_t) > buflen) { 210 #ifdef _KERNEL 211 int merr; 212 213 if (buflen != 0) 214 return 0; 215 A = m_xhalf((struct mbuf *)p, k, &merr); 216 continue; 217 #else 218 return 0; 219 #endif 220 } 221 A = EXTRACT_SHORT(&p[k]); 222 continue; 223 224 case BPF_LD|BPF_B|BPF_ABS: 225 k = pc->k; 226 if (k >= buflen) { 227 #ifdef _KERNEL 228 struct mbuf *m; 229 int len; 230 231 if (buflen != 0) 232 return 0; 233 m = (struct mbuf *)p; 234 MINDEX(len, m, k); 235 A = mtod(m, u_char *)[k]; 236 continue; 237 #else 238 return 0; 239 #endif 240 } 241 A = p[k]; 242 continue; 243 244 case BPF_LD|BPF_W|BPF_LEN: 245 A = wirelen; 246 continue; 247 248 case BPF_LDX|BPF_W|BPF_LEN: 249 X = wirelen; 250 continue; 251 252 case BPF_LD|BPF_W|BPF_IND: 253 k = X + pc->k; 254 if (k + sizeof(int32_t) > buflen) { 255 #ifdef _KERNEL 256 int merr; 257 258 if (buflen != 0) 259 return 0; 260 A = m_xword((struct mbuf *)p, k, &merr); 261 if (merr != 0) 262 return 0; 263 continue; 264 #else 265 return 0; 266 #endif 267 } 268 A = EXTRACT_LONG(&p[k]); 269 continue; 270 271 case BPF_LD|BPF_H|BPF_IND: 272 k = X + pc->k; 273 if (k + sizeof(int16_t) > buflen) { 274 #ifdef _KERNEL 275 int merr; 276 277 if (buflen != 0) 278 return 0; 279 A = m_xhalf((struct mbuf *)p, k, &merr); 280 if (merr != 0) 281 return 0; 282 continue; 283 #else 284 return 0; 285 #endif 286 } 287 A = EXTRACT_SHORT(&p[k]); 288 continue; 289 290 case BPF_LD|BPF_B|BPF_IND: 291 k = X + pc->k; 292 if (k >= buflen) { 293 #ifdef _KERNEL 294 struct mbuf *m; 295 int len; 296 297 if (buflen != 0) 298 return 0; 299 m = (struct mbuf *)p; 300 MINDEX(len, m, k); 301 A = mtod(m, u_char *)[k]; 302 continue; 303 #else 304 return 0; 305 #endif 306 } 307 A = p[k]; 308 continue; 309 310 case BPF_LDX|BPF_MSH|BPF_B: 311 k = pc->k; 312 if (k >= buflen) { 313 #ifdef _KERNEL 314 struct mbuf *m; 315 int len; 316 317 if (buflen != 0) 318 return 0; 319 m = (struct mbuf *)p; 320 MINDEX(len, m, k); 321 X = (mtod(m, char *)[k] & 0xf) << 2; 322 continue; 323 #else 324 return 0; 325 #endif 326 } 327 X = (p[pc->k] & 0xf) << 2; 328 continue; 329 330 case BPF_LD|BPF_IMM: 331 A = pc->k; 332 continue; 333 334 case BPF_LDX|BPF_IMM: 335 X = pc->k; 336 continue; 337 338 case BPF_LD|BPF_MEM: 339 A = mem[pc->k]; 340 continue; 341 342 case BPF_LDX|BPF_MEM: 343 X = mem[pc->k]; 344 continue; 345 346 case BPF_ST: 347 mem[pc->k] = A; 348 continue; 349 350 case BPF_STX: 351 mem[pc->k] = X; 352 continue; 353 354 case BPF_JMP|BPF_JA: 355 pc += pc->k; 356 continue; 357 358 case BPF_JMP|BPF_JGT|BPF_K: 359 pc += (A > pc->k) ? pc->jt : pc->jf; 360 continue; 361 362 case BPF_JMP|BPF_JGE|BPF_K: 363 pc += (A >= pc->k) ? pc->jt : pc->jf; 364 continue; 365 366 case BPF_JMP|BPF_JEQ|BPF_K: 367 pc += (A == pc->k) ? pc->jt : pc->jf; 368 continue; 369 370 case BPF_JMP|BPF_JSET|BPF_K: 371 pc += (A & pc->k) ? pc->jt : pc->jf; 372 continue; 373 374 case BPF_JMP|BPF_JGT|BPF_X: 375 pc += (A > X) ? pc->jt : pc->jf; 376 continue; 377 378 case BPF_JMP|BPF_JGE|BPF_X: 379 pc += (A >= X) ? pc->jt : pc->jf; 380 continue; 381 382 case BPF_JMP|BPF_JEQ|BPF_X: 383 pc += (A == X) ? pc->jt : pc->jf; 384 continue; 385 386 case BPF_JMP|BPF_JSET|BPF_X: 387 pc += (A & X) ? pc->jt : pc->jf; 388 continue; 389 390 case BPF_ALU|BPF_ADD|BPF_X: 391 A += X; 392 continue; 393 394 case BPF_ALU|BPF_SUB|BPF_X: 395 A -= X; 396 continue; 397 398 case BPF_ALU|BPF_MUL|BPF_X: 399 A *= X; 400 continue; 401 402 case BPF_ALU|BPF_DIV|BPF_X: 403 if (X == 0) 404 return 0; 405 A /= X; 406 continue; 407 408 case BPF_ALU|BPF_AND|BPF_X: 409 A &= X; 410 continue; 411 412 case BPF_ALU|BPF_OR|BPF_X: 413 A |= X; 414 continue; 415 416 case BPF_ALU|BPF_LSH|BPF_X: 417 A <<= X; 418 continue; 419 420 case BPF_ALU|BPF_RSH|BPF_X: 421 A >>= X; 422 continue; 423 424 case BPF_ALU|BPF_ADD|BPF_K: 425 A += pc->k; 426 continue; 427 428 case BPF_ALU|BPF_SUB|BPF_K: 429 A -= pc->k; 430 continue; 431 432 case BPF_ALU|BPF_MUL|BPF_K: 433 A *= pc->k; 434 continue; 435 436 case BPF_ALU|BPF_DIV|BPF_K: 437 A /= pc->k; 438 continue; 439 440 case BPF_ALU|BPF_AND|BPF_K: 441 A &= pc->k; 442 continue; 443 444 case BPF_ALU|BPF_OR|BPF_K: 445 A |= pc->k; 446 continue; 447 448 case BPF_ALU|BPF_LSH|BPF_K: 449 A <<= pc->k; 450 continue; 451 452 case BPF_ALU|BPF_RSH|BPF_K: 453 A >>= pc->k; 454 continue; 455 456 case BPF_ALU|BPF_NEG: 457 A = -A; 458 continue; 459 460 case BPF_MISC|BPF_TAX: 461 X = A; 462 continue; 463 464 case BPF_MISC|BPF_TXA: 465 A = X; 466 continue; 467 } 468 } 469 } 470 471 #ifdef _KERNEL 472 /* 473 * Return true if the 'fcode' is a valid filter program. 474 * The constraints are that each jump be forward and to a valid 475 * code. The code must terminate with either an accept or reject. 476 * 'valid' is an array for use by the routine (it must be at least 477 * 'len' bytes long). 478 * 479 * The kernel needs to be able to verify an application's filter code. 480 * Otherwise, a bogus program could easily crash the system. 481 */ 482 int 483 bpf_validate(struct bpf_insn *f, int len) 484 { 485 u_int i, from; 486 struct bpf_insn *p; 487 488 489 if (len < 1 || len > BPF_MAXINSNS) 490 return 0; 491 492 for (i = 0; i < len; ++i) { 493 p = &f[i]; 494 switch (BPF_CLASS(p->code)) { 495 /* 496 * Check that memory operations use valid addresses. 497 */ 498 case BPF_LD: 499 case BPF_LDX: 500 switch (BPF_MODE(p->code)) { 501 case BPF_MEM: 502 if (p->k >= BPF_MEMWORDS) 503 return 0; 504 break; 505 case BPF_ABS: 506 case BPF_IND: 507 case BPF_MSH: 508 case BPF_IMM: 509 case BPF_LEN: 510 break; 511 default: 512 return 0; 513 } 514 break; 515 case BPF_ST: 516 case BPF_STX: 517 if (p->k >= BPF_MEMWORDS) 518 return 0; 519 break; 520 case BPF_ALU: 521 switch (BPF_OP(p->code)) { 522 case BPF_ADD: 523 case BPF_SUB: 524 case BPF_OR: 525 case BPF_AND: 526 case BPF_LSH: 527 case BPF_RSH: 528 case BPF_NEG: 529 break; 530 case BPF_DIV: 531 /* 532 * Check for constant division by 0. 533 */ 534 if (BPF_RVAL(p->code) == BPF_K && p->k == 0) 535 return 0; 536 break; 537 default: 538 return 0; 539 } 540 break; 541 case BPF_JMP: 542 /* 543 * Check that jumps are within the code block, 544 * and that unconditional branches don't go 545 * backwards as a result of an overflow. 546 * Unconditional branches have a 32-bit offset, 547 * so they could overflow; we check to make 548 * sure they don't. Conditional branches have 549 * an 8-bit offset, and the from address is <= 550 * BPF_MAXINSNS, and we assume that BPF_MAXINSNS 551 * is sufficiently small that adding 255 to it 552 * won't overflow. 553 * 554 * We know that len is <= BPF_MAXINSNS, and we 555 * assume that BPF_MAXINSNS is < the maximum size 556 * of a u_int, so that i + 1 doesn't overflow. 557 */ 558 from = i + 1; 559 switch (BPF_OP(p->code)) { 560 case BPF_JA: 561 if (from + p->k < from || from + p->k >= len) 562 return 0; 563 break; 564 case BPF_JEQ: 565 case BPF_JGT: 566 case BPF_JGE: 567 case BPF_JSET: 568 if (from + p->jt >= len || from + p->jf >= len) 569 return 0; 570 break; 571 default: 572 return 0; 573 } 574 break; 575 case BPF_RET: 576 break; 577 case BPF_MISC: 578 break; 579 default: 580 return 0; 581 } 582 } 583 584 return BPF_CLASS(f[len - 1].code) == BPF_RET; 585 } 586 #endif 587
Indexes created Tue Sep 30 06:09:59 GMT 2025