bpf_filter.c revision 1.24
1 /* $NetBSD: bpf_filter.c,v 1.24 2005/11/30 23:14:38 rpaulo 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 1.24 2005/11/30 23:14:38 rpaulo 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 while (1) { 172 ++pc; 173 switch (pc->code) { 174 175 default: 176 #ifdef _KERNEL 177 return 0; 178 #else 179 abort(); 180 #endif 181 case BPF_RET|BPF_K: 182 return (u_int)pc->k; 183 184 case BPF_RET|BPF_A: 185 return (u_int)A; 186 187 case BPF_LD|BPF_W|BPF_ABS: 188 k = pc->k; 189 if (k + sizeof(int32_t) > buflen) { 190 #ifdef _KERNEL 191 int merr; 192 193 if (buflen != 0) 194 return 0; 195 A = m_xword((struct mbuf *)p, k, &merr); 196 if (merr != 0) 197 return 0; 198 continue; 199 #else 200 return 0; 201 #endif 202 } 203 A = EXTRACT_LONG(&p[k]); 204 continue; 205 206 case BPF_LD|BPF_H|BPF_ABS: 207 k = pc->k; 208 if (k + sizeof(int16_t) > buflen) { 209 #ifdef _KERNEL 210 int merr; 211 212 if (buflen != 0) 213 return 0; 214 A = m_xhalf((struct mbuf *)p, k, &merr); 215 continue; 216 #else 217 return 0; 218 #endif 219 } 220 A = EXTRACT_SHORT(&p[k]); 221 continue; 222 223 case BPF_LD|BPF_B|BPF_ABS: 224 k = pc->k; 225 if (k >= buflen) { 226 #ifdef _KERNEL 227 struct mbuf *m; 228 int len; 229 230 if (buflen != 0) 231 return 0; 232 m = (struct mbuf *)p; 233 MINDEX(len, m, k); 234 A = mtod(m, u_char *)[k]; 235 continue; 236 #else 237 return 0; 238 #endif 239 } 240 A = p[k]; 241 continue; 242 243 case BPF_LD|BPF_W|BPF_LEN: 244 A = wirelen; 245 continue; 246 247 case BPF_LDX|BPF_W|BPF_LEN: 248 X = wirelen; 249 continue; 250 251 case BPF_LD|BPF_W|BPF_IND: 252 k = X + pc->k; 253 if (k + sizeof(int32_t) > buflen) { 254 #ifdef _KERNEL 255 int merr; 256 257 if (buflen != 0) 258 return 0; 259 A = m_xword((struct mbuf *)p, k, &merr); 260 if (merr != 0) 261 return 0; 262 continue; 263 #else 264 return 0; 265 #endif 266 } 267 A = EXTRACT_LONG(&p[k]); 268 continue; 269 270 case BPF_LD|BPF_H|BPF_IND: 271 k = X + pc->k; 272 if (k + sizeof(int16_t) > buflen) { 273 #ifdef _KERNEL 274 int merr; 275 276 if (buflen != 0) 277 return 0; 278 A = m_xhalf((struct mbuf *)p, k, &merr); 279 if (merr != 0) 280 return 0; 281 continue; 282 #else 283 return 0; 284 #endif 285 } 286 A = EXTRACT_SHORT(&p[k]); 287 continue; 288 289 case BPF_LD|BPF_B|BPF_IND: 290 k = X + pc->k; 291 if (k >= buflen) { 292 #ifdef _KERNEL 293 struct mbuf *m; 294 int len; 295 296 if (buflen != 0) 297 return 0; 298 m = (struct mbuf *)p; 299 MINDEX(len, m, k); 300 A = mtod(m, u_char *)[k]; 301 continue; 302 #else 303 return 0; 304 #endif 305 } 306 A = p[k]; 307 continue; 308 309 case BPF_LDX|BPF_MSH|BPF_B: 310 k = pc->k; 311 if (k >= buflen) { 312 #ifdef _KERNEL 313 struct mbuf *m; 314 int len; 315 316 if (buflen != 0) 317 return 0; 318 m = (struct mbuf *)p; 319 MINDEX(len, m, k); 320 X = (mtod(m, char *)[k] & 0xf) << 2; 321 continue; 322 #else 323 return 0; 324 #endif 325 } 326 X = (p[pc->k] & 0xf) << 2; 327 continue; 328 329 case BPF_LD|BPF_IMM: 330 A = pc->k; 331 continue; 332 333 case BPF_LDX|BPF_IMM: 334 X = pc->k; 335 continue; 336 337 case BPF_LD|BPF_MEM: 338 A = mem[pc->k]; 339 continue; 340 341 case BPF_LDX|BPF_MEM: 342 X = mem[pc->k]; 343 continue; 344 345 case BPF_ST: 346 mem[pc->k] = A; 347 continue; 348 349 case BPF_STX: 350 mem[pc->k] = X; 351 continue; 352 353 case BPF_JMP|BPF_JA: 354 pc += pc->k; 355 continue; 356 357 case BPF_JMP|BPF_JGT|BPF_K: 358 pc += (A > pc->k) ? pc->jt : pc->jf; 359 continue; 360 361 case BPF_JMP|BPF_JGE|BPF_K: 362 pc += (A >= pc->k) ? pc->jt : pc->jf; 363 continue; 364 365 case BPF_JMP|BPF_JEQ|BPF_K: 366 pc += (A == pc->k) ? pc->jt : pc->jf; 367 continue; 368 369 case BPF_JMP|BPF_JSET|BPF_K: 370 pc += (A & pc->k) ? pc->jt : pc->jf; 371 continue; 372 373 case BPF_JMP|BPF_JGT|BPF_X: 374 pc += (A > X) ? pc->jt : pc->jf; 375 continue; 376 377 case BPF_JMP|BPF_JGE|BPF_X: 378 pc += (A >= X) ? pc->jt : pc->jf; 379 continue; 380 381 case BPF_JMP|BPF_JEQ|BPF_X: 382 pc += (A == X) ? pc->jt : pc->jf; 383 continue; 384 385 case BPF_JMP|BPF_JSET|BPF_X: 386 pc += (A & X) ? pc->jt : pc->jf; 387 continue; 388 389 case BPF_ALU|BPF_ADD|BPF_X: 390 A += X; 391 continue; 392 393 case BPF_ALU|BPF_SUB|BPF_X: 394 A -= X; 395 continue; 396 397 case BPF_ALU|BPF_MUL|BPF_X: 398 A *= X; 399 continue; 400 401 case BPF_ALU|BPF_DIV|BPF_X: 402 if (X == 0) 403 return 0; 404 A /= X; 405 continue; 406 407 case BPF_ALU|BPF_AND|BPF_X: 408 A &= X; 409 continue; 410 411 case BPF_ALU|BPF_OR|BPF_X: 412 A |= X; 413 continue; 414 415 case BPF_ALU|BPF_LSH|BPF_X: 416 A <<= X; 417 continue; 418 419 case BPF_ALU|BPF_RSH|BPF_X: 420 A >>= X; 421 continue; 422 423 case BPF_ALU|BPF_ADD|BPF_K: 424 A += pc->k; 425 continue; 426 427 case BPF_ALU|BPF_SUB|BPF_K: 428 A -= pc->k; 429 continue; 430 431 case BPF_ALU|BPF_MUL|BPF_K: 432 A *= pc->k; 433 continue; 434 435 case BPF_ALU|BPF_DIV|BPF_K: 436 A /= pc->k; 437 continue; 438 439 case BPF_ALU|BPF_AND|BPF_K: 440 A &= pc->k; 441 continue; 442 443 case BPF_ALU|BPF_OR|BPF_K: 444 A |= pc->k; 445 continue; 446 447 case BPF_ALU|BPF_LSH|BPF_K: 448 A <<= pc->k; 449 continue; 450 451 case BPF_ALU|BPF_RSH|BPF_K: 452 A >>= pc->k; 453 continue; 454 455 case BPF_ALU|BPF_NEG: 456 A = -A; 457 continue; 458 459 case BPF_MISC|BPF_TAX: 460 X = A; 461 continue; 462 463 case BPF_MISC|BPF_TXA: 464 A = X; 465 continue; 466 } 467 } 468 } 469 470 #ifdef _KERNEL 471 /* 472 * Return true if the 'fcode' is a valid filter program. 473 * The constraints are that each jump be forward and to a valid 474 * code. The code must terminate with either an accept or reject. 475 * 'valid' is an array for use by the routine (it must be at least 476 * 'len' bytes long). 477 * 478 * The kernel needs to be able to verify an application's filter code. 479 * Otherwise, a bogus program could easily crash the system. 480 */ 481 int 482 bpf_validate(struct bpf_insn *f, int len) 483 { 484 u_int i, from; 485 struct bpf_insn *p; 486 487 488 if (len < 1 || len > BPF_MAXINSNS) 489 return 0; 490 491 for (i = 0; i < len; ++i) { 492 p = &f[i]; 493 switch (BPF_CLASS(p->code)) { 494 /* 495 * Check that memory operations use valid addresses. 496 */ 497 case BPF_LD: 498 case BPF_LDX: 499 switch (BPF_MODE(p->code)) { 500 case BPF_ABS: 501 case BPF_IND: 502 case BPF_MSH: 503 /* 504 * More strict check with actual packet length 505 * is done runtime. 506 */ 507 if (p->k >= bpf_maxbufsize) 508 return 0; 509 break; 510 case BPF_MEM: 511 if (p->k >= BPF_MEMWORDS) 512 return 0; 513 break; 514 case BPF_IMM: 515 case BPF_LEN: 516 break; 517 default: 518 return 0; 519 } 520 break; 521 case BPF_ST: 522 case BPF_STX: 523 if (p->k >= BPF_MEMWORDS) 524 return 0; 525 break; 526 case BPF_ALU: 527 switch (BPF_OP(p->code)) { 528 case BPF_ADD: 529 case BPF_SUB: 530 case BPF_OR: 531 case BPF_AND: 532 case BPF_LSH: 533 case BPF_RSH: 534 case BPF_NEG: 535 break; 536 case BPF_DIV: 537 /* 538 * Check for constant division by 0. 539 */ 540 if (BPF_RVAL(p->code) == BPF_K && p->k == 0) 541 return 0; 542 default: 543 return 0; 544 } 545 break; 546 case BPF_JMP: 547 /* 548 * Check that jumps are within the code block, 549 * and that unconditional branches don't go 550 * backwards as a result of an overflow. 551 * Unconditional branches have a 32-bit offset, 552 * so they could overflow; we check to make 553 * sure they don't. Conditional branches have 554 * an 8-bit offset, and the from address is <= 555 * BPF_MAXINSNS, and we assume that BPF_MAXINSNS 556 * is sufficiently small that adding 255 to it 557 * won't overflow. 558 * 559 * We know that len is <= BPF_MAXINSNS, and we 560 * assume that BPF_MAXINSNS is < the maximum size 561 * of a u_int, so that i + 1 doesn't overflow. 562 */ 563 from = i + 1; 564 switch (BPF_OP(p->code)) { 565 case BPF_JA: 566 if (from + p->k < from || from + p->k >= len) 567 return 0; 568 break; 569 case BPF_JEQ: 570 case BPF_JGT: 571 case BPF_JGE: 572 case BPF_JSET: 573 if (from + p->jt >= len || from + p->jf >= len) 574 return 0; 575 break; 576 default: 577 return 0; 578 } 579 break; 580 case BPF_RET: 581 break; 582 case BPF_MISC: 583 break; 584 default: 585 return 0; 586 } 587 } 588 589 return BPF_CLASS(f[len - 1].code) == BPF_RET; 590 } 591 #endif 592
Indexes created Tue Sep 30 07:10:03 GMT 2025