bpf_filter.c revision 1.65
1 /* $NetBSD: bpf_filter.c,v 1.65 2014/06/25 09:51:34 alnsn 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 1.65 2014/06/25 09:51:34 alnsn 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 #include <sys/kmem.h> 52 #include <sys/endian.h> 53 54 #define __BPF_PRIVATE 55 #include <net/bpf.h> 56 57 #ifdef _KERNEL 58 59 bpf_ctx_t * 60 bpf_create(void) 61 { 62 return kmem_zalloc(sizeof(bpf_ctx_t), KM_SLEEP); 63 } 64 65 void 66 bpf_destroy(bpf_ctx_t *bc) 67 { 68 kmem_free(bc, sizeof(bpf_ctx_t)); 69 } 70 71 int 72 bpf_set_cop(bpf_ctx_t *bc, const bpf_copfunc_t *funcs, size_t n) 73 { 74 bc->copfuncs = funcs; 75 bc->nfuncs = n; 76 return 0; 77 } 78 79 int 80 bpf_set_extmem(bpf_ctx_t *bc, size_t nwords, bpf_memword_init_t preinited) 81 { 82 if (nwords > BPF_MAX_MEMWORDS || (preinited >> nwords) != 0) { 83 return EINVAL; 84 } 85 bc->extwords = nwords; 86 bc->preinited = preinited; 87 return 0; 88 } 89 90 #endif 91 92 #define EXTRACT_SHORT(p) be16dec(p) 93 #define EXTRACT_LONG(p) be32dec(p) 94 95 #ifdef _KERNEL 96 #include <sys/mbuf.h> 97 #define MINDEX(len, m, k) \ 98 { \ 99 len = m->m_len; \ 100 while (k >= len) { \ 101 k -= len; \ 102 m = m->m_next; \ 103 if (m == 0) \ 104 return 0; \ 105 len = m->m_len; \ 106 } \ 107 } 108 109 uint32_t m_xword(const struct mbuf *, uint32_t, int *); 110 uint32_t m_xhalf(const struct mbuf *, uint32_t, int *); 111 uint32_t m_xbyte(const struct mbuf *, uint32_t, int *); 112 113 #define xword(p, k, err) m_xword((const struct mbuf *)(p), (k), (err)) 114 #define xhalf(p, k, err) m_xhalf((const struct mbuf *)(p), (k), (err)) 115 #define xbyte(p, k, err) m_xbyte((const struct mbuf *)(p), (k), (err)) 116 117 uint32_t 118 m_xword(const struct mbuf *m, uint32_t k, int *err) 119 { 120 int len; 121 u_char *cp, *np; 122 struct mbuf *m0; 123 124 *err = 1; 125 MINDEX(len, m, k); 126 cp = mtod(m, u_char *) + k; 127 if (len >= k + 4) { 128 *err = 0; 129 return EXTRACT_LONG(cp); 130 } 131 m0 = m->m_next; 132 if (m0 == 0 || m0->m_len + len - k < 4) 133 return 0; 134 *err = 0; 135 np = mtod(m0, u_char *); 136 137 switch (len - k) { 138 case 1: 139 return (cp[0] << 24) | (np[0] << 16) | (np[1] << 8) | np[2]; 140 case 2: 141 return (cp[0] << 24) | (cp[1] << 16) | (np[0] << 8) | np[1]; 142 default: 143 return (cp[0] << 24) | (cp[1] << 16) | (cp[2] << 8) | np[0]; 144 } 145 } 146 147 uint32_t 148 m_xhalf(const struct mbuf *m, uint32_t k, int *err) 149 { 150 int len; 151 u_char *cp; 152 struct mbuf *m0; 153 154 *err = 1; 155 MINDEX(len, m, k); 156 cp = mtod(m, u_char *) + k; 157 if (len >= k + 2) { 158 *err = 0; 159 return EXTRACT_SHORT(cp); 160 } 161 m0 = m->m_next; 162 if (m0 == 0) 163 return 0; 164 *err = 0; 165 return (cp[0] << 8) | mtod(m0, u_char *)[0]; 166 } 167 168 uint32_t 169 m_xbyte(const struct mbuf *m, uint32_t k, int *err) 170 { 171 int len; 172 173 *err = 0; 174 MINDEX(len, m, k); 175 return mtod(m, u_char *)[k]; 176 } 177 #else /* _KERNEL */ 178 #include <stdlib.h> 179 #endif /* !_KERNEL */ 180 181 #include <net/bpf.h> 182 183 /* 184 * Execute the filter program starting at pc on the packet p 185 * wirelen is the length of the original packet 186 * buflen is the amount of data present 187 */ 188 #ifdef _KERNEL 189 190 u_int 191 bpf_filter(const struct bpf_insn *pc, const u_char *p, u_int wirelen, 192 u_int buflen) 193 { 194 uint32_t mem[BPF_MEMWORDS]; 195 bpf_args_t args = { 196 .pkt = p, 197 .wirelen = wirelen, 198 .buflen = buflen, 199 .mem = mem, 200 .arg = NULL 201 }; 202 203 return bpf_filter_ext(NULL, pc, &args); 204 } 205 206 u_int 207 bpf_filter_ext(const bpf_ctx_t *bc, const struct bpf_insn *pc, bpf_args_t *args) 208 #else 209 u_int 210 bpf_filter(const struct bpf_insn *pc, const u_char *p, u_int wirelen, 211 u_int buflen) 212 #endif 213 { 214 uint32_t A, X, k; 215 #ifndef _KERNEL 216 uint32_t mem[BPF_MEMWORDS]; 217 bpf_args_t args_store = { 218 .pkt = p, 219 .wirelen = wirelen, 220 .buflen = buflen, 221 .mem = mem, 222 .arg = NULL 223 }; 224 bpf_args_t * const args = &args_store; 225 #else 226 const uint8_t * const p = args->pkt; 227 #endif 228 if (pc == 0) { 229 /* 230 * No filter means accept all. 231 */ 232 return (u_int)-1; 233 } 234 235 /* 236 * Note: safe to leave memwords uninitialised, as the validation 237 * step ensures that it will not be read, if it was not written. 238 */ 239 A = 0; 240 X = 0; 241 --pc; 242 243 for (;;) { 244 ++pc; 245 switch (pc->code) { 246 247 default: 248 #ifdef _KERNEL 249 return 0; 250 #else 251 abort(); 252 /*NOTREACHED*/ 253 #endif 254 case BPF_RET|BPF_K: 255 return (u_int)pc->k; 256 257 case BPF_RET|BPF_A: 258 return (u_int)A; 259 260 case BPF_LD|BPF_W|BPF_ABS: 261 k = pc->k; 262 if (k > args->buflen || 263 sizeof(int32_t) > args->buflen - k) { 264 #ifdef _KERNEL 265 int merr; 266 267 if (args->buflen != 0) 268 return 0; 269 A = xword(args->pkt, k, &merr); 270 if (merr != 0) 271 return 0; 272 continue; 273 #else 274 return 0; 275 #endif 276 } 277 A = EXTRACT_LONG(&p[k]); 278 continue; 279 280 case BPF_LD|BPF_H|BPF_ABS: 281 k = pc->k; 282 if (k > args->buflen || 283 sizeof(int16_t) > args->buflen - k) { 284 #ifdef _KERNEL 285 int merr; 286 287 if (args->buflen != 0) 288 return 0; 289 A = xhalf(args->pkt, k, &merr); 290 if (merr != 0) 291 return 0; 292 continue; 293 #else 294 return 0; 295 #endif 296 } 297 A = EXTRACT_SHORT(&p[k]); 298 continue; 299 300 case BPF_LD|BPF_B|BPF_ABS: 301 k = pc->k; 302 if (k >= args->buflen) { 303 #ifdef _KERNEL 304 int merr; 305 306 if (args->buflen != 0) 307 return 0; 308 A = xbyte(args->pkt, k, &merr); 309 continue; 310 #else 311 return 0; 312 #endif 313 } 314 A = p[k]; 315 continue; 316 317 case BPF_LD|BPF_W|BPF_LEN: 318 A = args->wirelen; 319 continue; 320 321 case BPF_LDX|BPF_W|BPF_LEN: 322 X = args->wirelen; 323 continue; 324 325 case BPF_LD|BPF_W|BPF_IND: 326 k = X + pc->k; 327 if (pc->k > args->buflen || 328 X > args->buflen - pc->k || 329 sizeof(int32_t) > args->buflen - k) { 330 #ifdef _KERNEL 331 int merr; 332 333 if (args->buflen != 0) 334 return 0; 335 A = xword(args->pkt, k, &merr); 336 if (merr != 0) 337 return 0; 338 continue; 339 #else 340 return 0; 341 #endif 342 } 343 A = EXTRACT_LONG(&p[k]); 344 continue; 345 346 case BPF_LD|BPF_H|BPF_IND: 347 k = X + pc->k; 348 if (pc->k > args->buflen || 349 X > args->buflen - pc->k || 350 sizeof(int16_t) > args->buflen - k) { 351 #ifdef _KERNEL 352 int merr; 353 354 if (args->buflen != 0) 355 return 0; 356 A = xhalf(args->pkt, k, &merr); 357 if (merr != 0) 358 return 0; 359 continue; 360 #else 361 return 0; 362 #endif 363 } 364 A = EXTRACT_SHORT(&p[k]); 365 continue; 366 367 case BPF_LD|BPF_B|BPF_IND: 368 k = X + pc->k; 369 if (pc->k >= args->buflen || 370 X >= args->buflen - pc->k) { 371 #ifdef _KERNEL 372 int merr; 373 374 if (args->buflen != 0) 375 return 0; 376 A = xbyte(args->pkt, k, &merr); 377 continue; 378 #else 379 return 0; 380 #endif 381 } 382 A = p[k]; 383 continue; 384 385 case BPF_LDX|BPF_MSH|BPF_B: 386 k = pc->k; 387 if (k >= args->buflen) { 388 #ifdef _KERNEL 389 int merr; 390 391 if (args->buflen != 0) 392 return 0; 393 X = (xbyte(args->pkt, k, &merr) & 0xf) << 2; 394 continue; 395 #else 396 return 0; 397 #endif 398 } 399 X = (p[pc->k] & 0xf) << 2; 400 continue; 401 402 case BPF_LD|BPF_IMM: 403 A = pc->k; 404 continue; 405 406 case BPF_LDX|BPF_IMM: 407 X = pc->k; 408 continue; 409 410 case BPF_LD|BPF_MEM: 411 A = args->mem[pc->k]; 412 continue; 413 414 case BPF_LDX|BPF_MEM: 415 X = args->mem[pc->k]; 416 continue; 417 418 case BPF_ST: 419 args->mem[pc->k] = A; 420 continue; 421 422 case BPF_STX: 423 args->mem[pc->k] = X; 424 continue; 425 426 case BPF_JMP|BPF_JA: 427 pc += pc->k; 428 continue; 429 430 case BPF_JMP|BPF_JGT|BPF_K: 431 pc += (A > pc->k) ? pc->jt : pc->jf; 432 continue; 433 434 case BPF_JMP|BPF_JGE|BPF_K: 435 pc += (A >= pc->k) ? pc->jt : pc->jf; 436 continue; 437 438 case BPF_JMP|BPF_JEQ|BPF_K: 439 pc += (A == pc->k) ? pc->jt : pc->jf; 440 continue; 441 442 case BPF_JMP|BPF_JSET|BPF_K: 443 pc += (A & pc->k) ? pc->jt : pc->jf; 444 continue; 445 446 case BPF_JMP|BPF_JGT|BPF_X: 447 pc += (A > X) ? pc->jt : pc->jf; 448 continue; 449 450 case BPF_JMP|BPF_JGE|BPF_X: 451 pc += (A >= X) ? pc->jt : pc->jf; 452 continue; 453 454 case BPF_JMP|BPF_JEQ|BPF_X: 455 pc += (A == X) ? pc->jt : pc->jf; 456 continue; 457 458 case BPF_JMP|BPF_JSET|BPF_X: 459 pc += (A & X) ? pc->jt : pc->jf; 460 continue; 461 462 case BPF_ALU|BPF_ADD|BPF_X: 463 A += X; 464 continue; 465 466 case BPF_ALU|BPF_SUB|BPF_X: 467 A -= X; 468 continue; 469 470 case BPF_ALU|BPF_MUL|BPF_X: 471 A *= X; 472 continue; 473 474 case BPF_ALU|BPF_DIV|BPF_X: 475 if (X == 0) 476 return 0; 477 A /= X; 478 continue; 479 480 case BPF_ALU|BPF_AND|BPF_X: 481 A &= X; 482 continue; 483 484 case BPF_ALU|BPF_OR|BPF_X: 485 A |= X; 486 continue; 487 488 case BPF_ALU|BPF_LSH|BPF_X: 489 A <<= X; 490 continue; 491 492 case BPF_ALU|BPF_RSH|BPF_X: 493 A >>= X; 494 continue; 495 496 case BPF_ALU|BPF_ADD|BPF_K: 497 A += pc->k; 498 continue; 499 500 case BPF_ALU|BPF_SUB|BPF_K: 501 A -= pc->k; 502 continue; 503 504 case BPF_ALU|BPF_MUL|BPF_K: 505 A *= pc->k; 506 continue; 507 508 case BPF_ALU|BPF_DIV|BPF_K: 509 A /= pc->k; 510 continue; 511 512 case BPF_ALU|BPF_AND|BPF_K: 513 A &= pc->k; 514 continue; 515 516 case BPF_ALU|BPF_OR|BPF_K: 517 A |= pc->k; 518 continue; 519 520 case BPF_ALU|BPF_LSH|BPF_K: 521 A <<= pc->k; 522 continue; 523 524 case BPF_ALU|BPF_RSH|BPF_K: 525 A >>= pc->k; 526 continue; 527 528 case BPF_ALU|BPF_NEG: 529 A = -A; 530 continue; 531 532 case BPF_MISC|BPF_TAX: 533 X = A; 534 continue; 535 536 case BPF_MISC|BPF_TXA: 537 A = X; 538 continue; 539 540 case BPF_MISC|BPF_COP: 541 #ifdef _KERNEL 542 if (pc->k < bc->nfuncs) { 543 const bpf_copfunc_t fn = bc->copfuncs[pc->k]; 544 A = fn(bc, args, A); 545 continue; 546 } 547 #endif 548 return 0; 549 550 case BPF_MISC|BPF_COPX: 551 #ifdef _KERNEL 552 if (X < bc->nfuncs) { 553 const bpf_copfunc_t fn = bc->copfuncs[X]; 554 A = fn(bc, args, A); 555 continue; 556 } 557 #endif 558 return 0; 559 } 560 } 561 } 562 563 /* 564 * Return true if the 'fcode' is a valid filter program. 565 * The constraints are that each jump be forward and to a valid 566 * code, that memory accesses are within valid ranges (to the 567 * extent that this can be checked statically; loads of packet 568 * data have to be, and are, also checked at run time), and that 569 * the code terminates with either an accept or reject. 570 * 571 * The kernel needs to be able to verify an application's filter code. 572 * Otherwise, a bogus program could easily crash the system. 573 */ 574 575 #if defined(KERNEL) || defined(_KERNEL) 576 577 int 578 bpf_validate(const struct bpf_insn *f, int signed_len) 579 { 580 return bpf_validate_ext(NULL, f, signed_len); 581 } 582 583 int 584 bpf_validate_ext(const bpf_ctx_t *bc, const struct bpf_insn *f, int signed_len) 585 #else 586 int 587 bpf_validate(const struct bpf_insn *f, int signed_len) 588 #endif 589 { 590 u_int i, from, len, ok = 0; 591 const struct bpf_insn *p; 592 #if defined(KERNEL) || defined(_KERNEL) 593 bpf_memword_init_t *mem, invalid; 594 size_t size; 595 const size_t extwords = bc ? bc->extwords : 0; 596 const size_t memwords = extwords ? extwords : BPF_MEMWORDS; 597 const bpf_memword_init_t preinited = extwords ? bc->preinited : 0; 598 #else 599 const size_t memwords = BPF_MEMWORDS; 600 #endif 601 602 len = (u_int)signed_len; 603 if (len < 1) 604 return 0; 605 #if defined(KERNEL) || defined(_KERNEL) 606 if (len > BPF_MAXINSNS) 607 return 0; 608 #endif 609 if (BPF_CLASS(f[len - 1].code) != BPF_RET) 610 return 0; 611 612 #if defined(KERNEL) || defined(_KERNEL) 613 /* Note: only the pre-initialised is valid on startup */ 614 mem = kmem_zalloc(size = sizeof(*mem) * len, KM_SLEEP); 615 invalid = ~preinited; 616 #endif 617 618 for (i = 0; i < len; ++i) { 619 #if defined(KERNEL) || defined(_KERNEL) 620 /* blend in any invalid bits for current pc */ 621 invalid |= mem[i]; 622 #endif 623 p = &f[i]; 624 switch (BPF_CLASS(p->code)) { 625 /* 626 * Check that memory operations use valid addresses. 627 */ 628 case BPF_LD: 629 case BPF_LDX: 630 switch (BPF_MODE(p->code)) { 631 case BPF_MEM: 632 /* 633 * There's no maximum packet data size 634 * in userland. The runtime packet length 635 * check suffices. 636 */ 637 #if defined(KERNEL) || defined(_KERNEL) 638 /* 639 * More strict check with actual packet length 640 * is done runtime. 641 */ 642 if (p->k >= memwords) 643 goto out; 644 /* check for current memory invalid */ 645 if (invalid & BPF_MEMWORD_INIT(p->k)) 646 goto out; 647 #endif 648 break; 649 case BPF_ABS: 650 case BPF_IND: 651 case BPF_MSH: 652 case BPF_IMM: 653 case BPF_LEN: 654 break; 655 default: 656 goto out; 657 } 658 break; 659 case BPF_ST: 660 case BPF_STX: 661 if (p->k >= memwords) 662 goto out; 663 #if defined(KERNEL) || defined(_KERNEL) 664 /* validate the memory word */ 665 invalid &= ~BPF_MEMWORD_INIT(p->k); 666 #endif 667 break; 668 case BPF_ALU: 669 switch (BPF_OP(p->code)) { 670 case BPF_ADD: 671 case BPF_SUB: 672 case BPF_MUL: 673 case BPF_OR: 674 case BPF_AND: 675 case BPF_LSH: 676 case BPF_RSH: 677 case BPF_NEG: 678 break; 679 case BPF_DIV: 680 /* 681 * Check for constant division by 0. 682 */ 683 if (BPF_SRC(p->code) == BPF_K && p->k == 0) 684 goto out; 685 break; 686 default: 687 goto out; 688 } 689 break; 690 case BPF_JMP: 691 /* 692 * Check that jumps are within the code block, 693 * and that unconditional branches don't go 694 * backwards as a result of an overflow. 695 * Unconditional branches have a 32-bit offset, 696 * so they could overflow; we check to make 697 * sure they don't. Conditional branches have 698 * an 8-bit offset, and the from address is <= 699 * BPF_MAXINSNS, and we assume that BPF_MAXINSNS 700 * is sufficiently small that adding 255 to it 701 * won't overflow. 702 * 703 * We know that len is <= BPF_MAXINSNS, and we 704 * assume that BPF_MAXINSNS is < the maximum size 705 * of a u_int, so that i + 1 doesn't overflow. 706 * 707 * For userland, we don't know that the from 708 * or len are <= BPF_MAXINSNS, but we know that 709 * from <= len, and, except on a 64-bit system, 710 * it's unlikely that len, if it truly reflects 711 * the size of the program we've been handed, 712 * will be anywhere near the maximum size of 713 * a u_int. We also don't check for backward 714 * branches, as we currently support them in 715 * userland for the protochain operation. 716 */ 717 from = i + 1; 718 switch (BPF_OP(p->code)) { 719 case BPF_JA: 720 if (from + p->k >= len) 721 goto out; 722 #if defined(KERNEL) || defined(_KERNEL) 723 if (from + p->k < from) 724 goto out; 725 /* 726 * mark the currently invalid bits for the 727 * destination 728 */ 729 mem[from + p->k] |= invalid; 730 invalid = 0; 731 #endif 732 break; 733 case BPF_JEQ: 734 case BPF_JGT: 735 case BPF_JGE: 736 case BPF_JSET: 737 if (from + p->jt >= len || from + p->jf >= len) 738 goto out; 739 #if defined(KERNEL) || defined(_KERNEL) 740 /* 741 * mark the currently invalid bits for both 742 * possible jump destinations 743 */ 744 mem[from + p->jt] |= invalid; 745 mem[from + p->jf] |= invalid; 746 invalid = 0; 747 #endif 748 break; 749 default: 750 goto out; 751 } 752 break; 753 case BPF_RET: 754 break; 755 case BPF_MISC: 756 switch (BPF_MISCOP(p->code)) { 757 case BPF_COP: 758 case BPF_COPX: 759 /* In-kernel COP use only. */ 760 #if defined(KERNEL) || defined(_KERNEL) 761 if (bc == NULL || bc->copfuncs == NULL) 762 goto out; 763 if (BPF_MISCOP(p->code) == BPF_COP && 764 p->k >= bc->nfuncs) { 765 goto out; 766 } 767 break; 768 #else 769 goto out; 770 #endif 771 default: 772 break; 773 } 774 break; 775 default: 776 goto out; 777 } 778 } 779 ok = 1; 780 out: 781 #if defined(KERNEL) || defined(_KERNEL) 782 kmem_free(mem, size); 783 #endif 784 return ok; 785 } 786
Indexes created Tue Sep 30 07:10:03 GMT 2025