bpf_filter.c revision 1.47
1 /* $NetBSD: bpf_filter.c,v 1.47 2011/07/14 10:43:55 drochner 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 1.47 2011/07/14 10:43:55 drochner 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 EXTRACT_SHORT(p) be16dec(p) 55 #define EXTRACT_LONG(p) be32dec(p) 56 57 #ifdef _KERNEL 58 #include <sys/mbuf.h> 59 #define MINDEX(len, m, k) \ 60 { \ 61 len = m->m_len; \ 62 while (k >= len) { \ 63 k -= len; \ 64 m = m->m_next; \ 65 if (m == 0) \ 66 return 0; \ 67 len = m->m_len; \ 68 } \ 69 } 70 71 static int m_xword (const struct mbuf *, uint32_t, int *); 72 static int m_xhalf (const struct mbuf *, uint32_t, int *); 73 74 static int 75 m_xword(const struct mbuf *m, uint32_t k, int *err) 76 { 77 int len; 78 u_char *cp, *np; 79 struct mbuf *m0; 80 81 *err = 1; 82 MINDEX(len, m, k); 83 cp = mtod(m, u_char *) + k; 84 if (len >= k + 4) { 85 *err = 0; 86 return EXTRACT_LONG(cp); 87 } 88 m0 = m->m_next; 89 if (m0 == 0 || m0->m_len + len - k < 4) 90 return 0; 91 *err = 0; 92 np = mtod(m0, u_char *); 93 switch (len - k) { 94 95 case 1: 96 return (cp[0] << 24) | (np[0] << 16) | (np[1] << 8) | np[2]; 97 98 case 2: 99 return (cp[0] << 24) | (cp[1] << 16) | (np[0] << 8) | np[1]; 100 101 default: 102 return (cp[0] << 24) | (cp[1] << 16) | (cp[2] << 8) | np[0]; 103 } 104 } 105 106 static int 107 m_xhalf(const struct mbuf *m, uint32_t k, int *err) 108 { 109 int len; 110 u_char *cp; 111 struct mbuf *m0; 112 113 *err = 1; 114 MINDEX(len, m, k); 115 cp = mtod(m, u_char *) + k; 116 if (len >= k + 2) { 117 *err = 0; 118 return EXTRACT_SHORT(cp); 119 } 120 m0 = m->m_next; 121 if (m0 == 0) 122 return 0; 123 *err = 0; 124 return (cp[0] << 8) | mtod(m0, u_char *)[0]; 125 } 126 #else /* _KERNEL */ 127 #include <stdlib.h> 128 #endif /* !_KERNEL */ 129 130 #include <net/bpf.h> 131 132 /* 133 * Execute the filter program starting at pc on the packet p 134 * wirelen is the length of the original packet 135 * buflen is the amount of data present 136 */ 137 u_int 138 bpf_filter(const struct bpf_insn *pc, const u_char *p, u_int wirelen, 139 u_int buflen) 140 { 141 uint32_t A, X, k; 142 uint32_t mem[BPF_MEMWORDS]; 143 144 if (pc == 0) 145 /* 146 * No filter means accept all. 147 */ 148 return (u_int)-1; 149 A = 0; 150 X = 0; 151 memset(mem, 0, sizeof(mem)); 152 --pc; 153 for (;;) { 154 ++pc; 155 switch (pc->code) { 156 157 default: 158 #ifdef _KERNEL 159 return 0; 160 #else 161 abort(); 162 /*NOTREACHED*/ 163 #endif 164 case BPF_RET|BPF_K: 165 return (u_int)pc->k; 166 167 case BPF_RET|BPF_A: 168 return (u_int)A; 169 170 case BPF_LD|BPF_W|BPF_ABS: 171 k = pc->k; 172 if (k + sizeof(int32_t) > buflen) { 173 #ifdef _KERNEL 174 int merr = 0; /* XXX: GCC */ 175 176 if (buflen != 0) 177 return 0; 178 A = m_xword((const struct mbuf *)p, k, &merr); 179 if (merr != 0) 180 return 0; 181 continue; 182 #else 183 return 0; 184 #endif 185 } 186 A = EXTRACT_LONG(&p[k]); 187 continue; 188 189 case BPF_LD|BPF_H|BPF_ABS: 190 k = pc->k; 191 if (k + sizeof(int16_t) > buflen) { 192 #ifdef _KERNEL 193 int merr; 194 195 if (buflen != 0) 196 return 0; 197 A = m_xhalf((const struct mbuf *)p, k, &merr); 198 if (merr != 0) 199 return 0; 200 continue; 201 #else 202 return 0; 203 #endif 204 } 205 A = EXTRACT_SHORT(&p[k]); 206 continue; 207 208 case BPF_LD|BPF_B|BPF_ABS: 209 k = pc->k; 210 if (k >= buflen) { 211 #ifdef _KERNEL 212 const struct mbuf *m; 213 int len; 214 215 if (buflen != 0) 216 return 0; 217 m = (const struct mbuf *)p; 218 MINDEX(len, m, k); 219 A = mtod(m, u_char *)[k]; 220 continue; 221 #else 222 return 0; 223 #endif 224 } 225 A = p[k]; 226 continue; 227 228 case BPF_LD|BPF_W|BPF_LEN: 229 A = wirelen; 230 continue; 231 232 case BPF_LDX|BPF_W|BPF_LEN: 233 X = wirelen; 234 continue; 235 236 case BPF_LD|BPF_W|BPF_IND: 237 k = X + pc->k; 238 if (k + sizeof(int32_t) > buflen) { 239 #ifdef _KERNEL 240 int merr = 0; /* XXX: GCC */ 241 242 if (buflen != 0) 243 return 0; 244 A = m_xword((const struct mbuf *)p, k, &merr); 245 if (merr != 0) 246 return 0; 247 continue; 248 #else 249 return 0; 250 #endif 251 } 252 A = EXTRACT_LONG(&p[k]); 253 continue; 254 255 case BPF_LD|BPF_H|BPF_IND: 256 k = X + pc->k; 257 if (k + sizeof(int16_t) > buflen) { 258 #ifdef _KERNEL 259 int merr = 0; /* XXX: GCC */ 260 261 if (buflen != 0) 262 return 0; 263 A = m_xhalf((const struct mbuf *)p, k, &merr); 264 if (merr != 0) 265 return 0; 266 continue; 267 #else 268 return 0; 269 #endif 270 } 271 A = EXTRACT_SHORT(&p[k]); 272 continue; 273 274 case BPF_LD|BPF_B|BPF_IND: 275 k = X + pc->k; 276 if (k >= buflen) { 277 #ifdef _KERNEL 278 const struct mbuf *m; 279 int len; 280 281 if (buflen != 0) 282 return 0; 283 m = (const struct mbuf *)p; 284 MINDEX(len, m, k); 285 A = mtod(m, u_char *)[k]; 286 continue; 287 #else 288 return 0; 289 #endif 290 } 291 A = p[k]; 292 continue; 293 294 case BPF_LDX|BPF_MSH|BPF_B: 295 k = pc->k; 296 if (k >= buflen) { 297 #ifdef _KERNEL 298 const struct mbuf *m; 299 int len; 300 301 if (buflen != 0) 302 return 0; 303 m = (const struct mbuf *)p; 304 MINDEX(len, m, k); 305 X = (mtod(m, char *)[k] & 0xf) << 2; 306 continue; 307 #else 308 return 0; 309 #endif 310 } 311 X = (p[pc->k] & 0xf) << 2; 312 continue; 313 314 case BPF_LD|BPF_IMM: 315 A = pc->k; 316 continue; 317 318 case BPF_LDX|BPF_IMM: 319 X = pc->k; 320 continue; 321 322 case BPF_LD|BPF_MEM: 323 A = mem[pc->k]; 324 continue; 325 326 case BPF_LDX|BPF_MEM: 327 X = mem[pc->k]; 328 continue; 329 330 case BPF_ST: 331 mem[pc->k] = A; 332 continue; 333 334 case BPF_STX: 335 mem[pc->k] = X; 336 continue; 337 338 case BPF_JMP|BPF_JA: 339 pc += pc->k; 340 continue; 341 342 case BPF_JMP|BPF_JGT|BPF_K: 343 pc += (A > pc->k) ? pc->jt : pc->jf; 344 continue; 345 346 case BPF_JMP|BPF_JGE|BPF_K: 347 pc += (A >= pc->k) ? pc->jt : pc->jf; 348 continue; 349 350 case BPF_JMP|BPF_JEQ|BPF_K: 351 pc += (A == pc->k) ? pc->jt : pc->jf; 352 continue; 353 354 case BPF_JMP|BPF_JSET|BPF_K: 355 pc += (A & pc->k) ? pc->jt : pc->jf; 356 continue; 357 358 case BPF_JMP|BPF_JGT|BPF_X: 359 pc += (A > X) ? pc->jt : pc->jf; 360 continue; 361 362 case BPF_JMP|BPF_JGE|BPF_X: 363 pc += (A >= X) ? pc->jt : pc->jf; 364 continue; 365 366 case BPF_JMP|BPF_JEQ|BPF_X: 367 pc += (A == X) ? pc->jt : pc->jf; 368 continue; 369 370 case BPF_JMP|BPF_JSET|BPF_X: 371 pc += (A & X) ? pc->jt : pc->jf; 372 continue; 373 374 case BPF_ALU|BPF_ADD|BPF_X: 375 A += X; 376 continue; 377 378 case BPF_ALU|BPF_SUB|BPF_X: 379 A -= X; 380 continue; 381 382 case BPF_ALU|BPF_MUL|BPF_X: 383 A *= X; 384 continue; 385 386 case BPF_ALU|BPF_DIV|BPF_X: 387 if (X == 0) 388 return 0; 389 A /= X; 390 continue; 391 392 case BPF_ALU|BPF_AND|BPF_X: 393 A &= X; 394 continue; 395 396 case BPF_ALU|BPF_OR|BPF_X: 397 A |= X; 398 continue; 399 400 case BPF_ALU|BPF_LSH|BPF_X: 401 A <<= X; 402 continue; 403 404 case BPF_ALU|BPF_RSH|BPF_X: 405 A >>= X; 406 continue; 407 408 case BPF_ALU|BPF_ADD|BPF_K: 409 A += pc->k; 410 continue; 411 412 case BPF_ALU|BPF_SUB|BPF_K: 413 A -= pc->k; 414 continue; 415 416 case BPF_ALU|BPF_MUL|BPF_K: 417 A *= pc->k; 418 continue; 419 420 case BPF_ALU|BPF_DIV|BPF_K: 421 A /= pc->k; 422 continue; 423 424 case BPF_ALU|BPF_AND|BPF_K: 425 A &= pc->k; 426 continue; 427 428 case BPF_ALU|BPF_OR|BPF_K: 429 A |= pc->k; 430 continue; 431 432 case BPF_ALU|BPF_LSH|BPF_K: 433 A <<= pc->k; 434 continue; 435 436 case BPF_ALU|BPF_RSH|BPF_K: 437 A >>= pc->k; 438 continue; 439 440 case BPF_ALU|BPF_NEG: 441 A = -A; 442 continue; 443 444 case BPF_MISC|BPF_TAX: 445 X = A; 446 continue; 447 448 case BPF_MISC|BPF_TXA: 449 A = X; 450 continue; 451 } 452 } 453 } 454 455 /* 456 * Return true if the 'fcode' is a valid filter program. 457 * The constraints are that each jump be forward and to a valid 458 * code, that memory accesses are within valid ranges (to the 459 * extent that this can be checked statically; loads of packet 460 * data have to be, and are, also checked at run time), and that 461 * the code terminates with either an accept or reject. 462 * 463 * The kernel needs to be able to verify an application's filter code. 464 * Otherwise, a bogus program could easily crash the system. 465 */ 466 __CTASSERT(BPF_MEMWORDS == sizeof(uint16_t) * NBBY); 467 468 int 469 bpf_validate(const struct bpf_insn *f, int signed_len) 470 { 471 u_int i, from, len, ok = 0; 472 const struct bpf_insn *p; 473 #if defined(KERNEL) || defined(_KERNEL) 474 uint16_t *mem, invalid; 475 size_t size; 476 #endif 477 478 len = (u_int)signed_len; 479 if (len < 1) 480 return 0; 481 #if defined(KERNEL) || defined(_KERNEL) 482 if (len > BPF_MAXINSNS) 483 return 0; 484 #endif 485 if (BPF_CLASS(f[len - 1].code) != BPF_RET) 486 return 0; 487 488 #if defined(KERNEL) || defined(_KERNEL) 489 mem = kmem_zalloc(size = sizeof(*mem) * len, KM_SLEEP); 490 invalid = ~0; /* All is invalid on startup */ 491 #endif 492 493 for (i = 0; i < len; ++i) { 494 #if defined(KERNEL) || defined(_KERNEL) 495 /* blend in any invalid bits for current pc */ 496 invalid |= mem[i]; 497 #endif 498 p = &f[i]; 499 switch (BPF_CLASS(p->code)) { 500 /* 501 * Check that memory operations use valid addresses. 502 */ 503 case BPF_LD: 504 case BPF_LDX: 505 switch (BPF_MODE(p->code)) { 506 case BPF_MEM: 507 /* 508 * There's no maximum packet data size 509 * in userland. The runtime packet length 510 * check suffices. 511 */ 512 #if defined(KERNEL) || defined(_KERNEL) 513 /* 514 * More strict check with actual packet length 515 * is done runtime. 516 */ 517 if (p->k >= BPF_MEMWORDS) 518 goto out; 519 /* check for current memory invalid */ 520 if (invalid & (1 << p->k)) 521 goto out; 522 #endif 523 break; 524 case BPF_ABS: 525 case BPF_IND: 526 case BPF_MSH: 527 case BPF_IMM: 528 case BPF_LEN: 529 break; 530 default: 531 goto out; 532 } 533 break; 534 case BPF_ST: 535 case BPF_STX: 536 if (p->k >= BPF_MEMWORDS) 537 goto out; 538 #if defined(KERNEL) || defined(_KERNEL) 539 /* validate the memory word */ 540 invalid &= ~(1 << p->k); 541 #endif 542 break; 543 case BPF_ALU: 544 switch (BPF_OP(p->code)) { 545 case BPF_ADD: 546 case BPF_SUB: 547 case BPF_MUL: 548 case BPF_OR: 549 case BPF_AND: 550 case BPF_LSH: 551 case BPF_RSH: 552 case BPF_NEG: 553 break; 554 case BPF_DIV: 555 /* 556 * Check for constant division by 0. 557 */ 558 if (BPF_SRC(p->code) == BPF_K && p->k == 0) 559 goto out; 560 break; 561 default: 562 goto out; 563 } 564 break; 565 case BPF_JMP: 566 /* 567 * Check that jumps are within the code block, 568 * and that unconditional branches don't go 569 * backwards as a result of an overflow. 570 * Unconditional branches have a 32-bit offset, 571 * so they could overflow; we check to make 572 * sure they don't. Conditional branches have 573 * an 8-bit offset, and the from address is <= 574 * BPF_MAXINSNS, and we assume that BPF_MAXINSNS 575 * is sufficiently small that adding 255 to it 576 * won't overflow. 577 * 578 * We know that len is <= BPF_MAXINSNS, and we 579 * assume that BPF_MAXINSNS is < the maximum size 580 * of a u_int, so that i + 1 doesn't overflow. 581 * 582 * For userland, we don't know that the from 583 * or len are <= BPF_MAXINSNS, but we know that 584 * from <= len, and, except on a 64-bit system, 585 * it's unlikely that len, if it truly reflects 586 * the size of the program we've been handed, 587 * will be anywhere near the maximum size of 588 * a u_int. We also don't check for backward 589 * branches, as we currently support them in 590 * userland for the protochain operation. 591 */ 592 from = i + 1; 593 switch (BPF_OP(p->code)) { 594 case BPF_JA: 595 if (from + p->k >= len) 596 goto out; 597 #if defined(KERNEL) || defined(_KERNEL) 598 if (from + p->k < from) 599 goto out; 600 /* 601 * mark the currently invalid bits for the 602 * destination 603 */ 604 mem[from + p->k] |= invalid; 605 invalid = 0; 606 #endif 607 break; 608 case BPF_JEQ: 609 case BPF_JGT: 610 case BPF_JGE: 611 case BPF_JSET: 612 if (from + p->jt >= len || from + p->jf >= len) 613 goto out; 614 #if defined(KERNEL) || defined(_KERNEL) 615 /* 616 * mark the currently invalid bits for both 617 * possible jump destinations 618 */ 619 mem[from + p->jt] |= invalid; 620 mem[from + p->jf] |= invalid; 621 invalid = 0; 622 #endif 623 break; 624 default: 625 goto out; 626 } 627 break; 628 case BPF_RET: 629 break; 630 case BPF_MISC: 631 break; 632 default: 633 goto out; 634 } 635 } 636 ok = 1; 637 out: 638 #if defined(KERNEL) || defined(_KERNEL) 639 kmem_free(mem, size); 640 #endif 641 return ok; 642 } 643
Indexes created Tue Sep 30 06:09:59 GMT 2025