bpf_filter.c revision 1.48.2.1
1 /* $NetBSD: bpf_filter.c,v 1.48.2.1 2012/04/17 00:08:37 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 1.48.2.1 2012/04/17 00:08:37 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 #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 --pc; 152 for (;;) { 153 ++pc; 154 switch (pc->code) { 155 156 default: 157 #ifdef _KERNEL 158 return 0; 159 #else 160 abort(); 161 /*NOTREACHED*/ 162 #endif 163 case BPF_RET|BPF_K: 164 return (u_int)pc->k; 165 166 case BPF_RET|BPF_A: 167 return (u_int)A; 168 169 case BPF_LD|BPF_W|BPF_ABS: 170 k = pc->k; 171 if (k > buflen || sizeof(int32_t) > buflen - k) { 172 #ifdef _KERNEL 173 int merr = 0; /* XXX: GCC */ 174 175 if (buflen != 0) 176 return 0; 177 A = m_xword((const struct mbuf *)p, k, &merr); 178 if (merr != 0) 179 return 0; 180 continue; 181 #else 182 return 0; 183 #endif 184 } 185 A = EXTRACT_LONG(&p[k]); 186 continue; 187 188 case BPF_LD|BPF_H|BPF_ABS: 189 k = pc->k; 190 if (k > buflen || sizeof(int16_t) > buflen - k) { 191 #ifdef _KERNEL 192 int merr; 193 194 if (buflen != 0) 195 return 0; 196 A = m_xhalf((const 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_SHORT(&p[k]); 205 continue; 206 207 case BPF_LD|BPF_B|BPF_ABS: 208 k = pc->k; 209 if (k >= buflen) { 210 #ifdef _KERNEL 211 const struct mbuf *m; 212 int len; 213 214 if (buflen != 0) 215 return 0; 216 m = (const struct mbuf *)p; 217 MINDEX(len, m, k); 218 A = mtod(m, u_char *)[k]; 219 continue; 220 #else 221 return 0; 222 #endif 223 } 224 A = p[k]; 225 continue; 226 227 case BPF_LD|BPF_W|BPF_LEN: 228 A = wirelen; 229 continue; 230 231 case BPF_LDX|BPF_W|BPF_LEN: 232 X = wirelen; 233 continue; 234 235 case BPF_LD|BPF_W|BPF_IND: 236 k = X + pc->k; 237 if (pc->k > buflen || X > buflen - pc->k || 238 sizeof(int32_t) > buflen - k) { 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 (pc->k > buflen || X > buflen - pc->k || 258 sizeof(int16_t) > buflen - k) { 259 #ifdef _KERNEL 260 int merr = 0; /* XXX: GCC */ 261 262 if (buflen != 0) 263 return 0; 264 A = m_xhalf((const struct mbuf *)p, k, &merr); 265 if (merr != 0) 266 return 0; 267 continue; 268 #else 269 return 0; 270 #endif 271 } 272 A = EXTRACT_SHORT(&p[k]); 273 continue; 274 275 case BPF_LD|BPF_B|BPF_IND: 276 k = X + pc->k; 277 if (pc->k >= buflen || X >= buflen - pc->k) { 278 #ifdef _KERNEL 279 const struct mbuf *m; 280 int len; 281 282 if (buflen != 0) 283 return 0; 284 m = (const struct mbuf *)p; 285 MINDEX(len, m, k); 286 A = mtod(m, u_char *)[k]; 287 continue; 288 #else 289 return 0; 290 #endif 291 } 292 A = p[k]; 293 continue; 294 295 case BPF_LDX|BPF_MSH|BPF_B: 296 k = pc->k; 297 if (k >= buflen) { 298 #ifdef _KERNEL 299 const struct mbuf *m; 300 int len; 301 302 if (buflen != 0) 303 return 0; 304 m = (const struct mbuf *)p; 305 MINDEX(len, m, k); 306 X = (mtod(m, char *)[k] & 0xf) << 2; 307 continue; 308 #else 309 return 0; 310 #endif 311 } 312 X = (p[pc->k] & 0xf) << 2; 313 continue; 314 315 case BPF_LD|BPF_IMM: 316 A = pc->k; 317 continue; 318 319 case BPF_LDX|BPF_IMM: 320 X = pc->k; 321 continue; 322 323 case BPF_LD|BPF_MEM: 324 A = mem[pc->k]; 325 continue; 326 327 case BPF_LDX|BPF_MEM: 328 X = mem[pc->k]; 329 continue; 330 331 case BPF_ST: 332 mem[pc->k] = A; 333 continue; 334 335 case BPF_STX: 336 mem[pc->k] = X; 337 continue; 338 339 case BPF_JMP|BPF_JA: 340 pc += pc->k; 341 continue; 342 343 case BPF_JMP|BPF_JGT|BPF_K: 344 pc += (A > pc->k) ? pc->jt : pc->jf; 345 continue; 346 347 case BPF_JMP|BPF_JGE|BPF_K: 348 pc += (A >= pc->k) ? pc->jt : pc->jf; 349 continue; 350 351 case BPF_JMP|BPF_JEQ|BPF_K: 352 pc += (A == pc->k) ? pc->jt : pc->jf; 353 continue; 354 355 case BPF_JMP|BPF_JSET|BPF_K: 356 pc += (A & pc->k) ? pc->jt : pc->jf; 357 continue; 358 359 case BPF_JMP|BPF_JGT|BPF_X: 360 pc += (A > X) ? pc->jt : pc->jf; 361 continue; 362 363 case BPF_JMP|BPF_JGE|BPF_X: 364 pc += (A >= X) ? pc->jt : pc->jf; 365 continue; 366 367 case BPF_JMP|BPF_JEQ|BPF_X: 368 pc += (A == X) ? pc->jt : pc->jf; 369 continue; 370 371 case BPF_JMP|BPF_JSET|BPF_X: 372 pc += (A & X) ? pc->jt : pc->jf; 373 continue; 374 375 case BPF_ALU|BPF_ADD|BPF_X: 376 A += X; 377 continue; 378 379 case BPF_ALU|BPF_SUB|BPF_X: 380 A -= X; 381 continue; 382 383 case BPF_ALU|BPF_MUL|BPF_X: 384 A *= X; 385 continue; 386 387 case BPF_ALU|BPF_DIV|BPF_X: 388 if (X == 0) 389 return 0; 390 A /= X; 391 continue; 392 393 case BPF_ALU|BPF_AND|BPF_X: 394 A &= X; 395 continue; 396 397 case BPF_ALU|BPF_OR|BPF_X: 398 A |= X; 399 continue; 400 401 case BPF_ALU|BPF_LSH|BPF_X: 402 A <<= X; 403 continue; 404 405 case BPF_ALU|BPF_RSH|BPF_X: 406 A >>= X; 407 continue; 408 409 case BPF_ALU|BPF_ADD|BPF_K: 410 A += pc->k; 411 continue; 412 413 case BPF_ALU|BPF_SUB|BPF_K: 414 A -= pc->k; 415 continue; 416 417 case BPF_ALU|BPF_MUL|BPF_K: 418 A *= pc->k; 419 continue; 420 421 case BPF_ALU|BPF_DIV|BPF_K: 422 A /= pc->k; 423 continue; 424 425 case BPF_ALU|BPF_AND|BPF_K: 426 A &= pc->k; 427 continue; 428 429 case BPF_ALU|BPF_OR|BPF_K: 430 A |= pc->k; 431 continue; 432 433 case BPF_ALU|BPF_LSH|BPF_K: 434 A <<= pc->k; 435 continue; 436 437 case BPF_ALU|BPF_RSH|BPF_K: 438 A >>= pc->k; 439 continue; 440 441 case BPF_ALU|BPF_NEG: 442 A = -A; 443 continue; 444 445 case BPF_MISC|BPF_TAX: 446 X = A; 447 continue; 448 449 case BPF_MISC|BPF_TXA: 450 A = X; 451 continue; 452 } 453 } 454 } 455 456 /* 457 * Return true if the 'fcode' is a valid filter program. 458 * The constraints are that each jump be forward and to a valid 459 * code, that memory accesses are within valid ranges (to the 460 * extent that this can be checked statically; loads of packet 461 * data have to be, and are, also checked at run time), and that 462 * the code terminates with either an accept or reject. 463 * 464 * The kernel needs to be able to verify an application's filter code. 465 * Otherwise, a bogus program could easily crash the system. 466 */ 467 __CTASSERT(BPF_MEMWORDS == sizeof(uint16_t) * NBBY); 468 469 int 470 bpf_validate(const struct bpf_insn *f, int signed_len) 471 { 472 u_int i, from, len, ok = 0; 473 const struct bpf_insn *p; 474 #if defined(KERNEL) || defined(_KERNEL) 475 uint16_t *mem, invalid; 476 size_t size; 477 #endif 478 479 len = (u_int)signed_len; 480 if (len < 1) 481 return 0; 482 #if defined(KERNEL) || defined(_KERNEL) 483 if (len > BPF_MAXINSNS) 484 return 0; 485 #endif 486 if (BPF_CLASS(f[len - 1].code) != BPF_RET) 487 return 0; 488 489 #if defined(KERNEL) || defined(_KERNEL) 490 mem = kmem_zalloc(size = sizeof(*mem) * len, KM_SLEEP); 491 invalid = ~0; /* All is invalid on startup */ 492 #endif 493 494 for (i = 0; i < len; ++i) { 495 #if defined(KERNEL) || defined(_KERNEL) 496 /* blend in any invalid bits for current pc */ 497 invalid |= mem[i]; 498 #endif 499 p = &f[i]; 500 switch (BPF_CLASS(p->code)) { 501 /* 502 * Check that memory operations use valid addresses. 503 */ 504 case BPF_LD: 505 case BPF_LDX: 506 switch (BPF_MODE(p->code)) { 507 case BPF_MEM: 508 /* 509 * There's no maximum packet data size 510 * in userland. The runtime packet length 511 * check suffices. 512 */ 513 #if defined(KERNEL) || defined(_KERNEL) 514 /* 515 * More strict check with actual packet length 516 * is done runtime. 517 */ 518 if (p->k >= BPF_MEMWORDS) 519 goto out; 520 /* check for current memory invalid */ 521 if (invalid & (1 << p->k)) 522 goto out; 523 #endif 524 break; 525 case BPF_ABS: 526 case BPF_IND: 527 case BPF_MSH: 528 case BPF_IMM: 529 case BPF_LEN: 530 break; 531 default: 532 goto out; 533 } 534 break; 535 case BPF_ST: 536 case BPF_STX: 537 if (p->k >= BPF_MEMWORDS) 538 goto out; 539 #if defined(KERNEL) || defined(_KERNEL) 540 /* validate the memory word */ 541 invalid &= ~(1 << p->k); 542 #endif 543 break; 544 case BPF_ALU: 545 switch (BPF_OP(p->code)) { 546 case BPF_ADD: 547 case BPF_SUB: 548 case BPF_MUL: 549 case BPF_OR: 550 case BPF_AND: 551 case BPF_LSH: 552 case BPF_RSH: 553 case BPF_NEG: 554 break; 555 case BPF_DIV: 556 /* 557 * Check for constant division by 0. 558 */ 559 if (BPF_SRC(p->code) == BPF_K && p->k == 0) 560 goto out; 561 break; 562 default: 563 goto out; 564 } 565 break; 566 case BPF_JMP: 567 /* 568 * Check that jumps are within the code block, 569 * and that unconditional branches don't go 570 * backwards as a result of an overflow. 571 * Unconditional branches have a 32-bit offset, 572 * so they could overflow; we check to make 573 * sure they don't. Conditional branches have 574 * an 8-bit offset, and the from address is <= 575 * BPF_MAXINSNS, and we assume that BPF_MAXINSNS 576 * is sufficiently small that adding 255 to it 577 * won't overflow. 578 * 579 * We know that len is <= BPF_MAXINSNS, and we 580 * assume that BPF_MAXINSNS is < the maximum size 581 * of a u_int, so that i + 1 doesn't overflow. 582 * 583 * For userland, we don't know that the from 584 * or len are <= BPF_MAXINSNS, but we know that 585 * from <= len, and, except on a 64-bit system, 586 * it's unlikely that len, if it truly reflects 587 * the size of the program we've been handed, 588 * will be anywhere near the maximum size of 589 * a u_int. We also don't check for backward 590 * branches, as we currently support them in 591 * userland for the protochain operation. 592 */ 593 from = i + 1; 594 switch (BPF_OP(p->code)) { 595 case BPF_JA: 596 if (from + p->k >= len) 597 goto out; 598 #if defined(KERNEL) || defined(_KERNEL) 599 if (from + p->k < from) 600 goto out; 601 /* 602 * mark the currently invalid bits for the 603 * destination 604 */ 605 mem[from + p->k] |= invalid; 606 invalid = 0; 607 #endif 608 break; 609 case BPF_JEQ: 610 case BPF_JGT: 611 case BPF_JGE: 612 case BPF_JSET: 613 if (from + p->jt >= len || from + p->jf >= len) 614 goto out; 615 #if defined(KERNEL) || defined(_KERNEL) 616 /* 617 * mark the currently invalid bits for both 618 * possible jump destinations 619 */ 620 mem[from + p->jt] |= invalid; 621 mem[from + p->jf] |= invalid; 622 invalid = 0; 623 #endif 624 break; 625 default: 626 goto out; 627 } 628 break; 629 case BPF_RET: 630 break; 631 case BPF_MISC: 632 break; 633 default: 634 goto out; 635 } 636 } 637 ok = 1; 638 out: 639 #if defined(KERNEL) || defined(_KERNEL) 640 kmem_free(mem, size); 641 #endif 642 return ok; 643 } 644
Indexes created Tue Sep 30 06:09:59 GMT 2025