bpf_filter.c revision 1.44
1 /* $NetBSD: bpf_filter.c,v 1.44 2011/02/19 04:10:47 christos 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 1.44 2011/02/19 04:10:47 christos 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 /* CONSTCOND */ 153 while (1) { 154 ++pc; 155 switch (pc->code) { 156 157 default: 158 #ifdef _KERNEL 159 return 0; 160 #else 161 abort(); 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 + sizeof(int32_t) > buflen) { 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 + sizeof(int16_t) > buflen) { 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 (k + sizeof(int32_t) > buflen) { 238 #ifdef _KERNEL 239 int merr = 0; /* XXX: GCC */ 240 241 if (buflen != 0) 242 return 0; 243 A = m_xword((const struct mbuf *)p, k, &merr); 244 if (merr != 0) 245 return 0; 246 continue; 247 #else 248 return 0; 249 #endif 250 } 251 A = EXTRACT_LONG(&p[k]); 252 continue; 253 254 case BPF_LD|BPF_H|BPF_IND: 255 k = X + pc->k; 256 if (k + sizeof(int16_t) > buflen) { 257 #ifdef _KERNEL 258 int merr = 0; /* XXX: GCC */ 259 260 if (buflen != 0) 261 return 0; 262 A = m_xhalf((const struct mbuf *)p, k, &merr); 263 if (merr != 0) 264 return 0; 265 continue; 266 #else 267 return 0; 268 #endif 269 } 270 A = EXTRACT_SHORT(&p[k]); 271 continue; 272 273 case BPF_LD|BPF_B|BPF_IND: 274 k = X + pc->k; 275 if (k >= buflen) { 276 #ifdef _KERNEL 277 const struct mbuf *m; 278 int len; 279 280 if (buflen != 0) 281 return 0; 282 m = (const struct mbuf *)p; 283 MINDEX(len, m, k); 284 A = mtod(m, u_char *)[k]; 285 continue; 286 #else 287 return 0; 288 #endif 289 } 290 A = p[k]; 291 continue; 292 293 case BPF_LDX|BPF_MSH|BPF_B: 294 k = pc->k; 295 if (k >= buflen) { 296 #ifdef _KERNEL 297 const struct mbuf *m; 298 int len; 299 300 if (buflen != 0) 301 return 0; 302 m = (const struct mbuf *)p; 303 MINDEX(len, m, k); 304 X = (mtod(m, char *)[k] & 0xf) << 2; 305 continue; 306 #else 307 return 0; 308 #endif 309 } 310 X = (p[pc->k] & 0xf) << 2; 311 continue; 312 313 case BPF_LD|BPF_IMM: 314 A = pc->k; 315 continue; 316 317 case BPF_LDX|BPF_IMM: 318 X = pc->k; 319 continue; 320 321 case BPF_LD|BPF_MEM: 322 A = mem[pc->k]; 323 continue; 324 325 case BPF_LDX|BPF_MEM: 326 X = mem[pc->k]; 327 continue; 328 329 case BPF_ST: 330 mem[pc->k] = A; 331 continue; 332 333 case BPF_STX: 334 mem[pc->k] = X; 335 continue; 336 337 case BPF_JMP|BPF_JA: 338 pc += pc->k; 339 continue; 340 341 case BPF_JMP|BPF_JGT|BPF_K: 342 pc += (A > pc->k) ? pc->jt : pc->jf; 343 continue; 344 345 case BPF_JMP|BPF_JGE|BPF_K: 346 pc += (A >= pc->k) ? pc->jt : pc->jf; 347 continue; 348 349 case BPF_JMP|BPF_JEQ|BPF_K: 350 pc += (A == pc->k) ? pc->jt : pc->jf; 351 continue; 352 353 case BPF_JMP|BPF_JSET|BPF_K: 354 pc += (A & pc->k) ? pc->jt : pc->jf; 355 continue; 356 357 case BPF_JMP|BPF_JGT|BPF_X: 358 pc += (A > X) ? pc->jt : pc->jf; 359 continue; 360 361 case BPF_JMP|BPF_JGE|BPF_X: 362 pc += (A >= X) ? pc->jt : pc->jf; 363 continue; 364 365 case BPF_JMP|BPF_JEQ|BPF_X: 366 pc += (A == X) ? pc->jt : pc->jf; 367 continue; 368 369 case BPF_JMP|BPF_JSET|BPF_X: 370 pc += (A & X) ? pc->jt : pc->jf; 371 continue; 372 373 case BPF_ALU|BPF_ADD|BPF_X: 374 A += X; 375 continue; 376 377 case BPF_ALU|BPF_SUB|BPF_X: 378 A -= X; 379 continue; 380 381 case BPF_ALU|BPF_MUL|BPF_X: 382 A *= X; 383 continue; 384 385 case BPF_ALU|BPF_DIV|BPF_X: 386 if (X == 0) 387 return 0; 388 A /= X; 389 continue; 390 391 case BPF_ALU|BPF_AND|BPF_X: 392 A &= X; 393 continue; 394 395 case BPF_ALU|BPF_OR|BPF_X: 396 A |= X; 397 continue; 398 399 case BPF_ALU|BPF_LSH|BPF_X: 400 A <<= X; 401 continue; 402 403 case BPF_ALU|BPF_RSH|BPF_X: 404 A >>= X; 405 continue; 406 407 case BPF_ALU|BPF_ADD|BPF_K: 408 A += pc->k; 409 continue; 410 411 case BPF_ALU|BPF_SUB|BPF_K: 412 A -= pc->k; 413 continue; 414 415 case BPF_ALU|BPF_MUL|BPF_K: 416 A *= pc->k; 417 continue; 418 419 case BPF_ALU|BPF_DIV|BPF_K: 420 A /= pc->k; 421 continue; 422 423 case BPF_ALU|BPF_AND|BPF_K: 424 A &= pc->k; 425 continue; 426 427 case BPF_ALU|BPF_OR|BPF_K: 428 A |= pc->k; 429 continue; 430 431 case BPF_ALU|BPF_LSH|BPF_K: 432 A <<= pc->k; 433 continue; 434 435 case BPF_ALU|BPF_RSH|BPF_K: 436 A >>= pc->k; 437 continue; 438 439 case BPF_ALU|BPF_NEG: 440 A = -A; 441 continue; 442 443 case BPF_MISC|BPF_TAX: 444 X = A; 445 continue; 446 447 case BPF_MISC|BPF_TXA: 448 A = X; 449 continue; 450 } 451 } 452 } 453 454 /* 455 * Return true if the 'fcode' is a valid filter program. 456 * The constraints are that each jump be forward and to a valid 457 * code, that memory accesses are within valid ranges (to the 458 * extent that this can be checked statically; loads of packet 459 * data have to be, and are, also checked at run time), and that 460 * the code terminates with either an accept or reject. 461 * 462 * The kernel needs to be able to verify an application's filter code. 463 * Otherwise, a bogus program could easily crash the system. 464 */ 465 __CTASSERT(BPF_MEMWORDS == sizeof(uint16_t) * NBBY); 466 467 int 468 bpf_validate(const struct bpf_insn *f, int signed_len) 469 { 470 u_int i, from, len, ok = 0, size; 471 const struct bpf_insn *p; 472 #if defined(KERNEL) || defined(_KERNEL) 473 uint16_t *mem, invalid; 474 #endif 475 476 len = (u_int)signed_len; 477 if (len < 1) 478 return 0; 479 #if defined(KERNEL) || defined(_KERNEL) 480 if (len > BPF_MAXINSNS) 481 return 0; 482 #endif 483 if (BPF_CLASS(f[len - 1].code) != BPF_RET) 484 return 0; 485 486 #if defined(KERNEL) || defined(_KERNEL) 487 mem = kmem_zalloc(size = sizeof(*mem) * len, KM_SLEEP); 488 invalid = ~0; /* All is invalid on startup */ 489 #endif 490 491 for (i = 0; i < len; ++i) { 492 #if defined(KERNEL) || defined(_KERNEL) 493 /* blend in any invalid bits for current pc */ 494 invalid |= mem[i]; 495 #endif 496 p = &f[i]; 497 switch (BPF_CLASS(p->code)) { 498 /* 499 * Check that memory operations use valid addresses. 500 */ 501 case BPF_LD: 502 case BPF_LDX: 503 switch (BPF_MODE(p->code)) { 504 case BPF_MEM: 505 /* 506 * There's no maximum packet data size 507 * in userland. The runtime packet length 508 * check suffices. 509 */ 510 #if defined(KERNEL) || defined(_KERNEL) 511 /* 512 * More strict check with actual packet length 513 * is done runtime. 514 */ 515 if (p->k >= BPF_MEMWORDS) 516 goto out; 517 /* check for current memory invalid */ 518 if (invalid & (1 << p->k)) 519 goto out; 520 #endif 521 break; 522 case BPF_ABS: 523 case BPF_IND: 524 case BPF_MSH: 525 case BPF_IMM: 526 case BPF_LEN: 527 break; 528 default: 529 goto out; 530 } 531 break; 532 case BPF_ST: 533 case BPF_STX: 534 if (p->k >= BPF_MEMWORDS) 535 goto out; 536 #if defined(KERNEL) || defined(_KERNEL) 537 /* validate the memory word */ 538 invalid &= ~(1 << p->k); 539 #endif 540 break; 541 case BPF_ALU: 542 switch (BPF_OP(p->code)) { 543 case BPF_ADD: 544 case BPF_SUB: 545 case BPF_MUL: 546 case BPF_OR: 547 case BPF_AND: 548 case BPF_LSH: 549 case BPF_RSH: 550 case BPF_NEG: 551 break; 552 case BPF_DIV: 553 /* 554 * Check for constant division by 0. 555 */ 556 if (BPF_SRC(p->code) == BPF_K && p->k == 0) 557 goto out; 558 break; 559 default: 560 goto out; 561 } 562 break; 563 case BPF_JMP: 564 /* 565 * Check that jumps are within the code block, 566 * and that unconditional branches don't go 567 * backwards as a result of an overflow. 568 * Unconditional branches have a 32-bit offset, 569 * so they could overflow; we check to make 570 * sure they don't. Conditional branches have 571 * an 8-bit offset, and the from address is <= 572 * BPF_MAXINSNS, and we assume that BPF_MAXINSNS 573 * is sufficiently small that adding 255 to it 574 * won't overflow. 575 * 576 * We know that len is <= BPF_MAXINSNS, and we 577 * assume that BPF_MAXINSNS is < the maximum size 578 * of a u_int, so that i + 1 doesn't overflow. 579 * 580 * For userland, we don't know that the from 581 * or len are <= BPF_MAXINSNS, but we know that 582 * from <= len, and, except on a 64-bit system, 583 * it's unlikely that len, if it truly reflects 584 * the size of the program we've been handed, 585 * will be anywhere near the maximum size of 586 * a u_int. We also don't check for backward 587 * branches, as we currently support them in 588 * userland for the protochain operation. 589 */ 590 from = i + 1; 591 switch (BPF_OP(p->code)) { 592 case BPF_JA: 593 if (from + p->k >= len) 594 goto out; 595 #if defined(KERNEL) || defined(_KERNEL) 596 if (from + p->k < from) 597 goto out; 598 /* 599 * mark the currently invalid bits for the 600 * destination 601 */ 602 mem[from + p->k] |= invalid; 603 invalid = 0; 604 #endif 605 break; 606 case BPF_JEQ: 607 case BPF_JGT: 608 case BPF_JGE: 609 case BPF_JSET: 610 if (from + p->jt >= len || from + p->jf >= len) 611 goto out; 612 #if defined(KERNEL) || defined(_KERNEL) 613 /* 614 * mark the currently invalid bits for both 615 * possible jump destinations 616 */ 617 mem[from + p->jt] |= invalid; 618 mem[from + p->jf] |= invalid; 619 invalid = 0; 620 #endif 621 break; 622 default: 623 goto out; 624 } 625 break; 626 case BPF_RET: 627 break; 628 case BPF_MISC: 629 break; 630 default: 631 goto out; 632 } 633 } 634 ok = 1; 635 out: 636 #if defined(KERNEL) || defined(_KERNEL) 637 kmem_free(mem, size); 638 #endif 639 return ok; 640 } 641
Indexes created Tue Sep 30 07:10:03 GMT 2025