1 /* 2 * Copyright (c) 1990, 1991, 1993 3 * The Regents of the University of California. All rights reserved. 4 * 5 * This code is derived from the Stanford/CMU enet packet filter, 6 * (net/enet.c) distributed as part of 4.3BSD, and code contributed 7 * to Berkeley by Steven McCanne and Van Jacobson both of Lawrence 8 * Berkeley Laboratory. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 3. All advertising materials mentioning features or use of this software 19 * must display the following acknowledgement: 20 * This product includes software developed by the University of 21 * California, Berkeley and its contributors. 22 * 4. Neither the name of the University nor the names of its contributors 23 * may be used to endorse or promote products derived from this software 24 * without specific prior written permission. 25 * 26 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 27 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 28 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 29 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 30 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 31 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 32 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 33 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 34 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 35 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 36 * SUCH DAMAGE. 37 * 38 * @(#)bpf_filter.c 8.1 (Berkeley) 6/10/93 39 * 40 * $FreeBSD: src/sys/net/bpf_filter.c,v 1.17 1999/12/29 04:38:31 peter Exp $ 41 * $DragonFly: src/sys/net/bpf_filter.c,v 1.10 2008/01/02 12:30:34 sephe Exp $ 42 */ 43 44 #include <sys/param.h> 45 46 #if defined(sparc) || defined(mips) || defined(ibm032) 47 #define BPF_ALIGN 48 #endif 49 50 #ifndef BPF_ALIGN 51 #define EXTRACT_SHORT(p) ((u_int16_t)ntohs(*(u_int16_t *)p)) 52 #define EXTRACT_LONG(p) (ntohl(*(u_int32_t *)p)) 53 #else 54 #define EXTRACT_SHORT(p)\ 55 ((u_int16_t)\ 56 ((u_int16_t)*((u_char *)p+0)<<8|\ 57 (u_int16_t)*((u_char *)p+1)<<0)) 58 #define EXTRACT_LONG(p)\ 59 ((u_int32_t)*((u_char *)p+0)<<24|\ 60 (u_int32_t)*((u_char *)p+1)<<16|\ 61 (u_int32_t)*((u_char *)p+2)<<8|\ 62 (u_int32_t)*((u_char *)p+3)<<0) 63 #endif 64 65 #ifdef _KERNEL 66 #include <sys/mbuf.h> 67 #endif 68 #include <net/bpf.h> 69 #ifdef _KERNEL 70 #define MINDEX(m, k) \ 71 { \ 72 int len = m->m_len; \ 73 \ 74 while (k >= len) { \ 75 k -= len; \ 76 m = m->m_next; \ 77 if (m == 0) \ 78 return 0; \ 79 len = m->m_len; \ 80 } \ 81 } 82 83 extern int bpf_maxbufsize; 84 85 static u_int16_t m_xhalf (struct mbuf *m, bpf_u_int32 k, int *err); 86 static u_int32_t m_xword (struct mbuf *m, bpf_u_int32 k, int *err); 87 88 static u_int32_t 89 m_xword(struct mbuf *m, bpf_u_int32 k, int *err) 90 { 91 size_t len; 92 u_char *cp, *np; 93 struct mbuf *m0; 94 95 len = m->m_len; 96 while (k >= len) { 97 k -= len; 98 m = m->m_next; 99 if (m == 0) 100 goto bad; 101 len = m->m_len; 102 } 103 cp = mtod(m, u_char *) + k; 104 if (len - k >= 4) { 105 *err = 0; 106 return EXTRACT_LONG(cp); 107 } 108 m0 = m->m_next; 109 if (m0 == 0 || m0->m_len + len - k < 4) 110 goto bad; 111 *err = 0; 112 np = mtod(m0, u_char *); 113 switch (len - k) { 114 115 case 1: 116 return 117 ((u_int32_t)cp[0] << 24) | 118 ((u_int32_t)np[0] << 16) | 119 ((u_int32_t)np[1] << 8) | 120 (u_int32_t)np[2]; 121 122 case 2: 123 return 124 ((u_int32_t)cp[0] << 24) | 125 ((u_int32_t)cp[1] << 16) | 126 ((u_int32_t)np[0] << 8) | 127 (u_int32_t)np[1]; 128 129 default: 130 return 131 ((u_int32_t)cp[0] << 24) | 132 ((u_int32_t)cp[1] << 16) | 133 ((u_int32_t)cp[2] << 8) | 134 (u_int32_t)np[0]; 135 } 136 bad: 137 *err = 1; 138 return 0; 139 } 140 141 static u_int16_t 142 m_xhalf(struct mbuf *m, bpf_u_int32 k, int *err) 143 { 144 size_t len; 145 u_char *cp; 146 struct mbuf *m0; 147 148 len = m->m_len; 149 while (k >= len) { 150 k -= len; 151 m = m->m_next; 152 if (m == 0) 153 goto bad; 154 len = m->m_len; 155 } 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 goto bad; 164 *err = 0; 165 return (cp[0] << 8) | mtod(m0, u_char *)[0]; 166 bad: 167 *err = 1; 168 return 0; 169 } 170 #endif 171 172 /* 173 * Execute the filter program starting at pc on the packet p 174 * wirelen is the length of the original packet 175 * buflen is the amount of data present 176 */ 177 u_int 178 bpf_filter(const struct bpf_insn *pc, u_char *p, u_int wirelen, u_int buflen) 179 { 180 u_int32_t A = 0, X = 0; 181 bpf_u_int32 k; 182 int32_t mem[BPF_MEMWORDS]; 183 184 if (pc == 0) { 185 /* 186 * No filter means accept all. 187 */ 188 return (u_int)-1; 189 } 190 191 --pc; 192 while (1) { 193 ++pc; 194 switch (pc->code) { 195 196 default: 197 #ifdef _KERNEL 198 return 0; 199 #else 200 abort(); 201 #endif 202 case BPF_RET|BPF_K: 203 return (u_int)pc->k; 204 205 case BPF_RET|BPF_A: 206 return (u_int)A; 207 208 case BPF_LD|BPF_W|BPF_ABS: 209 k = pc->k; 210 if (k > buflen || sizeof(int32_t) > buflen - k) { 211 #ifdef _KERNEL 212 int merr; 213 214 if (buflen != 0) 215 return 0; 216 A = m_xword((struct mbuf *)p, k, &merr); 217 if (merr != 0) 218 return 0; 219 continue; 220 #else 221 return 0; 222 #endif 223 } 224 #ifdef BPF_ALIGN 225 if (((intptr_t)(p + k) & 3) != 0) 226 A = EXTRACT_LONG(&p[k]); 227 else 228 #endif 229 A = ntohl(*(int32_t *)(p + k)); 230 continue; 231 232 case BPF_LD|BPF_H|BPF_ABS: 233 k = pc->k; 234 if (k > buflen || sizeof(int16_t) > buflen - k) { 235 #ifdef _KERNEL 236 int merr; 237 238 if (buflen != 0) 239 return 0; 240 A = m_xhalf((struct mbuf *)p, k, &merr); 241 continue; 242 #else 243 return 0; 244 #endif 245 } 246 A = EXTRACT_SHORT(&p[k]); 247 continue; 248 249 case BPF_LD|BPF_B|BPF_ABS: 250 k = pc->k; 251 if (k >= buflen) { 252 #ifdef _KERNEL 253 struct mbuf *m; 254 255 if (buflen != 0) 256 return 0; 257 m = (struct mbuf *)p; 258 MINDEX(m, k); 259 A = mtod(m, u_char *)[k]; 260 continue; 261 #else 262 return 0; 263 #endif 264 } 265 A = p[k]; 266 continue; 267 268 case BPF_LD|BPF_W|BPF_LEN: 269 A = wirelen; 270 continue; 271 272 case BPF_LDX|BPF_W|BPF_LEN: 273 X = wirelen; 274 continue; 275 276 case BPF_LD|BPF_W|BPF_IND: 277 k = X + pc->k; 278 if (pc->k > buflen || X > buflen - pc->k || 279 sizeof(int32_t) > buflen - k) { 280 #ifdef _KERNEL 281 int merr; 282 283 if (buflen != 0) 284 return 0; 285 A = m_xword((struct mbuf *)p, k, &merr); 286 if (merr != 0) 287 return 0; 288 continue; 289 #else 290 return 0; 291 #endif 292 } 293 #ifdef BPF_ALIGN 294 if (((intptr_t)(p + k) & 3) != 0) 295 A = EXTRACT_LONG(&p[k]); 296 else 297 #endif 298 A = ntohl(*(int32_t *)(p + k)); 299 continue; 300 301 case BPF_LD|BPF_H|BPF_IND: 302 k = X + pc->k; 303 if (X > buflen || pc->k > buflen - X || 304 sizeof(int16_t) > buflen - k) { 305 #ifdef _KERNEL 306 int merr; 307 308 if (buflen != 0) 309 return 0; 310 A = m_xhalf((struct mbuf *)p, k, &merr); 311 if (merr != 0) 312 return 0; 313 continue; 314 #else 315 return 0; 316 #endif 317 } 318 A = EXTRACT_SHORT(&p[k]); 319 continue; 320 321 case BPF_LD|BPF_B|BPF_IND: 322 k = X + pc->k; 323 if (pc->k >= buflen || X >= buflen - pc->k) { 324 #ifdef _KERNEL 325 struct mbuf *m; 326 327 if (buflen != 0) 328 return 0; 329 m = (struct mbuf *)p; 330 MINDEX(m, k); 331 A = mtod(m, u_char *)[k]; 332 continue; 333 #else 334 return 0; 335 #endif 336 } 337 A = p[k]; 338 continue; 339 340 case BPF_LDX|BPF_MSH|BPF_B: 341 k = pc->k; 342 if (k >= buflen) { 343 #ifdef _KERNEL 344 struct mbuf *m; 345 346 if (buflen != 0) 347 return 0; 348 m = (struct mbuf *)p; 349 MINDEX(m, k); 350 X = (mtod(m, char *)[k] & 0xf) << 2; 351 continue; 352 #else 353 return 0; 354 #endif 355 } 356 X = (p[pc->k] & 0xf) << 2; 357 continue; 358 359 case BPF_LD|BPF_IMM: 360 A = pc->k; 361 continue; 362 363 case BPF_LDX|BPF_IMM: 364 X = pc->k; 365 continue; 366 367 case BPF_LD|BPF_MEM: 368 A = mem[pc->k]; 369 continue; 370 371 case BPF_LDX|BPF_MEM: 372 X = mem[pc->k]; 373 continue; 374 375 case BPF_ST: 376 mem[pc->k] = A; 377 continue; 378 379 case BPF_STX: 380 mem[pc->k] = X; 381 continue; 382 383 case BPF_JMP|BPF_JA: 384 pc += pc->k; 385 continue; 386 387 case BPF_JMP|BPF_JGT|BPF_K: 388 pc += (A > pc->k) ? pc->jt : pc->jf; 389 continue; 390 391 case BPF_JMP|BPF_JGE|BPF_K: 392 pc += (A >= pc->k) ? pc->jt : pc->jf; 393 continue; 394 395 case BPF_JMP|BPF_JEQ|BPF_K: 396 pc += (A == pc->k) ? pc->jt : pc->jf; 397 continue; 398 399 case BPF_JMP|BPF_JSET|BPF_K: 400 pc += (A & pc->k) ? pc->jt : pc->jf; 401 continue; 402 403 case BPF_JMP|BPF_JGT|BPF_X: 404 pc += (A > X) ? pc->jt : pc->jf; 405 continue; 406 407 case BPF_JMP|BPF_JGE|BPF_X: 408 pc += (A >= X) ? pc->jt : pc->jf; 409 continue; 410 411 case BPF_JMP|BPF_JEQ|BPF_X: 412 pc += (A == X) ? pc->jt : pc->jf; 413 continue; 414 415 case BPF_JMP|BPF_JSET|BPF_X: 416 pc += (A & X) ? pc->jt : pc->jf; 417 continue; 418 419 case BPF_ALU|BPF_ADD|BPF_X: 420 A += X; 421 continue; 422 423 case BPF_ALU|BPF_SUB|BPF_X: 424 A -= X; 425 continue; 426 427 case BPF_ALU|BPF_MUL|BPF_X: 428 A *= X; 429 continue; 430 431 case BPF_ALU|BPF_DIV|BPF_X: 432 if (X == 0) 433 return 0; 434 A /= X; 435 continue; 436 437 case BPF_ALU|BPF_AND|BPF_X: 438 A &= X; 439 continue; 440 441 case BPF_ALU|BPF_OR|BPF_X: 442 A |= X; 443 continue; 444 445 case BPF_ALU|BPF_LSH|BPF_X: 446 A <<= X; 447 continue; 448 449 case BPF_ALU|BPF_RSH|BPF_X: 450 A >>= X; 451 continue; 452 453 case BPF_ALU|BPF_ADD|BPF_K: 454 A += pc->k; 455 continue; 456 457 case BPF_ALU|BPF_SUB|BPF_K: 458 A -= pc->k; 459 continue; 460 461 case BPF_ALU|BPF_MUL|BPF_K: 462 A *= pc->k; 463 continue; 464 465 case BPF_ALU|BPF_DIV|BPF_K: 466 A /= pc->k; 467 continue; 468 469 case BPF_ALU|BPF_AND|BPF_K: 470 A &= pc->k; 471 continue; 472 473 case BPF_ALU|BPF_OR|BPF_K: 474 A |= pc->k; 475 continue; 476 477 case BPF_ALU|BPF_LSH|BPF_K: 478 A <<= pc->k; 479 continue; 480 481 case BPF_ALU|BPF_RSH|BPF_K: 482 A >>= pc->k; 483 continue; 484 485 case BPF_ALU|BPF_NEG: 486 A = -A; 487 continue; 488 489 case BPF_MISC|BPF_TAX: 490 X = A; 491 continue; 492 493 case BPF_MISC|BPF_TXA: 494 A = X; 495 continue; 496 } 497 } 498 } 499 500 #ifdef _KERNEL 501 /* 502 * Return true if the 'fcode' is a valid filter program. 503 * The constraints are that each jump be forward and to a valid 504 * code, that memory accesses are within valid ranges (to the 505 * extent that this can be checked statically; loads of packet 506 * data have to be, and are, also checked at run time), and that 507 * the code terminates with either an accept or reject. 508 * 509 * The kernel needs to be able to verify an application's filter code. 510 * Otherwise, a bogus program could easily crash the system. 511 */ 512 int 513 bpf_validate(const struct bpf_insn *f, int len) 514 { 515 u_int i, from; 516 const struct bpf_insn *p; 517 518 if (len < 1 || len > BPF_MAXINSNS) 519 return 0; 520 521 for (i = 0; i < len; ++i) { 522 p = &f[i]; 523 switch (BPF_CLASS(p->code)) { 524 /* 525 * Check that memory operations use valid addresses. 526 */ 527 case BPF_LD: 528 case BPF_LDX: 529 switch (BPF_MODE(p->code)) { 530 case BPF_IMM: 531 break; 532 case BPF_ABS: 533 case BPF_IND: 534 case BPF_MSH: 535 /* 536 * More strict check with actual packet length 537 * is done runtime. 538 */ 539 if (p->k >= bpf_maxbufsize) 540 return 0; 541 break; 542 case BPF_MEM: 543 if (p->k >= BPF_MEMWORDS) 544 return 0; 545 break; 546 case BPF_LEN: 547 break; 548 default: 549 return 0; 550 } 551 break; 552 case BPF_ST: 553 case BPF_STX: 554 if (p->k >= BPF_MEMWORDS) 555 return 0; 556 break; 557 case BPF_ALU: 558 switch (BPF_OP(p->code)) { 559 case BPF_ADD: 560 case BPF_SUB: 561 case BPF_MUL: 562 case BPF_OR: 563 case BPF_AND: 564 case BPF_LSH: 565 case BPF_RSH: 566 case BPF_NEG: 567 break; 568 case BPF_DIV: 569 /* 570 * Check for constant division by 0. 571 */ 572 if (BPF_SRC(p->code) == BPF_K && p->k == 0) 573 return 0; 574 break; 575 default: 576 return 0; 577 } 578 break; 579 case BPF_JMP: 580 /* 581 * Check that jumps are within the code block, 582 * and that unconditional branches don't go 583 * backwards as a result of an overflow. 584 * Unconditional branches have a 32-bit offset, 585 * so they could overflow; we check to make 586 * sure they don't. Conditional branches have 587 * an 8-bit offset, and the from address is <= 588 * BPF_MAXINSNS, and we assume that BPF_MAXINSNS 589 * is sufficiently small that adding 255 to it 590 * won't overflow. 591 * 592 * We know that len is <= BPF_MAXINSNS, and we 593 * assume that BPF_MAXINSNS is < the maximum size 594 * of a u_int, so that i + 1 doesn't overflow. 595 */ 596 from = i + 1; 597 switch (BPF_OP(p->code)) { 598 case BPF_JA: 599 if (from + p->k < from || from + p->k >= len) 600 return 0; 601 break; 602 case BPF_JEQ: 603 case BPF_JGT: 604 case BPF_JGE: 605 case BPF_JSET: 606 if (from + p->jt >= len || from + p->jf >= len) 607 return 0; 608 break; 609 default: 610 return 0; 611 } 612 break; 613 case BPF_RET: 614 break; 615 case BPF_MISC: 616 break; 617 default: 618 return 0; 619 } 620 } 621 return BPF_CLASS(f[len - 1].code) == BPF_RET; 622 } 623 #endif 624