Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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FreeBSD/Linux Kernel Cross Reference
sys/net/bpf_filter.c
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1 /* $NetBSD: bpf_filter.c,v 1.21.2.1 2006/10/23 17:48:04 ghen 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 1.21.2.1 2006/10/23 17:48:04 ghen 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 52 #if !defined(UNALIGNED_ACCESS) 53 #define BPF_ALIGN 54 #endif 55 56 #ifndef BPF_ALIGN 57 #define EXTRACT_SHORT(p) ((u_int16_t)ntohs(*(u_int16_t *)p)) 58 #define EXTRACT_LONG(p) (ntohl(*(u_int32_t *)p)) 59 #else 60 #define EXTRACT_SHORT(p)\ 61 ((u_int16_t)\ 62 ((u_int16_t)*((u_char *)p+0)<<8|\ 63 (u_int16_t)*((u_char *)p+1)<<0)) 64 #define EXTRACT_LONG(p)\ 65 ((u_int32_t)*((u_char *)p+0)<<24|\ 66 (u_int32_t)*((u_char *)p+1)<<16|\ 67 (u_int32_t)*((u_char *)p+2)<<8|\ 68 (u_int32_t)*((u_char *)p+3)<<0) 69 #endif 70 71 #ifdef _KERNEL 72 #include <sys/mbuf.h> 73 #define MINDEX(len, m, k) \ 74 { \ 75 len = m->m_len; \ 76 while (k >= len) { \ 77 k -= len; \ 78 m = m->m_next; \ 79 if (m == 0) \ 80 return 0; \ 81 len = m->m_len; \ 82 } \ 83 } 84 85 static int m_xword __P((struct mbuf *, int, int *)); 86 static int m_xhalf __P((struct mbuf *, int, int *)); 87 88 static int 89 m_xword(m, k, err) 90 struct mbuf *m; 91 int k, *err; 92 { 93 int len; 94 u_char *cp, *np; 95 struct mbuf *m0; 96 97 *err = 1; 98 MINDEX(len, m, k); 99 cp = mtod(m, u_char *) + k; 100 if (len - k >= 4) { 101 *err = 0; 102 return EXTRACT_LONG(cp); 103 } 104 m0 = m->m_next; 105 if (m0 == 0 || m0->m_len + len - k < 4) 106 return 0; 107 *err = 0; 108 np = mtod(m0, u_char *); 109 switch (len - k) { 110 111 case 1: 112 return (cp[0] << 24) | (np[0] << 16) | (np[1] << 8) | np[2]; 113 114 case 2: 115 return (cp[0] << 24) | (cp[1] << 16) | (np[0] << 8) | np[1]; 116 117 default: 118 return (cp[0] << 24) | (cp[1] << 16) | (cp[2] << 8) | np[0]; 119 } 120 } 121 122 static int 123 m_xhalf(m, k, err) 124 struct mbuf *m; 125 int k, *err; 126 { 127 int len; 128 u_char *cp; 129 struct mbuf *m0; 130 131 *err = 1; 132 MINDEX(len, m, k); 133 cp = mtod(m, u_char *) + k; 134 if (len - k >= 2) { 135 *err = 0; 136 return EXTRACT_SHORT(cp); 137 } 138 m0 = m->m_next; 139 if (m0 == 0) 140 return 0; 141 *err = 0; 142 return (cp[0] << 8) | mtod(m0, u_char *)[0]; 143 } 144 #else /* _KERNEL */ 145 #include <stdlib.h> 146 #endif /* !_KERNEL */ 147 148 #include <net/bpf.h> 149 150 /* 151 * Execute the filter program starting at pc on the packet p 152 * wirelen is the length of the original packet 153 * buflen is the amount of data present 154 */ 155 u_int 156 bpf_filter(pc, p, wirelen, buflen) 157 struct bpf_insn *pc; 158 u_char *p; 159 u_int wirelen; 160 u_int buflen; 161 { 162 u_int32_t A, X; 163 int k; 164 int32_t mem[BPF_MEMWORDS]; 165 166 if (pc == 0) 167 /* 168 * No filter means accept all. 169 */ 170 return (u_int)-1; 171 A = 0; 172 X = 0; 173 --pc; 174 while (1) { 175 ++pc; 176 switch (pc->code) { 177 178 default: 179 #ifdef _KERNEL 180 return 0; 181 #else 182 abort(); 183 #endif 184 case BPF_RET|BPF_K: 185 return (u_int)pc->k; 186 187 case BPF_RET|BPF_A: 188 return (u_int)A; 189 190 case BPF_LD|BPF_W|BPF_ABS: 191 k = pc->k; 192 if (k + sizeof(int32_t) > buflen) { 193 #ifdef _KERNEL 194 int merr; 195 196 if (buflen != 0) 197 return 0; 198 A = m_xword((struct mbuf *)p, k, &merr); 199 if (merr != 0) 200 return 0; 201 continue; 202 #else 203 return 0; 204 #endif 205 } 206 A = EXTRACT_LONG(&p[k]); 207 continue; 208 209 case BPF_LD|BPF_H|BPF_ABS: 210 k = pc->k; 211 if (k + sizeof(int16_t) > buflen) { 212 #ifdef _KERNEL 213 int merr; 214 215 if (buflen != 0) 216 return 0; 217 A = m_xhalf((struct mbuf *)p, k, &merr); 218 if (merr != 0) 219 return 0; 220 continue; 221 #else 222 return 0; 223 #endif 224 } 225 A = EXTRACT_SHORT(&p[k]); 226 continue; 227 228 case BPF_LD|BPF_B|BPF_ABS: 229 k = pc->k; 230 if (k >= buflen) { 231 #ifdef _KERNEL 232 struct mbuf *m; 233 int len; 234 235 if (buflen != 0) 236 return 0; 237 m = (struct mbuf *)p; 238 MINDEX(len, m, k); 239 A = mtod(m, u_char *)[k]; 240 continue; 241 #else 242 return 0; 243 #endif 244 } 245 A = p[k]; 246 continue; 247 248 case BPF_LD|BPF_W|BPF_LEN: 249 A = wirelen; 250 continue; 251 252 case BPF_LDX|BPF_W|BPF_LEN: 253 X = wirelen; 254 continue; 255 256 case BPF_LD|BPF_W|BPF_IND: 257 k = X + pc->k; 258 if (k + sizeof(int32_t) > buflen) { 259 #ifdef _KERNEL 260 int merr; 261 262 if (buflen != 0) 263 return 0; 264 A = m_xword((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_LONG(&p[k]); 273 continue; 274 275 case BPF_LD|BPF_H|BPF_IND: 276 k = X + pc->k; 277 if (k + sizeof(int16_t) > buflen) { 278 #ifdef _KERNEL 279 int merr; 280 281 if (buflen != 0) 282 return 0; 283 A = m_xhalf((struct mbuf *)p, k, &merr); 284 if (merr != 0) 285 return 0; 286 continue; 287 #else 288 return 0; 289 #endif 290 } 291 A = EXTRACT_SHORT(&p[k]); 292 continue; 293 294 case BPF_LD|BPF_B|BPF_IND: 295 k = X + pc->k; 296 if (k >= buflen) { 297 #ifdef _KERNEL 298 struct mbuf *m; 299 int len; 300 301 if (buflen != 0) 302 return 0; 303 m = (struct mbuf *)p; 304 MINDEX(len, m, k); 305 A = mtod(m, u_char *)[k]; 306 continue; 307 #else 308 return 0; 309 #endif 310 } 311 A = p[k]; 312 continue; 313 314 case BPF_LDX|BPF_MSH|BPF_B: 315 k = pc->k; 316 if (k >= buflen) { 317 #ifdef _KERNEL 318 struct mbuf *m; 319 int len; 320 321 if (buflen != 0) 322 return 0; 323 m = (struct mbuf *)p; 324 MINDEX(len, m, k); 325 X = (mtod(m, char *)[k] & 0xf) << 2; 326 continue; 327 #else 328 return 0; 329 #endif 330 } 331 X = (p[pc->k] & 0xf) << 2; 332 continue; 333 334 case BPF_LD|BPF_IMM: 335 A = pc->k; 336 continue; 337 338 case BPF_LDX|BPF_IMM: 339 X = pc->k; 340 continue; 341 342 case BPF_LD|BPF_MEM: 343 A = mem[pc->k]; 344 continue; 345 346 case BPF_LDX|BPF_MEM: 347 X = mem[pc->k]; 348 continue; 349 350 case BPF_ST: 351 mem[pc->k] = A; 352 continue; 353 354 case BPF_STX: 355 mem[pc->k] = X; 356 continue; 357 358 case BPF_JMP|BPF_JA: 359 pc += pc->k; 360 continue; 361 362 case BPF_JMP|BPF_JGT|BPF_K: 363 pc += (A > pc->k) ? pc->jt : pc->jf; 364 continue; 365 366 case BPF_JMP|BPF_JGE|BPF_K: 367 pc += (A >= pc->k) ? pc->jt : pc->jf; 368 continue; 369 370 case BPF_JMP|BPF_JEQ|BPF_K: 371 pc += (A == pc->k) ? pc->jt : pc->jf; 372 continue; 373 374 case BPF_JMP|BPF_JSET|BPF_K: 375 pc += (A & pc->k) ? pc->jt : pc->jf; 376 continue; 377 378 case BPF_JMP|BPF_JGT|BPF_X: 379 pc += (A > X) ? pc->jt : pc->jf; 380 continue; 381 382 case BPF_JMP|BPF_JGE|BPF_X: 383 pc += (A >= X) ? pc->jt : pc->jf; 384 continue; 385 386 case BPF_JMP|BPF_JEQ|BPF_X: 387 pc += (A == X) ? pc->jt : pc->jf; 388 continue; 389 390 case BPF_JMP|BPF_JSET|BPF_X: 391 pc += (A & X) ? pc->jt : pc->jf; 392 continue; 393 394 case BPF_ALU|BPF_ADD|BPF_X: 395 A += X; 396 continue; 397 398 case BPF_ALU|BPF_SUB|BPF_X: 399 A -= X; 400 continue; 401 402 case BPF_ALU|BPF_MUL|BPF_X: 403 A *= X; 404 continue; 405 406 case BPF_ALU|BPF_DIV|BPF_X: 407 if (X == 0) 408 return 0; 409 A /= X; 410 continue; 411 412 case BPF_ALU|BPF_AND|BPF_X: 413 A &= X; 414 continue; 415 416 case BPF_ALU|BPF_OR|BPF_X: 417 A |= X; 418 continue; 419 420 case BPF_ALU|BPF_LSH|BPF_X: 421 A <<= X; 422 continue; 423 424 case BPF_ALU|BPF_RSH|BPF_X: 425 A >>= X; 426 continue; 427 428 case BPF_ALU|BPF_ADD|BPF_K: 429 A += pc->k; 430 continue; 431 432 case BPF_ALU|BPF_SUB|BPF_K: 433 A -= pc->k; 434 continue; 435 436 case BPF_ALU|BPF_MUL|BPF_K: 437 A *= pc->k; 438 continue; 439 440 case BPF_ALU|BPF_DIV|BPF_K: 441 A /= pc->k; 442 continue; 443 444 case BPF_ALU|BPF_AND|BPF_K: 445 A &= pc->k; 446 continue; 447 448 case BPF_ALU|BPF_OR|BPF_K: 449 A |= pc->k; 450 continue; 451 452 case BPF_ALU|BPF_LSH|BPF_K: 453 A <<= pc->k; 454 continue; 455 456 case BPF_ALU|BPF_RSH|BPF_K: 457 A >>= pc->k; 458 continue; 459 460 case BPF_ALU|BPF_NEG: 461 A = -A; 462 continue; 463 464 case BPF_MISC|BPF_TAX: 465 X = A; 466 continue; 467 468 case BPF_MISC|BPF_TXA: 469 A = X; 470 continue; 471 } 472 } 473 } 474 475 #ifdef _KERNEL 476 /* 477 * Return true if the 'fcode' is a valid filter program. 478 * The constraints are that each jump be forward and to a valid 479 * code. The code must terminate with either an accept or reject. 480 * 'valid' is an array for use by the routine (it must be at least 481 * 'len' bytes long). 482 * 483 * The kernel needs to be able to verify an application's filter code. 484 * Otherwise, a bogus program could easily crash the system. 485 */ 486 int 487 bpf_validate(f, len) 488 struct bpf_insn *f; 489 int len; 490 { 491 int i; 492 struct bpf_insn *p; 493 494 for (i = 0; i < len; ++i) { 495 /* 496 * Check that that jumps are forward, and within 497 * the code block. 498 */ 499 p = &f[i]; 500 if (BPF_CLASS(p->code) == BPF_JMP) { 501 int from = i + 1; 502 503 if (BPF_OP(p->code) == BPF_JA) { 504 if ((p->k < 0) || 505 (from + p->k >= len) || 506 (from + p->k < 0)) 507 return 0; 508 } 509 else if (from + p->jt >= len || from + p->jf >= len) 510 return 0; 511 } 512 /* 513 * Check that memory operations use valid addresses. 514 */ 515 if ((BPF_CLASS(p->code) == BPF_ST || 516 (BPF_CLASS(p->code) == BPF_LD && 517 (p->code & 0xe0) == BPF_MEM)) && 518 (p->k >= BPF_MEMWORDS || p->k < 0)) 519 return 0; 520 /* 521 * Check for constant division by 0. 522 */ 523 if (p->code == (BPF_ALU|BPF_DIV|BPF_K) && p->k == 0) 524 return 0; 525 } 526 return BPF_CLASS(f[len - 1].code) == BPF_RET; 527 } 528 #endif
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