1 /* $NetBSD: bpf_filter.c,v 1.19 2001/11/15 09:48:25 lukem 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. All advertising materials mentioning features or use of this software 21 * must display the following acknowledgement: 22 * This product includes software developed by the University of 23 * California, Berkeley and its contributors. 24 * 4. Neither the name of the University nor the names of its contributors 25 * may be used to endorse or promote products derived from this software 26 * without specific prior written permission. 27 * 28 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 29 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 30 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 31 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 32 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 33 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 34 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 35 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 36 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 37 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 38 * SUCH DAMAGE. 39 * 40 * @(#)bpf_filter.c 8.1 (Berkeley) 6/10/93 41 */ 42 43 #include <sys/cdefs.h> 44 __KERNEL_RCSID(0, "$NetBSD: bpf_filter.c,v 1.19 2001/11/15 09:48:25 lukem Exp $"); 45 46 #if 0 47 #if !(defined(lint) || defined(KERNEL)) 48 static const char rcsid[] = 49 "@(#) Header: bpf_filter.c,v 1.33 97/04/26 13:37:18 leres Exp (LBL)"; 50 #endif 51 #endif 52 53 #include <sys/param.h> 54 #include <sys/time.h> 55 56 #if !defined(UNALIGNED_ACCESS) 57 #define BPF_ALIGN 58 #endif 59 60 #ifndef BPF_ALIGN 61 #define EXTRACT_SHORT(p) ((u_int16_t)ntohs(*(u_int16_t *)p)) 62 #define EXTRACT_LONG(p) (ntohl(*(u_int32_t *)p)) 63 #else 64 #define EXTRACT_SHORT(p)\ 65 ((u_int16_t)\ 66 ((u_int16_t)*((u_char *)p+0)<<8|\ 67 (u_int16_t)*((u_char *)p+1)<<0)) 68 #define EXTRACT_LONG(p)\ 69 ((u_int32_t)*((u_char *)p+0)<<24|\ 70 (u_int32_t)*((u_char *)p+1)<<16|\ 71 (u_int32_t)*((u_char *)p+2)<<8|\ 72 (u_int32_t)*((u_char *)p+3)<<0) 73 #endif 74 75 #ifdef _KERNEL 76 #include <sys/mbuf.h> 77 #define MINDEX(len, m, k) \ 78 { \ 79 len = m->m_len; \ 80 while (k >= len) { \ 81 k -= len; \ 82 m = m->m_next; \ 83 if (m == 0) \ 84 return 0; \ 85 len = m->m_len; \ 86 } \ 87 } 88 89 static int m_xword __P((struct mbuf *, int, int *)); 90 static int m_xhalf __P((struct mbuf *, int, int *)); 91 92 static int 93 m_xword(m, k, err) 94 struct mbuf *m; 95 int k, *err; 96 { 97 int len; 98 u_char *cp, *np; 99 struct mbuf *m0; 100 101 MINDEX(len, m, k); 102 cp = mtod(m, u_char *) + k; 103 if (len - k >= 4) { 104 *err = 0; 105 return EXTRACT_LONG(cp); 106 } 107 m0 = m->m_next; 108 if (m0 == 0 || m0->m_len + len - k < 4) 109 goto bad; 110 *err = 0; 111 np = mtod(m0, u_char *); 112 switch (len - k) { 113 114 case 1: 115 return (cp[0] << 24) | (np[0] << 16) | (np[1] << 8) | np[2]; 116 117 case 2: 118 return (cp[0] << 24) | (cp[1] << 16) | (np[0] << 8) | np[1]; 119 120 default: 121 return (cp[0] << 24) | (cp[1] << 16) | (cp[2] << 8) | np[0]; 122 } 123 bad: 124 *err = 1; 125 return 0; 126 } 127 128 static int 129 m_xhalf(m, k, err) 130 struct mbuf *m; 131 int k, *err; 132 { 133 int len; 134 u_char *cp; 135 struct mbuf *m0; 136 137 MINDEX(len, m, k); 138 cp = mtod(m, u_char *) + k; 139 if (len - k >= 2) { 140 *err = 0; 141 return EXTRACT_SHORT(cp); 142 } 143 m0 = m->m_next; 144 if (m0 == 0) 145 goto bad; 146 *err = 0; 147 return (cp[0] << 8) | mtod(m0, u_char *)[0]; 148 bad: 149 *err = 1; 150 return 0; 151 } 152 #else /* _KERNEL */ 153 #include <stdlib.h> 154 #endif /* !_KERNEL */ 155 156 #include <net/bpf.h> 157 158 /* 159 * Execute the filter program starting at pc on the packet p 160 * wirelen is the length of the original packet 161 * buflen is the amount of data present 162 */ 163 u_int 164 bpf_filter(pc, p, wirelen, buflen) 165 struct bpf_insn *pc; 166 u_char *p; 167 u_int wirelen; 168 u_int buflen; 169 { 170 u_int32_t A, X; 171 int k; 172 int32_t mem[BPF_MEMWORDS]; 173 174 if (pc == 0) 175 /* 176 * No filter means accept all. 177 */ 178 return (u_int)-1; 179 A = 0; 180 X = 0; 181 --pc; 182 while (1) { 183 ++pc; 184 switch (pc->code) { 185 186 default: 187 #ifdef _KERNEL 188 return 0; 189 #else 190 abort(); 191 #endif 192 case BPF_RET|BPF_K: 193 return (u_int)pc->k; 194 195 case BPF_RET|BPF_A: 196 return (u_int)A; 197 198 case BPF_LD|BPF_W|BPF_ABS: 199 k = pc->k; 200 if (k + sizeof(int32_t) > buflen) { 201 #ifdef _KERNEL 202 int merr; 203 204 if (buflen != 0) 205 return 0; 206 A = m_xword((struct mbuf *)p, k, &merr); 207 if (merr != 0) 208 return 0; 209 continue; 210 #else 211 return 0; 212 #endif 213 } 214 A = EXTRACT_LONG(&p[k]); 215 continue; 216 217 case BPF_LD|BPF_H|BPF_ABS: 218 k = pc->k; 219 if (k + sizeof(int16_t) > buflen) { 220 #ifdef _KERNEL 221 int merr; 222 223 if (buflen != 0) 224 return 0; 225 A = m_xhalf((struct mbuf *)p, k, &merr); 226 continue; 227 #else 228 return 0; 229 #endif 230 } 231 A = EXTRACT_SHORT(&p[k]); 232 continue; 233 234 case BPF_LD|BPF_B|BPF_ABS: 235 k = pc->k; 236 if (k >= buflen) { 237 #ifdef _KERNEL 238 struct mbuf *m; 239 int len; 240 241 if (buflen != 0) 242 return 0; 243 m = (struct mbuf *)p; 244 MINDEX(len, m, k); 245 A = mtod(m, u_char *)[k]; 246 continue; 247 #else 248 return 0; 249 #endif 250 } 251 A = p[k]; 252 continue; 253 254 case BPF_LD|BPF_W|BPF_LEN: 255 A = wirelen; 256 continue; 257 258 case BPF_LDX|BPF_W|BPF_LEN: 259 X = wirelen; 260 continue; 261 262 case BPF_LD|BPF_W|BPF_IND: 263 k = X + pc->k; 264 if (k + sizeof(int32_t) > buflen) { 265 #ifdef _KERNEL 266 int merr; 267 268 if (buflen != 0) 269 return 0; 270 A = m_xword((struct mbuf *)p, k, &merr); 271 if (merr != 0) 272 return 0; 273 continue; 274 #else 275 return 0; 276 #endif 277 } 278 A = EXTRACT_LONG(&p[k]); 279 continue; 280 281 case BPF_LD|BPF_H|BPF_IND: 282 k = X + pc->k; 283 if (k + sizeof(int16_t) > buflen) { 284 #ifdef _KERNEL 285 int merr; 286 287 if (buflen != 0) 288 return 0; 289 A = m_xhalf((struct mbuf *)p, k, &merr); 290 if (merr != 0) 291 return 0; 292 continue; 293 #else 294 return 0; 295 #endif 296 } 297 A = EXTRACT_SHORT(&p[k]); 298 continue; 299 300 case BPF_LD|BPF_B|BPF_IND: 301 k = X + pc->k; 302 if (k >= buflen) { 303 #ifdef _KERNEL 304 struct mbuf *m; 305 int len; 306 307 if (buflen != 0) 308 return 0; 309 m = (struct mbuf *)p; 310 MINDEX(len, m, k); 311 A = mtod(m, u_char *)[k]; 312 continue; 313 #else 314 return 0; 315 #endif 316 } 317 A = p[k]; 318 continue; 319 320 case BPF_LDX|BPF_MSH|BPF_B: 321 k = pc->k; 322 if (k >= buflen) { 323 #ifdef _KERNEL 324 struct mbuf *m; 325 int len; 326 327 if (buflen != 0) 328 return 0; 329 m = (struct mbuf *)p; 330 MINDEX(len, m, k); 331 X = (mtod(m, char *)[k] & 0xf) << 2; 332 continue; 333 #else 334 return 0; 335 #endif 336 } 337 X = (p[pc->k] & 0xf) << 2; 338 continue; 339 340 case BPF_LD|BPF_IMM: 341 A = pc->k; 342 continue; 343 344 case BPF_LDX|BPF_IMM: 345 X = pc->k; 346 continue; 347 348 case BPF_LD|BPF_MEM: 349 A = mem[pc->k]; 350 continue; 351 352 case BPF_LDX|BPF_MEM: 353 X = mem[pc->k]; 354 continue; 355 356 case BPF_ST: 357 mem[pc->k] = A; 358 continue; 359 360 case BPF_STX: 361 mem[pc->k] = X; 362 continue; 363 364 case BPF_JMP|BPF_JA: 365 pc += pc->k; 366 continue; 367 368 case BPF_JMP|BPF_JGT|BPF_K: 369 pc += (A > pc->k) ? pc->jt : pc->jf; 370 continue; 371 372 case BPF_JMP|BPF_JGE|BPF_K: 373 pc += (A >= pc->k) ? pc->jt : pc->jf; 374 continue; 375 376 case BPF_JMP|BPF_JEQ|BPF_K: 377 pc += (A == pc->k) ? pc->jt : pc->jf; 378 continue; 379 380 case BPF_JMP|BPF_JSET|BPF_K: 381 pc += (A & pc->k) ? pc->jt : pc->jf; 382 continue; 383 384 case BPF_JMP|BPF_JGT|BPF_X: 385 pc += (A > X) ? pc->jt : pc->jf; 386 continue; 387 388 case BPF_JMP|BPF_JGE|BPF_X: 389 pc += (A >= X) ? pc->jt : pc->jf; 390 continue; 391 392 case BPF_JMP|BPF_JEQ|BPF_X: 393 pc += (A == X) ? pc->jt : pc->jf; 394 continue; 395 396 case BPF_JMP|BPF_JSET|BPF_X: 397 pc += (A & X) ? pc->jt : pc->jf; 398 continue; 399 400 case BPF_ALU|BPF_ADD|BPF_X: 401 A += X; 402 continue; 403 404 case BPF_ALU|BPF_SUB|BPF_X: 405 A -= X; 406 continue; 407 408 case BPF_ALU|BPF_MUL|BPF_X: 409 A *= X; 410 continue; 411 412 case BPF_ALU|BPF_DIV|BPF_X: 413 if (X == 0) 414 return 0; 415 A /= X; 416 continue; 417 418 case BPF_ALU|BPF_AND|BPF_X: 419 A &= X; 420 continue; 421 422 case BPF_ALU|BPF_OR|BPF_X: 423 A |= X; 424 continue; 425 426 case BPF_ALU|BPF_LSH|BPF_X: 427 A <<= X; 428 continue; 429 430 case BPF_ALU|BPF_RSH|BPF_X: 431 A >>= X; 432 continue; 433 434 case BPF_ALU|BPF_ADD|BPF_K: 435 A += pc->k; 436 continue; 437 438 case BPF_ALU|BPF_SUB|BPF_K: 439 A -= pc->k; 440 continue; 441 442 case BPF_ALU|BPF_MUL|BPF_K: 443 A *= pc->k; 444 continue; 445 446 case BPF_ALU|BPF_DIV|BPF_K: 447 A /= pc->k; 448 continue; 449 450 case BPF_ALU|BPF_AND|BPF_K: 451 A &= pc->k; 452 continue; 453 454 case BPF_ALU|BPF_OR|BPF_K: 455 A |= pc->k; 456 continue; 457 458 case BPF_ALU|BPF_LSH|BPF_K: 459 A <<= pc->k; 460 continue; 461 462 case BPF_ALU|BPF_RSH|BPF_K: 463 A >>= pc->k; 464 continue; 465 466 case BPF_ALU|BPF_NEG: 467 A = -A; 468 continue; 469 470 case BPF_MISC|BPF_TAX: 471 X = A; 472 continue; 473 474 case BPF_MISC|BPF_TXA: 475 A = X; 476 continue; 477 } 478 } 479 } 480 481 #ifdef _KERNEL 482 /* 483 * Return true if the 'fcode' is a valid filter program. 484 * The constraints are that each jump be forward and to a valid 485 * code. The code must terminate with either an accept or reject. 486 * 'valid' is an array for use by the routine (it must be at least 487 * 'len' bytes long). 488 * 489 * The kernel needs to be able to verify an application's filter code. 490 * Otherwise, a bogus program could easily crash the system. 491 */ 492 int 493 bpf_validate(f, len) 494 struct bpf_insn *f; 495 int len; 496 { 497 int i; 498 struct bpf_insn *p; 499 500 for (i = 0; i < len; ++i) { 501 /* 502 * Check that that jumps are forward, and within 503 * the code block. 504 */ 505 p = &f[i]; 506 if (BPF_CLASS(p->code) == BPF_JMP) { 507 int from = i + 1; 508 509 if (BPF_OP(p->code) == BPF_JA) { 510 if ((p->k < 0) || 511 (from + p->k >= len) || 512 (from + p->k < 0)) 513 return 0; 514 } 515 else if (from + p->jt >= len || from + p->jf >= len) 516 return 0; 517 } 518 /* 519 * Check that memory operations use valid addresses. 520 */ 521 if ((BPF_CLASS(p->code) == BPF_ST || 522 (BPF_CLASS(p->code) == BPF_LD && 523 (p->code & 0xe0) == BPF_MEM)) && 524 (p->k >= BPF_MEMWORDS || p->k < 0)) 525 return 0; 526 /* 527 * Check for constant division by 0. 528 */ 529 if (p->code == (BPF_ALU|BPF_DIV|BPF_K) && p->k == 0) 530 return 0; 531 } 532 return BPF_CLASS(f[len - 1].code) == BPF_RET; 533 } 534 #endif 535