1 /* $NetBSD: bpf_filter.c,v 1.16 2000/04/12 04:21:22 chs 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 #if 0 44 #if !(defined(lint) || defined(KERNEL)) 45 static const char rcsid[] = 46 "@(#) Header: bpf_filter.c,v 1.33 97/04/26 13:37:18 leres Exp (LBL)"; 47 #endif 48 #endif 49 50 #include <sys/param.h> 51 #include <sys/types.h> 52 #include <sys/time.h> 53 54 #if !defined(UNALIGNED_ACCESS) 55 #define BPF_ALIGN 56 #endif 57 58 #ifndef BPF_ALIGN 59 #define EXTRACT_SHORT(p) ((u_int16_t)ntohs(*(u_int16_t *)p)) 60 #define EXTRACT_LONG(p) (ntohl(*(u_int32_t *)p)) 61 #else 62 #define EXTRACT_SHORT(p)\ 63 ((u_int16_t)\ 64 ((u_int16_t)*((u_char *)p+0)<<8|\ 65 (u_int16_t)*((u_char *)p+1)<<0)) 66 #define EXTRACT_LONG(p)\ 67 ((u_int32_t)*((u_char *)p+0)<<24|\ 68 (u_int32_t)*((u_char *)p+1)<<16|\ 69 (u_int32_t)*((u_char *)p+2)<<8|\ 70 (u_int32_t)*((u_char *)p+3)<<0) 71 #endif 72 73 #ifdef _KERNEL 74 #include <sys/mbuf.h> 75 #define MINDEX(len, m, k) \ 76 { \ 77 len = m->m_len; \ 78 while (k >= len) { \ 79 k -= len; \ 80 m = m->m_next; \ 81 if (m == 0) \ 82 return 0; \ 83 len = m->m_len; \ 84 } \ 85 } 86 87 static int m_xword __P((struct mbuf *, int, int *)); 88 static int m_xhalf __P((struct mbuf *, int, int *)); 89 90 static int 91 m_xword(m, k, err) 92 struct mbuf *m; 93 int k, *err; 94 { 95 int len; 96 u_char *cp, *np; 97 struct mbuf *m0; 98 99 MINDEX(len, m, k); 100 cp = mtod(m, u_char *) + k; 101 if (len - k >= 4) { 102 *err = 0; 103 return EXTRACT_LONG(cp); 104 } 105 m0 = m->m_next; 106 if (m0 == 0 || m0->m_len + len - k < 4) 107 goto bad; 108 *err = 0; 109 np = mtod(m0, u_char *); 110 switch (len - k) { 111 112 case 1: 113 return (cp[0] << 24) | (np[0] << 16) | (np[1] << 8) | np[2]; 114 115 case 2: 116 return (cp[0] << 24) | (cp[1] << 16) | (np[0] << 8) | np[1]; 117 118 default: 119 return (cp[0] << 24) | (cp[1] << 16) | (cp[2] << 8) | np[0]; 120 } 121 bad: 122 *err = 1; 123 return 0; 124 } 125 126 static int 127 m_xhalf(m, k, err) 128 struct mbuf *m; 129 int k, *err; 130 { 131 int len; 132 u_char *cp; 133 struct mbuf *m0; 134 135 MINDEX(len, m, k); 136 cp = mtod(m, u_char *) + k; 137 if (len - k >= 2) { 138 *err = 0; 139 return EXTRACT_SHORT(cp); 140 } 141 m0 = m->m_next; 142 if (m0 == 0) 143 goto bad; 144 *err = 0; 145 return (cp[0] << 8) | mtod(m0, u_char *)[0]; 146 bad: 147 *err = 1; 148 return 0; 149 } 150 #endif 151 152 #include <net/bpf.h> 153 154 /* 155 * Execute the filter program starting at pc on the packet p 156 * wirelen is the length of the original packet 157 * buflen is the amount of data present 158 */ 159 u_int 160 bpf_filter(pc, p, wirelen, buflen) 161 struct bpf_insn *pc; 162 u_char *p; 163 u_int wirelen; 164 u_int buflen; 165 { 166 u_int32_t A, X; 167 int k; 168 int32_t mem[BPF_MEMWORDS]; 169 170 if (pc == 0) 171 /* 172 * No filter means accept all. 173 */ 174 return (u_int)-1; 175 A = 0; 176 X = 0; 177 --pc; 178 while (1) { 179 ++pc; 180 switch (pc->code) { 181 182 default: 183 #ifdef _KERNEL 184 return 0; 185 #else 186 abort(); 187 #endif 188 case BPF_RET|BPF_K: 189 return (u_int)pc->k; 190 191 case BPF_RET|BPF_A: 192 return (u_int)A; 193 194 case BPF_LD|BPF_W|BPF_ABS: 195 k = pc->k; 196 if (k + sizeof(int32_t) > buflen) { 197 #ifdef _KERNEL 198 int merr; 199 200 if (buflen != 0) 201 return 0; 202 A = m_xword((struct mbuf *)p, k, &merr); 203 if (merr != 0) 204 return 0; 205 continue; 206 #else 207 return 0; 208 #endif 209 } 210 A = EXTRACT_LONG(&p[k]); 211 continue; 212 213 case BPF_LD|BPF_H|BPF_ABS: 214 k = pc->k; 215 if (k + sizeof(int16_t) > buflen) { 216 #ifdef _KERNEL 217 int merr; 218 219 if (buflen != 0) 220 return 0; 221 A = m_xhalf((struct mbuf *)p, k, &merr); 222 continue; 223 #else 224 return 0; 225 #endif 226 } 227 A = EXTRACT_SHORT(&p[k]); 228 continue; 229 230 case BPF_LD|BPF_B|BPF_ABS: 231 k = pc->k; 232 if (k >= buflen) { 233 #ifdef _KERNEL 234 struct mbuf *m; 235 int len; 236 237 if (buflen != 0) 238 return 0; 239 m = (struct mbuf *)p; 240 MINDEX(len, m, k); 241 A = mtod(m, u_char *)[k]; 242 continue; 243 #else 244 return 0; 245 #endif 246 } 247 A = p[k]; 248 continue; 249 250 case BPF_LD|BPF_W|BPF_LEN: 251 A = wirelen; 252 continue; 253 254 case BPF_LDX|BPF_W|BPF_LEN: 255 X = wirelen; 256 continue; 257 258 case BPF_LD|BPF_W|BPF_IND: 259 k = X + pc->k; 260 if (k + sizeof(int32_t) > buflen) { 261 #ifdef _KERNEL 262 int merr; 263 264 if (buflen != 0) 265 return 0; 266 A = m_xword((struct mbuf *)p, k, &merr); 267 if (merr != 0) 268 return 0; 269 continue; 270 #else 271 return 0; 272 #endif 273 } 274 A = EXTRACT_LONG(&p[k]); 275 continue; 276 277 case BPF_LD|BPF_H|BPF_IND: 278 k = X + pc->k; 279 if (k + sizeof(int16_t) > buflen) { 280 #ifdef _KERNEL 281 int merr; 282 283 if (buflen != 0) 284 return 0; 285 A = m_xhalf((struct mbuf *)p, k, &merr); 286 if (merr != 0) 287 return 0; 288 continue; 289 #else 290 return 0; 291 #endif 292 } 293 A = EXTRACT_SHORT(&p[k]); 294 continue; 295 296 case BPF_LD|BPF_B|BPF_IND: 297 k = X + pc->k; 298 if (k >= buflen) { 299 #ifdef _KERNEL 300 struct mbuf *m; 301 int len; 302 303 if (buflen != 0) 304 return 0; 305 m = (struct mbuf *)p; 306 MINDEX(len, m, k); 307 A = mtod(m, u_char *)[k]; 308 continue; 309 #else 310 return 0; 311 #endif 312 } 313 A = p[k]; 314 continue; 315 316 case BPF_LDX|BPF_MSH|BPF_B: 317 k = pc->k; 318 if (k >= buflen) { 319 #ifdef _KERNEL 320 struct mbuf *m; 321 int len; 322 323 if (buflen != 0) 324 return 0; 325 m = (struct mbuf *)p; 326 MINDEX(len, m, k); 327 X = (mtod(m, char *)[k] & 0xf) << 2; 328 continue; 329 #else 330 return 0; 331 #endif 332 } 333 X = (p[pc->k] & 0xf) << 2; 334 continue; 335 336 case BPF_LD|BPF_IMM: 337 A = pc->k; 338 continue; 339 340 case BPF_LDX|BPF_IMM: 341 X = pc->k; 342 continue; 343 344 case BPF_LD|BPF_MEM: 345 A = mem[pc->k]; 346 continue; 347 348 case BPF_LDX|BPF_MEM: 349 X = mem[pc->k]; 350 continue; 351 352 case BPF_ST: 353 mem[pc->k] = A; 354 continue; 355 356 case BPF_STX: 357 mem[pc->k] = X; 358 continue; 359 360 case BPF_JMP|BPF_JA: 361 pc += pc->k; 362 continue; 363 364 case BPF_JMP|BPF_JGT|BPF_K: 365 pc += (A > pc->k) ? pc->jt : pc->jf; 366 continue; 367 368 case BPF_JMP|BPF_JGE|BPF_K: 369 pc += (A >= pc->k) ? pc->jt : pc->jf; 370 continue; 371 372 case BPF_JMP|BPF_JEQ|BPF_K: 373 pc += (A == pc->k) ? pc->jt : pc->jf; 374 continue; 375 376 case BPF_JMP|BPF_JSET|BPF_K: 377 pc += (A & pc->k) ? pc->jt : pc->jf; 378 continue; 379 380 case BPF_JMP|BPF_JGT|BPF_X: 381 pc += (A > X) ? pc->jt : pc->jf; 382 continue; 383 384 case BPF_JMP|BPF_JGE|BPF_X: 385 pc += (A >= X) ? pc->jt : pc->jf; 386 continue; 387 388 case BPF_JMP|BPF_JEQ|BPF_X: 389 pc += (A == X) ? pc->jt : pc->jf; 390 continue; 391 392 case BPF_JMP|BPF_JSET|BPF_X: 393 pc += (A & X) ? pc->jt : pc->jf; 394 continue; 395 396 case BPF_ALU|BPF_ADD|BPF_X: 397 A += X; 398 continue; 399 400 case BPF_ALU|BPF_SUB|BPF_X: 401 A -= X; 402 continue; 403 404 case BPF_ALU|BPF_MUL|BPF_X: 405 A *= X; 406 continue; 407 408 case BPF_ALU|BPF_DIV|BPF_X: 409 if (X == 0) 410 return 0; 411 A /= X; 412 continue; 413 414 case BPF_ALU|BPF_AND|BPF_X: 415 A &= X; 416 continue; 417 418 case BPF_ALU|BPF_OR|BPF_X: 419 A |= X; 420 continue; 421 422 case BPF_ALU|BPF_LSH|BPF_X: 423 A <<= X; 424 continue; 425 426 case BPF_ALU|BPF_RSH|BPF_X: 427 A >>= X; 428 continue; 429 430 case BPF_ALU|BPF_ADD|BPF_K: 431 A += pc->k; 432 continue; 433 434 case BPF_ALU|BPF_SUB|BPF_K: 435 A -= pc->k; 436 continue; 437 438 case BPF_ALU|BPF_MUL|BPF_K: 439 A *= pc->k; 440 continue; 441 442 case BPF_ALU|BPF_DIV|BPF_K: 443 A /= pc->k; 444 continue; 445 446 case BPF_ALU|BPF_AND|BPF_K: 447 A &= pc->k; 448 continue; 449 450 case BPF_ALU|BPF_OR|BPF_K: 451 A |= pc->k; 452 continue; 453 454 case BPF_ALU|BPF_LSH|BPF_K: 455 A <<= pc->k; 456 continue; 457 458 case BPF_ALU|BPF_RSH|BPF_K: 459 A >>= pc->k; 460 continue; 461 462 case BPF_ALU|BPF_NEG: 463 A = -A; 464 continue; 465 466 case BPF_MISC|BPF_TAX: 467 X = A; 468 continue; 469 470 case BPF_MISC|BPF_TXA: 471 A = X; 472 continue; 473 } 474 } 475 } 476 477 #ifdef _KERNEL 478 /* 479 * Return true if the 'fcode' is a valid filter program. 480 * The constraints are that each jump be forward and to a valid 481 * code. The code must terminate with either an accept or reject. 482 * 'valid' is an array for use by the routine (it must be at least 483 * 'len' bytes long). 484 * 485 * The kernel needs to be able to verify an application's filter code. 486 * Otherwise, a bogus program could easily crash the system. 487 */ 488 int 489 bpf_validate(f, len) 490 struct bpf_insn *f; 491 int len; 492 { 493 int i; 494 struct bpf_insn *p; 495 496 for (i = 0; i < len; ++i) { 497 /* 498 * Check that that jumps are forward, and within 499 * the code block. 500 */ 501 p = &f[i]; 502 if (BPF_CLASS(p->code) == BPF_JMP) { 503 int from = i + 1; 504 505 if (BPF_OP(p->code) == BPF_JA) { 506 if ((p->k < 0) || 507 (from + p->k >= len) || 508 (from + p->k < 0)) 509 return 0; 510 } 511 else if (from + p->jt >= len || from + p->jf >= len) 512 return 0; 513 } 514 /* 515 * Check that memory operations use valid addresses. 516 */ 517 if ((BPF_CLASS(p->code) == BPF_ST || 518 (BPF_CLASS(p->code) == BPF_LD && 519 (p->code & 0xe0) == BPF_MEM)) && 520 (p->k >= BPF_MEMWORDS || p->k < 0)) 521 return 0; 522 /* 523 * Check for constant division by 0. 524 */ 525 if (p->code == (BPF_ALU|BPF_DIV|BPF_K) && p->k == 0) 526 return 0; 527 } 528 return BPF_CLASS(f[len - 1].code) == BPF_RET; 529 } 530 #endif 531