1 /* 2 * Copyright (c) 1990, 1991 Regents of the University of California. 3 * 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 * %sccs.include.redist.c% 11 * 12 * @(#)bpf_filter.c 7.6 (Berkeley) 06/04/93 13 * 14 * static char rcsid[] = 15 * "$Header: bpf_filter.c,v 1.16 91/10/27 21:22:35 mccanne Exp $"; 16 */ 17 18 #include <sys/param.h> 19 #include <sys/types.h> 20 #include <sys/time.h> 21 22 #ifdef sun 23 #include <netinet/in.h> 24 #endif 25 26 #if defined(sparc) || defined(mips) || defined(ibm032) 27 #define BPF_ALIGN 28 #endif 29 30 #ifndef BPF_ALIGN 31 #define EXTRACT_SHORT(p) ((u_short)ntohs(*(u_short *)p)) 32 #define EXTRACT_LONG(p) (ntohl(*(u_long *)p)) 33 #else 34 #define EXTRACT_SHORT(p)\ 35 ((u_short)\ 36 ((u_short)*((u_char *)p+0)<<8|\ 37 (u_short)*((u_char *)p+1)<<0)) 38 #define EXTRACT_LONG(p)\ 39 ((u_long)*((u_char *)p+0)<<24|\ 40 (u_long)*((u_char *)p+1)<<16|\ 41 (u_long)*((u_char *)p+2)<<8|\ 42 (u_long)*((u_char *)p+3)<<0) 43 #endif 44 45 #ifdef KERNEL 46 #include <sys/mbuf.h> 47 #define MINDEX(m, k) \ 48 { \ 49 register int len = m->m_len; \ 50 \ 51 while (k >= len) { \ 52 k -= len; \ 53 m = m->m_next; \ 54 if (m == 0) \ 55 return 0; \ 56 len = m->m_len; \ 57 } \ 58 } 59 60 static int 61 m_xword(m, k, err) 62 register struct mbuf *m; 63 register int k, *err; 64 { 65 register int len; 66 register u_char *cp, *np; 67 register struct mbuf *m0; 68 69 len = m->m_len; 70 while (k >= len) { 71 k -= len; 72 m = m->m_next; 73 if (m == 0) 74 goto bad; 75 len = m->m_len; 76 } 77 cp = mtod(m, u_char *) + k; 78 if (len - k >= 4) { 79 *err = 0; 80 return EXTRACT_LONG(cp); 81 } 82 m0 = m->m_next; 83 if (m0 == 0 || m0->m_len + len - k < 4) 84 goto bad; 85 *err = 0; 86 np = mtod(m0, u_char *); 87 switch (len - k) { 88 89 case 1: 90 return (cp[k] << 24) | (np[0] << 16) | (np[1] << 8) | np[2]; 91 92 case 2: 93 return (cp[k] << 24) | (cp[k + 1] << 16) | (np[0] << 8) | 94 np[1]; 95 96 default: 97 return (cp[k] << 24) | (cp[k + 1] << 16) | (cp[k + 2] << 8) | 98 np[0]; 99 } 100 bad: 101 *err = 1; 102 return 0; 103 } 104 105 static int 106 m_xhalf(m, k, err) 107 register struct mbuf *m; 108 register int k, *err; 109 { 110 register int len; 111 register u_char *cp; 112 register struct mbuf *m0; 113 114 len = m->m_len; 115 while (k >= len) { 116 k -= len; 117 m = m->m_next; 118 if (m == 0) 119 goto bad; 120 len = m->m_len; 121 } 122 cp = mtod(m, u_char *) + k; 123 if (len - k >= 2) { 124 *err = 0; 125 return EXTRACT_SHORT(cp); 126 } 127 m0 = m->m_next; 128 if (m0 == 0) 129 goto bad; 130 *err = 0; 131 return (cp[k] << 8) | mtod(m0, u_char *)[0]; 132 bad: 133 *err = 1; 134 return 0; 135 } 136 #endif 137 138 #include <net/bpf.h> 139 /* 140 * Execute the filter program starting at pc on the packet p 141 * wirelen is the length of the original packet 142 * buflen is the amount of data present 143 */ 144 u_int 145 bpf_filter(pc, p, wirelen, buflen) 146 register struct bpf_insn *pc; 147 register u_char *p; 148 u_int wirelen; 149 register u_int buflen; 150 { 151 register u_long A, X; 152 register int k; 153 long mem[BPF_MEMWORDS]; 154 155 if (pc == 0) 156 /* 157 * No filter means accept all. 158 */ 159 return (u_int)-1; 160 #ifdef lint 161 A = 0; 162 X = 0; 163 #endif 164 --pc; 165 while (1) { 166 ++pc; 167 switch (pc->code) { 168 169 default: 170 #ifdef KERNEL 171 return 0; 172 #else 173 abort(); 174 #endif 175 case BPF_RET|BPF_K: 176 return (u_int)pc->k; 177 178 case BPF_RET|BPF_A: 179 return (u_int)A; 180 181 case BPF_LD|BPF_W|BPF_ABS: 182 k = pc->k; 183 if (k + sizeof(long) > buflen) { 184 #ifdef KERNEL 185 int merr; 186 187 if (buflen != 0) 188 return 0; 189 A = m_xword((struct mbuf *)p, k, &merr); 190 if (merr != 0) 191 return 0; 192 continue; 193 #else 194 return 0; 195 #endif 196 } 197 #ifdef BPF_ALIGN 198 if (((int)(p + k) & 3) != 0) 199 A = EXTRACT_LONG(&p[k]); 200 else 201 #endif 202 A = ntohl(*(long *)(p + k)); 203 continue; 204 205 case BPF_LD|BPF_H|BPF_ABS: 206 k = pc->k; 207 if (k + sizeof(short) > buflen) { 208 #ifdef KERNEL 209 int merr; 210 211 if (buflen != 0) 212 return 0; 213 A = m_xhalf((struct mbuf *)p, k, &merr); 214 continue; 215 #else 216 return 0; 217 #endif 218 } 219 A = EXTRACT_SHORT(&p[k]); 220 continue; 221 222 case BPF_LD|BPF_B|BPF_ABS: 223 k = pc->k; 224 if (k >= buflen) { 225 #ifdef KERNEL 226 register struct mbuf *m; 227 228 if (buflen != 0) 229 return 0; 230 m = (struct mbuf *)p; 231 MINDEX(m, k); 232 A = mtod(m, u_char *)[k]; 233 continue; 234 #else 235 return 0; 236 #endif 237 } 238 A = p[k]; 239 continue; 240 241 case BPF_LD|BPF_W|BPF_LEN: 242 A = wirelen; 243 continue; 244 245 case BPF_LDX|BPF_W|BPF_LEN: 246 X = wirelen; 247 continue; 248 249 case BPF_LD|BPF_W|BPF_IND: 250 k = X + pc->k; 251 if (k + sizeof(long) > buflen) { 252 #ifdef KERNEL 253 int merr; 254 255 if (buflen != 0) 256 return 0; 257 A = m_xword((struct mbuf *)p, k, &merr); 258 if (merr != 0) 259 return 0; 260 continue; 261 #else 262 return 0; 263 #endif 264 } 265 #ifdef BPF_ALIGN 266 if (((int)(p + k) & 3) != 0) 267 A = EXTRACT_LONG(&p[k]); 268 else 269 #endif 270 A = ntohl(*(long *)(p + k)); 271 continue; 272 273 case BPF_LD|BPF_H|BPF_IND: 274 k = X + pc->k; 275 if (k + sizeof(short) > buflen) { 276 #ifdef KERNEL 277 int merr; 278 279 if (buflen != 0) 280 return 0; 281 A = m_xhalf((struct mbuf *)p, k, &merr); 282 if (merr != 0) 283 return 0; 284 continue; 285 #else 286 return 0; 287 #endif 288 } 289 A = EXTRACT_SHORT(&p[k]); 290 continue; 291 292 case BPF_LD|BPF_B|BPF_IND: 293 k = X + pc->k; 294 if (k >= buflen) { 295 #ifdef KERNEL 296 register struct mbuf *m; 297 298 if (buflen != 0) 299 return 0; 300 m = (struct mbuf *)p; 301 MINDEX(m, k); 302 A = mtod(m, char *)[k]; 303 continue; 304 #else 305 return 0; 306 #endif 307 } 308 A = p[k]; 309 continue; 310 311 case BPF_LDX|BPF_MSH|BPF_B: 312 k = pc->k; 313 if (k >= buflen) { 314 #ifdef KERNEL 315 register struct mbuf *m; 316 317 if (buflen != 0) 318 return 0; 319 m = (struct mbuf *)p; 320 MINDEX(m, k); 321 X = (mtod(m, char *)[k] & 0xf) << 2; 322 continue; 323 #else 324 return 0; 325 #endif 326 } 327 X = (p[pc->k] & 0xf) << 2; 328 continue; 329 330 case BPF_LD|BPF_IMM: 331 A = pc->k; 332 continue; 333 334 case BPF_LDX|BPF_IMM: 335 X = pc->k; 336 continue; 337 338 case BPF_LD|BPF_MEM: 339 A = mem[pc->k]; 340 continue; 341 342 case BPF_LDX|BPF_MEM: 343 X = mem[pc->k]; 344 continue; 345 346 case BPF_ST: 347 mem[pc->k] = A; 348 continue; 349 350 case BPF_STX: 351 mem[pc->k] = X; 352 continue; 353 354 case BPF_JMP|BPF_JA: 355 pc += pc->k; 356 continue; 357 358 case BPF_JMP|BPF_JGT|BPF_K: 359 pc += (A > pc->k) ? pc->jt : pc->jf; 360 continue; 361 362 case BPF_JMP|BPF_JGE|BPF_K: 363 pc += (A >= pc->k) ? pc->jt : pc->jf; 364 continue; 365 366 case BPF_JMP|BPF_JEQ|BPF_K: 367 pc += (A == pc->k) ? pc->jt : pc->jf; 368 continue; 369 370 case BPF_JMP|BPF_JSET|BPF_K: 371 pc += (A & pc->k) ? pc->jt : pc->jf; 372 continue; 373 374 case BPF_JMP|BPF_JGT|BPF_X: 375 pc += (A > X) ? pc->jt : pc->jf; 376 continue; 377 378 case BPF_JMP|BPF_JGE|BPF_X: 379 pc += (A >= X) ? pc->jt : pc->jf; 380 continue; 381 382 case BPF_JMP|BPF_JEQ|BPF_X: 383 pc += (A == X) ? pc->jt : pc->jf; 384 continue; 385 386 case BPF_JMP|BPF_JSET|BPF_X: 387 pc += (A & X) ? pc->jt : pc->jf; 388 continue; 389 390 case BPF_ALU|BPF_ADD|BPF_X: 391 A += X; 392 continue; 393 394 case BPF_ALU|BPF_SUB|BPF_X: 395 A -= X; 396 continue; 397 398 case BPF_ALU|BPF_MUL|BPF_X: 399 A *= X; 400 continue; 401 402 case BPF_ALU|BPF_DIV|BPF_X: 403 if (X == 0) 404 return 0; 405 A /= X; 406 continue; 407 408 case BPF_ALU|BPF_AND|BPF_X: 409 A &= X; 410 continue; 411 412 case BPF_ALU|BPF_OR|BPF_X: 413 A |= X; 414 continue; 415 416 case BPF_ALU|BPF_LSH|BPF_X: 417 A <<= X; 418 continue; 419 420 case BPF_ALU|BPF_RSH|BPF_X: 421 A >>= X; 422 continue; 423 424 case BPF_ALU|BPF_ADD|BPF_K: 425 A += pc->k; 426 continue; 427 428 case BPF_ALU|BPF_SUB|BPF_K: 429 A -= pc->k; 430 continue; 431 432 case BPF_ALU|BPF_MUL|BPF_K: 433 A *= pc->k; 434 continue; 435 436 case BPF_ALU|BPF_DIV|BPF_K: 437 A /= pc->k; 438 continue; 439 440 case BPF_ALU|BPF_AND|BPF_K: 441 A &= pc->k; 442 continue; 443 444 case BPF_ALU|BPF_OR|BPF_K: 445 A |= pc->k; 446 continue; 447 448 case BPF_ALU|BPF_LSH|BPF_K: 449 A <<= pc->k; 450 continue; 451 452 case BPF_ALU|BPF_RSH|BPF_K: 453 A >>= pc->k; 454 continue; 455 456 case BPF_ALU|BPF_NEG: 457 A = -A; 458 continue; 459 460 case BPF_MISC|BPF_TAX: 461 X = A; 462 continue; 463 464 case BPF_MISC|BPF_TXA: 465 A = X; 466 continue; 467 } 468 } 469 } 470 471 #ifdef KERNEL 472 /* 473 * Return true if the 'fcode' is a valid filter program. 474 * The constraints are that each jump be forward and to a valid 475 * code. The code must terminate with either an accept or reject. 476 * 'valid' is an array for use by the routine (it must be at least 477 * 'len' bytes long). 478 * 479 * The kernel needs to be able to verify an application's filter code. 480 * Otherwise, a bogus program could easily crash the system. 481 */ 482 int 483 bpf_validate(f, len) 484 struct bpf_insn *f; 485 int len; 486 { 487 register int i; 488 register struct bpf_insn *p; 489 490 for (i = 0; i < len; ++i) { 491 /* 492 * Check that that jumps are forward, and within 493 * the code block. 494 */ 495 p = &f[i]; 496 if (BPF_CLASS(p->code) == BPF_JMP) { 497 register int from = i + 1; 498 499 if (BPF_OP(p->code) == BPF_JA) { 500 if (from + p->k >= len) 501 return 0; 502 } 503 else if (from + p->jt >= len || from + p->jf >= len) 504 return 0; 505 } 506 /* 507 * Check that memory operations use valid addresses. 508 */ 509 if ((BPF_CLASS(p->code) == BPF_ST || 510 (BPF_CLASS(p->code) == BPF_LD && 511 (p->code & 0xe0) == BPF_MEM)) && 512 (p->k >= BPF_MEMWORDS || p->k < 0)) 513 return 0; 514 /* 515 * Check for constant division by 0. 516 */ 517 if (p->code == (BPF_ALU|BPF_DIV|BPF_K) && p->k == 0) 518 return 0; 519 } 520 return BPF_CLASS(f[len - 1].code) == BPF_RET; 521 } 522 #endif 523