sys/net/bpf_filter.c

   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_RVAL(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