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  */
  42
  43 #include <sys/systm.h>
  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 == NULL)
 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 == NULL || 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 == NULL)
 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 == NULL)
 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         bzero(mem, sizeof(mem));
 185
 186         if (pc == NULL) {
 187                 /*
 188                  * No filter means accept all.
 189                  */
 190                 return (u_int)-1;
 191         }
 192
 193         --pc;
 194         while (1) {
 195                 ++pc;
 196                 switch (pc->code) {
 197
 198                 default:
 199 #ifdef _KERNEL
 200                         return 0;
 201 #else
 202                         abort();
 203 #endif
 204                 case BPF_RET|BPF_K:
 205                         return (u_int)pc->k;
 206
 207                 case BPF_RET|BPF_A:
 208                         return (u_int)A;
 209
 210                 case BPF_LD|BPF_W|BPF_ABS:
 211                         k = pc->k;
 212                         if (k > buflen || sizeof(int32_t) > buflen - k) {
 213 #ifdef _KERNEL
 214                                 int merr;
 215
 216                                 if (buflen != 0)
 217                                         return 0;
 218                                 A = m_xword((struct mbuf *)p, k, &merr);
 219                                 if (merr != 0)
 220                                         return 0;
 221                                 continue;
 222 #else
 223                                 return 0;
 224 #endif
 225                         }
 226 #ifdef BPF_ALIGN
 227                         if (((intptr_t)(p + k) & 3) != 0)
 228                                 A = EXTRACT_LONG(&p[k]);
 229                         else
 230 #endif
 231                                 A = ntohl(*(int32_t *)(p + k));
 232                         continue;
 233
 234                 case BPF_LD|BPF_H|BPF_ABS:
 235                         k = pc->k;
 236                         if (k > buflen || sizeof(int16_t) > buflen - k) {
 237 #ifdef _KERNEL
 238                                 int merr;
 239
 240                                 if (buflen != 0)
 241                                         return 0;
 242                                 A = m_xhalf((struct mbuf *)p, k, &merr);
 243                                 continue;
 244 #else
 245                                 return 0;
 246 #endif
 247                         }
 248                         A = EXTRACT_SHORT(&p[k]);
 249                         continue;
 250
 251                 case BPF_LD|BPF_B|BPF_ABS:
 252                         k = pc->k;
 253                         if (k >= buflen) {
 254 #ifdef _KERNEL
 255                                 struct mbuf *m;
 256
 257                                 if (buflen != 0)
 258                                         return 0;
 259                                 m = (struct mbuf *)p;
 260                                 MINDEX(m, k);
 261                                 A = mtod(m, u_char *)[k];
 262                                 continue;
 263 #else
 264                                 return 0;
 265 #endif
 266                         }
 267                         A = p[k];
 268                         continue;
 269
 270                 case BPF_LD|BPF_W|BPF_LEN:
 271                         A = wirelen;
 272                         continue;
 273
 274                 case BPF_LDX|BPF_W|BPF_LEN:
 275                         X = wirelen;
 276                         continue;
 277
 278                 case BPF_LD|BPF_W|BPF_IND:
 279                         k = X + pc->k;
 280                         if (pc->k > buflen || X > buflen - pc->k ||
 281                             sizeof(int32_t) > buflen - k) {
 282 #ifdef _KERNEL
 283                                 int merr;
 284
 285                                 if (buflen != 0)
 286                                         return 0;
 287                                 A = m_xword((struct mbuf *)p, k, &merr);
 288                                 if (merr != 0)
 289                                         return 0;
 290                                 continue;
 291 #else
 292                                 return 0;
 293 #endif
 294                         }
 295 #ifdef BPF_ALIGN
 296                         if (((intptr_t)(p + k) & 3) != 0)
 297                                 A = EXTRACT_LONG(&p[k]);
 298                         else
 299 #endif
 300                                 A = ntohl(*(int32_t *)(p + k));
 301                         continue;
 302
 303                 case BPF_LD|BPF_H|BPF_IND:
 304                         k = X + pc->k;
 305                         if (X > buflen || pc->k > buflen - X ||
 306                             sizeof(int16_t) > buflen - k) {
 307 #ifdef _KERNEL
 308                                 int merr;
 309
 310                                 if (buflen != 0)
 311                                         return 0;
 312                                 A = m_xhalf((struct mbuf *)p, k, &merr);
 313                                 if (merr != 0)
 314                                         return 0;
 315                                 continue;
 316 #else
 317                                 return 0;
 318 #endif
 319                         }
 320                         A = EXTRACT_SHORT(&p[k]);
 321                         continue;
 322
 323                 case BPF_LD|BPF_B|BPF_IND:
 324                         k = X + pc->k;
 325                         if (pc->k >= buflen || X >= buflen - pc->k) {
 326 #ifdef _KERNEL
 327                                 struct mbuf *m;
 328
 329                                 if (buflen != 0)
 330                                         return 0;
 331                                 m = (struct mbuf *)p;
 332                                 MINDEX(m, k);
 333                                 A = mtod(m, u_char *)[k];
 334                                 continue;
 335 #else
 336                                 return 0;
 337 #endif
 338                         }
 339                         A = p[k];
 340                         continue;
 341
 342                 case BPF_LDX|BPF_MSH|BPF_B:
 343                         k = pc->k;
 344                         if (k >= buflen) {
 345 #ifdef _KERNEL
 346                                 struct mbuf *m;
 347
 348                                 if (buflen != 0)
 349                                         return 0;
 350                                 m = (struct mbuf *)p;
 351                                 MINDEX(m, k);
 352                                 X = (mtod(m, char *)[k] & 0xf) << 2;
 353                                 continue;
 354 #else
 355                                 return 0;
 356 #endif
 357                         }
 358                         X = (p[pc->k] & 0xf) << 2;
 359                         continue;
 360
 361                 case BPF_LD|BPF_IMM:
 362                         A = pc->k;
 363                         continue;
 364
 365                 case BPF_LDX|BPF_IMM:
 366                         X = pc->k;
 367                         continue;
 368
 369                 case BPF_LD|BPF_MEM:
 370                         A = mem[pc->k];
 371                         continue;
 372
 373                 case BPF_LDX|BPF_MEM:
 374                         X = mem[pc->k];
 375                         continue;
 376
 377                 case BPF_ST:
 378                         mem[pc->k] = A;
 379                         continue;
 380
 381                 case BPF_STX:
 382                         mem[pc->k] = X;
 383                         continue;
 384
 385                 case BPF_JMP|BPF_JA:
 386                         pc += pc->k;
 387                         continue;
 388
 389                 case BPF_JMP|BPF_JGT|BPF_K:
 390                         pc += (A > pc->k) ? pc->jt : pc->jf;
 391                         continue;
 392
 393                 case BPF_JMP|BPF_JGE|BPF_K:
 394                         pc += (A >= pc->k) ? pc->jt : pc->jf;
 395                         continue;
 396
 397                 case BPF_JMP|BPF_JEQ|BPF_K:
 398                         pc += (A == pc->k) ? pc->jt : pc->jf;
 399                         continue;
 400
 401                 case BPF_JMP|BPF_JSET|BPF_K:
 402                         pc += (A & pc->k) ? pc->jt : pc->jf;
 403                         continue;
 404
 405                 case BPF_JMP|BPF_JGT|BPF_X:
 406                         pc += (A > X) ? pc->jt : pc->jf;
 407                         continue;
 408
 409                 case BPF_JMP|BPF_JGE|BPF_X:
 410                         pc += (A >= X) ? pc->jt : pc->jf;
 411                         continue;
 412
 413                 case BPF_JMP|BPF_JEQ|BPF_X:
 414                         pc += (A == X) ? pc->jt : pc->jf;
 415                         continue;
 416
 417                 case BPF_JMP|BPF_JSET|BPF_X:
 418                         pc += (A & X) ? pc->jt : pc->jf;
 419                         continue;
 420
 421                 case BPF_ALU|BPF_ADD|BPF_X:
 422                         A += X;
 423                         continue;
 424
 425                 case BPF_ALU|BPF_SUB|BPF_X:
 426                         A -= X;
 427                         continue;
 428
 429                 case BPF_ALU|BPF_MUL|BPF_X:
 430                         A *= X;
 431                         continue;
 432
 433                 case BPF_ALU|BPF_DIV|BPF_X:
 434                         if (X == 0)
 435                                 return 0;
 436                         A /= X;
 437                         continue;
 438
 439                 case BPF_ALU|BPF_AND|BPF_X:
 440                         A &= X;
 441                         continue;
 442
 443                 case BPF_ALU|BPF_OR|BPF_X:
 444                         A |= X;
 445                         continue;
 446
 447                 case BPF_ALU|BPF_LSH|BPF_X:
 448                         A <<= X;
 449                         continue;
 450
 451                 case BPF_ALU|BPF_RSH|BPF_X:
 452                         A >>= X;
 453                         continue;
 454
 455                 case BPF_ALU|BPF_ADD|BPF_K:
 456                         A += pc->k;
 457                         continue;
 458
 459                 case BPF_ALU|BPF_SUB|BPF_K:
 460                         A -= pc->k;
 461                         continue;
 462
 463                 case BPF_ALU|BPF_MUL|BPF_K:
 464                         A *= pc->k;
 465                         continue;
 466
 467                 case BPF_ALU|BPF_DIV|BPF_K:
 468                         A /= pc->k;
 469                         continue;
 470
 471                 case BPF_ALU|BPF_AND|BPF_K:
 472                         A &= pc->k;
 473                         continue;
 474
 475                 case BPF_ALU|BPF_OR|BPF_K:
 476                         A |= pc->k;
 477                         continue;
 478
 479                 case BPF_ALU|BPF_LSH|BPF_K:
 480                         A <<= pc->k;
 481                         continue;
 482
 483                 case BPF_ALU|BPF_RSH|BPF_K:
 484                         A >>= pc->k;
 485                         continue;
 486
 487                 case BPF_ALU|BPF_NEG:
 488                         A = -A;
 489                         continue;
 490
 491                 case BPF_MISC|BPF_TAX:
 492                         X = A;
 493                         continue;
 494
 495                 case BPF_MISC|BPF_TXA:
 496                         A = X;
 497                         continue;
 498                 }
 499         }
 500 }
 501
 502 #ifdef _KERNEL
 503 /*
 504  * Return true if the 'fcode' is a valid filter program.
 505  * The constraints are that each jump be forward and to a valid
 506  * code, that memory accesses are within valid ranges (to the
 507  * extent that this can be checked statically; loads of packet
 508  * data have to be, and are, also checked at run time), and that
 509  * the code terminates with either an accept or reject.
 510  *
 511  * The kernel needs to be able to verify an application's filter code.
 512  * Otherwise, a bogus program could easily crash the system.
 513  */
 514 int
 515 bpf_validate(const struct bpf_insn *f, int len)
 516 {
 517         u_int i, from;
 518         const struct bpf_insn *p;
 519
 520         if (len < 1 || len > BPF_MAXINSNS)
 521                 return 0;
 522
 523         for (i = 0; i < len; ++i) {
 524                 p = &f[i];
 525                 switch (BPF_CLASS(p->code)) {
 526                 /*
 527                  * Check that memory operations use valid addresses.
 528                  */
 529                 case BPF_LD:
 530                 case BPF_LDX:
 531                         switch (BPF_MODE(p->code)) {
 532                         case BPF_IMM:
 533                                 break;
 534                         case BPF_ABS:
 535                         case BPF_IND:
 536                         case BPF_MSH:
 537                                 /*
 538                                  * More strict check with actual packet length
 539                                  * is done runtime.
 540                                  */
 541                                 if (p->k >= bpf_maxbufsize)
 542                                         return 0;
 543                                 break;
 544                         case BPF_MEM:
 545                                 if (p->k >= BPF_MEMWORDS)
 546                                         return 0;
 547                                 break;
 548                         case BPF_LEN:
 549                                 break;
 550                         default:
 551                                 return 0;
 552                         }
 553                         break;
 554                 case BPF_ST:
 555                 case BPF_STX:
 556                         if (p->k >= BPF_MEMWORDS)
 557                                 return 0;
 558                         break;
 559                 case BPF_ALU:
 560                         switch (BPF_OP(p->code)) {
 561                         case BPF_ADD:
 562                         case BPF_SUB:
 563                         case BPF_MUL:
 564                         case BPF_OR:
 565                         case BPF_AND:
 566                         case BPF_LSH:
 567                         case BPF_RSH:
 568                         case BPF_NEG:
 569                                 break;
 570                         case BPF_DIV:
 571                                 /*
 572                                  * Check for constant division by 0.
 573                                  */
 574                                 if (BPF_SRC(p->code) == BPF_K && p->k == 0)
 575                                         return 0;
 576                                 break;
 577                         default:
 578                                 return 0;
 579                         }
 580                         break;
 581                 case BPF_JMP:
 582                         /*
 583                          * Check that jumps are within the code block,
 584                          * and that unconditional branches don't go
 585                          * backwards as a result of an overflow.
 586                          * Unconditional branches have a 32-bit offset,
 587                          * so they could overflow; we check to make
 588                          * sure they don't.  Conditional branches have
 589                          * an 8-bit offset, and the from address is <=
 590                          * BPF_MAXINSNS, and we assume that BPF_MAXINSNS
 591                          * is sufficiently small that adding 255 to it
 592                          * won't overflow.
 593                          *
 594                          * We know that len is <= BPF_MAXINSNS, and we
 595                          * assume that BPF_MAXINSNS is < the maximum size
 596                          * of a u_int, so that i + 1 doesn't overflow.
 597                          */
 598                         from = i + 1;
 599                         switch (BPF_OP(p->code)) {
 600                         case BPF_JA:
 601                                 if (from + p->k < from || from + p->k >= len)
 602                                         return 0;
 603                                 break;
 604                         case BPF_JEQ:
 605                         case BPF_JGT:
 606                         case BPF_JGE:
 607                         case BPF_JSET:
 608                                 if (from + p->jt >= len || from + p->jf >= len)
 609                                         return 0;
 610                                 break;
 611                         default:
 612                                 return 0;
 613                         }
 614                         break;
 615                 case BPF_RET:
 616                         break;
 617                 case BPF_MISC:
 618                         break;
 619                 default:
 620                         return 0;
 621                 }
 622         }
 623         return BPF_CLASS(f[len - 1].code) == BPF_RET;
 624 }
 625 #endif