The Tcpdump Group git mirrors - libpcap/blob - bpf_filter.c

   1 /*-
   2  * Copyright (c) 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997
   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.c       7.5 (Berkeley) 7/15/91
  39  */
  40
  41 #ifdef HAVE_CONFIG_H
  42 #include <config.h>
  43 #endif
  44
  45 #include <pcap/pcap-inttypes.h>
  46 #include "pcap-types.h"
  47 #include "extract.h"
  48
  49 #define EXTRACT_SHORT   EXTRACT_BE_U_2
  50 #define EXTRACT_LONG    EXTRACT_BE_U_4
  51
  52 #ifndef _WIN32
  53 #include <sys/param.h>
  54 #include <sys/types.h>
  55 #include <sys/time.h>
  56 #endif /* _WIN32 */
  57
  58 #include <pcap-int.h>
  59
  60 #include <stdlib.h>
  61
  62 #ifdef __linux__
  63 #include <linux/types.h>
  64 #include <linux/if_packet.h>
  65 #include <linux/filter.h>
  66 #endif
  67
  68 enum {
  69         BPF_S_ANC_NONE,
  70         BPF_S_ANC_VLAN_TAG,
  71         BPF_S_ANC_VLAN_TAG_PRESENT,
  72 };
  73
  74 /*
  75  * Execute the filter program starting at pc on the packet p
  76  * wirelen is the length of the original packet
  77  * buflen is the amount of data present
  78  * aux_data is auxiliary data, currently used only when interpreting
  79  * filters intended for the Linux kernel in cases where the kernel
  80  * rejects the filter; it contains VLAN tag information
  81  * For the kernel, p is assumed to be a pointer to an mbuf if buflen is 0,
  82  * in all other cases, p is a pointer to a buffer and buflen is its size.
  83  *
  84  * Thanks to Ani Sinha <ani@arista.com> for providing initial implementation
  85  */
  86 #if defined(SKF_AD_VLAN_TAG_PRESENT)
  87 u_int
  88 pcap_filter_with_aux_data(const struct bpf_insn *pc, const u_char *p,
  89     u_int wirelen, u_int buflen, const struct bpf_aux_data *aux_data)
  90 #else
  91 u_int
  92 pcap_filter_with_aux_data(const struct bpf_insn *pc, const u_char *p,
  93     u_int wirelen, u_int buflen, const struct bpf_aux_data *aux_data _U_)
  94 #endif
  95 {
  96         register uint32_t A, X;
  97         register bpf_u_int32 k;
  98         uint32_t mem[BPF_MEMWORDS];
  99
 100         if (pc == 0)
 101                 /*
 102                  * No filter means accept all.
 103                  */
 104                 return (u_int)-1;
 105         A = 0;
 106         X = 0;
 107         --pc;
 108         for (;;) {
 109                 ++pc;
 110                 switch (pc->code) {
 111
 112                 default:
 113                         abort();
 114                 case BPF_RET|BPF_K:
 115                         return (u_int)pc->k;
 116
 117                 case BPF_RET|BPF_A:
 118                         return (u_int)A;
 119
 120                 case BPF_LD|BPF_W|BPF_ABS:
 121                         k = pc->k;
 122                         if (k > buflen || sizeof(int32_t) > buflen - k) {
 123                                 return 0;
 124                         }
 125                         A = EXTRACT_LONG(&p[k]);
 126                         continue;
 127
 128                 case BPF_LD|BPF_H|BPF_ABS:
 129                         k = pc->k;
 130                         if (k > buflen || sizeof(int16_t) > buflen - k) {
 131                                 return 0;
 132                         }
 133                         A = EXTRACT_SHORT(&p[k]);
 134                         continue;
 135
 136                 case BPF_LD|BPF_B|BPF_ABS:
 137                         switch (pc->k) {
 138
 139 #if defined(SKF_AD_VLAN_TAG_PRESENT)
 140                         case SKF_AD_OFF + SKF_AD_VLAN_TAG:
 141                                 if (!aux_data)
 142                                         return 0;
 143                                 A = aux_data->vlan_tag;
 144                                 break;
 145
 146                         case SKF_AD_OFF + SKF_AD_VLAN_TAG_PRESENT:
 147                                 if (!aux_data)
 148                                         return 0;
 149                                 A = aux_data->vlan_tag_present;
 150                                 break;
 151 #endif
 152                         default:
 153                                 k = pc->k;
 154                                 if (k >= buflen) {
 155                                         return 0;
 156                                 }
 157                                 A = p[k];
 158                                 break;
 159                         }
 160                         continue;
 161
 162                 case BPF_LD|BPF_W|BPF_LEN:
 163                         A = wirelen;
 164                         continue;
 165
 166                 case BPF_LDX|BPF_W|BPF_LEN:
 167                         X = wirelen;
 168                         continue;
 169
 170                 case BPF_LD|BPF_W|BPF_IND:
 171                         k = X + pc->k;
 172                         if (pc->k > buflen || X > buflen - pc->k ||
 173                             sizeof(int32_t) > buflen - k) {
 174                                 return 0;
 175                         }
 176                         A = EXTRACT_LONG(&p[k]);
 177                         continue;
 178
 179                 case BPF_LD|BPF_H|BPF_IND:
 180                         k = X + pc->k;
 181                         if (X > buflen || pc->k > buflen - X ||
 182                             sizeof(int16_t) > buflen - k) {
 183                                 return 0;
 184                         }
 185                         A = EXTRACT_SHORT(&p[k]);
 186                         continue;
 187
 188                 case BPF_LD|BPF_B|BPF_IND:
 189                         k = X + pc->k;
 190                         if (pc->k >= buflen || X >= buflen - pc->k) {
 191                                 return 0;
 192                         }
 193                         A = p[k];
 194                         continue;
 195
 196                 case BPF_LDX|BPF_MSH|BPF_B:
 197                         k = pc->k;
 198                         if (k >= buflen) {
 199                                 return 0;
 200                         }
 201                         X = (p[pc->k] & 0xf) << 2;
 202                         continue;
 203
 204                 case BPF_LD|BPF_IMM:
 205                         A = pc->k;
 206                         continue;
 207
 208                 case BPF_LDX|BPF_IMM:
 209                         X = pc->k;
 210                         continue;
 211
 212                 case BPF_LD|BPF_MEM:
 213                         A = mem[pc->k];
 214                         continue;
 215
 216                 case BPF_LDX|BPF_MEM:
 217                         X = mem[pc->k];
 218                         continue;
 219
 220                 case BPF_ST:
 221                         mem[pc->k] = A;
 222                         continue;
 223
 224                 case BPF_STX:
 225                         mem[pc->k] = X;
 226                         continue;
 227
 228                 case BPF_JMP|BPF_JA:
 229                         /*
 230                          * XXX - we currently implement "ip6 protochain"
 231                          * with backward jumps, so sign-extend pc->k.
 232                          */
 233                         pc += (bpf_int32)pc->k;
 234                         continue;
 235
 236                 case BPF_JMP|BPF_JGT|BPF_K:
 237                         pc += (A > pc->k) ? pc->jt : pc->jf;
 238                         continue;
 239
 240                 case BPF_JMP|BPF_JGE|BPF_K:
 241                         pc += (A >= pc->k) ? pc->jt : pc->jf;
 242                         continue;
 243
 244                 case BPF_JMP|BPF_JEQ|BPF_K:
 245                         pc += (A == pc->k) ? pc->jt : pc->jf;
 246                         continue;
 247
 248                 case BPF_JMP|BPF_JSET|BPF_K:
 249                         pc += (A & pc->k) ? pc->jt : pc->jf;
 250                         continue;
 251
 252                 case BPF_JMP|BPF_JGT|BPF_X:
 253                         pc += (A > X) ? pc->jt : pc->jf;
 254                         continue;
 255
 256                 case BPF_JMP|BPF_JGE|BPF_X:
 257                         pc += (A >= X) ? pc->jt : pc->jf;
 258                         continue;
 259
 260                 case BPF_JMP|BPF_JEQ|BPF_X:
 261                         pc += (A == X) ? pc->jt : pc->jf;
 262                         continue;
 263
 264                 case BPF_JMP|BPF_JSET|BPF_X:
 265                         pc += (A & X) ? pc->jt : pc->jf;
 266                         continue;
 267
 268                 case BPF_ALU|BPF_ADD|BPF_X:
 269                         A += X;
 270                         continue;
 271
 272                 case BPF_ALU|BPF_SUB|BPF_X:
 273                         A -= X;
 274                         continue;
 275
 276                 case BPF_ALU|BPF_MUL|BPF_X:
 277                         A *= X;
 278                         continue;
 279
 280                 case BPF_ALU|BPF_DIV|BPF_X:
 281                         if (X == 0)
 282                                 return 0;
 283                         A /= X;
 284                         continue;
 285
 286                 case BPF_ALU|BPF_MOD|BPF_X:
 287                         if (X == 0)
 288                                 return 0;
 289                         A %= X;
 290                         continue;
 291
 292                 case BPF_ALU|BPF_AND|BPF_X:
 293                         A &= X;
 294                         continue;
 295
 296                 case BPF_ALU|BPF_OR|BPF_X:
 297                         A |= X;
 298                         continue;
 299
 300                 case BPF_ALU|BPF_XOR|BPF_X:
 301                         A ^= X;
 302                         continue;
 303
 304                 case BPF_ALU|BPF_LSH|BPF_X:
 305                         if (X < 32)
 306                                 A <<= X;
 307                         else
 308                                 A = 0;
 309                         continue;
 310
 311                 case BPF_ALU|BPF_RSH|BPF_X:
 312                         if (X < 32)
 313                                 A >>= X;
 314                         else
 315                                 A = 0;
 316                         continue;
 317
 318                 case BPF_ALU|BPF_ADD|BPF_K:
 319                         A += pc->k;
 320                         continue;
 321
 322                 case BPF_ALU|BPF_SUB|BPF_K:
 323                         A -= pc->k;
 324                         continue;
 325
 326                 case BPF_ALU|BPF_MUL|BPF_K:
 327                         A *= pc->k;
 328                         continue;
 329
 330                 case BPF_ALU|BPF_DIV|BPF_K:
 331                         A /= pc->k;
 332                         continue;
 333
 334                 case BPF_ALU|BPF_MOD|BPF_K:
 335                         A %= pc->k;
 336                         continue;
 337
 338                 case BPF_ALU|BPF_AND|BPF_K:
 339                         A &= pc->k;
 340                         continue;
 341
 342                 case BPF_ALU|BPF_OR|BPF_K:
 343                         A |= pc->k;
 344                         continue;
 345
 346                 case BPF_ALU|BPF_XOR|BPF_K:
 347                         A ^= pc->k;
 348                         continue;
 349
 350                 case BPF_ALU|BPF_LSH|BPF_K:
 351                         A <<= pc->k;
 352                         continue;
 353
 354                 case BPF_ALU|BPF_RSH|BPF_K:
 355                         A >>= pc->k;
 356                         continue;
 357
 358                 case BPF_ALU|BPF_NEG:
 359                         /*
 360                          * Most BPF arithmetic is unsigned, but negation
 361                          * can't be unsigned; respecify it as subtracting
 362                          * the accumulator from 0U, so that 1) we don't
 363                          * get compiler warnings about negating an unsigned
 364                          * value and 2) don't get UBSan warnings about
 365                          * the result of negating 0x80000000 being undefined.
 366                          */
 367                         A = (0U - A);
 368                         continue;
 369
 370                 case BPF_MISC|BPF_TAX:
 371                         X = A;
 372                         continue;
 373
 374                 case BPF_MISC|BPF_TXA:
 375                         A = X;
 376                         continue;
 377                 }
 378         }
 379 }
 380
 381 u_int
 382 pcap_filter(const struct bpf_insn *pc, const u_char *p, u_int wirelen,
 383     u_int buflen)
 384 {
 385         return pcap_filter_with_aux_data(pc, p, wirelen, buflen, NULL);
 386 }
 387
 388 /*
 389  * Return true if the 'fcode' is a valid filter program.
 390  * The constraints are that each jump be forward and to a valid
 391  * code, that memory accesses are within valid ranges (to the
 392  * extent that this can be checked statically; loads of packet
 393  * data have to be, and are, also checked at run time), and that
 394  * the code terminates with either an accept or reject.
 395  *
 396  * The kernel needs to be able to verify an application's filter code.
 397  * Otherwise, a bogus program could easily crash the system.
 398  */
 399 int
 400 pcap_validate_filter(const struct bpf_insn *f, int len)
 401 {
 402         u_int i, from;
 403         const struct bpf_insn *p;
 404
 405         if (len < 1)
 406                 return 0;
 407
 408         for (i = 0; i < (u_int)len; ++i) {
 409                 p = &f[i];
 410                 switch (BPF_CLASS(p->code)) {
 411                 /*
 412                  * Check that memory operations use valid addresses.
 413                  */
 414                 case BPF_LD:
 415                 case BPF_LDX:
 416                         switch (BPF_MODE(p->code)) {
 417                         case BPF_IMM:
 418                                 break;
 419                         case BPF_ABS:
 420                         case BPF_IND:
 421                         case BPF_MSH:
 422                                 /*
 423                                  * There's no maximum packet data size
 424                                  * in userland.  The runtime packet length
 425                                  * check suffices.
 426                                  */
 427                                 break;
 428                         case BPF_MEM:
 429                                 if (p->k >= BPF_MEMWORDS)
 430                                         return 0;
 431                                 break;
 432                         case BPF_LEN:
 433                                 break;
 434                         default:
 435                                 return 0;
 436                         }
 437                         break;
 438                 case BPF_ST:
 439                 case BPF_STX:
 440                         if (p->k >= BPF_MEMWORDS)
 441                                 return 0;
 442                         break;
 443                 case BPF_ALU:
 444                         switch (BPF_OP(p->code)) {
 445                         case BPF_ADD:
 446                         case BPF_SUB:
 447                         case BPF_MUL:
 448                         case BPF_OR:
 449                         case BPF_AND:
 450                         case BPF_XOR:
 451                         case BPF_LSH:
 452                         case BPF_RSH:
 453                         case BPF_NEG:
 454                                 break;
 455                         case BPF_DIV:
 456                         case BPF_MOD:
 457                                 /*
 458                                  * Check for constant division or modulus
 459                                  * by 0.
 460                                  */
 461                                 if (BPF_SRC(p->code) == BPF_K && p->k == 0)
 462                                         return 0;
 463                                 break;
 464                         default:
 465                                 return 0;
 466                         }
 467                         break;
 468                 case BPF_JMP:
 469                         /*
 470                          * Check that jumps are within the code block,
 471                          * and that unconditional branches don't go
 472                          * backwards as a result of an overflow.
 473                          * Unconditional branches have a 32-bit offset,
 474                          * so they could overflow; we check to make
 475                          * sure they don't.  Conditional branches have
 476                          * an 8-bit offset, and the from address is <=
 477                          * BPF_MAXINSNS, and we assume that BPF_MAXINSNS
 478                          * is sufficiently small that adding 255 to it
 479                          * won't overflow.
 480                          *
 481                          * We know that len is <= BPF_MAXINSNS, and we
 482                          * assume that BPF_MAXINSNS is < the maximum size
 483                          * of a u_int, so that i + 1 doesn't overflow.
 484                          *
 485                          * For userland, we don't know that the from
 486                          * or len are <= BPF_MAXINSNS, but we know that
 487                          * from <= len, and, except on a 64-bit system,
 488                          * it's unlikely that len, if it truly reflects
 489                          * the size of the program we've been handed,
 490                          * will be anywhere near the maximum size of
 491                          * a u_int.  We also don't check for backward
 492                          * branches, as we currently support them in
 493                          * userland for the protochain operation.
 494                          */
 495                         from = i + 1;
 496                         switch (BPF_OP(p->code)) {
 497                         case BPF_JA:
 498                                 if (from + p->k >= (u_int)len)
 499                                         return 0;
 500                                 break;
 501                         case BPF_JEQ:
 502                         case BPF_JGT:
 503                         case BPF_JGE:
 504                         case BPF_JSET:
 505                                 if (from + p->jt >= (u_int)len || from + p->jf >= (u_int)len)
 506                                         return 0;
 507                                 break;
 508                         default:
 509                                 return 0;
 510                         }
 511                         break;
 512                 case BPF_RET:
 513                         break;
 514                 case BPF_MISC:
 515                         break;
 516                 default:
 517                         return 0;
 518                 }
 519         }
 520         return BPF_CLASS(f[len - 1].code) == BPF_RET;
 521 }
 522
 523 /*
 524  * Exported because older versions of libpcap exported them.
 525  */
 526 u_int
 527 bpf_filter(const struct bpf_insn *pc, const u_char *p, u_int wirelen,
 528     u_int buflen)
 529 {
 530         return pcap_filter(pc, p, wirelen, buflen);
 531 }
 532
 533 int
 534 bpf_validate(const struct bpf_insn *f, int len)
 535 {
 536         return pcap_validate_filter(f, len);
 537 }