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 #include "diag-control.h"
  49
  50 #define EXTRACT_SHORT   EXTRACT_BE_U_2
  51 #define EXTRACT_LONG    EXTRACT_BE_U_4
  52
  53 #ifndef _WIN32
  54 #include <sys/param.h>
  55 #include <sys/types.h>
  56 #include <sys/time.h>
  57 #endif /* _WIN32 */
  58
  59 #include <pcap-int.h>
  60
  61 #include <stdlib.h>
  62
  63 #ifdef __linux__
  64 #include <linux/types.h>
  65 #include <linux/if_packet.h>
  66 #include <linux/filter.h>
  67 #endif
  68
  69 enum {
  70         BPF_S_ANC_NONE,
  71         BPF_S_ANC_VLAN_TAG,
  72         BPF_S_ANC_VLAN_TAG_PRESENT,
  73 };
  74
  75 /*
  76  * Execute the filter program starting at pc on the packet p
  77  * wirelen is the length of the original packet
  78  * buflen is the amount of data present
  79  * aux_data is auxiliary data, currently used only when interpreting
  80  * filters intended for the Linux kernel in cases where the kernel
  81  * rejects the filter; it contains VLAN tag information
  82  * For the kernel, p is assumed to be a pointer to an mbuf if buflen is 0,
  83  * in all other cases, p is a pointer to a buffer and buflen is its size.
  84  *
  85  * Thanks to Ani Sinha <ani@arista.com> for providing initial implementation
  86  */
  87 #if defined(SKF_AD_VLAN_TAG_PRESENT)
  88 u_int
  89 pcap_filter_with_aux_data(const struct bpf_insn *pc, const u_char *p,
  90     u_int wirelen, u_int buflen, const struct pcap_bpf_aux_data *aux_data)
  91 #else
  92 u_int
  93 pcap_filter_with_aux_data(const struct bpf_insn *pc, const u_char *p,
  94     u_int wirelen, u_int buflen, const struct pcap_bpf_aux_data *aux_data _U_)
  95 #endif
  96 {
  97         register uint32_t A, X;
  98         register bpf_u_int32 k;
  99         uint32_t mem[BPF_MEMWORDS];
 100
 101         if (pc == 0)
 102                 /*
 103                  * No filter means accept all.
 104                  */
 105                 return (u_int)-1;
 106         A = 0;
 107         X = 0;
 108         --pc;
 109         for (;;) {
 110                 ++pc;
 111                 switch (pc->code) {
 112
 113                 default:
 114                         abort();
 115                 case BPF_RET|BPF_K:
 116                         return (u_int)pc->k;
 117
 118                 case BPF_RET|BPF_A:
 119                         return (u_int)A;
 120
 121                 case BPF_LD|BPF_W|BPF_ABS:
 122                         k = pc->k;
 123                         if (k > buflen || sizeof(int32_t) > buflen - k) {
 124                                 return 0;
 125                         }
 126                         A = EXTRACT_LONG(&p[k]);
 127                         continue;
 128
 129                 case BPF_LD|BPF_H|BPF_ABS:
 130                         k = pc->k;
 131                         if (k > buflen || sizeof(int16_t) > buflen - k) {
 132                                 return 0;
 133                         }
 134                         A = EXTRACT_SHORT(&p[k]);
 135                         continue;
 136
 137                 case BPF_LD|BPF_B|BPF_ABS:
 138                         /*
 139                          * Yes, we know, this switch doesn't do
 140                          * anything unless we're building for
 141                          * a Linux kernel with removed VLAN
 142                          * tags available as meta-data.
 143                          */
 144 DIAG_OFF_DEFAULT_ONLY_SWITCH
 145                         switch (pc->k) {
 146
 147 #if defined(SKF_AD_VLAN_TAG_PRESENT)
 148                         case SKF_AD_OFF + SKF_AD_VLAN_TAG:
 149                                 if (!aux_data)
 150                                         return 0;
 151                                 A = aux_data->vlan_tag;
 152                                 break;
 153
 154                         case SKF_AD_OFF + SKF_AD_VLAN_TAG_PRESENT:
 155                                 if (!aux_data)
 156                                         return 0;
 157                                 A = aux_data->vlan_tag_present;
 158                                 break;
 159 #endif
 160                         default:
 161                                 k = pc->k;
 162                                 if (k >= buflen) {
 163                                         return 0;
 164                                 }
 165                                 A = p[k];
 166                                 break;
 167                         }
 168 DIAG_ON_DEFAULT_ONLY_SWITCH
 169                         continue;
 170
 171                 case BPF_LD|BPF_W|BPF_LEN:
 172                         A = wirelen;
 173                         continue;
 174
 175                 case BPF_LDX|BPF_W|BPF_LEN:
 176                         X = wirelen;
 177                         continue;
 178
 179                 case BPF_LD|BPF_W|BPF_IND:
 180                         k = X + pc->k;
 181                         if (pc->k > buflen || X > buflen - pc->k ||
 182                             sizeof(int32_t) > buflen - k) {
 183                                 return 0;
 184                         }
 185                         A = EXTRACT_LONG(&p[k]);
 186                         continue;
 187
 188                 case BPF_LD|BPF_H|BPF_IND:
 189                         k = X + pc->k;
 190                         if (X > buflen || pc->k > buflen - X ||
 191                             sizeof(int16_t) > buflen - k) {
 192                                 return 0;
 193                         }
 194                         A = EXTRACT_SHORT(&p[k]);
 195                         continue;
 196
 197                 case BPF_LD|BPF_B|BPF_IND:
 198                         k = X + pc->k;
 199                         if (pc->k >= buflen || X >= buflen - pc->k) {
 200                                 return 0;
 201                         }
 202                         A = p[k];
 203                         continue;
 204
 205                 case BPF_LDX|BPF_MSH|BPF_B:
 206                         k = pc->k;
 207                         if (k >= buflen) {
 208                                 return 0;
 209                         }
 210                         X = (p[pc->k] & 0xf) << 2;
 211                         continue;
 212
 213                 case BPF_LD|BPF_IMM:
 214                         A = pc->k;
 215                         continue;
 216
 217                 case BPF_LDX|BPF_IMM:
 218                         X = pc->k;
 219                         continue;
 220
 221                 case BPF_LD|BPF_MEM:
 222                         A = mem[pc->k];
 223                         continue;
 224
 225                 case BPF_LDX|BPF_MEM:
 226                         X = mem[pc->k];
 227                         continue;
 228
 229                 case BPF_ST:
 230                         mem[pc->k] = A;
 231                         continue;
 232
 233                 case BPF_STX:
 234                         mem[pc->k] = X;
 235                         continue;
 236
 237                 case BPF_JMP|BPF_JA:
 238                         /*
 239                          * XXX - we currently implement "ip6 protochain"
 240                          * with backward jumps, so sign-extend pc->k.
 241                          */
 242                         pc += (bpf_int32)pc->k;
 243                         continue;
 244
 245                 case BPF_JMP|BPF_JGT|BPF_K:
 246                         pc += (A > pc->k) ? pc->jt : pc->jf;
 247                         continue;
 248
 249                 case BPF_JMP|BPF_JGE|BPF_K:
 250                         pc += (A >= pc->k) ? pc->jt : pc->jf;
 251                         continue;
 252
 253                 case BPF_JMP|BPF_JEQ|BPF_K:
 254                         pc += (A == pc->k) ? pc->jt : pc->jf;
 255                         continue;
 256
 257                 case BPF_JMP|BPF_JSET|BPF_K:
 258                         pc += (A & pc->k) ? pc->jt : pc->jf;
 259                         continue;
 260
 261                 case BPF_JMP|BPF_JGT|BPF_X:
 262                         pc += (A > X) ? pc->jt : pc->jf;
 263                         continue;
 264
 265                 case BPF_JMP|BPF_JGE|BPF_X:
 266                         pc += (A >= X) ? pc->jt : pc->jf;
 267                         continue;
 268
 269                 case BPF_JMP|BPF_JEQ|BPF_X:
 270                         pc += (A == X) ? pc->jt : pc->jf;
 271                         continue;
 272
 273                 case BPF_JMP|BPF_JSET|BPF_X:
 274                         pc += (A & X) ? pc->jt : pc->jf;
 275                         continue;
 276
 277                 case BPF_ALU|BPF_ADD|BPF_X:
 278                         A += X;
 279                         continue;
 280
 281                 case BPF_ALU|BPF_SUB|BPF_X:
 282                         A -= X;
 283                         continue;
 284
 285                 case BPF_ALU|BPF_MUL|BPF_X:
 286                         A *= X;
 287                         continue;
 288
 289                 case BPF_ALU|BPF_DIV|BPF_X:
 290                         if (X == 0)
 291                                 return 0;
 292                         A /= X;
 293                         continue;
 294
 295                 case BPF_ALU|BPF_MOD|BPF_X:
 296                         if (X == 0)
 297                                 return 0;
 298                         A %= X;
 299                         continue;
 300
 301                 case BPF_ALU|BPF_AND|BPF_X:
 302                         A &= X;
 303                         continue;
 304
 305                 case BPF_ALU|BPF_OR|BPF_X:
 306                         A |= X;
 307                         continue;
 308
 309                 case BPF_ALU|BPF_XOR|BPF_X:
 310                         A ^= X;
 311                         continue;
 312
 313                 case BPF_ALU|BPF_LSH|BPF_X:
 314                         if (X < 32)
 315                                 A <<= X;
 316                         else
 317                                 A = 0;
 318                         continue;
 319
 320                 case BPF_ALU|BPF_RSH|BPF_X:
 321                         if (X < 32)
 322                                 A >>= X;
 323                         else
 324                                 A = 0;
 325                         continue;
 326
 327                 case BPF_ALU|BPF_ADD|BPF_K:
 328                         A += pc->k;
 329                         continue;
 330
 331                 case BPF_ALU|BPF_SUB|BPF_K:
 332                         A -= pc->k;
 333                         continue;
 334
 335                 case BPF_ALU|BPF_MUL|BPF_K:
 336                         A *= pc->k;
 337                         continue;
 338
 339                 case BPF_ALU|BPF_DIV|BPF_K:
 340                         A /= pc->k;
 341                         continue;
 342
 343                 case BPF_ALU|BPF_MOD|BPF_K:
 344                         A %= pc->k;
 345                         continue;
 346
 347                 case BPF_ALU|BPF_AND|BPF_K:
 348                         A &= pc->k;
 349                         continue;
 350
 351                 case BPF_ALU|BPF_OR|BPF_K:
 352                         A |= pc->k;
 353                         continue;
 354
 355                 case BPF_ALU|BPF_XOR|BPF_K:
 356                         A ^= pc->k;
 357                         continue;
 358
 359                 case BPF_ALU|BPF_LSH|BPF_K:
 360                         A <<= pc->k;
 361                         continue;
 362
 363                 case BPF_ALU|BPF_RSH|BPF_K:
 364                         A >>= pc->k;
 365                         continue;
 366
 367                 case BPF_ALU|BPF_NEG:
 368                         /*
 369                          * Most BPF arithmetic is unsigned, but negation
 370                          * can't be unsigned; respecify it as subtracting
 371                          * the accumulator from 0U, so that 1) we don't
 372                          * get compiler warnings about negating an unsigned
 373                          * value and 2) don't get UBSan warnings about
 374                          * the result of negating 0x80000000 being undefined.
 375                          */
 376                         A = (0U - A);
 377                         continue;
 378
 379                 case BPF_MISC|BPF_TAX:
 380                         X = A;
 381                         continue;
 382
 383                 case BPF_MISC|BPF_TXA:
 384                         A = X;
 385                         continue;
 386                 }
 387         }
 388 }
 389
 390 u_int
 391 pcap_filter(const struct bpf_insn *pc, const u_char *p, u_int wirelen,
 392     u_int buflen)
 393 {
 394         return pcap_filter_with_aux_data(pc, p, wirelen, buflen, NULL);
 395 }
 396
 397 /*
 398  * Return true if the 'fcode' is a valid filter program.
 399  * The constraints are that each jump be forward and to a valid
 400  * code, that memory accesses are within valid ranges (to the
 401  * extent that this can be checked statically; loads of packet
 402  * data have to be, and are, also checked at run time), and that
 403  * the code terminates with either an accept or reject.
 404  *
 405  * The kernel needs to be able to verify an application's filter code.
 406  * Otherwise, a bogus program could easily crash the system.
 407  */
 408 int
 409 pcap_validate_filter(const struct bpf_insn *f, int len)
 410 {
 411         u_int i, from;
 412         const struct bpf_insn *p;
 413
 414         if (len < 1)
 415                 return 0;
 416
 417         for (i = 0; i < (u_int)len; ++i) {
 418                 p = &f[i];
 419                 switch (BPF_CLASS(p->code)) {
 420                 /*
 421                  * Check that memory operations use valid addresses.
 422                  */
 423                 case BPF_LD:
 424                 case BPF_LDX:
 425                         switch (BPF_MODE(p->code)) {
 426                         case BPF_IMM:
 427                                 break;
 428                         case BPF_ABS:
 429                         case BPF_IND:
 430                         case BPF_MSH:
 431                                 /*
 432                                  * There's no maximum packet data size
 433                                  * in userland.  The runtime packet length
 434                                  * check suffices.
 435                                  */
 436                                 break;
 437                         case BPF_MEM:
 438                                 if (p->k >= BPF_MEMWORDS)
 439                                         return 0;
 440                                 break;
 441                         case BPF_LEN:
 442                                 break;
 443                         default:
 444                                 return 0;
 445                         }
 446                         break;
 447                 case BPF_ST:
 448                 case BPF_STX:
 449                         if (p->k >= BPF_MEMWORDS)
 450                                 return 0;
 451                         break;
 452                 case BPF_ALU:
 453                         switch (BPF_OP(p->code)) {
 454                         case BPF_ADD:
 455                         case BPF_SUB:
 456                         case BPF_MUL:
 457                         case BPF_OR:
 458                         case BPF_AND:
 459                         case BPF_XOR:
 460                         case BPF_LSH:
 461                         case BPF_RSH:
 462                         case BPF_NEG:
 463                                 break;
 464                         case BPF_DIV:
 465                         case BPF_MOD:
 466                                 /*
 467                                  * Check for constant division or modulus
 468                                  * by 0.
 469                                  */
 470                                 if (BPF_SRC(p->code) == BPF_K && p->k == 0)
 471                                         return 0;
 472                                 break;
 473                         default:
 474                                 return 0;
 475                         }
 476                         break;
 477                 case BPF_JMP:
 478                         /*
 479                          * Check that jumps are within the code block,
 480                          * and that unconditional branches don't go
 481                          * backwards as a result of an overflow.
 482                          * Unconditional branches have a 32-bit offset,
 483                          * so they could overflow; we check to make
 484                          * sure they don't.  Conditional branches have
 485                          * an 8-bit offset, and the from address is <=
 486                          * BPF_MAXINSNS, and we assume that BPF_MAXINSNS
 487                          * is sufficiently small that adding 255 to it
 488                          * won't overflow.
 489                          *
 490                          * We know that len is <= BPF_MAXINSNS, and we
 491                          * assume that BPF_MAXINSNS is < the maximum size
 492                          * of a u_int, so that i + 1 doesn't overflow.
 493                          *
 494                          * For userland, we don't know that the from
 495                          * or len are <= BPF_MAXINSNS, but we know that
 496                          * from <= len, and, except on a 64-bit system,
 497                          * it's unlikely that len, if it truly reflects
 498                          * the size of the program we've been handed,
 499                          * will be anywhere near the maximum size of
 500                          * a u_int.  We also don't check for backward
 501                          * branches, as we currently support them in
 502                          * userland for the protochain operation.
 503                          */
 504                         from = i + 1;
 505                         switch (BPF_OP(p->code)) {
 506                         case BPF_JA:
 507                                 if (from + p->k >= (u_int)len)
 508                                         return 0;
 509                                 break;
 510                         case BPF_JEQ:
 511                         case BPF_JGT:
 512                         case BPF_JGE:
 513                         case BPF_JSET:
 514                                 if (from + p->jt >= (u_int)len || from + p->jf >= (u_int)len)
 515                                         return 0;
 516                                 break;
 517                         default:
 518                                 return 0;
 519                         }
 520                         break;
 521                 case BPF_RET:
 522                         break;
 523                 case BPF_MISC:
 524                         break;
 525                 default:
 526                         return 0;
 527                 }
 528         }
 529         return BPF_CLASS(f[len - 1].code) == BPF_RET;
 530 }
 531
 532 /*
 533  * Exported because older versions of libpcap exported them.
 534  */
 535 u_int
 536 bpf_filter(const struct bpf_insn *pc, const u_char *p, u_int wirelen,
 537     u_int buflen)
 538 {
 539         return pcap_filter(pc, p, wirelen, buflen);
 540 }
 541
 542 int
 543 bpf_validate(const struct bpf_insn *f, int len)
 544 {
 545         return pcap_validate_filter(f, len);
 546 }