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 #include <config.h>
  42
  43 #include <pcap/pcap-inttypes.h>
  44 #include "pcap-types.h"
  45 #include "extract.h"
  46 #include "diag-control.h"
  47
  48 #define EXTRACT_SHORT   EXTRACT_BE_U_2
  49 #define EXTRACT_LONG    EXTRACT_BE_U_4
  50
  51 #ifndef _WIN32
  52 #include <sys/param.h>
  53 #include <sys/types.h>
  54 #include <sys/time.h>
  55 #endif /* _WIN32 */
  56
  57 #include <pcap-int.h>
  58
  59 #include <stdlib.h>
  60
  61 #ifdef __linux__
  62 #include <linux/types.h>
  63 #include <linux/if_packet.h>
  64 #include <linux/filter.h>
  65 #endif
  66
  67 enum {
  68         BPF_S_ANC_NONE,
  69         BPF_S_ANC_VLAN_TAG,
  70         BPF_S_ANC_VLAN_TAG_PRESENT,
  71 };
  72
  73 /*
  74  * Execute the filter program starting at pc on the packet p
  75  * wirelen is the length of the original packet
  76  * buflen is the amount of data present
  77  * aux_data is auxiliary data, currently used only when interpreting
  78  * filters intended for the Linux kernel in cases where the kernel
  79  * rejects the filter; it contains VLAN tag information
  80  * For the kernel, p is assumed to be a pointer to an mbuf if buflen is 0,
  81  * in all other cases, p is a pointer to a buffer and buflen is its size.
  82  *
  83  * Thanks to Ani Sinha <ani@arista.com> for providing initial implementation
  84  */
  85 #if defined(SKF_AD_VLAN_TAG_PRESENT)
  86 u_int
  87 pcapint_filter_with_aux_data(const struct bpf_insn *pc, const u_char *p,
  88     u_int wirelen, u_int buflen, const struct pcap_bpf_aux_data *aux_data)
  89 #else
  90 u_int
  91 pcapint_filter_with_aux_data(const struct bpf_insn *pc, const u_char *p,
  92     u_int wirelen, u_int buflen, const struct pcap_bpf_aux_data *aux_data _U_)
  93 #endif
  94 {
  95         register uint32_t A, X;
  96         register bpf_u_int32 k;
  97
  98         if (pc == 0)
  99                 /*
 100                  * No filter means accept all.
 101                  */
 102                 return (u_int)-1;
 103         A = 0;
 104         X = 0;
 105         uint32_t mem[BPF_MEMWORDS] = {0};
 106         --pc;
 107         for (;;) {
 108                 ++pc;
 109                 switch (pc->code) {
 110
 111                 default:
 112                         abort();
 113                 case BPF_RET|BPF_K:
 114                         return (u_int)pc->k;
 115
 116                 case BPF_RET|BPF_A:
 117                         return (u_int)A;
 118
 119                 case BPF_LD|BPF_W|BPF_ABS:
 120                         k = pc->k;
 121                         if (k > buflen || sizeof(int32_t) > buflen - k) {
 122                                 return 0;
 123                         }
 124                         A = EXTRACT_LONG(&p[k]);
 125                         continue;
 126
 127                 case BPF_LD|BPF_H|BPF_ABS:
 128                         k = pc->k;
 129                         if (k > buflen || sizeof(int16_t) > buflen - k) {
 130                                 return 0;
 131                         }
 132                         A = EXTRACT_SHORT(&p[k]);
 133                         continue;
 134
 135                 case BPF_LD|BPF_B|BPF_ABS:
 136                         /*
 137                          * Yes, we know, this switch doesn't do
 138                          * anything unless we're building for
 139                          * a Linux kernel with removed VLAN
 140                          * tags available as meta-data.
 141                          */
 142 DIAG_OFF_DEFAULT_ONLY_SWITCH
 143                         switch (pc->k) {
 144
 145 #if defined(SKF_AD_VLAN_TAG_PRESENT)
 146                         case SKF_AD_OFF + SKF_AD_VLAN_TAG:
 147                                 if (!aux_data)
 148                                         return 0;
 149                                 A = aux_data->vlan_tag;
 150                                 break;
 151
 152                         case SKF_AD_OFF + SKF_AD_VLAN_TAG_PRESENT:
 153                                 if (!aux_data)
 154                                         return 0;
 155                                 A = aux_data->vlan_tag_present;
 156                                 break;
 157 #endif
 158                         default:
 159                                 k = pc->k;
 160                                 if (k >= buflen) {
 161                                         return 0;
 162                                 }
 163                                 A = p[k];
 164                                 break;
 165                         }
 166 DIAG_ON_DEFAULT_ONLY_SWITCH
 167                         continue;
 168
 169                 case BPF_LD|BPF_W|BPF_LEN:
 170                         A = wirelen;
 171                         continue;
 172
 173                 case BPF_LDX|BPF_W|BPF_LEN:
 174                         X = wirelen;
 175                         continue;
 176
 177                 case BPF_LD|BPF_W|BPF_IND:
 178                         k = X + pc->k;
 179                         if (pc->k > buflen || X > buflen - pc->k ||
 180                             sizeof(int32_t) > buflen - k) {
 181                                 return 0;
 182                         }
 183                         A = EXTRACT_LONG(&p[k]);
 184                         continue;
 185
 186                 case BPF_LD|BPF_H|BPF_IND:
 187                         k = X + pc->k;
 188                         if (X > buflen || pc->k > buflen - X ||
 189                             sizeof(int16_t) > buflen - k) {
 190                                 return 0;
 191                         }
 192                         A = EXTRACT_SHORT(&p[k]);
 193                         continue;
 194
 195                 case BPF_LD|BPF_B|BPF_IND:
 196                         k = X + pc->k;
 197                         if (pc->k >= buflen || X >= buflen - pc->k) {
 198                                 return 0;
 199                         }
 200                         A = p[k];
 201                         continue;
 202
 203                 case BPF_LDX|BPF_MSH|BPF_B:
 204                         k = pc->k;
 205                         if (k >= buflen) {
 206                                 return 0;
 207                         }
 208                         X = (p[pc->k] & 0xf) << 2;
 209                         continue;
 210
 211                 case BPF_LD|BPF_IMM:
 212                         A = pc->k;
 213                         continue;
 214
 215                 case BPF_LDX|BPF_IMM:
 216                         X = pc->k;
 217                         continue;
 218
 219                 case BPF_LD|BPF_MEM:
 220                         A = mem[pc->k];
 221                         continue;
 222
 223                 case BPF_LDX|BPF_MEM:
 224                         X = mem[pc->k];
 225                         continue;
 226
 227                 case BPF_ST:
 228                         mem[pc->k] = A;
 229                         continue;
 230
 231                 case BPF_STX:
 232                         mem[pc->k] = X;
 233                         continue;
 234
 235                 case BPF_JMP|BPF_JA:
 236                         /*
 237                          * XXX - we currently implement "ip6 protochain"
 238                          * with backward jumps, so sign-extend pc->k.
 239                          */
 240                         pc += (bpf_int32)pc->k;
 241                         continue;
 242
 243                 case BPF_JMP|BPF_JGT|BPF_K:
 244                         pc += (A > pc->k) ? pc->jt : pc->jf;
 245                         continue;
 246
 247                 case BPF_JMP|BPF_JGE|BPF_K:
 248                         pc += (A >= pc->k) ? pc->jt : pc->jf;
 249                         continue;
 250
 251                 case BPF_JMP|BPF_JEQ|BPF_K:
 252                         pc += (A == pc->k) ? pc->jt : pc->jf;
 253                         continue;
 254
 255                 case BPF_JMP|BPF_JSET|BPF_K:
 256                         pc += (A & pc->k) ? pc->jt : pc->jf;
 257                         continue;
 258
 259                 case BPF_JMP|BPF_JGT|BPF_X:
 260                         pc += (A > X) ? pc->jt : pc->jf;
 261                         continue;
 262
 263                 case BPF_JMP|BPF_JGE|BPF_X:
 264                         pc += (A >= X) ? pc->jt : pc->jf;
 265                         continue;
 266
 267                 case BPF_JMP|BPF_JEQ|BPF_X:
 268                         pc += (A == X) ? pc->jt : pc->jf;
 269                         continue;
 270
 271                 case BPF_JMP|BPF_JSET|BPF_X:
 272                         pc += (A & X) ? pc->jt : pc->jf;
 273                         continue;
 274
 275                 case BPF_ALU|BPF_ADD|BPF_X:
 276                         A += X;
 277                         continue;
 278
 279                 case BPF_ALU|BPF_SUB|BPF_X:
 280                         A -= X;
 281                         continue;
 282
 283                 case BPF_ALU|BPF_MUL|BPF_X:
 284                         A *= X;
 285                         continue;
 286
 287                 case BPF_ALU|BPF_DIV|BPF_X:
 288                         if (X == 0)
 289                                 return 0;
 290                         A /= X;
 291                         continue;
 292
 293                 case BPF_ALU|BPF_MOD|BPF_X:
 294                         if (X == 0)
 295                                 return 0;
 296                         A %= X;
 297                         continue;
 298
 299                 case BPF_ALU|BPF_AND|BPF_X:
 300                         A &= X;
 301                         continue;
 302
 303                 case BPF_ALU|BPF_OR|BPF_X:
 304                         A |= X;
 305                         continue;
 306
 307                 case BPF_ALU|BPF_XOR|BPF_X:
 308                         A ^= X;
 309                         continue;
 310
 311                 case BPF_ALU|BPF_LSH|BPF_X:
 312                         if (X < 32)
 313                                 A <<= X;
 314                         else
 315                                 A = 0;
 316                         continue;
 317
 318                 case BPF_ALU|BPF_RSH|BPF_X:
 319                         if (X < 32)
 320                                 A >>= X;
 321                         else
 322                                 A = 0;
 323                         continue;
 324
 325                 case BPF_ALU|BPF_ADD|BPF_K:
 326                         A += pc->k;
 327                         continue;
 328
 329                 case BPF_ALU|BPF_SUB|BPF_K:
 330                         A -= pc->k;
 331                         continue;
 332
 333                 case BPF_ALU|BPF_MUL|BPF_K:
 334                         A *= pc->k;
 335                         continue;
 336
 337                 case BPF_ALU|BPF_DIV|BPF_K:
 338                         A /= pc->k;
 339                         continue;
 340
 341                 case BPF_ALU|BPF_MOD|BPF_K:
 342                         A %= pc->k;
 343                         continue;
 344
 345                 case BPF_ALU|BPF_AND|BPF_K:
 346                         A &= pc->k;
 347                         continue;
 348
 349                 case BPF_ALU|BPF_OR|BPF_K:
 350                         A |= pc->k;
 351                         continue;
 352
 353                 case BPF_ALU|BPF_XOR|BPF_K:
 354                         A ^= pc->k;
 355                         continue;
 356
 357                 case BPF_ALU|BPF_LSH|BPF_K:
 358                         A <<= pc->k;
 359                         continue;
 360
 361                 case BPF_ALU|BPF_RSH|BPF_K:
 362                         A >>= pc->k;
 363                         continue;
 364
 365                 case BPF_ALU|BPF_NEG:
 366                         /*
 367                          * Most BPF arithmetic is unsigned, but negation
 368                          * can't be unsigned; respecify it as subtracting
 369                          * the accumulator from 0U, so that 1) we don't
 370                          * get compiler warnings about negating an unsigned
 371                          * value and 2) don't get UBSan warnings about
 372                          * the result of negating 0x80000000 being undefined.
 373                          */
 374                         A = (0U - A);
 375                         continue;
 376
 377                 case BPF_MISC|BPF_TAX:
 378                         X = A;
 379                         continue;
 380
 381                 case BPF_MISC|BPF_TXA:
 382                         A = X;
 383                         continue;
 384                 }
 385         }
 386 }
 387
 388 u_int
 389 pcapint_filter(const struct bpf_insn *pc, const u_char *p, u_int wirelen,
 390     u_int buflen)
 391 {
 392         return pcapint_filter_with_aux_data(pc, p, wirelen, buflen, NULL);
 393 }
 394
 395 /*
 396  * Return true if the 'fcode' is a valid filter program.
 397  * The constraints are that each jump be forward and to a valid
 398  * code, that memory accesses are within valid ranges (to the
 399  * extent that this can be checked statically; loads of packet
 400  * data have to be, and are, also checked at run time), and that
 401  * the code terminates with either an accept or reject.
 402  *
 403  * The kernel needs to be able to verify an application's filter code.
 404  * Otherwise, a bogus program could easily crash the system.
 405  */
 406 int
 407 pcapint_validate_filter(const struct bpf_insn *f, int len)
 408 {
 409         u_int i, from;
 410         const struct bpf_insn *p;
 411
 412         if (len < 1)
 413                 return 0;
 414
 415         for (i = 0; i < (u_int)len; ++i) {
 416                 p = &f[i];
 417                 switch (BPF_CLASS(p->code)) {
 418                 /*
 419                  * Check that memory operations use valid addresses.
 420                  */
 421                 case BPF_LD:
 422                 case BPF_LDX:
 423                         switch (BPF_MODE(p->code)) {
 424                         case BPF_IMM:
 425                                 break;
 426                         case BPF_ABS:
 427                         case BPF_IND:
 428                         case BPF_MSH:
 429                                 /*
 430                                  * There's no maximum packet data size
 431                                  * in userland.  The runtime packet length
 432                                  * check suffices.
 433                                  */
 434                                 break;
 435                         case BPF_MEM:
 436                                 if (p->k >= BPF_MEMWORDS)
 437                                         return 0;
 438                                 break;
 439                         case BPF_LEN:
 440                                 break;
 441                         default:
 442                                 return 0;
 443                         }
 444                         break;
 445                 case BPF_ST:
 446                 case BPF_STX:
 447                         if (p->k >= BPF_MEMWORDS)
 448                                 return 0;
 449                         break;
 450                 case BPF_ALU:
 451                         switch (BPF_OP(p->code)) {
 452                         case BPF_ADD:
 453                         case BPF_SUB:
 454                         case BPF_MUL:
 455                         case BPF_OR:
 456                         case BPF_AND:
 457                         case BPF_XOR:
 458                         case BPF_LSH:
 459                         case BPF_RSH:
 460                         case BPF_NEG:
 461                                 break;
 462                         case BPF_DIV:
 463                         case BPF_MOD:
 464                                 /*
 465                                  * Check for constant division or modulus
 466                                  * by 0.
 467                                  */
 468                                 if (BPF_SRC(p->code) == BPF_K && p->k == 0)
 469                                         return 0;
 470                                 break;
 471                         default:
 472                                 return 0;
 473                         }
 474                         break;
 475                 case BPF_JMP:
 476                         /*
 477                          * Check that jumps are within the code block,
 478                          * and that unconditional branches don't go
 479                          * backwards as a result of an overflow.
 480                          * Unconditional branches have a 32-bit offset,
 481                          * so they could overflow; we check to make
 482                          * sure they don't.  Conditional branches have
 483                          * an 8-bit offset, and the from address is <=
 484                          * BPF_MAXINSNS, and we assume that BPF_MAXINSNS
 485                          * is sufficiently small that adding 255 to it
 486                          * won't overflow.
 487                          *
 488                          * We know that len is <= BPF_MAXINSNS, and we
 489                          * assume that BPF_MAXINSNS is < the maximum size
 490                          * of a u_int, so that i + 1 doesn't overflow.
 491                          *
 492                          * For userland, we don't know that the from
 493                          * or len are <= BPF_MAXINSNS, but we know that
 494                          * from <= len, and, except on a 64-bit system,
 495                          * it's unlikely that len, if it truly reflects
 496                          * the size of the program we've been handed,
 497                          * will be anywhere near the maximum size of
 498                          * a u_int.  We also don't check for backward
 499                          * branches, as we currently support them in
 500                          * userland for the protochain operation.
 501                          */
 502                         from = i + 1;
 503                         switch (BPF_OP(p->code)) {
 504                         case BPF_JA:
 505                                 if (from + p->k >= (u_int)len)
 506                                         return 0;
 507                                 break;
 508                         case BPF_JEQ:
 509                         case BPF_JGT:
 510                         case BPF_JGE:
 511                         case BPF_JSET:
 512                                 if (from + p->jt >= (u_int)len || from + p->jf >= (u_int)len)
 513                                         return 0;
 514                                 break;
 515                         default:
 516                                 return 0;
 517                         }
 518                         break;
 519                 case BPF_RET:
 520                         break;
 521                 case BPF_MISC:
 522                         break;
 523                 default:
 524                         return 0;
 525                 }
 526         }
 527         return BPF_CLASS(f[len - 1].code) == BPF_RET;
 528 }
 529
 530 /*
 531  * Exported because older versions of libpcap exported them.
 532  */
 533 u_int
 534 bpf_filter(const struct bpf_insn *pc, const u_char *p, u_int wirelen,
 535     u_int buflen)
 536 {
 537         return pcapint_filter(pc, p, wirelen, buflen);
 538 }
 539
 540 int
 541 bpf_validate(const struct bpf_insn *f, int len)
 542 {
 543         return pcapint_validate_filter(f, len);
 544 }