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 1.7 2005/04/20 16:05:51 cpressey Exp $
  42  */
  43
  44 #include <sys/param.h>
  45
  46 #if defined(sparc) || defined(mips) || defined(ibm032) || defined(__alpha__)
  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 static u_int16_t        m_xhalf (struct mbuf *m, bpf_u_int32 k, int *err);
  84 static u_int32_t        m_xword (struct mbuf *m, bpf_u_int32 k, int *err);
  85
  86 static u_int32_t
  87 m_xword(struct mbuf *m, bpf_u_int32 k, int *err)
  88 {
  89         size_t len;
  90         u_char *cp, *np;
  91         struct mbuf *m0;
  92
  93         len = m->m_len;
  94         while (k >= len) {
  95                 k -= len;
  96                 m = m->m_next;
  97                 if (m == 0)
  98                         goto bad;
  99                 len = m->m_len;
 100         }
 101         cp = mtod(m, u_char *) + k;
 102         if (len - k >= 4) {
 103                 *err = 0;
 104                 return EXTRACT_LONG(cp);
 105         }
 106         m0 = m->m_next;
 107         if (m0 == 0 || m0->m_len + len - k < 4)
 108                 goto bad;
 109         *err = 0;
 110         np = mtod(m0, u_char *);
 111         switch (len - k) {
 112
 113         case 1:
 114                 return
 115                     ((u_int32_t)cp[0] << 24) |
 116                     ((u_int32_t)np[0] << 16) |
 117                     ((u_int32_t)np[1] << 8)  |
 118                     (u_int32_t)np[2];
 119
 120         case 2:
 121                 return
 122                     ((u_int32_t)cp[0] << 24) |
 123                     ((u_int32_t)cp[1] << 16) |
 124                     ((u_int32_t)np[0] << 8) |
 125                     (u_int32_t)np[1];
 126
 127         default:
 128                 return
 129                     ((u_int32_t)cp[0] << 24) |
 130                     ((u_int32_t)cp[1] << 16) |
 131                     ((u_int32_t)cp[2] << 8) |
 132                     (u_int32_t)np[0];
 133         }
 134     bad:
 135         *err = 1;
 136         return 0;
 137 }
 138
 139 static u_int16_t
 140 m_xhalf(struct mbuf *m, bpf_u_int32 k, int *err)
 141 {
 142         size_t len;
 143         u_char *cp;
 144         struct mbuf *m0;
 145
 146         len = m->m_len;
 147         while (k >= len) {
 148                 k -= len;
 149                 m = m->m_next;
 150                 if (m == 0)
 151                         goto bad;
 152                 len = m->m_len;
 153         }
 154         cp = mtod(m, u_char *) + k;
 155         if (len - k >= 2) {
 156                 *err = 0;
 157                 return EXTRACT_SHORT(cp);
 158         }
 159         m0 = m->m_next;
 160         if (m0 == 0)
 161                 goto bad;
 162         *err = 0;
 163         return (cp[0] << 8) | mtod(m0, u_char *)[0];
 164  bad:
 165         *err = 1;
 166         return 0;
 167 }
 168 #endif
 169
 170 /*
 171  * Execute the filter program starting at pc on the packet p
 172  * wirelen is the length of the original packet
 173  * buflen is the amount of data present
 174  */
 175 u_int
 176 bpf_filter(const struct bpf_insn *pc, u_char *p, u_int wirelen, u_int buflen)
 177 {
 178         u_int32_t A = 0, X = 0;
 179         bpf_u_int32 k;
 180         int32_t mem[BPF_MEMWORDS];
 181
 182         if (pc == 0) {
 183                 /*
 184                  * No filter means accept all.
 185                  */
 186                 return (u_int)-1;
 187         }
 188
 189         --pc;
 190         while (1) {
 191                 ++pc;
 192                 switch (pc->code) {
 193
 194                 default:
 195 #ifdef _KERNEL
 196                         return 0;
 197 #else
 198                         abort();
 199 #endif
 200                 case BPF_RET|BPF_K:
 201                         return (u_int)pc->k;
 202
 203                 case BPF_RET|BPF_A:
 204                         return (u_int)A;
 205
 206                 case BPF_LD|BPF_W|BPF_ABS:
 207                         k = pc->k;
 208                         if (k > buflen || sizeof(int32_t) > buflen - k) {
 209 #ifdef _KERNEL
 210                                 int merr;
 211
 212                                 if (buflen != 0)
 213                                         return 0;
 214                                 A = m_xword((struct mbuf *)p, k, &merr);
 215                                 if (merr != 0)
 216                                         return 0;
 217                                 continue;
 218 #else
 219                                 return 0;
 220 #endif
 221                         }
 222 #ifdef BPF_ALIGN
 223                         if (((intptr_t)(p + k) & 3) != 0)
 224                                 A = EXTRACT_LONG(&p[k]);
 225                         else
 226 #endif
 227                                 A = ntohl(*(int32_t *)(p + k));
 228                         continue;
 229
 230                 case BPF_LD|BPF_H|BPF_ABS:
 231                         k = pc->k;
 232                         if (k > buflen || sizeof(int16_t) > buflen - k) {
 233 #ifdef _KERNEL
 234                                 int merr;
 235
 236                                 if (buflen != 0)
 237                                         return 0;
 238                                 A = m_xhalf((struct mbuf *)p, k, &merr);
 239                                 continue;
 240 #else
 241                                 return 0;
 242 #endif
 243                         }
 244                         A = EXTRACT_SHORT(&p[k]);
 245                         continue;
 246
 247                 case BPF_LD|BPF_B|BPF_ABS:
 248                         k = pc->k;
 249                         if (k >= buflen) {
 250 #ifdef _KERNEL
 251                                 struct mbuf *m;
 252
 253                                 if (buflen != 0)
 254                                         return 0;
 255                                 m = (struct mbuf *)p;
 256                                 MINDEX(m, k);
 257                                 A = mtod(m, u_char *)[k];
 258                                 continue;
 259 #else
 260                                 return 0;
 261 #endif
 262                         }
 263                         A = p[k];
 264                         continue;
 265
 266                 case BPF_LD|BPF_W|BPF_LEN:
 267                         A = wirelen;
 268                         continue;
 269
 270                 case BPF_LDX|BPF_W|BPF_LEN:
 271                         X = wirelen;
 272                         continue;
 273
 274                 case BPF_LD|BPF_W|BPF_IND:
 275                         k = X + pc->k;
 276                         if (pc->k > buflen || X > buflen - pc->k ||
 277                             sizeof(int32_t) > buflen - k) {
 278 #ifdef _KERNEL
 279                                 int merr;
 280
 281                                 if (buflen != 0)
 282                                         return 0;
 283                                 A = m_xword((struct mbuf *)p, k, &merr);
 284                                 if (merr != 0)
 285                                         return 0;
 286                                 continue;
 287 #else
 288                                 return 0;
 289 #endif
 290                         }
 291 #ifdef BPF_ALIGN
 292                         if (((intptr_t)(p + k) & 3) != 0)
 293                                 A = EXTRACT_LONG(&p[k]);
 294                         else
 295 #endif
 296                                 A = ntohl(*(int32_t *)(p + k));
 297                         continue;
 298
 299                 case BPF_LD|BPF_H|BPF_IND:
 300                         k = X + pc->k;
 301                         if (X > buflen || pc->k > buflen - X ||
 302                             sizeof(int16_t) > buflen - k) {
 303 #ifdef _KERNEL
 304                                 int merr;
 305
 306                                 if (buflen != 0)
 307                                         return 0;
 308                                 A = m_xhalf((struct mbuf *)p, k, &merr);
 309                                 if (merr != 0)
 310                                         return 0;
 311                                 continue;
 312 #else
 313                                 return 0;
 314 #endif
 315                         }
 316                         A = EXTRACT_SHORT(&p[k]);
 317                         continue;
 318
 319                 case BPF_LD|BPF_B|BPF_IND:
 320                         k = X + pc->k;
 321                         if (pc->k >= buflen || X >= buflen - pc->k) {
 322 #ifdef _KERNEL
 323                                 struct mbuf *m;
 324
 325                                 if (buflen != 0)
 326                                         return 0;
 327                                 m = (struct mbuf *)p;
 328                                 MINDEX(m, k);
 329                                 A = mtod(m, char *)[k];
 330                                 continue;
 331 #else
 332                                 return 0;
 333 #endif
 334                         }
 335                         A = p[k];
 336                         continue;
 337
 338                 case BPF_LDX|BPF_MSH|BPF_B:
 339                         k = pc->k;
 340                         if (k >= buflen) {
 341 #ifdef _KERNEL
 342                                 struct mbuf *m;
 343
 344                                 if (buflen != 0)
 345                                         return 0;
 346                                 m = (struct mbuf *)p;
 347                                 MINDEX(m, k);
 348                                 X = (mtod(m, char *)[k] & 0xf) << 2;
 349                                 continue;
 350 #else
 351                                 return 0;
 352 #endif
 353                         }
 354                         X = (p[pc->k] & 0xf) << 2;
 355                         continue;
 356
 357                 case BPF_LD|BPF_IMM:
 358                         A = pc->k;
 359                         continue;
 360
 361                 case BPF_LDX|BPF_IMM:
 362                         X = pc->k;
 363                         continue;
 364
 365                 case BPF_LD|BPF_MEM:
 366                         A = mem[pc->k];
 367                         continue;
 368
 369                 case BPF_LDX|BPF_MEM:
 370                         X = mem[pc->k];
 371                         continue;
 372
 373                 case BPF_ST:
 374                         mem[pc->k] = A;
 375                         continue;
 376
 377                 case BPF_STX:
 378                         mem[pc->k] = X;
 379                         continue;
 380
 381                 case BPF_JMP|BPF_JA:
 382                         pc += pc->k;
 383                         continue;
 384
 385                 case BPF_JMP|BPF_JGT|BPF_K:
 386                         pc += (A > pc->k) ? pc->jt : pc->jf;
 387                         continue;
 388
 389                 case BPF_JMP|BPF_JGE|BPF_K:
 390                         pc += (A >= pc->k) ? pc->jt : pc->jf;
 391                         continue;
 392
 393                 case BPF_JMP|BPF_JEQ|BPF_K:
 394                         pc += (A == pc->k) ? pc->jt : pc->jf;
 395                         continue;
 396
 397                 case BPF_JMP|BPF_JSET|BPF_K:
 398                         pc += (A & pc->k) ? pc->jt : pc->jf;
 399                         continue;
 400
 401                 case BPF_JMP|BPF_JGT|BPF_X:
 402                         pc += (A > X) ? pc->jt : pc->jf;
 403                         continue;
 404
 405                 case BPF_JMP|BPF_JGE|BPF_X:
 406                         pc += (A >= X) ? pc->jt : pc->jf;
 407                         continue;
 408
 409                 case BPF_JMP|BPF_JEQ|BPF_X:
 410                         pc += (A == X) ? pc->jt : pc->jf;
 411                         continue;
 412
 413                 case BPF_JMP|BPF_JSET|BPF_X:
 414                         pc += (A & X) ? pc->jt : pc->jf;
 415                         continue;
 416
 417                 case BPF_ALU|BPF_ADD|BPF_X:
 418                         A += X;
 419                         continue;
 420
 421                 case BPF_ALU|BPF_SUB|BPF_X:
 422                         A -= X;
 423                         continue;
 424
 425                 case BPF_ALU|BPF_MUL|BPF_X:
 426                         A *= X;
 427                         continue;
 428
 429                 case BPF_ALU|BPF_DIV|BPF_X:
 430                         if (X == 0)
 431                                 return 0;
 432                         A /= X;
 433                         continue;
 434
 435                 case BPF_ALU|BPF_AND|BPF_X:
 436                         A &= X;
 437                         continue;
 438
 439                 case BPF_ALU|BPF_OR|BPF_X:
 440                         A |= X;
 441                         continue;
 442
 443                 case BPF_ALU|BPF_LSH|BPF_X:
 444                         A <<= X;
 445                         continue;
 446
 447                 case BPF_ALU|BPF_RSH|BPF_X:
 448                         A >>= X;
 449                         continue;
 450
 451                 case BPF_ALU|BPF_ADD|BPF_K:
 452                         A += pc->k;
 453                         continue;
 454
 455                 case BPF_ALU|BPF_SUB|BPF_K:
 456                         A -= pc->k;
 457                         continue;
 458
 459                 case BPF_ALU|BPF_MUL|BPF_K:
 460                         A *= pc->k;
 461                         continue;
 462
 463                 case BPF_ALU|BPF_DIV|BPF_K:
 464                         A /= pc->k;
 465                         continue;
 466
 467                 case BPF_ALU|BPF_AND|BPF_K:
 468                         A &= pc->k;
 469                         continue;
 470
 471                 case BPF_ALU|BPF_OR|BPF_K:
 472                         A |= pc->k;
 473                         continue;
 474
 475                 case BPF_ALU|BPF_LSH|BPF_K:
 476                         A <<= pc->k;
 477                         continue;
 478
 479                 case BPF_ALU|BPF_RSH|BPF_K:
 480                         A >>= pc->k;
 481                         continue;
 482
 483                 case BPF_ALU|BPF_NEG:
 484                         A = -A;
 485                         continue;
 486
 487                 case BPF_MISC|BPF_TAX:
 488                         X = A;
 489                         continue;
 490
 491                 case BPF_MISC|BPF_TXA:
 492                         A = X;
 493                         continue;
 494                 }
 495         }
 496 }
 497
 498 #ifdef _KERNEL
 499 /*
 500  * Return true if the 'fcode' is a valid filter program.
 501  * The constraints are that jump and memory accesses are within valid
 502  * ranges, and that the code terminates with either an accept or reject.
 503  *
 504  * The kernel needs to be able to verify an application's filter code.
 505  * Otherwise, a bogus program could easily crash the system.
 506  */
 507 int
 508 bpf_validate(const struct bpf_insn *f, int len)
 509 {
 510         int i;
 511         const struct bpf_insn *p;
 512
 513         for (i = 0; i < len; ++i) {
 514                 /*
 515                  * Check that that jumps are within the code block.
 516                  */
 517                 p = &f[i];
 518                 if (BPF_CLASS(p->code) == BPF_JMP) {
 519                         int from = i + 1;
 520
 521                         if (BPF_OP(p->code) == BPF_JA) {
 522                                 if (from >= len || p->k >= len - from)
 523                                         return 0;
 524                         }
 525                         else if (from >= len || p->jt >= len - from ||
 526                                  p->jf >= len - from)
 527                                 return 0;
 528                 }
 529                 /*
 530                  * Check that memory operations use valid addresses.
 531                  */
 532                 if ((BPF_CLASS(p->code) == BPF_ST ||
 533                      (BPF_CLASS(p->code) == BPF_LD &&
 534                       (p->code & 0xe0) == BPF_MEM)) &&
 535                     p->k >= BPF_MEMWORDS)
 536                         return 0;
 537                 /*
 538                  * Check for constant division by 0.
 539                  */
 540                 if (p->code == (BPF_ALU|BPF_DIV|BPF_K) && p->k == 0)
 541                         return 0;
 542         }
 543         return BPF_CLASS(f[len - 1].code) == BPF_RET;
 544 }
 545 #endif