The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/net/bpf_filter.c

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    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  * 4. Neither the name of the University nor the names of its contributors
   19  *    may be used to endorse or promote products derived from this software
   20  *    without specific prior written permission.
   21  *
   22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   32  * SUCH DAMAGE.
   33  *
   34  *      @(#)bpf_filter.c        8.1 (Berkeley) 6/10/93
   35  */
   36 
   37 #include <sys/cdefs.h>
   38 __FBSDID("$FreeBSD: releng/8.1/sys/net/bpf_filter.c 182456 2008-08-29 20:00:55Z jkim $");
   39 
   40 #include <sys/param.h>
   41 
   42 #if !defined(_KERNEL) || defined(sun)
   43 #include <netinet/in.h>
   44 #endif
   45 
   46 #ifndef __i386__
   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 #else
   68 #include <stdlib.h>
   69 #endif
   70 #include <net/bpf.h>
   71 #ifdef _KERNEL
   72 #define MINDEX(m, k) \
   73 { \
   74         register int len = m->m_len; \
   75  \
   76         while (k >= len) { \
   77                 k -= len; \
   78                 m = m->m_next; \
   79                 if (m == 0) \
   80                         return (0); \
   81                 len = m->m_len; \
   82         } \
   83 }
   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 == 0)
  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 == 0 || m0->m_len + len - k < 4)
  110                 goto bad;
  111         *err = 0;
  112         np = mtod(m0, u_char *);
  113         switch (len - k) {
  114         case 1:
  115                 return (((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 (((u_int32_t)cp[0] << 24) |
  122                     ((u_int32_t)cp[1] << 16) |
  123                     ((u_int32_t)np[0] << 8) |
  124                     (u_int32_t)np[1]);
  125 
  126         default:
  127                 return (((u_int32_t)cp[0] << 24) |
  128                     ((u_int32_t)cp[1] << 16) |
  129                     ((u_int32_t)cp[2] << 8) |
  130                     (u_int32_t)np[0]);
  131         }
  132     bad:
  133         *err = 1;
  134         return (0);
  135 }
  136 
  137 static u_int16_t
  138 m_xhalf(struct mbuf *m, bpf_u_int32 k, int *err)
  139 {
  140         size_t len;
  141         u_char *cp;
  142         struct mbuf *m0;
  143 
  144         len = m->m_len;
  145         while (k >= len) {
  146                 k -= len;
  147                 m = m->m_next;
  148                 if (m == 0)
  149                         goto bad;
  150                 len = m->m_len;
  151         }
  152         cp = mtod(m, u_char *) + k;
  153         if (len - k >= 2) {
  154                 *err = 0;
  155                 return (EXTRACT_SHORT(cp));
  156         }
  157         m0 = m->m_next;
  158         if (m0 == 0)
  159                 goto bad;
  160         *err = 0;
  161         return ((cp[0] << 8) | mtod(m0, u_char *)[0]);
  162  bad:
  163         *err = 1;
  164         return (0);
  165 }
  166 #endif
  167 
  168 /*
  169  * Execute the filter program starting at pc on the packet p
  170  * wirelen is the length of the original packet
  171  * buflen is the amount of data present
  172  */
  173 u_int
  174 bpf_filter(const struct bpf_insn *pc, u_char *p, u_int wirelen, u_int buflen)
  175 {
  176         u_int32_t A = 0, X = 0;
  177         bpf_u_int32 k;
  178         u_int32_t mem[BPF_MEMWORDS];
  179 
  180         if (pc == NULL)
  181                 /*
  182                  * No filter means accept all.
  183                  */
  184                 return ((u_int)-1);
  185 
  186         --pc;
  187         while (1) {
  188                 ++pc;
  189                 switch (pc->code) {
  190                 default:
  191 #ifdef _KERNEL
  192                         return (0);
  193 #else
  194                         abort();
  195 #endif
  196 
  197                 case BPF_RET|BPF_K:
  198                         return ((u_int)pc->k);
  199 
  200                 case BPF_RET|BPF_A:
  201                         return ((u_int)A);
  202 
  203                 case BPF_LD|BPF_W|BPF_ABS:
  204                         k = pc->k;
  205                         if (k > buflen || sizeof(int32_t) > buflen - k) {
  206 #ifdef _KERNEL
  207                                 int merr;
  208 
  209                                 if (buflen != 0)
  210                                         return (0);
  211                                 A = m_xword((struct mbuf *)p, k, &merr);
  212                                 if (merr != 0)
  213                                         return (0);
  214                                 continue;
  215 #else
  216                                 return (0);
  217 #endif
  218                         }
  219 #ifdef BPF_ALIGN
  220                         if (((intptr_t)(p + k) & 3) != 0)
  221                                 A = EXTRACT_LONG(&p[k]);
  222                         else
  223 #endif
  224                                 A = ntohl(*(int32_t *)(p + k));
  225                         continue;
  226 
  227                 case BPF_LD|BPF_H|BPF_ABS:
  228                         k = pc->k;
  229                         if (k > buflen || sizeof(int16_t) > buflen - k) {
  230 #ifdef _KERNEL
  231                                 int merr;
  232 
  233                                 if (buflen != 0)
  234                                         return (0);
  235                                 A = m_xhalf((struct mbuf *)p, k, &merr);
  236                                 continue;
  237 #else
  238                                 return (0);
  239 #endif
  240                         }
  241                         A = EXTRACT_SHORT(&p[k]);
  242                         continue;
  243 
  244                 case BPF_LD|BPF_B|BPF_ABS:
  245                         k = pc->k;
  246                         if (k >= buflen) {
  247 #ifdef _KERNEL
  248                                 struct mbuf *m;
  249 
  250                                 if (buflen != 0)
  251                                         return (0);
  252                                 m = (struct mbuf *)p;
  253                                 MINDEX(m, k);
  254                                 A = mtod(m, u_char *)[k];
  255                                 continue;
  256 #else
  257                                 return (0);
  258 #endif
  259                         }
  260                         A = p[k];
  261                         continue;
  262 
  263                 case BPF_LD|BPF_W|BPF_LEN:
  264                         A = wirelen;
  265                         continue;
  266 
  267                 case BPF_LDX|BPF_W|BPF_LEN:
  268                         X = wirelen;
  269                         continue;
  270 
  271                 case BPF_LD|BPF_W|BPF_IND:
  272                         k = X + pc->k;
  273                         if (pc->k > buflen || X > buflen - pc->k ||
  274                             sizeof(int32_t) > buflen - k) {
  275 #ifdef _KERNEL
  276                                 int merr;
  277 
  278                                 if (buflen != 0)
  279                                         return (0);
  280                                 A = m_xword((struct mbuf *)p, k, &merr);
  281                                 if (merr != 0)
  282                                         return (0);
  283                                 continue;
  284 #else
  285                                 return (0);
  286 #endif
  287                         }
  288 #ifdef BPF_ALIGN
  289                         if (((intptr_t)(p + k) & 3) != 0)
  290                                 A = EXTRACT_LONG(&p[k]);
  291                         else
  292 #endif
  293                                 A = ntohl(*(int32_t *)(p + k));
  294                         continue;
  295 
  296                 case BPF_LD|BPF_H|BPF_IND:
  297                         k = X + pc->k;
  298                         if (X > buflen || pc->k > buflen - X ||
  299                             sizeof(int16_t) > buflen - k) {
  300 #ifdef _KERNEL
  301                                 int merr;
  302 
  303                                 if (buflen != 0)
  304                                         return (0);
  305                                 A = m_xhalf((struct mbuf *)p, k, &merr);
  306                                 if (merr != 0)
  307                                         return (0);
  308                                 continue;
  309 #else
  310                                 return (0);
  311 #endif
  312                         }
  313                         A = EXTRACT_SHORT(&p[k]);
  314                         continue;
  315 
  316                 case BPF_LD|BPF_B|BPF_IND:
  317                         k = X + pc->k;
  318                         if (pc->k >= buflen || X >= buflen - pc->k) {
  319 #ifdef _KERNEL
  320                                 struct mbuf *m;
  321 
  322                                 if (buflen != 0)
  323                                         return (0);
  324                                 m = (struct mbuf *)p;
  325                                 MINDEX(m, k);
  326                                 A = mtod(m, u_char *)[k];
  327                                 continue;
  328 #else
  329                                 return (0);
  330 #endif
  331                         }
  332                         A = p[k];
  333                         continue;
  334 
  335                 case BPF_LDX|BPF_MSH|BPF_B:
  336                         k = pc->k;
  337                         if (k >= buflen) {
  338 #ifdef _KERNEL
  339                                 register struct mbuf *m;
  340 
  341                                 if (buflen != 0)
  342                                         return (0);
  343                                 m = (struct mbuf *)p;
  344                                 MINDEX(m, k);
  345                                 X = (mtod(m, u_char *)[k] & 0xf) << 2;
  346                                 continue;
  347 #else
  348                                 return (0);
  349 #endif
  350                         }
  351                         X = (p[pc->k] & 0xf) << 2;
  352                         continue;
  353 
  354                 case BPF_LD|BPF_IMM:
  355                         A = pc->k;
  356                         continue;
  357 
  358                 case BPF_LDX|BPF_IMM:
  359                         X = pc->k;
  360                         continue;
  361 
  362                 case BPF_LD|BPF_MEM:
  363                         A = mem[pc->k];
  364                         continue;
  365 
  366                 case BPF_LDX|BPF_MEM:
  367                         X = mem[pc->k];
  368                         continue;
  369 
  370                 case BPF_ST:
  371                         mem[pc->k] = A;
  372                         continue;
  373 
  374                 case BPF_STX:
  375                         mem[pc->k] = X;
  376                         continue;
  377 
  378                 case BPF_JMP|BPF_JA:
  379                         pc += pc->k;
  380                         continue;
  381 
  382                 case BPF_JMP|BPF_JGT|BPF_K:
  383                         pc += (A > pc->k) ? pc->jt : pc->jf;
  384                         continue;
  385 
  386                 case BPF_JMP|BPF_JGE|BPF_K:
  387                         pc += (A >= pc->k) ? pc->jt : pc->jf;
  388                         continue;
  389 
  390                 case BPF_JMP|BPF_JEQ|BPF_K:
  391                         pc += (A == pc->k) ? pc->jt : pc->jf;
  392                         continue;
  393 
  394                 case BPF_JMP|BPF_JSET|BPF_K:
  395                         pc += (A & pc->k) ? pc->jt : pc->jf;
  396                         continue;
  397 
  398                 case BPF_JMP|BPF_JGT|BPF_X:
  399                         pc += (A > X) ? pc->jt : pc->jf;
  400                         continue;
  401 
  402                 case BPF_JMP|BPF_JGE|BPF_X:
  403                         pc += (A >= X) ? pc->jt : pc->jf;
  404                         continue;
  405 
  406                 case BPF_JMP|BPF_JEQ|BPF_X:
  407                         pc += (A == X) ? pc->jt : pc->jf;
  408                         continue;
  409 
  410                 case BPF_JMP|BPF_JSET|BPF_X:
  411                         pc += (A & X) ? pc->jt : pc->jf;
  412                         continue;
  413 
  414                 case BPF_ALU|BPF_ADD|BPF_X:
  415                         A += X;
  416                         continue;
  417 
  418                 case BPF_ALU|BPF_SUB|BPF_X:
  419                         A -= X;
  420                         continue;
  421 
  422                 case BPF_ALU|BPF_MUL|BPF_X:
  423                         A *= X;
  424                         continue;
  425 
  426                 case BPF_ALU|BPF_DIV|BPF_X:
  427                         if (X == 0)
  428                                 return (0);
  429                         A /= X;
  430                         continue;
  431 
  432                 case BPF_ALU|BPF_AND|BPF_X:
  433                         A &= X;
  434                         continue;
  435 
  436                 case BPF_ALU|BPF_OR|BPF_X:
  437                         A |= X;
  438                         continue;
  439 
  440                 case BPF_ALU|BPF_LSH|BPF_X:
  441                         A <<= X;
  442                         continue;
  443 
  444                 case BPF_ALU|BPF_RSH|BPF_X:
  445                         A >>= X;
  446                         continue;
  447 
  448                 case BPF_ALU|BPF_ADD|BPF_K:
  449                         A += pc->k;
  450                         continue;
  451 
  452                 case BPF_ALU|BPF_SUB|BPF_K:
  453                         A -= pc->k;
  454                         continue;
  455 
  456                 case BPF_ALU|BPF_MUL|BPF_K:
  457                         A *= pc->k;
  458                         continue;
  459 
  460                 case BPF_ALU|BPF_DIV|BPF_K:
  461                         A /= pc->k;
  462                         continue;
  463 
  464                 case BPF_ALU|BPF_AND|BPF_K:
  465                         A &= pc->k;
  466                         continue;
  467 
  468                 case BPF_ALU|BPF_OR|BPF_K:
  469                         A |= pc->k;
  470                         continue;
  471 
  472                 case BPF_ALU|BPF_LSH|BPF_K:
  473                         A <<= pc->k;
  474                         continue;
  475 
  476                 case BPF_ALU|BPF_RSH|BPF_K:
  477                         A >>= pc->k;
  478                         continue;
  479 
  480                 case BPF_ALU|BPF_NEG:
  481                         A = -A;
  482                         continue;
  483 
  484                 case BPF_MISC|BPF_TAX:
  485                         X = A;
  486                         continue;
  487 
  488                 case BPF_MISC|BPF_TXA:
  489                         A = X;
  490                         continue;
  491                 }
  492         }
  493 }
  494 
  495 #ifdef _KERNEL
  496 static const u_short    bpf_code_map[] = {
  497         0x10ff, /* 0x00-0x0f: 1111111100001000 */
  498         0x3070, /* 0x10-0x1f: 0000111000001100 */
  499         0x3131, /* 0x20-0x2f: 1000110010001100 */
  500         0x3031, /* 0x30-0x3f: 1000110000001100 */
  501         0x3131, /* 0x40-0x4f: 1000110010001100 */
  502         0x1011, /* 0x50-0x5f: 1000100000001000 */
  503         0x1013, /* 0x60-0x6f: 1100100000001000 */
  504         0x1010, /* 0x70-0x7f: 0000100000001000 */
  505         0x0093, /* 0x80-0x8f: 1100100100000000 */
  506         0x0000, /* 0x90-0x9f: 0000000000000000 */
  507         0x0000, /* 0xa0-0xaf: 0000000000000000 */
  508         0x0002, /* 0xb0-0xbf: 0100000000000000 */
  509         0x0000, /* 0xc0-0xcf: 0000000000000000 */
  510         0x0000, /* 0xd0-0xdf: 0000000000000000 */
  511         0x0000, /* 0xe0-0xef: 0000000000000000 */
  512         0x0000  /* 0xf0-0xff: 0000000000000000 */
  513 };
  514 
  515 #define BPF_VALIDATE_CODE(c)    \
  516     ((c) <= 0xff && (bpf_code_map[(c) >> 4] & (1 << ((c) & 0xf))) != 0)
  517 
  518 /*
  519  * Return true if the 'fcode' is a valid filter program.
  520  * The constraints are that each jump be forward and to a valid
  521  * code.  The code must terminate with either an accept or reject.
  522  *
  523  * The kernel needs to be able to verify an application's filter code.
  524  * Otherwise, a bogus program could easily crash the system.
  525  */
  526 int
  527 bpf_validate(const struct bpf_insn *f, int len)
  528 {
  529         register int i;
  530         register const struct bpf_insn *p;
  531 
  532         /* Do not accept negative length filter. */
  533         if (len < 0)
  534                 return (0);
  535 
  536         /* An empty filter means accept all. */
  537         if (len == 0)
  538                 return (1);
  539 
  540         for (i = 0; i < len; ++i) {
  541                 p = &f[i];
  542                 /*
  543                  * Check that the code is valid.
  544                  */
  545                 if (!BPF_VALIDATE_CODE(p->code))
  546                         return (0);
  547                 /*
  548                  * Check that that jumps are forward, and within
  549                  * the code block.
  550                  */
  551                 if (BPF_CLASS(p->code) == BPF_JMP) {
  552                         register u_int offset;
  553 
  554                         if (p->code == (BPF_JMP|BPF_JA))
  555                                 offset = p->k;
  556                         else
  557                                 offset = p->jt > p->jf ? p->jt : p->jf;
  558                         if (offset >= (u_int)(len - i) - 1)
  559                                 return (0);
  560                         continue;
  561                 }
  562                 /*
  563                  * Check that memory operations use valid addresses.
  564                  */
  565                 if (p->code == BPF_ST || p->code == BPF_STX ||
  566                     p->code == (BPF_LD|BPF_MEM) ||
  567                     p->code == (BPF_LDX|BPF_MEM)) {
  568                         if (p->k >= BPF_MEMWORDS)
  569                                 return (0);
  570                         continue;
  571                 }
  572                 /*
  573                  * Check for constant division by 0.
  574                  */
  575                 if (p->code == (BPF_ALU|BPF_DIV|BPF_K) && p->k == 0)
  576                         return (0);
  577         }
  578         return (BPF_CLASS(f[len - 1].code) == BPF_RET);
  579 }
  580 #endif

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