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  * $FreeBSD: releng/7.3/sys/net/bpf_filter.c 182761 2008-09-04 15:18:32Z jkim $
   37  */
   38 
   39 #include <sys/param.h>
   40 
   41 #ifdef sun
   42 #include <netinet/in.h>
   43 #endif
   44 
   45 #ifndef __i386__
   46 #define BPF_ALIGN
   47 #endif
   48 
   49 #ifndef BPF_ALIGN
   50 #define EXTRACT_SHORT(p)        ((u_int16_t)ntohs(*(u_int16_t *)p))
   51 #define EXTRACT_LONG(p)         (ntohl(*(u_int32_t *)p))
   52 #else
   53 #define EXTRACT_SHORT(p)\
   54         ((u_int16_t)\
   55                 ((u_int16_t)*((u_char *)p+0)<<8|\
   56                  (u_int16_t)*((u_char *)p+1)<<0))
   57 #define EXTRACT_LONG(p)\
   58                 ((u_int32_t)*((u_char *)p+0)<<24|\
   59                  (u_int32_t)*((u_char *)p+1)<<16|\
   60                  (u_int32_t)*((u_char *)p+2)<<8|\
   61                  (u_int32_t)*((u_char *)p+3)<<0)
   62 #endif
   63 
   64 #ifdef _KERNEL
   65 #include <sys/mbuf.h>
   66 #endif
   67 #include <net/bpf.h>
   68 #ifdef _KERNEL
   69 #define MINDEX(m, k) \
   70 { \
   71         register int len = m->m_len; \
   72  \
   73         while (k >= len) { \
   74                 k -= len; \
   75                 m = m->m_next; \
   76                 if (m == 0) \
   77                         return 0; \
   78                 len = m->m_len; \
   79         } \
   80 }
   81 
   82 static u_int16_t        m_xhalf(struct mbuf *m, bpf_u_int32 k, int *err);
   83 static u_int32_t        m_xword(struct mbuf *m, bpf_u_int32 k, int *err);
   84 
   85 static u_int32_t
   86 m_xword(struct mbuf *m, bpf_u_int32 k, int *err)
   87 {
   88         size_t len;
   89         u_char *cp, *np;
   90         struct mbuf *m0;
   91 
   92         len = m->m_len;
   93         while (k >= len) {
   94                 k -= len;
   95                 m = m->m_next;
   96                 if (m == 0)
   97                         goto bad;
   98                 len = m->m_len;
   99         }
  100         cp = mtod(m, u_char *) + k;
  101         if (len - k >= 4) {
  102                 *err = 0;
  103                 return EXTRACT_LONG(cp);
  104         }
  105         m0 = m->m_next;
  106         if (m0 == 0 || m0->m_len + len - k < 4)
  107                 goto bad;
  108         *err = 0;
  109         np = mtod(m0, u_char *);
  110         switch (len - k) {
  111         case 1:
  112                 return
  113                     ((u_int32_t)cp[0] << 24) |
  114                     ((u_int32_t)np[0] << 16) |
  115                     ((u_int32_t)np[1] << 8)  |
  116                     (u_int32_t)np[2];
  117 
  118         case 2:
  119                 return
  120                     ((u_int32_t)cp[0] << 24) |
  121                     ((u_int32_t)cp[1] << 16) |
  122                     ((u_int32_t)np[0] << 8) |
  123                     (u_int32_t)np[1];
  124 
  125         default:
  126                 return
  127                     ((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 /*
  497  * Return true if the 'fcode' is a valid filter program.
  498  * The constraints are that each jump be forward and to a valid
  499  * code.  The code must terminate with either an accept or reject.
  500  *
  501  * The kernel needs to be able to verify an application's filter code.
  502  * Otherwise, a bogus program could easily crash the system.
  503  */
  504 int
  505 bpf_validate(f, len)
  506         const struct bpf_insn *f;
  507         int len;
  508 {
  509         register int i;
  510         register const struct bpf_insn *p;
  511 
  512         /* Do not accept negative length filter. */
  513         if (len < 0)
  514                 return 0;
  515 
  516         /* An empty filter means accept all. */
  517         if (len == 0)
  518                 return 1;
  519 
  520         for (i = 0; i < len; ++i) {
  521                 /*
  522                  * Check that that jumps are forward, and within
  523                  * the code block.
  524                  */
  525                 p = &f[i];
  526                 if (BPF_CLASS(p->code) == BPF_JMP) {
  527                         register int from = i + 1;
  528 
  529                         if (BPF_OP(p->code) == BPF_JA) {
  530                                 if (from >= len || p->k >= len - from)
  531                                         return 0;
  532                         }
  533                         else if (from >= len || p->jt >= len - from ||
  534                                  p->jf >= len - from)
  535                                 return 0;
  536                 }
  537                 /*
  538                  * Check that memory operations use valid addresses.
  539                  */
  540                 if ((BPF_CLASS(p->code) == BPF_ST ||
  541                      BPF_CLASS(p->code) == BPF_STX ||
  542                      ((BPF_CLASS(p->code) == BPF_LD ||
  543                        BPF_CLASS(p->code) == BPF_LDX) &&
  544                       (p->code & 0xe0) == BPF_MEM)) &&
  545                     p->k >= BPF_MEMWORDS)
  546                         return 0;
  547                 /*
  548                  * Check for constant division by 0.
  549                  */
  550                 if (p->code == (BPF_ALU|BPF_DIV|BPF_K) && p->k == 0)
  551                         return 0;
  552         }
  553         return BPF_CLASS(f[len - 1].code) == BPF_RET;
  554 }
  555 #endif

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