The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: 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  * 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 1.21 2002/07/05 00:06:08 peter Exp $
   41  */
   42 
   43 #include <sys/param.h>
   44 
   45 #ifdef sun
   46 #include <netinet/in.h>
   47 #endif
   48 
   49 #ifndef __i386__
   50 #define BPF_ALIGN
   51 #endif
   52 
   53 #ifndef BPF_ALIGN
   54 #define EXTRACT_SHORT(p)        ((u_int16_t)ntohs(*(u_int16_t *)p))
   55 #define EXTRACT_LONG(p)         (ntohl(*(u_int32_t *)p))
   56 #else
   57 #define EXTRACT_SHORT(p)\
   58         ((u_int16_t)\
   59                 ((u_int16_t)*((u_char *)p+0)<<8|\
   60                  (u_int16_t)*((u_char *)p+1)<<0))
   61 #define EXTRACT_LONG(p)\
   62                 ((u_int32_t)*((u_char *)p+0)<<24|\
   63                  (u_int32_t)*((u_char *)p+1)<<16|\
   64                  (u_int32_t)*((u_char *)p+2)<<8|\
   65                  (u_int32_t)*((u_char *)p+3)<<0)
   66 #endif
   67 
   68 #ifdef _KERNEL
   69 #include <sys/mbuf.h>
   70 #endif
   71 #include <net/bpf.h>
   72 #ifdef _KERNEL
   73 #define MINDEX(m, k) \
   74 { \
   75         register int len = m->m_len; \
   76  \
   77         while (k >= len) { \
   78                 k -= len; \
   79                 m = m->m_next; \
   80                 if (m == 0) \
   81                         return 0; \
   82                 len = m->m_len; \
   83         } \
   84 }
   85 
   86 static u_int16_t        m_xhalf(struct mbuf *m, bpf_u_int32 k, int *err);
   87 static u_int32_t        m_xword(struct mbuf *m, bpf_u_int32 k, int *err);
   88 
   89 static u_int32_t
   90 m_xword(m, k, err)
   91         register struct mbuf *m;
   92         register bpf_u_int32 k;
   93         register int *err;
   94 {
   95         register size_t len;
   96         register u_char *cp, *np;
   97         register struct mbuf *m0;
   98 
   99         len = m->m_len;
  100         while (k >= len) {
  101                 k -= len;
  102                 m = m->m_next;
  103                 if (m == 0)
  104                         goto bad;
  105                 len = m->m_len;
  106         }
  107         cp = mtod(m, u_char *) + k;
  108         if (len - k >= 4) {
  109                 *err = 0;
  110                 return EXTRACT_LONG(cp);
  111         }
  112         m0 = m->m_next;
  113         if (m0 == 0 || m0->m_len + len - k < 4)
  114                 goto bad;
  115         *err = 0;
  116         np = mtod(m0, u_char *);
  117         switch (len - k) {
  118 
  119         case 1:
  120                 return
  121                     ((u_int32_t)cp[0] << 24) |
  122                     ((u_int32_t)np[0] << 16) |
  123                     ((u_int32_t)np[1] << 8)  |
  124                     (u_int32_t)np[2];
  125 
  126         case 2:
  127                 return
  128                     ((u_int32_t)cp[0] << 24) |
  129                     ((u_int32_t)cp[1] << 16) |
  130                     ((u_int32_t)np[0] << 8) |
  131                     (u_int32_t)np[1];
  132 
  133         default:
  134                 return
  135                     ((u_int32_t)cp[0] << 24) |
  136                     ((u_int32_t)cp[1] << 16) |
  137                     ((u_int32_t)cp[2] << 8) |
  138                     (u_int32_t)np[0];
  139         }
  140     bad:
  141         *err = 1;
  142         return 0;
  143 }
  144 
  145 static u_int16_t
  146 m_xhalf(m, k, err)
  147         register struct mbuf *m;
  148         register bpf_u_int32 k;
  149         register int *err;
  150 {
  151         register size_t len;
  152         register u_char *cp;
  153         register struct mbuf *m0;
  154 
  155         len = m->m_len;
  156         while (k >= len) {
  157                 k -= len;
  158                 m = m->m_next;
  159                 if (m == 0)
  160                         goto bad;
  161                 len = m->m_len;
  162         }
  163         cp = mtod(m, u_char *) + k;
  164         if (len - k >= 2) {
  165                 *err = 0;
  166                 return EXTRACT_SHORT(cp);
  167         }
  168         m0 = m->m_next;
  169         if (m0 == 0)
  170                 goto bad;
  171         *err = 0;
  172         return (cp[0] << 8) | mtod(m0, u_char *)[0];
  173  bad:
  174         *err = 1;
  175         return 0;
  176 }
  177 #endif
  178 
  179 /*
  180  * Execute the filter program starting at pc on the packet p
  181  * wirelen is the length of the original packet
  182  * buflen is the amount of data present
  183  */
  184 u_int
  185 bpf_filter(pc, p, wirelen, buflen)
  186         register const struct bpf_insn *pc;
  187         register u_char *p;
  188         u_int wirelen;
  189         register u_int buflen;
  190 {
  191         register u_int32_t A = 0, X = 0;
  192         register bpf_u_int32 k;
  193         int32_t mem[BPF_MEMWORDS];
  194 
  195         if (pc == 0)
  196                 /*
  197                  * No filter means accept all.
  198                  */
  199                 return (u_int)-1;
  200 
  201         --pc;
  202         while (1) {
  203                 ++pc;
  204                 switch (pc->code) {
  205 
  206                 default:
  207 #ifdef _KERNEL
  208                         return 0;
  209 #else
  210                         abort();
  211 #endif
  212                 case BPF_RET|BPF_K:
  213                         return (u_int)pc->k;
  214 
  215                 case BPF_RET|BPF_A:
  216                         return (u_int)A;
  217 
  218                 case BPF_LD|BPF_W|BPF_ABS:
  219                         k = pc->k;
  220                         if (k > buflen || sizeof(int32_t) > buflen - k) {
  221 #ifdef _KERNEL
  222                                 int merr;
  223 
  224                                 if (buflen != 0)
  225                                         return 0;
  226                                 A = m_xword((struct mbuf *)p, k, &merr);
  227                                 if (merr != 0)
  228                                         return 0;
  229                                 continue;
  230 #else
  231                                 return 0;
  232 #endif
  233                         }
  234 #ifdef BPF_ALIGN
  235                         if (((intptr_t)(p + k) & 3) != 0)
  236                                 A = EXTRACT_LONG(&p[k]);
  237                         else
  238 #endif
  239                                 A = ntohl(*(int32_t *)(p + k));
  240                         continue;
  241 
  242                 case BPF_LD|BPF_H|BPF_ABS:
  243                         k = pc->k;
  244                         if (k > buflen || sizeof(int16_t) > buflen - k) {
  245 #ifdef _KERNEL
  246                                 int merr;
  247 
  248                                 if (buflen != 0)
  249                                         return 0;
  250                                 A = m_xhalf((struct mbuf *)p, k, &merr);
  251                                 continue;
  252 #else
  253                                 return 0;
  254 #endif
  255                         }
  256                         A = EXTRACT_SHORT(&p[k]);
  257                         continue;
  258 
  259                 case BPF_LD|BPF_B|BPF_ABS:
  260                         k = pc->k;
  261                         if (k >= buflen) {
  262 #ifdef _KERNEL
  263                                 register struct mbuf *m;
  264 
  265                                 if (buflen != 0)
  266                                         return 0;
  267                                 m = (struct mbuf *)p;
  268                                 MINDEX(m, k);
  269                                 A = mtod(m, u_char *)[k];
  270                                 continue;
  271 #else
  272                                 return 0;
  273 #endif
  274                         }
  275                         A = p[k];
  276                         continue;
  277 
  278                 case BPF_LD|BPF_W|BPF_LEN:
  279                         A = wirelen;
  280                         continue;
  281 
  282                 case BPF_LDX|BPF_W|BPF_LEN:
  283                         X = wirelen;
  284                         continue;
  285 
  286                 case BPF_LD|BPF_W|BPF_IND:
  287                         k = X + pc->k;
  288                         if (pc->k > buflen || X > buflen - pc->k ||
  289                             sizeof(int32_t) > buflen - k) {
  290 #ifdef _KERNEL
  291                                 int merr;
  292 
  293                                 if (buflen != 0)
  294                                         return 0;
  295                                 A = m_xword((struct mbuf *)p, k, &merr);
  296                                 if (merr != 0)
  297                                         return 0;
  298                                 continue;
  299 #else
  300                                 return 0;
  301 #endif
  302                         }
  303 #ifdef BPF_ALIGN
  304                         if (((intptr_t)(p + k) & 3) != 0)
  305                                 A = EXTRACT_LONG(&p[k]);
  306                         else
  307 #endif
  308                                 A = ntohl(*(int32_t *)(p + k));
  309                         continue;
  310 
  311                 case BPF_LD|BPF_H|BPF_IND:
  312                         k = X + pc->k;
  313                         if (X > buflen || pc->k > buflen - X ||
  314                             sizeof(int16_t) > buflen - k) {
  315 #ifdef _KERNEL
  316                                 int merr;
  317 
  318                                 if (buflen != 0)
  319                                         return 0;
  320                                 A = m_xhalf((struct mbuf *)p, k, &merr);
  321                                 if (merr != 0)
  322                                         return 0;
  323                                 continue;
  324 #else
  325                                 return 0;
  326 #endif
  327                         }
  328                         A = EXTRACT_SHORT(&p[k]);
  329                         continue;
  330 
  331                 case BPF_LD|BPF_B|BPF_IND:
  332                         k = X + pc->k;
  333                         if (pc->k >= buflen || X >= buflen - pc->k) {
  334 #ifdef _KERNEL
  335                                 register struct mbuf *m;
  336 
  337                                 if (buflen != 0)
  338                                         return 0;
  339                                 m = (struct mbuf *)p;
  340                                 MINDEX(m, k);
  341                                 A = mtod(m, char *)[k];
  342                                 continue;
  343 #else
  344                                 return 0;
  345 #endif
  346                         }
  347                         A = p[k];
  348                         continue;
  349 
  350                 case BPF_LDX|BPF_MSH|BPF_B:
  351                         k = pc->k;
  352                         if (k >= buflen) {
  353 #ifdef _KERNEL
  354                                 register struct mbuf *m;
  355 
  356                                 if (buflen != 0)
  357                                         return 0;
  358                                 m = (struct mbuf *)p;
  359                                 MINDEX(m, k);
  360                                 X = (mtod(m, char *)[k] & 0xf) << 2;
  361                                 continue;
  362 #else
  363                                 return 0;
  364 #endif
  365                         }
  366                         X = (p[pc->k] & 0xf) << 2;
  367                         continue;
  368 
  369                 case BPF_LD|BPF_IMM:
  370                         A = pc->k;
  371                         continue;
  372 
  373                 case BPF_LDX|BPF_IMM:
  374                         X = pc->k;
  375                         continue;
  376 
  377                 case BPF_LD|BPF_MEM:
  378                         A = mem[pc->k];
  379                         continue;
  380 
  381                 case BPF_LDX|BPF_MEM:
  382                         X = mem[pc->k];
  383                         continue;
  384 
  385                 case BPF_ST:
  386                         mem[pc->k] = A;
  387                         continue;
  388 
  389                 case BPF_STX:
  390                         mem[pc->k] = X;
  391                         continue;
  392 
  393                 case BPF_JMP|BPF_JA:
  394                         pc += pc->k;
  395                         continue;
  396 
  397                 case BPF_JMP|BPF_JGT|BPF_K:
  398                         pc += (A > pc->k) ? pc->jt : pc->jf;
  399                         continue;
  400 
  401                 case BPF_JMP|BPF_JGE|BPF_K:
  402                         pc += (A >= pc->k) ? pc->jt : pc->jf;
  403                         continue;
  404 
  405                 case BPF_JMP|BPF_JEQ|BPF_K:
  406                         pc += (A == pc->k) ? pc->jt : pc->jf;
  407                         continue;
  408 
  409                 case BPF_JMP|BPF_JSET|BPF_K:
  410                         pc += (A & pc->k) ? pc->jt : pc->jf;
  411                         continue;
  412 
  413                 case BPF_JMP|BPF_JGT|BPF_X:
  414                         pc += (A > X) ? pc->jt : pc->jf;
  415                         continue;
  416 
  417                 case BPF_JMP|BPF_JGE|BPF_X:
  418                         pc += (A >= X) ? pc->jt : pc->jf;
  419                         continue;
  420 
  421                 case BPF_JMP|BPF_JEQ|BPF_X:
  422                         pc += (A == X) ? pc->jt : pc->jf;
  423                         continue;
  424 
  425                 case BPF_JMP|BPF_JSET|BPF_X:
  426                         pc += (A & X) ? pc->jt : pc->jf;
  427                         continue;
  428 
  429                 case BPF_ALU|BPF_ADD|BPF_X:
  430                         A += X;
  431                         continue;
  432 
  433                 case BPF_ALU|BPF_SUB|BPF_X:
  434                         A -= X;
  435                         continue;
  436 
  437                 case BPF_ALU|BPF_MUL|BPF_X:
  438                         A *= X;
  439                         continue;
  440 
  441                 case BPF_ALU|BPF_DIV|BPF_X:
  442                         if (X == 0)
  443                                 return 0;
  444                         A /= X;
  445                         continue;
  446 
  447                 case BPF_ALU|BPF_AND|BPF_X:
  448                         A &= X;
  449                         continue;
  450 
  451                 case BPF_ALU|BPF_OR|BPF_X:
  452                         A |= X;
  453                         continue;
  454 
  455                 case BPF_ALU|BPF_LSH|BPF_X:
  456                         A <<= X;
  457                         continue;
  458 
  459                 case BPF_ALU|BPF_RSH|BPF_X:
  460                         A >>= X;
  461                         continue;
  462 
  463                 case BPF_ALU|BPF_ADD|BPF_K:
  464                         A += pc->k;
  465                         continue;
  466 
  467                 case BPF_ALU|BPF_SUB|BPF_K:
  468                         A -= pc->k;
  469                         continue;
  470 
  471                 case BPF_ALU|BPF_MUL|BPF_K:
  472                         A *= pc->k;
  473                         continue;
  474 
  475                 case BPF_ALU|BPF_DIV|BPF_K:
  476                         A /= pc->k;
  477                         continue;
  478 
  479                 case BPF_ALU|BPF_AND|BPF_K:
  480                         A &= pc->k;
  481                         continue;
  482 
  483                 case BPF_ALU|BPF_OR|BPF_K:
  484                         A |= pc->k;
  485                         continue;
  486 
  487                 case BPF_ALU|BPF_LSH|BPF_K:
  488                         A <<= pc->k;
  489                         continue;
  490 
  491                 case BPF_ALU|BPF_RSH|BPF_K:
  492                         A >>= pc->k;
  493                         continue;
  494 
  495                 case BPF_ALU|BPF_NEG:
  496                         A = -A;
  497                         continue;
  498 
  499                 case BPF_MISC|BPF_TAX:
  500                         X = A;
  501                         continue;
  502 
  503                 case BPF_MISC|BPF_TXA:
  504                         A = X;
  505                         continue;
  506                 }
  507         }
  508 }
  509 
  510 #ifdef _KERNEL
  511 /*
  512  * Return true if the 'fcode' is a valid filter program.
  513  * The constraints are that each jump be forward and to a valid
  514  * code.  The code must terminate with either an accept or reject.
  515  *
  516  * The kernel needs to be able to verify an application's filter code.
  517  * Otherwise, a bogus program could easily crash the system.
  518  */
  519 int
  520 bpf_validate(f, len)
  521         const struct bpf_insn *f;
  522         int len;
  523 {
  524         register int i;
  525         register const struct bpf_insn *p;
  526 
  527         for (i = 0; i < len; ++i) {
  528                 /*
  529                  * Check that that jumps are forward, and within
  530                  * the code block.
  531                  */
  532                 p = &f[i];
  533                 if (BPF_CLASS(p->code) == BPF_JMP) {
  534                         register int from = i + 1;
  535 
  536                         if (BPF_OP(p->code) == BPF_JA) {
  537                                 if (from >= len || p->k >= len - from)
  538                                         return 0;
  539                         }
  540                         else if (from >= len || p->jt >= len - from ||
  541                                  p->jf >= len - from)
  542                                 return 0;
  543                 }
  544                 /*
  545                  * Check that memory operations use valid addresses.
  546                  */
  547                 if ((BPF_CLASS(p->code) == BPF_ST ||
  548                      (BPF_CLASS(p->code) == BPF_LD &&
  549                       (p->code & 0xe0) == BPF_MEM)) &&
  550                     p->k >= BPF_MEMWORDS)
  551                         return 0;
  552                 /*
  553                  * Check for constant division by 0.
  554                  */
  555                 if (p->code == (BPF_ALU|BPF_DIV|BPF_K) && p->k == 0)
  556                         return 0;
  557         }
  558         return BPF_CLASS(f[len - 1].code) == BPF_RET;
  559 }
  560 #endif

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