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  * $FreeBSD$
   41  */
   42 
   43 #include <sys/param.h>
   44 
   45 #ifdef sun
   46 #include <netinet/in.h>
   47 #endif
   48 
   49 #if defined(sparc) || defined(mips) || defined(ibm032) || defined(__alpha__)
   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 __P((struct mbuf *m, bpf_u_int32 k, int *err));
   87 static u_int32_t        m_xword __P((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 || sizeof(int32_t) > buflen - k) {
  289 #ifdef KERNEL
  290                                 int merr;
  291 
  292                                 if (buflen != 0)
  293                                         return 0;
  294                                 A = m_xword((struct mbuf *)p, k, &merr);
  295                                 if (merr != 0)
  296                                         return 0;
  297                                 continue;
  298 #else
  299                                 return 0;
  300 #endif
  301                         }
  302 #ifdef BPF_ALIGN
  303                         if (((intptr_t)(p + k) & 3) != 0)
  304                                 A = EXTRACT_LONG(&p[k]);
  305                         else
  306 #endif
  307                                 A = ntohl(*(int32_t *)(p + k));
  308                         continue;
  309 
  310                 case BPF_LD|BPF_H|BPF_IND:
  311                         k = X + pc->k;
  312                         if (X > buflen || pc->k > buflen - X || sizeof(int16_t) > buflen - k) {
  313 #ifdef KERNEL
  314                                 int merr;
  315 
  316                                 if (buflen != 0)
  317                                         return 0;
  318                                 A = m_xhalf((struct mbuf *)p, k, &merr);
  319                                 if (merr != 0)
  320                                         return 0;
  321                                 continue;
  322 #else
  323                                 return 0;
  324 #endif
  325                         }
  326                         A = EXTRACT_SHORT(&p[k]);
  327                         continue;
  328 
  329                 case BPF_LD|BPF_B|BPF_IND:
  330                         k = X + pc->k;
  331                         if (pc->k >= buflen || X >= buflen - pc->k) {
  332 #ifdef KERNEL
  333                                 register struct mbuf *m;
  334 
  335                                 if (buflen != 0)
  336                                         return 0;
  337                                 m = (struct mbuf *)p;
  338                                 MINDEX(m, k);
  339                                 A = mtod(m, char *)[k];
  340                                 continue;
  341 #else
  342                                 return 0;
  343 #endif
  344                         }
  345                         A = p[k];
  346                         continue;
  347 
  348                 case BPF_LDX|BPF_MSH|BPF_B:
  349                         k = pc->k;
  350                         if (k >= buflen) {
  351 #ifdef KERNEL
  352                                 register struct mbuf *m;
  353 
  354                                 if (buflen != 0)
  355                                         return 0;
  356                                 m = (struct mbuf *)p;
  357                                 MINDEX(m, k);
  358                                 X = (mtod(m, char *)[k] & 0xf) << 2;
  359                                 continue;
  360 #else
  361                                 return 0;
  362 #endif
  363                         }
  364                         X = (p[pc->k] & 0xf) << 2;
  365                         continue;
  366 
  367                 case BPF_LD|BPF_IMM:
  368                         A = pc->k;
  369                         continue;
  370 
  371                 case BPF_LDX|BPF_IMM:
  372                         X = pc->k;
  373                         continue;
  374 
  375                 case BPF_LD|BPF_MEM:
  376                         A = mem[pc->k];
  377                         continue;
  378 
  379                 case BPF_LDX|BPF_MEM:
  380                         X = mem[pc->k];
  381                         continue;
  382 
  383                 case BPF_ST:
  384                         mem[pc->k] = A;
  385                         continue;
  386 
  387                 case BPF_STX:
  388                         mem[pc->k] = X;
  389                         continue;
  390 
  391                 case BPF_JMP|BPF_JA:
  392                         pc += pc->k;
  393                         continue;
  394 
  395                 case BPF_JMP|BPF_JGT|BPF_K:
  396                         pc += (A > pc->k) ? pc->jt : pc->jf;
  397                         continue;
  398 
  399                 case BPF_JMP|BPF_JGE|BPF_K:
  400                         pc += (A >= pc->k) ? pc->jt : pc->jf;
  401                         continue;
  402 
  403                 case BPF_JMP|BPF_JEQ|BPF_K:
  404                         pc += (A == pc->k) ? pc->jt : pc->jf;
  405                         continue;
  406 
  407                 case BPF_JMP|BPF_JSET|BPF_K:
  408                         pc += (A & pc->k) ? pc->jt : pc->jf;
  409                         continue;
  410 
  411                 case BPF_JMP|BPF_JGT|BPF_X:
  412                         pc += (A > X) ? pc->jt : pc->jf;
  413                         continue;
  414 
  415                 case BPF_JMP|BPF_JGE|BPF_X:
  416                         pc += (A >= X) ? pc->jt : pc->jf;
  417                         continue;
  418 
  419                 case BPF_JMP|BPF_JEQ|BPF_X:
  420                         pc += (A == X) ? pc->jt : pc->jf;
  421                         continue;
  422 
  423                 case BPF_JMP|BPF_JSET|BPF_X:
  424                         pc += (A & X) ? pc->jt : pc->jf;
  425                         continue;
  426 
  427                 case BPF_ALU|BPF_ADD|BPF_X:
  428                         A += X;
  429                         continue;
  430 
  431                 case BPF_ALU|BPF_SUB|BPF_X:
  432                         A -= X;
  433                         continue;
  434 
  435                 case BPF_ALU|BPF_MUL|BPF_X:
  436                         A *= X;
  437                         continue;
  438 
  439                 case BPF_ALU|BPF_DIV|BPF_X:
  440                         if (X == 0)
  441                                 return 0;
  442                         A /= X;
  443                         continue;
  444 
  445                 case BPF_ALU|BPF_AND|BPF_X:
  446                         A &= X;
  447                         continue;
  448 
  449                 case BPF_ALU|BPF_OR|BPF_X:
  450                         A |= X;
  451                         continue;
  452 
  453                 case BPF_ALU|BPF_LSH|BPF_X:
  454                         A <<= X;
  455                         continue;
  456 
  457                 case BPF_ALU|BPF_RSH|BPF_X:
  458                         A >>= X;
  459                         continue;
  460 
  461                 case BPF_ALU|BPF_ADD|BPF_K:
  462                         A += pc->k;
  463                         continue;
  464 
  465                 case BPF_ALU|BPF_SUB|BPF_K:
  466                         A -= pc->k;
  467                         continue;
  468 
  469                 case BPF_ALU|BPF_MUL|BPF_K:
  470                         A *= pc->k;
  471                         continue;
  472 
  473                 case BPF_ALU|BPF_DIV|BPF_K:
  474                         A /= pc->k;
  475                         continue;
  476 
  477                 case BPF_ALU|BPF_AND|BPF_K:
  478                         A &= pc->k;
  479                         continue;
  480 
  481                 case BPF_ALU|BPF_OR|BPF_K:
  482                         A |= pc->k;
  483                         continue;
  484 
  485                 case BPF_ALU|BPF_LSH|BPF_K:
  486                         A <<= pc->k;
  487                         continue;
  488 
  489                 case BPF_ALU|BPF_RSH|BPF_K:
  490                         A >>= pc->k;
  491                         continue;
  492 
  493                 case BPF_ALU|BPF_NEG:
  494                         A = -A;
  495                         continue;
  496 
  497                 case BPF_MISC|BPF_TAX:
  498                         X = A;
  499                         continue;
  500 
  501                 case BPF_MISC|BPF_TXA:
  502                         A = X;
  503                         continue;
  504                 }
  505         }
  506 }
  507 
  508 #ifdef KERNEL
  509 /*
  510  * Return true if the 'fcode' is a valid filter program.
  511  * The constraints are that each jump be forward and to a valid
  512  * code.  The code must terminate with either an accept or reject.
  513  *
  514  * The kernel needs to be able to verify an application's filter code.
  515  * Otherwise, a bogus program could easily crash the system.
  516  */
  517 int
  518 bpf_validate(f, len)
  519         const struct bpf_insn *f;
  520         int len;
  521 {
  522         register int i;
  523         register const struct bpf_insn *p;
  524 
  525         for (i = 0; i < len; ++i) {
  526                 /*
  527                  * Check that that jumps are forward, and within
  528                  * the code block.
  529                  */
  530                 p = &f[i];
  531                 if (BPF_CLASS(p->code) == BPF_JMP) {
  532                         register int from = i + 1;
  533 
  534                         if (BPF_OP(p->code) == BPF_JA) {
  535                                 if (from >= len || p->k >= len - from)
  536                                         return 0;
  537                         }
  538                         else if (from >= len || p->jt >= len - from || p->jf >= len - from)
  539                                 return 0;
  540                 }
  541                 /*
  542                  * Check that memory operations use valid addresses.
  543                  */
  544                 if ((BPF_CLASS(p->code) == BPF_ST ||
  545                      (BPF_CLASS(p->code) == BPF_LD &&
  546                       (p->code & 0xe0) == BPF_MEM)) &&
  547                     p->k >= BPF_MEMWORDS)
  548                         return 0;
  549                 /*
  550                  * Check for constant division by 0.
  551                  */
  552                 if (p->code == (BPF_ALU|BPF_DIV|BPF_K) && p->k == 0)
  553                         return 0;
  554         }
  555         return BPF_CLASS(f[len - 1].code) == BPF_RET;
  556 }
  557 #endif
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FreeBSD/Linux Kernel Cross Reference sys/net/bpf_filter.c

FreeBSD/Linux Kernel Cross Reference
sys/net/bpf_filter.c
