net/core/filter.c

   1 /*
   2  * Linux Socket Filter - Kernel level socket filtering
   3  *
   4  * Author:
   5  *     Jay Schulist <jschlst@samba.org>
   6  *
   7  * Based on the design of:
   8  *     - The Berkeley Packet Filter
   9  *
  10  * This program is free software; you can redistribute it and/or
  11  * modify it under the terms of the GNU General Public License
  12  * as published by the Free Software Foundation; either version
  13  * 2 of the License, or (at your option) any later version.
  14  *
  15  * Andi Kleen - Fix a few bad bugs and races.
  16  */
  17
  18 #include <linux/config.h>
  19 #if defined(CONFIG_FILTER)
  20
  21 #include <linux/module.h>
  22 #include <linux/types.h>
  23 #include <linux/sched.h>
  24 #include <linux/mm.h>
  25 #include <linux/fcntl.h>
  26 #include <linux/socket.h>
  27 #include <linux/in.h>
  28 #include <linux/inet.h>
  29 #include <linux/netdevice.h>
  30 #include <linux/if_packet.h>
  31 #include <net/ip.h>
  32 #include <net/protocol.h>
  33 #include <linux/skbuff.h>
  34 #include <net/sock.h>
  35 #include <linux/errno.h>
  36 #include <linux/timer.h>
  37 #include <asm/system.h>
  38 #include <asm/uaccess.h>
  39 #include <linux/filter.h>
  40
  41 /* No hurry in this branch */
  42
  43 static u8 *load_pointer(struct sk_buff *skb, int k)
  44 {
  45         u8 *ptr = NULL;
  46
  47         if (k>=SKF_NET_OFF)
  48                 ptr = skb->nh.raw + k - SKF_NET_OFF;
  49         else if (k>=SKF_LL_OFF)
  50                 ptr = skb->mac.raw + k - SKF_LL_OFF;
  51
  52         if (ptr >= skb->head && ptr < skb->tail)
  53                 return ptr;
  54         return NULL;
  55 }
  56
  57 /**
  58  *      sk_run_filter   -       run a filter on a socket
  59  *      @skb: buffer to run the filter on
  60  *      @filter: filter to apply
  61  *      @flen: length of filter
  62  *
  63  * Decode and apply filter instructions to the skb->data.
  64  * Return length to keep, 0 for none. skb is the data we are
  65  * filtering, filter is the array of filter instructions, and
  66  * len is the number of filter blocks in the array.
  67  */
  68
  69 int sk_run_filter(struct sk_buff *skb, struct sock_filter *filter, int flen)
  70 {
  71         unsigned char *data = skb->data;
  72         /* len is UNSIGNED. Byte wide insns relies only on implicit
  73            type casts to prevent reading arbitrary memory locations.
  74          */
  75         unsigned int len = skb->len-skb->data_len;
  76         struct sock_filter *fentry;     /* We walk down these */
  77         u32 A = 0;                      /* Accumulator */
  78         u32 X = 0;                      /* Index Register */
  79         u32 mem[BPF_MEMWORDS];          /* Scratch Memory Store */
  80         int k;
  81         int pc;
  82
  83         /*
  84          * Process array of filter instructions.
  85          */
  86
  87         for(pc = 0; pc < flen; pc++)
  88         {
  89                 fentry = &filter[pc];
  90
  91                 switch(fentry->code)
  92                 {
  93                         case BPF_ALU|BPF_ADD|BPF_X:
  94                                 A += X;
  95                                 continue;
  96
  97                         case BPF_ALU|BPF_ADD|BPF_K:
  98                                 A += fentry->k;
  99                                 continue;
 100
 101                         case BPF_ALU|BPF_SUB|BPF_X:
 102                                 A -= X;
 103                                 continue;
 104
 105                         case BPF_ALU|BPF_SUB|BPF_K:
 106                                 A -= fentry->k;
 107                                 continue;
 108
 109                         case BPF_ALU|BPF_MUL|BPF_X:
 110                                 A *= X;
 111                                 continue;
 112
 113                         case BPF_ALU|BPF_MUL|BPF_K:
 114                                 A *= fentry->k;
 115                                 continue;
 116
 117                         case BPF_ALU|BPF_DIV|BPF_X:
 118                                 if(X == 0)
 119                                         return (0);
 120                                 A /= X;
 121                                 continue;
 122
 123                         case BPF_ALU|BPF_DIV|BPF_K:
 124                                 if(fentry->k == 0)
 125                                         return (0);
 126                                 A /= fentry->k;
 127                                 continue;
 128
 129                         case BPF_ALU|BPF_AND|BPF_X:
 130                                 A &= X;
 131                                 continue;
 132
 133                         case BPF_ALU|BPF_AND|BPF_K:
 134                                 A &= fentry->k;
 135                                 continue;
 136
 137                         case BPF_ALU|BPF_OR|BPF_X:
 138                                 A |= X;
 139                                 continue;
 140
 141                         case BPF_ALU|BPF_OR|BPF_K:
 142                                 A |= fentry->k;
 143                                 continue;
 144
 145                         case BPF_ALU|BPF_LSH|BPF_X:
 146                                 A <<= X;
 147                                 continue;
 148
 149                         case BPF_ALU|BPF_LSH|BPF_K:
 150                                 A <<= fentry->k;
 151                                 continue;
 152
 153                         case BPF_ALU|BPF_RSH|BPF_X:
 154                                 A >>= X;
 155                                 continue;
 156
 157                         case BPF_ALU|BPF_RSH|BPF_K:
 158                                 A >>= fentry->k;
 159                                 continue;
 160
 161                         case BPF_ALU|BPF_NEG:
 162                                 A = -A;
 163                                 continue;
 164
 165                         case BPF_JMP|BPF_JA:
 166                                 pc += fentry->k;
 167                                 continue;
 168
 169                         case BPF_JMP|BPF_JGT|BPF_K:
 170                                 pc += (A > fentry->k) ? fentry->jt : fentry->jf;
 171                                 continue;
 172
 173                         case BPF_JMP|BPF_JGE|BPF_K:
 174                                 pc += (A >= fentry->k) ? fentry->jt : fentry->jf;
 175                                 continue;
 176
 177                         case BPF_JMP|BPF_JEQ|BPF_K:
 178                                 pc += (A == fentry->k) ? fentry->jt : fentry->jf;
 179                                 continue;
 180
 181                         case BPF_JMP|BPF_JSET|BPF_K:
 182                                 pc += (A & fentry->k) ? fentry->jt : fentry->jf;
 183                                 continue;
 184
 185                         case BPF_JMP|BPF_JGT|BPF_X:
 186                                 pc += (A > X) ? fentry->jt : fentry->jf;
 187                                 continue;
 188
 189                         case BPF_JMP|BPF_JGE|BPF_X:
 190                                 pc += (A >= X) ? fentry->jt : fentry->jf;
 191                                 continue;
 192
 193                         case BPF_JMP|BPF_JEQ|BPF_X:
 194                                 pc += (A == X) ? fentry->jt : fentry->jf;
 195                                 continue;
 196
 197                         case BPF_JMP|BPF_JSET|BPF_X:
 198                                 pc += (A & X) ? fentry->jt : fentry->jf;
 199                                 continue;
 200
 201                         case BPF_LD|BPF_W|BPF_ABS:
 202                                 k = fentry->k;
 203 load_w:
 204                                 if(k >= 0 && (unsigned int)(k+sizeof(u32)) <= len) {
 205                                         A = ntohl(*(u32*)&data[k]);
 206                                         continue;
 207                                 }
 208                                 if (k<0) {
 209                                         u8 *ptr;
 210
 211                                         if (k>=SKF_AD_OFF)
 212                                                 break;
 213                                         if ((ptr = load_pointer(skb, k)) != NULL) {
 214                                                 A = ntohl(*(u32*)ptr);
 215                                                 continue;
 216                                         }
 217                                 } else {
 218                                         u32 tmp;
 219                                         if (!skb_copy_bits(skb, k, &tmp, 4)) {
 220                                                 A = ntohl(tmp);
 221                                                 continue;
 222                                         }
 223                                 }
 224                                 return 0;
 225
 226                         case BPF_LD|BPF_H|BPF_ABS:
 227                                 k = fentry->k;
 228 load_h:
 229                                 if(k >= 0 && (unsigned int) (k + sizeof(u16)) <= len) {
 230                                         A = ntohs(*(u16*)&data[k]);
 231                                         continue;
 232                                 }
 233                                 if (k<0) {
 234                                         u8 *ptr;
 235
 236                                         if (k>=SKF_AD_OFF)
 237                                                 break;
 238                                         if ((ptr = load_pointer(skb, k)) != NULL) {
 239                                                 A = ntohs(*(u16*)ptr);
 240                                                 continue;
 241                                         }
 242                                 } else {
 243                                         u16 tmp;
 244                                         if (!skb_copy_bits(skb, k, &tmp, 2)) {
 245                                                 A = ntohs(tmp);
 246                                                 continue;
 247                                         }
 248                                 }
 249                                 return 0;
 250
 251                         case BPF_LD|BPF_B|BPF_ABS:
 252                                 k = fentry->k;
 253 load_b:
 254                                 if(k >= 0 && (unsigned int)k < len) {
 255                                         A = data[k];
 256                                         continue;
 257                                 }
 258                                 if (k<0) {
 259                                         u8 *ptr;
 260
 261                                         if (k>=SKF_AD_OFF)
 262                                                 break;
 263                                         if ((ptr = load_pointer(skb, k)) != NULL) {
 264                                                 A = *ptr;
 265                                                 continue;
 266                                         }
 267                                 } else {
 268                                         u8 tmp;
 269                                         if (!skb_copy_bits(skb, k, &tmp, 1)) {
 270                                                 A = tmp;
 271                                                 continue;
 272                                         }
 273                                 }
 274                                 return 0;
 275
 276                         case BPF_LD|BPF_W|BPF_LEN:
 277                                 A = len;
 278                                 continue;
 279
 280                         case BPF_LDX|BPF_W|BPF_LEN:
 281                                 X = len;
 282                                 continue;
 283
 284                         case BPF_LD|BPF_W|BPF_IND:
 285                                 k = X + fentry->k;
 286                                 goto load_w;
 287
 288                        case BPF_LD|BPF_H|BPF_IND:
 289                                 k = X + fentry->k;
 290                                 goto load_h;
 291
 292                        case BPF_LD|BPF_B|BPF_IND:
 293                                 k = X + fentry->k;
 294                                 goto load_b;
 295
 296                         case BPF_LDX|BPF_B|BPF_MSH:
 297                                 k = fentry->k;
 298                                 if(k >= 0 && (unsigned int)k >= len)
 299                                         return (0);
 300                                 X = (data[k] & 0xf) << 2;
 301                                 continue;
 302
 303                         case BPF_LD|BPF_IMM:
 304                                 A = fentry->k;
 305                                 continue;
 306
 307                         case BPF_LDX|BPF_IMM:
 308                                 X = fentry->k;
 309                                 continue;
 310
 311                         case BPF_LD|BPF_MEM:
 312                                 A = mem[fentry->k];
 313                                 continue;
 314
 315                         case BPF_LDX|BPF_MEM:
 316                                 X = mem[fentry->k];
 317                                 continue;
 318
 319                         case BPF_MISC|BPF_TAX:
 320                                 X = A;
 321                                 continue;
 322
 323                         case BPF_MISC|BPF_TXA:
 324                                 A = X;
 325                                 continue;
 326
 327                         case BPF_RET|BPF_K:
 328                                 return ((unsigned int)fentry->k);
 329
 330                         case BPF_RET|BPF_A:
 331                                 return ((unsigned int)A);
 332
 333                         case BPF_ST:
 334                                 mem[fentry->k] = A;
 335                                 continue;
 336
 337                         case BPF_STX:
 338                                 mem[fentry->k] = X;
 339                                 continue;
 340
 341                         default:
 342                                 /* Invalid instruction counts as RET */
 343                                 return (0);
 344                 }
 345
 346                 /* Handle ancillary data, which are impossible
 347                    (or very difficult) to get parsing packet contents.
 348                  */
 349                 switch (k-SKF_AD_OFF) {
 350                 case SKF_AD_PROTOCOL:
 351                         A = htons(skb->protocol);
 352                         continue;
 353                 case SKF_AD_PKTTYPE:
 354                         A = skb->pkt_type;
 355                         continue;
 356                 case SKF_AD_IFINDEX:
 357                         A = skb->dev->ifindex;
 358                         continue;
 359                 default:
 360                         return 0;
 361                 }
 362         }
 363
 364         return (0);
 365 }
 366
 367 /**
 368  *      sk_chk_filter - verify socket filter code
 369  *      @filter: filter to verify
 370  *      @flen: length of filter
 371  *
 372  * Check the user's filter code. If we let some ugly
 373  * filter code slip through kaboom! The filter must contain
 374  * no references or jumps that are out of range, no illegal instructions
 375  * and no backward jumps. It must end with a RET instruction
 376  *
 377  * Returns 0 if the rule set is legal or a negative errno code if not.
 378  */
 379
 380 int sk_chk_filter(struct sock_filter *filter, int flen)
 381 {
 382         struct sock_filter *ftest;
 383         int pc;
 384
 385         if ((unsigned int) flen >= (~0U / sizeof(struct sock_filter)))
 386                 return -EINVAL;
 387
 388        /*
 389         * Check the filter code now.
 390         */
 391         for(pc = 0; pc < flen; pc++)
 392         {
 393                 /*
 394                  *      All jumps are forward as they are not signed
 395                  */
 396
 397                 ftest = &filter[pc];
 398                 if(BPF_CLASS(ftest->code) == BPF_JMP)
 399                 {
 400                         /*
 401                          *      But they mustn't jump off the end.
 402                          */
 403                         if(BPF_OP(ftest->code) == BPF_JA)
 404                         {
 405                                 /* Note, the large ftest->k might cause
 406                                    loops. Compare this with conditional
 407                                    jumps below, where offsets are limited. --ANK (981016)
 408                                  */
 409                                 if (ftest->k >= (unsigned)(flen-pc-1))
 410                                         return -EINVAL;
 411                         }
 412                         else
 413                         {
 414                                 /*
 415                                  *      For conditionals both must be safe
 416                                  */
 417                                 if(pc + ftest->jt +1 >= flen || pc + ftest->jf +1 >= flen)
 418                                         return -EINVAL;
 419                         }
 420                 }
 421
 422                 /*
 423                  *      Check that memory operations use valid addresses.
 424                  */
 425
 426                 if (ftest->k >= BPF_MEMWORDS)
 427                 {
 428                         /*
 429                          *      But it might not be a memory operation...
 430                          */
 431                         switch (ftest->code) {
 432                         case BPF_ST:
 433                         case BPF_STX:
 434                         case BPF_LD|BPF_MEM:
 435                         case BPF_LDX|BPF_MEM:
 436                                 return -EINVAL;
 437                         }
 438                 }
 439         }
 440
 441         /*
 442          *      The program must end with a return. We don't care where they
 443          *      jumped within the script (its always forwards) but in the
 444          *      end they _will_ hit this.
 445          */
 446
 447         return (BPF_CLASS(filter[flen - 1].code) == BPF_RET)?0:-EINVAL;
 448 }
 449
 450 /**
 451  *      sk_attach_filter - attach a socket filter
 452  *      @fprog: the filter program
 453  *      @sk: the socket to use
 454  *
 455  * Attach the user's filter code. We first run some sanity checks on
 456  * it to make sure it does not explode on us later. If an error
 457  * occurs or there is insufficient memory for the filter a negative
 458  * errno code is returned. On success the return is zero.
 459  */
 460
 461 int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk)
 462 {
 463         struct sk_filter *fp;
 464         unsigned int fsize = sizeof(struct sock_filter) * fprog->len;
 465         int err;
 466
 467         /* Make sure new filter is there and in the right amounts. */
 468         if (fprog->filter == NULL || fprog->len > BPF_MAXINSNS)
 469                 return (-EINVAL);
 470
 471         fp = (struct sk_filter *)sock_kmalloc(sk, fsize+sizeof(*fp), GFP_KERNEL);
 472         if(fp == NULL)
 473                 return (-ENOMEM);
 474
 475         if (copy_from_user(fp->insns, fprog->filter, fsize)) {
 476                 sock_kfree_s(sk, fp, fsize+sizeof(*fp));
 477                 return -EFAULT;
 478         }
 479
 480         atomic_set(&fp->refcnt, 1);
 481         fp->len = fprog->len;
 482
 483         if ((err = sk_chk_filter(fp->insns, fp->len))==0) {
 484                 struct sk_filter *old_fp;
 485
 486                 spin_lock_bh(&sk->lock.slock);
 487                 old_fp = sk->filter;
 488                 sk->filter = fp;
 489                 spin_unlock_bh(&sk->lock.slock);
 490                 fp = old_fp;
 491         }
 492
 493         if (fp)
 494                 sk_filter_release(sk, fp);
 495
 496         return (err);
 497 }
 498 #endif /* CONFIG_FILTER */