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  * Kris Katterjohn - Added many additional checks in sk_chk_filter()
  17  */
  18
  19 #include <linux/module.h>
  20 #include <linux/types.h>
  21 #include <linux/mm.h>
  22 #include <linux/fcntl.h>
  23 #include <linux/socket.h>
  24 #include <linux/in.h>
  25 #include <linux/inet.h>
  26 #include <linux/netdevice.h>
  27 #include <linux/if_packet.h>
  28 #include <net/ip.h>
  29 #include <net/protocol.h>
  30 #include <linux/skbuff.h>
  31 #include <net/sock.h>
  32 #include <linux/errno.h>
  33 #include <linux/timer.h>
  34 #include <asm/system.h>
  35 #include <asm/uaccess.h>
  36 #include <asm/unaligned.h>
  37 #include <linux/filter.h>
  38
  39 /* No hurry in this branch */
  40 static void *__load_pointer(struct sk_buff *skb, int k)
  41 {
  42         u8 *ptr = NULL;
  43
  44         if (k >= SKF_NET_OFF)
  45                 ptr = skb_network_header(skb) + k - SKF_NET_OFF;
  46         else if (k >= SKF_LL_OFF)
  47                 ptr = skb_mac_header(skb) + k - SKF_LL_OFF;
  48
  49         if (ptr >= skb->head && ptr < skb_tail_pointer(skb))
  50                 return ptr;
  51         return NULL;
  52 }
  53
  54 static inline void *load_pointer(struct sk_buff *skb, int k,
  55                                  unsigned int size, void *buffer)
  56 {
  57         if (k >= 0)
  58                 return skb_header_pointer(skb, k, size, buffer);
  59         else {
  60                 if (k >= SKF_AD_OFF)
  61                         return NULL;
  62                 return __load_pointer(skb, k);
  63         }
  64 }
  65
  66 /**
  67  *      sk_run_filter - run a filter on a socket
  68  *      @skb: buffer to run the filter on
  69  *      @filter: filter to apply
  70  *      @flen: length of filter
  71  *
  72  * Decode and apply filter instructions to the skb->data.
  73  * Return length to keep, 0 for none. skb is the data we are
  74  * filtering, filter is the array of filter instructions, and
  75  * len is the number of filter blocks in the array.
  76  */
  77 unsigned int sk_run_filter(struct sk_buff *skb, struct sock_filter *filter, int flen)
  78 {
  79         struct sock_filter *fentry;     /* We walk down these */
  80         void *ptr;
  81         u32 A = 0;                      /* Accumulator */
  82         u32 X = 0;                      /* Index Register */
  83         u32 mem[BPF_MEMWORDS];          /* Scratch Memory Store */
  84         u32 tmp;
  85         int k;
  86         int pc;
  87
  88         /*
  89          * Process array of filter instructions.
  90          */
  91         for (pc = 0; pc < flen; pc++) {
  92                 fentry = &filter[pc];
  93
  94                 switch (fentry->code) {
  95                 case BPF_ALU|BPF_ADD|BPF_X:
  96                         A += X;
  97                         continue;
  98                 case BPF_ALU|BPF_ADD|BPF_K:
  99                         A += fentry->k;
 100                         continue;
 101                 case BPF_ALU|BPF_SUB|BPF_X:
 102                         A -= X;
 103                         continue;
 104                 case BPF_ALU|BPF_SUB|BPF_K:
 105                         A -= fentry->k;
 106                         continue;
 107                 case BPF_ALU|BPF_MUL|BPF_X:
 108                         A *= X;
 109                         continue;
 110                 case BPF_ALU|BPF_MUL|BPF_K:
 111                         A *= fentry->k;
 112                         continue;
 113                 case BPF_ALU|BPF_DIV|BPF_X:
 114                         if (X == 0)
 115                                 return 0;
 116                         A /= X;
 117                         continue;
 118                 case BPF_ALU|BPF_DIV|BPF_K:
 119                         A /= fentry->k;
 120                         continue;
 121                 case BPF_ALU|BPF_AND|BPF_X:
 122                         A &= X;
 123                         continue;
 124                 case BPF_ALU|BPF_AND|BPF_K:
 125                         A &= fentry->k;
 126                         continue;
 127                 case BPF_ALU|BPF_OR|BPF_X:
 128                         A |= X;
 129                         continue;
 130                 case BPF_ALU|BPF_OR|BPF_K:
 131                         A |= fentry->k;
 132                         continue;
 133                 case BPF_ALU|BPF_LSH|BPF_X:
 134                         A <<= X;
 135                         continue;
 136                 case BPF_ALU|BPF_LSH|BPF_K:
 137                         A <<= fentry->k;
 138                         continue;
 139                 case BPF_ALU|BPF_RSH|BPF_X:
 140                         A >>= X;
 141                         continue;
 142                 case BPF_ALU|BPF_RSH|BPF_K:
 143                         A >>= fentry->k;
 144                         continue;
 145                 case BPF_ALU|BPF_NEG:
 146                         A = -A;
 147                         continue;
 148                 case BPF_JMP|BPF_JA:
 149                         pc += fentry->k;
 150                         continue;
 151                 case BPF_JMP|BPF_JGT|BPF_K:
 152                         pc += (A > fentry->k) ? fentry->jt : fentry->jf;
 153                         continue;
 154                 case BPF_JMP|BPF_JGE|BPF_K:
 155                         pc += (A >= fentry->k) ? fentry->jt : fentry->jf;
 156                         continue;
 157                 case BPF_JMP|BPF_JEQ|BPF_K:
 158                         pc += (A == fentry->k) ? fentry->jt : fentry->jf;
 159                         continue;
 160                 case BPF_JMP|BPF_JSET|BPF_K:
 161                         pc += (A & fentry->k) ? fentry->jt : fentry->jf;
 162                         continue;
 163                 case BPF_JMP|BPF_JGT|BPF_X:
 164                         pc += (A > X) ? fentry->jt : fentry->jf;
 165                         continue;
 166                 case BPF_JMP|BPF_JGE|BPF_X:
 167                         pc += (A >= X) ? fentry->jt : fentry->jf;
 168                         continue;
 169                 case BPF_JMP|BPF_JEQ|BPF_X:
 170                         pc += (A == X) ? fentry->jt : fentry->jf;
 171                         continue;
 172                 case BPF_JMP|BPF_JSET|BPF_X:
 173                         pc += (A & X) ? fentry->jt : fentry->jf;
 174                         continue;
 175                 case BPF_LD|BPF_W|BPF_ABS:
 176                         k = fentry->k;
 177 load_w:
 178                         ptr = load_pointer(skb, k, 4, &tmp);
 179                         if (ptr != NULL) {
 180                                 A = ntohl(get_unaligned((__be32 *)ptr));
 181                                 continue;
 182                         }
 183                         break;
 184                 case BPF_LD|BPF_H|BPF_ABS:
 185                         k = fentry->k;
 186 load_h:
 187                         ptr = load_pointer(skb, k, 2, &tmp);
 188                         if (ptr != NULL) {
 189                                 A = ntohs(get_unaligned((__be16 *)ptr));
 190                                 continue;
 191                         }
 192                         break;
 193                 case BPF_LD|BPF_B|BPF_ABS:
 194                         k = fentry->k;
 195 load_b:
 196                         ptr = load_pointer(skb, k, 1, &tmp);
 197                         if (ptr != NULL) {
 198                                 A = *(u8 *)ptr;
 199                                 continue;
 200                         }
 201                         break;
 202                 case BPF_LD|BPF_W|BPF_LEN:
 203                         A = skb->len;
 204                         continue;
 205                 case BPF_LDX|BPF_W|BPF_LEN:
 206                         X = skb->len;
 207                         continue;
 208                 case BPF_LD|BPF_W|BPF_IND:
 209                         k = X + fentry->k;
 210                         goto load_w;
 211                 case BPF_LD|BPF_H|BPF_IND:
 212                         k = X + fentry->k;
 213                         goto load_h;
 214                 case BPF_LD|BPF_B|BPF_IND:
 215                         k = X + fentry->k;
 216                         goto load_b;
 217                 case BPF_LDX|BPF_B|BPF_MSH:
 218                         ptr = load_pointer(skb, fentry->k, 1, &tmp);
 219                         if (ptr != NULL) {
 220                                 X = (*(u8 *)ptr & 0xf) << 2;
 221                                 continue;
 222                         }
 223                         return 0;
 224                 case BPF_LD|BPF_IMM:
 225                         A = fentry->k;
 226                         continue;
 227                 case BPF_LDX|BPF_IMM:
 228                         X = fentry->k;
 229                         continue;
 230                 case BPF_LD|BPF_MEM:
 231                         A = mem[fentry->k];
 232                         continue;
 233                 case BPF_LDX|BPF_MEM:
 234                         X = mem[fentry->k];
 235                         continue;
 236                 case BPF_MISC|BPF_TAX:
 237                         X = A;
 238                         continue;
 239                 case BPF_MISC|BPF_TXA:
 240                         A = X;
 241                         continue;
 242                 case BPF_RET|BPF_K:
 243                         return fentry->k;
 244                 case BPF_RET|BPF_A:
 245                         return A;
 246                 case BPF_ST:
 247                         mem[fentry->k] = A;
 248                         continue;
 249                 case BPF_STX:
 250                         mem[fentry->k] = X;
 251                         continue;
 252                 default:
 253                         WARN_ON(1);
 254                         return 0;
 255                 }
 256
 257                 /*
 258                  * Handle ancillary data, which are impossible
 259                  * (or very difficult) to get parsing packet contents.
 260                  */
 261                 switch (k-SKF_AD_OFF) {
 262                 case SKF_AD_PROTOCOL:
 263                         A = ntohs(skb->protocol);
 264                         continue;
 265                 case SKF_AD_PKTTYPE:
 266                         A = skb->pkt_type;
 267                         continue;
 268                 case SKF_AD_IFINDEX:
 269                         A = skb->dev->ifindex;
 270                         continue;
 271                 default:
 272                         return 0;
 273                 }
 274         }
 275
 276         return 0;
 277 }
 278
 279 /**
 280  *      sk_chk_filter - verify socket filter code
 281  *      @filter: filter to verify
 282  *      @flen: length of filter
 283  *
 284  * Check the user's filter code. If we let some ugly
 285  * filter code slip through kaboom! The filter must contain
 286  * no references or jumps that are out of range, no illegal
 287  * instructions, and must end with a RET instruction.
 288  *
 289  * All jumps are forward as they are not signed.
 290  *
 291  * Returns 0 if the rule set is legal or -EINVAL if not.
 292  */
 293 int sk_chk_filter(struct sock_filter *filter, int flen)
 294 {
 295         struct sock_filter *ftest;
 296         int pc;
 297
 298         if (flen == 0 || flen > BPF_MAXINSNS)
 299                 return -EINVAL;
 300
 301         /* check the filter code now */
 302         for (pc = 0; pc < flen; pc++) {
 303                 ftest = &filter[pc];
 304
 305                 /* Only allow valid instructions */
 306                 switch (ftest->code) {
 307                 case BPF_ALU|BPF_ADD|BPF_K:
 308                 case BPF_ALU|BPF_ADD|BPF_X:
 309                 case BPF_ALU|BPF_SUB|BPF_K:
 310                 case BPF_ALU|BPF_SUB|BPF_X:
 311                 case BPF_ALU|BPF_MUL|BPF_K:
 312                 case BPF_ALU|BPF_MUL|BPF_X:
 313                 case BPF_ALU|BPF_DIV|BPF_X:
 314                 case BPF_ALU|BPF_AND|BPF_K:
 315                 case BPF_ALU|BPF_AND|BPF_X:
 316                 case BPF_ALU|BPF_OR|BPF_K:
 317                 case BPF_ALU|BPF_OR|BPF_X:
 318                 case BPF_ALU|BPF_LSH|BPF_K:
 319                 case BPF_ALU|BPF_LSH|BPF_X:
 320                 case BPF_ALU|BPF_RSH|BPF_K:
 321                 case BPF_ALU|BPF_RSH|BPF_X:
 322                 case BPF_ALU|BPF_NEG:
 323                 case BPF_LD|BPF_W|BPF_ABS:
 324                 case BPF_LD|BPF_H|BPF_ABS:
 325                 case BPF_LD|BPF_B|BPF_ABS:
 326                 case BPF_LD|BPF_W|BPF_LEN:
 327                 case BPF_LD|BPF_W|BPF_IND:
 328                 case BPF_LD|BPF_H|BPF_IND:
 329                 case BPF_LD|BPF_B|BPF_IND:
 330                 case BPF_LD|BPF_IMM:
 331                 case BPF_LDX|BPF_W|BPF_LEN:
 332                 case BPF_LDX|BPF_B|BPF_MSH:
 333                 case BPF_LDX|BPF_IMM:
 334                 case BPF_MISC|BPF_TAX:
 335                 case BPF_MISC|BPF_TXA:
 336                 case BPF_RET|BPF_K:
 337                 case BPF_RET|BPF_A:
 338                         break;
 339
 340                 /* Some instructions need special checks */
 341
 342                 case BPF_ALU|BPF_DIV|BPF_K:
 343                         /* check for division by zero */
 344                         if (ftest->k == 0)
 345                                 return -EINVAL;
 346                         break;
 347
 348                 case BPF_LD|BPF_MEM:
 349                 case BPF_LDX|BPF_MEM:
 350                 case BPF_ST:
 351                 case BPF_STX:
 352                         /* check for invalid memory addresses */
 353                         if (ftest->k >= BPF_MEMWORDS)
 354                                 return -EINVAL;
 355                         break;
 356
 357                 case BPF_JMP|BPF_JA:
 358                         /*
 359                          * Note, the large ftest->k might cause loops.
 360                          * Compare this with conditional jumps below,
 361                          * where offsets are limited. --ANK (981016)
 362                          */
 363                         if (ftest->k >= (unsigned)(flen-pc-1))
 364                                 return -EINVAL;
 365                         break;
 366
 367                 case BPF_JMP|BPF_JEQ|BPF_K:
 368                 case BPF_JMP|BPF_JEQ|BPF_X:
 369                 case BPF_JMP|BPF_JGE|BPF_K:
 370                 case BPF_JMP|BPF_JGE|BPF_X:
 371                 case BPF_JMP|BPF_JGT|BPF_K:
 372                 case BPF_JMP|BPF_JGT|BPF_X:
 373                 case BPF_JMP|BPF_JSET|BPF_K:
 374                 case BPF_JMP|BPF_JSET|BPF_X:
 375                         /* for conditionals both must be safe */
 376                         if (pc + ftest->jt + 1 >= flen ||
 377                             pc + ftest->jf + 1 >= flen)
 378                                 return -EINVAL;
 379                         break;
 380
 381                 default:
 382                         return -EINVAL;
 383                 }
 384         }
 385
 386         return (BPF_CLASS(filter[flen - 1].code) == BPF_RET) ? 0 : -EINVAL;
 387 }
 388
 389 /**
 390  *      sk_filter_rcu_release: Release a socket filter by rcu_head
 391  *      @rcu: rcu_head that contains the sk_filter to free
 392  */
 393 static void sk_filter_rcu_release(struct rcu_head *rcu)
 394 {
 395         struct sk_filter *fp = container_of(rcu, struct sk_filter, rcu);
 396
 397         sk_filter_release(fp);
 398 }
 399
 400 static void sk_filter_delayed_uncharge(struct sock *sk, struct sk_filter *fp)
 401 {
 402         unsigned int size = sk_filter_len(fp);
 403
 404         atomic_sub(size, &sk->sk_omem_alloc);
 405         call_rcu_bh(&fp->rcu, sk_filter_rcu_release);
 406 }
 407
 408 /**
 409  *      sk_attach_filter - attach a socket filter
 410  *      @fprog: the filter program
 411  *      @sk: the socket to use
 412  *
 413  * Attach the user's filter code. We first run some sanity checks on
 414  * it to make sure it does not explode on us later. If an error
 415  * occurs or there is insufficient memory for the filter a negative
 416  * errno code is returned. On success the return is zero.
 417  */
 418 int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk)
 419 {
 420         struct sk_filter *fp, *old_fp;
 421         unsigned int fsize = sizeof(struct sock_filter) * fprog->len;
 422         int err;
 423
 424         /* Make sure new filter is there and in the right amounts. */
 425         if (fprog->filter == NULL)
 426                 return -EINVAL;
 427
 428         fp = sock_kmalloc(sk, fsize+sizeof(*fp), GFP_KERNEL);
 429         if (!fp)
 430                 return -ENOMEM;
 431         if (copy_from_user(fp->insns, fprog->filter, fsize)) {
 432                 sock_kfree_s(sk, fp, fsize+sizeof(*fp));
 433                 return -EFAULT;
 434         }
 435
 436         atomic_set(&fp->refcnt, 1);
 437         fp->len = fprog->len;
 438
 439         err = sk_chk_filter(fp->insns, fp->len);
 440         if (err) {
 441                 sk_filter_uncharge(sk, fp);
 442                 return err;
 443         }
 444
 445         rcu_read_lock_bh();
 446         old_fp = rcu_dereference(sk->sk_filter);
 447         rcu_assign_pointer(sk->sk_filter, fp);
 448         rcu_read_unlock_bh();
 449
 450         if (old_fp)
 451                 sk_filter_delayed_uncharge(sk, old_fp);
 452         return 0;
 453 }
 454
 455 int sk_detach_filter(struct sock *sk)
 456 {
 457         int ret = -ENOENT;
 458         struct sk_filter *filter;
 459
 460         rcu_read_lock_bh();
 461         filter = rcu_dereference(sk->sk_filter);
 462         if (filter) {
 463                 rcu_assign_pointer(sk->sk_filter, NULL);
 464                 sk_filter_delayed_uncharge(sk, filter);
 465                 ret = 0;
 466         }
 467         rcu_read_unlock_bh();
 468         return ret;
 469 }
 470
 471 EXPORT_SYMBOL(sk_chk_filter);
 472 EXPORT_SYMBOL(sk_run_filter);