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 <net/netlink.h>
  31 #include <linux/skbuff.h>
  32 #include <net/sock.h>
  33 #include <linux/errno.h>
  34 #include <linux/timer.h>
  35 #include <asm/system.h>
  36 #include <asm/uaccess.h>
  37 #include <asm/unaligned.h>
  38 #include <linux/filter.h>
  39
  40 /* No hurry in this branch */
  41 static void *__load_pointer(struct sk_buff *skb, int k)
  42 {
  43         u8 *ptr = NULL;
  44
  45         if (k >= SKF_NET_OFF)
  46                 ptr = skb_network_header(skb) + k - SKF_NET_OFF;
  47         else if (k >= SKF_LL_OFF)
  48                 ptr = skb_mac_header(skb) + k - SKF_LL_OFF;
  49
  50         if (ptr >= skb->head && ptr < skb_tail_pointer(skb))
  51                 return ptr;
  52         return NULL;
  53 }
  54
  55 static inline void *load_pointer(struct sk_buff *skb, int k,
  56                                  unsigned int size, void *buffer)
  57 {
  58         if (k >= 0)
  59                 return skb_header_pointer(skb, k, size, buffer);
  60         else {
  61                 if (k >= SKF_AD_OFF)
  62                         return NULL;
  63                 return __load_pointer(skb, k);
  64         }
  65 }
  66
  67 /**
  68  *      sk_filter - run a packet through a socket filter
  69  *      @sk: sock associated with &sk_buff
  70  *      @skb: buffer to filter
  71  *      @needlock: set to 1 if the sock is not locked by caller.
  72  *
  73  * Run the filter code and then cut skb->data to correct size returned by
  74  * sk_run_filter. If pkt_len is 0 we toss packet. If skb->len is smaller
  75  * than pkt_len we keep whole skb->data. This is the socket level
  76  * wrapper to sk_run_filter. It returns 0 if the packet should
  77  * be accepted or -EPERM if the packet should be tossed.
  78  *
  79  */
  80 int sk_filter(struct sock *sk, struct sk_buff *skb)
  81 {
  82         int err;
  83         struct sk_filter *filter;
  84
  85         err = security_sock_rcv_skb(sk, skb);
  86         if (err)
  87                 return err;
  88
  89         rcu_read_lock_bh();
  90         filter = rcu_dereference(sk->sk_filter);
  91         if (filter) {
  92                 unsigned int pkt_len = sk_run_filter(skb, filter->insns,
  93                                 filter->len);
  94                 err = pkt_len ? pskb_trim(skb, pkt_len) : -EPERM;
  95         }
  96         rcu_read_unlock_bh();
  97
  98         return err;
  99 }
 100 EXPORT_SYMBOL(sk_filter);
 101
 102 /**
 103  *      sk_run_filter - run a filter on a socket
 104  *      @skb: buffer to run the filter on
 105  *      @filter: filter to apply
 106  *      @flen: length of filter
 107  *
 108  * Decode and apply filter instructions to the skb->data.
 109  * Return length to keep, 0 for none. skb is the data we are
 110  * filtering, filter is the array of filter instructions, and
 111  * len is the number of filter blocks in the array.
 112  */
 113 unsigned int sk_run_filter(struct sk_buff *skb, struct sock_filter *filter, int flen)
 114 {
 115         struct sock_filter *fentry;     /* We walk down these */
 116         void *ptr;
 117         u32 A = 0;                      /* Accumulator */
 118         u32 X = 0;                      /* Index Register */
 119         u32 mem[BPF_MEMWORDS];          /* Scratch Memory Store */
 120         u32 tmp;
 121         int k;
 122         int pc;
 123
 124         /*
 125          * Process array of filter instructions.
 126          */
 127         for (pc = 0; pc < flen; pc++) {
 128                 fentry = &filter[pc];
 129
 130                 switch (fentry->code) {
 131                 case BPF_ALU|BPF_ADD|BPF_X:
 132                         A += X;
 133                         continue;
 134                 case BPF_ALU|BPF_ADD|BPF_K:
 135                         A += fentry->k;
 136                         continue;
 137                 case BPF_ALU|BPF_SUB|BPF_X:
 138                         A -= X;
 139                         continue;
 140                 case BPF_ALU|BPF_SUB|BPF_K:
 141                         A -= fentry->k;
 142                         continue;
 143                 case BPF_ALU|BPF_MUL|BPF_X:
 144                         A *= X;
 145                         continue;
 146                 case BPF_ALU|BPF_MUL|BPF_K:
 147                         A *= fentry->k;
 148                         continue;
 149                 case BPF_ALU|BPF_DIV|BPF_X:
 150                         if (X == 0)
 151                                 return 0;
 152                         A /= X;
 153                         continue;
 154                 case BPF_ALU|BPF_DIV|BPF_K:
 155                         A /= fentry->k;
 156                         continue;
 157                 case BPF_ALU|BPF_AND|BPF_X:
 158                         A &= X;
 159                         continue;
 160                 case BPF_ALU|BPF_AND|BPF_K:
 161                         A &= fentry->k;
 162                         continue;
 163                 case BPF_ALU|BPF_OR|BPF_X:
 164                         A |= X;
 165                         continue;
 166                 case BPF_ALU|BPF_OR|BPF_K:
 167                         A |= fentry->k;
 168                         continue;
 169                 case BPF_ALU|BPF_LSH|BPF_X:
 170                         A <<= X;
 171                         continue;
 172                 case BPF_ALU|BPF_LSH|BPF_K:
 173                         A <<= fentry->k;
 174                         continue;
 175                 case BPF_ALU|BPF_RSH|BPF_X:
 176                         A >>= X;
 177                         continue;
 178                 case BPF_ALU|BPF_RSH|BPF_K:
 179                         A >>= fentry->k;
 180                         continue;
 181                 case BPF_ALU|BPF_NEG:
 182                         A = -A;
 183                         continue;
 184                 case BPF_JMP|BPF_JA:
 185                         pc += fentry->k;
 186                         continue;
 187                 case BPF_JMP|BPF_JGT|BPF_K:
 188                         pc += (A > fentry->k) ? fentry->jt : fentry->jf;
 189                         continue;
 190                 case BPF_JMP|BPF_JGE|BPF_K:
 191                         pc += (A >= fentry->k) ? fentry->jt : fentry->jf;
 192                         continue;
 193                 case BPF_JMP|BPF_JEQ|BPF_K:
 194                         pc += (A == fentry->k) ? fentry->jt : fentry->jf;
 195                         continue;
 196                 case BPF_JMP|BPF_JSET|BPF_K:
 197                         pc += (A & fentry->k) ? fentry->jt : fentry->jf;
 198                         continue;
 199                 case BPF_JMP|BPF_JGT|BPF_X:
 200                         pc += (A > X) ? fentry->jt : fentry->jf;
 201                         continue;
 202                 case BPF_JMP|BPF_JGE|BPF_X:
 203                         pc += (A >= X) ? fentry->jt : fentry->jf;
 204                         continue;
 205                 case BPF_JMP|BPF_JEQ|BPF_X:
 206                         pc += (A == X) ? fentry->jt : fentry->jf;
 207                         continue;
 208                 case BPF_JMP|BPF_JSET|BPF_X:
 209                         pc += (A & X) ? fentry->jt : fentry->jf;
 210                         continue;
 211                 case BPF_LD|BPF_W|BPF_ABS:
 212                         k = fentry->k;
 213 load_w:
 214                         ptr = load_pointer(skb, k, 4, &tmp);
 215                         if (ptr != NULL) {
 216                                 A = get_unaligned_be32(ptr);
 217                                 continue;
 218                         }
 219                         break;
 220                 case BPF_LD|BPF_H|BPF_ABS:
 221                         k = fentry->k;
 222 load_h:
 223                         ptr = load_pointer(skb, k, 2, &tmp);
 224                         if (ptr != NULL) {
 225                                 A = get_unaligned_be16(ptr);
 226                                 continue;
 227                         }
 228                         break;
 229                 case BPF_LD|BPF_B|BPF_ABS:
 230                         k = fentry->k;
 231 load_b:
 232                         ptr = load_pointer(skb, k, 1, &tmp);
 233                         if (ptr != NULL) {
 234                                 A = *(u8 *)ptr;
 235                                 continue;
 236                         }
 237                         break;
 238                 case BPF_LD|BPF_W|BPF_LEN:
 239                         A = skb->len;
 240                         continue;
 241                 case BPF_LDX|BPF_W|BPF_LEN:
 242                         X = skb->len;
 243                         continue;
 244                 case BPF_LD|BPF_W|BPF_IND:
 245                         k = X + fentry->k;
 246                         goto load_w;
 247                 case BPF_LD|BPF_H|BPF_IND:
 248                         k = X + fentry->k;
 249                         goto load_h;
 250                 case BPF_LD|BPF_B|BPF_IND:
 251                         k = X + fentry->k;
 252                         goto load_b;
 253                 case BPF_LDX|BPF_B|BPF_MSH:
 254                         ptr = load_pointer(skb, fentry->k, 1, &tmp);
 255                         if (ptr != NULL) {
 256                                 X = (*(u8 *)ptr & 0xf) << 2;
 257                                 continue;
 258                         }
 259                         return 0;
 260                 case BPF_LD|BPF_IMM:
 261                         A = fentry->k;
 262                         continue;
 263                 case BPF_LDX|BPF_IMM:
 264                         X = fentry->k;
 265                         continue;
 266                 case BPF_LD|BPF_MEM:
 267                         A = mem[fentry->k];
 268                         continue;
 269                 case BPF_LDX|BPF_MEM:
 270                         X = mem[fentry->k];
 271                         continue;
 272                 case BPF_MISC|BPF_TAX:
 273                         X = A;
 274                         continue;
 275                 case BPF_MISC|BPF_TXA:
 276                         A = X;
 277                         continue;
 278                 case BPF_RET|BPF_K:
 279                         return fentry->k;
 280                 case BPF_RET|BPF_A:
 281                         return A;
 282                 case BPF_ST:
 283                         mem[fentry->k] = A;
 284                         continue;
 285                 case BPF_STX:
 286                         mem[fentry->k] = X;
 287                         continue;
 288                 default:
 289                         WARN_ON(1);
 290                         return 0;
 291                 }
 292
 293                 /*
 294                  * Handle ancillary data, which are impossible
 295                  * (or very difficult) to get parsing packet contents.
 296                  */
 297                 switch (k-SKF_AD_OFF) {
 298                 case SKF_AD_PROTOCOL:
 299                         A = ntohs(skb->protocol);
 300                         continue;
 301                 case SKF_AD_PKTTYPE:
 302                         A = skb->pkt_type;
 303                         continue;
 304                 case SKF_AD_IFINDEX:
 305                         A = skb->dev->ifindex;
 306                         continue;
 307                 case SKF_AD_NLATTR: {
 308                         struct nlattr *nla;
 309
 310                         if (skb_is_nonlinear(skb))
 311                                 return 0;
 312                         if (A > skb->len - sizeof(struct nlattr))
 313                                 return 0;
 314
 315                         nla = nla_find((struct nlattr *)&skb->data[A],
 316                                        skb->len - A, X);
 317                         if (nla)
 318                                 A = (void *)nla - (void *)skb->data;
 319                         else
 320                                 A = 0;
 321                         continue;
 322                 }
 323                 default:
 324                         return 0;
 325                 }
 326         }
 327
 328         return 0;
 329 }
 330 EXPORT_SYMBOL(sk_run_filter);
 331
 332 /**
 333  *      sk_chk_filter - verify socket filter code
 334  *      @filter: filter to verify
 335  *      @flen: length of filter
 336  *
 337  * Check the user's filter code. If we let some ugly
 338  * filter code slip through kaboom! The filter must contain
 339  * no references or jumps that are out of range, no illegal
 340  * instructions, and must end with a RET instruction.
 341  *
 342  * All jumps are forward as they are not signed.
 343  *
 344  * Returns 0 if the rule set is legal or -EINVAL if not.
 345  */
 346 int sk_chk_filter(struct sock_filter *filter, int flen)
 347 {
 348         struct sock_filter *ftest;
 349         int pc;
 350
 351         if (flen == 0 || flen > BPF_MAXINSNS)
 352                 return -EINVAL;
 353
 354         /* check the filter code now */
 355         for (pc = 0; pc < flen; pc++) {
 356                 ftest = &filter[pc];
 357
 358                 /* Only allow valid instructions */
 359                 switch (ftest->code) {
 360                 case BPF_ALU|BPF_ADD|BPF_K:
 361                 case BPF_ALU|BPF_ADD|BPF_X:
 362                 case BPF_ALU|BPF_SUB|BPF_K:
 363                 case BPF_ALU|BPF_SUB|BPF_X:
 364                 case BPF_ALU|BPF_MUL|BPF_K:
 365                 case BPF_ALU|BPF_MUL|BPF_X:
 366                 case BPF_ALU|BPF_DIV|BPF_X:
 367                 case BPF_ALU|BPF_AND|BPF_K:
 368                 case BPF_ALU|BPF_AND|BPF_X:
 369                 case BPF_ALU|BPF_OR|BPF_K:
 370                 case BPF_ALU|BPF_OR|BPF_X:
 371                 case BPF_ALU|BPF_LSH|BPF_K:
 372                 case BPF_ALU|BPF_LSH|BPF_X:
 373                 case BPF_ALU|BPF_RSH|BPF_K:
 374                 case BPF_ALU|BPF_RSH|BPF_X:
 375                 case BPF_ALU|BPF_NEG:
 376                 case BPF_LD|BPF_W|BPF_ABS:
 377                 case BPF_LD|BPF_H|BPF_ABS:
 378                 case BPF_LD|BPF_B|BPF_ABS:
 379                 case BPF_LD|BPF_W|BPF_LEN:
 380                 case BPF_LD|BPF_W|BPF_IND:
 381                 case BPF_LD|BPF_H|BPF_IND:
 382                 case BPF_LD|BPF_B|BPF_IND:
 383                 case BPF_LD|BPF_IMM:
 384                 case BPF_LDX|BPF_W|BPF_LEN:
 385                 case BPF_LDX|BPF_B|BPF_MSH:
 386                 case BPF_LDX|BPF_IMM:
 387                 case BPF_MISC|BPF_TAX:
 388                 case BPF_MISC|BPF_TXA:
 389                 case BPF_RET|BPF_K:
 390                 case BPF_RET|BPF_A:
 391                         break;
 392
 393                 /* Some instructions need special checks */
 394
 395                 case BPF_ALU|BPF_DIV|BPF_K:
 396                         /* check for division by zero */
 397                         if (ftest->k == 0)
 398                                 return -EINVAL;
 399                         break;
 400
 401                 case BPF_LD|BPF_MEM:
 402                 case BPF_LDX|BPF_MEM:
 403                 case BPF_ST:
 404                 case BPF_STX:
 405                         /* check for invalid memory addresses */
 406                         if (ftest->k >= BPF_MEMWORDS)
 407                                 return -EINVAL;
 408                         break;
 409
 410                 case BPF_JMP|BPF_JA:
 411                         /*
 412                          * Note, the large ftest->k might cause loops.
 413                          * Compare this with conditional jumps below,
 414                          * where offsets are limited. --ANK (981016)
 415                          */
 416                         if (ftest->k >= (unsigned)(flen-pc-1))
 417                                 return -EINVAL;
 418                         break;
 419
 420                 case BPF_JMP|BPF_JEQ|BPF_K:
 421                 case BPF_JMP|BPF_JEQ|BPF_X:
 422                 case BPF_JMP|BPF_JGE|BPF_K:
 423                 case BPF_JMP|BPF_JGE|BPF_X:
 424                 case BPF_JMP|BPF_JGT|BPF_K:
 425                 case BPF_JMP|BPF_JGT|BPF_X:
 426                 case BPF_JMP|BPF_JSET|BPF_K:
 427                 case BPF_JMP|BPF_JSET|BPF_X:
 428                         /* for conditionals both must be safe */
 429                         if (pc + ftest->jt + 1 >= flen ||
 430                             pc + ftest->jf + 1 >= flen)
 431                                 return -EINVAL;
 432                         break;
 433
 434                 default:
 435                         return -EINVAL;
 436                 }
 437         }
 438
 439         return (BPF_CLASS(filter[flen - 1].code) == BPF_RET) ? 0 : -EINVAL;
 440 }
 441 EXPORT_SYMBOL(sk_chk_filter);
 442
 443 /**
 444  *      sk_filter_rcu_release: Release a socket filter by rcu_head
 445  *      @rcu: rcu_head that contains the sk_filter to free
 446  */
 447 static void sk_filter_rcu_release(struct rcu_head *rcu)
 448 {
 449         struct sk_filter *fp = container_of(rcu, struct sk_filter, rcu);
 450
 451         sk_filter_release(fp);
 452 }
 453
 454 static void sk_filter_delayed_uncharge(struct sock *sk, struct sk_filter *fp)
 455 {
 456         unsigned int size = sk_filter_len(fp);
 457
 458         atomic_sub(size, &sk->sk_omem_alloc);
 459         call_rcu_bh(&fp->rcu, sk_filter_rcu_release);
 460 }
 461
 462 /**
 463  *      sk_attach_filter - attach a socket filter
 464  *      @fprog: the filter program
 465  *      @sk: the socket to use
 466  *
 467  * Attach the user's filter code. We first run some sanity checks on
 468  * it to make sure it does not explode on us later. If an error
 469  * occurs or there is insufficient memory for the filter a negative
 470  * errno code is returned. On success the return is zero.
 471  */
 472 int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk)
 473 {
 474         struct sk_filter *fp, *old_fp;
 475         unsigned int fsize = sizeof(struct sock_filter) * fprog->len;
 476         int err;
 477
 478         /* Make sure new filter is there and in the right amounts. */
 479         if (fprog->filter == NULL)
 480                 return -EINVAL;
 481
 482         fp = sock_kmalloc(sk, fsize+sizeof(*fp), GFP_KERNEL);
 483         if (!fp)
 484                 return -ENOMEM;
 485         if (copy_from_user(fp->insns, fprog->filter, fsize)) {
 486                 sock_kfree_s(sk, fp, fsize+sizeof(*fp));
 487                 return -EFAULT;
 488         }
 489
 490         atomic_set(&fp->refcnt, 1);
 491         fp->len = fprog->len;
 492
 493         err = sk_chk_filter(fp->insns, fp->len);
 494         if (err) {
 495                 sk_filter_uncharge(sk, fp);
 496                 return err;
 497         }
 498
 499         rcu_read_lock_bh();
 500         old_fp = rcu_dereference(sk->sk_filter);
 501         rcu_assign_pointer(sk->sk_filter, fp);
 502         rcu_read_unlock_bh();
 503
 504         if (old_fp)
 505                 sk_filter_delayed_uncharge(sk, old_fp);
 506         return 0;
 507 }
 508
 509 int sk_detach_filter(struct sock *sk)
 510 {
 511         int ret = -ENOENT;
 512         struct sk_filter *filter;
 513
 514         rcu_read_lock_bh();
 515         filter = rcu_dereference(sk->sk_filter);
 516         if (filter) {
 517                 rcu_assign_pointer(sk->sk_filter, NULL);
 518                 sk_filter_delayed_uncharge(sk, filter);
 519                 ret = 0;
 520         }
 521         rcu_read_unlock_bh();
 522         return ret;
 523 }