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  *
  72  * Run the filter code and then cut skb->data to correct size returned by
  73  * sk_run_filter. If pkt_len is 0 we toss packet. If skb->len is smaller
  74  * than pkt_len we keep whole skb->data. This is the socket level
  75  * wrapper to sk_run_filter. It returns 0 if the packet should
  76  * be accepted or -EPERM if the packet should be tossed.
  77  *
  78  */
  79 int sk_filter(struct sock *sk, struct sk_buff *skb)
  80 {
  81         int err;
  82         struct sk_filter *filter;
  83
  84         err = security_sock_rcv_skb(sk, skb);
  85         if (err)
  86                 return err;
  87
  88         rcu_read_lock_bh();
  89         filter = rcu_dereference(sk->sk_filter);
  90         if (filter) {
  91                 unsigned int pkt_len = sk_run_filter(skb, filter->insns,
  92                                 filter->len);
  93                 err = pkt_len ? pskb_trim(skb, pkt_len) : -EPERM;
  94         }
  95         rcu_read_unlock_bh();
  96
  97         return err;
  98 }
  99 EXPORT_SYMBOL(sk_filter);
 100
 101 /**
 102  *      sk_run_filter - run a filter on a socket
 103  *      @skb: buffer to run the filter on
 104  *      @filter: filter to apply
 105  *      @flen: length of filter
 106  *
 107  * Decode and apply filter instructions to the skb->data.
 108  * Return length to keep, 0 for none. skb is the data we are
 109  * filtering, filter is the array of filter instructions, and
 110  * len is the number of filter blocks in the array.
 111  */
 112 unsigned int sk_run_filter(struct sk_buff *skb, struct sock_filter *filter, int flen)
 113 {
 114         struct sock_filter *fentry;     /* We walk down these */
 115         void *ptr;
 116         u32 A = 0;                      /* Accumulator */
 117         u32 X = 0;                      /* Index Register */
 118         u32 mem[BPF_MEMWORDS];          /* Scratch Memory Store */
 119         u32 tmp;
 120         int k;
 121         int pc;
 122
 123         /*
 124          * Process array of filter instructions.
 125          */
 126         for (pc = 0; pc < flen; pc++) {
 127                 fentry = &filter[pc];
 128
 129                 switch (fentry->code) {
 130                 case BPF_ALU|BPF_ADD|BPF_X:
 131                         A += X;
 132                         continue;
 133                 case BPF_ALU|BPF_ADD|BPF_K:
 134                         A += fentry->k;
 135                         continue;
 136                 case BPF_ALU|BPF_SUB|BPF_X:
 137                         A -= X;
 138                         continue;
 139                 case BPF_ALU|BPF_SUB|BPF_K:
 140                         A -= fentry->k;
 141                         continue;
 142                 case BPF_ALU|BPF_MUL|BPF_X:
 143                         A *= X;
 144                         continue;
 145                 case BPF_ALU|BPF_MUL|BPF_K:
 146                         A *= fentry->k;
 147                         continue;
 148                 case BPF_ALU|BPF_DIV|BPF_X:
 149                         if (X == 0)
 150                                 return 0;
 151                         A /= X;
 152                         continue;
 153                 case BPF_ALU|BPF_DIV|BPF_K:
 154                         A /= fentry->k;
 155                         continue;
 156                 case BPF_ALU|BPF_AND|BPF_X:
 157                         A &= X;
 158                         continue;
 159                 case BPF_ALU|BPF_AND|BPF_K:
 160                         A &= fentry->k;
 161                         continue;
 162                 case BPF_ALU|BPF_OR|BPF_X:
 163                         A |= X;
 164                         continue;
 165                 case BPF_ALU|BPF_OR|BPF_K:
 166                         A |= fentry->k;
 167                         continue;
 168                 case BPF_ALU|BPF_LSH|BPF_X:
 169                         A <<= X;
 170                         continue;
 171                 case BPF_ALU|BPF_LSH|BPF_K:
 172                         A <<= fentry->k;
 173                         continue;
 174                 case BPF_ALU|BPF_RSH|BPF_X:
 175                         A >>= X;
 176                         continue;
 177                 case BPF_ALU|BPF_RSH|BPF_K:
 178                         A >>= fentry->k;
 179                         continue;
 180                 case BPF_ALU|BPF_NEG:
 181                         A = -A;
 182                         continue;
 183                 case BPF_JMP|BPF_JA:
 184                         pc += fentry->k;
 185                         continue;
 186                 case BPF_JMP|BPF_JGT|BPF_K:
 187                         pc += (A > fentry->k) ? fentry->jt : fentry->jf;
 188                         continue;
 189                 case BPF_JMP|BPF_JGE|BPF_K:
 190                         pc += (A >= fentry->k) ? fentry->jt : fentry->jf;
 191                         continue;
 192                 case BPF_JMP|BPF_JEQ|BPF_K:
 193                         pc += (A == fentry->k) ? fentry->jt : fentry->jf;
 194                         continue;
 195                 case BPF_JMP|BPF_JSET|BPF_K:
 196                         pc += (A & fentry->k) ? fentry->jt : fentry->jf;
 197                         continue;
 198                 case BPF_JMP|BPF_JGT|BPF_X:
 199                         pc += (A > X) ? fentry->jt : fentry->jf;
 200                         continue;
 201                 case BPF_JMP|BPF_JGE|BPF_X:
 202                         pc += (A >= X) ? fentry->jt : fentry->jf;
 203                         continue;
 204                 case BPF_JMP|BPF_JEQ|BPF_X:
 205                         pc += (A == X) ? fentry->jt : fentry->jf;
 206                         continue;
 207                 case BPF_JMP|BPF_JSET|BPF_X:
 208                         pc += (A & X) ? fentry->jt : fentry->jf;
 209                         continue;
 210                 case BPF_LD|BPF_W|BPF_ABS:
 211                         k = fentry->k;
 212 load_w:
 213                         ptr = load_pointer(skb, k, 4, &tmp);
 214                         if (ptr != NULL) {
 215                                 A = get_unaligned_be32(ptr);
 216                                 continue;
 217                         }
 218                         break;
 219                 case BPF_LD|BPF_H|BPF_ABS:
 220                         k = fentry->k;
 221 load_h:
 222                         ptr = load_pointer(skb, k, 2, &tmp);
 223                         if (ptr != NULL) {
 224                                 A = get_unaligned_be16(ptr);
 225                                 continue;
 226                         }
 227                         break;
 228                 case BPF_LD|BPF_B|BPF_ABS:
 229                         k = fentry->k;
 230 load_b:
 231                         ptr = load_pointer(skb, k, 1, &tmp);
 232                         if (ptr != NULL) {
 233                                 A = *(u8 *)ptr;
 234                                 continue;
 235                         }
 236                         break;
 237                 case BPF_LD|BPF_W|BPF_LEN:
 238                         A = skb->len;
 239                         continue;
 240                 case BPF_LDX|BPF_W|BPF_LEN:
 241                         X = skb->len;
 242                         continue;
 243                 case BPF_LD|BPF_W|BPF_IND:
 244                         k = X + fentry->k;
 245                         goto load_w;
 246                 case BPF_LD|BPF_H|BPF_IND:
 247                         k = X + fentry->k;
 248                         goto load_h;
 249                 case BPF_LD|BPF_B|BPF_IND:
 250                         k = X + fentry->k;
 251                         goto load_b;
 252                 case BPF_LDX|BPF_B|BPF_MSH:
 253                         ptr = load_pointer(skb, fentry->k, 1, &tmp);
 254                         if (ptr != NULL) {
 255                                 X = (*(u8 *)ptr & 0xf) << 2;
 256                                 continue;
 257                         }
 258                         return 0;
 259                 case BPF_LD|BPF_IMM:
 260                         A = fentry->k;
 261                         continue;
 262                 case BPF_LDX|BPF_IMM:
 263                         X = fentry->k;
 264                         continue;
 265                 case BPF_LD|BPF_MEM:
 266                         A = mem[fentry->k];
 267                         continue;
 268                 case BPF_LDX|BPF_MEM:
 269                         X = mem[fentry->k];
 270                         continue;
 271                 case BPF_MISC|BPF_TAX:
 272                         X = A;
 273                         continue;
 274                 case BPF_MISC|BPF_TXA:
 275                         A = X;
 276                         continue;
 277                 case BPF_RET|BPF_K:
 278                         return fentry->k;
 279                 case BPF_RET|BPF_A:
 280                         return A;
 281                 case BPF_ST:
 282                         mem[fentry->k] = A;
 283                         continue;
 284                 case BPF_STX:
 285                         mem[fentry->k] = X;
 286                         continue;
 287                 default:
 288                         WARN_ON(1);
 289                         return 0;
 290                 }
 291
 292                 /*
 293                  * Handle ancillary data, which are impossible
 294                  * (or very difficult) to get parsing packet contents.
 295                  */
 296                 switch (k-SKF_AD_OFF) {
 297                 case SKF_AD_PROTOCOL:
 298                         A = ntohs(skb->protocol);
 299                         continue;
 300                 case SKF_AD_PKTTYPE:
 301                         A = skb->pkt_type;
 302                         continue;
 303                 case SKF_AD_IFINDEX:
 304                         A = skb->dev->ifindex;
 305                         continue;
 306                 case SKF_AD_MARK:
 307                         A = skb->mark;
 308                         continue;
 309                 case SKF_AD_NLATTR: {
 310                         struct nlattr *nla;
 311
 312                         if (skb_is_nonlinear(skb))
 313                                 return 0;
 314                         if (A > skb->len - sizeof(struct nlattr))
 315                                 return 0;
 316
 317                         nla = nla_find((struct nlattr *)&skb->data[A],
 318                                        skb->len - A, X);
 319                         if (nla)
 320                                 A = (void *)nla - (void *)skb->data;
 321                         else
 322                                 A = 0;
 323                         continue;
 324                 }
 325                 case SKF_AD_NLATTR_NEST: {
 326                         struct nlattr *nla;
 327
 328                         if (skb_is_nonlinear(skb))
 329                                 return 0;
 330                         if (A > skb->len - sizeof(struct nlattr))
 331                                 return 0;
 332
 333                         nla = (struct nlattr *)&skb->data[A];
 334                         if (nla->nla_len > A - skb->len)
 335                                 return 0;
 336
 337                         nla = nla_find_nested(nla, X);
 338                         if (nla)
 339                                 A = (void *)nla - (void *)skb->data;
 340                         else
 341                                 A = 0;
 342                         continue;
 343                 }
 344                 default:
 345                         return 0;
 346                 }
 347         }
 348
 349         return 0;
 350 }
 351 EXPORT_SYMBOL(sk_run_filter);
 352
 353 /**
 354  *      sk_chk_filter - verify socket filter code
 355  *      @filter: filter to verify
 356  *      @flen: length of filter
 357  *
 358  * Check the user's filter code. If we let some ugly
 359  * filter code slip through kaboom! The filter must contain
 360  * no references or jumps that are out of range, no illegal
 361  * instructions, and must end with a RET instruction.
 362  *
 363  * All jumps are forward as they are not signed.
 364  *
 365  * Returns 0 if the rule set is legal or -EINVAL if not.
 366  */
 367 int sk_chk_filter(struct sock_filter *filter, int flen)
 368 {
 369         struct sock_filter *ftest;
 370         int pc;
 371
 372         if (flen == 0 || flen > BPF_MAXINSNS)
 373                 return -EINVAL;
 374
 375         /* check the filter code now */
 376         for (pc = 0; pc < flen; pc++) {
 377                 ftest = &filter[pc];
 378
 379                 /* Only allow valid instructions */
 380                 switch (ftest->code) {
 381                 case BPF_ALU|BPF_ADD|BPF_K:
 382                 case BPF_ALU|BPF_ADD|BPF_X:
 383                 case BPF_ALU|BPF_SUB|BPF_K:
 384                 case BPF_ALU|BPF_SUB|BPF_X:
 385                 case BPF_ALU|BPF_MUL|BPF_K:
 386                 case BPF_ALU|BPF_MUL|BPF_X:
 387                 case BPF_ALU|BPF_DIV|BPF_X:
 388                 case BPF_ALU|BPF_AND|BPF_K:
 389                 case BPF_ALU|BPF_AND|BPF_X:
 390                 case BPF_ALU|BPF_OR|BPF_K:
 391                 case BPF_ALU|BPF_OR|BPF_X:
 392                 case BPF_ALU|BPF_LSH|BPF_K:
 393                 case BPF_ALU|BPF_LSH|BPF_X:
 394                 case BPF_ALU|BPF_RSH|BPF_K:
 395                 case BPF_ALU|BPF_RSH|BPF_X:
 396                 case BPF_ALU|BPF_NEG:
 397                 case BPF_LD|BPF_W|BPF_ABS:
 398                 case BPF_LD|BPF_H|BPF_ABS:
 399                 case BPF_LD|BPF_B|BPF_ABS:
 400                 case BPF_LD|BPF_W|BPF_LEN:
 401                 case BPF_LD|BPF_W|BPF_IND:
 402                 case BPF_LD|BPF_H|BPF_IND:
 403                 case BPF_LD|BPF_B|BPF_IND:
 404                 case BPF_LD|BPF_IMM:
 405                 case BPF_LDX|BPF_W|BPF_LEN:
 406                 case BPF_LDX|BPF_B|BPF_MSH:
 407                 case BPF_LDX|BPF_IMM:
 408                 case BPF_MISC|BPF_TAX:
 409                 case BPF_MISC|BPF_TXA:
 410                 case BPF_RET|BPF_K:
 411                 case BPF_RET|BPF_A:
 412                         break;
 413
 414                 /* Some instructions need special checks */
 415
 416                 case BPF_ALU|BPF_DIV|BPF_K:
 417                         /* check for division by zero */
 418                         if (ftest->k == 0)
 419                                 return -EINVAL;
 420                         break;
 421
 422                 case BPF_LD|BPF_MEM:
 423                 case BPF_LDX|BPF_MEM:
 424                 case BPF_ST:
 425                 case BPF_STX:
 426                         /* check for invalid memory addresses */
 427                         if (ftest->k >= BPF_MEMWORDS)
 428                                 return -EINVAL;
 429                         break;
 430
 431                 case BPF_JMP|BPF_JA:
 432                         /*
 433                          * Note, the large ftest->k might cause loops.
 434                          * Compare this with conditional jumps below,
 435                          * where offsets are limited. --ANK (981016)
 436                          */
 437                         if (ftest->k >= (unsigned)(flen-pc-1))
 438                                 return -EINVAL;
 439                         break;
 440
 441                 case BPF_JMP|BPF_JEQ|BPF_K:
 442                 case BPF_JMP|BPF_JEQ|BPF_X:
 443                 case BPF_JMP|BPF_JGE|BPF_K:
 444                 case BPF_JMP|BPF_JGE|BPF_X:
 445                 case BPF_JMP|BPF_JGT|BPF_K:
 446                 case BPF_JMP|BPF_JGT|BPF_X:
 447                 case BPF_JMP|BPF_JSET|BPF_K:
 448                 case BPF_JMP|BPF_JSET|BPF_X:
 449                         /* for conditionals both must be safe */
 450                         if (pc + ftest->jt + 1 >= flen ||
 451                             pc + ftest->jf + 1 >= flen)
 452                                 return -EINVAL;
 453                         break;
 454
 455                 default:
 456                         return -EINVAL;
 457                 }
 458         }
 459
 460         return (BPF_CLASS(filter[flen - 1].code) == BPF_RET) ? 0 : -EINVAL;
 461 }
 462 EXPORT_SYMBOL(sk_chk_filter);
 463
 464 /**
 465  *      sk_filter_rcu_release: Release a socket filter by rcu_head
 466  *      @rcu: rcu_head that contains the sk_filter to free
 467  */
 468 static void sk_filter_rcu_release(struct rcu_head *rcu)
 469 {
 470         struct sk_filter *fp = container_of(rcu, struct sk_filter, rcu);
 471
 472         sk_filter_release(fp);
 473 }
 474
 475 static void sk_filter_delayed_uncharge(struct sock *sk, struct sk_filter *fp)
 476 {
 477         unsigned int size = sk_filter_len(fp);
 478
 479         atomic_sub(size, &sk->sk_omem_alloc);
 480         call_rcu_bh(&fp->rcu, sk_filter_rcu_release);
 481 }
 482
 483 /**
 484  *      sk_attach_filter - attach a socket filter
 485  *      @fprog: the filter program
 486  *      @sk: the socket to use
 487  *
 488  * Attach the user's filter code. We first run some sanity checks on
 489  * it to make sure it does not explode on us later. If an error
 490  * occurs or there is insufficient memory for the filter a negative
 491  * errno code is returned. On success the return is zero.
 492  */
 493 int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk)
 494 {
 495         struct sk_filter *fp, *old_fp;
 496         unsigned int fsize = sizeof(struct sock_filter) * fprog->len;
 497         int err;
 498
 499         /* Make sure new filter is there and in the right amounts. */
 500         if (fprog->filter == NULL)
 501                 return -EINVAL;
 502
 503         fp = sock_kmalloc(sk, fsize+sizeof(*fp), GFP_KERNEL);
 504         if (!fp)
 505                 return -ENOMEM;
 506         if (copy_from_user(fp->insns, fprog->filter, fsize)) {
 507                 sock_kfree_s(sk, fp, fsize+sizeof(*fp));
 508                 return -EFAULT;
 509         }
 510
 511         atomic_set(&fp->refcnt, 1);
 512         fp->len = fprog->len;
 513
 514         err = sk_chk_filter(fp->insns, fp->len);
 515         if (err) {
 516                 sk_filter_uncharge(sk, fp);
 517                 return err;
 518         }
 519
 520         rcu_read_lock_bh();
 521         old_fp = rcu_dereference(sk->sk_filter);
 522         rcu_assign_pointer(sk->sk_filter, fp);
 523         rcu_read_unlock_bh();
 524
 525         if (old_fp)
 526                 sk_filter_delayed_uncharge(sk, old_fp);
 527         return 0;
 528 }
 529
 530 int sk_detach_filter(struct sock *sk)
 531 {
 532         int ret = -ENOENT;
 533         struct sk_filter *filter;
 534
 535         rcu_read_lock_bh();
 536         filter = rcu_dereference(sk->sk_filter);
 537         if (filter) {
 538                 rcu_assign_pointer(sk->sk_filter, NULL);
 539                 sk_filter_delayed_uncharge(sk, filter);
 540                 ret = 0;
 541         }
 542         rcu_read_unlock_bh();
 543         return ret;
 544 }