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 <linux/gfp.h>
  29 #include <net/ip.h>
  30 #include <net/protocol.h>
  31 #include <net/netlink.h>
  32 #include <linux/skbuff.h>
  33 #include <net/sock.h>
  34 #include <linux/errno.h>
  35 #include <linux/timer.h>
  36 #include <asm/system.h>
  37 #include <asm/uaccess.h>
  38 #include <asm/unaligned.h>
  39 #include <linux/filter.h>
  40 #include <linux/reciprocal_div.h>
  41
  42 /* No hurry in this branch */
  43 static void *__load_pointer(const struct sk_buff *skb, int k, unsigned int size)
  44 {
  45         u8 *ptr = NULL;
  46
  47         if (k >= SKF_NET_OFF)
  48                 ptr = skb_network_header(skb) + k - SKF_NET_OFF;
  49         else if (k >= SKF_LL_OFF)
  50                 ptr = skb_mac_header(skb) + k - SKF_LL_OFF;
  51
  52         if (ptr >= skb->head && ptr + size <= skb_tail_pointer(skb))
  53                 return ptr;
  54         return NULL;
  55 }
  56
  57 static inline void *load_pointer(const struct sk_buff *skb, int k,
  58                                  unsigned int size, void *buffer)
  59 {
  60         if (k >= 0)
  61                 return skb_header_pointer(skb, k, size, buffer);
  62         return __load_pointer(skb, k, size);
  63 }
  64
  65 /**
  66  *      sk_filter - run a packet through a socket filter
  67  *      @sk: sock associated with &sk_buff
  68  *      @skb: buffer to filter
  69  *
  70  * Run the filter code and then cut skb->data to correct size returned by
  71  * sk_run_filter. If pkt_len is 0 we toss packet. If skb->len is smaller
  72  * than pkt_len we keep whole skb->data. This is the socket level
  73  * wrapper to sk_run_filter. It returns 0 if the packet should
  74  * be accepted or -EPERM if the packet should be tossed.
  75  *
  76  */
  77 int sk_filter(struct sock *sk, struct sk_buff *skb)
  78 {
  79         int err;
  80         struct sk_filter *filter;
  81
  82         err = security_sock_rcv_skb(sk, skb);
  83         if (err)
  84                 return err;
  85
  86         rcu_read_lock();
  87         filter = rcu_dereference(sk->sk_filter);
  88         if (filter) {
  89                 unsigned int pkt_len = SK_RUN_FILTER(filter, skb);
  90
  91                 err = pkt_len ? pskb_trim(skb, pkt_len) : -EPERM;
  92         }
  93         rcu_read_unlock();
  94
  95         return err;
  96 }
  97 EXPORT_SYMBOL(sk_filter);
  98
  99 /**
 100  *      sk_run_filter - run a filter on a socket
 101  *      @skb: buffer to run the filter on
 102  *      @fentry: filter to apply
 103  *
 104  * Decode and apply filter instructions to the skb->data.
 105  * Return length to keep, 0 for none. @skb is the data we are
 106  * filtering, @filter is the array of filter instructions.
 107  * Because all jumps are guaranteed to be before last instruction,
 108  * and last instruction guaranteed to be a RET, we dont need to check
 109  * flen. (We used to pass to this function the length of filter)
 110  */
 111 unsigned int sk_run_filter(const struct sk_buff *skb,
 112                            const struct sock_filter *fentry)
 113 {
 114         void *ptr;
 115         u32 A = 0;                      /* Accumulator */
 116         u32 X = 0;                      /* Index Register */
 117         u32 mem[BPF_MEMWORDS];          /* Scratch Memory Store */
 118         u32 tmp;
 119         int k;
 120
 121         /*
 122          * Process array of filter instructions.
 123          */
 124         for (;; fentry++) {
 125 #if defined(CONFIG_X86_32)
 126 #define K (fentry->k)
 127 #else
 128                 const u32 K = fentry->k;
 129 #endif
 130
 131                 switch (fentry->code) {
 132                 case BPF_S_ALU_ADD_X:
 133                         A += X;
 134                         continue;
 135                 case BPF_S_ALU_ADD_K:
 136                         A += K;
 137                         continue;
 138                 case BPF_S_ALU_SUB_X:
 139                         A -= X;
 140                         continue;
 141                 case BPF_S_ALU_SUB_K:
 142                         A -= K;
 143                         continue;
 144                 case BPF_S_ALU_MUL_X:
 145                         A *= X;
 146                         continue;
 147                 case BPF_S_ALU_MUL_K:
 148                         A *= K;
 149                         continue;
 150                 case BPF_S_ALU_DIV_X:
 151                         if (X == 0)
 152                                 return 0;
 153                         A /= X;
 154                         continue;
 155                 case BPF_S_ALU_DIV_K:
 156                         A = reciprocal_divide(A, K);
 157                         continue;
 158                 case BPF_S_ALU_AND_X:
 159                         A &= X;
 160                         continue;
 161                 case BPF_S_ALU_AND_K:
 162                         A &= K;
 163                         continue;
 164                 case BPF_S_ALU_OR_X:
 165                         A |= X;
 166                         continue;
 167                 case BPF_S_ALU_OR_K:
 168                         A |= K;
 169                         continue;
 170                 case BPF_S_ALU_LSH_X:
 171                         A <<= X;
 172                         continue;
 173                 case BPF_S_ALU_LSH_K:
 174                         A <<= K;
 175                         continue;
 176                 case BPF_S_ALU_RSH_X:
 177                         A >>= X;
 178                         continue;
 179                 case BPF_S_ALU_RSH_K:
 180                         A >>= K;
 181                         continue;
 182                 case BPF_S_ALU_NEG:
 183                         A = -A;
 184                         continue;
 185                 case BPF_S_JMP_JA:
 186                         fentry += K;
 187                         continue;
 188                 case BPF_S_JMP_JGT_K:
 189                         fentry += (A > K) ? fentry->jt : fentry->jf;
 190                         continue;
 191                 case BPF_S_JMP_JGE_K:
 192                         fentry += (A >= K) ? fentry->jt : fentry->jf;
 193                         continue;
 194                 case BPF_S_JMP_JEQ_K:
 195                         fentry += (A == K) ? fentry->jt : fentry->jf;
 196                         continue;
 197                 case BPF_S_JMP_JSET_K:
 198                         fentry += (A & K) ? fentry->jt : fentry->jf;
 199                         continue;
 200                 case BPF_S_JMP_JGT_X:
 201                         fentry += (A > X) ? fentry->jt : fentry->jf;
 202                         continue;
 203                 case BPF_S_JMP_JGE_X:
 204                         fentry += (A >= X) ? fentry->jt : fentry->jf;
 205                         continue;
 206                 case BPF_S_JMP_JEQ_X:
 207                         fentry += (A == X) ? fentry->jt : fentry->jf;
 208                         continue;
 209                 case BPF_S_JMP_JSET_X:
 210                         fentry += (A & X) ? fentry->jt : fentry->jf;
 211                         continue;
 212                 case BPF_S_LD_W_ABS:
 213                         k = K;
 214 load_w:
 215                         ptr = load_pointer(skb, k, 4, &tmp);
 216                         if (ptr != NULL) {
 217                                 A = get_unaligned_be32(ptr);
 218                                 continue;
 219                         }
 220                         return 0;
 221                 case BPF_S_LD_H_ABS:
 222                         k = K;
 223 load_h:
 224                         ptr = load_pointer(skb, k, 2, &tmp);
 225                         if (ptr != NULL) {
 226                                 A = get_unaligned_be16(ptr);
 227                                 continue;
 228                         }
 229                         return 0;
 230                 case BPF_S_LD_B_ABS:
 231                         k = K;
 232 load_b:
 233                         ptr = load_pointer(skb, k, 1, &tmp);
 234                         if (ptr != NULL) {
 235                                 A = *(u8 *)ptr;
 236                                 continue;
 237                         }
 238                         return 0;
 239                 case BPF_S_LD_W_LEN:
 240                         A = skb->len;
 241                         continue;
 242                 case BPF_S_LDX_W_LEN:
 243                         X = skb->len;
 244                         continue;
 245                 case BPF_S_LD_W_IND:
 246                         k = X + K;
 247                         goto load_w;
 248                 case BPF_S_LD_H_IND:
 249                         k = X + K;
 250                         goto load_h;
 251                 case BPF_S_LD_B_IND:
 252                         k = X + K;
 253                         goto load_b;
 254                 case BPF_S_LDX_B_MSH:
 255                         ptr = load_pointer(skb, K, 1, &tmp);
 256                         if (ptr != NULL) {
 257                                 X = (*(u8 *)ptr & 0xf) << 2;
 258                                 continue;
 259                         }
 260                         return 0;
 261                 case BPF_S_LD_IMM:
 262                         A = K;
 263                         continue;
 264                 case BPF_S_LDX_IMM:
 265                         X = K;
 266                         continue;
 267                 case BPF_S_LD_MEM:
 268                         A = mem[K];
 269                         continue;
 270                 case BPF_S_LDX_MEM:
 271                         X = mem[K];
 272                         continue;
 273                 case BPF_S_MISC_TAX:
 274                         X = A;
 275                         continue;
 276                 case BPF_S_MISC_TXA:
 277                         A = X;
 278                         continue;
 279                 case BPF_S_RET_K:
 280                         return K;
 281                 case BPF_S_RET_A:
 282                         return A;
 283                 case BPF_S_ST:
 284                         mem[K] = A;
 285                         continue;
 286                 case BPF_S_STX:
 287                         mem[K] = X;
 288                         continue;
 289                 case BPF_S_ANC_PROTOCOL:
 290                         A = ntohs(skb->protocol);
 291                         continue;
 292                 case BPF_S_ANC_PKTTYPE:
 293                         A = skb->pkt_type;
 294                         continue;
 295                 case BPF_S_ANC_IFINDEX:
 296                         if (!skb->dev)
 297                                 return 0;
 298                         A = skb->dev->ifindex;
 299                         continue;
 300                 case BPF_S_ANC_MARK:
 301                         A = skb->mark;
 302                         continue;
 303                 case BPF_S_ANC_QUEUE:
 304                         A = skb->queue_mapping;
 305                         continue;
 306                 case BPF_S_ANC_HATYPE:
 307                         if (!skb->dev)
 308                                 return 0;
 309                         A = skb->dev->type;
 310                         continue;
 311                 case BPF_S_ANC_RXHASH:
 312                         A = skb->rxhash;
 313                         continue;
 314                 case BPF_S_ANC_CPU:
 315                         A = raw_smp_processor_id();
 316                         continue;
 317                 case BPF_S_ANC_NLATTR: {
 318                         struct nlattr *nla;
 319
 320                         if (skb_is_nonlinear(skb))
 321                                 return 0;
 322                         if (A > skb->len - sizeof(struct nlattr))
 323                                 return 0;
 324
 325                         nla = nla_find((struct nlattr *)&skb->data[A],
 326                                        skb->len - A, X);
 327                         if (nla)
 328                                 A = (void *)nla - (void *)skb->data;
 329                         else
 330                                 A = 0;
 331                         continue;
 332                 }
 333                 case BPF_S_ANC_NLATTR_NEST: {
 334                         struct nlattr *nla;
 335
 336                         if (skb_is_nonlinear(skb))
 337                                 return 0;
 338                         if (A > skb->len - sizeof(struct nlattr))
 339                                 return 0;
 340
 341                         nla = (struct nlattr *)&skb->data[A];
 342                         if (nla->nla_len > A - skb->len)
 343                                 return 0;
 344
 345                         nla = nla_find_nested(nla, X);
 346                         if (nla)
 347                                 A = (void *)nla - (void *)skb->data;
 348                         else
 349                                 A = 0;
 350                         continue;
 351                 }
 352                 default:
 353                         WARN_ON(1);
 354                         return 0;
 355                 }
 356         }
 357
 358         return 0;
 359 }
 360 EXPORT_SYMBOL(sk_run_filter);
 361
 362 /*
 363  * Security :
 364  * A BPF program is able to use 16 cells of memory to store intermediate
 365  * values (check u32 mem[BPF_MEMWORDS] in sk_run_filter())
 366  * As we dont want to clear mem[] array for each packet going through
 367  * sk_run_filter(), we check that filter loaded by user never try to read
 368  * a cell if not previously written, and we check all branches to be sure
 369  * a malicious user doesn't try to abuse us.
 370  */
 371 static int check_load_and_stores(struct sock_filter *filter, int flen)
 372 {
 373         u16 *masks, memvalid = 0; /* one bit per cell, 16 cells */
 374         int pc, ret = 0;
 375
 376         BUILD_BUG_ON(BPF_MEMWORDS > 16);
 377         masks = kmalloc(flen * sizeof(*masks), GFP_KERNEL);
 378         if (!masks)
 379                 return -ENOMEM;
 380         memset(masks, 0xff, flen * sizeof(*masks));
 381
 382         for (pc = 0; pc < flen; pc++) {
 383                 memvalid &= masks[pc];
 384
 385                 switch (filter[pc].code) {
 386                 case BPF_S_ST:
 387                 case BPF_S_STX:
 388                         memvalid |= (1 << filter[pc].k);
 389                         break;
 390                 case BPF_S_LD_MEM:
 391                 case BPF_S_LDX_MEM:
 392                         if (!(memvalid & (1 << filter[pc].k))) {
 393                                 ret = -EINVAL;
 394                                 goto error;
 395                         }
 396                         break;
 397                 case BPF_S_JMP_JA:
 398                         /* a jump must set masks on target */
 399                         masks[pc + 1 + filter[pc].k] &= memvalid;
 400                         memvalid = ~0;
 401                         break;
 402                 case BPF_S_JMP_JEQ_K:
 403                 case BPF_S_JMP_JEQ_X:
 404                 case BPF_S_JMP_JGE_K:
 405                 case BPF_S_JMP_JGE_X:
 406                 case BPF_S_JMP_JGT_K:
 407                 case BPF_S_JMP_JGT_X:
 408                 case BPF_S_JMP_JSET_X:
 409                 case BPF_S_JMP_JSET_K:
 410                         /* a jump must set masks on targets */
 411                         masks[pc + 1 + filter[pc].jt] &= memvalid;
 412                         masks[pc + 1 + filter[pc].jf] &= memvalid;
 413                         memvalid = ~0;
 414                         break;
 415                 }
 416         }
 417 error:
 418         kfree(masks);
 419         return ret;
 420 }
 421
 422 /**
 423  *      sk_chk_filter - verify socket filter code
 424  *      @filter: filter to verify
 425  *      @flen: length of filter
 426  *
 427  * Check the user's filter code. If we let some ugly
 428  * filter code slip through kaboom! The filter must contain
 429  * no references or jumps that are out of range, no illegal
 430  * instructions, and must end with a RET instruction.
 431  *
 432  * All jumps are forward as they are not signed.
 433  *
 434  * Returns 0 if the rule set is legal or -EINVAL if not.
 435  */
 436 int sk_chk_filter(struct sock_filter *filter, int flen)
 437 {
 438         /*
 439          * Valid instructions are initialized to non-0.
 440          * Invalid instructions are initialized to 0.
 441          */
 442         static const u8 codes[] = {
 443                 [BPF_ALU|BPF_ADD|BPF_K]  = BPF_S_ALU_ADD_K,
 444                 [BPF_ALU|BPF_ADD|BPF_X]  = BPF_S_ALU_ADD_X,
 445                 [BPF_ALU|BPF_SUB|BPF_K]  = BPF_S_ALU_SUB_K,
 446                 [BPF_ALU|BPF_SUB|BPF_X]  = BPF_S_ALU_SUB_X,
 447                 [BPF_ALU|BPF_MUL|BPF_K]  = BPF_S_ALU_MUL_K,
 448                 [BPF_ALU|BPF_MUL|BPF_X]  = BPF_S_ALU_MUL_X,
 449                 [BPF_ALU|BPF_DIV|BPF_X]  = BPF_S_ALU_DIV_X,
 450                 [BPF_ALU|BPF_AND|BPF_K]  = BPF_S_ALU_AND_K,
 451                 [BPF_ALU|BPF_AND|BPF_X]  = BPF_S_ALU_AND_X,
 452                 [BPF_ALU|BPF_OR|BPF_K]   = BPF_S_ALU_OR_K,
 453                 [BPF_ALU|BPF_OR|BPF_X]   = BPF_S_ALU_OR_X,
 454                 [BPF_ALU|BPF_LSH|BPF_K]  = BPF_S_ALU_LSH_K,
 455                 [BPF_ALU|BPF_LSH|BPF_X]  = BPF_S_ALU_LSH_X,
 456                 [BPF_ALU|BPF_RSH|BPF_K]  = BPF_S_ALU_RSH_K,
 457                 [BPF_ALU|BPF_RSH|BPF_X]  = BPF_S_ALU_RSH_X,
 458                 [BPF_ALU|BPF_NEG]        = BPF_S_ALU_NEG,
 459                 [BPF_LD|BPF_W|BPF_ABS]   = BPF_S_LD_W_ABS,
 460                 [BPF_LD|BPF_H|BPF_ABS]   = BPF_S_LD_H_ABS,
 461                 [BPF_LD|BPF_B|BPF_ABS]   = BPF_S_LD_B_ABS,
 462                 [BPF_LD|BPF_W|BPF_LEN]   = BPF_S_LD_W_LEN,
 463                 [BPF_LD|BPF_W|BPF_IND]   = BPF_S_LD_W_IND,
 464                 [BPF_LD|BPF_H|BPF_IND]   = BPF_S_LD_H_IND,
 465                 [BPF_LD|BPF_B|BPF_IND]   = BPF_S_LD_B_IND,
 466                 [BPF_LD|BPF_IMM]         = BPF_S_LD_IMM,
 467                 [BPF_LDX|BPF_W|BPF_LEN]  = BPF_S_LDX_W_LEN,
 468                 [BPF_LDX|BPF_B|BPF_MSH]  = BPF_S_LDX_B_MSH,
 469                 [BPF_LDX|BPF_IMM]        = BPF_S_LDX_IMM,
 470                 [BPF_MISC|BPF_TAX]       = BPF_S_MISC_TAX,
 471                 [BPF_MISC|BPF_TXA]       = BPF_S_MISC_TXA,
 472                 [BPF_RET|BPF_K]          = BPF_S_RET_K,
 473                 [BPF_RET|BPF_A]          = BPF_S_RET_A,
 474                 [BPF_ALU|BPF_DIV|BPF_K]  = BPF_S_ALU_DIV_K,
 475                 [BPF_LD|BPF_MEM]         = BPF_S_LD_MEM,
 476                 [BPF_LDX|BPF_MEM]        = BPF_S_LDX_MEM,
 477                 [BPF_ST]                 = BPF_S_ST,
 478                 [BPF_STX]                = BPF_S_STX,
 479                 [BPF_JMP|BPF_JA]         = BPF_S_JMP_JA,
 480                 [BPF_JMP|BPF_JEQ|BPF_K]  = BPF_S_JMP_JEQ_K,
 481                 [BPF_JMP|BPF_JEQ|BPF_X]  = BPF_S_JMP_JEQ_X,
 482                 [BPF_JMP|BPF_JGE|BPF_K]  = BPF_S_JMP_JGE_K,
 483                 [BPF_JMP|BPF_JGE|BPF_X]  = BPF_S_JMP_JGE_X,
 484                 [BPF_JMP|BPF_JGT|BPF_K]  = BPF_S_JMP_JGT_K,
 485                 [BPF_JMP|BPF_JGT|BPF_X]  = BPF_S_JMP_JGT_X,
 486                 [BPF_JMP|BPF_JSET|BPF_K] = BPF_S_JMP_JSET_K,
 487                 [BPF_JMP|BPF_JSET|BPF_X] = BPF_S_JMP_JSET_X,
 488         };
 489         int pc;
 490
 491         if (flen == 0 || flen > BPF_MAXINSNS)
 492                 return -EINVAL;
 493
 494         /* check the filter code now */
 495         for (pc = 0; pc < flen; pc++) {
 496                 struct sock_filter *ftest = &filter[pc];
 497                 u16 code = ftest->code;
 498
 499                 if (code >= ARRAY_SIZE(codes))
 500                         return -EINVAL;
 501                 code = codes[code];
 502                 if (!code)
 503                         return -EINVAL;
 504                 /* Some instructions need special checks */
 505                 switch (code) {
 506                 case BPF_S_ALU_DIV_K:
 507                         /* check for division by zero */
 508                         if (ftest->k == 0)
 509                                 return -EINVAL;
 510                         ftest->k = reciprocal_value(ftest->k);
 511                         break;
 512                 case BPF_S_LD_MEM:
 513                 case BPF_S_LDX_MEM:
 514                 case BPF_S_ST:
 515                 case BPF_S_STX:
 516                         /* check for invalid memory addresses */
 517                         if (ftest->k >= BPF_MEMWORDS)
 518                                 return -EINVAL;
 519                         break;
 520                 case BPF_S_JMP_JA:
 521                         /*
 522                          * Note, the large ftest->k might cause loops.
 523                          * Compare this with conditional jumps below,
 524                          * where offsets are limited. --ANK (981016)
 525                          */
 526                         if (ftest->k >= (unsigned)(flen-pc-1))
 527                                 return -EINVAL;
 528                         break;
 529                 case BPF_S_JMP_JEQ_K:
 530                 case BPF_S_JMP_JEQ_X:
 531                 case BPF_S_JMP_JGE_K:
 532                 case BPF_S_JMP_JGE_X:
 533                 case BPF_S_JMP_JGT_K:
 534                 case BPF_S_JMP_JGT_X:
 535                 case BPF_S_JMP_JSET_X:
 536                 case BPF_S_JMP_JSET_K:
 537                         /* for conditionals both must be safe */
 538                         if (pc + ftest->jt + 1 >= flen ||
 539                             pc + ftest->jf + 1 >= flen)
 540                                 return -EINVAL;
 541                         break;
 542                 case BPF_S_LD_W_ABS:
 543                 case BPF_S_LD_H_ABS:
 544                 case BPF_S_LD_B_ABS:
 545 #define ANCILLARY(CODE) case SKF_AD_OFF + SKF_AD_##CODE:        \
 546                                 code = BPF_S_ANC_##CODE;        \
 547                                 break
 548                         switch (ftest->k) {
 549                         ANCILLARY(PROTOCOL);
 550                         ANCILLARY(PKTTYPE);
 551                         ANCILLARY(IFINDEX);
 552                         ANCILLARY(NLATTR);
 553                         ANCILLARY(NLATTR_NEST);
 554                         ANCILLARY(MARK);
 555                         ANCILLARY(QUEUE);
 556                         ANCILLARY(HATYPE);
 557                         ANCILLARY(RXHASH);
 558                         ANCILLARY(CPU);
 559                         }
 560                 }
 561                 ftest->code = code;
 562         }
 563
 564         /* last instruction must be a RET code */
 565         switch (filter[flen - 1].code) {
 566         case BPF_S_RET_K:
 567         case BPF_S_RET_A:
 568                 return check_load_and_stores(filter, flen);
 569         }
 570         return -EINVAL;
 571 }
 572 EXPORT_SYMBOL(sk_chk_filter);
 573
 574 /**
 575  *      sk_filter_release_rcu - Release a socket filter by rcu_head
 576  *      @rcu: rcu_head that contains the sk_filter to free
 577  */
 578 void sk_filter_release_rcu(struct rcu_head *rcu)
 579 {
 580         struct sk_filter *fp = container_of(rcu, struct sk_filter, rcu);
 581
 582         bpf_jit_free(fp);
 583         kfree(fp);
 584 }
 585 EXPORT_SYMBOL(sk_filter_release_rcu);
 586
 587 /**
 588  *      sk_attach_filter - attach a socket filter
 589  *      @fprog: the filter program
 590  *      @sk: the socket to use
 591  *
 592  * Attach the user's filter code. We first run some sanity checks on
 593  * it to make sure it does not explode on us later. If an error
 594  * occurs or there is insufficient memory for the filter a negative
 595  * errno code is returned. On success the return is zero.
 596  */
 597 int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk)
 598 {
 599         struct sk_filter *fp, *old_fp;
 600         unsigned int fsize = sizeof(struct sock_filter) * fprog->len;
 601         int err;
 602
 603         /* Make sure new filter is there and in the right amounts. */
 604         if (fprog->filter == NULL)
 605                 return -EINVAL;
 606
 607         fp = sock_kmalloc(sk, fsize+sizeof(*fp), GFP_KERNEL);
 608         if (!fp)
 609                 return -ENOMEM;
 610         if (copy_from_user(fp->insns, fprog->filter, fsize)) {
 611                 sock_kfree_s(sk, fp, fsize+sizeof(*fp));
 612                 return -EFAULT;
 613         }
 614
 615         atomic_set(&fp->refcnt, 1);
 616         fp->len = fprog->len;
 617         fp->bpf_func = sk_run_filter;
 618
 619         err = sk_chk_filter(fp->insns, fp->len);
 620         if (err) {
 621                 sk_filter_uncharge(sk, fp);
 622                 return err;
 623         }
 624
 625         bpf_jit_compile(fp);
 626
 627         old_fp = rcu_dereference_protected(sk->sk_filter,
 628                                            sock_owned_by_user(sk));
 629         rcu_assign_pointer(sk->sk_filter, fp);
 630
 631         if (old_fp)
 632                 sk_filter_uncharge(sk, old_fp);
 633         return 0;
 634 }
 635 EXPORT_SYMBOL_GPL(sk_attach_filter);
 636
 637 int sk_detach_filter(struct sock *sk)
 638 {
 639         int ret = -ENOENT;
 640         struct sk_filter *filter;
 641
 642         filter = rcu_dereference_protected(sk->sk_filter,
 643                                            sock_owned_by_user(sk));
 644         if (filter) {
 645                 rcu_assign_pointer(sk->sk_filter, NULL);
 646                 sk_filter_uncharge(sk, filter);
 647                 ret = 0;
 648         }
 649         return ret;
 650 }
 651 EXPORT_SYMBOL_GPL(sk_detach_filter);