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/module.h>
  19 #include <linux/types.h>
  20 #include <linux/sched.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 <linux/filter.h>
  37
  38 /* No hurry in this branch */
  39 static void *__load_pointer(struct sk_buff *skb, int k)
  40 {
  41         u8 *ptr = NULL;
  42
  43         if (k >= SKF_NET_OFF)
  44                 ptr = skb->nh.raw + k - SKF_NET_OFF;
  45         else if (k >= SKF_LL_OFF)
  46                 ptr = skb->mac.raw + k - SKF_LL_OFF;
  47
  48         if (ptr >= skb->head && ptr < skb->tail)
  49                 return ptr;
  50         return NULL;
  51 }
  52
  53 static inline void *load_pointer(struct sk_buff *skb, int k,
  54                                  unsigned int size, void *buffer)
  55 {
  56         if (k >= 0)
  57                 return skb_header_pointer(skb, k, size, buffer);
  58         else {
  59                 if (k >= SKF_AD_OFF)
  60                         return NULL;
  61                 return __load_pointer(skb, k);
  62         }
  63 }
  64
  65 /**
  66  *      sk_run_filter   -       run a filter on a socket
  67  *      @skb: buffer to run the filter on
  68  *      @filter: filter to apply
  69  *      @flen: length of filter
  70  *
  71  * Decode and apply filter instructions to the skb->data.
  72  * Return length to keep, 0 for none. skb is the data we are
  73  * filtering, filter is the array of filter instructions, and
  74  * len is the number of filter blocks in the array.
  75  */
  76
  77 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                         if (fentry->k == 0)
 120                                 return 0;
 121                         A /= fentry->k;
 122                         continue;
 123                 case BPF_ALU|BPF_AND|BPF_X:
 124                         A &= X;
 125                         continue;
 126                 case BPF_ALU|BPF_AND|BPF_K:
 127                         A &= fentry->k;
 128                         continue;
 129                 case BPF_ALU|BPF_OR|BPF_X:
 130                         A |= X;
 131                         continue;
 132                 case BPF_ALU|BPF_OR|BPF_K:
 133                         A |= fentry->k;
 134                         continue;
 135                 case BPF_ALU|BPF_LSH|BPF_X:
 136                         A <<= X;
 137                         continue;
 138                 case BPF_ALU|BPF_LSH|BPF_K:
 139                         A <<= fentry->k;
 140                         continue;
 141                 case BPF_ALU|BPF_RSH|BPF_X:
 142                         A >>= X;
 143                         continue;
 144                 case BPF_ALU|BPF_RSH|BPF_K:
 145                         A >>= fentry->k;
 146                         continue;
 147                 case BPF_ALU|BPF_NEG:
 148                         A = -A;
 149                         continue;
 150                 case BPF_JMP|BPF_JA:
 151                         pc += fentry->k;
 152                         continue;
 153                 case BPF_JMP|BPF_JGT|BPF_K:
 154                         pc += (A > fentry->k) ? fentry->jt : fentry->jf;
 155                         continue;
 156                 case BPF_JMP|BPF_JGE|BPF_K:
 157                         pc += (A >= fentry->k) ? fentry->jt : fentry->jf;
 158                         continue;
 159                 case BPF_JMP|BPF_JEQ|BPF_K:
 160                         pc += (A == fentry->k) ? fentry->jt : fentry->jf;
 161                         continue;
 162                 case BPF_JMP|BPF_JSET|BPF_K:
 163                         pc += (A & fentry->k) ? fentry->jt : fentry->jf;
 164                         continue;
 165                 case BPF_JMP|BPF_JGT|BPF_X:
 166                         pc += (A > X) ? fentry->jt : fentry->jf;
 167                         continue;
 168                 case BPF_JMP|BPF_JGE|BPF_X:
 169                         pc += (A >= X) ? fentry->jt : fentry->jf;
 170                         continue;
 171                 case BPF_JMP|BPF_JEQ|BPF_X:
 172                         pc += (A == X) ? fentry->jt : fentry->jf;
 173                         continue;
 174                 case BPF_JMP|BPF_JSET|BPF_X:
 175                         pc += (A & X) ? fentry->jt : fentry->jf;
 176                         continue;
 177                 case BPF_LD|BPF_W|BPF_ABS:
 178                         k = fentry->k;
 179  load_w:
 180                         ptr = load_pointer(skb, k, 4, &tmp);
 181                         if (ptr != NULL) {
 182                                 A = ntohl(*(u32 *)ptr);
 183                                 continue;
 184                         }
 185                         break;
 186                 case BPF_LD|BPF_H|BPF_ABS:
 187                         k = fentry->k;
 188  load_h:
 189                         ptr = load_pointer(skb, k, 2, &tmp);
 190                         if (ptr != NULL) {
 191                                 A = ntohs(*(u16 *)ptr);
 192                                 continue;
 193                         }
 194                         break;
 195                 case BPF_LD|BPF_B|BPF_ABS:
 196                         k = fentry->k;
 197 load_b:
 198                         ptr = load_pointer(skb, k, 1, &tmp);
 199                         if (ptr != NULL) {
 200                                 A = *(u8 *)ptr;
 201                                 continue;
 202                         }
 203                         break;
 204                 case BPF_LD|BPF_W|BPF_LEN:
 205                         A = skb->len;
 206                         continue;
 207                 case BPF_LDX|BPF_W|BPF_LEN:
 208                         X = skb->len;
 209                         continue;
 210                 case BPF_LD|BPF_W|BPF_IND:
 211                         k = X + fentry->k;
 212                         goto load_w;
 213                 case BPF_LD|BPF_H|BPF_IND:
 214                         k = X + fentry->k;
 215                         goto load_h;
 216                 case BPF_LD|BPF_B|BPF_IND:
 217                         k = X + fentry->k;
 218                         goto load_b;
 219                 case BPF_LDX|BPF_B|BPF_MSH:
 220                         ptr = load_pointer(skb, fentry->k, 1, &tmp);
 221                         if (ptr != NULL) {
 222                                 X = (*(u8 *)ptr & 0xf) << 2;
 223                                 continue;
 224                         }
 225                         return 0;
 226                 case BPF_LD|BPF_IMM:
 227                         A = fentry->k;
 228                         continue;
 229                 case BPF_LDX|BPF_IMM:
 230                         X = fentry->k;
 231                         continue;
 232                 case BPF_LD|BPF_MEM:
 233                         A = mem[fentry->k];
 234                         continue;
 235                 case BPF_LDX|BPF_MEM:
 236                         X = mem[fentry->k];
 237                         continue;
 238                 case BPF_MISC|BPF_TAX:
 239                         X = A;
 240                         continue;
 241                 case BPF_MISC|BPF_TXA:
 242                         A = X;
 243                         continue;
 244                 case BPF_RET|BPF_K:
 245                         return ((unsigned int)fentry->k);
 246                 case BPF_RET|BPF_A:
 247                         return ((unsigned int)A);
 248                 case BPF_ST:
 249                         mem[fentry->k] = A;
 250                         continue;
 251                 case BPF_STX:
 252                         mem[fentry->k] = X;
 253                         continue;
 254                 default:
 255                         /* Invalid instruction counts as RET */
 256                         return 0;
 257                 }
 258
 259                 /*
 260                  * Handle ancillary data, which are impossible
 261                  * (or very difficult) to get parsing packet contents.
 262                  */
 263                 switch (k-SKF_AD_OFF) {
 264                 case SKF_AD_PROTOCOL:
 265                         A = htons(skb->protocol);
 266                         continue;
 267                 case SKF_AD_PKTTYPE:
 268                         A = skb->pkt_type;
 269                         continue;
 270                 case SKF_AD_IFINDEX:
 271                         A = skb->dev->ifindex;
 272                         continue;
 273                 default:
 274                         return 0;
 275                 }
 276         }
 277
 278         return 0;
 279 }
 280
 281 /**
 282  *      sk_chk_filter - verify socket filter code
 283  *      @filter: filter to verify
 284  *      @flen: length of filter
 285  *
 286  * Check the user's filter code. If we let some ugly
 287  * filter code slip through kaboom! The filter must contain
 288  * no references or jumps that are out of range, no illegal instructions
 289  * and no backward jumps. It must end with a RET instruction
 290  *
 291  * Returns 0 if the rule set is legal or a negative errno code 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 (((unsigned int)flen >= (~0U / sizeof(struct sock_filter))) || flen == 0)
 299                 return -EINVAL;
 300
 301         /* check the filter code now */
 302         for (pc = 0; pc < flen; pc++) {
 303                 /* all jumps are forward as they are not signed */
 304                 ftest = &filter[pc];
 305                 if (BPF_CLASS(ftest->code) == BPF_JMP) {
 306                         /* but they mustn't jump off the end */
 307                         if (BPF_OP(ftest->code) == BPF_JA) {
 308                                 /*
 309                                  * Note, the large ftest->k might cause loops.
 310                                  * Compare this with conditional jumps below,
 311                                  * where offsets are limited. --ANK (981016)
 312                                  */
 313                                 if (ftest->k >= (unsigned)(flen-pc-1))
 314                                         return -EINVAL;
 315                         } else {
 316                                 /* for conditionals both must be safe */
 317                                 if (pc + ftest->jt +1 >= flen ||
 318                                     pc + ftest->jf +1 >= flen)
 319                                         return -EINVAL;
 320                         }
 321                 }
 322
 323                 /* check that memory operations use valid addresses. */
 324                 if (ftest->k >= BPF_MEMWORDS) {
 325                         /* but it might not be a memory operation... */
 326                         switch (ftest->code) {
 327                         case BPF_ST:
 328                         case BPF_STX:
 329                         case BPF_LD|BPF_MEM:
 330                         case BPF_LDX|BPF_MEM:
 331                                 return -EINVAL;
 332                         }
 333                 }
 334         }
 335
 336         /*
 337          * The program must end with a return. We don't care where they
 338          * jumped within the script (its always forwards) but in the end
 339          * they _will_ hit this.
 340          */
 341         return (BPF_CLASS(filter[flen - 1].code) == BPF_RET) ? 0 : -EINVAL;
 342 }
 343
 344 /**
 345  *      sk_attach_filter - attach a socket filter
 346  *      @fprog: the filter program
 347  *      @sk: the socket to use
 348  *
 349  * Attach the user's filter code. We first run some sanity checks on
 350  * it to make sure it does not explode on us later. If an error
 351  * occurs or there is insufficient memory for the filter a negative
 352  * errno code is returned. On success the return is zero.
 353  */
 354 int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk)
 355 {
 356         struct sk_filter *fp;
 357         unsigned int fsize = sizeof(struct sock_filter) * fprog->len;
 358         int err;
 359
 360         /* Make sure new filter is there and in the right amounts. */
 361         if (fprog->filter == NULL || fprog->len > BPF_MAXINSNS)
 362                 return -EINVAL;
 363
 364         fp = sock_kmalloc(sk, fsize+sizeof(*fp), GFP_KERNEL);
 365         if (!fp)
 366                 return -ENOMEM;
 367         if (copy_from_user(fp->insns, fprog->filter, fsize)) {
 368                 sock_kfree_s(sk, fp, fsize+sizeof(*fp));
 369                 return -EFAULT;
 370         }
 371
 372         atomic_set(&fp->refcnt, 1);
 373         fp->len = fprog->len;
 374
 375         err = sk_chk_filter(fp->insns, fp->len);
 376         if (!err) {
 377                 struct sk_filter *old_fp;
 378
 379                 spin_lock_bh(&sk->sk_lock.slock);
 380                 old_fp = sk->sk_filter;
 381                 sk->sk_filter = fp;
 382                 spin_unlock_bh(&sk->sk_lock.slock);
 383                 fp = old_fp;
 384         }
 385
 386         if (fp)
 387                 sk_filter_release(sk, fp);
 388         return err;
 389 }
 390
 391 EXPORT_SYMBOL(sk_chk_filter);
 392 EXPORT_SYMBOL(sk_run_filter);