2 * Linux Socket Filter - Kernel level socket filtering
5 * Jay Schulist <jschlst@samba.org>
7 * Based on the design of:
8 * - The Berkeley Packet Filter
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.
15 * Andi Kleen - Fix a few bad bugs and races.
16 * Kris Katterjohn - Added many additional checks in sk_chk_filter()
19 #include <linux/module.h>
20 #include <linux/types.h>
22 #include <linux/fcntl.h>
23 #include <linux/socket.h>
25 #include <linux/inet.h>
26 #include <linux/netdevice.h>
27 #include <linux/if_packet.h>
28 #include <linux/gfp.h>
30 #include <net/protocol.h>
31 #include <net/netlink.h>
32 #include <linux/skbuff.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>
90 /* No hurry in this branch */
91 static void *__load_pointer(struct sk_buff *skb, int k)
96 ptr = skb_network_header(skb) + k - SKF_NET_OFF;
97 else if (k >= SKF_LL_OFF)
98 ptr = skb_mac_header(skb) + k - SKF_LL_OFF;
100 if (ptr >= skb->head && ptr < skb_tail_pointer(skb))
105 static inline void *load_pointer(struct sk_buff *skb, int k,
106 unsigned int size, void *buffer)
109 return skb_header_pointer(skb, k, size, buffer);
113 return __load_pointer(skb, k);
118 * sk_filter - run a packet through a socket filter
119 * @sk: sock associated with &sk_buff
120 * @skb: buffer to filter
122 * Run the filter code and then cut skb->data to correct size returned by
123 * sk_run_filter. If pkt_len is 0 we toss packet. If skb->len is smaller
124 * than pkt_len we keep whole skb->data. This is the socket level
125 * wrapper to sk_run_filter. It returns 0 if the packet should
126 * be accepted or -EPERM if the packet should be tossed.
129 int sk_filter(struct sock *sk, struct sk_buff *skb)
132 struct sk_filter *filter;
134 err = security_sock_rcv_skb(sk, skb);
139 filter = rcu_dereference_bh(sk->sk_filter);
141 unsigned int pkt_len = sk_run_filter(skb, filter->insns);
143 err = pkt_len ? pskb_trim(skb, pkt_len) : -EPERM;
145 rcu_read_unlock_bh();
149 EXPORT_SYMBOL(sk_filter);
152 * sk_run_filter - run a filter on a socket
153 * @skb: buffer to run the filter on
154 * @filter: filter to apply
156 * Decode and apply filter instructions to the skb->data.
157 * Return length to keep, 0 for none. @skb is the data we are
158 * filtering, @filter is the array of filter instructions.
159 * Because all jumps are guaranteed to be before last instruction,
160 * and last instruction guaranteed to be a RET, we dont need to check
161 * flen. (We used to pass to this function the length of filter)
163 unsigned int sk_run_filter(struct sk_buff *skb, const struct sock_filter *fentry)
166 u32 A = 0; /* Accumulator */
167 u32 X = 0; /* Index Register */
168 u32 mem[BPF_MEMWORDS]; /* Scratch Memory Store */
169 unsigned long memvalid = 0;
173 BUILD_BUG_ON(BPF_MEMWORDS > BITS_PER_LONG);
175 * Process array of filter instructions.
178 #if defined(CONFIG_X86_32)
179 #define K (fentry->k)
181 const u32 K = fentry->k;
184 switch (fentry->code) {
185 case BPF_S_ALU_ADD_X:
188 case BPF_S_ALU_ADD_K:
191 case BPF_S_ALU_SUB_X:
194 case BPF_S_ALU_SUB_K:
197 case BPF_S_ALU_MUL_X:
200 case BPF_S_ALU_MUL_K:
203 case BPF_S_ALU_DIV_X:
208 case BPF_S_ALU_DIV_K:
209 A = reciprocal_divide(A, K);
211 case BPF_S_ALU_AND_X:
214 case BPF_S_ALU_AND_K:
223 case BPF_S_ALU_LSH_X:
226 case BPF_S_ALU_LSH_K:
229 case BPF_S_ALU_RSH_X:
232 case BPF_S_ALU_RSH_K:
241 case BPF_S_JMP_JGT_K:
242 fentry += (A > K) ? fentry->jt : fentry->jf;
244 case BPF_S_JMP_JGE_K:
245 fentry += (A >= K) ? fentry->jt : fentry->jf;
247 case BPF_S_JMP_JEQ_K:
248 fentry += (A == K) ? fentry->jt : fentry->jf;
250 case BPF_S_JMP_JSET_K:
251 fentry += (A & K) ? fentry->jt : fentry->jf;
253 case BPF_S_JMP_JGT_X:
254 fentry += (A > X) ? fentry->jt : fentry->jf;
256 case BPF_S_JMP_JGE_X:
257 fentry += (A >= X) ? fentry->jt : fentry->jf;
259 case BPF_S_JMP_JEQ_X:
260 fentry += (A == X) ? fentry->jt : fentry->jf;
262 case BPF_S_JMP_JSET_X:
263 fentry += (A & X) ? fentry->jt : fentry->jf;
268 ptr = load_pointer(skb, k, 4, &tmp);
270 A = get_unaligned_be32(ptr);
277 ptr = load_pointer(skb, k, 2, &tmp);
279 A = get_unaligned_be16(ptr);
286 ptr = load_pointer(skb, k, 1, &tmp);
295 case BPF_S_LDX_W_LEN:
307 case BPF_S_LDX_B_MSH:
308 ptr = load_pointer(skb, K, 1, &tmp);
310 X = (*(u8 *)ptr & 0xf) << 2;
321 A = (memvalid & (1UL << K)) ?
325 X = (memvalid & (1UL << K)) ?
339 memvalid |= 1UL << K;
343 memvalid |= 1UL << K;
352 * Handle ancillary data, which are impossible
353 * (or very difficult) to get parsing packet contents.
355 switch (k-SKF_AD_OFF) {
356 case SKF_AD_PROTOCOL:
357 A = ntohs(skb->protocol);
365 A = skb->dev->ifindex;
371 A = skb->queue_mapping;
382 A = raw_smp_processor_id();
384 case SKF_AD_NLATTR: {
387 if (skb_is_nonlinear(skb))
389 if (A > skb->len - sizeof(struct nlattr))
392 nla = nla_find((struct nlattr *)&skb->data[A],
395 A = (void *)nla - (void *)skb->data;
400 case SKF_AD_NLATTR_NEST: {
403 if (skb_is_nonlinear(skb))
405 if (A > skb->len - sizeof(struct nlattr))
408 nla = (struct nlattr *)&skb->data[A];
409 if (nla->nla_len > A - skb->len)
412 nla = nla_find_nested(nla, X);
414 A = (void *)nla - (void *)skb->data;
426 EXPORT_SYMBOL(sk_run_filter);
429 * sk_chk_filter - verify socket filter code
430 * @filter: filter to verify
431 * @flen: length of filter
433 * Check the user's filter code. If we let some ugly
434 * filter code slip through kaboom! The filter must contain
435 * no references or jumps that are out of range, no illegal
436 * instructions, and must end with a RET instruction.
438 * All jumps are forward as they are not signed.
440 * Returns 0 if the rule set is legal or -EINVAL if not.
442 int sk_chk_filter(struct sock_filter *filter, int flen)
445 * Valid instructions are initialized to non-0.
446 * Invalid instructions are initialized to 0.
448 static const u8 codes[] = {
449 [BPF_ALU|BPF_ADD|BPF_K] = BPF_S_ALU_ADD_K,
450 [BPF_ALU|BPF_ADD|BPF_X] = BPF_S_ALU_ADD_X,
451 [BPF_ALU|BPF_SUB|BPF_K] = BPF_S_ALU_SUB_K,
452 [BPF_ALU|BPF_SUB|BPF_X] = BPF_S_ALU_SUB_X,
453 [BPF_ALU|BPF_MUL|BPF_K] = BPF_S_ALU_MUL_K,
454 [BPF_ALU|BPF_MUL|BPF_X] = BPF_S_ALU_MUL_X,
455 [BPF_ALU|BPF_DIV|BPF_X] = BPF_S_ALU_DIV_X,
456 [BPF_ALU|BPF_AND|BPF_K] = BPF_S_ALU_AND_K,
457 [BPF_ALU|BPF_AND|BPF_X] = BPF_S_ALU_AND_X,
458 [BPF_ALU|BPF_OR|BPF_K] = BPF_S_ALU_OR_K,
459 [BPF_ALU|BPF_OR|BPF_X] = BPF_S_ALU_OR_X,
460 [BPF_ALU|BPF_LSH|BPF_K] = BPF_S_ALU_LSH_K,
461 [BPF_ALU|BPF_LSH|BPF_X] = BPF_S_ALU_LSH_X,
462 [BPF_ALU|BPF_RSH|BPF_K] = BPF_S_ALU_RSH_K,
463 [BPF_ALU|BPF_RSH|BPF_X] = BPF_S_ALU_RSH_X,
464 [BPF_ALU|BPF_NEG] = BPF_S_ALU_NEG,
465 [BPF_LD|BPF_W|BPF_ABS] = BPF_S_LD_W_ABS,
466 [BPF_LD|BPF_H|BPF_ABS] = BPF_S_LD_H_ABS,
467 [BPF_LD|BPF_B|BPF_ABS] = BPF_S_LD_B_ABS,
468 [BPF_LD|BPF_W|BPF_LEN] = BPF_S_LD_W_LEN,
469 [BPF_LD|BPF_W|BPF_IND] = BPF_S_LD_W_IND,
470 [BPF_LD|BPF_H|BPF_IND] = BPF_S_LD_H_IND,
471 [BPF_LD|BPF_B|BPF_IND] = BPF_S_LD_B_IND,
472 [BPF_LD|BPF_IMM] = BPF_S_LD_IMM,
473 [BPF_LDX|BPF_W|BPF_LEN] = BPF_S_LDX_W_LEN,
474 [BPF_LDX|BPF_B|BPF_MSH] = BPF_S_LDX_B_MSH,
475 [BPF_LDX|BPF_IMM] = BPF_S_LDX_IMM,
476 [BPF_MISC|BPF_TAX] = BPF_S_MISC_TAX,
477 [BPF_MISC|BPF_TXA] = BPF_S_MISC_TXA,
478 [BPF_RET|BPF_K] = BPF_S_RET_K,
479 [BPF_RET|BPF_A] = BPF_S_RET_A,
480 [BPF_ALU|BPF_DIV|BPF_K] = BPF_S_ALU_DIV_K,
481 [BPF_LD|BPF_MEM] = BPF_S_LD_MEM,
482 [BPF_LDX|BPF_MEM] = BPF_S_LDX_MEM,
484 [BPF_STX] = BPF_S_STX,
485 [BPF_JMP|BPF_JA] = BPF_S_JMP_JA,
486 [BPF_JMP|BPF_JEQ|BPF_K] = BPF_S_JMP_JEQ_K,
487 [BPF_JMP|BPF_JEQ|BPF_X] = BPF_S_JMP_JEQ_X,
488 [BPF_JMP|BPF_JGE|BPF_K] = BPF_S_JMP_JGE_K,
489 [BPF_JMP|BPF_JGE|BPF_X] = BPF_S_JMP_JGE_X,
490 [BPF_JMP|BPF_JGT|BPF_K] = BPF_S_JMP_JGT_K,
491 [BPF_JMP|BPF_JGT|BPF_X] = BPF_S_JMP_JGT_X,
492 [BPF_JMP|BPF_JSET|BPF_K] = BPF_S_JMP_JSET_K,
493 [BPF_JMP|BPF_JSET|BPF_X] = BPF_S_JMP_JSET_X,
497 if (flen == 0 || flen > BPF_MAXINSNS)
500 /* check the filter code now */
501 for (pc = 0; pc < flen; pc++) {
502 struct sock_filter *ftest = &filter[pc];
503 u16 code = ftest->code;
505 if (code >= ARRAY_SIZE(codes))
510 /* Some instructions need special checks */
512 case BPF_S_ALU_DIV_K:
513 /* check for division by zero */
516 ftest->k = reciprocal_value(ftest->k);
522 /* check for invalid memory addresses */
523 if (ftest->k >= BPF_MEMWORDS)
528 * Note, the large ftest->k might cause loops.
529 * Compare this with conditional jumps below,
530 * where offsets are limited. --ANK (981016)
532 if (ftest->k >= (unsigned)(flen-pc-1))
535 case BPF_S_JMP_JEQ_K:
536 case BPF_S_JMP_JEQ_X:
537 case BPF_S_JMP_JGE_K:
538 case BPF_S_JMP_JGE_X:
539 case BPF_S_JMP_JGT_K:
540 case BPF_S_JMP_JGT_X:
541 case BPF_S_JMP_JSET_X:
542 case BPF_S_JMP_JSET_K:
543 /* for conditionals both must be safe */
544 if (pc + ftest->jt + 1 >= flen ||
545 pc + ftest->jf + 1 >= flen)
552 /* last instruction must be a RET code */
553 switch (filter[flen - 1].code) {
560 EXPORT_SYMBOL(sk_chk_filter);
563 * sk_filter_rcu_release - Release a socket filter by rcu_head
564 * @rcu: rcu_head that contains the sk_filter to free
566 static void sk_filter_rcu_release(struct rcu_head *rcu)
568 struct sk_filter *fp = container_of(rcu, struct sk_filter, rcu);
570 sk_filter_release(fp);
573 static void sk_filter_delayed_uncharge(struct sock *sk, struct sk_filter *fp)
575 unsigned int size = sk_filter_len(fp);
577 atomic_sub(size, &sk->sk_omem_alloc);
578 call_rcu_bh(&fp->rcu, sk_filter_rcu_release);
582 * sk_attach_filter - attach a socket filter
583 * @fprog: the filter program
584 * @sk: the socket to use
586 * Attach the user's filter code. We first run some sanity checks on
587 * it to make sure it does not explode on us later. If an error
588 * occurs or there is insufficient memory for the filter a negative
589 * errno code is returned. On success the return is zero.
591 int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk)
593 struct sk_filter *fp, *old_fp;
594 unsigned int fsize = sizeof(struct sock_filter) * fprog->len;
597 /* Make sure new filter is there and in the right amounts. */
598 if (fprog->filter == NULL)
601 fp = sock_kmalloc(sk, fsize+sizeof(*fp), GFP_KERNEL);
604 if (copy_from_user(fp->insns, fprog->filter, fsize)) {
605 sock_kfree_s(sk, fp, fsize+sizeof(*fp));
609 atomic_set(&fp->refcnt, 1);
610 fp->len = fprog->len;
612 err = sk_chk_filter(fp->insns, fp->len);
614 sk_filter_uncharge(sk, fp);
618 old_fp = rcu_dereference_protected(sk->sk_filter,
619 sock_owned_by_user(sk));
620 rcu_assign_pointer(sk->sk_filter, fp);
623 sk_filter_delayed_uncharge(sk, old_fp);
626 EXPORT_SYMBOL_GPL(sk_attach_filter);
628 int sk_detach_filter(struct sock *sk)
631 struct sk_filter *filter;
633 filter = rcu_dereference_protected(sk->sk_filter,
634 sock_owned_by_user(sk));
636 rcu_assign_pointer(sk->sk_filter, NULL);
637 sk_filter_delayed_uncharge(sk, filter);
642 EXPORT_SYMBOL_GPL(sk_detach_filter);