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>
41 /* No hurry in this branch */
42 static void *__load_pointer(struct sk_buff *skb, int k)
47 ptr = skb_network_header(skb) + k - SKF_NET_OFF;
48 else if (k >= SKF_LL_OFF)
49 ptr = skb_mac_header(skb) + k - SKF_LL_OFF;
51 if (ptr >= skb->head && ptr < skb_tail_pointer(skb))
56 static inline void *load_pointer(struct sk_buff *skb, int k,
57 unsigned int size, void *buffer)
60 return skb_header_pointer(skb, k, size, buffer);
64 return __load_pointer(skb, k);
69 * sk_filter - run a packet through a socket filter
70 * @sk: sock associated with &sk_buff
71 * @skb: buffer to filter
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.
80 int sk_filter(struct sock *sk, struct sk_buff *skb)
83 struct sk_filter *filter;
85 err = security_sock_rcv_skb(sk, skb);
90 filter = rcu_dereference_bh(sk->sk_filter);
92 unsigned int pkt_len = sk_run_filter(skb, filter->insns,
94 err = pkt_len ? pskb_trim(skb, pkt_len) : -EPERM;
100 EXPORT_SYMBOL(sk_filter);
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
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.
113 unsigned int sk_run_filter(struct sk_buff *skb, struct sock_filter *filter, int flen)
115 struct sock_filter *fentry; /* We walk down these */
117 u32 A = 0; /* Accumulator */
118 u32 X = 0; /* Index Register */
119 u32 mem[BPF_MEMWORDS]; /* Scratch Memory Store */
125 * Process array of filter instructions.
127 for (pc = 0; pc < flen; pc++) {
128 fentry = &filter[pc];
130 switch (fentry->code) {
131 case BPF_ALU|BPF_ADD|BPF_X:
134 case BPF_ALU|BPF_ADD|BPF_K:
137 case BPF_ALU|BPF_SUB|BPF_X:
140 case BPF_ALU|BPF_SUB|BPF_K:
143 case BPF_ALU|BPF_MUL|BPF_X:
146 case BPF_ALU|BPF_MUL|BPF_K:
149 case BPF_ALU|BPF_DIV|BPF_X:
154 case BPF_ALU|BPF_DIV|BPF_K:
157 case BPF_ALU|BPF_AND|BPF_X:
160 case BPF_ALU|BPF_AND|BPF_K:
163 case BPF_ALU|BPF_OR|BPF_X:
166 case BPF_ALU|BPF_OR|BPF_K:
169 case BPF_ALU|BPF_LSH|BPF_X:
172 case BPF_ALU|BPF_LSH|BPF_K:
175 case BPF_ALU|BPF_RSH|BPF_X:
178 case BPF_ALU|BPF_RSH|BPF_K:
181 case BPF_ALU|BPF_NEG:
187 case BPF_JMP|BPF_JGT|BPF_K:
188 pc += (A > fentry->k) ? fentry->jt : fentry->jf;
190 case BPF_JMP|BPF_JGE|BPF_K:
191 pc += (A >= fentry->k) ? fentry->jt : fentry->jf;
193 case BPF_JMP|BPF_JEQ|BPF_K:
194 pc += (A == fentry->k) ? fentry->jt : fentry->jf;
196 case BPF_JMP|BPF_JSET|BPF_K:
197 pc += (A & fentry->k) ? fentry->jt : fentry->jf;
199 case BPF_JMP|BPF_JGT|BPF_X:
200 pc += (A > X) ? fentry->jt : fentry->jf;
202 case BPF_JMP|BPF_JGE|BPF_X:
203 pc += (A >= X) ? fentry->jt : fentry->jf;
205 case BPF_JMP|BPF_JEQ|BPF_X:
206 pc += (A == X) ? fentry->jt : fentry->jf;
208 case BPF_JMP|BPF_JSET|BPF_X:
209 pc += (A & X) ? fentry->jt : fentry->jf;
211 case BPF_LD|BPF_W|BPF_ABS:
214 ptr = load_pointer(skb, k, 4, &tmp);
216 A = get_unaligned_be32(ptr);
220 case BPF_LD|BPF_H|BPF_ABS:
223 ptr = load_pointer(skb, k, 2, &tmp);
225 A = get_unaligned_be16(ptr);
229 case BPF_LD|BPF_B|BPF_ABS:
232 ptr = load_pointer(skb, k, 1, &tmp);
238 case BPF_LD|BPF_W|BPF_LEN:
241 case BPF_LDX|BPF_W|BPF_LEN:
244 case BPF_LD|BPF_W|BPF_IND:
247 case BPF_LD|BPF_H|BPF_IND:
250 case BPF_LD|BPF_B|BPF_IND:
253 case BPF_LDX|BPF_B|BPF_MSH:
254 ptr = load_pointer(skb, fentry->k, 1, &tmp);
256 X = (*(u8 *)ptr & 0xf) << 2;
263 case BPF_LDX|BPF_IMM:
269 case BPF_LDX|BPF_MEM:
272 case BPF_MISC|BPF_TAX:
275 case BPF_MISC|BPF_TXA:
294 * Handle ancillary data, which are impossible
295 * (or very difficult) to get parsing packet contents.
297 switch (k-SKF_AD_OFF) {
298 case SKF_AD_PROTOCOL:
299 A = ntohs(skb->protocol);
305 A = skb->dev->ifindex;
311 A = skb->queue_mapping;
313 case SKF_AD_NLATTR: {
316 if (skb_is_nonlinear(skb))
318 if (A > skb->len - sizeof(struct nlattr))
321 nla = nla_find((struct nlattr *)&skb->data[A],
324 A = (void *)nla - (void *)skb->data;
329 case SKF_AD_NLATTR_NEST: {
332 if (skb_is_nonlinear(skb))
334 if (A > skb->len - sizeof(struct nlattr))
337 nla = (struct nlattr *)&skb->data[A];
338 if (nla->nla_len > A - skb->len)
341 nla = nla_find_nested(nla, X);
343 A = (void *)nla - (void *)skb->data;
355 EXPORT_SYMBOL(sk_run_filter);
358 * sk_chk_filter - verify socket filter code
359 * @filter: filter to verify
360 * @flen: length of filter
362 * Check the user's filter code. If we let some ugly
363 * filter code slip through kaboom! The filter must contain
364 * no references or jumps that are out of range, no illegal
365 * instructions, and must end with a RET instruction.
367 * All jumps are forward as they are not signed.
369 * Returns 0 if the rule set is legal or -EINVAL if not.
371 int sk_chk_filter(struct sock_filter *filter, int flen)
373 struct sock_filter *ftest;
376 if (flen == 0 || flen > BPF_MAXINSNS)
379 /* check the filter code now */
380 for (pc = 0; pc < flen; pc++) {
383 /* Only allow valid instructions */
384 switch (ftest->code) {
385 case BPF_ALU|BPF_ADD|BPF_K:
386 case BPF_ALU|BPF_ADD|BPF_X:
387 case BPF_ALU|BPF_SUB|BPF_K:
388 case BPF_ALU|BPF_SUB|BPF_X:
389 case BPF_ALU|BPF_MUL|BPF_K:
390 case BPF_ALU|BPF_MUL|BPF_X:
391 case BPF_ALU|BPF_DIV|BPF_X:
392 case BPF_ALU|BPF_AND|BPF_K:
393 case BPF_ALU|BPF_AND|BPF_X:
394 case BPF_ALU|BPF_OR|BPF_K:
395 case BPF_ALU|BPF_OR|BPF_X:
396 case BPF_ALU|BPF_LSH|BPF_K:
397 case BPF_ALU|BPF_LSH|BPF_X:
398 case BPF_ALU|BPF_RSH|BPF_K:
399 case BPF_ALU|BPF_RSH|BPF_X:
400 case BPF_ALU|BPF_NEG:
401 case BPF_LD|BPF_W|BPF_ABS:
402 case BPF_LD|BPF_H|BPF_ABS:
403 case BPF_LD|BPF_B|BPF_ABS:
404 case BPF_LD|BPF_W|BPF_LEN:
405 case BPF_LD|BPF_W|BPF_IND:
406 case BPF_LD|BPF_H|BPF_IND:
407 case BPF_LD|BPF_B|BPF_IND:
409 case BPF_LDX|BPF_W|BPF_LEN:
410 case BPF_LDX|BPF_B|BPF_MSH:
411 case BPF_LDX|BPF_IMM:
412 case BPF_MISC|BPF_TAX:
413 case BPF_MISC|BPF_TXA:
418 /* Some instructions need special checks */
420 case BPF_ALU|BPF_DIV|BPF_K:
421 /* check for division by zero */
427 case BPF_LDX|BPF_MEM:
430 /* check for invalid memory addresses */
431 if (ftest->k >= BPF_MEMWORDS)
437 * Note, the large ftest->k might cause loops.
438 * Compare this with conditional jumps below,
439 * where offsets are limited. --ANK (981016)
441 if (ftest->k >= (unsigned)(flen-pc-1))
445 case BPF_JMP|BPF_JEQ|BPF_K:
446 case BPF_JMP|BPF_JEQ|BPF_X:
447 case BPF_JMP|BPF_JGE|BPF_K:
448 case BPF_JMP|BPF_JGE|BPF_X:
449 case BPF_JMP|BPF_JGT|BPF_K:
450 case BPF_JMP|BPF_JGT|BPF_X:
451 case BPF_JMP|BPF_JSET|BPF_K:
452 case BPF_JMP|BPF_JSET|BPF_X:
453 /* for conditionals both must be safe */
454 if (pc + ftest->jt + 1 >= flen ||
455 pc + ftest->jf + 1 >= flen)
464 return (BPF_CLASS(filter[flen - 1].code) == BPF_RET) ? 0 : -EINVAL;
466 EXPORT_SYMBOL(sk_chk_filter);
469 * sk_filter_rcu_release: Release a socket filter by rcu_head
470 * @rcu: rcu_head that contains the sk_filter to free
472 static void sk_filter_rcu_release(struct rcu_head *rcu)
474 struct sk_filter *fp = container_of(rcu, struct sk_filter, rcu);
476 sk_filter_release(fp);
479 static void sk_filter_delayed_uncharge(struct sock *sk, struct sk_filter *fp)
481 unsigned int size = sk_filter_len(fp);
483 atomic_sub(size, &sk->sk_omem_alloc);
484 call_rcu_bh(&fp->rcu, sk_filter_rcu_release);
488 * sk_attach_filter - attach a socket filter
489 * @fprog: the filter program
490 * @sk: the socket to use
492 * Attach the user's filter code. We first run some sanity checks on
493 * it to make sure it does not explode on us later. If an error
494 * occurs or there is insufficient memory for the filter a negative
495 * errno code is returned. On success the return is zero.
497 int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk)
499 struct sk_filter *fp, *old_fp;
500 unsigned int fsize = sizeof(struct sock_filter) * fprog->len;
503 /* Make sure new filter is there and in the right amounts. */
504 if (fprog->filter == NULL)
507 fp = sock_kmalloc(sk, fsize+sizeof(*fp), GFP_KERNEL);
510 if (copy_from_user(fp->insns, fprog->filter, fsize)) {
511 sock_kfree_s(sk, fp, fsize+sizeof(*fp));
515 atomic_set(&fp->refcnt, 1);
516 fp->len = fprog->len;
518 err = sk_chk_filter(fp->insns, fp->len);
520 sk_filter_uncharge(sk, fp);
525 old_fp = rcu_dereference_bh(sk->sk_filter);
526 rcu_assign_pointer(sk->sk_filter, fp);
527 rcu_read_unlock_bh();
530 sk_filter_delayed_uncharge(sk, old_fp);
533 EXPORT_SYMBOL_GPL(sk_attach_filter);
535 int sk_detach_filter(struct sock *sk)
538 struct sk_filter *filter;
541 filter = rcu_dereference_bh(sk->sk_filter);
543 rcu_assign_pointer(sk->sk_filter, NULL);
544 sk_filter_delayed_uncharge(sk, filter);
547 rcu_read_unlock_bh();
550 EXPORT_SYMBOL_GPL(sk_detach_filter);