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>
29 #include <net/protocol.h>
30 #include <net/netlink.h>
31 #include <linux/skbuff.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>
40 /* No hurry in this branch */
41 static void *__load_pointer(struct sk_buff
*skb
, int k
)
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
;
50 if (ptr
>= skb
->head
&& ptr
< skb_tail_pointer(skb
))
55 static inline void *load_pointer(struct sk_buff
*skb
, int k
,
56 unsigned int size
, void *buffer
)
59 return skb_header_pointer(skb
, k
, size
, buffer
);
63 return __load_pointer(skb
, k
);
68 * sk_filter - run a packet through a socket filter
69 * @sk: sock associated with &sk_buff
70 * @skb: buffer to filter
71 * @needlock: set to 1 if the sock is not locked by caller.
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(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
= ntohl(get_unaligned((__be32
*)ptr
));
220 case BPF_LD
|BPF_H
|BPF_ABS
:
223 ptr
= load_pointer(skb
, k
, 2, &tmp
);
225 A
= ntohs(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
;
307 case SKF_AD_NLATTR
: {
310 if (skb_is_nonlinear(skb
))
312 if (A
> skb
->len
- sizeof(struct nlattr
))
315 nla
= nla_find((struct nlattr
*)&skb
->data
[A
],
318 A
= (void *)nla
- (void *)skb
->data
;
330 EXPORT_SYMBOL(sk_run_filter
);
333 * sk_chk_filter - verify socket filter code
334 * @filter: filter to verify
335 * @flen: length of filter
337 * Check the user's filter code. If we let some ugly
338 * filter code slip through kaboom! The filter must contain
339 * no references or jumps that are out of range, no illegal
340 * instructions, and must end with a RET instruction.
342 * All jumps are forward as they are not signed.
344 * Returns 0 if the rule set is legal or -EINVAL if not.
346 int sk_chk_filter(struct sock_filter
*filter
, int flen
)
348 struct sock_filter
*ftest
;
351 if (flen
== 0 || flen
> BPF_MAXINSNS
)
354 /* check the filter code now */
355 for (pc
= 0; pc
< flen
; pc
++) {
358 /* Only allow valid instructions */
359 switch (ftest
->code
) {
360 case BPF_ALU
|BPF_ADD
|BPF_K
:
361 case BPF_ALU
|BPF_ADD
|BPF_X
:
362 case BPF_ALU
|BPF_SUB
|BPF_K
:
363 case BPF_ALU
|BPF_SUB
|BPF_X
:
364 case BPF_ALU
|BPF_MUL
|BPF_K
:
365 case BPF_ALU
|BPF_MUL
|BPF_X
:
366 case BPF_ALU
|BPF_DIV
|BPF_X
:
367 case BPF_ALU
|BPF_AND
|BPF_K
:
368 case BPF_ALU
|BPF_AND
|BPF_X
:
369 case BPF_ALU
|BPF_OR
|BPF_K
:
370 case BPF_ALU
|BPF_OR
|BPF_X
:
371 case BPF_ALU
|BPF_LSH
|BPF_K
:
372 case BPF_ALU
|BPF_LSH
|BPF_X
:
373 case BPF_ALU
|BPF_RSH
|BPF_K
:
374 case BPF_ALU
|BPF_RSH
|BPF_X
:
375 case BPF_ALU
|BPF_NEG
:
376 case BPF_LD
|BPF_W
|BPF_ABS
:
377 case BPF_LD
|BPF_H
|BPF_ABS
:
378 case BPF_LD
|BPF_B
|BPF_ABS
:
379 case BPF_LD
|BPF_W
|BPF_LEN
:
380 case BPF_LD
|BPF_W
|BPF_IND
:
381 case BPF_LD
|BPF_H
|BPF_IND
:
382 case BPF_LD
|BPF_B
|BPF_IND
:
384 case BPF_LDX
|BPF_W
|BPF_LEN
:
385 case BPF_LDX
|BPF_B
|BPF_MSH
:
386 case BPF_LDX
|BPF_IMM
:
387 case BPF_MISC
|BPF_TAX
:
388 case BPF_MISC
|BPF_TXA
:
393 /* Some instructions need special checks */
395 case BPF_ALU
|BPF_DIV
|BPF_K
:
396 /* check for division by zero */
402 case BPF_LDX
|BPF_MEM
:
405 /* check for invalid memory addresses */
406 if (ftest
->k
>= BPF_MEMWORDS
)
412 * Note, the large ftest->k might cause loops.
413 * Compare this with conditional jumps below,
414 * where offsets are limited. --ANK (981016)
416 if (ftest
->k
>= (unsigned)(flen
-pc
-1))
420 case BPF_JMP
|BPF_JEQ
|BPF_K
:
421 case BPF_JMP
|BPF_JEQ
|BPF_X
:
422 case BPF_JMP
|BPF_JGE
|BPF_K
:
423 case BPF_JMP
|BPF_JGE
|BPF_X
:
424 case BPF_JMP
|BPF_JGT
|BPF_K
:
425 case BPF_JMP
|BPF_JGT
|BPF_X
:
426 case BPF_JMP
|BPF_JSET
|BPF_K
:
427 case BPF_JMP
|BPF_JSET
|BPF_X
:
428 /* for conditionals both must be safe */
429 if (pc
+ ftest
->jt
+ 1 >= flen
||
430 pc
+ ftest
->jf
+ 1 >= flen
)
439 return (BPF_CLASS(filter
[flen
- 1].code
) == BPF_RET
) ? 0 : -EINVAL
;
441 EXPORT_SYMBOL(sk_chk_filter
);
444 * sk_filter_rcu_release: Release a socket filter by rcu_head
445 * @rcu: rcu_head that contains the sk_filter to free
447 static void sk_filter_rcu_release(struct rcu_head
*rcu
)
449 struct sk_filter
*fp
= container_of(rcu
, struct sk_filter
, rcu
);
451 sk_filter_release(fp
);
454 static void sk_filter_delayed_uncharge(struct sock
*sk
, struct sk_filter
*fp
)
456 unsigned int size
= sk_filter_len(fp
);
458 atomic_sub(size
, &sk
->sk_omem_alloc
);
459 call_rcu_bh(&fp
->rcu
, sk_filter_rcu_release
);
463 * sk_attach_filter - attach a socket filter
464 * @fprog: the filter program
465 * @sk: the socket to use
467 * Attach the user's filter code. We first run some sanity checks on
468 * it to make sure it does not explode on us later. If an error
469 * occurs or there is insufficient memory for the filter a negative
470 * errno code is returned. On success the return is zero.
472 int sk_attach_filter(struct sock_fprog
*fprog
, struct sock
*sk
)
474 struct sk_filter
*fp
, *old_fp
;
475 unsigned int fsize
= sizeof(struct sock_filter
) * fprog
->len
;
478 /* Make sure new filter is there and in the right amounts. */
479 if (fprog
->filter
== NULL
)
482 fp
= sock_kmalloc(sk
, fsize
+sizeof(*fp
), GFP_KERNEL
);
485 if (copy_from_user(fp
->insns
, fprog
->filter
, fsize
)) {
486 sock_kfree_s(sk
, fp
, fsize
+sizeof(*fp
));
490 atomic_set(&fp
->refcnt
, 1);
491 fp
->len
= fprog
->len
;
493 err
= sk_chk_filter(fp
->insns
, fp
->len
);
495 sk_filter_uncharge(sk
, fp
);
500 old_fp
= rcu_dereference(sk
->sk_filter
);
501 rcu_assign_pointer(sk
->sk_filter
, fp
);
502 rcu_read_unlock_bh();
505 sk_filter_delayed_uncharge(sk
, old_fp
);
509 int sk_detach_filter(struct sock
*sk
)
512 struct sk_filter
*filter
;
515 filter
= rcu_dereference(sk
->sk_filter
);
517 rcu_assign_pointer(sk
->sk_filter
, NULL
);
518 sk_filter_delayed_uncharge(sk
, filter
);
521 rcu_read_unlock_bh();