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>
41 #include <linux/ratelimit.h>
43 /* No hurry in this branch */
44 static void *__load_pointer(const struct sk_buff
*skb
, int k
, unsigned int size
)
49 ptr
= skb_network_header(skb
) + k
- SKF_NET_OFF
;
50 else if (k
>= SKF_LL_OFF
)
51 ptr
= skb_mac_header(skb
) + k
- SKF_LL_OFF
;
53 if (ptr
>= skb
->head
&& ptr
+ size
<= skb_tail_pointer(skb
))
58 static inline void *load_pointer(const struct sk_buff
*skb
, int k
,
59 unsigned int size
, void *buffer
)
62 return skb_header_pointer(skb
, k
, size
, buffer
);
63 return __load_pointer(skb
, k
, size
);
67 * sk_filter - run a packet through a socket filter
68 * @sk: sock associated with &sk_buff
69 * @skb: buffer to filter
71 * Run the filter code and then cut skb->data to correct size returned by
72 * sk_run_filter. If pkt_len is 0 we toss packet. If skb->len is smaller
73 * than pkt_len we keep whole skb->data. This is the socket level
74 * wrapper to sk_run_filter. It returns 0 if the packet should
75 * be accepted or -EPERM if the packet should be tossed.
78 int sk_filter(struct sock
*sk
, struct sk_buff
*skb
)
81 struct sk_filter
*filter
;
83 err
= security_sock_rcv_skb(sk
, skb
);
88 filter
= rcu_dereference(sk
->sk_filter
);
90 unsigned int pkt_len
= SK_RUN_FILTER(filter
, skb
);
92 err
= pkt_len
? pskb_trim(skb
, pkt_len
) : -EPERM
;
98 EXPORT_SYMBOL(sk_filter
);
101 * sk_run_filter - run a filter on a socket
102 * @skb: buffer to run the filter on
103 * @fentry: filter to apply
105 * Decode and apply filter instructions to the skb->data.
106 * Return length to keep, 0 for none. @skb is the data we are
107 * filtering, @filter is the array of filter instructions.
108 * Because all jumps are guaranteed to be before last instruction,
109 * and last instruction guaranteed to be a RET, we dont need to check
110 * flen. (We used to pass to this function the length of filter)
112 unsigned int sk_run_filter(const struct sk_buff
*skb
,
113 const struct sock_filter
*fentry
)
116 u32 A
= 0; /* Accumulator */
117 u32 X
= 0; /* Index Register */
118 u32 mem
[BPF_MEMWORDS
]; /* Scratch Memory Store */
123 * Process array of filter instructions.
126 #if defined(CONFIG_X86_32)
127 #define K (fentry->k)
129 const u32 K
= fentry
->k
;
132 switch (fentry
->code
) {
133 case BPF_S_ALU_ADD_X
:
136 case BPF_S_ALU_ADD_K
:
139 case BPF_S_ALU_SUB_X
:
142 case BPF_S_ALU_SUB_K
:
145 case BPF_S_ALU_MUL_X
:
148 case BPF_S_ALU_MUL_K
:
151 case BPF_S_ALU_DIV_X
:
156 case BPF_S_ALU_DIV_K
:
157 A
= reciprocal_divide(A
, K
);
159 case BPF_S_ALU_AND_X
:
162 case BPF_S_ALU_AND_K
:
171 case BPF_S_ALU_LSH_X
:
174 case BPF_S_ALU_LSH_K
:
177 case BPF_S_ALU_RSH_X
:
180 case BPF_S_ALU_RSH_K
:
189 case BPF_S_JMP_JGT_K
:
190 fentry
+= (A
> K
) ? fentry
->jt
: fentry
->jf
;
192 case BPF_S_JMP_JGE_K
:
193 fentry
+= (A
>= K
) ? fentry
->jt
: fentry
->jf
;
195 case BPF_S_JMP_JEQ_K
:
196 fentry
+= (A
== K
) ? fentry
->jt
: fentry
->jf
;
198 case BPF_S_JMP_JSET_K
:
199 fentry
+= (A
& K
) ? fentry
->jt
: fentry
->jf
;
201 case BPF_S_JMP_JGT_X
:
202 fentry
+= (A
> X
) ? fentry
->jt
: fentry
->jf
;
204 case BPF_S_JMP_JGE_X
:
205 fentry
+= (A
>= X
) ? fentry
->jt
: fentry
->jf
;
207 case BPF_S_JMP_JEQ_X
:
208 fentry
+= (A
== X
) ? fentry
->jt
: fentry
->jf
;
210 case BPF_S_JMP_JSET_X
:
211 fentry
+= (A
& X
) ? fentry
->jt
: fentry
->jf
;
216 ptr
= load_pointer(skb
, k
, 4, &tmp
);
218 A
= get_unaligned_be32(ptr
);
225 ptr
= load_pointer(skb
, k
, 2, &tmp
);
227 A
= get_unaligned_be16(ptr
);
234 ptr
= load_pointer(skb
, k
, 1, &tmp
);
243 case BPF_S_LDX_W_LEN
:
255 case BPF_S_LDX_B_MSH
:
256 ptr
= load_pointer(skb
, K
, 1, &tmp
);
258 X
= (*(u8
*)ptr
& 0xf) << 2;
290 case BPF_S_ANC_PROTOCOL
:
291 A
= ntohs(skb
->protocol
);
293 case BPF_S_ANC_PKTTYPE
:
296 case BPF_S_ANC_IFINDEX
:
299 A
= skb
->dev
->ifindex
;
304 case BPF_S_ANC_QUEUE
:
305 A
= skb
->queue_mapping
;
307 case BPF_S_ANC_HATYPE
:
312 case BPF_S_ANC_RXHASH
:
316 A
= raw_smp_processor_id();
318 case BPF_S_ANC_NLATTR
: {
321 if (skb_is_nonlinear(skb
))
323 if (A
> skb
->len
- sizeof(struct nlattr
))
326 nla
= nla_find((struct nlattr
*)&skb
->data
[A
],
329 A
= (void *)nla
- (void *)skb
->data
;
334 case BPF_S_ANC_NLATTR_NEST
: {
337 if (skb_is_nonlinear(skb
))
339 if (A
> skb
->len
- sizeof(struct nlattr
))
342 nla
= (struct nlattr
*)&skb
->data
[A
];
343 if (nla
->nla_len
> A
- skb
->len
)
346 nla
= nla_find_nested(nla
, X
);
348 A
= (void *)nla
- (void *)skb
->data
;
354 WARN_RATELIMIT(1, "Unknown code:%u jt:%u tf:%u k:%u\n",
355 fentry
->code
, fentry
->jt
,
356 fentry
->jf
, fentry
->k
);
363 EXPORT_SYMBOL(sk_run_filter
);
367 * A BPF program is able to use 16 cells of memory to store intermediate
368 * values (check u32 mem[BPF_MEMWORDS] in sk_run_filter())
369 * As we dont want to clear mem[] array for each packet going through
370 * sk_run_filter(), we check that filter loaded by user never try to read
371 * a cell if not previously written, and we check all branches to be sure
372 * a malicious user doesn't try to abuse us.
374 static int check_load_and_stores(struct sock_filter
*filter
, int flen
)
376 u16
*masks
, memvalid
= 0; /* one bit per cell, 16 cells */
379 BUILD_BUG_ON(BPF_MEMWORDS
> 16);
380 masks
= kmalloc(flen
* sizeof(*masks
), GFP_KERNEL
);
383 memset(masks
, 0xff, flen
* sizeof(*masks
));
385 for (pc
= 0; pc
< flen
; pc
++) {
386 memvalid
&= masks
[pc
];
388 switch (filter
[pc
].code
) {
391 memvalid
|= (1 << filter
[pc
].k
);
395 if (!(memvalid
& (1 << filter
[pc
].k
))) {
401 /* a jump must set masks on target */
402 masks
[pc
+ 1 + filter
[pc
].k
] &= memvalid
;
405 case BPF_S_JMP_JEQ_K
:
406 case BPF_S_JMP_JEQ_X
:
407 case BPF_S_JMP_JGE_K
:
408 case BPF_S_JMP_JGE_X
:
409 case BPF_S_JMP_JGT_K
:
410 case BPF_S_JMP_JGT_X
:
411 case BPF_S_JMP_JSET_X
:
412 case BPF_S_JMP_JSET_K
:
413 /* a jump must set masks on targets */
414 masks
[pc
+ 1 + filter
[pc
].jt
] &= memvalid
;
415 masks
[pc
+ 1 + filter
[pc
].jf
] &= memvalid
;
426 * sk_chk_filter - verify socket filter code
427 * @filter: filter to verify
428 * @flen: length of filter
430 * Check the user's filter code. If we let some ugly
431 * filter code slip through kaboom! The filter must contain
432 * no references or jumps that are out of range, no illegal
433 * instructions, and must end with a RET instruction.
435 * All jumps are forward as they are not signed.
437 * Returns 0 if the rule set is legal or -EINVAL if not.
439 int sk_chk_filter(struct sock_filter
*filter
, int flen
)
442 * Valid instructions are initialized to non-0.
443 * Invalid instructions are initialized to 0.
445 static const u8 codes
[] = {
446 [BPF_ALU
|BPF_ADD
|BPF_K
] = BPF_S_ALU_ADD_K
,
447 [BPF_ALU
|BPF_ADD
|BPF_X
] = BPF_S_ALU_ADD_X
,
448 [BPF_ALU
|BPF_SUB
|BPF_K
] = BPF_S_ALU_SUB_K
,
449 [BPF_ALU
|BPF_SUB
|BPF_X
] = BPF_S_ALU_SUB_X
,
450 [BPF_ALU
|BPF_MUL
|BPF_K
] = BPF_S_ALU_MUL_K
,
451 [BPF_ALU
|BPF_MUL
|BPF_X
] = BPF_S_ALU_MUL_X
,
452 [BPF_ALU
|BPF_DIV
|BPF_X
] = BPF_S_ALU_DIV_X
,
453 [BPF_ALU
|BPF_AND
|BPF_K
] = BPF_S_ALU_AND_K
,
454 [BPF_ALU
|BPF_AND
|BPF_X
] = BPF_S_ALU_AND_X
,
455 [BPF_ALU
|BPF_OR
|BPF_K
] = BPF_S_ALU_OR_K
,
456 [BPF_ALU
|BPF_OR
|BPF_X
] = BPF_S_ALU_OR_X
,
457 [BPF_ALU
|BPF_LSH
|BPF_K
] = BPF_S_ALU_LSH_K
,
458 [BPF_ALU
|BPF_LSH
|BPF_X
] = BPF_S_ALU_LSH_X
,
459 [BPF_ALU
|BPF_RSH
|BPF_K
] = BPF_S_ALU_RSH_K
,
460 [BPF_ALU
|BPF_RSH
|BPF_X
] = BPF_S_ALU_RSH_X
,
461 [BPF_ALU
|BPF_NEG
] = BPF_S_ALU_NEG
,
462 [BPF_LD
|BPF_W
|BPF_ABS
] = BPF_S_LD_W_ABS
,
463 [BPF_LD
|BPF_H
|BPF_ABS
] = BPF_S_LD_H_ABS
,
464 [BPF_LD
|BPF_B
|BPF_ABS
] = BPF_S_LD_B_ABS
,
465 [BPF_LD
|BPF_W
|BPF_LEN
] = BPF_S_LD_W_LEN
,
466 [BPF_LD
|BPF_W
|BPF_IND
] = BPF_S_LD_W_IND
,
467 [BPF_LD
|BPF_H
|BPF_IND
] = BPF_S_LD_H_IND
,
468 [BPF_LD
|BPF_B
|BPF_IND
] = BPF_S_LD_B_IND
,
469 [BPF_LD
|BPF_IMM
] = BPF_S_LD_IMM
,
470 [BPF_LDX
|BPF_W
|BPF_LEN
] = BPF_S_LDX_W_LEN
,
471 [BPF_LDX
|BPF_B
|BPF_MSH
] = BPF_S_LDX_B_MSH
,
472 [BPF_LDX
|BPF_IMM
] = BPF_S_LDX_IMM
,
473 [BPF_MISC
|BPF_TAX
] = BPF_S_MISC_TAX
,
474 [BPF_MISC
|BPF_TXA
] = BPF_S_MISC_TXA
,
475 [BPF_RET
|BPF_K
] = BPF_S_RET_K
,
476 [BPF_RET
|BPF_A
] = BPF_S_RET_A
,
477 [BPF_ALU
|BPF_DIV
|BPF_K
] = BPF_S_ALU_DIV_K
,
478 [BPF_LD
|BPF_MEM
] = BPF_S_LD_MEM
,
479 [BPF_LDX
|BPF_MEM
] = BPF_S_LDX_MEM
,
481 [BPF_STX
] = BPF_S_STX
,
482 [BPF_JMP
|BPF_JA
] = BPF_S_JMP_JA
,
483 [BPF_JMP
|BPF_JEQ
|BPF_K
] = BPF_S_JMP_JEQ_K
,
484 [BPF_JMP
|BPF_JEQ
|BPF_X
] = BPF_S_JMP_JEQ_X
,
485 [BPF_JMP
|BPF_JGE
|BPF_K
] = BPF_S_JMP_JGE_K
,
486 [BPF_JMP
|BPF_JGE
|BPF_X
] = BPF_S_JMP_JGE_X
,
487 [BPF_JMP
|BPF_JGT
|BPF_K
] = BPF_S_JMP_JGT_K
,
488 [BPF_JMP
|BPF_JGT
|BPF_X
] = BPF_S_JMP_JGT_X
,
489 [BPF_JMP
|BPF_JSET
|BPF_K
] = BPF_S_JMP_JSET_K
,
490 [BPF_JMP
|BPF_JSET
|BPF_X
] = BPF_S_JMP_JSET_X
,
494 if (flen
== 0 || flen
> BPF_MAXINSNS
)
497 /* check the filter code now */
498 for (pc
= 0; pc
< flen
; pc
++) {
499 struct sock_filter
*ftest
= &filter
[pc
];
500 u16 code
= ftest
->code
;
502 if (code
>= ARRAY_SIZE(codes
))
507 /* Some instructions need special checks */
509 case BPF_S_ALU_DIV_K
:
510 /* check for division by zero */
513 ftest
->k
= reciprocal_value(ftest
->k
);
519 /* check for invalid memory addresses */
520 if (ftest
->k
>= BPF_MEMWORDS
)
525 * Note, the large ftest->k might cause loops.
526 * Compare this with conditional jumps below,
527 * where offsets are limited. --ANK (981016)
529 if (ftest
->k
>= (unsigned)(flen
-pc
-1))
532 case BPF_S_JMP_JEQ_K
:
533 case BPF_S_JMP_JEQ_X
:
534 case BPF_S_JMP_JGE_K
:
535 case BPF_S_JMP_JGE_X
:
536 case BPF_S_JMP_JGT_K
:
537 case BPF_S_JMP_JGT_X
:
538 case BPF_S_JMP_JSET_X
:
539 case BPF_S_JMP_JSET_K
:
540 /* for conditionals both must be safe */
541 if (pc
+ ftest
->jt
+ 1 >= flen
||
542 pc
+ ftest
->jf
+ 1 >= flen
)
548 #define ANCILLARY(CODE) case SKF_AD_OFF + SKF_AD_##CODE: \
549 code = BPF_S_ANC_##CODE; \
556 ANCILLARY(NLATTR_NEST
);
567 /* last instruction must be a RET code */
568 switch (filter
[flen
- 1].code
) {
571 return check_load_and_stores(filter
, flen
);
575 EXPORT_SYMBOL(sk_chk_filter
);
578 * sk_filter_release_rcu - Release a socket filter by rcu_head
579 * @rcu: rcu_head that contains the sk_filter to free
581 void sk_filter_release_rcu(struct rcu_head
*rcu
)
583 struct sk_filter
*fp
= container_of(rcu
, struct sk_filter
, rcu
);
588 EXPORT_SYMBOL(sk_filter_release_rcu
);
591 * sk_attach_filter - attach a socket filter
592 * @fprog: the filter program
593 * @sk: the socket to use
595 * Attach the user's filter code. We first run some sanity checks on
596 * it to make sure it does not explode on us later. If an error
597 * occurs or there is insufficient memory for the filter a negative
598 * errno code is returned. On success the return is zero.
600 int sk_attach_filter(struct sock_fprog
*fprog
, struct sock
*sk
)
602 struct sk_filter
*fp
, *old_fp
;
603 unsigned int fsize
= sizeof(struct sock_filter
) * fprog
->len
;
606 /* Make sure new filter is there and in the right amounts. */
607 if (fprog
->filter
== NULL
)
610 fp
= sock_kmalloc(sk
, fsize
+sizeof(*fp
), GFP_KERNEL
);
613 if (copy_from_user(fp
->insns
, fprog
->filter
, fsize
)) {
614 sock_kfree_s(sk
, fp
, fsize
+sizeof(*fp
));
618 atomic_set(&fp
->refcnt
, 1);
619 fp
->len
= fprog
->len
;
620 fp
->bpf_func
= sk_run_filter
;
622 err
= sk_chk_filter(fp
->insns
, fp
->len
);
624 sk_filter_uncharge(sk
, fp
);
630 old_fp
= rcu_dereference_protected(sk
->sk_filter
,
631 sock_owned_by_user(sk
));
632 rcu_assign_pointer(sk
->sk_filter
, fp
);
635 sk_filter_uncharge(sk
, old_fp
);
638 EXPORT_SYMBOL_GPL(sk_attach_filter
);
640 int sk_detach_filter(struct sock
*sk
)
643 struct sk_filter
*filter
;
645 filter
= rcu_dereference_protected(sk
->sk_filter
,
646 sock_owned_by_user(sk
));
648 rcu_assign_pointer(sk
->sk_filter
, NULL
);
649 sk_filter_uncharge(sk
, filter
);
654 EXPORT_SYMBOL_GPL(sk_detach_filter
);