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>
93 BPF_S_ANC_NLATTR_NEST
,
101 /* No hurry in this branch */
102 static void *__load_pointer(const struct sk_buff
*skb
, int k
, unsigned int size
)
106 if (k
>= SKF_NET_OFF
)
107 ptr
= skb_network_header(skb
) + k
- SKF_NET_OFF
;
108 else if (k
>= SKF_LL_OFF
)
109 ptr
= skb_mac_header(skb
) + k
- SKF_LL_OFF
;
111 if (ptr
>= skb
->head
&& ptr
+ size
<= skb_tail_pointer(skb
))
116 static inline void *load_pointer(const struct sk_buff
*skb
, int k
,
117 unsigned int size
, void *buffer
)
120 return skb_header_pointer(skb
, k
, size
, buffer
);
121 return __load_pointer(skb
, k
, size
);
125 * sk_filter - run a packet through a socket filter
126 * @sk: sock associated with &sk_buff
127 * @skb: buffer to filter
129 * Run the filter code and then cut skb->data to correct size returned by
130 * sk_run_filter. If pkt_len is 0 we toss packet. If skb->len is smaller
131 * than pkt_len we keep whole skb->data. This is the socket level
132 * wrapper to sk_run_filter. It returns 0 if the packet should
133 * be accepted or -EPERM if the packet should be tossed.
136 int sk_filter(struct sock
*sk
, struct sk_buff
*skb
)
139 struct sk_filter
*filter
;
141 err
= security_sock_rcv_skb(sk
, skb
);
146 filter
= rcu_dereference_bh(sk
->sk_filter
);
148 unsigned int pkt_len
= sk_run_filter(skb
, filter
->insns
);
150 err
= pkt_len
? pskb_trim(skb
, pkt_len
) : -EPERM
;
152 rcu_read_unlock_bh();
156 EXPORT_SYMBOL(sk_filter
);
159 * sk_run_filter - run a filter on a socket
160 * @skb: buffer to run the filter on
161 * @fentry: filter to apply
163 * Decode and apply filter instructions to the skb->data.
164 * Return length to keep, 0 for none. @skb is the data we are
165 * filtering, @filter is the array of filter instructions.
166 * Because all jumps are guaranteed to be before last instruction,
167 * and last instruction guaranteed to be a RET, we dont need to check
168 * flen. (We used to pass to this function the length of filter)
170 unsigned int sk_run_filter(const struct sk_buff
*skb
,
171 const struct sock_filter
*fentry
)
174 u32 A
= 0; /* Accumulator */
175 u32 X
= 0; /* Index Register */
176 u32 mem
[BPF_MEMWORDS
]; /* Scratch Memory Store */
181 * Process array of filter instructions.
184 #if defined(CONFIG_X86_32)
185 #define K (fentry->k)
187 const u32 K
= fentry
->k
;
190 switch (fentry
->code
) {
191 case BPF_S_ALU_ADD_X
:
194 case BPF_S_ALU_ADD_K
:
197 case BPF_S_ALU_SUB_X
:
200 case BPF_S_ALU_SUB_K
:
203 case BPF_S_ALU_MUL_X
:
206 case BPF_S_ALU_MUL_K
:
209 case BPF_S_ALU_DIV_X
:
214 case BPF_S_ALU_DIV_K
:
215 A
= reciprocal_divide(A
, K
);
217 case BPF_S_ALU_AND_X
:
220 case BPF_S_ALU_AND_K
:
229 case BPF_S_ALU_LSH_X
:
232 case BPF_S_ALU_LSH_K
:
235 case BPF_S_ALU_RSH_X
:
238 case BPF_S_ALU_RSH_K
:
247 case BPF_S_JMP_JGT_K
:
248 fentry
+= (A
> K
) ? fentry
->jt
: fentry
->jf
;
250 case BPF_S_JMP_JGE_K
:
251 fentry
+= (A
>= K
) ? fentry
->jt
: fentry
->jf
;
253 case BPF_S_JMP_JEQ_K
:
254 fentry
+= (A
== K
) ? fentry
->jt
: fentry
->jf
;
256 case BPF_S_JMP_JSET_K
:
257 fentry
+= (A
& K
) ? fentry
->jt
: fentry
->jf
;
259 case BPF_S_JMP_JGT_X
:
260 fentry
+= (A
> X
) ? fentry
->jt
: fentry
->jf
;
262 case BPF_S_JMP_JGE_X
:
263 fentry
+= (A
>= X
) ? fentry
->jt
: fentry
->jf
;
265 case BPF_S_JMP_JEQ_X
:
266 fentry
+= (A
== X
) ? fentry
->jt
: fentry
->jf
;
268 case BPF_S_JMP_JSET_X
:
269 fentry
+= (A
& X
) ? fentry
->jt
: fentry
->jf
;
274 ptr
= load_pointer(skb
, k
, 4, &tmp
);
276 A
= get_unaligned_be32(ptr
);
283 ptr
= load_pointer(skb
, k
, 2, &tmp
);
285 A
= get_unaligned_be16(ptr
);
292 ptr
= load_pointer(skb
, k
, 1, &tmp
);
301 case BPF_S_LDX_W_LEN
:
313 case BPF_S_LDX_B_MSH
:
314 ptr
= load_pointer(skb
, K
, 1, &tmp
);
316 X
= (*(u8
*)ptr
& 0xf) << 2;
348 case BPF_S_ANC_PROTOCOL
:
349 A
= ntohs(skb
->protocol
);
351 case BPF_S_ANC_PKTTYPE
:
354 case BPF_S_ANC_IFINDEX
:
357 A
= skb
->dev
->ifindex
;
362 case BPF_S_ANC_QUEUE
:
363 A
= skb
->queue_mapping
;
365 case BPF_S_ANC_HATYPE
:
370 case BPF_S_ANC_RXHASH
:
374 A
= raw_smp_processor_id();
376 case BPF_S_ANC_NLATTR
: {
379 if (skb_is_nonlinear(skb
))
381 if (A
> skb
->len
- sizeof(struct nlattr
))
384 nla
= nla_find((struct nlattr
*)&skb
->data
[A
],
387 A
= (void *)nla
- (void *)skb
->data
;
392 case BPF_S_ANC_NLATTR_NEST
: {
395 if (skb_is_nonlinear(skb
))
397 if (A
> skb
->len
- sizeof(struct nlattr
))
400 nla
= (struct nlattr
*)&skb
->data
[A
];
401 if (nla
->nla_len
> A
- skb
->len
)
404 nla
= nla_find_nested(nla
, X
);
406 A
= (void *)nla
- (void *)skb
->data
;
419 EXPORT_SYMBOL(sk_run_filter
);
423 * A BPF program is able to use 16 cells of memory to store intermediate
424 * values (check u32 mem[BPF_MEMWORDS] in sk_run_filter())
425 * As we dont want to clear mem[] array for each packet going through
426 * sk_run_filter(), we check that filter loaded by user never try to read
427 * a cell if not previously written, and we check all branches to be sure
428 * a malicious user doesnt try to abuse us.
430 static int check_load_and_stores(struct sock_filter
*filter
, int flen
)
432 u16
*masks
, memvalid
= 0; /* one bit per cell, 16 cells */
435 BUILD_BUG_ON(BPF_MEMWORDS
> 16);
436 masks
= kmalloc(flen
* sizeof(*masks
), GFP_KERNEL
);
439 memset(masks
, 0xff, flen
* sizeof(*masks
));
441 for (pc
= 0; pc
< flen
; pc
++) {
442 memvalid
&= masks
[pc
];
444 switch (filter
[pc
].code
) {
447 memvalid
|= (1 << filter
[pc
].k
);
451 if (!(memvalid
& (1 << filter
[pc
].k
))) {
457 /* a jump must set masks on target */
458 masks
[pc
+ 1 + filter
[pc
].k
] &= memvalid
;
461 case BPF_S_JMP_JEQ_K
:
462 case BPF_S_JMP_JEQ_X
:
463 case BPF_S_JMP_JGE_K
:
464 case BPF_S_JMP_JGE_X
:
465 case BPF_S_JMP_JGT_K
:
466 case BPF_S_JMP_JGT_X
:
467 case BPF_S_JMP_JSET_X
:
468 case BPF_S_JMP_JSET_K
:
469 /* a jump must set masks on targets */
470 masks
[pc
+ 1 + filter
[pc
].jt
] &= memvalid
;
471 masks
[pc
+ 1 + filter
[pc
].jf
] &= memvalid
;
482 * sk_chk_filter - verify socket filter code
483 * @filter: filter to verify
484 * @flen: length of filter
486 * Check the user's filter code. If we let some ugly
487 * filter code slip through kaboom! The filter must contain
488 * no references or jumps that are out of range, no illegal
489 * instructions, and must end with a RET instruction.
491 * All jumps are forward as they are not signed.
493 * Returns 0 if the rule set is legal or -EINVAL if not.
495 int sk_chk_filter(struct sock_filter
*filter
, int flen
)
498 * Valid instructions are initialized to non-0.
499 * Invalid instructions are initialized to 0.
501 static const u8 codes
[] = {
502 [BPF_ALU
|BPF_ADD
|BPF_K
] = BPF_S_ALU_ADD_K
,
503 [BPF_ALU
|BPF_ADD
|BPF_X
] = BPF_S_ALU_ADD_X
,
504 [BPF_ALU
|BPF_SUB
|BPF_K
] = BPF_S_ALU_SUB_K
,
505 [BPF_ALU
|BPF_SUB
|BPF_X
] = BPF_S_ALU_SUB_X
,
506 [BPF_ALU
|BPF_MUL
|BPF_K
] = BPF_S_ALU_MUL_K
,
507 [BPF_ALU
|BPF_MUL
|BPF_X
] = BPF_S_ALU_MUL_X
,
508 [BPF_ALU
|BPF_DIV
|BPF_X
] = BPF_S_ALU_DIV_X
,
509 [BPF_ALU
|BPF_AND
|BPF_K
] = BPF_S_ALU_AND_K
,
510 [BPF_ALU
|BPF_AND
|BPF_X
] = BPF_S_ALU_AND_X
,
511 [BPF_ALU
|BPF_OR
|BPF_K
] = BPF_S_ALU_OR_K
,
512 [BPF_ALU
|BPF_OR
|BPF_X
] = BPF_S_ALU_OR_X
,
513 [BPF_ALU
|BPF_LSH
|BPF_K
] = BPF_S_ALU_LSH_K
,
514 [BPF_ALU
|BPF_LSH
|BPF_X
] = BPF_S_ALU_LSH_X
,
515 [BPF_ALU
|BPF_RSH
|BPF_K
] = BPF_S_ALU_RSH_K
,
516 [BPF_ALU
|BPF_RSH
|BPF_X
] = BPF_S_ALU_RSH_X
,
517 [BPF_ALU
|BPF_NEG
] = BPF_S_ALU_NEG
,
518 [BPF_LD
|BPF_W
|BPF_ABS
] = BPF_S_LD_W_ABS
,
519 [BPF_LD
|BPF_H
|BPF_ABS
] = BPF_S_LD_H_ABS
,
520 [BPF_LD
|BPF_B
|BPF_ABS
] = BPF_S_LD_B_ABS
,
521 [BPF_LD
|BPF_W
|BPF_LEN
] = BPF_S_LD_W_LEN
,
522 [BPF_LD
|BPF_W
|BPF_IND
] = BPF_S_LD_W_IND
,
523 [BPF_LD
|BPF_H
|BPF_IND
] = BPF_S_LD_H_IND
,
524 [BPF_LD
|BPF_B
|BPF_IND
] = BPF_S_LD_B_IND
,
525 [BPF_LD
|BPF_IMM
] = BPF_S_LD_IMM
,
526 [BPF_LDX
|BPF_W
|BPF_LEN
] = BPF_S_LDX_W_LEN
,
527 [BPF_LDX
|BPF_B
|BPF_MSH
] = BPF_S_LDX_B_MSH
,
528 [BPF_LDX
|BPF_IMM
] = BPF_S_LDX_IMM
,
529 [BPF_MISC
|BPF_TAX
] = BPF_S_MISC_TAX
,
530 [BPF_MISC
|BPF_TXA
] = BPF_S_MISC_TXA
,
531 [BPF_RET
|BPF_K
] = BPF_S_RET_K
,
532 [BPF_RET
|BPF_A
] = BPF_S_RET_A
,
533 [BPF_ALU
|BPF_DIV
|BPF_K
] = BPF_S_ALU_DIV_K
,
534 [BPF_LD
|BPF_MEM
] = BPF_S_LD_MEM
,
535 [BPF_LDX
|BPF_MEM
] = BPF_S_LDX_MEM
,
537 [BPF_STX
] = BPF_S_STX
,
538 [BPF_JMP
|BPF_JA
] = BPF_S_JMP_JA
,
539 [BPF_JMP
|BPF_JEQ
|BPF_K
] = BPF_S_JMP_JEQ_K
,
540 [BPF_JMP
|BPF_JEQ
|BPF_X
] = BPF_S_JMP_JEQ_X
,
541 [BPF_JMP
|BPF_JGE
|BPF_K
] = BPF_S_JMP_JGE_K
,
542 [BPF_JMP
|BPF_JGE
|BPF_X
] = BPF_S_JMP_JGE_X
,
543 [BPF_JMP
|BPF_JGT
|BPF_K
] = BPF_S_JMP_JGT_K
,
544 [BPF_JMP
|BPF_JGT
|BPF_X
] = BPF_S_JMP_JGT_X
,
545 [BPF_JMP
|BPF_JSET
|BPF_K
] = BPF_S_JMP_JSET_K
,
546 [BPF_JMP
|BPF_JSET
|BPF_X
] = BPF_S_JMP_JSET_X
,
550 if (flen
== 0 || flen
> BPF_MAXINSNS
)
553 /* check the filter code now */
554 for (pc
= 0; pc
< flen
; pc
++) {
555 struct sock_filter
*ftest
= &filter
[pc
];
556 u16 code
= ftest
->code
;
558 if (code
>= ARRAY_SIZE(codes
))
563 /* Some instructions need special checks */
565 case BPF_S_ALU_DIV_K
:
566 /* check for division by zero */
569 ftest
->k
= reciprocal_value(ftest
->k
);
575 /* check for invalid memory addresses */
576 if (ftest
->k
>= BPF_MEMWORDS
)
581 * Note, the large ftest->k might cause loops.
582 * Compare this with conditional jumps below,
583 * where offsets are limited. --ANK (981016)
585 if (ftest
->k
>= (unsigned)(flen
-pc
-1))
588 case BPF_S_JMP_JEQ_K
:
589 case BPF_S_JMP_JEQ_X
:
590 case BPF_S_JMP_JGE_K
:
591 case BPF_S_JMP_JGE_X
:
592 case BPF_S_JMP_JGT_K
:
593 case BPF_S_JMP_JGT_X
:
594 case BPF_S_JMP_JSET_X
:
595 case BPF_S_JMP_JSET_K
:
596 /* for conditionals both must be safe */
597 if (pc
+ ftest
->jt
+ 1 >= flen
||
598 pc
+ ftest
->jf
+ 1 >= flen
)
604 #define ANCILLARY(CODE) case SKF_AD_OFF + SKF_AD_##CODE: \
605 code = BPF_S_ANC_##CODE; \
612 ANCILLARY(NLATTR_NEST
);
623 /* last instruction must be a RET code */
624 switch (filter
[flen
- 1].code
) {
627 return check_load_and_stores(filter
, flen
);
631 EXPORT_SYMBOL(sk_chk_filter
);
634 * sk_filter_release_rcu - Release a socket filter by rcu_head
635 * @rcu: rcu_head that contains the sk_filter to free
637 void sk_filter_release_rcu(struct rcu_head
*rcu
)
639 struct sk_filter
*fp
= container_of(rcu
, struct sk_filter
, rcu
);
643 EXPORT_SYMBOL(sk_filter_release_rcu
);
646 * sk_attach_filter - attach a socket filter
647 * @fprog: the filter program
648 * @sk: the socket to use
650 * Attach the user's filter code. We first run some sanity checks on
651 * it to make sure it does not explode on us later. If an error
652 * occurs or there is insufficient memory for the filter a negative
653 * errno code is returned. On success the return is zero.
655 int sk_attach_filter(struct sock_fprog
*fprog
, struct sock
*sk
)
657 struct sk_filter
*fp
, *old_fp
;
658 unsigned int fsize
= sizeof(struct sock_filter
) * fprog
->len
;
661 /* Make sure new filter is there and in the right amounts. */
662 if (fprog
->filter
== NULL
)
665 fp
= sock_kmalloc(sk
, fsize
+sizeof(*fp
), GFP_KERNEL
);
668 if (copy_from_user(fp
->insns
, fprog
->filter
, fsize
)) {
669 sock_kfree_s(sk
, fp
, fsize
+sizeof(*fp
));
673 atomic_set(&fp
->refcnt
, 1);
674 fp
->len
= fprog
->len
;
676 err
= sk_chk_filter(fp
->insns
, fp
->len
);
678 sk_filter_uncharge(sk
, fp
);
682 old_fp
= rcu_dereference_protected(sk
->sk_filter
,
683 sock_owned_by_user(sk
));
684 rcu_assign_pointer(sk
->sk_filter
, fp
);
687 sk_filter_uncharge(sk
, old_fp
);
690 EXPORT_SYMBOL_GPL(sk_attach_filter
);
692 int sk_detach_filter(struct sock
*sk
)
695 struct sk_filter
*filter
;
697 filter
= rcu_dereference_protected(sk
->sk_filter
,
698 sock_owned_by_user(sk
));
700 rcu_assign_pointer(sk
->sk_filter
, NULL
);
701 sk_filter_uncharge(sk
, filter
);
706 EXPORT_SYMBOL_GPL(sk_detach_filter
);