Vulnerability: The (1) BPF_S_ANC_NLATTR and (2) BPF_S_ANC_NLATTR_NEST extension implementations in the sk_run_filter function in net/core/filter.c in the Linux kernel through 3.14.3 do not check whether a certain length value is sufficiently large, which allows local users to cause a denial of service (integer underflow and system crash) via crafted BPF instructions.  NOTE: the affected code was moved to the __skb_get_nlattr and __skb_get_nlattr_nest functions before the vulnerability was announced.
Vulnerability ID: CVE-2014-3144
CWE: CWE-190
Severity score: 6.9
Project: https://github.com/torvalds/linux
Published: 2014-05-11
File: net/core/filter.c
Commit message: filter: prevent nla extensions to peek beyond the end of the message

The BPF_S_ANC_NLATTR and BPF_S_ANC_NLATTR_NEST extensions fail to check
for a minimal message length before testing the supplied offset to be
within the bounds of the message. This allows the subtraction of the nla
header to underflow and therefore -- as the data type is unsigned --
allowing far to big offset and length values for the search of the
netlink attribute.

The remainder calculation for the BPF_S_ANC_NLATTR_NEST extension is
also wrong. It has the minuend and subtrahend mixed up, therefore
calculates a huge length value, allowing to overrun the end of the
message while looking for the netlink attribute.

The following three BPF snippets will trigger the bugs when attached to
a UNIX datagram socket and parsing a message with length 1, 2 or 3.

 ,-[ PoC for missing size check in BPF_S_ANC_NLATTR ]--
 | ld	#0x87654321
 | ldx	#42
 | ld	#nla
 | ret	a
 `---

 ,-[ PoC for the same bug in BPF_S_ANC_NLATTR_NEST ]--
 | ld	#0x87654321
 | ldx	#42
 | ld	#nlan
 | ret	a
 `---

 ,-[ PoC for wrong remainder calculation in BPF_S_ANC_NLATTR_NEST ]--
 | ; (needs a fake netlink header at offset 0)
 | ld	#0
 | ldx	#42
 | ld	#nlan
 | ret	a
 `---

Fix the first issue by ensuring the message length fulfills the minimal
size constrains of a nla header. Fix the second bug by getting the math
for the remainder calculation right.

Fixes: 4738c1db15 ("[SKFILTER]: Add SKF_ADF_NLATTR instruction")
Fixes: d214c7537b ("filter: add SKF_AD_NLATTR_NEST to look for nested..")
Cc: Patrick McHardy <kaber@trash.net>
Cc: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Mathias Krause <minipli@googlemail.com>
Acked-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Commit author: Mathias Krause

Vulnerable version (before fix):
 static u64 __skb_get_nlattr(u64 ctx, u64 A, u64 X, u64 r4, u64 r5) 	if (skb_is_nonlinear(skb)) 		return 0;  	if (A > skb->len - sizeof(struct nlattr)) 		return 0;  static u64 __skb_get_nlattr_nest(u64 ctx, u64 A, u64 X, u64 r4, u64 r5) 	if (skb_is_nonlinear(skb)) 		return 0;  	if (A > skb->len - sizeof(struct nlattr)) 		return 0;  	nla = (struct nlattr *) &skb->data[A]; 	if (nla->nla_len > A - skb->len) 		return 0;  	nla = nla_find_nested(nla, X);

Fixed version (after fix):
 static u64 __skb_get_nlattr(u64 ctx, u64 A, u64 X, u64 r4, u64 r5) 	if (skb_is_nonlinear(skb)) 		return 0;  	if (skb->len < sizeof(struct nlattr)) 		return 0;  	if (A > skb->len - sizeof(struct nlattr)) 		return 0;  static u64 __skb_get_nlattr_nest(u64 ctx, u64 A, u64 X, u64 r4, u64 r5) 	if (skb_is_nonlinear(skb)) 		return 0;  	if (skb->len < sizeof(struct nlattr)) 		return 0;  	if (A > skb->len - sizeof(struct nlattr)) 		return 0;  	nla = (struct nlattr *) &skb->data[A]; 	if (nla->nla_len > skb->len - A) 		return 0;  	nla = nla_find_nested(nla, X);

Patch:
patch: @@ -600,6 +600,9 @@ static u64 __skb_get_nlattr(u64 ctx, u64 A, u64 X, u64 r4, u64 r5)
 	if (skb_is_nonlinear(skb))
 		return 0;
 
+	if (skb->len < sizeof(struct nlattr))
+		return 0;
+
 	if (A > skb->len - sizeof(struct nlattr))
 		return 0;
 
@@ -618,11 +621,14 @@ static u64 __skb_get_nlattr_nest(u64 ctx, u64 A, u64 X, u64 r4, u64 r5)
 	if (skb_is_nonlinear(skb))
 		return 0;
 
+	if (skb->len < sizeof(struct nlattr))
+		return 0;
+
 	if (A > skb->len - sizeof(struct nlattr))
 		return 0;
 
 	nla = (struct nlattr *) &skb->data[A];
-	if (nla->nla_len > A - skb->len)
+	if (nla->nla_len > skb->len - A)
 		return 0;
 
 	nla = nla_find_nested(nla, X);
path: net/core/filter.c