CVE-2014-3144 (published 2014-05-11T21:55Z)

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.

Severity: MEDIUM
CVSS v2 base score: 4.9 (AV:L/AC:L/Au:N/C:N/I:N/A:C)

Weakness information:
cwe_id: CWE-190
cwe_name: Integer Overflow or Wraparound
description: The product performs a calculation that can
         produce an integer overflow or wraparound when the logic
         assumes that the resulting value will always be larger than
         the original value. This occurs when an integer value is
         incremented to a value that is too large to store in the
         associated representation. When this occurs, the value may
         become a very small or negative number.
extended_description: 
            
            
            
            
         
         

Fix information:
repo_url: https://github.com/torvalds/linux
commit_details: repo_url: https://github.com/torvalds/linux
author: Mathias Krause
author_date: 2014-04-13 18:23:33+02:00
msg: 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>
repository: repo_url: https://github.com/torvalds/linux
repo_name: torvalds/linux
description: Linux kernel source tree
repo_language: C
owner: torvalds
file_changes: filename: filter.c
change_type: ModificationType.MODIFY
diff: @@ -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);

programming_language: C