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filter: prevent nla extensions to peek beyond the end of the message

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[ Upstream commit 05ab8f2647 ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

CVE-2014-3145

Change-Id: Ib04d8987304986b206ef86d5158e9b8c5787cf55
(cherry picked from commit 314760e66c)
This commit is contained in:
Mathias Krause 2014-04-13 18:23:33 +02:00 committed by Sean McCreary
parent 401717e104
commit 69e670b2b5
1 changed files with 5 additions and 1 deletions
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6
net/core/filter.c
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@ -323,6 +323,8 @@ load_b:
if (skb_is_nonlinear(skb))
return 0;
if (skb->len < sizeof(struct nlattr))
return 0;
if (A > skb->len - sizeof(struct nlattr))
return 0;
@ -339,11 +341,13 @@ load_b:
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);