3.14-stable review patch. If anyone has any objections, please let me know.
------------------
From: Mathias Krause <minipli@xxxxxxxxxxxxxx>
[ Upstream commit 05ab8f2647e4221cbdb3856dd7d32bd5407316b3 ]
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@xxxxxxxxx>
Cc: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
Signed-off-by: Mathias Krause <minipli@xxxxxxxxxxxxxx>
Acked-by: Daniel Borkmann <dborkman@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
net/core/filter.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -355,6 +355,8 @@ 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;
@@ -371,11 +373,13 @@ 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);
--
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