Re: [PATCH 3.4 022/214] filter: prevent nla extensions to peek beyond the end of the message

[Mathias Krause]

On 5 June 2014 15:33, Luis Henriques <luis.henriques@xxxxxxxxxxxxx> wrote:
> On Wed, Jun 04, 2014 at 09:16:25PM -0700, Greg Kroah-Hartman wrote:
>> 3.4-stable review patch.  If anyone has any objections, please let me know.
>> [...]
>> --- a/net/core/filter.c
>> +++ b/net/core/filter.c
>> @@ -338,11 +338,15 @@ load_b:
>>
>>                       if (skb_is_nonlinear(skb))
>>                               return 0;
>> +                     if (skb->len < sizeof(struct nlattr))
>> +                             return 0;
>> +                     if (skb->len < sizeof(struct nlattr))
>> +                             return 0;
>
> There above code is duplicated this backport.  The same comment
> applies to the 3.2.y backport (I've added Ben to the CC list).
>

Good catch! The diff should look more like the the one in the
attachment. I guess patch(1) just failed here to find the right place
to apply the hunk to.

Thanks,
Mathias
diff --git a/net/core/filter.c b/net/core/filter.c
index 6f755cc..3b7398a 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -322,6 +322,8 @@ 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;
 
@@ -338,11 +340,13 @@ 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);