netdev - Re: x25: remote-triggerable heap overflow in call user data processing

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Date:	Mon, 3 Oct 2011 17:51:53 +1100
From:	Andrew Hendry <andrew.hendry@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	matt d <mattjd@...il.com>, netdev@...r.kernel.org
Subject: Re: x25: remote-triggerable heap overflow in call user data processing

x25_in.c looks straightforward.
with af_x25.c we might want to move the incoming call user data check
before the call accept block above.
Otherwise it could send call accept/call clear right next to each
other and it might get bad state

On Mon, Oct 3, 2011 at 4:45 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> Le lundi 03 octobre 2011 à 16:23 +1300, matt d a écrit :
>> Refer to the x25 packet layer's handling of incoming call user data,
>> namely at these two locations, in x25_rx_call_request and
>> x25_state1_machine:
>> https://github.com/mirrors/linux/blob/master/net/x25/af_x25.c#L1039
>> https://github.com/mirrors/linux/blob/master/net/x25/x25_in.c#L126
>>
>> Call user data from an incoming message is copied into
>> (make)x25->calluserdata.cuddata buffers, which are 128 bytes long.
>> However, the length copied is based on the remaining message length,
>> and is not limited to the output buffer size. This allows a remote
>> attacker to overflow data onto the heap.
>>
>> There is an appropriate constant defined for the length, but it
>> seemingly isn't used there:
>> https://github.com/mirrors/linux/blob/master/include/net/x25.h#L104
>>
>> It seems this issue was noticed some time ago:
>> http://www.spinics.net/lists/linux-x25/msg00043.html
>> http://patchwork.ozlabs.org/patch/23917/
>> ...however nothing was done about the bigger problem.
>>
>> I have written a simple exploit for this vulnerability if it needs to
>> be posted, however I think the problem is pretty straightforward to
>> see as-is.
>
> Please send a patch, it seems you have everything done to do it
> properly ;)
>
>
>
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