netdev - Re: [BUG] null pointer dereference in tcp_gso

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Date:	Wed, 22 Jan 2014 23:02:49 +0100
From:	arno@...isbad.org (Arnaud Ebalard)
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Daniel Borkmann <dborkman@...hat.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Willy Tarreau <w@....eu>, netdev@...r.kernel.org
Subject: Re: [BUG] null pointer dereference in tcp_gso_segment()

Hi Eric,

Eric Dumazet <eric.dumazet@...il.com> writes:

>> Unless there is an assumption I missed somewhere in the function, the
>> problem may occur during the first round of the loop, because (unlike
>> the 'while' condition does at line 21) skb->next is not checked against
>> null at lines 17 above before it is passed to tcp_hdr() at line 18.
>> 
>> To be honest, I am asking because I am not familiar w/ the code and it
>> is somewhat old so I wonder why noone got hit before. AFAICT,
>> f4c50d990dcf ([NET]: Add software TSOv4) added TSOv4 support in 2006 via
>> introduction of tcp_tso_segmen() (with the same kind of deref but
>> possibly different assumptions) which was more recently modified via
>> 28850dc7c7 (net: tcp: move GRO/GSO functions to tcp_offload) to become
>> tcp_gso_segment().
>> 
>> David, can you confirm the analysis and possibly comment on the
>> conditions needed for the bug to manifest?
>
> A gso packet contains at least 2 segments.

By whom / where is it enforced?

Cheers,

a+


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