netdev - Re: [PATCH net] net: ipv6: tcp: fix potential use after free in tcp_v6_do

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Message-Id: <20130904.145704.1474150306960456668.davem@davemloft.net>
Date:	Wed, 04 Sep 2013 14:57:04 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	dborkman@...hat.com
Cc:	netdev@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH net] net: ipv6: tcp: fix potential use after free in
 tcp_v6_do_rcv

From: Daniel Borkmann <dborkman@...hat.com>
Date: Tue,  3 Sep 2013 19:29:12 +0200

> In tcp_v6_do_rcv() code, when processing pkt options, we soley work
> on our skb clone opt_skb that we've created earlier before entering
> tcp_rcv_established() on our way. However, only in condition ...
> 
>   if (np->rxopt.bits.rxtclass)
>     np->rcv_tclass = ipv6_get_dsfield(ipv6_hdr(skb));
> 
> ... we work on skb itself. As we extract every other information out
> of opt_skb in ipv6_pktoptions path, this seems wrong, since skb can
> already be released by tcp_rcv_established() earlier on. When we try
> to access it in ipv6_hdr(), we will dereference freed skb.
> 
> Signed-off-by: Daniel Borkmann <dborkman@...hat.com>
> Cc: Eric Dumazet <eric.dumazet@...il.com>

Applied.
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