linux-kernel - Re: [PATCH net v2] tcp: prevent fetching dst twice in early demux code

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Message-Id: <20150323.223946.1369598595861439895.davem@davemloft.net>
Date:	Mon, 23 Mar 2015 22:39:46 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	mkubecek@...e.cz
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	edumazet@...gle.com, kuznet@....inr.ac.ru, jmorris@...ei.org,
	yoshfuji@...ux-ipv6.org, kaber@...sh.net
Subject: Re: [PATCH net v2] tcp: prevent fetching dst twice in early demux
 code

From: Michal Kubecek <mkubecek@...e.cz>
Date: Mon, 23 Mar 2015 15:14:00 +0100 (CET)

> On s390x, gcc 4.8 compiles this part of tcp_v6_early_demux()
> 
>         struct dst_entry *dst = sk->sk_rx_dst;
> 
>         if (dst)
>                 dst = dst_check(dst, inet6_sk(sk)->rx_dst_cookie);
> 
> to code reading sk->sk_rx_dst twice, once for the test and once for
> the argument of ip6_dst_check() (dst_check() is inline). This allows
> ip6_dst_check() to be called with null first argument, causing a crash.
> 
> Protect sk->sk_rx_dst access by READ_ONCE() both in IPv4 and IPv6
> TCP early demux code.
> 
> Fixes: 41063e9dd119 ("ipv4: Early TCP socket demux.")
> Fixes: c7109986db3c ("ipv6: Early TCP socket demux")
> Signed-off-by: Michal Kubecek <mkubecek@...e.cz>

Applied and queued up for -stable.
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