netdev - Re: [PATCH] netfilter: conntrack: death_by

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Date:	Fri, 19 Jun 2009 13:15:12 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	Ingo Molnar <mingo@...e.hu>, David Miller <davem@...emloft.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Pablo Neira Ayuso <pablo@...filter.org>
Subject: Re: [PATCH] netfilter: conntrack: death_by_timeout() fix

Eric Dumazet wrote:
> [PATCH] netfilter: conntrack: death_by_timeout() fix
> 
> death_by_timeout() might delete a conntrack from hash list
> and insert it in dying list.
> 
>  nf_ct_delete_from_lists(ct);
>  nf_ct_insert_dying_list(ct);
> 
> I believe a (lockless) reader could *catch* ct while doing a lookup 
> and miss the end of its chain.
> (nulls lookup algo must check the null value at the end of lookup and
> should restart if the null value is not the expected one.
> cf Documentation/RCU/rculist_nulls.txt for details)
> 
> We need to change nf_conntrack_init_net() and use a different "null" value,
> guaranteed not being used in regular lists. Choose very large values, since
> hash table uses [0..size-1] null values.

Applied, thanks Eric.
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