netdev - Re: [PATCH 1/1] neighbour: Fixed race condition at tbl->nht

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Message-Id: <20120221.162905.83071433719723123.davem@davemloft.net>
Date:	Tue, 21 Feb 2012 16:29:05 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	michel@...irati.com.br, netdev@...r.kernel.org
Subject: Re: [PATCH 1/1] neighbour: Fixed race condition at tbl->nht

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Tue, 21 Feb 2012 22:25:22 +0100

> Le mardi 21 février 2012 à 16:04 -0500, Michel Machado a écrit :
>> When the fixed race condition happens:
>> 
>> 1. While function neigh_periodic_work scans the neighbor hash table
>> pointed by field tbl->nht, it unlocks and locks tbl->lock between
>> buckets in order to call cond_resched.
>> 
>> 2. Assume that function neigh_periodic_work calls cond_resched, that is,
>> the lock tbl->lock is available, and function neigh_hash_grow runs.
>> 
>> 3. Once function neigh_hash_grow finishes, and RCU calls
>> neigh_hash_free_rcu, the original struct neigh_hash_table that function
>> neigh_periodic_work was using doesn't exist anymore.
>> 
>> 4. Once back at neigh_periodic_work, whenever the old struct
>> neigh_hash_table is accessed, things can go badly.
>> 
>> Signed-off-by: Michel Machado <michel@...irati.com.br>
 ...
> Nice catch !
> 
> Bug introduced in 2.6.37 in commit d6bf781712a (net neigh: RCU
> conversion of neigh hash table)
> 
> Acked-by: Eric Dumazet <eric.dumazet@...il.com>

Applied, and queued up for -stable, thanks.
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