netdev - Re: [PATCH net-next] tcp/dccp: fix hashdance race for passive sessions

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Message-Id: <20151023.054306.857450545092417631.davem@davemloft.net>
Date:	Fri, 23 Oct 2015 05:43:06 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH net-next] tcp/dccp: fix hashdance race for passive
 sessions

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Thu, 22 Oct 2015 08:20:46 -0700

> From: Eric Dumazet <edumazet@...gle.com>
> 
> Multiple cpus can process duplicates of incoming ACK messages
> matching a SYN_RECV request socket. This is a rare event under
> normal operations, but definitely can happen.
> 
> Only one must win the race, otherwise corruption would occur.
> 
> To fix this without adding new atomic ops, we use logic in
> inet_ehash_nolisten() to detect the request was present in the same
> ehash bucket where we try to insert the new child.
> 
> If request socket was not found, we have to undo the child creation. 
> 
> This actually removes a spin_lock()/spin_unlock() pair in
> reqsk_queue_unlink() for the fast path.
> 
> Fixes: e994b2f0fb92 ("tcp: do not lock listener to process SYN packets")
> Fixes: 079096f103fa ("tcp/dccp: install syn_recv requests into ehash table")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Applied, thanks.
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