netdev - Re: [PATCH net-next] tcp: syncookies: extend validity range

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Message-Id: <20150514.223321.1648157993009055494.davem@davemloft.net>
Date:	Thu, 14 May 2015 22:33:21 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org, fw@...len.de, ncardwell@...gle.com,
	ycheng@...gle.com
Subject: Re: [PATCH net-next] tcp: syncookies: extend validity range

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Thu, 14 May 2015 14:26:56 -0700

> From: Eric Dumazet <edumazet@...gle.com>
> 
> Now we allow storing more request socks per listener, we might
> hit syncookie mode less often and hit following bug in our stack :
> 
> When we send a burst of syncookies, then exit this mode,
> tcp_synq_no_recent_overflow() can return false if the ACK packets coming
> from clients are coming three seconds after the end of syncookie
> episode.
> 
> This is a way too strong requirement and conflicts with rest of
> syncookie code which allows ACK to be aged up to 2 minutes.
> 
> Perfectly valid ACK packets are dropped just because clients might be
> in a crowded wifi environment or on another planet.
> 
> So let's fix this, and also change tcp_synq_overflow() to not
> dirty a cache line for every syncookie we send, as we are under attack.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Applied, thanks.
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