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

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Message-ID: <20150514214544.GF6179@breakpoint.cc>
Date:	Thu, 14 May 2015 23:45:44 +0200
From:	Florian Westphal <fw@...len.de>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>, Florian Westphal <fw@...len.de>,
	Neal Cardwell <ncardwell@...gle.com>,
	Yuchung Cheng <ycheng@...gle.com>
Subject: Re: [PATCH net-next] tcp: syncookies: extend validity range

Eric Dumazet <eric.dumazet@...il.com> wrote:
> 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.

Heh.  Indeed.  This dates back to original from 1997...

> 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>
> ---
> As this is an old bug, I chose net-next tree.

Looks great, thanks Eric!

Acked-by: Florian Westphal <fw@...len.de>
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