netdev - Re: [PATCH v3 -next 1/2] tcp: syncookies: reduce cookie lifetime to 128 seconds

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Message-Id: <20130924.104012.113351985998037405.davem@davemloft.net>
Date:	Tue, 24 Sep 2013 10:40:12 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	fw@...len.de
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH v3 -next 1/2] tcp: syncookies: reduce cookie lifetime
 to 128 seconds

From: Florian Westphal <fw@...len.de>
Date: Fri, 20 Sep 2013 22:32:55 +0200

> We currently accept cookies that were created less than 4 minutes ago
> (ie, cookies with counter delta 0-3).  Combined with the 8 mss table
> values, this yields 32 possible values (out of 2**32) that will be valid.
> 
> Reducing the lifetime to < 2 minutes halves the guessing chance while
> still providing a large enough period.
> 
> While at it, get rid of jiffies value -- they overflow too quickly on
> 32 bit platforms.
> 
> getnstimeofday is used to create a counter that increments every 64s.
> perf shows getnstimeofday cost is negible compared to sha_transform;
> normal tcp initial sequence number generation uses getnstimeofday, too.
> 
> Reported-by: Jakob Lell <jakob@...oblell.com>
> Signed-off-by: Florian Westphal <fw@...len.de>

Applied.
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