netdev - Re: [PATCH 1/3] [RFC] TCP syncookies: slow down timer to mitigate spoofing attacks

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Message-ID: <20130816214706.GF5154@breakpoint.cc>
Date:	Fri, 16 Aug 2013 23:47:06 +0200
From:	Florian Westphal <fw@...len.de>
To:	Jiri Bohac <jbohac@...e.cz>
Cc:	Jakob Lell <jakob@...oblell.com>, netdev@...r.kernel.org,
	davem@...emloft.net
Subject: Re: [PATCH 1/3] [RFC] TCP syncookies: slow down timer to mitigate
 spoofing attacks

Jiri Bohac <jbohac@...e.cz> wrote:
> This patch slows down the timer used in syncookies from 1/60 Hz to 1/60/4 Hz
> so that at any moment only two differrent timer values can be accepted.
> As a result, 1 bit of sequence number entropy is gained.
> 
> This changes the maximum cookie age limit from 4 - 5 minutes to 4 - 8 minutes.

I think we should just cap at 2 minutes (i.e, accept 0 and 1 minute delta).

A cookie is not validated if the last syn overflow is more than 3
seconds in the past anyway.
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