netdev - Re: [PATCH net] ipv6: remove max_addresses check from ipv6_create

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Date:	Tue, 20 Aug 2013 00:12:10 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	hannes@...essinduktion.org
Cc:	netdev@...r.kernel.org, dingtianhong@...wei.com, kargig@...d.gr,
	ppandit@...hat.com, yoshfuji@...ux-ipv6.org
Subject: Re: [PATCH net] ipv6: remove max_addresses check from
 ipv6_create_tempaddr

From: Hannes Frederic Sowa <hannes@...essinduktion.org>
Date: Fri, 16 Aug 2013 13:02:27 +0200

> Because of the max_addresses check attackers were able to disable privacy
> extensions on an interface by creating enough autoconfigured addresses:
> 
> <http://seclists.org/oss-sec/2012/q4/292>
> 
> But the check is not actually needed: max_addresses protects the
> kernel to install too many ipv6 addresses on an interface and guards
> addrconf_prefix_rcv to install further addresses as soon as this limit
> is reached. We only generate temporary addresses in direct response of
> a new address showing up. As soon as we filled up the maximum number of
> addresses of an interface, we stop installing more addresses and thus
> also stop generating more temp addresses.
> 
> Even if the attacker tries to generate a lot of temporary addresses
> by announcing a prefix and removing it again (lifetime == 0) we won't
> install more temp addresses, because the temporary addresses do count
> to the maximum number of addresses, thus we would stop installing new
> autoconfigured addresses when the limit is reached.
> 
> This patch fixes CVE-2013-0343 (but other layer-2 attacks are still
> possible).
> 
> Thanks to Ding Tianhong to bring this topic up again.
> 
> Cc: Ding Tianhong <dingtianhong@...wei.com>
> Cc: George Kargiotakis <kargig@...d.gr>
> Cc: P J P <ppandit@...hat.com>
> Cc: YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org>
> Signed-off-by: Hannes Frederic Sowa <hannes@...essinduktion.org>

Applied and queued up for -stable, thanks.
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