netdev - Re: [PATCH net] ip: make IP identifiers less predictable

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Date:	Fri, 25 Jul 2014 20:09:11 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jeffrey Knockel <jeffk@...unm.edu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	"Jedidiah R. Crandall" <crandall@...unm.edu>,
	Willy Tarreau <w@....eu>,
	"security@...nel.org" <security@...nel.org>
Subject: Re: [PATCH net] ip: make IP identifiers less predictable

On Fri, 2014-07-25 at 09:55 -0600, Jeffrey Knockel wrote:

> So my thoughts in a nutshell:  I believe that this proposed patch solves
> the original problem of attackers being able to infer the value of
> counters via a side-channel.  However, in the post-73f156a6e8c1 world,
> there's also a new problem which we might care about too where we have
> an attacker who controls a large number of addresses.  This patch also
> happens to help with this problem too, but maybe not enough, depending
> on how sophisticated of an attacker we want to protect against.

What do you mean by "an attacker who controls a large number of
addresses" ?

The hash(daddr) -> slot function is not known, as we use a Jenkin hash
with a secret ( ip_idents_hashrnd & ip6_idents_hashrnd )

We might change the hash to use both daddr & saddr to increase
protection.

pre-73f156a6e8c1 was horrible, because it was easy to fill inetpeer
table to force a garbage collection. Then when an ID was needed for a
peer that had been evicted, we started again from a fixed base ID
( secure_ip_id() )

Thanks.


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