netdev - Re: [PATCH 1/2] net: Toeplitz library functions

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Message-ID: <20130924160014.GA26769@order.stressinduktion.org>
Date:	Tue, 24 Sep 2013 18:00:14 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Tom Herbert <therbert@...gle.com>
Cc:	David Miller <davem@...hat.com>,
	David Laight <David.Laight@...lab.com>,
	Linux Netdev List <netdev@...r.kernel.org>,
	"Brandeburg, Jesse" <jesse.brandeburg@...el.com>
Subject: Re: [PATCH 1/2] net: Toeplitz library functions

On Tue, Sep 24, 2013 at 08:54:24AM -0700, Tom Herbert wrote:
> On Tue, Sep 24, 2013 at 8:39 AM, David Miller <davem@...hat.com> wrote:
> > From: Tom Herbert <therbert@...gle.com>
> > Date: Tue, 24 Sep 2013 08:22:55 -0700
> >
> >> We use this value for steering, and could use it for other uses like
> >> connection lookup.
> >
> > For security reasons we absolutely cannot use it for that purpose,
> > please stop claiming this.
> >
> > Any hash function which an attacker can reproduce is attackable.
> 
> The Toeplitz function uses a secret key whose length is based on the
> input length.  96 bits in IPv4, 320 bits in IPv6.  I don't see how an
> attacker can reproduce this if the key is random.  If the problem is
> that devices are not being configured with a sufficiently random key
> (some actually are using a fixed key :-( ), that's a separate issue
> that should be addressed.  It is possible to DoS attack through the
> steering mechanism.

I agree, my first comment on the second patch was wrong. I did not assume that
the hashing function does seed itself. We also do not rehash the connection
tables. So if Eric's comments would be addressed its use could be fine.


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