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

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Message-ID: <CA+mtBx83=X6k42oe4=-hD_coRoX72bJ05Kb5dDfRCDCdTzOH+A@mail.gmail.com>
Date:	Tue, 24 Sep 2013 11:24:59 -0700
From:	Tom Herbert <therbert@...gle.com>
To:	Ben Hutchings <bhutchings@...arflare.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 11:10 AM, Ben Hutchings
<bhutchings@...arflare.com> wrote:
> On Tue, 2013-09-24 at 14:03 -0400, David Miller wrote:
>> From: Tom Herbert <therbert@...gle.com>
>> Date: Tue, 24 Sep 2013 08:54:24 -0700
>>
>> > 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.
>>
>> All of them are using a fixed, defined, key.
>
> This is certainly false, as I know sfc randomises the key.  And the
> Microsoft RSS spec appears to require that the key is programmable.
>
There are some drivers are using fixed keys.  This is not good.  I'll
take a look at those.  It should be sufficient to randomly set the key
once at initialization.


> Ben.
>
> --
> Ben Hutchings, Staff Engineer, Solarflare
> Not speaking for my employer; that's the marketing department's job.
> They asked us to note that Solarflare product names are trademarked.
>
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