linux-kernel - Re: [kernel-hardening] Re: [PATCH v7 3/6] random: use SipHash in place of MD5

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Message-ID: <1482421900.2673.3.camel@stressinduktion.org>
Date:   Thu, 22 Dec 2016 16:51:40 +0100
From:   Hannes Frederic Sowa <hannes@...essinduktion.org>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     kernel-hardening@...ts.openwall.com, Theodore Ts'o <tytso@....edu>,
        Andy Lutomirski <luto@...capital.net>,
        Netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        David Laight <David.Laight@...lab.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Eric Biggers <ebiggers3@...il.com>,
        Tom Herbert <tom@...bertland.com>,
        Andi Kleen <ak@...ux.intel.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jean-Philippe Aumasson <jeanphilippe.aumasson@...il.com>
Subject: Re: [kernel-hardening] Re: [PATCH v7 3/6] random: use SipHash in
 place of MD5

On Thu, 2016-12-22 at 16:41 +0100, Jason A. Donenfeld wrote:
> Hi Hannes,
> 
> On Thu, Dec 22, 2016 at 4:33 PM, Hannes Frederic Sowa
> <hannes@...essinduktion.org> wrote:
> > IPv6 you cannot touch anymore. The hashing algorithm is part of uAPI.
> > You don't want to give people new IPv6 addresses with the same stable
> > secret (across reboots) after a kernel upgrade. Maybe they lose
> > connectivity then and it is extra work?
> 
> Ahh, too bad. So it goes.

If no other users survive we can put it into the ipv6 module.

> > The bpf hash stuff can be changed during this merge window, as it is
> > not yet in a released kernel. Albeit I would probably have preferred
> > something like sha256 here, which can be easily replicated by user
> > space tools (minus the problem of patching out references to not
> > hashable data, which must be zeroed).
> 
> Oh, interesting, so time is of the essence then. Do you want to handle
> changing the new eBPF code to something not-SHA1 before it's too late,
> as part of a new patchset that can fast track itself to David? And
> then I can preserve my large series for the next merge window.

This algorithm should be a non-seeded algorithm, because the hashes
should be stable and verifiable by user space tooling. Thus this would
need a hashing algorithm that is hardened against pre-image
attacks/collision resistance, which siphash is not. I would prefer some
higher order SHA algorithm for that actually.

Bye,
Hannes