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

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Message-ID: <CAADnVQ+memUT2zcc-wunP0QgWSLWpmnSJNRJZmfDdc+FBb=gEg@mail.gmail.com>
Date:   Thu, 22 Dec 2016 11:34:36 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Hannes Frederic Sowa <hannes@...essinduktion.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        "Theodore Ts'o" <tytso@....edu>, 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: BPF hash algo (Re: [kernel-hardening] Re: [PATCH v7 3/6] random:
 use SipHash in place of MD5)

On Thu, Dec 22, 2016 at 9:25 AM, Andy Lutomirski <luto@...capital.net> wrote:
> On Thu, Dec 22, 2016 at 8:59 AM, Hannes Frederic Sowa
> <hannes@...essinduktion.org> wrote:
>> On Thu, 2016-12-22 at 08:07 -0800, Andy Lutomirski wrote:
>>
>> We don't prevent ebpf programs being loaded based on the digest but
>> just to uniquely identify loaded programs from user space and match up
>> with their source.
>
> The commit log talks about using the hash to see if the program has
> already been compiled and JITted.  If that's done, then a collision
> will directly cause the kernel to malfunction.

Andy, please read the code.
we could have used jhash there just as well.
Collisions are fine.