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From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date: Thu, 22 Dec 2016 11:34:36 -0800
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Subject: Re: BPF hash algo (Re: [kernel-hardening] Re: [PATCH v7 3/6] random:
 use SipHash in place of MD5)
To: Andy Lutomirski <luto@amacapital.net>
Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        "Jason A. Donenfeld" <Jason@zx2c4.com>,
        "kernel-hardening@lists.openwall.com" 
        <kernel-hardening@lists.openwall.com>,
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        LKML <linux-kernel@vger.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
        David Laight <David.Laight@aculab.com>,
        Eric Dumazet <edumazet@google.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Eric Biggers <ebiggers3@gmail.com>, Tom Herbert <tom@herbertland.com>,
        Andi Kleen <ak@linux.intel.com>,
        "David S. Miller" <davem@davemloft.net>,
        Jean-Philippe Aumasson <jeanphilippe.aumasson@gmail.com>
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On Thu, Dec 22, 2016 at 9:25 AM, Andy Lutomirski <luto@amacapital.net> wrote:
> On Thu, Dec 22, 2016 at 8:59 AM, Hannes Frederic Sowa
> <hannes@stressinduktion.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.