From: Thomas Graf <tgraf@suug.ch>
To: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Daniel Borkmann <dborkman@redhat.com>,
"David S. Miller" <davem@davemloft.net>,
Theodore Ts'o <tytso@mit.edu>,
netdev@vger.kernel.org,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Where exactly will arch_fast_hash be used
Date: Thu, 4 Dec 2014 15:26:37 +0000 [thread overview]
Message-ID: <20141204152637.GA32140@casper.infradead.org> (raw)
In-Reply-To: <20141204081147.GA19030@gondor.apana.org.au>
On 12/04/14 at 04:11pm, Herbert Xu wrote:
> Hi:
>
> While working on rhashtable it came to me that this whole concept
> of arch_fast_hash is flawed. CRCs are linear functions so it's
> fairly easy for an attacker to identify collisions or at least
> eliminate a large amount of search space (e.g., controlling the
> last bit of the hash result is almost trivial, even when you add
> a random seed).
>
> So what exactly are we going to use arch_fast_hash for? Presumably
> it's places where security is never goint to be an issue, right?
>
> Even if security wasn't an issue, straight CRC32 has really poor
> lower-order bit distribution, which makes it a terrible choice for
> a hash table that simply uses the lower-order bits.
As Daniel pointed out, this work originated for the OVS edge use
case where security is of less concern and the rehashing is
sufficient. Identifying collisions is less of interest as the user
space fall back provides a greater surface for an attack.
next prev parent reply other threads:[~2014-12-04 15:26 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-12-04 8:11 Where exactly will arch_fast_hash be used Herbert Xu
2014-12-04 12:34 ` Hannes Frederic Sowa
2014-12-04 13:14 ` Daniel Borkmann
2014-12-04 15:26 ` Thomas Graf [this message]
2014-12-04 15:29 ` Herbert Xu
2014-12-04 15:39 ` Thomas Graf
2014-12-04 15:43 ` Daniel Borkmann
2014-12-04 15:47 ` Herbert Xu
2014-12-04 15:51 ` Daniel Borkmann
2014-12-04 15:56 ` David Laight
2014-12-04 16:10 ` Herbert Xu
-- strict thread matches above, loose matches on Subject: below --
2014-12-07 5:20 George Spelvin
2014-12-07 9:28 ` Herbert Xu
2014-12-07 10:02 ` George Spelvin
2014-12-07 12:51 ` Herbert Xu
2014-12-07 13:23 ` George Spelvin
2014-12-07 14:06 ` Hannes Frederic Sowa
2014-12-07 21:33 ` George Spelvin
2014-12-08 11:25 ` Hannes Frederic Sowa
2014-12-08 16:19 ` George Spelvin
2014-12-08 16:32 ` Hannes Frederic Sowa
2014-12-09 14:24 ` Herbert Xu
2014-12-07 13:14 ` Hannes Frederic Sowa
2014-12-07 13:30 ` George Spelvin
2014-12-07 13:41 ` Hannes Frederic Sowa
2014-12-07 13:52 ` Hannes Frederic Sowa
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