netdev - Re: Where exactly will arch_fast

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Message-ID: <20141204153938.GC32140@casper.infradead.org>
Date:	Thu, 4 Dec 2014 15:39:38 +0000
From:	Thomas Graf <tgraf@...g.ch>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Daniel Borkmann <dborkman@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Theodore Ts'o <tytso@....edu>, netdev@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Where exactly will arch_fast_hash be used

On 12/04/14 at 11:29pm, Herbert Xu wrote:
> On Thu, Dec 04, 2014 at 03:26:37PM +0000, Thomas Graf wrote:
> >
> > 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.
> 
> Well in that case the current setup I think is very misleading.
> It's inviting unsuspecting kernel developers to use it as a hash
> function for general hash tables, which AFAICS is something that
> it fails at miserably.

Well, it's called fast hash and not secure hash ;-) but a clear hint
definitely wouldn't hurt.

I wasn't aware of the distribution weakness of the lower bits. Do
you have a reference to more information?
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