linux-kernel - RE: Where exactly will arch_fast

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Date:	Thu, 4 Dec 2014 15:56:30 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Herbert Xu' <herbert@...dor.apana.org.au>,
	Daniel Borkmann <dborkman@...hat.com>
CC:	Thomas Graf <tgraf@...g.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Theodore Ts'o <tytso@....edu>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: RE: Where exactly will arch_fast_hash be used

From: Herbert Xu
> On Thu, Dec 04, 2014 at 04:43:31PM +0100, Daniel Borkmann wrote:
> >
> > Hm, I thought the kernel doc on arch_fast_hash() in include/linux/hash.h
> > would give enough of a hint ...
> 
> I think something more explicit like "do not use this in a hash
> table unless you know what you're doing" might be needed.

That isn't really helpful. Maybe something more like:

"This CRC algorithm used by this hash is 'linear', ie hash(a xor b) ==
hash(a) xor hash(b). This means that it is relatively easy for a remote
attacker to generate multiple items with the same hash."

	David



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