linux-kernel - Re: [PATCH 07/12] random: use the arch-specific rng in xfer_secondary

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Date:	Sun, 08 Jul 2012 03:06:31 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Theodore Ts'o <tytso@....edu>
Cc:	Linux Kernel Developers List <linux-kernel@...r.kernel.org>,
	ewust@...ch.edu, zakir@...ch.edu, nadiah@...ucsd.edu,
	jhalderm@...ch.edu, stable@...r.kernel.org
Subject: Re: [PATCH 07/12] random: use the arch-specific rng in
 xfer_secondary_pool

On Sat, 2012-07-07 at 21:41 -0400, Theodore Ts'o wrote:
> On Sun, Jul 08, 2012 at 02:06:46AM +0100, Ben Hutchings wrote:
> > 
> > Surely the number of random bytes being added is i * sizeof(long), not
> > sizeof(u.hwrand)?
> > 
> 
> Meh; Kees Cook has made the same observation.  Basically, in the
> unlikely case where RDRAND fails, we'll end up mixing in stack
> garbage.  It's not a security vulnerability, since the contents of the
> entropy pool never gets exposed.  In fact, one could argue that mixing
> in some unknown garbage from the kernel stack might actually help a
> little; but it can't hurt.

Sorry, I realised after reading further that there's no entropy being
credited.  However, I expect that kmemcheck will complain unless you
limit the used length or call kmemcheck_mark_initialized().

Ben.

-- 
Ben Hutchings
Life would be so much easier if we could look at the source code.

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