linux-kernel - Re: [PATCH] [char] random: fix priming of last

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Date:	Tue, 19 Mar 2013 13:12:09 -0400
From:	Jarod Wilson <jarod@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	Herbert Xu <herbert@...dor.hengli.com.au>,
	Neil Horman <nhorman@...driver.com>,
	"David S. Miller" <davem@...emloft.net>,
	Matt Mackall <mpm@...enic.com>,
	"Theodore Ts'o" <tytso@....edu>, linux-crypto@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH] [char] random: fix priming of last_data

On Tue, Mar 19, 2013 at 12:18:09PM -0400, Jarod Wilson wrote:
> Commit ec8f02da9e added priming of last_data per fips requirements.
> Unfortuantely, it did so in a way that can lead to multiple threads all
> incrementing nbytes, but only one actually doing anything with the extra
> data, which leads to some fun  random corruption and panics.
> 
> The fix is to simply do everything needed to prime last_data in a single
> shot, so there's no window for multiple cpus to increment nbytes -- in
> fact, we won't even increment or decrement nbytes anymore, we'll just
> extract the needed EXTRACT_BYTES one time per pool and then carry on with
                             ^^^^^
		     EXTRACT_SIZE

Error in the description, if anyone actually cares. Oops.

> the normal routine.
> 
> All these changes have been tested across multiple hosts and architectures
> where panics were previously encoutered. The code changes are are strictly
> limited to areas only touched when when booted in fips mode.
> 
> This change should also go into 3.8-stable, to make the myriads of fips
> users on 3.8.x happy.

-- 
Jarod Wilson
jarod@...hat.com

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