linux-kernel - Re: [PATCH] random: add blocking facility to urandom

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Message-ID: <4E67C7AD.9050903@redhat.com>
Date:	Wed, 07 Sep 2011 15:36:13 -0400
From:	Jarod Wilson <jarod@...hat.com>
To:	"Ted Ts'o" <tytso@....edu>, Jarod Wilson <jarod@...hat.com>,
	Sasha Levin <levinsasha928@...il.com>,
	linux-crypto@...r.kernel.org, Matt Mackall <mpm@...enic.com>,
	Neil Horman <nhorman@...hat.com>,
	Herbert Xu <herbert.xu@...hat.com>,
	Steve Grubb <sgrubb@...hat.com>,
	Stephan Mueller <stephan.mueller@...ec.com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] random: add blocking facility to urandom

Ted Ts'o wrote:
> On Wed, Sep 07, 2011 at 02:26:35PM -0400, Jarod Wilson wrote:
>> We're looking for a generic solution here that doesn't require
>> re-educating every single piece of userspace. And anything done in
>> userspace is going to be full of possible holes -- there needs to be
>> something in place that actually *enforces* the policy, and
>> centralized accounting/tracking, lest you wind up with multiple
>> processes racing to grab the entropy.
>
> Yeah, but there are userspace programs that depend on urandom not
> blocking... so your proposed change would break them.

But only if you've set the sysctl to a non-zero value, and even then, 
only if someone is actively draining entropy from /dev/random. 
Otherwise, in practice, it behaves the same as always. Granted, I 
haven't tested with all possible userspace to see how it might fall 
down, but suggestions for progs to try would be welcomed.

But again, I want to stress that out of the box, there's absolutely no 
change to the way urandom behaves, no blocking, this *only* kicks in if 
you twiddle the sysctl because you have some sort of security 
requirement that mandates it.


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


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