Re: [PATCH] random: add blocking facility to urandom

Jarod Wilson
2011-09-07T19:36:20Z

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@redhat.com