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

Sasha Levin
2011-09-07T20:01:06Z

On Wed, 2011-09-07 at 15:30 -0400, Jarod Wilson wrote:
> Sasha Levin wrote:
> > On Wed, 2011-09-07 at 14:26 -0400, Jarod Wilson wrote:
> >> Sasha Levin wrote:
> >> [..] And anything done in
> >> userspace is going to be full of possible holes [..]
> >
> > Such as? Is there an example of a case which can't be handled in
> > userspace?
>
> How do you mandate preventing reads from urandom when there isn't
> sufficient entropy? You likely wind up needing to restrict access to the
> actual urandom via permissions and selinux policy or similar, and then
> run a daemon or something that provides a pseudo-urandom that brokers
> access to the real urandom. Get the permissions or policy wrong, and
> havoc ensues. An issue with the initscript or udev rule to hide the real
> urandom, and things can fall down. Its a whole lot more fragile than
> this approach, and a lot more involved in setting it up.

Replace /dev/urandom with a simple CUSE driver, redirect reads to the
real urandom after applying your threshold.

--

Sasha.