[libvirt] RFC: virtio-rng and /dev/urandom

[Yaniv Kaul]

On Fri, Apr 15, 2016 at 6:47 PM, Eric Blake <eblake at redhat.com> wrote:

> On 04/15/2016 04:41 AM, Cole Robinson wrote:
> > Libvirt currently rejects using host /dev/urandom as an input source for
> a
> > virtio-rng device. The only accepted sources are /dev/random and
> /dev/hwrng.
> > This is the result of discussions on qemu-devel around when the feature
> was
> > first added (2013). Examples:
> >
> > http://lists.gnu.org/archive/html/qemu-devel/2012-09/msg02387.html
> > https://lists.gnu.org/archive/html/qemu-devel/2013-03/threads.html#00023
> >
> > libvirt's rejection of /dev/urandom has generated some complaints from
> users:
> >
> > https://bugzilla.redhat.com/show_bug.cgi?id=1074464
> > * cited: http://www.2uo.de/myths-about-urandom/
> > http://www.redhat.com/archives/libvir-list/2016-March/msg01062.html
> > http://www.redhat.com/archives/libvir-list/2016-April/msg00186.html
> >
> > I think it's worth having another discussion about this, at least with a
> > recent argument in one place so we can put it to bed. I'm CCing a bunch
> of
> > people. I think the questions are:
> >
> > 1) is the original recommendation to never use virtio-rng+/dev/urandom
> correct?
>
> That I'm not sure about - and the answer may be context-dependent (for
> example a FIPS user may care more than an ordinary user)
>
> >
> > 2) regardless of #1, should we continue to reject that config in libvirt?
>
> This one, I have a pretty strong opinion: libvirt should NOT enforce
> policy.  If someone has a valid use case for doing it, we should permit
> them to do it, even if it lets someone else shoot themselves in the
> foot.  So I think we should relax libvirt to allow users that source
> their virtio-rng from /dev/urandom.
>

+1
I'd personally be happy (for some specific test-dev use case) with
/dev/zero - I don't care about the security, but I want the entropy
collection to be done as fast as possible.
Y.


>
> --
> Eric Blake   eblake redhat com    +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
>
>
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