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



On 04/15/2016 06:41 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?
> 
> 2) regardless of #1, should we continue to reject that config in libvirt?
> 

Even though there's still a debate about whether use of /dev/urandom here is
sensible, several people suggested removing the libvirt path restriction, and
nobody really spoke up to defend it. So I've posted a patch to fully drop
libvirt's rng path whitelist:

http://www.redhat.com/archives/libvir-list/2016-April/msg01362.html

- Cole


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