[libvirt] [PATCH] Add hw random number generator (/dev/hwrng) to default qemu cgroup ACL

[Daniel P. Berrange]

On Mon, Nov 18, 2013 at 09:05:21AM -0700, Eric Blake wrote:
> On 11/18/2013 08:20 AM, Daniel P. Berrange wrote:
> 
> >>  static const char *const defaultDeviceACL[] = {
> >>      "/dev/null", "/dev/full", "/dev/zero",
> >> -    "/dev/random", "/dev/urandom",
> >> +    "/dev/random", "/dev/urandom", "/dev/hwrng",
> >>      "/dev/ptmx", "/dev/kvm", "/dev/kqemu",
> >>      "/dev/rtc", "/dev/hpet", "/dev/vfio/vfio",
> >>      NULL,
> > 
> > NACK, for any device listed in the XML, we should add it in the per-VM
> > cgroups setup code.
> > 
> > The existing /dev/random & /dev/urandom devices are there because they
> > are used for basic crypto libraries unrelated to the XML config.
> 
> /dev/urandom, probably.  /dev/random - really?  Isn't that a DoS
> potential for one guest to starve entropy from other guests, in spite of
> sVirt?

It is a tradeoff between providing the crypto libraries a weaker
entropy source vs DOS potential via entropy starvation. Given that
/dev/random is world writable on Linux in general, I think it is
acceptable to allow QEMU access by default. Paranoid admins can
always set the cgroups device ACL in /etc/libvirt/.qemu.conf if
they want to restrict it.

Daniel
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