Debian: DSA-2650-2 Critical Libvirt KVM Access Regression

The recent security update for libvirt was found to cause a regression.
The kvm/qemu processes weren't run as the `kvm` user anymore in order to
fix the file/device ownership changes, but the processes where not
correctly configured to use the `kvm` group either. When the user would
try to run a virtual machine, the process was denied access to the
/dev/kvm device node, preventing the virtual machine to run.

For the stable distribution (squeeze), this problem has been fixed in
version 0.8.3-5+squeeze5.

We recommend that you upgrade your libvirt packages.

Further information about Debian Security Advisories, how to apply
these updates to your system and frequently asked questions can be
found at: http://www.debian.org/security/