libvirtd in privileged (root) mode runs qemu/kvm guests with a different
user. It set owner/group of storage used by this guests to this user and
group. In Debian this is libvirt-qemu:kvm.
| brw-rw---T 1 libvirt-qemu kvm 254, 11 Feb 25 17:08 /dev/dm-11
| brw-rw---T 1 libvirt-qemu kvm 254, 12 Feb 25 17:50 /dev/dm-12
The kvm group is used for generic access control on /dev/kvm, so a lot
of users may have access to this group.
| crw-rw---T 1 root kvm 10, 232 Feb 25 18:04 kvm
This allows write access to unrelated users to this storage.
Affected is at least Debian Squeeze (0.8.3-5+squeeze2) and Debian
This issue did not affect the versions of the libvirt package as shipped with Red Hat Enterprise Linux 5 and 6.