USN-1831-1 fixed a vulnerability in OpenStack Nova. The upstream fix introduced a regression where instances using uncached QCOW2 images would fail to start. This update fixes the problem.
We apologize for the inconvenience.
Original advisory details:
Loganathan Parthipan discovered that Nova did not verify the size of QCOW2 instance storage. An authenticated attacker could exploit this to cause a denial of service by creating an image with a large virtual size with little data, then filling the virtual disk.