When doing a live snapshot, the libvirt driver creates an intermediate
qcow2 file with the same backing file as the original disk. However,
it calls qemu-img info without specifying the input format explicitly.
An authenticated user can write data to a raw disk which will cause
this code to misinterpret the disk as a qcow2 file with a
user-specified backing file on the host, and return an arbitrary host
file as the backing file.
This bug does not appear to result in a data leak in this case, but
this is hard to verify. It certainly results in corrupt output.
Closes-Bug: #1524274
Change-Id: I11485f077d28f4e97529a691e55e3e3c0bea8872
915fdbbfb8