qcow2: Prevent allocating compressed clusters at offset 0
If the refcount data is corrupted then we can end up trying to
allocate a new compressed cluster at offset 0 in the image, triggering
an assertion in qcow2_alloc_bytes() that would crash QEMU:
qcow2_alloc_bytes: Assertion `offset' failed.
This patch adds an explicit check for this scenario and a new test
case.
Signed-off-by: Alberto Garcia <berto@igalia.com>
Message-id:
fb53467cf48e95ff3330def1cf1003a5b862b7d9.
1509718618.git.berto@igalia.com
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>