Comment 1 for bug 361938

http://git.kernel.org/?p=virt/kvm/kvm-userspace.git;a=commitdiff;h=385aae33c08e17ec63671b9fa1c503c21283bc1f;hp=b335c2b5762259c827bae487dca26441497a96cb

qcow2's get_cluster_offset() scans forward in the l2 table to find other
clusters that have the same allocation status as the first cluster.
This is used by (among others) qcow_is_allocated().

Unfortunately, it was not checking to be sure that it didn't fall off
the end of the l2 table. This patch adds that check.

The symptom that motivated me to look into this was that
bdrv_is_allocated() was returning false when there was in fact data
there. This is one of many ways this bug could lead to data corruption.

I checked the other place that scans for consecutive unallocated blocks
(alloc_cluster_offset()) and it appears to be OK:
    nb_clusters = MIN(nb_clusters, s->l2_size - l2_index);
appears to prevent the same problem from occurring.

Signed-off-by: Nolan Leake <nolan <at> sigbus.net>
Signed-off-by: Anthony Liguori <email address hidden>