On 11/10/2017 02:31 PM, Max Reitz wrote: > Instead of using an assertion, it is better to emit a corruption event > here. Checking all offsets for correct alignment can be tedious and it > is easily possible to forget to do so. qcow2_cache_do_get() is a > function every L2 and refblock access has to go through, so this is a > good central point to add such a check. > > And for good measure, let us also add an assertion that the offset is > non-zero. Making this a corruption event is not feasible, because a > zero offset usually means something special (such as the cluster is > unused), so all callers should be checking this anyway. If they do not, > it is their fault, hence the assertion here. > > Signed-off-by: Max Reitz > --- > block/qcow2-cache.c | 21 +++++++++++++++++++++ > tests/qemu-iotests/060 | 21 +++++++++++++++++++++ > tests/qemu-iotests/060.out | 29 +++++++++++++++++++++++++++++ > 3 files changed, 71 insertions(+) > > +--- Repairing --- > +Repairing refcount block 1 is outside image > +ERROR refcount block 2 is not cluster aligned; refcount table entry corrupted > +qcow2: Marking image as corrupt: Refblock offset 0x200 unaligned (reftable index: 0x2); further corruption events will be suppressed > +Can't get refcount for cluster 1048576: Input/output error Trying to understand this: we have a double corruption, because we encountered a refblock that points outside of the image, but fixing the refblock in turn encounters a second refblock that points within the image but to an unaligned area. Of course, you should never encounter these bad refblocks in normal usage, but when it comes to dealing with untrusted images, being robust is always worth it. Reviewed-by: Eric Blake -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org