Re: [Qemu-block] [Qemu-devel] [PATCH for-2.11 5/5] qcow2: Refuse to get unaligned offsets from cache

[Eric Blake]

On 11/10/2017 04:00 PM, Max Reitz wrote:
>> 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.
> 
> No, it's the very same.  As far as I've seen it, the repair function
> tries to fix the "refblock is outside image" error by resizing the image
> so the refblock is inside the image.  However, the subsequent
> bdrv_truncate() detects the alignment corruption, too, and thus marks
> the image corrupt.

Is resizing the image to be larger always a wise thing compared to just
rebuilding the refcount?  If I stick a large enough out-of-image value
in the table, can I cause a denial-of-service by making qemu try to
allocate petabytes of storage just to bring it into range?

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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