Re: [Qemu-devel] Image probing: how it can be insecure, and what we could do about it

[Eric Blake]

On 11/05/2014 09:38 AM, Max Reitz wrote:

>> Note that specifying just the top image's format is not enough, you also
>> have to specify any backing images' formats.  QCOW2 can optionally store
>> the backing image format in the image.  The other COW formats can't.
> 
> Well, they can, with "json:". *cough*
> 
>> Example of insecure usage: -hda bar.vmdk, where bar.vmdk is a VMDK image
>> with a raw backing file.
> 
> Yesterday I found out that doesn't seem possible. You apparently can
> only use VMDK with VMDK backing files. Other than that, we only have
> qcow1 and qed as COW formats which should not be used anyway.

Actually, qed requires the backing format to be recorded (it is
non-optional) and is therefore immune to probing problems of backing
files.  That's one thing it got right.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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