[PATCH v2 1/3] iotests: Specify explicit backing format where sensible

Eric Blake eblake at redhat.com
Thu Feb 27 13:08:50 UTC 2020


On 2/27/20 3:19 AM, Ján Tomko wrote:
> On a Wednesday in 2020, Eric Blake wrote:
>> There are many existing qcow2 images that specify a backing file but
>> no format.  This has been the source of CVEs in the past, but has
>> become more prominent of a problem now that libvirt has switched to
>> -blockdev.  With older -drive, at least the probing was always done by
>> qemu (so the only risk of a changed format between successive boots of
>> a guest was if qemu was upgraded and probed differently).  But with
>> newer -blockdev, libvirt must specify a format; if libvirt guesses raw
>> where the image was formatted, this results in data corruption visible
>> to the guest; conversely, if libvirt guesses qcow2 where qemu was
>> using raw, this can result in potential security holes, so modern
>> libvirt instead refuses to use images without explicit backing format.
>>
>> The change in libvirt to reject images without explicit backing format
>> has pointed out that a number of tools have been far too reliant on
>> probing in the past.  It's time to set a better example in our own
>> iotests of properly setting this parameter.
>>
>> iotest calls to create, rebase, convert, and amend are all impacted to
>> some degree.  It's a bit annoying that we are inconsistent on command
>> line - while all of those accept -o backing_file=...,backing_fmt=...,
>> the shortcuts are different: create and rebase have -b and -F, convert
>> has -B but no -F, and amend has no shortcuts.
>>
>> Signed-off-by: Eric Blake <eblake at redhat.com>
>> ---
> 
> [...]
> 
> Test #225 still uses -b without a format:
> 
> ./check -vmdk 225

Oh, good catch (I only ran ./check -qcow2, -nbd, and -raw).

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org




More information about the libvir-list mailing list