Re: [PATCH v6 08/10] iotests: Specify explicit backing format where sensible

[Eric Blake <eblake@redhat.com>]

On 7/7/20 11:07 AM, Kevin Wolf wrote:
> Am 06.07.2020 um 22:39 hat Eric Blake geschrieben:
>> 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, and convert 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, while
>> convert has -B but no -F.  (amend has no shortcuts, but the previous
>> patch just deprecated the use of amend to change backing chains).
>>
>> Signed-off-by: Eric Blake <eblake@redhat.com>
> 
> This breaks at least 024 and 043 for qed because qemu-img info can't
> print the backing file format there (qed only saves a flag whether it's
> raw or non-raw).

Shoot.  I tend to avoid tests of qed and qcow (because they take so 
long), so while I may have tested them around v1 or v2 of the series, 
all the rebasing has changed the results by now.  Such is life.

> 
> We can fix the output filtering during the freeze, though.

Yes indeed, and I'll post such patches soon, now that you've pointed it out.

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