Re: [Xen-devel] [PATCH v3] libxl: QED disks support

[Cedric Bosdonnat <cbosdonnat@xxxxxxxx>]

Hi Ian,

On Mon, 2016-12-12 at 17:36 +0000, Ian Jackson wrote:
> Cédric Bosdonnat writes ("[PATCH v3] libxl: QED disks support"):
> > Qdisk supports qcow and qcow2, extend it to also support qed disk
> > format.
> 
> The patch is good.
> 
> I have a qualm, though.  I think this would increase our security
> support footprint to include the qemu qed disk format driver.
> 
> Specifically:
> 
>  * Does the qed format contain a builtin way to refer to other files,
>    like qcow does ?  Paradoxically, if it does not, then it is a
>    bigger risk for us: because then it might be reasonable for a user
>    to feed an untrusted qed image file to xl, for use with a
>    likewise-untrusted guest.  That means that image-handling bugs in
>    qed would be security bugs which we might have to do security
>    response for.

QED does support backing files, not sure if this is a good or bad news
on the security topic.

>  * We should at least consider the possibility that qed might be
>    vulnerable to anomalous guest behaviour.  I don't know enough about
>    qed to say much about that.
> 
> So I would be happy with this patch if it came with a hunk editing
> docs/misc/qemu-xen-security to say something like:
> 
>  +  - backing storage image format: raw, qcow, qcow2, vhd
> 
> (And we might want to drop vhd...)

I'm not the one deciding what is supported and what is not. Just tell
me what I should add in the patch regarding that and I'll add it.

--
Cedric

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