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

[Ian Jackson <ian.jackson@xxxxxxxxxxxxx>]

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.

 * 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...)

Ian.

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