[virt-tools-list] [PATCH 22/22] spice: hook into QMP port

[Daniel P. Berrangé]

On Tue, Jul 31, 2018 at 03:41:25PM +0200, marcandre.lureau at redhat.com wrote:
> From: Marc-André Lureau <marcandre.lureau at redhat.com>
> 
> If the "org.qemu.monitor.qmp.0" port is available:
> - enable the VM UI
> - get and follow the VM state
> - send the requested VM actions
> 
> This adds a json-glib dependency on spice-gtk display. If necessary,
> we could make it optional.

This patch is something I much don't much like the precedent / idea
of. Its only stop/pause/resume right now, but over time this will
inevitably expand and end up re-implementing much of libvirt's QMP
monitor handling, but worse. For example, the patch below has a CVE
in it because it is not limiting the amount of data it reads before
the \r\n pair, so a malicious QEMU can make it consume GB worth of RAM.

I would suggest it should use libvirt for these actions, but that
kind of defeats the goal of what you're trying to achieve by providing
a UI that is usable by standalone QEMU.

The other thing that occurs to me is that the idea of remote power
control is interesting / useful for pretty much all uses of SPICE and
VNC with QEMU, even when libvirt is managing QEMU.

As it stands we would not want to expose the monitor over SPICE in
many cases as it gives the SPICE user way too high privileges, but
remote power control is useful especially for cloud users. A way
to force a reboot of a dead/hung guest from the SPICE client instad
of having to jump out to openstack CLI API for example.

In VNC there was a 3rd party extension defined to allow remote power
control actions over VNC.

Thus I think SPICE could define a remote power control extension of
its own that could be safely enabled in all cases, even where the
remote user is unprivileged. This is portable to all SPICE server
side impls that care to provide it since it would not be QMP.


Regards,
Daniel
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