[libvirt] Adding support to limit client connections for vnc/spice display driver

[Patil, Tushar]

On Wed, Mar 19, 2014 at 06:41:16PM +0000, Patil, Tushar wrote:
> >
>> We are using KVM hypervisor driver for running OpenStack IaaS. Couple
>> of months back we have reported one security issue [1] in OS. Basically
>> we want to limit on the number of vnc client connections that can be
>> opened by users for a given VM. I know that there is share policy where
>> you can specify "VNC_SHARE_MODE_EXCLUSIVE" share mode. But it only allows
>> one client connection to the vnc console, it will disconnect all previously
>> opened vnc client connections. Since vnc display driver already has the
>> data of client connections, it would be possible to add the logic to limit
>> on the number of client connections.
>>
>> What we want is the ability to specify threshold how many vnc client
>> connections should be allowed at any given point of time in the domain
>> xml for graphics device (especially for vnc/spice)?
>>
>> Example
> ><graphics type="vnc" autoport="yes" keymap="en-us" listen="127.0.0.1"/, share-policy="limit-connections", connections="5">
>>
>> Add support to accept new share policy "limit-connections'.
>> So in the above example, when user tries to open vnc display for the 6th
>>time, then the request should be rejected.
>>
>> I need your expert opinion in deciding whether it's a good idea to add
>> this support in the vnc/spice display driver or this kind of constraint
>> should be imposed outside libvirt?

> Libvirt isn't at all involved in vnc/spice connections. They happen
> directly between QEMU & the client app, optionally via Nova's proxy
> service. If QEMU had a setting for such a limit then libvirt could
> set it, but AFAIK none exists, so there's nothing libvirt can do
> about this currently. So options are either todo work in QEMU to
> add this config feature, then wire it into libvirt, or address it in
> the Nova proxy service.

Thanks for your advice. I will add a new feature request in qemu. After this feature is added to qemu, I will then add a request in libvirt to use the newly added parameters.

Thanks and Best Regards,
Tushar

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