[libvirt] [Qemu-devel] Re: Libvirt debug API

[Anthony Liguori]

On 04/26/2010 08:31 AM, Daniel P. Berrange wrote:
> What you describe is not inherant to the daemon model. This is why we have
> two separate models in libvirt. The system instance is pre-spawned with
> high privileges, to allow use of hosts resources which require high
> privileges to access. The session instance is auto-spawned when the app
> connects to libvirt, thus it inherits the privileges of the app that is
> using it.
>
> I don't deny that the system instance has a new attack surface, because it
> is running privileged. If the app needs to connect VMs to privileged
> resources, then the architecture has to have some privileged component
> to give access to those resoruces. You don't want the VM to be privileged,
> nor the whole management app to be privileged. The system daemon is thus the
> arbitrator for this privileged access. If you don't need todo anything that
> requires higher privileges though, just use the session instance which
> always matches the apps privileges.
>    

I regret saying "more secure" because I think it's a difficult concept 
to really quantify and that makes it hard to meaningfully discuss.

The reason I lean toward the direct launch model is that it gives the 
user a lot of flexibility in terms of using things like namespaces, DAC, 
cgroups, capabilities, etc.  A lot of potential features are lost when 
you do indirect launch because you have to teach the daemon how to 
support each of these features.

Regards,

Anthony Liguori

> Daniel
>