[libvirt-users] libvirtd via unix socket using system uri

[Michal Privoznik]

On 4/30/19 3:15 PM, Peter Crowther wrote:
> On Tue, 30 Apr 2019 at 10:48, Daniel P. Berrangé <berrange at redhat.com>
> wrote:
> 
>> On Tue, Apr 30, 2019 at 10:45:03AM +0100, Peter Crowther wrote:
>>> On Tue, 30 Apr 2019 at 10:40, Michal Privoznik <mprivozn at redhat.com>
>> wrote:
>>>
>>>> Is there any problem running libvirtd as root?
>>>>
>>>> Yes, in the regulated environment in which I work!  I have to do far
>> more
>>> thorough threat analysis than I would do if I knew which capabilities it
>>> had.  So far, we've accepted the extra work; but it would be wonderful to
>>> be able to run a locked-down virtualisation environment.
>>
>> Libvirtd system mode will want cap_net_admin in order to setup TAP devices
>> and cap_sys_admin to manage disk permissions to grant QEMU access, at which
>> point you've lost any security benefit of running it unprivileged with
>> selective capabilities.
>>
>> Would it fail hard without these, even if using (for example) pre-created
> Ceph block storage, which is our use case?  Or would it only fail when it
> tried to make use of a capability that wasn't present?  My reading of
> capabilities is that behaviour is indistinguishable until you get an EPERM?
> 
> I agree that CAP_DAC_OVERRIDE (per your later mail) is game over for any

CAP_DAC_OVERRIDE won't be required if you don't need libvirt to 
chown()/setfilecon() disk images (dynamic_ownership in qemu.conf).
CAP_SYS_ADMIN is going to be required if you want libvirt to mount some 
nfs based storage pools/create namespaces (note that libvirt creates a 
small namespace for qemu to run in - might need CAP_MKNOD then).

Long story short, why bother with /system if you can't use it and not 
use /session instead?

Michal