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Re: [libvirt] [PATCH 0/4] RFC: grant KVM guests retain arbitrary capabilities



On Tue, Dec 20, 2011 at 04:40:54PM +0900, Taku Izumi wrote:
> Hi all,
> 
> This patchset adds an option for KVM guests to retain arbitrary capabilities.
> 
> I want KVM guests to retain "cap_sys_rawio" capability, so I tried to
> run qemu as root user. However because libvirt clears all capability 
> of KVM guest by default, even if guest is running as root user,
> it doesn't have any capability.  I can fulfill my requirement by 
> disabling "clear_emulator_capabilities" option, but it's not 
> good idea considering security risk. I'm happy libvirt could clear
> unnecessary capabilities instead of clearing all. That is a motivator
> for creating this patch.
> 
> By adding "domain_capabilities" element and to domain XML, its domain
> can retain specified capabilities  like the following:
> 
> ; VM can retain cap_sys_rawio capability
> # virsh edit VM
> ...
>   </features>
>   <domain_capabilities>
>     <cap_sys_rawio/>
>   </domain_capabilities>
>   <clock offset='utc'/>

We could do with a feature like this for LXC too. Though I'd prefer
the XML to be a little more concise. Perhaps

    <process>
       <cap_sys_rawio/>
    </process>

One potential concern is that the capability names are OS specific,
so perhaps rather than allow them as element names, we should use
string attribute values for them

    <process>
      <cap name='sys_rawio'/>
    </process>

and declare the attribute values are potentially OS dependant, and
then expose the list of allowed OS capabilities values in the capabilities
XML.

Daniel
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