passt SELinux labelling (was: Re: [PATCH v2 1/3] qemu_passt: Don't make passt transition to svirt_t/libvirt_domain on start)

[Daniel P. Berrangé]

On Fri, Mar 03, 2023 at 10:18:39AM -0800, Andrea Bolognani wrote:
> On Fri, Mar 03, 2023 at 06:06:05PM +0000, Daniel P. Berrangé wrote:
> > On Fri, Mar 03, 2023 at 09:56:55AM -0800, Andrea Bolognani wrote:
> > > Right, but wouldn't the idea of poking at the filesystem to retrieve
> > > the label from the binary (passt_exec_t) and then applying a text
> > > transformation to obtain the runtime label (passt_t) go directly
> > > against the idea of not hardcoding information about a specific
> > > policy implementation into libvirt?
> >
> > I'm not suggesting applying a text transformation. The example code
> > using libselinux I described in the other reply actually askes the
> > kernel to tell us what the target type will be when a process
> > labelled passt_exec_t is execd.
> 
> Yeah, that's a lot better.
> 
> > > As I understand it, such a policy would allow virtqemud (virtd_t) to
> > > execute passt (passt_exec_t) and automatically result in a transition
> > > of the process to the desired context (passt_t).
> >
> > Yes, and I'm saying we must ask the kernel to tell us what that target
> > context will be for the loaded policy, given the source file context.
> 
> I still don't understand why we can't simply execute passt and let
> the domain transition defined in the policy take care of switching to
> the appropriate label from us, like we do for dnsmasq and other
> tools? Why do we need to do things differently for passt?

That won't get the per-VM label applied. It will end up running
passt_t:s0:c0.c1023, but we want it to be passt_t:s0:c342,155.
To transition from non-MCS to MCS, you have to explicitly tell
the kernel what to do instead of relying on the plain automatic
transition.


With regards,
Daniel
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