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

On 3/3/23 1:36 PM, Daniel P. Berrangé wrote: > 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. Since you've brought up dnsmasq as an example, note that the dnsmasq processes don't have any MCS (which I guess is the right thing, since a single dnsmasq might be used by many/any/all guests, contrasting with passt, or the slirp-helper or tpm, which have one instance per guest device. This does make dnsmasq a "not ideal" example when figuring out what is needed for passt though (in some ways, but not others)(I think? I still can't claim to fully grok all the details of this).