Re: [PATCH v5 0/9] virtiofsd: Add support for file security context at file creation

[Vivek Goyal]

On Mon, Feb 07, 2022 at 01:05:16PM +0000, Daniel P. Berrangé wrote:
> On Wed, Feb 02, 2022 at 02:39:26PM -0500, Vivek Goyal wrote:
> > Hi,
> > 
> > This is V5 of the patches. I posted V4 here.
> > 
> > https://listman.redhat.com/archives/virtio-fs/2022-January/msg00041.html
> > 
> > These will allow us to support SELinux with virtiofs. This will send
> > SELinux context at file creation to server and server can set it on
> > file.
> 
> I've not entirely figured it out from the code, so easier for me
> to ask...
> 
> How is the SELinux labelled stored on the host side ? It is stored
> directly in the security.* xattr namespace, or is is subject to
> xattr remapping that virtiofsd already supports.
> 
> Storing directly means virtiofsd has to run in an essentially
> unconfined context, to let it do arbitrary  changes on security.*
> xattrs without being blocked by SELinux) and has risk that guest
> initiated changes can open holes in the host confinement if
> the exported FS is generally visible to processes on the host.
> 
> 
> Using remapping lets virtiofsd be strictly isolated by SELinux
> policy on the host, and ensures that guest context changes
> can't open up holes in the host.
> 
> Both are valid use cases, so I'd ultimately expect us to want
> to support both, but my preference for a "default" behaviour
> would be remapping.

I am expecting users to configure virtiofsd to remap "security.selinux"
to "trusted.virtiofsd.security.selinux" and that will allow guest
and host security selinux to co-exist and allow separate SELinux policies
for guest and host.

I agree that my preference for a default behavior is remapping as well.
That makes most sense. 

One downside of mapping to trusted namespace is that it requires
CAP_SYS_ADMIN for virtiofsd.

Having said that, these patches don't enforce the remapping default. That
has to come from the user because it also needs to be given CAP_SYS_ADMIN.
So out of box default is no remapping and passthrough SELinux.

Thanks
Vivek

> 
> Regards,
> Daniel
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