Re: [Virtio-fs] virtiofs mounted filesystems & SELinux

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Link Dupont (link@sub-pop.net) wrote:
> Adding the <binary xattr='on'> element to the <filesystem> device does seem
> to spawn virtiofsd with the option string "source=/home,xattr". My guest can
> no longer mount the device though.
> 
> It errors with:
> 
> [ 170.225553] 9pnet_virtio: no channels available
> mount: mount(2) failed: No such file or directory
> 
> I think what this is doing is causing libvirt to create the device as a
> virtiofs device instead of a 9p device. The EL7 kernel doesn't have a
> virtiofs driver, so it can't mount virtiofs devices.
> 
> My knowledge is unfortunately limited about the nuances between 9p and
> virtiofs. So I'm mostly experimenting by trial-and-error here.

They're almost entirely different implementations; if you have a
virtiofsd then you're running virtiofs, not 9p, and yes RHEL7 won't like
that.

(I'm not sure el7 had 9p either??)

Dave


> On Wed, Jun 2 2021 at 03:55:40 PM -0500, Connor Kuehl <ckuehl@redhat.com>
> wrote:
> > On 5/21/21 11:59 AM, Link Dupont wrote:
> > 
> > Adding the virtio-fs mailing list.
> > 
> > >  I am mounting a filesystem into a domain using the virtiofs driver.
> > > 
> > >  <filesystem accessmode="passthrough" type="mount">
> > >        <source dir="/home"/>
> > >        <target dir="/home"/>
> > >        <driver type="virtiofs"/>
> > >  </filesystem>
> > > 
> > >  Both my host (Fedora 34) and guest (CentOS 8.4) are running with
> > > SELinux
> > >  enforcing. From my host, I can see that the SELinux context type is
> > > set to
> > >  user_home_dir_t.
> > > 
> > >  $ ls -ldZ /home/link
> > >  drwxr-xr-x. 61 link link system_u:object_r:user_home_dir_t:s0 8192
> > > May 21
> > >  12:41 /home/link
> > > 
> > > > From within the guest however, the volume is unlabeled_t
> > > 
> > >  $ ls -lZd /home/link
> > >  drwxr-xr-x. 61 link link system_u:object_r:unlabeled_t:s0 8192 May
> > > 21 12:53 /
> > >  home/link
> > > 
> > >  Is there a way to pass the SELinux context through to the guest? Or
> > > mount the
> > >  volume with the correct options to map SELinux contexts?
> > > 
> > > 
> > 
> > Hi,
> > 
> > I'm afraid I actually don't know that much about SELinux but I read
> > that it relies on using extended attributes in the file system to
> > accomplish its labeling.
> > 
> > Do you still experience this issue when you enable extended attribute
> > support[1] in virtiofsd? The example in the optional parameters snippet
> > enables extended attributes with the xattr='on' element.
> > 
> > Connor
> > 
> > [1] https://libvirt.org/kbase/virtiofs.html#optional-parameters
> > 
> 
> 
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-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK