[Virtio-fs] restorcon/SELinux virtiofs question

[Vivek Goyal]

On Thu, Nov 19, 2020 at 01:38:41PM -0500, Vivek Goyal wrote:
> On Thu, Nov 19, 2020 at 12:27:20PM -0600, Harry G. Coin wrote:
> > 
> > On 11/19/20 12:16 PM, Vivek Goyal wrote:
> > > On Thu, Nov 19, 2020 at 10:52:51AM -0600, Harry G. Coin wrote:
> > >> Hello virtiofs team.  I need clarification about a 'restorecon' selinux
> > >> guest giving an 'operation not supported' response.
> > >>
> > >> If the host fs is btrfs (with xattr enabled in virtiofsd) but not
> > >> running SELinux,
> > > I suspect that on host setxattr(security.selinux) is failing with 
> > > "operation not supported". 
> > >
> > > What do you mean by host "not running SELinux". SElinux is not compiled
> > > in? Or it is disabled or in passive mode?
> > >
> > > Is it working with filesystems other than btrfs, say ext4 or xfs.
> > >
> > > Now qemu supports xattr remapping. You might want to run virtiofsd
> > > to remap security.selinux. I think that might get you going till
> > > the root cause of the issue is found.
> > >
> > > Vivek
> > 
> > Thank you for the focus.   The host os in this instance is not from the
> > fedora/rhel/centos world with selinux running.  My case is a debian
> > sourced distro (ubuntu).  That world uses 'apparmor' by default, not
> > selinux.   I think it's reasonable to suppose there are a lot of servers
> > out there not running selinux that have lots of vms running on them, not
> > all using virtiofs.  There should be a documented way to allow the
> > 'restorcon' command on one of many guests on such hosts to work.  I
> > suppose to wrap this up:
> > 
> > For the future readers who got here by searching,  could you give the
> > first kernel version that supports a non-selinux host supporting an
> > selinux enabled guest and the virtiofsd command line necessary to get
> > the restorecon command to work normally?
> 
> I don't know yet. Because I don't know what's the root cause of the
> issue.
> 
> The way you are explaining it, looks like host kernel somehow is
> blocking setxattr(security.selinux). And I have no idea why. Is it
> apparmor or something else.
> 
> If no selinux module is loaded on host, then as long as virtiofsd
> process has CAP_SYS_ADMIN, it should be able to set security.selinux.
> 
> "Operation not supported" means error "EOPNOTSUP". I am assuming
> you are running virtiofsd with "-o xattr" to make sure virtiofsd
> supports xattr. If that's the case somehow kernel is returning
> "EOPNOTSUP".
> 
> Can you run virtiofsd with debug option -d and try to install that
> package in guest and capture outout of virtiofsd and post here. It
> might confirm that host kernel is returning error.

I tried doing "chcon unconfined_u:object_r:admin_home_t:s0 bar.txt" 
on a file in virtiofs and got "Operation not supported". I think
guest kernel failed this. Will need to debug further.

Vivek