[Libguestfs] [common PATCH 3/3] mlcustomize: do not relabel if not enforcing (RHBZ#1828952)

[Daniel P. Berrangé]

On Thu, Sep 24, 2020 at 11:15:29AM +0100, Richard W.M. Jones wrote:
> On Wed, Sep 23, 2020 at 05:57:50PM +0200, Pino Toscano wrote:
> > Do not attempt to relabel a guest in case its SELinux enforcing mode is
> > not "enforcing", as it is either pointless, or it may fail because of an
> > invalid policy configured.

If invalid policy is configured, you're doomed whether you do labelling
or not. 

If valid policy is configured, and you don't do labelling you're creating
a new failure mode.

IOW, always doing labelling is the right thing, because at least one of
the 4 scenarios will be an improvement, and it isn't creating any downsides
other than the time required to do the labelling.

> > ---
> >  mlcustomize/SELinux_relabel.ml | 26 +++++++++++++++++++++++++-
> >  1 file changed, 25 insertions(+), 1 deletion(-)
> > 
> > diff --git a/mlcustomize/SELinux_relabel.ml b/mlcustomize/SELinux_relabel.ml
> > index 647aeda..db00e59 100644
> > --- a/mlcustomize/SELinux_relabel.ml
> > +++ b/mlcustomize/SELinux_relabel.ml
> > @@ -24,6 +24,9 @@ open Printf
> >  
> >  module G = Guestfs
> >  
> > +exception SELinux_not_enforcing
> > +(* Interal exception to signal a non-enforcing SELinux. *)
> > +
> >  (* Simple reimplementation of Array.mem, available only with OCaml >= 4.03. *)
> >  let array_find a l =
> >    List.mem a (Array.to_list l)
> > @@ -35,12 +38,18 @@ let rec relabel (g : G.guestfs) =
> >        use_setfiles g;
> >        (* That worked, so we don't need to autorelabel. *)
> >        g#rm_f "/.autorelabel"
> > -    with Failure _ ->
> > +    with
> > +    | Failure _ ->
> >        (* This is the fallback in case something in the setfiles
> >         * method didn't work.  That includes the case where a non-SELinux
> >         * host is processing an SELinux guest, and other things.
> >         *)
> >        g#touch "/.autorelabel"
> > +    | SELinux_not_enforcing ->
> > +      (* This means that SELinux was not configured to be in enforcing mode,
> > +       * so silently accept this.
> > +       *)
> > +      ()
> >    )
> >  
> >  and is_selinux_guest g =
> > @@ -59,6 +68,21 @@ and use_setfiles g =
> >    g#aug_load ();
> >    debug_augeas_errors g;
> >  
> > +  (* Get the SELinux enforcing mode, eg "enforcing", "permissive",
> > +   * "disabled".
> > +   * Use "disabled" if not specified, just like libselinux seems to do.
> > +   *)
> > +  let typ = read_selinux_config_key g "SELINUX" "disabled" in
> > +  (* Do not attempt any relabelling if the SELinux is not "enforcing":
> > +   * - in "permissive" mode SELinux is still running, however nothing is
> > +   *   enforced: this means labels can be wrong, and "it is fine"
> 
> I don't think it's fine.  As I showed here:
> 
> https://www.redhat.com/archives/libguestfs/2020-June/msg00115.html
> 
> in permissive mode labels are still being updated on disk.
> 
> TBH I don't understand what you said here:
> 
> https://www.redhat.com/archives/libguestfs/2020-June/msg00117.html
> 
> about "both the labels and the policy may be all wrong".  If the
> administrator set the policy to permissive then labels ought still to
> be updated when the guest is running, and we ought to try to keep them
> updated if we can in v2v.  It's also fine for an administrator to
> switch a system to permissive and then back to enforcing without
> relabelling or rebooting.

Yep, in permissive mode apps / admins should still work on the
assumption that SELinux is operating normally. ie assume you
can be switched to enforcing mode at any time. You certainly
want to continue to apply labelling as normal on disk.

If you don't care about labelling to be updated, it means you
are not likely to ever switch to enforcing, and that's what the
"disabled" state is for.



> 
> > +   * - when "disabled" means SELinux is not running, so any relabelling
> > +   *   is pointless (other than potentially fail due to an invalid
> > +   *   SELINUXTYPE configuration)
> 
> Here you're correct.  Once the admin disabled SELinux, labels are
> going to quickly get out of step with reality, and so attempting to
> relabel in virt-v2v is indeed a waste of time.
> 
> I'd accept this series if you changed "not enforcing" to
> "not enforcing or permissive".


Regards,
Daniel
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