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Re: [Libguestfs] [PATCH v2 3/5] launch: libvirt: Allow the SELinux label to be set on qcow2 overlay files.



On Fri, 2013-03-01 at 10:49 +0000, Richard W.M. Jones wrote:
> On Fri, Mar 01, 2013 at 10:22:14AM +0000, Matthew Booth wrote:
> > On Thu, 2013-02-28 at 16:02 +0000, Richard W.M. Jones wrote:
> > > From: "Richard W.M. Jones" <rjones redhat com>
> > > 
> > > When a disk is opened readonly, the libvirt attach-method privately
> > > creates a qcow2 overlay on top.
> > > 
> > > This commit lets that overlay get an SELinux label, and sets it to the
> > > imagelabel specified by guestfs_internal_set_libvirt_selinux_label.
> > > 
> > > The above only applies to the libvirt attach-method.
> > > ---
> > >  src/launch-libvirt.c | 28 ++++++++++++++++++++--------
> > >  1 file changed, 20 insertions(+), 8 deletions(-)
> > > 
> > > diff --git a/src/launch-libvirt.c b/src/launch-libvirt.c
> > > index 318847a..b692fd6 100644
> > > --- a/src/launch-libvirt.c
> > > +++ b/src/launch-libvirt.c
> > > @@ -133,8 +133,8 @@ static int is_custom_qemu (guestfs_h *g);
> > >  static int is_blk (const char *path);
> > >  static int random_chars (char *ret, size_t len);
> > >  static void ignore_errors (void *ignore, virErrorPtr ignore2);
> > > -static char *make_qcow2_overlay (guestfs_h *g, const char *path, const char *format);
> > > -static int make_qcow2_overlay_for_drive (guestfs_h *g, struct drive *drv);
> > > +static char *make_qcow2_overlay (guestfs_h *g, const char *path, const char *format, const char *selinux_imagelabel);
> > > +static int make_qcow2_overlay_for_drive (guestfs_h *g, struct drive *drv, const char *selinux_imagelabel);
> > >  static void drive_free_priv (void *);
> > >  static void set_socket_create_context (guestfs_h *g);
> > >  static void clear_socket_create_context (guestfs_h *g);
> > > @@ -235,13 +235,13 @@ launch_libvirt (guestfs_h *g, const char *libvirt_uri)
> > >     * Note that appliance can be NULL if using the old-style appliance.
> > >     */
> > >    if (appliance) {
> > > -    params.appliance_overlay = make_qcow2_overlay (g, appliance, "raw");
> > > +    params.appliance_overlay = make_qcow2_overlay (g, appliance, "raw", NULL);
> > >      if (!params.appliance_overlay)
> > >        goto cleanup;
> > >    }
> > 
> > I remain convinced that this is going to bite us at some point in the
> > future. The fact that it works now is essentially a quirk of the default
> > SELinux policy. I still don't understand at all how the confined guest
> > can access the underlying appliance image, which libvirt presumably
> > doesn't relabel.
> 
> There's no mystery.  Because the appliance disk has a <shareable/>
> tag, libvirt labels it as Dan explains here:
> 
> https://www.redhat.com/archives/libguestfs/2013-February/msg00139.html

Actually, that doesn't clear it up.

Firstly, the <shareable/> attribute uses an alternative labelling. This
alternative labelling still requires support from the policy, so it
remains policy-specific.

Secondly, it doesn't explain if/how the backing file is relabelled. If
it isn't, why is it accessible? Again, this would be a quirk of the
default policy.

Dan?

Matt


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