On Wed, Jun 3, 2020 at 3:12 PM Stephen Smalley
<stephen.smalley.work@xxxxxxxxx> wrote:
> On Wed, Jun 3, 2020 at 4:23 AM Ondrej Mosnacek <omosnace@xxxxxxxxxx> wrote:
> >
> > On Tue, Jun 2, 2020 at 7:42 PM Stephen Smalley
> > <stephen.smalley.work@xxxxxxxxx> wrote:
> > > This is required to pass the tests for kernels that include
> > > commit a3c751a50fe6 ("vfs: allow unprivileged whiteout creation"),
> > > which changed vfs_mknod() to permit whiteout creation without
> > > requiring CAP_MKNOD and then switched vfs_whiteout() to use vfs_mknod()
> > > rather than calling i_op->mknod() directly, which was originally done
> > > to avoid such checking. However, vfs_mknod() still calls the LSM hook
> > > and therefore applies SELinux checks on whiteout creation. Since
> > > vfs_whiteout() now calls vfs_mknod(), SELinux :chr_file create permission
> > > is now required for such whiteout creation by overlayfs. Skipping the LSM
> > > hook call or SELinux check entirely seems unsafe since we otherwise would
> > > never check whether the process was allowed to create a file in that label;
> > > even though the whiteout device cannot be read/written, it can be used as
> > > a channel wrt its existence and attributes.
> > >
> > > See the discussion in:
> > > https://lore.kernel.org/linux-fsdevel/20200409212859.GH28467@xxxxxxxxxxxxxxxxxxxxxxxxx/
> > >
> > > Signed-off-by: Stephen Smalley <stephen.smalley.work@xxxxxxxxx>
> > > ---
> > > policy/test_overlayfs.te | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > Thanks, this looks good and fixes the failure for me.
> >
> > >
> > > diff --git a/policy/test_overlayfs.te b/policy/test_overlayfs.te
> > > index b29621e..c844b82 100644
> > > --- a/policy/test_overlayfs.te
> > > +++ b/policy/test_overlayfs.te
> > > @@ -88,7 +88,7 @@ manage_dirs_pattern(test_overlay_mounter_t, test_overlay_mounter_files_t, test_o
> > > #
> > > # Needed to remove a transition file
> >
> > Just please also update this comment ("...to create and remove..." or similar).
>
> That wouldn't be correct. The additional :chr_file create permission
> is needed to remove the transition file because removing a file from
> overlayfs creates a whiteout device file. It isn't to create the
> transition file.
Ah, I see... In that case the patch is fine as-is, so:
Acked-by: Ondrej Mosnacek <omosnace@xxxxxxxxxx>
--
Ondrej Mosnacek
Software Engineer, Platform Security - SELinux kernel
Red Hat, Inc.
