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.
