Re: [PATCH RFC 0/2] Fix setting of security labels over NFSv4.2

["J . Bruce Fields" <bfields@fieldses.org>]

On Fri, May 26, 2017 at 10:48:17AM -0400, Stephen Smalley wrote:
> On Thu, 2017-05-25 at 17:07 -0400, Scott Mayhew wrote:
> > Red Hat QE reported that chcon fails over NFSv4.2 on recent kernels.
> > The problem is related to how filesystems are mounted in NFSv4.
> 
> What kernel version and what is a reproducer for the problem?  I don't
> seem to see it on e.g. Fedora 25 with 4.10, unless I misunderstand.

Basically just mount an export with security_label set, mount over NFS,
"ls -Z" will (correctly) show you the server-side security labels, but
"chcon" will fail with ENOTSUP.

If that's not reproducing, maybe you chould show us "exports -v" and
"mount" output--it might not reproduce if you have an "fsid=0" export or
if you're mounting with a protocol version older than 4.2.

--b.

> 
> > 
> > When an NFSv4 client performs a mount operation, it first mounts the
> > NFSv4 root and then does path walk to the exported path and performs
> > a
> > submount on that, cloning the security mount options from the root's
> > superblock to the submount's superblock in the process.
> > 
> > Unless the NFS server has an explicit fsid=0 export with the
> > "security_label" option, the NFSv4 root superblock will not have
> > SBLABEL_MNT set, and neither will the submount superblock after
> > cloning
> > the security mount options.  As a result, setxattr's of security
> > labels
> > over NFSv4.2 will fail.
> > 
> > NFS servers with a modern nfs-utils package will automatically create
> > a
> > pseudo fs to fill in the gaps (including the root itself) leading up
> > to
> > the actual export, so it is uncommon these days for an NFS server to
> > have an explicit fsid=0 export.
> > 
> > Allowing the NFSv4 client to override the SECURITY_LSM_NATIVE_LABELS
> > flag on an initialized superblock would ensure that SBLABEL_MNT is
> > set
> > when the client traverses from an exported path without the
> > "security_label" option to one with the "security_label" option.
> > 
> > Scott Mayhew (2):
> >   selinux: allow SECURITY_LSM_NATIVE_LABELS to be set on an already
> >     initialized superblock
> >   nfs: update labeling behavior on a superblock when submounting
> > 
> >  fs/nfs/super.c           | 23 ++++++++++++++++++++++-
> >  security/selinux/hooks.c |  4 ++--
> >  2 files changed, 24 insertions(+), 3 deletions(-)
> >