On Wed, Apr 21, 2021 at 1:14 PM Ondrej Mosnacek [off-list ref] wrote:

This series aims to correct a design flaw in the original anon_inode
SELinux support that would make it hard to write policies for anonymous
inodes once more types of them are supported (currently only userfaultfd
inodes are). A more detailed rationale is provided in the second patch.

The first patch extends the anon_inode_getfd_secure() function to accept
an additional numeric identifier that represents the type of the
anonymous inode being created, which is passed to the LSMs via
security_inode_init_security_anon().

The second patch then introduces a new SELinux policy capability that
allow policies to opt-in to have a separate class used for each type of
anon inode. That means that the "old way" will still

... will what? :)

I think it would be a very good idea if you could provide some
concrete examples of actual policy problems encountered using the
current approach.  I haven't looked at these patches very seriously
yet, but my initial reaction is not "oh yes, we definitely need this".

I wish I had realized the practical consequences earlier, while the
patches were still under review, but it only started to sink in after
the authors themselves later raised the issue in an off-list
conversation. Even then, I still hoped it wouldn't be that bad, but the
more I thought about how to apply this in an actual policy, the more I
realized how much pain it would be to work with the current design, so
I decided to propose these changes.

I hope this will be an acceptable solution.

A selinux-testsuite patch that adapts the userfaultfd test to work also
with the new policy capability enabled will follow.

Ondrej Mosnacek (2):
  LSM,anon_inodes: explicitly distinguish anon inode types
  selinux: add capability to map anon inode types to separate classes

 fs/anon_inodes.c                           | 42 +++++++++++++---------
 fs/userfaultfd.c                           |  6 ++--
 include/linux/anon_inodes.h                |  4 ++-
 include/linux/lsm_hook_defs.h              |  3 +-
 include/linux/security.h                   | 19 ++++++++++
 security/security.c                        |  3 +-
 security/selinux/hooks.c                   | 28 ++++++++++++++-
 security/selinux/include/classmap.h        |  2 ++
 security/selinux/include/policycap.h       |  1 +
 security/selinux/include/policycap_names.h |  3 +-
 security/selinux/include/security.h        |  7 ++++
 11 files changed, 95 insertions(+), 23 deletions(-)

--
2.30.2

-- 
paul moore
www.paul-moore.com