Re: [RFC PATCH 0/2] selinux,anon_inodes: Use a separate SELinux class for each type of anon inode

From: Paul Moore <paul@paul-moore.com>
To: Ondrej Mosnacek <omosnace@redhat.com>
Cc: selinux@vger.kernel.org, linux-security-module@vger.kernel.org,
	linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Lokesh Gidra <lokeshgidra@google.com>,
	Stephen Smalley <stephen.smalley.work@gmail.com>
Subject: Re: [RFC PATCH 0/2] selinux,anon_inodes: Use a separate SELinux class for each type of anon inode
Date: Wed, 21 Apr 2021 16:38:20 -0400	[thread overview]
Message-ID: <CAHC9VhTFPHO7YtTxSZNcEZwoy4R3RXVu-4RrAHRtv8BVEw-zGA@mail.gmail.com> (raw)
In-Reply-To: <20210421171446.785507-1-omosnace@redhat.com>

On Wed, Apr 21, 2021 at 1:14 PM Ondrej Mosnacek <omosnace@redhat.com> 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