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

From: Ondrej Mosnacek <omosnace@redhat.com>
To: Paul Moore <paul@paul-moore.com>
Cc: SElinux list <selinux@vger.kernel.org>,
	Linux Security Module list 
	<linux-security-module@vger.kernel.org>,
	linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
	Linux kernel mailing list <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: Thu, 22 Apr 2021 13:39:39 +0200	[thread overview]
Message-ID: <CAFqZXNts94w-hMhzCjKW5sHrVw2pw2w7cMQ3+Q2suJ_XUUpUwg@mail.gmail.com> (raw)
In-Reply-To: <CAHC9VhTFPHO7YtTxSZNcEZwoy4R3RXVu-4RrAHRtv8BVEw-zGA@mail.gmail.com>

On Wed, Apr 21, 2021 at 10:38 PM Paul Moore <paul@paul-moore.com> wrote:
> 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? :)

Whoops, I thought I had gone over all the text enough times, but
apparently not :) It should have said something along the lines of:

...will still work and will be used by default.

>
> 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".

An example is provided in patch 2. It is a generalized problem that we
would eventually run into in Fedora policy (at least) with the
unconfined_domain_type attribute and so far only hypothetical future
types of anon inodes.

-- 
Ondrej Mosnacek
Software Engineer, Linux Security - SELinux kernel
Red Hat, Inc.