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 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 09:48:41 -0400	[thread overview]
Message-ID: <CAHC9VhS8F-3X6p2pmjvd0ripnpf=oRAA0G5bmE4yrdi-4sDyDw@mail.gmail.com> (raw)
In-Reply-To: <CAFqZXNts94w-hMhzCjKW5sHrVw2pw2w7cMQ3+Q2suJ_XUUpUwg@mail.gmail.com>

On Thu, Apr 22, 2021 at 7:40 AM Ondrej Mosnacek <omosnace@redhat.com> wrote:
> 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.

That's what I figured from my quick glance at the code, but I wanted
to make sure.

> > 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.

Yes, I read the example you provided in patch 2, but it was still a
little too abstract for my liking.  I have the same concern that
Stephen mentioned, I was just giving you an opportunity to show that
in this case the additional object classes were warranted.

-- 
paul moore
www.paul-moore.com