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From:   Stephen Smalley <stephen.smalley.work@gmail.com>
Date:   Mon, 31 Aug 2020 10:47:02 -0400
Message-ID: <CAEjxPJ6GkUot29g5qq2GVYzmY2xwfTvVJkNP2kK54OcW7tkz1Q@mail.gmail.com>
Subject: Re: [PATCH] SELinux: Measure state and hash of policy using IMA
To:     Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
Cc:     Paul Moore <paul@paul-moore.com>,
        Ondrej Mosnacek <omosnace@redhat.com>,
        Mimi Zohar <zohar@linux.ibm.com>,
        Casey Schaufler <casey@schaufler-ca.com>,
        Tyler Hicks <tyhicks@linux.microsoft.com>,
        tusharsu@linux.microsoft.com, Sasha Levin <sashal@kernel.org>,
        James Morris <jmorris@namei.org>,
        linux-integrity@vger.kernel.org,
        SElinux list <selinux@vger.kernel.org>,
        LSM List <linux-security-module@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
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On Wed, Aug 26, 2020 at 8:51 AM Stephen Smalley
<stephen.smalley.work@gmail.com> wrote:
>
> On Tue, Aug 25, 2020 at 4:49 PM Lakshmi Ramasubramanian
> <nramas@linux.microsoft.com> wrote:
> >
> > On 8/24/20 3:18 PM, Paul Moore wrote:
> >
> > Hi Paul,
> >
> > >>>>> Is Ondrej's re-try approach I need to use to workaround policy reload issue?
> > >>>>
> > >>>> No, I think perhaps we should move the mutex to selinux_state instead
> > >>>> of selinux_fs_info.  selinux_fs_info has a pointer to selinux_state so
> > >>>> it can then use it indirectly.  Note that your patches are going to
> > >>>> conflict with other ongoing work in the selinux next branch that is
> > >>>> refactoring policy load and converting the policy rwlock to RCU.
> > >>>
> > >>> Yeah, and I'm experimenting with a patch on top of Stephen's RCU work
> > >>> that would allow you to do this in a straightforward way without even
> > >>> messing with the fsi->mutex. My patch may or may not be eventually
> > >>> committed, but either way I'd recommend holding off on this for a
> > >>> while until the dust settles around the RCU conversion.
> > >>
> > >> I can make the SELinux\IMA changes in "selinux next branch" taking
> > >> dependencies on Stephen's patches + relevant IMA patches.
> > >
> > > I know it can be frustrating to hear what I'm about to say, but the
> > > best option is probably just to wait a little to let things settle in
> > > the SELinux -next branch.  There is a lot of stuff going on right now
> > > with patches flooding in (at least "flooding" from a SELinux kernel
> > > development perspective) and we/I've haven't gotten through all of
> > > them yet.
> > >
> >
> > Could you please let me know when the current set of changes in SELinux
> > next branch would be completed and be ready to take new changes?
> >
> > I mean, roughly - would it be a month from now or you expect that to
> > take longer?
>
> I can't speak for Paul but I would expect it to be sooner rather than
> later. Ondrej has some follow ups on top of my policy rcu conversion
> but then it should be good to go.

I think the major changes are now merged although there are still a
couple of changes coming from Ondrej that could affect your code.  For
your purposes, the important things to note are:

1) The mutex has moved from selinux_fs_info to selinux_state and is
now named policy_mutex.  You will need to take it around your call to
security_read_policy_kernel().

2) security_policydb_len() was removed and security_read_policy() just
directly reads the policydb len.  You can do the same from your
security_read_policy_kernel() variant.

3) Ondrej has a pending change to move the policycap[] array from
selinux_state to selinux_policy so that it can be atomically updated
with the policy.

4) Ondrej has a pending change to eliminate the separate initialized
boolean from selinux_state and just test whether selinux_state.policy
is non-NULL but as long as you are using selinux_initialized() to
test, your code should be unaffected.