From: Paul Moore <paul@paul-moore.com>
To: Daniel Borkmann <daniel@iogearbox.net>
Cc: Ondrej Mosnacek <omosnace@redhat.com>,
linux-security-module@vger.kernel.org,
James Morris <jmorris@namei.org>,
Steven Rostedt <rostedt@goodmis.org>,
Ingo Molnar <mingo@redhat.com>,
Stephen Smalley <stephen.smalley.work@gmail.com>,
selinux@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
linux-fsdevel@vger.kernel.org, bpf@vger.kernel.org,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
Casey Schaufler <casey@schaufler-ca.com>,
jolsa@redhat.com
Subject: Re: [PATCH v2] lockdown,selinux: avoid bogus SELinux lockdown permission checks
Date: Wed, 2 Jun 2021 11:13:27 -0400 [thread overview]
Message-ID: <CAHC9VhTuPnPs1wMTmoGUZ4fvyy-es9QJpE7O_yTs2JKos4fgbw@mail.gmail.com> (raw)
In-Reply-To: <3ca181e3-df32-9ae0-12c6-efb899b7ce7a@iogearbox.net>
On Wed, Jun 2, 2021 at 8:40 AM Daniel Borkmann <daniel@iogearbox.net> wrote:
> On 6/1/21 10:47 PM, Paul Moore wrote:
> > The thing I'm worried about would be the case where a LSM policy
> > change requires that an existing BPF program be removed or disabled.
> > I'm guessing based on the refcounting that there is not presently a
> > clean way to remove a BPF program from the system, but is this
> > something we could resolve? If we can't safely remove a BPF program
> > from the system, can we replace/swap it with an empty/NULL BPF
> > program?
>
> Removing progs would somehow mean destroying those references from an
> async event and then /safely/ guaranteeing that nothing is accessing
> them anymore. But then if policy changes once more where they would
> be allowed again we would need to revert back to the original state,
> which brings us to your replace/swap question with an empty/null prog.
> It's not feasible either, because there are different BPF program types
> and they can have different return code semantics that lead to subsequent
> actions. If we were to replace them with an empty/NULL program, then
> essentially this will get us into an undefined system state given it's
> unclear what should be a default policy for each program type, etc.
> Just to pick one simple example, outside of tracing, that comes to mind:
> say, you attached a program with tc to a given device ingress hook. That
> program implements firewalling functionality, and potentially deep down
> in that program there is functionality to record/sample packets along
> with some meta data. Part of what is exported to the ring buffer to the
> user space reader may be a struct net_device field that is otherwise not
> available (or at least not yet), hence it's probe-read with mentioned
> helpers. If you were now to change the SELinux policy for that tc loader
> application, and therefore replace/swap the progs in the kernel that were
> loaded with it (given tc's lockdown policy was recorded in their sec blob)
> with an empty/NULL program, then either you say allow-all or drop-all,
> but either way, you break the firewalling functionality completely by
> locking yourself out of the machine or letting everything through. There
> is no sane way where we could reason about the context/internals of a
> given program where it would be safe to replace with a simple empty/NULL
> prog.
Help me out here, is your answer that the access check can only be
done at BPF program load time? That isn't really a solution from a
SELinux perspective as far as I'm concerned.
I understand the ideas I've tossed out aren't practical from a BPF
perspective, but it would be nice if we could find something that does
work. Surely you BPF folks can think of some way to provide a
runtime, not load time, check?
--
paul moore
www.paul-moore.com
next prev parent reply other threads:[~2021-06-02 15:14 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-17 9:20 [PATCH v2] lockdown,selinux: avoid bogus SELinux lockdown permission checks Ondrej Mosnacek
2021-05-17 11:00 ` Michael Ellerman
2021-05-26 11:44 ` Ondrej Mosnacek
2021-05-27 4:28 ` James Morris
2021-05-27 14:18 ` Paul Moore
2021-05-28 1:37 ` Paul Moore
2021-05-28 7:09 ` Daniel Borkmann
2021-05-28 9:53 ` Jiri Olsa
2021-05-28 9:56 ` Daniel Borkmann
2021-05-28 10:16 ` Jiri Olsa
2021-05-28 11:47 ` Jiri Olsa
2021-05-28 11:54 ` Daniel Borkmann
2021-05-28 13:42 ` Ondrej Mosnacek
2021-05-28 14:20 ` Daniel Borkmann
2021-05-28 15:54 ` Paul Moore
2021-05-28 15:47 ` Paul Moore
2021-05-28 18:10 ` Daniel Borkmann
2021-05-28 22:52 ` Paul Moore
2021-05-29 18:48 ` Paul Moore
2021-05-31 8:24 ` Daniel Borkmann
2021-06-01 20:47 ` Paul Moore
2021-06-02 12:40 ` Daniel Borkmann
2021-06-02 15:13 ` Paul Moore [this message]
2021-06-03 18:52 ` Daniel Borkmann
2021-06-04 4:50 ` Paul Moore
2021-06-04 18:02 ` Daniel Borkmann
2021-06-04 23:34 ` Paul Moore
2021-06-05 0:08 ` Alexei Starovoitov
2021-06-05 18:10 ` Casey Schaufler
2021-06-05 18:17 ` Linus Torvalds
2021-06-06 2:11 ` Paul Moore
2021-06-06 1:30 ` Paul Moore
2021-06-02 13:39 ` Ondrej Mosnacek
2021-06-03 17:46 ` Paul Moore
2021-06-08 11:01 ` Ondrej Mosnacek
2021-06-09 2:40 ` Paul Moore
2021-05-28 13:58 ` Steven Rostedt
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