Re: [PATCH v2] lockdown,selinux: avoid bogus SELinux lockdown permission checks

[Jiri Olsa]

On Fri, May 28, 2021 at 11:56:02AM +0200, Daniel Borkmann wrote:

SNIP

> 
> Ondrej / Paul / Jiri: at least for the BPF tracing case specifically (I haven't looked
> at the rest but it's also kind of independent), the attached fix should address both
> reported issues, please take a look & test.
> 
> Thanks a lot,
> Daniel

> From 5893ad528dc0a0a68933b8f2a81b18d3f539660d Mon Sep 17 00:00:00 2001
> From: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> Date: Fri, 28 May 2021 09:16:31 +0000
> Subject: [PATCH bpf] bpf, audit, lockdown: Fix bogus SELinux lockdown permission checks
> 
> Commit 59438b46471a ("security,lockdown,selinux: implement SELinux lockdown")
> added an implementation of the locked_down LSM hook to SELinux, with the aim
> to restrict which domains are allowed to perform operations that would breach
> lockdown. This is indirectly also getting audit subsystem involved to report
> events. The latter is problematic, as reported by Ondrej and Serhei, since it
> can bring down the whole system via audit:
> 
>   i) The audit events that are triggered due to calls to security_locked_down()
>      can OOM kill a machine, see below details [0].
> 
>  ii) It seems to be causing a deadlock via slow_avc_audit() -> audit_log_end()
>      when presumingly trying to wake up kauditd [1].
> 
> Fix both at the same time by taking a completely different approach, that is,
> move the check into the program verification phase where we actually retrieve
> the func proto. This also reliably gets the task (current) that is trying to
> install the tracing program, e.g. bpftrace/bcc/perf/systemtap/etc, and it also
> fixes the OOM since we're moving this out of the BPF helpers which can be called
> millions of times per second.

nice idea.. I'll try to reproduce and test

jirka