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@iogearbox.net>
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