linux-kernel - Re: [PATCH 1/2] audit: show user land backtrace as part of audit context messages

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Date:   Tue, 2 Feb 2021 23:11:12 +0100
From:   Ondrej Mosnacek <omosnace@...hat.com>
To:     Paul Moore <paul@...l-moore.com>
Cc:     "Daniel Walker (danielwa)" <danielwa@...co.com>,
        "Victor Kamensky (kamensky)" <kamensky@...co.com>,
        "Ruslan Bilovol -X (rbilovol - GLOBALLOGIC INC at Cisco)" 
        <rbilovol@...co.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-audit@...hat.com" <linux-audit@...hat.com>,
        "xe-linux-external(mailer list)" <xe-linux-external@...co.com>
Subject: Re: [PATCH 1/2] audit: show user land backtrace as part of audit
 context messages

On Tue, Feb 2, 2021 at 10:46 PM Paul Moore <paul@...l-moore.com> wrote:
> On Tue, Feb 2, 2021 at 4:44 PM Daniel Walker (danielwa)
> <danielwa@...co.com> wrote:
> > On Tue, Feb 02, 2021 at 04:35:42PM -0500, Paul Moore wrote:
> > > On Tue, Feb 2, 2021 at 4:29 PM Daniel Walker <danielwa@...co.com> wrote:
> > > > From: Victor Kamensky <kamensky@...co.com>
> > > >
> > > > To efficiently find out where SELinux AVC denial is comming from
> > > > take backtrace of user land process and display it as type=UBACKTRACE
> > > > message that comes as audit context for SELinux AVC and other audit
> > > > messages ...
> > >
> > > Have you tried the new perf tracepoint for SELinux AVC decisions that
> > > trigger an audit event?  It's a new feature for v5.10 and looks to
> > > accomplish most of what you are looking for with this patch.
> > >
> > > * https://www.paul-moore.com/blog/d/2020/12/linux_v510.html
> >
> > We haven't tried it, but I can look into it. We're not using v5.10 extensively
> > yet.
>
> Let us know if that works for you, and if it doesn't, let us know what
> might be missing.  I hate seeing the kernel grow multiple features
> which do the same thing.

I agree - I played around with this new tracepoint recently and you
can use it to achieve what you want quite easily:

# collect traces for denials (just interrupt/kill the sleep process
when done) - will create a perf.data file you can analyze later
perf record -a -e avc:selinux_audited -g --call-graph=dwarf sleep infinity
# dump all collected backtraces from the perf.data file
perf script

It's a bit complicated if you want to have it running in the
background permanently as a service (you need to tell perf to dump the
recorded data before you can read it), but perf already has some
command-line options to help with that use case.

--
Ondrej Mosnacek
Software Engineer, Linux Security - SELinux kernel
Red Hat, Inc.