linux-kernel - Re: [PATCH 2/2] audit: show (grand)parents information of an audit context

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Date:   Wed, 3 Feb 2021 18:57:04 +0000
From:   "Daniel Walker (danielwa)" <danielwa@...co.com>
To:     Paul Moore <paul@...l-moore.com>
CC:     Eric Paris <eparis@...hat.com>,
        "Phil Zhang (xuanyzha)" <xuanyzha@...co.com>,
        "xe-linux-external(mailer list)" <xe-linux-external@...co.com>,
        "linux-audit@...hat.com" <linux-audit@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] audit: show (grand)parents information of an audit
 context

On Tue, Feb 02, 2021 at 04:44:47PM -0500, Paul Moore wrote:
> On Tue, Feb 2, 2021 at 4:29 PM Daniel Walker <danielwa@...co.com> wrote:
> > From: Phil Zhang <xuanyzha@...co.com>
> >
> > To ease the root cause analysis of SELinux AVCs, this new feature
> > traverses task structs to iteratively find all parent processes
> > starting with the denied process and ending at the kernel. Meanwhile,
> > it prints out the command lines and subject contexts of those parents.
> >
> > This provides developers a clear view of how processes were spawned
> > and where transitions happened, without the need to reproduce the
> > issue and manually audit interesting events.
> >
> > Example on bash over ssh:
> >     $ runcon -u system_u -r system_r -t polaris_hm_t ls
> >     ...
> >     type=PARENT msg=audit(1610548241.033:255): subj=root:unconfined_r:unconfined_t:s0-s0:c0.c1023  cmdline="-bash"
> >     type=PARENT msg=audit(1610548241.033:255): subj=system_u:system_r:sshd_t:s0-s0:c0.c1023        cmdline="sshd: root@.../0"
> >     type=PARENT msg=audit(1610548241.033:255): subj=system_u:system_r:sshd_t:s0-s0:c0.c1023        cmdline="/tmp/sw/rp/0/0/rp_security/mount/usr/sbin/sshd
> >     type=PARENT msg=audit(1610548241.033:255): subj=system_u:system_r:init_t:s0                    cmdline="/init"
> >     type=PARENT msg=audit(1610548241.033:255): subj=system_u:system_r:kernel_t:s0
> >     ...
> >
> > Cc: xe-linux-external@...co.com
> > Signed-off-by: Phil Zhang <xuanyzha@...co.com>
> > Signed-off-by: Daniel Walker <danielwa@...co.com>
> > ---
> >  include/uapi/linux/audit.h |  5 ++-
> >  init/Kconfig               |  7 +++++
> >  kernel/audit.c             |  3 +-
> >  kernel/auditsc.c           | 64 ++++++++++++++++++++++++++++++++++++++
> >  4 files changed, 77 insertions(+), 2 deletions(-)
> 
> This is just for development/testing of SELinux policy, right?  It
> seems like this is better done in userspace to me through a
> combination of policy analysis and just understanding of how your
> system is put together.
 
That's why the patch was create to better understand the system.

> If you really need this information in the audit log for some
> production use, it seems like you could audit the various
> fork()/exec() syscalls to get an understanding of the various process
> (sub)trees on the system.  It would require a bit of work to sift
> through the audit log and reconstruct the events that led to a process
> being started, and generating the AVC you are interested in debugging,
> but folks who live The Audit Life supposedly do this sort of thing a
> lot (this sort of thing being tracing a process/session).

We have a very complex and constantly changing system, and we use shell scripts
some of the time. If a shell script triggers an AVC it will typically show the
tool called instead of the shell script which triggered calling the tool.

We do have audit enabled in production systems, and I think we collect these
logs in case of issues on the production system. Phil is better to address this.

We're willing to try alternatives like what you suggested above.

Daniel