Re: [PATCH] Don't audit SECCOMP_KILL/RET_ERRNO when syscall auditing is disabled

[Andi Kleen <ak@linux.intel.com>]

On Sun, Apr 10, 2016 at 06:17:53PM -0400, Paul Moore wrote:
> On Sat, Apr 9, 2016 at 10:41 PM, Andi Kleen <andi@firstfloor.org> wrote:
> >> What kernel version are you using?  I believe we fixed that in Linux
> >> 4.5 with the following:
> >
> > This is 4.6-rc2.
> >>
> >>   commit 96368701e1c89057bbf39222e965161c68a85b4b
> >>   From: Paul Moore <pmoore@redhat.com>
> >>   Date: Wed, 13 Jan 2016 10:18:55 -0400 (09:18 -0500)
> >>
> >>   audit: force seccomp event logging to honor the audit_enabled flag
> >
> > No you didn't fix it because audit_enabled is always enabled by systemd
> > for user space auditing, see the original description of my patch.
> 
> [NOTE: adding the audit list to the CC line]

This mailing list is marked subscriber only in MAINTAINERS so I
intentionally didn't add it. It's unlikely that my emails
will make it through.

> Sorry, I read your email too quickly; you are correct, that commit
> fixed a different problem.
> 
> Let me think on this a bit more.  Technically I don't see this as a
> bug with the kernel, userspace is enabling audit and you are getting
> audit messages as a result; from my opinion this is the expected

It's a bug in the kernel because seccomp is different from everything else.

The kernel only produces audit messages when audit rules are set
for every other case.

The only exception is this seccomp message which is produced 
unconditionally. Doesn't make sense to treat seccomp special
here. It should only be audited when some kind of rule is set.

> behavior.  However, we've talked in the past about providing better
> control over seccomp's auditing/logging and that work would allow you
> to quiet all seccomp messages if you desired.
> 
> If you are interested, I started tracking this issue at the link below:
> 
>  * https://github.com/linux-audit/audit-kernel/issues/13

Making it a sysctl is fine for me as long as it is disabled by default
so that user space doesn't need to be modified to make seccomp
stop spamming.

Audit should always be opt-in, not opt-out.

However I think making it conditional on syscall auditing like
in my patch is equivalent and much simpler.

If you really insist on the sysctl I can send patch.

-Andi