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

[Richard Guy Briggs]

On 16/04/10, Andi Kleen wrote:
> 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@xxxxxxxxxxxxxx> 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@xxxxxxxxxx>
> > >>   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.

> > 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.

I can think of other examples, such as CONFIG_CHANGE, LOGIN,
NETFILTER_CFG, MAC_*, AVC and surely others, if I am understanding your
point.

> 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.

We had the opposite problem with AUDIT_USER_AVC and maybe also with
AUDIT_USER_SELINUX_ERR.

> > 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.

Not for those who rely on it...

> 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

- RGB

--
Richard Guy Briggs <rgb@xxxxxxxxxx>
Kernel Security Engineering, Base Operating Systems, Red Hat
Remote, Ottawa, Canada
Voice: +1.647.777.2635, Internal: (81) 32635