[PATCH] capabilities: do not audit log BPRM_FCAPS on set*id

[Richard Guy Briggs]

On 2017-04-11 15:36, Paul Moore wrote:
> On Wed, Mar 29, 2017 at 6:29 AM, Richard Guy Briggs <rgb at redhat.com> wrote:
> > On 2017-03-09 09:34, Steve Grubb wrote:
> >> On Tuesday, March 7, 2017 4:10:49 PM EST Richard Guy Briggs wrote:
> >> > > > > > one possibly audit-worth case which (if I read correctly) this will
> >> > > > > > skip is where a setuid-root binary has filecaps which *limit* its
> >> > > > > > privs.
> >> > > > > > Does that matter?
> >> > > > >
> >> > > > > I hadn't thought of that case, but I did consider in the setuid case
> >> > > > > comparing before and after without setuid forcing the drop of all
> >> > > > > capabilities via "ambient".  Mind you, this bug has been around before
> >> > > > > Luto's patch that adds the ambient capabilities set.
> >> > > >
> >> > > > Can you suggest a scenario where that might happen?
> >> > >
> >> > > Sorry, do you mean the case I brought up, or the one you mentioned?  I
> >> > > don't quite understnad the one you brought up.  For mine it's pretty
> >> > > simple to reproduce, just
> >> >
> >> > I was talking about the case you brought up, but they could be the same
> >> > case.
> >> >
> >> > I was thinking of a case where the caps actually change, but are
> >> > overridden by the blanket full permissions of setuid.
> >>
> >> If there actually is a change in capability bits besides the implied change of
> >> capabilities based on the change of the uid alone, then it should be logged.
> >
> > Are you speaking of a change in pP' only from pI, or also pI', pE' and pA'?
> >
> > Something like ( pP' xor pI ) not empty?
> >
> > The previous patch I'd sent was reasonably easy to understand, but I'm
> > having trouble adding this new twist to the logic expression in question
> > due to the inverted combination of pre-existing items.  I'm having
> > trouble visualizing a 5 or more-dimensional Karnaugh map...
> >
> > While I am at it, I notice pA is missing from the audit record.  The
> > record contains fields "old_pp", "old_pi", "old_pe", "new_pp", "new_pi",
> > "new_pe" so in keeping with the previous record normalizations, I'd like
> > to change the "new_*" variants to simply drop the "new_" prefix.
> >
> >         https://github.com/linux-audit/audit-kernel/issues/40
> 
> Yes, there is the separate ambient capabilities record patch, but
> where do we stand with this patch?  From what I gather there is still
> some uncertainty here?

Yes, I put this on my back burner thinking about how best to re-approach
this, hoping others would offer some insight or advice how to attack
this, otherwise I'm going to end up with a horrendous conditional
expression, I fear.

Steve, I was hoping to get a clarification from you about which
capability bits had changed.

Serge, do you have any suggestions on how to approach the conditional
logic?

> paul moore

- RGB

--
Richard Guy Briggs <rgb at redhat.com>
Sr. S/W Engineer, Kernel Security, Base Operating Systems
Remote, Ottawa, Red Hat Canada
IRC: rgb, SunRaycer
Voice: +1.647.777.2635, Internal: (81) 32635