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

[Richard Guy Briggs]

On 2017-04-12 14:49, Steve Grubb wrote:
> On Wednesday, April 12, 2017 2:43:21 AM EDT Richard Guy Briggs wrote:
> > 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?

This is what I'm trying to clarify.

> > > > 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.
> 
> I am not sure what you are asking of me.

I'm trying to understand exactly which capability sets should be
compared to determine if there was a material change, but perhaps that
question is better asked of Serge.  What does the certification care
about in terms that helps me code this?

> -Steve

- 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
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