Re: [PATCH ghak90 V8 07/16] audit: add contid support for signalling the audit daemon

[Paul Moore <paul@paul-moore.com>]

On Wed, Mar 18, 2020 at 5:56 PM Richard Guy Briggs <rgb@redhat.com> wrote:
> On 2020-03-18 17:42, Paul Moore wrote:
> > On Wed, Mar 18, 2020 at 5:27 PM Richard Guy Briggs <rgb@redhat.com> wrote:
> > > On 2020-03-18 16:56, Paul Moore wrote:
> > > > On Fri, Mar 13, 2020 at 2:59 PM Richard Guy Briggs <rgb@redhat.com> wrote:
> > > > > On 2020-03-13 12:29, Paul Moore wrote:
> > > > > > On Thu, Mar 12, 2020 at 3:30 PM Richard Guy Briggs <rgb@redhat.com> wrote:
> > > > > > > On 2020-02-13 16:44, Paul Moore wrote:
> > > > > > > > This is a bit of a thread-hijack, and for that I apologize, but
> > > > > > > > another thought crossed my mind while thinking about this issue
> > > > > > > > further ... Once we support multiple auditd instances, including the
> > > > > > > > necessary record routing and duplication/multiple-sends (the host
> > > > > > > > always sees *everything*), we will likely need to find a way to "trim"
> > > > > > > > the audit container ID (ACID) lists we send in the records.  The
> > > > > > > > auditd instance running on the host/initns will always see everything,
> > > > > > > > so it will want the full container ACID list; however an auditd
> > > > > > > > instance running inside a container really should only see the ACIDs
> > > > > > > > of any child containers.
> > > > > > >
> > > > > > > Agreed.  This should be easy to check and limit, preventing an auditd
> > > > > > > from seeing any contid that is a parent of its own contid.
> > > > > > >
> > > > > > > > For example, imagine a system where the host has containers 1 and 2,
> > > > > > > > each running an auditd instance.  Inside container 1 there are
> > > > > > > > containers A and B.  Inside container 2 there are containers Y and Z.
> > > > > > > > If an audit event is generated in container Z, I would expect the
> > > > > > > > host's auditd to see a ACID list of "1,Z" but container 1's auditd
> > > > > > > > should only see an ACID list of "Z".  The auditd running in container
> > > > > > > > 2 should not see the record at all (that will be relatively
> > > > > > > > straightforward).  Does that make sense?  Do we have the record
> > > > > > > > formats properly designed to handle this without too much problem (I'm
> > > > > > > > not entirely sure we do)?
> > > > > > >
> > > > > > > I completely agree and I believe we have record formats that are able to
> > > > > > > handle this already.
> > > > > >
> > > > > > I'm not convinced we do.  What about the cases where we have a field
> > > > > > with a list of audit container IDs?  How do we handle that?
> > > > >
> > > > > I don't understand the problem.  (I think you crossed your 1/2 vs
> > > > > A/B/Y/Z in your example.) ...
> > > >
> > > > It looks like I did, sorry about that.
> > > >
> > > > > ... Clarifying the example above, if as you
> > > > > suggest an event happens in container Z, the hosts's auditd would report
> > > > >         Z,^2
> > > > > and the auditd in container 2 would report
> > > > >         Z,^2
> > > > > but if there were another auditd running in container Z it would report
> > > > >         Z
> > > > > while the auditd in container 1 or A/B would see nothing.
> > > >
> > > > Yes.  My concern is how do we handle this to minimize duplicating and
> > > > rewriting the records?  It isn't so much about the format, although
> > > > the format is a side effect.
> > >
> > > Are you talking about caching, or about divulging more information than
> > > necessary or even information leaks?  Or even noticing that records that
> > > need to be generated to two audit daemons share the same contid field
> > > values and should be generated at the same time or information shared
> > > between them?  I'd see any of these as optimizations that don't affect
> > > the api.
> >
> > Imagine a record is generated in a container which has more than one
> > auditd in it's ancestry that should receive this record, how do we
> > handle that without completely killing performance?  That's my
> > concern.  If you've already thought up a plan for this - excellent,
> > please share :)
>
> No, I haven't given that much thought other than the correctness and
> security issues of making sure that each audit daemon is sufficiently
> isolated to do its job but not jeopardize another audit domain.  Audit
> already kills performance, according to some...
>
> We currently won't have that problem since there can only be one so far.
> Fixing and optimizing this is part of the next phase of the challenge of
> adding a second audit daemon.
>
> Let's work on correctness and reasonable efficiency for this phase and
> not focus on a problem we don't yet have.  I wouldn't consider this
> incurring technical debt at this point.

I agree, one stage at a time, but the choice we make here is going to
have a significant impact on what we can do later.  We need to get
this as "right" as possible; this isn't something we should dismiss
with a hand-wave as a problem for the next stage.  We don't need an
implementation, but I would like to see a rough design of how we would
address this problem.

> I could see cacheing a contid string from one starting point, but it may
> be more work to search that cached string to truncate it or add to it
> when another audit daemon requests a copy of a similar string.  I
> suppose every full contid string could be generated the first time it is
> used and parts of it used (start/finish) as needed but that
> search/indexing may not be worth it.

I hope we can do better than string manipulations in the kernel.  I'd
much rather defer generating the ACID list (if possible), than
generating a list only to keep copying and editing it as the record is
sent.

-- 
paul moore
www.paul-moore.com