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Date:   Thu, 30 May 2019 20:20:58 -0400
From:   Richard Guy Briggs <rgb@redhat.com>
To:     Paul Moore <paul@paul-moore.com>
Cc:     Tycho Andersen <tycho@tycho.ws>,
        "Serge E. Hallyn" <serge@hallyn.com>,
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        simo@redhat.com, Eric Paris <eparis@parisplace.org>,
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Subject: Re: [PATCH ghak90 V6 02/10] audit: add container id
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On 2019-05-30 19:26, Paul Moore wrote:
> On Thu, May 30, 2019 at 5:29 PM Tycho Andersen <tycho@tycho.ws> wrote:
> > On Thu, May 30, 2019 at 03:29:32PM -0400, Paul Moore wrote:
> > >
> > > [REMINDER: It is an "*audit* container ID" and not a general
> > > "container ID" ;)  Smiley aside, I'm not kidding about that part.]
> >
> > This sort of seems like a distinction without a difference; presumably
> > audit is going to want to differentiate between everything that people
> > in userspace call a container. So you'll have to support all this
> > insanity anyway, even if it's "not a container ID".
> 
> That's not quite right.  Audit doesn't care about what a container is,
> or is not, it also doesn't care if the "audit container ID" actually
> matches the ID used by the container engine in userspace and I think
> that is a very important line to draw.  Audit is simply given a value
> which it calls the "audit container ID", it ensures that the value is
> inherited appropriately (e.g. children inherit their parent's audit
> container ID), and it uses the value in audit records to provide some
> additional context for log analysis.  The distinction isn't limited to
> the value itself, but also to how it is used; it is an "audit
> container ID" and not a "container ID" because this value is
> exclusively for use by the audit subsystem.  We are very intentionally
> not adding a generic container ID to the kernel.  If the kernel does
> ever grow a general purpose container ID we will be one of the first
> ones in line to make use of it, but we are not going to be the ones to
> generically add containers to the kernel.  Enough people already hate
> audit ;)
> 
> > > I'm not interested in supporting/merging something that isn't useful;
> > > if this doesn't work for your use case then we need to figure out what
> > > would work.  It sounds like nested containers are much more common in
> > > the lxc world, can you elaborate a bit more on this?
> > >
> > > As far as the possible solutions you mention above, I'm not sure I
> > > like the per-userns audit container IDs, I'd much rather just emit the
> > > necessary tracking information via the audit record stream and let the
> > > log analysis tools figure it out.  However, the bigger question is how
> > > to limit (re)setting the audit container ID when you are in a non-init
> > > userns.  For reasons already mentioned, using capable() is a non
> > > starter for everything but the initial userns, and using ns_capable()
> > > is equally poor as it essentially allows any userns the ability to
> > > munge it's audit container ID (obviously not good).  It appears we
> > > need a different method for controlling access to the audit container
> > > ID.
> >
> > One option would be to make it a string, and have it be append only.
> > That should be safe with no checks.
> >
> > I know there was a long thread about what type to make this thing. I
> > think you could accomplish the append-only-ness with a u64 if you had
> > some rule about only allowing setting lower order bits than those that
> > are already set. With 4 bits for simplicity:
> >
> > 1100         # initial container id
> > 1100 -> 1011 # not allowed
> > 1100 -> 1101 # allowed, but now 1101 is set in stone since there are
> >              # no lower order bits left
> >
> > There are probably fancier ways to do it if you actually understand
> > math :)
> 
>  ;)
> 
> > Since userns nesting is limited to 32 levels (right now, IIRC), and
> > you have 64 bits, this might be reasonable. You could just teach
> > container engines to use the first say N bits for themselves, with a 1
> > bit for the barrier at the end.
> 
> I like the creativity, but I worry that at some point these
> limitations are going to be raised (limits have a funny way of doing
> that over time) and we will be in trouble.  I say "trouble" because I
> want to be able to quickly do an audit container ID comparison and
> we're going to pay a penalty for these larger values (we'll need this
> when we add multiple auditd support and the requisite record routing).
> 
> Thinking about this makes me also realize we probably need to think a
> bit longer about audit container ID conflicts between orchestrators.
> Right now we just take the value that is given to us by the
> orchestrator, but if we want to allow multiple container orchestrators
> to work without some form of cooperation in userspace (I think we have
> to assume the orchestrators will not talk to each other) we likely
> need to have some way to block reuse of an audit container ID.  We
> would either need to prevent the orchestrator from explicitly setting
> an audit container ID to a currently in use value, or instead generate
> the audit container ID in the kernel upon an event triggered by the
> orchestrator (e.g. a write to a /proc file).  I suspect we should
> start looking at the idr code, I think we will need to make use of it.

My first reaction to using the IDR code is that once an idr is given up,
it can be reused.  I suppose we request IDRs and then never give them up
to avoid reuse...

I already had some ideas of preventing an existing ID from being reused,
but that makes the practice of some container engines injecting
processes into existing containers difficult if not impossible.

> paul moore
> www.paul-moore.com

- RGB

--
Richard Guy Briggs <rgb@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