On Tue, Jul 16, 2019 at 6:03 PM Richard Guy Briggs <rgb@xxxxxxxxxx> wrote: > On 2019-07-15 17:04, Paul Moore wrote: > > On Mon, Jul 8, 2019 at 2:06 PM Richard Guy Briggs <rgb@xxxxxxxxxx> wrote: ... > > > If we can't trust ns_capable() then why are we passing on > > > CAP_AUDIT_CONTROL? It is being passed down and not stripped purposely > > > by the orchestrator/engine. If ns_capable() isn't inherited how is it > > > gained otherwise? Can it be inserted by cotainer image? I think the > > > answer is "no". Either we trust ns_capable() or we have audit > > > namespaces (recommend based on user namespace) (or both). > > > > My thinking is that since ns_capable() checks the credentials with > > respect to the current user namespace we can't rely on it to control > > access since it would be possible for a privileged process running > > inside an unprivileged container to manipulate the audit container ID > > (containerized process has CAP_AUDIT_CONTROL, e.g. running as root in > > the container, while the container itself does not). > > What makes an unprivileged container unprivileged? "root", or "CAP_*"? My understanding is that when most people refer to an unprivileged container they are referring to a container run without capabilities or a container run by a user other than root. I'm sure there are better definitions out there, by folks much smarter than me on these things, but that's my working definition. > If CAP_AUDIT_CONTROL is granted, does "root" matter? Our discussions here have been about capabilities, not UIDs. The only reason root might matter is that it generally has the full capability set. > Does it matter what user namespace it is in? What likely matters is what check is called: capable() or ns_capable(). Those can yield very different results. > I understand that root is *gained* in an > unprivileged user namespace, but capabilities are inherited or permitted > and that process either has it or it doesn't and an unprivileged user > namespace can't gain a capability that has been rescinded. Different > subsystems use the userid or capabilities or both to determine > privileges. Once again, I believe the important thing to focus on here is capable() vs ns_capable(). We can't safely rely on ns_capable() for the audit container ID policy since that is easily met inside the container regardless of the process' creds which started the container. > In this case, is the userid relevant? We don't do UID checks, we do capability checks, so yes, the UID is irrelevant. > > > At this point I would say we are at an impasse unless we trust > > > ns_capable() or we implement audit namespaces. > > > > I'm not sure how we can trust ns_capable(), but if you can think of a > > way I would love to hear it. I'm also not sure how namespacing audit > > is helpful (see my above comments), but if you think it is please > > explain. > > So if we are not namespacing, why do we not trust capabilities? We can trust capable(CAP_AUDIT_CONTROL) for enforcing audit container ID policy, we can not trust ns_capable(CAP_AUDIT_CONTROL). -- paul moore www.paul-moore.com
