Re: [PATCH v3 3/3] selinux: add permission names to trace event

[Paul Moore]

On Fri, Aug 21, 2020 at 8:29 AM Stephen Smalley
<stephen.smalley.work@xxxxxxxxx> wrote:
> On Thu, Aug 20, 2020 at 10:31 PM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> > On Wed, 19 Aug 2020 09:11:08 -0400
> > Stephen Smalley <stephen.smalley.work@xxxxxxxxx> wrote:
> >
> > > So we'll need to update this plugin whenever we modify
> > > security/selinux/include/classmap.h to keep them in sync.  Is that a
> > > concern?  I don't suppose the plugin could directly include classmap.h?
> > > I guess we'd have to export it as a public header. It isn't considered
> > > to be part of the kernel API/ABI and can change anytime (but in practice
> > > changes are not that frequent, and usually just additive in nature).
> >
> > Yes, it would require some stability between userspace and the plugin.
> > If the value indexes don't change then that would work fine. If you add
> > new ones, that too should be OK, just have a way to state "unknown" in
> > the plugin.
>
> Since we introduced the dynamic class/perm mapping support, it has
> been possible for the values of existing classes/permissions to
> change, and that has happened at time, e.g. when we added watch
> permissions to the common file perms, that shifted the values of the
> class file perms like entrypoint, when we added the process2 class
> right after the process class, it shifted the values of all the
> subsequent classes in the classmap.h.  So you can't rely on those
> values remaining stable across kernel versions.

I think it is becoming increasingly clear that generating the
permission set string in userspace isn't really workable without
breaking the dynamic class/permission mapping to some degree.
Unfortunately I don't see these perf changes as a big enough "win" to
offset the loss of the dynamic mapping loss.

I'm okay with merging patches 1/3 and 2/3 wth the changes Stephen
suggested, but I think we will need to leave patch 3/3 out of this for
now.

-- 
paul moore
www.paul-moore.com