linux-kernel - Re: [PATCH] capabilities: add capability cgroup controller

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Date:	Fri, 24 Jun 2016 10:59:16 -0500
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Topi Miettinen <toiwoton@...il.com>, linux-kernel@...r.kernel.org,
	luto@...nel.org, serge@...lyn.com, keescook@...omium.org,
	Jonathan Corbet <corbet@....net>,
	Li Zefan <lizefan@...wei.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	James Morris <james.l.morris@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Howells <dhowells@...hat.com>,
	David Woodhouse <David.Woodhouse@...el.com>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Petr Mladek <pmladek@...e.com>,
	"open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
	"open list:CONTROL GROUP (CGROUP)" <cgroups@...r.kernel.org>,
	"open list:CAPABILITIES" <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH] capabilities: add capability cgroup controller

Quoting Tejun Heo (tj@...nel.org):
> Hello,
> 
> On Fri, Jun 24, 2016 at 12:22:54AM +0000, Topi Miettinen wrote:
> > > This doesn't have anything to do with resource control and I don't
> > > think it's a good idea to add arbitrary monitoring mechanisms to
> > > cgroup just because it's easy to add interface there.  Given that
> > > capabilities are inherited and modified through the process hierarchy,
> > > shouldn't this be part of that?
> > 
> > With per process tracking, it's easy to miss if a short-lived process
> > exercised capabilities. Especially with ambient capabilities, the parent
> > process could be a shell script which might not use capabilities at all,
> > but its children do the heavy lifting.
> 
> But isn't being recursive orthogonal to using cgroup?  Why not account
> usages recursively along the process hierarchy?  Capabilities don't
> have much to do with cgroup but everything with process hierarchy.
> That's how they're distributed and modified.  If monitoring their
> usages is necessary, it makes sense to do it in the same structure.

That was my argument against using cgroups to enforce a new bounding
set.  For tracking though, the cgroup process tracking seems as applicable
to this as it does to systemd tracking of services.  It tracks a task and
the children it forks.