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

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Date:	Fri, 24 Jun 2016 00:22:54 +0000
From:	Topi Miettinen <toiwoton@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	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

On 06/23/16 21:38, Tejun Heo wrote:
> Hello,
> 
> On Thu, Jun 23, 2016 at 06:07:10PM +0300, Topi Miettinen wrote:
>> There are many basic ways to control processes, including capabilities,
>> cgroups and resource limits. However, there are far fewer ways to find
>> out useful values for the limits, except blind trial and error.
>>
>> Currently, there is no way to know which capabilities are actually used.
>> Even the source code is only implicit, in-depth knowledge of each
>> capability must be used when analyzing a program to judge which
>> capabilities the program will exercise.
>>
>> Add a new cgroup controller for monitoring of capabilities
>> in the cgroup.
>>
>> Test case demonstrating basic capability monitoring and how the
>> capabilities are combined at next level (boot to rdshell):
> 
> 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.

Per process tracking (like in the version I sent earlier) could still be
added on top of this to complement cgroup level tracking, but I think
cgroup approach is more flexible as it can cover anything from a single
task to a collection of processes.

-Topi

> 
> Thanks.
>