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

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Date:	Mon, 27 Jun 2016 19:10:21 +0000
From:	Topi Miettinen <toiwoton@...il.com>
To:	"Serge E. Hallyn" <serge@...lyn.com>, Tejun Heo <tj@...nel.org>
Cc:	lkml <linux-kernel@...r.kernel.org>, luto@...nel.org,
	Kees Cook <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 06/27/16 14:54, Serge E. Hallyn wrote:
> Quoting Tejun Heo (tj@...nel.org):
>> Hello, Topi.
>>
>> On Sun, Jun 26, 2016 at 3:14 PM, Topi Miettinen <toiwoton@...il.com> wrote:
>>> The parent might be able do it if proc/pid/xyz files are still
>>> accessible after child exit but before its exit status is collected. But
>>> if the parent doesn't do it (and you are not able to change it to do it)
>>> and it collects the exit status without collecting other info, can you
>>> suggest a different way how another process could collect it 100% reliably?
>>
>> I'm not saying that there's such mechanism now. I'm suggesting that
>> that'd be a more fitting way of implementing a new mechanism to track
>> capability usages.
> 
> Hi Topi,
> 
> I think Eric was right a few emails earlier that the audit subsystem is
> really the most appropriate answer to this.  (Perhaps sysctl-controllered?)
> Combined with taskstats it would give you what you need.  Or you could even
> use an empty new named cgroup controller, say 'none,name=caps', and then
> look only at audit results for cgroup '/myapp' in the caps hierarchy.
> 

I'll have to study these more. But from what I saw so far, it looks to
me that a separate tool would be needed to read taskstats and if that
tool is not taken by distros, the users would not be any wiser, right?
With cgroup (or /proc), no new tools would be needed.

-Topi