linux-kernel - Re: [RFC PATCH] cgroup namespaces: add a 'nsroot=' mountinfo field

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Date:	Wed, 13 Apr 2016 14:01:52 -0500
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	"Serge E. Hallyn" <serge@...lyn.com>, linux-api@...r.kernel.org,
	adityakali@...gle.com,
	Linux Containers <containers@...ts.osdl.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	cgroups@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] cgroup namespaces: add a 'nsroot=' mountinfo field

Quoting Tejun Heo (tj@...nel.org):
> Hello, Serge.
> 
> On Wed, Apr 13, 2016 at 01:46:39PM -0500, Serge E. Hallyn wrote:
> > It's not a leak of any information we're trying to hide.  I realize
> > something like 8 years have passed, but I still basically go by the
> > ksummit guidance that containers are ok but the kernel's first priority
> > is to facilitate containers but not trick containers into thinking
> > they're not containerized.  So long as the container is properly set
> > up, I don't think there's anything the workload could do with the
> > nsroot= info other than *know* that it is in a ns cgroup.
> > 
> > If we did change that guidance, there's a slew of proc info that we
> > could better virtualize :)
> 
> I see.  I'm just wondering because the information here seems a bit
> gratuituous.  Isn't the only thing necessary telling whether the root
> is bind mounted or namescoped?  Wouldn't simple "nsroot" work for that
> purpose?

I don't think so - we could be in a cgroup namespace but still have
access only to bind-mounted cgroups.  So we need to compare the
superblock dentry root field to the nsroot= value.