linux-kernel - Re: call_usermodehelper in containers

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Message-ID: <20131119095116.1254aeaa@tlielax.poochiereds.net>
Date:	Tue, 19 Nov 2013 09:51:16 -0500
From:	Jeff Layton <jlayton@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Stanislav Kinsbursky <skinsbursky@...allels.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-nfs@...r.kernel.org, devel@...nvz.org, bfields@...ldses.org,
	bharrosh@...asas.com
Subject: Re: call_usermodehelper in containers

On Mon, 18 Nov 2013 19:02:59 +0100
Oleg Nesterov <oleg@...hat.com> wrote:

> On 11/18, Oleg Nesterov wrote:
> >
> > On 11/15, Eric W. Biederman wrote:
> > >
> > > I don't understand that one.  Having a preforked thread with the proper
> > > environment that can act like kthreadd in terms of spawning user mode
> > > helpers works and is simple.
> >
> > Can't we ask ->child_reaper to create the non-daemonized kernel thread
> > with the "right" ->nsproxy, ->fs, etc?
> >
> > IOW. Please the the "patch" below. It is obviously incomplete and wrong,
> > and it can be more clear/clean. And probably we need another API. Just
> > to explain what I mean.
> 
> Or, perhaps UMH_IN_MY_NS should only work if ->child_reaper explicitly
> does, say, prctl(PR_SPAWN_UMH_IN_NS_HELPER) which forks the non-daemonized
> kernel kthread_worker thread, I dunno.
> 
> Oleg.
> 

Neat idea.

So is it always the case that tasks in a container have the same
namespace settings and capabilities as the child_reaper?

We'll still have the basic problem for nfsd that we'll need to keep
track of what the child_reaper is when nfsd is started, but I think
that's not too hard to solve.

-- 
Jeff Layton <jlayton@...hat.com>
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