linux-kernel - Re: call_usermodehelper in containers

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Date:	Wed, 24 Feb 2016 08:55:16 +0800
From:	Ian Kent <raven@...maw.net>
To:	"J. Bruce Fields" <bfields@...ldses.org>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Stanislav Kinsbursky <skinsbursky@...allels.com>,
	Jeff Layton <jlayton@...hat.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-nfs@...r.kernel.org, devel@...nvz.org, bharrosh@...asas.com,
	Linux Containers <containers@...ts.linux-foundation.org>
Subject: Re: call_usermodehelper in containers

On Tue, 2016-02-23 at 09:36 -0500, J. Bruce Fields wrote:
> On Tue, Feb 23, 2016 at 10:55:30AM +0800, Ian Kent wrote:
> > You know, wrt. the mechanism Oleg suggested, I've been wondering if
> > it's
> > even necessary to capture process template information for
> > execution.
> > 
> > Isn't the main issue the execution of unknown arbitrary objects
> > getting
> > access to a privileged context?
> > 
> > Then perhaps it is sufficient to require registration of an SHA hash
> > (of
> > some sort) for these objects by a suitably privileged process and
> > only
> > allow helper execution of valid objects.
> 
> That executable probably also depends on libraries, services, and tons
> of other miscellaneous stuff in its environment.  The NFSv4 client
> idmapper, for example, may be doing ldap calls.  Unless the helper is
> created with incredible care, I don't think that it's enough just to
> verify that you're executing the correct helper.

Yeah, I was thinking the logistics of keeping something like this up to
date would be hard but calculating this for every call would be too much
overhead I think.

> 
> --b.
> 
> > 
> > If that is sufficient then helper execution from within a container
> > or
> > user namespace could just use the callers environment itself.
> > 
> > What else do we need to be wary of, any thoughts Eric?
> > 
> > Ian