linux-kernel - Re: [rfc] fcntl: Add F_GETOWNER

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Date:	Fri, 30 Mar 2012 16:15:00 +0000
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
Cc:	Serge Hallyn <serge.hallyn@...onical.com>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Oleg Nesterov <oleg@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pavel Emelyanov <xemul@...allels.com>, keescook@...omium.org
Subject: Re: [rfc] fcntl: Add F_GETOWNER_UIDS option

Quoting Cyrill Gorcunov (gorcunov@...nvz.org):
> On Fri, Mar 30, 2012 at 09:12:19AM -0500, Serge Hallyn wrote:
> ...
> > > 
> > > Yes, I wanna take a look on Eric's set first just to get right
> > > "picture" of everything. And I wanted to find a minimal solution
> > > with current kernel code base which could be extended in future.
> > > 
> > > That said I guess the current init-ns-only approach should do the
> > > trick for a while. And (thanks for pointing) I need to add a test
> > > if a caller which tries to obtain uids has enought credentials
> > > for that (probably CAP_FOWNER), right?
> > 
> > Sorry, I'm not sure which caller you mean.  Neither f_setown nor
> > f_getown require privilege right now.  Oh, you mean at restart?
> 
> I meant the dumper. Yes, at moment f_get/setown requires no privileges
> but I'm not sure if uid/euid is same or less sensible information
> than pid, that's why I though CAP_FOWNER might be worth to add, no?

Hmm, I would say no, but that might be a good question for kees.

IMO it's not sensitive information and so no sense requiring privilege
(and encouraging handing out of extra privilage to get at the info)

Cc:ing kees.

> > f_setown to someone else's uid/pid means you may cause a signal to
> > be sent to them.  So CAP_KILL might be good?  You do through that
> > signal get *some* info about the file writes, though not contents.
> > So yeah, maybe (CAP_KILL|CAP_FOWNER).
> ...
> > > I suspect operating with kuid's will be a way more easier.
> > 
> > Yeah, I keep going back and forth on which makes more sense.  But
> > kuid's probably make more sense, even though they aren't what
> > userspace in container will see.  When you restore, the mapping
> > will give userspace what it expects;  and if you're going to
> > restart in a container with a different mapping, then you'll
> > have to convert the filesystem as well since its inodes will
> > store kuids, so may as well also convert the kuids in the
> > checkpoint image then.
> 
> Agreed (if only I'm not missimg somethig ;)
> 
> 	Cyrill
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