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

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Date:	Wed, 28 Mar 2012 10:48:38 +0400
From:	Cyrill Gorcunov <gorcunov@...nvz.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	"Serge E. Hallyn" <serge@...lyn.com>,
	Oleg Nesterov <oleg@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	"Serge E. Hallyn" <serge.hallyn@...onical.com>
Subject: Re: [rfc] fcntl: Add F_GETOWNER_UIDS option

On Tue, Mar 27, 2012 at 07:22:48PM -0700, Eric W. Biederman wrote:
> >> Hi Serge, thanks for info. But if it will be unconverted uid, can't
> >> be there some security problem with that which I missed?
> 
> I would suggest the easy route and create a KCONFIG dependency
> on !CONFIG_USER_NS until the code for that is a little farther along.
> 
> Hopefully later this week or begginning of next week I should be posting
> my patches and seeing how well the rest of the world takes them.
> 

CC me on them, please.

> > Noone is really using the user namespaces right now, but rather than
> > adding the cred (and refcounting concerns), my suggestion for now
> > would be to hardcode a check in modown() that current_user_ns() ==
> > &init_user_ns.

OK, thanks

> >
> > I *did* have a patch in the past which added the cred to fown, but
> > no idea where it is right now...
> 
> So I guess there are two questions.
> - Does it make sense besides translation to add a cred here in general?
> 

I personally fail to find a reason except uids translation.

> - How will it work with the user_namespace?
> 
>   I am just about ready to post a patchset that at the edges of
>   userspace maps all uid and gids into uid and gids in the initial user
>   namespace.

So, we could map tme into initial user namesapce right? And we could
require for a while that F_GETOWNER_UIDS should be called from initial
user namespace only. Then we could extend it for being called from any
user-namespace if such need appear. Or I miss something?

	Cyrill
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