linux-kernel - [PATCH 0/2] (Was: user namespace: make signal.c respect user namespaces)

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Date:	Tue, 20 Sep 2011 16:39:20 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Serge E. Hallyn" <serge@...lyn.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Howells <dhowells@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	"Serge E. Hallyn" <serge.hallyn@...onical.com>,
	lkml <linux-kernel@...r.kernel.org>, richard@....at,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Tejun Heo <tj@...nel.org>
Subject: [PATCH 0/2] (Was: user namespace: make signal.c respect user
	namespaces)

On 09/20, Oleg Nesterov wrote:
>
> On 09/20, Serge E. Hallyn wrote:
> >
> > Quoting Oleg Nesterov (oleg@...hat.com):
> > >
> > > 	static inline uid_t good_name(struct task_struct *from, struct task_struct *to)
> > > 	{
> > > 		// the caller does rcu_read_lock() if needed
> > > 		const struct cred *from_cred = __task_cred(from);
> > > 		return user_ns_map_uid(task_cred_xxx(to, user_ns),
> > > 					from_cred, from_cred->uid);
> > > 	}
> >
> > That looks great, thanks.  I couldn't think it up myself, but now that
> > I see it in your email, I see this would be very valuable in helping
> > make this code more readable  :)
>
> Damn ;) The problem is, "the caller does rcu_read_lock() if needed"
> can't shut up __rcu_dereference_check(). current_cred() passes c == true
> to do this.
>
> This reminds me, __task_cred()->task_is_dead() should go away. Probably
> we can replace it with (__t == current). Otherwise send_signal() needs
> rcu_read_lock() to avoid the warning from lockdep, or the helper needs
> the unconditional rcu_read_lock().

IOW, I think we need 2 simple patches first.

The problem is, I have no idea how can I really test these changes ;)
David, Paul, may be you can review...

Oleg.

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