linux-kernel - Re: [PATCH review 08/16] userns: Kill task_user

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Date:	Mon, 19 Nov 2012 14:34:50 -0800
From:	Kees Cook <keescook@...omium.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Linux Containers <containers@...ts.linux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	"Serge E. Hallyn" <serge@...lyn.com>,
	James Morris <james.l.morris@...cle.com>
Subject: Re: [PATCH review 08/16] userns: Kill task_user_ns

On Mon, Nov 19, 2012 at 7:12 AM, Eric W. Biederman
<ebiederm@...ssion.com> wrote:
> From: "Eric W. Biederman" <ebiederm@...ssion.com>
>
> The task_user_ns function hides the fact that it is getting the user
> namespace from struct cred on the task.  struct cred may go away as
> soon as the rcu lock is released.  This leads to a race where we
> can dereference a stale user namespace pointer.
>
> To make it obvious a struct cred is involved kill task_user_ns.
>
> To kill the race modify the users of task_user_ns to only
> reference the user namespace while the rcu lock is held.
>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: James Morris <james.l.morris@...cle.com>
> Acked-by: Serge Hallyn <serge.hallyn@...onical.com>
> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>

Nice catch! This is disappointingly messy looking, but I do not see
any sensible way to clean it up better than you've already done.

Acked-by: Kees Cook <keescook@...omium.org>

-Kees

-- 
Kees Cook
Chrome OS Security
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