Re: [PATCH review 08/16] userns: Kill task_user_ns

Kees Cook
2012-11-19T22:34:53Z

On Mon, Nov 19, 2012 at 7:12 AM, Eric W. Biederman
<ebiederm@xmission.com> wrote:
> From: "Eric W. Biederman" <ebiederm@xmission.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@chromium.org>
> Cc: James Morris <james.l.morris@oracle.com>
> Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.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@chromium.org>

-Kees

--
Kees Cook
Chrome OS Security