linux-kernel - [PATCH 0/1] pid_namespace: pidns_get() should check task_active_pid

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Message-ID: <20140402154447.GA29857@redhat.com>
Date:	Wed, 2 Apr 2014 17:44:47 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Matthew Dempsky <mdempsky@...omium.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Kees Cook <keescook@...omium.org>,
	Julien Tinnes <jln@...omium.org>,
	Roland McGrath <mcgrathr@...omium.org>,
	Jan Kratochvil <jan.kratochvil@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 0/1] pid_namespace: pidns_get() should check
	task_active_pid_ns() != NULL

On 04/02, Oleg Nesterov wrote:
>
> Especially because this code needs a fix. Yes, rcu_read_lock() should
> be enough to ensure that ->parent and its namespace (if !NULL) can not
> go away, but task_active_pid_ns() can return NULL release_task(->parent)
> was already (although this race is pure theoretical). So this helper
> should also check it is !NULL under rcu_read_lock(), afaics.
>
> (Hmm... off-topic, but get_pidns looks buggy by the same reason, I'll
>  send a fix).

Eric, I have to admit that I din't bother to actually verify this, but
pidns_get() looks "obviously buggy". Could you ack/nack ?

Oleg.

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