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

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Message-ID: <87eh1fisfm.fsf@x220.int.ebiederm.org>
Date:	Wed, 02 Apr 2014 09:53:33 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Matthew Dempsky <mdempsky@...omium.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	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: Re: [PATCH 1/1] pid_namespace: pidns_get() should check task_active_pid_ns() != NULL

Oleg Nesterov <oleg@...hat.com> writes:

> pidns_get()->get_pid_ns() can hit ns == NULL. This task_struct can't
> go away, but task_active_pid_ns(task) is NULL if release_task(task)
> was already called. Alternatively we could change get_pid_ns(ns) to
> check ns != NULL, but it seems that other callers are fine.

get_pid_ns already has a ns == NULL check, so no code changes should be
needed.

Eric

>
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
>
> --- x/kernel/pid_namespace.c
> +++ x/kernel/pid_namespace.c
> @@ -318,7 +318,9 @@ static void *pidns_get(struct task_struct *task)
>  	struct pid_namespace *ns;
>  
>  	rcu_read_lock();
> -	ns = get_pid_ns(task_active_pid_ns(task));
> +	ns = task_active_pid_ns(task);
> +	if (ns)
> +		get_pid_ns(ns);
>  	rcu_read_unlock();
>  
>  	return ns;
--
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