linux-kernel - Re: [PATCH] apparmor: remove the "task" arg from may_change_ptraced

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Date:	Thu, 26 Sep 2013 09:25:19 -0400
From:	Richard Guy Briggs <rgb@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	John Johansen <john.johansen@...onical.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] apparmor: remove the "task" arg from
 may_change_ptraced_domain()

On Tue, Sep 24, 2013 at 06:44:42PM +0200, Oleg Nesterov wrote:
> On 09/23, Richard Guy Briggs wrote:
> >
> > On Mon, Sep 16, 2013 at 04:20:35PM +0200, Oleg Nesterov wrote:
> > > Unless task == current ptrace_parent(task) is not safe even under
> > > rcu_read_lock() and most of the current users are not right.
> >
> > Could you point to an explanation of this?
> 
> If this task exits before rcu_read_lock() ->parent can point to the
> already freed/reused memory.

Ok, understood.  So even though the task may have exited, the task
struct pointer is still valid, but not the contents of the task struct
to which it points.

> (in the long term we should probably clear
>  ->parent/real_parent/group_leader/more in __unhash_process(), but
>  lets not discuss this right now ;)

...so that the contents are valid in a task struct of a task that has
exited.

Thanks for the (more obvious to me now) explanation.

> Oleg.

- RGB

--
Richard Guy Briggs <rbriggs@...hat.com>
Senior Software Engineer
Kernel Security
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