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Date: Mon, 25 May 2009 21:39:32 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Christoph Hellwig <hch@infradead.org>, Ingo Molnar <mingo@elte.hu>,
       Pavel Emelyanov <xemul@openvz.org>, Roland McGrath <roland@redhat.com>,
       Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/1] ptrace: do_notify_parent_cldstop: fix the wrong
	->nsproxy usage
Message-ID: <20090525193932.GA22261@redhat.com>
References: <20090525185502.GA20781@redhat.com>
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On 05/25, Oleg Nesterov wrote:
>
> If the non-traced sub-thread calls do_notify_parent_cldstop(), we send the
> notification to group_leader->real_parent and we report group_leader's pid.
>
> But, if group_leader is traced we use the wrong ->parent->nsproxy->pid_ns,
> the tracer and parent can live in different namespaces. Change the code
> to use "parent" instead of tsk->parent.
>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
>
> --- PTRACE/kernel/signal.c~CLDSTOP_NS	2009-05-25 20:24:50.000000000 +0200
> +++ PTRACE/kernel/signal.c	2009-05-25 20:33:37.000000000 +0200
> @@ -1496,7 +1496,7 @@ static void do_notify_parent_cldstop(str
>  	 * see comment in do_notify_parent() abot the following 3 lines
>  	 */
>  	rcu_read_lock();
> -	info.si_pid = task_pid_nr_ns(tsk, tsk->parent->nsproxy->pid_ns);
> +	info.si_pid = task_pid_nr_ns(tsk, parent->nsproxy->pid_ns);


While this change is correct in any case (I hope), I wonder whether
we need another one:

	--- a/kernel/signal.c
	+++ b/kernel/signal.c
	@@ -1483,12 +1483,12 @@ static void do_notify_parent_cldstop(str
		struct task_struct *parent;
		struct sighand_struct *sighand;
	 
	+	if (!task_ptrace(tsk))
	+		tsk = tsk->group_leader;
	+
	+	parent = tsk->real_parent;
		if (task_ptrace(tsk))
			parent = tsk->parent;
	-	else {
	-		tsk = tsk->group_leader;
	-		parent = tsk->real_parent;
	-	}
	 
		info.si_signo = SIGCHLD;
		info.si_errno = 0;

If the sub-thread is not traced, but ->group_leader is, perhaps it makes
more sense to notify the leader's tracer, not parent?

Not that I think this is really important. Just curious about what was
the intent.

Oleg.