linux-kernel - Re: [PATCH 1/1] ptrace: do_notify_parent_cldstop: fix the wrong ->nsproxy usage

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Date:	Mon, 1 Jun 2009 21:54:18 -0700
From:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
To:	Roland McGrath <roland@...hat.com>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Hellwig <hch@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Pavel Emelyanov <xemul@...nvz.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] ptrace: do_notify_parent_cldstop: fix the wrong
	->nsproxy usage

Roland McGrath [roland@...hat.com] wrote:
| > Yes. Perhaps it would be nice to add a helper,
| 
| I agree.
| 
| > > sys_kill, do_tkill all look wrong to me.
| > 
| > They should be fine, note the
| > 
| > 	if (from_ancestor_ns)
| > 		q->info.si_pid = 0;
| > 
| > in __send_signal(). If we send the signal "down" to the sub-namespace,
| > si_pid == 0 is correct. And, unlike do_notify_parent/ptrace_notify/etc
| > kill/tkill can't send the signal "up".
| 
| Ah, right.  I knew there was something around this I was forgetting.

Setting si_pid to task_tgid_vnr(current); in places like do_tkill() is
slightly misleading bc, it can get modified later in send_signal().  We
can't set si_pid correctly in do_tkill() since we must first establish
pid-namespace relationship and that can mess up control flow.

Maybe a comment will help.
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