linux-kernel - Re: [RFC] fs, proc: Introduce /proc/<pid>/task/<tid>/children entry v5

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Date:	Sun, 15 Jan 2012 19:48:06 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Tejun Heo <tj@...nel.org>, Andrew Vagin <avagin@...nvz.org>,
	Vasiliy Kulikov <segoon@...nwall.com>
Subject: Re: [RFC] fs, proc: Introduce /proc/<pid>/task/<tid>/children
	entry v5

On 01/15, Cyrill Gorcunov wrote:
>
> On Sun, Jan 15, 2012 at 07:07:21PM +0100, Oleg Nesterov wrote:
> >
> > Again. I simply can't understand what ptrace_may_access() actually
> > means. Why do we use the possible child, not parent?
> >
> > IOW. I have no idea if we really need any security check at all.
> > You can find the children pids without this patch anyway via.
> > grep PPid /proc/*/status.
> >
>
> OK, I see. I am actually not sure which behaviour should be there.
> What should we do if say we have a task with a number of children,
> which changed permissions of own and some of children. Look what I mean.
>
> We have say tid A, which has children B C D, and when we read
> /proc/pid/task/tid/children we should see "B C D" here. But
> what if say A started with roots rights, then changed own permission
> so everyone could read this /proc/pid/task/<A>/children, but
> left C with root permissions only. So should we list C here?

Why not? What is the problem to know the pid of this child? And once
again, you can list all children without this patch anyway.

Perhaps I missed something, but I simply don't understand the problem.

Oleg.

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