linux-kernel - Re: [RESEND PATCH] pid_ns: Fix proc_flush_task() accessing freed proc

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Message-ID: <20100625183733.GA2627@us.ibm.com>
Date:	Fri, 25 Jun 2010 11:37:33 -0700
From:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Containers <containers@...ts.osdl.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH] pid_ns: Fix proc_flush_task() accessing freed
	proc_mnt

Louis Rilling [Louis.Rilling@...labs.com] wrote:
| - proc_pid_readdir():
|   Needs similar check and protection to proc_pid_lookup(), but there is another
|   issue: next_tgid() can find a dying task:

Hmm, I thought proc_pid_readdir() would be a problem too but convinced myself
that it would not - since a process running proc_pid_readdir() would have
a reference to the pid namespace, in which case destroy_pid_ns() would not
be called.
| 
|   next_tgid() finds a task
|                                    task dies
|                                    last reference to ns is dropped
|                                    destroy_pid_namespace()

caller of next_tgid() holds a ref to pid-ns right ?

Sukadev
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