linux-kernel - Re: [PATCH] xacct_add_tsk: fix pure theoretical ->mm use-after-free

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Message-ID: <20061030204125.GB677@oleg>
Date:	Mon, 30 Oct 2006 23:41:25 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Jay Lan <jlan@...r.sgi.com>
Cc:	Andrew Morton <akpm@...l.org>,
	Shailabh Nagar <nagar@...son.ibm.com>,
	Balbir Singh <balbir@...ibm.com>, Jay Lan <jlan@....com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xacct_add_tsk: fix pure theoretical ->mm use-after-free

On 10/30, Jay Lan wrote:
>
> Oleg Nesterov wrote:
> > Paranoid fix. The task can free its ->mm after the 'if (p->mm)' check.
> 
> Why this change is necessary? This routine is indirectly invoked by
> taskstats_exit_send() routine called inside do_exit():

Not only, please note

	taskstats_user_cmd(TASKSTATS_CMD_ATTR_PID)->fill_pid()->xacct_add_tsk()

path. This tsk is not 'current', it was found by find_task_by_pid(), and
it may exit at any time.

Oleg.

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