linux-kernel - Re: [PATCH 1/3] ptrace: ptrace_attach: check PF_KTHREAD + exit

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Date:	Tue, 5 May 2009 16:47:33 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	chrisw@...s-sol.org, roland@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] ptrace: ptrace_attach: check PF_KTHREAD +
 exit_state instead of ->mm

On Wed, 6 May 2009 00:47:22 +0200
Oleg Nesterov <oleg@...hat.com> wrote:

> - Add PF_KTHREAD check to prevent attaching to the kernel thread
>   with a borrowed ->mm.
> 
>   With or without this change we can race with daemonize() which
>   can set PF_KTHREAD or clear ->mm after ptrace_attach() does the
>   check, but this doesn't matter because reparent_to_kthreadd()
>   does ptrace_unlink().
> 
> - Kill "!task->mm" check. We don't really care about ->mm != NULL,
>   and the task can call exit_mm() right after we drop task_lock().
>   What we need is to make sure we can't attach after exit_notify(),
>   check task->exit_state != 0 instead.
> 

These patches make a mess of utrace-core.patch.  Do we really want to do that?
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