linux-kernel - Re: [PATCH 1/1] kthread: introduce kthread_get_run() to fix __nbd

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Message-ID: <20151028152715.GA22672@redhat.com>
Date:	Wed, 28 Oct 2015 16:27:15 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Markus Pargmann <mpa@...gutronix.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>, nbd-general@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] kthread: introduce kthread_get_run() to fix
	__nbd_ioctl()

Markus,

sorry for delay, I didn't have email access two days,

On 10/26, Markus Pargmann wrote:
>
> On Sun, Oct 25, 2015 at 03:27:13PM +0100, Oleg Nesterov wrote:
> > It is not safe to use the task_struct returned by kthread_run(threadfn)
> > if threadfn() can exit before the "owner" does kthread_stop(), nothing
> > protects this task_struct.
> >
> > So __nbd_ioctl() looks buggy; a killed nbd_thread_send() can exit, free
> > its task_struct, and then kthread_stop() can use the freed/reused memory.
> >
> > Add the new trivial helper, kthread_get_run(). Hopefully it will have more
> > users, this patch changes __nbd_ioctl() as an example.
>
> Thanks.
>
> Acked-by: Markus Pargmann <mpa@...gutronix.de>
>
> However I am not sure this is important for 4.3 final. This bug is
> present since at least 2008 (didn't look further).

Ah yes, I din't bother to check the history of this code, thanks.

So this bug is very old, no need to push the fix into 4.3.

Oleg.

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