Re: [Nbd] [PATCH 1/1] kthread: introduce kthread_get_run() to fix __nbd_ioctl()
- To: Markus Pargmann <mpa@...1897...>
- Cc: Tejun Heo <tj@...1285...>, nbd-general@lists.sourceforge.net, Andrew Morton <akpm@...133...>, linux-kernel@...25...
- Subject: Re: [Nbd] [PATCH 1/1] kthread: introduce kthread_get_run() to fix __nbd_ioctl()
- From: Oleg Nesterov <oleg@...696...>
- Date: Wed, 28 Oct 2015 16:27:15 +0100
- Message-id: <20151028152715.GA22672@...696...>
- In-reply-to: <20151026073314.GD16521@...1897...>
- References: <20151025142655.GA30961@...696...> <20151025142713.GA30965@...696...> <20151026073314.GD16521@...1897...>
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@...1897...>
>
> 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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