Re: [Nbd] [PATCH 1/1] kthread: introduce kthread_get_run() to fix __nbd_ioctl()
- To: Oleg Nesterov <oleg@...696...>
- Cc: Tejun Heo <tj@...1285...>, Andrew Morton <akpm@...133...>, nbd-general@lists.sourceforge.net, linux-kernel@...25...
- Subject: Re: [Nbd] [PATCH 1/1] kthread: introduce kthread_get_run() to fix __nbd_ioctl()
- From: Christoph Hellwig <hch@...1270...>
- Date: Mon, 26 Oct 2015 17:26:42 -0700
- Message-id: <20151027002642.GA32444@...1270...>
- In-reply-to: <20151025142713.GA30965@...696...>
- References: <20151025142655.GA30961@...696...> <20151025142713.GA30965@...696...>
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.
This looks horrible. I think the real problem is that nbd is totally
abusing signals for kthreads and that needs to go away.
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