Re: [PATCH v2 5/5] md: protect md_thread with a new disk level spin lock

[Guoqing Jiang <guoqing.jiang@linux.dev>]

On 3/15/23 14:18, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@huawei.com>
>
> Our test reports a uaf for 'mddev->sync_thread':
>
> T1                      T2
> md_start_sync
>   md_register_thread
> 			raid1d
> 			 md_check_recovery
> 			  md_reap_sync_thread
> 			   md_unregister_thread
> 			    kfree
>
>   md_wakeup_thread
>    wake_up
>    ->sync_thread was freed

Better to provide the relevant uaf (user after free perhaps you mean)
log from the test.

> Currently, a global spinlock 'pers_lock' is borrowed to protect
> 'mddev->thread', this problem can be fixed likewise, however, there might
> be similar problem for other md_thread, and I really don't like the idea to
> borrow a global lock.
>
> This patch use a disk level spinlock to protect md_thread in relevant apis.

It is array level I think, and you probably want to remove the comment.

* pers_lockdoes extra service to protect accesses to
* mddev->thread when the mutex cannot be held.

Thanks,
Guoqing