linux-kernel - Re: [PATCH v2] io_uring: fix use-after-free of sq->thread in __io_uring_show

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Message-ID: <aEh9DxZ0AQSSranB@kbusch-mbp>
Date: Tue, 10 Jun 2025 12:44:31 -0600
From: Keith Busch <kbusch@...nel.org>
To: Penglei Jiang <superman.xpt@...il.com>
Cc: axboe@...nel.dk, io-uring@...r.kernel.org, linux-kernel@...r.kernel.org,
	syzbot+531502bbbe51d2f769f4@...kaller.appspotmail.com
Subject: Re: [PATCH v2] io_uring: fix use-after-free of sq->thread in
 __io_uring_show_fdinfo()

On Tue, Jun 10, 2025 at 10:18:01AM -0700, Penglei Jiang wrote:
> @@ -379,7 +380,8 @@ static int io_sq_thread(void *data)
>  		io_sq_tw(&retry_list, UINT_MAX);
>  
>  	io_uring_cancel_generic(true, sqd);
> -	sqd->thread = NULL;
> +	rcu_assign_pointer(sqd->thread, NULL);

I believe this will fail a sparse check without adding the "__rcu" type
annotation on the struct's "thread" member.