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

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Message-ID: <48f61e8e-1de6-4737-9e58-145d4599b0c0@kernel.dk>
Date: Tue, 10 Jun 2025 12:56:31 -0600
From: Jens Axboe <axboe@...nel.dk>
To: Keith Busch <kbusch@...nel.org>, Penglei Jiang <superman.xpt@...il.com>
Cc: 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 6/10/25 12:44 PM, Keith Busch wrote:
> 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.

I think that only happens the other way around, eg accessing them directly
when marked with __rcu. I could be entirely wrong, though...

-- 
Jens Axboe