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Subject: Re: [PATCH] io_uring: Fix NULL pointer dereference in
 io_sq_wq_submit_work()
From:   Jens Axboe <axboe@kernel.dk>
To:     yinxin_1989 <yinxin_1989@aliyun.com>,
        viro <viro@zeniv.linux.org.uk>
Cc:     linux-block <linux-block@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
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 <ae9f3887-5205-8aa8-afa7-4e01d03921bc@kernel.dk>
 <67f27d17-81fa-43a8-baa9-429b1ccd65d0.yinxin_1989@aliyun.com>
 <4eeefb43-488c-dc90-f47c-10defe6f9278@kernel.dk>
Message-ID: <98f2cbbf-4f6f-501b-2f4e-1b8b803ce6a6@kernel.dk>
Date:   Tue, 1 Sep 2020 14:01:59 -0600
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On 9/1/20 8:52 AM, Jens Axboe wrote:
> On 8/31/20 10:59 PM, yinxin_1989 wrote:
>>
>>> On 8/31/20 7:54 PM, Xin Yin wrote:
>>>> the commit <1c4404efcf2c0> ("<io_uring: make sure async workqueue
>>>> is canceled on exit>") caused a crash in io_sq_wq_submit_work().
>>>> when io_ring-wq get a req form async_list, which may not have been
>>>> added to task_list. Then try to delete the req from task_list will caused
>>>> a "NULL pointer dereference".
>>>
>>> Hmm, do you have a reproducer for this?
>>
>> I update code to linux5.4.y , and I can reproduce this issue on an arm
>> board and my x86 pc by fio tools.
> 
> Right, I figured this was 5.4 stable, as that's the only version that
> has this patch.

I took a closer look, and I think your patch can basically be boiled down
to this single hunk. If you agree, can you resend your patch with the
description based on that, then I'll get it queued up for 5.4-stable.
Thanks!

diff --git a/fs/io_uring.c b/fs/io_uring.c
index fada14ee1cdc..cbbcd85780c4 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2378,6 +2378,16 @@ static bool io_add_to_prev_work(struct async_list *list, struct io_kiocb *req)
 		list_del_init(&req->list);
 		ret = false;
 	}
+
+	if (ret) {
+		struct io_ring_ctx *ctx = req->ctx;
+		unsigned long flags;
+
+		spin_lock_irqsave(&ctx->task_lock, flags);
+		list_add(&req->task_list, &ctx->task_list);
+		req->work_task = NULL;
+		spin_unlock_irqrestore(&ctx->task_lock, flags);
+	}
 	spin_unlock(&list->lock);
 	return ret;
 }

-- 
Jens Axboe