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Subject: Re: [PATCH] usb: dwc2: fix possible NULL pointer dereference caused
 by driver concurrency
To:     Greg KH <gregkh@linuxfoundation.org>
Cc:     hminas@synopsys.com, linux-usb@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <2023092552-tulip-yo-yo-cbb3@gregkh>
From:   Jia-Ju Bai <baijiaju@buaa.edu.cn>
Message-ID: <e8ee2457-0d43-834c-8bdb-69791dc9fc34@buaa.edu.cn>
Date:   Mon, 25 Sep 2023 18:11:05 +0800
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Thanks for the reply :)

On 2023/9/25 17:38, Greg KH wrote:
> On Mon, Sep 25, 2023 at 05:17:41PM +0800, Jia-Ju Bai wrote:
>> In _dwc2_hcd_urb_enqueue(), "urb->hcpriv = NULL" is executed without
>> holding the lock "hsotg->lock". In _dwc2_hcd_urb_dequeue():
>>
>>      spin_lock_irqsave(&hsotg->lock, flags);
>>      ...
>> 	if (!urb->hcpriv) {
>> 		dev_dbg(hsotg->dev, "## urb->hcpriv is NULL ##\n");
>> 		goto out;
>> 	}
>>      rc = dwc2_hcd_urb_dequeue(hsotg, urb->hcpriv); // Use urb->hcpriv
>>      ...
>> out:
>>      spin_unlock_irqrestore(&hsotg->lock, flags);
>>
>> When _dwc2_hcd_urb_enqueue() and _dwc2_hcd_urb_dequeue() are
>> concurrently executed, the NULL check of "urb->hcpriv" can be executed
>> before "urb->hcpriv = NULL". After urb->hcpriv is NULL, it can be used
>> in the function call to dwc2_hcd_urb_dequeue(), which can cause a NULL
>> pointer dereference.
> Odd trailing spaces in your changelog text, is that intentional?

They are caused by the configuration of my file editor, and I changed it 
just now.

>
>> To fix this possible bug, "urb->hcpriv = NULL" should be executed with
>> holding the lock "hsotg->lock".
>>
>> Signed-off-by: Jia-Ju Bai <baijiaju@buaa.edu.cn>
>> ---
>>   drivers/usb/dwc2/hcd.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/usb/dwc2/hcd.c b/drivers/usb/dwc2/hcd.c
>> index 657f1f659ffa..35c7a4df8e71 100644
>> --- a/drivers/usb/dwc2/hcd.c
>> +++ b/drivers/usb/dwc2/hcd.c
>> @@ -4769,8 +4769,8 @@ static int _dwc2_hcd_urb_enqueue(struct usb_hcd *hcd, struct urb *urb,
>>   	if (qh_allocated && qh->channel && qh->channel->qh == qh)
>>   		qh->channel->qh = NULL;
>>   fail2:
>> -	spin_unlock_irqrestore(&hsotg->lock, flags);
>>   	urb->hcpriv = NULL;
>> +	spin_unlock_irqrestore(&hsotg->lock, flags);
>>   	kfree(qtd);
>>   fail1:
>>   	if (qh_allocated) {
>> -- 
>> 2.34.1
>>
> What commit id does this fix?
>
> And how did you test this to verify it works properly?
>
> And how was it found?

I sent a v2 patch to add these details and fix the mistakes about 
trailing spaces.


Thanks,
Jia-Ju Bai