linux-kernel - Re: [PATCH] usb: dwc2: fix possible NULL pointer dereference caused by driver concurrency

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Message-ID: <2023092552-tulip-yo-yo-cbb3@gregkh>
Date:   Mon, 25 Sep 2023 11:38:38 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Jia-Ju Bai <baijiaju@...a.edu.cn>
Cc:     hminas@...opsys.com, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: dwc2: fix possible NULL pointer dereference caused
 by driver concurrency

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?

> 
> To fix this possible bug, "urb->hcpriv = NULL" should be executed with
> holding the lock "hsotg->lock".
> 
> Signed-off-by: Jia-Ju Bai <baijiaju@...a.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?

thanks,

greg k-h