linux-kernel - Re: [RFC PATCH] usb: dwc3: gadget: Fix NULL pointer dereference in dwc3_gadget

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Date: Wed, 17 Jan 2024 01:19:01 +0000
From: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To: Uttkarsh Aggarwal <quic_uaggarwa@...cinc.com>
CC: Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: Re: [RFC PATCH] usb: dwc3: gadget: Fix NULL pointer dereference in
 dwc3_gadget_suspend

Hi,

On Wed, Jan 10, 2024, Uttkarsh Aggarwal wrote:
> In current scenario if Plug-out and Plug-In performed continuously
> there could be a chance while checking for dwc->gadget_driver in
> dwc3_gadget_suspend, a NULL pointer dereference may occur.
> 
> Call Stack:
> 
> 	CPU1:                           CPU2:
> 	gadget_unbind_driver            dwc3_suspend_common
> 	dw3_gadget_stop                 dwc3_gadget_suspend
>                                         dwc3_disconnect_gadget
> 
> CPU1 basically clears the variable and CPU2 checks the variable.
> Consider CPU1 is running and right before gadget_driver is cleared
> and in parallel CPU2 executes dwc3_gadget_suspend where it finds
> dwc->gadget_driver which is not NULL and resumes execution and then
> CPU1 completes execution. CPU2 executes dwc3_disconnect_gadget where
> it checks dwc->gadget_driver is already NULL because of which the
> NULL pointer deference occur.
> 
> To prevent this, moving NULL pointer check inside of spin_lock.
> 
> Signed-off-by: Uttkarsh Aggarwal <quic_uaggarwa@...cinc.com>
> ---
>  drivers/usb/dwc3/gadget.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> index 019368f8e9c4..564976b3e2b9 100644
> --- a/drivers/usb/dwc3/gadget.c
> +++ b/drivers/usb/dwc3/gadget.c
> @@ -4709,15 +4709,13 @@ int dwc3_gadget_suspend(struct dwc3 *dwc)
>  	unsigned long flags;
>  	int ret;
>  
> -	if (!dwc->gadget_driver)
> -		return 0;
> -
>  	ret = dwc3_gadget_soft_disconnect(dwc);
>  	if (ret)
>  		goto err;
>  
>  	spin_lock_irqsave(&dwc->lock, flags);
> -	dwc3_disconnect_gadget(dwc);
> +	if (dwc->gadget_driver)
> +		dwc3_disconnect_gadget(dwc);
>  	spin_unlock_irqrestore(&dwc->lock, flags);
>  
>  	return 0;
> -- 
> 2.17.1
> 

Do you have the dmesg log of this NULL pointer dereference?

Thanks,
Thinh