Re: [PATCH] usb: gadget: udc: Add null pointer check for udc in gadget_match_driver

[Alan Stern]

On Fri, Aug 30, 2024 at 06:16:12PM +0530, Selvarasu Ganesan wrote:
> Hi Alan,
> 
> Thanks for your comments. I understand your suggestions. We already have 
> a similar reference check with the udc name before calling 
> usb_gadget_register_driver.
> In the drivers/usb/gadget/configfs.c file, I am wondering if there might 
> be an issue with the check of udc_name before 
> usb_gadget_register_driver. This is the only way to allow 
> gadget_register to be called before releasing or unregistering an 
> existing udc. Do you think we need to add an additional check here, 
> referencing the UDC, to prevent gadget_register from being called before 
> the existing UDC is released?

I don't understand what you're saying.  There is no routine named 
"gadget_register".  (And there is no variable named "udc_name" in the 
code below, although there is gi->composite.gadget_driver.udc_name -- 
but that's not a variable, it is a field in a structure.)

> drivers/usb/gadget/configfs.c : gadget_dev_desc_UDC_store()
> ===========================================================
> if (gi->composite.gadget_driver.udc_name) {
>                          ret = -EBUSY;
>                          goto err;
>                  }
> gi->composite.gadget_driver.udc_name = name;

Are you talking about this check and assignment?  Why do you think there 
might be a problem here?

Are you worried that some UDC might be released while this code is 
running?  If that happens, why would it be a problem?

> ret = usb_gadget_register_driver(&gi->composite.gadget_driver);

Alan Stern