Re: [PATCH] usb: usbip: fix null pointer dereference

[Sudip Mukherjee]

On Friday 03 June 2016 09:29 AM, Krzysztof Opasiak wrote:
> On 06/02/2016 03:22 PM, Sudip Mukherjee wrote:
> > We have been dereferencing udc before checking it. Lets use it after it
> > has been checked.
>
> To be honest I have mixed feelings about this patch.
>
> On one hand it prevents us from dereferencing potential NULL ptr what is
> generally good. But on the other hand it seems to be a little bit
> pointless overhead. This function is called only in one place, it's
> internal function of vudc driver and in addition generally it is
> currently impossible that this function will get NULL ptr as parameter
> as it's value is taken from container_of(). Not to mention that if this
> is NULL or garbage we will end up in NULL ptr dereference much earlier
> before calling this function.
>
> So if there is something that you would like to fix with this patch and
> you have a real problem with this function could you please provide us
> some more details (for example stack trace)? If this patch is just to
> prevent us from something that will never happen then I would rather to
> not submit this. In my opinion if we get a NULL in this function this
> means that we have some serious problem in UDC core and this check will
> just mask this error.

Yes, I should have seen earlier that the only caller has already 
dereferenced udc. So maybe the following will be appropriate in this 
situation.

Regards
Sudip

diff --git a/drivers/usb/usbip/vudc_sysfs.c b/drivers/usb/usbip/vudc_sysfs.c
index 99397fa..0f98f2c 100644
--- a/drivers/usb/usbip/vudc_sysfs.c
+++ b/drivers/usb/usbip/vudc_sysfs.c
@@ -40,7 +40,7 @@ int get_gadget_descs(struct vudc *udc)
 	struct usb_ctrlrequest req;
 	int ret;
 
-	if (!udc || !udc->driver || !udc->pullup)
+	if (!udc->driver || !udc->pullup)
 		return -EINVAL;
 
 	req.bRequestType = USB_DIR_IN | USB_TYPE_STANDARD | USB_RECIP_DEVICE;