linux-kernel - Re: [PATCH] usb: cdnsp: Fixes error: uninitialized symbol 'len'

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Date:   Wed, 5 Apr 2023 19:41:53 +0200
From:   Oliver Neukum <oneukum@...e.com>
To:     Greg KH <gregkh@...uxfoundation.org>,
        Pawel Laszczak <pawell@...ence.com>
Cc:     peter.chen@...nel.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] usb: cdnsp: Fixes error: uninitialized symbol 'len'

On 05.04.23 19:23, Greg KH wrote:
> On Fri, Mar 31, 2023 at 05:06:00AM -0400, Pawel Laszczak wrote:

>>   {
>>   	struct usb_ctrlrequest *ctrl = &pdev->setup;
>> -	int ret = 0;
>> +	int ret = -EINVAL;
>>   	u16 len;
>>   
>>   	trace_cdnsp_ctrl_req(ctrl);
>> @@ -424,7 +424,6 @@ void cdnsp_setup_analyze(struct cdnsp_device *pdev)
>>   
>>   	if (pdev->gadget.state == USB_STATE_NOTATTACHED) {
>>   		dev_err(pdev->dev, "ERR: Setup detected in unattached state\n");
>> -		ret = -EINVAL;
> 
> That's a nice change, but I don't see the original error here that you
> are saying this change fixes.
> 
> What am I missing?

The function has this check at its beginning:

        if (!pdev->gadget_driver)
                 goto out;

ret is initialized to 0 and len is uninitialized.
The jump goes to:

out:
         if (ret < 0)
                 cdnsp_ep0_stall(pdev);
         else if (!len && pdev->ep0_stage != CDNSP_STATUS_STAGE)
                 cdnsp_status_stage(pdev);


The compiler (and an analysis tool) can determine that len will be
evaluated in an uninitialized state. Setting ret to something
negative prevents that. I must say this is convoluted, even though
it is correct.

	HTH
		Oliver