Re: [RFC 1/4] Add usb_get_address and usb_set_address support

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Aug 20, 2019 at 10:18:42PM +0000, Charles.Hyde@dellteam.com wrote:
> +int usb_get_address(struct usb_device *dev, unsigned char * mac)
> +{
> +	int ret = -ENOMEM;
> +	unsigned char *tbuf = kmalloc(256, GFP_NOIO);

On a technical level, why are you asking for 256 bytes here, and in the
control message, yet assuming you will only get 6 back for a correct
message?  Shouldn't you be only asking for 6 bytes?

> +
> +	if (!tbuf)
> +		return -ENOMEM;
> +
> +	ret = usb_control_msg(dev, usb_sndctrlpipe(dev, 0),
> +			USB_CDC_GET_NET_ADDRESS,
> +			USB_DIR_IN | USB_TYPE_CLASS | USB_RECIP_INTERFACE,
> +			0, USB_REQ_SET_ADDRESS, tbuf, 256,
> +			USB_CTRL_GET_TIMEOUT);
> +	if (ret == 6)
> +		memcpy(mac, tbuf, 6);
> +
> +	kfree(tbuf);
> +	return ret;

So if 100 is returned by the device (not likely, but let's say 7), then
you return 7 bytes, yet you did not copy the data into the pointer given
to you.

SHouldn't you report a real error for when this happens (hint, it will.)

thanks,

greg k-h