Re: [PATCH v1 1/1] USB: serial: Add boundry check for read_urbs array access

[sathyanarayanan kuppuswamy]

On 03/08/2018 03:43 PM, Greg KH wrote:
> On Thu, Mar 08, 2018 at 03:29:48PM -0800, sathyanarayanan kuppuswamy wrote:
> > On 03/08/2018 12:54 AM, Oliver Neukum wrote:
> > > Am Mittwoch, den 07.03.2018, 13:41 -0800 schrieb sathyanarayanan
> > > kuppuswamy       :
> > > > On 03/07/2018 12:58 PM, Greg KH wrote:
> > > > > So I don't see why your check is needed, what other code path would ever
> > > > > call this function in a way that the bounds check would be needed?
> > > > void usb_serial_generic_read_bulk_callback(struct urb *urb)
> > > >
> > > > 385ÂÂÂÂÂÂÂÂ for (i = 0; i < ARRAY_SIZE(port->read_urbs); ++i) {
> > > > 386ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ if (urb == port->read_urbs[i])
> > > > 387ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ break;
> > > > 388ÂÂÂÂÂÂÂÂ }
> > > >
> > > > In here, after this for loop is done (without any matching urb), i value
> > > > will be equal to ARRAY_SIZE(port->read_urbs). So there is a possibility
> > > > of usb_serial_generic_submit_read_urb() getting called with this invalid
> > > > index.
> > > If this happens the function was called for a stray URB.
> > > Your check comes to late. We have called set_bit with an invalid index
> > > and other shit.
> > > We definitely do not just want to return an error in that case.
> > In that case do you think we should use some WARN_ON() for invalid index in
> > usb_serial_generic_read_bulk_callback()?
> No, again, how could that ever happen?
>
> Don't add pointless error checking for things that are impossible to
> ever hit :)
Thanks Greg.
> thanks,
>
> greg k-h
> --
> To unsubscribe from this list: send the line "unsubscribe linux-usb" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

--
Sathyanarayanan Kuppuswamy
Linux kernel developer