[alsa-devel] usb/sound/bcd2000: warning in bcd2000_init_device

[Johan Hovold]

On Wed, Oct 04, 2017 at 08:10:59AM +0200, Takashi Iwai wrote:
> On Tue, 03 Oct 2017 19:42:21 +0200,
> Greg Kroah-Hartman wrote:
> > 
> > On Tue, Oct 03, 2017 at 12:50:08PM -0400, Alan Stern wrote:
> > > On Tue, 3 Oct 2017, Takashi Iwai wrote:
> > > 
> > > > > It's a dev_WARN because it indicates a potentially serious error in the 
> > > > > driver: The driver has submitted an interrupt URB to a bulk endpoint.  
> > > > > That may not sound bad, but the same check gets triggered if a driver 
> > > > > submits a bulk URB to an isochronous endpoint, or any other invalid 
> > > > > combination.
> > > > > 
> > > > > Most likely the explanation here is that the driver doesn't bother to
> > > > > check the endpoint type because it expects the endpoint will always be
> > > > > interrupt.  But that is not a safe strategy.  USB devices and their
> > > > > firmware should not be trusted unnecessarily.
> > > > > 
> > > > > The best fix is, like you said, to add a sanity check in the caller.
> > > > 
> > > > OK, but then do we have some handy helper for the check?
> > > > As other bug reports by syzkaller suggest, there are a few other
> > > > drivers that do the same, submitting a urb with naive assumption of
> > > > the fixed EP for specific devices.  In the end we'll need to put the
> > > > very same checks there in multiple places.
> > > 
> > > Perhaps we could add a helper routine that would take a list of 
> > > expected endpoint types and check that the actual endpoints match the 
> > > types.  But of course, all the drivers you're talking about would have 
> > > to add a call to this helper routine.
> > 
> > We have almost this type of function, usb_find_common_endpoints(),
> > what's wrong with using that?  Johan has already swept the tree and
> > added a lot of these checks, odds are no one looked at the sound/
> > subdir...

Yeah, I only swept the tree for instances were a missing endpoint could
lead to a NULL-deref. This is not the case here were the endpoint
addresses are hardcoded in the driver.

I also never got around to applying the new helper outside of
drivers/usb.

> Well, what I had in my mind is just a snippet from usb_submit_urb(),
> something like:
> 
> bool usb_sanity_check_urb_pipe(struct urb *urb)
> {
> 	struct usb_host_endpoint *ep;
> 	int xfertype;
> 	static const int pipetypes[4] = {
> 		PIPE_CONTROL, PIPE_ISOCHRONOUS, PIPE_BULK, PIPE_INTERRUPT
> 	};
> 
> 	ep = usb_pipe_endpoint(urb->dev, urb->pipe);
> 	xfertype = usb_endpoint_type(&ep->desc);
> 	return usb_pipetype(urb->pipe) != pipetypes[xfertype];
> }
> 
> And calling this before usb_submit_urb() in each place that assigns
> the fixed EP as device-specific quirks.
> Does it make sense?

Not really. Your driver should not even bind to an interface which lacks
the expected endpoints (rather than check this at a potentially later
point in time when URBs are submitted).

The new helper which Greg mentioned would allow this to implemented with
just a few lines of code. Just add it to bcd2000_init_midi() or similar.  

Thanks,
Johan