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SubjectRe: usb/sound/bcd2000: warning in bcd2000_init_device
On Wed, 04 Oct 2017 11:24:42 +0200,
Johan Hovold wrote:
>
> 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 endpoint may exist but it may be invalid, as the problem is
triggered by a VM. It doesn't parse but tries a fixed EP as it's no
compliant device.

> 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.

Could you give an example? Then I can ask Andrey whether such a call
really addresses the issue.


thanks,

Takashi

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