Re: [PATCH 4/4] HID: logitech-hidpp: disable io in probe error path

[Peter Wu <peter@lekensteyn.nl>]

On Thursday 11 December 2014 09:37:06 Andrew de los Reyes wrote:
> On Thu Dec 11 2014 at 7:31:43 AM Benjamin Tissoires
> <benjamin.tissoires@redhat.com> wrote:
> >
> > On Dec 11 2014 or thereabouts, Peter Wu wrote:
> > > Balance a hid_device_io_start() call with hid_device_io_stop() in the
> > > error path. This avoids processing of HID reports when the probe fails
> > > which possibly leads to invalid memory access in hid_device_probe() as
> > > report_enum->report_id_hash might already be freed via
> > > hid_close_report().
> >
> > Well spotted too!
> >
> > >
> > > hid_set_drvdata() is called before wtp_allocate, be consistent and clear
> > > drvdata too on the error path of wtp_allocate.
> >
> > This is not strictly speaking required. We will have a dangling value in
> > hdev->private_data, but this should be overwritten before the next use.
> >
> > Anyway, it makes sense to clean up after a failure, so the patch is
> > Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
> >
> > Cheers,
> > Benjamin
> >
> > >
> > > Signed-off-by: Peter Wu <peter@lekensteyn.nl>
> > > ---
> > > Hi Andrew,
> > >
> > > There are few users of hid_device_io_start/stop, this is the first one
> > > to get start/stop out of sync. Should the comment of
> > > hid_device_io_start() be updated to ensure that hid_device_io_stop()
> > > gets called before probe() returns? Or should the hid-core be changed to
> > > handle this out-of-sync issue:
> 
> I do not have a strong opinion on this, and will defer to others. The
> reason I needed to communicate during probe() was to have the driver
> probe the actual device for details. In this use case, I would be okay
> to disable IO at the end of probe() and have it become reenabled via
> the normal (default) methods.
> 
> -andrew

Keeping the reports enabled when the probe succeeds is fine, I am
referring to the error path. If the probe fails, then reports should
never be accepted or a corruption may occur (if I see it correctly).

Is this analysis correct?

 hid_device_probe()
   hid_device_io_start()
   return FAILURE
 hid_close_report(device)
   report_enum = device
        ->report_enum[i]
   hid_free_report(report_enum
        ->report_id_hash[j])    <-- NOTE: freed
                    ... interrupt occurs ...
                                    hid_input_report()
                                      hid_get_report()
                                        report = report_enum->report_id_hash[n];
                                                 ^ NOTE: use-after-free
                                        return report if not NULL
                                      hdrv->raw_event(report) <--- BOOM?
   kfree(device->rdesc)
 device->driver = NULL

Kind regards,
Peter

> > >
> > >               if (ret) {
> > >                       if (hdev->io_started))
> > >                               down(&hdev->driver_input_lock);
> > >                       hid_close_report(hdev);
> > >                       hdev->driver = NULL;
> > >               }
> > >
> > > Is my observation correct or not that HID reports can arrive during
> > > hid_close_report() when io_started == true?
> > >
> > > Kind regards,
> > > Peter
> > > ---
> > >  drivers/hid/hid-logitech-hidpp.c | 4 +++-
> > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/hid/hid-logitech-hidpp.c b/drivers/hid/hid-logitech-hidpp.c
> > > index 4292cc3..2f420c0 100644
> > > --- a/drivers/hid/hid-logitech-hidpp.c
> > > +++ b/drivers/hid/hid-logitech-hidpp.c
> > > @@ -1121,7 +1121,7 @@ static int hidpp_probe(struct hid_device *hdev, const struct hid_device_id *id)
> > >       if (hidpp->quirks & HIDPP_QUIRK_CLASS_WTP) {
> > >               ret = wtp_allocate(hdev, id);
> > >               if (ret)
> > > -                     return ret;
> > > +                     goto wtp_allocate_fail;
> > >       }
> > >
> > >       INIT_WORK(&hidpp->work, delayed_work_cb);
> > > @@ -1141,6 +1141,7 @@ static int hidpp_probe(struct hid_device *hdev, const struct hid_device_id *id)
> > >       if (id->group != HID_GROUP_LOGITECH_DJ_DEVICE) {
> > >               if (!connected) {
> > >                       hid_err(hdev, "Device not connected");
> > > +                     hid_device_io_stop(hdev);
> > >                       goto hid_parse_fail;
> > >               }
> > >
> > > @@ -1186,6 +1187,7 @@ hid_hw_start_fail:
> > >  hid_parse_fail:
> > >       cancel_work_sync(&hidpp->work);
> > >       mutex_destroy(&hidpp->send_mutex);
> > > +wtp_allocate_fail:
> > >       hid_set_drvdata(hdev, NULL);
> > >       return ret;
> > >  }
> > > --
> > > 2.1.3
> > >