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

[Andrew de los Reyes]

I would think you'd need to call hid_device_io_stop in probe before
returning just to make sure the hid->driver_input_lock is in the right
state. You may be able to consult hid->io_started in the probe thread
after calling probe, and do the appropriate cleanup if probe returned
error. IMHO I like to keep things like lock/unlock in pairs near each
other, so it seems preferable to require that drivers handle calling
hid_device_io_stop themselves if probe will fail. I don't know in
general what the Linux stance is, tho.

-andrew

On Thu, Dec 11, 2014 at 9:53 AM, Peter Wu <peter@xxxxxxxxxxxxx> wrote:
> 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@xxxxxxxxxx> 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@xxxxxxxxxx>
>> >
>> > Cheers,
>> > Benjamin
>> >
>> > >
>> > > Signed-off-by: Peter Wu <peter@xxxxxxxxxxxxx>
>> > > ---
>> > > 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
>> > >
>
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