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

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Date:	Thu, 11 Dec 2014 10:31:18 -0500
From:	Benjamin Tissoires <benjamin.tissoires@...hat.com>
To:	Peter Wu <peter@...ensteyn.nl>
Cc:	Jiri Kosina <jkosina@...e.cz>,
	Nestor Lopez Casado <nlopezcasad@...itech.com>,
	Andrew de los Reyes <adlr@...omium.org>,
	Peter Hutterer <peter.hutterer@...-t.net>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] HID: logitech-hidpp: disable io in probe error path

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@...hat.com>

Cheers,
Benjamin

> 
> Signed-off-by: Peter Wu <peter@...ensteyn.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:
> 
> 		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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