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HID: wacom: Ignore attempts to overwrite the touch_max value from HID

Message ID 20210216194154.111950-1-jason.gerecke@wacom.com (mailing list archive)
State Mainlined
Commit 88f38846bfb1a452a3d47e38aeab20a4ceb74294
Delegated to: Jiri Kosina
Headers show
Series HID: wacom: Ignore attempts to overwrite the touch_max value from HID | expand

Commit Message

Jason Gerecke Feb. 16, 2021, 7:41 p.m. UTC
The `wacom_feature_mapping` function is careful to only set the the
touch_max value a single time, but this care does not extend to the
`wacom_wac_finger_event` function. In particular, if a device sends
multiple HID_DG_CONTACTMAX items in a single feature report, the
driver will end up retaining the value of last item.

The HID descriptor for the Cintiq Companion 2 does exactly this. It
incorrectly sets a "Report Count" of 2, which will cause the driver
to process two HID_DG_CONTACTCOUNT items. The first item has the actual
count, while the second item should have been declared as a constant
zero. The constant zero is the value the driver ends up using, however,
since it is the last HID_DG_CONTACTCOUNT in the report.

    Report ID (16),
    Usage (Contact Count Maximum),  ; Contact count maximum (55h, static value)
    Report Count (2),
    Logical Maximum (10),
    Feature (Variable),

To address this, we add a check that the touch_max is not already set
within the `wacom_wac_finger_event` function that processes the
HID_DG_TOUCHMAX item. We emit a warning if the value is set and ignore
the updated value.

This could potentially cause problems if there is a tablet which has
a similar issue but requires the last item to be used. This is unlikely,
however, since it would have to have a different non-zero value for
HID_DG_CONTACTMAX earlier in the same report, which makes no sense
except in the case of a firmware bug. Note that cases where the
HID_DG_CONTACTMAX items are in different reports is already handled
(and similarly ignored) by `wacom_feature_mapping` as mentioned above.

Link: https://github.com/linuxwacom/input-wacom/issues/223
Fixes: 184eccd40389 ("HID: wacom: generic: read HID_DG_CONTACTMAX from any feature report")
Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>
CC: stable@vger.kernel.org
---
 drivers/hid/wacom_wac.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

Comments

Jiri Kosina Feb. 18, 2021, 8:36 a.m. UTC | #1
On Tue, 16 Feb 2021, Jason Gerecke wrote:

> The `wacom_feature_mapping` function is careful to only set the the
> touch_max value a single time, but this care does not extend to the
> `wacom_wac_finger_event` function. In particular, if a device sends
> multiple HID_DG_CONTACTMAX items in a single feature report, the
> driver will end up retaining the value of last item.
> 
> The HID descriptor for the Cintiq Companion 2 does exactly this. It
> incorrectly sets a "Report Count" of 2, which will cause the driver
> to process two HID_DG_CONTACTCOUNT items. The first item has the actual
> count, while the second item should have been declared as a constant
> zero. The constant zero is the value the driver ends up using, however,
> since it is the last HID_DG_CONTACTCOUNT in the report.
> 
>     Report ID (16),
>     Usage (Contact Count Maximum),  ; Contact count maximum (55h, static value)
>     Report Count (2),
>     Logical Maximum (10),
>     Feature (Variable),
> 
> To address this, we add a check that the touch_max is not already set
> within the `wacom_wac_finger_event` function that processes the
> HID_DG_TOUCHMAX item. We emit a warning if the value is set and ignore
> the updated value.
> 
> This could potentially cause problems if there is a tablet which has
> a similar issue but requires the last item to be used. This is unlikely,
> however, since it would have to have a different non-zero value for
> HID_DG_CONTACTMAX earlier in the same report, which makes no sense
> except in the case of a firmware bug. Note that cases where the
> HID_DG_CONTACTMAX items are in different reports is already handled
> (and similarly ignored) by `wacom_feature_mapping` as mentioned above.
> 
> Link: https://github.com/linuxwacom/input-wacom/issues/223
> Fixes: 184eccd40389 ("HID: wacom: generic: read HID_DG_CONTACTMAX from any feature report")
> Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>
> CC: stable@vger.kernel.org
> ---
>  drivers/hid/wacom_wac.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hid/wacom_wac.c b/drivers/hid/wacom_wac.c
> index 1bd0eb71559c..44d715c12f6a 100644
> --- a/drivers/hid/wacom_wac.c
> +++ b/drivers/hid/wacom_wac.c
> @@ -2600,7 +2600,12 @@ static void wacom_wac_finger_event(struct hid_device *hdev,
>  		wacom_wac->is_invalid_bt_frame = !value;
>  		return;
>  	case HID_DG_CONTACTMAX:
> -		features->touch_max = value;
> +		if (!features->touch_max) {
> +			features->touch_max = value;
> +		} else {
> +			hid_warn(hdev, "%s: ignoring attempt to overwrite non-zero touch_max "
> +				 "%d -> %d\n", __func__, features->touch_max, value);
> +		}
>  		return;

Applied, thanks Jason.
diff mbox series

Patch

diff --git a/drivers/hid/wacom_wac.c b/drivers/hid/wacom_wac.c
index 1bd0eb71559c..44d715c12f6a 100644
--- a/drivers/hid/wacom_wac.c
+++ b/drivers/hid/wacom_wac.c
@@ -2600,7 +2600,12 @@  static void wacom_wac_finger_event(struct hid_device *hdev,
 		wacom_wac->is_invalid_bt_frame = !value;
 		return;
 	case HID_DG_CONTACTMAX:
-		features->touch_max = value;
+		if (!features->touch_max) {
+			features->touch_max = value;
+		} else {
+			hid_warn(hdev, "%s: ignoring attempt to overwrite non-zero touch_max "
+				 "%d -> %d\n", __func__, features->touch_max, value);
+		}
 		return;
 	}