HID: wacom: Interpret tilt data from Intuos Pro BT as signed values

commit 49a397ad24ee5e2c53a59dada2780d7e71bd3f77 upstream.

The tilt data contained in the Bluetooth packets of an Intuos Pro are
supposed to be interpreted as signed values. Simply casting the values
to type `char` is not guaranteed to work since it is implementation-
defined whether it is signed or unsigned. At least one user has noticed
the data being reported incorrectly on their system. To ensure that the
data is interpreted properly, we specifically cast to `signed char`
instead.

Link: https://github.com/linuxwacom/input-wacom/issues/445
Fixes: 4922cd26f03c ("HID: wacom: Support 2nd-gen Intuos Pro's Bluetooth classic interface")
CC: stable@vger.kernel.org # 4.11+
Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/hid/wacom_wac.c b/drivers/hid/wacom_wac.c
index 7a16c65f20148ac1a9b3d229349bdb460734e4ba..001d7f996dc85d10c6a80af4d627f00260bd3705 100644 (file)
--- a/drivers/hid/wacom_wac.c
+++ b/drivers/hid/wacom_wac.c
@@ -1353,9 +1353,9 @@ static void wacom_intuos_pro2_bt_pen(struct wacom_wac *wacom)
                                        rotation -= 1800;
 
                                input_report_abs(pen_input, ABS_TILT_X,
-                                                (char)frame[7]);
+                                                (signed char)frame[7]);
                                input_report_abs(pen_input, ABS_TILT_Y,
-                                                (char)frame[8]);
+                                                (signed char)frame[8]);
                                input_report_abs(pen_input, ABS_Z, rotation);
                                input_report_abs(pen_input, ABS_WHEEL,
                                                 get_unaligned_le16(&frame[11]));