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 fe4051024db3d8a10bf96b768563d1a24d4ab45a..f0f6e8de025ab2775bc30a01cc321a338bfc9140 100644 (file)
--- a/drivers/hid/wacom_wac.c
+++ b/drivers/hid/wacom_wac.c
@@ -1321,9 +1321,9 @@ 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]));