[PATCH] Input: focaltech - use signed coordinates to prevent underflow

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

focaltech_finger_state stores finger coordinates x and y as unsigned
int. When processing relative packets, negative deltas can cause
unsigned integer underflow if the finger moves past the left or bottom
boundary of the touchpad, wrapping the coordinates to values near
UINT_MAX.

When clamping the coordinates in focaltech_report_state(), these
underflowed values are clamped against priv->x_max / priv->y_max instead
of 0, causing the cursor to jump erratically to the opposite edge of the
touchpad.

Change the coordinate variables and limits to signed int so that
negative values resulting from relative movements clamp correctly to 0.

Fixes: 05be1d079ec0 ("Input: psmouse - support for the FocalTech PS/2 protocol extensions")
Reported-by: sashiko-bot@kernel.org
Assisted-by: Antigravity:gemini-3.6-flash
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
---
 drivers/input/mouse/focaltech.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/input/mouse/focaltech.c b/drivers/input/mouse/focaltech.c
index d3ad4af5aa09..c6f6540e3e29 100644
--- a/drivers/input/mouse/focaltech.c
+++ b/drivers/input/mouse/focaltech.c
@@ -78,8 +78,8 @@ struct focaltech_finger_state {
 	 * Absolute position (from the bottom left corner) of the
 	 * finger.
 	 */
-	unsigned int x;
-	unsigned int y;
+	int x;
+	int y;
 };
 
 /*
@@ -108,7 +108,7 @@ struct focaltech_hw_state {
 };
 
 struct focaltech_data {
-	unsigned int x_max, y_max;
+	int x_max, y_max;
 	struct focaltech_hw_state state;
 };
 
@@ -126,14 +126,14 @@ static void focaltech_report_state(struct psmouse *psmouse)
 		input_mt_slot(dev, i);
 		input_mt_report_slot_state(dev, MT_TOOL_FINGER, active);
 		if (active) {
-			unsigned int clamped_x, clamped_y;
+			int clamped_x, clamped_y;
 			/*
 			 * The touchpad might report invalid data, so we clamp
 			 * the resulting values so that we do not confuse
 			 * userspace.
 			 */
-			clamped_x = clamp(finger->x, 0U, priv->x_max);
-			clamped_y = clamp(finger->y, 0U, priv->y_max);
+			clamped_x = clamp(finger->x, 0, priv->x_max);
+			clamped_y = clamp(finger->y, 0, priv->y_max);
 			input_report_abs(dev, ABS_MT_POSITION_X, clamped_x);
 			input_report_abs(dev, ABS_MT_POSITION_Y,
 					 priv->y_max - clamped_y);
-- 
2.55.0.508.g3f0d502094-goog


-- 
Dmitry