[PATCH 2/3] Input: stmfts - validate slot ID in touch events

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

Both FTS4 and FTS5 contact and release reporting functions extract a
4-bit slot/touch ID (values 0 to 15) from the event payload. However,
the driver initializes only STMFTS_MAX_FINGERS (10) multi-touch slots.

Passing a slot ID greater than or equal to STMFTS_MAX_FINGERS to
input_mt_slot() is silently rejected by the input core without updating
mt->slot, which causes subsequent slot state, coordinate, or release
reports to corrupt or release the previously active slot.

Validate that the slot ID is strictly less than STMFTS_MAX_FINGERS in
stmfts_report_contact_event(), stmfts_report_contact_release(),
stmfts5_report_contact_event(), and stmfts5_report_contact_release(),
logging a warning and returning early when an invalid slot ID is
encountered.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
---
 drivers/input/touchscreen/stmfts.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/drivers/input/touchscreen/stmfts.c b/drivers/input/touchscreen/stmfts.c
index 3613c7f2ab15..25d127aa8642 100644
--- a/drivers/input/touchscreen/stmfts.c
+++ b/drivers/input/touchscreen/stmfts.c
@@ -232,6 +232,12 @@ static void stmfts_report_contact_event(struct stmfts_data *sdata,
 	u8 orientation = event[6];
 	u8 area = event[7];
 
+	if (slot_id >= STMFTS_MAX_FINGERS) {
+		dev_warn(&sdata->client->dev,
+			 "invalid slot ID %u\n", slot_id);
+		return;
+	}
+
 	input_mt_slot(sdata->input, slot_id);
 
 	input_mt_report_slot_state(sdata->input, MT_TOOL_FINGER, true);
@@ -250,6 +256,12 @@ static void stmfts_report_contact_release(struct stmfts_data *sdata,
 {
 	u8 slot_id = (event[0] & STMFTS_MASK_TOUCH_ID) >> 4;
 
+	if (slot_id >= STMFTS_MAX_FINGERS) {
+		dev_warn(&sdata->client->dev,
+			 "invalid slot ID %u\n", slot_id);
+		return;
+	}
+
 	input_mt_slot(sdata->input, slot_id);
 	input_mt_report_slot_inactive(sdata->input);
 
@@ -282,6 +294,12 @@ static void stmfts5_report_contact_event(struct stmfts_data *sdata,
 	int distance = 0;
 	unsigned int tool;
 
+	if (touch_id >= STMFTS_MAX_FINGERS) {
+		dev_warn(&sdata->client->dev,
+			 "invalid slot ID %u\n", touch_id);
+		return;
+	}
+
 	switch (touch_type) {
 	case STMFTS_TOUCH_TYPE_STYLUS:
 		tool = MT_TOOL_PEN;
@@ -340,6 +358,12 @@ static void stmfts5_report_contact_release(struct stmfts_data *sdata,
 	/* format: touch ID is in high 4 bits of event[1] */
 	u8 touch_id = (event[1] & STMFTS_MASK_TOUCH_ID) >> 4;
 
+	if (touch_id >= STMFTS_MAX_FINGERS) {
+		dev_warn(&sdata->client->dev,
+			 "invalid slot ID %u\n", touch_id);
+		return;
+	}
+
 	input_mt_slot(sdata->input, touch_id);
 	input_mt_report_slot_inactive(sdata->input);
 }
-- 
2.56.0.385.gac671c819a-goog