[PATCH] HID: wacom: avoid overflows in sequence number tracking

[Aldo Ariel Panzardo]

The dropped-packet calculation derives the sequence range in signed
int arithmetic. A sequence field whose logical range spans all signed
32-bit values makes the range calculation wrap to zero, so the following
modulo triggers a divide exception.

Do the range and delta calculations in s64, and normalize the delta after
the modulo. Also avoid overflowing value + 1 when the received value is at
the logical maximum.

Fixes: 359673ea3a20 ("HID: wacom: Support sequence numbers smaller than 16-bit")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Aldo Ariel Panzardo <qwe.aldo@xxxxxxxxx>
---
 drivers/hid/wacom_wac.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/drivers/hid/wacom_wac.c b/drivers/hid/wacom_wac.c
index da1f0ea856..39ffe5e7c7 100644
--- a/drivers/hid/wacom_wac.c
+++ b/drivers/hid/wacom_wac.c
@@ -2530,13 +2530,21 @@ static void wacom_wac_pen_event(struct hid_device *hdev, struct hid_field *field
 	case WACOM_HID_WD_SEQUENCENUMBER:
 		if (wacom_wac->hid_data.sequence_number != value &&
 		    wacom_wac->hid_data.sequence_number >= 0) {
-			int sequence_size = field->logical_maximum - field->logical_minimum + 1;
-			int drop_count = (value - wacom_wac->hid_data.sequence_number) % sequence_size;
-			hid_warn(hdev, "Dropped %d packets", drop_count);
+			s64 sequence_size = (s64)field->logical_maximum -
+					    field->logical_minimum + 1;
+			s64 drop_count = (s64)value -
+					 wacom_wac->hid_data.sequence_number;
+
+			drop_count %= sequence_size;
+			if (drop_count < 0)
+				drop_count += sequence_size;
+			hid_warn(hdev, "Dropped %lld packets",
+				 (long long)drop_count);
 		}
-		wacom_wac->hid_data.sequence_number = value + 1;
-		if (wacom_wac->hid_data.sequence_number > field->logical_maximum)
+		if (value >= field->logical_maximum)
 			wacom_wac->hid_data.sequence_number = field->logical_minimum;
+		else
+			wacom_wac->hid_data.sequence_number = value + 1;
 		return;
 	}
 
-- 
2.43.0