[PATCH v3] HID: wacom: avoid overflows in sequence number tracking

[Aldo Ariel Panzardo <qwe.aldo@gmail.com>]

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

Normalize the maximum and current value according to the HID parser's
signedness rule, and keep the sequence state and arithmetic in s64. Use
div64_s64() for the remainder to avoid __moddi3 link failures on 32-bit
architectures. This also avoids overflowing value + 1 at the logical
maximum.

Fixes: 359673ea3a20 ("HID: wacom: Support sequence numbers smaller than 16-bit")
Cc: stable@vger.kernel.org
Signed-off-by: Aldo Ariel Panzardo <qwe.aldo@gmail.com>
---

Changes in v3:
  - Replace raw s64 modulo with div64_s64()-based remainder to avoid
    __moddi3 link failure on 32-bit architectures (i386, arm32).
    Reported by Sashiko AI review.

Changes in v2:
  - Normalize logical_maximum/value as unsigned when logical_minimum >= 0,
    matching HID parser signedness. Store sequence state as s64.
    Fixes unsigned 0..UINT32_MAX range that broke v1.

 drivers/hid/wacom_wac.c | 33 ++++++++++++++++++++++++---------
 drivers/hid/wacom_wac.h |  2 +-
 2 files changed, 25 insertions(+), 10 deletions(-)

diff --git a/drivers/hid/wacom_wac.c b/drivers/hid/wacom_wac.c
index da1f0ea856..af94f59a5d 100644
--- a/drivers/hid/wacom_wac.c
+++ b/drivers/hid/wacom_wac.c
@@ -7,6 +7,7 @@
 #include "wacom.h"
 #include <linux/input/mt.h>
 #include <linux/jiffies.h>
+#include <linux/math64.h>

 /* resolution for penabled devices */
 #define WACOM_PL_RES		20
@@ -2527,18 +2528,33 @@ static void wacom_wac_pen_event(struct hid_device *hdev, struct hid_field *field
 	case WACOM_HID_WD_BARRELSWITCH3:
 		wacom_wac->hid_data.barrelswitch3 = value;
 		return;
-	case WACOM_HID_WD_SEQUENCENUMBER:
-		if (wacom_wac->hid_data.sequence_number != value &&
+	case WACOM_HID_WD_SEQUENCENUMBER: {
+		s64 sequence_minimum = field->logical_minimum;
+		s64 sequence_maximum = sequence_minimum < 0 ?
+			(s64)field->logical_maximum :
+			(s64)(u32)field->logical_maximum;
+		s64 sequence_value = sequence_minimum < 0 ?
+			(s64)value : (s64)(u32)value;
+
+		if (wacom_wac->hid_data.sequence_number != sequence_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 = sequence_maximum -
+					    sequence_minimum + 1;
+			s64 drop_count = sequence_value -
+					 wacom_wac->hid_data.sequence_number;
+
+			drop_count -= div64_s64(drop_count, sequence_size) *
+				      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)
-			wacom_wac->hid_data.sequence_number = field->logical_minimum;
+		if (sequence_value >= sequence_maximum)
+			wacom_wac->hid_data.sequence_number = sequence_minimum;
+		else
+			wacom_wac->hid_data.sequence_number = sequence_value + 1;
 		return;
 	}
+	}

 	/* send pen events only when touch is up or forced out
 	 * or touch arbitration is off
diff --git a/drivers/hid/wacom_wac.h b/drivers/hid/wacom_wac.h
index 126bec6e5c..74e7c5a04a 100644
--- a/drivers/hid/wacom_wac.h
+++ b/drivers/hid/wacom_wac.h
@@ -324,7 +324,7 @@ struct hid_data {
 	int bat_connected;
 	int ps_connected;
 	bool pad_input_event_flag;
-	int sequence_number;
+	s64 sequence_number;
 	ktime_t time_delayed;
 };

--
2.43.0