[PATCH v3] HID: wacom: avoid overflows in sequence number tracking
From: Aldo Ariel Panzardo <hidden>
Date: 2026-09-15 14:52:49
Also in:
lkml, stable
Subsystem:
hid core layer, hid wacom driver, the rest · Maintainers:
Jiri Kosina, Benjamin Tissoires, Ping Cheng, Jason Gerecke, Linus Torvalds
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 <redacted>
---
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