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

[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@vger.kernel.org
Signed-off-by: Aldo Ariel Panzardo <qwe.aldo@gmail.com>
---
 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

[PATCH v2] 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 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. 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>
---
 drivers/hid/wacom_wac.c | 32 ++++++++++++++++++++++++--------
 drivers/hid/wacom_wac.h |  2 +-
 2 files changed, 25 insertions(+), 9 deletions(-)

diff --git a/drivers/hid/wacom_wac.c b/drivers/hid/wacom_wac.c
index da1f0ea856..428ac7077a 100644
--- a/drivers/hid/wacom_wac.c
+++ b/drivers/hid/wacom_wac.c
@@ -2527,18 +2527,34 @@ 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 %= 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

Re: [PATCH v2] HID: wacom: avoid overflows in sequence number tracking

[kernel test robot]

Hi Aldo,

kernel test robot noticed the following build errors:

[auto build test ERROR on hid/for-next]
[also build test ERROR on linus/master v7.3-rc3 next-20260914]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Aldo-Ariel-Panzardo/HID-wacom-avoid-overflows-in-sequence-number-tracking/20260915-111621
base:   https://git.kernel.org/pub/scm/linux/kernel/git/hid/hid.git for-next
patch link:    https://lore.kernel.org/r/20260915141621.3011011-1-qwe.aldo%40gmail.com
patch subject: [PATCH v2] HID: wacom: avoid overflows in sequence number tracking
config: arm-randconfig-1001-20260916 (https://download.01.org/0day-ci/archive/20260917/202609170218.u9lMtoL0-lkp@intel.com/config)
compiler: arm-linux-gnueabi-gcc (GCC) 8.5.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260917/202609170218.u9lMtoL0-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202609170218.u9lMtoL0-lkp@intel.com/

All errors (new ones prefixed by >>, old ones prefixed by <<):

>> ERROR: modpost: drivers/hid/wacom.ko: symbol '__aeabi_ldivmod' undefined!

--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH v2] HID: wacom: avoid overflows in sequence number tracking

[kernel test robot]

Hi Aldo,

kernel test robot noticed the following build errors:

[auto build test ERROR on hid/for-next]
[also build test ERROR on linus/master v7.3-rc3]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Aldo-Ariel-Panzardo/HID-wacom-avoid-overflows-in-sequence-number-tracking/20260915-111621
base:   https://git.kernel.org/pub/scm/linux/kernel/git/hid/hid.git for-next
patch link:    https://lore.kernel.org/r/20260915141621.3011011-1-qwe.aldo%40gmail.com
patch subject: [PATCH v2] HID: wacom: avoid overflows in sequence number tracking
config: hexagon-allmodconfig (https://download.01.org/0day-ci/archive/20260917/202609171246.TbpsuolV-lkp@intel.com/config)
compiler: clang version 24.0.0git (https://github.com/llvm/llvm-project 148ee2b266b73a49f1f31d0bd17d4818b91bee9f)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260917/202609171246.TbpsuolV-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202609171246.TbpsuolV-lkp@intel.com/

All errors (new ones prefixed by >>, old ones prefixed by <<):

>> ERROR: modpost: drivers/hid/wacom.ko: symbol '__hexagon_moddi3' undefined!

--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

[PATCH v3] 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 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