[PATCH] Input: elan_i2c - prevent division by zero on invalid device parameters

[PATCH] Input: elan_i2c - prevent division by zero on invalid device parameters

[Ranjan Kumar]

The Elan I2C touchpad driver queries the device for its physical
dimensions and trace counts to calculate the device resolution and width.
However, if the device firmware or device tree provides invalid zero
values for x_traces, y_traces, x_mm, or y_mm, it results in a fatal
division-by-zero exception leading to a kernel panic during device probe.

Add sanity checks to ensure these physical parameters are non-zero
before performing the division. If invalid values are detected, log an
error and return -EINVAL to gracefully abort the initialization and
maintain system stability.

Fixes: 6696777c6506 ("Input: add driver for Elan I2C/SMbus touchpad")
Fixes: e3a9a1290688 ("Input: elan_i2c - do not query the info if they are provided")
Signed-off-by: Ranjan Kumar <kumarranja@chromium.org>
---
 drivers/input/mouse/elan_i2c_core.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/drivers/input/mouse/elan_i2c_core.c b/drivers/input/mouse/elan_i2c_core.c
index fee1796da3d0..b5fd63928afd 100644
--- a/drivers/input/mouse/elan_i2c_core.c
+++ b/drivers/input/mouse/elan_i2c_core.c
@@ -425,6 +425,14 @@ static int elan_query_device_parameters(struct elan_tp_data *data)
 		if (error)
 			return error;
 	}
+
+	if (unlikely(x_traces == 0 || y_traces == 0)) {
+		dev_err(&client->dev,
+			"Invalid trace numbers: x=%u, y=%u\n",
+			x_traces, y_traces);
+		return -EINVAL;
+	}
+
 	data->width_x = data->max_x / x_traces;
 	data->width_y = data->max_y / y_traces;
 
@@ -440,6 +448,14 @@ static int elan_query_device_parameters(struct elan_tp_data *data)
 		data->x_res = elan_convert_resolution(hw_x_res, data->pattern);
 		data->y_res = elan_convert_resolution(hw_y_res, data->pattern);
 	} else {
+
+		if (unlikely(x_mm == 0 || y_mm == 0)) {
+			dev_err(&client->dev,
+				"Invalid physical dimensions: x_mm=%u, y_mm=%u\n",
+				x_mm, y_mm);
+			return -EINVAL;
+		}
+
 		data->x_res = (data->max_x + 1) / x_mm;
 		data->y_res = (data->max_y + 1) / y_mm;
 	}
-- 
2.54.0.563.g4f69b47b94-goog

Re: [PATCH] Input: elan_i2c - prevent division by zero on invalid device parameters

[Dmitry Torokhov]

Hi Ranjan,

On Wed, May 13, 2026 at 07:39:08AM +0000, Ranjan Kumar wrote:
> The Elan I2C touchpad driver queries the device for its physical
> dimensions and trace counts to calculate the device resolution and width.
> However, if the device firmware or device tree provides invalid zero
> values for x_traces, y_traces, x_mm, or y_mm, it results in a fatal
> division-by-zero exception leading to a kernel panic during device probe.
> 

Neither crashing nor aborting probe with -EINVAL is great as we will not
be able to flash another firmware.

How do we get into this state? Is this something actually observed or
just theoretical?

> Add sanity checks to ensure these physical parameters are non-zero
> before performing the division. If invalid values are detected, log an
> error and return -EINVAL to gracefully abort the initialization and
> maintain system stability.

That is hardly "stability" for a laptop when its pointer is not working.

Thanks.

-- 
Dmitry

[PATCH v2] Input: elan_i2c - prevent division by zero on invalid device parameters

[Ranjan Kumar]

The Elan I2C touchpad driver queries the device for its physical
dimensions and trace counts to calculate the device resolution and width.
However, if the device firmware or device tree provides invalid zero
values for x_traces, y_traces, x_mm, or y_mm, it results in a fatal
division-by-zero exception leading to a kernel panic during device probe.

Add sanity checks to ensure these physical parameters are non-zero
before performing the division. If invalid values are detected, log a
warning and fall back to safe default values (1) to safely bypass the
division.

This prevents the kernel panic while allowing the probe to complete
successfully. Completing the probe ensures the sysfs nodes are created,
keeping the firmware update path intact so a recovery firmware can be
flashed to the device.

Fixes: 6696777c6506 ("Input: add driver for Elan I2C/SMbus touchpad")
Fixes: e3a9a1290688 ("Input: elan_i2c - do not query the info if they are provided")
Signed-off-by: Ranjan Kumar <kumarranja@chromium.org>
---
Changes in v2:
 - Changed error handling from aborting probe with -EINVAL to logging a
   warning and falling back to default values (1).
 - Bypassing the division instead of aborting preserves the sysfs
   interface for firmware updates and keeps the pointer functional.

 drivers/input/mouse/elan_i2c_core.c | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/drivers/input/mouse/elan_i2c_core.c b/drivers/input/mouse/elan_i2c_core.c
index fee1796da3d0..32b2849ab36a 100644
--- a/drivers/input/mouse/elan_i2c_core.c
+++ b/drivers/input/mouse/elan_i2c_core.c
@@ -425,8 +425,17 @@ static int elan_query_device_parameters(struct elan_tp_data *data)
 		if (error)
 			return error;
 	}
-	data->width_x = data->max_x / x_traces;
-	data->width_y = data->max_y / y_traces;
+
+	if (unlikely(x_traces == 0 || y_traces == 0)) {
+		dev_warn(&client->dev,
+			 "invalid trace numbers: x=%u, y=%u\n",
+			 x_traces, y_traces);
+		data->width_x = 1;
+		data->width_y = 1;
+	} else {
+		data->width_x = data->max_x / x_traces;
+		data->width_y = data->max_y / y_traces;
+	}
 
 	if (device_property_read_u32(&client->dev,
 				     "touchscreen-x-mm", &x_mm) ||
@@ -440,8 +449,16 @@ static int elan_query_device_parameters(struct elan_tp_data *data)
 		data->x_res = elan_convert_resolution(hw_x_res, data->pattern);
 		data->y_res = elan_convert_resolution(hw_y_res, data->pattern);
 	} else {
-		data->x_res = (data->max_x + 1) / x_mm;
-		data->y_res = (data->max_y + 1) / y_mm;
+		if (unlikely(x_mm == 0 || y_mm == 0)) {
+			dev_warn(&client->dev,
+				 "invalid physical dimensions: x_mm=%u, y_mm=%u\n",
+				 x_mm, y_mm);
+			data->x_res = 1;
+			data->y_res = 1;
+		} else {
+			data->x_res = (data->max_x + 1) / x_mm;
+			data->y_res = (data->max_y + 1) / y_mm;
+		}
 	}
 
 	if (device_property_read_bool(&client->dev, "elan,clickpad"))
-- 
2.54.0.563.g4f69b47b94-goog

Re: [PATCH v2] Input: elan_i2c - prevent division by zero on invalid device parameters

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Setting `width_x` and `width_y` to 1 as a fallback introduces a severe arithmetic underflow when calculating touch area sizes.
--

commit 592cc1df694c917c489ca1a6dcea8bd8b7a8d985
Author: Ranjan Kumar <kumarranja@chromium.org>

Input: elan_i2c - prevent division by zero on invalid device parameters

The Elan I2C touchpad driver queries the device for its physical dimensions
and trace counts to calculate the device resolution and width. If the device
provides invalid zero values, this commit adds checks to fall back to safe
default values of 1 to bypass the division and prevent a kernel panic.

> diff --git a/drivers/input/mouse/elan_i2c_core.c b/drivers/input/mouse/elan_i2c_core.c
> index fee1796da3d08..32b2849ab36a7 100644
> --- a/drivers/input/mouse/elan_i2c_core.c
> +++ b/drivers/input/mouse/elan_i2c_core.c
> @@ -425,8 +425,17 @@ static int elan_query_device_parameters(struct elan_tp_data *data)
>  		if (error)
>  			return error;
>  	}
> -	data->width_x = data->max_x / x_traces;
> -	data->width_y = data->max_y / y_traces;
> +
> +	if (unlikely(x_traces == 0 || y_traces == 0)) {
> +		dev_warn(&client->dev,
> +			 "invalid trace numbers: x=%u, y=%u\n",
> +			 x_traces, y_traces);
> +		data->width_x = 1;
> +		data->width_y = 1;

Does setting these fallback values to 1 introduce an arithmetic underflow
regression when calculating touch area sizes?

In elan_report_absolute() and elan_report_contact(), the touch area sizes are
calculated using an expression like:

    area_x = mk_x * (data->width_x - ETP_FWIDTH_REDUCE);

Since ETP_FWIDTH_REDUCE is 90 and data->width_x is an unsigned int, setting
the width to 1 causes the subtraction to underflow, resulting in a massive
unsigned integer.

When passed to input_report_abs(), this value is cast back to a negative
number, violating the 0 minimum boundary configured for ABS_MT_TOUCH_MAJOR.

Could this confuse userspace input handlers and trigger unwanted behaviors?

To prevent this underflow while maintaining the firmware update fallback path,
should the fallback value be at least ETP_FWIDTH_REDUCE (90) instead of 1?

[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260515065235.1913403-1-kumarranja@chromium.org?part=1