[PATCH v3] Input: elan_i2c - prevent division by zero on invalid device parameters

[PATCH v3] 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 trace values are detected,
log a warning and fall back to ETP_FWIDTH_REDUCE to prevent arithmetic
underflow during touch reporting. For invalid physical dimensions, fall
back to a safe default of 1.

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 v3:
 - Changed trace fallback values from 1 to ETP_FWIDTH_REDUCE to prevent 
   an unsigned integer underflow in elan_report_absolute(). 
 Changes in v2:
 - Changed error handling from aborting probe with -EINVAL to logging a
   warning and falling back to default values.

 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..c64e1dd1e60b 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 = ETP_FWIDTH_REDUCE;
+		data->width_y = ETP_FWIDTH_REDUCE;
+	} 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 v3] Input: elan_i2c - prevent division by zero on invalid device parameters

[Dmitry Torokhov]

Hi Ranjan,

On Mon, May 18, 2026 at 06:26:24AM +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.
> 
> Add sanity checks to ensure these physical parameters are non-zero
> before performing the division. If invalid trace values are detected,
> log a warning and fall back to ETP_FWIDTH_REDUCE to prevent arithmetic
> underflow during touch reporting.

I would define some defaults that are not necessarily the same as
ETP_FWIDTH_REDUCE. The arithmetic overflow should be handled separately,
as it may still happen if we read (or set up via device tree) some small
(but non-zero) values.

> For invalid physical dimensions, fall
> back to a safe default of 1.
> 
> 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 v3:
>  - Changed trace fallback values from 1 to ETP_FWIDTH_REDUCE to prevent 
>    an unsigned integer underflow in elan_report_absolute(). 
>  Changes in v2:
>  - Changed error handling from aborting probe with -EINVAL to logging a
>    warning and falling back to default values.
> 
>  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..c64e1dd1e60b 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)) {

I'd say "if (!x_traces || !y_traces) ...". This is not hot path so
annotating with unlikely does not buy us anything.

I wonder if we should be comparing with some threshold instead of 0.
Something above 90 I guess.

Thanks.

-- 
Dmitry