hwmon: (max16065) Use local variable to avoid TOCTOU

[PATCH] hwmon: (max16065) Use local variable to avoid TOCTOU

Posted by Gui-Dong Han 3 days, 8 hours ago

In max16065_current_show, data->curr_sense is read twice: once for the
error check and again for the calculation. Since
i2c_smbus_read_byte_data returns negative error codes on failure, if the
data changes to an error code between the check and the use, ADC_TO_CURR
results in an incorrect calculation.

Read data->curr_sense into a local variable to ensure consistency. Note
that data->curr_gain is constant and safe to access directly.

This aligns max16065_current_show with max16065_input_show, which
already uses a local variable for the same reason.

Link: https://lore.kernel.org/all/CALbr=LYJ_ehtp53HXEVkSpYoub+XYSTU8Rg=o1xxMJ8=5z8B-g@mail.gmail.com/
Fixes: f5bae2642e3d ("hwmon: Driver for MAX16065 System Manager and compatibles")
Cc: stable@vger.kernel.org
Signed-off-by: Gui-Dong Han <hanguidong02@gmail.com>
---
Based on the discussion in the link, I will submit a series of patches to
address TOCTOU issues in the hwmon subsystem by converting macros to
functions or adjusting locking where appropriate.
---
 drivers/hwmon/max16065.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/hwmon/max16065.c b/drivers/hwmon/max16065.c
index 0ccb5eb596fc..4c9e7892a73c 100644
--- a/drivers/hwmon/max16065.c
+++ b/drivers/hwmon/max16065.c
@@ -216,12 +216,13 @@ static ssize_t max16065_current_show(struct device *dev,
 				     struct device_attribute *da, char *buf)
 {
 	struct max16065_data *data = max16065_update_device(dev);
+	int curr_sense = data->curr_sense;
 
-	if (unlikely(data->curr_sense < 0))
-		return data->curr_sense;
+	if (unlikely(curr_sense < 0))
+		return curr_sense;
 
 	return sysfs_emit(buf, "%d\n",
-			  ADC_TO_CURR(data->curr_sense, data->curr_gain));
+			  ADC_TO_CURR(curr_sense, data->curr_gain));
 }
 
 static ssize_t max16065_limit_store(struct device *dev,
-- 
2.43.0

Re: [PATCH] hwmon: (max16065) Use local variable to avoid TOCTOU

Posted by Guenter Roeck 3 days, 4 hours ago

On Fri, Nov 28, 2025 at 08:47:09PM +0800, Gui-Dong Han wrote:
> In max16065_current_show, data->curr_sense is read twice: once for the
> error check and again for the calculation. Since
> i2c_smbus_read_byte_data returns negative error codes on failure, if the
> data changes to an error code between the check and the use, ADC_TO_CURR
> results in an incorrect calculation.
> 
> Read data->curr_sense into a local variable to ensure consistency. Note
> that data->curr_gain is constant and safe to access directly.
> 
> This aligns max16065_current_show with max16065_input_show, which
> already uses a local variable for the same reason.
> 
> Link: https://lore.kernel.org/all/CALbr=LYJ_ehtp53HXEVkSpYoub+XYSTU8Rg=o1xxMJ8=5z8B-g@mail.gmail.com/
> Fixes: f5bae2642e3d ("hwmon: Driver for MAX16065 System Manager and compatibles")
> Cc: stable@vger.kernel.org
> Signed-off-by: Gui-Dong Han <hanguidong02@gmail.com>

Applied.

Thanks,
Guenter