Commit 4faaa77d authored by Gui-Dong Han's avatar Gui-Dong Han Committed by Guenter Roeck
Browse files

hwmon: (emc2103) Add locking to avoid TOCTOU 

The functions fan1_input_show and fan1_target_show check shared data for
zero before using it as a divisor. These accesses are currently
lockless. If the data changes to zero between the check and the
division, it causes a divide-by-zero error.

Explicitly acquire the update lock around these checks and calculations
to ensure the data remains stable, preventing Time-of-Check to
Time-of-Use (TOCTOU) race conditions.

Link: https://lore.kernel.org/all/CALbr=LYJ_ehtp53HXEVkSpYoub+XYSTU8Rg=o1xxMJ8=5z8B-g@mail.gmail.com/


Signed-off-by: default avatarGui-Dong Han <hanguidong02@gmail.com>
Link: https://lore.kernel.org/r/20251124165508.4667-1-hanguidong02@gmail.com


Signed-off-by: default avatarGuenter Roeck <linux@roeck-us.net>
parent edbce49e

drivers/hwmon/emc2103.c

+4 −0
Original line number Diff line number Diff line
@@ -277,8 +277,10 @@ fan1_input_show(struct device *dev, struct device_attribute *da, char *buf) 
{

	struct emc2103_data *data = emc2103_update_device(dev);

	int rpm = 0;

	mutex_lock(&data->update_lock);

	if (data->fan_tach != 0)

		rpm = (FAN_RPM_FACTOR * data->fan_multiplier) / data->fan_tach;

	mutex_unlock(&data->update_lock);

	return sprintf(buf, "%d\n", rpm);

}
@@ -363,10 +365,12 @@ fan1_target_show(struct device *dev, struct device_attribute *da, char *buf) 
	struct emc2103_data *data = emc2103_update_device(dev);

	int rpm = 0;



	mutex_lock(&data->update_lock);

	/* high byte of 0xff indicates disabled so return 0 */

	if ((data->fan_target != 0) && ((data->fan_target & 0x1fe0) != 0x1fe0))

		rpm = (FAN_RPM_FACTOR * data->fan_multiplier)

			/ data->fan_target;

	mutex_unlock(&data->update_lock);



	return sprintf(buf, "%d\n", rpm);

}