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hwmon: (emc2103) Add locking to avoid TOCTOU

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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: Gui-Dong Han <hanguidong02@gmail.com>
Link: https://lore.kernel.org/r/20251124165508.4667-1-hanguidong02@gmail.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
This commit is contained in:
Gui-Dong Han
2025-11-25 00:55:08 +08:00
committed by Guenter Roeck
parent edbce49ea6
commit 4faaa77d6b
1 changed files with 4 additions and 0 deletions
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4
drivers/hwmon/emc2103.c
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@@ -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);
}