Commit be89cf78 authored by Gui-Dong Han's avatar Gui-Dong Han Committed by Guenter Roeck
Browse files

hwmon: (lm87) Convert macros to functions to avoid TOCTOU 

The macro FAN_FROM_REG evaluates its arguments multiple times. When used
in lockless contexts involving shared driver data, this causes
Time-of-Check to Time-of-Use (TOCTOU) race conditions.

Convert the macro to a static function. This guarantees that arguments
are evaluated only once (pass-by-value), preventing the race
conditions.

Adhere to the principle of minimal changes by only converting macros
that evaluate arguments multiple times and are used in lockless
contexts.

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/20251126113542.9968-1-hanguidong02@gmail.com


Signed-off-by: default avatarGuenter Roeck <linux@roeck-us.net>
parent fe5dbe31

drivers/hwmon/lm87.c

+11 −5
Original line number Diff line number Diff line
@@ -116,8 +116,14 @@ static u8 LM87_REG_TEMP_LOW[3] = { 0x3A, 0x38, 0x2C }; 
				 (((val) < 0 ? (val) - 500 : \

				   (val) + 500) / 1000))



#define FAN_FROM_REG(reg, div)	((reg) == 255 || (reg) == 0 ? 0 : \

				 (1350000 + (reg)*(div) / 2) / ((reg) * (div)))

static int fan_from_reg(int reg, int div)

{

	if (reg == 255 || reg == 0)

		return 0;



	return (1350000 + reg * div / 2) / (reg * div);

}



#define FAN_TO_REG(val, div)	((val) * (div) * 255 <= 1350000 ? 255 : \

				 (1350000 + (val)*(div) / 2) / ((val) * (div)))
@@ -465,7 +471,7 @@ static ssize_t fan_input_show(struct device *dev, 
	struct lm87_data *data = lm87_update_device(dev);

	int nr = to_sensor_dev_attr(attr)->index;



	return sprintf(buf, "%d\n", FAN_FROM_REG(data->fan[nr],

	return sprintf(buf, "%d\n", fan_from_reg(data->fan[nr],

		       FAN_DIV_FROM_REG(data->fan_div[nr])));

}
@@ -475,7 +481,7 @@ static ssize_t fan_min_show(struct device *dev, struct device_attribute *attr, 
	struct lm87_data *data = lm87_update_device(dev);

	int nr = to_sensor_dev_attr(attr)->index;



	return sprintf(buf, "%d\n", FAN_FROM_REG(data->fan_min[nr],

	return sprintf(buf, "%d\n", fan_from_reg(data->fan_min[nr],

		       FAN_DIV_FROM_REG(data->fan_div[nr])));

}
@@ -534,7 +540,7 @@ static ssize_t fan_div_store(struct device *dev, 
		return err;



	mutex_lock(&data->update_lock);

	min = FAN_FROM_REG(data->fan_min[nr],

	min = fan_from_reg(data->fan_min[nr],

			   FAN_DIV_FROM_REG(data->fan_div[nr]));



	switch (val) {