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: Gui-Dong Han <hanguidong02@gmail.com>
Link: https://lore.kernel.org/r/20251126113542.9968-1-hanguidong02@gmail.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

diff --git a/drivers/hwmon/lm87.c b/drivers/hwmon/lm87.c
index d2d970e73c61653e49f386921568d734db92bf7a..37bf2d1d3d099897c71e49381940d924c374041c 100644 (file)
--- a/drivers/hwmon/lm87.c
+++ b/drivers/hwmon/lm87.c
@@ -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) {