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hwmon: (w83791d) 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 leads to
Time-of-Check to Time-of-Use (TOCTOU) race conditions, potentially
causing divide-by-zero errors.

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

Additionally, in store_fan_div, move the calculation of the minimum
limit inside the update lock. This ensures that the read-modify-write
sequence operates on consistent data.

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/
Fixes: 9873964d6e ("[PATCH] HWMON: w83791d: New hardware monitoring driver for the Winbond W83791D")
Cc: stable@vger.kernel.org
Signed-off-by: Gui-Dong Han <hanguidong02@gmail.com>
Link: https://lore.kernel.org/r/20251202180105.12842-1-hanguidong02@gmail.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
pull/1354/merge
Gui-Dong Han 2025-12-03 02:01:05 +08:00 committed by Guenter Roeck
parent 67a454e6b1
commit 670d7ef945
1 changed files with 12 additions and 7 deletions
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19
drivers/hwmon/w83791d.c
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@ -218,9 +218,14 @@ static u8 fan_to_reg(long rpm, int div)
return clamp_val((1350000 + rpm * div / 2) / (rpm * div), 1, 254);
}
#define FAN_FROM_REG(val, div) ((val) == 0 ? -1 : \
((val) == 255 ? 0 : \
1350000 / ((val) * (div))))
static int fan_from_reg(int val, int div)
{
if (val == 0)
return -1;
if (val == 255)
return 0;
return 1350000 / (val * div);
}
/* for temp1 which is 8-bit resolution, LSB = 1 degree Celsius */
#define TEMP1_FROM_REG(val) ((val) * 1000)
@ -521,7 +526,7 @@ static ssize_t show_##reg(struct device *dev, struct device_attribute *attr, \
struct w83791d_data *data = w83791d_update_device(dev); \
int nr = sensor_attr->index; \
return sprintf(buf, "%d\n", \
FAN_FROM_REG(data->reg[nr], DIV_FROM_REG(data->fan_div[nr]))); \
fan_from_reg(data->reg[nr], DIV_FROM_REG(data->fan_div[nr]))); \
}
show_fan_reg(fan);
@ -585,10 +590,10 @@ static ssize_t store_fan_div(struct device *dev, struct device_attribute *attr,
if (err)
return err;
/* Save fan_min */
min = FAN_FROM_REG(data->fan_min[nr], DIV_FROM_REG(data->fan_div[nr]));
mutex_lock(&data->update_lock);
/* Save fan_min */
min = fan_from_reg(data->fan_min[nr], DIV_FROM_REG(data->fan_div[nr]));
data->fan_div[nr] = div_to_reg(nr, val);
switch (nr) {