hwmon: (lm63) Add locking to avoid TOCTOU

The functions show_fan(), show_pwm1(), show_temp11(),
temp2_crit_hyst_show(), and show_lut_temp_hyst() access shared cached
data without holding the update lock. This can cause TOCTOU races if
the cached values change between the checks and the later calculations.

Those cached values are updated in lm63_update_device(). In the general
case, the affected functions combine multiple cached values without
locking and can therefore observe a mixed old/new snapshot. In
addition, show_fan() reads data->fan[nr] locklessly while
lm63_update_device() updates data->fan[0] in two steps, which can
expose an intermediate torn value and potentially trigger a
divide-by-zero error. This means that converting the macro to a
function is not sufficient to fix show_fan().

Hold the update lock across the whole read and calculation sequence so
that the values remain stable.

Check the other functions in the driver as well. Keep them unchanged
because they either do not access shared cached values multiple times
or already do so under lock.

Link: https://lore.kernel.org/linux-hwmon/CALbr=LYJ_ehtp53HXEVkSpYoub+XYSTU8Rg=o1xxMJ8=5z8B-g@mail.gmail.com/
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Fixes: e872c91e726e ("hwmon: (lm63) Add support for unsigned upper temperature limits")
Fixes: d216f6809eb6 ("hwmon: (lm63) Expose automatic fan speed control lookup table")
Signed-off-by: Gui-Dong Han <hanguidong02@gmail.com>
Link: https://lore.kernel.org/r/20260416135703.53262-1-hanguidong02@gmail.com
[groeck: Use lm63_update_device() to get driver data in temp2_crit_hyst_store]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

0 files changed, 0 insertions, 0 deletions