thermal: add sanity check for the passive attribute

Values below 1000 milli-celsius don't make sense and can cause the
system to go into a thermal heart attack: the actual temperature
will always be lower and thus the system will be throttled down to
its lowest setting.

An additional problem is that values below 1000 will show as 0 in
/proc/acpi/thermal/TZx/trip_points:passive.

cat passive
0
echo -n 90 >passive
bash: echo: write error: Invalid argument
echo -n 90000 >passive
cat passive
90000

Signed-off-by: Frans Pop <elendil@planet.nl>
Acked-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Len Brown <len.brown@intel.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/drivers/thermal/thermal_sys.c b/drivers/thermal/thermal_sys.c
index 6f8d8f971212..310e40ab00b6 100644
--- a/drivers/thermal/thermal_sys.c
+++ b/drivers/thermal/thermal_sys.c
@@ -225,6 +225,12 @@ passive_store(struct device *dev, struct device_attribute *attr,
         if (!sscanf(buf, "%d\n", &state))
                 return -EINVAL;
 
+        /* sanity check: values below 1000 millicelcius don't make sense
+         * and can cause the system to go into a thermal heart attack
+         */
+        if (state && state < 1000)
+                return -EINVAL;
+
         if (state && !tz->forced_passive) {
                 mutex_lock(&thermal_list_lock);
                 list_for_each_entry(cdev, &thermal_cdev_list, node) {