[PATCH v2] hwmon: (asus-ec-sensors) add WARN_ONCE() on invalid sensor index

[Alexei Safin]

Prevent undefined behavior by adding WARN_ONCE() when find_ec_sensor_index()
returns a negative value.

Even though unsupported attributes are filtered out by asus_ec_hwmon_is_visible(),
a programming error could still cause an invalid sensor access.

Instead of silently returning an error, log a warning to highlight the problem,
and propagate the original error code.

Update both asus_ec_hwmon_read() and asus_ec_hwmon_read_string() accordingly.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: d0ddfd241e57 ("hwmon: (asus-ec-sensors) add driver for ASUS EC")
Signed-off-by: Alexei Safin <a.safin@xxxxxxx>
---
v2: Use WARN_ONCE() instead of returning -EINVAL, and update
    both asus_ec_hwmon_read() and asus_ec_hwmon_read_string()
    as suggested by Eugene Shalygin.
    
 drivers/hwmon/asus-ec-sensors.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/hwmon/asus-ec-sensors.c b/drivers/hwmon/asus-ec-sensors.c
index d893cfd1cb82..a563d7acef2e 100644
--- a/drivers/hwmon/asus-ec-sensors.c
+++ b/drivers/hwmon/asus-ec-sensors.c
@@ -820,9 +820,8 @@ static int asus_ec_hwmon_read(struct device *dev, enum hwmon_sensor_types type,
 	struct ec_sensors_data *state = dev_get_drvdata(dev);
 	int sidx = find_ec_sensor_index(state, type, channel);
 
-	if (sidx < 0) {
+	if (WARN_ONCE(sidx < 0, "asus-ec-sensors: sensor not found\n"))
 		return sidx;
-	}
 
 	ret = get_cached_value_or_update(dev, sidx, state, &value);
 	if (!ret) {
@@ -839,6 +838,10 @@ static int asus_ec_hwmon_read_string(struct device *dev,
 {
 	struct ec_sensors_data *state = dev_get_drvdata(dev);
 	int sensor_index = find_ec_sensor_index(state, type, channel);
+
+	if (WARN_ONCE(sensor_index < 0, "asus-ec-sensors: sensor not found\n"))
+		return sensor_index;
+
 	*str = get_sensor_info(state, sensor_index)->label;
 
 	return 0;
-- 
2.39.5 (Apple Git-154)