[PATCH 11/15] iio: hid-sensors: fix a division by zero

[Greg Kroah-Hartman]

From: Josef Bacik <josef@xxxxxxxxxxxxxx>

convert_to_vtf_format() divides the micro part of a value by
10^(6 + exp).  The unit exponent of a HID field is a nibble and goes
down to -8.  For -7 and -8 the argument of int_pow() is negative, which
the unsigned parameter turns into a huge power of ten: 0 modulo 2^64.
The division by it is a divide error.  The exponent comes from the report
descriptor of the sensor hub, the value from a write to the hysteresis
attribute of the IIO device.

Multiply by 10^(-exp - 6) in these two cases.

Fixes: 73c6768b710a ("iio: hid-sensors: Common attribute and trigger")
Cc: stable <stable@xxxxxxxxxx>
Cc: David Lechner <dlechner@xxxxxxxxxxxx>
Cc: "Nuno Sá" <nuno.sa@xxxxxxxxxx>
Cc: Andy Shevchenko <andy@xxxxxxxxxx>
Cc: Sanjay Chitroda <sanjayembeddedse@xxxxxxxxx>
Cc: Shi Hao <i.shihao.999@xxxxxxxxx>
Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/iio/common/hid-sensors/hid-sensor-attributes.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/iio/common/hid-sensors/hid-sensor-attributes.c b/drivers/iio/common/hid-sensors/hid-sensor-attributes.c
index 9e7c26e37880..3b0985d500ae 100644
--- a/drivers/iio/common/hid-sensors/hid-sensor-attributes.c
+++ b/drivers/iio/common/hid-sensors/hid-sensor-attributes.c
@@ -140,7 +140,10 @@ static u32 convert_to_vtf_format(int size, int exp, int val1, int val2)
 	if (val1 < 0 || val2 < 0)
 		sign = -1;
 	exp = hid_sensor_convert_exponent(exp);
-	if (exp < 0) {
+	if (exp < -6) {
+		value = abs(val1) * int_pow(10, -exp);
+		value += abs(val2) * int_pow(10, -exp - 6);
+	} else if (exp < 0) {
 		divisor = int_pow(10, 6 + exp);
 		value = abs(val1) * int_pow(10, -exp);
 		value += abs(val2) / divisor;

-- 
2.56.0