iio: dac: ad5686: fix input raw value check

commit d01220ee5e43c65a206df827b39bf5cf5f7b9dce upstream.

Fix range check for input raw value, which is off by one, i.e., for a
10-bit DAC the max valid value is 1023, but 1 << 10 equals 1024, which
passes the previous check, allowing an out-of-range write. The issue
exists since the ad5686 driver was first introduced.

Fixes: c2f37c8dca ("iio: dac: New driver for AD5686R, AD5685R, AD5684R Digital to analog converters")
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Rodrigo Alencar <rodrigo.alencar@analog.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ulrich Hecht <uli@kernel.org>

drivers/iio/dac/ad5686.c

@@ -146,7 +146,7 @@ static int ad5686_write_raw(struct iio_dev *indio_dev,
 
 	switch (mask) {
 	case IIO_CHAN_INFO_RAW:
-		if (val > (1 << chan->scan_type.realbits) || val < 0)
+		if (val >= (1 << chan->scan_type.realbits) || val < 0)
 			return -EINVAL;
 
 		mutex_lock(&indio_dev->mlock);