iio: accel: fxls8962af: clamp the device-reported FIFO sample count

fxls8962af_fifo_flush() transfers the sample count the device reports in
BUF_STATUS into an on-stack buffer sized for FXLS8962AF_FIFO_LENGTH (32)
samples, but the count is a 6-bit field (0..63) that is only checked for
zero. A device, or an attacker on the I2C/SPI bus, reporting 33..63
overflows the buffer by up to 186 bytes: a stack out-of-bounds write.

Clamp the count to FXLS8962AF_FIFO_LENGTH before the transfer, mirroring
the clamp already applied in fxls8962af_set_watermark(). Conforming
hardware reports at most that many samples and is unaffected.

Signed-off-by: Bryam Vargas <hexlabsecurity@proton.me>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/accel/fxls8962af-core.c

@@ -970,6 +970,8 @@ static int fxls8962af_fifo_flush(struct iio_dev *indio_dev)
 	if (!count)
 		return 0;
 
+	count = min(count, FXLS8962AF_FIFO_LENGTH);
+
 	data->old_timestamp = data->timestamp;
 	data->timestamp = iio_get_time_ns(indio_dev);