iio: adc: ad7124: Fix potential overflow due to non sequential channel numbers

Channel numbering must start at 0 and then not have any holes, or
it is possible to overflow the available storage.  Note this bug was
introduced as part of a fix to ensure we didn't rely on the ordering
of child nodes.  So we need to support arbitrary ordering but they all
need to be there somewhere.

Note I hit this when using qemu to test the rest of this series.
Arguably this isn't the best fix, but it is probably the most minimal
option for backporting etc.

Alexandru's sign-off is here because he carried this patch in a larger
set that Jonathan then applied.

Fixes: d7857e4 ("iio: adc: ad7124: Fix DT channel configuration")
Reviewed-by: Alexandru Ardelean <[email protected]>
Signed-off-by: Jonathan Cameron <[email protected]>
Signed-off-by: Alexandru Ardelean <[email protected]>
Cc: <[email protected]>

Author: jic23

drivers/iio/adc/ad7124.c

@@ -771,6 +771,13 @@ static int ad7124_of_parse_channel_config(struct iio_dev *indio_dev,
 		if (ret)
 			goto err;
 
+		if (channel >= indio_dev->num_channels) {
+			dev_err(indio_dev->dev.parent,
+				"Channel index >= number of channels\n");
+			ret = -EINVAL;
+			goto err;
+		}
+
 		ret = of_property_read_u32_array(child, "diff-channels",
 						 ain, 2);
 		if (ret)