iio: adc: xilinx-ams: fix out-of-bounds channel lookup in event handling

ams_event_to_channel() may return a pointer past the end of
dev->channels when no matching scan_index is found. This can lead
to invalid memory access in ams_handle_event().

Add a bounds check in ams_event_to_channel() and return NULL when
no channel is found. Also guard the caller to safely handle this
case.

Fixes: d5c7062 ("iio: adc: Add Xilinx AMS driver")
Signed-off-by: Guilherme Ivo Bozi <guilherme.bozi@usp.br>
Reviewed-by: Salih Erim <salih.erim@amd.com>
Tested-by: Salih Erim <salih.erim@amd.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Author: guilhermeivo

drivers/iio/adc/xilinx-ams.c

@@ -871,6 +871,9 @@ static const struct iio_chan_spec *ams_event_to_channel(struct iio_dev *dev,
 		if (dev->channels[i].scan_index == scan_index)
 			break;
 
+	if (i == dev->num_channels)
+		return NULL;
+
 	return &dev->channels[i];
 }
 
@@ -1012,6 +1015,8 @@ static void ams_handle_event(struct iio_dev *indio_dev, u32 event)
 	const struct iio_chan_spec *chan;
 
 	chan = ams_event_to_channel(indio_dev, event);
+	if (!chan)
+		return;
 
 	if (chan->type == IIO_TEMP) {
 		/*