iio: inkern: add error case in iio_channel_get()

 The datasheet name is defined in the IIO driver.
 On the other hand, the adc_channel_label is configured in
 the platform side.
 If the datasheet name is not matched with any adc_channel_label,
 the iio_channel_get() should be returned as error for preventing
 invalid channel data access.

 This can be handled either way.
 (a) checking null data when using it : in the xxx_read_raw()
 or
 (b) error returns when the channel is requested : this patch

 The IIO consumer can't use the channel with invalid channel spec.
 Therefore case (b) is more reasonable.
Signed-off-by: Milo(Woogyom) Kim <milo.kim@ti.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/inkern.c

@@ -136,12 +136,21 @@ struct iio_channel *iio_channel_get(const char *name, const char *channel_name)
 
 	channel->indio_dev = c->indio_dev;
 
-	if (c->map->adc_channel_label)
+	if (c->map->adc_channel_label) {
 		channel->channel =
 			iio_chan_spec_from_name(channel->indio_dev,
 						c->map->adc_channel_label);
 
+		if (channel->channel == NULL)
+			goto error_no_chan;
+	}
+
 	return channel;
+
+error_no_chan:
+	iio_device_put(c->indio_dev);
+	kfree(channel);
+	return ERR_PTR(-EINVAL);
 }
 EXPORT_SYMBOL_GPL(iio_channel_get);