[PATCH] iio: st_sensors: add __counted_by_ptr to struct st_sensor_settings

[Bill Wendling <morbo@google.com>]

Annotate the "ch" pointer member of "struct st_sensor_settings" with the
"__counted_by_ptr" attribute. The elements of "ch" are counted by the
"num_ch" member in the same struct.

All instances of "struct st_sensor_settings" are defined as "static
const" arrays across the ST sensor core drivers. For pressure sensors,
"num_ch" is explicitly initialized with the size of the respective
channel array using "ARRAY_SIZE(...)" during static definition.

For accelerometer, gyroscope, and magnetometer sensors, "num_ch" is not
explicitly initialized (and thus defaults to 0). This is because those
drivers hardcode the channel count to "ST_SENSORS_NUMBER_ALL_CHANNELS"
rather than using "num_ch" from the settings struct.

Since these structures are static const, both "ch" and "num_ch" are
fully initialized at compile time and available immediately at boot
time.  The only accesses to the "ch" field of "st_sensor_settings" occur
when assigning it to "indio_dev->channels" during device probing.

Because "sensor_settings->ch" is never dereferenced or accessed as an
array, adding the "__counted_by_ptr" annotation does not cause any
runtime panics or false-positive bounds checks under KASAN or UBSAN.

Cc: codemender-patching+linux@google.com
Assisted-by: LLM
Signed-off-by: Bill Wendling <morbo@google.com>
---
 include/linux/iio/common/st_sensors.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/iio/common/st_sensors.h b/include/linux/iio/common/st_sensors.h
index 1ba496f0fea5..6e914ed49529 100644
--- a/include/linux/iio/common/st_sensors.h
+++ b/include/linux/iio/common/st_sensors.h
@@ -206,7 +206,7 @@ struct st_sensor_settings {
 	u8 wai;
 	u8 wai_addr;
 	char sensors_supported[ST_SENSORS_MAX_4WAI][ST_SENSORS_MAX_NAME];
-	struct iio_chan_spec *ch;
+	struct iio_chan_spec *ch __counted_by_ptr(num_ch);
 	int num_ch;
 	struct st_sensor_odr odr;
 	struct st_sensor_power pw;
-- 
2.55.0.1082.g2b9226bbc0-goog