[PATCH v2] leds: pwm: Annotate leds[] with __counted_by()

[Mert Seftali <mertsftl@gmail.com>]

From: Mert Seftali <mertsftl@gmail.com>

Add the __counted_by() attribute to the flexible array member leds[] in
struct led_pwm_priv so the compiler and runtime (e.g. FORTIFY_SOURCE,
UBSAN_BOUNDS) can bounds-check accesses against num_leds.

While here, pass the led_pwm_data element into led_pwm_add() instead of
the whole led_pwm_priv, so the helper no longer needs to index the array
itself. num_leds is incremented in the caller as each LED is added and
doubles as the index.

No functional change intended.

Suggested-by: Lee Jones <lee@kernel.org>
Signed-off-by: Mert Seftali <mertsftl@gmail.com>
---
Changes in v2 (per Lee Jones review):
- Pass the led_pwm_data element into led_pwm_add() so it drops the priv
  and index arguments; increment num_leds in the caller, where it also
  serves as the array index.

Build-tested only (also with FORTIFY_SOURCE and UBSAN_BOUNDS enabled).

 drivers/leds/leds-pwm.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/leds/leds-pwm.c b/drivers/leds/leds-pwm.c
index 6c1f2f50ff85..dabdf0423582 100644
--- a/drivers/leds/leds-pwm.c
+++ b/drivers/leds/leds-pwm.c
@@ -36,7 +36,7 @@ struct led_pwm_data {
 
 struct led_pwm_priv {
 	int num_leds;
-	struct led_pwm_data leds[];
+	struct led_pwm_data leds[] __counted_by(num_leds);
 };
 
 static int led_pwm_set(struct led_classdev *led_cdev,
@@ -81,10 +81,9 @@ static int led_pwm_default_brightness_get(struct fwnode_handle *fwnode,
 }
 
 __attribute__((nonnull))
-static int led_pwm_add(struct device *dev, struct led_pwm_priv *priv,
+static int led_pwm_add(struct device *dev, struct led_pwm_data *led_data,
 		       struct led_pwm *led, struct fwnode_handle *fwnode)
 {
-	struct led_pwm_data *led_data = &priv->leds[priv->num_leds];
 	struct led_init_data init_data = { .fwnode = fwnode };
 	int ret;
 
@@ -167,7 +166,6 @@ static int led_pwm_add(struct device *dev, struct led_pwm_priv *priv,
 		}
 	}
 
-	priv->num_leds++;
 	return 0;
 }
 
@@ -193,9 +191,10 @@ static int led_pwm_create_fwnode(struct device *dev, struct led_pwm_priv *priv)
 
 		led.default_state = led_init_default_state_get(fwnode);
 
-		ret = led_pwm_add(dev, priv, &led, fwnode);
+		ret = led_pwm_add(dev, &priv->leds[priv->num_leds], &led, fwnode);
 		if (ret)
 			return ret;
+		priv->num_leds++;
 	}
 
 	return 0;
-- 
2.55.0