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.
For the annotation to be correct, num_leds must equal the number of allocated elements before leds[] is accessed. Even taking the address &priv->leds[i] is bounds-checked against num_leds under UBSAN_BOUNDS. The driver allocates device_get_child_node_count() elements up front, so set num_leds to that count right after allocation. 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; the caller walks a led_pwm_data pointer over priv->leds. No functional change intended. Suggested-by: Lee Jones <[email protected]> Signed-off-by: Mert Seftali <[email protected]> --- Changes in v3: - v2 followed the review suggestion to pass the element and increment num_leds in the caller. That is exactly what Sashiko caught: with __counted_by(num_leds), &priv->leds[num_leds] is bounds-checked, so incrementing num_leds from 0 as the loop runs trips UBSAN_BOUNDS on probe. num_leds is now set to the full count up front and the caller walks a led_pwm_data pointer, which keeps the element-passing and the dropped index variable, just without the running counter. 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. Build-tested only (no PWM-LED hardware). The __counted_by bounds behaviour that motivated v3 was verified with a standalone UBSAN reproducer on gcc and clang. drivers/leds/leds-pwm.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/drivers/leds/leds-pwm.c b/drivers/leds/leds-pwm.c index 6c1f2f50ff85..d1116a5cb2b2 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; @@ -167,12 +166,12 @@ static int led_pwm_add(struct device *dev, struct led_pwm_priv *priv, } } - priv->num_leds++; return 0; } static int led_pwm_create_fwnode(struct device *dev, struct led_pwm_priv *priv) { + struct led_pwm_data *led_data = priv->leds; struct led_pwm led; int ret; @@ -193,7 +192,7 @@ 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, led_data++, &led, fwnode); if (ret) return ret; } @@ -217,6 +216,8 @@ static int led_pwm_probe(struct platform_device *pdev) if (!priv) return -ENOMEM; + priv->num_leds = count; + ret = led_pwm_create_fwnode(&pdev->dev, priv); if (ret) -- 2.55.0
