Hello Andy Could you please take a look at this patch series?
I've just found your post on habr about devres API misusing and I think this is just another case.
On 10/25/23 16:07, George Stark wrote:
Lots of drivers use devm_led_classdev_register() to register their led objects and let the kernel free those leds at the driver's remove stage. It can lead to a problem due to led_classdev_unregister() implementation calls led_set_brightness() to turn off the led. led_set_brightness() may call one of the module's brightness_set callbacks. If that callback uses module's resources allocated without using devm funcs() then those resources will be already freed at module's remove() callback and we may have use-after-free situation. Here is an example: module_probe() { devm_led_classdev_register(module_brightness_set_cb); mutex_init(&mutex); } module_brightness_set_cb() { mutex_lock(&mutex); do_set_brightness(); mutex_unlock(&mutex); } module_remove() { mutex_destroy(&mutex); } at rmmod: module_remove() ->mutex_destroy(&mutex); devres_release_all() ->led_classdev_unregister(); ->led_set_brightness(); ->module_brightness_set_cb(); ->mutex_lock(&mutex); /* use-after-free */ I think it's an architectural issue and should be discussed thoroughly. Some thoughts about fixing it as a start: 1) drivers can use devm_led_classdev_unregister() to explicitly free leds before dependend resources are freed. devm_led_classdev_register() remains being useful to simplify probe implementation. As a proof of concept I examined all drivers from drivers/leds and prepared patches where it's needed. Sometimes it was not as clean as just calling devm_led_classdev_unregister() because several drivers do not track their leds object at all - they can call devm_led_classdev_register() and drop the returned pointer. In that case I used devres group API. Drivers outside drivers/leds should be checked too after discussion. 2) remove led_set_brightness from led_classdev_unregister() and force the drivers to turn leds off at shutdown. May be add check that led's brightness is 0 at led_classdev_unregister() and put a warning to dmesg if it's not. Actually in many cases it doesn't really need to turn off the leds manually one-by-one if driver shutdowns whole led controller. For the last case to disable the warning new flag can be brought in e.g LED_AUTO_OFF_AT_SHUTDOWN (similar to LED_RETAIN_AT_SHUTDOWN). George Stark (8): leds: powernv: explicitly unregister LEDs at module's shutdown leds: nic78bx: explicitly unregister LEDs at module's shutdown leds: an30259a: explicitly unregister LEDs at module's shutdown leds: mlxreg: explicitly unregister LEDs at module's shutdown leds: aw200xx: explicitly unregister LEDs at module's shutdown leds: aw2013: explicitly unregister LEDs at module's shutdown leds: lp3952: explicitly unregister LEDs at module's shutdown leds: lm3532: explicitly unregister LEDs at module's shutdown drivers/leds/leds-an30259a.c | 4 ++++ drivers/leds/leds-aw200xx.c | 4 ++++ drivers/leds/leds-aw2013.c | 4 ++++ drivers/leds/leds-lm3532.c | 6 ++++++ drivers/leds/leds-lp3952.c | 5 +++++ drivers/leds/leds-mlxreg.c | 12 +++++++++++- drivers/leds/leds-nic78bx.c | 4 ++++ drivers/leds/leds-powernv.c | 7 +++++++ 8 files changed, 45 insertions(+), 1 deletion(-)
-- Best regards George