In the Linux kernel, the following vulnerability has been resolved: HID: appletb-kbd: fix UAF in...

In the Linux kernel, the following vulnerability has been resolved:

HID: appletb-kbd: fix UAF in inactivity-timer cleanup path

Commit 38224c472a03 ("HID: appletb-kbd: fix slab use-after-free bug in appletb_kbd_probe") added timer_delete_sync(&kbd->inactivity_timer) to both the probe close_hw error path and appletb_kbd_remove(), but the way it was wired in left the inactivity timer reachable during driver tear-down via two distinct windows.

Window A -- put_device() before timer_delete_sync():

put_device(&kbd->backlight_dev->dev);
timer_delete_sync(&kbd->inactivity_timer);

The inactivity_timer softirq reads kbd->backlight_dev and calls backlight_device_set_brightness() -> mutex_lock(&ops_lock). If a concurrent hid_appletb_bl unbind drops the last devm reference between these two calls, the backlight_device is freed and the mutex_lock() touches freed memory.

Window B -- backlight cleanup before hid_hw_stop():

if (kbd->backlight_dev) {
	timer_delete_sync(...);
	put_device(...);
}
hid_hw_close(hdev);
hid_hw_stop(hdev);

Even after Window A is closed, hid_hw_close()/hid_hw_stop() still run afterwards, so a late ".event" callback from the HID core (USB URB completion on real Apple hardware) can arrive after timer_delete_sync() drained the softirq but before put_device() drops the reference. That callback reaches reset_inactivity_timer(), which calls mod_timer() and re-arms the timer. The freshly re-armed timer can then fire on the about-to-be-freed backlight_device.

Both windows produce the same KASAN slab-use-after-free:

BUG: KASAN: slab-use-after-free in __mutex_lock+0x1aab/0x21c0 Read of size 8 at addr ffff88803ee9a108 by task swapper/0/0 Call Trace: __mutex_lock backlight_device_set_brightness appletb_inactivity_timer call_timer_fn run_timer_softirq handle_softirqs Allocated by task N: devm_backlight_device_register appletb_bl_probe Freed by task M: (concurrent hid_appletb_bl unbind path)

Close both windows at once by reworking the tear-down in appletb_kbd_remove() and in the probe close_hw error path so that

1. hid_hw_close()/hid_hw_stop() run before the backlight cleanup, guaranteeing no further .event callback can fire and re-arm the timer, and
2. inside the "if (kbd->backlight_dev)" block, timer_delete_sync() runs before put_device(), so the softirq is drained before the final reference is dropped.