From 4db2af929279c799b5653a39eb0795c72baffca4 Mon Sep 17 00:00:00 2001 From: Sangyun Kim Date: Mon, 20 Apr 2026 14:13:17 +0900 Subject: [PATCH] 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. Fixes: 38224c472a03 ("HID: appletb-kbd: fix slab use-after-free bug in appletb_kbd_probe") Cc: stable@vger.kernel.org Signed-off-by: Sangyun Kim Signed-off-by: Jiri Kosina --- drivers/hid/hid-appletb-kbd.c | 18 +++++++++--------- 1 file changed, 9 insertions(+), 9 deletions(-) diff --git a/drivers/hid/hid-appletb-kbd.c b/drivers/hid/hid-appletb-kbd.c index 0fdc0968b9ef..8feac9e3589b 100644 --- a/drivers/hid/hid-appletb-kbd.c +++ b/drivers/hid/hid-appletb-kbd.c @@ -440,13 +440,13 @@ static int appletb_kbd_probe(struct hid_device *hdev, const struct hid_device_id unregister_handler: input_unregister_handler(&kbd->inp_handler); close_hw: - if (kbd->backlight_dev) { - put_device(&kbd->backlight_dev->dev); - timer_delete_sync(&kbd->inactivity_timer); - } hid_hw_close(hdev); stop_hw: hid_hw_stop(hdev); + if (kbd->backlight_dev) { + timer_delete_sync(&kbd->inactivity_timer); + put_device(&kbd->backlight_dev->dev); + } return ret; } @@ -457,13 +457,13 @@ static void appletb_kbd_remove(struct hid_device *hdev) appletb_kbd_set_mode(kbd, APPLETB_KBD_MODE_OFF); input_unregister_handler(&kbd->inp_handler); - if (kbd->backlight_dev) { - put_device(&kbd->backlight_dev->dev); - timer_delete_sync(&kbd->inactivity_timer); - } - hid_hw_close(hdev); hid_hw_stop(hdev); + + if (kbd->backlight_dev) { + timer_delete_sync(&kbd->inactivity_timer); + put_device(&kbd->backlight_dev->dev); + } } static int appletb_kbd_suspend(struct hid_device *hdev, pm_message_t msg)