HID: appletb-kbd: fix slab use-after-free bug in appletb_kbd_probe

JIRA: https://issues.redhat.com/browse/RHEL-101770
Upstream Status: 6.16-rc
Tested: with the hid-tools test suite and some hardware

commit 38224c4
Author: Qasim Ijaz <qasdev00@gmail.com>
Date:   Tue Jun 24 13:52:56 2025 +0100

    HID: appletb-kbd: fix slab use-after-free bug in appletb_kbd_probe

    In probe appletb_kbd_probe() a "struct appletb_kbd *kbd" is allocated
    via devm_kzalloc() to store touch bar keyboard related data.
    Later on if backlight_device_get_by_name() finds a backlight device
    with name "appletb_backlight" a timer (kbd->inactivity_timer) is setup
    with appletb_inactivity_timer() and the timer is armed to run after
    appletb_tb_dim_timeout (60) seconds.

    A use-after-free is triggered when failure occurs after the timer is
    armed. This ultimately means probe failure occurs and as a result the
    "struct appletb_kbd *kbd" which is device managed memory is freed.
    After 60 seconds the timer will have expired and __run_timers will
    attempt to access the timer (kbd->inactivity_timer) however the kdb
    structure has been freed causing a use-after free.

    [   71.636938] ==================================================================
    [   71.637915] BUG: KASAN: slab-use-after-free in __run_timers+0x7ad/0x890
    [   71.637915] Write of size 8 at addr ffff8881178c5958 by task swapper/1/0
    [   71.637915]
    [   71.637915] CPU: 1 UID: 0 PID: 0 Comm: swapper/1 Not tainted 6.16.0-rc2-00318-g739a6c93cc75-dirty #12 PREEMPT(voluntary)
    [   71.637915] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
    [   71.637915] Call Trace:
    [   71.637915]  <IRQ>
    [   71.637915]  dump_stack_lvl+0x53/0x70
    [   71.637915]  print_report+0xce/0x670
    [   71.637915]  ? __run_timers+0x7ad/0x890
    [   71.637915]  kasan_report+0xce/0x100
    [   71.637915]  ? __run_timers+0x7ad/0x890
    [   71.637915]  __run_timers+0x7ad/0x890
    [   71.637915]  ? __pfx___run_timers+0x10/0x10
    [   71.637915]  ? update_process_times+0xfc/0x190
    [   71.637915]  ? __pfx_update_process_times+0x10/0x10
    [   71.637915]  ? _raw_spin_lock_irq+0x80/0xe0
    [   71.637915]  ? _raw_spin_lock_irq+0x80/0xe0
    [   71.637915]  ? __pfx__raw_spin_lock_irq+0x10/0x10
    [   71.637915]  run_timer_softirq+0x141/0x240
    [   71.637915]  ? __pfx_run_timer_softirq+0x10/0x10
    [   71.637915]  ? __pfx___hrtimer_run_queues+0x10/0x10
    [   71.637915]  ? kvm_clock_get_cycles+0x18/0x30
    [   71.637915]  ? ktime_get+0x60/0x140
    [   71.637915]  handle_softirqs+0x1b8/0x5c0
    [   71.637915]  ? __pfx_handle_softirqs+0x10/0x10
    [   71.637915]  irq_exit_rcu+0xaf/0xe0
    [   71.637915]  sysvec_apic_timer_interrupt+0x6c/0x80
    [   71.637915]  </IRQ>
    [   71.637915]
    [   71.637915] Allocated by task 39:
    [   71.637915]  kasan_save_stack+0x33/0x60
    [   71.637915]  kasan_save_track+0x14/0x30
    [   71.637915]  __kasan_kmalloc+0x8f/0xa0
    [   71.637915]  __kmalloc_node_track_caller_noprof+0x195/0x420
    [   71.637915]  devm_kmalloc+0x74/0x1e0
    [   71.637915]  appletb_kbd_probe+0x37/0x3c0
    [   71.637915]  hid_device_probe+0x2d1/0x680
    [   71.637915]  really_probe+0x1c3/0x690
    [   71.637915]  __driver_probe_device+0x247/0x300
    [   71.637915]  driver_probe_device+0x49/0x210
    [...]
    [   71.637915]
    [   71.637915] Freed by task 39:
    [   71.637915]  kasan_save_stack+0x33/0x60
    [   71.637915]  kasan_save_track+0x14/0x30
    [   71.637915]  kasan_save_free_info+0x3b/0x60
    [   71.637915]  __kasan_slab_free+0x37/0x50
    [   71.637915]  kfree+0xcf/0x360
    [   71.637915]  devres_release_group+0x1f8/0x3c0
    [   71.637915]  hid_device_probe+0x315/0x680
    [   71.637915]  really_probe+0x1c3/0x690
    [   71.637915]  __driver_probe_device+0x247/0x300
    [   71.637915]  driver_probe_device+0x49/0x210
    [...]

    The root cause of the issue is that the timer is not disarmed
    on failure paths leading to it remaining active and accessing
    freed memory. To fix this call timer_delete_sync() to deactivate
    the timer.

    Another small issue is that timer_delete_sync is called
    unconditionally in appletb_kbd_remove(), fix this by checking
    for a valid kbd->backlight_dev before calling timer_delete_sync.

    Fixes: 93a0fc4 ("HID: hid-appletb-kbd: add support for automatic brightness control while using the touchbar")
    Cc: stable@vger.kernel.org
    Signed-off-by: Qasim Ijaz <qasdev00@gmail.com>
    Reviewed-by: Aditya Garg <gargaditya08@live.com>
    Signed-off-by: Jiri Kosina <jkosina@suse.com>

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

Author: bentiss

drivers/hid/hid-appletb-kbd.c

@@ -437,8 +437,10 @@ 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)
+	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);
@@ -452,10 +454,10 @@ static void appletb_kbd_remove(struct hid_device *hdev)
 	appletb_kbd_set_mode(kbd, APPLETB_KBD_MODE_OFF);
 
 	input_unregister_handler(&kbd->inp_handler);
-	timer_delete_sync(&kbd->inactivity_timer);
-
-	if (kbd->backlight_dev)
+	if (kbd->backlight_dev) {
 		put_device(&kbd->backlight_dev->dev);
+		timer_delete_sync(&kbd->inactivity_timer);
+	}
 
 	hid_hw_close(hdev);
 	hid_hw_stop(hdev);