HID: appletb-kbd: fix slab use-after-free bug in appletb_kbd_probe
CVE: CVE-2025-38378
Component: kernel
Severity: None
Release date: 2025-07-25T00:00:00+00:00

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

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.


Remediation: