linux-kernel - Re: [PATCH v2] HID: appletb-kbd: fix slab use-after-free bug in appletb_kbd

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Message-ID:
 <PN3PR01MB95971AF4986E61E0A5A29DC7B878A@PN3PR01MB9597.INDPRD01.PROD.OUTLOOK.COM>
Date: Tue, 24 Jun 2025 18:41:56 +0530
From: Aditya Garg <gargaditya08@...e.com>
To: Qasim Ijaz <qasdev00@...il.com>, jikos@...nel.org, bentiss@...nel.org
Cc: linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
 stable@...r.kernel.org
Subject: Re: [PATCH v2] HID: appletb-kbd: fix slab use-after-free bug in
 appletb_kbd_probe



On 24/06/25 6:22 pm, Qasim Ijaz wrote:
> 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: 93a0fc489481 ("HID: hid-appletb-kbd: add support for automatic brightness control while using the touchbar")
> Cc: stable@...r.kernel.org
> Signed-off-by: Qasim Ijaz <qasdev00@...il.com>

Reviewed-by: Aditya Garg <gargaditya08@...e.com>

> ---
> v2:
> - Add backlight check in remove() since we don't want to unconditionally call timer_delete_sync
> 
>  drivers/hid/hid-appletb-kbd.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
>