CVE-2025-38394: HID: appletb-kbd: fix memory corruption of input_handler_list
In the Linux kernel, the following vulnerability has been resolved:

HID: appletb-kbd: fix memory corruption of input_handler_list

In appletb_kbd_probe an input handler is initialised and then registered
with input core through input_register_handler(). When this happens input
core will add the input handler (specifically its node) to the global
input_handler_list. The input_handler_list is central to the functionality
of input core and is traversed in various places in input core. An example
of this is when a new input device is plugged in and gets registered with
input core.

The input_handler in probe is allocated as device managed memory. If a
probe failure occurs after input_register_handler() the input_handler
memory is freed, yet it will remain in the input_handler_list. This
effectively means the input_handler_list contains a dangling pointer
to data belonging to a freed input handler.

This causes an issue when any other input device is plugged in - in my
case I had an old PixArt HP USB optical mouse and I decided to
plug it in after a failure occurred after input_register_handler().
This lead to the registration of this input device via
input_register_device which involves traversing over every handler
in the corrupted input_handler_list and calling input_attach_handler(),
giving each handler a chance to bind to newly registered device.

The core of this bug is a UAF which causes memory corruption of
input_handler_list and to fix it we must ensure the input handler is
unregistered from input core, this is done through
input_unregister_handler().

[   63.191597] ==================================================================
[   63.192094] BUG: KASAN: slab-use-after-free in input_attach_handler.isra.0+0x1a9/0x1e0
[   63.192094] Read of size 8 at addr ffff888105ea7c80 by task kworker/0:2/54
[   63.192094]
[   63.192094] CPU: 0 UID: 0 PID: 54 Comm: kworker/0:2 Not tainted 6.16.0-rc2-00321-g2aa6621d
[   63.192094] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.164
[   63.192094] Workqueue: usb_hub_wq hub_event
[   63.192094] Call Trace:
[   63.192094]  <TASK>
[   63.192094]  dump_stack_lvl+0x53/0x70
[   63.192094]  print_report+0xce/0x670
[   63.192094]  kasan_report+0xce/0x100
[   63.192094]  input_attach_handler.isra.0+0x1a9/0x1e0
[   63.192094]  input_register_device+0x76c/0xd00
[   63.192094]  hidinput_connect+0x686d/0xad60
[   63.192094]  hid_connect+0xf20/0x1b10
[   63.192094]  hid_hw_start+0x83/0x100
[   63.192094]  hid_device_probe+0x2d1/0x680
[   63.192094]  really_probe+0x1c3/0x690
[   63.192094]  __driver_probe_device+0x247/0x300
[   63.192094]  driver_probe_device+0x49/0x210
[   63.192094]  __device_attach_driver+0x160/0x320
[   63.192094]  bus_for_each_drv+0x10f/0x190
[   63.192094]  __device_attach+0x18e/0x370
[   63.192094]  bus_probe_device+0x123/0x170
[   63.192094]  device_add+0xd4d/0x1460
[   63.192094]  hid_add_device+0x30b/0x910
[   63.192094]  usbhid_probe+0x920/0xe00
[   63.192094]  usb_probe_interface+0x363/0x9a0
[   63.192094]  really_probe+0x1c3/0x690
[   63.192094]  __driver_probe_device+0x247/0x300
[   63.192094]  driver_probe_device+0x49/0x210
[   63.192094]  __device_attach_driver+0x160/0x320
[   63.192094]  bus_for_each_drv+0x10f/0x190
[   63.192094]  __device_attach+0x18e/0x370
[   63.192094]  bus_probe_device+0x123/0x170
[   63.192094]  device_add+0xd4d/0x1460
[   63.192094]  usb_set_configuration+0xd14/0x1880
[   63.192094]  usb_generic_driver_probe+0x78/0xb0
[   63.192094]  usb_probe_device+0xaa/0x2e0
[   63.192094]  really_probe+0x1c3/0x690
[   63.192094]  __driver_probe_device+0x247/0x300
[   63.192094]  driver_probe_device+0x49/0x210
[   63.192094]  __device_attach_driver+0x160/0x320
[   63.192094]  bus_for_each_drv+0x10f/0x190
[   63.192094]  __device_attach+0x18e/0x370
[   63.192094]  bus_probe_device+0x123/0x170
[   63.192094]  device_add+0xd4d/0x1460
[   63.192094]  usb_new_device+0x7b4/0x1000
[   63.192094]  hub_event+0x234d/0x3
---truncated---
CVSS v3.1: 7.8