CVE-2025-38394

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] [ 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—

Weakness

The product writes data past the end, or before the beginning, of the intended buffer.

Affected Software

Potential Mitigations

• Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.

• For example, many languages that perform their own memory management, such as Java and Perl, are not subject to buffer overflows. Other languages, such as Ada and C#, typically provide overflow protection, but the protection can be disabled by the programmer.

• Be wary that a language’s interface to native code may still be subject to overflows, even if the language itself is theoretically safe.

• Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.

• Examples include the Safe C String Library (SafeStr) by Messier and Viega [REF-57], and the Strsafe.h library from Microsoft [REF-56]. These libraries provide safer versions of overflow-prone string-handling functions.

• Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking.

• D3-SFCV (Stack Frame Canary Validation) from D3FEND [REF-1334] discusses canary-based detection in detail.

• Consider adhering to the following rules when allocating and managing an application’s memory:

• Run or compile the software using features or extensions that randomly arrange the positions of a program’s executable and libraries in memory. Because this makes the addresses unpredictable, it can prevent an attacker from reliably jumping to exploitable code.

• Examples include Address Space Layout Randomization (ASLR) [REF-58] [REF-60] and Position-Independent Executables (PIE) [REF-64]. Imported modules may be similarly realigned if their default memory addresses conflict with other modules, in a process known as “rebasing” (for Windows) and “prelinking” (for Linux) [REF-1332] using randomly generated addresses. ASLR for libraries cannot be used in conjunction with prelink since it would require relocating the libraries at run-time, defeating the whole purpose of prelinking.

• For more information on these techniques see D3-SAOR (Segment Address Offset Randomization) from D3FEND [REF-1335].

• Use a CPU and operating system that offers Data Execution Protection (using hardware NX or XD bits) or the equivalent techniques that simulate this feature in software, such as PaX [REF-60] [REF-61]. These techniques ensure that any instruction executed is exclusively at a memory address that is part of the code segment.

• For more information on these techniques see D3-PSEP (Process Segment Execution Prevention) from D3FEND [REF-1336].

References

• https://git.kernel.org/stable/c/6ad40b07e15c29712d9a4b8096914ccd82e3fc17
• https://git.kernel.org/stable/c/c80f2b047d5cc42fbd2dff9d1942d4ba7545100f