Re: [PATCH] HID: pidff: fix OOB write when hid->inputs is empty

[Jiri Kosina]

On Sun, 26 Jul 2026, Baul Lee wrote:

> hid_pidff_init_with_quirks() derives its input_dev from
> 
> 	list_entry(hid->inputs.next, struct hid_input, list)
> 
> without first checking that hid->inputs is non-empty.  The list member
> of struct hid_input is at offset 0, so on an empty list list_entry()
> yields &hid->inputs itself and the following hidinput->input load reads
> an unrelated member of struct hid_device.  dev is then a type-confused
> pointer, and force-feedback init writes through it: each
> set_bit(FF_*, dev->ffbit) stores 8 bytes at dev + 192, past the end of
> the object dev actually aliases, and input_ff_create() adds further
> writes of a heap pointer and two function pointers.
> 
> Until hid-universal-pidff the only caller was hid_pidff_init() from
> usbhid, which runs under HID_CLAIMED_INPUT and therefore always has at
> least one hid_input.  universal_pidff_probe() starts the device with
> HID_CONNECT_DEFAULT & ~HID_CONNECT_FF and then calls
> hid_pidff_init_with_quirks() directly whenever the descriptor carries a
> PID usage page, bypassing that gate.  A report descriptor whose only
> application collection is on HID_UP_PID leaves hid->inputs empty while
> hid_connect() still succeeds through the hidraw claim, so probe reaches
> the unguarded list_entry().
> 
> The write happens in the USB probe path, on the hotplug workqueue, so
> plugging in a malicious device is enough to trigger it; no attacker
> software and no logged-in user are required.  KASAN reports an 8-byte
> out-of-bounds write in hid_pidff_init_with_quirks() reached from
> universal_pidff_probe().
> 
> Check for an empty list before deriving dev and return -ENODEV, as the
> other HID force-feedback drivers already do.  universal_pidff_probe()
> propagates the error and unwinds.
> 
> Discovered by XBOW, triaged by Baul Lee <baul.lee@xxxxxxxx>
> 
> Fixes: f06bf8d94fff ("HID: Add hid-universal-pidff driver and supported device ids")
> Reported-by: Federico Kirschbaum <federico.kirschbaum@xxxxxxxx>
> Reported-by: Baul Lee <baul.lee@xxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Baul Lee <baul.lee@xxxxxxxx>

Applied, thanks.

-- 
Jiri Kosina
SUSE Labs