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

On Sun, 2026-07-26 at 15:25 +0900, Baul Lee wrote:
> hid_pidff_init_with_quirks() derives its input_dev from
>=20
> 	list_entry(hid->inputs.next, struct hid_input, list)
>=20
> 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.
>=20
> 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().
>=20
> 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().
>=20
> 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.
>=20
> Discovered by XBOW, triaged by Baul Lee <[email protected]>
>=20
> Fixes: f06bf8d94fff ("HID: Add hid-universal-pidff driver and supported d=
evice ids")
> Reported-by: Federico Kirschbaum <[email protected]>
> Reported-by: Baul Lee <[email protected]>
> Cc: [email protected]
> Signed-off-by: Baul Lee <[email protected]>
> ---
>  drivers/hid/usbhid/hid-pidff.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
>=20
> diff --git a/drivers/hid/usbhid/hid-pidff.c b/drivers/hid/usbhid/hid-pidf=
f.c
> index 5f4395f7c645..22951b7ecd17 100644
> --- a/drivers/hid/usbhid/hid-pidff.c
> +++ b/drivers/hid/usbhid/hid-pidff.c
> @@ -1539,13 +1539,20 @@ static int pidff_check_autocenter(struct pidff_de=
vice *pidff,
>  int hid_pidff_init_with_quirks(struct hid_device *hid, u32 initial_quirk=
s)
>  {
>  	struct pidff_device *pidff;
> -	struct hid_input *hidinput =3D
> -		list_entry(hid->inputs.next, struct hid_input, list);
> -	struct input_dev *dev =3D hidinput->input;
> +	struct hid_input *hidinput;
> +	struct input_dev *dev;
>  	struct ff_device *ff;
>  	int max_effects;
>  	int error;
> =20
> +	if (list_empty(&hid->inputs)) {
> +		hid_err(hid, "no inputs found\n");
> +		return -ENODEV;
> +	}
> +
> +	hidinput =3D list_first_entry(&hid->inputs, struct hid_input, list);
> +	dev =3D hidinput->input;
> +
>  	hid_dbg(hid, "starting pid init\n");
> =20
>  	if (list_empty(&hid->report_enum[HID_OUTPUT_REPORT].report_list)) {

Looks good, doesn't break anything and will help in such scenario.
Thanks!
--=20
Reviewed-by: Tomasz Paku=C5=82a <[email protected]>