Re: [PATCH] HID: lg4ff: validate report length before fixed offsets

[Jiri Kosina]

On Fri, 24 Jul 2026, Jiancheng Huang wrote:

> lg4ff_raw_event() rewrites fixed report offsets when combined pedals are
> enabled. It currently assumes that each product report contains every
> source and destination byte used by the rewrite.
> 
> Return without rewriting a short report before each product-specific
> access. Apply the same bound to the computed offset path.
> 
> Fixes: c832f86effbc ("HID: hid-logitech: Add combined pedal support Logitech wheels")
> Signed-off-by: Jiancheng Huang <jchuang@xxxxxxxxxx>
> Assisted-by: Codex:gpt-5.6-luna

Thanks for the patch. Next time please CC at least some relevant 
mailinglists as well.

CCing now LKML and applying.

> ---
> Evidence (v7.2-rc4 KUnit/KASAN oracle under bounded QEMU):
> Source: confirmed/hid_lg4ff_short_report_oob_raw_excerpt.log
> 
> [    2.638792] KTAP version 1
> [    2.638888] 1..1
> [    2.641100]     KTAP version 1
> [    2.641235]     # Subtest: hid-lg4ff-exploration
> [    2.641784]     # module: hid_logitech
> [    2.641962]     1..1
> [    2.644581] ==================================================================
> [    2.645008] BUG: KASAN: slab-out-of-bounds in lg4ff_raw_event+0x2fd/0x410
> [    2.645369] Read of size 1 at addr ffff88800229fc63 by task kunit_try_catch/67
> [    2.645369] 
> [    2.645369] CPU: 1 UID: 0 PID: 67 Comm: kunit_try_catch Tainted: G                 N  7.2.0-rc4-dirty #3 PREEMPT(full) 
> [    2.645369] Tainted: [N]=TEST
> [    2.645369] Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
> [    2.645369] Call Trace:
> [    2.645369]  <TASK>
> [    2.645369]  dump_stack_lvl+0x53/0x70
> [    2.645369]  print_report+0xd0/0x630
> [    2.645369]  ? __pfx__raw_spin_lock_irqsave+0x10/0x10
> [    2.645369]  ? lg4ff_raw_event+0x2fd/0x410
> [    2.645369]  kasan_report+0xe5/0x120
> [    2.645369]  ? lg4ff_raw_event+0x2fd/0x410
> [    2.645369]  lg4ff_raw_event+0x2fd/0x410
> [    2.645369]  lg4ff_short_report_oob_test+0x14e/0x250
> 
>  drivers/hid/hid-lg4ff.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/hid/hid-lg4ff.c b/drivers/hid/hid-lg4ff.c
> index e901fdb7d..62f99a932 100644
> --- a/drivers/hid/hid-lg4ff.c
> +++ b/drivers/hid/hid-lg4ff.c
> @@ -336,6 +336,8 @@ int lg4ff_raw_event(struct hid_device *hdev, struct hid_report *report,
>  	if (entry->wdata.combine) {
>  		switch (entry->wdata.product_id) {
>  		case USB_DEVICE_ID_LOGITECH_WHEEL:
> +			if (size < 7)
> +				return 0;
>  			rd[5] = rd[3];
>  			rd[6] = 0x7F;
>  			return 1;
> @@ -343,10 +345,14 @@ int lg4ff_raw_event(struct hid_device *hdev, struct hid_report *report,
>  		case USB_DEVICE_ID_LOGITECH_WINGMAN_FFG:
>  		case USB_DEVICE_ID_LOGITECH_MOMO_WHEEL:
>  		case USB_DEVICE_ID_LOGITECH_MOMO_WHEEL2:
> +			if (size < 6)
> +				return 0;
>  			rd[4] = rd[3];
>  			rd[5] = 0x7F;
>  			return 1;
>  		case USB_DEVICE_ID_LOGITECH_DFP_WHEEL:
> +			if (size < 7)
> +				return 0;
>  			rd[5] = rd[4];
>  			rd[6] = 0x7F;
>  			return 1;
> @@ -366,6 +372,8 @@ int lg4ff_raw_event(struct hid_device *hdev, struct hid_report *report,
>  		}
>  
>  		/* Compute a combined axis when wheel does not supply it */
> +		if (size <= offset + 1)
> +			return 0;
>  		rd[offset] = (0xFF + rd[offset] - rd[offset+1]) >> 1;
>  		rd[offset+1] = 0x7F;
>  		return 1;
> -- 
> 2.43.0
> 

-- 
Jiri Kosina
SUSE Labs