[PATCH] Bluetooth: btmtk: accept too short WMT FUNC_CTRL events

[Luiz Augusto von Dentz]

Hi Pauli, Tristan,

On Fri, Apr 24, 2026 at 3:25 PM Pauli Virtanen <pav at iki.fi> wrote:
>
> MT7925 (USB ID 0e8d:e025) on fw version 20260106153314 sends WMT
> FUNC_CTRL events that are missing the status field.
>
> Prior to commit 006b9943b982 ("Bluetooth: btmtk: validate WMT event SKB
> length before struct access") the status was read from out-of-bounds of
> SKB data, which usually would result to success with
> BTMTK_WMT_ON_UNDONE, although I don't know the intent here.  The bounds
> check added in that commit returns with error instead, producing
> "Bluetooth: hci0: Failed to send wmt func ctrl (-22)" and makes the
> device unusable.
>
> Fix the regression by interpreting too short packet as status
> BTMTK_WMT_ON_UNDONE, which makes the device work normally again.
>
> Fixes: 006b9943b982 ("Bluetooth: btmtk: validate WMT event SKB length before struct access")
> Signed-off-by: Pauli Virtanen <pav at iki.fi>
> ---
>
> Notes:
>     AFAICS the commit is not yet pulled and is only in bluetooth-next, so
>     maybe this should be just fixup?

Yeah, I'll most likely fix it in place and add your Signed-off-by.

>  drivers/bluetooth/btmtk.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/bluetooth/btmtk.c b/drivers/bluetooth/btmtk.c
> index ab34f1dd42bc..68a32d11e5ec 100644
> --- a/drivers/bluetooth/btmtk.c
> +++ b/drivers/bluetooth/btmtk.c
> @@ -719,8 +719,8 @@ static int btmtk_usb_hci_wmt_sync(struct hci_dev *hdev,
>         case BTMTK_WMT_FUNC_CTRL:
>                 if (!skb_pull_data(data->evt_skb,
>                                    sizeof(wmt_evt_funcc->status))) {
> -                       err = -EINVAL;
> -                       goto err_free_skb;
> +                       status = BTMTK_WMT_ON_UNDONE;
> +                       break;

This probably means the original change was never tested on real
hardware. We likely need input from the MediaTek team on how to handle
these events, as I don't think a public spec exists.

>                 }
>
>                 wmt_evt_funcc = (struct btmtk_hci_wmt_evt_funcc *)wmt_evt;
> --
> 2.53.0
>


-- 
Luiz Augusto von Dentz