Re: [PATCH] Bluetooth: btusb: mediatek: Avoid btusb_mtk_claim_iso_intf() NULL deref

[Incog <incogcyberpunk@gmail.com>]

From: IncogCyberpunk <incogcyberpunk@proton.me>

On  Wed, 19 Nov 2025 08:53:55 -0800 , Douglas Anderson <dianders@chromium.org> wrote:

> In btusb_mtk_setup(), we set `btmtk_data->isopkt_intf` to:
>   usb_ifnum_to_if(data->udev, MTK_ISO_IFNUM)
> 
> That function can return NULL in some cases. Even when it returns
> NULL, though, we still go on to call btusb_mtk_claim_iso_intf().
> 
> As of commit e9087e828827 ("Bluetooth: btusb: mediatek: Add locks for
> usb_driver_claim_interface()"), calling btusb_mtk_claim_iso_intf()
> when `btmtk_data->isopkt_intf` is NULL will cause a crash because
> we'll end up passing a bad pointer to device_lock(). Prior to that
> commit we'd pass the NULL pointer directly to
> usb_driver_claim_interface() which would detect it and return an
> error, which was handled.
> 
> Resolve the crash in btusb_mtk_claim_iso_intf() by adding a NULL check
> at the start of the function. This makes the code handle a NULL
> `btmtk_data->isopkt_intf` the same way it did before the problematic
> commit (just with a slight change to the error message printed).


Proposed patch:

> index a722446ec73d..1466e0f1865d 100644
> --- a/drivers/bluetooth/btusb.c
> +++ b/drivers/bluetooth/btusb.c
> @@ -2714,6 +2714,11 @@ static void btusb_mtk_claim_iso_intf(struct btusb_data *data)
>  	struct btmtk_data *btmtk_data = hci_get_priv(data->hdev);
>  	int err;
>  
> +	if (!btmtk_data->isopkt_intf) {
> +		bt_dev_err(data->hdev, "Can't claim NULL iso interface");
> +		return;
> +	}
> +
>  	/*
>  	 * The function usb_driver_claim_interface() is documented to need
>  	 * locks held if it's not called from a probe routine. The code here


I tested this patch by manually updating the drivers/bluetooth/btusb.c file with the proposed patches as above ; which solves a REGRESSION issue `bluetooth adapter provided by btusb not being recognized and hence bluetooth not working` since kernel version 6.13.2 .
This REGRESSION issue has been present in both the stable and the mainline kernels since 6.13.2 release due to the below mentioned commit in v6.13.2 :

Troublesome Commit Details:
- Title: Bluetooth: btusb: mediatek: Add locks for usb_driver_claim_interface()
- commit id: 4194766ec8756f4f654d595ae49962acbac49490
- [ Upstream commit e9087e828827e5a5c85e124ce77503f2b81c3491 ]
- Author: Douglas Anderson <dianders@chromium.org>
- Date:   Wed Jan 15 19:36:36 2025 -0800

Tested-by: IncogCyberpunk <incogcyberpunk@proton.me>

Regards,
IncogCyberpunk