Re: [PATCH v3] Bluetooth: btusb: mediatek: Avoid btusb_mtk_claim_iso_intf() NULL deref

[Paul Menzel <pmenzel@molgen.mpg.de>]

Dear Douglas,


Thank you for your patch.

Am 20.11.25 um 17:12 schrieb Douglas Anderson:
> 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).
> 
> Reported-by: IncogCyberpunk <incogcyberpunk@proton.me>
> Closes: http://lore.kernel.org/r/a380d061-479e-4713-bddd-1d6571ca7e86@leemhuis.info
> Fixes: e9087e828827 ("Bluetooth: btusb: mediatek: Add locks for usb_driver_claim_interface()")
> Cc: stable@vger.kernel.org
> Tested-by: IncogCyberpunk <incogcyberpunk@proton.me>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
> 
> Changes in v3:
> - Added Cc to stable.
> - Added IncogCyberpunk Tested-by tag.
> - v2: https://patch.msgid.link/20251119092641.v2.1.I1ae7aebc967e52c7c4be7aa65fbd81736649568a@changeid
> 
> Changes in v2:
> - Rebase atop commit 529ac8e706c3 ("Bluetooth: ... mtk iso interface")
> - v1: https://patch.msgid.link/20251119085354.1.I1ae7aebc967e52c7c4be7aa65fbd81736649568a@changeid
> 
>   drivers/bluetooth/btusb.c | 5 +++++
>   1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/bluetooth/btusb.c b/drivers/bluetooth/btusb.c
> index fcc62e2fb641..683ac02e964b 100644
> --- a/drivers/bluetooth/btusb.c
> +++ b/drivers/bluetooth/btusb.c
> @@ -2751,6 +2751,11 @@ static void btusb_mtk_claim_iso_intf(struct btusb_data *data)
>   	if (!btmtk_data)
>   		return;
>   
> +	if (!btmtk_data->isopkt_intf) {
> +		bt_dev_err(data->hdev, "Can't claim NULL iso interface");

As an error is printed now, what should be done about? Do drivers need 
fixing? Is it broken hardware?

> +		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

Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>


Kind regards,

Paul