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

[Doug Anderson]

Hi,

On Wed, Nov 19, 2025 at 8:54 AM Douglas Anderson <dianders at 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).
>
> Reported-by: IncogCyberpunk <incogcyberpunk at 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()")
> Signed-off-by: Douglas Anderson <dianders at chromium.org>
> ---
> I have no way to test this commit myself other than to compile it. It
> looks fairly straightforward, though, so I'm hopeful it will fix the
> problem.
>
>  drivers/bluetooth/btusb.c | 5 +++++
>  1 file changed, 5 insertions(+)

Ugh, the bluetooth bot properly told me that my patch doesn't apply to
bt-next. I'll send a v2 right away. Sorry for the noise.

-Doug