linux-kernel - Re: [PATCH v3] Bluetooth: btusb: mediatek: Avoid btusb_mtk_claim_iso

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Message-ID: <CAD=FV=W1D7ksbS-q1c6cHQSxx3=Z5yfC8duiBGh8S01NhLPLUg@mail.gmail.com>
Date: Thu, 20 Nov 2025 09:13:07 -0800
From: Doug Anderson <dianders@...omium.org>
To: Paul Menzel <pmenzel@...gen.mpg.de>
Cc: Marcel Holtmann <marcel@...tmann.org>, Luiz Augusto von Dentz <luiz.dentz@...il.com>, 
	Matthias Brugger <matthias.bgg@...il.com>, 
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, 
	Thorsten Leemhuis <regressions@...mhuis.info>, regressions@...ts.linux.dev, 
	incogcyberpunk@...ton.me, johan.hedberg@...il.com, sean.wang@...iatek.com, 
	stable@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-bluetooth@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH v3] Bluetooth: btusb: mediatek: Avoid btusb_mtk_claim_iso_intf()
 NULL deref

Hi,

On Thu, Nov 20, 2025 at 9:04 AM Paul Menzel <pmenzel@...gen.mpg.de> wrote:
>
> > 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,

An error was also printed before commit e9087e828827 ("Bluetooth:
btusb: mediatek: Add locks for usb_driver_claim_interface()") too, it
was just a different error message. Previously the NULL would have
been noticed by usb_driver_claim_interface(), which would have
returned -ENODEV. That error would have been noticed and the message
printed would have been:

Failed to claim iso interface: -19

So that error is merely changed into:

Can't claim NULL iso interface

> what should be done about? Do drivers need
> fixing? Is it broken hardware?

Personally, I have no idea. I was mostly trying to get the regression
fixed and, after looking at the code, I was convinced that this would
get us back to working at least as well as we did before commit
e9087e828827 ("Bluetooth: btusb: mediatek: Add locks for
usb_driver_claim_interface()"), plus we'd still have the device_lock()
in place to avoid the problems I noticed earlier. It sounds as if,
even with the error printed, things were working well enough for
IncogCyberpunk.

If someone wants to analyze how / why `btmtk_data->isopkt_intf` would
be NULL in this case and if we should do something better to handle
it, I'd certainly support it!

> > +             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@...gen.mpg.de>

Thanks!

-Doug