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()")
Signed-off-by: Douglas Anderson <dianders@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(+)

diff --git a/drivers/bluetooth/btusb.c b/drivers/bluetooth/btusb.c
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
-- 
2.52.0.rc1.455.g30608eb744-goog

On Wed, Nov 19, 2025 at 08:53:55AM -0800, Douglas Anderson 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@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@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.

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
a patch that has triggered this response.  He used to manually respond
to these common problems, but in order to save his sanity (he kept
writing the same thing over and over, yet to different people), I was
created.  Hopefully you will not take offence and will fix the problem
in your patch and resubmit it so that it can be accepted into the Linux
kernel tree.

You are receiving this message because of the following common error(s)
as indicated below:

- You have marked a patch with a "Fixes:" tag for a commit that is in an
  older released kernel, yet you do not have a cc: stable line in the
  signed-off-by area at all, which means that the patch will not be
  applied to any older kernel releases.  To properly fix this, please
  follow the documented rules in the
  Documentation/process/stable-kernel-rules.rst file for how to resolve
  this.

If you wish to discuss this problem further, or you have questions about
how to resolve this issue, please feel free to respond to this email and
Greg will reply once he has dug out from the pending patches received
from other developers.

thanks,

greg k-h's patch email bot

Hi,

On Wed, Nov 19, 2025 at 11:12 PM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> - You have marked a patch with a "Fixes:" tag for a commit that is in an
>   older released kernel, yet you do not have a cc: stable line in the
>   signed-off-by area at all, which means that the patch will not be
>   applied to any older kernel releases.  To properly fix this, please
>   follow the documented rules in the
>   Documentation/process/stable-kernel-rules.rst file for how to resolve
>   this.

Sure. I'll send a v3 with the Cc to stable added and collect
IncogCyberpunk's Tested-by tag that was given in response to v1.

-Doug

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

Hi,

On Wed, Nov 19, 2025 at 8:54 AM 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).
>
> 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()")
> Signed-off-by: Douglas Anderson <dianders@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