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

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Message-ID: <20251119085354.1.I1ae7aebc967e52c7c4be7aa65fbd81736649568a@changeid>
Date: Wed, 19 Nov 2025 08:53:55 -0800
From: Douglas Anderson <dianders@...omium.org>
To: 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>
Cc: Thorsten Leemhuis <regressions@...mhuis.info>,
	incogcyberpunk@...ton.me,
	johan.hedberg@...il.com,
	regressions@...ts.linux.dev,
	sean.wang@...iatek.com,
	Douglas Anderson <dianders@...omium.org>,
	linux-arm-kernel@...ts.infradead.org,
	linux-bluetooth@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-mediatek@...ts.infradead.org
Subject: [PATCH] Bluetooth: btusb: mediatek: Avoid btusb_mtk_claim_iso_intf() NULL deref

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@...ton.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@...omium.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