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

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Message-ID: <20251120081227.v3.1.I1ae7aebc967e52c7c4be7aa65fbd81736649568a@changeid>
Date: Thu, 20 Nov 2025 08:12:28 -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>,
	regressions@...ts.linux.dev,
	incogcyberpunk@...ton.me,
	johan.hedberg@...il.com,
	sean.wang@...iatek.com,
	Douglas Anderson <dianders@...omium.org>,
	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: [PATCH v3] 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()")
Cc: stable@...r.kernel.org
Tested-by: IncogCyberpunk <incogcyberpunk@...ton.me>
Signed-off-by: Douglas Anderson <dianders@...omium.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");
+		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