linux-kernel - [PATCH] Bluetooth: btusb: revert use of devm

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Message-ID: <20251210160228.29074-2-rpthibeault@gmail.com>
Date: Wed, 10 Dec 2025 11:02:28 -0500
From: Raphael Pinsonneault-Thibeault <rpthibeault@...il.com>
To: marcel@...tmann.org,
	luiz.dentz@...il.com
Cc: oliver@...kum.org,
	linux-bluetooth@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Raphael Pinsonneault-Thibeault <rpthibeault@...il.com>
Subject: [PATCH] Bluetooth: btusb: revert use of devm_kzalloc in btusb

This reverts commit 98921dbd00c4e ("Bluetooth: Use devm_kzalloc in
btusb.c file").

In btusb_probe(), we use devm_kzalloc() to allocate the btusb data. This
ties the lifetime of all the btusb data to the binding of a driver to
one interface, INTF. In a driver that binds to other interfaces, ISOC
and DIAG, this is an accident waiting to happen.

The issue is revealed in btusb_disconnect(), where calling
usb_driver_release_interface(&btusb_driver, data->intf) will have devm
free the data that is also being used by the other interfaces of the
driver that may not be released yet.

To fix this, revert the use of devm and go back to freeing memory
explicitly.

Signed-off-by: Raphael Pinsonneault-Thibeault <rpthibeault@...il.com>
---
Syzbot reported this UAF already and my commit 23d22f2f7176
("Bluetooth: btusb: reorder cleanup in btusb_disconnect to avoid UAF")
provided a fix that rearranged the
usb_driver_release_interface() calls so INTF was released last because
I (wrongly) assumed using devm like this was intentional.

This patch is motivated by a discussion prompted by Oliver Neukum:
https://lore.kernel.org/linux-bluetooth/aee37797-a280-47ea-91ac-487ddc124ac7@neukum.org/

link to patch for 23d22f2f7176:
https://lore.kernel.org/linux-bluetooth/20251105192839.895418-3-rpthibeault@gmail.com/

 drivers/bluetooth/btusb.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/bluetooth/btusb.c b/drivers/bluetooth/btusb.c
index 8ed3883ab8ee..ded09e94d296 100644
--- a/drivers/bluetooth/btusb.c
+++ b/drivers/bluetooth/btusb.c
@@ -4052,7 +4052,7 @@ static int btusb_probe(struct usb_interface *intf,
 			return -ENODEV;
 	}
 
-	data = devm_kzalloc(&intf->dev, sizeof(*data), GFP_KERNEL);
+	data = kzalloc(sizeof(*data), GFP_KERNEL);
 	if (!data)
 		return -ENOMEM;
 
@@ -4075,8 +4075,10 @@ static int btusb_probe(struct usb_interface *intf,
 		}
 	}
 
-	if (!data->intr_ep || !data->bulk_tx_ep || !data->bulk_rx_ep)
+	if (!data->intr_ep || !data->bulk_tx_ep || !data->bulk_rx_ep) {
+		kfree(data);
 		return -ENODEV;
+	}
 
 	if (id->driver_info & BTUSB_AMP) {
 		data->cmdreq_type = USB_TYPE_CLASS | 0x01;
@@ -4131,8 +4133,10 @@ static int btusb_probe(struct usb_interface *intf,
 	data->recv_acl = hci_recv_frame;
 
 	hdev = hci_alloc_dev_priv(priv_size);
-	if (!hdev)
+	if (!hdev) {
+		kfree(data);
 		return -ENOMEM;
+	}
 
 	hdev->bus = HCI_USB;
 	hci_set_drvdata(hdev, data);
@@ -4406,6 +4410,7 @@ static int btusb_probe(struct usb_interface *intf,
 	if (data->reset_gpio)
 		gpiod_put(data->reset_gpio);
 	hci_free_dev(hdev);
+	kfree(data);
 	return err;
 }
 
@@ -4454,6 +4459,7 @@ static void btusb_disconnect(struct usb_interface *intf)
 	}
 
 	hci_free_dev(hdev);
+	kfree(data);
 }
 
 #ifdef CONFIG_PM

base-commit: 9d588a1140b9ae211581a7a154d0b806d8cd8238
-- 
2.43.0