Bluetooth: Fix double free in hci_conn_cleanup

syzbot reports a slab use-after-free in hci_conn_hash_flush [1].
After releasing an object using hci_conn_del_sysfs in the
hci_conn_cleanup function, releasing the same object again
using the hci_dev_put and hci_conn_put functions causes a double free.
Here's a simplified flow:

hci_conn_del_sysfs:
  hci_dev_put
    put_device
      kobject_put
        kref_put
          kobject_release
            kobject_cleanup
              kfree_const
                kfree(name)

hci_dev_put:
  ...
    kfree(name)

hci_conn_put:
  put_device
    ...
      kfree(name)

This patch drop the hci_dev_put and hci_conn_put function
call in hci_conn_cleanup function, because the object is
freed in hci_conn_del_sysfs function.

This patch also fixes the refcounting in hci_conn_add_sysfs() and
hci_conn_del_sysfs() to take into account device_add() failures.

This fixes CVE-2023-28464.

Link: https://syzkaller.appspot.com/bug?id=1bb51491ca5df96a5f724899d1dbb87afda61419 [1]

Signed-off-by: ZhengHan Wang <[email protected]>
Co-developed-by: Luiz Augusto von Dentz <[email protected]>
Signed-off-by: Luiz Augusto von Dentz <[email protected]>

Author: unrav31

net/bluetooth/hci_conn.c

@@ -172,13 +172,11 @@ static void hci_conn_cleanup(struct hci_conn *conn)
 			hdev->notify(hdev, HCI_NOTIFY_CONN_DEL);
 	}
 
-	hci_conn_del_sysfs(conn);
-
 	debugfs_remove_recursive(conn->debugfs);
 
-	hci_dev_put(hdev);
+	hci_conn_del_sysfs(conn);
 
-	hci_conn_put(conn);
+	hci_dev_put(hdev);
 }
 
 static void hci_acl_create_connection(struct hci_conn *conn)

net/bluetooth/hci_sysfs.c

@@ -35,7 +35,7 @@ void hci_conn_init_sysfs(struct hci_conn *conn)
 {
 	struct hci_dev *hdev = conn->hdev;
 
-	BT_DBG("conn %p", conn);
+	bt_dev_dbg(hdev, "conn %p", conn);
 
 	conn->dev.type = &bt_link;
 	conn->dev.class = &bt_class;
@@ -48,27 +48,30 @@ void hci_conn_add_sysfs(struct hci_conn *conn)
 {
 	struct hci_dev *hdev = conn->hdev;
 
-	BT_DBG("conn %p", conn);
+	bt_dev_dbg(hdev, "conn %p", conn);
 
 	if (device_is_registered(&conn->dev))
 		return;
 
 	dev_set_name(&conn->dev, "%s:%d", hdev->name, conn->handle);
 
-	if (device_add(&conn->dev) < 0) {
+	if (device_add(&conn->dev) < 0)
 		bt_dev_err(hdev, "failed to register connection device");
-		return;
-	}
-
-	hci_dev_hold(hdev);
 }
 
 void hci_conn_del_sysfs(struct hci_conn *conn)
 {
 	struct hci_dev *hdev = conn->hdev;
 
-	if (!device_is_registered(&conn->dev))
+	bt_dev_dbg(hdev, "conn %p", conn);
+
+	if (!device_is_registered(&conn->dev)) {
+		/* If device_add() has *not* succeeded, use *only* put_device()
+		 * to drop the reference count.
+		 */
+		put_device(&conn->dev);
 		return;
+	}
 
 	while (1) {
 		struct device *dev;
@@ -80,9 +83,7 @@ void hci_conn_del_sysfs(struct hci_conn *conn)
 		put_device(dev);
 	}
 
-	device_del(&conn->dev);
-
-	hci_dev_put(hdev);
+	device_unregister(&conn->dev);
 }
 
 static void bt_host_release(struct device *dev)