Bluetooth: hci_ldisc: Initialize hci_dev before open()

The hci_dev struct hdev is referenced in work queues and timers started
by open() in some protocols. This creates a race between the
initialization function and the work or timer which can result hdev
being dereferenced while it is still null.

The syzbot report contains a reliable reproducer which causes a null
pointer dereference of hdev in hci_uart_write_work() by making the
memory allocation for hdev fail.

To fix this, ensure hdev is valid from before calling a protocol's
open() until after calling a protocol's close().

Reported-by: syzbot+257790c15bcdef6fe00c@syzkaller.appspotmail.com
Signed-off-by: Jeremy Cline <jcline@redhat.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

drivers/bluetooth/hci_ldisc.c

@@ -207,11 +207,11 @@ void hci_uart_init_work(struct work_struct *work)
 	err = hci_register_dev(hu->hdev);
 	if (err < 0) {
 		BT_ERR("Can't register HCI device");
+		clear_bit(HCI_UART_PROTO_READY, &hu->flags);
+		hu->proto->close(hu);
 		hdev = hu->hdev;
 		hu->hdev = NULL;
 		hci_free_dev(hdev);
-		clear_bit(HCI_UART_PROTO_READY, &hu->flags);
-		hu->proto->close(hu);
 		return;
 	}
 
@@ -616,6 +616,7 @@ static void hci_uart_tty_receive(struct tty_struct *tty, const u8 *data,
 static int hci_uart_register_dev(struct hci_uart *hu)
 {
 	struct hci_dev *hdev;
+	int err;
 
 	BT_DBG("");
 
@@ -659,11 +660,22 @@ static int hci_uart_register_dev(struct hci_uart *hu)
 	else
 		hdev->dev_type = HCI_PRIMARY;
 
+	/* Only call open() for the protocol after hdev is fully initialized as
+	 * open() (or a timer/workqueue it starts) may attempt to reference it.
+	 */
+	err = hu->proto->open(hu);
+	if (err) {
+		hu->hdev = NULL;
+		hci_free_dev(hdev);
+		return err;
+	}
+
 	if (test_bit(HCI_UART_INIT_PENDING, &hu->hdev_flags))
 		return 0;
 
 	if (hci_register_dev(hdev) < 0) {
 		BT_ERR("Can't register HCI device");
+		hu->proto->close(hu);
 		hu->hdev = NULL;
 		hci_free_dev(hdev);
 		return -ENODEV;
@@ -683,17 +695,12 @@ static int hci_uart_set_proto(struct hci_uart *hu, int id)
 	if (!p)
 		return -EPROTONOSUPPORT;
 
-	err = p->open(hu);
-	if (err)
-		return err;
-
 	hu->proto = p;
 	set_bit(HCI_UART_PROTO_READY, &hu->flags);
 
 	err = hci_uart_register_dev(hu);
 	if (err) {
 		clear_bit(HCI_UART_PROTO_READY, &hu->flags);
-		p->close(hu);
 		return err;
 	}