Bluetooth: hci_ldisc: Fix null pointer derefence in case of early data

BugLink: https://bugs.launchpad.net/bugs/1853881

commit 84cb3df0 upstream.

HCI_UART_PROTO_SET flag is set before hci_uart_set_proto call. If we
receive data from tty layer during this procedure, proto pointer may
not be assigned yet, leading to null pointer dereference in rx method
hci_uart_tty_receive.

This patch fixes this issue by introducing HCI_UART_PROTO_READY flag in
order to avoid any proto operation before proto opening and assignment.
Signed-off-by: Loic Poulain <loic.poulain@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Cc: Ralph Siemsen <ralph.siemsen@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

drivers/bluetooth/hci_ldisc.c

@@ -227,7 +227,7 @@ static int hci_uart_flush(struct hci_dev *hdev)
 	tty_ldisc_flush(tty);
 	tty_driver_flush_buffer(tty);
 
-	if (test_bit(HCI_UART_PROTO_SET, &hu->flags))
+	if (test_bit(HCI_UART_PROTO_READY, &hu->flags))
 		hu->proto->flush(hu);
 
 	return 0;
@@ -506,7 +506,7 @@ static void hci_uart_tty_close(struct tty_struct *tty)
 
 	cancel_work_sync(&hu->write_work);
 
-	if (test_and_clear_bit(HCI_UART_PROTO_SET, &hu->flags)) {
+	if (test_and_clear_bit(HCI_UART_PROTO_READY, &hu->flags)) {
 		if (hdev) {
 			if (test_bit(HCI_UART_REGISTERED, &hu->flags))
 				hci_unregister_dev(hdev);
@@ -514,6 +514,7 @@ static void hci_uart_tty_close(struct tty_struct *tty)
 		}
 		hu->proto->close(hu);
 	}
+	clear_bit(HCI_UART_PROTO_SET, &hu->flags);
 
 	kfree(hu);
 }
@@ -540,7 +541,7 @@ static void hci_uart_tty_wakeup(struct tty_struct *tty)
 	if (tty != hu->tty)
 		return;
 
-	if (test_bit(HCI_UART_PROTO_SET, &hu->flags))
+	if (test_bit(HCI_UART_PROTO_READY, &hu->flags))
 		hci_uart_tx_wakeup(hu);
 }
 
@@ -564,7 +565,7 @@ static void hci_uart_tty_receive(struct tty_struct *tty, const u8 *data,
 	if (!hu || tty != hu->tty)
 		return;
 
-	if (!test_bit(HCI_UART_PROTO_SET, &hu->flags))
+	if (!test_bit(HCI_UART_PROTO_READY, &hu->flags))
 		return;
 
 	/* It does not need a lock here as it is already protected by a mutex in
@@ -652,9 +653,11 @@ static int hci_uart_set_proto(struct hci_uart *hu, int id)
 		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;
 	}

drivers/bluetooth/hci_uart.h

@@ -94,6 +94,7 @@ struct hci_uart {
 /* HCI_UART proto flag bits */
 #define HCI_UART_PROTO_SET	0
 #define HCI_UART_REGISTERED	1
+#define HCI_UART_PROTO_READY	2
 
 /* TX states  */
 #define HCI_UART_SENDING	1