[PATCH] Bluetooth: hci_ldisc: Postpone HCI_UART_PROTO_READY bit set in hci_uart_set_proto()

[Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>]

task A:                                task B:
hci_uart_set_proto                     flush_to_ldisc
 - p->open(hu) -> h5_open  //alloc h5  - receive_buf
 - set_bit HCI_UART_PROTO_READY         - tty_port_default_receive_buf
 - hci_uart_register_dev                 - tty_ldisc_receive_buf
                                          - hci_uart_tty_receive
				           - test_bit HCI_UART_PROTO_READY
				            - h5_recv
 - clear_bit HCI_UART_PROTO_READY             while() {
 - p->open(hu) -> h5_close //free h5
				              - h5_rx_3wire_hdr
				               - h5_reset()  //use-after-free
                                              }

It could use ioctl to set hci uart proto, but there is
a use-after-free issue when hci_uart_register_dev() fail in
hci_uart_set_proto(), see stack above, fix this by setting
HCI_UART_PROTO_READY bit only when hci_uart_register_dev()
return success.

Reported-by: syzbot+899a33dc0fa0dbaf06a6@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
---
 drivers/bluetooth/hci_ldisc.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
index 4918fefc4a6f..9562e72c1ae5 100644
--- a/drivers/bluetooth/hci_ldisc.c
+++ b/drivers/bluetooth/hci_ldisc.c
@@ -696,14 +696,13 @@ static int hci_uart_set_proto(struct hci_uart *hu, int id)
 		return -EPROTONOSUPPORT;
 
 	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);
 		return err;
 	}
 
+	set_bit(HCI_UART_PROTO_READY, &hu->flags);
 	return 0;
 }
 
-- 
2.20.1