Bluetooth: hci_ldisc: Postpone HCI_UART_PROTO_READY bit set in hci_uart_set_proto()

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@syzkaller.appspotmail.com
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Reviewed-by: Jeremy Cline <jcline@redhat.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
static int hci_uart_tty_ioctl(struct tty_struct *tty, struct file *file,
			      unsigned int cmd, unsigned long arg)
{
	struct hci_uart *hu = tty->disc_data;
	int err = 0;

	BT_DBG("");

	/* Verify the status of the device */
	if (!hu)
		return -EBADF;

	switch (cmd) {
	case HCIUARTSETPROTO:
		if (!test_and_set_bit(HCI_UART_PROTO_SET, &hu->flags)) {
			err = hci_uart_set_proto(hu, arg);
			if (err)
				clear_bit(HCI_UART_PROTO_SET, &hu->flags);
		} else
			err = -EBUSY;
		break;

	case HCIUARTGETPROTO:
		if (test_bit(HCI_UART_PROTO_SET, &hu->flags))
			err = hu->proto->id;
		else
			err = -EUNATCH;
		break;

	case HCIUARTGETDEVICE:
		if (test_bit(HCI_UART_REGISTERED, &hu->flags))
			err = hu->hdev->id;
		else
			err = -EUNATCH;
		break;

	case HCIUARTSETFLAGS:
		if (test_bit(HCI_UART_PROTO_SET, &hu->flags))
			err = -EBUSY;
		else
			err = hci_uart_set_flags(hu, arg);
		break;

	case HCIUARTGETFLAGS:
		err = hu->hdev_flags;
		break;

	default:
		err = n_tty_ioctl_helper(tty, file, cmd, arg);
		break;
	}

	return err;
}

static int hci_uart_tty_ioctl(struct tty_struct *tty, struct file *file,
			      unsigned int cmd, unsigned long arg)
{
	struct hci_uart *hu = tty->disc_data;
	int err = 0;

	BT_DBG("");

	/* Verify the status of the device */
	if (!hu)
		return -EBADF;

	switch (cmd) {
	case HCIUARTSETPROTO:
		if (!test_and_set_bit(HCI_UART_PROTO_SET, &hu->flags)) {
			err = hci_uart_set_proto(hu, arg);
			if (err)
				clear_bit(HCI_UART_PROTO_SET, &hu->flags);
		} else
			err = -EBUSY;
		break;

	case HCIUARTGETPROTO:
		if (test_bit(HCI_UART_PROTO_SET, &hu->flags))
			err = hu->proto->id;
		else
			err = -EUNATCH;
		break;

	case HCIUARTGETDEVICE:
		if (test_bit(HCI_UART_REGISTERED, &hu->flags))
			err = hu->hdev->id;
		else
			err = -EUNATCH;
		break;

	case HCIUARTSETFLAGS:
		if (test_bit(HCI_UART_PROTO_SET, &hu->flags))
			err = -EBUSY;
		else
			err = hci_uart_set_flags(hu, arg);
		break;

	case HCIUARTGETFLAGS:
		err = hu->hdev_flags;
		break;

	default:
		err = n_tty_ioctl_helper(tty, file, cmd, arg);
		break;
	}

	return err;
}
