USB: xhci: dbc: fix tty registration race

Make sure to allocate resources before registering the tty device to
avoid having a racing open() and write() fail to enable rx or
dereference a NULL pointer when accessing the uninitialised fifo.

Fixes: dfba2174dc42 ("usb: xhci: Add DbC support in xHCI driver")
Cc: stable@vger.kernel.org      # 4.16
Cc: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20211008092547.3996295-4-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/host/xhci-dbgtty.c b/drivers/usb/host/xhci-dbgtty.c
index 6e784f2..eb46e64 100644 (file)
--- a/drivers/usb/host/xhci-dbgtty.c
+++ b/drivers/usb/host/xhci-dbgtty.c
@@ -408,40 +408,38 @@ static int xhci_dbc_tty_register_device(struct xhci_dbc *dbc)
                return -EBUSY;
 
        xhci_dbc_tty_init_port(dbc, port);
-       tty_dev = tty_port_register_device(&port->port,
-                                          dbc_tty_driver, 0, NULL);
-       if (IS_ERR(tty_dev)) {
-               ret = PTR_ERR(tty_dev);
-               goto register_fail;
-       }
 
        ret = kfifo_alloc(&port->write_fifo, DBC_WRITE_BUF_SIZE, GFP_KERNEL);
        if (ret)
-               goto buf_alloc_fail;
+               goto err_exit_port;
 
        ret = xhci_dbc_alloc_requests(dbc, BULK_IN, &port->read_pool,
                                      dbc_read_complete);
        if (ret)
-               goto request_fail;
+               goto err_free_fifo;
 
        ret = xhci_dbc_alloc_requests(dbc, BULK_OUT, &port->write_pool,
                                      dbc_write_complete);
        if (ret)
-               goto request_fail;
+               goto err_free_requests;
+
+       tty_dev = tty_port_register_device(&port->port,
+                                          dbc_tty_driver, 0, NULL);
+       if (IS_ERR(tty_dev)) {
+               ret = PTR_ERR(tty_dev);
+               goto err_free_requests;
+       }
 
        port->registered = true;
 
        return 0;
 
-request_fail:
+err_free_requests:
        xhci_dbc_free_requests(&port->read_pool);
        xhci_dbc_free_requests(&port->write_pool);
+err_free_fifo:
        kfifo_free(&port->write_fifo);
-
-buf_alloc_fail:
-       tty_unregister_device(dbc_tty_driver, 0);
-
-register_fail:
+err_exit_port:
        xhci_dbc_tty_exit_port(port);
 
        dev_err(dbc->dev, "can't register tty port, err %d\n", ret);