[PATCH 4.4 81/86] USB: serial: cyberjack: fix write-URB completion race

[Greg Kroah-Hartman]

From: Johan Hovold <jo...@kernel.org>

commit 985616f0457d9f555fff417d0da56174f70cc14f upstream.

The write-URB busy flag was being cleared before the completion handler
was done with the URB, something which could lead to corrupt transfers
due to a racing write request if the URB is resubmitted.

Fixes: 507ca9bc0476 ("[PATCH] USB: add ability for usb-serial drivers to 
determine if their write urb is currently being used.")
Cc: stable <sta...@vger.kernel.org>     # 2.6.13
Reviewed-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
Signed-off-by: Johan Hovold <jo...@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 drivers/usb/serial/cyberjack.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/drivers/usb/serial/cyberjack.c
+++ b/drivers/usb/serial/cyberjack.c
@@ -368,11 +368,12 @@ static void cyberjack_write_bulk_callbac
        struct cyberjack_private *priv = usb_get_serial_port_data(port);
        struct device *dev = &port->dev;
        int status = urb->status;
+       bool resubmitted = false;
 
-       set_bit(0, &port->write_urbs_free);
        if (status) {
                dev_dbg(dev, "%s - nonzero write bulk status received: %d\n",
                        __func__, status);
+               set_bit(0, &port->write_urbs_free);
                return;
        }
 
@@ -405,6 +406,8 @@ static void cyberjack_write_bulk_callbac
                        goto exit;
                }
 
+               resubmitted = true;
+
                dev_dbg(dev, "%s - priv->wrsent=%d\n", __func__, priv->wrsent);
                dev_dbg(dev, "%s - priv->wrfilled=%d\n", __func__, 
priv->wrfilled);
 
@@ -421,6 +424,8 @@ static void cyberjack_write_bulk_callbac
 
 exit:
        spin_unlock(&priv->lock);
+       if (!resubmitted)
+               set_bit(0, &port->write_urbs_free);
        usb_serial_port_softint(port);
 }