usb: usbip: set buffer pointers to NULL after free

BugLink: http://bugs.launchpad.net/bugs/1705238

commit b3b51417 upstream.

The usbip stack dynamically allocates the transfer_buffer and
setup_packet of each urb that got generated by the tcp to usb stub code.
As these pointers are always used only once we will set them to NULL
after use. This is done likewise to the free_urb code in vudc_dev.c.
This patch fixes double kfree situations where the usbip remote side
added the URB_FREE_BUFFER.
Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Acked-by: Shuah Khan <shuahkh@osg.samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

drivers/usb/usbip/stub_main.c

@@ -262,7 +262,11 @@ void stub_device_cleanup_urbs(struct stub_device *sdev)
 		kmem_cache_free(stub_priv_cache, priv);
 
 		kfree(urb->transfer_buffer);
+		urb->transfer_buffer = NULL;
+
 		kfree(urb->setup_packet);
+		urb->setup_packet = NULL;
+
 		usb_free_urb(urb);
 	}
 }

drivers/usb/usbip/stub_tx.c

@@ -28,7 +28,11 @@ static void stub_free_priv_and_urb(struct stub_priv *priv)
 	struct urb *urb = priv->urb;
 
 	kfree(urb->setup_packet);
+	urb->setup_packet = NULL;
+
 	kfree(urb->transfer_buffer);
+	urb->transfer_buffer = NULL;
+
 	list_del(&priv->list);
 	kmem_cache_free(stub_priv_cache, priv);
 	usb_free_urb(urb);