[media] airspy: fix error logic during device register

This patch addresses CVE-2016-5400, a local DOS vulnerability caused by
a memory leak in the airspy usb device driver.

The vulnerability is triggered when more than 64 usb devices register
with v4l2 of type VFL_TYPE_SDR or VFL_TYPE_SUBDEV.A badusb device can
emulate 64 of these devices then through continual emulated
connect/disconnect of the 65th device, cause the kernel to run out of
RAM and crash the kernel.

The vulnerability exists in kernel versions from 3.17 to current 4.7.

The memory leak is caused by the probe function of the airspy driver
mishandeling errors and not freeing the corresponding control structures
when an error occours registering the device to v4l2 core.

Signed-off-by: James Patrick-Evans <james@jmp-e.com>
Cc: stable@vger.kernel.org # Up to Kernel 3.17
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/usb/airspy/airspy.c

@@ -1072,7 +1072,7 @@ static int airspy_probe(struct usb_interface *intf,
 	if (ret) {
 		dev_err(s->dev, "Failed to register as video device (%d)\n",
 				ret);
-		goto err_unregister_v4l2_dev;
+		goto err_free_controls;
 	}
 	dev_info(s->dev, "Registered as %s\n",
 			video_device_node_name(&s->vdev));