media: fix airspy usb probe error path

Fix a memory leak on probe error of the airspy usb device driver.

The problem is triggered when more than 64 usb devices register with
v4l2 of type VFL_TYPE_SDR or VFL_TYPE_SUBDEV.

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.

A badusb device can emulate 64 of these devices, and then through
continual emulated connect/disconnect of the 65th device, cause the
kernel to run out of RAM and crash the kernel, thus causing a local DOS
vulnerability.

Fixes CVE-2016-5400
Signed-off-by: James Patrick-Evans <james@jmp-e.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: stable@vger.kernel.org # 3.17+
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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));
@@ -1081,7 +1081,6 @@ static int airspy_probe(struct usb_interface *intf,
 
 err_free_controls:
 	v4l2_ctrl_handler_free(&s->hdl);
-err_unregister_v4l2_dev:
 	v4l2_device_unregister(&s->v4l2_dev);
 err_free_mem:
 	kfree(s);