vhost-user-gpu: fix memory leak while calling 'vg_resource_unref' (CVE-2021-3544)

If the guest trigger following sequences, the attach_backing will be leaked:

	vg_resource_create_2d
	vg_resource_attach_backing
	vg_resource_unref

This patch fix this by freeing 'res->iov' in vg_resource_destroy.

Fixes: CVE-2021-3544
Reported-by: Li Qiang <liq3ea@163.com>
virtio-gpu fix: 5e8e3c4c ("virtio-gpu: fix resource leak
in virgl_cmd_resource_unref")

Reviewed-by: Prasad J Pandit <pjp@fedoraproject.org>
Signed-off-by: Li Qiang <liq3ea@163.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20210516030403.107723-5-liq3ea@163.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

contrib/vhost-user-gpu/vhost-user-gpu.c

@@ -400,6 +400,7 @@ vg_resource_destroy(VuGpu *g,
     }
 
     vugbm_buffer_destroy(&res->buffer);
+    g_free(res->iov);
     pixman_image_unref(res->image);
     QTAILQ_REMOVE(&g->reslist, res, next);
     g_free(res);