vhost-user-gpu: fix memory leak in 'virgl_cmd_resource_unref' (CVE-2021-3544)

vhost-user-gpu: fix memory leak in 'virgl_cmd_resource_unref' (CVE-2021-3544)

The 'res->iov' will be leaked if the guest trigger following sequences:

	virgl_cmd_create_resource_2d
	virgl_resource_attach_backing
	virgl_cmd_resource_unref

This patch fixes this.

Fixes: CVE-2021-3544
Reported-by: Li Qiang <liq3ea@163.com>
virtio-gpu fix: 5e8e3c4c75 ("virtio-gpu: fix resource leak
in virgl_cmd_resource_unref"

Signed-off-by: Li Qiang <liq3ea@163.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20210516030403.107723-6-liq3ea@163.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
(cherry picked from commit f6091d86ba9ea05f4e111b9b42ee0005c37a6779)
Signed-off-by: Michael Roth <michael.roth@amd.com>