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

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

If 'virgl_renderer_resource_attach_iov' failed, the 'res_iovs' will
be leaked.

Fixes: CVE-2021-3544
Reported-by: Li Qiang <liq3ea@163.com>
virtio-gpu fix: 33243031da ("virtio-gpu-3d: fix memory leak
in resource attach backing")

Signed-off-by: Li Qiang <liq3ea@163.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20210516030403.107723-7-liq3ea@163.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
(cherry picked from commit 63736af5a6571d9def93769431e0d7e38c6677bf)
Signed-off-by: Michael Roth <michael.roth@amd.com>