You're running into that permission error because of how Docker handles file permissions between the host and the container. It's by design for security reasons. The user inside the container likely doesn't have access to the mounted directory unless the UID and GID match what's on the host. You can work around it, but it's locked down intentionally.
Also, what's the use case here? What do you need file sharing via Samba in a Docker container for? If it's just about moving files in and out, docker cp or docker exec -it container /bin/bash might be easier.