This will not work. sudo cp aaa bbb will work but su -c cp aaa bbb will complain that the user aaa does not exist, you need to quote them instead, like su -c "cp aaa bbb".
I searched it up, and apparently "$@" and expands to "foo" "bar" while "$*" expands to "foo bar", and the latter is what we want. From a quick test on my machine, that replacement in in your function definition seems to fix it :).
