With this property - dfs.permissions.supergroup, dfs.permissions.superusergroup
CM lets you control/assign superuser for Hadoop environment. But if left as is, I notice directories owned by group for ex: hdfs:supergroup.
Now CM creates it at the time of Hadoop cluster installation, but who are all the users under this supergroup?
When directories or files show group as "supergroup" that means that noone except superusers would have access via group permission. It is merely a convention. If there is no OS group named supergroup (or LDAP if you are using LDAP groups mapping) then only the "hdfs" user has access.
In short, there is no group named "supergroup" by default. If you are a superuser, you would have access to the file/directory anyway since permissions would not apply to a superuser.