https://docs.oracle.com/cd/B28359_01/server.111/b28310/ds_concepts002.htm#ADMIN12085 Database links are either private or public. If they are private, then only the user who created the link has access; if they are public, then all database users have access.
https://docs.oracle.com/database/121/SQLRF/statements_5006.htm#SQLRF01205