The installation scripts in the Gentoo dev-db/mysql, dev-db/mariadb, dev-db/percona-server, dev-db/mysql-cluster, and dev-db/mariadb-galera…

The installation scripts in the Gentoo dev-db/mysql, dev-db/mariadb, dev-db/percona-server, dev-db/mysql-cluster, and dev-db/mariadb-galera packages before 2017-09-29 have chown calls for user-writable directory trees, which allows local users to gain privileges by leveraging access to the mysql account for creation of a link.