You can try this and it should lock them to their folder only.
Open vsftpd configuration file - /etc/vsftpd/vsftpd.conf
# vi /etc/vsftpd/vsftpd.conf

Make sure following line exists (and uncommented):
chroot_local_user=YES

Save and close the file. Restart vsftpd.
# /etc/init.d/vsftpd restart