Tente
passwd_chroot_enable=yes
passwd_chroot_enable
If enabled, along with chroot_local_user , then a chroot() jail location may be specified on a per-user basis. Each user's jail is derived from their home directory string in /etc/passwd. The occurrence of /./ in the home directory string denotes that the jail is at that particular location in the path.
Observe também que o AFAIR vsftp tem que ser executado como root para permitir que qualquer configuração chroot funcione!
Veja também
run_as_launching_user
[...] Specifically, vsftpd does not / cannot use chroot technology to restrict file access when this option is set (even if launched by root). [...]