I think this is what chroot_local_user=YES does.
Note from man vsftpd.conf
If set to YES, local users will be (by default) placed in a chroot() jail in their home direc-
tory after login. Warning: This option has security implications, especially if the users
have upload permission, or shell access. Only enable if you know what you are doing. Note
that these security implications are not vsftpd specific. They apply to all FTP daemons which
offer to put local users in chroot() jails.
Perhaps someone else can give some colour on what these security implications are. Lat time I tried googling for an answer, I got nowhere much