1 open holes in the firewall
Use OpenWRT's web interface (luci): open tcp:20 and tcp:21 for plain old unencrypted ftp.
2 install vsftpd
opkg install vsftpd
3 create the ftp directory
mkdir -p /home/ftp_user/storage
chown ftp_user /home/ftp_user/storage
Note: Don't chown the ftp_user dir, because later we will jail the user.
4 add the user to the system
Add a user by editing /etc/passwd, useradd doesn't add a shell, so don't use it.
"/bin/false" - no ssh login possible
to change the password of that user
5 configure vsftpd
Config, add these to /etc/vsftpd.conf, so the anon user points to the right location
6 jail the user
7 start and enable
to start and make it autostart at boot:
Basically OpenWRT has issues in terms of scripts and commands, but it's amazing how many things are already implemented.