Whitelist CloudFlare's IPs on port your selection of ports
This script supports Fedora, RHEL, CentOS, Debian,and Ubuntu.
bash <(curl -sSL https://raw.githubusercontent.com/tommytran732/Cloudflare-IPWhitelist/master/cloudflare.sh)
Before you run the script, makes sure you have not opened those ports to all IPs as it will make this script useless.
If you run SSHD on a port different from 22, make sure you have it opened or just change the command ufw allow 22 to your appropriate port.