Xen: firewall DomU from Dom0

Posted by valqk on
Have you ever wondered how to force some firewall rules on a xen DomU and the DomU root won't be able to use some ports etc?
Well, the only proper way is to firewall DomU from the Dom0 machine.
Here is a way to do it.
This script is just an example. It should be made more universal and can apply to ALL of your DomU's for their protection :-) or logging specific traffic.
#!/bin/bash
vifname=$1;
/sbin/iptables -N vps
#outbound traffic redirect to vps - a per DomU chain.
/sbin/iptables -I FORWARD -m physdev  --physdev-out peth0 --physdev-in $vifname -j vps
#log some of the traffic
/sbin/iptables -A "vps" -j LOG -m  tcp --dport 80,110,113 --log-level 4 --log-prefix '*DomUNameHere-shows-in-logs*'
#allow some ports
/sbin/iptables -A "vps" -p tcp -m tcp --dport 20 -j RETURN
/sbin/iptables -A "vps" -p tcp -m tcp --dport 21 -j RETURN
/sbin/iptables -A "vps" -p tcp -m tcp --dport 22 -j RETURN
/sbin/iptables -A "vps" -p tcp -m tcp --dport 80 -j RETURN
/sbin/iptables -A "vps" -p tcp -m tcp --dport 443 -j RETURN
/sbin/iptables -A "vps" -p tcp -m tcp --dport 6666 -j RETURN
/sbin/iptables -A "vps" -p tcp -m tcp --dport 6667 -j RETURN
/sbin/iptables -A "vps" -p tcp -m tcp --dport 6668 -j RETURN
/sbin/iptables -A "vps" -p tcp -m tcp --dport 6669 -j RETURN
/sbin/iptables -A "vps" -p udp -m udp --dport 53 -j RETURN
#allow establieshed connections from inside the DomU to go back in
/sbin/iptables -A "vps" -p tcp -m state --state RELATED,ESTABLISHED -j RETURN
#drop all other traffic.
/sbin/iptables -A "vps" -p tcp -j DROP

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