Re: Setting Deny Forward Rules with Firewalld

On Fri, Dec 31, 2021 at 02:49:09AM -0000, Sean Zimmermann wrote:

Hi everyone,

I'm trying to setup a firewall so one of my VMs is barred from accessing the LAN (if saddr = VM Address and daddr = 192.168.0.0/16, deny input and forward). I was able to do this in nftables here:

table inet ext_only { chain input { type filter hook input priority filter - 10; policy accept; ct state new ip saddr 192.168.100.100 drop }

    chain forward {
            type filter hook forward priority filter - 10; policy accept;
            ct state new ip saddr 192.168.100.100 ip daddr 192.168.0.0/16 drop
    }

}

However, I've been having trouble trying to figure out the correct way to do this for firewalld. I know I can move the VM IP to its own zone, and I can then block input, but I couldn't figure out how to write a forward deny rule.

What is the recommended way to handle dropping forwarded packets?

Policy objects are available in v0.9.0 and later. They allow forward and output filtering.

- https://firewalld.org/2020/09/policy-objects-introduction - https://firewalld.org/2020/09/policy-objects-filtering-container-and-vm-traf...

You probably want something like this (untested):

# firewalld-cmd --permanent --add-policy noForwardToLan # firewalld-cmd --permanent --policy noForwardToLan --add-ingress-zone <zone_of_vm> # firewalld-cmd --permanent --policy noForwardToLan --add-egress-zone <zone_of_lan> # firewalld-cmd --permanent --policy noForwardToLan --set-target REJECT

This will reject all traffic originating from <zone_of_vm> and destined to <zone_of_lan>. It would allow the VM to connect to the internet if your uplink is in yet another zone, e.g. public or external.

Hope that helps. Eric.