[Libvir] [PATCH] Re: iptables masquerade rule overexpansive

[Charles Duffy <cduffy messageone com>]

Daniel P. Berrange wrote:
> Instead of having the separate ACCEPT rule I think it would be sufficient
> to replace  the 0.0.0.0/0 target with  ! 192.168.65.0/24, eg
>
> iptables -t nat -A POSTROUTING
>                 --source 192.168.65.0/24 
>                 --destination ! 192.168.65.0/24
>                 -j MASQUERADE
>
> so it will masquerade traffic which is leaving the ip range of the virtual
> network only, and leave ip traffic between the VMs & VM<->host alone.

I considered that -- but while it will work as long as the default 
forward rule is ACCEPT, it could result in hosts being unable to 
communicate with each other if the default rule for the table is otherwise.

That said, it's certainly easier... patch attached.

diff -ru libvirt-0.4.0.orig/src/iptables.c libvirt-0.4.0/src/iptables.c
--- libvirt-0.4.0.orig/src/iptables.c	2007-12-12 07:30:49.000000000 -0600
+++ libvirt-0.4.0/src/iptables.c	2008-03-27 15:31:29.000000000 -0500
@@ -1047,6 +1047,7 @@
         return iptablesAddRemoveRule(ctx->nat_postrouting,
                                      action,
                                      "--source", network,
+                                     "--destination", "!", network,
                                      "--out-interface", physdev,
                                      "--jump", "MASQUERADE",
                                      NULL);
@@ -1054,6 +1055,7 @@
         return iptablesAddRemoveRule(ctx->nat_postrouting,
                                      action,
                                      "--source", network,
+                                     "--destination", "!", network,
                                      "--jump", "MASQUERADE",
                                      NULL);
     }