3:08 p.m.
On Thu, May 12, 2022 at 08:04:28PM +0100, Daniel P. Berrangé wrote:
On Thu, May 12, 2022 at 07:00:09PM +0100, Daniel P. Berrangé wrote:
> On Wed, May 11, 2022 at 11:41:51AM -0400, Eric Garver wrote:
> > This series fixes routed networks when a newer firewalld (>= 1.0.0) is
> > present [1]. Firewalld 1.0.0 included a change that disallows implicit
> > forwarding between zones [2]. libvirt was relying on this behavior to
> > allow routed networks to function.
> >
> > New firewalld policies are added. This is done to use common rules
> > between NAT and routed networks. Policies have been supported since
> > firewalld 0.9.0.
>
> For those following along, there's a helpful description of policies
> here, specifically explaining how its useful to the libvirt scenario:
>
> https://firewalld.org/2020/09/policy-objects-introduction
In reviewing these patches I've come to realize I'm still not
confident I'm understanding the interaction between traffic
we're managing at the firewalld zones/policies.
It's confusing because it's a combination of iptables (libvirt) and
firewalld (nftables). And they filter independently. Think of it as
having to pass through two firewalls.
Hopefully I got it all correct below.
For illustration let me assume the following setup:
[
* Remote host on LAN (remote host IP 10.0.0.2)
* eth0 public facing ethernet on the LAN (local host IP 10.0.0.5)
* virbr0 isolated bridge device (local host IP 192.168.122.1)
* vnet0 TAP device for a guest (guest IP 192.168.122.5)
Remote host Local host
+----------+ LAN +----------+ IP forward +---------------+
| 10.0.0.2 | -------- | 10.0.0.5 | --------------| 192.168.122.1 |
| eth0 | | eth0 | w/ NAT | virbr0 |
+----------+ +----------+ +---------------+
|
| bridge port
|
+---------------+
| 192.168.122.5 |
| host: vnet0 |
| guest: eth0 |
+---------------+
IIUC zones are
* 'libvirt' containing 'virbr0'
* 'FedoraWorkstation' containing 'eth0'
Is 'vnet0' in a zone or not ?
No. Only the bridge interface is added to the zone. The vnet* interfaces
don't have addresses.
Traffic flows
* LAN Remote host (10.0.0.2) -> local host (10.0.0.5)
Normal traffic nothing to do with libvirt
Rules in <zone> FedoraWorkstation apply
True.
* LAN Remote host (10.0.0.2) -> guest (192.168.122.5)
IP layer forwarding via eth0 (with conntrack match for NAT zone)
ingress=FedoraWorkstation
egress=libvirt
Rules in <policy> libvirt-host-in apply ?
False. There are no explicit firewalld rules for this.
Existing connections would be implicitly allowed by a top-level "ct
state" match in FORWARD.
* Local host (192.168.122.1) -> guest (192.168.122.5)
Rules in <zone> libvirt apply ?
False. No rules explicit rules apply.
Firewalld allows outbound by default.
* Local host (10.0.0.5) -> guest (192.168.122.5)
NB, shouldn't happen as traffic should have originated
from 192.168.122.1 instead.
ingress=FedoraWorkstation
egress=libvirt
Rules in <policy> libvirt-host-in apply ?
False. There are no explicit firewalld rules for this.
New connections would be denied. Existing (originating from VM) would be
allowed.
* Guest (192.168.122.5) -> Local host (192.168.122.1)
Rules in <zone> libvirt apply ?
Need to allow dhcp, dns, ssh. Feels like this
should still be rules in the <zone> ?
True. This is handled by the current zone definition.
This series moves them into libvirt-to-host. You used the name
libvirt-host-in, which may be a better name for the policy. :)
* Guest (192.168.122.5) -> Local host (10.0.0.5)
NB, shouldn't happen as guest generally won't be
aware of host's eth0 IP address.
ingress=libvirt
egress=FedoraWorkstation
Rules in <policy> libvirt-nat-out apply ?
Should not allow anything special related to virt,
as dhcp/dns stuff should only be serviced from virbr0.
So the libvirt-nat-out policy feels wrong for this
case.
False. I think this is still considered INPUT traffic since it's going
to the local network stack.
So the "libvirt" zone and libvirt-to-host would apply.
Would be
ingress=libvirt
egress=HOST
* Guest (192.168.122.5) -> LAN remote host (10.0.0.2)
ingress=libvirt
egress=FedoraWorkstation
Rules in <policy> libvirt-nat-out apply ?
Need to allow all traffic
True.
Is the above right, or any I getting mixed up somewhere ?
Answered all inline.