On 07/08/2013 10:59 AM, Sven Schwedas wrote:
Hi,
I'm trying to configure nwfilter for KVM, but so far I haven't managed
to figure out a working configuration.
Network setup: The dom0 (Debian 7.1, kernel 3.2.46-1, libvirt 0.9.12) is
connected via eth0, part of the external subnet 192.168.17.0/24, and has
an additional subnet 192.168.128.160/28 routed to its main address
192.168.17.125.
The host's subnet is configured as bridge in virsh:
<network>
<name>foo</name>
<forward dev='eth0' mode='route'>
<interface dev='eth0'/>
</forward>
<bridge name='foo-br0' stp='off' delay='0' />
<ip address='192.168.128.161' netmask='255.255.255.240'>
</ip>
</network>
The domU is configured to use this bridge (static IP configured in DomU):
<interface type='network'>
<source network='foo'/>
<target dev='vnet0'/>
<model type='virtio'/>
<filterref filter='test-eth0'>
<parameter name='CTRL_IP_LEARNING' value='none'/>
<parameter name='IP' value='192.168.128.162'/>
</filterref>
<alias name='net0'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
</interface>
With an empty filter, connectivity is working fine. Now, if I add the
example ruleset suggested in the documentation (
http://libvirt.org/formatnwfilter.html#nwfwriteexample ), *incoming*
ICMP works (but not outgoing), and inbound SSH traffic is blocked,
together with outbound DNS.
The linked rules produce the following iptables chains:
Chain INPUT (policy ACCEPT)
target prot opt source destination
libvirt-host-in all -- 0.0.0.0/0 0.0.0.0/0
ACCEPT udp -- 0.0.0.0/0 0.0.0.0/0 udp dpt:53
ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:53
ACCEPT udp -- 0.0.0.0/0 0.0.0.0/0 udp dpt:67
ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:67
Chain FORWARD (policy ACCEPT)
target prot opt source destination
libvirt-in all -- 0.0.0.0/0 0.0.0.0/0
libvirt-out all -- 0.0.0.0/0 0.0.0.0/0
libvirt-in-post all -- 0.0.0.0/0 0.0.0.0/0
ACCEPT all -- 0.0.0.0/0 192.168.128.160/28
ACCEPT all -- 192.168.128.160/28 0.0.0.0/0
ACCEPT all -- 0.0.0.0/0 0.0.0.0/0
REJECT all -- 0.0.0.0/0 0.0.0.0/0 reject-with icmp-port-unreachable
REJECT all -- 0.0.0.0/0 0.0.0.0/0 reject-with icmp-port-unreachable
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
Chain FI-vnet0 (1 references)
target prot opt source destination
RETURN tcp -- 0.0.0.0/0 0.0.0.0/0 tcp spt:22 state ESTABLISHED ctdir ORIGINAL
RETURN tcp -- 0.0.0.0/0 0.0.0.0/0 tcp spt:80 state ESTABLISHED ctdir ORIGINAL
RETURN icmp -- 0.0.0.0/0 0.0.0.0/0 state NEW,ESTABLISHED ctdir REPLY
RETURN udp -- 0.0.0.0/0 0.0.0.0/0 udp dpt:53 state NEW,ESTABLISHED ctdir REPLY
DROP all -- 0.0.0.0/0 0.0.0.0/0
Chain FO-vnet0 (1 references)
target prot opt source destination
ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:22 state NEW,ESTABLISHED ctdir REPLY
ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:80 state NEW,ESTABLISHED ctdir REPLY
ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 state ESTABLISHED ctdir ORIGINAL
ACCEPT udp -- 0.0.0.0/0 0.0.0.0/0 udp spt:53 state ESTABLISHED ctdir ORIGINAL
DROP all -- 0.0.0.0/0 0.0.0.0/0
Chain HI-vnet0 (1 references)
target prot opt source destination
RETURN tcp -- 0.0.0.0/0 0.0.0.0/0 tcp spt:22 state ESTABLISHED ctdir ORIGINAL
RETURN tcp -- 0.0.0.0/0 0.0.0.0/0 tcp spt:80 state ESTABLISHED ctdir ORIGINAL
RETURN icmp -- 0.0.0.0/0 0.0.0.0/0 state NEW,ESTABLISHED ctdir REPLY
RETURN udp -- 0.0.0.0/0 0.0.0.0/0 udp dpt:53 state NEW,ESTABLISHED ctdir REPLY
DROP all -- 0.0.0.0/0 0.0.0.0/0
Chain libvirt-host-in (1 references)
target prot opt source destination
HI-vnet0 all -- 0.0.0.0/0 0.0.0.0/0 [goto] PHYSDEV match --physdev-in vnet0
Chain libvirt-in (1 references)
target prot opt source destination
FI-vnet0 all -- 0.0.0.0/0 0.0.0.0/0 [goto] PHYSDEV match --physdev-in vnet0
Chain libvirt-in-post (1 references)
target prot opt source destination
ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 PHYSDEV match --physdev-in vnet0
Chain libvirt-out (1 references)
target prot opt source destination
FO-vnet0 all -- 0.0.0.0/0 0.0.0.0/0 [goto] PHYSDEV match --physdev-out vnet0
I've tried fidgeting with the configuration (direction inout instead of
in/out, etc.), but I didn't find a setup that works as intended. What am
I missing?
Depending on the settings of your Linux distribution you may need to
echo 1 > /proc/sys/net/bridge/bridge-nf-call-iptables
to enable iptables filtering for traffic traversing the bridge. Does
this get it to work?
Stefan
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