[openstack-dev] [OSSN 0029] Neutron FWaaS rules lack port restrictions when using protocol 'any'

Nathan Kinder nkinder at redhat.com
Wed Sep 24 16:58:39 UTC 2014

Hash: SHA1

Neutron FWaaS rules lack port restrictions when using protocol 'any'
- ---

### Summary ###
A bug in the Neutron FWaaS (Firewall as a Service) code results in
iptables rules being generated that do not reflect desired port
restrictions. This behaviour is triggered when a protocol other than
'udp' or 'tcp' is specified, e.g. 'any'.

The scope of this bug is limited to Neutron FWaaS and systems built upon
it. Security Groups are not affected.

### Affected Services / Software ###
Neutron FWaaS, Grizzly, Havana, Icehouse

### Discussion ###
When specifying firewall rules using Neutron that should match multiple
protocols, it is convenient to specify a protocol of 'any' in place of
defining multiple specific rules.

For example, in order to allow DNS (TCP and UDP) requests, the following
rule might be defined:

neutron firewall-rule-create --protocol any --destination-port 53 \
    --action allow

However, this rule results in the generation of iptables firewall rules
that do not reflect the desired port restriction. An example generated
iptables rule might look like the following:

- -A neutron-l3-agent-iv441c58eb2 -j ACCEPT

Note that the restriction on port 53 is missing. As a result, the
generated rule will match and accept any traffic being processed by the
rule chain to which it belongs.

Additionally, iptables arranges sets of rules into chains and processes
packets entering a chain one rule at a time. Rule matching stops at the
first matched exit condition (e.g. accept or drop). Since, the generated
rule above will match and accept all packets, it will effectively short
circuit any filtering rules lower down in the chain. Consequently, this
can break other firewall rules regardless of the protocol specified when
defining those rules with Neutron. They simply need to appear later in
the generated iptables rule chain.

This bug is triggered when any protocol other than 'tcp' or 'udp' is
specified in conjunction with a source or destination port number.

### Recommended Actions ###
Avoid the use of 'any' when specifying the protocol for Neutron FWaaS
rules. Instead, create multiple rules for both 'tcp' and 'udp' protocols

A fix has been submitted to Juno.

### Contacts / References ###
This OSSN : https://wiki.openstack.org/wiki/OSSN/OSSN-0029
Original LaunchPad Bug : https://bugs.launchpad.net/neutron/+bug/1365961
OpenStack Security ML : openstack-security at lists.openstack.org
OpenStack Security Group : https://launchpad.net/~openstack-ossg
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