Re: [libvirt] [PATCH 0/13] [RFC] Network filtering (ACL) extensions for libvirt

Hi! The following set of patches add network filtering (ACL) extensions to libvirt and enable network traffic filtering for VMs using ebtables and, depending on the networking technology being used (tap, but not macvtap), also iptables. Usage of either is optional and controlled through filters that a VM is referencing. The ebtables-level filtering is based on the XML derived from the CIM network slide 10 (filtering) from the DMTF website (http://www.dmtf.org/standards/cim/cim_schema_v2230/CIM_Network.pdf). The XML we derived from this was discussed on the list before. On the ebtables level we currently handle filtering of IPv4 and ARP traffic.

The iptables-level filtering is based on similar XML where XML nodes described the particular protocol to filter for. Its extensions enable the filtering of traffic using iptables for tcp, udp, icmp, igmp, sctp and 'all' types of traffic. This list of protocols maps to the features supported by iptables and only excludes protocols like 'esp' and 'ah'. Currently only bridging mode is supported and based on availability of the physdev match. The filtering framework adds new libvirt virsh commands for managing the filters. The 5 new commands are: - virsh nwfilter-list - virsh nwfilter-dumpxml <name of filter> - virsh nwfilter-define <name of file containing filter desc.> - virsh nwfilter-undefine <name of filter> - virsh nwfilter-edit <name of filter> Above commands are similar to commands for already existing pools and as such much of the code directly related to the above commands could be borrowed from other drivers. The network filters can either contain rules using the above mentioned XML or contain references to other filters in order to build more complex filters that form some sort of filter tree or can contain both. An example for a filter referencing other filters would be this one here: <filter name='demofilter4' chain='root'> <uuid>66f62d1d-34c1-1421-824f-c62d5ee5e8b6</uuid> <filterref filter='no-mac-spoofing'/> <filterref filter='no-mac-broadcast'/> <filterref filter='no-arp-spoofing'/> <filterref filter='allow-dhcp'> <parameter name='DHCPSERVER' value='10.0.0.1'/> </filterref> <filterref filter='no-other-l2-traffic'/> <filterref filter='recv-only-vm-ipaddress'/> <filterref filter='recv-only-vm-macaddress'/> <filterref filter='l3-test'/> </filter> A filter containing actual rules would look like this: <filter name='no-mac-broadcast' chain='ipv4'> <uuid>ffe2ccd6-edec-7360-1852-6b5ccb553234</uuid> <rule action='drop' direction='out' priority='500'> <mac dstmacaddr='ff:ff:ff:ff:ff:ff'/> </rule> </filter> The filter XML now also holds a priority attribute in the rule. This provides control over the ordering of the applied ebtables/iptables rules beyond their appearance in the XML. The domain XML has been extended to reference a top level filter from within each <interface> XML node. A valid reference to such a top level filter looks like this: <interface type='bridge'> <source bridge='static'/> <filterref filter='demofilter4'> <parameter name='IP' value='9.59.241.151'/> </filterref> </interface> In this XML a parameter IP is passed for instantiation of the referenced filters, that may require the availability of this parameter. In the above case the IP parameter's value describes the value of the IP address of the VM and allows to enable those filters to be instantiated that require this 'IP' variable. If a filter requires a parameter that is not provided, the VM will not start or the interface will not attach to a running VM. Any names of parameters can be provided for instantiation of filters and their names and values only need to pass a regular expression test. Currently only MAC and IP addresses and port numbers can be replaced with variables inside the filter XML. In a subsequent patch we will be adding capability to allow users to omit the IP parameter (only) and enable libvirt to learn the IP address of the VM and have it instantiate the filter once it knows it. While virtual machines are running, it is possible to update their filters. For that all running VMs' filter 'trees' are traversed to detect whether the updated filter is referenced by the VM. If so, its ebtables/iptable rules are applied. If one of the VMs' update fails allupdates are rolled back and the filter XML update is rejected.

One comment about the instantiation of the rules: Since the XML allows to create nearly any possible combination of parameters to ebtables or iptables commands, I haven't used the ebtables or iptables wrappers. Instead, I am writing ebtables/iptables command into a buffer, add command line options to each one of them as described in the rule's XML, write the buffer into a file and run it as a script. For those commands that are not allowed to fail I am using the following format to run them: cmd="ebtables <some options>" r=`${cmd}` if [ $? -ne 0 ]; then echo "Failure in command ${cmd}." exit 1 fi cmd="..." [...] If one of the command fails in such a batch, the libvirt code is going pick up the error code '1', tear down anything previously established and report an error back. The actual error message shown above is currently not reported back, but can be later on with some changes to the commands running external programs that need to read the script's stdout.