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

Stefan Berger stefanb at us.ibm.com
Fri Mar 12 12:58:42 UTC 2010

One note: the attached patches must be compiled with --without-lxc support 
due to a linking problem. Will fix this for the next post.


> 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=''/>
>   </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=''/>
>   </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.
> One comment to patch 13: It currently #include's a .c file into a .c
> file only for the reason so I don't have to change too much code once I
> change code in the underlying patch. So this has to be changed. The
> patch series works without patch 13, but then only supports ebtables.
> The patches apply to the current tip. They pass 'make syntax-check' and
> have been frequently run in valgrind for memory leak checks. The order
> in which I apply the patches is as follows:
> add_recursive_locks.diff
> add_build_support.diff
> add_public_api.diff
> add_internal_api.diff
> impl_pub_api.diff
> def_wire_protocol_format.diff
> impl_rpc_client.c
> impl_srv_dispatch.diff
> add_virsh_support.diff
> add_xml_parsing.diff
> add_qemu_support.diff
> impl_driver.diff
> add_iptables_support.diff
> Looking forward to your feedback on the patches. 
> Thanks and regards,
>     Stefan and Gerhard
> --
> libvir-list mailing list
> libvir-list at redhat.com
> https://www.redhat.com/mailman/listinfo/libvir-list
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