7:06 a.m.
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.
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