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



On Thu, Mar 11, 2010 at 08:06:04AM -0500, Stefan Berger wrote:
> 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. 

It is planned to cover IPv6 too, either at ebtables or ip6tables
level ?
 
>   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.


I've not looked at the actual code in detail yet, but the public API,
virsh commands, XML etc all looks generally good to me. I'll try and
get you a detailed code review friday/monday once I get through my
current work items.

> 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.

I understand why you can't use the ebtables/iptables APIs we currently
have there, but I'm not much of a fan of using the shell script. Isn't
it just as easy to directly call  virRun() with each set of ARGV to be
exec'd ?


Regards,
Daniel
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