On Tue, Mar 30, 2010 at 01:56:52PM -0400, Stefan Berger wrote: > Subject: Support for learning a VM's IP address > A caveat: The algorithm does not know which one is the appropriate IP > address of a VM. If the VM spoofs an IP address in its first ARP traffic > or IPv4 packets its filtering rules will be instantiated for this IP > address, thus 'locking' it to the found IP address. So, it's still > 'safer' to explicitly provide the IP address of a VM's interface in the > filter description if it is known beforehand. While this code is very clever, I'm not really convinced that having a learning capability that snifs arbitrary IP packets for an address is desirable. The primary task of the nwfilter mechanism is to provide secure isolation of the VM from other VMs & network protocols. Basing this ontop of a learning mode that we know can be trivially poisoned/exploited by sending fake ARPs just doesn't seem like a good plan - it is providing users a false sense of security. The only way I could see this working in a reasonably secure manner is to start from the assigned MAC address that we know & can trust. Then listen for DHCP OFFERS (IPv4/6) matching the MAC address, and extract the IP from that. This assumes DHCP OFFERS come from a trusted server, so we need to make sure that other VMs can't spoof DHCP OFFERS. Either the admin could include a DHCP blocking rule in the nwfilter config for all VMs (needs to be on all hosts), or have a host config parameter for nwfilter to specify the trusted DHCP server address. If done right, this gives a IP addr learning mode which the VM can't poison with an IP of its choosing. For IPv6 the network might use DHCPv6 which we can procss in much the same way, or it might be doing stateless autoconfig. So we'd need some host level config parameter to specify whether to learn based on DHCPv6, or based on the router advertisments. In the latter case a VM auto-assigns itself an IPv6 address based on the router prefix + its MAC address. So if we spot the router prefix + know the MAC addr we can safely set the IPv6 addr filter Regards, Daniel -- |: Red Hat, Engineering, London -o- http://people.redhat.com/berrange/ :| |: http://libvirt.org -o- http://virt-manager.org -o- http://deltacloud.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: GnuPG: 7D3B9505 -o- F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :| -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list