5f1e6a7d48
Historically firewall rules for virtual networks were added straight
into the base chains. This works but has a number of bugs and design
limitations:
- It is inflexible for admins wanting to add extra rules ahead
of libvirt's rules, via hook scripts.
- It is not clear to the admin that the rules were created by
libvirt
- Each rule must be deleted by libvirt individually since they
are all directly in the builtin chains
- The ordering of rules in the forward chain is incorrect
when multiple networks are created, allowing traffic to
mistakenly flow between networks in one direction.
To address all of these problems, libvirt needs to move to creating
rules in its own private chains. In the top level builtin chains,
libvirt will add links to its own private top level chains.
Addressing the traffic ordering bug requires some extra steps. With
everything going into the FORWARD chain there was interleaving of rules
for outbound traffic and inbound traffic for each network:
-A FORWARD -d 192.168.3.0/24 -o virbr1 -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A FORWARD -s 192.168.3.0/24 -i virbr1 -j ACCEPT
-A FORWARD -i virbr1 -o virbr1 -j ACCEPT
-A FORWARD -o virbr1 -j REJECT --reject-with icmp-port-unreachable
-A FORWARD -i virbr1 -j REJECT --reject-with icmp-port-unreachable
-A FORWARD -d 192.168.2.0/24 -o virbr0 -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A FORWARD -s 192.168.2.0/24 -i virbr0 -j ACCEPT
-A FORWARD -i virbr0 -o virbr0 -j ACCEPT
-A FORWARD -o virbr0 -j REJECT --reject-with icmp-port-unreachable
-A FORWARD -i virbr0 -j REJECT --reject-with icmp-port-unreachable
The rule allowing outbound traffic from virbr1 would mistakenly
allow packets from virbr1 to virbr0, before the rule denying input
to virbr0 gets a chance to run.
What we really need todo is group the forwarding rules into three
distinct sets:
* Cross rules - LIBVIRT_FWX
-A FORWARD -i virbr1 -o virbr1 -j ACCEPT
-A FORWARD -i virbr0 -o virbr0 -j ACCEPT
* Incoming rules - LIBVIRT_FWI
-A FORWARD -d 192.168.3.0/24 -o virbr1 -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A FORWARD -o virbr1 -j REJECT --reject-with icmp-port-unreachable
-A FORWARD -d 192.168.2.0/24 -o virbr0 -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A FORWARD -o virbr0 -j REJECT --reject-with icmp-port-unreachable
* Outgoing rules - LIBVIRT_FWO
-A FORWARD -s 192.168.3.0/24 -i virbr1 -j ACCEPT
-A FORWARD -i virbr1 -j REJECT --reject-with icmp-port-unreachable
-A FORWARD -s 192.168.2.0/24 -i virbr0 -j ACCEPT
-A FORWARD -i virbr0 -j REJECT --reject-with icmp-port-unreachable
There is thus no risk of outgoing rules for one network mistakenly
allowing incoming traffic for another network, as all incoming rules
are evalated first.
With this in mind, we'll thus need three distinct chains linked from
the FORWARD chain, so we end up with:
INPUT --> LIBVIRT_INP (filter)
OUTPUT --> LIBVIRT_OUT (filter)
FORWARD +-> LIBVIRT_FWX (filter)
+-> LIBVIRT_FWO
\-> LIBVIRT_FWI
POSTROUTING --> LIBVIRT_PRT (nat & mangle)
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Libvirt API for virtualization
Libvirt provides a portable, long term stable C API for managing the virtualization technologies provided by many operating systems. It includes support for QEMU, KVM, Xen, LXC, bhyve, Virtuozzo, VMware vCenter and ESX, VMware Desktop, Hyper-V, VirtualBox and the POWER Hypervisor.
For some of these hypervisors, it provides a stateful management daemon which runs on the virtualization host allowing access to the API both by non-privileged local users and remote users.
Layered packages provide bindings of the libvirt C API into other languages including Python, Perl, PHP, Go, Java, OCaml, as well as mappings into object systems such as GObject, CIM and SNMP.
Further information about the libvirt project can be found on the website:
License
The libvirt C API is distributed under the terms of GNU Lesser General
Public License, version 2.1 (or later). Some parts of the code that are
not part of the C library may have the more restrictive GNU General
Public License, version 2.1 (or later). See the files COPYING.LESSER
and COPYING for full license terms & conditions.
Installation
Libvirt uses the GNU Autotools build system, so in general can be built and installed with the usual commands. For example, to build in a manner that is suitable for installing as root, use:
$ ./configure --prefix=/usr --sysconfdir=/etc --localstatedir=/var
$ make
$ sudo make install
While to build & install as an unprivileged user
$ ./configure --prefix=$HOME/usr
$ make
$ make install
The libvirt code relies on a large number of 3rd party libraries. These will
be detected during execution of the configure script and a summary printed
which lists any missing (optional) dependencies.
Contributing
The libvirt project welcomes contributions in many ways. For most components the best way to contribute is to send patches to the primary development mailing list. Further guidance on this can be found on the website:
https://libvirt.org/contribute.html
Contact
The libvirt project has two primary mailing lists:
- libvirt-users@redhat.com (for user discussions)
- libvir-list@redhat.com (for development only)
Further details on contacting the project are available on the website: