Uruk rc file

default
The simplest valid rc file is the empty file. This rc file blocks all TCP and UDP connection attempts to services on our host: this is the default behaviour.

simplest
The simplest rc file which does allow traffic to our services looks like e.g.:

interfaces=eth0 ips_eth0=default ip_eth0_default=192.168.26.27 net_eth0_default=192.168.0.0/16 ip6_eth0_default=2001:db8::1/64 net6_eth0_default=2001:db8::/32 services_eth0_default_tcp=local ports_eth0_default_tcp_local="0:65535" sources_eth0_default_tcp_local="0.0.0.0/0 ::/0" services_eth0_default_udp=local ports_eth0_default_udp_local="0:65535" sources_eth0_default_udp_local="0.0.0.0/0"

This rc file allows all IPv4 and IPv6 UDP and TCP traffic from publicly routable IPs to eth0's IP.

realistic
If you'd like to block traffic on wlan0 and allow traffic to ssh on your wired interface, and don't like to explicitly set your IPs in rc:

# list of interfaces you'd like uruk to protect interfaces=eth0 wlan0 # set variables ip{,6}_eth0_default and net{,6}_eth0_default . /lib/uruk/init/autodetect-ips # names for eth0's 2 IPv4 addresses ips_eth0="default dhcp" # allow access to our sshd on eth0's primary IP on tcp port 443 # from anywhere services_eth0_default_tcp=ssh ports_eth0_default_tcp_ssh=443 sources_eth0_default_tcp_ssh="0.0.0.0/0 ::/0" # we get a static IPv4 via dhcp ip_eth0_dhcp=10.0.0.3 net_eth0_dhcp=10./8 services_eth0_dhcp_tcp=http ports_eth0_dhcp_tcp_http=http sources_eth0_dhcp_tcp_http=$net_eth0_dhcp # we leave services_wlan0_default_{tcp,udp} unset: don't allow any # incoming connections on wlan0's default IP

autodetect-ips
The script autodetect-ips --as used in the previous example-- looks for files /etc/sysconfig/network-scripts/ifcfg-* (commonly found at e.g. Red Hat and Fedora systems) and /etc/network/interfaces (as found at e.g. Debian and Ubuntu systems), and, for each interface nic, and each found IPv4 and IPv6 address and network, sets variables ip_nic_default, ip6_nic_default, net_nic_default and net6_nic_default . Then it calls ip(8) and adds any other found nic, ip and net triplets (for IPv4 and, for IPv6, only addresses in scope "global").

The script autodetect-ips is useful if you'd like to share your rc file among different hosts.

another example
For an even more reasonable rc file, look at the well-commented example rc file in /usr/share/doc/uruk/examples/rc.

IPv4 AND IPv6

You can mix IPv4 and IPv6-addresses in sources_*. E.g.:

ips_eth0='default private' ip_eth0_default=1.2.3.4 ip6_eth0_default= services_eth0_default_tcp='mail local' sources_eth0_default_tcp_mail='10.0.0.0/24 192.0.32.0/24 192.168.6.26' sources_eth0_default_tcp_local='192.0.32.0/24 svejk.example.com 2001:db8::/32' ports_eth0_default_tcp_mail=smtp ports_eth0_default_tcp_local='ssh ftp'

If svejk.example.com has both an IPv4 PTR record in DNS, as well as an IPv6 PTR record, connection attempts from svejk to the ssh and ftp TCP ports are allowed, via both IPv4 and IPv6.

Uruk used to require variables sources6_* to be set to support ip6tables. Since uruk version 20140319 (The Alfama Release), this is no longer needed; setting sources_* suffices. To be precise, the semantics since uruk version 20140319 is: 1) If both sources_* and sources6_* are defined (even if they're just empty), each is used for its respective address family. (This ensures backwards compatibility.) 2) If sources6_* is undefined, sources_* is used for both v4 and v6. 3) In either case, v4 literals in v6 context and v6 literals in v4 context are silently (!) ignored.

HOOKS

Uruk offers hooks for inserting your own code between iptables invocations. Examples will show the usefulness of these hooks.

allowing broadcasts
In rc, there is:

rc_b=$etcdir/bootp

while the file bootp reads

iptables —A INPUT —m state ——state NEW —i eth0 \ ——protocol udp ——destination-port bootps —j ACCEPT

. This enables one to add rules for packets with broadcast addresses in their destination. (Uruk has no support for this in its regular rc.)

allowing non-matching returntraffic
In rc there is:

rc_d=$etcdir/dns

while the file dns reads

for source in 10.5.0.27 10.56.0.40 do $iptables -A INPUT -i eth0 --protocol udp \ --source "$source" --source-port domain \ --destination "$ip_eth0" \ --destination-port 30000: -j ACCEPT done

This allows one to allow (return)traffic, disregarding the state. (Uruk has no support for this in its regular rc.)

allowing NAT
In rc there is:

rc_a=${etcdir}/nat

while the file nat reads

$iptables -t nat -A POSTROUTING \ --out-interface eth0 -j SNAT \ --to-source $ip_eth0

This allows Network Address Translation. However, beware! Like all extensive use of hooks, this will break the uruk-save script. If you make sure your active iptables rules are wiped, and invoke uruk manually to load new rules, you're safe. Using the init script with its default settings is safe too.

allowing IPv6 tunneling
In rc there is:

rc_b=${etcdir}/proto_41

while the file proto_41 reads

$iptables -A INPUT -i ppp0 --protocol 41 --destination $ip_ppp0 -j ACCEPT

This allows IP protocol 41, typically used for this kind of tunneling.

allowing any traffic on an interface
In rc there is:

interfaces_unprotect="lo eth2"

This allows any traffic on eth2 (and on lo, the default), including any ICMP packets and packets from any source address.

using multiple hooks at one entry point in the main uruk process
In case rc_a, rc_b, ... , or rc_i does not have a file as its value, but a directory, all files matching "$rc_x"/*.rc will get sourced. This helps configuration management in complex situations involving lots of uruk configuration files for lots of hosts.

See the section "THE GORY DETAILS: uruk INTERNALS" in uruk(8) (or the uruk source) to find out which hook (there are hooks rc_a, rc_b, ... , rc_i) to use.

NETWORK INTERFACES WITH MULTIPLE IP ADDRESSES

Uruk supports situations where a network interface has more than one IP address attached. Variables ips_nic and bcasts_nic are used for this.

If ips_nic is set, e.g. like

ips_eth0="ip0 ip1 ip2"

we assume multiple (three in this example) IPs are assigned to eth0. If this variable is not set only one IP is supported on eth0.

In multiple-IP mode, IP addresses are listed as e.g.

ip_eth0_ip0="137.56.247.16"

(If you're used to the Linux ifconfig(8) output, you could use the name ip for eth0, and ip0 for eth0:0.) The ports, services and sources variables look like e.g.

services_eth0_ip2_tcp=local ports_eth0_ip2_tcp_local=smtp sources_eth0_ip2_tcp_local=$localnet

and, similarly,

net_eth0_ip1=192.168.0.0/16

Furthermore, for dropping broadcast packets, specify e.g.

bcasts_eth0="ip0 ip2" # yes, possibly a subset of ips_eth0 bcast_eth0_ip0="10.0.0.255" bcast_eth0_ip2="10.0.255.255"

As an additional feature, if you have multiple IP addresses that all need to get the same rules, you can assign them to a single name:

ip_eth0_ip0="137.56.247.16 137.56.247.17 137.56.247.18"

LOGGING AND DEBUGGING

Uruk has support for logging network packets, and for debugging the uruk script.

Logging
By default, uruk logs denied packets. This is adjustable using the loglevel variable. The settings are:

•

"zero": be silent; do not log any packet. rc file features loglevel=10.

•

"low": log denied packets, which are targeted at one of our IPs. rc file features loglevel=30.

•

"medium": log denied non-broadcast packets. This is the default: loglevel is unset or rc file features loglevel=50.

•

"fascist": log all packets. rc file features loglevel=90.

Debugging
To debug the uruk script, invoke uruk as

sh -x /sbin/uruk

this shows what is done, along with executing it. (Like an uruk '-v' option.)

If you'd rather prefer not to execute, but just watch what would've been done, invoke uruk as

URUK_IPTABLES='echo iptables' URUK_IP6TABLES='echo ip6tables' uruk

(Like an uruk '-n' option.) If you have this statement set, you can run uruk under a non-priviliged user account.

If you'd like to test a new rc file before installing it, run something like:

URUK_CONFIG=/path/to/new/uruk/rc/file uruk

Of course, all these tweaks can be combined.

VARIABLES

The uruk script honors the following variables in rc files:

•

"version" Uruk version compatibility of this rc file

•

"loglevel"

•

"iptables" Full pathname of iptables executable.

•

"ip6tables" Full pathname of ip6tables executable.

•

"interfaces" List of network interfaces.

More variables are available. For now, you'll have to take a look at the example rc file in /usr/share/doc/uruk/examples/rc for more details.

ENVIRONMENT VARIABLES

See uruk(8) for a list of honored environment variables.

FILES

/etc/uruk/rc

COPYRIGHT

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see http://www.gnu.org/licenses/.

AUTHOR

Joost van Baal-Ilić <joostvb-uruk@mdcc.cx>

NAME

SYNOPSIS

DESCRIPTION

EXAMPLES