eb6e1310b8
svn path=/nixos/trunk/; revision=29285
282 lines
8.8 KiB
Nix
282 lines
8.8 KiB
Nix
/* This module enables a simple firewall.
|
||
|
||
The firewall can be customised in arbitrary ways by setting
|
||
‘networking.firewall.extraCommands’. For modularity, the firewall
|
||
uses several chains:
|
||
|
||
- ‘nixos-fw-input’ is the main chain for input packet processing.
|
||
|
||
- ‘nixos-fw-log-refuse’ and ‘nixos-fw-refuse’ are called for
|
||
refused packets. (The former jumps to the latter after logging
|
||
the packet.) If you want additional logging, or want to accept
|
||
certain packets anyway, you can insert rules at the start of
|
||
these chain.
|
||
|
||
- ‘nixos-fw-accept’ is called for accepted packets. If you want
|
||
additional logging, or want to reject certain packets anyway, you
|
||
can insert rules at the start of this chain.
|
||
|
||
*/
|
||
|
||
|
||
|
||
{ config, pkgs, ... }:
|
||
|
||
with pkgs.lib;
|
||
|
||
let
|
||
|
||
cfg = config.networking.firewall;
|
||
|
||
helpers =
|
||
''
|
||
# Helper command to manipulate both the IPv4 and IPv6 tables.
|
||
ip46tables() {
|
||
iptables "$@"
|
||
ip6tables "$@"
|
||
}
|
||
'';
|
||
|
||
in
|
||
|
||
{
|
||
|
||
###### interface
|
||
|
||
options = {
|
||
|
||
networking.firewall.enable = mkOption {
|
||
default = false;
|
||
description =
|
||
''
|
||
Whether to enable the firewall. This is a simple stateful
|
||
firewall that blocks connection attempts to unauthorised TCP
|
||
or UDP ports on this machine. It does not affect packet
|
||
forwarding.
|
||
'';
|
||
};
|
||
|
||
networking.firewall.logRefusedConnections = mkOption {
|
||
default = true;
|
||
description =
|
||
''
|
||
Whether to log rejected or dropped incoming connections.
|
||
'';
|
||
};
|
||
|
||
networking.firewall.logRefusedPackets = mkOption {
|
||
default = false;
|
||
description =
|
||
''
|
||
Whether to log all rejected or dropped incoming packets.
|
||
This tends to give a lot of log messages, so it's mostly
|
||
useful for debugging.
|
||
'';
|
||
};
|
||
|
||
networking.firewall.logRefusedUnicastsOnly = mkOption {
|
||
default = true;
|
||
description =
|
||
''
|
||
If <option>networking.firewall.logRefusedPackets</option>
|
||
and this option are enabled, then only log packets
|
||
specifically directed at this machine, i.e., not broadcasts
|
||
or multicasts.
|
||
'';
|
||
};
|
||
|
||
networking.firewall.rejectPackets = mkOption {
|
||
default = false;
|
||
description =
|
||
''
|
||
If set, forbidden packets are rejected rather than dropped
|
||
(ignored). This means that a ICMP "port unreachable" error
|
||
message is sent back to the client. Rejecting packets makes
|
||
port scanning somewhat easier.
|
||
'';
|
||
};
|
||
|
||
networking.firewall.allowedTCPPorts = mkOption {
|
||
default = [];
|
||
example = [ 22 80 ];
|
||
type = types.list types.int;
|
||
description =
|
||
''
|
||
List of TCP ports on which incoming connections are
|
||
accepted.
|
||
'';
|
||
};
|
||
|
||
networking.firewall.allowedUDPPorts = mkOption {
|
||
default = [];
|
||
example = [ 53 ];
|
||
type = types.list types.int;
|
||
description =
|
||
''
|
||
List of open UDP ports.
|
||
'';
|
||
};
|
||
|
||
networking.firewall.allowPing = mkOption {
|
||
default = false;
|
||
type = types.bool;
|
||
description =
|
||
''
|
||
Whether to respond to incoming ICMPv4 echo requests
|
||
("pings"). ICMPv6 pings are always allowed because the
|
||
larger address space of IPv6 makes network scanning much
|
||
less effective.
|
||
'';
|
||
};
|
||
|
||
networking.firewall.extraCommands = mkOption {
|
||
default = "";
|
||
example = "iptables -A INPUT -p icmp -j ACCEPT";
|
||
description =
|
||
''
|
||
Additional shell commands executed as part of the firewall
|
||
initialisation script. These are executed just before the
|
||
final "reject" firewall rule is added, so they can be used
|
||
to allow packets that would otherwise be refused.
|
||
'';
|
||
};
|
||
|
||
};
|
||
|
||
|
||
###### implementation
|
||
|
||
# !!! Maybe if `enable' is false, the firewall should still be built
|
||
# but not started by default. However, currently nixos-rebuild
|
||
# doesn't deal with such Upstart jobs properly (it starts them if
|
||
# they are changed, regardless of whether the start condition
|
||
# holds).
|
||
config = mkIf cfg.enable {
|
||
|
||
environment.systemPackages = [ pkgs.iptables ];
|
||
|
||
boot.kernelModules = [ "nf_conntrack_ftp" ];
|
||
|
||
jobs.firewall =
|
||
{ startOn = "started network-interfaces";
|
||
|
||
path = [ pkgs.iptables ];
|
||
|
||
preStart =
|
||
''
|
||
${helpers}
|
||
set -x
|
||
|
||
# Flush the old firewall rules. !!! Ideally, updating the
|
||
# firewall would be atomic. Apparently that's possible
|
||
# with iptables-restore.
|
||
ip46tables -D INPUT -j nixos-fw || true
|
||
for chain in nixos-fw nixos-fw-accept nixos-fw-log-refuse nixos-fw-refuse FW_REFUSE; do
|
||
ip46tables -F "$chain" || true
|
||
ip46tables -X "$chain" || true
|
||
done
|
||
|
||
|
||
# The "nixos-fw-accept" chain just accepts packets.
|
||
ip46tables -N nixos-fw-accept
|
||
ip46tables -A nixos-fw-accept -j ACCEPT
|
||
|
||
|
||
# The "nixos-fw-refuse" chain rejects or drops packets.
|
||
ip46tables -N nixos-fw-refuse
|
||
|
||
${if cfg.rejectPackets then ''
|
||
# Send a reset for existing TCP connections that we've
|
||
# somehow forgotten about. Send ICMP "port unreachable"
|
||
# for everything else.
|
||
ip46tables -A nixos-fw-refuse -p tcp ! --syn -j REJECT --reject-with tcp-reset
|
||
ip46tables -A nixos-fw-refuse -j REJECT
|
||
'' else ''
|
||
ip46tables -A nixos-fw-refuse -j DROP
|
||
''}
|
||
|
||
|
||
# The "nixos-fw-log-refuse" chain performs logging, then
|
||
# jumps to the "nixos-fw-refuse" chain.
|
||
ip46tables -N nixos-fw-log-refuse
|
||
|
||
${optionalString cfg.logRefusedConnections ''
|
||
ip46tables -A nixos-fw-log-refuse -p tcp --syn -j LOG --log-level info --log-prefix "rejected connection: "
|
||
''}
|
||
${optionalString (cfg.logRefusedPackets && !cfg.logRefusedUnicastsOnly) ''
|
||
ip46tables -A nixos-fw-log-refuse -m pkttype --pkt-type broadcast \
|
||
-j LOG --log-level info --log-prefix "rejected broadcast: "
|
||
ip46tables -A nixos-fw-log-refuse -m pkttype --pkt-type multicast \
|
||
-j LOG --log-level info --log-prefix "rejected multicast: "
|
||
''}
|
||
ip46tables -A nixos-fw-log-refuse -m pkttype ! --pkt-type unicast -j nixos-fw-refuse
|
||
${optionalString cfg.logRefusedPackets ''
|
||
ip46tables -A nixos-fw-log-refuse \
|
||
-j LOG --log-level info --log-prefix "rejected packet: "
|
||
''}
|
||
ip46tables -A nixos-fw-log-refuse -j nixos-fw-refuse
|
||
|
||
|
||
# The "nixos-fw" chain does the actual work.
|
||
ip46tables -N nixos-fw
|
||
|
||
# Accept all traffic on the loopback interface.
|
||
ip46tables -A nixos-fw -i lo -j nixos-fw-accept
|
||
|
||
# Accept packets from established or related connections.
|
||
ip46tables -A nixos-fw -m conntrack --ctstate ESTABLISHED,RELATED -j nixos-fw-accept
|
||
|
||
# Accept connections to the allowed TCP ports.
|
||
${concatMapStrings (port:
|
||
''
|
||
ip46tables -A nixos-fw -p tcp --dport ${toString port} -j nixos-fw-accept
|
||
''
|
||
) cfg.allowedTCPPorts
|
||
}
|
||
|
||
# Accept packets on the allowed UDP ports.
|
||
${concatMapStrings (port:
|
||
''
|
||
ip46tables -A nixos-fw -p udp --dport ${toString port} -j nixos-fw-accept
|
||
''
|
||
) cfg.allowedUDPPorts
|
||
}
|
||
|
||
# Accept IPv4 multicast. Not a big security risk since
|
||
# probably nobody is listening anyway.
|
||
#iptables -A nixos-fw -d 224.0.0.0/4 -j nixos-fw-accept
|
||
|
||
# Optionally respond to ICMPv4 pings.
|
||
${optionalString cfg.allowPing ''
|
||
iptables -A nixos-fw -p icmp --icmp-type echo-request -j nixos-fw-accept
|
||
''}
|
||
|
||
# Accept all ICMPv6 messages except redirects and node
|
||
# information queries (type 139). See RFC 4890, section
|
||
# 4.4.
|
||
ip6tables -A nixos-fw -p icmpv6 --icmpv6-type redirect -j DROP
|
||
ip6tables -A nixos-fw -p icmpv6 --icmpv6-type 139 -j DROP
|
||
ip6tables -A nixos-fw -p icmpv6 -j nixos-fw-accept
|
||
|
||
${cfg.extraCommands}
|
||
|
||
# Reject/drop everything else.
|
||
ip46tables -A nixos-fw -j nixos-fw-log-refuse
|
||
|
||
|
||
# Enable the firewall.
|
||
ip46tables -A INPUT -j nixos-fw
|
||
'';
|
||
|
||
postStop =
|
||
''
|
||
${helpers}
|
||
ip46tables -D INPUT -j nixos-fw || true
|
||
#ip46tables -P INPUT ACCEPT
|
||
'';
|
||
};
|
||
|
||
};
|
||
|
||
}
|