X-Git-Url: https://git.distorted.org.uk/~mdw/firewall/blobdiff_plain/0291d6d55d3dc38a12d61abc007dda5cc3aa5110..3a68f6887e27cd5e9369a9c421e417e59acef08b:/local.m4

diff --git a/local.m4 b/local.m4
index 5e27449..f6b5f46 100644
--- a/local.m4
+++ b/local.m4
@@ -1,4 +1,4 @@
-### -*-m4-*-
+### -*-sh-*-
 ###
 ### Local firewall configuration
 ###
@@ -51,46 +51,70 @@ defiface $if_trusted \
 	safe:172.29.199.64/27 \
 	untrusted:default
 
+## Default NTP servers.
+ntp_servers="158.152.1.76 158.152.1.204 194.159.253.2 195.173.57.232"
+
 m4_divert(60)m4_dnl
 ###--------------------------------------------------------------------------
 ### Special forwarding exemptions.
 
+## Only allow these packets if they're not fragmented.  (Don't trust safe
+## hosts's fragment reassembly to be robust against malicious fragments.)
+## There's a hideous bug in iptables 1.4.11.1 which botches the meaning of
+## `! -f', so we do the negation using early return from a subchain.
+clearchain fwd-spec-nofrag
+run iptables -A fwd-spec-nofrag -j RETURN --fragment
+run ip6tables -A fwd-spec-nofrag -j RETURN \
+	-m ipv6header --soft --header frag
+run iptables -A FORWARD -j fwd-spec-nofrag
+
 ## Allow ping from safe/noloop to untrusted networks.
-run iptables -A FORWARD -j ACCEPT \
-	-p icmp ! -f --icmp-type echo-request \
+run iptables -A fwd-spec-nofrag -j ACCEPT \
+	-p icmp --icmp-type echo-request \
 	-m mark --mark $to_untrusted/$MASK_TO
-run iptables -A FORWARD -j ACCEPT \
-	-p icmp ! -f --icmp-type echo-reply \
+run iptables -A fwd-spec-nofrag -j ACCEPT \
+	-p icmp --icmp-type echo-reply \
 	-m mark --mark $from_untrusted/$MASK_FROM \
 	-m state --state ESTABLISHED
-run ip6tables -A FORWARD -j ACCEPT \
+run ip6tables -A fwd-spec-nofrag -j ACCEPT \
 	-p ipv6-icmp --icmpv6-type echo-request \
-	-m ipv6header --soft ! --header frag \
 	-m mark --mark $to_untrusted/$MASK_TO
-run ip6tables -A FORWARD -j ACCEPT \
+run ip6tables -A fwd-spec-nofrag -j ACCEPT \
 	-p ipv6-icmp --icmpv6-type echo-reply \
-	-m ipv6header --soft ! --header frag \
 	-m mark --mark $from_untrusted/$MASK_FROM \
 	-m state --state ESTABLISHED
 
 ## Allow SSH from safe/noloop to untrusted networks.
-run iptables -A FORWARD -j ACCEPT \
-	-p tcp ! -f --destination-port $port_ssh \
+run iptables -A fwd-spec-nofrag -j ACCEPT \
+	-p tcp --destination-port $port_ssh \
 	-m mark --mark $to_untrusted/$MASK_TO
-run iptables -A FORWARD -j ACCEPT \
-	-p tcp ! -f --source-port $port_ssh \
+run iptables -A fwd-spec-nofrag -j ACCEPT \
+	-p tcp --source-port $port_ssh \
 	-m mark --mark $from_untrusted/$MASK_FROM \
 	-m state --state ESTABLISHED
-run ip6tables -A FORWARD -j ACCEPT \
+run ip6tables -A fwd-spec-nofrag -j ACCEPT \
 	-p tcp --destination-port $port_ssh \
-	-m ipv6header --soft ! --header frag \
 	-m mark --mark $to_untrusted/$MASK_TO
-run ip6tables -A FORWARD -j ACCEPT \
+run ip6tables -A fwd-spec-nofrag -j ACCEPT \
 	-p tcp --source-port $port_ssh \
-	-m ipv6header --soft ! --header frag \
 	-m mark --mark $from_untrusted/$MASK_FROM \
 	-m state --state ESTABLISHED
 
+m4_divert(60)m4_dnl
+###--------------------------------------------------------------------------
+### Kill things we don't understand properly.
+###
+### I don't like having to do this, but since I don't know how to do proper
+### multicast filtering, I'm just going to ban it from being forwarded.
+
+errorchain poorly-understood REJECT
+
+## Ban multicast destination addresses in forwarding.
+run iptables -A FORWARD -g poorly-understood \
+	-d 224.0.0.0/4
+run ip6tables -A FORWARD -g poorly-understood \
+	-d ff::/8
+
 m4_divert(80)m4_dnl
 ###--------------------------------------------------------------------------
 ### Locally-bound packet inspection.
@@ -110,6 +134,13 @@ run iptables -A inbound -j ACCEPT \
 	-s 172.29.198.0/23 \
 	-p udp --source-port $port_bootpc --destination-port $port_bootps
 
+## Incoming broadcast multicast on a network interface associated with the
+## trusted network is OK, since it must have originated there (or been
+## forwarded, but we don't do that yet).
+run iptables -A inbound -j ACCEPT \
+	-s 0.0.0.0 -d 224.0.0.0/24 \
+	-i $if_trusted
+
 ## Allow incoming ping.  This is the only ICMP left.
 run ip46tables -A inbound -j ACCEPT -p icmp