###--------------------------------------------------------------------------
### 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
-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