3 ### Initialization and finishing touches for firewall scripts
5 ### (c) 2008 Mark Wooding
8 ###----- Licensing notice ---------------------------------------------------
10 ### This program is free software; you can redistribute it and/or modify
11 ### it under the terms of the GNU General Public License as published by
12 ### the Free Software Foundation; either version 2 of the License, or
13 ### (at your option) any later version.
15 ### This program is distributed in the hope that it will be useful,
16 ### but WITHOUT ANY WARRANTY; without even the implied warranty of
17 ### MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
18 ### GNU General Public License for more details.
20 ### You should have received a copy of the GNU General Public License
21 ### along with this program; if not, write to the Free Software Foundation,
22 ### Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
25 ###--------------------------------------------------------------------------
26 ### Clear existing firewall rules.
28 ## The main chains: set policy to drop, and then clear the rules. For a
29 ## while, incoming packets will be silently dropped, but we should have got
30 ## everything going before anyone actually hits a timeout.
32 ## We don't control some of the chains, so we should preserve them. This
33 ## introduces a whole bunch of problems.
35 ## Chains we're meant to preserve
36 preserve_chains="filter:fail2ban filter:fail2ban-* $preserve_chains"
38 ## Take the various IP versions in turn.
41 for table in $(cat /proc/net/${ip}_tables_names); do
43 ## Step 1: clear out the builtin chains.
44 ${ip}tables -nL -t $table |
45 sed -n '/^Chain \([^ ]\+\) (policy .*$/ s//\1/p ' |
51 run ${ip}tables -t $table -P $chain $policy
52 run ${ip}tables -t $table -F $chain
55 ## Step 2: clear out user chains. Unfortunately, we can only clear
56 ## chains which have no references to them, so work through picking off
57 ## unreferenced chains which aren't meant to be preserved until there are
61 ${ip}tables -nL -t $table |
62 sed -n '/^Chain \([^ ]\+\) (0 references)$/ s//\1/p ' \
63 >/var/run/firewall-chains.tmp
66 for pat in $preserve_chains; do
67 case "$table:$chain" in $pat) match=t ;; esac
71 run ${ip}tables -t $table -F $chain
72 run ${ip}tables -t $table -X $chain
76 done </var/run/firewall-chains.tmp
77 case $progress in nil) break ;; esac
80 ## Step 3: report on uncleared user chains. This means that there's a
82 ${ip}tables -nL -t $table |
83 sed -n '/^Chain \([^ ]\+\) (\([1-9][0-9]*\) references)$/ s//\1 \2/p ' \
84 >/var/run/firewall-chains.tmp
85 while read chain refs; do
87 for pat in $preserve_chains; do
88 case "$table:$chain" in $pat) match=t ;; esac
92 echo >&2 "$0: can't clear referenced $ip chain \`$table:$chain'"
96 done </var/run/firewall-chains.tmp
99 rm -f /var/run/firewall-chains.tmp
100 case $unref in t) exit 1 ;; esac
103 ###--------------------------------------------------------------------------
104 ### Set safe IP options.
106 ## Set forwarding options. Apparently setting ip_forward clobbers other
107 ## settings, so put this first.
108 case $host_type_<::>FWHOST in
112 setopt ip_forward $forward
113 setdevopt forwarding $forward
115 ## Set dynamic port allocation.
116 setopt ip_local_port_range $open_port_min $open_port_max
118 ## Deploy SYN-cookies if necessary.
119 setopt tcp_syncookies 1
121 ## Allow broadcast and multicast ping, because it's a useful diagnostic tool.
122 setopt icmp_echo_ignore_broadcasts 0
124 ## Turn off iptables filtering for bridges. We'll use ebtables if we need
125 ## to; but right now the model is that we do filtering at the borders, and
126 ## are tolerant of things which are local.
127 if [ -x /sbin/brctl ]; then
129 if [ -d /proc/sys/net/bridge ]; then
130 for filter in arptables iptables ip6tables; do
131 run sysctl -q net.bridge.bridge-nf-call-$filter=0
136 ## Turn off the reverse-path filter. It's basically useless: the filter does
137 ## nothing at all for single-homed hosts; and multi-homed hosts tend to have
138 ## routing aysmmetries if there's any kind of cycle.
139 setdevopt rp_filter 0
140 setdevopt log_martians 0
142 ## Turn off things which can mess with our routing decisions.
143 setdevopt accept_source_route 0
144 setdevopt accept_redirects 0
146 ## If we're maent to stop the firewall, then now is the time to do it.
150 ###--------------------------------------------------------------------------
151 ### Establish error chains.
153 errorchain forbidden REJECT
154 ## Generic `not allowed' chain.
156 errorchain tcp-fragment REJECT
157 ## Chain for logging fragmented TCP segements.
159 errorchain bad-tcp REJECT -p tcp --reject-with tcp-reset
160 ## Bad TCP segments (e.g., for unknown connections). Sends a TCP reset.
162 errorchain mangle:bad-source-address DROP
163 errorchain bad-source-address DROP
164 ## Packet arrived on wrong interface for its source address. Drops the
165 ## packet, since there's nowhere sensible to send an error.
167 errorchain bad-destination-address REJECT
168 ## Packet arrived on non-loopback interface with loopback destination.
170 errorchain interesting ACCEPT
171 ## Not an error, just log interesting packets.
174 ###--------------------------------------------------------------------------
175 ### Standard filtering.
177 ## Don't clobber local traffic
178 run ip46tables -A INPUT -i lo -j ACCEPT
180 ## We really shouldn't see packets destined for localhost on any interface
181 ## other than the loopback.
182 run iptables -A INPUT -g bad-destination-address \
184 run ip6tables -A INPUT -g bad-destination-address \
187 ## We shouldn't be asked to forward things with link-local addresses.
190 run iptables -A FORWARD -g bad-source-address \
192 run iptables -A FORWARD -g bad-destination-address \
194 run ip6tables -A FORWARD -g bad-source-address \
196 run ip6tables -A FORWARD -g bad-destination-address \
201 ## Also, don't forward link-local broadcast or multicast.
204 run iptables -A FORWARD -g bad-destination-address \
206 run iptables -A FORWARD -g bad-destination-address \
207 -m addrtype --dst-type BROADCAST
208 run iptables -A FORWARD -g bad-destination-address \
210 for x in 0 1 2 3 4 5 6 7 8 9 a b c d e f; do
211 run ip6tables -A FORWARD -g bad-destination-address \
217 ## Add a hook for fail2ban.
219 run ip46tables -A INPUT -j fail2ban
222 ###--------------------------------------------------------------------------
223 ### Finishing touches.
226 ## Locally generated packets are all OK.
227 run ip46tables -P OUTPUT ACCEPT
229 ## Other incoming things are forbidden.
230 for chain in INPUT FORWARD; do
231 run ip46tables -A $chain -g forbidden
234 ## Allow stuff through unknown tables.
236 for table in $(cat /proc/net/${ip}_tables_names); do
237 case $table in mangle | filter) continue ;; esac
238 ${ip}tables -nL -t $table |
239 sed -n '/^Chain \([^ ]\+\) (policy .*$/ s//\1/p ' |
241 run ${ip}tables -t $table -P $chain ACCEPT
246 ## Dump the resulting configuration.
247 if [ "$FW_DEBUG" ]; then
249 for table in mangle filter; do
250 echo "----- $ip $table -----"
252 ${ip}tables -t $table -nvL
259 ###----- That's all, folks --------------------------------------------------