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
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12 ### the Free Software Foundation; either version 2 of the License, or
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18 ### GNU General Public License for more details.
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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 setopt ip_forward $forward
109 setdevopt forwarding $forward
111 ## Set dynamic port allocation.
112 setopt ip_local_port_range $open_port_min $open_port_max
114 ## Deploy SYN-cookies if necessary.
115 setopt tcp_syncookies 1
117 ## Allow broadcast and multicast ping, because it's a useful diagnostic tool.
118 setopt icmp_echo_ignore_broadcasts 0
120 ## Turn off iptables filtering for bridges. We'll use ebtables if we need
121 ## to; but right now the model is that we do filtering at the borders, and
122 ## are tolerant of things which are local.
123 if [ -x /sbin/brctl ]; then
125 if [ -d /proc/sys/net/bridge ]; then
126 for filter in arptables iptables ip6tables; do
127 run sysctl -q net.bridge.bridge-nf-call-$filter=0
132 ## Turn on the reverse-path filter, and log weird things.
133 setdevopt rp_filter $rp_filter
134 setdevopt log_martians $log_martians
136 ## Turn off things which can mess with our routing decisions.
137 setdevopt accept_source_route 0
138 setdevopt accept_redirects 0
140 ## If we're maent to stop the firewall, then now is the time to do it.
144 ###--------------------------------------------------------------------------
145 ### Establish error chains.
147 errorchain forbidden REJECT
148 ## Generic `not allowed' chain.
150 errorchain tcp-fragment REJECT
151 ## Chain for logging fragmented TCP segements.
153 errorchain bad-tcp REJECT -p tcp --reject-with tcp-reset
154 ## Bad TCP segments (e.g., for unknown connections). Sends a TCP reset.
156 errorchain mangle:bad-source-address DROP
157 errorchain bad-source-address DROP
158 ## Packet arrived on wrong interface for its source address. Drops the
159 ## packet, since there's nowhere sensible to send an error.
161 errorchain bad-destination-address REJECT
162 ## Packet arrived on non-loopback interface with loopback destination.
164 errorchain interesting ACCEPT
165 ## Not an error, just log interesting packets.
168 ###--------------------------------------------------------------------------
169 ### Standard filtering.
171 ## Don't clobber local traffic
172 run ip46tables -A INPUT -i lo -j ACCEPT
174 ## We really shouldn't see packets destined for localhost on any interface
175 ## other than the loopback.
176 run iptables -A INPUT -g bad-destination-address \
178 run ip6tables -A INPUT -g bad-destination-address \
181 ## We shouldn't be asked to forward things with link-local addresses.
182 run iptables -A FORWARD -g bad-source-address \
184 run iptables -A FORWARD -g bad-destination-address \
186 run ip6tables -A FORWARD -g bad-source-address \
188 run ip6tables -A FORWARD -g bad-destination-address \
191 ## Also, don't forward link-local broadcast or multicast.
192 run iptables -A FORWARD -g bad-destination-address \
194 run iptables -A FORWARD -g bad-destination-address \
195 -m addrtype --dst-type BROADCAST
196 run iptables -A FORWARD -g bad-destination-address \
198 for x in 0 1 2 3 4 5 6 7 8 9 a b c d e f; do
199 run ip6tables -A FORWARD -g bad-destination-address \
203 ## Add a hook for fail2ban.
205 run ip46tables -A INPUT -j fail2ban
208 ###--------------------------------------------------------------------------
209 ### Finishing touches.
212 ## Locally generated packets are all OK.
213 run ip46tables -P OUTPUT ACCEPT
215 ## Other incoming things are forbidden.
216 for chain in INPUT FORWARD; do
217 run ip46tables -A $chain -g forbidden
220 ## Allow stuff through unknown tables.
222 for table in $(cat /proc/net/${ip}_tables_names); do
223 case $table in mangle | filter) continue ;; esac
224 ${ip}tables -nL -t $table |
225 sed -n '/^Chain \([^ ]\+\) (policy .*$/ s//\1/p ' |
227 run ${ip}tables -t $table -P $chain ACCEPT
233 ###----- That's all, folks --------------------------------------------------