[firewall] / bookends.m4

### -*-sh-*-
###
### Initialization and finishing touches for firewall scripts
###
### (c) 2008 Mark Wooding
###

###----- Licensing notice ---------------------------------------------------
###
### This program is free software; you can redistribute it and/or modify
### it under the terms of the GNU General Public License as published by
### the Free Software Foundation; either version 2 of the License, or
### (at your option) any later version.
###
### This program is distributed in the hope that it will be useful,
### but WITHOUT ANY WARRANTY; without even the implied warranty of
### MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
### GNU General Public License for more details.
###
### You should have received a copy of the GNU General Public License
### along with this program; if not, write to the Free Software Foundation,
### Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

m4_divert(30)m4_dnl
###--------------------------------------------------------------------------
### Clear existing firewall rules.

## The main chains: set policy to drop, and then clear the rules.  For a
## while, incoming packets will be silently dropped, but we should have got
## everything going before anyone actually hits a timeout.
##
## We don't control some of the chains, so we should preserve them.  This
## introduces a whole bunch of problems.

## Chains we're meant to preserve
preserve_chains="filter:fail2ban filter:fail2ban-* $preserve_chains"

## Take the various IP versions in turn.
unref=nil
for ip in ip ip6; do
  for table in $(cat /proc/net/${ip}_tables_names); do

    ## Step 1: clear out the builtin chains.
    ${ip}tables -nL -t $table |
    sed -n '/^Chain \([^ ]\+\) (policy .*$/ s//\1/p ' |
    while read chain; do
      case $table in
	nat) policy=ACCEPT ;;
	*) policy=DROP ;;
      esac
      run ${ip}tables -t $table -P $chain $policy
      run ${ip}tables -t $table -F $chain
    done

    ## Step 2: clear out user chains.  Unfortunately, we can only clear
    ## chains which have no references to them, so work through picking off
    ## unreferenced chains which aren't meant to be preserved until there are
    ## none left.
    while :; do
      progress=nil
      ${ip}tables -nL -t $table |
      sed -n '/^Chain \([^ ]\+\) (0 references)$/ s//\1/p ' \
	>/var/run/firewall-chains.tmp
      while read chain; do
	match=nil
	for pat in $preserve_chains; do
	  case "$table:$chain" in $pat) match=t ;; esac
	done
	case $match in
	  nil)
	    run ${ip}tables -t $table -F $chain
	    run ${ip}tables -t $table -X $chain
	    progress=t
	    ;;
	esac
      done </var/run/firewall-chains.tmp
      case $progress in nil) break ;; esac
    done

    ## Step 3: report on uncleared user chains.  This means that there's a
    ## serious problem.
    ${ip}tables -nL -t $table |
    sed -n '/^Chain \([^ ]\+\) (\([1-9][0-9]*\) references)$/ s//\1 \2/p ' \
      >/var/run/firewall-chains.tmp
    while read chain refs; do
      match=nil
      for pat in $preserve_chains; do
	case "$table:$chain" in $pat) match=t ;; esac
      done
      case $match in
	nil)
	  echo >&2 "$0: can't clear referenced $ip chain \`$table:$chain'"
	  unref=t
	  ;;
      esac
    done </var/run/firewall-chains.tmp
  done
done
rm -f /var/run/firewall-chains.tmp
case $unref in t) exit 1 ;; esac

m4_divert(32)m4_dnl
###--------------------------------------------------------------------------
### Set safe IP options.

## Set forwarding options.  Apparently setting ip_forward clobbers other
## settings, so put this first.
case $host_type_<::>FWHOST in
  router) forward=1 ;;
  *) forward=0 ;;
esac
setopt ip_forward $forward
setdevopt forwarding $forward
case $forward in
  0) inchains="INPUT" ;;
  1) inchains="INPUT FORWARD" ;;
esac

## Set dynamic port allocation.
setopt ip_local_port_range $open_port_min $open_port_max

## Deploy SYN-cookies if necessary.
setopt tcp_syncookies 1

## Allow broadcast and multicast ping, because it's a useful diagnostic tool.
setopt icmp_echo_ignore_broadcasts 0

## Turn off iptables filtering for bridges.  We'll use ebtables if we need
## to; but right now the model is that we do filtering at the borders, and
## are tolerant of things which are local.
if [ -x /sbin/brctl ]; then
  modprobe bridge || :
  if [ -d /proc/sys/net/bridge ]; then
    for filter in arptables iptables ip6tables; do
      run sysctl -q net.bridge.bridge-nf-call-$filter=0
    done
  fi
fi

## Turn off the reverse-path filter.  It's basically useless: the filter does
## nothing at all for single-homed hosts; and multi-homed hosts tend to have
## routing aysmmetries if there's any kind of cycle.
setdevopt rp_filter 0
setdevopt log_martians 0

## Turn off things which can mess with our routing decisions.
setdevopt accept_source_route 0
setdevopt accept_redirects 0

## If we're maent to stop the firewall, then now is the time to do it.
$exit_after_clearing

m4_divert(34)m4_dnl
###--------------------------------------------------------------------------
### Establish error chains.

errorchain forbidden REJECT
## Generic `not allowed' chain.

errorchain tcp-fragment REJECT
## Chain for logging fragmented TCP segements.

errorchain bad-tcp REJECT -p tcp --reject-with tcp-reset
## Bad TCP segments (e.g., for unknown connections).  Sends a TCP reset.

errorchain mangle:bad-source-address DROP
errorchain bad-source-address DROP
## Packet arrived on wrong interface for its source address.  Drops the
## packet, since there's nowhere sensible to send an error.

errorchain bad-destination-address REJECT
## Packet arrived on non-loopback interface with loopback destination.

errorchain interesting ACCEPT
## Not an error, just log interesting packets.

m4_divert(50)m4_dnl
###--------------------------------------------------------------------------
### Standard filtering.

## Don't clobber local traffic
run ip46tables -A INPUT -i lo -j ACCEPT

## We really shouldn't see packets destined for localhost on any interface
## other than the loopback.
run iptables -A INPUT -g bad-destination-address \
	-d 127.0.0.0/8
run ip6tables -A INPUT -g bad-destination-address \
	-d ::1

## We shouldn't be asked to forward things with link-local addresses.
case $forward in
  1)
    run iptables -A FORWARD -g bad-source-address \
	    -s 169.254.0.0/16
    run iptables -A FORWARD -g bad-destination-address \
	    -d 169.254.0.0/16
    run ip6tables -A FORWARD -g bad-source-address \
	    -s fe80::/10
    run ip6tables -A FORWARD -g bad-destination-address \
	    -d fe80::/10
    ;;
esac

## Also, don't forward link-local broadcast or multicast.
case $forward in
  1)
    run iptables -A FORWARD -g bad-destination-address \
	    -d 255.255.255.255
    run iptables -A FORWARD -g bad-destination-address \
	    -m addrtype --dst-type BROADCAST
    run iptables -A FORWARD -g bad-destination-address \
	    -d 224.0.0.0/24
    for x in 0 1 2 3 4 5 6 7 8 9 a b c d e f; do
      run ip6tables -A FORWARD -g bad-destination-address \
	    -d fe${x}2::/16
    done
    ;;
esac

## Add a hook for fail2ban.
clearchain fail2ban
run ip46tables -A INPUT -j fail2ban

m4_divert(90)m4_dnl
###--------------------------------------------------------------------------
### Finishing touches.

m4_divert(94)m4_dnl
## Locally generated packets are all OK.
run ip46tables -P OUTPUT ACCEPT

## Other incoming things are forbidden.
for chain in INPUT FORWARD; do
  run ip46tables -A $chain -g forbidden
done

## Allow stuff through unknown tables.
for ip in ip ip6; do
  for table in $(cat /proc/net/${ip}_tables_names); do
    case $table in mangle | filter) continue ;; esac
    ${ip}tables -nL -t $table |
    sed -n '/^Chain \([^ ]\+\) (policy .*$/ s//\1/p ' |
    while read chain; do
      run ${ip}tables -t $table -P $chain ACCEPT
    done
  done
done

## Dump the resulting configuration.
if [ "$FW_DEBUG" ]; then
  for ip in ip ip6; do
    for table in mangle filter; do
      echo "----- $ip $table -----"
      echo
      ${ip}tables -t $table -nvL
      echo
    done
  done
fi

m4_divert(-1)
###----- That's all, folks --------------------------------------------------
Commit	Line	Data
775bd287	1	### --sh--
bfdc045d MW	2	###
	3	### Initialization and finishing touches for firewall scripts
	4	###
	5	### (c) 2008 Mark Wooding
	6	###
	7
	8	###----- Licensing notice ---------------------------------------------------
	9	###
	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.
	14	###
	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.
	19	###
	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.
	23
	24	m4_divert(30)m4_dnl
	25	###--------------------------------------------------------------------------
	26	### Clear existing firewall rules.
	27
	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.
42dae9ae MW	31	##
	32	## We don't control some of the chains, so we should preserve them. This
	33	## introduces a whole bunch of problems.
	34
	35	## Chains we're meant to preserve
	36	preserve_chains="filter:fail2ban filter:fail2ban-* $preserve_chains"
	37
	38	## Take the various IP versions in turn.
	39	unref=nil
	40	for ip in ip ip6; do
	41	for table in $(cat /proc/net/${ip}_tables_names); do
	42
	43	## Step 1: clear out the builtin chains.
	44	${ip}tables -nL -t $table \|
	45	sed -n '/^Chain \([^ ]\+\) (policy .*$/ s//\1/p ' \|
	46	while read chain; do
	47	case $table in
	48	nat) policy=ACCEPT ;;
	49	*) policy=DROP ;;
	50	esac
	51	run ${ip}tables -t $table -P $chain $policy
	52	run ${ip}tables -t $table -F $chain
	53	done
	54
	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
	58	## none left.
	59	while :; do
	60	progress=nil
	61	${ip}tables -nL -t $table \|
	62	sed -n '/^Chain \([^ ]\+\) (0 references)$/ s//\1/p ' \
	63	>/var/run/firewall-chains.tmp
	64	while read chain; do
	65	match=nil
	66	for pat in $preserve_chains; do
	67	case "$table:$chain" in $pat) match=t ;; esac
	68	done
	69	case $match in
	70	nil)
	71	run ${ip}tables -t $table -F $chain
	72	run ${ip}tables -t $table -X $chain
	73	progress=t
	74	;;
	75	esac
	76	done </var/run/firewall-chains.tmp
	77	case $progress in nil) break ;; esac
	78	done
	79
	80	## Step 3: report on uncleared user chains. This means that there's a
	81	## serious problem.
	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
	86	match=nil
	87	for pat in $preserve_chains; do
	88	case "$table:$chain" in $pat) match=t ;; esac
	89	done
	90	case $match in
	91	nil)
	92	echo >&2 "$0: can't clear referenced $ip chain \`$table:$chain'"
	93	unref=t
	94	;;
95	esac
96	done </var/run/firewall-chains.tmp
bfdc045d	97	done
bfdc045d	98	done
42dae9ae MW	99	rm -f /var/run/firewall-chains.tmp
42dae9ae MW	100	case $unref in t) exit 1 ;; esac
bfdc045d MW	101
	102	m4_divert(32)m4_dnl
	103	###--------------------------------------------------------------------------
	104	### Set safe IP options.
	105
	106	## Set forwarding options. Apparently setting ip_forward clobbers other
	107	## settings, so put this first.
78af294c MW	108	case $host_type_<::>FWHOST in
	109	router) forward=1 ;;
	110	*) forward=0 ;;
	111	esac
bfdc045d MW	112	setopt ip_forward $forward
bfdc045d MW	113	setdevopt forwarding $forward
f0033e07 MW	114	case $forward in
	115	0) inchains="INPUT" ;;
	116	1) inchains="INPUT FORWARD" ;;
	117	esac
bfdc045d MW	118
	119	## Set dynamic port allocation.
	120	setopt ip_local_port_range $open_port_min $open_port_max
	121
	122	## Deploy SYN-cookies if necessary.
	123	setopt tcp_syncookies 1
	124
c8d422ec MW	125	## Allow broadcast and multicast ping, because it's a useful diagnostic tool.
	126	setopt icmp_echo_ignore_broadcasts 0
	127
429f4314 MW	128	## Turn off iptables filtering for bridges. We'll use ebtables if we need
	129	## to; but right now the model is that we do filtering at the borders, and
	130	## are tolerant of things which are local.
6d47692a MW	131	if [ -x /sbin/brctl ]; then
	132	modprobe bridge \|\| :
	133	if [ -d /proc/sys/net/bridge ]; then
	134	for filter in arptables iptables ip6tables; do
	135	run sysctl -q net.bridge.bridge-nf-call-$filter=0
	136	done
	137	fi
	138	fi
429f4314	139
78af294c MW	140	## Turn off the reverse-path filter. It's basically useless: the filter does
	141	## nothing at all for single-homed hosts; and multi-homed hosts tend to have
	142	## routing aysmmetries if there's any kind of cycle.
	143	setdevopt rp_filter 0
	144	setdevopt log_martians 0
bfdc045d MW	145
	146	## Turn off things which can mess with our routing decisions.
	147	setdevopt accept_source_route 0
	148	setdevopt accept_redirects 0
	149
	150	## If we're maent to stop the firewall, then now is the time to do it.
	151	$exit_after_clearing
	152
	153	m4_divert(34)m4_dnl
	154	###--------------------------------------------------------------------------
	155	### Establish error chains.
	156
0291d6d5 MW	157	errorchain forbidden REJECT
0291d6d5 MW	158	## Generic `not allowed' chain.
bfdc045d	159
0291d6d5 MW	160	errorchain tcp-fragment REJECT
0291d6d5 MW	161	## Chain for logging fragmented TCP segements.
bfdc045d MW	162
	163	errorchain bad-tcp REJECT -p tcp --reject-with tcp-reset
	164	## Bad TCP segments (e.g., for unknown connections). Sends a TCP reset.
	165
	166	errorchain mangle:bad-source-address DROP
0291d6d5	167	errorchain bad-source-address DROP
bfdc045d MW	168	## Packet arrived on wrong interface for its source address. Drops the
	169	## packet, since there's nowhere sensible to send an error.
	170
0291d6d5 MW	171	errorchain bad-destination-address REJECT
0291d6d5 MW	172	## Packet arrived on non-loopback interface with loopback destination.
f381cc0a	173
bfdc045d MW	174	errorchain interesting ACCEPT
	175	## Not an error, just log interesting packets.
	176
a4d8cae3	177	m4_divert(50)m4_dnl
bfdc045d	178	###--------------------------------------------------------------------------
f543dab7	179	### Standard filtering.
bfdc045d	180
f381cc0a	181	## Don't clobber local traffic
0291d6d5	182	run ip46tables -A INPUT -i lo -j ACCEPT
bfdc045d	183
f381cc0a MW	184	## We really shouldn't see packets destined for localhost on any interface
	185	## other than the loopback.
	186	run iptables -A INPUT -g bad-destination-address \
	187	-d 127.0.0.0/8
0291d6d5 MW	188	run ip6tables -A INPUT -g bad-destination-address \
	189	-d ::1
	190
	191	## We shouldn't be asked to forward things with link-local addresses.
78af294c MW	192	case $forward in
	193	1)
	194	run iptables -A FORWARD -g bad-source-address \
	195	-s 169.254.0.0/16
	196	run iptables -A FORWARD -g bad-destination-address \
	197	-d 169.254.0.0/16
	198	run ip6tables -A FORWARD -g bad-source-address \
	199	-s fe80::/10
	200	run ip6tables -A FORWARD -g bad-destination-address \
	201	-d fe80::/10
	202	;;
	203	esac
f381cc0a	204
429f4314	205	## Also, don't forward link-local broadcast or multicast.
78af294c MW	206	case $forward in
	207	1)
	208	run iptables -A FORWARD -g bad-destination-address \
	209	-d 255.255.255.255
	210	run iptables -A FORWARD -g bad-destination-address \
	211	-m addrtype --dst-type BROADCAST
	212	run iptables -A FORWARD -g bad-destination-address \
	213	-d 224.0.0.0/24
	214	for x in 0 1 2 3 4 5 6 7 8 9 a b c d e f; do
	215	run ip6tables -A FORWARD -g bad-destination-address \
	216	-d fe${x}2::/16
	217	done
	218	;;
	219	esac
429f4314	220
f543dab7 MW	221	## Add a hook for fail2ban.
	222	clearchain fail2ban
	223	run ip46tables -A INPUT -j fail2ban
	224
bfdc045d MW	225	m4_divert(90)m4_dnl
	226	###--------------------------------------------------------------------------
	227	### Finishing touches.
	228
	229	m4_divert(94)m4_dnl
	230	## Locally generated packets are all OK.
c1c877c2	231	run ip46tables -P OUTPUT ACCEPT
bfdc045d MW	232
	233	## Other incoming things are forbidden.
	234	for chain in INPUT FORWARD; do
c1c877c2	235	run ip46tables -A $chain -g forbidden
bfdc045d MW	236	done
bfdc045d MW	237
86c975b5 MW	238	## Allow stuff through unknown tables.
	239	for ip in ip ip6; do
	240	for table in $(cat /proc/net/${ip}_tables_names); do
	241	case $table in mangle \| filter) continue ;; esac
	242	${ip}tables -nL -t $table \|
	243	sed -n '/^Chain \([^ ]\+\) (policy .*$/ s//\1/p ' \|
	244	while read chain; do
	245	run ${ip}tables -t $table -P $chain ACCEPT
	246	done
	247	done
	248	done
	249
d8852323 MW	250	## Dump the resulting configuration.
	251	if [ "$FW_DEBUG" ]; then
	252	for ip in ip ip6; do
	253	for table in mangle filter; do
	254	echo "----- $ip $table -----"
	255	echo
	256	${ip}tables -t $table -nvL
	257	echo
	258	done
	259	done
	260	fi
	261
bfdc045d MW	262	m4_divert(-1)
bfdc045d MW	263	###----- That's all, folks --------------------------------------------------