[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 host=0 ;;
  server) forward=0 host=0 ;;
  client) forward=0 host=1 ;;
esac
setopt ip_forward $forward
setdevopt forwarding $forward
for i in \
  accept_ra accept_ra_defrtr accept_ra_pinfo accept_ra_info_max_plen
do
  setdevopt $i $host
done
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 $forward in
  1)
    run iptables -A FORWARD -g bad-destination-address \
	    -d 255.255.255.255
    run iptables -A FORWARD -g bad-destination-address \
	    -m addrtype --dst-type BROADCAST
    run iptables -A FORWARD -g bad-destination-address \
	    -d 224.0.0.0/24
    clearchain check-fwd-multi
    for x in 0 1 2 3 4 5 6 7 8 9 a b c d e f; do
      run ip6tables -A check-fwd-multi -g bad-destination-address \
	    -d ff${x}2::/16
    done
    ip6tables -A FORWARD -j check-fwd-multi -d ff00::/8
    ;;
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	108	case $host_type_<::>FWHOST in
dc005150 MW	109	router) forward=1 host=0 ;;
	110	server) forward=0 host=0 ;;
	111	client) forward=0 host=1 ;;
78af294c	112	esac
bfdc045d MW	113	setopt ip_forward $forward
bfdc045d MW	114	setdevopt forwarding $forward
dc005150 MW	115	for i in \
	116	accept_ra accept_ra_defrtr accept_ra_pinfo accept_ra_info_max_plen
	117	do
	118	setdevopt $i $host
	119	done
f0033e07 MW	120	case $forward in
	121	0) inchains="INPUT" ;;
	122	1) inchains="INPUT FORWARD" ;;
	123	esac
bfdc045d MW	124
	125	## Set dynamic port allocation.
	126	setopt ip_local_port_range $open_port_min $open_port_max
	127
	128	## Deploy SYN-cookies if necessary.
	129	setopt tcp_syncookies 1
	130
c8d422ec MW	131	## Allow broadcast and multicast ping, because it's a useful diagnostic tool.
	132	setopt icmp_echo_ignore_broadcasts 0
	133
429f4314 MW	134	## Turn off iptables filtering for bridges. We'll use ebtables if we need
	135	## to; but right now the model is that we do filtering at the borders, and
	136	## are tolerant of things which are local.
6d47692a MW	137	if [ -x /sbin/brctl ]; then
	138	modprobe bridge \|\| :
	139	if [ -d /proc/sys/net/bridge ]; then
	140	for filter in arptables iptables ip6tables; do
	141	run sysctl -q net.bridge.bridge-nf-call-$filter=0
	142	done
	143	fi
	144	fi
429f4314	145
78af294c MW	146	## Turn off the reverse-path filter. It's basically useless: the filter does
	147	## nothing at all for single-homed hosts; and multi-homed hosts tend to have
	148	## routing aysmmetries if there's any kind of cycle.
	149	setdevopt rp_filter 0
	150	setdevopt log_martians 0
bfdc045d MW	151
	152	## Turn off things which can mess with our routing decisions.
	153	setdevopt accept_source_route 0
	154	setdevopt accept_redirects 0
	155
	156	## If we're maent to stop the firewall, then now is the time to do it.
	157	$exit_after_clearing
	158
	159	m4_divert(34)m4_dnl
	160	###--------------------------------------------------------------------------
	161	### Establish error chains.
	162
0291d6d5 MW	163	errorchain forbidden REJECT
0291d6d5 MW	164	## Generic `not allowed' chain.
bfdc045d	165
0291d6d5 MW	166	errorchain tcp-fragment REJECT
0291d6d5 MW	167	## Chain for logging fragmented TCP segements.
bfdc045d MW	168
	169	errorchain bad-tcp REJECT -p tcp --reject-with tcp-reset
	170	## Bad TCP segments (e.g., for unknown connections). Sends a TCP reset.
	171
	172	errorchain mangle:bad-source-address DROP
0291d6d5	173	errorchain bad-source-address DROP
bfdc045d MW	174	## Packet arrived on wrong interface for its source address. Drops the
	175	## packet, since there's nowhere sensible to send an error.
	176
0291d6d5 MW	177	errorchain bad-destination-address REJECT
0291d6d5 MW	178	## Packet arrived on non-loopback interface with loopback destination.
f381cc0a	179
bfdc045d MW	180	errorchain interesting ACCEPT
	181	## Not an error, just log interesting packets.
	182
a4d8cae3	183	m4_divert(50)m4_dnl
bfdc045d	184	###--------------------------------------------------------------------------
f543dab7	185	### Standard filtering.
bfdc045d	186
f381cc0a	187	## Don't clobber local traffic
0291d6d5	188	run ip46tables -A INPUT -i lo -j ACCEPT
bfdc045d	189
f381cc0a MW	190	## We really shouldn't see packets destined for localhost on any interface
	191	## other than the loopback.
	192	run iptables -A INPUT -g bad-destination-address \
	193	-d 127.0.0.0/8
0291d6d5 MW	194	run ip6tables -A INPUT -g bad-destination-address \
	195	-d ::1
	196
	197	## We shouldn't be asked to forward things with link-local addresses.
78af294c MW	198	case $forward in
	199	1)
	200	run iptables -A FORWARD -g bad-source-address \
	201	-s 169.254.0.0/16
	202	run iptables -A FORWARD -g bad-destination-address \
	203	-d 169.254.0.0/16
	204	run ip6tables -A FORWARD -g bad-source-address \
	205	-s fe80::/10
	206	run ip6tables -A FORWARD -g bad-destination-address \
	207	-d fe80::/10
	208	;;
	209	esac
f381cc0a	210
429f4314	211	## Also, don't forward link-local broadcast or multicast.
78af294c MW	212	case $forward in
	213	1)
	214	run iptables -A FORWARD -g bad-destination-address \
	215	-d 255.255.255.255
	216	run iptables -A FORWARD -g bad-destination-address \
	217	-m addrtype --dst-type BROADCAST
	218	run iptables -A FORWARD -g bad-destination-address \
	219	-d 224.0.0.0/24
e6d64b67	220	clearchain check-fwd-multi
78af294c	221	for x in 0 1 2 3 4 5 6 7 8 9 a b c d e f; do
e6d64b67 MW	222	run ip6tables -A check-fwd-multi -g bad-destination-address \
e6d64b67 MW	223	-d ff${x}2::/16
78af294c	224	done
e6d64b67	225	ip6tables -A FORWARD -j check-fwd-multi -d ff00::/8
78af294c MW	226	;;
78af294c MW	227	esac
429f4314	228
f543dab7 MW	229	## Add a hook for fail2ban.
	230	clearchain fail2ban
	231	run ip46tables -A INPUT -j fail2ban
	232
bfdc045d MW	233	m4_divert(90)m4_dnl
	234	###--------------------------------------------------------------------------
	235	### Finishing touches.
	236
	237	m4_divert(94)m4_dnl
	238	## Locally generated packets are all OK.
c1c877c2	239	run ip46tables -P OUTPUT ACCEPT
bfdc045d MW	240
	241	## Other incoming things are forbidden.
	242	for chain in INPUT FORWARD; do
c1c877c2	243	run ip46tables -A $chain -g forbidden
bfdc045d MW	244	done
bfdc045d MW	245
86c975b5 MW	246	## Allow stuff through unknown tables.
	247	for ip in ip ip6; do
	248	for table in $(cat /proc/net/${ip}_tables_names); do
	249	case $table in mangle \| filter) continue ;; esac
	250	${ip}tables -nL -t $table \|
	251	sed -n '/^Chain \([^ ]\+\) (policy .*$/ s//\1/p ' \|
	252	while read chain; do
	253	run ${ip}tables -t $table -P $chain ACCEPT
	254	done
	255	done
	256	done
	257
d8852323 MW	258	## Dump the resulting configuration.
	259	if [ "$FW_DEBUG" ]; then
	260	for ip in ip ip6; do
	261	for table in mangle filter; do
	262	echo "----- $ip $table -----"
	263	echo
	264	${ip}tables -t $table -nvL
	265	echo
	266	done
	267	done
	268	fi
	269
bfdc045d MW	270	m4_divert(-1)
bfdc045d MW	271	###----- That's all, folks --------------------------------------------------