[PATCH] ipsec: Add block rules to avoid conntrack entries

[Michael Tremer <michael.tremer@ipfire.org>]

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If an IPsec VPN connections is not established, there are
rare cases when packets are supposed to be sent through
that said tunnel and incorrectly handled.

Those packets are sent to the default gateway an entry
for this connection is created in the connection tracking
table (usually only happens to UDP). All following packets
are sent the same route even after the tunnel has been
brought up. That leads to SIP phones not being able to
register among other things.

This patch adds firewall rules that these packets are
rejected. That will sent a notification to the client
that the tunnel is not up and avoid the connection to
be added to the connection tracking table.

Apart from a small performance penalty there should
be no other side-effects.

Fixes: #10908

Signed-off-by: Michael Tremer <michael.tremer(a)ipfire.org>
Cc: tomvend(a)rymes.com
Cc: daniel.weismueller(a)ipfire.org
Cc: morlix(a)morlix.de
---
 config/firewall/ipsec-block           | 59 +++++++++++++++++++++++++++++++++++
 config/rootfiles/common/stage2        |  1 +
 config/rootfiles/common/x86_64/stage2 |  1 +
 lfs/stage2                            |  2 ++
 src/initscripts/init.d/firewall       |  8 +++++
 src/misc-progs/ipsecctrl.c            |  4 +++
 6 files changed, 75 insertions(+)
 create mode 100644 config/firewall/ipsec-block

diff --git a/config/firewall/ipsec-block b/config/firewall/ipsec-block
new file mode 100644
index 0000000..9fa8e1a
--- /dev/null
+++ b/config/firewall/ipsec-block
@@ -0,0 +1,59 @@
+#!/bin/bash
+###############################################################################
+#                                                                             #
+# IPFire.org - A linux based firewall                                         #
+# Copyright (C) 2015 IPFire Team                                              #
+#                                                                             #
+# 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 3 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, see <http://www.gnu.org/licenses/>.       #
+#                                                                             #
+###############################################################################
+
+VPN_CONFIG="/var/ipfire/vpn/config"
+
+block_subnet() {
+	local subnet="${1}"
+
+	# Don't block a wildcard subnet
+	if [ "${subnet}" = "0.0.0.0/0" ] || [ "${subnet}" = "0.0.0.0/0.0.0.0" ]; then
+		return 0
+	fi
+
+	iptables -A IPSECBLOCK -d "${subnet}" -j REJECT --reject-with icmp-net-unreachable
+}
+
+block_ipsec() {
+	# Flush all exists rules
+	iptables -F IPSECBLOCK
+
+	local id status name lefthost type ctype unknown1 unknown2 unknown3
+	local leftsubnets unknown4 righthost rightsubnets rest
+	while IFS="," read -r id status name lefthost type ctype unkown1 unknown2 unknown3 \
+			leftsubnets unknown4 righthost rightsubnets rest; do
+		# Check if the connection is enabled
+		[ "${status}" = "on" ] || continue
+
+		# Check if this a net-to-net connection
+		[ "${type}" = "net" ] || continue
+
+		# Split multiple subnets
+		rightsubnets="${rightsubnets//\|/ }"
+
+		local rightsubnet
+		for rightsubnet in ${rightsubnets}; do
+			block_subnet "${rightsubnet}"
+		done
+	done < "${VPN_CONFIG}"
+}
+
+block_ipsec || exit $?
diff --git a/config/rootfiles/common/stage2 b/config/rootfiles/common/stage2
index 90e28d9..4021caf 100644
--- a/config/rootfiles/common/stage2
+++ b/config/rootfiles/common/stage2
@@ -73,6 +73,7 @@ run
 #usr/lib
 usr/lib/firewall
 usr/lib/firewall/firewall-lib.pl
+usr/lib/firewall/ipsec-block
 usr/lib/firewall/rules.pl
 #usr/lib/libgcc_s.so
 usr/lib/libgcc_s.so.1
diff --git a/config/rootfiles/common/x86_64/stage2 b/config/rootfiles/common/x86_64/stage2
index 0ac9ab5..531daaa 100644
--- a/config/rootfiles/common/x86_64/stage2
+++ b/config/rootfiles/common/x86_64/stage2
@@ -74,6 +74,7 @@ run
 #usr/lib
 usr/lib/firewall
 usr/lib/firewall/firewall-lib.pl
+usr/lib/firewall/ipsec-block
 usr/lib/firewall/rules.pl
 #usr/lib/libgcc_s.so
 usr/lib/libgcc_s.so.1
diff --git a/lfs/stage2 b/lfs/stage2
index 3244fa3..ec5d117 100644
--- a/lfs/stage2
+++ b/lfs/stage2
@@ -114,6 +114,8 @@ endif
 		/usr/lib/firewall/rules.pl
 	install -m 644 $(DIR_SRC)/config/firewall/firewall-lib.pl \
 		/usr/lib/firewall/firewall-lib.pl
+	install -m 755 $(DIR_SRC)/config/firewall/ipsec-block \
+		/usr/lib/firewall/ipsec-block
 
 	# Nobody user
 	-mkdir -p /home/nobody
diff --git a/src/initscripts/init.d/firewall b/src/initscripts/init.d/firewall
index 8ca02bc..2d462d7 100644
--- a/src/initscripts/init.d/firewall
+++ b/src/initscripts/init.d/firewall
@@ -115,6 +115,11 @@ iptables_init() {
 	iptables -A INPUT -j GUARDIAN
 	iptables -A FORWARD -j GUARDIAN
 
+	# Block non-established IPsec networks
+	iptables -N IPSECBLOCK
+	iptables -A FORWARD -m policy --dir out --pol none -j IPSECBLOCK
+	iptables -A OUTPUT  -m policy --dir out --pol none -j IPSECBLOCK
+
 	# Block OpenVPN transfer networks
 	iptables -N OVPNBLOCK
 	iptables -A INPUT   -i tun+ -j OVPNBLOCK
@@ -270,6 +275,9 @@ iptables_init() {
 	iptables -t nat -N REDNAT
 	iptables -t nat -A POSTROUTING -j REDNAT
 
+	# Populate IPsec block chain
+	/usr/lib/firewall/ipsec-block
+
 	# Apply OpenVPN firewall rules
 	/usr/local/bin/openvpnctrl --firewall-rules
 
diff --git a/src/misc-progs/ipsecctrl.c b/src/misc-progs/ipsecctrl.c
index e99202d..7499e94 100644
--- a/src/misc-progs/ipsecctrl.c
+++ b/src/misc-progs/ipsecctrl.c
@@ -144,6 +144,9 @@ void turn_connection_on(char *name, char *type) {
                 "/usr/sbin/ipsec down %s >/dev/null", name);
         safe_system(command);
 
+	// Reload the IPsec block chain
+	safe_system("/usr/lib/firewall/ipsec-block >/dev/null");
+
 	// Reload the configuration into the daemon (#10339).
 	ipsec_reload();
 
@@ -302,6 +305,7 @@ int main(int argc, char *argv[]) {
 
         // start the system
         if ((argc == 2) && strcmp(argv[1], "S") == 0) {
+		safe_system("/usr/lib/firewall/ipsec-block >/dev/null");
 		safe_system("/usr/sbin/ipsec restart >/dev/null");
                 exit(0);
         }
-- 
2.4.4