Add a preflight check for the precence of ip_tables. Check if the kernel has ipv6_tables support and if the module is present load it. If ipv6 support isn't available and we have a public ipv6 address warn the user that the system has no ipv6 firewall

setup/preflight.sh

@@ -60,3 +60,24 @@ if [ -z "$ARM" ]; then
 	exit
 fi
 fi
+
+# Check that the kernel supports at least ipv4 ip_tables, either by a module or by being
+# compiled directly in the kernel
+#
+# If this isn't supported tell the user to compile the kernel module or disable the firewall
+# and inform of the risk of doing so.
+if
+	[ ! -e /proc/net/ip_tables_names ] &&
+	[ ! -e /lib/modules/`uname -r`/kernel/net/ipv4/netfilter/ip_tables.ko ] &&
+	[ -z "$DISABLE_FIREWALL" ]
+then
+	echo "Your system doesn't support at least ipv4 ip_tables. You will either need to compile"
+	echo "a kernel that supports it, or compile the kernel module"
+	echo
+	echo "If you would like to continue without a firewall you can set 'export DISABLE_FIREWALL=1' at the"
+	echo "command line. However, doing this prevents Mail-in-a-Box to activate fail2ban. This service"
+	echo "protects the system from bruteforce attacks on the exposed network services. Also services "
+	echo "that shouldn't be exposed are now exposed if you don't use a different (external) firewall"
+	exit
+fi
+

setup/system.sh

@@ -227,10 +227,42 @@ if [ -z "$DISABLE_FIREWALL" ]; then
 	# Install `ufw` which provides a simple firewall configuration.
 	apt_install ufw
 
-	# Some providers don't load the ip6_tables kernel module (Scaleway)
+	# Check if the ip_tables has ipv6 support on this system, prefilght has
-	if [ -z "`lsmod | grep ^ip6_tables`" ]; then
+	# taken care of ipv4.
-		echo ip6_tables >> /etc/modules
+	#
-		modprobe ip6_tables
+	# We check if:
+	#	- the kernel has support built-in
+	#	- the module is present on the system.
+	#
+	# If no ipv6 support is available we disable the ipv6 firewall
+	#
+	# If ipv6 is supported on the system we load the module if necessary and activate the
+	# ipv6 firewall.
+	if
+	        [ ! -e /proc/net/ip6_tables_names ] &&
+		[ ! -e /lib/modules/`uname -r`/kernel/net/ipv6/netfilter/ip6_tables.ko ]
+	then
+		# If we have a public ipv6 address we should notify the user that no ipv6 firewall is available
+		if [ ! -z "$PUBLIC_IPV6" ]; then
+			echo "WARNING: There is a public ipv6 address but no ipv6 firewall available in the kernel"
+		fi
+
+		# Disable the IPV6 firewall
+		sed -i "s/IPV6.*/IPV6=no/" /etc/default/ufw
+	else
+		# Check if the ipv6 ip_tables is not active in the kernel or that the module
+		# isn't loaded. Some providers fail to load the module by default (Scaleway)
+		if
+			[ ! -e /proc/net/ip6_tables_names ] &&
+			[ -z "`lsmod | grep ^ip6_tables`" ]
+		then
+			# Load the ip6_tables kernel module, previous step made sure it exists
+			echo ip6_tables >> /etc/modules
+			modprobe ip6_tables
+		fi
+
+		# Enable the IPV6 firewall
+                sed -i "s/IPV6.*/IPV6=yes/" /etc/default/ufw
 	fi
 
 	# Allow incoming connections to SSH.