ebtables-segment-mld: Segment IGMP/MLD domain

This patch adds a new gluon-ebtables package to filter IGMP/MLD messages
via ebtables.

For one thing this reduces multicast overhead: About one third of all
ICMPv6 multicast traffic in Lübeck or Hamburg is MLD.

Furthermore it removes a potential Distributed Denial-of-Service vector
(see Gluon ticket #553).

Finally, it is a prerequisite for enabling bridge multicast snooping in
a decentral and robust fashion.

Note that IGMP/MLD are filtered for multicast traffic coming from
the mesh, too (new MULTICAST_IN), as unfortunately there seem to
be other queriers somewhere in the mesh at least for Freifunk
Lübeck. Also adding these rules to be prepared to anyone intentionally
or unintentionally disabling these filters on his/her node.

Node operators not running Gluon (for instance gateway nodes) should
make sure to either enable multicast_router towards bat0 or disable
multicast snooping entirely if they have a bridge on top of bat0.

Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>

docs/package/gluon-ebtables-segment-mld.rst

@@ -0,0 +1,16 @@
+gluon-ebtables-segment-mld
+==========================
+
+These filters drop IGMP/MLD packets before they enter the mesh and
+filter any IGMP/MLD packets coming from the mesh.
+
+IGMP/MLD have the concept of a local, elected Querier. For more
+decentralization and increased robustness, the idea of this package is
+to split the IGMP/MLD domain a querier is responsible for, allowing to
+have a querier per node. The split IGMP/MLD domain will also reduce
+overhead for this packet type, increasing scalability.
+
+Beware of the consequences of using this package though: You might need
+to explicitly, manually mark ports on snooping switches leading towards
+your mesh node as multicast router ports for now (Multicast Router
+Discovery, MRD, not implemented yet).

package/gluon-ebtables-filter-multicast/files/lib/gluon/ebtables/100-mcast-chain

@@ -1 +0,0 @@
-chain('MULTICAST_OUT', 'DROP')

package/gluon-ebtables-filter-multicast/files/lib/gluon/ebtables/110-mcast-allow-icmpv6

@@ -1,3 +1,3 @@
-rule 'MULTICAST_OUT -p IPv6 --ip6-protocol ipv6-icmp --ip6-icmp-type echo-request -j DROP'
+rule 'MULTICAST_OUT_ICMPV6 -p IPv6 --ip6-protocol ipv6-icmp --ip6-icmp-type echo-request -j RETURN'
-rule 'MULTICAST_OUT -p IPv6 --ip6-protocol ipv6-icmp --ip6-icmp-type 139 -j DROP'
+rule 'MULTICAST_OUT_ICMPV6 -p IPv6 --ip6-protocol ipv6-icmp --ip6-icmp-type 139 -j RETURN' -- ICMP Node Information Query
-rule 'MULTICAST_OUT -p IPv6 --ip6-protocol ipv6-icmp -j RETURN'
+rule 'MULTICAST_OUT_ICMPV6 -j ACCEPT'

package/gluon-ebtables-filter-multicast/files/lib/gluon/ebtables/300-mcast

@@ -1,2 +0,0 @@
-rule 'FORWARD --logical-out br-client -o bat0 -d Multicast -j MULTICAST_OUT'
-rule 'OUTPUT --logical-out br-client -o bat0 -d Multicast -j MULTICAST_OUT'

package/gluon-ebtables-filter-multicast/files/lib/gluon/ebtables/355-mcast-drop

@@ -0,0 +1 @@
+rule ('MULTICAST_OUT -j DROP')

package/gluon-ebtables-segment-mld/Makefile

@@ -0,0 +1,51 @@
+include $(TOPDIR)/rules.mk
+
+PKG_NAME:=gluon-ebtables-segment-mld
+PKG_VERSION:=1
+PKG_RELEASE:=1
+
+PKG_BUILD_DIR := $(BUILD_DIR)/$(PKG_NAME)
+
+include $(INCLUDE_DIR)/package.mk
+
+define Package/gluon-ebtables-segment-mld
+  SECTION:=gluon
+  CATEGORY:=Gluon
+  TITLE:=Ebtables filters for IGMP/MLD packets
+  DEPENDS:=+gluon-core +gluon-ebtables
+endef
+
+define Package/gluon-ebtables-segment-mld/description
+	Gluon community wifi mesh firmware framework: Ebtables filters for
+	IGMP/MLD packets
+
+	These filters drop IGMP/MLD packets before they enter the mesh and
+	filter any IGMP/MLD packets coming from the mesh.
+
+	IGMP/MLD have the concept of a local, elected Querier. For more
+	decentralization and increased robustness, the idea of this package is
+	to split the IGMP/MLD domain a querier is responsible for, allowing to
+	have a querier per node. The split IGMP/MLD domain will also reduce
+	overhead for this packet type, increasing scalability.
+
+	Beware of the consequences of using this package though: You might need
+	to explicitly, manually mark ports on snooping switches leading towards
+	your mesh node as multicast router ports for now (Multicast Router
+	Discovery, MRD, not implemented yet).
+endef
+
+define Build/Prepare
+	mkdir -p $(PKG_BUILD_DIR)
+endef
+
+define Build/Configure
+endef
+
+define Build/Compile
+endef
+
+define Package/gluon-ebtables-segment-mld/install
+	$(CP) ./files/* $(1)/
+endef
+
+$(eval $(call BuildPackage,gluon-ebtables-segment-mld))

package/gluon-ebtables-segment-mld/files/lib/gluon/ebtables/100-mcast-in-chain

@@ -0,0 +1,2 @@
+chain('MULTICAST_IN', 'RETURN', 'nat')
+chain('MULTICAST_IN_ICMPV6', 'RETURN', 'nat')

package/gluon-ebtables-segment-mld/files/lib/gluon/ebtables/101-mcast-in-rule

@@ -0,0 +1,2 @@
+rule ('PREROUTING -d Multicast --logical-in br-client -i bat0 -j MULTICAST_IN', 'nat')
+rule ('MULTICAST_IN -p IPv6 --ip6-protocol ipv6-icmp -j MULTICAST_IN_ICMPV6', 'nat')

package/gluon-ebtables-segment-mld/files/lib/gluon/ebtables/105-mcast-drop-igmp

@@ -0,0 +1,2 @@
+rule('MULTICAST_OUT -p IPv4 --ip-protocol igmp -j DROP')
+rule('MULTICAST_IN -p IPv4 --ip-protocol igmp -j DROP', 'nat')

package/gluon-ebtables-segment-mld/files/lib/gluon/ebtables/105-mcast-drop-mld

@@ -0,0 +1,9 @@
+rule('MULTICAST_OUT_ICMPV6 -p IPv6 --ip6-protocol ipv6-icmp --ip6-icmp-type 130 -j DROP') -- MLD Query
+rule('MULTICAST_OUT_ICMPV6 -p IPv6 --ip6-protocol ipv6-icmp --ip6-icmp-type 131 -j DROP') -- MLDv1 Report
+rule('MULTICAST_OUT_ICMPV6 -p IPv6 --ip6-protocol ipv6-icmp --ip6-icmp-type 132 -j DROP') -- MLDv1 Done
+rule('MULTICAST_OUT_ICMPV6 -p IPv6 --ip6-protocol ipv6-icmp --ip6-icmp-type 143 -j DROP') -- MLDv2 Report
+
+rule('MULTICAST_IN_ICMPV6 -p IPv6 --ip6-protocol ipv6-icmp --ip6-icmp-type 130 -j DROP', 'nat') -- MLD Query
+rule('MULTICAST_IN_ICMPV6 -p IPv6 --ip6-protocol ipv6-icmp --ip6-icmp-type 131 -j DROP', 'nat') -- MLDv1 Report
+rule('MULTICAST_IN_ICMPV6 -p IPv6 --ip6-protocol ipv6-icmp --ip6-icmp-type 132 -j DROP', 'nat') -- MLDv1 Done
+rule('MULTICAST_IN_ICMPV6 -p IPv6 --ip6-protocol ipv6-icmp --ip6-icmp-type 143 -j DROP', 'nat') -- MLDv2 Report

package/gluon-ebtables/files/etc/init.d/gluon-ebtables

@@ -24,12 +24,15 @@ exec_file() {
 	local file="$1"
 
 	/usr/bin/lua -e "
-		function rule(command)
+		function rule(command, table)
+			table = table or 'filter'
 			os.execute($EBTABLES_RULE)
 		end
-		function chain(name, policy)
+		function chain(name, policy, table)
+			table = table or 'filter'
 			os.execute($EBTABLES_CHAIN)
 		end
+
 	" "$file"
 }
 
@@ -48,8 +51,8 @@ exec_all() {
 
 start() {
 	(
-		export EBTABLES_RULE='"ebtables -A " .. command'
+		export EBTABLES_RULE='"ebtables -t " .. table .. " -A " .. command'
-		export EBTABLES_CHAIN='"ebtables -N " .. name .. " -P " .. policy'
+		export EBTABLES_CHAIN='"ebtables -t " .. table .. "  -N " .. name .. " -P " .. policy'
 
 		if [ -z "$1" ]; then
 			exec_all ''
@@ -61,8 +64,8 @@ start() {
 
 stop() {
 	(
-		export EBTABLES_RULE='"ebtables -D " .. command'
+		export EBTABLES_RULE='"ebtables -t " ..	table .. " -D " .. command'
-		export EBTABLES_CHAIN='"ebtables -X " .. name'
+		export EBTABLES_CHAIN='"ebtables -t " .. table .. " -X " .. name'
 
 		if [ -z "$1" ]; then
 			exec_all '-r'

package/gluon-ebtables/files/lib/gluon/ebtables/100-dir-chain

@@ -1,2 +1,5 @@
 chain('IN_ONLY', 'RETURN')
 chain('OUT_ONLY', 'RETURN')
+
+chain('MULTICAST_OUT', 'RETURN')
+chain('MULTICAST_OUT_ICMPV6', 'RETURN')

package/gluon-ebtables/files/lib/gluon/ebtables/350-mcast-dir-rules

@@ -0,0 +1,4 @@
+rule 'OUTPUT -d Multicast --logical-out br-client -o bat0 -j MULTICAST_OUT'
+rule 'FORWARD -d Multicast --logical-out br-client -o bat0 -j MULTICAST_OUT'
+
+rule 'MULTICAST_OUT -p IPv6 --ip6-protocol ipv6-icmp -j MULTICAST_OUT_ICMPV6'