Overhaul address classification for link-local and non-unicast addresses.

[firewall] / classify.m4

diff --git a/classify.m4 b/classify.m4
index 606d90d..59ac3d9 100644 (file)
--- a/classify.m4
+++ b/classify.m4
@@ -65,6 +65,17 @@ m4_divert(40)m4_dnl
 clearchain mangle:in-classify mangle:in-default mangle:out-classify
 clearchain mangle:local-source
 
+## An unpleasant hack.  We can't reject packets from the mangle table, so
+## we mark packets with a bad destination and then detect this in the
+## filter table.
+clearchain mangle:bad-destination-address
+BAD_DEST=0xf6f377d2
+ip46tables -t mangle -A bad-destination-address -j MARK --set-mark $BAD_DEST
+ip46tables -t mangle -A bad-destination-address -j ACCEPT
+for i in $inchains; do
+  ip46tables -A $i -m mark --mark $BAD_DEST -g bad-destination-address
+done
+
 ## Packets over the loopback interface are automatically trusted.  All manner
 ## of weird stuff happens on lo, and it's best not to second-guess it.
 run ip46tables -t mangle -A in-classify -i lo -j ACCEPT
@@ -98,15 +109,6 @@ for addr in $host_6addrs; do
          -s $addr
 done
 
-## It's not valid to have a multicast address as a packet source: multicast
-## routing is done away from the source, so a multicast address would make
-## this impossible to do.  So discard these packets.  Also discard class-E
-## IPv4 addresses, since they aren't assigned.
-run iptables -t mangle -A in-classify -g bad-source-address \
-       -s 224.0.0.0/3
-run ip6tables -t mangle -A in-classify -g bad-source-address \
-       -s ff00::/8
-
 m4_divert(41)m4_dnl
 ## Define the important networks.
 for pass in 1 2; do
@@ -115,6 +117,56 @@ m4_divert(42)m4_dnl
 done
 
 m4_divert(46)m4_dnl
+## Special IPv4 source addresses.  Forbid broadcast and multicast sources.
+## Mark the special zero address and link-local addresses as such.  (This
+## also matches class-E addresses, which are probably permanently invalid.)
+for i in 0.0.0.0 169.254.0.0/16; do
+  run iptables -t mangle -A in-classify -g mark-from-link -s $i
+done
+run iptables -t mangle -A in-classify -g bad-source-address \
+       -s 224.0.0.0/3
+run iptables -t mangle -A in-classify -g bad-source-address \
+       -m addrtype --src-type BROADCAST \
+
+## Special IPv6 addresses.  Format multicast sources, and mark zero and
+## link local addresses.
+for i in :: fe80::/10; do
+  run ip6tables -t mangle -A in-classify -g mark-from-link -s $i
+done
+run ip6tables -t mangle -A in-classify -g bad-source-address \
+       -s ff00::/8
+
+## Special IPv4 destination addresses.  The zero address is invalid; mark
+## link-local and recognized broadcast addresses as link-local.  We leave
+## multicast for later.
+for i in 0.0.0.0 240.0.0.0/4; do
+  run iptables -t mangle -A out-classify -g bad-destination-address -d $i
+done
+run iptables -t mangle -A out-classify -g mark-to-link -d 169.254.0.0/16
+run iptables -t mangle -A out-classify -g mark-to-link \
+       -m addrtype --dst-type BROADCAST
+
+## Special IPv6 destination addressses.  The zero address is again invalid;
+## mark link local addresses.  We do multicast later.
+run ip6tables -t mangle -A out-classify -g bad-destination-address \
+       -d ::
+run ip6tables -t mangle -A out-classify -g mark-to-link -d fe80::/10
+
+## Now deal with multicast.  Link-local multicast is detected as being
+## link-local, so that we can prevent it being forwarded correctly.
+clearchain mangle:out-classify-mcast
+run iptables -t mangle -A out-classify-mcast -g mark-to-link \
+       -d 224.0.0.0/24
+for i in 0 1 2 3 4 5 6 7 8 9 a b c d e f; do
+  run ip6tables -t mangle -A out-classify-mcast -g mark-to-link \
+         -d ff${i}2::/16
+done
+run ip46tables -t mangle -A out-classify-mcast -g mark-to-mcast
+run iptables -t mangle -A out-classify -g out-classify-mcast \
+       -d 224.0.0.0/4
+run ip6tables -t mangle -A out-classify -g out-classify-mcast \
+       -d ff00::/8
+
 ## Build the input classification chains.  There's one chain `in-IFACE' for
 ## each local interface.  This chain does a further dispatch on the source
 ## address to the appropriate `mark-from-CLASS' chain for the source network
@@ -268,6 +320,14 @@ run ip46tables -t mangle -A out-classify -g mark-to-$net_class_default
 run ip46tables -t mangle -A PREROUTING -j in-classify
 run ip46tables -t mangle -A PREROUTING -j out-classify
 
+## Incoming stuff to or from a link-local address is OK.
+run ip46tables -t mangle -A INPUT \
+       -m mark --mark $to_link/$MASK_TO \
+       -j MARK --or-mark $fwd_link
+run ip46tables -t mangle -A INPUT \
+       -m mark --mark $from_link/$MASK_FROM \
+       -j MARK --or-mark $fwd_link
+
 ## Now it's safe to let stuff through.
 for i in PREROUTING INPUT FORWARD OUTPUT POSTROUTING; do
   run ip46tables -t mangle -P $i ACCEPT