| 1 | ### -*-m4-*- |
| 2 | ### |
| 3 | ### Classify packets according to source and destination networks. |
| 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(40)m4_dnl |
| 25 | ###-------------------------------------------------------------------------- |
| 26 | ### Address classification. |
| 27 | ### |
| 28 | ### The objective of address classification is to work out what kind of |
| 29 | ### networks a packet is travelling between, in order to make filtering |
| 30 | ### decisions easier. |
| 31 | ### |
| 32 | ### Address classification is done in the mangle table, by attaching |
| 33 | ### appropriate marks to the packet. We split the Internet into a number of |
| 34 | ### address classes, and make forwarding decisions based on the classes of |
| 35 | ### the source and destination addresses. |
| 36 | ### |
| 37 | ### The mark word is split into three fields: the FROM and TO fields simply |
| 38 | ### record the source and destination classes numerically; the MASK field is |
| 39 | ### used to determine whether forwarding should occur. There is a mask bit |
| 40 | ### for each address class. Source classification sets mask bits according |
| 41 | ### to the forwarding policy for the source address class. Destination |
| 42 | ### classification clears all of the mask bits except for the one |
| 43 | ### corresponding to the actual destination class. Therefore, forwarding is |
| 44 | ### permitted if and only if the mask bits are not all zero. |
| 45 | ### |
| 46 | ### The mangle chains are arranged as follows. |
| 47 | ### |
| 48 | ### The PREROUTING hook simply invokes in-classify and out-classify chains as |
| 49 | ### subroutines. These will tail-call appropriate classification chains. |
| 50 | ### |
| 51 | ### The in-classify chain is responsible for both source address |
| 52 | ### classification and verifying that the packet arrived from the correct |
| 53 | ### interface. It does an initial dispatch on the source interface, to |
| 54 | ### in-IFACE. The in-IFACE chain dispatches to mark-from-CLASS when it |
| 55 | ### recognizes an address belonging to the CLASS; if no matches succeed, it |
| 56 | ### goes to bad-source-address, which logs a message and drops the packet. |
| 57 | ### The default interface is special. If no explicit matches are found, it |
| 58 | ### dispatches to in-default which forbids a few obviously evil things and |
| 59 | ### finally dispatches to mark-from-untrusted. |
| 60 | ### |
| 61 | ### The out-classify is simpler because it doesn't care about the interface. |
| 62 | ### It simply checks each network range in turn, dispatching to mark-to-CLASS |
| 63 | ### on a match or mark-to-DEFAULT (probably untrusted) if there is no match. |
| 64 | |
| 65 | clearchain mangle:in-classify mangle:in-default mangle:out-classify |
| 66 | clearchain mangle:local-source |
| 67 | |
| 68 | ## Packets over the loopback interface are automatically trusted. All manner |
| 69 | ## of weird stuff happens on lo, and it's best not to second-guess it. |
| 70 | run iptables -t mangle -A in-classify -i lo -j ACCEPT |
| 71 | |
| 72 | ## Local bootp packets have bizarre addresses. Don't block them just because |
| 73 | ## of this. |
| 74 | run iptables -t mangle -A in-classify -j RETURN \ |
| 75 | -s 0.0.0.0 -d 255.255.255.255 \ |
| 76 | -p udp --source-port $port_bootpc --destination-port $port_bootps |
| 77 | |
| 78 | ## Since packets with source and destination addresses both local will go |
| 79 | ## over the loopback interface, I shouldn't see a packet from me over any |
| 80 | ## other interface. Except that I will if I sent a broadcast or multicast. |
| 81 | ## Allow the broadcasts, and remember not to trust them. |
| 82 | run iptables -t mangle -A local-source -j RETURN \ |
| 83 | -m addrtype --dst-type BROADCAST |
| 84 | run iptables -t mangle -A local-source -j RETURN \ |
| 85 | -m addrtype --dst-type MULTICAST |
| 86 | run iptables -t mangle -A local-source -g bad-source-address |
| 87 | run iptables -t mangle -A in-classify -j local-source \ |
| 88 | -m addrtype --src-type LOCAL |
| 89 | |
| 90 | m4_divert(41)m4_dnl |
| 91 | ## Define the important networks. |
| 92 | for pass in 1 2; do |
| 93 | netclassindex=0 |
| 94 | m4_divert(42)m4_dnl |
| 95 | done |
| 96 | |
| 97 | m4_divert(46)m4_dnl |
| 98 | ## Mark addresses reachable on non-default interfaces as not reachable on the |
| 99 | ## default interface. |
| 100 | trace "nets = $allnets" |
| 101 | for net in $allnets; do |
| 102 | case $net in |
| 103 | "$defaultiface":*) |
| 104 | ;; |
| 105 | *) |
| 106 | run iptables -t mangle -A in-$defaultiface \ |
| 107 | -s ${net#*:} -g bad-source-address |
| 108 | ;; |
| 109 | esac |
| 110 | done |
| 111 | |
| 112 | ## Fill in the black holes in the network. |
| 113 | for addr in \ |
| 114 | 10.0.0.0/8 172.16.0.0/12 192.168.0.0/16 \ |
| 115 | 127.0.0.0/8 192.0.2.0/24 |
| 116 | do |
| 117 | run iptables -t mangle -A in-default -s $addr -g bad-source-address |
| 118 | done |
| 119 | |
| 120 | m4_divert(92)m4_dnl |
| 121 | ## Put the final default decision on the in-default chain, and attach the |
| 122 | ## classification chains to the PREROUTING hook. |
| 123 | run iptables -t mangle -A in-$defaultiface -g mark-from-$defaultclass |
| 124 | run iptables -t mangle -A PREROUTING -j in-classify |
| 125 | run iptables -t mangle -A PREROUTING -j out-classify |
| 126 | |
| 127 | ## Now it's safe to let stuff through. |
| 128 | for i in PREROUTING INPUT FORWARD OUTPUT POSTROUTING; do |
| 129 | run iptables -t mangle -P $i ACCEPT |
| 130 | done |
| 131 | |
| 132 | m4_divert(-1) |
| 133 | ###----- That's all, folks -------------------------------------------------- |