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authorHarald Welte <laforge@gnumonks.org>2015-10-25 21:00:20 +0100
committerHarald Welte <laforge@gnumonks.org>2015-10-25 21:00:20 +0100
commitfca59bea770346cf1c1f9b0e00cb48a61b44a8f3 (patch)
treea2011270df48d3501892ac1a56015c8be57e8a7d /2003/netfilter-programming-clt2003
import of old now defunct presentation slides svn repo
Diffstat (limited to '2003/netfilter-programming-clt2003')
-rw-r--r--2003/netfilter-programming-clt2003/abstract70
-rw-r--r--2003/netfilter-programming-clt2003/ipt_workshop.c54
-rw-r--r--2003/netfilter-programming-clt2003/ipt_workshop.h6
-rw-r--r--2003/netfilter-programming-clt2003/libipt_workshop.c102
-rw-r--r--2003/netfilter-programming-clt2003/netfilter-programming-clt2003.mgp636
-rw-r--r--2003/netfilter-programming-clt2003/nf_workshop.c57
6 files changed, 925 insertions, 0 deletions
diff --git a/2003/netfilter-programming-clt2003/abstract b/2003/netfilter-programming-clt2003/abstract
new file mode 100644
index 0000000..d4e2cac
--- /dev/null
+++ b/2003/netfilter-programming-clt2003/abstract
@@ -0,0 +1,70 @@
+Kurz-Paper zum Vortrag "Programmierung von netfilter/iptables-Erweiterungen"
+(Schluessel 3b911575)
+
+1. Warum ist dieses Thema fuer die Besucher interessant?
+
+ Das Thema ist aus unterschiedlichen Gruenden interessant.
+
+ Zum einen is vielen fortgeschrittenen Administratoren einfach nicht klar,
+ was sich durch eigene Erweiterungsmodule fuer Moeglichkeiten erschliessen.
+ Zu vielen denken noch in der alten, starren, monolithischen 'ipchains'-Welt.
+
+ Zum anderen ist es auch eine ideale Moeglichkeit, ein bisschen in die Welt
+ der Kernel-Programmierung hereinzuschnuppern. Viele der komplexen
+ Zusammenhaenge (locking, etc.) werden weitestgehend vom netfilter/iptables
+ core uebernommen, so dass wirklich lediglich C-Programmierkenntnisse noetig
+ sind, und man bisher den Kernel noch nicht angefasst haben muss.
+
+ Und nicht zuletzt waere dieser Vortrag erst die zweite Moeglichkeit,
+ sich anstatt RTFM durch einen Workshop mit diesem Thema zu beschaeftigen ;)
+
+2. Warum beschaeftigen Sie sich mit dem Thema?
+
+ Weil ich ein Mitglied des netfilter core teams und der gegenwaertige
+ Maintainer des Linux Firewalling Subsystems bin.
+
+ Warum ich nun das bin, ist eine laengere Geschichte. Ich finde es jedenfalls
+ wichtig, an der Weiterentwicklung des Linux-Firewallings zu arbeiten.
+ Netzwerke, und insbesondere Netzwerksicherheit war schon immer mein
+ Lieblingsthema.
+
+3. Welche Struktur/Gliederung soll der Vortrag bzw. Workshop haben?
+
+ Zunaechst kommt eine kurze Uebersicht ueber die interne Architektur
+ des netfilter- und iptables- subsystem.
+
+ Im zweiten Teil werden die im Rahmen dieser Architektur zur Verfuegung
+ stehenden API's besprochen, u.a. auch mit Code-Beispielen von existierenden
+ iptables matches/targets, sowie conntrack und NAT helper-Modulen.
+
+ Im driten Teil folgt dann eine schritt-fuer-schritt-Entwicklung eines
+ iptables-Erweiterungsmoduls.
+
+4. Planen Sie auch eine praktische Vorfuehrung im Rahmen des Beitrages?
+
+ Nunja, nach dem es sich um eine Art Programmier-Tutorial handelt werden
+ wir nach dem Theoretischen Teil (einer Einfuehrung in die API's) zusammen
+ ein solches Erweiterungsmodul schreiben. Ich denke das zaehlt als
+ "praktische Vorfuehrung"
+
+5. Welche einschlaegigen Webseiten gibt es zum Tema?
+
+ Die Homepage des netfilter/iptables-Projekts unter http://www.netfilter.org/,
+ insbesondere das netfilter-hacking-HOWTO unter
+ http://www.netfilter.org/documentation/HOWTO/netfilter-hacking-HOWTO.html ist
+ als relevant zu bezeichnen.
+
+6. Haben Sie schon einmal ueber dieses Thema referiert?
+
+ Ich habe zahlreiche Vortraege und Tutorials run um das Thema
+ netfilter/iptables auf internationalen Konferenzen gehalten (unter anderem
+ Linuxtag, Linux-Kongress, Ottawa Linux Symposium, Sao Paulo Linux Expo, ...).
+ Eine unvollstaendige Liste ist unter http://www.netfilter.org/events.html
+
+ Dabei war auch bereits ein eintaegiger Workshop, in dem von den Grundlagen
+ der Anwendung bis zur Programmierung von Erweiterungsmodule der komplette
+ Themenbereich abgedeckt war.
+
+Sonstiges:
+
+ Der Workshop kann in deutsch oder englisch angeboten werden.
diff --git a/2003/netfilter-programming-clt2003/ipt_workshop.c b/2003/netfilter-programming-clt2003/ipt_workshop.c
new file mode 100644
index 0000000..3a6c802
--- /dev/null
+++ b/2003/netfilter-programming-clt2003/ipt_workshop.c
@@ -0,0 +1,54 @@
+#include <linux/module.h>
+#include <linux/sk_buff.h>
+#include <linux/netfilter_ipv4/ip_tables.h>
+#include <linux/netfilter_ipv4/ipt_workshop.h>
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
+MODULE_DESCRIPTION("5CLT workshop iptables module");
+
+static int ws_match(const struct sk_buff *skb, const struct net_device *in,
+ const struct net_device *out, const void *matchinfo,
+ int offset, const void *hdr, u_int16_t datalen,
+ int *hotdrop)
+{
+ const struct ipt_ws_info *info = matchinfo;
+ const struct iphdr *iph = skb->nh.iph;
+
+ if (iph->ttl == info->ttl)
+ return 1;
+
+ return 0;
+}
+
+static int ws_checkentry(const char *tablename, const struct ipt_ip *ip,
+ void *matchinfo, unsigned int matchsize,
+ unsigned int hook_mask)
+{
+ if (matchsize != IPT_ALIGN(sizeof(struct ipt_ws_info)))
+ return 0;
+
+ return 1;
+}
+
+static struct ipt_match ws_match = {
+ .list = { .prev = NULL, .next = NULL },
+ .name = "workshop",
+ .match = &ws_match,
+ .checkentry = &ws_checkentry,
+ .destroy = NULL,
+ .me = THIS_MODULE
+};
+
+static int __init init(void)
+{
+ return ipt_register_match(&ws_match);
+}
+
+static void __exit fini(void)
+{
+ ipt_unregister_match(&ws_match);
+}
+
+module_init(init);
+module_exit(fini);
diff --git a/2003/netfilter-programming-clt2003/ipt_workshop.h b/2003/netfilter-programming-clt2003/ipt_workshop.h
new file mode 100644
index 0000000..f707703
--- /dev/null
+++ b/2003/netfilter-programming-clt2003/ipt_workshop.h
@@ -0,0 +1,6 @@
+#ifndef _IPT_WORKSHOP_H
+#define _IPT_WORKSHOP_H
+struct ipt_ws_info {
+ u_int8_t ttl;
+};
+#endif
diff --git a/2003/netfilter-programming-clt2003/libipt_workshop.c b/2003/netfilter-programming-clt2003/libipt_workshop.c
new file mode 100644
index 0000000..6254334
--- /dev/null
+++ b/2003/netfilter-programming-clt2003/libipt_workshop.c
@@ -0,0 +1,102 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <getopt.h>
+#include <linux/netfilter_ipv4/ip_tables.h>
+#include <linux/netfilter_ipv4/ipt_workshop.h>
+
+static void help(void)
+{
+ printf(
+"workshop match v%s options:\n"
+" --ttl TTL value\n"
+, IPTABLES_VERSION);
+}
+
+static void init(struct ipt_entry_match *m, unsigned int *nfcache)
+{
+ /* caching not implemented yet */
+ *nfcache |= NFC_UNKNOWN;
+}
+
+static int parse(int c, char **argv, int invert, unsigned int *flags,
+ const struct ipt_entry *entry, unsigned int *nfcache,
+ struct ipt_entry_match **match)
+{
+ struct ipt_ws_info *info = (struct ipt_ws_info *) (*match)->data;
+
+ check_inverse(optarg, &invert, &optind, 0);
+
+ if (invert)
+ exit_error(PARAMETER_PROBLEM, "invert not supported");
+
+ if (*flags)
+ exit_error(PARAMETER_PROBLEM,
+ "workshop: can't specify parameter twice");
+
+ if (!optarg)
+ exit_error(PARAMETER_PROBLEM,
+ "workshop: you must specify a value");
+
+ switch (c) {
+ case 'z':
+ info->ttl = atoi(optarg);
+ /* FIXME: range 0-255 */
+ *flags = 1;
+ break;
+ default:
+ return 0;
+ }
+
+ return 1;
+}
+
+static void final_check(unsigned int flags)
+{
+ if (!flags)
+ exit_error(PARAMETER_PROBLEM,
+ "workshop match: you must specify foo");
+}
+
+static void print(const struct ipt_ip *ip,
+ const struct ipt_entry_match *match,
+ int numeric)
+{
+ const struct ipt_ws_info *info = (struct ipt_ws_info *) match->data;
+
+ printf("workshop match TTL=%u ", info->ttl);
+
+}
+
+static void save(const struct ipt_ip *ip,
+ const struct ipt_entry_match *match)
+{
+ const struct ipt_ws_info *info = (struct ipt_ws_info *) match->data;
+
+ printf("--ttl %u ", info->ttl);
+}
+
+static struct option opts[] = {
+ { "ttl", 1, 0, 'z' },
+ { 0 }
+};
+
+static struct iptables_match ws = {
+ .next = NULL,
+ .name = "workshop",
+ .version = IPTABLES_VERSION,
+ .size = IPT_ALIGN(sizeof(struct ipt_ws_info)),
+ .userspacesize = IPT_ALIGN(sizeof(struct ipt_ws_info)),
+ .help = &help,
+ .init = &init,
+ .parse = &parse,
+ .final_check = &final_check,
+ .print = &print,
+ .save = &save,
+ .extra_opts = opts
+};
+
+void _init(void)
+{
+ register_match(&ws);
+}
diff --git a/2003/netfilter-programming-clt2003/netfilter-programming-clt2003.mgp b/2003/netfilter-programming-clt2003/netfilter-programming-clt2003.mgp
new file mode 100644
index 0000000..e700cf8
--- /dev/null
+++ b/2003/netfilter-programming-clt2003/netfilter-programming-clt2003.mgp
@@ -0,0 +1,636 @@
+%include "default.mgp"
+%default 1 bgrad
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%deffont "typewriter" tfont "MONOTYPE.TTF"
+%page
+%nodefault
+%back "blue"
+
+%center
+%size 7
+
+
+Programming netfilter/iptables
+extensions
+
+
+%center
+%size 4
+by
+
+Harald Welte <laforge@netfilter.org>
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+The netfilter/iptables architecture
+Contents
+
+
+ Introduction
+ The netfilter/iptables architecture
+ Netfilter hooks in protocol stacks
+ Packet selection based on IP Tables
+ The Connection Tracking Subsystem
+ The NAT Subsystem based on netfilter + iptables
+ Packet filtering using the 'filter' table
+ Packet mangling using the 'mangle' table
+ Advanced netfilter concepts
+ Current development and Future
+ Developing a netfilter module
+ Developing a new iptables match
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+The netfilter/iptables architecture
+Introduction
+
+Why did we need netfilter/iptables?
+Because ipchains...
+
+ has no infrastructure for passing packets to userspace
+ makes transparent proxying extremely difficult
+ has interface address dependent Packet filter rules
+ has Masquerading implemented as part of packet filtering
+ code is too complex and intermixed with core ipv4 stack
+ is neither modular nor extensible
+ only barely supports one special case of NAT (masquerading)
+ has only stateless packet filtering
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+The netfilter/iptables architecture
+Introduction
+
+Who's behind netfilter/iptables
+ Paul 'Rusty' Russel
+ co-author of iptables in Linux 2.2
+ was paid by Watchguard for about one Year of development
+ James Morris
+ userspace queuing (kernel, library and tools)
+ REJECT target
+ Marc Boucher
+ NAT and packet filtering controlled by one command
+ Mangle table
+ Harald Welte
+ Conntrack+NAT helper infrastructure (newnat)
+ Userspace packet logging (ULOG)
+ PPTP and IRC conntrack/NAT helpers
+ Jozsef Kadlecsik
+ TCP window tracking
+ H.323 conntrack + NAT helper
+ Continued newnat development
+ Non-core team contributors
+ http://www.netfilter.org/scoreboard/
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+The netfilter/iptables architecture
+Netfilter Hooks
+
+What is netfilter?
+
+ System of callback functions within network stack
+ Callback function to be called for every packet traversing certain point (hook) within network stack
+ Protocol independent framework
+ Hooks in layer 3 stacks (IPv4, IPv6, DECnet, ARP)
+ Multiple kernel modules can register with each of the hooks
+ Asynchronous packet handling in userspace (ip_queue)
+
+Traditional packet filtering, NAT, ... is implemented on top of this framework
+
+Can be used for other stuff interfacing with the core network stack, like DECnet routing daemon.
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+The netfilter/iptables architecture
+Netfilter Hooks
+
+Netfilter architecture in IPv4
+%font "typewriter"
+
+ --->[1]--->[ROUTE]--->[3]--->[4]--->
+ | ^
+ | |
+ | [ROUTE]
+ v |
+ [2] [5]
+ | ^
+ | |
+ v |
+
+%font "standard"
+1=NF_IP_PRE_ROUTING
+2=NF_IP_LOCAL_IN
+3=NF_IP_FORWARD
+4=NF_IP_POST_ROUTING
+5=NF_IP_LOCAL_OUT
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+The netfilter/iptables architecture
+Netfilter Hooks
+
+Netfilter Hooks
+
+ Any kernel module may register a callback function at any of the hooks
+
+ The module has to return one of the following constants
+
+ NF_ACCEPT continue traversal as normal
+ NF_DROP drop the packet, do not continue
+ NF_STOLEN I've taken over the packet do not continue
+ NF_QUEUE enqueue packet to userspace
+ NF_REPEAT call this hook again
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+The netfilter/iptables architecture
+IP tables
+
+Packet selection using IP tables
+
+ The kernel provides generic IP tables support
+
+ Each kernel module may create it's own IP table
+
+ The three major parts of 2.4 firewalling subsystem are implemented using IP tables
+ Packet filtering table 'filter'
+ NAT table 'nat'
+ Packet mangling table 'mangle'
+
+ Can potentially be used for other stuff, i.e. IPsec SPDB
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+The netfilter/iptables architecture
+IP Tables
+
+Managing chains and tables
+
+ An IP table consists out of multiple chains
+ A chain consists out of a list of rules
+ Every single rule in a chain consists out of
+ match[es] (rule executed if all matches true)
+ target (what to do if the rule is matched)
+
+%size 4
+matches and targets can either be builtin or implemented as kernel modules
+
+%size 6
+ The userspace tool iptables is used to control IP tables
+ handles all different kinds of IP tables
+ supports a plugin/shlib interface for target/match specific options
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+The netfilter/iptables architecture
+IP Tables
+
+Basic iptables commands
+
+ To build a complete iptables command, we must specify
+ which table to work with
+ which chain in this table to use
+ an operation (insert, add, delete, modify)
+ one or more matches (optional)
+ a target
+
+The syntax is
+%font "typewriter"
+%size 3
+iptables -t table -Operation chain -j target match(es)
+%font "standard"
+%size 5
+
+Example:
+%font "typewriter"
+%size 3
+iptables -t filter -A INPUT -j ACCEPT -p tcp --dport smtp
+%font "standard"
+%size 5
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+The netfilter/iptables architecture
+IP Tables
+
+Matches
+ Basic matches
+ -p protocol (tcp/udp/icmp/...)
+ -s source address (ip/mask)
+ -d destination address (ip/mask)
+ -i incoming interface
+ -o outgoing interface
+
+ Match extensions (examples)
+ tcp/udp TCP/udp source/destination port
+ icmp ICMP code/type
+ ah/esp AH/ESP SPID match
+ mac source MAC address
+ mark nfmark
+ length match on length of packet
+ limit rate limiting (n packets per timeframe)
+ owner owner uid of the socket sending the packet
+ tos TOS field of IP header
+ ttl TTL field of IP header
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+The netfilter/iptables architecture
+IP Tables
+
+Targets
+ very dependent on the particular table.
+
+ Table specific targets will be discussed later
+
+ Generic Targets, always available
+ ACCEPT accept packet within chain
+ DROP silently drop packet
+ QUEUE enqueue packet to userspace
+ LOG log packet via syslog
+ ULOG log packet via ulogd
+ RETURN return to previous (calling) chain
+ foobar jump to user defined chain
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+The netfilter/iptables architecture
+Packet Filtering
+
+Overview
+
+ Implemented as 'filter' table
+ Registers with three netfilter hooks
+
+ NF_IP_LOCAL_IN (packets destined for the local host)
+ NF_IP_FORWARD (packets forwarded by local host)
+ NF_IP_LOCAL_OUT (packets from the local host)
+
+Each of the three hooks has attached one chain (INPUT, FORWARD, OUTPUT)
+
+Every packet passes exactly one of the three chains. Note that this is very different compared to the old 2.2.x ipchains behaviour.
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+The netfilter/iptables architecture
+Packet Filtering
+
+Targets available within 'filter' table
+
+ Builtin Targets to be used in filter table
+ ACCEPT accept the packet
+ DROP silently drop the packet
+ QUEUE enqueue packet to userspace
+ RETURN return to previous (calling) chain
+ foobar user defined chain
+
+ Targets implemented as loadable modules
+ REJECT drop the packet but inform sender
+ MIRROR change source/destination IP and resend
+ LOG log via syslog
+ ULOG log via userspace
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+The netfilter/iptables architecture
+Connection Tracking Subsystem
+
+ Connection tracking...
+
+ implemented seperately from NAT
+ enables stateful filtering
+ implementation
+ hooks into NF_IP_PRE_ROUTING to track packets
+ hooks into NF_IP_POST_ROUTING and NF_IP_LOCAL_IN to see if packet passed filtering rules
+ protocol modules (currently TCP/UDP/ICMP)
+ application helpers currently (FTP,IRC,H.323,talk,SNMP)
+ divides packets in the following four categories
+ NEW - would establish new connection
+ ESTABLISHED - part of already established connection
+ RELATED - is related to established connection
+ INVALID - (multicast, errors...)
+ does _NOT_ filter packets itself
+ can be utilized by iptables using the 'state' match
+ is used by NAT Subsystem
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+HA for netfillter/iptables
+Connection Tracking Subsystem
+
+Common structures
+ struct ip_conntrack_tuple, representing unidirectional flow
+ layer 3 src + dst
+ layer 4 protocol
+ layer 4 src + dst
+
+
+ connetions represented as struct ip_conntrack
+ original tuple
+ reply tuple
+ timeout
+ l4 state private data
+ app helper
+ app helper private data
+ expected connections
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+HA for netfillter/iptables
+Connection Tracking Subsystem
+
+Flow of events for new packet
+ packet enters NF_IP_PRE_ROUTING
+ tuple is derived from packet
+ lookup conntrack hash table with hash(tuple) -> fails
+ new ip_conntrack is allocated
+ fill in original and reply == inverted(original) tuple
+ initialize timer
+ assign app helper if applicable
+ see if we've been expected -> fails
+ call layer 4 helper 'new' function
+
+ ...
+
+ packet enters NF_IP_POST_ROUTING
+ do hashtable lookup for packet -> fails
+ place struct ip_conntrack in hashtable
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+HA for netfillter/iptables
+Connection Tracking Subsystem
+
+Flow of events for packet part of existing connection
+ packet enters NF_IP_PRE_ROUTING
+ tuple is derived from packet
+ lookup conntrack hash table with hash(tuple)
+ assosiate conntrack entry with skb->nfct
+ call l4 protocol helper 'packet' function
+ do l4 state tracking
+ update timeouts as needed [i.e. TCP TIME_WAIT,...]
+
+ ...
+
+ packet enters NF_IP_POST_ROUTING
+ do hashtable lookup for packet -> succeds
+ do nothing else
+
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+The netfilter/iptables architecture
+Network Address Translation
+
+Overview
+
+ Previous Linux Kernels only implemented one special case of NAT: Masquerading
+ Linux 2.4.x can do any kind of NAT.
+ NAT subsystem implemented on top of netfilter, iptables and conntrack
+ NAT subsystem registers with all five netfilter hooks
+ 'nat' Table registers chains PREROUTING, POSTROUTING and OUTPUT
+ Following targets available within 'nat' Table
+ SNAT changes the packet's source whille passing NF_IP_POST_ROUTING
+ DNAT changes the packet's destination while passing NF_IP_PRE_ROUTING
+ MASQUERADE is a special case of SNAT
+ REDIRECT is a special case of DNAT
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+The netfilter/iptables architecture
+Network Address Translation
+
+flow of events for NEW packet:
+ packet enters NF_IP_PRE_ROUTING after conntrack
+ resolve conntrack entry for packet
+ if (expectfn of helper) call it
+ else iterate over rules in PREROUTING chain of nat table
+ save respective NAT mappings in conntrack
+ apply the NAT mappings to the packet
+ call NAT helper function, if there is one for this proto
+
+ ...
+
+ packet enters NF_IP_POST_ROUTING
+ resolve conntrack entry for packet
+ iterate over rules in POSTROUTING chain of nat table
+ save respectiva NAT mappings in conntrack
+ apply the NAT mappings to the packet
+ call NAT helper function, if there is one for this proto
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+The netfilter/iptables architecture
+Network Address Translation
+
+flow of events for ESTABLISHED packets:
+ packet enters NF_IP_PRE_ROUTING after conntrack
+ reseolve conntrack entry for packet
+ apply the NAT mappings (read from conntrack entry) to the packet
+ call NAT helper function, if there is one for this proto
+
+ ...
+
+ packet enters NF_IP_POST_ROUTING
+ resolve conntrack entry for packet
+ apply the NAT mappings (read from conntrack entry) to the packet
+ call NAT helper function, if there is one for this proto
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+The netfilter/iptables architecture
+Network Address Translation
+
+ Source NAT
+ SNAT Example:
+%font "typewriter"
+%size 3
+iptables -t nat -A POSTROUTING -j SNAT --to-source 1.2.3.4 -s 10.0.0.0/8
+%font "standard"
+%size 4
+
+ MASQUERADE Example:
+%font "typewriter"
+%size 3
+iptables -t nat -A POSTROUTING -j MASQUERADE -o ppp0
+%font "standard"
+%size 5
+
+ Destination NAT
+ DNAT example
+%font "typewriter"
+%size 3
+iptables -t nat -A PREROUTING -j DNAT --to-destination 1.2.3.4:8080 -p tcp --dport 80 -i eth1
+%font "standard"
+%size 4
+
+ REDIRECT example
+%font "typewriter"
+%size 3
+iptables -t nat -A PREROUTING -j REDIRECT --to-port 3128 -i eth1 -p tcp --dport 80
+%font "standard"
+%size 5
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+The netfilter/iptables architecture
+Packet Mangling
+
+ Purpose of mangle table
+ packet manipulation except address manipulation
+
+ Integration with netfilter
+ 'mangle' table hooks in all five netfilter hooks
+ priority: after conntrack
+
+ Targets specific to the 'mangle' table:
+ DSCP - manipulate DSCP field
+ IPV4OPTSSTRIP - strip IPv4 options
+ MARK - change the nfmark field of the skb
+ TCPMSS - set TCP MSS option
+ TOS - manipulate the TOS bits
+ TTL - set / increase / decrease TTL field
+
+Simple example:
+%font "typewriter"
+%size 3
+iptables -t mangle -A PREROUTING -j MARK --set-mark 10 -p tcp --dport 80
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+The netfilter/iptables architecture
+Advanced Netfilter concepts
+
+%size 4
+ Userspace logging
+ flexible replacement for old syslog-based logging
+ packets to userspace via multicast netlink sockets
+ easy-to-use library (libipulog)
+ plugin-extensible userspace logging daemon (ulogd)
+ Can even be used to directly log into MySQL
+
+ Queuing
+ reliable asynchronous packet handling
+ packets to userspace via unicast netlink socket
+ easy-to-use library (libipq)
+ provides Perl bindings
+ experimental queue multiplex daemon (ipqmpd)
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+The netfilter/iptables architecture
+Current Development and Future
+
+Netfilter (although it proved very stable) is still work in progress.
+
+ Areas of current development
+ infrastructure for conntrack manipulation from userspace
+ failover of stateful firewalls
+ making iptables layer3 independent (pkttables)
+ new userspace library (libiptables) to hide plugins from apps
+ more matches and targets for advanced functions (pool, hashslot)
+ more conntrack and NAT modules (RPC, SNMP, SMB, ...)
+ better IPv6 support (conntrack, more matches / targets)
+ conntrack hash optimizations
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+Developing netfilter/iptables extensions
+Developing a netfilter module
+
+ Netfilter modules are very low-layer
+ Get called for every packet passing the hook in this l3prot
+ Examples of netfilter modules are: ip_tables, ip_conntrack, iptable_nat
+ API for netfilter <linux/netfilter.h>:
+%font "typewriter"
+ nf_register_hook(struct nf_hook_ops *reg)
+ nf_unregister_hook(struct nf_hook_ops *reg)
+ struct nf_hook_ops:
+ struct list_head list; /* list header {NULL,NULL}) */
+ nf_hookfn *hook; /* the callback function */
+ int pf; /* protocol family */
+ int hooknum; /* hook to register with */
+ int priority; /* priority, determines order */
+%font "standard"
+ Example code see "nf_workshop.c"
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+Developing netfilter/iptables extensions
+Developing an ip_tables match module
+
+ ip_tables modules are at a high layer
+ Get called for every packet iterating a rule with this match
+ Examples of iptables modules are: ipt_ttl, ipt_tos, ipt_tcpmss
+ API for iptables matches <linux/netfilter_ipv4/ip_tables.h>:
+%font "typewriter"
+ ipt_register_match(struct ipt_match *match)
+ ipt_unregister_match(struct ipt_match *match)
+ struct ipt_match:
+ struct list_head list; /* list header {NULL,NULL} */
+ const char name[]; /* name of the match */
+ int (*match); /* called when pkt is matched */
+ int (*checkentry); /* called when entry inserted */
+ void (*destroy); /* called when entry deleted */
+ struct modulea *me; /* set to THIS_MODULE */
+%font "standard"
+ Example code see "ipt_workshop.c"
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+Developing netfilter/iptables extensions
+Developing an iptables match module
+
+ Something has to parse the commandline optins for ipt_workshop.c
+ Solution: libpt_workshop.c as iptables plugin
+ API for iptables-command plugins <iptables.h>:
+%font "typewriter"
+ register_match(struct iptables_match)
+ struct iptables_match:
+ struct iptables_match *next; /* next one */
+ ipt_chainlabel name; /* name */
+ const char *version; /* version */
+ size_t size; /* size of match data */
+ size_t userspacesize; /* size for userspace */
+ void (*help); /* print help message */
+ void (*init); /* init the matchinfo */
+ int (*parse); /* parse getopt chars */
+ void (*final_check); /* consistency check */
+ void (*print); /* print (iptables -L) */
+ void (*save); /* iptables-save */
+ struct option extra_opts; /* getopt-style opts */
+%font "typewriter"
+ Example code see "libipt_workshop.c"
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+Future of Linux packet filtering
+Thanks
+ The slides and the an according paper of this presentation are available at http://www.gnumonks.org/
+
+ The netfilter homepage http://www.netfilter.org/
+
+ Thanks to
+ the BBS people, Z-Netz, FIDO, ...
+ for heavily increasing my computer usage in 1992
+ KNF
+ for bringing me in touch with the internet as early as 1994
+ for providing a playground for technical people
+ for telling me about the existance of Linux!
+ Alan Cox, Alexey Kuznetsov, David Miller, Andi Kleen
+ for implementing (one of?) the world's best TCP/IP stacks
+ Paul 'Rusty' Russell
+ for starting the netfilter/iptables project
+ for trusting me to maintain it today
+ Astaro AG
+ for sponsoring parts of my netfilter work
+ for sponsoring my travel cost to 5CLT
+
diff --git a/2003/netfilter-programming-clt2003/nf_workshop.c b/2003/netfilter-programming-clt2003/nf_workshop.c
new file mode 100644
index 0000000..7ea8520
--- /dev/null
+++ b/2003/netfilter-programming-clt2003/nf_workshop.c
@@ -0,0 +1,57 @@
+#include <linux/module.h>
+#include <linux/config.h>
+#include <linux/skbuff.h>
+#include <linux/ip.h>
+
+#include <linux/netfilter.h>
+#include <linux/netfilter_ipv4.h>
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
+MODULE_DESCRIPTION("5CLT workshop module");
+
+static unsigned int
+workshop_fn(unsigned int hooknum,
+ struct sk_buff **pskb,
+ const struct net_device *in,
+ const struct net_device *out,
+ int (*okfn)(struct sk_buff *))
+{
+ struct iphdr *iph = (*pskb)->nh.iph;
+ /* do whatever we want to do */
+
+ printk(KERN_NOTICE "packet from %u.%u.%u.%u received\n",
+ NIPQUAD(iph->saddr));
+
+ return NF_ACCEPT;
+}
+
+static struct nf_hook_ops workshop_ops = {
+ .list = { .prev = NULL, .next = NULL },
+ .hook = &workshop_fn,
+ .pf = PF_INET,
+ .hooknum = NF_IP_PRE_ROUTING,
+ .priority = NF_IP_PRI_LAST-1
+};
+
+static int __init init(void)
+{
+ int ret = 0;
+
+ ret = nf_register_hook(&workshop_ops);
+ if (ret < 0) {
+ printk(KERN_ERR "something went wrong while registering\n");
+ return ret;
+ }
+
+ printk(KERN_DEBUG "workshop netfilter module successfully loaded\n");
+ return ret;
+}
+
+static void __exit fini(void)
+{
+ nf_unregister_hook(&workshop_ops);
+}
+
+module_init(init);
+module_exit(fini);
personal git repositories of Harald Welte. Your mileage may vary