diff options
Diffstat (limited to '2003/netfilter-internals-kiblix2003')
| -rw-r--r-- | 2003/netfilter-internals-kiblix2003/abstract | 49 | ||||
| -rw-r--r-- | 2003/netfilter-internals-kiblix2003/biography | 22 | ||||
| -rw-r--r-- | 2003/netfilter-internals-kiblix2003/netfilter-internals-kiblix2003.mgp | 509 |
3 files changed, 580 insertions, 0 deletions
diff --git a/2003/netfilter-internals-kiblix2003/abstract b/2003/netfilter-internals-kiblix2003/abstract new file mode 100644 index 0000000..56a19a5 --- /dev/null +++ b/2003/netfilter-internals-kiblix2003/abstract @@ -0,0 +1,49 @@ +Linux 2.4.x netfilter/iptables firewalling internals + + The Linux 2.4.x kernel series has introduced a totally new kernel firewalling subsystem. It is much more than a plain successor of ipfwadm or ipchains. + + The netfilter/iptables project has a very modular design and it's +sub-projects can be split in several parts: netfilter, iptables, connection +tracking, NAT and packet mangling. + + While most users will already have learned how to use the basic functions +of netfilter/iptables in order to convert their old ipchains firewalls to +iptables, there's more advanced but less used functionality in +netfilter/iptables. + + The presentation covers the design principles behind the netfilter/iptables +implementation. This knowledge enables us to understand how the individual +parts of netfilter/iptables fit together, and for which potential applications +this is useful. + +Topics covered: + +- overview about the internal netfilter/iptables architecture + - the netfilter hooks inside the network protocol stacks + - packet selection with IP tables + - how is connection tracking and NAT integrated into the framework +- the connection tracking system + - how good does it track the TCP state? + - how does it track ICMP and UDP state at all? + - layer 4 protocol helpers (GRE, ...) + - application helpers (ftp, irc, h323, ...) + - restrictions/limitations +- the NAT system + - how does it interact with connection tracking? + - layer 4 protocol helpers + - application helpers (ftp, irc, ...) +- misc + - how far is IPv6 firewalling with ip6tables? + - advances in failover/HA of stateful firewalls + - ivisible firewalls with iptables on a bridge + - userspace packet queueing with QUEUE + - userspace packet logging with ULOG + +Requirements: +- knowledge about the TCP/IP protocol family +- knowledge about general firewalling and packet filtering concepts +- prior experience with linux packet filters + +Audience: +- firewall administrators +- network developers diff --git a/2003/netfilter-internals-kiblix2003/biography b/2003/netfilter-internals-kiblix2003/biography new file mode 100644 index 0000000..d027c14 --- /dev/null +++ b/2003/netfilter-internals-kiblix2003/biography @@ -0,0 +1,22 @@ + <a href="http://gnumonks.org/users/laforge/">Harald Welte</a> is one +of the five <a href="http://www.netfilter.org/">netfilter/iptables</a> core +team members, and the current Linux 2.4.x firewalling maintainer. + + His main interest in computing has always been networking. In the few time +left besides netfilter/iptables related work, he's writing obscure documents +like the <a href="http://www.gnumonks.org/ftp/pub/doc/uucp-over-ssl.html"> UUCP +over SSL HOWTO</a>. Other kernel-related projects he has been contributing are +user mode linux and the international (crypto) kernel patch. + + In the past he has been working as an independent IT Consultant working on +closed-source projecst for various companies ranging from banks to +manufacturers of networking gear. During the year 2001 he was living in +Curitiba (Brazil), where he got sponsored for his Linux related work by +<a href="http://www.conectiva.com/">Conectiva Inc.</a>. + + Starting with February 2002, Harald has been contracted part-time by +<a href="http://www.astaro.com/">Astaro AG</a>, who are sponsoring him for his +current netfilter/iptables work. + + Harald is living in Berlin, Germany. + diff --git a/2003/netfilter-internals-kiblix2003/netfilter-internals-kiblix2003.mgp b/2003/netfilter-internals-kiblix2003/netfilter-internals-kiblix2003.mgp new file mode 100644 index 0000000..2aa408b --- /dev/null +++ b/2003/netfilter-internals-kiblix2003/netfilter-internals-kiblix2003.mgp @@ -0,0 +1,509 @@ +%include "default.mgp" +%default 1 bgrad +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +%nodefault +%back "blue" + +%center +%size 7 + + +Linux 2.4.x netfilter/iptables +firewalling internals + + +%center +%size 4 +by + +Harald Welte <laforge@netfilter.org> + + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables in Linux 2.4 +Contents + + + Introduction + 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 + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables in Linux 2.4 +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 +netfilter/iptables in Linux 2.4 +Introduction + +Who's behind netfilter/iptables + Paul 'Rusty' Russell + 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) + Marc Boucher + NAT and packet filtering controlled by one command + Mangle table + Harald Welte + Conntrack+NAT helper infrastructure (newnat) + Userspace packet logging (ULOG) + Jozsef Kadlecsik + TCP window tracking + H.323 conntrack + NAT helper + Non-core team contributors + http://www.netfilter.org/scoreboard/ +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables in Linux 2.4 +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 +netfilter/iptables in Linux 2.4 +Netfilter Hooks + +Netfilter architecture in IPv4 +%font "typewriter" +%size 4 + + --->[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 +netfilter/iptables in Linux 2.4 +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 +netfilter/iptables in Linux 2.4 +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 +netfilter/iptables in Linux 2.4 +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 5 + 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 +netfilter/iptables in Linux 2.4 +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 +netfilter/iptables in Linux 2.4 +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 +netfilter/iptables in Linux 2.4 +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 +netfilter/iptables in Linux 2.4 +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 +netfilter/iptables in Linux 2.4 +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 +netfilter/iptables in Linux 2.4 +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 +netfilter/iptables in Linux 2.4 +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 +netfilter/iptables in Linux 2.4 +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 +netfilter/iptables in Linux 2.4 +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 +netfilter/iptables in Linux 2.4 +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 +netfilter/iptables in Linux 2.4 +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 (conntrack sync) + 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) + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +Future of Linux packet filtering +Thanks + + 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 +%size 3 + The slides and the an according paper of this presentation are available at http://www.gnumonks.org/ +%size 3 + The netfilter homepage http://www.netfilter.org/ + |