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Diffstat (limited to '2002/netfilter-curdevel-lk2002')
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diff --git a/2002/netfilter-curdevel-lk2002/netfilter-curdevel-lk2002.mgp b/2002/netfilter-curdevel-lk2002/netfilter-curdevel-lk2002.mgp new file mode 100644 index 0000000..987162b --- /dev/null +++ b/2002/netfilter-curdevel-lk2002/netfilter-curdevel-lk2002.mgp @@ -0,0 +1,374 @@ +%include "default.mgp" +%default 1 bgrad +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +%nodefault +%back "blue" + +%center +%size 7 + + +The future of Linux packet filtering +targeted for kernel 2.6 and beyond + + +%center +%size 4 +by + +Harald Welte <laforge@gnumonks.org> + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +Future of Linux packet filtering +Contents + + + Problems with current 2.4.x netfilter/iptables + Solution to code replication + Solution for dynamic rulesets + Solution for API to GUI's and other management programs + + HA for stateful firewalling + What's special about firewalling HA + Poor man's failover + Real state replication + + Other current work + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +Future of Linux packet filtering +Problems with 2.4.x netfilter/iptables + + code replication between iptables/ip6tables/arptables + iptables was never meant for other protocols, but people did copy+paste 'ports' + replication of + core kernel code + layer 3 independent matches (mac, interface, ...) + userspace library (libiptc) + userspace tool (iptables) + userspace plugins (libipt_xxx.so) + + doesn't suit the needs for dynamically changing rulesets + dynamic rulesets becomming more common due (service selection, IDS) + a whole table is created in userspace and sent as blob to kernel + for every ruleset the table needs to be copied to userspace and back + inside kernel consistency checks on whole table, loop detection + + too extensible for writing any forward-compatible GUI + new extensions showing up all the time + a frontend would need to know about the options and use of a new extension + thus frontends are always incomplete and out-of-date + no high-level API other than piping to iptables-restore + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +Future of Linux packet filtering +Reducing code replication + + code replication is a real problem: unclean, bugfixes missed + we need layer 3 independent layer for + submitting rules to the kernel + traversing packet-rulesets supporting match/target modules + registering matches/targets + layer 3 specific (like matching ipv4 address) + layer 3 independent (like matching MAC address) + + solution + pkt_tables inside kernel + pkt_tables_ipv4 registers layer 3 handler with pkt_tables + pkt_tables_ipv6 registers layer 3 handler with pkt_tables + everybody registering a pkt_table (like iptable_filter) needs to specify the l3 protocol + libraries in userspace (see later) + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +Future of Linux packet filtering +Supporting dynamic rulesets + + atomic table-replacement turned out to be bad idea + need new interface for sending individual rules to kernel + policy routing has the same problem and good solution: rtnetlink + solution: nfnetlink + multicast-netlink based packet-orinented socket between kernel and userspace + has extra benefit that other userspace processes get notified of rule changes [just like routing daemons] + nfnetlink is a low-layer below all kernel/userspace communication + pkttnetlink [aka iptnetlink] + ctnetlink + ulog + ip_queue + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +Future of Linux packet filtering +Communication with other programs + +whole set of libraries + libnfnetlink for low-layer communication + libpkttnetlink for rule modifications + will handle all plugins [which are currently part of iptables] + query functions about avaliable matches/targets + query functions about parameters + query functions for help messages about specific match/parameter of a match + generic structure from which rules can be built + conversion functions to parse generic structure into in-kernel structure + conversion functiosn to perse kernel structure into generic structure + functions to convert generic structure in plain text + libipq will stay API-compatible to current version + libipulog will stay API-compatible to current version + libiptc will go away [compatibility layer extremely difficult] + + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +HA for netfillter/iptables +Introduction + +What is special about firewall failover? + + Nothing, in case of the stateless packet filter + Common IP takeover solutions can be used + VRRP + Hartbeat + + Distribution of packet filtering ruleset no problem + can be done manually + or implemented with simple userspace process + + Problems arise with stateful packet filters + Connection state only on active node + NAT mappings only on active node + + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +HA for netfillter/iptables +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 +HA for netfillter/iptables +Poor man's failover + +Poor man's failover + principle + let every node do it's own tracking rather than replicating state + two possible implementations + connect every node to shared media (i.e. real ethernet) + forwarding only turned on on active node + slave nodes use promiscuous mode to sniff packets + copy all traffic to slave nodes + active master needs to copy all traffic to other nodes + disadvantage: high load, sync traffic == payload traffic + IMHO stupid way of solving the problem + advantages + very easy implementation + only addition of sniffing mode to conntrack needed + existing means of address takeover can be used + same load on active master and slave nodes + no additional load on active master + disadvantages + can only be used with real shared media (no switches, ...) + can not be used with NAT + remaining problem + no initial state sync after reboot of slave node! + + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +HA for netfillter/iptables +Real state replication + +Parts needed + state replication protocol + multicast based + sequence numbers for detection of packet loss + NACK-based retransmission + no security, since private ethernet segment to be used + event interface on active node + calling out to callback function at all state changes + exported interface to manipulate conntrack hash table + kernel thread for sending conntrack state protocol messages + registers with event interface + creates and accumulates state replication packets + sends them via in-kernel sockets api + kernel thread for receiving conntrack state replication messages + receives state replication packets via in-kernel sockets + uses conntrack hashtable manipulation interface + + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +HA for netfillter/iptables +Real state replication + + Flow of events in chronological order: + on active node, inside the network RX softirq + connection tracking code is analyzing a forwarded packet + connection tracking gathers some new state information + connection tracking updates local connection tracking database + connection tracking sends event message to event API + on active node, inside the conntrack-sync kernel thread + conntrack sync daemon receives event through event API + conntrack sync daemon aggregates multiple event messages into a state replication protocol message, removing possible redundancy + conntrack sync daemon generates state replication protocol message + conntrack sync daemon sends state replication protocol message + on slave node(s), inside network RX softirq + connection tracking code ignores packets coming from the interface attached to the private conntrac sync network + state replication protocol messages is appended to socket receive queue of conntrack-sync kernel thread + on slave node(s), inside conntrack-sync kernel thread + conntrack sync daemon receives state replication message + conntrack sync daemon creates/updates conntrack entry + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +HA for netfillter/iptables +Neccessary changes to kernel + +Neccessary changes to current conntrack core + + event generation (callback functions) for all state changes + + conntrack hashtable manipulation API + is needed (and already implemented) for 'ctnetlink' API + + conntrack exemptions + needed to _not_ track conntrack state replication packets + is needed for other cases as well + currently being developed by Jozsef Kadlecsik + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +HA for netfillter/iptables +Other current work + + optimizing the conntrack code + hash function optimization + current hash function not good for even hash bucket count + other hash functions in development + hash function evaluation tool [cttest] avaliable + introduce per-system randomness to prevent hash attack + code optimization (locking/timers/...) + + getting our work submitted into the mainstream kernel + turns out to be more difficult + e.g. newnat api now waiting for three months + + discussions about multiple targets/actions per rule + technical implementation easy + however, not everybody convinced that it fits into the concept + + using tc for firewalling + Jamal Hadi Selim uses iptables targets from within TC + leads to discussion of generic classification engine API in kernel + + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%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 + |