linux/include/net/netfilter
Pablo Neira Ayuso dd7669a92c netfilter: conntrack: optional reliable conntrack event delivery
This patch improves ctnetlink event reliability if one broadcast
listener has set the NETLINK_BROADCAST_ERROR socket option.

The logic is the following: if an event delivery fails, we keep
the undelivered events in the missed event cache. Once the next
packet arrives, we add the new events (if any) to the missed
events in the cache and we try a new delivery, and so on. Thus,
if ctnetlink fails to deliver an event, we try to deliver them
once we see a new packet. Therefore, we may lose state
transitions but the userspace process gets in sync at some point.

At worst case, if no events were delivered to userspace, we make
sure that destroy events are successfully delivered. Basically,
if ctnetlink fails to deliver the destroy event, we remove the
conntrack entry from the hashes and we insert them in the dying
list, which contains inactive entries. Then, the conntrack timer
is added with an extra grace timeout of random32() % 15 seconds
to trigger the event again (this grace timeout is tunable via
/proc). The use of a limited random timeout value allows
distributing the "destroy" resends, thus, avoiding accumulating
lots "destroy" events at the same time. Event delivery may
re-order but we can identify them by means of the tuple plus
the conntrack ID.

The maximum number of conntrack entries (active or inactive) is
still handled by nf_conntrack_max. Thus, we may start dropping
packets at some point if we accumulate a lot of inactive conntrack
entries that did not successfully report the destroy event to
userspace.

During my stress tests consisting of setting a very small buffer
of 2048 bytes for conntrackd and the NETLINK_BROADCAST_ERROR socket
flag, and generating lots of very small connections, I noticed
very few destroy entries on the fly waiting to be resend.

A simple way to test this patch consist of creating a lot of
entries, set a very small Netlink buffer in conntrackd (+ a patch
which is not in the git tree to set the BROADCAST_ERROR flag)
and invoke `conntrack -F'.

For expectations, no changes are introduced in this patch.
Currently, event delivery is only done for new expectations (no
events from expectation expiration, removal and confirmation).
In that case, they need a per-expectation event cache to implement
the same idea that is exposed in this patch.

This patch can be useful to provide reliable flow-accouting. We
still have to add a new conntrack extension to store the creation
and destroy time.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Patrick McHardy <kaber@trash.net>
2009-06-13 12:30:52 +02:00
..
ipv4 netfilter: nf_ct_icmp: keep the ICMP ct entries longer 2009-06-08 15:53:43 +02:00
ipv6 netfilter: nf_ct_icmp: keep the ICMP ct entries longer 2009-06-08 15:53:43 +02:00
nf_conntrack.h netfilter: conntrack: optional reliable conntrack event delivery 2009-06-13 12:30:52 +02:00
nf_conntrack_acct.h netfilter: netns nf_conntrack: per-netns conntrack accounting 2008-10-08 11:35:09 +02:00
nf_conntrack_core.h netfilter: conntrack: don't deliver events for racy packets 2009-03-16 15:06:42 +01:00
nf_conntrack_ecache.h netfilter: conntrack: optional reliable conntrack event delivery 2009-06-13 12:30:52 +02:00
nf_conntrack_expect.h netfilter: ctnetlink: fix regression in expectation handling 2009-04-06 17:47:20 +02:00
nf_conntrack_extend.h netfilter: conntrack: move event caching to conntrack extension infrastructure 2009-06-13 12:26:29 +02:00
nf_conntrack_helper.h netfilter: conntrack: move helper destruction to nf_ct_helper_destroy() 2009-06-13 12:28:22 +02:00
nf_conntrack_l3proto.h netfilter: ctnetlink: add callbacks to the per-proto nlattrs 2009-03-25 18:24:48 +01:00
nf_conntrack_l4proto.h netfilter: nf_conntrack: use per-conntrack locks for protocol data 2009-06-10 14:32:47 +02:00
nf_conntrack_tuple.h netfilter: nf_conntrack: use SLAB_DESTROY_BY_RCU and get rid of call_rcu() 2009-03-25 21:05:46 +01:00
nf_log.h netfilter: use a linked list of loggers 2009-03-16 14:54:21 +01:00
nf_nat.h netfilter: nf_nat: add support for persistent mappings 2009-04-16 18:33:01 +02:00
nf_nat_core.h netfilter: ctnetlink: remove bogus module dependency between ctnetlink and nf_nat 2008-10-14 11:58:31 -07:00
nf_nat_helper.h [NETFILTER]: nf_nat: kill helper and seq_adjust hooks 2008-04-14 11:15:52 +02:00
nf_nat_protocol.h [NETFILTER]: nf_nat: use bool type in nf_nat_proto 2008-04-14 11:15:53 +02:00
nf_nat_rule.h [NETFILTER]: nf_nat: don't add NAT extension for confirmed conntracks 2008-04-14 11:15:51 +02:00
nf_queue.h netfilter: Use unsigned types for hooknum and pf vars 2008-10-08 11:35:00 +02:00
nf_tproxy_core.h netfilter: iptables tproxy core 2008-10-08 11:35:12 +02:00
nfnetlink_log.h netfilter: nfnetlink_log: fix warning and prototype mismatch 2008-11-18 12:16:52 +01:00
xt_rateest.h [NETFILTER]: x_tables: add RATEEST target 2008-01-28 14:56:02 -08:00