netfilter: nf_ct_helper: allow to disable automatic helper assignment

This patch allows you to disable automatic conntrack helper
lookup based on TCP/UDP ports, eg.

echo 0 > /proc/sys/net/netfilter/nf_conntrack_helper

[ Note: flows that already got a helper will keep using it even
  if automatic helper assignment has been disabled ]

Once this behaviour has been disabled, you have to explicitly
use the iptables CT target to attach helper to flows.

There are good reasons to stop supporting automatic helper
assignment, for further information, please read:

http://www.netfilter.org/news.html#2012-04-03

This patch also adds one message to inform that automatic helper
assignment is deprecated and it will be removed soon (this is
spotted only once, with the first flow that gets a helper attached
to make it as less annoying as possible).

Signed-off-by: Eric Leblond <eric@regit.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/include/net/netns/conntrack.h b/include/net/netns/conntrack.h
index 7a911ec..a053a19 100644
--- a/include/net/netns/conntrack.h
+++ b/include/net/netns/conntrack.h
@@ -26,11 +26,14 @@
 	int			sysctl_tstamp;
 	int			sysctl_checksum;
 	unsigned int		sysctl_log_invalid; /* Log invalid packets */
+	int			sysctl_auto_assign_helper;
+	bool			auto_assign_helper_warned;
 #ifdef CONFIG_SYSCTL
 	struct ctl_table_header	*sysctl_header;
 	struct ctl_table_header	*acct_sysctl_header;
 	struct ctl_table_header	*tstamp_sysctl_header;
 	struct ctl_table_header	*event_sysctl_header;
+	struct ctl_table_header	*helper_sysctl_header;
 #endif
 	char			*slabname;
 };