netfilter: ctnetlink: make event listener tracking global

pernet tracking doesn't work correctly because other netns might have
set NETLINK_LISTEN_ALL_NSID on its event socket.

In this case its expected that events originating in other net
namespaces are also received.

Making pernet-tracking work while also honoring NETLINK_LISTEN_ALL_NSID
requires much more intrusive changes both in netlink and nfnetlink,
f.e. adding a 'setsockopt' callback that lets nfnetlink know that the
event socket entered (or left) ALL_NSID mode.

Move to global tracking instead: if there is an event socket anywhere
on the system, all net namespaces which have conntrack enabled and
use autobind mode will allocate the ecache extension.

netlink_has_listeners() returns false only if the given group has no
subscribers in any net namespace, the 'net' argument passed to
nfnetlink_has_listeners is only used to derive the protocol (nfnetlink),
it has no other effect.

For proper NETLINK_LISTEN_ALL_NSID-aware pernet tracking of event
listeners a new netlink_has_net_listeners() is also needed.

Fixes: 90d1daa45849 ("netfilter: conntrack: add nf_conntrack_events autodetect mode")
Reported-by: Bryce Kahle <bryce.kahle@datadoghq.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/include/linux/netfilter.h b/include/linux/netfilter.h
index d8817d381c14..bef8db9d6c08 100644
--- a/include/linux/netfilter.h
+++ b/include/linux/netfilter.h
@@ -488,4 +488,9 @@ extern const struct nfnl_ct_hook __rcu *nfnl_ct_hook;
  */
 DECLARE_PER_CPU(bool, nf_skb_duplicated);
 
+/**
+ * Contains bitmask of ctnetlink event subscribers, if any.
+ * Can't be pernet due to NETLINK_LISTEN_ALL_NSID setsockopt flag.
+ */
+extern u8 nf_ctnetlink_has_listener;
 #endif /*__LINUX_NETFILTER_H*/