From: Florian Westphal <fw@xxxxxxxxx>
At this time, every new conntrack gets the 'event cache extension'
enabled for it.
This is because the 'net.netfilter.nf_conntrack_events' sysctl defaults
to 1.
Changing the default to 0 means that commands that rely on the event
notification extension, e.g. 'conntrack -E' or conntrackd, stop working.
We COULD detect if there is a listener by means of
'nfnetlink_has_listeners()' and only add the extension if this is true.
The downside is a dependency from conntrack module to nfnetlink module.
This adds a different way: inc/dec a counter whenever a ctnetlink group
is being (un)subscribed and toggle a flag in struct net.
Next patches will take advantage of this and will only add the event
extension if the flag is set.
Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
---
include/net/netns/conntrack.h | 1 +
net/netfilter/nfnetlink.c | 40 ++++++++++++++++++++++++++++++++---
2 files changed, 38 insertions(+), 3 deletions(-)
diff --git a/include/net/netns/conntrack.h b/include/net/netns/conntrack.h
index a71cfd4e2f21..0677cd3de034 100644
--- a/include/net/netns/conntrack.h
+++ b/include/net/netns/conntrack.h
@@ -95,6 +95,7 @@ struct nf_ip_net {
struct netns_ct {
#ifdef CONFIG_NF_CONNTRACK_EVENTS
+ bool ctnetlink_has_listener;
bool ecache_dwork_pending;
#endif
u8 sysctl_log_invalid; /* Log invalid packets */
diff --git a/net/netfilter/nfnetlink.c b/net/netfilter/nfnetlink.c
index 7e2c8dd01408..ad3bbe34ca88 100644
--- a/net/netfilter/nfnetlink.c
+++ b/net/netfilter/nfnetlink.c
@@ -45,6 +45,7 @@ MODULE_DESCRIPTION("Netfilter messages via netlink socket");
static unsigned int nfnetlink_pernet_id __read_mostly;
struct nfnl_net {
+ unsigned int ctnetlink_listeners;
struct sock *nfnl;
};
@@ -654,7 +655,6 @@ static void nfnetlink_rcv(struct sk_buff *skb)
netlink_rcv_skb(skb, nfnetlink_rcv_msg);
}
-#ifdef CONFIG_MODULES
static int nfnetlink_bind(struct net *net, int group)
{
const struct nfnetlink_subsystem *ss;
@@ -670,9 +670,44 @@ static int nfnetlink_bind(struct net *net, int group)
rcu_read_unlock();
if (!ss)
request_module_nowait("nfnetlink-subsys-%d", type);
+
+#ifdef CONFIG_NF_CONNTRACK_EVENTS
+ if (type == NFNL_SUBSYS_CTNETLINK) {
+ struct nfnl_net *nfnlnet = nfnl_pernet(net);
+
+ nfnl_lock(NFNL_SUBSYS_CTNETLINK);
+
+ if (WARN_ON_ONCE(nfnlnet->ctnetlink_listeners == UINT_MAX)) {
+ nfnl_unlock(NFNL_SUBSYS_CTNETLINK);
+ return -EOVERFLOW;
+ }
+
+ nfnlnet->ctnetlink_listeners++;
+ if (nfnlnet->ctnetlink_listeners == 1)
+ WRITE_ONCE(net->ct.ctnetlink_has_listener, true);
+ nfnl_unlock(NFNL_SUBSYS_CTNETLINK);
+ }
+#endif
return 0;
}
+
+static void nfnetlink_unbind(struct net *net, int group)
+{
+#ifdef CONFIG_NF_CONNTRACK_EVENTS
+ int type = nfnl_group2type[group];
+
+ if (type == NFNL_SUBSYS_CTNETLINK) {
+ struct nfnl_net *nfnlnet = nfnl_pernet(net);
+
+ nfnl_lock(NFNL_SUBSYS_CTNETLINK);
+ WARN_ON_ONCE(nfnlnet->ctnetlink_listeners == 0);
+ nfnlnet->ctnetlink_listeners--;
+ if (nfnlnet->ctnetlink_listeners == 0)
+ WRITE_ONCE(net->ct.ctnetlink_has_listener, false);
+ nfnl_unlock(NFNL_SUBSYS_CTNETLINK);
+ }
#endif
+}
static int __net_init nfnetlink_net_init(struct net *net)
{
@@ -680,9 +715,8 @@ static int __net_init nfnetlink_net_init(struct net *net)
struct netlink_kernel_cfg cfg = {
.groups = NFNLGRP_MAX,
.input = nfnetlink_rcv,
-#ifdef CONFIG_MODULES
.bind = nfnetlink_bind,
-#endif
+ .unbind = nfnetlink_unbind,
};
nfnlnet->nfnl = netlink_kernel_create(net, NETLINK_NETFILTER, &cfg);
--
2.30.2
