netfilter: bridge: move br_netfilter out of the core

Jesper reported that br_netfilter always registers the hooks since
this is part of the bridge core. This harms performance for people that
don't need this.

This patch modularizes br_netfilter so it can be rmmod'ed, thus,
the hooks can be unregistered. I think the bridge netfilter should have
been a separated module since the beginning, Patrick agreed on that.

Note that this is breaking compatibility for users that expect that
bridge netfilter is going to be available after explicitly 'modprobe
bridge' or via automatic load through brctl.

However, the damage can be easily undone by modprobing br_netfilter.
The bridge core also spots a message to provide a clue to people that
didn't notice that this has been deprecated.

On top of that, the plan is that nftables will not rely on this software
layer, but integrate the connection tracking into the bridge layer to
enable stateful filtering and NAT, which is was bridge netfilter users
seem to require.

This patch still keeps the fake_dst_ops in the bridge core, since this
is required by when the bridge port is initialized. So we can safely
modprobe/rmmod br_netfilter anytime.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Acked-by: Florian Westphal <fw@strlen.de>

1 files changed, 6 insertions, 6 deletions

diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
index 62a7fa2e3569..d304d752c091 100644
--- a/net/bridge/br_private.h
+++ b/net/bridge/br_private.h
@@ -221,7 +221,7 @@ struct net_bridge
 	struct pcpu_sw_netstats		__percpu *stats;
 	spinlock_t			hash_lock;
 	struct hlist_head		hash[BR_HASH_SIZE];
-#ifdef CONFIG_BRIDGE_NETFILTER
+#if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
 	struct rtable 			fake_rtable;
 	bool				nf_call_iptables;
 	bool				nf_call_ip6tables;
@@ -751,13 +751,13 @@ static inline int br_vlan_enabled(struct net_bridge *br)
 #endif
 
 /* br_netfilter.c */
-#ifdef CONFIG_BRIDGE_NETFILTER
-int br_netfilter_init(void);
-void br_netfilter_fini(void);
+#if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
+int br_nf_core_init(void);
+void br_nf_core_fini(void);
 void br_netfilter_rtable_init(struct net_bridge *);
 #else
-#define br_netfilter_init()	(0)
-#define br_netfilter_fini()	do { } while (0)
+static inline int br_nf_core_init(void) { return 0; }
+static inline void br_nf_core_fini(void) {}
 #define br_netfilter_rtable_init(x)
 #endif