netfilter: bridge: use rcu hook to resolve br_netfilter dependency

e5de75b ("netfilter: bridge: move DNAT helper to br_netfilter") results
in the following link problem:

net/bridge/br_device.c:29: undefined reference to `br_nf_prerouting_finish_bridge`

Moreover it creates a hard dependency between br_netfilter and the
bridge core, which is what we've been trying to avoid so far.

Resolve this problem by using a hook structure so we reduce #ifdef
pollution and keep bridge netfilter specific code under br_netfilter.c
which was the original intention.

Reported-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 6 insertions, 1 deletions

diff --git a/net/bridge/br_device.c b/net/bridge/br_device.c
index 294cbcc49263..4ff77a16956c 100644
--- a/net/bridge/br_device.c
+++ b/net/bridge/br_device.c
@@ -25,6 +25,9 @@
 #define COMMON_FEATURES (NETIF_F_SG | NETIF_F_FRAGLIST | NETIF_F_HIGHDMA | \
                          NETIF_F_GSO_MASK | NETIF_F_HW_CSUM)
 
+const struct nf_br_ops __rcu *nf_br_ops __read_mostly;
+EXPORT_SYMBOL_GPL(nf_br_ops);
+
 /* net device transmit always called with BH disabled */
 netdev_tx_t br_dev_xmit(struct sk_buff *skb, struct net_device *dev)
 {
@@ -33,10 +36,12 @@ netdev_tx_t br_dev_xmit(struct sk_buff *skb, struct net_device *dev)
         struct net_bridge_fdb_entry *dst;
         struct net_bridge_mdb_entry *mdst;
         struct pcpu_sw_netstats *brstats = this_cpu_ptr(br->stats);
+        const struct nf_br_ops *nf_ops;
         u16 vid = 0;
 
         rcu_read_lock();
-        if (br_nf_prerouting_finish_bridge(skb)) {
+        nf_ops = rcu_dereference(nf_br_ops);
+        if (nf_ops && nf_ops->br_dev_xmit_hook(skb)) {
                 rcu_read_unlock();
                 return NETDEV_TX_OK;
         }