bridge: use br_port_get_rtnl within rtnl lock

current br_port_get_rcu is problematic in bridging path
(NULL deref). Change these calls in netlink path first.
Signed-off-by: Hong Zhiguo <zhiguohong@tencent.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/br_netlink.c

@@ -207,7 +207,7 @@ int br_getlink(struct sk_buff *skb, u32 pid, u32 seq,
 	       struct net_device *dev, u32 filter_mask)
 {
 	int err = 0;
-	struct net_bridge_port *port = br_port_get_rcu(dev);
+	struct net_bridge_port *port = br_port_get_rtnl(dev);
 
 	/* not a bridge port and  */
 	if (!port && !(filter_mask & RTEXT_FILTER_BRVLAN))
@@ -451,7 +451,7 @@ static size_t br_get_link_af_size(const struct net_device *dev)
 	struct net_port_vlans *pv;
 
 	if (br_port_exists(dev))
-		pv = nbp_get_vlan_info(br_port_get_rcu(dev));
+		pv = nbp_get_vlan_info(br_port_get_rtnl(dev));
 	else if (dev->priv_flags & IFF_EBRIDGE)
 		pv = br_get_vlan_info((struct net_bridge *)netdev_priv(dev));
 	else

net/bridge/br_private.h

@@ -208,7 +208,7 @@ static inline struct net_bridge_port *br_port_get_rcu(const struct net_device *d
 	return br_port_exists(dev) ? port : NULL;
 }
 
-static inline struct net_bridge_port *br_port_get_rtnl(struct net_device *dev)
+static inline struct net_bridge_port *br_port_get_rtnl(const struct net_device *dev)
 {
 	return br_port_exists(dev) ?
 		rtnl_dereference(dev->rx_handler_data) : NULL;