rtnetlink: allow rtnl_fill_link_netnsid() to run under RCU protection

We want to be able to run rtnl_fill_ifinfo() under RCU protection
instead of RTNL in the future.

All rtnl_link_ops->get_link_net() methods already using dev_net()
are ready. I added READ_ONCE() annotations on others.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/ppp/ppp_generic.c

@@ -1357,7 +1357,7 @@ static struct net *ppp_nl_get_link_net(const struct net_device *dev)
 {
 	struct ppp *ppp = netdev_priv(dev);
 
-	return ppp->ppp_net;
+	return READ_ONCE(ppp->ppp_net);
 }
 
 static struct rtnl_link_ops ppp_link_ops __read_mostly = {

drivers/net/vxlan/vxlan_core.c

@@ -4569,7 +4569,7 @@ static struct net *vxlan_get_link_net(const struct net_device *dev)
 {
 	struct vxlan_dev *vxlan = netdev_priv(dev);
 
-	return vxlan->net;
+	return READ_ONCE(vxlan->net);
 }
 
 static struct rtnl_link_ops vxlan_link_ops __read_mostly = {

net/core/rtnetlink.c

@@ -1923,9 +1923,6 @@ static int rtnl_fill_ifinfo(struct sk_buff *skb,
 			goto nla_put_failure;
 	}
 
-	if (rtnl_fill_link_netnsid(skb, dev, src_net, gfp))
-		goto nla_put_failure;
-
 	if (new_nsid &&
 	    nla_put_s32(skb, IFLA_NEW_NETNSID, *new_nsid) < 0)
 		goto nla_put_failure;
@@ -1938,6 +1935,8 @@ static int rtnl_fill_ifinfo(struct sk_buff *skb,
 		goto nla_put_failure;
 
 	rcu_read_lock();
+	if (rtnl_fill_link_netnsid(skb, dev, src_net, GFP_ATOMIC))
+		goto nla_put_failure_rcu;
 	qdisc = rcu_dereference(dev->qdisc);
 	if (qdisc && nla_put_string(skb, IFLA_QDISC, qdisc->ops->id))
 		goto nla_put_failure_rcu;

net/ipv4/ip_tunnel.c

@@ -1120,7 +1120,7 @@ struct net *ip_tunnel_get_link_net(const struct net_device *dev)
 {
 	struct ip_tunnel *tunnel = netdev_priv(dev);
 
-	return tunnel->net;
+	return READ_ONCE(tunnel->net);
 }
 EXPORT_SYMBOL(ip_tunnel_get_link_net);
 

net/ipv6/ip6_tunnel.c

@@ -2146,7 +2146,7 @@ struct net *ip6_tnl_get_link_net(const struct net_device *dev)
 {
 	struct ip6_tnl *tunnel = netdev_priv(dev);
 
-	return tunnel->net;
+	return READ_ONCE(tunnel->net);
 }
 EXPORT_SYMBOL(ip6_tnl_get_link_net);
 

net/xfrm/xfrm_interface_core.c

@@ -926,7 +926,7 @@ static struct net *xfrmi_get_link_net(const struct net_device *dev)
 {
 	struct xfrm_if *xi = netdev_priv(dev);
 
-	return xi->net;
+	return READ_ONCE(xi->net);
 }
 
 static const struct nla_policy xfrmi_policy[IFLA_XFRM_MAX + 1] = {