gtp: Use for_each_netdev_rcu() in gtp_genl_dump_pdp().

gtp_newlink() links the gtp device to a list in dev_net(dev).

However, even after the gtp device is moved to another netns,
it stays on the list but should be invisible.

Let's use for_each_netdev_rcu() for netdev traversal in
gtp_genl_dump_pdp().

Note that gtp_dev_list is no longer used under RCU, so list
helpers are converted to the non-RCU variant.

Fixes: 459aa66 ("gtp: add initial driver for datapath of GPRS Tunneling Protocol (GTP-U)")
Reported-by: Xiao Liang <shaw.leon@gmail.com>
Closes: https://lore.kernel.org/netdev/CABAhCOQdBL6h9M2C+kd+bGivRJ9Q72JUxW+-gur0nub_=PmFPA@mail.gmail.com/
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/gtp.c

@@ -1525,7 +1525,7 @@ static int gtp_newlink(struct net *src_net, struct net_device *dev,
 	}
 
 	gn = net_generic(dev_net(dev), gtp_net_id);
-	list_add_rcu(&gtp->list, &gn->gtp_dev_list);
+	list_add(&gtp->list, &gn->gtp_dev_list);
 	dev->priv_destructor = gtp_destructor;
 
 	netdev_dbg(dev, "registered new GTP interface\n");
@@ -1551,7 +1551,7 @@ static void gtp_dellink(struct net_device *dev, struct list_head *head)
 		hlist_for_each_entry_safe(pctx, next, &gtp->tid_hash[i], hlist_tid)
 			pdp_context_delete(pctx);
 
-	list_del_rcu(&gtp->list);
+	list_del(&gtp->list);
 	unregister_netdevice_queue(dev, head);
 }
 
@@ -2271,16 +2271,19 @@ static int gtp_genl_dump_pdp(struct sk_buff *skb,
 	struct gtp_dev *last_gtp = (struct gtp_dev *)cb->args[2], *gtp;
 	int i, j, bucket = cb->args[0], skip = cb->args[1];
 	struct net *net = sock_net(skb->sk);
+	struct net_device *dev;
 	struct pdp_ctx *pctx;
-	struct gtp_net *gn;
-
-	gn = net_generic(net, gtp_net_id);
 
 	if (cb->args[4])
 		return 0;
 
 	rcu_read_lock();
-	list_for_each_entry_rcu(gtp, &gn->gtp_dev_list, list) {
+	for_each_netdev_rcu(net, dev) {
+		if (dev->rtnl_link_ops != &gtp_link_ops)
+			continue;
+
+		gtp = netdev_priv(dev);
+
 		if (last_gtp && last_gtp != gtp)
 			continue;
 		else
@@ -2475,9 +2478,9 @@ static void __net_exit gtp_net_exit_batch_rtnl(struct list_head *net_list,
 
 	list_for_each_entry(net, net_list, exit_list) {
 		struct gtp_net *gn = net_generic(net, gtp_net_id);
-		struct gtp_dev *gtp;
+		struct gtp_dev *gtp, *gtp_next;
 
-		list_for_each_entry(gtp, &gn->gtp_dev_list, list)
+		list_for_each_entry_safe(gtp, gtp_next, &gn->gtp_dev_list, list)
 			gtp_dellink(gtp->dev, dev_to_kill);
 	}
 }