netdev - [PATCH net-next] veth: report NEWLINK event when moving the peer device in a new namespace

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Message-Id: <51722660f2ef860779e227541dab77046496f135.1535712096.git.lorenzo.bianconi@redhat.com>
Date:   Fri, 31 Aug 2018 13:43:50 +0200
From:   Lorenzo Bianconi <lorenzo.bianconi@...hat.com>
To:     davem@...emloft.net
Cc:     netdev@...r.kernel.org
Subject: [PATCH net-next] veth: report NEWLINK event when moving the peer device in a new namespace

When moving a veth device to another namespace, userspace receives a
RTM_DELLINK message indicating the device has been removed from current
netns. However, the other peer does not receive a netlink event
containing new values for IFLA_LINK_NETNSID and IFLA_LINK veth
attributes.
Fix that behaviour sending to userspace a RTM_NEWLINK message in the peer
namespace to report new IFLA_LINK_NETNSID/IFLA_LINK values

Reviewed-by: Stefano Brivio <sbrivio@...hat.com>
Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@...hat.com>
---
Changes since RFC:
- export rtmsg_ifinfo_build_skb() symbol and do not use rtmsg_ifinfo_newnet()
  directly
---
 drivers/net/veth.c   | 66 +++++++++++++++++++++++++++++++++++++++++++-
 net/core/rtnetlink.c |  1 +
 2 files changed, 66 insertions(+), 1 deletion(-)

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index 8d679c8b7f25..0caffc93d74d 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -1242,18 +1242,82 @@ static struct rtnl_link_ops veth_link_ops = {
 	.get_link_net	= veth_get_link_net,
 };
 
+static int veth_notify(struct notifier_block *this,
+		       unsigned long event, void *ptr)
+{
+	struct net_device *peer, *dev = netdev_notifier_info_to_dev(ptr);
+	struct net *peer_net, *net = dev_net(dev);
+	int nsid, ret = NOTIFY_DONE;
+	struct veth_priv *priv;
+	struct sk_buff *skb;
+
+	if (dev->netdev_ops != &veth_netdev_ops)
+		return NOTIFY_DONE;
+
+	if (event != NETDEV_REGISTER)
+		return NOTIFY_DONE;
+
+	priv = netdev_priv(dev);
+
+	rcu_read_lock();
+
+	peer = rcu_dereference(priv->peer);
+	if (!peer)
+		goto out;
+
+	peer_net = dev_net(peer);
+	/* do not forward events if both veth devices
+	 * are in the same namespace
+	 */
+	if (peer_net == net)
+		goto out;
+
+	/* notify on peer namespace new IFLA_LINK_NETNSID
+	 * and IFLA_LINK values
+	 */
+	nsid = peernet2id_alloc(peer_net, net);
+	skb = rtmsg_ifinfo_build_skb(RTM_NEWLINK, peer, ~0U,
+				     IFLA_EVENT_NONE, GFP_ATOMIC,
+				     &nsid, dev->ifindex);
+	if (skb) {
+		rtnl_notify(skb, peer_net, 0, RTNLGRP_LINK, NULL,
+			    GFP_ATOMIC);
+		ret = NOTIFY_OK;
+	}
+
+out:
+	rcu_read_unlock();
+
+	return ret;
+}
+
+static struct notifier_block veth_notifier = {
+	.notifier_call = veth_notify,
+};
+
 /*
  * init/fini
  */
 
 static __init int veth_init(void)
 {
-	return rtnl_link_register(&veth_link_ops);
+	int err;
+
+	err = register_netdevice_notifier(&veth_notifier);
+	if (err < 0)
+		return err;
+
+	err = rtnl_link_register(&veth_link_ops);
+	if (err < 0)
+		unregister_netdevice_notifier(&veth_notifier);
+
+	return err;
 }
 
 static __exit void veth_exit(void)
 {
 	rtnl_link_unregister(&veth_link_ops);
+	unregister_netdevice_notifier(&veth_notifier);
 }
 
 module_init(veth_init);
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 24431e578310..b2df84db7670 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -3326,6 +3326,7 @@ struct sk_buff *rtmsg_ifinfo_build_skb(int type, struct net_device *dev,
 		rtnl_set_sk_err(net, RTNLGRP_LINK, err);
 	return NULL;
 }
+EXPORT_SYMBOL(rtmsg_ifinfo_build_skb);
 
 void rtmsg_ifinfo_send(struct sk_buff *skb, struct net_device *dev, gfp_t flags)
 {
-- 
2.17.1