net: Fix userspace RTM_NEWLINK notifications.

I received some bug reports about userspace programs having problems
because after RTM_NEWLINK was received they could not immediate access
files under /proc/sys/net/ because they had not been registered yet.

The original problem was trivially fixed by moving the userspace
notification from rtnetlink_event() to the end of
register_netdevice().

When testing that change I discovered I was still getting RTM_NEWLINK
events before I could access proc and I was also getting RTM_NEWLINK
events after I was seeing RTM_DELLINK.  Things practically guaranteed
to confuse userspace.

After a little more investigation these extra notifications proved to
be from the new notifiers NETDEV_POST_INIT and NETDEV_UNREGISTER_BATCH
hitting the default case in rtnetlink_event, and triggering
unnecessary RTM_NEWLINK messages.

rtnetlink_event now explicitly handles NETDEV_UNREGISTER_BATCH and
NETDEV_POST_INIT to avoid sending the incorrect userspace
notifications.

Signed-off-by: Eric W. Biederman <ebiederm@aristanetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 14 insertions, 3 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 6fe7d739e59b..be9924f60ec3 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5035,6 +5035,11 @@ int register_netdevice(struct net_device *dev)
                 rollback_registered(dev);
                 dev->reg_state = NETREG_UNREGISTERED;
         }
+        /*
+         *      Prevent userspace races by waiting until the network
+         *      device is fully setup before sending notifications.
+         */
+        rtmsg_ifinfo(RTM_NEWLINK, dev, ~0U);
 
 out:
         return ret;
@@ -5597,6 +5602,12 @@ int dev_change_net_namespace(struct net_device *dev, struct net *net, const char
         /* Notify protocols, that a new device appeared. */
         call_netdevice_notifiers(NETDEV_REGISTER, dev);
 
+        /*
+         *      Prevent userspace races by waiting until the network
+         *      device is fully setup before sending notifications.
+         */
+        rtmsg_ifinfo(RTM_NEWLINK, dev, ~0U);
+
         synchronize_net();
         err = 0;
 out:
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 33148a568199..794bcb897ff0 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1364,15 +1364,15 @@ static int rtnetlink_event(struct notifier_block *this, unsigned long event, voi
         case NETDEV_UNREGISTER:
                 rtmsg_ifinfo(RTM_DELLINK, dev, ~0U);
                 break;
-        case NETDEV_REGISTER:
-                rtmsg_ifinfo(RTM_NEWLINK, dev, ~0U);
-                break;
         case NETDEV_UP:
         case NETDEV_DOWN:
                 rtmsg_ifinfo(RTM_NEWLINK, dev, IFF_UP|IFF_RUNNING);
                 break;
+        case NETDEV_POST_INIT:
+        case NETDEV_REGISTER:
         case NETDEV_CHANGE:
         case NETDEV_GOING_DOWN:
+        case NETDEV_UNREGISTER_BATCH:
                 break;
         default:
                 rtmsg_ifinfo(RTM_NEWLINK, dev, 0);