net: Fix NETDEV_CHANGE notifier usage causing spurious arp flush

net: Fix NETDEV_CHANGE notifier usage causing spurious arp flush

[ Upstream commit 54951194656e4853e441266fd095f880bc0398f3 ]

A bug was introduced in NETDEV_CHANGE notifier sequence causing the
arp table to be sometimes spuriously cleared (including manual arp
entries marked permanent), upon network link carrier changes.

The changed argument for the notifier was applied only to a single
caller of NETDEV_CHANGE, missing among others netdev_state_change().
So upon net_carrier events induced by the network, which are
triggering a call to netdev_state_change(), arp_netdev_event() would
decide whether to clear or not arp cache based on random/junk stack
values (a kind of read buffer overflow).

Fixes: be9efd365328 ("net: pass changed flags along with NETDEV_CHANGE event")
Fixes: 6c8b4e3ff81b ("arp: flush arp cache on IFF_NOARP change")
Signed-off-by: Loic Prylli <loicp@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>