ipv4: arp_notify address list bug

This fixes a bug with arp_notify.

If arp_notify is enabled, kernel will crash if address is changed
and no IP address is assigned.
  http://bugzilla.kernel.org/show_bug.cgi?id=14330

Reported-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 10 insertions, 6 deletions

diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index e92f1fd28aa5..5df2f6a0b0f0 100644
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -1077,12 +1077,16 @@ static int inetdev_event(struct notifier_block *this, unsigned long event,
                 ip_mc_up(in_dev);
                 /* fall through */
         case NETDEV_CHANGEADDR:
-                if (IN_DEV_ARP_NOTIFY(in_dev))
-                        arp_send(ARPOP_REQUEST, ETH_P_ARP,
-                                 in_dev->ifa_list->ifa_address,
-                                 dev,
-                                 in_dev->ifa_list->ifa_address,
-                                 NULL, dev->dev_addr, NULL);
+                /* Send gratuitous ARP to notify of link change */
+                if (IN_DEV_ARP_NOTIFY(in_dev)) {
+                        struct in_ifaddr *ifa = in_dev->ifa_list;
+
+                        if (ifa)
+                                arp_send(ARPOP_REQUEST, ETH_P_ARP,
+                                         ifa->ifa_address, dev,
+                                         ifa->ifa_address, NULL,
+                                         dev->dev_addr, NULL);
+                }
                 break;
         case NETDEV_DOWN:
                 ip_mc_down(in_dev);