net: sysfs: ethtool_ops can be NULL

commit d519e17e2d01a0ee9abe083019532061b4438065
(net: export device speed and duplex via sysfs)
made the wrong assumption that netdev->ethtool_ops was always set.

This makes possible to crash kernel and let rtnl in locked state.

modprobe dummy
ip link set dummy0 up
(udev runs and crash)

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Andy Gospodarek <andy@greyhouse.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/net-sysfs.c

@@ -139,7 +139,9 @@ static ssize_t show_speed(struct device *dev,
 	if (!rtnl_trylock())
 		return restart_syscall();
 
-	if (netif_running(netdev) && netdev->ethtool_ops->get_settings) {
+	if (netif_running(netdev) &&
+	    netdev->ethtool_ops &&
+	    netdev->ethtool_ops->get_settings) {
 		struct ethtool_cmd cmd = { ETHTOOL_GSET };
 
 		if (!netdev->ethtool_ops->get_settings(netdev, &cmd))
@@ -158,7 +160,9 @@ static ssize_t show_duplex(struct device *dev,
 	if (!rtnl_trylock())
 		return restart_syscall();
 
-	if (netif_running(netdev) && netdev->ethtool_ops->get_settings) {
+	if (netif_running(netdev) &&
+	    netdev->ethtool_ops &&
+	    netdev->ethtool_ops->get_settings) {
 		struct ethtool_cmd cmd = { ETHTOOL_GSET };
 
 		if (!netdev->ethtool_ops->get_settings(netdev, &cmd))