net: Zero terminate ifr_name in dev_ifname().

The ifr.ifr_name is passed around and assumed to be NULL terminated.
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/dev_ioctl.c

@@ -28,6 +28,7 @@ static int dev_ifname(struct net *net, struct ifreq __user *arg)
 
 	if (copy_from_user(&ifr, arg, sizeof(struct ifreq)))
 		return -EFAULT;
+	ifr.ifr_name[IFNAMSIZ-1] = 0;
 
 	error = netdev_get_name(net, ifr.ifr_name, ifr.ifr_ifindex);
 	if (error)