net: dev_close() should check IFF_UP

Commit 443457242b (factorize sync-rcu call in
unregister_netdevice_many) mistakenly removed one test from dev_close()

Following actions trigger a BUG :

modprobe bonding
modprobe dummy
ifconfig bond0 up
ifenslave bond0 dummy0
rmmod dummy

dev_close() must not close a non IFF_UP device.

With help from Frank Blaschka and Einar EL Lueck

Reported-by: Frank Blaschka <blaschka@linux.vnet.ibm.com>
Reported-by: Einar EL Lueck <ELELUECK@de.ibm.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -1284,11 +1284,13 @@ static int dev_close_many(struct list_head *head)
  */
 int dev_close(struct net_device *dev)
 {
-	LIST_HEAD(single);
+	if (dev->flags & IFF_UP) {
+		LIST_HEAD(single);
 
-	list_add(&dev->unreg_list, &single);
-	dev_close_many(&single);
-	list_del(&single);
+		list_add(&dev->unreg_list, &single);
+		dev_close_many(&single);
+		list_del(&single);
+	}
 	return 0;
 }
 EXPORT_SYMBOL(dev_close);