dev: Fix network device ifindex allocation

index 8658074..dae8010 100644
@@ -7491,7 +7491,7 @@ int register_netdevice(struct net_device *dev)
 	}
 
 	ret = -EBUSY;
-	if (!dev->ifindex)
+	if (dev->ifindex <= 0)
 		dev->ifindex = dev_new_index(net);
 	else if (__dev_get_by_index(net, dev->ifindex))
 		goto err_uninit;

index dae8010..6f573f7 100644
@@ -7014,7 +7014,9 @@ int dev_change_xdp_fd(struct net_device *dev, struct netlink_ext_ack *extack,
  *	@net: the applicable net namespace
  *
  *	Returns a suitable unique value for a new device interface
- *	number.  The caller must hold the rtnl semaphore or the
+ *	number or zero in case of no free indexes in net namespace.
+ *
+ *	The caller must hold the rtnl mutex or the
  *	dev_base_lock to be sure it remains unique.
  */
 static int dev_new_index(struct net *net)

@@ -7023,7 +7025,7 @@ static int dev_new_index(struct net *net)
 
 	for (;;) {
 		if (++ifindex <= 0)
-			ifindex = 1;
+			return 0;
 		if (!__dev_get_by_index(net, ifindex))
 			return net->ifindex = ifindex;
 	}

@@ -7491,9 +7493,12 @@ int register_netdevice(struct net_device *dev)
 	}
 
 	ret = -EBUSY;
-	if (dev->ifindex <= 0)
-		dev->ifindex = dev_new_index(net);
-	else if (__dev_get_by_index(net, dev->ifindex))
+	if (dev->ifindex <= 0) {
+		int ifindex = dev_new_index(net);
+		if (!ifindex)
+			goto err_uninit;
+		dev->ifindex = ifindex;
+	} else if (__dev_get_by_index(net, dev->ifindex))
 		goto err_uninit;
 
 	/* Transfer changeable features to wanted_features and enable

@@ -8174,6 +8179,7 @@ void unregister_netdev(struct net_device *dev)
 
 int dev_change_net_namespace(struct net_device *dev, struct net *net, const char *pat)
 {
+	int ifindex = 0;
 	int err;
 
 	ASSERT_RTNL();

@@ -8192,6 +8198,14 @@ int dev_change_net_namespace(struct net_device *dev, struct net *net, const char
 	if (net_eq(dev_net(dev), net))
 		goto out;
 
+	/* If there is an ifindex conflict assign a new one */
+	err = -EBUSY;
+	if (__dev_get_by_index(net, dev->ifindex)) {
+		ifindex = dev_new_index(net);
+		if (!ifindex)
+			goto out;
+	}
+
 	/* Pick the destination device name, and ensure
 	 * we can use it in the destination network namespace.
 	 */

@@ -8245,9 +8259,9 @@ int dev_change_net_namespace(struct net_device *dev, struct net *net, const char
 	/* Actually switch the network namespace */
 	dev_net_set(dev, net);
 
-	/* If there is an ifindex conflict assign a new one */
-	if (__dev_get_by_index(net, dev->ifindex))
-		dev->ifindex = dev_new_index(net);
+	/* Actually change the ifindex */
+	if (ifindex)
+		dev->ifindex = ifindex;
 
 	/* Send a netdev-add uevent to the new namespace */
 	kobject_uevent(&dev->dev.kobj, KOBJ_ADD);

index 6f573f7..e1714e7 100644
@@ -7031,6 +7031,24 @@ static int dev_new_index(struct net *net)
 	}
 }
 
+/**
+ *	dev_free_index	-	free an ifindex
+ *	@dev: the network device whose index to free
+ *
+ *	Sets network namespace last allocated index to the value
+ *	proceed to the ifindex we want to free.  The caller
+ *	must hold the rtnl semaphore or the dev_base_lock to be
+ *	sure it remains unique.
+ */
+static void dev_free_index(struct net_device *dev)
+{
+	struct net *net = dev_net(dev);
+	int ifindex = dev->ifindex;
+
+	if (--ifindex < net->ifindex)
+		net->ifindex = ifindex;
+}
+
 /* Delayed registration/unregisteration */
 static LIST_HEAD(net_todo_list);
 DECLARE_WAIT_QUEUE_HEAD(netdev_unregistering_wq);

@@ -7454,8 +7472,9 @@ void netif_tx_stop_all_queues(struct net_device *dev)
 
 int register_netdevice(struct net_device *dev)
 {
-	int ret;
 	struct net *net = dev_net(dev);
+	int ifindex = 0;
+	int ret;
 
 	BUG_ON(dev_boot_phase);
 	ASSERT_RTNL();

@@ -7494,7 +7513,7 @@ int register_netdevice(struct net_device *dev)
 
 	ret = -EBUSY;
 	if (dev->ifindex <= 0) {
-		int ifindex = dev_new_index(net);
+		ifindex = dev_new_index(net);
 		if (!ifindex)
 			goto err_uninit;
 		dev->ifindex = ifindex;

@@ -7573,10 +7592,9 @@ int register_netdevice(struct net_device *dev)
 	/* Notify protocols, that a new device appeared. */
 	ret = call_netdevice_notifiers(NETDEV_REGISTER, dev);
 	ret = notifier_to_errno(ret);
-	if (ret) {
-		rollback_registered(dev);
-		dev->reg_state = NETREG_UNREGISTERED;
-	}
+	if (ret)
+		goto err_rollback;
+
 	/*
 	 *	Prevent userspace races by waiting until the network
 	 *	device is fully setup before sending notifications.

@@ -7593,6 +7611,14 @@ int register_netdevice(struct net_device *dev)
 		dev->netdev_ops->ndo_uninit(dev);
 	if (dev->priv_destructor)
 		dev->priv_destructor(dev);
+	goto err_free_index;
+
+err_rollback:
+	rollback_registered(dev);
+	dev->reg_state = NETREG_UNREGISTERED;
+err_free_index:
+	if (ifindex)
+		dev_free_index(dev);
 	goto out;
 }
 EXPORT_SYMBOL(register_netdevice);

@@ -7805,9 +7831,11 @@ void netdev_run_todo(void)
 		if (dev->needs_free_netdev)
 			free_netdev(dev);
 
-		/* Report a network device has been unregistered */
 		rtnl_lock();
+		/* Report a network device has been unregistered */
 		dev_net(dev)->dev_unreg_count--;
+		/* Reclaim a network device index */
+		dev_free_index(dev);
 		__rtnl_unlock();
 		wake_up(&netdev_unregistering_wq);
 

@@ -8256,6 +8284,9 @@ int dev_change_net_namespace(struct net_device *dev, struct net *net, const char
 	kobject_uevent(&dev->dev.kobj, KOBJ_REMOVE);
 	netdev_adjacent_del_links(dev);
 
+	/* Free network device index */
+	dev_free_index(dev);
+
 	/* Actually switch the network namespace */
 	dev_net_set(dev, net);
 

index 0156fe8..0689433 100644
@@ -405,7 +405,7 @@ static int veth_newlink(struct net *src_net, struct net_device *dev,
 	if (tbp[IFLA_ADDRESS] == NULL)
 		eth_hw_addr_random(peer);
 
-	if (ifmp && (dev->ifindex != 0))
+	if (ifmp && dev->ifindex > 0)
 		peer->ifindex = ifmp->ifi_index;
 
 	err = register_netdevice(peer);