net: introduce a function to check if a netdev name is in use

__dev_get_by_name is currently used to either retrieve a net device
reference using its name or to check if a name is already used by a
registered net device (per ns). In the later case there is no need to
return a reference to a net device.

Introduce a new helper, netdev_name_in_use, to check if a name is
currently used by a registered net device without leaking a reference
the corresponding net device. This helper uses netdev_name_node_lookup
instead of __dev_get_by_name as we don't need the extra logic retrieving
a reference to the corresponding net device.
Signed-off-by: NAntoine Tenart <atenart@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -2955,6 +2955,7 @@ struct net_device *__dev_get_by_flags(struct net *net, unsigned short flags,
 struct net_device *dev_get_by_name(struct net *net, const char *name);
 struct net_device *dev_get_by_name_rcu(struct net *net, const char *name);
 struct net_device *__dev_get_by_name(struct net *net, const char *name);
+bool netdev_name_in_use(struct net *net, const char *name);
 int dev_alloc_name(struct net_device *dev, const char *name);
 int dev_open(struct net_device *dev, struct netlink_ext_ack *extack);
 void dev_close(struct net_device *dev);

net/core/dev.c

@@ -303,6 +303,12 @@ static struct netdev_name_node *netdev_name_node_lookup_rcu(struct net *net,
 	return NULL;
 }
 
+bool netdev_name_in_use(struct net *net, const char *name)
+{
+	return netdev_name_node_lookup(net, name);
+}
+EXPORT_SYMBOL(netdev_name_in_use);
+
 int netdev_name_node_alt_create(struct net_device *dev, const char *name)
 {
 	struct netdev_name_node *name_node;
@@ -1133,7 +1139,7 @@ static int __dev_alloc_name(struct net *net, const char *name, char *buf)
 	}
 
 	snprintf(buf, IFNAMSIZ, name, i);
-	if (!__dev_get_by_name(net, buf))
+	if (!netdev_name_in_use(net, buf))
 		return i;
 
 	/* It is possible to run out of possible slots
@@ -1187,7 +1193,7 @@ static int dev_get_valid_name(struct net *net, struct net_device *dev,
 
 	if (strchr(name, '%'))
 		return dev_alloc_name_ns(net, dev, name);
-	else if (__dev_get_by_name(net, name))
+	else if (netdev_name_in_use(net, name))
 		return -EEXIST;
 	else if (dev->name != name)
 		strlcpy(dev->name, name, IFNAMSIZ);
@@ -11153,7 +11159,7 @@ int __dev_change_net_namespace(struct net_device *dev, struct net *net,
 	 * we can use it in the destination network namespace.
 	 */
 	err = -EEXIST;
-	if (__dev_get_by_name(net, dev->name)) {
+	if (netdev_name_in_use(net, dev->name)) {
 		/* We get here if we can't use the current device name */
 		if (!pat)
 			goto out;
@@ -11506,7 +11512,7 @@ static void __net_exit default_device_exit(struct net *net)
 
 		/* Push remaining network devices to init_net */
 		snprintf(fb_name, IFNAMSIZ, "dev%d", dev->ifindex);
-		if (__dev_get_by_name(&init_net, fb_name))
+		if (netdev_name_in_use(&init_net, fb_name))
 			snprintf(fb_name, IFNAMSIZ, "dev%%d");
 		err = dev_change_net_namespace(dev, &init_net, fb_name);
 		if (err) {