net: replace dev_addr_sem with netdev instance lock

Lockdep reports possible circular dependency in [0]. Instead of
fixing the ordering, replace global dev_addr_sem with netdev
instance lock. Most of the paths that set/get mac are RTNL
protected. Two places where it's not, convert to explicit
locking:
- sysfs address_show
- dev_get_mac_address via dev_ioctl

0: https://netdev-3.bots.linux.dev/vmksft-forwarding-dbg/results/993321/24-router-bridge-1d-lag-sh/stderr

Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20250305163732.2766420-12-sdf@fomichev.me
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/tap.c

@@ -1017,7 +1017,7 @@ static long tap_ioctl(struct file *file, unsigned int cmd,
 			rtnl_unlock();
 			return -ENOLINK;
 		}
-		ret = dev_set_mac_address_user(tap->dev, &sa, NULL);
+		ret = dev_set_mac_address(tap->dev, &sa, NULL);
 		tap_put_tap_dev(tap);
 		rtnl_unlock();
 		return ret;

drivers/net/tun.c

@@ -3175,7 +3175,7 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 
 	case SIOCSIFHWADDR:
 		/* Set hw address */
-		ret = dev_set_mac_address_user(tun->dev, &ifr.ifr_hwaddr, NULL);
+		ret = dev_set_mac_address(tun->dev, &ifr.ifr_hwaddr, NULL);
 		break;
 
 	case TUNGETSNDBUF:

include/linux/netdevice.h

@@ -2492,7 +2492,7 @@ struct net_device {
 	 *
 	 * Protects:
 	 *	@gro_flush_timeout, @napi_defer_hard_irqs, @napi_list,
-	 *	@net_shaper_hierarchy, @reg_state, @threaded
+	 *	@net_shaper_hierarchy, @reg_state, @threaded, @dev_addr
 	 *
 	 * Partially protects (writers must hold both @lock and rtnl_lock):
 	 *	@up
@@ -4262,10 +4262,6 @@ int netif_set_mac_address(struct net_device *dev, struct sockaddr *sa,
 			  struct netlink_ext_ack *extack);
 int dev_set_mac_address(struct net_device *dev, struct sockaddr *sa,
 			struct netlink_ext_ack *extack);
-int netif_set_mac_address_user(struct net_device *dev, struct sockaddr *sa,
-			       struct netlink_ext_ack *extack);
-int dev_set_mac_address_user(struct net_device *dev, struct sockaddr *sa,
-			     struct netlink_ext_ack *extack);
 int dev_get_mac_address(struct sockaddr *sa, struct net *net, char *dev_name);
 int dev_get_port_parent_id(struct net_device *dev,
 			   struct netdev_phys_item_id *ppid, bool recurse);

net/core/dev.c

@@ -1058,6 +1058,28 @@ struct net_device *netdev_get_by_index_lock(struct net *net, int ifindex)
 	return __netdev_put_lock(dev);
 }
 
+/**
+ * netdev_get_by_name_lock() - find a device by its name
+ * @net: the applicable net namespace
+ * @name: name of device
+ *
+ * Search for an interface by name. If a valid device
+ * with @name is found it will be returned with netdev->lock held.
+ * netdev_unlock() must be called to release it.
+ *
+ * Return: pointer to a device with lock held, NULL if not found.
+ */
+struct net_device *netdev_get_by_name_lock(struct net *net, const char *name)
+{
+	struct net_device *dev;
+
+	dev = dev_get_by_name(net, name);
+	if (!dev)
+		return NULL;
+
+	return __netdev_put_lock(dev);
+}
+
 struct net_device *
 netdev_xa_find_lock(struct net *net, struct net_device *dev,
 		    unsigned long *index)
@@ -9589,44 +9611,24 @@ int netif_set_mac_address(struct net_device *dev, struct sockaddr *sa,
 	return 0;
 }
 
-DECLARE_RWSEM(dev_addr_sem);
-
-int netif_set_mac_address_user(struct net_device *dev, struct sockaddr *sa,
-			       struct netlink_ext_ack *extack)
-{
-	int ret;
-
-	down_write(&dev_addr_sem);
-	ret = netif_set_mac_address(dev, sa, extack);
-	up_write(&dev_addr_sem);
-	return ret;
-}
-
 int dev_get_mac_address(struct sockaddr *sa, struct net *net, char *dev_name)
 {
 	size_t size = sizeof(sa->sa_data_min);
 	struct net_device *dev;
-	int ret = 0;
 
-	down_read(&dev_addr_sem);
+	dev = netdev_get_by_name_lock(net, dev_name);
-	rcu_read_lock();
+	if (!dev)
+		return -ENODEV;
 
-	dev = dev_get_by_name_rcu(net, dev_name);
-	if (!dev) {
-		ret = -ENODEV;
-		goto unlock;
-	}
 	if (!dev->addr_len)
 		memset(sa->sa_data, 0, size);
 	else
 		memcpy(sa->sa_data, dev->dev_addr,
 		       min_t(size_t, size, dev->addr_len));
 	sa->sa_family = dev->type;
+	netdev_unlock(dev);
 
-unlock:
+	return 0;
-	rcu_read_unlock();
-	up_read(&dev_addr_sem);
-	return ret;
 }
 EXPORT_SYMBOL(dev_get_mac_address);
 

net/core/dev.h

@@ -28,6 +28,7 @@ netdev_napi_by_id_lock(struct net *net, unsigned int napi_id);
 struct net_device *dev_get_by_napi_id(unsigned int napi_id);
 
 struct net_device *netdev_get_by_index_lock(struct net *net, int ifindex);
+struct net_device *netdev_get_by_name_lock(struct net *net, const char *name);
 struct net_device *__netdev_put_lock(struct net_device *dev);
 struct net_device *
 netdev_xa_find_lock(struct net *net, struct net_device *dev,
@@ -69,8 +70,6 @@ extern int		weight_p;
 extern int		dev_weight_rx_bias;
 extern int		dev_weight_tx_bias;
 
-extern struct rw_semaphore dev_addr_sem;
-
 /* rtnl helpers */
 extern struct list_head net_todo_list;
 void netdev_run_todo(void);

net/core/dev_api.c

@@ -82,19 +82,6 @@ void dev_set_group(struct net_device *dev, int new_group)
 	netdev_unlock_ops(dev);
 }
 
-int dev_set_mac_address_user(struct net_device *dev, struct sockaddr *sa,
-			     struct netlink_ext_ack *extack)
-{
-	int ret;
-
-	netdev_lock_ops(dev);
-	ret = netif_set_mac_address_user(dev, sa, extack);
-	netdev_unlock_ops(dev);
-
-	return ret;
-}
-EXPORT_SYMBOL(dev_set_mac_address_user);
-
 /**
  * dev_change_net_namespace() - move device to different nethost namespace
  * @dev: device
@@ -310,9 +297,9 @@ int dev_set_mac_address(struct net_device *dev, struct sockaddr *sa,
 {
 	int ret;
 
-	netdev_lock_ops(dev);
+	netdev_lock(dev);
 	ret = netif_set_mac_address(dev, sa, extack);
-	netdev_unlock_ops(dev);
+	netdev_unlock(dev);
 
 	return ret;
 }

net/core/dev_ioctl.c

@@ -574,7 +574,7 @@ static int dev_ifsioc(struct net *net, struct ifreq *ifr, void __user *data,
 	case SIOCSIFHWADDR:
 		if (dev->addr_len > sizeof(struct sockaddr))
 			return -EINVAL;
-		return dev_set_mac_address_user(dev, &ifr->ifr_hwaddr, NULL);
+		return dev_set_mac_address(dev, &ifr->ifr_hwaddr, NULL);
 
 	case SIOCSIFHWBROADCAST:
 		if (ifr->ifr_hwaddr.sa_family != dev->type)

net/core/net-sysfs.c

@@ -262,14 +262,11 @@ static ssize_t address_show(struct device *dev, struct device_attribute *attr,
 	struct net_device *ndev = to_net_dev(dev);
 	ssize_t ret = -EINVAL;
 
-	down_read(&dev_addr_sem);
+	netdev_lock(ndev);
-
-	rcu_read_lock();
 	if (dev_isalive(ndev))
 		ret = sysfs_format_mac(buf, ndev->dev_addr, ndev->addr_len);
-	rcu_read_unlock();
+	netdev_unlock(ndev);
 
-	up_read(&dev_addr_sem);
 	return ret;
 }
 static DEVICE_ATTR_RO(address);

net/core/rtnetlink.c

@@ -3089,7 +3089,11 @@ static int do_setlink(const struct sk_buff *skb, struct net_device *dev,
 		sa->sa_family = dev->type;
 		memcpy(sa->sa_data, nla_data(tb[IFLA_ADDRESS]),
 		       dev->addr_len);
-		err = netif_set_mac_address_user(dev, sa, extack);
+		if (!netdev_need_ops_lock(dev))
+			netdev_lock(dev);
+		err = netif_set_mac_address(dev, sa, extack);
+		if (!netdev_need_ops_lock(dev))
+			netdev_unlock(dev);
 		kfree(sa);
 		if (err)
 			goto errout;