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>

1 files changed, 27 insertions, 25 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 404047d4d943..a0f75a1d1f5a 100644
--- a/net/core/dev.c
+++ b/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);
-	rcu_read_lock();
+	dev = netdev_get_by_name_lock(net, dev_name);
+	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:
-	rcu_read_unlock();
-	up_read(&dev_addr_sem);
-	return ret;
+	return 0;
 }
 EXPORT_SYMBOL(dev_get_mac_address);