Merge branch 'net-bring-back-dev_addr_sem'

Stanislav Fomichev says:

====================
net: bring back dev_addr_sem

Kohei reports an issue with dev_addr_sem conversion to netdev instance
lock in [0]. Based on the discussion, switching to netdev instance
lock to protect the address might not work for the devices that
are not using netdev ops lock.
Bring dev_addr_sem instance lock back but fix the ordering.

0: https://lore.kernel.org/netdev/[e-mail]
====================

Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Paolo Abeni <[e-mail]>

drivers/net/tap.c

···
 			rtnl_unlock();
 			return -ENOLINK;
 		}
-		ret = dev_set_mac_address(tap->dev, &sa, NULL);
+		ret = dev_set_mac_address_user(tap->dev, &sa, NULL);
 		tap_put_tap_dev(tap);
 		rtnl_unlock();
 		return ret;

drivers/net/tun.c

···
 
 	case SIOCSIFHWADDR:
 		/* Set hw address */
-		ret = dev_set_mac_address(tun->dev, &ifr.ifr_hwaddr, NULL);
+		ret = dev_set_mac_address_user(tun->dev, &ifr.ifr_hwaddr, NULL);
 		break;
 
 	case TUNGETSNDBUF:

include/linux/netdevice.h

···
 	 *
 	 * Protects:
 	 *	@gro_flush_timeout, @napi_defer_hard_irqs, @napi_list,
-	 *	@net_shaper_hierarchy, @reg_state, @threaded, @dev_addr
+	 *	@net_shaper_hierarchy, @reg_state, @threaded
 	 *
 	 * Partially protects (writers must hold both @lock and rtnl_lock):
 	 *	@up
···
 			  struct netlink_ext_ack *extack);
 int dev_set_mac_address(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

···
 	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)
···
 	return 0;
 }
 
+DECLARE_RWSEM(dev_addr_sem);
+
 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;
 
-	dev = netdev_get_by_name_lock(net, dev_name);
-	if (!dev)
-		return -ENODEV;
+	down_read(&dev_addr_sem);
+	rcu_read_lock();
 
+	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);
 
-	return 0;
+unlock:
+	rcu_read_unlock();
+	up_read(&dev_addr_sem);
+	return ret;
 }
 EXPORT_SYMBOL(dev_get_mac_address);
 

net/core/dev.h

···
 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,
···
 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;

net/core/dev_api.c

···
 	netdev_unlock_ops(dev);
 }
 
+int dev_set_mac_address_user(struct net_device *dev, struct sockaddr *sa,
+			     struct netlink_ext_ack *extack)
+{
+	int ret;
+
+	down_write(&dev_addr_sem);
+	netdev_lock_ops(dev);
+	ret = netif_set_mac_address(dev, sa, extack);
+	netdev_unlock_ops(dev);
+	up_write(&dev_addr_sem);
+
+	return ret;
+}
+EXPORT_SYMBOL(dev_set_mac_address_user);
+
 /**
  * dev_change_net_namespace() - move device to different nethost namespace
  * @dev: device
···
 {
 	int ret;
 
-	netdev_lock(dev);
+	netdev_lock_ops(dev);
 	ret = netif_set_mac_address(dev, sa, extack);
-	netdev_unlock(dev);
+	netdev_unlock_ops(dev);
 
 	return ret;
 }

net/core/dev_ioctl.c

···
 	case SIOCSIFHWADDR:
 		if (dev->addr_len > sizeof(struct sockaddr))
 			return -EINVAL;
-		return dev_set_mac_address(dev, &ifr->ifr_hwaddr, NULL);
+		return dev_set_mac_address_user(dev, &ifr->ifr_hwaddr, NULL);
 
 	case SIOCSIFHWBROADCAST:
 		if (ifr->ifr_hwaddr.sa_family != dev->type)

net/core/net-sysfs.c

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

net/core/rtnetlink.c

···
 			goto errout;
 		}
 		sa->sa_family = dev->type;
+
+		netdev_unlock_ops(dev);
+
+		/* dev_addr_sem is an outer lock, enforce proper ordering */
+		down_write(&dev_addr_sem);
+		netdev_lock_ops(dev);
+
 		memcpy(sa->sa_data, nla_data(tb[IFLA_ADDRESS]),
 		       dev->addr_len);
-		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)
+		if (err) {
+			up_write(&dev_addr_sem);
 			goto errout;
+		}
 		status |= DO_SETLINK_MODIFIED;
+
+		up_write(&dev_addr_sem);
 	}
 
 	if (tb[IFLA_MTU]) {