dev: Hold rtnl_net_lock() for dev_ifsioc().

Basically, dev_ifsioc() operates on the passed single netns (except
for netdev notifier chains with lower/upper devices for which we will
need more changes).

Let's hold rtnl_net_lock() for dev_ifsioc().

Now that NETDEV_CHANGENAME is always triggered under rtnl_net_lock()
of the device's netns. (do_setlink() and dev_ifsioc())

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250115095545.52709-4-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/core/dev.c

@@ -1348,16 +1348,13 @@ static int dev_get_valid_name(struct net *net, struct net_device *dev,
  */
 int dev_change_name(struct net_device *dev, const char *newname)
 {
+	struct net *net = dev_net(dev);
 	unsigned char old_assign_type;
 	char oldname[IFNAMSIZ];
 	int err = 0;
 	int ret;
-	struct net *net;
-
-	ASSERT_RTNL();
-	BUG_ON(!dev_net(dev));
 
-	net = dev_net(dev);
+	ASSERT_RTNL_NET(net);
 
 	if (!strncmp(newname, dev->name, IFNAMSIZ))
 		return 0;

net/core/dev_ioctl.c

@@ -543,7 +543,7 @@ static int dev_siocwandev(struct net_device *dev, struct if_settings *ifs)
 }
 
 /*
- *	Perform the SIOCxIFxxx calls, inside rtnl_lock()
+ *	Perform the SIOCxIFxxx calls, inside rtnl_net_lock()
  */
 static int dev_ifsioc(struct net *net, struct ifreq *ifr, void __user *data,
 		      unsigned int cmd)
@@ -620,11 +620,14 @@ static int dev_ifsioc(struct net *net, struct ifreq *ifr, void __user *data,
 			return -ENODEV;
 		if (!netif_is_bridge_master(dev))
 			return -EOPNOTSUPP;
+
 		netdev_hold(dev, &dev_tracker, GFP_KERNEL);
-		rtnl_unlock();
+		rtnl_net_unlock(net);
+
 		err = br_ioctl_call(net, netdev_priv(dev), cmd, ifr, NULL);
+
 		netdev_put(dev, &dev_tracker);
-		rtnl_lock();
+		rtnl_net_lock(net);
 		return err;
 
 	case SIOCDEVPRIVATE ... SIOCDEVPRIVATE + 15:
@@ -770,9 +773,11 @@ int dev_ioctl(struct net *net, unsigned int cmd, struct ifreq *ifr,
 		dev_load(net, ifr->ifr_name);
 		if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
 			return -EPERM;
-		rtnl_lock();
+
+		rtnl_net_lock(net);
 		ret = dev_ifsioc(net, ifr, data, cmd);
-		rtnl_unlock();
+		rtnl_net_unlock(net);
+
 		if (colon)
 			*colon = ':';
 		return ret;
@@ -816,9 +821,11 @@ int dev_ioctl(struct net *net, unsigned int cmd, struct ifreq *ifr,
 	case SIOCBONDSLAVEINFOQUERY:
 	case SIOCBONDINFOQUERY:
 		dev_load(net, ifr->ifr_name);
-		rtnl_lock();
+
+		rtnl_net_lock(net);
 		ret = dev_ifsioc(net, ifr, data, cmd);
-		rtnl_unlock();
+		rtnl_net_unlock(net);
+
 		if (need_copyout)
 			*need_copyout = false;
 		return ret;
@@ -841,9 +848,10 @@ int dev_ioctl(struct net *net, unsigned int cmd, struct ifreq *ifr,
 		    (cmd >= SIOCDEVPRIVATE &&
 		     cmd <= SIOCDEVPRIVATE + 15)) {
 			dev_load(net, ifr->ifr_name);
-			rtnl_lock();
+
+			rtnl_net_lock(net);
 			ret = dev_ifsioc(net, ifr, data, cmd);
-			rtnl_unlock();
+			rtnl_net_unlock(net);
 			return ret;
 		}
 		return -ENOTTY;

net/core/rtnl_net_debug.c

@@ -27,7 +27,6 @@ static int rtnl_net_debug_event(struct notifier_block *nb,
 	case NETDEV_CHANGEADDR:
 	case NETDEV_PRE_CHANGEADDR:
 	case NETDEV_GOING_DOWN:
-	case NETDEV_CHANGENAME:
 	case NETDEV_FEAT_CHANGE:
 	case NETDEV_BONDING_FAILOVER:
 	case NETDEV_PRE_UP:
@@ -60,18 +59,10 @@ static int rtnl_net_debug_event(struct notifier_block *nb,
 		ASSERT_RTNL();
 		break;
 
-	/* Once an event fully supports RTNL_NET, move it here
-	 * and remove "if (0)" below.
-	 *
-	 * case NETDEV_XXX:
-	 *	ASSERT_RTNL_NET(net);
-	 *	break;
-	 */
-	}
-
-	/* Just to avoid unused-variable error for dev and net. */
-	if (0)
+	case NETDEV_CHANGENAME:
 		ASSERT_RTNL_NET(net);
+		break;
+	}
 
 	return NOTIFY_DONE;
 }