hsr: hold rcu and dev lock for hsr_get_port_ndev

hsr_get_port_ndev calls hsr_for_each_port, which need to hold rcu lock.
On the other hand, before return the port device, we need to hold the
device reference to avoid UaF in the caller function.

Suggested-by: Paolo Abeni <pabeni@redhat.com>
Fixes: 9c10dd8 ("net: hsr: Create and export hsr_get_port_ndev()")
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250905091533.377443-4-liuhangbin@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: liuhangbin

drivers/net/ethernet/ti/icssg/icssg_prueth.c

@@ -654,7 +654,7 @@ static void icssg_prueth_hsr_fdb_add_del(struct prueth_emac *emac,
 
 static int icssg_prueth_hsr_add_mcast(struct net_device *ndev, const u8 *addr)
 {
-	struct net_device *real_dev;
+	struct net_device *real_dev, *port_dev;
 	struct prueth_emac *emac;
 	u8 vlan_id, i;
 
@@ -663,11 +663,15 @@ static int icssg_prueth_hsr_add_mcast(struct net_device *ndev, const u8 *addr)
 
 	if (is_hsr_master(real_dev)) {
 		for (i = HSR_PT_SLAVE_A; i < HSR_PT_INTERLINK; i++) {
-			emac = netdev_priv(hsr_get_port_ndev(real_dev, i));
-			if (!emac)
+			port_dev = hsr_get_port_ndev(real_dev, i);
+			emac = netdev_priv(port_dev);
+			if (!emac) {
+				dev_put(port_dev);
 				return -EINVAL;
+			}
 			icssg_prueth_hsr_fdb_add_del(emac, addr, vlan_id,
 						     true);
+			dev_put(port_dev);
 		}
 	} else {
 		emac = netdev_priv(real_dev);
@@ -679,7 +683,7 @@ static int icssg_prueth_hsr_add_mcast(struct net_device *ndev, const u8 *addr)
 
 static int icssg_prueth_hsr_del_mcast(struct net_device *ndev, const u8 *addr)
 {
-	struct net_device *real_dev;
+	struct net_device *real_dev, *port_dev;
 	struct prueth_emac *emac;
 	u8 vlan_id, i;
 
@@ -688,11 +692,15 @@ static int icssg_prueth_hsr_del_mcast(struct net_device *ndev, const u8 *addr)
 
 	if (is_hsr_master(real_dev)) {
 		for (i = HSR_PT_SLAVE_A; i < HSR_PT_INTERLINK; i++) {
-			emac = netdev_priv(hsr_get_port_ndev(real_dev, i));
-			if (!emac)
+			port_dev = hsr_get_port_ndev(real_dev, i);
+			emac = netdev_priv(port_dev);
+			if (!emac) {
+				dev_put(port_dev);
 				return -EINVAL;
+			}
 			icssg_prueth_hsr_fdb_add_del(emac, addr, vlan_id,
 						     false);
+			dev_put(port_dev);
 		}
 	} else {
 		emac = netdev_priv(real_dev);

net/hsr/hsr_device.c

@@ -675,9 +675,14 @@ struct net_device *hsr_get_port_ndev(struct net_device *ndev,
 	struct hsr_priv *hsr = netdev_priv(ndev);
 	struct hsr_port *port;
 
+	rcu_read_lock();
 	hsr_for_each_port(hsr, port)
-		if (port->type == pt)
+		if (port->type == pt) {
+			dev_hold(port->dev);
+			rcu_read_unlock();
 			return port->dev;
+		}
+	rcu_read_unlock();
 	return NULL;
 }
 EXPORT_SYMBOL(hsr_get_port_ndev);