Merge: vrf: use RCU protection in l3mdev_l3_out()

MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9/-/merge_requests/6566

JIRA: https://issues.redhat.com/browse/RHEL-81542


Upstream Status: linux.git
CVE: CVE-2025-21791

Signed-off-by: Guillaume Nault <gnault@redhat.com>

Approved-by: Antoine Tenart <atenart@redhat.com>
Approved-by: Florian Westphal <fwestpha@redhat.com>
Approved-by: CKI KWF Bot <cki-ci-bot+kwf-gitlab-com@redhat.com>

Merged-by: Augusto Caringi <acaringi@redhat.com>

include/net/l3mdev.h

@@ -209,10 +209,12 @@ struct sk_buff *l3mdev_l3_out(struct sock *sk, struct sk_buff *skb, u16 proto)
 	if (netif_is_l3_slave(dev)) {
 		struct net_device *master;
 
+		rcu_read_lock();
 		master = netdev_master_upper_dev_get_rcu(dev);
 		if (master && master->l3mdev_ops->l3mdev_l3_out)
 			skb = master->l3mdev_ops->l3mdev_l3_out(master, sk,
 								skb, proto);
+		rcu_read_unlock();
 	}
 
 	return skb;