openvswitch: use RCU protection in ovs_vport_cmd_fill_info()

ovs_vport_cmd_fill_info() can be called without RTNL or RCU.

Use RCU protection and dev_net_rcu() to avoid potential UAF.

Fixes: 9354d45 ("openvswitch: reliable interface indentification in port dumps")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250207135841.1948589-6-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: edumazet

net/openvswitch/datapath.c

@@ -2101,6 +2101,7 @@ static int ovs_vport_cmd_fill_info(struct vport *vport, struct sk_buff *skb,
 {
 	struct ovs_header *ovs_header;
 	struct ovs_vport_stats vport_stats;
+	struct net *net_vport;
 	int err;
 
 	ovs_header = genlmsg_put(skb, portid, seq, &dp_vport_genl_family,
@@ -2117,12 +2118,15 @@ static int ovs_vport_cmd_fill_info(struct vport *vport, struct sk_buff *skb,
 	    nla_put_u32(skb, OVS_VPORT_ATTR_IFINDEX, vport->dev->ifindex))
 		goto nla_put_failure;
 
-	if (!net_eq(net, dev_net(vport->dev))) {
-		int id = peernet2id_alloc(net, dev_net(vport->dev), gfp);
+	rcu_read_lock();
+	net_vport = dev_net_rcu(vport->dev);
+	if (!net_eq(net, net_vport)) {
+		int id = peernet2id_alloc(net, net_vport, GFP_ATOMIC);
 
 		if (nla_put_s32(skb, OVS_VPORT_ATTR_NETNSID, id))
-			goto nla_put_failure;
+			goto nla_put_failure_unlock;
 	}
+	rcu_read_unlock();
 
 	ovs_vport_get_stats(vport, &vport_stats);
 	if (nla_put_64bit(skb, OVS_VPORT_ATTR_STATS,
@@ -2143,6 +2147,8 @@ static int ovs_vport_cmd_fill_info(struct vport *vport, struct sk_buff *skb,
 	genlmsg_end(skb, ovs_header);
 	return 0;
 
+nla_put_failure_unlock:
+	rcu_read_unlock();
 nla_put_failure:
 	err = -EMSGSIZE;
 error: