From: Jiri Pirko <jiri@resnulli.us>
Date: Sat, 27 Jul 2019 11:44:57 +0200

+	if ((netns_pid_attr && (netns_fd_attr || netns_id_attr)) ||
+	    (netns_fd_attr && (netns_pid_attr || netns_id_attr)) ||
+	    (netns_id_attr && (netns_pid_attr || netns_fd_attr))) {
+		NL_SET_ERR_MSG(info->extack, "multiple netns identifying attributes specified");
+		return ERR_PTR(-EINVAL);
+	}

How about:

	if (!!a + !!b + !!c > 1) {
	...

+
+	if (netns_pid_attr) {
+		net = get_net_ns_by_pid(nla_get_u32(netns_pid_attr));
+	} else if (netns_fd_attr) {
+		net = get_net_ns_by_fd(nla_get_u32(netns_fd_attr));
+	} else if (netns_id_attr) {
+		net = get_net_ns_by_id(sock_net(skb->sk),
+				       nla_get_u32(netns_id_attr));
+		if (!net)
+			net = ERR_PTR(-EINVAL);
+	}
+	if (IS_ERR(net)) {

I think this is going to be one of those cases where a compiler won't be able
to prove that 'net' is guaranteed to be initialized at this spot.  Please
rearrange this code somehow so that is unlikely to happen.

Thanks.