nexthop: Use a dedicated policy for nh_valid_get_del_req()

This function uses the global nexthop policy only to then bounce all
arguments except for NHA_ID. Instead, just create a new policy that
only includes the one allowed attribute.
Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/nexthop.c

@@ -36,6 +36,10 @@ static const struct nla_policy rtm_nh_policy[NHA_MAX + 1] = {
 	[NHA_FDB]		= { .type = NLA_FLAG },
 };
 
+static const struct nla_policy rtm_nh_policy_get[] = {
+	[NHA_ID]		= { .type = NLA_U32 },
+};
+
 static bool nexthop_notifiers_is_empty(struct net *net)
 {
 	return !net->nexthop.notifier_chain.head;
@@ -1842,28 +1846,16 @@ static int nh_valid_get_del_req(struct nlmsghdr *nlh, u32 *id,
 				struct netlink_ext_ack *extack)
 {
 	struct nhmsg *nhm = nlmsg_data(nlh);
-	struct nlattr *tb[NHA_MAX + 1];
-	int err, i;
+	struct nlattr *tb[ARRAY_SIZE(rtm_nh_policy_get)];
+	int err;
 
-	err = nlmsg_parse(nlh, sizeof(*nhm), tb, NHA_MAX, rtm_nh_policy,
-			  extack);
+	err = nlmsg_parse(nlh, sizeof(*nhm), tb,
+			  ARRAY_SIZE(rtm_nh_policy_get) - 1,
+			  rtm_nh_policy_get, extack);
 	if (err < 0)
 		return err;
 
 	err = -EINVAL;
-	for (i = 0; i < __NHA_MAX; ++i) {
-		if (!tb[i])
-			continue;
-
-		switch (i) {
-		case NHA_ID:
-			break;
-		default:
-			NL_SET_ERR_MSG_ATTR(extack, tb[i],
-					    "Unexpected attribute in request");
-			goto out;
-		}
-	}
 	if (nhm->nh_protocol || nhm->resvd || nhm->nh_scope || nhm->nh_flags) {
 		NL_SET_ERR_MSG(extack, "Invalid values in header");
 		goto out;