nexthop: Only parse NHA_OP_FLAGS for get messages that require it

The attribute is parsed into 'op_flags' in nh_valid_get_del_req() which
is called from the handlers of three message types: RTM_DELNEXTHOP,
RTM_GETNEXTHOPBUCKET and RTM_GETNEXTHOP. The attribute is only used by
the latter and rejected by the policies of the other two.

Pass 'op_flags' as NULL from the handlers of the other two and only
parse the attribute when the argument is not NULL.

This is a preparation for a subsequent patch.

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20240311162307.545385-2-idosch@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: idosch

net/ipv4/nexthop.c

@@ -3230,10 +3230,12 @@ static int nh_valid_get_del_req(const struct nlmsghdr *nlh,
 		return -EINVAL;
 	}
 
-	if (tb[NHA_OP_FLAGS])
-		*op_flags = nla_get_u32(tb[NHA_OP_FLAGS]);
-	else
-		*op_flags = 0;
+	if (op_flags) {
+		if (tb[NHA_OP_FLAGS])
+			*op_flags = nla_get_u32(tb[NHA_OP_FLAGS]);
+		else
+			*op_flags = 0;
+	}
 
 	return 0;
 }
@@ -3250,7 +3252,6 @@ static int rtm_del_nexthop(struct sk_buff *skb, struct nlmsghdr *nlh,
 		.portid = NETLINK_CB(skb).portid,
 	};
 	struct nexthop *nh;
-	u32 op_flags;
 	int err;
 	u32 id;
 
@@ -3259,7 +3260,7 @@ static int rtm_del_nexthop(struct sk_buff *skb, struct nlmsghdr *nlh,
 	if (err < 0)
 		return err;
 
-	err = nh_valid_get_del_req(nlh, tb, &id, &op_flags, extack);
+	err = nh_valid_get_del_req(nlh, tb, &id, NULL, extack);
 	if (err)
 		return err;
 
@@ -3716,15 +3717,14 @@ static int nh_valid_get_bucket_req(const struct nlmsghdr *nlh,
 				   struct netlink_ext_ack *extack)
 {
 	struct nlattr *tb[NHA_MAX + 1];
-	u32 op_flags;
 	int err;
 
 	err = nlmsg_parse(nlh, sizeof(struct nhmsg), tb, NHA_MAX,
 			  rtm_nh_policy_get_bucket, extack);
 	if (err < 0)
 		return err;
 
-	err = nh_valid_get_del_req(nlh, tb, id, &op_flags, extack);
+	err = nh_valid_get_del_req(nlh, tb, id, NULL, extack);
 	if (err)
 		return err;