asset/*: fix ip address calculations

The issue was a result of IPNet's ParseCIDR() always returning a 16-byte
address, while some third-party libraries assume that the address length
corresponds to whether or not IPv6 is in use.

pkg/asset/manifests/kube-core-operator.go

@@ -2,7 +2,6 @@ package manifests
 
 import (
 	"fmt"
-	"net"
 	"strings"
 
 	"github.com/ghodss/yaml"
@@ -85,8 +84,7 @@ func (kco *kubeCoreOperator) coreConfig() (*kubecore.OperatorConfig, error) {
 	coreConfig.AuthConfig.OIDCGroupsClaim = authConfigOIDCGroupsClaim
 	coreConfig.AuthConfig.OIDCUsernameClaim = authConfigOIDCUsernameClaim
 
-	svcCidr := kco.installConfig.Networking.ServiceCIDR
-	ip, err := cidr.Host(&net.IPNet{IP: svcCidr.IP, Mask: svcCidr.Mask}, 10)
+	ip, err := cidr.Host(&kco.installConfig.Networking.ServiceCIDR.IPNet, 10)
 	if err != nil {
 		return nil, err
 	}

pkg/ipnet/ipnet.go

@@ -52,7 +52,19 @@ func (ipnet *IPNet) UnmarshalJSON(b []byte) (err error) {
 	if err != nil {
 		return err
 	}
-	ipnet.IP = ip
+
+	// This check is needed in order to work around a strange quirk in the Go
+	// standard library. All of the addresses returned by net.ParseCIDR() are
+	// 16-byte addresses. This does _not_ imply that they are IPv6 addresses,
+	// which is what some libraries (e.g. github.com/apparentlymart/go-cidr)
+	// assume. By forcing the address to be the expected length, we can work
+	// around these bugs.
+	if ip.To4() != nil {
+		ipnet.IP = ip.To4()
+	} else {
+		ipnet.IP = ip
+	}
 	ipnet.Mask = net.Mask
+
 	return nil
 }