Remove localhost calls from external names

Signed-off-by: Ricardo Pchevuzinske Katz <ricardo.katz@gmail.com>

.github/workflows/ci.yaml

@@ -159,7 +159,7 @@ jobs:
 
     strategy:
       matrix:
-        k8s: [v1.16.15, v1.17.17, v1.18.19, v1.19.11, v1.20.7, v1.21.0]
+        k8s: [v1.16.15, v1.17.17, v1.18.15, v1.19.7, v1.20.2]
 
     steps:
 

internal/ingress/controller/endpoints.go

@@ -50,6 +50,12 @@ func getEndpoints(s *corev1.Service, port *corev1.ServicePort, proto corev1.Prot
 
 	// ExternalName services
 	if s.Spec.Type == corev1.ServiceTypeExternalName {
+		if ip := net.ParseIP(s.Spec.ExternalName); s.Spec.ExternalName == "localhost" ||
+			(ip != nil && ip.IsLoopback()) {
+			klog.Errorf("Invalid attempt to use localhost name %s in %q", s.Spec.ExternalName, svcKey)
+			return upsServers
+		}
+
 		klog.V(3).Infof("Ingress using Service %q of type ExternalName.", svcKey)
 		targetPort := port.TargetPort.IntValue()
 		// if the externalName is not an IP address we need to validate is a valid FQDN

internal/ingress/controller/endpoints_test.go

@@ -78,6 +78,54 @@ func TestGetEndpoints(t *testing.T) {
 			},
 			[]ingress.Endpoint{},
 		},
+		{
+			"a service type ServiceTypeExternalName service with localhost in name should return 0 endpoint",
+			&corev1.Service{
+				Spec: corev1.ServiceSpec{
+					Type:         corev1.ServiceTypeExternalName,
+					ExternalName: "localhost",
+					Ports: []corev1.ServicePort{
+						{
+							Name:       "default",
+							TargetPort: intstr.FromInt(443),
+						},
+					},
+				},
+			},
+			&corev1.ServicePort{
+				Name:       "default",
+				TargetPort: intstr.FromInt(80),
+			},
+			corev1.ProtocolTCP,
+			func(string) (*corev1.Endpoints, error) {
+				return &corev1.Endpoints{}, nil
+			},
+			[]ingress.Endpoint{},
+		},
+		{
+			"a service type ServiceTypeExternalName service with 127.0.0.1 in name should return 0 endpoint",
+			&corev1.Service{
+				Spec: corev1.ServiceSpec{
+					Type:         corev1.ServiceTypeExternalName,
+					ExternalName: "127.0.0.1",
+					Ports: []corev1.ServicePort{
+						{
+							Name:       "default",
+							TargetPort: intstr.FromInt(443),
+						},
+					},
+				},
+			},
+			&corev1.ServicePort{
+				Name:       "default",
+				TargetPort: intstr.FromInt(80),
+			},
+			corev1.ProtocolTCP,
+			func(string) (*corev1.Endpoints, error) {
+				return &corev1.Endpoints{}, nil
+			},
+			[]ingress.Endpoint{},
+		},
 		{
 			"a service type ServiceTypeExternalName with a valid port should return one endpoint",
 			&corev1.Service{

rootfs/etc/nginx/lua/balancer.lua

@@ -35,6 +35,9 @@ local IMPLEMENTATIONS = {
   ewma = ewma,
 }
 
+local PROHIBITED_LOCALHOST_PORT = configuration.prohibited_localhost_port or '10246'
+local PROHIBITED_PEER_PATTERN = "^127.*:" .. PROHIBITED_LOCALHOST_PORT .. "$"
+
 local _M = {}
 local balancers = {}
 local backends_with_external_name = {}
@@ -317,6 +320,11 @@ function _M.balance()
     return
   end
 
+  if peer:match(PROHIBITED_PEER_PATTERN) then
+    ngx.log(ngx.ERR, "attempted to proxy to self, balancer: ", balancer.name, ", peer: ", peer)
+    return
+  end
+
   ngx_balancer.set_more_tries(1)
 
   local ok, err = ngx_balancer.set_current_peer(peer)

rootfs/etc/nginx/lua/tcp_udp_balancer.lua

@@ -25,6 +25,9 @@ local IMPLEMENTATIONS = {
   round_robin = round_robin
 }
 
+local PROHIBITED_LOCALHOST_PORT = configuration.prohibited_localhost_port or '10246'
+local PROHIBITED_PEER_PATTERN = "^127.*:" .. PROHIBITED_LOCALHOST_PORT .. "$"
+
 local _M = {}
 local balancers = {}
 local backends_with_external_name = {}
@@ -181,6 +184,11 @@ function _M.balance()
     return
   end
 
+  if peer:match(PROHIBITED_PEER_PATTERN) then
+    ngx.log(ngx.ERR, "attempted to proxy to self, balancer: ", balancer.name, ", peer: ", peer)
+    return
+  end
+
   ngx_balancer.set_more_tries(1)
 
   local ok, err = ngx_balancer.set_current_peer(peer)

rootfs/etc/nginx/template/nginx.tmpl

@@ -84,6 +84,7 @@ http {
           error("require failed: " .. tostring(res))
         else
           configuration = res
+          configuration.prohibited_localhost_port = '{{ .StatusPort }}'
         end
 
         ok, res = pcall(require, "balancer")
@@ -713,6 +714,8 @@ stream {
           error("require failed: " .. tostring(res))
         else
           tcp_udp_configuration = res
+          tcp_udp_configuration.prohibited_localhost_port = '{{ .StatusPort }}'
+
         end
 
         ok, res = pcall(require, "tcp_udp_balancer")