acl: introduce package to enable global config

This introduces an `acl` package in `internal` which globally configures
the allowance to namespaced references, instead of having to pass on a
variable everywhere.

For the sake of security, the default behavior of the package itself is
to _not_ allow cross namespace references. However, the behavior of the
controller remains unchanged, and the configuration flag still enables
the allowance by default.

Signed-off-by: Hidde Beydals <hidde@hhh.computer>

internal/acl/acl.go

@@ -0,0 +1,43 @@
+/*
+Copyright 2023 The Flux authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package acl
+
+import (
+	"fmt"
+
+	"k8s.io/apimachinery/pkg/types"
+	"sigs.k8s.io/controller-runtime/pkg/client"
+
+	"github.com/fluxcd/pkg/runtime/acl"
+)
+
+var (
+	// AllowCrossNamespaceRef is a global flag that can be used to allow
+	// cross-namespace references.
+	AllowCrossNamespaceRef = false
+)
+
+// AllowsAccessTo returns an error if the object does not allow access to the
+// given reference.
+func AllowsAccessTo(obj client.Object, kind string, ref types.NamespacedName) error {
+	if !AllowCrossNamespaceRef && obj.GetNamespace() != ref.Namespace {
+		return acl.AccessDeniedError(fmt.Sprintf("cross-namespace references are not allowed: cannot access %s %s",
+			kind, ref.String(),
+		))
+	}
+	return nil
+}

internal/acl/acl_test.go

@@ -0,0 +1,93 @@
+/*
+Copyright 2023 The Flux authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package acl
+
+import (
+	v2 "github.com/fluxcd/helm-controller/api/v2beta2"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/types"
+	"sigs.k8s.io/controller-runtime/pkg/client"
+	"testing"
+)
+
+func TestAllowsAccessTo(t *testing.T) {
+	tests := []struct {
+		name    string
+		allow   bool
+		obj     client.Object
+		ref     types.NamespacedName
+		wantErr bool
+	}{
+		{
+			name:  "allow cross-namespace reference",
+			allow: true,
+			obj: &v2.HelmRelease{
+				ObjectMeta: metav1.ObjectMeta{
+					Name:      "some-name",
+					Namespace: "some-namespace",
+				},
+			},
+			ref: types.NamespacedName{
+				Name:      "some-name",
+				Namespace: "some-other-namespace",
+			},
+			wantErr: false,
+		},
+		{
+			name:  "disallow cross-namespace reference",
+			allow: false,
+			obj: &v2.HelmRelease{
+				ObjectMeta: metav1.ObjectMeta{
+					Name:      "some-name",
+					Namespace: "some-namespace",
+				},
+			},
+			ref: types.NamespacedName{
+				Name:      "some-name",
+				Namespace: "some-other-namespace",
+			},
+			wantErr: true,
+		},
+		{
+			name:  "allow same-namespace reference",
+			allow: false,
+			obj: &v2.HelmRelease{
+				ObjectMeta: metav1.ObjectMeta{
+					Name:      "some-name",
+					Namespace: "some-namespace",
+				},
+			},
+			ref: types.NamespacedName{
+				Name:      "some-name",
+				Namespace: "some-namespace",
+			},
+			wantErr: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			curAllow := AllowCrossNamespaceRef
+			AllowCrossNamespaceRef = tt.allow
+			t.Cleanup(func() { AllowCrossNamespaceRef = curAllow })
+
+			if err := AllowsAccessTo(tt.obj, "mock", tt.ref); (err != nil) != tt.wantErr {
+				t.Errorf("AllowsAccessTo() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}