PodSecurity: runAsNonRoot: cleanup

Improve message and details
Add unit tests
Consolidate integration test fixtures

staging/src/k8s.io/pod-security-admission/policy/check_runAsNonRoot.go

@@ -17,6 +17,7 @@ limitations under the License.
 package policy
 
 import (
+	"fmt"
 	"strings"
 
 	corev1 "k8s.io/api/core/v1"
@@ -34,7 +35,9 @@ spec.securityContext.runAsNonRoot
 spec.containers[*].securityContext.runAsNonRoot
 spec.initContainers[*].securityContext.runAsNonRoot
 
-**Allowed Values:** true
+**Allowed Values:**
+true
+undefined/null at container-level if pod-level is set to true
 */
 
 func init() {
@@ -57,47 +60,68 @@ func CheckRunAsNonRoot() Check {
 }
 
 func runAsNonRoot_1_0(podMetadata *metav1.ObjectMeta, podSpec *corev1.PodSpec) CheckResult {
-	var forbiddenPaths []string
+	// things that explicitly set runAsNonRoot=false
+	var badSetters []string
 
-	// TODO: how to check ephemeral containers
-
-	containerCount := 0
-	containerRunAsNonRootCount := 0
 	podRunAsNonRoot := false
-
-	visitContainersWithPath(podSpec, field.NewPath("spec"), func(container *corev1.Container, path *field.Path) {
-		containerCount++
-		if container.SecurityContext != nil && container.SecurityContext.RunAsNonRoot != nil {
-			if !*container.SecurityContext.RunAsNonRoot {
-				forbiddenPaths = append(forbiddenPaths, path.Child("securityContext", "runAsNonRoot").String())
-			} else {
-				containerRunAsNonRootCount++
-			}
-		}
-	})
-
 	if podSpec.SecurityContext != nil && podSpec.SecurityContext.RunAsNonRoot != nil {
 		if !*podSpec.SecurityContext.RunAsNonRoot {
-			forbiddenPaths = append(forbiddenPaths, field.NewPath("spec").Child("securityContext", "runAsNonRoot").String())
+			badSetters = append(badSetters, "pod")
 		} else {
 			podRunAsNonRoot = true
 		}
 	}
 
+	// containers that explicitly set runAsNonRoot=false
+	var explicitlyBadContainers []string
+	// containers that didn't set runAsNonRoot and aren't caught by a pod-level runAsNonRoot=true
+	var implicitlyBadContainers []string
+
+	visitContainersWithPath(podSpec, field.NewPath("spec"), func(container *corev1.Container, path *field.Path) {
+		if container.SecurityContext != nil && container.SecurityContext.RunAsNonRoot != nil {
+			// container explicitly set runAsNonRoot
+			if !*container.SecurityContext.RunAsNonRoot {
+				// container explicitly set runAsNonRoot to a bad value
+				explicitlyBadContainers = append(explicitlyBadContainers, container.Name)
+			}
+		} else {
+			// container did not explicitly set runAsNonRoot
+			if !podRunAsNonRoot {
+				// no pod-level runAsNonRoot=true, so this container implicitly has a bad value
+				implicitlyBadContainers = append(implicitlyBadContainers, container.Name)
+			}
+		}
+	})
+
+	if len(explicitlyBadContainers) > 0 {
+		badSetters = append(
+			badSetters,
+			fmt.Sprintf(
+				"%s %s",
+				pluralize("container", "containers", len(explicitlyBadContainers)),
+				joinQuote(explicitlyBadContainers),
+			),
+		)
+	}
 	// pod or containers explicitly set runAsNonRoot=false
-	if len(forbiddenPaths) > 0 {
+	if len(badSetters) > 0 {
 		return CheckResult{
 			Allowed:         false,
-			ForbiddenReason: "runAsNonRoot != false",
-			ForbiddenDetail: strings.Join(forbiddenPaths, ", "),
+			ForbiddenReason: "runAsNonRoot != true",
+			ForbiddenDetail: fmt.Sprintf("%s must not set securityContext.runAsNonRoot=false", strings.Join(badSetters, " and ")),
 		}
 	}
 
 	// pod didn't set runAsNonRoot and not all containers opted into runAsNonRoot
-	if podRunAsNonRoot == false && containerCount > containerRunAsNonRootCount {
+	if len(implicitlyBadContainers) > 0 {
 		return CheckResult{
 			Allowed:         false,
-			ForbiddenReason: "runAsNonRoot != false",
+			ForbiddenReason: "runAsNonRoot != true",
+			ForbiddenDetail: fmt.Sprintf(
+				"pod or %s %s must set securityContext.runAsNonRoot=true",
+				pluralize("container", "containers", len(implicitlyBadContainers)),
+				joinQuote(implicitlyBadContainers),
+			),
 		}
 	}
 

staging/src/k8s.io/pod-security-admission/policy/check_runAsNonRoot_test.go

@@ -0,0 +1,99 @@
+/*
+Copyright 2021 The Kubernetes 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 policy
+
+import (
+	"testing"
+
+	corev1 "k8s.io/api/core/v1"
+	utilpointer "k8s.io/utils/pointer"
+)
+
+func TestRunAsNonRoot(t *testing.T) {
+	tests := []struct {
+		name         string
+		pod          *corev1.Pod
+		expectReason string
+		expectDetail string
+	}{
+		{
+			name: "no explicit runAsNonRoot",
+			pod: &corev1.Pod{Spec: corev1.PodSpec{
+				Containers: []corev1.Container{
+					{Name: "a"},
+				},
+			}},
+			expectReason: `runAsNonRoot != true`,
+			expectDetail: `pod or container "a" must set securityContext.runAsNonRoot=true`,
+		},
+		{
+			name: "pod runAsNonRoot=false",
+			pod: &corev1.Pod{Spec: corev1.PodSpec{
+				SecurityContext: &corev1.PodSecurityContext{RunAsNonRoot: utilpointer.Bool(false)},
+				Containers: []corev1.Container{
+					{Name: "a", SecurityContext: nil},
+				},
+			}},
+			expectReason: `runAsNonRoot != true`,
+			expectDetail: `pod must not set securityContext.runAsNonRoot=false`,
+		},
+		{
+			name: "containers runAsNonRoot=false",
+			pod: &corev1.Pod{Spec: corev1.PodSpec{
+				SecurityContext: &corev1.PodSecurityContext{RunAsNonRoot: utilpointer.Bool(true)},
+				Containers: []corev1.Container{
+					{Name: "a", SecurityContext: nil},
+					{Name: "b", SecurityContext: &corev1.SecurityContext{}},
+					{Name: "c", SecurityContext: &corev1.SecurityContext{RunAsNonRoot: utilpointer.Bool(false)}},
+					{Name: "d", SecurityContext: &corev1.SecurityContext{RunAsNonRoot: utilpointer.Bool(false)}},
+					{Name: "e", SecurityContext: &corev1.SecurityContext{RunAsNonRoot: utilpointer.Bool(true)}},
+					{Name: "f", SecurityContext: &corev1.SecurityContext{RunAsNonRoot: utilpointer.Bool(true)}},
+				},
+			}},
+			expectReason: `runAsNonRoot != true`,
+			expectDetail: `containers "c", "d" must not set securityContext.runAsNonRoot=false`,
+		},
+		{
+			name: "pod nil, container fallthrough",
+			pod: &corev1.Pod{Spec: corev1.PodSpec{
+				Containers: []corev1.Container{
+					{Name: "a", SecurityContext: nil},
+					{Name: "b", SecurityContext: &corev1.SecurityContext{}},
+					{Name: "d", SecurityContext: &corev1.SecurityContext{RunAsNonRoot: utilpointer.Bool(true)}},
+					{Name: "e", SecurityContext: &corev1.SecurityContext{RunAsNonRoot: utilpointer.Bool(true)}},
+				},
+			}},
+			expectReason: `runAsNonRoot != true`,
+			expectDetail: `pod or containers "a", "b" must set securityContext.runAsNonRoot=true`,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			result := runAsNonRoot_1_0(&tc.pod.ObjectMeta, &tc.pod.Spec)
+			if result.Allowed {
+				t.Fatal("expected disallowed")
+			}
+			if e, a := tc.expectReason, result.ForbiddenReason; e != a {
+				t.Errorf("expected\n%s\ngot\n%s", e, a)
+			}
+			if e, a := tc.expectDetail, result.ForbiddenDetail; e != a {
+				t.Errorf("expected\n%s\ngot\n%s", e, a)
+			}
+		})
+	}
+}

staging/src/k8s.io/pod-security-admission/test/fixtures_runAsNonRoot.go

@@ -52,12 +52,6 @@ func init() {
 					p.Spec.Containers[0].SecurityContext.RunAsNonRoot = pointer.BoolPtr(true)
 					p.Spec.InitContainers[0].SecurityContext.RunAsNonRoot = pointer.BoolPtr(true)
 				}),
-				// set at pod level and containers
-				tweak(p, func(p *corev1.Pod) {
-					p.Spec.SecurityContext.RunAsNonRoot = pointer.BoolPtr(true)
-					p.Spec.Containers[0].SecurityContext.RunAsNonRoot = pointer.BoolPtr(true)
-					p.Spec.InitContainers[0].SecurityContext.RunAsNonRoot = pointer.BoolPtr(true)
-				}),
 			}
 		},
 		generateFail: func(p *corev1.Pod) []*corev1.Pod {
@@ -74,12 +68,6 @@ func init() {
 				// explicit false on containers
 				tweak(p, func(p *corev1.Pod) { p.Spec.Containers[0].SecurityContext.RunAsNonRoot = pointer.BoolPtr(false) }),
 				tweak(p, func(p *corev1.Pod) { p.Spec.InitContainers[0].SecurityContext.RunAsNonRoot = pointer.BoolPtr(false) }),
-				// nil security contexts
-				tweak(p, func(p *corev1.Pod) {
-					p.Spec.SecurityContext = nil
-					p.Spec.Containers[0].SecurityContext = nil
-					p.Spec.InitContainers[0].SecurityContext = nil
-				}),
 			}
 		},
 	}