PodSecurity: procMount: cleanup

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

@@ -27,6 +27,18 @@ import (
 	"k8s.io/pod-security-admission/api"
 )
 
+/*
+
+The default /proc masks are set up to reduce attack surface, and should be required.
+
+**Restricted Fields:**
+spec.containers[*].securityContext.procMount
+spec.initContainers[*].securityContext.procMount
+
+**Allowed Values:** undefined/null, "Default"
+
+*/
+
 func init() {
 	addCheck(CheckProcMount)
 }
@@ -41,14 +53,14 @@ func CheckProcMount() Check {
 		Versions: []VersionedCheck{
 			{
 				MinimumVersion: api.MajorMinorVersion(1, 0),
-				CheckPod:       checkProcMount_1_0,
+				CheckPod:       procMount_1_0,
 			},
 		},
 	}
 }
 
-func checkProcMount_1_0(podMetadata *metav1.ObjectMeta, podSpec *corev1.PodSpec) CheckResult {
+func procMount_1_0(podMetadata *metav1.ObjectMeta, podSpec *corev1.PodSpec) CheckResult {
-	forbiddenContainers := sets.NewString()
+	var badContainers []string
 	forbiddenProcMountTypes := sets.NewString()
 	visitContainersWithPath(podSpec, field.NewPath("spec"), func(container *corev1.Container, path *field.Path) {
 		// allow if the security context is nil.
@@ -61,18 +73,19 @@ func checkProcMount_1_0(podMetadata *metav1.ObjectMeta, podSpec *corev1.PodSpec)
 		}
 		// check if the value of the proc mount type is valid.
 		if *container.SecurityContext.ProcMount != v1.DefaultProcMount {
-			forbiddenContainers.Insert(container.Name)
+			badContainers = append(badContainers, container.Name)
 			forbiddenProcMountTypes.Insert(string(*container.SecurityContext.ProcMount))
 		}
 	})
-	if len(forbiddenContainers) > 0 {
+	if len(badContainers) > 0 {
 		return CheckResult{
 			Allowed:         false,
-			ForbiddenReason: "forbidden procMount",
+			ForbiddenReason: "procMount",
 			ForbiddenDetail: fmt.Sprintf(
-				"containers %q have forbidden procMount types %q",
+				"%s %s must not set securityContext.procMount to %s",
-				forbiddenContainers.List(),
+				pluralize("container", "containers", len(badContainers)),
-				forbiddenProcMountTypes.List(),
+				joinQuote(badContainers),
+				joinQuote(forbiddenProcMountTypes.List()),
 			),
 		}
 	}

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

@@ -0,0 +1,66 @@
+/*
+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"
+)
+
+func TestProcMount(t *testing.T) {
+	defaultValue := corev1.DefaultProcMount
+	unmaskedValue := corev1.UnmaskedProcMount
+	otherValue := corev1.ProcMountType("other")
+
+	tests := []struct {
+		name         string
+		pod          *corev1.Pod
+		expectReason string
+		expectDetail string
+	}{
+		{
+			name: "procMount",
+			pod: &corev1.Pod{Spec: corev1.PodSpec{
+				Containers: []corev1.Container{
+					{Name: "a", SecurityContext: nil},
+					{Name: "b", SecurityContext: &corev1.SecurityContext{}},
+					{Name: "c", SecurityContext: &corev1.SecurityContext{ProcMount: &defaultValue}},
+					{Name: "d", SecurityContext: &corev1.SecurityContext{ProcMount: &unmaskedValue}},
+					{Name: "e", SecurityContext: &corev1.SecurityContext{ProcMount: &otherValue}},
+				},
+			}},
+			expectReason: `procMount`,
+			expectDetail: `containers "d", "e" must not set securityContext.procMount to "Unmasked", "other"`,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			result := procMount_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_procMount.go

@@ -25,7 +25,7 @@ import (
 
 func init() {
 	fixtureData_1_0 := fixtureGenerator{
-		expectErrorSubstring: "forbidden procMount",
+		expectErrorSubstring: "procMount",
 		generatePass: func(p *v1.Pod) []*v1.Pod {
 			p = ensureSecurityContext(p)
 			return []*corev1.Pod{
@@ -43,13 +43,13 @@ func init() {
 			return []*corev1.Pod{
 				// set proc mount of container to a forbidden value
 				tweak(p, func(copy *v1.Pod) {
-					inValidProcMountType := v1.UnmaskedProcMount
+					unmaskedProcMountType := v1.UnmaskedProcMount
-					copy.Spec.Containers[0].SecurityContext.ProcMount = &inValidProcMountType
+					copy.Spec.Containers[0].SecurityContext.ProcMount = &unmaskedProcMountType
 				}),
 				// set proc mount of init container to a forbidden value
 				tweak(p, func(copy *v1.Pod) {
-					inValidProcMountType := v1.UnmaskedProcMount
+					unmaskedProcMountType := v1.UnmaskedProcMount
-					copy.Spec.InitContainers[0].SecurityContext.ProcMount = &inValidProcMountType
+					copy.Spec.InitContainers[0].SecurityContext.ProcMount = &unmaskedProcMountType
 				}),
 			}
 		},