PodSecurity: baseline capabilities: cleanup

Rename to capabilities_baseline
Add unit test exercising forbidden reason and details
Consolidate integration test fixtures

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

@@ -26,20 +26,32 @@ import (
 	"k8s.io/pod-security-admission/api"
 )
 
+/*
+Adding NET_RAW or capabilities beyond the default set must be disallowed.
+
+**Restricted Fields:**
+spec.containers[*].securityContext.capabilities.add
+spec.initContainers[*].securityContext.capabilities.add
+
+**Allowed Values:**
+undefined / empty
+values from the default set "AUDIT_WRITE", "CHOWN", "DAC_OVERRIDE","FOWNER", "FSETID", "KILL", "MKNOD", "NET_BIND_SERVICE", "SETFCAP", "SETGID", "SETPCAP", "SETUID", "SYS_CHROOT"
+*/
+
 func init() {
-	addCheck(CheckAddCapabilities)
+	addCheck(CheckCapabilitiesBaseline)
 }
 
-// CheckAddCapabilities returns a baseline level check
+// CheckCapabilitiesBaseline returns a baseline level check
 // that limits the capabilities that can be added in 1.0+
-func CheckAddCapabilities() Check {
+func CheckCapabilitiesBaseline() Check {
 	return Check{
-		ID:    "addCapabilities",
+		ID:    "capabilities_baseline",
 		Level: api.LevelBaseline,
 		Versions: []VersionedCheck{
 			{
 				MinimumVersion: api.MajorMinorVersion(1, 0),
-				CheckPod:       addCapabilities_1_0,
+				CheckPod:       capabilitiesBaseline_1_0,
 			},
 		},
 	}
@@ -63,28 +75,33 @@ var (
 	)
 )
 
-func addCapabilities_1_0(podMetadata *metav1.ObjectMeta, podSpec *corev1.PodSpec) CheckResult {
+func capabilitiesBaseline_1_0(podMetadata *metav1.ObjectMeta, podSpec *corev1.PodSpec) CheckResult {
-	forbiddenContainers := sets.NewString()
+	var badContainers []string
-	forbiddenCapabilities := sets.NewString()
+	nonDefaultCapabilities := sets.NewString()
 	visitContainersWithPath(podSpec, field.NewPath("spec"), func(container *corev1.Container, path *field.Path) {
 		if container.SecurityContext != nil && container.SecurityContext.Capabilities != nil {
+			valid := true
 			for _, c := range container.SecurityContext.Capabilities.Add {
 				if !capabilities_allowed_1_0.Has(string(c)) {
-					forbiddenContainers.Insert(container.Name)
+					valid = false
-					forbiddenCapabilities.Insert(string(c))
+					nonDefaultCapabilities.Insert(string(c))
 				}
 			}
+			if !valid {
+				badContainers = append(badContainers, container.Name)
+			}
 		}
 	})
 
-	if len(forbiddenCapabilities) > 0 {
+	if len(badContainers) > 0 {
 		return CheckResult{
 			Allowed:         false,
-			ForbiddenReason: "forbidden capabilities",
+			ForbiddenReason: "non-default capabilities",
 			ForbiddenDetail: fmt.Sprintf(
-				"containers %q added %q",
+				"%s %s must not include %s in securityContext.capabilities.add",
-				forbiddenContainers.List(),
+				pluralize("container", "containers", len(badContainers)),
-				forbiddenCapabilities.List(),
+				joinQuote(badContainers),
+				joinQuote(nonDefaultCapabilities.List()),
 			),
 		}
 	}

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

@@ -0,0 +1,58 @@
+/*
+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 TestCapabilitiesBaseline(t *testing.T) {
+	tests := []struct {
+		name         string
+		pod          *corev1.Pod
+		expectReason string
+		expectDetail string
+	}{
+		{
+			name: "multiple containers",
+			pod: &corev1.Pod{Spec: corev1.PodSpec{
+				Containers: []corev1.Container{
+					{Name: "a", SecurityContext: &corev1.SecurityContext{Capabilities: &corev1.Capabilities{Add: []corev1.Capability{"FOO", "BAR"}}}},
+					{Name: "b", SecurityContext: &corev1.SecurityContext{Capabilities: &corev1.Capabilities{Add: []corev1.Capability{"BAR", "BAZ"}}}},
+				}}},
+			expectReason: `non-default capabilities`,
+			expectDetail: `containers "a", "b" must not include "BAR", "BAZ", "FOO" in securityContext.capabilities.add`,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			result := capabilitiesBaseline_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_capabilities_baseline.go

@@ -47,7 +47,7 @@ func ensureCapabilities(p *corev1.Pod) *corev1.Pod {
 
 func init() {
 	fixtureData_1_0 := fixtureGenerator{
-		expectErrorSubstring: "forbidden capabilities",
+		expectErrorSubstring: "non-default capabilities",
 		generatePass: func(p *corev1.Pod) []*corev1.Pod {
 			// don't generate fixtures if minimal valid pod drops ALL
 			if p.Spec.Containers[0].SecurityContext != nil && p.Spec.Containers[0].SecurityContext.Capabilities != nil {
@@ -65,8 +65,6 @@ func init() {
 					p.Spec.Containers[0].SecurityContext.Capabilities.Add = []corev1.Capability{
 						"AUDIT_WRITE", "CHOWN", "DAC_OVERRIDE", "FOWNER", "FSETID", "KILL", "MKNOD", "NET_BIND_SERVICE", "SETFCAP", "SETGID", "SETPCAP", "SETUID", "SYS_CHROOT",
 					}
-				}),
-				tweak(p, func(p *corev1.Pod) {
 					p.Spec.InitContainers[0].SecurityContext.Capabilities.Add = []corev1.Capability{
 						"AUDIT_WRITE", "CHOWN", "DAC_OVERRIDE", "FOWNER", "FSETID", "KILL", "MKNOD", "NET_BIND_SERVICE", "SETFCAP", "SETGID", "SETPCAP", "SETUID", "SYS_CHROOT",
 					}
@@ -80,6 +78,7 @@ func init() {
 				tweak(p, func(p *corev1.Pod) {
 					p.Spec.Containers[0].SecurityContext.Capabilities.Add = []corev1.Capability{"NET_RAW"}
 				}),
+				// ensure init container is enforced
 				tweak(p, func(p *corev1.Pod) {
 					p.Spec.InitContainers[0].SecurityContext.Capabilities.Add = []corev1.Capability{"NET_RAW"}
 				}),
@@ -87,29 +86,16 @@ func init() {
 				tweak(p, func(p *corev1.Pod) {
 					p.Spec.Containers[0].SecurityContext.Capabilities.Add = []corev1.Capability{"chown"}
 				}),
-				tweak(p, func(p *corev1.Pod) {
-					p.Spec.InitContainers[0].SecurityContext.Capabilities.Add = []corev1.Capability{"chown"}
-				}),
-				// unknown capability
-				tweak(p, func(p *corev1.Pod) {
-					p.Spec.Containers[0].SecurityContext.Capabilities.Add = []corev1.Capability{"bogus"}
-				}),
-				tweak(p, func(p *corev1.Pod) {
-					p.Spec.InitContainers[0].SecurityContext.Capabilities.Add = []corev1.Capability{"bogus"}
-				}),
 				// CAP_ prefix
 				tweak(p, func(p *corev1.Pod) {
 					p.Spec.Containers[0].SecurityContext.Capabilities.Add = []corev1.Capability{"CAP_CHOWN"}
 				}),
-				tweak(p, func(p *corev1.Pod) {
-					p.Spec.InitContainers[0].SecurityContext.Capabilities.Add = []corev1.Capability{"CAP_CHOWN"}
-				}),
 			}
 		},
 	}
 
 	registerFixtureGenerator(
-		fixtureKey{level: api.LevelBaseline, version: api.MajorMinorVersion(1, 0), check: "addCapabilities"},
+		fixtureKey{level: api.LevelBaseline, version: api.MajorMinorVersion(1, 0), check: "capabilities_baseline"},
 		fixtureData_1_0,
 	)
 }