fix: crash when applying unquoted null (#8081)

Signed-off-by: Charles-Edouard Brétéché <charles.edouard@nirmata.com>

pkg/validation/policy/validate.go

@@ -639,6 +639,17 @@ func validateMatchKindHelper(rule kyvernov1.Rule) error {
 	return fmt.Errorf("at least one element must be specified in a kind block, the kind attribute is mandatory when working with the resources element")
 }
 
+// isMapStringString goes through a map to verify values are string
+func isMapStringString(m map[string]interface{}) bool {
+	// range over labels
+	for _, val := range m {
+		if val == nil || reflect.TypeOf(val).String() != "string" {
+			return false
+		}
+	}
+	return true
+}
+
 // isLabelAndAnnotationsString :- Validate if labels and annotations contains only string values
 func isLabelAndAnnotationsString(rule kyvernov1.Rule) bool {
 	checkLabelAnnotation := func(metaKey map[string]interface{}) bool {
@@ -646,21 +657,15 @@ func isLabelAndAnnotationsString(rule kyvernov1.Rule) bool {
 			if mk == "labels" {
 				labelKey, ok := metaKey[mk].(map[string]interface{})
 				if ok {
-					// range over labels
-					for _, val := range labelKey {
-						if reflect.TypeOf(val).String() != "string" {
-							return false
-						}
+					if !isMapStringString(labelKey) {
+						return false
 					}
 				}
 			} else if mk == "annotations" {
 				annotationKey, ok := metaKey[mk].(map[string]interface{})
 				if ok {
-					// range over annotations
-					for _, val := range annotationKey {
-						if reflect.TypeOf(val).String() != "string" {
-							return false
-						}
+					if !isMapStringString(annotationKey) {
+						return false
 					}
 				}
 			}

pkg/validation/policy/validate_test.go

@@ -3295,3 +3295,60 @@ func Test_ImmutableGenerateFields(t *testing.T) {
 		assert.Assert(t, (err != nil) == test.expectedErr, test.name, err)
 	}
 }
+
+func Test_isMapStringString(t *testing.T) {
+	type args struct {
+		m map[string]interface{}
+	}
+	tests := []struct {
+		name string
+		args args
+		want bool
+	}{{
+		name: "nil",
+		args: args{
+			m: nil,
+		},
+		want: true,
+	}, {
+		name: "empty",
+		args: args{
+			m: map[string]interface{}{},
+		},
+		want: true,
+	}, {
+		name: "string values",
+		args: args{
+			m: map[string]interface{}{
+				"a": "b",
+				"c": "d",
+			},
+		},
+		want: true,
+	}, {
+		name: "int value",
+		args: args{
+			m: map[string]interface{}{
+				"a": "b",
+				"c": 123,
+			},
+		},
+		want: false,
+	}, {
+		name: "nil value",
+		args: args{
+			m: map[string]interface{}{
+				"a": "b",
+				"c": nil,
+			},
+		},
+		want: false,
+	}}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := isMapStringString(tt.args.m); got != tt.want {
+				t.Errorf("checkLabelAnnotation() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}