annotation validation: validate regex in common name annotation (#10657)

* fix common name validation

* add tests

internal/ingress/annotations/parser/validators.go

@@ -117,6 +117,20 @@ func ValidateRegex(regex *regexp.Regexp, removeSpace bool) AnnotationValidator {
 	}
 }
 
+// CommonNameAnnotationValidator checks whether the annotation value starts with
+// 'CN=' and is followed by a valid regex.
+func CommonNameAnnotationValidator(s string) error {
+	if !strings.HasPrefix(s, "CN=") {
+		return fmt.Errorf("value %s is not a valid Common Name annotation: missing prefix 'CN='", s)
+	}
+
+	if _, err := regexp.Compile(s[3:]); err != nil {
+		return fmt.Errorf("value %s is not a valid regex: %w", s, err)
+	}
+
+	return nil
+}
+
 // ValidateOptions receives an array of valid options that can be the value of annotation.
 // If no valid option is found, it will return an error
 func ValidateOptions(options []string, caseSensitive, trimSpace bool) AnnotationValidator {

internal/ingress/annotations/parser/validators_test.go

@@ -307,3 +307,59 @@ func TestCheckAnnotationRisk(t *testing.T) {
 		})
 	}
 }
+
+func TestCommonNameAnnotationValidator(t *testing.T) {
+	tests := []struct {
+		name       string
+		annotation string
+		wantErr    bool
+	}{
+		{
+			name:       "correct example",
+			annotation: `CN=(my\.common\.name)`,
+			wantErr:    false,
+		},
+		{
+			name:       "no CN= prefix",
+			annotation: `(my\.common\.name)`,
+			wantErr:    true,
+		},
+		{
+			name:       "invalid prefix",
+			annotation: `CN(my\.common\.name)`,
+			wantErr:    true,
+		},
+		{
+			name:       "invalid regex",
+			annotation: `CN=(my\.common\.name]`,
+			wantErr:    true,
+		},
+		{
+			name:       "wildcard regex",
+			annotation: `CN=(my\..*\.name)`,
+			wantErr:    false,
+		},
+		{
+			name:       "somewhat complex regex",
+			annotation: "CN=(my\\.app\\.dev|.*\\.bbb\\.aaaa\\.tld)",
+			wantErr:    false,
+		},
+		{
+			name:       "another somewhat complex regex",
+			annotation: `CN=(my-app.*\.c\.defg\.net|other.app.com)`,
+			wantErr:    false,
+		},
+		{
+			name:       "nested parenthesis regex",
+			annotation: `CN=(api-one\.(asdf)?qwer\.webpage\.organization\.org)`,
+			wantErr:    false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if err := CommonNameAnnotationValidator(tt.annotation); (err != nil) != tt.wantErr {
+				t.Errorf("CommonNameAnnotationValidator() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}