fix(initdata): reject combined certs in extra_root_certificates entries

Each array entry must contain exactly one certificate; bundles are now
caught early with a clear error naming the offending index.

Signed-off-by: Pradipta Banerjee <pradipta.banerjee@gmail.com>

Author: bpradipt

cmd/initdata/common.go

@@ -286,7 +286,15 @@ func extractCertsFromInitdata(data map[string]string) ([]certEntry, error) {
 			if extra, ok := img["extra_root_certificates"].([]interface{}); ok {
 				for i, c := range extra {
 					if cert, ok := c.(string); ok && cert != "" {
-						pemSources = append(pemSources, pemSource{cert, fmt.Sprintf("cdh.toml/image.extra_root_certificates[%d]", i)})
+						source := fmt.Sprintf("cdh.toml/image.extra_root_certificates[%d]", i)
+						certs, err := parsePEMCerts([]byte(cert))
+						if err != nil {
+							return nil, fmt.Errorf("%s: failed to parse: %w", source, err)
+						}
+						if len(certs) > 1 {
+							return nil, fmt.Errorf("%s: contains %d certificates; each array entry must contain exactly one certificate", source, len(certs))
+						}
+						pemSources = append(pemSources, pemSource{cert, source})
 					}
 				}
 			}

cmd/initdata/validate_test.go

@@ -132,6 +132,44 @@ func TestRunValidate_WithBothCACerts(t *testing.T) {
 	}
 }
 
+func TestRunValidate_CombinedExtraRootCertRejected(t *testing.T) {
+	_, _, pem1 := makeTestCACert(t)
+	_, _, pem2 := makeTestCACert(t)
+	combined := strings.ReplaceAll(string(append(pem1, pem2...)), "\n", "\\n")
+
+	tomlContent := `version = "0.1.0"
+algorithm = "sha256"
+
+[data]
+"aa.toml" = '''
+[token_configs]
+[token_configs.kbs]
+url = "http://kbs.example.svc:8080"
+'''
+"cdh.toml" = '''
+[kbc]
+name = "cc_kbc"
+url = "http://kbs.example.svc:8080"
+
+[image]
+extra_root_certificates = ["` + combined + `"]
+'''
+`
+	dir := t.TempDir()
+	path := dir + "/initdata.toml"
+	_ = os.WriteFile(path, []byte(tomlContent), 0600)
+	validateFile = path
+	defer func() { validateFile = "" }()
+
+	stderr, err := runValidateStderr(t)
+	if err == nil {
+		t.Fatal("expected validation failure for combined extra_root_certificates entry")
+	}
+	if !strings.Contains(stderr, "extra_root_certificates[0]") || !strings.Contains(stderr, "exactly one certificate") {
+		t.Errorf("expected 'extra_root_certificates[0]' and 'exactly one certificate' in stderr, got: %q", stderr)
+	}
+}
+
 func TestRunValidate_InvalidEmbeddedCert(t *testing.T) {
 	validateFile = "testdata/invalid-leaf-no-san.toml"
 	defer func() { validateFile = "" }()