kubeadm: add validation to verify that the CertificateKey is a valid hex encoded AES key

cmd/kubeadm/app/apis/kubeadm/validation/validation.go

@@ -17,6 +17,7 @@ limitations under the License.
 package validation
 
 import (
+	"encoding/hex"
 	"fmt"
 	"net"
 	"net/url"
@@ -54,7 +55,7 @@ func ValidateInitConfiguration(c *kubeadm.InitConfiguration) field.ErrorList {
 	allErrs = append(allErrs, ValidateClusterConfiguration(&c.ClusterConfiguration)...)
 	// TODO(Arvinderpal): update advertiseAddress validation for dual-stack once it's implemented.
 	allErrs = append(allErrs, ValidateAPIEndpoint(&c.LocalAPIEndpoint, field.NewPath("localAPIEndpoint"))...)
-	// TODO: Maybe validate that .CertificateKey is a valid hex encoded AES key
+	allErrs = append(allErrs, ValidateCertificateKey(c.CertificateKey, field.NewPath("certificateKey"))...)
 	return allErrs
 }
 
@@ -98,7 +99,7 @@ func ValidateJoinControlPlane(c *kubeadm.JoinControlPlane, fldPath *field.Path)
 	allErrs := field.ErrorList{}
 	if c != nil {
 		allErrs = append(allErrs, ValidateAPIEndpoint(&c.LocalAPIEndpoint, fldPath.Child("localAPIEndpoint"))...)
-		// TODO: Maybe validate that .CertificateKey is a valid hex encoded AES key
+		allErrs = append(allErrs, ValidateCertificateKey(c.CertificateKey, field.NewPath("certificateKey"))...)
 	}
 	return allErrs
 }
@@ -594,6 +595,25 @@ func ValidateAPIEndpoint(c *kubeadm.APIEndpoint, fldPath *field.Path) field.Erro
 	return allErrs
 }
 
+// ValidateCertificateKey validates the certificate key is a valid hex encoded AES key
+func ValidateCertificateKey(certificateKey string, fldPath *field.Path) field.ErrorList {
+	allErrs := field.ErrorList{}
+
+	if len(certificateKey) > 0 {
+		decodedKey, err := hex.DecodeString(certificateKey)
+		if err != nil {
+			return append(allErrs, field.Invalid(fldPath, certificateKey, fmt.Sprintf("certificate key decoding error: %v", err)))
+		}
+
+		k := len(decodedKey)
+		if k != constants.CertificateKeySize {
+			allErrs = append(allErrs, field.Invalid(fldPath, certificateKey, fmt.Sprintf("invalid certificate key size %d, the key must be an AES key of size %d", k, constants.CertificateKeySize)))
+		}
+	}
+
+	return allErrs
+}
+
 // ValidateIgnorePreflightErrors validates duplicates in:
 // - ignore-preflight-errors flag and
 // - ignorePreflightErrors field in {Init,Join}Configuration files.

cmd/kubeadm/app/apis/kubeadm/validation/validation_test.go

@@ -455,6 +455,42 @@ func TestValidateAPIEndpoint(t *testing.T) {
 	}
 }
 
+func TestValidateCertificateKey(t *testing.T) {
+	var tests = []struct {
+		name           string
+		certificateKey string
+		expected       bool
+	}{
+		{
+			name:           "Valid certificate key",
+			certificateKey: "e6a2eb8581237ab72a4f494f30285ec12a9694d750b9785706a83bfcbbbd2204",
+			expected:       true,
+		},
+		{
+			name:           "Invalid hex encoded string",
+			certificateKey: "z6a2eb8581237ab72a4f494f30285ec12a9694d750b9785706a83bfcbbbd2204",
+			expected:       false,
+		},
+		{
+			name:           "Invalid AES key size",
+			certificateKey: "e6a2",
+			expected:       false,
+		},
+	}
+	for _, rt := range tests {
+		actual := ValidateCertificateKey(rt.certificateKey, nil)
+		t.Log(actual)
+		if (len(actual) == 0) != rt.expected {
+			t.Errorf(
+				"%s test case failed:\n\texpected: %t\n\t  actual: %t",
+				rt.name,
+				rt.expected,
+				(len(actual) == 0),
+			)
+		}
+	}
+}
+
 // TODO: Create a separated test for ValidateClusterConfiguration
 func TestValidateInitConfiguration(t *testing.T) {
 	nodename := "valid-nodename"