crypto: don't let builtin aes crash if no IV is provided

If no IV is provided, then use a default IV of all-zeros
instead of crashing. This gives parity with gcrypt and
nettle backends.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

crypto/cipher-builtin.c

@@ -25,8 +25,7 @@ typedef struct QCryptoCipherBuiltinAES QCryptoCipherBuiltinAES;
 struct QCryptoCipherBuiltinAES {
     AES_KEY encrypt_key;
     AES_KEY decrypt_key;
-    uint8_t *iv;
-    size_t niv;
+    uint8_t iv[AES_BLOCK_SIZE];
 };
 typedef struct QCryptoCipherBuiltinDESRFB QCryptoCipherBuiltinDESRFB;
 struct QCryptoCipherBuiltinDESRFB {
@@ -61,7 +60,6 @@ static void qcrypto_cipher_free_aes(QCryptoCipher *cipher)
 {
     QCryptoCipherBuiltin *ctxt = cipher->opaque;
 
-    g_free(ctxt->state.aes.iv);
     g_free(ctxt);
     cipher->opaque = NULL;
 }
@@ -145,15 +143,13 @@ static int qcrypto_cipher_setiv_aes(QCryptoCipher *cipher,
                                      Error **errp)
 {
     QCryptoCipherBuiltin *ctxt = cipher->opaque;
-    if (niv != 16) {
-        error_setg(errp, "IV must be 16 bytes not %zu", niv);
+    if (niv != AES_BLOCK_SIZE) {
+        error_setg(errp, "IV must be %d bytes not %zu",
+                   AES_BLOCK_SIZE, niv);
         return -1;
     }
 
-    g_free(ctxt->state.aes.iv);
-    ctxt->state.aes.iv = g_new0(uint8_t, niv);
-    memcpy(ctxt->state.aes.iv, iv, niv);
-    ctxt->state.aes.niv = niv;
+    memcpy(ctxt->state.aes.iv, iv, AES_BLOCK_SIZE);
 
     return 0;
 }

tests/test-crypto-cipher.c

@@ -287,6 +287,32 @@ static void test_cipher(const void *opaque)
     qcrypto_cipher_free(cipher);
 }
 
+
+static void test_cipher_null_iv(void)
+{
+    QCryptoCipher *cipher;
+    uint8_t key[32] = { 0 };
+    uint8_t plaintext[32] = { 0 };
+    uint8_t ciphertext[32] = { 0 };
+
+    cipher = qcrypto_cipher_new(
+        QCRYPTO_CIPHER_ALG_AES_256,
+        QCRYPTO_CIPHER_MODE_CBC,
+        key, sizeof(key),
+        &error_abort);
+    g_assert(cipher != NULL);
+
+    /* Don't call qcrypto_cipher_setiv */
+
+    qcrypto_cipher_encrypt(cipher,
+                           plaintext,
+                           ciphertext,
+                           sizeof(plaintext),
+                           &error_abort);
+
+    qcrypto_cipher_free(cipher);
+}
+
 int main(int argc, char **argv)
 {
     size_t i;
@@ -298,5 +324,9 @@ int main(int argc, char **argv)
     for (i = 0; i < G_N_ELEMENTS(test_data); i++) {
         g_test_add_data_func(test_data[i].path, &test_data[i], test_cipher);
     }
+
+    g_test_add_func("/crypto/cipher/null-iv",
+                    test_cipher_null_iv);
+
     return g_test_run();
 }