crypto: add sanity checking of plaintext/ciphertext length

When encrypting/decrypting data, the plaintext/ciphertext
buffers are required to be a multiple of the cipher block
size. If this is not done, nettle will abort and gcrypt
will report an error. To get consistent behaviour add
explicit checks upfront for the buffer sizes.

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

crypto/cipher-builtin.c

@@ -39,6 +39,7 @@ struct QCryptoCipherBuiltin {
         QCryptoCipherBuiltinAES aes;
         QCryptoCipherBuiltinDESRFB desrfb;
     } state;
+    size_t blocksize;
     void (*free)(QCryptoCipher *cipher);
     int (*setiv)(QCryptoCipher *cipher,
                  const uint8_t *iv, size_t niv,
@@ -181,6 +182,7 @@ static int qcrypto_cipher_init_aes(QCryptoCipher *cipher,
         goto error;
     }
 
+    ctxt->blocksize = AES_BLOCK_SIZE;
     ctxt->free = qcrypto_cipher_free_aes;
     ctxt->setiv = qcrypto_cipher_setiv_aes;
     ctxt->encrypt = qcrypto_cipher_encrypt_aes;
@@ -282,6 +284,7 @@ static int qcrypto_cipher_init_des_rfb(QCryptoCipher *cipher,
     memcpy(ctxt->state.desrfb.key, key, nkey);
     ctxt->state.desrfb.nkey = nkey;
 
+    ctxt->blocksize = 8;
     ctxt->free = qcrypto_cipher_free_des_rfb;
     ctxt->setiv = qcrypto_cipher_setiv_des_rfb;
     ctxt->encrypt = qcrypto_cipher_encrypt_des_rfb;
@@ -370,6 +373,12 @@ int qcrypto_cipher_encrypt(QCryptoCipher *cipher,
 {
     QCryptoCipherBuiltin *ctxt = cipher->opaque;
 
+    if (len % ctxt->blocksize) {
+        error_setg(errp, "Length %zu must be a multiple of block size %zu",
+                   len, ctxt->blocksize);
+        return -1;
+    }
+
     return ctxt->encrypt(cipher, in, out, len, errp);
 }
 
@@ -382,6 +391,12 @@ int qcrypto_cipher_decrypt(QCryptoCipher *cipher,
 {
     QCryptoCipherBuiltin *ctxt = cipher->opaque;
 
+    if (len % ctxt->blocksize) {
+        error_setg(errp, "Length %zu must be a multiple of block size %zu",
+                   len, ctxt->blocksize);
+        return -1;
+    }
+
     return ctxt->decrypt(cipher, in, out, len, errp);
 }
 

crypto/cipher-gcrypt.c

@@ -34,6 +34,11 @@ bool qcrypto_cipher_supports(QCryptoCipherAlgorithm alg)
     }
 }
 
+typedef struct QCryptoCipherGcrypt QCryptoCipherGcrypt;
+struct QCryptoCipherGcrypt {
+    gcry_cipher_hd_t handle;
+    size_t blocksize;
+};
 
 QCryptoCipher *qcrypto_cipher_new(QCryptoCipherAlgorithm alg,
                                   QCryptoCipherMode mode,
@@ -41,7 +46,7 @@ QCryptoCipher *qcrypto_cipher_new(QCryptoCipherAlgorithm alg,
                                   Error **errp)
 {
     QCryptoCipher *cipher;
-    gcry_cipher_hd_t handle;
+    QCryptoCipherGcrypt *ctx;
     gcry_error_t err;
     int gcryalg, gcrymode;
 
@@ -87,7 +92,9 @@ QCryptoCipher *qcrypto_cipher_new(QCryptoCipherAlgorithm alg,
     cipher->alg = alg;
     cipher->mode = mode;
 
-    err = gcry_cipher_open(&handle, gcryalg, gcrymode, 0);
+    ctx = g_new0(QCryptoCipherGcrypt, 1);
+
+    err = gcry_cipher_open(&ctx->handle, gcryalg, gcrymode, 0);
     if (err != 0) {
         error_setg(errp, "Cannot initialize cipher: %s",
                    gcry_strerror(err));
@@ -100,10 +107,12 @@ QCryptoCipher *qcrypto_cipher_new(QCryptoCipherAlgorithm alg,
          * bizarre RFB variant of DES :-)
          */
         uint8_t *rfbkey = qcrypto_cipher_munge_des_rfb_key(key, nkey);
-        err = gcry_cipher_setkey(handle, rfbkey, nkey);
+        err = gcry_cipher_setkey(ctx->handle, rfbkey, nkey);
         g_free(rfbkey);
+        ctx->blocksize = 8;
     } else {
-        err = gcry_cipher_setkey(handle, key, nkey);
+        err = gcry_cipher_setkey(ctx->handle, key, nkey);
+        ctx->blocksize = 16;
     }
     if (err != 0) {
         error_setg(errp, "Cannot set key: %s",
@@ -111,11 +120,12 @@ QCryptoCipher *qcrypto_cipher_new(QCryptoCipherAlgorithm alg,
         goto error;
     }
 
-    cipher->opaque = handle;
+    cipher->opaque = ctx;
     return cipher;
 
  error:
-    gcry_cipher_close(handle);
+    gcry_cipher_close(ctx->handle);
+    g_free(ctx);
     g_free(cipher);
     return NULL;
 }
@@ -123,12 +133,13 @@ QCryptoCipher *qcrypto_cipher_new(QCryptoCipherAlgorithm alg,
 
 void qcrypto_cipher_free(QCryptoCipher *cipher)
 {
-    gcry_cipher_hd_t handle;
+    QCryptoCipherGcrypt *ctx;
     if (!cipher) {
         return;
     }
-    handle = cipher->opaque;
+    ctx = cipher->opaque;
-    gcry_cipher_close(handle);
+    gcry_cipher_close(ctx->handle);
+    g_free(ctx);
     g_free(cipher);
 }
 
@@ -139,10 +150,16 @@ int qcrypto_cipher_encrypt(QCryptoCipher *cipher,
                            size_t len,
                            Error **errp)
 {
-    gcry_cipher_hd_t handle = cipher->opaque;
+    QCryptoCipherGcrypt *ctx = cipher->opaque;
     gcry_error_t err;
 
-    err = gcry_cipher_encrypt(handle,
+    if (len % ctx->blocksize) {
+        error_setg(errp, "Length %zu must be a multiple of block size %zu",
+                   len, ctx->blocksize);
+        return -1;
+    }
+
+    err = gcry_cipher_encrypt(ctx->handle,
                               out, len,
                               in, len);
     if (err != 0) {
@@ -161,10 +178,16 @@ int qcrypto_cipher_decrypt(QCryptoCipher *cipher,
                            size_t len,
                            Error **errp)
 {
-    gcry_cipher_hd_t handle = cipher->opaque;
+    QCryptoCipherGcrypt *ctx = cipher->opaque;
     gcry_error_t err;
 
-    err = gcry_cipher_decrypt(handle,
+    if (len % ctx->blocksize) {
+        error_setg(errp, "Length %zu must be a multiple of block size %zu",
+                   len, ctx->blocksize);
+        return -1;
+    }
+
+    err = gcry_cipher_decrypt(ctx->handle,
                               out, len,
                               in, len);
     if (err != 0) {
@@ -180,11 +203,17 @@ int qcrypto_cipher_setiv(QCryptoCipher *cipher,
                          const uint8_t *iv, size_t niv,
                          Error **errp)
 {
-    gcry_cipher_hd_t handle = cipher->opaque;
+    QCryptoCipherGcrypt *ctx = cipher->opaque;
     gcry_error_t err;
 
-    gcry_cipher_reset(handle);
+    if (niv != ctx->blocksize) {
-    err = gcry_cipher_setiv(handle, iv, niv);
+        error_setg(errp, "Expected IV size %zu not %zu",
+                   ctx->blocksize, niv);
+        return -1;
+    }
+
+    gcry_cipher_reset(ctx->handle);
+    err = gcry_cipher_setiv(ctx->handle, iv, niv);
     if (err != 0) {
         error_setg(errp, "Cannot set IV: %s",
                    gcry_strerror(err));

crypto/cipher-nettle.c

@@ -69,7 +69,7 @@ struct QCryptoCipherNettle {
     nettle_cipher_func *alg_encrypt;
     nettle_cipher_func *alg_decrypt;
     uint8_t *iv;
-    size_t niv;
+    size_t blocksize;
 };
 
 bool qcrypto_cipher_supports(QCryptoCipherAlgorithm alg)
@@ -125,7 +125,7 @@ QCryptoCipher *qcrypto_cipher_new(QCryptoCipherAlgorithm alg,
         ctx->alg_encrypt = des_encrypt_wrapper;
         ctx->alg_decrypt = des_decrypt_wrapper;
 
-        ctx->niv = DES_BLOCK_SIZE;
+        ctx->blocksize = DES_BLOCK_SIZE;
         break;
 
     case QCRYPTO_CIPHER_ALG_AES_128:
@@ -140,14 +140,14 @@ QCryptoCipher *qcrypto_cipher_new(QCryptoCipherAlgorithm alg,
         ctx->alg_encrypt = aes_encrypt_wrapper;
         ctx->alg_decrypt = aes_decrypt_wrapper;
 
-        ctx->niv = AES_BLOCK_SIZE;
+        ctx->blocksize = AES_BLOCK_SIZE;
         break;
     default:
         error_setg(errp, "Unsupported cipher algorithm %d", alg);
         goto error;
     }
 
-    ctx->iv = g_new0(uint8_t, ctx->niv);
+    ctx->iv = g_new0(uint8_t, ctx->blocksize);
     cipher->opaque = ctx;
 
     return cipher;
@@ -184,6 +184,12 @@ int qcrypto_cipher_encrypt(QCryptoCipher *cipher,
 {
     QCryptoCipherNettle *ctx = cipher->opaque;
 
+    if (len % ctx->blocksize) {
+        error_setg(errp, "Length %zu must be a multiple of block size %zu",
+                   len, ctx->blocksize);
+        return -1;
+    }
+
     switch (cipher->mode) {
     case QCRYPTO_CIPHER_MODE_ECB:
         ctx->alg_encrypt(ctx->ctx_encrypt, len, out, in);
@@ -191,7 +197,7 @@ int qcrypto_cipher_encrypt(QCryptoCipher *cipher,
 
     case QCRYPTO_CIPHER_MODE_CBC:
         cbc_encrypt(ctx->ctx_encrypt, ctx->alg_encrypt,
-                    ctx->niv, ctx->iv,
+                    ctx->blocksize, ctx->iv,
                     len, out, in);
         break;
     default:
@@ -211,6 +217,12 @@ int qcrypto_cipher_decrypt(QCryptoCipher *cipher,
 {
     QCryptoCipherNettle *ctx = cipher->opaque;
 
+    if (len % ctx->blocksize) {
+        error_setg(errp, "Length %zu must be a multiple of block size %zu",
+                   len, ctx->blocksize);
+        return -1;
+    }
+
     switch (cipher->mode) {
     case QCRYPTO_CIPHER_MODE_ECB:
         ctx->alg_decrypt(ctx->ctx_decrypt ? ctx->ctx_decrypt : ctx->ctx_encrypt,
@@ -219,7 +231,7 @@ int qcrypto_cipher_decrypt(QCryptoCipher *cipher,
 
     case QCRYPTO_CIPHER_MODE_CBC:
         cbc_decrypt(ctx->ctx_decrypt ? ctx->ctx_decrypt : ctx->ctx_encrypt,
-                    ctx->alg_decrypt, ctx->niv, ctx->iv,
+                    ctx->alg_decrypt, ctx->blocksize, ctx->iv,
                     len, out, in);
         break;
     default:
@@ -235,9 +247,9 @@ int qcrypto_cipher_setiv(QCryptoCipher *cipher,
                          Error **errp)
 {
     QCryptoCipherNettle *ctx = cipher->opaque;
-    if (niv != ctx->niv) {
+    if (niv != ctx->blocksize) {
         error_setg(errp, "Expected IV size %zu not %zu",
-                   ctx->niv, niv);
+                   ctx->blocksize, niv);
         return -1;
     }
     memcpy(ctx->iv, iv, niv);

tests/test-crypto-cipher.c

@@ -313,6 +313,53 @@ static void test_cipher_null_iv(void)
     qcrypto_cipher_free(cipher);
 }
 
+static void test_cipher_short_plaintext(void)
+{
+    Error *err = NULL;
+    QCryptoCipher *cipher;
+    uint8_t key[32] = { 0 };
+    uint8_t plaintext1[20] = { 0 };
+    uint8_t ciphertext1[20] = { 0 };
+    uint8_t plaintext2[40] = { 0 };
+    uint8_t ciphertext2[40] = { 0 };
+    int ret;
+
+    cipher = qcrypto_cipher_new(
+        QCRYPTO_CIPHER_ALG_AES_256,
+        QCRYPTO_CIPHER_MODE_CBC,
+        key, sizeof(key),
+        &error_abort);
+    g_assert(cipher != NULL);
+
+    /* Should report an error as plaintext is shorter
+     * than block size
+     */
+    ret = qcrypto_cipher_encrypt(cipher,
+                                 plaintext1,
+                                 ciphertext1,
+                                 sizeof(plaintext1),
+                                 &err);
+    g_assert(ret == -1);
+    g_assert(err != NULL);
+
+    error_free(err);
+    err = NULL;
+
+    /* Should report an error as plaintext is larger than
+     * block size, but not a multiple of block size
+     */
+    ret = qcrypto_cipher_encrypt(cipher,
+                                 plaintext2,
+                                 ciphertext2,
+                                 sizeof(plaintext2),
+                                 &err);
+    g_assert(ret == -1);
+    g_assert(err != NULL);
+
+    error_free(err);
+    qcrypto_cipher_free(cipher);
+}
+
 int main(int argc, char **argv)
 {
     size_t i;
@@ -328,5 +375,8 @@ int main(int argc, char **argv)
     g_test_add_func("/crypto/cipher/null-iv",
                     test_cipher_null_iv);
 
+    g_test_add_func("/crypto/cipher/short-plaintext",
+                    test_cipher_short_plaintext);
+
     return g_test_run();
 }