CTR_DRBG: deprecate mbedtls_ctr_drbg_update because it ignores errors

Deprecate mbedtls_ctr_drbg_update (which returns void) in favor of a
new function mbedtls_ctr_drbg_update_ret which reports error.

include/mbedtls/ctr_drbg.h

@@ -248,9 +248,12 @@ int mbedtls_ctr_drbg_reseed( mbedtls_ctr_drbg_context *ctx,
  * \param additional   The data to update the state with.
  * \param add_len      Length of \p additional data.
  *
+ * \return             \c 0 on success.
+ * \return             An error from the underlying AES cipher on failure.
  */
-void mbedtls_ctr_drbg_update( mbedtls_ctr_drbg_context *ctx,
+int mbedtls_ctr_drbg_update_ret( mbedtls_ctr_drbg_context *ctx,
-                      const unsigned char *additional, size_t add_len );
+                                 const unsigned char *additional,
+                                 size_t add_len );
 
 /**
  * \brief   This function updates a CTR_DRBG instance with additional
@@ -290,6 +293,35 @@ int mbedtls_ctr_drbg_random_with_add( void *p_rng,
 int mbedtls_ctr_drbg_random( void *p_rng,
                      unsigned char *output, size_t output_len );
 
+
+#if ! defined(MBEDTLS_DEPRECATED_REMOVED)
+#if defined(MBEDTLS_DEPRECATED_WARNING)
+#define MBEDTLS_DEPRECATED    __attribute__((deprecated))
+#else
+#define MBEDTLS_DEPRECATED
+#endif
+/**
+ * \brief              This function updates the state of the CTR_DRBG context.
+ *
+ * \deprecated         Superseded by mbedtls_ctr_drbg_update_ret()
+ *                     in 2.16.0.
+ *
+ * \note               If \p add_len is greater than
+ *                     #MBEDTLS_CTR_DRBG_MAX_SEED_INPUT, only the first
+ *                     #MBEDTLS_CTR_DRBG_MAX_SEED_INPUT Bytes are used.
+ *                     The remaining Bytes are silently discarded.
+ *
+ * \param ctx          The CTR_DRBG context.
+ * \param additional   The data to update the state with.
+ * \param add_len      Length of \p additional data.
+ */
+MBEDTLS_DEPRECATED void mbedtls_ctr_drbg_update(
+    mbedtls_ctr_drbg_context *ctx,
+    const unsigned char *additional,
+    size_t add_len );
+#undef MBEDTLS_DEPRECATED
+#endif /* !MBEDTLS_DEPRECATED_REMOVED */
+
 #if defined(MBEDTLS_FS_IO)
 /**
  * \brief               This function writes a seed file.

library/ctr_drbg.c

@@ -331,24 +331,39 @@ exit:
  * and with outputs
  *   ctx = initial_working_state
  */
-void mbedtls_ctr_drbg_update( mbedtls_ctr_drbg_context *ctx,
+int mbedtls_ctr_drbg_update_ret( mbedtls_ctr_drbg_context *ctx,
-                      const unsigned char *additional, size_t add_len )
+                                 const unsigned char *additional,
+                                 size_t add_len )
 {
     unsigned char add_input[MBEDTLS_CTR_DRBG_SEEDLEN];
+    int ret;
 
-    if( add_len > 0 )
+    if( add_len == 0 )
-    {
+        return( 0 );
-        /* MAX_INPUT would be more logical here, but we have to match
-         * block_cipher_df()'s limits since we can't propagate errors */
-        if( add_len > MBEDTLS_CTR_DRBG_MAX_SEED_INPUT )
-            add_len = MBEDTLS_CTR_DRBG_MAX_SEED_INPUT;
 
-        block_cipher_df( add_input, additional, add_len );
+    if( ( ret = block_cipher_df( add_input, additional, add_len ) ) != 0 )
-        ctr_drbg_update_internal( ctx, add_input );
+        goto exit;
-        mbedtls_platform_zeroize( add_input, sizeof( add_input ) );
+    if( ( ret = ctr_drbg_update_internal( ctx, add_input ) ) != 0 )
-    }
+        goto exit;
+
+exit:
+    mbedtls_platform_zeroize( add_input, sizeof( add_input ) );
+    return( ret );
 }
 
+#if !defined(MBEDTLS_DEPRECATED_REMOVED)
+void mbedtls_ctr_drbg_update( mbedtls_ctr_drbg_context *ctx,
+                              const unsigned char *additional,
+                              size_t add_len )
+{
+    /* MAX_INPUT would be more logical here, but we have to match
+     * block_cipher_df()'s limits since we can't propagate errors */
+    if( add_len > MBEDTLS_CTR_DRBG_MAX_SEED_INPUT )
+        add_len = MBEDTLS_CTR_DRBG_MAX_SEED_INPUT;
+    (void) mbedtls_ctr_drbg_update_ret( ctx, additional, add_len );
+}
+#endif /* MBEDTLS_DEPRECATED_REMOVED */
+
 /* CTR_DRBG_Reseed with derivation function (SP 800-90A §10.2.1.4.2)
  * mbedtls_ctr_drbg_reseed(ctx, additional, len)
  * implements
@@ -573,7 +588,7 @@ int mbedtls_ctr_drbg_update_seed_file( mbedtls_ctr_drbg_context *ctx, const char
     if( fread( buf, 1, n, f ) != n )
         ret = MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR;
     else
-        mbedtls_ctr_drbg_update( ctx, buf, n );
+        ret = mbedtls_ctr_drbg_update_ret( ctx, buf, n );
 
     fclose( f );
 

tests/suites/test_suite_ctr_drbg.function

@@ -244,9 +244,11 @@ void ctr_drbg_entropy_usage(  )
     }
     TEST_ASSERT( last_idx == test_offset_idx );
 
-    /* Call update with too much data (sizeof entropy > MAX(_SEED)_INPUT)
+    /* Call update with too much data (sizeof entropy > MAX(_SEED)_INPUT).
-     * (just make sure it doesn't cause memory corruption) */
+     * Make sure it's detected as an error and doesn't cause memory
-    mbedtls_ctr_drbg_update( &ctx, entropy, sizeof( entropy ) );
+     * corruption. */
+    TEST_ASSERT( mbedtls_ctr_drbg_update_ret(
+                     &ctx, entropy, sizeof( entropy ) ) != 0 );
 
     /* Now enable PR, so the next few calls should all reseed */
     mbedtls_ctr_drbg_set_prediction_resistance( &ctx, MBEDTLS_CTR_DRBG_PR_ON );