test-rand: return failure on not enough data, allow parent

The test-rand RNG was returning success when it had some but insufficient data.
Now, it returns failure and doesn't advance the data pointer.

The test-rand RNG was failing when a parent was specified.  This case is now
ignored.

Fixes #16785

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/16905)

doc/man7/EVP_RAND-TEST-RAND.pod

@@ -52,9 +52,8 @@ they can all be set as well as read.
 =item "test_entropy" (B<OSSL_RAND_PARAM_TEST_ENTROPY>) <octet string>
 
 Sets the bytes returned when the test generator is sent an entropy request.
-When entropy is requested, these bytes are treated as a cyclic buffer and they
-are repeated as required.  The current position is remembered across generate
-calls.
+The current position is remembered across generate calls.
+If there are insufficient data present to satisfy a call, an error is returned.
 
 =item "test_nonce" (B<OSSL_RAND_PARAM_TEST_NONCE>) <octet string>
 

providers/implementations/rands/test_rng.c

@@ -52,9 +52,6 @@ static void *test_rng_new(void *provctx, void *parent,
 {
     PROV_TEST_RNG *t;
 
-    if (parent != NULL)
-        return NULL;
-
     t = OPENSSL_zalloc(sizeof(*t));
     if (t == NULL)
         return NULL;
@@ -107,16 +104,11 @@ static int test_rng_generate(void *vtest, unsigned char *out, size_t outlen,
                              const unsigned char *adin, size_t adin_len)
 {
     PROV_TEST_RNG *t = (PROV_TEST_RNG *)vtest;
-    size_t i;
 
-    if (strength > t->strength)
+    if (strength > t->strength || t->entropy_len - t->entropy_pos < outlen)
         return 0;
-
-    for (i = 0; i < outlen; i++) {
-        out[i] = t->entropy[t->entropy_pos++];
-        if (t->entropy_pos >= t->entropy_len)
-            break;
-    }
+    memcpy(out, t->entropy + t->entropy_pos, outlen);
+    t->entropy_pos += outlen;
     return 1;
 }
 

test/build.info

@@ -62,7 +62,7 @@ IF[{- !$disabled{tests} -}]
           context_internal_test aesgcmtest params_test evp_pkey_dparams_test \
           keymgmt_internal_test hexstr_test provider_status_test defltfips_test \
           bio_readbuffer_test user_property_test pkcs7_test upcallstest \
-          provfetchtest prov_config_test
+          provfetchtest prov_config_test rand_test
 
   IF[{- !$disabled{'deprecated-3.0'} -}]
     PROGRAMS{noinst}=enginetest
@@ -84,6 +84,10 @@ IF[{- !$disabled{tests} -}]
   INCLUDE[sanitytest]=../include ../apps/include
   DEPEND[sanitytest]=../libcrypto libtestutil.a
 
+  SOURCE[rand_test]=rand_test.c
+  INCLUDE[rand_test]=../include ../apps/include
+  DEPEND[rand_test]=../libcrypto libtestutil.a
+
   SOURCE[rsa_complex]=rsa_complex.c
   INCLUDE[rsa_complex]=../include ../apps/include
 

test/rand_test.c

@@ -0,0 +1,56 @@
+/*
+ * Copyright 2021 The OpenSSL Project Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License 2.0 (the >License>).  You may not use
+ * this file except in compliance with the License.  You can obtain a copy
+ * in the file LICENSE in the source distribution or at
+ * https://www.openssl.org/source/license.html
+ */
+
+#include <openssl/evp.h>
+#include <openssl/rand.h>
+#include <openssl/bio.h>
+#include <openssl/core_names.h>
+#include "testutil.h"
+
+static int test_rand(void)
+{
+    EVP_RAND_CTX *privctx;
+    OSSL_PARAM params[2], *p = params;
+    unsigned char entropy1[] = { 0x00, 0x01, 0x02, 0x03, 0x04, 0x05 };
+    unsigned char entropy2[] = { 0xff, 0xfe, 0xfd };
+    unsigned char outbuf[3];
+
+    if (!TEST_ptr(privctx = RAND_get0_private(NULL)))
+        return 0;
+
+    *p++ = OSSL_PARAM_construct_octet_string(OSSL_RAND_PARAM_TEST_ENTROPY,
+                                             entropy1, sizeof(entropy1));
+    *p = OSSL_PARAM_construct_end();
+
+    if (!TEST_ptr(privctx = RAND_get0_private(NULL))
+            || !TEST_true(EVP_RAND_CTX_set_params(privctx, params))
+            || !TEST_int_gt(RAND_priv_bytes(outbuf, sizeof(outbuf)), 0)
+            || !TEST_mem_eq(outbuf, sizeof(outbuf), entropy1, sizeof(outbuf))
+            || !TEST_int_le(RAND_priv_bytes(outbuf, sizeof(outbuf) + 1), 0)
+            || !TEST_int_gt(RAND_priv_bytes(outbuf, sizeof(outbuf)), 0)
+            || !TEST_mem_eq(outbuf, sizeof(outbuf),
+                            entropy1 + sizeof(outbuf), sizeof(outbuf)))
+        return 0;
+
+    *params = OSSL_PARAM_construct_octet_string(OSSL_RAND_PARAM_TEST_ENTROPY,
+                                                entropy2, sizeof(entropy2));
+    if (!TEST_true(EVP_RAND_CTX_set_params(privctx, params))
+            || !TEST_int_gt(RAND_priv_bytes(outbuf, sizeof(outbuf)), 0)
+            || !TEST_mem_eq(outbuf, sizeof(outbuf), entropy2, sizeof(outbuf)))
+        return 0;
+    return 1;
+}
+
+int setup_tests(void)
+{
+    if (!TEST_true(RAND_set_DRBG_type(NULL, "TEST-RAND", NULL, NULL, NULL)))
+        return 0;
+    ADD_TEST(test_rand);
+    return 1;
+}

test/recipes/05-test_rand.t

@@ -11,8 +11,9 @@ use warnings;
 use OpenSSL::Test;
 use OpenSSL::Test::Utils;
 
-plan tests => 2;
+plan tests => 3;
 setup("test_rand");
 
+ok(run(test(["rand_test"])));
 ok(run(test(["drbgtest"])));
 ok(run(test(["rand_status_test"])));