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)

1 files changed, 3 insertions, 11 deletions

diff --git a/providers/implementations/rands/test_rng.c b/providers/implementations/rands/test_rng.c
index bdad7ac9ac..4e7fed0fc7 100644
--- a/providers/implementations/rands/test_rng.c
+++ b/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;
 }