[test] Make sm2_internal_test less fragile to changes in the ec module

Since these are KATs, the trailing randomness consumed by the ec module
does not really matter. So make the fake random buffer circular.

(cherry picked from commit 09736245b174a37abb87fb7ceb55462d940ff2bb)

Reviewed-by: Nicola Tuveri <nic.tuv@gmail.com>
Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
(Merged from https://github.com/openssl/openssl/pull/11435)

1 files changed, 9 insertions, 10 deletions

diff --git a/test/sm2_internal_test.c b/test/sm2_internal_test.c
index 952f688e8b..f7e4e38d03 100644
--- a/test/sm2_internal_test.c
+++ b/test/sm2_internal_test.c
@@ -32,17 +32,18 @@ static size_t fake_rand_size = 0;
 
 static int get_faked_bytes(unsigned char *buf, int num)
 {
-    int i;
-
     if (fake_rand_bytes == NULL)
         return saved_rand->bytes(buf, num);
 
-    if (!TEST_size_t_le(fake_rand_bytes_offset + num, fake_rand_size))
+    if (!TEST_size_t_gt(fake_rand_size, 0))
         return 0;
 
-    for (i = 0; i != num; ++i)
-        buf[i] = fake_rand_bytes[fake_rand_bytes_offset + i];
-    fake_rand_bytes_offset += num;
+    while (num-- > 0) {
+        if (fake_rand_bytes_offset >= fake_rand_size)
+            fake_rand_bytes_offset = 0;
+        *buf++ = fake_rand_bytes[fake_rand_bytes_offset++];
+    }
+
     return 1;
 }
 
@@ -175,8 +176,7 @@ static int test_sm2_crypt(const EC_GROUP *group,
 
     start_fake_rand(k_hex);
     if (!TEST_true(sm2_encrypt(key, digest, (const uint8_t *)message, msg_len,
-                               ctext, &ctext_len))
-            || !TEST_size_t_eq(fake_rand_bytes_offset, fake_rand_size)) {
+                               ctext, &ctext_len))) {
         restore_rand();
         goto done;
     }
@@ -296,8 +296,7 @@ static int test_sm2_sign(const EC_GROUP *group,
     start_fake_rand(k_hex);
     sig = sm2_do_sign(key, EVP_sm3(), (const uint8_t *)userid, strlen(userid),
                       (const uint8_t *)message, msg_len);
-    if (!TEST_ptr(sig)
-            || !TEST_size_t_eq(fake_rand_bytes_offset, fake_rand_size)) {
+    if (!TEST_ptr(sig)) {
         restore_rand();
         goto done;
     }