test/evp_test.c: Check too big output buffer sizes in PKEYKDF tests

EVP_PKEY_derive() should be able to cope with a too big buffer for fixed
size outputs.  However, we don't test that.

This change modifies the PKEYKDF tests to ask EVP_PKEY_derive() what the
desired output buffer size is, and as long as the returned value isn't
absurd (indicating that anything goes), the output buffer is made to be
twice as big as what is expected.

Tests openssl#18517

Reviewed-by: Paul Dale <[email protected]>
Reviewed-by: Tomas Mraz <[email protected]>
(Merged from openssl#18533)

(cherry picked from commit a0587aa)

Author: levitte

test/evp_test.c

@@ -2897,7 +2897,23 @@ static int pkey_kdf_test_run(EVP_TEST *t)
 {
     PKEY_KDF_DATA *expected = t->data;
     unsigned char *got = NULL;
-    size_t got_len = expected->output_len;
+    size_t got_len = 0;
+
+    /* Find out the KDF output size */
+    if (EVP_PKEY_derive(expected->ctx, NULL, &got_len) <= 0) {
+        t->err = "INTERNAL_ERROR";
+        goto err;
+    }
+
+    /*
+     * We may get an absurd output size, which signals that anything goes.
+     * If not, we specify a too big buffer for the output, to test that
+     * EVP_PKEY_derive() can cope with it.
+     */
+    if (got_len == SIZE_MAX || got_len == 0)
+        got_len = expected->output_len;
+    else
+        got_len = expected->output_len * 2;
 
     if (!TEST_ptr(got = OPENSSL_malloc(got_len == 0 ? 1 : got_len))) {
         t->err = "INTERNAL_ERROR";