tests/external_override: Add override test for internal implementations

This adds a test to check if the internal implementation is not used
when it is not supposed to be used.

To be able to override functions using LD_PRELOAD, a shared version of
the torture library was added, as well as a shared library for each
of the algorithms implemented internally (ChaCha20, Poly1305,
curve25519, and ed25519).

Signed-off-by: Anderson Toshiyuki Sasaki <ansasaki@redhat.com>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>

tests/external_override/curve25519_override.h

@@ -0,0 +1,31 @@
+/*
+ * This file is part of the SSH Library
+ *
+ * Copyright (c) 2021 by Anderson Toshiyuki Sasaki - Red Hat, Inc.
+ *
+ * The SSH Library is free software: you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation, either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * The SSH Library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with the SSH Library; see the file COPYING. If not,
+ * see <https://www.gnu.org/licenses/>.
+ */
+
+#include "libssh/curve25519.h"
+
+int __wrap_crypto_scalarmult_base(unsigned char *q,
+                                  const unsigned char *n);
+
+int __wrap_crypto_scalarmult(unsigned char *q,
+                             const unsigned char *n,
+                             const unsigned char *p);
+
+bool internal_curve25519_function_called(void);
+void reset_curve25519_function_called(void);