Fix memory leak in library deinit

ENGINE_cleanup calls CRYPTO_free_ex_data and therefore,
CRYPTO_cleanup_all_ex_data - which cleans up the method pointers - must
run after ENGINE_cleanup.

Additionally, don't needlessly initialize the EX_CALLBACKS stack during
e.g. CRYPTO_free_ex_data. The only time this is actually needed is when
reserving the first ex data index. Specifically, since sk_num returns -1
on NULL input, the rest of the code already handles a NULL method stack
correctly.

Reviewed-by: Rich Salz <rsalz@openssl.org>

crypto/init.c

@@ -474,12 +474,17 @@ void OPENSSL_cleanup(void)
                     "RAND_cleanup()\n");
 
 #endif
-    CRYPTO_cleanup_all_ex_data();
-    EVP_cleanup();
-    CONF_modules_free();
+/*
+ * Note that cleanup order is important.
+ * For example, ENGINEs use CRYPTO_EX_DATA and therefore, must be cleaned up
+ * before the ex data handlers are wiped in CRYPTO_cleanup_all_ex_data().
+ */
 #ifndef OPENSSL_NO_ENGINE
     ENGINE_cleanup();
 #endif
+    CRYPTO_cleanup_all_ex_data();
+    EVP_cleanup();
+    CONF_modules_free();
     RAND_cleanup();
     base_inited = 0;
 }
@@ -628,5 +633,3 @@ int OPENSSL_atexit(void (*handler)(void))
 
     return 1;
 }
-
-