UI: Ensure there will be no race condition when getting the UI_METHOD ex_data

Reviewed-by: NMatt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2222)

crypto/ui/ui_util.c

@@ -8,6 +8,7 @@
  */
 
 #include <string.h>
+#include "internal/thread_once.h"
 #include "ui_locl.h"
 
 #ifndef BUFSIZ
@@ -83,18 +84,12 @@ static void ui_free_method_data(void *parent, void *ptr, CRYPTO_EX_DATA *ad,
     OPENSSL_free(ptr);
 }
 
-static int ui_method_data_index()
+static CRYPTO_ONCE get_index_once = CRYPTO_ONCE_STATIC_INIT;
+DEFINE_RUN_ONCE_STATIC(ui_method_data_index)
 {
-    static int idx = -1;
-
-    if (idx == -1)
-        idx = CRYPTO_get_ex_new_index(CRYPTO_EX_INDEX_UI_METHOD,
-                                      0, NULL,
-                                      ui_new_method_data,
-                                      ui_dup_method_data,
-                                      ui_free_method_data);
-
-    return idx;
+    return CRYPTO_get_ex_new_index(CRYPTO_EX_INDEX_UI_METHOD, 0, NULL,
+                                   ui_new_method_data, ui_dup_method_data,
+                                   ui_free_method_data);
 }
 
 static int ui_open(UI *ui)
@@ -109,7 +104,8 @@ static int ui_read(UI *ui, UI_STRING *uis)
             char result[PEM_BUFSIZE];
             const struct pem_password_cb_data *data =
                 UI_method_get_ex_data(UI_get_method(ui),
-                                      ui_method_data_index());
+                                      RUN_ONCE(&get_index_once,
+                                               ui_method_data_index));
             int maxsize = UI_get_result_maxsize(uis);
             int len = data->cb(result,
                                maxsize > PEM_BUFSIZE ? PEM_BUFSIZE : maxsize,
@@ -143,6 +139,7 @@ UI_METHOD *UI_UTIL_wrap_read_pem_callback(pem_password_cb *cb, int rwflag)
 {
     struct pem_password_cb_data *data = NULL;
     UI_METHOD *ui_method = NULL;
+    int idx = 0;
 
     if ((data = OPENSSL_zalloc(sizeof(*data))) == NULL
         || (ui_method = UI_create_method("PEM password callback wrapper")) == NULL
@@ -150,7 +147,8 @@ UI_METHOD *UI_UTIL_wrap_read_pem_callback(pem_password_cb *cb, int rwflag)
         || UI_method_set_reader(ui_method, ui_read) < 0
         || UI_method_set_writer(ui_method, ui_write) < 0
         || UI_method_set_closer(ui_method, ui_close) < 0
-        || UI_method_set_ex_data(ui_method, ui_method_data_index(), data) < 0) {
+        || (idx = RUN_ONCE(&get_index_once, ui_method_data_index)) <= 0
+        || UI_method_set_ex_data(ui_method, idx, data) < 0) {
         UI_destroy_method(ui_method);
         OPENSSL_free(data);
         return NULL;