Bug #30191834: SERVER CAN MAKE CLIENT LOAD AUTH-PLUGIN FROM ANY DIRECTORY

Post push fix.
i_mysql_client_test was failing because of invalid address access.

RB#23351

Author: Bharathy Satish

sql-common/client_plugin.cc

@@ -405,6 +405,7 @@ struct st_mysql_client_plugin *mysql_load_plugin_v(MYSQL *mysql,
   void *sym, *dlhandle;
   struct st_mysql_client_plugin *plugin;
   const char *plugindir;
+  const CHARSET_INFO *cs = nullptr;
   size_t len = (name ? strlen(name) : 0);
   int well_formed_error;
   size_t res = 0;
@@ -435,15 +436,18 @@ struct st_mysql_client_plugin *mysql_load_plugin_v(MYSQL *mysql,
       plugindir = PLUGINDIR;
     }
   }
+  if (mysql && mysql->charset)
+    cs = mysql->charset;
+  else
+    cs = &my_charset_utf8mb4_bin;
   /* check if plugin name does not have any directory separator character */
-  if ((my_strcspn(mysql->charset, name, name + len, FN_DIRSEP,
-                  strlen(FN_DIRSEP))) < len) {
+  if ((my_strcspn(cs, name, name + len, FN_DIRSEP, strlen(FN_DIRSEP))) < len) {
     errmsg = "No paths allowed for shared library";
     goto err;
   }
   /* check if plugin name does not exceed its maximum length */
-  res = mysql->charset->cset->well_formed_len(
-      mysql->charset, name, name + len, NAME_CHAR_LEN, &well_formed_error);
+  res = cs->cset->well_formed_len(cs, name, name + len, NAME_CHAR_LEN,
+                                  &well_formed_error);
 
   if (well_formed_error || len != res) {
     errmsg = "Invalid plugin name";
@@ -453,7 +457,7 @@ struct st_mysql_client_plugin *mysql_load_plugin_v(MYSQL *mysql,
     check if length of(plugin_dir + plugin name) does not exceed its maximum
     length
   */
-  if (strlen(plugindir) + len + 1 >= FN_REFLEN) {
+  if ((strlen(plugindir) + len + 1) >= FN_REFLEN) {
     errmsg = "Invalid path";
     goto err;
   }