Bug#49894 shifted MYSQL_REPLICATION_PLUGIN number

The number for MYSQL_REPLICATION_PLUGIN was shifted when backporting
because MYSQL_AUDIT_PLUGIN was not backported.

This problem is fixed by backporting only the number of audit plugin
and print an error when trying to load audit plugins. Note that
replication plugins compiled against old MYSQL_REPLICATION_PLUGIN
number will also be recognized as audit plugin and be rejected.

include/mysql/plugin.h:
  backporting the number of audit plugin (MYSQL_AUDIT_PLUGIN)
sql/sql_plugin.cc:
  backporting the number of audit plugin (MYSQL_AUDIT_PLUGIN)
  print an error when trying to load audit plugins

include/mysql/plugin.h

@@ -80,8 +80,9 @@ typedef struct st_mysql_xid MYSQL_XID;
 #define MYSQL_FTPARSER_PLUGIN        2  /* Full-text parser plugin      */
 #define MYSQL_DAEMON_PLUGIN          3  /* The daemon/raw plugin type */
 #define MYSQL_INFORMATION_SCHEMA_PLUGIN  4  /* The I_S plugin type */
-#define MYSQL_REPLICATION_PLUGIN     5	/* The replication plugin type */
-#define MYSQL_MAX_PLUGIN_TYPE_NUM    6  /* The number of plugin types   */
+#define MYSQL_AUDIT_PLUGIN           5  /* The Audit plugin type        */
+#define MYSQL_REPLICATION_PLUGIN     6	/* The replication plugin type */
+#define MYSQL_MAX_PLUGIN_TYPE_NUM    7  /* The number of plugin types   */
 
 /* We use the following strings to define licenses for plugins */
 #define PLUGIN_LICENSE_PROPRIETARY 0

sql/sql_plugin.cc

@@ -47,6 +47,7 @@ const LEX_STRING plugin_type_names[MYSQL_MAX_PLUGIN_TYPE_NUM]=
   { C_STRING_WITH_LEN("FTPARSER") },
   { C_STRING_WITH_LEN("DAEMON") },
   { C_STRING_WITH_LEN("INFORMATION SCHEMA") },
+  { C_STRING_WITH_LEN("AUDIT") },
   { C_STRING_WITH_LEN("REPLICATION") },
 };
 
@@ -87,6 +88,7 @@ static int min_plugin_info_interface_version[MYSQL_MAX_PLUGIN_TYPE_NUM]=
   MYSQL_FTPARSER_INTERFACE_VERSION,
   MYSQL_DAEMON_INTERFACE_VERSION,
   MYSQL_INFORMATION_SCHEMA_INTERFACE_VERSION,
+  0x0000, /* place holder for audit plugin */
   MYSQL_REPLICATION_INTERFACE_VERSION,
 };
 static int cur_plugin_info_interface_version[MYSQL_MAX_PLUGIN_TYPE_NUM]=
@@ -96,6 +98,7 @@ static int cur_plugin_info_interface_version[MYSQL_MAX_PLUGIN_TYPE_NUM]=
   MYSQL_FTPARSER_INTERFACE_VERSION,
   MYSQL_DAEMON_INTERFACE_VERSION,
   MYSQL_INFORMATION_SCHEMA_INTERFACE_VERSION,
+  0x0000, /* place holder for audit plugin */
   MYSQL_REPLICATION_INTERFACE_VERSION,
 };
 
@@ -738,6 +741,14 @@ static bool plugin_add(MEM_ROOT *tmp_root,
                        name_len))
     {
       struct st_plugin_int *tmp_plugin_ptr;
+
+      if (plugin->type == MYSQL_AUDIT_PLUGIN)
+      {
+        /* Bug#49894 */
+        sql_print_error("Plugin type 'AUDIT' not supported by this server.");
+        goto err;
+      }
+
       if (*(int*)plugin->info <
           min_plugin_info_interface_version[plugin->type] ||
           ((*(int*)plugin->info) >> 8) >