A fix and a test case for Bug#16365 "Prepared Statements: DoS with

too many open statements". The patch adds a new global variable
@@max_prepared_stmt_count. This variable limits the total number
of prepared statements in the server. The default value of
@@max_prepared_stmt_count is 16382. 16382 small statements
(a select against 3 tables with GROUP, ORDER and LIMIT) consume 
100MB of RAM. Once this limit has been reached, the server will 
refuse to prepare a new statement and return ER_UNKNOWN_ERROR 
(unfortunately, we can't add new errors to 4.1 without breaking 5.0). The limit is changeable after startup
and can accept any value from 0 to 1 million. In case
the new value of the limit is less than the current
statement count, no new statements can be added, while the old
still can be used. Additionally, the current count of prepared 
statements is now available through a global read-only variable 
@@prepared_stmt_count.


mysql-test/r/ps.result:
  Test results fixed (a test case for Bug#16365)
mysql-test/t/ps.test:
  A test case for Bug#16365 "Prepared Statements: DoS with too many 
  open statements". Also fix statement leaks in other tests.
sql/mysql_priv.h:
  Add declarations for new global variables.
sql/mysqld.cc:
  Add definitions of max_prepared_stmt_count, prepared_stmt_count.
sql/set_var.cc:
  Implement support for @@prepared_stmt_count and 
  @@max_prepared_stmt_count. Currently these variables are queried
  without acquiring LOCK_prepared_stmt_count due to limitations of
  the set_var/sys_var class design. Updates are, however, protected 
  with a lock.
sql/set_var.h:
  New declarations to add support for @@max_prepared_stmt_count.
  Implement a new class, where the lock to be used when updating
  a variable is a parameter.
sql/sql_class.cc:
  Add accounting of the total number of prepared statements in the
  server to the methods of Statement_map.
sql/sql_class.h:
  Add accounting of the total number of prepared statements in the
  server to the methods of Statement_map.
sql/sql_prepare.cc:
  Statement_map::insert will now send a message in case of an
  error.

1 files changed, 37 insertions, 5 deletions

diff --git a/sql/set_var.cc b/sql/set_var.cc
index e10bfda62b7..681c70c4c02 100644
--- a/sql/set_var.cc
+++ b/sql/set_var.cc
@@ -118,6 +118,7 @@ static KEY_CACHE *create_key_cache(const char *name, uint length);
 void fix_sql_mode_var(THD *thd, enum_var_type type);
 static byte *get_error_count(THD *thd);
 static byte *get_warning_count(THD *thd);
+static byte *get_prepared_stmt_count(THD *thd);
 static byte *get_have_innodb(THD *thd);
 
 /*
@@ -239,6 +240,10 @@ sys_var_thd_ha_rows	sys_sql_max_join_size("sql_max_join_size",
 					      &SV::max_join_size,
 					      fix_max_join_size);
 #endif
+static sys_var_long_ptr_global
+sys_max_prepared_stmt_count("max_prepared_stmt_count",
+                            &max_prepared_stmt_count,
+                            &LOCK_prepared_stmt_count);
 sys_var_long_ptr	sys_max_relay_log_size("max_relay_log_size",
                                                &max_relay_log_size,
                                                fix_max_relay_log_size);
@@ -472,6 +477,9 @@ static sys_var_readonly		sys_warning_count("warning_count",
 						  OPT_SESSION,
 						  SHOW_LONG,
 						  get_warning_count);
+static sys_var_readonly	sys_prepared_stmt_count("prepared_stmt_count",
+                                                OPT_GLOBAL, SHOW_LONG,
+                                                get_prepared_stmt_count);
 
 /* alias for last_insert_id() to be compatible with Sybase */
 #ifdef HAVE_REPLICATION
@@ -569,6 +577,7 @@ sys_var *sys_variables[]=
   &sys_max_heap_table_size,
   &sys_max_join_size,
   &sys_max_length_for_sort_data,
+  &sys_max_prepared_stmt_count,
   &sys_max_relay_log_size,
   &sys_max_seeks_for_key,
   &sys_max_sort_length,
@@ -589,6 +598,7 @@ sys_var *sys_variables[]=
   &sys_new_mode,
   &sys_old_passwords,
   &sys_preload_buff_size,
+  &sys_prepared_stmt_count,
   &sys_pseudo_thread_id,
   &sys_query_alloc_block_size,
   &sys_query_cache_size,
@@ -801,6 +811,8 @@ struct show_var_st init_vars[]= {
   {sys_max_join_size.name,	(char*) &sys_max_join_size,	    SHOW_SYS},
   {sys_max_length_for_sort_data.name, (char*) &sys_max_length_for_sort_data,
    SHOW_SYS},
+  {sys_max_prepared_stmt_count.name, (char*) &sys_max_prepared_stmt_count,
+    SHOW_SYS},
   {sys_max_relay_log_size.name, (char*) &sys_max_relay_log_size,    SHOW_SYS},
   {sys_max_seeks_for_key.name,  (char*) &sys_max_seeks_for_key,	    SHOW_SYS},
   {sys_max_sort_length.name,	(char*) &sys_max_sort_length,	    SHOW_SYS},
@@ -838,6 +850,7 @@ struct show_var_st init_vars[]= {
   {sys_old_passwords.name,    (char*) &sys_old_passwords,           SHOW_SYS},
   {"open_files_limit",	      (char*) &open_files_limit,	    SHOW_LONG},
   {"pid_file",                (char*) pidfile_name,                 SHOW_CHAR},
+  {sys_prepared_stmt_count.name, (char*) &sys_prepared_stmt_count, SHOW_SYS},
   {"port",                    (char*) &mysqld_port,                  SHOW_INT},
   {sys_preload_buff_size.name, (char*) &sys_preload_buff_size,      SHOW_SYS},
   {"protocol_version",        (char*) &protocol_version,            SHOW_INT},
@@ -1251,29 +1264,40 @@ static void fix_server_id(THD *thd, enum_var_type type)
   server_id_supplied = 1;
 }
 
-bool sys_var_long_ptr::check(THD *thd, set_var *var)
+
+sys_var_long_ptr::
+sys_var_long_ptr(const char *name_arg, ulong *value_ptr,
+                 sys_after_update_func after_update_arg)
+  :sys_var_long_ptr_global(name_arg, value_ptr,
+                           &LOCK_global_system_variables, after_update_arg)
+{}
+
+
+bool sys_var_long_ptr_global::check(THD *thd, set_var *var)
 {
   longlong v= var->value->val_int();
   var->save_result.ulonglong_value= v < 0 ? 0 : v;
   return 0;
 }
 
-bool sys_var_long_ptr::update(THD *thd, set_var *var)
+bool sys_var_long_ptr_global::update(THD *thd, set_var *var)
 {
   ulonglong tmp= var->save_result.ulonglong_value;
-  pthread_mutex_lock(&LOCK_global_system_variables);
+  pthread_mutex_lock(guard);
   if (option_limits)
     *value= (ulong) getopt_ull_limit_value(tmp, option_limits);
   else
     *value= (ulong) tmp;
-  pthread_mutex_unlock(&LOCK_global_system_variables);
+  pthread_mutex_unlock(guard);
   return 0;
 }
 
 
-void sys_var_long_ptr::set_default(THD *thd, enum_var_type type)
+void sys_var_long_ptr_global::set_default(THD *thd, enum_var_type type)
 {
+  pthread_mutex_lock(guard);
   *value= (ulong) option_limits->def_value;
+  pthread_mutex_unlock(guard);
 }
 
 
@@ -2642,6 +2666,14 @@ static byte *get_have_innodb(THD *thd)
 }
 
 
+static byte *get_prepared_stmt_count(THD *thd)
+{
+  pthread_mutex_lock(&LOCK_prepared_stmt_count);
+  thd->sys_var_tmp.ulong_value= prepared_stmt_count;
+  pthread_mutex_unlock(&LOCK_prepared_stmt_count);
+  return (byte*) &thd->sys_var_tmp.ulong_value;
+}
+
 /****************************************************************************
   Main handling of variables:
   - Initialisation