Bug #15954872 "MAKE MDL SUBSYSTEM AND TABLE DEFINITION CACHE

ROBUST AGAINST BUGS IN CALLERS".

Both MDL subsystems and Table Definition Cache code assume
that callers ensure that names of objects passed to them are
not longer than NAME_LEN bytes. Unfortunately due to bugs in
callers this assumption might be broken in some cases. As
result we get nasty bugs causing buffer overruns when we
construct MDL key or TDC key from object names.

This patch makes MDL and TDC code more robust against such
bugs by ensuring that we always checking size of result
buffer when constructing MDL and TDC keys. This doesn't
free its callers from ensuring that both db and table names
are shorter than NAME_LEN bytes. But at least these steps
prevents buffer overruns in case of bug in caller, replacing
them with less harmful behavior.

This is 5.5-only version of patch.

Changed code of MDL_key::mdl_key_init() to take into account
size of buffer for the key.

Introduced new version of create_table_def_key() helper function
which constructs TDC key without risk of result buffer overrun.
Places in code that construct TDC keys were changed to use this
function.

Also changed rm_temporary_table() and open_new_frm() functions
to avoid use of "unsafe" strmov() and strxmov() functions and
use safer strnxmov() instead.

sql/mdl.h

@@ -241,8 +241,14 @@ public:
                     const char *db, const char *name)
   {
     m_ptr[0]= (char) mdl_namespace;
-    m_db_name_length= (uint16) (strmov(m_ptr + 1, db) - m_ptr - 1);
-    m_length= (uint16) (strmov(m_ptr + m_db_name_length + 2, name) - m_ptr + 1);
+    /*
+      It is responsibility of caller to ensure that db and object names
+      are not longer than NAME_LEN. Still we play safe and try to avoid
+      buffer overruns.
+    */
+    m_db_name_length= (uint16) (strmake(m_ptr + 1, db, NAME_LEN) - m_ptr - 1);
+    m_length= (uint16) (strmake(m_ptr + m_db_name_length + 2, name, NAME_LEN) -
+                        m_ptr + 1);
   }
   void mdl_key_init(const MDL_key *rhs)
   {

sql/sql_base.cc

@@ -316,8 +316,9 @@ uint create_table_def_key(THD *thd, char *key,
                           const TABLE_LIST *table_list,
                           bool tmp_table)
 {
-  uint key_length= (uint) (strmov(strmov(key, table_list->db)+1,
-                                  table_list->table_name)-key)+1;
+  uint key_length= create_table_def_key(key, table_list->db,
+                                        table_list->table_name);
+
   if (tmp_table)
   {
     int4store(key + key_length, thd->server_id);
@@ -815,13 +816,10 @@ void release_table_share(TABLE_SHARE *share)
 TABLE_SHARE *get_cached_table_share(const char *db, const char *table_name)
 {
   char key[NAME_LEN*2+2];
-  TABLE_LIST table_list;
   uint key_length;
   mysql_mutex_assert_owner(&LOCK_open);
 
-  table_list.db= (char*) db;
-  table_list.table_name= (char*) table_name;
-  key_length= create_table_def_key((THD*) 0, key, &table_list, 0);
+  key_length= create_table_def_key(key, db, table_name);
   return (TABLE_SHARE*) my_hash_search(&table_def_cache,
                                        (uchar*) key, key_length);
 }  
@@ -3168,7 +3166,7 @@ err_unlock:
 TABLE *find_locked_table(TABLE *list, const char *db, const char *table_name)
 {
   char	key[MAX_DBKEY_LENGTH];
-  uint key_length=(uint) (strmov(strmov(key,db)+1,table_name)-key)+1;
+  uint key_length= create_table_def_key(key, db, table_name);
 
   for (TABLE *table= list; table ; table=table->next)
   {
@@ -5994,17 +5992,27 @@ TABLE *open_table_uncached(THD *thd, const char *path, const char *db,
 }
 
 
-bool rm_temporary_table(handlerton *base, char *path)
+/**
+  Delete a temporary table.
+
+  @param base  Handlerton for table to be deleted.
+  @param path  Path to the table to be deleted (i.e. path
+               to its .frm without an extension).
+
+  @retval false - success.
+  @retval true  - failure.
+*/
+
+bool rm_temporary_table(handlerton *base, const char *path)
 {
   bool error=0;
   handler *file;
-  char *ext;
+  char frm_path[FN_REFLEN + 1];
   DBUG_ENTER("rm_temporary_table");
 
-  strmov(ext= strend(path), reg_ext);
-  if (mysql_file_delete(key_file_frm, path, MYF(0)))
+  strxnmov(frm_path, sizeof(frm_path) - 1, path, reg_ext, NullS);
+  if (mysql_file_delete(key_file_frm, frm_path, MYF(0)))
     error=1; /* purecov: inspected */
-  *ext= 0;				// remove extension
   file= get_new_handler((TABLE_SHARE*) 0, current_thd->mem_root, base);
   if (file && file->ha_delete_table(path))
   {
@@ -8943,7 +8951,7 @@ void tdc_remove_table(THD *thd, enum_tdc_remove_table_type remove_type,
               thd->mdl_context.is_lock_owner(MDL_key::TABLE, db, table_name,
                                              MDL_EXCLUSIVE));
 
-  key_length=(uint) (strmov(strmov(key,db)+1,table_name)-key)+1;
+  key_length= create_table_def_key(key, db, table_name);
 
   if ((share= (TABLE_SHARE*) my_hash_search(&table_def_cache,(uchar*) key,
                                             key_length)))
@@ -9056,12 +9064,14 @@ open_new_frm(THD *thd, TABLE_SHARE *share, const char *alias,
 {
   LEX_STRING pathstr;
   File_parser *parser;
-  char path[FN_REFLEN];
+  char path[FN_REFLEN+1];
   DBUG_ENTER("open_new_frm");
 
   /* Create path with extension */
-  pathstr.length= (uint) (strxmov(path, share->normalized_path.str, reg_ext,
-                                  NullS)- path);
+  pathstr.length= (uint) (strxnmov(path, sizeof(path) - 1,
+                                   share->normalized_path.str,
+                                   reg_ext,
+                                   NullS) - path);
   pathstr.str=    path;
 
   if ((parser= sql_parse_prepare(&pathstr, mem_root, 1)))

sql/sql_base.h

@@ -81,6 +81,31 @@ uint cached_table_definitions(void);
 uint create_table_def_key(THD *thd, char *key,
                           const TABLE_LIST *table_list,
                           bool tmp_table);
+
+/**
+  Create a table cache key for non-temporary table.
+
+  @param key         Buffer for key (must be at least NAME_LEN*2+2 bytes).
+  @param db          Database name.
+  @param table_name  Table name.
+
+  @return Length of key.
+
+  @sa create_table_def_key(thd, char *, table_list, bool)
+*/
+
+inline uint
+create_table_def_key(char *key, const char *db, const char *table_name)
+{
+  /*
+    In theory caller should ensure that both db and table_name are
+    not longer than NAME_LEN bytes. In practice we play safe to avoid
+    buffer overruns.
+  */
+  return (uint)(strmake(strmake(key, db, NAME_LEN) + 1, table_name,
+                        NAME_LEN) - key + 1);
+}
+
 TABLE_SHARE *get_table_share(THD *thd, TABLE_LIST *table_list, char *key,
                              uint key_length, uint db_flags, int *error,
                              my_hash_value_type hash_value);
@@ -157,7 +182,7 @@ thr_lock_type read_lock_type_for_table(THD *thd,
                                        TABLE_LIST *table_list);
 
 my_bool mysql_rm_tmp_tables(void);
-bool rm_temporary_table(handlerton *base, char *path);
+bool rm_temporary_table(handlerton *base, const char *path);
 void close_tables_for_reopen(THD *thd, TABLE_LIST **tables,
                              const MDL_savepoint &start_of_statement_svp);
 TABLE_LIST *find_table_in_list(TABLE_LIST *table,

sql/sql_cache.cc

@@ -2786,8 +2786,8 @@ void Query_cache::invalidate_table(THD *thd, TABLE_LIST *table_list)
     char key[MAX_DBKEY_LENGTH];
     uint key_length;
 
-    key_length=(uint) (strmov(strmov(key,table_list->db)+1,
-			      table_list->table_name) -key)+ 1;
+    key_length= create_table_def_key(key, table_list->db,
+                                     table_list->table_name);
 
     // We don't store temporary tables => no key_length+=4 ...
     invalidate_table(thd, (uchar *)key, key_length);
@@ -2904,8 +2904,8 @@ Query_cache::register_tables_from_list(TABLE_LIST *tables_used,
       DBUG_PRINT("qcache", ("view: %s  db: %s",
                             tables_used->view_name.str,
                             tables_used->view_db.str));
-      key_length= (uint) (strmov(strmov(key, tables_used->view_db.str) + 1,
-                                 tables_used->view_name.str) - key) + 1;
+      key_length= create_table_def_key(key, tables_used->view_db.str,
+                                       tables_used->view_name.str);
       /*
         There are not callback function for for VIEWs
       */
@@ -4137,8 +4137,9 @@ uint Query_cache::filename_2_table_key (char *key, const char *path,
   *db_length= (filename - dbname) - 1;
   DBUG_PRINT("qcache", ("table '%-.*s.%s'", *db_length, dbname, filename));
 
-  DBUG_RETURN((uint) (strmov(strmake(key, dbname, *db_length) + 1,
-			     filename) -key) + 1);
+  DBUG_RETURN((uint) (strmake(strmake(key, dbname,
+                                      min(*db_length, NAME_LEN)) + 1,
+                              filename, NAME_LEN) - key) + 1);
 }
 
 /****************************************************************************