Bug#13003736 CRASH IN ITEM_REF::WALK WITH SUBQUERIES

Problem: Some queries with subqueries and a HAVING clause that
consists only of a column not in the select or grouping lists causes
the server to crash.

During parsing, an Item_ref is constructed for the HAVING column. The
name of the column is resolved when JOIN::prepare calls fix_fields()
on its having clause. Since the column is not mentioned in the select
or grouping lists, a ref pointer is not found and a new Item_field is
created instead. The Item_ref is replaced by the Item_field in the
tree of HAVING clauses. Since the tree consists only of this item, the
pointer that is updated is JOIN::having. However,
st_select_lex::having still points to the Item_ref as the root of the
tree of HAVING clauses.

The bug is triggered when doing filesort for create_sort_index(). When
find_all_keys() calls select->cond->walk() it eventually reaches
Item_subselect::walk() where it continues to walk the having clauses
from lex->having. This means that it finds the Item_ref instead of the
new Item_field, and Item_ref::walk() tries to dereference the ref
pointer, which is still null.

The crash is reproducible only in 5.5, but the problem lies latent in
5.1 and trunk as well.

Fix: After calling fix_fields on the having clause in JOIN::prepare(),
set select_lex::having to point to the same item as JOIN::having.

This patch also fixes a bug in 5.1 and 5.5 that is triggered if the
query is executed as a prepared statement. The Item_field is created
in the runtime arena when the query is prepared, and the pointer to
the item is saved by st_select_lex::fix_prepare_information() and
brought back as a dangling pointer when the query is executed, after
the runtime arena has been reclaimed.

Fix: Backport fix from trunk that switches to the permanent arena
before calling Item_ref::fix_fields() in JOIN::prepare().


sql/item.cc:
  Set context when creating Item_field.
sql/sql_select.cc:
  Switch to permanent arena and update select_lex->having.

sql/item.cc

@@ -6010,7 +6010,7 @@ bool Item_ref::fix_fields(THD *thd, Item **reference)
       if (from_field != not_found_field)
       {
         Item_field* fld;
-        if (!(fld= new Item_field(from_field)))
+        if (!(fld= new Item_field(thd, last_checked_context, from_field)))
           goto error;
         thd->change_item_tree(reference, fld);
         mark_as_dependent(thd, last_checked_context->select_lex,

sql/sql_select.cc

@@ -528,6 +528,8 @@ JOIN::prepare(Item ***rref_pointer_array,
   
   if (having)
   {
+    Query_arena backup, *arena;
+    arena= thd->activate_stmt_arena_if_needed(&backup);
     nesting_map save_allow_sum_func= thd->lex->allow_sum_func;
     thd->where="having clause";
     thd->lex->allow_sum_func|= 1 << select_lex_arg->nest_level;
@@ -536,6 +538,10 @@ JOIN::prepare(Item ***rref_pointer_array,
 			 (having->fix_fields(thd, &having) ||
 			  having->check_cols(1)));
     select_lex->having_fix_field= 0;
+    select_lex->having= having;
+    if (arena)
+      thd->restore_active_arena(arena, &backup);
+
     if (having_fix_rc || thd->is_error())
       DBUG_RETURN(-1);				/* purecov: inspected */
     thd->lex->allow_sum_func= save_allow_sum_func;