MDEV-26412 Server crash in Item_field::fix_outer_field for INSERT SELECT

IF an INSERT/REPLACE SELECT statement contained an ON expression in the top
level select and this expression used a subquery with a column reference
that could not be resolved then an attempt to resolve this reference as
an outer reference caused a crash of the server. This happened because the
outer context field in the Name_resolution_context structure was not set
to NULL for such references. Rather it pointed to the first element in
the select_stack.

Note that starting from 10.4 we cannot use the SELECT_LEX::outer_select()
method when parsing a SELECT construct.

Approved by Oleksandr Byelkin <sanja@mariadb.com>

mysql-test/main/insert.result

@@ -751,3 +751,19 @@ REPLACE INTO v1 SET f = NULL;
 ERROR 22007: Truncated incorrect DOUBLE value: 'foo'
 DROP VIEW v1;
 DROP TABLE t1;
+# End of 10.0 tests
+#
+# MDEV-26412: INSERT CREATE with subquery in ON expression
+#
+create table t1 (a int);
+create table t2 (b int);
+create table t3 (c int);
+create table t4 (d1 int, d2 int);
+insert into t4
+select * from t1 left join t2 on (select t1.i from t3);
+ERROR 42S22: Unknown column 't1.i' in 'field list'
+replace t4
+select * from t1 left join t2 on (select t1.i from t3);
+ERROR 42S22: Unknown column 't1.i' in 'field list'
+drop table t1,t2,t3,t4;
+# End of 10.4 tests

mysql-test/main/insert.test

@@ -612,3 +612,25 @@ CREATE VIEW v1 AS SELECT * FROM t1 WHERE f <=> 'foo' WITH CHECK OPTION;
 REPLACE INTO v1 SET f = NULL;
 DROP VIEW v1;
 DROP TABLE t1;
+
+--echo # End of 10.0 tests
+
+--echo #
+--echo # MDEV-26412: INSERT CREATE with subquery in ON expression
+--echo #
+
+create table t1 (a int);
+create table t2 (b int);
+create table t3 (c int);
+create table t4 (d1 int, d2 int);
+
+--error ER_BAD_FIELD_ERROR
+insert into t4
+  select * from t1 left join t2 on (select t1.i from t3);
+--error ER_BAD_FIELD_ERROR
+replace t4
+  select * from t1 left join t2 on (select t1.i from t3);
+
+drop table t1,t2,t3,t4;
+
+--echo # End of 10.4 tests

sql/sql_lex.cc

@@ -701,6 +701,7 @@ void LEX::start(THD *thd_arg)
   context_stack.empty();
   //empty select_stack
   select_stack_top= 0;
+  select_stack_outer_barrier= 0;
   unit.init_query();
   current_select_number= 0;
   curr_with_clause= 0;

sql/sql_lex.h

@@ -3246,6 +3246,12 @@ struct LEX: public Query_tables_list
   List<Name_resolution_context> context_stack;
   SELECT_LEX *select_stack[MAX_SELECT_NESTING + 1];
   uint select_stack_top;
+  /*
+    Usually this is set to 0, but for INSERT/REPLACE SELECT it is set to 1.
+    When parsing such statements the pointer to the most outer select is placed
+    into the second element of select_stack rather than into the first.
+  */
+  uint select_stack_outer_barrier;
 
   SQL_I_List<ORDER> proc_list;
   SQL_I_List<TABLE_LIST> auxiliary_table_list, save_list;
@@ -3686,6 +3692,17 @@ struct LEX: public Query_tables_list
 
   bool copy_db_to(LEX_CSTRING *to);
 
+  void inc_select_stack_outer_barrier()
+  {
+    select_stack_outer_barrier++;
+  }
+
+  SELECT_LEX *parser_current_outer_select()
+  {
+    return select_stack_top - 1 == select_stack_outer_barrier ?
+             0 : select_stack[select_stack_top - 1];
+  }
+
   Name_resolution_context *current_context()
   {
     return context_stack.head();

sql/sql_parse.cc

@@ -9015,9 +9015,7 @@ push_new_name_resolution_context(THD *thd,
     right_op->last_leaf_for_name_resolution();
   LEX *lex= thd->lex;
   on_context->select_lex = lex->current_select;
-  st_select_lex *curr_select= lex->pop_select();
-  st_select_lex *outer_sel= lex->select_stack_head();
-  lex->push_select(curr_select);
+  st_select_lex *outer_sel= lex->parser_current_outer_select();
   on_context->outer_context = outer_sel ? &outer_sel->context : 0;
   return lex->push_context(on_context);
 }

sql/sql_yacc.yy

@@ -13608,6 +13608,7 @@ insert:
             if (Lex->main_select_push())
               MYSQL_YYABORT;
             mysql_init_select(lex);
+            lex->inc_select_stack_outer_barrier();
             lex->current_select->parsing_place= BEFORE_OPT_LIST;
           }
           insert_lock_option
@@ -13634,6 +13635,7 @@ replace:
             if (Lex->main_select_push())
               MYSQL_YYABORT;
             mysql_init_select(lex);
+            lex->inc_select_stack_outer_barrier();
             lex->current_select->parsing_place= BEFORE_OPT_LIST;
           }
           replace_lock_option insert2