From 082aea7742455246fdcfd112a392b78c793dfebc Mon Sep 17 00:00:00 2001
From: Sergei Golubchik <serg@mariadb.org>
Date: Sat, 21 Oct 2023 17:33:29 +0200
Subject: [PATCH] MDEV-31112 vcol circular references lead to stack overflow

---
 mysql-test/suite/vcol/r/vcol_misc.result | 11 +++++++++++
 mysql-test/suite/vcol/t/vcol_misc.test   | 13 +++++++++++++
 sql/item.cc                              |  7 ++++---
 3 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/mysql-test/suite/vcol/r/vcol_misc.result b/mysql-test/suite/vcol/r/vcol_misc.result
index 0a86d68b3ad87..8038f18ffc702 100644
--- a/mysql-test/suite/vcol/r/vcol_misc.result
+++ b/mysql-test/suite/vcol/r/vcol_misc.result
@@ -569,3 +569,14 @@ drop table t1;
 #
 # End of 10.3 tests
 #
+#
+# MDEV-31112 vcol circular references lead to stack overflow
+#
+create table t (a int, c int as (a));
+alter table t alter column c drop default;
+alter table t modify column a int as (c) stored;
+ERROR 01000: Expression for field `a` is referring to uninitialized field `c`
+drop table t;
+#
+# End of 10.4 tests
+#
diff --git a/mysql-test/suite/vcol/t/vcol_misc.test b/mysql-test/suite/vcol/t/vcol_misc.test
index f696d5d581465..3bbed408f6f81 100644
--- a/mysql-test/suite/vcol/t/vcol_misc.test
+++ b/mysql-test/suite/vcol/t/vcol_misc.test
@@ -536,3 +536,16 @@ drop table t1;
 --echo #
 --echo # End of 10.3 tests
 --echo #
+
+--echo #
+--echo # MDEV-31112 vcol circular references lead to stack overflow
+--echo #
+create table t (a int, c int as (a));
+alter table t alter column c drop default;
+--error ER_EXPRESSION_REFERS_TO_UNINIT_FIELD
+alter table t modify column a int as (c) stored;
+drop table t;
+
+--echo #
+--echo # End of 10.4 tests
+--echo #
diff --git a/sql/item.cc b/sql/item.cc
index f9d8ac490aed9..34272156aade2 100644
--- a/sql/item.cc
+++ b/sql/item.cc
@@ -908,14 +908,15 @@ bool Item_field::register_field_in_write_map(void *arg)
 
   This is used by fix_vcol_expr() when a table is opened
 
-  We don't have to check fields that are marked as NO_DEFAULT_VALUE
-  as the upper level will ensure that all these will be given a value.
+  We don't have to check non-virtual fields that are marked as
+  NO_DEFAULT_VALUE as the upper level will ensure that all these
+  will be given a value.
 */
 
 bool Item_field::check_field_expression_processor(void *arg)
 {
   Field *org_field= (Field*) arg;
-  if (field->flags & NO_DEFAULT_VALUE_FLAG)
+  if (field->flags & NO_DEFAULT_VALUE_FLAG && !field->vcol_info)
     return 0;
   if ((field->default_value && field->default_value->flags) || field->vcol_info)
   {