MDEV-6743 crash in GROUP_CONCAT(IF () ORDER BY 1)

mysql-test/r/func_group.result:
  Test case
mysql-test/t/func_group.test:
  Test case
sql/item_sum.cc:
  Restore ORDER for prepared statements

mysql-test/r/func_group.result

-drop table if exists t1,t2;
+drop table if exists t1,t2,t3,t4,t5,t6;
 set @sav_dpi= @@div_precision_increment;
 set div_precision_increment= 5;
 show variables like 'div_precision_increment';
@@ -2239,3 +2239,34 @@ explain select MIN(b) from t1 where b >= inet_aton('192.168.119.32');
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
 DROP TABLE t1;
+#
+# MDEV-6743 crash in GROUP_CONCAT(IF () ORDER BY 1)
+#
+CREATE TABLE t1 (pk INT, t2_id INT, t5_id INT, PRIMARY KEY (pk));
+INSERT INTO t1 VALUES (1,3,12),(2,3,15);
+CREATE TABLE t2 (pk INT, PRIMARY KEY (pk));
+INSERT INTO t2 VALUES (4),(5);
+CREATE TABLE t3 (t2_id INT, t4_id INT);
+INSERT INTO t3 VALUES (6,11),(7,12);
+CREATE TABLE t4 (id INT);
+INSERT INTO t4 VALUES (13),(14);
+CREATE TABLE t5 (pk INT, f VARCHAR(50), t6_id INT, PRIMARY KEY (pk));
+INSERT INTO t5 VALUES (9,'FOO',NULL);
+CREATE TABLE t6 (pk INT, f VARCHAR(120), b TINYINT(4), PRIMARY KEY (pk));
+PREPARE stmt FROM "
+  SELECT      t1.t2_id, GROUP_CONCAT(IF (t6.b, t6.f, t5.f) ORDER BY 1)
+  FROM        t1
+  JOIN        t2 ON t1.t2_id = t2.pk
+  JOIN        t3 ON t2.pk = t3.t2_id
+  JOIN        t4 ON t4.id = t3.t4_id
+  JOIN        t5 ON t1.t5_id = t5.pk
+  LEFT JOIN   t6 ON t6.pk = t5.t6_id
+  GROUP BY    t1.t2_id
+";
+EXECUTE stmt;
+t2_id	GROUP_CONCAT(IF (t6.b, t6.f, t5.f) ORDER BY 1)
+EXECUTE stmt;
+t2_id	GROUP_CONCAT(IF (t6.b, t6.f, t5.f) ORDER BY 1)
+EXECUTE stmt;
+t2_id	GROUP_CONCAT(IF (t6.b, t6.f, t5.f) ORDER BY 1)
+DROP TABLE t1,t2,t3,t4,t5,t6;

mysql-test/t/func_group.test

@@ -3,7 +3,7 @@
 #
 
 --disable_warnings
-drop table if exists t1,t2;
+drop table if exists t1,t2,t3,t4,t5,t6;
 --enable_warnings
 
 set @sav_dpi= @@div_precision_increment;
@@ -1528,3 +1528,40 @@ insert into t1 (b) values (INET_ATON('192.168.200.200'));
 explain select MIN(b) from t1 where b >= inet_aton('192.168.119.32');
 DROP TABLE t1;
 
+--echo #
+--echo # MDEV-6743 crash in GROUP_CONCAT(IF () ORDER BY 1)
+--echo #
+
+CREATE TABLE t1 (pk INT, t2_id INT, t5_id INT, PRIMARY KEY (pk));
+INSERT INTO t1 VALUES (1,3,12),(2,3,15);
+
+CREATE TABLE t2 (pk INT, PRIMARY KEY (pk));
+INSERT INTO t2 VALUES (4),(5);
+
+CREATE TABLE t3 (t2_id INT, t4_id INT);
+INSERT INTO t3 VALUES (6,11),(7,12);
+
+CREATE TABLE t4 (id INT);
+INSERT INTO t4 VALUES (13),(14);
+
+CREATE TABLE t5 (pk INT, f VARCHAR(50), t6_id INT, PRIMARY KEY (pk));
+INSERT INTO t5 VALUES (9,'FOO',NULL);
+
+CREATE TABLE t6 (pk INT, f VARCHAR(120), b TINYINT(4), PRIMARY KEY (pk));
+
+PREPARE stmt FROM "
+  SELECT      t1.t2_id, GROUP_CONCAT(IF (t6.b, t6.f, t5.f) ORDER BY 1)
+  FROM        t1
+  JOIN        t2 ON t1.t2_id = t2.pk
+  JOIN        t3 ON t2.pk = t3.t2_id
+  JOIN        t4 ON t4.id = t3.t4_id
+  JOIN        t5 ON t1.t5_id = t5.pk
+  LEFT JOIN   t6 ON t6.pk = t5.t6_id
+  GROUP BY    t1.t2_id
+";
+
+EXECUTE stmt;
+EXECUTE stmt;
+EXECUTE stmt;
+
+DROP TABLE t1,t2,t3,t4,t5,t6;

sql/item_sum.cc

@@ -3181,19 +3181,13 @@ Item_func_group_concat(Name_resolution_context *context_arg,
   /*
     We need to allocate:
     args - arg_count_field+arg_count_order
-           (for possible order items in temporare tables)
+           (for possible order items in temporary tables)
     order - arg_count_order
   */
-  if (!(args= (Item**) sql_alloc(sizeof(Item*) * arg_count +
+  if (!(args= (Item**) sql_alloc(sizeof(Item*) * arg_count * 2 +
                                  sizeof(ORDER*)*arg_count_order)))
     return;
 
-  if (!(orig_args= (Item **) sql_alloc(sizeof(Item *) * arg_count)))
-  {
-    args= NULL;
-    return;
-  }
-
   order= (ORDER**)(args + arg_count);
 
   /* fill args items of show and sort */
@@ -3214,6 +3208,9 @@ Item_func_group_concat(Name_resolution_context *context_arg,
       order_item->item= arg_ptr++;
     }
   }
+
+  /* orig_args is only used for print() */
+  orig_args= (Item**) (order + arg_count_order);
   memcpy(orig_args, args, sizeof(Item*) * arg_count);
 }
 
@@ -3297,6 +3294,19 @@ void Item_func_group_concat::cleanup()
     }
     DBUG_ASSERT(tree == 0);
   }
+
+  /*
+    For prepared statements we have to restore pointers for ORDER BY as
+    they may point to areas that are freed at cleanup().
+  */
+  if (!current_thd->stmt_arena->is_conventional() && arg_count_order)
+  {
+    memcpy(args + arg_count_field, orig_args + arg_count_field,
+           sizeof(Item*) * arg_count_order);
+
+    for (uint i= 0 ; i < arg_count_order ; i++)
+      order[i]->item = args + arg_count_field + i;
+  }
   DBUG_VOID_RETURN;
 }