Bug #29878 Garbage data generation when executing SESSION_USER() on a slave.

Item_func_user doesn't calculate anything in it's val_str() method,
just returns saved str_value.
Though Item::save_in_field method can destroy str_value, relying on
val_str() return. As a result we get the garbage stored in field.

We cannot use Item::save_in_field implementation for Item_func_user,
reimplement it in simpler way.

1 files changed, 5 insertions, 1 deletions

diff --git a/sql/item.h b/sql/item.h
index 5b1a80a5f03..72236cb5e63 100644
--- a/sql/item.h
+++ b/sql/item.h
@@ -612,6 +612,7 @@ public:
 
   int save_time_in_field(Field *field);
   int save_date_in_field(Field *field);
+  int save_str_value_in_field(Field *field, String *result);
 
   virtual Field *get_tmp_table_field() { return 0; }
   /* This is also used to create fields in CREATE ... SELECT: */
@@ -2166,7 +2167,10 @@ public:
   my_decimal *val_decimal(my_decimal *);
   void make_field(Send_field *field) { item->make_field(field); }
   void copy();
-  int save_in_field(Field *field, bool no_conversions);
+  int save_in_field(Field *field, bool no_conversions)
+  {
+    return save_str_value_in_field(field, &str_value);
+  }
   table_map used_tables() const { return (table_map) 1L; }
   bool const_item() const { return 0; }
   bool is_null() { return null_value; }