MDEV-14750 Valgrind Invalid read, ASAN heap-use-after-free in Item_ident::print upon SHOW CREATE on partitioned table

items in the partitioning function were taking
the table name from the table's field
(in set_field(from_field) in Item_field::fix_fields)
and field's table_name is TABLE::alias.

But alias is changed for every statement, and
can be realloced if next statement uses a longer
alias. But partitioning items are fixed once
and live as long as the TABLE does. So if
an alias is realloced, pointers to the old
alias string will become invalid.

Fix partitioning item table_name to point to
the actual table name instead.

1 files changed, 4 insertions, 0 deletions

diff --git a/sql/item.cc b/sql/item.cc
index fbc4ec22c6e..68761293682 100644
--- a/sql/item.cc
+++ b/sql/item.cc
@@ -5766,6 +5766,10 @@ bool Item_field::post_fix_fields_part_expr_processor(void *int_arg)
   DBUG_ASSERT(fixed);
   if (field->vcol_info)
     field->vcol_info->mark_as_in_partitioning_expr();
+  /*
+    Update table_name to be real table name, not the alias. Because alias is
+    reallocated for every statement, and this item has a long life time */
+  table_name= field->table->s->table_name.str;
   return FALSE;
 }