MDEV-24868 Server crashes in optimize_schema_tables_memory_usage after select from information_schema.innodb_sys_columns

optimize_schema_tables_memory_usage() crashed when its argument included
TABLE struct that was not fully initialized.

To prevent such a crash, we check if a table is an information schema table at
the beginning of each iteration.

Closes #1768

1 files changed, 8 insertions, 3 deletions

diff --git a/sql/sql_show.cc b/sql/sql_show.cc
index e6b5461e5af..469f28acf6c 100644
--- a/sql/sql_show.cc
+++ b/sql/sql_show.cc
@@ -8672,14 +8672,19 @@ end:
 
 bool optimize_schema_tables_memory_usage(List<TABLE_LIST> &tables)
 {
+  DBUG_ENTER("optimize_schema_tables_memory_usage");
+
   List_iterator<TABLE_LIST> tli(tables);
 
   while (TABLE_LIST *table_list= tli++)
   {
+    if (!table_list->schema_table)
+      continue;
+
     TABLE *table= table_list->table;
     THD *thd=table->in_use;
 
-    if (!table_list->schema_table || !thd->fill_information_schema_tables())
+    if (!thd->fill_information_schema_tables())
       continue;
 
     if (!table->is_created())
@@ -8726,10 +8731,10 @@ bool optimize_schema_tables_memory_usage(List<TABLE_LIST> &tables)
       // TODO switch from Aria to Memory if all blobs were optimized away?
       if (instantiate_tmp_table(table, p->keyinfo, p->start_recinfo, &p->recinfo,
                    table_list->select_lex->options | thd->variables.option_bits))
-        return 1;
+        DBUG_RETURN(1);
     }
   }
-  return 0;
+  DBUG_RETURN(0);
 }