MDEV-25906 : SIGSEGV in flush_tables_with_read_lock on FTWRL or FTFE | SIGSEGV in ha_maria::extrabb-10.6-MDEV-25906

Problem was that flush_tables_with_read_lock did not check
is base table database information_schema or performance_schema
where FLUSH is not supported. Furthermore, it did not check
is there even any base table.

3 files changed, 88 insertions, 16 deletions

diff --git a/mysql-test/main/flush.result b/mysql-test/main/flush.result
index 941dc63e3da..0630a424e1c 100644
--- a/mysql-test/main/flush.result
+++ b/mysql-test/main/flush.result
@@ -615,3 +615,28 @@ show status like "Threads_cached";
 Variable_name	Value
 Threads_cached	0
 set @@global.thread_cache_size=@save_thread_cache_size;
+#
+# MDEV-25906: SIGSEGV in flush_tables_with_read_lock on FTWRL or FTFE | SIGSEGV in ha_maria::extra
+#
+CREATE VIEW v AS SELECT 1 FROM (SELECT 1) AS d;
+CREATE VIEW v2 AS SELECT * FROM v;
+FLUSH TABLE v WITH READ LOCK;
+ERROR HY000: 'test.v' is not of type 'BASE TABLE'
+FLUSH TABLE v FOR EXPORT;
+ERROR HY000: 'test.v' is not of type 'BASE TABLE'
+FLUSH TABLE v2 WITH READ LOCK;
+ERROR HY000: 'test.v2' is not of type 'BASE TABLE'
+DROP VIEW v2;
+DROP VIEW v;
+CREATE VIEW v(c) AS SELECT column_name FROM information_schema.columns;
+FLUSH TABLE v WITH READ LOCK;
+ERROR 42000: Access denied for user 'root'@'localhost' to database 'information_schema'
+FLUSH TABLE v FOR EXPORT;
+ERROR 42000: Access denied for user 'root'@'localhost' to database 'information_schema'
+DROP VIEW v;
+CREATE VIEW v(u) AS SELECT user FROM performance_schema.accounts;
+FLUSH TABLE v WITH READ LOCK;
+ERROR 42000: Access denied for user 'root'@'localhost' to database 'performance_schema'
+FLUSH TABLE v FOR EXPORT;
+ERROR 42000: Access denied for user 'root'@'localhost' to database 'performance_schema'
+DROP VIEW v;
diff --git a/mysql-test/main/flush.test b/mysql-test/main/flush.test
index 97830238b0e..dd488070ce8 100644
--- a/mysql-test/main/flush.test
+++ b/mysql-test/main/flush.test
@@ -1,3 +1,5 @@
+--source include/have_perfschema.inc
+
 connect (con1,localhost,root,,);
 connect (con2,localhost,root,,);
 connection con1;
@@ -732,3 +734,32 @@ set @@global.thread_cache_size=0;
 flush threads;
 show status like "Threads_cached";
 set @@global.thread_cache_size=@save_thread_cache_size;
+
+--echo #
+--echo # MDEV-25906: SIGSEGV in flush_tables_with_read_lock on FTWRL or FTFE | SIGSEGV in ha_maria::extra
+--echo #
+
+CREATE VIEW v AS SELECT 1 FROM (SELECT 1) AS d;
+CREATE VIEW v2 AS SELECT * FROM v;
+--error ER_WRONG_OBJECT
+FLUSH TABLE v WITH READ LOCK;
+--error ER_WRONG_OBJECT
+FLUSH TABLE v FOR EXPORT;
+--error ER_WRONG_OBJECT
+FLUSH TABLE v2 WITH READ LOCK;
+DROP VIEW v2;
+DROP VIEW v;
+
+CREATE VIEW v(c) AS SELECT column_name FROM information_schema.columns;
+--error ER_DBACCESS_DENIED_ERROR
+FLUSH TABLE v WITH READ LOCK;
+--error ER_DBACCESS_DENIED_ERROR
+FLUSH TABLE v FOR EXPORT;
+DROP VIEW v;
+
+CREATE VIEW v(u) AS SELECT user FROM performance_schema.accounts;
+--error ER_DBACCESS_DENIED_ERROR
+FLUSH TABLE v WITH READ LOCK;
+--error ER_DBACCESS_DENIED_ERROR
+FLUSH TABLE v FOR EXPORT;
+DROP VIEW v;
diff --git a/sql/sql_reload.cc b/sql/sql_reload.cc
index 0fa2fa10df8..91695f37906 100644
--- a/sql/sql_reload.cc
+++ b/sql/sql_reload.cc
@@ -586,29 +586,45 @@ bool flush_tables_with_read_lock(THD *thd, TABLE_LIST *all_tables)
                            &lock_tables_prelocking_strategy))
     goto error_reset_bits;
 
-  if (thd->lex->type & REFRESH_FOR_EXPORT)
+  // Iterate all tables
+  for (auto table_list= all_tables; table_list;
+       table_list= table_list->next_global)
   {
-    // Check if all storage engines support FOR EXPORT.
-    for (TABLE_LIST *table_list= all_tables; table_list;
-         table_list= table_list->next_global)
+    // FLUSH [WITH READ LOCK|FOR EXPORT] not supported
+    // for information_schema or performance_schema tables
+    if (is_infoschema_db(&table_list->db) ||
+	is_perfschema_db(&table_list->db))
+    {
+      my_error(ER_DBACCESS_DENIED_ERROR, MYF(0),
+               thd->security_ctx->priv_user,
+               thd->security_ctx->priv_host,
+               table_list->db.str);
+      goto error_reset_bits;
+    }
+    // FLUSH [WITH READ LOCK|FOR EXPORT] not supported
+    // if there is no base table
+    if (!table_list->is_view() && !table_list->table)
     {
-      if (!(table_list->is_view() ||
-            table_list->table->file->ha_table_flags() & HA_CAN_EXPORT))
+      TABLE_LIST *view= table_list->top_table();
+
+      my_error(ER_WRONG_OBJECT, MYF(0),
+               view ? view->db.str : all_tables->db.str,
+               view ? view->table_name.str : all_tables->table_name.str,
+               "BASE TABLE");
+      goto error_reset_bits;
+    }
+    if (!table_list->is_view())
+    {
+      // Check if storage engine support FOR EXPORT.
+      if ((thd->lex->type & REFRESH_FOR_EXPORT) &&
+          !(table_list->table->file->ha_table_flags() & HA_CAN_EXPORT))
       {
         my_error(ER_ILLEGAL_HA, MYF(0),table_list->table->file->table_type(),
                  table_list->db.str, table_list->table_name.str);
         goto error_reset_bits;
       }
-    }
-  }
-
-  if (thd->lex->type & REFRESH_READ_LOCK)
-  {
-    for (auto table_list= all_tables; table_list;
-         table_list= table_list->next_global)
-    {
-      if (!table_list->is_view() &&
-          table_list->table->file->extra(HA_EXTRA_FLUSH))
+      else if ((thd->lex->type & REFRESH_READ_LOCK) &&
+               table_list->table->file->extra(HA_EXTRA_FLUSH))
         goto error_reset_bits;
     }
   }