MDEV-12666: CURRENT_ROLE() and DATABASE() does not work in a view

The problem lies in how CURRENT_ROLE is defined. The
Item_func_current_role inherits from Item_func_sysconst, which defines
a safe_charset_converter to be a const_charset_converter.

During view creation, if there is no role previously set, the current_role()
function returns NULL.

This is captured on item instantiation and the
const_charset_converter call subsequently returns an Item_null.
In turn, the function is replaced with Item_null and the view is
then created with an Item_null instead of Item_func_current_role.

Without this patch, the first SHOW CREATE VIEW from the testcase would
have a where clause of WHERE role_name = NULL, while the second SHOW
CREATE VIEW would show a correctly created view.

The same applies for the DATABASE function, as it can change as well.

There is an additional problem with CURRENT_ROLE() when used in a
prepared statement. During prepared statement creation we used to set
the string_value of the function to the current role as well as the
null_value flag. During execution, if CURRENT_ROLE was not null, the
null_value flag was never set to not-null during fix_fields.

Item_func_current_user however can never be NULL so it did not show this
problem in a view before. At the same time, the CURRENT_USER() can not
be changed between prepared statement execution and creation so the
implementation where the value is stored during fix_fields is
sufficient.

Note also that DATABASE() function behaves differently during prepared
statements. See bug 25843 for details or commit
7e0ad09edff587dadc3e9855fc81e1b7de8f2199

1 files changed, 24 insertions, 3 deletions

diff --git a/sql/item_strfunc.cc b/sql/item_strfunc.cc
index 7cd712cc5e1..08b9ded80f5 100644
--- a/sql/item_strfunc.cc
+++ b/sql/item_strfunc.cc
@@ -2344,6 +2344,7 @@ String *Item_func_database::val_str(String *str)
   }
   else
     str->copy(thd->db, thd->db_length, system_charset_info);
+  null_value= 0;
   return str;
 }
 
@@ -2378,6 +2379,28 @@ bool Item_func_user::init(const char *user, const char *host)
 }
 
 
+Item *Item_func_sysconst::safe_charset_converter(CHARSET_INFO *tocs)
+{
+  /*
+   During view or prepared statement creation, the item should not
+   make use of const_charset_converter as it would imply substitution
+   with constant items which is not correct. Functions can have different
+   values during view creation and view execution based on context.
+
+   Return the identical item during view creation and prepare.
+  */
+  if (!Item_func_sysconst::const_item())
+    return this;
+  return const_charset_converter(tocs, true, fully_qualified_func_name());
+}
+
+bool Item_func_sysconst::const_item() const
+{
+  if (current_thd->lex->is_ps_or_view_context_analysis())
+    return false;
+  return true;
+}
+
 bool Item_func_user::fix_fields(THD *thd, Item **ref)
 {
   return (Item_func_sysconst::fix_fields(thd, ref) ||
@@ -2403,21 +2426,19 @@ bool Item_func_current_role::fix_fields(THD *thd, Item **ref)
 
   Security_context *ctx= context->security_ctx
                           ? context->security_ctx : thd->security_ctx;
-
   if (ctx->priv_role[0])
   {
     if (str_value.copy(ctx->priv_role, strlen(ctx->priv_role),
                        system_charset_info))
       return 1;
-
     str_value.mark_as_const();
+    null_value= maybe_null= 0;
     return 0;
   }
   null_value= maybe_null= 1;
   return 0;
 }
 
-
 void Item_func_soundex::fix_length_and_dec()
 {
   uint32 char_length= args[0]->max_char_length();