A patch for Bug#34820: log_output can be set to illegal value.

We have "set" variables, which can accept empty values
(like sql_mode), and which can not (like log_output). The problem
was that the code does not distinguish them and allow empty
values for every set variable.

The fix is to introduce an attribute of a set variable telling
whether it can accept empty values.


mysql-test/r/variables.result:
  Update result file.
mysql-test/t/variables.test:
  A test case for Bug#34820: log_output can be set to illegal value.
sql/set_var.cc:
  Don't allow empty values if it is prohibitted.
sql/set_var.h:
  Add a flag (m_allow_empty_value) telling if an empty value is
  acceptable for this variable.

1 files changed, 15 insertions, 3 deletions

diff --git a/sql/set_var.h b/sql/set_var.h
index b33a3a968bb..c4fc13f1321 100644
--- a/sql/set_var.h
+++ b/sql/set_var.h
@@ -74,7 +74,8 @@ public:
   sys_var(const char *name_arg, sys_after_update_func func= NULL,
           Binlog_status_enum binlog_status_arg= NOT_IN_BINLOG)
     :name(name_arg), after_update(func), no_support_one_shot(1),
-    binlog_status(binlog_status_arg)
+    binlog_status(binlog_status_arg),
+    m_allow_empty_value(TRUE)
   {}
   virtual ~sys_var() {}
   void chain_sys_var(sys_var_chain *chain_arg)
@@ -109,8 +110,16 @@ public:
   virtual bool is_readonly() const { return 0; }
   virtual sys_var_pluginvar *cast_pluginvar() { return 0; }
 
+protected:
+  void set_allow_empty_value(bool allow_empty_value)
+  {
+    m_allow_empty_value= allow_empty_value;
+  }
+
 private:
   const Binlog_status_enum binlog_status;
+
+  bool m_allow_empty_value;
 };
 
 
@@ -878,8 +887,11 @@ public:
   sys_var_log_output(sys_var_chain *chain, const char *name_arg, ulong *value_arg,
                      TYPELIB *typelib, sys_after_update_func func)
     :sys_var(name_arg,func), value(value_arg), enum_names(typelib)
-  { chain_sys_var(chain); }
-  bool check(THD *thd, set_var *var)
+  {
+    chain_sys_var(chain);
+    set_allow_empty_value(FALSE);
+  }
+  virtual bool check(THD *thd, set_var *var)
   {
     return check_set(thd, var, enum_names);
   }