MDEV-23841: Memory leak in innodb_monitor_validate()

innodb_monitor_validate(): Let item_val_str() allocate the memory
in THD, so that it will be available to innodb_monitor_update().
In this way, there is no need to allocate another buffer, and
no problem if the call to innodb_monitor_update() is skipped due
to an invalid value that is passed to another configuration parameter.

There are some other callers to st_mysql_sys_var::val_str()
that validate configuration parameters that are related to FULLTEXT INDEX,
but they will allocate memory by invoking thd_strmake().

mysql-test/suite/innodb/r/monitor.result

@@ -637,6 +637,8 @@ LIKE 'buffer_page_written_index_leaf';
 NAME	COUNT > 0
 buffer_page_written_index_leaf	0
 SET GLOBAL innodb_monitor_enable='%';
+SET GLOBAL innodb_monitor_reset_all= '%', innodb_compression_algorithm= foo;
+ERROR 42000: Variable 'innodb_compression_algorithm' can't be set to the value of 'foo'
 INSERT INTO t1 VALUES (5), (6), (7), (8);
 FLUSH TABLES t1 FOR EXPORT;
 UNLOCK TABLES;

mysql-test/suite/innodb/t/monitor.test

@@ -408,6 +408,8 @@ SELECT NAME, COUNT > 0 FROM INFORMATION_SCHEMA.INNODB_METRICS WHERE NAME
 LIKE 'buffer_page_written_index_leaf';
 
 SET GLOBAL innodb_monitor_enable='%';
+--error ER_WRONG_VALUE_FOR_VAR
+SET GLOBAL innodb_monitor_reset_all= '%', innodb_compression_algorithm= foo;
 INSERT INTO t1 VALUES (5), (6), (7), (8); FLUSH TABLES t1 FOR EXPORT;
 UNLOCK TABLES;
 SELECT NAME, COUNT > 0 FROM INFORMATION_SCHEMA.INNODB_METRICS WHERE NAME

storage/innobase/handler/ha_innodb.cc

@@ -17808,13 +17808,7 @@ innodb_monitor_validate_wildcard_name(
 Validate the passed in monitor name, find and save the
 corresponding monitor name in the function parameter "save".
 @return 0 if monitor name is valid */
-static
-int
-innodb_monitor_valid_byname(
-/*========================*/
-	void*			save,	/*!< out: immediate result
-					for update function */
-	const char*		name)	/*!< in: incoming monitor name */
+static int innodb_monitor_valid_byname(const char *name)
 {
 	ulint		use;
 	monitor_info_t*	monitor_info;
@@ -17862,9 +17856,6 @@ innodb_monitor_valid_byname(
 		}
 	}
 
-	/* Save the configure name for innodb_monitor_update() */
-	*static_cast<const char**>(save) = name;
-
 	return(0);
 }
 /*************************************************************//**
@@ -17880,41 +17871,18 @@ innodb_monitor_validate(
 						for update function */
 	struct st_mysql_value*		value)	/*!< in: incoming string */
 {
-	const char*	name;
-	char*		monitor_name;
-	char		buff[STRING_BUFFER_USUAL_SIZE];
-	int		len = sizeof(buff);
-	int		ret;
+  int ret= 0;
 
-	ut_a(save != NULL);
-	ut_a(value != NULL);
-
-	name = value->val_str(value, buff, &len);
-
-	/* monitor_name could point to memory from MySQL
-	or buff[]. Always dup the name to memory allocated
-	by InnoDB, so we can access it in another callback
-	function innodb_monitor_update() and free it appropriately */
-	if (name) {
-		monitor_name = my_strdup(//PSI_INSTRUMENT_ME,
-                                         name, MYF(0));
-	} else {
-		return(1);
-	}
-
-	ret = innodb_monitor_valid_byname(save, monitor_name);
-
-	if (ret) {
-		/* Validation failed */
-		my_free(monitor_name);
-	} else {
-		/* monitor_name will be freed in separate callback function
-		innodb_monitor_update(). Assert "save" point to
-		the "monitor_name" variable */
-		ut_ad(*static_cast<char**>(save) == monitor_name);
-	}
+  if (const char *name= value->val_str(value, nullptr, &ret))
+  {
+    ret= innodb_monitor_valid_byname(name);
+    if (!ret)
+      *static_cast<const char**>(save)= name;
+  }
+  else
+    ret= 1;
 
-	return(ret);
+  return ret;
 }
 
 /****************************************************************//**
@@ -17930,11 +17898,9 @@ innodb_monitor_update(
 						formal string goes */
 	const void*		save,		/*!< in: immediate result
 						from check function */
-	mon_option_t		set_option,	/*!< in: the set option,
+	mon_option_t		set_option)	/*!< in: the set option,
 						whether to turn on/off or
 						reset the counter */
-	ibool			free_mem)	/*!< in: whether we will
-						need to free the memory */
 {
 	monitor_info_t*	monitor_info;
 	ulint		monitor_id;
@@ -18018,12 +17984,6 @@ innodb_monitor_update(
 		sql_print_warning("InnoDB: Monitor %s is already enabled.",
 				  srv_mon_get_name((monitor_id_t) err_monitor));
 	}
-
-	if (free_mem && name) {
-		my_free((void*) name);
-	}
-
-	return;
 }
 
 #ifdef UNIV_DEBUG
@@ -18114,7 +18074,7 @@ innodb_enable_monitor_update(
 	const void*			save)	/*!< in: immediate result
 						from check function */
 {
-	innodb_monitor_update(thd, var_ptr, save, MONITOR_TURN_ON, TRUE);
+	innodb_monitor_update(thd, var_ptr, save, MONITOR_TURN_ON);
 }
 
 /****************************************************************//**
@@ -18131,7 +18091,7 @@ innodb_disable_monitor_update(
 	const void*			save)	/*!< in: immediate result
 						from check function */
 {
-	innodb_monitor_update(thd, var_ptr, save, MONITOR_TURN_OFF, TRUE);
+	innodb_monitor_update(thd, var_ptr, save, MONITOR_TURN_OFF);
 }
 
 /****************************************************************//**
@@ -18149,7 +18109,7 @@ innodb_reset_monitor_update(
 	const void*			save)	/*!< in: immediate result
 						from check function */
 {
-	innodb_monitor_update(thd, var_ptr, save, MONITOR_RESET_VALUE, TRUE);
+	innodb_monitor_update(thd, var_ptr, save, MONITOR_RESET_VALUE);
 }
 
 /****************************************************************//**
@@ -18167,8 +18127,7 @@ innodb_reset_all_monitor_update(
 	const void*			save)	/*!< in: immediate result
 						from check function */
 {
-	innodb_monitor_update(thd, var_ptr, save, MONITOR_RESET_ALL_VALUE,
-			      TRUE);
+	innodb_monitor_update(thd, var_ptr, save, MONITOR_RESET_ALL_VALUE);
 }
 
 static
@@ -18213,10 +18172,9 @@ innodb_enable_monitor_at_startup(
 	for (char* option = my_strtok_r(str, sep, &last);
 	     option;
 	     option = my_strtok_r(NULL, sep, &last)) {
-		char*	option_name;
-		if (!innodb_monitor_valid_byname(&option_name, option)) {
+		if (!innodb_monitor_valid_byname(option)) {
 			innodb_monitor_update(NULL, NULL, &option,
-					      MONITOR_TURN_ON, FALSE);
+					      MONITOR_TURN_ON);
 		} else {
 			sql_print_warning("Invalid monitor counter"
 					  " name: '%s'", option);