MDEV-25237 crash after setting global session_track_system_variables to an invalid value

Fix of typo in checking variable list corectness.

Fix of error handling in case of variable list parse error

mysql-test/main/mysqltest_tracking_info.result

@@ -57,3 +57,33 @@ ERROR 42000: Variable 'session_track_system_variables' can't be set to the value
 SET SESSION session_track_system_variables=NULL;
 ERROR 42000: Variable 'session_track_system_variables' can't be set to the value of 'NULL'
 # End of 10.3 tests
+#
+# MDEV-25237: crash after setting global session_track_system_variables
+# to an invalid value
+#
+SET GLOBAL session_track_system_variables='a';
+ERROR HY000: Unknown system variable 'a'
+SET GLOBAL event_scheduler=1;
+# check that value really returns as it was
+set GLOBAL session_track_system_variables='character_set_connection';
+SET GLOBAL session_track_system_variables='a';
+ERROR HY000: Unknown system variable 'a'
+connect  con,localhost,root,,test;
+SET NAMES 'utf8';
+-- Tracker : SESSION_TRACK_SYSTEM_VARIABLES
+-- character_set_connection
+-- utf8
+
+SET NAMES 'big5';
+-- Tracker : SESSION_TRACK_SYSTEM_VARIABLES
+-- character_set_connection
+-- big5
+
+select @@session_track_system_variables;
+@@session_track_system_variables
+character_set_connection
+connection default;
+disconnect con;
+SET GLOBAL session_track_system_variables=default;
+SET GLOBAL event_scheduler=default;
+# End of 10.4 test

mysql-test/main/mysqltest_tracking_info.test

@@ -60,3 +60,35 @@ SET @@GLOBAL.session_track_system_variables=NULL;
 SET SESSION session_track_system_variables=NULL;
 
 --echo # End of 10.3 tests
+
+--echo #
+--echo # MDEV-25237: crash after setting global session_track_system_variables
+--echo # to an invalid value
+--echo #
+
+--error ER_UNKNOWN_SYSTEM_VARIABLE
+SET GLOBAL session_track_system_variables='a';
+SET GLOBAL event_scheduler=1;
+
+
+--echo # check that value really returns as it was
+
+set GLOBAL session_track_system_variables='character_set_connection';
+--error ER_UNKNOWN_SYSTEM_VARIABLE
+SET GLOBAL session_track_system_variables='a';
+
+connect (con,localhost,root,,test);
+--enable_session_track_info
+SET NAMES 'utf8';
+SET NAMES 'big5';
+--disable_session_track_info
+
+select @@session_track_system_variables;
+
+connection default;
+disconnect con;
+
+SET GLOBAL session_track_system_variables=default;
+SET GLOBAL event_scheduler=default;
+
+--echo # End of 10.4 test

mysql-test/main/mysqltest_tracking_info_debug.result

+set @save_session_track_system_variables=@@session_track_system_variables;
+#
+# MDEV-25237: Assertion `global_system_variables.
+# session_track_system_variables' failed in
+# Session_sysvars_tracker::init | SIGSEGV's in __strlen_avx2 |
+# UBSAN: runtime error: null pointer passed as argument 1, which
+# is declared to never be null in my_strdup
+#
+# check that that parser problems do not lead to crash
+SET @old_debug= @@session.debug;
+set debug_dbug="+d,dbug_session_tracker_parse_error";
+SET GLOBAL session_track_system_variables='query_cache_size';
+ERROR HY001: Out of memory; restart server and try again (needed 1 bytes)
+set debug_dbug=@old_debug;
+SELECT @@global.session_track_system_variables;
+@@global.session_track_system_variables
+NULL
+SET GLOBAL event_scheduler=1;
+SET GLOBAL session_track_system_variables=default;
+SET GLOBAL event_scheduler=default;
+# End of 10.4 test

mysql-test/main/mysqltest_tracking_info_debug.test

+
+--source include/have_debug.inc
+--source include/no_protocol.inc
+--source include/not_embedded.inc
+
+
+set @save_session_track_system_variables=@@session_track_system_variables;
+
+--echo #
+--echo # MDEV-25237: Assertion `global_system_variables.
+--echo # session_track_system_variables' failed in
+--echo # Session_sysvars_tracker::init | SIGSEGV's in __strlen_avx2 |
+--echo # UBSAN: runtime error: null pointer passed as argument 1, which
+--echo # is declared to never be null in my_strdup
+--echo #
+
+--echo # check that that parser problems do not lead to crash
+SET @old_debug= @@session.debug;
+set debug_dbug="+d,dbug_session_tracker_parse_error";
+--error ER_OUTOFMEMORY
+SET GLOBAL session_track_system_variables='query_cache_size';
+set debug_dbug=@old_debug;
+SELECT @@global.session_track_system_variables;
+
+SET GLOBAL event_scheduler=1;
+
+SET GLOBAL session_track_system_variables=default;
+SET GLOBAL event_scheduler=default;
+
+--echo # End of 10.4 test

sql/session_tracker.cc

@@ -221,7 +221,7 @@ bool sysvartrack_validate_value(THD *thd, const char *str, size_t len)
     /* Remove leading/trailing whitespace. */
     trim_whitespace(system_charset_info, &var);
 
-    if (!strcmp(var.str, "*") && !find_sys_var(thd, var.str, var.length))
+    if (strcmp(var.str, "*") && !find_sys_var(thd, var.str, var.length))
       return true;
 
     if (lasts)
@@ -331,9 +331,8 @@ void Session_sysvars_tracker::init(THD *thd)
   mysql_mutex_assert_owner(&LOCK_global_system_variables);
   DBUG_ASSERT(thd->variables.session_track_system_variables ==
               global_system_variables.session_track_system_variables);
-  DBUG_ASSERT(global_system_variables.session_track_system_variables);
   thd->variables.session_track_system_variables=
-    my_strdup(global_system_variables.session_track_system_variables,
+    my_strdup(safe_str(global_system_variables.session_track_system_variables),
               MYF(MY_WME | MY_THREAD_SPECIFIC));
 }
 
@@ -572,6 +571,12 @@ bool sysvartrack_global_update(THD *thd, char *str, size_t len)
 {
   LEX_STRING tmp= { str, len };
   Session_sysvars_tracker::vars_list dummy;
+  DBUG_EXECUTE_IF("dbug_session_tracker_parse_error",
+                  {
+                    my_error(ER_OUTOFMEMORY, MYF(0), 1);
+                    return true;
+                  });
+
   if (!dummy.parse_var_list(thd, tmp, false, system_charset_info))
   {
     dummy.construct_var_list(str, len + 1);

sql/sys_vars.inl

@@ -620,8 +620,12 @@ class Sys_var_sesvartrack: public Sys_var_charptr_base
     {
       if (sysvartrack_global_update(thd, new_val,
                                     var->save_result.string_value.length))
+      {
+        if (new_val)
+          my_free(new_val);
         new_val= 0;
       }
+    }
     global_update_finish(new_val);
     return (new_val == 0 && var->save_result.string_value.str != 0);
   }