MDEV-25197: The statement set password=password('') executed in PS mode fails in case it is run by a user with expired password

A user connected to a server with an expired password
can't change password with the statement "SET password=..."
if this statement is run in PS mode. In mentioned use case a user
gets the error ER_MUST_CHANGE_PASSWORD on attempt to run
the statement  PREPARE stmt FOR "SET password=...";

The reason of failure to reset password by a locked user using the
statement PREPARE stmt FOR "SET password=..." is that PS-related
statements are not listed among the commands allowed for execution
by a user with expired password. However, simple adding of PS-related
statements (PREPARE FOR/EXECUTE/DEALLOCATE PREPARE ) to the list of
statements allowed for execution by a locked user is not enough
to solve problems, since it opens the opportunity for a locked user
to execute any statement in the PS mode.

To exclude this opportunity, additional checking that the statement
being prepared for execution in PS-mode is the SET statement has to be added.
This extra checking has been added by this patch into the method
Prepared_statement::prepared() that executed on preparing any statement
for execution in PS-mode.

mysql-test/main/ps.result

@@ -5536,5 +5536,37 @@ DEALLOCATE PREPARE stmt;
 DROP VIEW v1;
 DROP TABLE t1;
 #
+# MDEV-25197: The statement set password=password('') executed in PS mode
+#             fails in case it is run by a user with expired password
+#
+CREATE USER user1@localhost PASSWORD EXPIRE;
+SET @disconnect_on_expired_password_save=@@global.disconnect_on_expired_password;
+SET GLOBAL disconnect_on_expired_password=OFF;
+connect con1,localhost,user1;
+connection con1;
+# Check that no regular statement like SELECT can be prepared
+# by a user with an expired password
+PREPARE stmt FROM "SELECT 1";
+ERROR HY000: You must SET PASSWORD before executing this statement
+# Check that the DEALLOCATE PREPARE statement can be run by a user
+# with an expired password
+PREPARE stmt FROM "SET password=password('')";
+DEALLOCATE PREPARE stmt;
+# Check that the SET PASSWORD statement can be executed in PS mode by
+# a user with an expired password
+PREPARE stmt FROM "SET password=password('')";
+EXECUTE stmt;
+PREPARE stmt FROM "SELECT 1";
+# Check that user's password is not expired anymore
+EXECUTE stmt;
+1
+1
+DEALLOCATE PREPARE stmt;
+# Clean up
+disconnect con1;
+connection default;
+SET GLOBAL disconnect_on_expired_password=@disconnect_on_expired_password_save;
+DROP USER user1@localhost;
+#
 # End of 10.4 tests
 #

mysql-test/main/ps.test

@@ -4979,6 +4979,43 @@ DEALLOCATE PREPARE stmt;
 DROP VIEW v1;
 DROP TABLE t1;
 
+--echo #
+--echo # MDEV-25197: The statement set password=password('') executed in PS mode
+--echo #             fails in case it is run by a user with expired password
+--echo #
+CREATE USER user1@localhost PASSWORD EXPIRE;
+
+SET @disconnect_on_expired_password_save=@@global.disconnect_on_expired_password;
+SET GLOBAL disconnect_on_expired_password=OFF;
+
+connect(con1,localhost,user1);
+connection con1;
+--echo # Check that no regular statement like SELECT can be prepared
+--echo # by a user with an expired password
+--error ER_MUST_CHANGE_PASSWORD
+PREPARE stmt FROM "SELECT 1";
+
+--echo # Check that the DEALLOCATE PREPARE statement can be run by a user
+--echo # with an expired password
+PREPARE stmt FROM "SET password=password('')";
+DEALLOCATE PREPARE stmt;
+
+--echo # Check that the SET PASSWORD statement can be executed in PS mode by
+--echo # a user with an expired password
+PREPARE stmt FROM "SET password=password('')";
+EXECUTE stmt;
+PREPARE stmt FROM "SELECT 1";
+--echo # Check that user's password is not expired anymore
+EXECUTE stmt;
+DEALLOCATE PREPARE stmt;
+
+--echo # Clean up
+disconnect con1;
+connection default;
+
+SET GLOBAL disconnect_on_expired_password=@disconnect_on_expired_password_save;
+DROP USER user1@localhost;
+
 --echo #
 --echo # End of 10.4 tests
 --echo #

sql/sql_parse.cc

@@ -1641,7 +1641,9 @@ bool dispatch_command(enum enum_server_command command, THD *thd,
   if (unlikely(thd->security_ctx->password_expired &&
                command != COM_QUERY &&
                command != COM_PING &&
-               command != COM_QUIT))
+               command != COM_QUIT &&
+               command != COM_STMT_PREPARE &&
+               command != COM_STMT_EXECUTE))
   {
     my_error(ER_MUST_CHANGE_PASSWORD, MYF(0));
     goto dispatch_end;
@@ -3490,7 +3492,10 @@ mysql_execute_command(THD *thd)
               first_table->for_insert_data);
 
   if (thd->security_ctx->password_expired &&
-      lex->sql_command != SQLCOM_SET_OPTION)
+      lex->sql_command != SQLCOM_SET_OPTION &&
+      lex->sql_command != SQLCOM_PREPARE &&
+      lex->sql_command != SQLCOM_EXECUTE &&
+      lex->sql_command != SQLCOM_DEALLOCATE_PREPARE)
   {
     my_error(ER_MUST_CHANGE_PASSWORD, MYF(0));
     DBUG_RETURN(1);

sql/sql_prepare.cc

@@ -4217,6 +4217,15 @@ bool Prepared_statement::prepare(const char *packet, uint packet_len)
           thd->is_error() ||
           init_param_array(this));
 
+  if (thd->security_ctx->password_expired &&
+      lex->sql_command != SQLCOM_SET_OPTION)
+  {
+    thd->restore_backup_statement(this, &stmt_backup);
+    thd->restore_active_arena(this, &stmt_backup);
+    thd->stmt_arena= old_stmt_arena;
+    my_error(ER_MUST_CHANGE_PASSWORD, MYF(0));
+    DBUG_RETURN(true);
+  }
   lex->set_trg_event_type_for_tables();
 
   /*