MDEV-28367: BACKUP LOCKS on table to be accessible to those with database LOCK TABLES privileges

- Allow database level access via `LOCK TABLES` to execute statement
`BACKUP [un]LOCK <object>`
- `BACKUP UNLOCK` works only with `RELOAD` privilege.
  In case there is `LOCK TABLES` privilege without `RELOAD` privilege,
  we check if backup lock is taken before.
  If it is not we raise an error of missing `RELOAD` privilege.
- We had to remove any error/warnings from calling functions because
`thd->get_stmt_da()->m_status` will be set to error and will break
`my_ok()`.
- Added missing test coverage of `RELOAD` privilege to `main.grant.test`
Reviewer: <daniel@mariadb.org>

mysql-test/main/backup_locks.result

@@ -163,5 +163,82 @@ ERROR HY000: Can't execute the query because you have a conflicting read lock
 BACKUP UNLOCK;
 DROP TABLE t3;
 #
+#  MDEV-28367: BACKUP LOCKS on table to be accessible to those
+#              with database LOCK TABLES privileges
+#
+create database db1;
+create table db1.t1(t int);
+create user user1@localhost;
+select user,host from mysql.user where user='user1';
+User	Host
+user1	localhost
+connect(localhost,user1,,db1,MASTER_PORT,MASTER_SOCKET);
+connect  con1, localhost, user1, ,db1;
+ERROR 42000: Access denied for user 'user1'@'localhost' to database 'db1'
+grant reload on *.* to user1@localhost;
+grant select on db1.* to user1@localhost;
+show grants for user1@localhost;
+Grants for user1@localhost
+GRANT RELOAD ON *.* TO `user1`@`localhost`
+GRANT SELECT ON `db1`.* TO `user1`@`localhost`
+connect  con1, localhost, user1, ,db1;
+BACKUP UNLOCK;
+BACKUP LOCK db1.t1;
+SELECT LOCK_MODE, LOCK_TYPE, TABLE_SCHEMA, TABLE_NAME FROM information_schema.metadata_lock_info;
+LOCK_MODE	LOCK_TYPE	TABLE_SCHEMA	TABLE_NAME
+MDL_SHARED_HIGH_PRIO	Table metadata lock	db1	t1
+BACKUP UNLOCK;
+SELECT LOCK_MODE, LOCK_TYPE, TABLE_SCHEMA, TABLE_NAME FROM information_schema.metadata_lock_info;
+LOCK_MODE	LOCK_TYPE	TABLE_SCHEMA	TABLE_NAME
+connection default;
+disconnect con1;
+grant lock tables on db1.* to user1@localhost;
+show grants for user1@localhost;
+Grants for user1@localhost
+GRANT RELOAD ON *.* TO `user1`@`localhost`
+GRANT SELECT, LOCK TABLES ON `db1`.* TO `user1`@`localhost`
+connect  con1, localhost, user1, ,db1;
+BACKUP UNLOCK;
+BACKUP LOCK db1.t1;
+SELECT LOCK_MODE, LOCK_TYPE, TABLE_SCHEMA, TABLE_NAME FROM information_schema.metadata_lock_info;
+LOCK_MODE	LOCK_TYPE	TABLE_SCHEMA	TABLE_NAME
+MDL_SHARED_HIGH_PRIO	Table metadata lock	db1	t1
+BACKUP UNLOCK;
+SELECT LOCK_MODE, LOCK_TYPE, TABLE_SCHEMA, TABLE_NAME FROM information_schema.metadata_lock_info;
+LOCK_MODE	LOCK_TYPE	TABLE_SCHEMA	TABLE_NAME
+connection default;
+disconnect con1;
+revoke reload on *.* from user1@localhost;
+show grants for user1@localhost;
+Grants for user1@localhost
+GRANT USAGE ON *.* TO `user1`@`localhost`
+GRANT SELECT, LOCK TABLES ON `db1`.* TO `user1`@`localhost`
+connect  con1, localhost, user1, ,db1;
+BACKUP UNLOCK;
+ERROR 42000: Access denied; you need (at least one of) the RELOAD, LOCK TABLES privilege(s) for this operation
+BACKUP LOCK db1.t1;
+SELECT LOCK_MODE, LOCK_TYPE, TABLE_SCHEMA, TABLE_NAME FROM information_schema.metadata_lock_info;
+LOCK_MODE	LOCK_TYPE	TABLE_SCHEMA	TABLE_NAME
+MDL_SHARED_HIGH_PRIO	Table metadata lock	db1	t1
+BACKUP UNLOCK;
+SELECT LOCK_MODE, LOCK_TYPE, TABLE_SCHEMA, TABLE_NAME FROM information_schema.metadata_lock_info;
+LOCK_MODE	LOCK_TYPE	TABLE_SCHEMA	TABLE_NAME
+connection default;
+disconnect con1;
+revoke lock tables on db1.* from user1@localhost;
+show grants for user1@localhost;
+Grants for user1@localhost
+GRANT USAGE ON *.* TO `user1`@`localhost`
+GRANT SELECT ON `db1`.* TO `user1`@`localhost`
+connect  con1, localhost, user1, ,db1;
+BACKUP LOCK db1.t1;
+ERROR 42000: Access denied; you need (at least one of) the RELOAD, LOCK TABLES privilege(s) for this operation
+BACKUP UNLOCK;
+ERROR 42000: Access denied; you need (at least one of) the RELOAD, LOCK TABLES privilege(s) for this operation
+connection default;
+disconnect con1;
+drop database db1;
+drop user user1@localhost;
+#
 # End of MariaDB 10.4 tests
 #

mysql-test/main/backup_locks.test

@@ -188,6 +188,79 @@ DROP TABLE t3;
 BACKUP UNLOCK;
 DROP TABLE t3;
 
+--echo #
+--echo #  MDEV-28367: BACKUP LOCKS on table to be accessible to those
+--echo #              with database LOCK TABLES privileges
+--echo #
+
+--source include/have_metadata_lock_info.inc
+create database db1;
+create table db1.t1(t int);
+create user user1@localhost;
+select user,host from mysql.user where user='user1';
+--replace_result $MASTER_MYSOCK MASTER_SOCKET $MASTER_MYPORT MASTER_PORT
+--error ER_DBACCESS_DENIED_ERROR
+--connect (con1, localhost, user1, ,db1)
+
+grant reload on *.* to user1@localhost;
+# To access DB one need select privileges
+grant select on db1.* to user1@localhost;
+show grants for user1@localhost;
+--connect (con1, localhost, user1, ,db1)
+
+# This should work we have RELOAD privilege
+BACKUP UNLOCK;
+BACKUP LOCK db1.t1;
+SELECT LOCK_MODE, LOCK_TYPE, TABLE_SCHEMA, TABLE_NAME FROM information_schema.metadata_lock_info;
+BACKUP UNLOCK;
+SELECT LOCK_MODE, LOCK_TYPE, TABLE_SCHEMA, TABLE_NAME FROM information_schema.metadata_lock_info;
+
+# Add LOCK TABLES DB privileges (all privileges for BACKUP LOCK are there)
+connection default;
+disconnect con1;
+grant lock tables on db1.* to user1@localhost;
+show grants for user1@localhost;
+--connect (con1, localhost, user1, ,db1)
+# This should work we have RELOAD & LOCK privilege
+BACKUP UNLOCK;
+BACKUP LOCK db1.t1;
+SELECT LOCK_MODE, LOCK_TYPE, TABLE_SCHEMA, TABLE_NAME FROM information_schema.metadata_lock_info;
+BACKUP UNLOCK;
+SELECT LOCK_MODE, LOCK_TYPE, TABLE_SCHEMA, TABLE_NAME FROM information_schema.metadata_lock_info;
+
+# Remove reload privilege, leave only LOCK TABLES privilege
+connection default;
+disconnect con1;
+revoke reload on *.* from user1@localhost;
+show grants for user1@localhost;
+--connect (con1, localhost, user1, ,db1)
+# There is no reload priv needed for unlock and there is no mdl_backup_lock taken
+--error ER_SPECIFIC_ACCESS_DENIED_ERROR
+BACKUP UNLOCK;
+# BACKUP LOCK should work, since we have LOCK privilege
+BACKUP LOCK db1.t1;
+SELECT LOCK_MODE, LOCK_TYPE, TABLE_SCHEMA, TABLE_NAME FROM information_schema.metadata_lock_info;
+# This works since there was taken mdl_backup_lock before
+BACKUP UNLOCK;
+SELECT LOCK_MODE, LOCK_TYPE, TABLE_SCHEMA, TABLE_NAME FROM information_schema.metadata_lock_info;
+
+# Remove LOCK TABLES privilege
+connection default;
+disconnect con1;
+revoke lock tables on db1.* from user1@localhost;
+show grants for user1@localhost;
+--connect (con1, localhost, user1, ,db1)
+--error ER_SPECIFIC_ACCESS_DENIED_ERROR
+BACKUP LOCK db1.t1;
+--error ER_SPECIFIC_ACCESS_DENIED_ERROR
+BACKUP UNLOCK;
+
+connection default;
+disconnect con1;
+
+drop database db1;
+drop user user1@localhost;
+
 --echo #
 --echo # End of MariaDB 10.4 tests
 --echo #

mysql-test/main/grant.result

@@ -1951,6 +1951,11 @@ GRANT EXECUTE                 ON mysqltest_db1.* TO mysqltest_u1@localhost;
 GRANT FILE                    ON *.* TO mysqltest_u1@localhost;
 GRANT CREATE USER             ON *.* TO mysqltest_u1@localhost;
 GRANT PROCESS                 ON *.* TO mysqltest_u1@localhost;
+GRANT RELOAD                  ON mysqltest_db1.* TO mysqltest_u1@localhost;
+ERROR HY000: Incorrect usage of DB GRANT and GLOBAL PRIVILEGES
+connect(localhost,mysqltest_u1,,db1,MASTER_PORT,MASTER_SOCKET);
+connect  con1, localhost, mysqltest_u1, ,db1;
+ERROR 42000: Access denied for user 'mysqltest_u1'@'localhost' to database 'db1'
 GRANT RELOAD                  ON *.* TO mysqltest_u1@localhost;
 GRANT REPLICATION CLIENT      ON *.* TO mysqltest_u1@localhost;
 GRANT REPLICATION SLAVE       ON *.* TO mysqltest_u1@localhost;

mysql-test/main/grant.test

@@ -1821,6 +1821,13 @@ GRANT EXECUTE                 ON mysqltest_db1.* TO mysqltest_u1@localhost;
 GRANT FILE                    ON *.* TO mysqltest_u1@localhost;
 GRANT CREATE USER             ON *.* TO mysqltest_u1@localhost;
 GRANT PROCESS                 ON *.* TO mysqltest_u1@localhost;
+# Global privileges should be granted to all schemas, not individual DB
+--error ER_WRONG_USAGE
+GRANT RELOAD                  ON mysqltest_db1.* TO mysqltest_u1@localhost;
+# Select privilege is needed beside RELOAD privilege
+--replace_result $MASTER_MYSOCK MASTER_SOCKET $MASTER_MYPORT MASTER_PORT
+--error ER_DBACCESS_DENIED_ERROR
+--connect (con1, localhost, mysqltest_u1, ,db1)
 GRANT RELOAD                  ON *.* TO mysqltest_u1@localhost;
 GRANT REPLICATION CLIENT      ON *.* TO mysqltest_u1@localhost;
 GRANT REPLICATION SLAVE       ON *.* TO mysqltest_u1@localhost;

sql/sql_parse.cc

@@ -5153,9 +5153,55 @@ mysql_execute_command(THD *thd)
       my_ok(thd);
     break;
   case SQLCOM_BACKUP_LOCK:
-    if (check_global_access(thd, RELOAD_ACL))
-      goto error;
-    /* first table is set for lock. For unlock the list is empty */
+    if (check_global_access(thd, RELOAD_ACL, true))
+    {
+#ifndef NO_EMBEDDED_ACCESS_CHECKS
+      /*
+        In case there is no global privilege, check DB privilege for LOCK TABLES.
+      */
+      if (first_table) // BACKUP LOCK
+      {
+        if (check_single_table_access(thd, LOCK_TABLES_ACL, first_table, true))
+        {
+          char command[30];
+          get_privilege_desc(command, sizeof(command), RELOAD_ACL|LOCK_TABLES_ACL);
+          my_error(ER_SPECIFIC_ACCESS_DENIED_ERROR, MYF(0), command);
+          goto error;
+        }
+      }
+      else // BACKUP UNLOCK
+      {
+        /*
+          We test mdl_backup_lock here because, if a user could obtain a lock
+          it would be silly to error and say `you can't BACKUP UNLOCK`
+          (because its obvious you did a `BACKUP LOCK`).
+          As `BACKUP UNLOCK` doesn't have a database reference,
+          there's no way we can check if the `BACKUP LOCK` privilege is missing.
+          Testing `thd->db` would involve faking a `TABLE_LIST` structure,
+          which because of the depth of inspection
+          in `check_single_table_access` makes the faking likely to cause crashes,
+          or unintended effects. The outcome of this is,
+          if a user does an `BACKUP UNLOCK` without a `BACKUP LOCKED` table,
+          there may be a` ER_SPECIFIC_ACCESS_DENIED` error even though
+          user has the privilege.
+          Its a bit different to what happens if the user has RELOAD_ACL,
+          where the error is silently ignored.
+        */
+        if (!thd->mdl_backup_lock)
+        {
+
+          char command[30];
+          get_privilege_desc(command, sizeof(command), RELOAD_ACL|LOCK_TABLES_ACL);
+          my_error(ER_SPECIFIC_ACCESS_DENIED_ERROR, MYF(0), command);
+          goto error;
+        }
+      }
+#endif
+    }
+    /*
+      There is reload privilege, first table is set for lock.
+      For unlock the list is empty
+    */
     if (first_table)
       res= backup_lock(thd, first_table);
     else