Calling procedure dynamically, from different schema, permissions issue

Question

Hi,
I have a 'master_user' schema that needs to run DDL on a 'secondary_user' schema.
There appears to be some kind of permissions subtlety that I'm missing. Here are the simplified steps to create, test and troubleshoot:
Secondary schema has a procedure defined:
-- Run as SYSTEM (at build time)
CREATE OR REPLACE PROCEDURE secondary_user.execute_immediate(p_sql_statement IN VARCHAR2)
IS
BEGIN
    EXECUTE IMMEDIATE p_sql_statement;
END;
GRANT EXECUTE ON secondary_user.execute_immediate TO master_user;
I then want to call this procedure from master_user to execute DDL dynamically in secondary_user.
- Run as master_user
BEGIN
    EXECUTE IMMEDIATE ' BEGIN secondary_user.execute_immediate(''DROP TABLE test1''); END;';
END;
ERROR at line 1:
ORA-00942: table or view does not exist
ORA-06512: at SECONDARY_USER.EXECUTE_IMMEDIATE", line 5
ORA-06512: at line 1
ORA-06512: at line 2
TROUBLESHOOTING SO FAR:
Now I can call this procedure directly:
-- As master_user
EXEC secondary_user.execute_immediate('drop table test1')
PL/SQL procedure successfully completed.
I can call the wrapped procedure as different users:
-- As secondary_user
BEGIN
    EXECUTE IMMEDIATE ' BEGIN secondary_user.execute_immediate(''DROP TABLE test1''); END;';
END;
PL/SQL procedure successfully completed.
-- As SYSTEM
BEGIN
    EXECUTE IMMEDIATE ' BEGIN secondary_user.execute_immediate(''DROP TABLE test1''); END;';
END;
PL/SQL procedure successfully completed.
Can you shed any light on this behaviour? The master_user clearly has permission to run the procedure, but it cannot see it from within an anonymous block. However SYSTEM can so what permission does SYSTEM have that master_user does not?
Much appreciated,
Si

Answer 1

Something doesn't add up:
SCOTT@orcl > create user secondary_user
  2  identified by secondary_user
  3  default tablespace users
  4  quota unlimited on users
  5  /
User created.
SCOTT@orcl > grant create session to secondary_user
  2  /
Grant succeeded.
SCOTT@orcl > create user master_user
  2  identified by master_user
  3  default tablespace users
  4  quota unlimited on users
  5  /
User created.
SCOTT@orcl > grant create session to master_user
  2  /
Grant succeeded.
SCOTT@orcl > CREATE OR REPLACE PROCEDURE secondary_user.execute_immediate(p_sql_statement IN VARCHAR2)
  2
  3  IS
  4
  5  BEGIN
  6
  7      EXECUTE IMMEDIATE p_sql_statement;
  8
  9  END;
10
11  /
Procedure created.
SCOTT@orcl > GRANT EXECUTE ON secondary_user.execute_immediate TO master_user;
Grant succeeded.
SCOTT@orcl >
SCOTT@orcl > create table secondary_user.test1(n number)
  2  /
Table created.
SCOTT@orcl > connect master_user@orcl
Enter password:
Connected.
MASTER_USER@orcl > BEGIN
  2
  3      EXECUTE IMMEDIATE ' BEGIN secondary_user.execute_immediate(''DROP TABLE test1''); END;';
  4
  5  END;
  6
  7  /
PL/SQL procedure successfully completed.
MASTER_USER@orcl >
Make sure table secondary_user.test1 exists when you run SP. And, as you can see, neither secondary_user nor master_user have any privs besides create session.
SY.