How to check users are not trying to change other users passwords

The trigger below will check to see that user George is only changing his own password and not trying to change other peoples passwords.

create procedure
reset_password (p_username in varchar2,
p_password in varchar2)
as
begin

if (USER=’GEORGE’ and p_username in (‘MARY’,’BILL’,’SUE’))
then
execute immediate
‘alter user ‘ || p_username ||
‘ identified by ‘ || p_password;
else

send_email_to_admin
(‘George is trying to amend ‘ || p_username || ‘ password’);
raise_application_error
(-20001, ‘George, you cannot change other peoples passwords’);
end if;
end;
/
grant execute on reset_password to george;