如何授予非超级用户特权以执行函数pg_read_binary_file？

Question

In PostgreSQL I have a database with a custom function witch loads binary content of the file in database table by using the system function pg_read_binary_file .

If I ran this custom funtion under a user with superuser rights, it executes successfuly. But when the user does not have superuser rights, I receive an error:

permission denied for function pg_read_binary_file

I thought that all that I need is to simply GRANT permissions to EXECUTE the funtion for such user, so I did the following:

GRANT EXECUTE ON FUNCTION pg_read_binary_file(text,bigint,bigint,boolean) TO someuser;
GRANT EXECUTE ON FUNCTION pg_read_binary_file(text,bigint,bigint) TO someuser; 
GRANT EXECUTE ON FUNCTION pg_read_binary_file(text) TO someuser;

If I check the permissions by

SELECT proacl FROM pg_proc WHERE proname='pg_read_binary_file';

I get:

{postgres=X/postgres,someuser=X/postgres}
{postgres=X/postgres,someuser=X/postgres}
{postgres=X/postgres,someuser=X/postgres}

As I understand, now someuser has permission to execute the function pg_read_binary_file . But when I try to run my custom function, I still receive the same error:

permission denied for function pg_read_binary_file

So the question is how to give permission to a non-superuser to execute the function pg_read_binary_file ? Maybe there are some additional permissions that must be granted, but it is not obvious.

In the documentation on Portgres system functions for pg_read_binary_file it is written that:

Restricted to superusers by default, but other users can be granted EXECUTE to run the function.

I searched for some additional information about the way how can I give such permissions, but without luck.

Answer 1

There are three possibilities:

1. You are using an old PostgreSQL version.

   Before commit e79350fef2917522571add750e3e21af293b50fe , this was not governed by permissions on the functions, but by hard-coded checks in the function itself.

   This doesn't seem to be your case, however, because the error messages would then read:

    ERROR: must be superuser to read files 

2. You are not someuser when you try to execute the function. Test with

    SELECT current_user; 

3. You are connected to a different database (eg, you changed the permissions in the postgres database, but someuser connects to a different database).