Обсуждение: Why does pg_rewind deny permission for pg_read_binary_file() other than 'dbname=postgres'?

BTW rewinder is another USER that I made for control variable:

$ pg_rewind -D /pgdata --source-server='host=172.17.1.2 port=5432 user=rewinder dbname=postgres connect_timeout=5'
pg_rewind: source and target cluster are on the same timeline
pg_rewind: no rewind required
$ pg_rewind -D /pgdata --source-server='host=172.17.1.2 port=5432 user=rewinder dbname=repmgr   connect_timeout=5'
pg_rewind: error: could not fetch remote file "global/pg_control": ERROR:  permission denied for function pg_read_binary_file

---------- Forwarded message ---------
From: Zhaoxun Yan <yan.zhaoxun@gmail.com>
Date: Thu, Oct 12, 2023 at 4:44 PM
Subject: Why does pg_rewind deny permission for pg_read_binary_file() other than 'dbname=postgres'?
To: Pgsql-admin <pgsql-admin@lists.postgresql.org>

Hi there!

I am using repmgr and I have to use the command repmgr node rejoin --force-rewind under 'dbname=repmgr'. It always fail on using pg_rewind, the error is like this:
pg_rewind: error: could not fetch remote file "global/pg_control": ERROR:  permission denied for function pg_read_binary_file

I look into pg_rewind, and found that for a rewind user defined like
https://www.postgresql.org/docs/16/app-pgrewind.html

It always encounters such a problem if database != postgres but functions when 'dbname=postgres'

$ pg_rewind -D /pgdata --source-server='host=172.17.1.2 port=5432 user=rep dbname=repmgr connect_timeout=5'
pg_rewind: error: could not fetch remote file "global/pg_control": ERROR:  permission denied for function pg_read_binary_file
$ pg_rewind -D /pgdata --source-server='host=172.17.1.2 port=5432 user=rep dbname=postgres connect_timeout=5'
pg_rewind: source and target cluster are on the same timeline
pg_rewind: no rewind required

What is the problem with it?

BTW, below is what I have done to USER rewinder:

CREATE USER rewinder;
GRANT EXECUTE ON function pg_catalog.pg_ls_dir(text, boolean, boolean) TO rewinder;
GRANT EXECUTE ON function pg_catalog.pg_stat_file(text, boolean) TO rewinder;
GRANT EXECUTE ON function pg_catalog.pg_read_binary_file(text) TO rewinder;
GRANT EXECUTE ON function pg_catalog.pg_read_binary_file(text, bigint, bigint, boolean) TO rewinder;

# below is irrelevant to postgresql's pg_rewind

GRANT ALL PRIVILEGES ON DATABASE repmgr TO rewinder;
GRANT ALL PRIVILEGES ON SCHEMA repmgr TO rewinder;
GRANT pg_read_all_stats TO rewinder;
GRANT ALL ON SCHEMA repmgr TO rewinder;
GRANT SELECT  ON DATABASE repmgr TO rewinder;
GRANT SELECT ON ALL TABLES IN SCHEMA repmgr TO rewinder;
GRANT SELECT ON SCHEMA repmgr TO rewinder;

Hi Ron,

I forgot to tell you that during setting up repmgr, I have created database repmgr (possibly schema repmgr depending on what extension repmgr did)

CREATE USER rep replication;

CREATE database repmgr WITH OWNER rep;

CREATE EXTENSION repmgr;

On Thu, Oct 12, 2023 at 5:22 PM Ron <ronljohnsonjr@gmail.com> wrote:

"rewinder" is a user, not a database.  "dbname=postgres" explicitly means that the database name is "postgres".

On 10/12/23 03:48, Zhaoxun Yan wrote:

BTW rewinder is another USER that I made for control variable:

$ pg_rewind -D /pgdata --source-server='host=172.17.1.2 port=5432 user=rewinder dbname=postgres connect_timeout=5'
pg_rewind: source and target cluster are on the same timeline
pg_rewind: no rewind required
$ pg_rewind -D /pgdata --source-server='host=172.17.1.2 port=5432 user=rewinder dbname=repmgr   connect_timeout=5'
pg_rewind: error: could not fetch remote file "global/pg_control": ERROR:  permission denied for function pg_read_binary_file

---------- Forwarded message ---------
From: Zhaoxun Yan <yan.zhaoxun@gmail.com>
Date: Thu, Oct 12, 2023 at 4:44 PM
Subject: Why does pg_rewind deny permission for pg_read_binary_file() other than 'dbname=postgres'?
To: Pgsql-admin <pgsql-admin@lists.postgresql.org>

Hi there!

I am using repmgr and I have to use the command repmgr node rejoin --force-rewind under 'dbname=repmgr'. It always fail on using pg_rewind, the error is like this:
pg_rewind: error: could not fetch remote file "global/pg_control": ERROR:  permission denied for function pg_read_binary_file

I look into pg_rewind, and found that for a rewind user defined like
https://www.postgresql.org/docs/16/app-pgrewind.html

It always encounters such a problem if database != postgres but functions when 'dbname=postgres'

$ pg_rewind -D /pgdata --source-server='host=172.17.1.2 port=5432 user=rep dbname=repmgr connect_timeout=5'
pg_rewind: error: could not fetch remote file "global/pg_control": ERROR:  permission denied for function pg_read_binary_file
$ pg_rewind -D /pgdata --source-server='host=172.17.1.2 port=5432 user=rep dbname=postgres connect_timeout=5'
pg_rewind: source and target cluster are on the same timeline
pg_rewind: no rewind required

What is the problem with it?

BTW, below is what I have done to USER rewinder:

CREATE USER rewinder;
GRANT EXECUTE ON function pg_catalog.pg_ls_dir(text, boolean, boolean) TO rewinder;
GRANT EXECUTE ON function pg_catalog.pg_stat_file(text, boolean) TO rewinder;
GRANT EXECUTE ON function pg_catalog.pg_read_binary_file(text) TO rewinder;
GRANT EXECUTE ON function pg_catalog.pg_read_binary_file(text, bigint, bigint, boolean) TO rewinder;

# below is irrelevant to postgresql's pg_rewind

GRANT ALL PRIVILEGES ON DATABASE repmgr TO rewinder;
GRANT ALL PRIVILEGES ON SCHEMA repmgr TO rewinder;
GRANT pg_read_all_stats TO rewinder;
GRANT ALL ON SCHEMA repmgr TO rewinder;
GRANT SELECT  ON DATABASE repmgr TO rewinder;
GRANT SELECT ON ALL TABLES IN SCHEMA repmgr TO rewinder;
GRANT SELECT ON SCHEMA repmgr TO rewinder;

--
Born in Arizona, moved to Babylonia.

Zhaoxun Yan <yan.zhaoxun@gmail.com> writes:
> The results are the same, 'dbname=repmgr' is the root cause of the error,
> since 'dbname=postgres' went well with both 'user=rep' and 'user=rewinder',
> while 'dbname=repmgr' generates exactly the same error.

As far as I can tell, you granted permissions on that function
in the postgres database, but not any other database.  Function
permissions, like most others, are database-local in Postgres.

            regards, tom lane

Now pg_rewind has no problem when user=rewinder & dbname=repmgr:
$ pg_rewind -D /pgdata --source-server='host=172.17.1.2 port=5432 user=rewinder dbname=repmgr   connect_timeout=5'
pg_rewind: source and target cluster are on the same timeline
pg_rewind: no rewind required

Still, I wish psql can specify this database limitation explicitly, either enforcing the command with 'IN DATABASE [dbname]', or emphasize it in feedback rather than a simple 'GRANT'.