Horton

Re: Possibility to disable `ALTER SYSTEM`

Andrew Dunstan <andrew@dunslane.net>

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From: Andrew Dunstan <andrew@dunslane.net>
To: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: PostgreSQL Hackers <pgsql-hackers@postgresql.org>, Jelte Fennema-Nio <postgres@jeltef.nl>, Daniel Gustafsson <daniel@yesql.se>, Bruce Momjian <bruce@momjian.us>, Tom Lane <tgl@sss.pgh.pa.us>, Joel Jacobson <joel@compiler.org>, Gabriele Bartolini <gabriele.bartolini@enterprisedb.com>, Magnus Hagander <magnus.hagander@redpill-linpro.com>, Maciek Sakrejda <m.sakrejda@gmail.com>, Robert Haas <robertmhaas@gmail.com>
Date: 2024-03-19T11:49:10Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Add allow_alter_system GUC.

  2. Rename COMPAT_OPTIONS_CLIENT to COMPAT_OPTIONS_OTHER.

  3. Remove support for version-0 calling conventions.

On Tue, Mar 19, 2024 at 5:26 AM Heikki Linnakangas <hlinnaka@iki.fi> wrote:

> I want to remind everyone of this from Gabriele's first message that
> started this thread:
>
> > At the moment, a possible workaround is that `ALTER SYSTEM` can be
> blocked
> > by making the postgresql.auto.conf read only, but the returned message is
> > misleading and that’s certainly bad user experience (which is very
> > important in a cloud native environment):
> >
> >
> > ```
> > postgres=# ALTER SYSTEM SET wal_level TO minimal;
> > ERROR:  could not open file "postgresql.auto.conf": Permission denied
> > ```
>
> I think making the config file read-only is a fine solution. If you
> don't want postgres to mess with the config files, forbid it with the
> permission system.
>
> Problems with pg_rewind, pg_basebackup were mentioned with that
> approach. I think if you want the config files to be managed outside
> PostgreSQL, by kubernetes, patroni or whatever, it would be good for
> them to be read-only to the postgres user anyway, even if we had a
> mechanism to disable ALTER SYSTEM. So it would be good to fix the
> problems with those tools anyway.
>
> The error message is not great, I agree with that. Can we improve it?
> Maybe just add a HINT like this:
>
> postgres=# ALTER SYSTEM SET wal_level TO minimal;
> ERROR:  could not open file "postgresql.auto.conf" for writing:
> Permission denied
> HINT:  Configuration might be managed outside PostgreSQL
>
>
> Perhaps we could make that even better with a GUC though. I propose a
> GUC called 'configuration_managed_externally = true / false". If you set
> it to true, we prevent ALTER SYSTEM and make the error message more
> definitive:
>
> postgres=# ALTER SYSTEM SET wal_level TO minimal;
> ERROR:  configuration is managed externally
>
> As a bonus, if that GUC is set, we could even check at server startup
> that all the configuration files are not writable by the postgres user,
> and print a warning or refuse to start up if they are.
>
> (Another way to read this proposal is to rename the GUC that's been
> discussed in this thread to 'configuration_managed_externally'. That
> makes it look less like a security feature, and describes the intended
> use case.)
>
>
>

I agree with pretty much all of this.

cheers

andrew