Re: Possibility to disable `ALTER SYSTEM`

On Tue, 19 Mar 2024 at 15:52, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> I like this idea. The "bonus" is not optional though, because
> setting the files' ownership/permissions is the only way to be
> sure that the prohibition is even a little bit bulletproof.

I don't agree with this. The only "normal" way of modifying
postgresql.auto.conf from within postgres is using ALTER SYSTEM, so
simply disabling ALTER SYSTEM seems enough to me.

> Another question is whether this should be one-size-fits-all for
> all the configuration files. I can imagine situations where
> you'd like to lock down postgresql[.auto].conf but not pg_hba.conf.
> But maybe that can wait for somebody to show up with a use-case.

Afaik there's no way to modify pg_hba.conf from within postgres, only
read it. (except for COPY TO FILE/PROGRAM etc) So, I don't think we
need to worry about this now.

On Tue, 19 Mar 2024 at 15:52, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> Heikki Linnakangas <hlinnaka(at)iki(dot)fi> writes:
> > 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.
>
> I like this idea. The "bonus" is not optional though, because
> setting the files' ownership/permissions is the only way to be
> sure that the prohibition is even a little bit bulletproof.
>
> One small issue: how do we make that work on Windows? Have recent
> versions grown anything that looks like real file permissions?
>
> Another question is whether this should be one-size-fits-all for
> all the configuration files. I can imagine situations where
> you'd like to lock down postgresql[.auto].conf but not pg_hba.conf.
> But maybe that can wait for somebody to show up with a use-case.
>
> regards, tom lane