Re: pg18: Virtual generated columns are not (yet) safe when superuser selects from them

On Thu, Jun 5, 2025 at 10:39 PM Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
> On Thu, Jun 5, 2025 at 6:49 AM Peter Eisentraut <peter(at)eisentraut(dot)org> wrote:
> > I propose to address this by not allowing the use of user-defined
> > functions in generation expressions for now. The attached patch
> > implements this. This assumes that all built-in functions are
> > trustworthy, for this purpose, which seems likely true and likely desirable.
> >
> > I think the feature is still useful like that, and this approach
> > provides a path to add new functionality in the future that grows this
> > set of allowed functions, for example by allowing some configurable set
> > of "trusted" functions or whatever.
>
> I don't think this is sufficient to fix the problem. We have built-in
> functions that are unsafe. These include LO functions like loread(),
> lowrite(), lo_unlink(); functions that change session state like
> set_config() and setseed(); functions that allow arbitrary query
> execution like query_to_xml(); slot-manipulation functions like
> pg_drop_replication_slot(); and maybe other things.
>
> Even if it worked, I think it's an unappealing solution -- we've
> worked really hard at extensibility and making decisions based on
> object properties rather than what's built-in and what's provided by a
> user or an extension. But I also don't think it works.
>

I think it will work.
because we already require the generated column expression to be
immutable functions.

The above functions you mentioned are all not immutable.