Re: Prevent crash when calling pgstat functions with unregistered stats kind

Hi,

On Thu, Jul 02, 2026 at 01:10:18PM +0900, Michael Paquier wrote:
> On Thu, Jul 02, 2026 at 04:06:01AM +0000, Bertrand Drouvot wrote:
> > I agree that the responsibility should primarily be in the extension. However,
> > the issue is that the NULL dereference happens inside core code (pgstat_prep_pending_entry,
> > etc.), and the resulting segfault(s) cause the postmaster to terminate all
> > backends (not just the offending session).
> >
> > Given that one misconfigured extension can crash all connections on the server,
> > a defensive check in core seems reasonable (kind of similar to 341e9a05e7b).
>
> Nope, this was a different thing, doable in a couple of steps:
> - Load the library.
> - Write custom stats.
> - Stop the server, flush the stats.
> - Edit the configuration, not loading the library.
> - Restart the server, loading failed.
>
> The problem of this thread ought to be blocked at its source, in the
> extension itself: let's not give free hands to an extension to do what
> it should not be allowed to do. There is a similar defense in
> test_custom_rmgrs, as one example. We should just map to that.

Ok but what about extensions that don't call pgstat_register_kind() at all? Your
point is that they would see the issue during the development of the extension? (If
so, I think I could agree).

Regards,

--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
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