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From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
To: Michael Paquier <michael@paquier.xyz>
Cc: Ewan Young <kdbase.hack@gmail.com>
Cc: pgsql-hackers@lists.postgresql.org
Subject: Re: Prevent crash when calling pgstat functions with unregistered stats kind
Date: Thu, 2 Jul 2026 04:23:16 +0000
Message-ID: <akXntNv2344hoc6L@bdtpg> (raw)
In-Reply-To: <akXkqov6wLbKwpAd@paquier.xyz>
References: <akS/ldidWeqG1FWk@bdtpg>
	<CAON2xHOA23Oq8EERoV9ERBZof1O_vN-tYf0q58TwdkrTNZ-SPg@mail.gmail.com>
	<akXalpb3zjPX3ZEl@bdtpg>
	<akXebziFr_eQgQi8@paquier.xyz>
	<akXjqbXRTLNcwHyE@bdtpg>
	<akXkqov6wLbKwpAd@paquier.xyz>

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
Amazon Web Services: https://aws.amazon.com

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