Thread

Re: Server crash: Use-after-free in AfterTriggerEndQuery()

amit <amitlangote09@gmail.com> — 2026-05-07T09:09:36Z

Hi Anthonin,

On Wed, May 6, 2026 at 5:14 PM Anthonin Bonnefoy
<anthonin.bonnefoy@datadoghq.com> wrote:
> On Tue, May 5, 2026 at 8:38 AM Amul Sul <sulamul@gmail.com> wrote:
> > Here is the reproducible test that has an AFTER INSERT trigger on a
> > referenced table that recursively inserts rows into itself:
> >
> > --
> > create table trigger_recursive_pk (id int primary key);
> > create table trigger_recursive_fk (id int references trigger_recursive_pk(id));
> > insert into trigger_recursive_pk select g from generate_series(1, 15) g;
> >
> > create function trigger_recursive_fn() returns trigger language plpgsql as $$
> > begin
> >     if new.id < 10 then
> >         insert into trigger_recursive_fk values (new.id + 1);
> >     end if;
> >     return new;
> > end$$;
> >
> > create trigger trigger_recursive after insert on trigger_recursive_fk
> >     for each row execute function trigger_recursive_fn();
> >
> > insert into trigger_recursive_fk values (1);
> > --
>
> I've managed to reproduce the issue on the current HEAD thanks to the
> script. Doing a git bissect, the failure was introduced with
> 34a30786293005 when the batch_callbacks list was added.
>
> > The attached patch fixes the reported issue by recomputing qs
> > immediately before calling FireAfterTriggerBatchCallbacks().
>
> The patch fixes the issue and the change looks reasonable.

Thanks for the review.  I agree.

Attached v2.  I simplified the test because the FK isn't really needed
to reproduce the bug, since the use-after-free is the stale qs load
itself.  Also reworded the comment above the recompute and tweaked the
commit message a bit.

Will push tomorrow barring objections.  Thanks again, Amul, for the patch.

-- 
Thanks, Amit Langote