Re: Procedures versus the "fastpath" API

On Tue, 2021-03-09 at 14:15 -0500, Tom Lane wrote:
> The security team received a report from Theodor-Arsenij
> Larionov-Trichkin of PostgresPro that it's possible to crash the
> backend with an assertion or null-pointer dereference by trying to
> call a window function via the "fast path function call" protocol
> message.
> 
> So the questthemion on the table is what to do about this.
> 
> As for procedures, I'm of the opinion that we should just reject those
> too, but some other security team members were not happy with that
> idea.  Conceivably we could attempt to make the case actually work,
> but is it worth the trouble?  Given the lack of field complaints
> about the "invalid transaction termination" failure, it seems unlikely
> that it's occurred to anyone to try to call procedures this way.
> We'd need special infrastructure to test the case, too, since psql
> offers no access to fastpath calls.
> 
> A compromise suggestion was to prohibit calling procedures via
> fastpath as of HEAD, but leave existing releases as they are,
> in case anyone is using a case that happens to work.

The "invalid transaction termination" failure alone doesn't
worry or surprise me - transaction handling in procedures only works
under rather narrow conditions anyway (no SELECT on the call stack,
no explicit transaction was started outside the procedure).

If that is the only problem, I'd just document it.  The hard work is
of course that there is no other problem with calling procedures that
way.  If anybody wants to do that work, and transaction handling is
the only thing that doesn't work with the fastpath API, we can call
it supported and document the exception.

In case of doubt, I would agree with you and forbid it in HEAD
as a corner case with little real-world use.

Yours,
Laurenz Albe