Re: Assert in pageinspect with NULL pages

On Sun, Mar 27, 2022 at 2:02 PM Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Sun, Mar 27, 2022 at 4:26 PM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
> > We're not dealing
> > with adversarial page images here.
>
> I think it's bad that we have to make that assumption, considering
> that there's nothing whatever to keep users from supplying arbitrary
> page images to pageinspect.

Maybe it isn't strictly necessary for bt_page_items(), but making that
level of guarantee is really hard, and not particularly useful. And
that's the easy case for pageinspect: gist_page_items() takes a raw
bytea, and puts it through the underlying types output functions.

I think that it might actually be fundamentally impossible to
guarantee that that'll be safe, because we have no idea what the
output function might be doing. It's arbitrary user-defined code that
could easily be implemented in C. Combined with an arbitrary page
image.

> But I also agree that if we're unable or
> unwilling to make things perfect, it's still good to make them better.

I think that most of the functions can approach being perfectly
robust, with a little work. In practical terms they can almost
certainly be made so robust that no real user of bt_page_items() will
ever crash the server. Somebody that goes out of their way to do that
*might* find a way (even with the easier cases), but that doesn't
particularly concern me.

--
Peter Geoghegan