Re: can we mark upper/lower/textlike functions leakproof?

On Wed, Jul 31, 2024 at 2:03 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> The problem here is that marking these functions leakproof is a
> promise about a *whole bunch* of code, much of it not under our
> control; worse, there's no reason to think all that code is stable.
> A large fraction of it didn't even exist a few versions ago.

I think it's a fair critique. It could be reasonable to say, well, a
particular user could reasonably judge that the risk of marking
upper() as leak-proof is acceptable, but it's a little too risky for
us to want to do it as a project. After all, they can know things like
"we don't even use ICU," which we as a project cannot know.

However, the risk is that an end-user is going to be much less able to
evaluate what is and isn't safe than we are. I think some people are
going to be like -- well the core project doesn't mark enough stuff
leakproof, so I'll just go add markings to a bunch of stuff myself.
And they probably won't stop at stuff like UPPER which is almost
leakproof. They might add it to stuff such as LIKE which results in
immediately giving away the farm. By not giving people any guidance,
we invite them to make up their own rules.

Perhaps it's still right to be conservative; after all, no matter what
an end-user does, it's not a CVE for us, and CVEs suck. On the other
hand, shipping a system that is not useful in practice until you
modify a bunch of stuff also sucks, especially when it's not at all
clear which things are safe to modify.

I'm not sure what the right thing to do here is, but I think that it's
wrong to imagine that being unwilling to endorse probably-leakproof
things as leakproof -- or unwilling to put in the work to MAKE them
leakproof if they currently aren't -- has no security costs.

--
Robert Haas
EDB: http://www.enterprisedb.com