Re: Proposed patch for key managment

On Sat, Dec 5, 2020 at 09:54:33PM +0900, Michael Paquier wrote:
> On Fri, Dec 04, 2020 at 10:52:29PM -0500, Bruce Momjian wrote:
> > OK, I worked with Sawada-san and added the attached patch. The updated
> > full patch is at the same URL: :-)
> >
> > https://github.com/postgres/postgres/compare/master...bmomjian:key.diff
>
> Oh, I see that you use SHA256 during firstboot, which is why you
> bypass the resowner paths in cryptohash_openssl.c. Wouldn't it be
> better to use IsBootstrapProcessingMode() then?

I tried that, but we also use the resource references before the
resource system is started even in non-bootstrap mode. Maybe we should
be creating a resource owner for this, but it is so early in the boot
process I don't know if that is safe.

> > @@ -72,14 +72,15 @@ pg_cryptohash_create(pg_cryptohash_type type)
> > ctx = ALLOC(sizeof(pg_cryptohash_ctx));
> > if (ctx == NULL)
> > return NULL;
> > + explicit_bzero(ctx, sizeof(pg_cryptohash_ctx));
> >
> > state = ALLOC(sizeof(pg_cryptohash_state));
> > if (state == NULL)
> > {
> > - explicit_bzero(ctx, sizeof(pg_cryptohash_ctx));
> > FREE(ctx);
> > return NULL;
> > }
> > + explicit_bzero(state, sizeof(pg_cryptohash_state));
>
> explicit_bzero() is used to give the guarantee that any sensitive data
> gets cleaned up after an error or on free. So I think that your use
> is incorrect here for an initialization.

It turns out what we were missing was a clear of state->resowner in
cases where the resowner was null. I removed the bzero calls completely
and it now runs fine.

> > if (state->evpctx == NULL)
> > {
> > - explicit_bzero(state, sizeof(pg_cryptohash_state));
> > - explicit_bzero(ctx, sizeof(pg_cryptohash_ctx));
> > #ifndef FRONTEND
> > ereport(ERROR,
> > (errcode(ERRCODE_OUT_OF_MEMORY),
>
> And this original position is IMO more correct.

Do we even need them?

> Anyway, at quick glance, the backtrace of upthread is indicating a
> double-free with an attempt to free a resource owner that has been
> already free'd.

I think that is now fixed too. Updated patch at the same URL:

https://github.com/postgres/postgres/compare/master...bmomjian:key.diff

--
Bruce Momjian <bruce(at)momjian(dot)us> https://momjian.us
EnterpriseDB https://enterprisedb.com

The usefulness of a cup is in its emptiness, Bruce Lee