Re: Bytea PL/Perl transform

út 30. 1. 2024 v 16:43 odesílatel Dagfinn Ilmari Mannsåker <
ilmari(at)ilmari(dot)org> napsal:

> Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> writes:
>
> > I inserted perl reference support - hstore_plperl and json_plperl does
> it.
> >
> > +<->/* Dereference references recursively. */
> > +<->while (SvROK(in))
> > +<-><-->in = SvRV(in);
>
> That code in hstore_plperl and json_plperl is only relevant because they
> deal with non-scalar values (hashes for hstore, and also arrays for
> json) which must be passed as references. The recursive nature of the
> dereferencing is questionable, and masked the bug fixed by commit
> 1731e3741cbbf8e0b4481665d7d523bc55117f63.
>
> bytea_plperl only deals with scalars (specifically strings), so should
> not concern itself with references. In fact, this code breaks returning
> objects with overloaded stringification, for example:
>
> CREATE FUNCTION plperlu_overload() RETURNS bytea LANGUAGE plperlu
> TRANSFORM FOR TYPE bytea
> AS $$
> package StringOverload { use overload '""' => sub { "stuff" }; }
> return bless {}, "StringOverload";
> $$;
>
> This makes the server crash with an assertion failure from Perl because
> SvPVbyte() was passed a non-scalar value:
>
> postgres: ilmari regression_bytea_plperl [local] SELECT: sv.c:2865:
> Perl_sv_2pv_flags:
> Assertion `SvTYPE(sv) != SVt_PVAV && SvTYPE(sv) != SVt_PVHV && SvTYPE(sv)
> != SVt_PVFM' failed.
>
> If I remove the dereferincing loop it succeeds:
>
> SELECT encode(plperlu_overload(), 'escape') AS string;
> string
> --------
> stuff
> (1 row)
>
> Attached is a v2 patch which removes the dereferencing and includes the
> above example as a test.
>

But without dereference it returns bad value.

Maybe there should be a check so references cannot be returned? Probably is
not safe pass pointers between Perl and Postgres.

>
> - ilmari
>
>