Re: BUG #18276: Heap-buffer-overflow triggered in src/backend/utils/adt/datum.c:163

PG Bug reporting form <noreply@postgresql.org> writes:
> My fuzzer finds a heap-buffer-overflow bug in PostgreSQL 17devel, which
> makes PostgreSQL crash.

All I see here is a datatype declaration that doesn't match what the
C functions expect.  You wrote:

> CREATE TYPE widget (
>    input = widget_in,
>    output = widget_out,
>    alignment = double
> );

but the declaration that the regress.so functions expect is what's in
src/test/regress/sql/create_type.sql:

CREATE TYPE widget (
   internallength = 24,
   input = widget_in,
   output = widget_out,
   typmod_in = numerictypmodin,
   typmod_out = numerictypmodout,
   alignment = double
);

That is, widget_in expects it should produce a fixed-length Datum
(24 bytes long, with no length word).  But you declared the type
as variable-length, meaning that datumCopy expects to find a length
word.  That discrepancy leads directly to the reported crash.

            regards, tom lane