[postgis-devel] st_asflatgeobuf detoast crash

[Julien Rouhaud]

Hi,

On Sat, Jun 18, 2022 at 06:52:10AM -0500, Justin Pryzby wrote:
> An instance running pg15beta1 crashed while running one of sqlsmith's appalling
> queries.  I reproduced with this, simplified query:
> 
> 	select st_asflatgeobuf(row(1), false, '')
> 	over () from information_schema.table_privileges
> 
> Program terminated with signal 11, Segmentation fault.
> #0  pg_detoast_datum_copy (datum=0x514) at fmgr.c:1719

All versions of st_asflatgeobuf have the same problem, so you can reduce the
reproducer to:

select st_asflatgeobuf(row(1)) from pg_class;

AFAICT, inspect_table() doesn't check that a geometry column was indeed found,
leading to the problem.

Some like that fixes the crash for me:

diff --git a/postgis/flatgeobuf.c b/postgis/flatgeobuf.c
index 1b502e546..545442f31 100644
--- a/postgis/flatgeobuf.c
+++ b/postgis/flatgeobuf.c
@@ -110,6 +110,9 @@ static void inspect_table(struct flatgeobuf_agg_ctx *ctx)
        columns_size++;
    }

+   if (!geom_found)
+       elog(ERROR, "no geom column found");
+
    if (columns_size > 0) {
        ctx->ctx->columns = columns;
        ctx->ctx->columns_size = columns_size;