Re: Use-after-free issue in postgres_fdw

On Sat, Mar 21, 2026 at 1:14 AM Matheus Alcantara
<matheusssilv97@gmail.com> wrote:
> On 20/03/26 05:27, Chao Li wrote:
> > I am not very familiar with the FDW code, so I am not ready to suggest a concrete fix. But it seems wrong to let later paths keep using PgFdwScanState->conn after select * from ft1 has already failed with connection loss. My guess is that we either need to invalidate all dependent state when disconnect_pg_server() runs, or otherwise prevent later cleanup paths from touching the cached PGconn *.
>
> Although I agree with this I think that it will be a quite invasive
> change to fix this issue, considering that it should be back-ported.
>
> I see two ways to implement this:
>
> 1. ForeignScanState->conn points to a ConnCacheEntry and it access the
> PGConn via ConnCacheEntry->conn, so it can check if != NULL before using.
>
> 2. Make pgfdw_reject_incomplete_xact_state_change() or
> disconnect_pg_server() receive a PgFdwConnState and add a new field on
> this state to represent that the connection is closed and them check
> this field on the proper code paths.
>
> With the patch proposed on the previous email the server don't crash
> and any use of PgFdwScanState->conn will make the command to fail with
> something like this:
>
>     ERROR:  08006: no connection to the server
>     CONTEXT:  remote SQL command: CLOSE c1
>     LOCATION:  pgfdw_report_internal, connection.c:1059
>
>
> So I don't think that this change would be worth, or I'm missing
> something? What do you think?

I don't feel the need to do these, either, for the reason mentioned upthread.

Thanks again!

Best regards,
Etsuro Fujita