Thread: segfault when disconnecting from db with server side prepare

If I enable server side prepare (UseServerSidePrepare=1 in my DSN) and connect to the database, execute a query, then
disconnect,the following code path is taken: 
SQL_Disconnect calls PGAPI_Disconnect
PGAPI_Disconnect calls CC_Cleanup
CC_Cleanup iterates through its statements:

/* Free all the stmts on this connection */
for (i = 0; i < self->num_stmts; i++)
{
        stmt = self->stmts[i];
        if (stmt)
        {
                stmt->hdbc = NULL;      /* prevent any more dbase interactions */
                SC_Destructor(stmt);
                self->stmts[i] = NULL;
        }
}

SC_Destructor calls SC_initialize_stmts(self, TRUE)
SC_Initialize_stmts calls SC_set_prepared(self, FALSE), which dereferences the hdbc pointer, which was set to null in
thecode block above: 

void
SC_set_prepared(StatementClass *stmt, BOOL prepared)
{
        if (prepared == stmt->prepared)
                return;
        if (!prepared)
        {
                ConnectionClass *conn = SC_get_conn(stmt);
*** CRASH ***   if (CONN_CONNECTED == conn->status)
                {
                        QResultClass    *res;
                        char dealloc_stmt[128];

                        sprintf(dealloc_stmt, "DEALLOCATE _PLAN%0x", stmt);
                        res = CC_send_query(conn, dealloc_stmt, NULL, 0);
                        if (res)
                                QR_Destructor(res);
                }
        }
        stmt->prepared = prepared;
}


The SC_set_prepared function is trying to deallocate the query plan on the server side - is this necessary if we're
shuttingdown the connection? (anyway, the socket has already been closed before the statements are deallocated.) 

I think the proper way to fix this is to simply add a check for a null pointer in the SC_set_prepared function, but I
wantedto ask here first since I don't know if this will have any unforseen consequences. 

> -----Original Message-----
> From: pgsql-odbc-owner@postgresql.org
> [mailto:pgsql-odbc-owner@postgresql.org] On Behalf Of Scot Loach
> Sent: 19 September 2004 15:29
> To: pgsql-odbc@postgresql.org
> Subject: [ODBC] segfault when disconnecting from db with
> server side prepare
>
> I think the proper way to fix this is to simply add a check
> for a null pointer in the SC_set_prepared function, but I
> wanted to ask here first since I don't know if this will have
> any unforseen consequences.

Sounds fine to me - it's not like you would ever intentionally want conn
== null in there.

Can you supply a patch?

Regards, Dave

I took a closer look at the CVS and it appears that this is in fact already fixed, I guess I need to update my CVS.

Thanks anyway.

scot.


-----Original Message-----
From: Dave Page [mailto:dpage@vale-housing.co.uk]
Sent: Monday, September 20, 2004 3:39 AM
To: Scot Loach; pgsql-odbc@postgresql.org
Subject: RE: [ODBC] segfault when disconnecting from db with server side
prepare




> -----Original Message-----
> From: pgsql-odbc-owner@postgresql.org
> [mailto:pgsql-odbc-owner@postgresql.org] On Behalf Of Scot Loach
> Sent: 19 September 2004 15:29
> To: pgsql-odbc@postgresql.org
> Subject: [ODBC] segfault when disconnecting from db with
> server side prepare
>
> I think the proper way to fix this is to simply add a check
> for a null pointer in the SC_set_prepared function, but I
> wanted to ask here first since I don't know if this will have
> any unforseen consequences.

Sounds fine to me - it's not like you would ever intentionally want conn
== null in there.

Can you supply a patch?

Regards, Dave