Message-ID: <gh-postgresql-interfaces-psqlodbc-113-c2841390272@github.com>
From: "harukat (@harukat)" <noreply+harukat@github.com>
To: "postgresql-interfaces/psqlodbc" <noreply+postgresql-interfaces-psqlodbc@github.com>
Date: Wed, 30 Apr 2025 09:36:29 +0000
Subject: Re: [postgresql-interfaces/psqlodbc] PR #113: SQLFreeStmt(stmt,SQL_DROP) now returns an error when it's conn has been disconnected.
In-Reply-To: <gh-postgresql-interfaces-psqlodbc-113@github.com>
References: <gh-postgresql-interfaces-psqlodbc-113@github.com>
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X-GitHub-Issue: 113
X-GitHub-Repo: postgresql-interfaces/psqlodbc
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@davecramer 
Information was obtained about the crash after the fix.

Although this fix reduces the frequency of occurrence, it does not seem to completely prevent the driver manager from attempting to execute SQLFreeStmt(hstmt,SQL_DROP) twice for same hstmt.

When connection pooling was enabled and clients were repeatedly connecting, querying, and disconnecting, stopping the PostgreSQL server and having clients repeatedly try to connect could cause hstmt dereference to fail or double free.

The following is an excerpt from the call stack as it occurs:
```
(hstmt dereference failure case)
podbc35w!SQLFreeStmt
odbc32!DisconnectCleanup
odbc32!SQLDisconnect
System_Data_6e170000
clr!CallDescrWorkerInternal

(double free case)
ntdll!RtlpLogHeapFailure
ntdll!RtlFreeHeap
ucrtbase!_free_base
ucrtbase!free
podbc35w!SC_clear_error
podbc35w!PGAPI_FreeStmt
podbc35w!SQLFreeStmt
odbc32!DisconnectCleanup
odbc32!SQLDisconnect
System_Data_6da30000
clr!CallDescrWorkerInternal
```

The following is the tail of debug log as it occurs: (hstmt dereference failure case)
```
[1096-27.344]odbcapi30w[SQLGetConnectAttrW]76: Entering
[1096-27.344] pgapi30.c[PGAPI_GetConnectAttr]411: entering 1209
[1096-27.344] odbcapi.c[SQLMoreResults]1189: Entering
[1096-27.344]statement.[SC_log_error]2502: STATEMENT ERROR: func=SQLMoreResults, desc='', errnum=35, errmsg='SQLMoreResults unable due to the connection lost'
[1096-27.344]connection[CC_log_error]2641: CONN ERROR: func=SQLMoreResults, desc='', errnum=0, errmsg='(NULL)'
[1096-27.344] odbcapi.c[SQLFreeStmt]395: Entering
[1096-27.344]statement.[PGAPI_FreeStmt]248: entering...hstmt=06D925A0, fOption=0
[1096-27.344]statement.[SC_recycle_statement]881: entering self=06D925A0
[1096-27.344] qresult.c[QR_Destructor]356: entering
[1096-27.344]    bind.c[PDATA_free_params]676: entering self=06D92780
[1096-27.344]odbcapi30.[SQLFreeHandle]264: Entering
[1096-27.344]statement.[PGAPI_FreeStmt]248: entering...hstmt=06D925A0, fOption=1
[1096-27.344] qresult.c[QR_Destructor]356: entering
[1096-27.344]statement.[SC_init_Result]555: leaving(06D925A0)
[1096-27.344]statement.[SC_Destructor]491: entering self=06D925A0, self->result=00000000, self->hdbc=06D932F8
[1096-27.344]statement.[SC_log_error]2502: STATEMENT ERROR: func=SC_Destructor, desc='', errnum=35, errmsg='connection error.'
[1096-27.344]connection[CC_log_error]2641: CONN ERROR: func=SC_Destructor, desc='', errnum=0, errmsg='(NULL)'
[1096-27.344]    bind.c[APD_free_params]656: entering self=06D926B8
[1096-27.344]    bind.c[IPD_free_params]711: entering self=06D926F8
[1096-27.344]    bind.c[PDATA_free_params]676: entering self=06D92780
[1096-27.344]statement.[SC_Destructor]545: leaving
[1096-28.015] odbcapi.c[SQLFreeStmt]395: Entering
[1096-28.015]statement.[PGAPI_FreeStmt]248: entering...hstmt=06D925A0, fOption=1
```