Re: crash bug on closed connection

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От Jade Koskela
Тема Re: crash bug on closed connection
Дата
Msg-id CAN5ZvqwLXs3z0pxAQOKDthLBdRkP_Md+bryiexdtAHtp0rFBng@mail.gmail.com
обсуждение исходный текст
Ответ на Re: crash bug on closed connection  (Jade Koskela <jkoskela0@gmail.com>)
Ответы Re: crash bug on closed connection
Список pgsql-odbc
Дерево обсуждения
Here is the end of the log. 
I've done some debugging, when CC_send_query_append is called here, it correctly identifies that there was an error, and exits the function.

res = CC_send_query_append(conn, self->stmt_with_params, qryi, qflag, SC_get_ancestor(self), appendq); (statement.c:2069)

The result which is returned is not handled correctly (statement.c:2078)

if (appendq)
{
    QResultClass    *qres, *nres;

    if ( res->rstatus == PORES_EMPTY_QUERY && !res->next)
        res = NULL;

    for (qres = res; qres;)
    {
        if (qres->command && strnicmp(qres->command, fetch_cmd, 5) == 0)
        {
            res = qres;
            break;
        }
        nres = qres->next;
        if (nres && QR_get_notice(qres) != NULL)
        {
            if (QR_command_successful(nres) &&
                QR_command_nonfatal(qres))
            {
                QR_set_rstatus(nres, PORES_NONFATAL_ERROR);
            }
            QR_add_notice(nres, QR_get_notice(qres));
        }
        qres->next = NULL;
        QR_Destructor(qres);
        qres = nres;
    }
}

There is only a single result, with result.next == NULL.
This part of the code calls the destructor on the only result, but res is still left pointing at it. After that fun things happen.
It gets a long way before it actually crashes in Exec_with_parameters_resolved.



On Mon, Oct 13, 2014 at 10:27 PM, Jade Koskela <jkoskela0@gmail.com> wrote:
Also the mac/pc isn't relevant information in the repro that I posted. It might as well just be client/server.

On Mon, Oct 13, 2014 at 10:26 PM, Jade Koskela <jkoskela0@gmail.com> wrote:
Some of these steps might not be necessary. It might could be accomplished with a kill -9 on postgres. I tried running Postgres on Windows, and force killing it, but then the client always knew the connection was down.

When this occurs "in the wild", it is usually related to a timeout, so the fix that was checked in recently for setting tcpKeepAlive might be a workaround.

On Mon, Oct 13, 2014 at 4:44 PM, Jade Koskela <jkoskela0@gmail.com> wrote:
I have been looking into this crash for a while now, and I finally have a good repro.

After digging through it with wireshark I observed this
client tries to send a query
 retransmit query
 retransmit query
 ...
client sends TCP [RST],[ACK]
Now it has crashed, so we restart it again and begin another connection successfully.

It seems that the connection has dropped, but the client was never informed, and it doesn't handle this gracefully. 

I reproed it like this:

On my mac running postgres server:
  Setup port forwarding to emulate a proxy or firewall problem
  ssh -L [public ip]:5433:localhost:5432 -N localhost

On my windows machine:
  Connect to port 5433 on my mac
  Run a query

On my mac:
  Kill the ssh proxy
  sighup postgres
  open the ssh proxy again

On my windows machine:
  Run another query (machine still thinks connection is ok)
  Crash in psqlodbcw.dll   

> psqlodbc35w.dll!Exec_with_parameters_resolved(StatementClass_ * stmt=0x0a6f4fa0, int * exec_end=0x083bf3dc)  Line 606 + 0x1b bytes C
  psqlodbc35w.dll!PGAPI_Execute(void * hstmt=0x0a6f4fa0, unsigned short flag=1)  Line 1147 + 0xd bytes C
  psqlodbc35w.dll!SQLExecute(void * StatementHandle=0x0a6f4fa0)  Line 386 + 0xe bytes C
  odbc32.dll!_SQLExecute@4()  + 0x2c1 bytes

> if (sscanf(cmd , "UPDATE %d", &count) == 1) // here cmd is junk but not null (0xddddddd)






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