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Bug #42068 zend_mm_heap corrupted error when freeing resultset (Works with PDO ODBC)
Submitted: 2007-07-22 14:17 UTC Modified: 2009-11-16 01:00 UTC
Votes:14
Avg. Score:4.2 ± 1.2
Reproduced:11 of 12 (91.7%)
Same Version:3 (27.3%)
Same OS:6 (54.5%)
From: macuyiko at gmail dot com Assigned:
Status: No Feedback Package: ODBC related
PHP Version: 5.2.3 OS: Linux (64bit)
Private report: No CVE-ID:
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 [2007-07-22 14:17 UTC] macuyiko at gmail dot com
Description:
------------
Using Intersystems' Cache 64 bit ODBC driver (libcacheodbc.so) with unixODBC causes PHP 5.2.3 to crash. (I never had a problem with the 32 bit driver.) Also, using another ODBC tool, like isql, works fine.

I have managed to track down this problem in PHP's source code, in php_odbc.c, in the function PHP_FUNCTION(odbc_free_result), there are the following lines:

//...start fragment...
ZEND_FETCH_RESOURCE(result, odbc_result *, pv_res, -1, "ODBC result", le_result);
if (result->values) {
 for (i = 0; i < result->numcols; i++) {
  if (result->values[i].value) { 
   efree(result->values[i].value);
  }
 }
 efree(result->values);
 result->values = NULL;
}
//...end fragment...

Commenting out the line:
efree(result->values);
causes PHP to Segfault.

Commenting out the line:
efree(result->values[i].value);
still gives the zend_mm_heap corrupted error.

When I comment out both lines, the problem disappears. But I fear that this might not be good practice.

So what could be causing this problem? It is only with the 64 bit driver/PHP/Linux that this error occurs. Using the 32 bit driver works. Other databases' ODBC drivers work fine too.

Note: this error was also present in PHP 5.2.1. In PHP 5.1.6, I got a "glibc double free detected"-error.

Reproduce code:
---------------
<?php
echo "Opening connection...\n";
$connection = odbc_connect($dsn,"",""); //connect to dsn
echo "Executing SQL...\n";
$result = odbc_do($connection,$sqlstring);
//optional code to do something with resultset here
/*the following line crashes PHP with zend_mm_heap corrupted
commenting out this line doesn't help (since the result will be freed
automatically anyway*/
echo "Freeing...\n";
odbc_free_result($result);
echo "Closing...\n";
odbc_close($connection);
echo "Done.\n";
?>

Expected result:
----------------
Opening connection...
Executing SQL...
Freeing...
Closing...
Done.

Actual result:
--------------
Opening connection...
Executing SQL...
Freeing...
zend_mm_heap corrupted

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History

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 [2007-07-24 12:01 UTC] jani@php.net
Try using the PDO ODBC instead. It is known to work better in most cases.
 [2007-07-24 14:25 UTC] macuyiko at gmail dot com
Using pdo-odbc works. I still use the normal odbc functions a lot though, but at least I have an alternative now.

I still wonder what could be causing this crash though.
 [2009-11-08 16:09 UTC] felipe@php.net
Please try using this snapshot:

  http://snaps.php.net/php5.2-latest.tar.gz
 
For Windows:

  http://windows.php.net/snapshots/

I can't reproduce it.
 [2009-11-16 01:00 UTC] php-bugs at lists dot php dot net
No feedback was provided for this bug for over a week, so it is
being suspended automatically. If you are able to provide the
information that was originally requested, please do so and change
the status of the bug back to "Open".
 
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