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Bug #57191 Apache Segfaults when storing PDO statements in static variables
Submitted: 2006-08-21 12:10 UTC Modified: 2006-10-25 17:33 UTC
From: wolff at 21st dot de Assigned:
Status: Closed Package: APC (PECL)
PHP Version: 5.1.4 OS: Ubuntu Dapper
Private report: No CVE-ID: None
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From: wolff at 21st dot de
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 [2006-08-21 12:10 UTC] wolff at 21st dot de 
Description:
------------
This is with APC 3.0.10 - I'm storing a prepared statement 
object in a static object variable to act as a statement 
cache. When I do that, PHP seems to make a clean exit, but 
Apache segfaults and just displays a blank page.

This seems not to occur on the first request after a fresh 
Apache restart, though - but on all subsequent ones.

Additional discussion of the bug can be found here:
http://blog.wolff-hamburg.de/index.php?url=archives/9-UPDATE-Bug-found-kinda.html
...only I came to the conclusion that it was APC's 
wrong-doing after I already submitted the blog post.

Bug *may* be somehow related to this one:
http://pecl.php.net/bugs/bug.php?id=8324

...but for me it only happens when storing prepared 
statements in static variables.

Reproduce code:
---------------
class SegFault {
    static protected $cache = array();
    public function execute() {
        $pdo = new PDO('mysql:host=localhost;dbname=mysql', 'root');
        $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        $stmt = $pdo->prepare('SELECT user FROM user WHERE host=:hostname');
        self::$cache[] = $stmt; // this is the culprit, remove this line and all is well
        
        $bindings = array(':hostname' => 'localhost');
        $stmt->execute($bindings);
        return $stmt;
    }    
}

$crash = new SegFault();
echo "<p>Timestamp: ".time()."</p><pre>";
foreach($crash->execute() as $row) {
    print_r($row);
}
echo "</pre>";

Expected result:
----------------
A page should be served containing the current timestamp 
and a printout of all MySQL users for localhost.

Actual result:
--------------
Apache segfaults:
[Mon Aug 21 17:40:58 2006] [notice] child pid 27755 exit 
signal Segmentation fault (11)

Either disabling APC or commenting out the line "self::
$cache[] = $stmt;" will fix the problem.

Patches

Pull Requests

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 [2006-08-21 12:15 UTC] rasmus@php.net 
Right, so please try 3.0.11
 [2006-08-21 17:56 UTC] gopalv82 at yahoo dot com 
A direct duplicate of http://bugs.php.net/bug.php?id=37445 ?

Here's the patch, apply and retest - http://news.php.net/php.cvs/39679.

APC probably doesn't have anything to do with this particular bug :)
 [2006-08-23 08:04 UTC] wolff at 21st dot de 
Ok, I installed APC 3.0.11 now (sorry for not trying this 
earlier) and I still get the exact same behavior.
 [2006-08-29 00:24 UTC] gopalv82 at yahoo dot com 
Please upgrade your php build. This is a known bug which was introduced in 5.1.4 and fixed in 5.1.6.

Please feel free to ask for this bug to re-opened if the problem persists.
 [2006-10-10 16:41 UTC] florian dot herlitschke at creaflex dot de 
I just got the same error and created a test case

$test = new test();
echo "hello world";

class test
{
  public function __construct() 
  {
    $dsn = 'mysql:host=localhost;dbname=mydb';
    $dbh = new PDO($dsn,'foo','****');
    $x = $dbh->prepare('SELECT * FROM table');
    self::$cache = $x; // remove me
  }
}


deactivating apc didnt work. First request after apache restart works well, second request end up with a blank page. PHP Version 5.1.6-pl4-gentoo with (or without) APC 3.0.12p2
 [2006-10-10 17:03 UTC] florian dot herlitschke at creaflex dot de 
Sorry, my fault, deactivating APC works pretty well for my example. But with activated APC I have to restart Apache or edit my script with a space or a blank line to get it work once again! But only for one request!

Apache error_log says:
[Tue Oct 10 23:13:57 2006] [notice] child pid 15218 exit signal Segmentation fault (11)
 [2006-10-11 02:04 UTC] gopalv82 at yahoo dot com 
Moving back to Open.

Thanks for the update.
 [2006-10-11 07:26 UTC] gopalv82 at yahoo dot com 
Actually this is not really APC's wrong-doing.

There seems to be some code in PDO land which depends on the destroy_class cleaning up static members before the standard deactivation cleanups start.

I'm investigating on how to fix this in both places.
 [2006-10-25 17:33 UTC] gopalv82 at yahoo dot com 
This patch fixes the APC part of the story

http://news.php.net/php.pecl.cvs/6545

This "fixes" the segv by re-ordering the destructors, though not the correct fix, still prevents a few memory leaks (if nothing else).
 
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