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Bug #16278 reference to $_SESSION causes seg-fault
Submitted: 2002-03-26 00:02 UTC Modified: 2002-03-26 03:25 UTC
From: bhlyons at mail dot com Assigned:
Status: Not a bug Package: Reproducible crash
PHP Version: 4.1.2 OS: Linux 2.2.16 (redhat 7.0)
Private report: No CVE-ID: None
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 [2002-03-26 00:02 UTC] bhlyons at mail dot com 
Configuration:
./configure --with-apxs --enable-debug
php.ini = php.ini-recommended
Apache 1.3.12

I have been using a procedure to create nicely-formatted tables of arrays and their contents for a long time.  It works very well under 4.1.2 (and previous 4.* verions) for displaying $GLOBALS if session_start has not been called.  If session_start has been called, it causes a seg-fault when the $HTTP_SESSION_VARS and/or $_SESSION is processed.

My normal script is much more elaborate, but I've stripped it to the bare minimum to make the bugs more obvious.  There are four 'fix' comments in the code - implementing any one will make the problem go away, but none should be necessary.

I have compiled 4.2.0rc1 with the same ./configure options and used the 4.2.0rc1-supplied php.ini-recommended file as part of a further test.  The output is the same, but the seg-fault is not reported to the error log with 4.2.0rc1.

------------ index.php -------------------

<?PHP

# fix 1 is to pass the array by value
function CVTT (&$array, $depth=0) {
  if($depth==0) {
    print "<PRE>\n";
  }
  while(list($key,$value)=each($array)) {
# fix 2 is to skip both instances of the session variables array
### If this session-skipping block is enabled, there are no problems
#    if($key=="_SESSION" || $key=="HTTP_SESSION_VARS") {
#      print "skipping $key\n";
#      continue;
#    }
### End of session-skipping block
    for($c=0;$c<$depth*5;$c++) {
      print " ";
    }
    print "$key=";
    if(is_array($value)) {
      $valuestring="Array";
    } elseif(is_object($value)) {
      $valuestring="Object";
    } elseif(is_bool($value)) {
      if($value) {
        $valuestring="Boolean True";
      } else {
        $valuestring="Boolean False";
      }
    } else {
      $valuestring=$value;
    }
    print "$valuestring\n";
    if(is_array($array[$key])) {
# fix 3 is to pass $value instead of $array[$key]
      CVTT($array[$key], $depth+1);
    }
  }
  if($depth==0) {
    print "</PRE>\n";
  }
}

# fix 4 is to eliminate the session_start
session_start();

$_SESSION['one']="two";

?>
<HTML>
<HEAD>
</HEAD>
<BODY>

<?PHP

CVTT($GLOBALS)

?>

</BODY>
</HTML>

---------------end of index.php -------------

I was not able to get a backtrace by following the instructions in the php documentation.  I'd be happy to try again with more-detailed instructions.

If there is any further testing you would like, please let me know.

Sincerely,
Bryan

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 [2002-03-26 03:20 UTC] sniper@php.net 
So you're saying that with PHP 4.2.0RC1 it works?
 [2002-03-26 03:25 UTC] tal@php.net 
According to you, it wroks fine with 4.2.0rc1. So that doesn't really matter.
 [2002-03-26 09:43 UTC] bhlyons at mail dot com 
NO, I am saying that it does NOT work in PHP >= 4.1.0, including 4.2.0rc1.

What I meant by the 'output is the same' is that the stream sent to the browser gets prematurely truncated (when PHP dies) at roughly the same point in 4.1.2 and 4.2.0rc1.  With 4.1.2, the seg-fault gets reported to the error log.  With 4.2.0rc1, the seg-fault does not get reported to the error log, but it has definitely died prematurely.

This is a simple function that has worked for a long time, and works great now if session_start isn't called.  There is something peculiar about HTTP_SESSION_VARS and _SESSION when sessions are active that is causing the problem.  The SERVER/POST/GET vars, in both HTTP_ and _var forms are fine.  As a matter of fact, if session_start is not called, you can even create HTTP_SESSION_VARS and _SESSION arrays and they'll work fine, too, so it isn't just the name.

session_start does something to HTTP_SESSION_VARS and _SESSION and cause PHP to die under this code.  Paste my sample code into a file and see it for yourself.  Look carefully, the truncation is right near the end.  To make it more obvious, add a "<P>DONE</P>" just before </BODY> - you'll never see that text in the output.

Sincerely,
Bryan
 
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