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Bug #24858 proc_open() leaves zombie processes if user cancels page load
Submitted: 2003-07-29 13:51 UTC Modified: 2003-08-01 14:51 UTC
From: jr-php2 at quo dot to Assigned:
Status: Not a bug Package: Program Execution
PHP Version: 4.3.3RC2-dev OS: Red Hat Linux 9.0, kernel 2.4.21
Private report: No CVE-ID: None
 [2003-07-29 13:51 UTC] jr-php2 at quo dot to
Description:
------------
Apache version: 1.3.28
PHP version: 4.3.2, used as a CGI binary:
./configure --prefix=/usr/local/php-cgi --enable-track-vars --with-mysql --with-zlib --enable-discard-path

I have found that if page loading is cancelled by the user (e.g. by closing the Internet Explorer window) before fclose() & proc_close() are called, a zombie process is left behind.

Try the code below (save it as 'testx.cgi'). During normal execution, you'll see this:

27551 ?        S      0:00 /usr/local/php-cgi/bin/php testx.cgi
22800 ?        Z      0:00 [ls <defunct>]

If you let the page load completely, both processes go away from the process list.

If, however, you close the browser window before the sleep() call finishes, about 70% of the time a zombie process is left behind:

27551 ?        Z      0:00 [testx.cgi <defunct>]

I have to restart Apache (1.3.28) to kill this process.

Reproduce code:
---------------
#!/usr/local/php-cgi/bin/php
<?php
$descriptorspec = array(
   0 => array("pipe", "r"),  // stdin is a pipe that the child will read from
   1 => array("pipe", "w"),  // stdout is a pipe that the child will write to
   2 => array("file", "/dev/null", "a"), // stderr is a file to write to
);
$process = proc_open('/bin/ls -al /tmp', $descriptorspec, $pipes);
if (!is_resource($process)) die("Error: proc_open failed");

sleep(10);

fclose($pipes[0]);

fpassthru($pipes[1]);
fclose($pipes[1]);

proc_close($process);
?>

Expected result:
----------------
There should be no zombie process left over when the user cancels the page load.


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 [2003-07-29 14:36 UTC] jr-php2 at quo dot to
FYI, I tried adding a "ignore_user_abort(1);" call to the top of the script but it did not help. I guess ignore_user_abort() probably has no effect when PHP is used as a CGI binary?
 [2003-07-30 02:42 UTC] jr-php2 at quo dot to
Same problem exists in php4-STABLE-200307300530.
 [2003-08-01 14:51 UTC] jr-php2 at quo dot to
Good news:

I found I couldn't reproduce the problem after downgrading Apache to 1.3.27. Then I came across this bug report for Apache 1.3.28:

http://nagoya.apache.org/bugzilla/show_bug.cgi?id=21737

I applied the second patch there, and so far haven't had any more lingering zombie processes.

Why I could only reproduce the problem when I used proc_open() remains a mystery... Sorry for the false alarm.
 
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