PHP is_readable returns true for non-readable file

Question

I have an image processor PHP script, and it contains the following code:

        if (!is_dir($fullFile)) {
            if (is_readable($fullFile)) {
                $im = getimagesize($fullFile); // Will be FALSE if not an image

In some instances, the script will fail at getimagesize with the following error:

getimagesize(/path/to/file.jpg) [function.getimagesize]: failed to open stream: Permission denied at www.yada.yada/page.php

In this case, the permissions for /path/to/file.jpg are definitely prohibitive (400), so I'd have expected the is_readable test to prevent me getting to that point. Aside from setting permissions differently, what might I do in order to resolve this? Why does it seem that is_readable has an incorrect result? Is it possible that is_readable is operating with the EUID of the file owner, while getimagesize is not? That's the only explanation that makes sense to me, but even that knowledge doesn't help resolve.

Prompted by @hek2mgl I created this ultra-complex script, named readable.php:

<?php echo is_readable("/stora2/Pics/2009/2009-07-26/DSC00532.JPG") . "\n\n"; ?>

Then I switched user to the web server user (actually www-data on this server) and ran it. Result was

1

Then I ran strace as that same user. These are the commands I used. The result is a 70KB+ file, and SO won't let me post it in its entirety, so it is posted at http://pastebin.com/mFqiSBiz

dennis@luke:~$ sudo su - www-data

$ ls -l "/stora2/Pics/2009/2009-07-26/DSC00532.JPG"
-rw------- 1 dennis dennis 524288 2012-02-11 08:18 /stora2/Pics/2009/2009-07-26/DSC00532.JPG

$ file "/stora2/Pics/2009/2009-07-26/DSC00532.JPG"
/stora2/Pics/2009/2009-07-26/DSC00532.JPG: writable, regular file, no read permission

$ php /home/dennis/readable.php
1

$ strace php /home/dennis/readable.php > /tmp/strace.out 2>&1

Not sure what I'm looking for. Please advise.

Answer 1

Depending on what version of php you are running, this could be a bug, as hek2mgl said in the comments. If you want to workaround this, you can add logic based on the file permissions, with fileperms