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Request #28947 open_basedir misfunction with symbolic links
Submitted: 2004-06-28 12:51 UTC Modified: 2013-10-28 10:59 UTC
Votes:12
Avg. Score:4.1 ± 1.0
Reproduced:12 of 12 (100.0%)
Same Version:0 (0.0%)
Same OS:0 (0.0%)
From: johnsteed99 at yahoo dot it Assigned: krakjoe (profile)
Status: Closed Package: *General Issues
PHP Version: 4.3.7 OS: Linux Red Hat 7.2.2
Private report: No CVE-ID: None
 [2004-06-28 12:51 UTC] johnsteed99 at yahoo dot it
Description:
------------
We have a symbolic link to apache's htdocs:
/WWW -> /usr/local/apache2/htdocs
We are not in safe mode, but we set open_basedir. If we try to use a function that has to create a file (move_uploaded_file, tempnam, fopen in W mode, copy, etc.) and we specify a path using the symbolic link (/WWW/mysite/upl), php does not allow us to proceed, alerting that open_basedir restriction is in effect. If the file is present so it has only to be opened, everything is fine. If we specify the real path (/usr/local/apache2/htdocs/mysite/upl), it works both in creation and opening. No problems found when opening files in read mode.
Specifying open_basedir as link or real path does not affect the problem. We think the bug should be in fopen_wrappers.c, function expand_filepath().

Reproduce code:
---------------
<?
    if ($_POST["action"] == 'save')
    {
        $upl_dir = '/WWW/mysite/upl';
        $upl_file = $upl_dir.$_FILES['userfile']['name'];
        if (! move_uploaded_file( $_FILES['userfile']['tmp_name'], $upl_file))
            echo "failed<br>";
    }
?>
<html>
<body bgcolor="#FFFFFF">
    <form method="post" action="<? echo $PHP_SELF; ?>?action=save" enctype="multipart/form-data">
        Send a file:
        <input type="file" name="userfile" />
        <input type="submit" name="Submit" value="Send" />
    </form>
</body>
</html>


Expected result:
----------------
Resolved destination directory is in open_basedir, so it should be allowed to create a file.

Actual result:
--------------
When affected file is not existent, php does not allow to create it if a directory in its path is specified using a symbolic link.

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 [2004-06-28 14:40 UTC] johnsteed99 at yahoo dot it
In the code, $upl_dir misses last slash, so line 4 should be
$upl_dir = '/WWW/mysite/upl/';
 [2004-06-28 22:06 UTC] iliaa@php.net
Thank you for taking the time to write to us, but this is not
a bug. Please double-check the documentation available at
http://www.php.net/manual/ and the instructions on how to report
a bug at http://bugs.php.net/how-to-report.php

The open_basedir is applied on the resolved name, which 
prevents the use of symlinks to create open_basedir 
bypasses. This is intended & expected behavior. 
 [2004-06-29 10:46 UTC] johnsteed99 at yahoo dot it
The point is that the resolved name of the path (/usr/local/apache2/htdocs/mysite) is present in open_basedir, and it makes no difference whether open_basedir is written as /WWW/mysite (symb. link) or /usr/local/apache2/htdocs/mysite (resolved name) - but it makes difference writing the path as symbolic link or resolved name.
Then, since it gives no open_basedir restriction when the file is already present even if path is written as symbolic link, we think that this is actually a bug.
This is a schema of php behaviour, where you can find the only two cases where restriction applies: 
open_basedir  S  S  R  R  S  S  R  R
path          S  S  S  S  R  R  R  R
file exists   Y  N  Y  N  Y  N  Y  N
restriction   N  Y  N  Y  N  N  N  N
(S:written as symb. link, R: written as resolved name)
 [2004-06-29 17:47 UTC] iliaa@php.net
Please provide the necessary directory/file structure and a 
simple script that can be used to duplicate the behavior. 
 [2004-06-30 13:19 UTC] johnsteed99 at yahoo dot it
Apache has its document root in /usr/local/apache2/htdocs, and there is a symbolic link pointing to this directory 
(/WWW -> /usr/local/apache2/htdocs).

Test site has this virtual host configuration in httpd.conf:
<VirtualHost xxx.xxx.xxx.xxx:80>
    ServerName test.mysite.com
    DocumentRoot /WWW/mysite
    php_admin_value open_basedir "/WWW/mysite"
</VirtualHost>

In the file system, we have:
/usr/local/apache2/htdocs/mysite/test, a directory with 777 permissions
/usr/local/apache2/htdocs/mysite/testupload.php, a script with the following code:

<?
    if ($_GET["action"] == 'save')
    {
        $upl_dir = '/WWW/mysite/test/';
//        $upl_dir = '/usr/local/apache2/htdocs/mysite/test/';
        $upl_file = $upl_dir.$_FILES['userfile']['name'];
        echo "src file: ".$_FILES['userfile']['tmp_name'].", dst file: $upl_file<br>";
        if (! move_uploaded_file( $_FILES['userfile']['tmp_name'], $upl_file))
            echo "failed<br>";
    }
?>
<html>
<body bgcolor="#FFFFFF">
    <form method="post" action="<? echo $PHP_SELF; ?>?action=save" enctype="multipart/form-data">
        Send a file:
        <input type="file" name="userfile" />
        <input type="submit" name="Submit" value="Send" />
    </form>
</body>
</html>

You can switch between the two $upl_dir to test the behaviour with symbolic link [S] and resolved name [R]. As 
previously stated, you should get this schema (we avoid to specify the way open_basedir is specified, since using [S] or [R] does not seem to affect the problem):

path          S  S  R  R
file exists   Y  N  Y  N
restriction   N  Y  N  N

Testing the problem on a different server, we found another strange behaviour with Apache/1.3.29 on Red Hat Linux 7.2 2.96-112.7.1 (php 4.3.7). Using the same configuration as before (just substituting the string 'apache2' with 'apache'), we get this schema:

path          S  S  R  R
file exists   Y  N  Y  N
restriction   Y* Y  N  N

When the destination file is already existent, restriction applies but the existing file is deleted anyway.

In both cases, we should expect no restriction using the symbolic link in the destination file path, having specified 
the symbolic link (or its the resolved name) in the open_basedir setting. We think that path's symbolic link is 
correctly resolved to prevent open_basedir bypasses, but then it should be tested with the resolved open_basedir 
settings to set the restriction.
 [2004-11-10 17:35 UTC] martijn at sipo dot nl
I run into this exact problem with PHP 4.3.9 on Debian Woody. 

Opening an existing file for reading or writing works as expected; creating a new file or a directory fails with a warning about an open_basedir restriction. The resolved path of the file I try to create, is in open_basedir.
 [2004-11-10 18:04 UTC] tony2001@php.net
All symbolic links are resolved, so you need to add real path to open_basedir instead of link path.
 [2006-04-11 13:51 UTC] johnsteed99 at yahoo dot it
One year and a half later, I decided to re-open the bug. I had several mail from people complaining to have the same problem I reported, asking me direction to solve it. Unfortunately, I have no solution. So once again I am here asking to have a look at this bug, that is not bogus.
Please spend 5 minutes to check it, as you can see it has a 100% rate of reproduction.
 [2013-10-28 10:59 UTC] krakjoe@php.net
-Status: Open +Status: Closed -Package: Feature/Change Request +Package: *General Issues -Assigned To: +Assigned To: krakjoe
 [2013-10-28 10:59 UTC] krakjoe@php.net
open_basedir accepts a real path.

Closing, again.
 
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