Question

Here’s an idea. I’m trying to create file from PHP script. File may be created in any public place on server (in public root or in its subdirectories). Bottom of line, I want to write function like this (it must work on both unix and windows servers).

function create_file($path, $filename, $content, $overwrite=false) {
  # body
  ...

  }

Parameters:

• $path – file-path (empty or ends with /)
• $filename – any valid file-name (requires dot+extension)
• $content – file-content (anything)
• $overwrite – if set true, existing file will be overwritten (default. false).

Result:

Function returns TRUE and creates file with content, or FALSE if file-creation was not possible for any reason.

Description of problem:

I expect this function to return true and create file $filename on path $path, or false if it wasn’t possible for any reason. Also if file was successfully opened for writing, need to put $content in it.

Argument $path is relative path to public directory, and $filename is any valid filename. Of course, I want to avoid creating files if path points outside of public directory. Function may be called from subdirectory-scripts like this example

# php script: /scripts/test.php
create_file('../data/', 'test.info', 'some contents');
# result file: /data/test.info

What have I tried so far?

I’ve tried doing this with fopen() and fwrite() functions and that works on some servers, and doesn’t work on some. I guess there’s problem with writing privileges and chmod() but to be honest I’m not very familiar with chmod attributes. Also I couldn’t check if $path points outside of server’s public directory.

In short, I want this function to create file and return TRUE if file doesn’t exist, or file exists and $owerwrite=true. Otherwise, nothing happens and function returns FALSE.

Additionally, I would like to know reason why file can’t be created on some path (just in theory). Incorrect path/filename is only thing I have on my mind and I’m sure there’s more about this problem.

Thanks in advance for any sample/example/suggestion.

update code

So far I have this code…

  function create_file($path, $filename, $content, $overwrite=false) {
    $reldir = explode('/', trim(str_replace('\\', '/', dirname($_SERVER['PHP_SELF'])), '/'));
    $dirdepth = sizeof($reldir);
    $rpadd = $dirdepth > 0 ? '(\.\./){0,' . $dirdepth . '}' : '';
    $ptpath = '#^/?' . $rpadd . '([a-z0-9]\w*/)*$#i';
    $ptname = '/^[a-z]\w*\.[a-z0-9]+$/i'; 
    if ($res = preg_match($ptpath, $path) && preg_match($ptname, $filename)) {
      $res = false;
      if ($overwrite === true || !file_exists($path.$filename)) {
        if ($f = @fopen($path.$filename, 'w')) {
          fwrite($f, $content);
          fclose($f);
          $res = true;
          }
        }
      }
    return $res;
    }

Answer 1

Some suggestions:

1. set the owner of the web server document root: chown -R apache:apache /var/www (i suppose /var/www is your document root and that the web server apache runs with user apache). Set the privilegies of the document root like this in order to have all directories under document look with privilegies 755 (only owner which is user apache can write in folders /var/www and sub folders)
2. Block paths that point out of your /var/www document root: you are under the issue known as http://en.wikipedia.org/wiki/Directory_traversal_attack. What about if the $path is something like: /var/www/../../../etc/passwd?
   Basename php function can help you identifying this kind of malignous paths. Look this post: php directory traversal issue
3. To check wheter a file already exists or not: http://php.net/manual/en/function.file-exists.php