Safely chroot the current process and drop privileges.

Bind a TCP server to a privileged port, chroot and drop privileges to "wwwuser".

var net = require('net');
var chroot = require('chroot');

var server = net.createServer();
server.listen(80, function(err) {
  if (err) { throw err; }

  try {
    chroot('/var/empty', 'wwwuser');
    console.log('changed root to "/var/empty" and user to "wwwuser"');
  } catch(err) {
    console.error('changing root or user failed', err);
    process.exit(1);
  }
});

Note: the process must be started as the super user.

$ npm install chroot

• newRoot {String} The path to the new root directory for this process. The whole path should be owned by the super user and may not be writable by the group owner or others.
• user {String|Number} The user to switch to after changing the root directory. Can be either a name or an id.
• group {String|Number} The group to switch to after changing the root directory. Can be either a name or an id of any group the user belongs to (see /etc/groups). Defaults to the users primary group (see /etc/passwd).

Change the root directory of the current process. A normal user must be provided since changing root without dropping privileges makes no sense from a security point of view.

• The current working dir is updated to "/".
• If the environment variable PWD is set, it will be updated to "/".
• Open file descriptors are not closed and environment variables and argv are not cleared, use child_process.fork() to accomplish that.

Chrooting a program is not a security solution. It is only one aspect of the much broader principle of least privilege. When done right it can be used as a mitigation to seriously hinder a compromised process in further compromising the system. Keep the following things in mind when setting up and using a chroot:

• Anything that is stored in the chroot can be used against you. Use an empty non-writable directory if possible.
• Include modules before chrooting.
• Create a separate user account used only for running the chrooted process.
• Use child_process.fork() to clear the environment and close file descriptors.

Further reading:

• http://www.unixwiz.net/techtips/chroot-practices.html
• http://www.dwheeler.com/secure-programs/Secure-Programs-HOWTO/minimize-privileges.html

ISC

Copyright (c) 2014, 2015 Tim Kuijsten

Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted, provided that the above copyright notice and this permission notice appear in all copies.

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