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Chroot Jails Made Easy
GonzoJohn writes "There are always difficult jobs to do as a GNU/Linux system administrator. Sometimes the difficulty lies in finding out how to do a particular job, not necessarily the job itself. This can be particularly true in the open source world where documentation can often take a back seat to implementation. But once in a while, you can stumble on a real gem that simplifies even the most difficult administration tasks. One such gem is the Jail Chroot Project. Linux Orbit introduces you to creating chroot-ed environments in this article."
I must have spent a week working through various docs trying to learn this, and most of what I read was either impossible to understand or just inaccurate. Finally I happened upon this, and I refer to it often. Here's the jist of it:
====================
Introduction
Jail Chroot Project is an attempt of write a tool that builds a chrooted environment. The main goal of Jail is to be as simple as possible, and highly portable. The most difficult step when building a chrooted environment is to set up the right libraries and files. Here, Jail comes to the rescue with a tool to automagically configures & builds all the required files, directories and libraries. Jail is licensed under the GNU General Public License.
Jail program has been written using C, and the setup script has been written using a bash script and perl. Jail has been tested under Linux (Debian 2.1 & 2.2, RedHat 6.1, 6.2 and 7.0 and Caldera Openlinux 7.0), Solaris (2.6), IRIX (6.5) and FreeBSD 4.3. Some people has contributed to jail with patches and ideas. Thanks to all of them.
Jail supports lots of interesting features:
Runs on Linux, Solaris, IRIX and freeBSD (tested) and should run in any of the flavours of these operating systems.
Modular design, so you can port Jail in an easy way.
Support for multiple users in a single chrooted environment.
Fully customizable user shell.
Support for multiple servers: telnetd, sshd, ftpd...
Easy to install thanks to the enviroment creation script.
Should work in any UNIX.
Ease of porting.
Allows run any kind of program as a shell.
An html version of the mailing list has been added to the web site. Now you can read all the user contributions, ideas and patches here.
In the long run, though, I hope the standard aproach becomes User Mode Linux.
"A language that doesn't affect the way you think about programming, is not worth knowing" - Alan Perlis
First he fried my data
...... Supreme court.. here I come
Then he formatted my drive
Then he garbled my project
But.. I am *not* going to let him put me in jail too! Rise ye users. This is a conspiracy by all admins to jail us. they are violating our DMCA RIAA CIAA BIDA
My Aurora : http://www.youtube.com/watch?v=o91ZsGwJYyg
FB : https://www.facebook.com/TanveersPhotography
Jail is a term taken from BSD.
/something bin, and /something becomes root direcorty (/) of run program. This program can't open for example /etc/passwd, because _real_ /etc doesn't exist in it's /. Chrooted program's /etc is in fact /something/etc. /dev) inside chroot, mount it, and ... voila! You have access to whole disk. Chroot is broken. Of course, you must have access for making file, but must chroot have.
In BSD, jail and chroot are two different things, althrough very similar. There exist two syscalls - jail() and chroot().
What's the difference?
Chroot is ordinary chroot, the same as in linux. You do chroot
But if you goot root priviledges you can easily break chroot. Just make a special file named 'hda1' beeing a device node (like those in
Jail is slightly different. It not only hold process in some directory. It's also *restrict* certain *syscalls*. So you can't mount anything, change network settings and some more. Jail is more restrictive and probably you can't break it even if you have root access in jail.
Jail, because of blocking syscalls, must have some help from kernel. Right now, there is a jail() in FreeBSD and probably NetBSD. OpenBSD don't have it - Theo says it's too complicated to be secure. Also Linux don't have jail().
If you want more information, browse FreeBSD man pages, avaiable online.
:wq
From the site:
Again, not to minimize the outstanding work here, but what if I want to create chroot jails for the LAMP class I'm teaching (I'm not really, but this seems like a cool application) so they can all have their own Apache installations? It sounds like chroot will know to move the httpd binary and the required shared libraries, but what about the rest of the admin shell scripts, server root, shared icons dir, mime types file, etc.?
Then what happens if I want to upgrade? My guess is a fair amount of bootstrapping needs to be done in the new root....
What might be really cool is for addjailsw to be RPM-aware so I could do a addjailsw mod_ssl-2.8.7-6 which would get a list of necessary files and package dependencies and install them in the new root and update the RPM DB in the new root as well.
Maybe just wishful thinking....
moto411.com
Although they are a step towards higher security, chroot jails are not infallible.
If there's a security hole in an application, it's still possible for an attacker to get root (but yes, they'll be confined to the chroot environment).
But then, under Linux, at least, the attacked will still be able to mount /proc, if they find a way of getting binaries into the machine, which will enable a number of possible attacks on the machine, by altering stuff under /proc/sys.
It may also be possible for the attacker to create device files (eg, /dev/hda) and write directly to the disk.
So, all in all, even if you're running in a chroot jail, it helps to make sure your apps are running as non-root, if you can. authbind is your friend.
-- Even if a god did exist, why the fsck should I worship it?
Though it seems like a virtual system, a chroot cell is not totally virtual, and there can still be plenty of comprosmises.
h tml
Like usual, all you need is access to a compiler, and you can make a jailbreak. In fact, there's a whole guide to it here:
http://www.bpfh.net/simes/computing/chroot-break.
If the whole jail resided in its own actual virtual Linux machine, where nasty things cannot break the account, just the session, they would be quite a bit more effective.
The chroot environment is trivial to get out of if you're still running as root. Obviously if there's an exploit that lets you get root access even inside a chroot environment, then you can get out of that chroot environment.
The C source code is here.
now we need to go OSS in diesel cars
I have been using chroot for many years, mostly with the big three (Apache bind and sendmail). However, I would never rely solely on chroot for security.
It is rediculous to do a Maxwell Smart and put 10 locks on your front door when the window is wide open. You are always better to rely upon a locked box, inside a locked box, inside a locked box etcetera, Rather than OUMF lock!
OUMF??? you say (new proposed acromyn)...
Just think of Arnie in Predator when he says to the alien "You're one ugly mother f......"
From excellent karma to terible karma with a single +5 funny post...
Yes !
In the beginning, I want to call myself the assembler man, but I have a very poor english at 14' (I'm spanish) and I didn't know what 'ass' means XD. But yes, I'm assman.
Note that there is a project that attempts to add jail-syscall-like functionality to the Linux kernel: vserver.
I haven't tested it yet, but it looks very promising.
Sig (appended to the end of comments I post, 54 chars)
The Medusa project allows the implementation of system call policies in Linux. Google for it. I think with smart rulesets; chroot and jail are all redundant. For example, denying untrusted user set*id access (toppled by smart fileaccess privileges) renders most "security" attacks useless for that user (he cannot cause any real damage other than DoS, which can also be stopped by implementing thread/fork timers for that user).
Sooo Assman...
Does your code have any back-doors?
sorry, it had to be said.