From: Rob Landley <rob@landley.net>
Organization: Boundaries Unlimited
To: Al Boldi <a1426z@gawab.com>
Subject: Re: [PATCH 12/18] shared mount handling: bind and rbind
Date: Wed, 16 Nov 2005 02:47:15 -0600
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Cc: Linus Torvalds <torvalds@osdl.org>, Ram Pai <linuxram@us.ibm.com>,
       Miklos Szeredi <miklos@szeredi.hu>, Al Viro <viro@ftp.linux.org.uk>,
       linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
References: <E1EZInj-0001Ez-AV@ZenIV.linux.org.uk> <Pine.LNX.4.64.0511151948570.13959@g5.osdl.org> <200511160835.28636.a1426z@gawab.com>
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On Tuesday 15 November 2005 23:35, Al Boldi wrote:
> Linus Torvalds wrote:
> > This is why we have "pivot_root()" and "chroot()", which can both be used
> > to do what you want to do. You mount the new root somewhere else, and
> > then you chroot (or pivot-root) to it. And THEN you do 'chdir("/")' to
> > move the cwd into the new root too (and only at that point have you
> > "lost" the old root - although you can actually get it back if you have
> > some file descriptor open to it).
>
> Wouldn't this constitute a security flaw?
>
> Shouldn't chroot jail you?

A few years ago I had a build script that compiled a new Linux From Scratch 
system I could chroot into, and one of the things in the new chroot 
environment was a different boot loader.  And for testing purposes (and with 
a boot CD standing by) I would chroot into this new environment and run the 
lilo in it to add the new test kernel into the boot option list.

One day, I upgraded to a new kernel version and it stopped working, because 
chroot had acquired some unwanted security feature that prevented lilo from 
properly talking to /dev/hda from within a chroot environment.

I remember being rather put out by this.

Chroot is sometimes used for other purposes than "security".

Rob
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