Re: [PATCH 12/18] shared mount handling: bind and rbind

From: Rob Landley
Date: Wed Nov 16 2005 - 03:47:47 EST

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".

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