Re: [PATCH][CFT] per-process namespaces for Linux

[Alexander Viro]

On Mon, 26 Feb 2001, Marco d'Itri wrote:

> On Feb 26, Alexander Viro <[e-mail]> wrote:
> 
>  >There is no way to implement them without credentials' cache. Which needs
>  >to be done for many other reasons, but that's a separate patch and
>  >separate story. If it's done - no serious penalty involved. However,
>  >I doubt that we want a union on / itself. /dev - sure, /bin and /lib -
>  >maybe, but /... What for?
> What I'd really like to do is remount / somewhere with mount --bind,
> mount over it another skeleton file system which hides setuid programs
> and some directories and then run a chrooted sshd in the new root.
> If I'm not missing something, this would make creation of secure chroot
> environments very easy.

I'm making NOSUID per-mountpoint. So
	pid = clone(CLONE_NEWNS,0);
	if (!pid) {
		...
		remount everything with nosuid
		exec sshd
	}
should be OK
As for hiding the directories - also easy, mount --bind an empty 
immutable directory over each of them.

NODEV is also easy to make per-mountpoint, but readonly may be trickier;
we need permission() to take vfsmount+dentry instead of inode for that.
Doable, but will touch quite a few places.