linux-kernel - Re: [PATCH 4/4] Allow unprivileged chroot when safe

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Message-ID: <20120116200618.GN23916@ZenIV.linux.org.uk>
Date:	Mon, 16 Jan 2012 20:06:18 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Casey Schaufler <casey@...aufler-ca.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jamie Lokier <jamie@...reable.org>,
	Will Drewry <wad@...omium.org>, linux-kernel@...r.kernel.org,
	keescook@...omium.org, john.johansen@...onical.com,
	serge.hallyn@...onical.com, coreyb@...ux.vnet.ibm.com,
	pmoore@...hat.com, eparis@...hat.com, djm@...drot.org,
	segoon@...nwall.com, rostedt@...dmis.org, jmorris@...ei.org,
	scarybeasts@...il.com, avi@...hat.com, penberg@...helsinki.fi,
	mingo@...e.hu, akpm@...ux-foundation.org, khilman@...com,
	borislav.petkov@....com, amwang@...hat.com, oleg@...hat.com,
	ak@...ux.intel.com, eric.dumazet@...il.com, gregkh@...e.de,
	dhowells@...hat.com, daniel.lezcano@...e.fr,
	linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org, olofj@...omium.org,
	mhalcrow@...gle.com, dlaor@...hat.com, corbet@....net,
	alan@...rguk.ukuu.org.uk
Subject: Re: [PATCH 4/4] Allow unprivileged chroot when safe

On Sun, Jan 15, 2012 at 04:37:21PM -0800, Andy Lutomirski wrote:

> +	is_chrooted = (fs->root.mnt->mnt_mountpoint !=
> +		       fs->root.mnt->mnt_parent->mnt_root ||
> +		       fs->root.dentry != fs->root.mnt->mnt_root);

Folks, is it _that_ hard to at least try to compile your patches?  Hint:
this one will *not*.  That sad detail aside, this test would have been
a pile of garbage even on the kernels that used to have mnt_mountpoint
in struct vfsmount.  What *are* you trying to test here?  The last part
at least does make some sense - it's "process root happens to be the
root of some vfsmount".  The first part, though, makes no sense whatsoever;
it's "... and that vfsmount is mounted on top of root of some other
vfsmount".

Grr...  NAKed, with extreme prejudice.
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