Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752966Ab3JEXTW (ORCPT ); Sat, 5 Oct 2013 19:19:22 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:52761 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752390Ab3JEXTU (ORCPT ); Sat, 5 Oct 2013 19:19:20 -0400 Date: Sun, 6 Oct 2013 00:19:15 +0100 From: Al Viro To: Rob Landley Cc: "Eric W. Biederman" , Miklos Szeredi , "Serge E. Hallyn" , Linux-Fsdevel , Kernel Mailing List , Andy Lutomirski , Linus Torvalds Subject: Re: [RFC][PATCH 0/3] vfs: Detach mounts on unlink. Message-ID: <20131005231915.GW13318@ZenIV.linux.org.uk> References: <87li281wx6.fsf_-_@xmission.com> <1381014462.1974.162@driftwood> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1381014462.1974.162@driftwood> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1432 Lines: 33 On Sat, Oct 05, 2013 at 06:07:42PM -0500, Rob Landley wrote: > A todo item I've had _forever_ is fixing chroot() to not be broken > so that you can trivially break out of a chroot via: > > chdir("/"); > mkdir("sub"); > chroot("sub"); > chdir("./../../../../../../../.."); > > (Because chroot() affects where "/" points but NOT where "." points > to, and chdir does an == check with the dentry "/" points at to know > when to stop, so if you move "/" under "." you can back up to the > actual root of the tree.) > > The above is why lxc uses pivot_root() instead of chroot(). > > These days, we have multiple mount trees so there's no reason > chroot() can't trim the process local mount tree (creating a new > bind mount if necessary). Except my todo list runneth over and I > haven't had a chance to dig in and see what would be involved. (Last > time I brought this up people were wondering why chroot() didn't > just move "." to the new "/" if it wasn't under it. I had no idea, > still don't.) 1) RTFUNIXFAQ. chroot() never has been root-proof. 2) your "fix" isn't - it will lead to mounts done by chrooted process not affecting other processes in the same namespace. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/