Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933199AbaJUQeu (ORCPT ); Tue, 21 Oct 2014 12:34:50 -0400 Received: from mail-oi0-f43.google.com ([209.85.218.43]:32962 "EHLO mail-oi0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932382AbaJUQet (ORCPT ); Tue, 21 Oct 2014 12:34:49 -0400 Date: Tue, 21 Oct 2014 11:34:26 -0500 From: Seth Forshee To: Andy Lutomirski Cc: "Eric W. Biederman" , Linux FS Devel , linux-kernel@vger.kernel.org, Michael j Theall , fuse-devel@lists.sourceforge.net, Miklos Szeredi , "Serge H. Hallyn" Subject: Re: [PATCH v3] fs: Treat foreign mounts as nosuid Message-ID: <20141021163426.GB68568@ubuntu-hedt> Mail-Followup-To: Andy Lutomirski , "Eric W. Biederman" , Linux FS Devel , linux-kernel@vger.kernel.org, Michael j Theall , fuse-devel@lists.sourceforge.net, Miklos Szeredi , "Serge H. Hallyn" References: <252a4d87d99fc2b5fe4411c838f65b312c4e13cd.1413330857.git.luto@amacapital.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <252a4d87d99fc2b5fe4411c838f65b312c4e13cd.1413330857.git.luto@amacapital.net> 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 On Tue, Oct 14, 2014 at 04:54:47PM -0700, Andy Lutomirski wrote: > If a process gets access to a mount from a different namespace user > namespace, that process should not be able to take advantage of > setuid files or selinux entrypoints from that filesystem. > Technically, trusting mounts created by the same or ancestor user > namespaces ought to be safe, but it's simpler to distrust all > foreign mounts. > > This will make it safer to allow more complex filesystems to be > mounted in non-root user namespaces. > > This does not remove the need for MNT_LOCK_NOSUID. The setuid, > setgid, and file capability bits can no longer be abused if code in > a user namespace were to clear nosuid on an untrusted filesystem, > but this patch, by itself, is insufficient to protect the system > from abuse of files that, when execed, would increase MAC privilege. > > As a more concrete explanation, any task that can manipulate a > vfsmount associated with a given user namespace already has > capabilities in that namespace and all of its descendents. If they > can cause a malicious setuid, setgid, or file-caps executable to > appear in that mount, then that executable will only allow them to > elevate privileges in exactly the set of namespaces in which they > are already privileges. > > On the other hand, if they can cause a malicious executable to > appear with a dangerous MAC label, running it could change the > caller's security context in a way that should not have been > possible, even inside the namespace in which the task is confined. > > As a hardening measure, this would have made CVE-2014-5207 much > more difficult to exploit. > > Signed-off-by: Andy Lutomirski Now that I'm back from plumbers I've finally had a chance to play around with this and it seems to be working as expected. I'll be considering this patch a prerequisite for the next round of fuse userns patches. Acked-by: Seth Forshee -- 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/