From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932317AbaGUNJR (ORCPT ); Mon, 21 Jul 2014 09:09:17 -0400 Received: from mail-qg0-f44.google.com ([209.85.192.44]:56717 "EHLO mail-qg0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754541AbaGUNJQ (ORCPT ); Mon, 21 Jul 2014 09:09:16 -0400 MIME-Version: 1.0 X-Originating-IP: [46.139.80.5] In-Reply-To: <20140721124725.GB111224@ubuntu-hedt> References: <1405365496-58404-1-git-send-email-seth.forshee@canonical.com> <1405365496-58404-4-git-send-email-seth.forshee@canonical.com> <20140721124725.GB111224@ubuntu-hedt> Date: Mon, 21 Jul 2014 15:09:14 +0200 Message-ID: Subject: Re: [PATCH 3/3] fuse: Allow mounts from user namespaces From: Miklos Szeredi To: Miklos Szeredi , Kernel Mailing List , fuse-devel , lxc-devel@lists.linuxcontainers.org, "Eric W. Biederman" , Serge Hallyn , "Michael H. Warfield" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 21, 2014 at 2:47 PM, Seth Forshee wrote: > On Fri, Jul 18, 2014 at 05:33:23PM +0200, Miklos Szeredi wrote: >> On Mon, Jul 14, 2014 at 9:18 PM, Seth Forshee >> wrote: >> > Update fuse to allow mounts from user namespaces. During mount >> > current_user_ns() is stashed away, >> >> Same thing here. While practically this may work, it's theoretically >> wrong, and possibly may go wrong in special situations. In fuse >> there's no official "server process", so storing information, like >> namespace, about one is going to be wrong. > > What you're suggesting would probably work fine when dealing with pids. > It's not going to work though for the checks I've added in > fuse_allow_current_process() that the process is in the mount owner's > user ns, and without those checks or something similar I don't think > it's safe to permit allow_other for user ns mounts. You can add that check in fuse_dev_do_read() as well. If the fsuid/fsgid doesn't exist in the "server's" namespace, then set req->out.h.error and call request_end(). > Can you elaborate on what special situations might violate these > assumptions or otherwise cause problems? What's preventing a fuse fs implementation from handling FUSE_INIT in one process and then handling the rest in a different process (possibly in a different namespace)? Thanks, Miklos