From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm@xmission.com (Eric W. Biederman) Subject: Re: [PATCH 01/15] add Documentation/namespaces/user_namespace.txt (v3) Date: Mon, 03 Oct 2011 12:53:48 -0700 Message-ID: References: <1314993400-6910-1-git-send-email-serge@hallyn.com> <1314993400-6910-4-git-send-email-serge@hallyn.com> <20110926191737.GA4562@albatros> <20110927132157.GB3111@sergelap> <20110927155659.GA22532@albatros> <20111001170047.GA2935@sergelap> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Vasiliy Kulikov , Serge Hallyn , akpm@osdl.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, containers@lists.linux-foundation.org, dhowells@redhat.com, rdunlap@xenotime.net, kernel-hardening@lists.openwall.com To: "Serge E. Hallyn" Return-path: Received: from out01.mta.xmission.com ([166.70.13.231]:46855 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757458Ab1JCTxj (ORCPT ); Mon, 3 Oct 2011 15:53:39 -0400 In-Reply-To: (Eric W. Biederman's message of "Sun, 02 Oct 2011 18:46:06 -0700") Sender: netdev-owner@vger.kernel.org List-ID: ebiederm@xmission.com (Eric W. Biederman) writes: > "Serge E. Hallyn" writes: > >> Quoting Vasiliy Kulikov (segoon@openwall.com): >>> On Tue, Sep 27, 2011 at 08:21 -0500, Serge E. Hallyn wrote: >>> > > First, the patches by design expose much kernel code to unprivileged >>> > > userspace processes. This code doesn't expect malformed data (e.g. VFS, >>> > > specific filesystems, block layer, char drivers, sysadmin part of LSMs, >>> > > etc. etc.). By relaxing permission rules you greatly increase attack >>> > > surface of the kernel from unprivileged users. Are you (or somebody >>> > > else) planning to audit this code? > > Well in theory this codes does expose this code to unprivileged user > space in a way that increases the attack surface. However right now > there are a lot of cases where because the kernel lacks a sufficient > mechanism people are just given root provileges so that can get things > done. Network manager controlling the network stack as an unprivileged > user. Random filesystems on usb sticks being mounted and unmounted > automatically when the usb sticks are inserted and removed. > > I completely agree that auditing and looking at the code is necessary I > think most of what will happen is that we will start directly supporting > how the kernel is actually used in the real world. Which should > actually reduce our level of vulnerability, because we give up the > delusion that large classes of operations don't need careful > attention because only root can perform them. Operations which the > user space authors turn around and write a suid binary for and > unprivileged user space performs those operations all day long. > >>> > I had wanted to (but didn't) propose a discussion at ksummit about how >>> > best to approach the filesystem code. That's not even just for user >>> > namespaces - patches have been floated in the past to make mount an >>> > unprivileged operation depending on the FS and the user's permission >>> > over the device and target. >>> >>> This is a dangerous operation by itself. >> >> Of course it is :) And it's been a while since it has been brought up, >> but it *was* quite well thought through and throrougly discussed - see >> i.e. https://lkml.org/lkml/2008/1/8/131 >> >> Oh, that's right. In the end the reason it didn't go in had to do with >> the ability for an unprivileged user to prevent a privileged user from >> unmounting trees by leaving a busy mount in a hidden namespace. >> >> Eric, in the past we didn't know what to do about that, but I wonder >> if setns could be used in some clever way to solve it from userspace. > > Oh. That is a good objection. I had not realized that unprivileged > mounts had that problem. I just re-read the discussion you are referring to and that wasn't it. Fuse already has something like a revoke in it's umount -f implementation. Eric