Date: Mon, 3 Oct 2011 15:04:23 -0500 From: "Serge E. Hallyn" <serge.hallyn@...onical.com> To: "Eric W. Biederman" <ebiederm@...ssion.com> Cc: Vasiliy Kulikov <segoon@...nwall.com>, Serge Hallyn <serge@...lyn.com>, akpm@...l.org, linux-kernel@...r.kernel.org, netdev@...r.kernel.org, containers@...ts.linux-foundation.org, dhowells@...hat.com, rdunlap@...otime.net, kernel-hardening@...ts.openwall.com Subject: Re: [PATCH 01/15] add Documentation/namespaces/user_namespace.txt (v3) Quoting Eric W. Biederman (ebiederm@...ssion.com): > ebiederm@...ssion.com (Eric W. Biederman) writes: > > > "Serge E. Hallyn" <serge.hallyn@...onical.com> writes: > > > >> Quoting Vasiliy Kulikov (segoon@...nwall.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 The one I linked was one discussion, but not the final one. https://lkml.org/lkml/2008/10/6/72 is the one where the need for revoke is brought up. > it. Fuse already has something like a revoke in it's umount -f > implementation. I'll have to (haven't yet) take a look at it. -serge
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