On Fri, Apr 21, 2017 at 11:51 PM, Andy Lutomirski <luto@xxxxxxxxxx> wrote: > On Fri, Apr 21, 2017 at 5:12 PM, Djalal Harouni <tixxdz@xxxxxxxxx> wrote: >> On Sat, Apr 22, 2017 at 1:51 AM, Andy Lutomirski <luto@xxxxxxxxxx> wrote: >> [...] >>>>> I personally like my implicit_rights idea, and it might be interesting >>>>> to prototype it. >>>> >>>> I don't like blocking a needed feature behind a large super-feature >>>> that doesn't exist yet. We'd be able to refactor this code into using >>>> such a thing in the future, so I'd prefer to move ahead with this >>>> since it would stop actual exploits. >>> >>> I don't think the super-feature is so hard, and I think we should not >>> add the per-task thing the way it's done in this patch. Let's not add >>> per-task things where the best argument for their security is "not >>> sure how it would be exploited". >> >> Actually the XFRM framework CVE-2017-7184 [1] is one real example, of >> course there are others. The exploit was used on a generic distro >> during a security contest that distro is Ubuntu. That distro will >> never provide a module autoloading restriction by default to not harm >> it's users. Consumers or containers/sandboxes then can run their >> confined apps using such facilities. >> >> These bugs will stay in embedded devices that use these generic >> distros for ever. >> >>> Anyway, I think the sysctl is really the important bit. The per-task >>> setting is icing on the cake IMO. One upon a time autoload was more >>> important, but these days modaliases are supposed to do most of the >>> work. I bet that modern distros don't need unprivileged autoload at >>> all. >> >> Actually I think they do and we can't just change that. Users may >> depend on it, it is a well established facility. >> >> Now the other problem is CAP_NET_ADMIN which does lot of things, it is >> more like the CAP_SYS_ADMIN. >> >> This is a quick list that I got from only the past months, I'm pretty >> sure there are more: >> >> * DCCP use after free CVE-2017-6074 >> * n_hldc CVE-2017-2636 >> * XFRM framework CVE-2017-7184 >> * L2TPv3 CVE-2016-10200 >> >> Most of these need CAP_NET_ADMIN to be autoloaded, however we also >> need CAP_NET_ADMIN for other things... therefore it is better to have >> an extra facility that could coexist with CAP_NET_ADMIN and other >> sandbox features. >> > > I agree that the feature is important, but I think your implementation > is needlessly dangerous. I imagine that the main uses that you care > about involve containers. How about doing it in a safer way that > works for containers? I can think of a few. For example: > > 1. A sysctl that, if set, prevents autoloading outside the root > userns. This isn't very flexible at all, but it might work. > > 2. Your patch, but require privilege within the calling namespace to > set the prctl. How about CAP_SYS_ADMIN || no_new_privs? -Kees > > 3. A per-user-ns sysctl. -- Kees Cook Pixel Security -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
