From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AD3EAC2BCA1 for ; Fri, 7 Jun 2019 21:06:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 88102208C0 for ; Fri, 7 Jun 2019 21:06:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730251AbfFGVGo (ORCPT ); Fri, 7 Jun 2019 17:06:44 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34046 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730342AbfFGVGn (ORCPT ); Fri, 7 Jun 2019 17:06:43 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 202B581DEB; Fri, 7 Jun 2019 21:06:43 +0000 (UTC) Received: from localhost.localdomain (ovpn-112-50.rdu2.redhat.com [10.10.112.50]) by smtp.corp.redhat.com (Postfix) with ESMTP id 787565D9C6; Fri, 7 Jun 2019 21:06:39 +0000 (UTC) Reply-To: dwalsh@redhat.com Subject: Re: New Container vulnerability could potentially use an SELinux fix. To: Stephen Smalley , Miloslav Trmac , selinux@vger.kernel.org References: <7ca438c7-4a41-4daa-fc3f-a46a2e0af945@redhat.com> <9313f92a-46cf-c65c-6cfb-1373917de02b@tycho.nsa.gov> From: Daniel Walsh Openpgp: preference=signencrypt Autocrypt: addr=dwalsh@redhat.com; prefer-encrypt=mutual; keydata= mQENBFsaqOEBCADBSnZCZpi262vX8m7iL/OdHKP9G9dhS28FR60cjd8nMPqHDNhQJBjLMZra 66L2cCIEhc4HEItail7KU1BckrMc4laFaxL8tLoVTKHZwb74n2OcAJ4FtgzkNNlB1XJvSwC/ 909uwt7cpDqwXpJvyP3t17iuklB1OY0EEjTDt9aU4+0QjHzV18L4Cpd9iQ4ksu+EHT+pjlBk DdQB+hKoAjxPl11Eh6pZfrAcrNWpYBBk0A3XE9Jb6ghbmHWltNgVOsCa9GcswJHUEeFiOup6 J5DTv6Xzwt0t6QB8nIs+wDJH+VxqAXcrxscnAhViIfGGS2AtxzjnVOz/J+UZPaauIGXTABEB AAG0LERhbmllbCBKIFdhbHNoIChGb3IgR2l0KSA8ZHdhbHNoQHJlZGhhdC5jb20+iQE4BBMB AgAiBQJbGqjhAhsDBgsJCAcDAgYVCAIJCgsEFgIDAQIeAQIXgAAKCRCi35Adq+LAKHuJB/98 nZB5RmNjMWua4Ms8q5a1R9XWlDAb3mrST6JeL+uV/M0fa18e2Aw4/hi/WZHjAjoypLmcuaRx GeCbC8iYdpfRDUG79Y956Qq+Vs8c6VfNDMY1mvtfb00eeTaYoOCu0Aa9LDeR9iLKh2g0RI+N Zr3EU45RxZdacIs1v6mU8pGpyUq/FvuTGK9GzR9d1YeVCuSpQKN4ckHNZHJUXyk0vOZft1oO nSgLqM9EDWA+yz1JLmRYwbNsim7IvfVOav5mCgnKzHcL2mLv8qCnMFZjoQV8aGny/W739Z3a YJo1CdOg6zSu5SOvmq9idYrBRkwEtyLXss2oceTVBs0MxqQ/9mLPuQENBFsaqOEBCADDl2hl bUpqJGgwt2eQvs0Z0DCx/7nn0hlLfEn4WAv2HqP25AjIRXUX31Mzu68C4QnsvNtY4zN+FGRC EfUpYsjiL7vBYlRePhIohyMYU4RLp5eXFQKahHO/9Xlhe8mwueQNwYxNBPfMQ65U2AuqxpcS scx4s5w208mhqHoKz6IB2LuKeflhYfH5Y1FNAtVGHfhg22xlcAdupPPcxGuS4fBEW6PD/SDf Y4HT5iUHsyksQKjM0IFalqZ7YuLfXBl07OD2zU7WI9c3W0dwkvwIRjt3aD4iAah544uOLff+ BzfxWghXeo80S2a1WCL0S/2qR0NVct/ExaDWboYr/bKpTa/1ABEBAAGJAR8EGAECAAkFAlsa qOECGwwACgkQot+QHaviwCi2hgf/XRvrt+VBmp1ZFxQAR9E6S7AtRT8KSytjFiqEC7TpOx3r 2OZ4gZ3ZiW4TMW8hS7aYRgF1uYpLzl7BbrCfCHfAWEcXZ+uG8vayg8G/mLAcNlLY+JE76ATs 53ziEY9R2Vb/wLMFd2nNBdqfwGcRH9N9VOej9vP76nCP01ZolY8Nms2hE383/+1Quxp5EedU BN5W5l7x9riBJyqCA63hr4u8wNsTuQgrDyhm/U1IvYeLtMopgotjnIR3KiTKOElbppLeXW3w EO/sQTPk+vQ4vcsJYY9Dnf1NlvHE4klj60GHjtjitsBEHzdE7s+J9FOxPmt8l+gMogGumKpN Y4lO0pfTyg== Organization: Red Hat Message-ID: Date: Fri, 7 Jun 2019 17:06:38 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <9313f92a-46cf-c65c-6cfb-1373917de02b@tycho.nsa.gov> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Fri, 07 Jun 2019 21:06:43 +0000 (UTC) Sender: selinux-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: selinux@vger.kernel.org On 6/7/19 12:44 PM, Stephen Smalley wrote: > On 6/7/19 11:42 AM, Daniel Walsh wrote: >> We have periodic vulnerablities around bad container images having >> symbolic link attacks against the host. >> >> One came out last week about doing a `podman cp` >> >> Which would copy content from the host into the container.  The issue >> was that if the container was running, it could trick the processes >> copying content into it to follow a symbolic link to external of the >> container image. >> >> The question came up, is there a way to use SELinux to prevent this. And >> sadly the answer right now is no, because we have no way to know what >> the label of the process attempting to update the container file system >> is running as.  Usually it will be running as unconfined_t. >> >> One idea would be to add a rule to policy that control the following of >> symbolic links to only those specified in policy. >> >> >> Something like >> >> SPECIALRESTRICTED TYPE container_file_t >> >> allow container_file_t container_file_t:symlink follow; >> >> Then if a process attempted to copy content onto a symbolic link from >> container_file_t to a non container_file_t type, the kernel would deny >> access. >> >> Thoughts? > > SELinux would prevent it if you didn't allow unconfined_t (or other > privileged domains) to follow untrustworthy symlinks (e.g. don't allow > unconfined_t container_file_t:lnk_file read; in the first place). > That's the right way to prevent it. > > Trying to apply a check between symlink and its target as you suggest > is problematic; we don't generally have them both at the same point.  > If we are allowed to follow the symlink, we read its contents and > perform a path walk on that, and that could be a multi-component > pathname lookup that itself spans further symlinks, mount points, > etc.  I think that would be challenging to support in the kernel, > subject to races, and certainly would require changes outside of just > SELinux. > > If you truly cannot impose such restrictions on unconfined_t, then > maybe podman should run in its own domain. > This is not an issue with just podman.  Podman can mount the image and the tools can just read/write content into the mountpoint. I thought I recalled a LSM that prefented symlink attacks when users would link a file in the homedir against /etc/shadow and then attempt to get the admin to modify the file in his homedir? I was thinking that if that existed we could build more controls on it based on Labels rather then just UIDs matching.