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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 4EBB8C4741F for ; Fri, 30 Oct 2020 16:09:09 +0000 (UTC) Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [63.128.21.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 7183720724 for ; Fri, 30 Oct 2020 16:09:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7183720724 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=hallyn.com Authentication-Results: mail.kernel.org; spf=tempfail smtp.mailfrom=linux-audit-bounces@redhat.com Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-588-RJDU40c4Pqy2226SuHiIQw-1; Fri, 30 Oct 2020 12:09:04 -0400 X-MC-Unique: RJDU40c4Pqy2226SuHiIQw-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 456F219080A6; Fri, 30 Oct 2020 16:08:50 +0000 (UTC) Received: from colo-mx.corp.redhat.com (colo-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.20]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 1E75A5C1C4; Fri, 30 Oct 2020 16:08:50 +0000 (UTC) Received: from lists01.pubmisc.prod.ext.phx2.redhat.com (lists01.pubmisc.prod.ext.phx2.redhat.com [10.5.19.33]) by colo-mx.corp.redhat.com (Postfix) with ESMTP id 8D8DD1826D36; Fri, 30 Oct 2020 16:08:49 +0000 (UTC) Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) by lists01.pubmisc.prod.ext.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id 09UG3ifR016757 for ; Fri, 30 Oct 2020 12:03:45 -0400 Received: by smtp.corp.redhat.com (Postfix) id CB27B1004176; Fri, 30 Oct 2020 16:03:44 +0000 (UTC) Received: from mimecast-mx02.redhat.com (mimecast06.extmail.prod.ext.rdu2.redhat.com [10.11.55.22]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C630D1004165 for ; Fri, 30 Oct 2020 16:03:41 +0000 (UTC) Received: from us-smtp-1.mimecast.com (us-smtp-2.mimecast.com [207.211.31.81]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-SHA384 (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id B4AD4185A790 for ; Fri, 30 Oct 2020 16:03:41 +0000 (UTC) Received: from mail.hallyn.com (mail.hallyn.com [178.63.66.53]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-11-ikb1yYf2N_yTQwbn-TTXfQ-1; Fri, 30 Oct 2020 12:03:36 -0400 X-MC-Unique: ikb1yYf2N_yTQwbn-TTXfQ-1 Received: by mail.hallyn.com (Postfix, from userid 1001) id 0CBD712C3; Fri, 30 Oct 2020 11:03:32 -0500 (CDT) Date: Fri, 30 Oct 2020 11:03:32 -0500 From: "Serge E. Hallyn" To: Seth Forshee Subject: Re: [PATCH 00/34] fs: idmapped mounts Message-ID: <20201030160332.GA30083@mail.hallyn.com> References: <20201029003252.2128653-1-christian.brauner@ubuntu.com> <87pn51ghju.fsf@x220.int.ebiederm.org> <20201029155148.5odu4j2kt62ahcxq@yavin.dot.cyphar.com> <87361xdm4c.fsf@x220.int.ebiederm.org> <20201030150748.GA176340@ubuntu-x1> MIME-Version: 1.0 In-Reply-To: <20201030150748.GA176340@ubuntu-x1> User-Agent: Mutt/1.9.4 (2018-02-28) X-Mimecast-Impersonation-Protect: Policy=CLT - Impersonation Protection Definition; Similar Internal Domain=false; Similar Monitored External Domain=false; Custom External Domain=false; Mimecast External Domain=false; Newly Observed Domain=false; Internal User Name=false; Custom Display Name List=false; Reply-to Address Mismatch=false; Targeted Threat Dictionary=false; Mimecast Threat Dictionary=false; Custom Threat Dictionary=false X-Scanned-By: MIMEDefang 2.78 on 10.11.54.3 X-loop: linux-audit@redhat.com X-Mailman-Approved-At: Fri, 30 Oct 2020 12:08:47 -0400 Cc: Phil Estes , Lennart Poettering , Amir Goldstein , Mimi Zohar , David Howells , Andreas Dilger , containers@lists.linux-foundation.org, Christian Brauner , Tycho Andersen , Miklos Szeredi , James Morris , smbarber@chromium.org, Christoph Hellwig , linux-ext4@vger.kernel.org, Mrunal Patel , Serge Hallyn , Arnd Bergmann , Jann Horn , selinux@vger.kernel.org, Josh Triplett , linux-fsdevel@vger.kernel.org, Aleksa Sarai , Alexander Viro , Andy Lutomirski , OGAWA Hirofumi , Geoffrey Thomas , James Bottomley , John Johansen , Theodore Tso , Dmitry Kasatkin , Jonathan Corbet , linux-unionfs@vger.kernel.org, linux-security-module@vger.kernel.org, linux-audit@redhat.com, "Eric W. Biederman" , linux-api@vger.kernel.org, Alban Crequy , linux-integrity@vger.kernel.org, =?iso-8859-1?Q?St=E9phane?= Graber , Todd Kjos X-BeenThere: linux-audit@redhat.com X-Mailman-Version: 2.1.12 Precedence: junk List-Id: Linux Audit Discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linux-audit-bounces@redhat.com Errors-To: linux-audit-bounces@redhat.com X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=linux-audit-bounces@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On Fri, Oct 30, 2020 at 10:07:48AM -0500, Seth Forshee wrote: > On Thu, Oct 29, 2020 at 11:37:23AM -0500, Eric W. Biederman wrote: > > First and foremost: A uid shift on write to a filesystem is a security > > bug waiting to happen. This is especially in the context of facilities > > like iouring, that play very agressive games with how process context > > makes it to system calls. > > > > The only reason containers were not immediately exploitable when iouring > > was introduced is because the mechanisms are built so that even if > > something escapes containment the security properties still apply. > > Changes to the uid when writing to the filesystem does not have that > > property. The tiniest slip in containment will be a security issue. > > > > This is not even the least bit theoretical. I have seem reports of how > > shitfs+overlayfs created a situation where anyone could read > > /etc/shadow. > > This bug was the result of a complex interaction with several > contributing factors. It's fair to say that one component was overlayfs > writing through an id-shifted mount, but the primary cause was related > to how copy-up was done coupled with allowing unprivileged overlayfs > mounts in a user ns. Checks that the mounter had access to the lower fs > file were not done before copying data up, and so the file was copied up > temporarily to the id shifted upperdir. Even though it was immediately > removed, other factors made it possible for the user to get the file > contents from the upperdir. > > Regardless, I do think you raise a good point. We need to be wary of any > place the kernel could open files through a shifted mount, especially > when the open could be influenced by userspace. > > Perhaps kernel file opens through shifted mounts should to be opt-in. > I.e. unless a flag is passed, or a different open interface used, the > open will fail if the dentry being opened is subject to id shifting. > This way any kernel writes which would be subject to id shifting will > only happen through code which as been written to take it into account. For my use cases, it would be fine to require opt-in at original fs mount time by init_user_ns admin. I.e. mount -o allow_idmap /dev/mapper/whoozit /whatzit I'm quite certain I would always be sharing a separate LV or loopback or tmpfs. -serge -- Linux-audit mailing list Linux-audit@redhat.com https://www.redhat.com/mailman/listinfo/linux-audit