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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 7965AC6379D for ; Tue, 24 Nov 2020 22:45:32 +0000 (UTC) Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id C3BFE20872 for ; Tue, 24 Nov 2020 22:45:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C3BFE20872 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ubuntu.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-453-uXJbiixqMaet1SyjTJVI6Q-1; Tue, 24 Nov 2020 17:45:28 -0500 X-MC-Unique: uXJbiixqMaet1SyjTJVI6Q-1 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 mimecast-mx01.redhat.com (Postfix) with ESMTPS id 0C86681C464; Tue, 24 Nov 2020 22:45:25 +0000 (UTC) Received: from colo-mx.corp.redhat.com (colo-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.21]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 164735D9CA; Tue, 24 Nov 2020 22:45:24 +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 ED6DB4E58E; Tue, 24 Nov 2020 22:45:21 +0000 (UTC) Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) by lists01.pubmisc.prod.ext.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id 0AOCUvA0008875 for ; Tue, 24 Nov 2020 07:30:58 -0500 Received: by smtp.corp.redhat.com (Postfix) id DED6F2166B2B; Tue, 24 Nov 2020 12:30:57 +0000 (UTC) Received: from mimecast-mx02.redhat.com (mimecast03.extmail.prod.ext.rdu2.redhat.com [10.11.55.19]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D8CB42166B2A for ; Tue, 24 Nov 2020 12:30:54 +0000 (UTC) Received: from us-smtp-1.mimecast.com (us-smtp-delivery-1.mimecast.com [205.139.110.120]) (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 A92FB811E86 for ; Tue, 24 Nov 2020 12:30:54 +0000 (UTC) Received: from youngberry.canonical.com (youngberry.canonical.com [91.189.89.112]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-506-4tKqbJyiOQ-Ze9R8QLC8QA-1; Tue, 24 Nov 2020 07:30:51 -0500 X-MC-Unique: 4tKqbJyiOQ-Ze9R8QLC8QA-1 Received: from ip5f5af0a0.dynamic.kabel-deutschland.de ([95.90.240.160] helo=wittgenstein) by youngberry.canonical.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.86_2) (envelope-from ) id 1khXSv-0004ea-Op; Tue, 24 Nov 2020 12:30:37 +0000 Date: Tue, 24 Nov 2020 13:30:35 +0100 From: Christian Brauner To: Tycho Andersen Subject: Re: [PATCH v2 07/39] mount: attach mappings to mounts Message-ID: <20201124123035.hbv4sstyoucht7xp@wittgenstein> References: <20201115103718.298186-1-christian.brauner@ubuntu.com> <20201115103718.298186-8-christian.brauner@ubuntu.com> <20201123154719.GD4025434@cisco> <20201123162428.GA24807@cisco> MIME-Version: 1.0 In-Reply-To: <20201123162428.GA24807@cisco> 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 10.11.54.6 X-loop: linux-audit@redhat.com X-Mailman-Approved-At: Tue, 24 Nov 2020 17:45:20 -0500 Cc: Andy Lutomirski , Mimi Zohar , James Bottomley , Andreas Dilger , Christoph Hellwig , Jonathan Corbet , smbarber@chromium.org, Christoph Hellwig , Alban Crequy , linux-ext4@vger.kernel.org, Mrunal Patel , Arnd Bergmann , Jann Horn , selinux@vger.kernel.org, Josh Triplett , Seth Forshee , Aleksa Sarai , Alexander Viro , Lennart Poettering , OGAWA Hirofumi , Geoffrey Thomas , David Howells , John Johansen , Theodore Tso , Dmitry Kasatkin , containers@lists.linux-foundation.org, linux-security-module@vger.kernel.org, linux-audit@redhat.com, "Eric W. Biederman" , linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-integrity@vger.kernel.org, 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 10.5.11.14 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 Mon, Nov 23, 2020 at 11:24:28AM -0500, Tycho Andersen wrote: > On Mon, Nov 23, 2020 at 10:47:19AM -0500, Tycho Andersen wrote: > > On Sun, Nov 15, 2020 at 11:36:46AM +0100, Christian Brauner wrote: > > > +static inline struct user_namespace *mnt_user_ns(const struct vfsmount *mnt) > > > +{ > > > + return mnt->mnt_user_ns; > > > +} > > > > I think you might want a READ_ONCE() here. Right now it seems ok, since the > > mnt_user_ns can't change, but if we ever allow it to change (and I see you have > > a idmapped_mounts_wip_v2_allow_to_change_idmapping branch on your public tree > > :D), the pattern of, > > > > user_ns = mnt_user_ns(path->mnt); > > if (mnt_idmapped(path->mnt)) { > > uid = kuid_from_mnt(user_ns, uid); > > gid = kgid_from_mnt(user_ns, gid); > > } > > > > could race. > > Actually, isn't a race possible now? > > kuid_from_mnt(mnt_user_ns(path->mnt) /* &init_user_ns */); > WRITE_ONCE(mnt->mnt.mnt_user_ns, user_ns); > WRITE_ONCE(m->mnt.mnt_flags, flags); > kgid_from_mnt(mnt_user_ns(path->mnt) /* the right user ns */); > > So maybe it should be: > > if (mnt_idmapped(path->mnt)) { > barrier(); > user_ns = mnt_user_ns(path->mnt); > uid = kuid_from_mnt(user_ns, uid); > gid = kgid_from_mnt(user_ns, gid); > } > > since there's no data dependency between mnt_idmapped() and > mnt_user_ns()? I think I had something to handle this case in another branch of mine. The READ_ONCE() you mentioned in another patch I had originally dropped because I wasn't sure whether it works on pointers but after talking to Jann and David it seems that it handles pointers fine. Let me take a look and fix it in the next version. I just finished porting the test suite to xfstests as Christoph requested and I'm looking at this now. Thanks! Christian -- Linux-audit mailing list Linux-audit@redhat.com https://www.redhat.com/mailman/listinfo/linux-audit