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=-0.8 required=3.0 tests=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 6C747C3402A for ; Mon, 17 Feb 2020 21:20:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 40875207FD for ; Mon, 17 Feb 2020 21:20:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729141AbgBQVUg (ORCPT ); Mon, 17 Feb 2020 16:20:36 -0500 Received: from youngberry.canonical.com ([91.189.89.112]:55236 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728254AbgBQVUg (ORCPT ); Mon, 17 Feb 2020 16:20:36 -0500 Received: from ip5f5bf7ec.dynamic.kabel-deutschland.de ([95.91.247.236] helo=wittgenstein) by youngberry.canonical.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.86_2) (envelope-from ) id 1j3noV-0004NS-OY; Mon, 17 Feb 2020 21:20:23 +0000 Date: Mon, 17 Feb 2020 22:20:22 +0100 From: Christian Brauner To: James Bottomley Cc: =?utf-8?B?U3TDqXBoYW5l?= Graber , "Eric W. Biederman" , Aleksa Sarai , Jann Horn , Kees Cook , Jonathan Corbet , linux-kernel@vger.kernel.org, containers@lists.linux-foundation.org, smbarber@chromium.org, Seth Forshee , linux-security-module@vger.kernel.org, Alexander Viro , linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, Alexey Dobriyan Subject: Re: [PATCH v2 00/28] user_namespace: introduce fsid mappings Message-ID: <20200217212022.2rfex3qsdjyyqrq7@wittgenstein> References: <20200214183554.1133805-1-christian.brauner@ubuntu.com> <1581973568.24289.6.camel@HansenPartnership.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <1581973568.24289.6.camel@HansenPartnership.com> Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: On Mon, Feb 17, 2020 at 01:06:08PM -0800, James Bottomley wrote: > On Fri, 2020-02-14 at 19:35 +0100, Christian Brauner wrote: > [...] > > People not as familiar with user namespaces might not be aware that > > fsid mappings already exist. Right now, fsid mappings are always > > identical to id mappings. Specifically, the kernel will lookup fsuids > > in the uid mappings and fsgids in the gid mappings of the relevant > > user namespace. > > This isn't actually entirely true: today we have the superblock user > namespace, which can be used for fsid remapping on filesystems that > support it (currently f2fs and fuse). Since this is a single shift, Note that this states "the relevant" user namespace not the caller's user namespace. And the point is true even for such filesystems. fuse does call make_kuid(fc->user_ns, attr->uid) and hence looks up the mapping in the id mappings.. This would be replaced by make_kfsuid(). > how is it going to play with s_user_ns? Do you have to understand the > superblock mapping to use this shift, or are we simply using this to > replace s_user_ns? I'm not sure what you mean by understand the superblock mapping. The case is not different from the devpts patch in this series. Fuse needs to be changed to call make_kfsuid() since it is mountable inside user namespaces at which point everthing just works.