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=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 C7920C63697 for ; Sat, 21 Nov 2020 09:45:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9F80F22253 for ; Sat, 21 Nov 2020 09:45:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727367AbgKUJpH (ORCPT ); Sat, 21 Nov 2020 04:45:07 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41312 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727257AbgKUJpG (ORCPT ); Sat, 21 Nov 2020 04:45:06 -0500 Received: from smtp-42ab.mail.infomaniak.ch (smtp-42ab.mail.infomaniak.ch [IPv6:2001:1600:3:17::42ab]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5DF9EC061A49; Sat, 21 Nov 2020 01:45:06 -0800 (PST) Received: from smtp-3-0001.mail.infomaniak.ch (unknown [10.4.36.108]) by smtp-2-3000.mail.infomaniak.ch (Postfix) with ESMTPS id 4CdT6R6RqJzlhrhL; Sat, 21 Nov 2020 10:45:03 +0100 (CET) Received: from ns3096276.ip-94-23-54.eu (unknown [94.23.54.103]) by smtp-3-0001.mail.infomaniak.ch (Postfix) with ESMTPA id 4CdT6P5kbjzlh8TD; Sat, 21 Nov 2020 10:45:01 +0100 (CET) Subject: Re: [PATCH v24 02/12] landlock: Add ruleset and domain management To: Jann Horn Cc: James Morris , "Serge E . Hallyn" , Al Viro , Andy Lutomirski , Anton Ivanov , Arnd Bergmann , Casey Schaufler , Jeff Dike , Jonathan Corbet , Kees Cook , Michael Kerrisk , Richard Weinberger , Shuah Khan , Vincent Dagonneau , Kernel Hardening , Linux API , linux-arch , "open list:DOCUMENTATION" , linux-fsdevel , kernel list , "open list:KERNEL SELFTEST FRAMEWORK" , linux-security-module , the arch/x86 maintainers , =?UTF-8?Q?Micka=c3=abl_Sala=c3=bcn?= References: <20201112205141.775752-1-mic@digikod.net> <20201112205141.775752-3-mic@digikod.net> From: =?UTF-8?Q?Micka=c3=abl_Sala=c3=bcn?= Message-ID: <28499c4b-d388-7bd1-046e-a775c326e156@digikod.net> Date: Sat, 21 Nov 2020 10:45:01 +0100 User-Agent: MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 21/11/2020 08:00, Jann Horn wrote: > On Thu, Nov 12, 2020 at 9:51 PM Mickaël Salaün wrote: >> A Landlock ruleset is mainly a red-black tree with Landlock rules as >> nodes. This enables quick update and lookup to match a requested >> access, e.g. to a file. A ruleset is usable through a dedicated file >> descriptor (cf. following commit implementing syscalls) which enables a >> process to create and populate a ruleset with new rules. >> >> A domain is a ruleset tied to a set of processes. This group of rules >> defines the security policy enforced on these processes and their future >> children. A domain can transition to a new domain which is the >> intersection of all its constraints and those of a ruleset provided by >> the current process. This modification only impact the current process. >> This means that a process can only gain more constraints (i.e. lose >> accesses) over time. >> >> Cc: James Morris >> Cc: Jann Horn >> Cc: Kees Cook >> Cc: Serge E. Hallyn >> Signed-off-by: Mickaël Salaün >> --- >> >> Changes since v23: >> * Always intersect access rights. Following the filesystem change >> logic, make ruleset updates more consistent by always intersecting >> access rights (boolean AND) instead of combining them (boolean OR) for >> the same layer. > > This seems wrong to me. If some software e.g. builds a policy that > allows it to execute specific libraries and to open input files > specified on the command line, and the user then specifies a library > as an input file, this change will make that fail unless the software > explicitly deduplicates the rules. > Userspace will be forced to add extra complexity to work around this. That's a valid use case I didn't think about. Reverting this change is not an issue. > >> This defensive approach could also help avoid user >> space to inadvertently allow multiple access rights for the same >> object (e.g. write and execute access on a path hierarchy) instead of >> dealing with such inconsistency. This can happen when there is no >> deduplication of objects (e.g. paths and underlying inodes) whereas >> they get different access rights with landlock_add_rule(2). > > I don't see why that's an issue. If userspace wants to be able to > access the same object in different ways for different purposes, it > should be able to do that, no? > > I liked the semantics from the previous version. > I agree, but the real issue is with the ruleset layers applied to the filesystem, cf. patch 7.