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=-9.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, 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 7FAE4C55179 for ; Thu, 29 Oct 2020 09:30:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2F43C2076B for ; Thu, 29 Oct 2020 09:30:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726460AbgJ2JaQ (ORCPT ); Thu, 29 Oct 2020 05:30:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46782 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726701AbgJ2JaK (ORCPT ); Thu, 29 Oct 2020 05:30:10 -0400 Received: from smtp-42ad.mail.infomaniak.ch (smtp-42ad.mail.infomaniak.ch [IPv6:2001:1600:3:17::42ad]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5C5BAC0613D2 for ; Thu, 29 Oct 2020 02:30:10 -0700 (PDT) Received: from smtp-2-0001.mail.infomaniak.ch (unknown [10.5.36.108]) by smtp-2-3000.mail.infomaniak.ch (Postfix) with ESMTPS id 4CMKsq0bfrzljf95; Thu, 29 Oct 2020 10:30:07 +0100 (CET) Received: from ns3096276.ip-94-23-54.eu (unknown [94.23.54.103]) by smtp-2-0001.mail.infomaniak.ch (Postfix) with ESMTPA id 4CMKsn1t98zlh8Tj; Thu, 29 Oct 2020 10:30:05 +0100 (CET) Subject: Re: [PATCH v22 01/12] landlock: Add object 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: <20201027200358.557003-1-mic@digikod.net> <20201027200358.557003-2-mic@digikod.net> From: =?UTF-8?Q?Micka=c3=abl_Sala=c3=bcn?= Message-ID: Date: Thu, 29 Oct 2020 10:30:04 +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 29/10/2020 02:05, Jann Horn wrote: > On Tue, Oct 27, 2020 at 9:04 PM Mickaël Salaün wrote: >> A Landlock object enables to identify a kernel object (e.g. an inode). >> A Landlock rule is a set of access rights allowed on an object. Rules >> are grouped in rulesets that may be tied to a set of processes (i.e. >> subjects) to enforce a scoped access-control (i.e. a domain). >> >> Because Landlock's goal is to empower any process (especially >> unprivileged ones) to sandbox themselves, we cannot rely on a >> system-wide object identification such as file extended attributes. >> Indeed, we need innocuous, composable and modular access-controls. >> >> The main challenge with these constraints is to identify kernel objects >> while this identification is useful (i.e. when a security policy makes >> use of this object). But this identification data should be freed once >> no policy is using it. This ephemeral tagging should not and may not be >> written in the filesystem. We then need to manage the lifetime of a >> rule according to the lifetime of its objects. To avoid a global lock, >> this implementation make use of RCU and counters to safely reference >> objects. >> >> A following commit uses this generic object management for inodes. >> >> Cc: James Morris >> Cc: Jann Horn >> Cc: Kees Cook >> Cc: Serge E. Hallyn >> Signed-off-by: Mickaël Salaün > > Reviewed-by: Jann Horn Thanks for the review. > > except for some minor nits: > > [...] >> diff --git a/security/landlock/object.c b/security/landlock/object.c > [...] >> +void landlock_put_object(struct landlock_object *const object) >> +{ >> + /* >> + * The call to @object->underops->release(object) might sleep e.g., > > s/ e.g.,/, e.g./ I indeed prefer the comma preceding the "e.g.", but it seems that there is a difference between UK english and US english: https://english.stackexchange.com/questions/16172/should-i-always-use-a-comma-after-e-g-or-i-e Looking at the kernel documentation makes it clear: $ git grep -F 'e.g. ' | wc -l 1179 $ git grep -F 'e.g., ' | wc -l 160 I'll apply your fix in the whole patch series. > >> + * because of iput(). >> + */ >> + might_sleep(); >> + if (!object) >> + return; > [...] >> +} >> diff --git a/security/landlock/object.h b/security/landlock/object.h > [...] >> +struct landlock_object { >> + /** >> + * @usage: This counter is used to tie an object to the rules matching >> + * it or to keep it alive while adding a new rule. If this counter >> + * reaches zero, this struct must not be modified, but this counter can >> + * still be read from within an RCU read-side critical section. When >> + * adding a new rule to an object with a usage counter of zero, we must >> + * wait until the pointer to this object is set to NULL (or recycled). >> + */ >> + refcount_t usage; >> + /** >> + * @lock: Guards against concurrent modifications. This lock must be > > s/must be/must be held/ ? Right. > >> + * from the time @usage drops to zero until any weak references from >> + * @underobj to this object have been cleaned up. >> + * >> + * Lock ordering: inode->i_lock nests inside this. >> + */ >> + spinlock_t lock; > [...] >> +}; >> + >> +struct landlock_object *landlock_create_object( >> + const struct landlock_object_underops *const underops, >> + void *const underojb); > > nit: "underobj" > Good catch!