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 B1827CA9EC9 for ; Mon, 4 Nov 2019 23:41:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8287421D71 for ; Mon, 4 Nov 2019 23:41:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730016AbfKDXl4 (ORCPT ); Mon, 4 Nov 2019 18:41:56 -0500 Received: from out01.mta.xmission.com ([166.70.13.231]:58128 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729817AbfKDXl4 (ORCPT ); Mon, 4 Nov 2019 18:41:56 -0500 Received: from in02.mta.xmission.com ([166.70.13.52]) by out01.mta.xmission.com with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.87) (envelope-from ) id 1iRlys-0003Z2-Cb; Mon, 04 Nov 2019 16:41:54 -0700 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95] helo=x220.xmission.com) by in02.mta.xmission.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.87) (envelope-from ) id 1iRlyr-0000zR-Ha; Mon, 04 Nov 2019 16:41:54 -0700 From: ebiederm@xmission.com (Eric W. Biederman) To: Topi Miettinen Cc: Luis Chamberlain , Kees Cook , Alexey Dobriyan , "linux-kernel\@vger.kernel.org" , "open list\:FILESYSTEMS \(VFS and infrastructure\)" References: <74a91362-247c-c749-5200-7bdce704ed9e@gmail.com> <87d0e8g5f4.fsf@x220.int.ebiederm.org> <87h83jejei.fsf@x220.int.ebiederm.org> Date: Mon, 04 Nov 2019 17:41:40 -0600 In-Reply-To: (Topi Miettinen's message of "Mon, 4 Nov 2019 19:58:55 +0200") Message-ID: <87tv7jciq3.fsf@x220.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1iRlyr-0000zR-Ha;;;mid=<87tv7jciq3.fsf@x220.int.ebiederm.org>;;;hst=in02.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX18AaWiq4pZEpAPJi78BflGOh+DMoEBcnOg= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [PATCH] Allow restricting permissions in /proc/sys X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Topi Miettinen writes: > On 4.11.2019 17.44, Eric W. Biederman wrote: >> Topi Miettinen writes: >> >>> On 3.11.2019 20.50, Eric W. Biederman wrote: >>>> Topi Miettinen writes: >>>> >>>>> Several items in /proc/sys need not be accessible to unprivileged >>>>> tasks. Let the system administrator change the permissions, but only >>>>> to more restrictive modes than what the sysctl tables allow. >>>> >>>> This looks quite buggy. You neither update table->mode nor >>>> do you ever read from table->mode to initialize the inode. >>>> I am missing something in my quick reading of your patch? >>> >>> inode->i_mode gets initialized in proc_sys_make_inode(). >>> >>> I didn't want to touch the table, so that the original permissions can >>> be used to restrict the changes made. In case the restrictions are >>> removed as suggested by Theodore Ts'o, table->mode could be >>> changed. Otherwise I'd rather add a new field to store the current >>> mode and the mode field can remain for reference. As the original >>> author of the code from 2007, would you let the administrator to >>> chmod/chown the items in /proc/sys without restrictions (e.g. 0400 -> >>> 0777)? >> >> At an architectural level I think we need to do this carefully and have >> a compelling reason. The code has survived nearly the entire life of >> linux without this capability. > > I'd be happy with only allowing restrictions to access for > now. Perhaps later with more analysis, also relaxing changes and maybe > UID/GID changes can be allowed. Let's find the use case where someone cares before we think about that. >> I think right now the common solution is to mount another file over the >> file you are trying to hide/limit. Changing the permissions might be >> better but that is not at all clear. >> >> Do you have specific examples of the cases where you would like to >> change the permissions? > > Unprivileged applications typically do not need to access most items > in /proc/sys, so I'd like to gradually find out which are needed. So > far I've seen no problems with 0500 mode for directories abi, crypto, > debug, dev, fs, user or vm. But if there is no problem in letting everyone access the information why reduce the permissions? > I'm also using systemd's InaccessiblePaths to limit access (which > mounts an inaccessible directory over the path), but that's a bit too > big hammer. For example there are over 100 files in /proc/sys/kernel, > perhaps there will be issues when creating a mount for each, and that > multiplied by a number of services. My sense is that if there is any kind of compelling reason to make world-readable values not world-readable, and it doesn't break anything (except malicious applications) than a kernel patch is probably the way to go. Policy knobs like this on proc tend to break in normal maintenance because they are not used enough so I am not a big fan of adding policy knobs just because we can. > I see no problems by using Firejail (which uses PID namespacing) with > v2, the permissions in /proc/sys are the same as outside the > namespace. Thank you for testing. Eric