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=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 8C3B2C433E0 for ; Wed, 27 May 2020 14:14:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6BE2020899 for ; Wed, 27 May 2020 14:14:29 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="AKAalPVw" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388594AbgE0OO2 (ORCPT ); Wed, 27 May 2020 10:14:28 -0400 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:48021 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2388413AbgE0OOY (ORCPT ); Wed, 27 May 2020 10:14:24 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1590588863; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=dctxeA759qsefX6QIwxwGGafAWwHT3wkT86+72lNh4I=; b=AKAalPVw95f6tS/LjkeMRs7EQTvwPOYH6Ld7pzfqGuV9LFc6zNUjDiq/N7UKuWGJDi2wf4 VArN/XLl+/no47mes2Pe1SQuxaEKfk+hUstvCD1pw5zpuRdDwKWBO8XvPD/Vp9Ks0heFxE fFolfgLpBxDS/Sr4MXThb+/zgvani98= 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-494-cCwpMpz8MJGNDHIv5dmS8w-1; Wed, 27 May 2020 10:14:19 -0400 X-MC-Unique: cCwpMpz8MJGNDHIv5dmS8w-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 7862C8018A7; Wed, 27 May 2020 14:14:16 +0000 (UTC) Received: from dcbz.redhat.com (ovpn-113-73.ams2.redhat.com [10.36.113.73]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A4C705C1B0; Wed, 27 May 2020 14:14:05 +0000 (UTC) Date: Wed, 27 May 2020 16:14:03 +0200 From: Adrian Reber To: "Eric W. Biederman" Cc: Casey Schaufler , Christian Brauner , Pavel Emelyanov , Oleg Nesterov , Dmitry Safonov <0x7f454c46@gmail.com>, Andrei Vagin , Nicolas Viennot , =?utf-8?B?TWljaGHFgiBDxYJhcGnFhHNraQ==?= , Kamil Yurtsever , Dirk Petersen , Christine Flood , Mike Rapoport , Radostin Stoyanov , Cyrill Gorcunov , Serge Hallyn , Stephen Smalley , Sargun Dhillon , Arnd Bergmann , linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, selinux@vger.kernel.org, Eric Paris , Jann Horn Subject: Re: [PATCH] capabilities: Introduce CAP_RESTORE Message-ID: <20200527141403.GC250149@dcbz.redhat.com> References: <20200522055350.806609-1-areber@redhat.com> <20200525080541.GF104922@dcbz.redhat.com> <877dwybxvi.fsf@x220.int.ebiederm.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <877dwybxvi.fsf@x220.int.ebiederm.org> X-Operating-System: Linux (5.6.11-300.fc32.x86_64) X-Load-Average: 0.82 0.68 0.60 X-Unexpected: The Spanish Inquisition X-GnuPG-Key: gpg --recv-keys D3C4906A Organization: Red Hat X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: On Tue, May 26, 2020 at 08:59:29AM -0500, Eric W. Biederman wrote: > Adrian Reber writes: > > > On Fri, May 22, 2020 at 09:40:37AM -0700, Casey Schaufler wrote: > > >> What are the other blockers? Are you going to suggest additional new > >> capabilities to clear them? > > > > As mentioned somewhere else access to /proc//map_files/ would be > > helpful. Right now I am testing with a JVM and it works without root > > just with the attached patch. Without access to /proc//map_files/ > > not everything CRIU can do will actually work, but we are a lot closer > > to what our users have been asking for. > > The current permission checks on /proc//map_files/ are simply > someone being over-cautious. > > Someone needs to think through the threat landscape and figure out what > permission checks are actually needed. > > Making the permission check ns_capable instead of capable is a > no-brainer. Figuring out which user_ns to test against might be a > we bit harder. > > We could probably even allow the owner of the process to open the files > but that requires someone doing the work of thinking through how > being able to opening files that you have mmaped might be a problem. As mentioned in the other thread, CRIU can work with read access to map_files. > >> > There are probably a few more things guarded by CAP_SYS_ADMIN required > >> > to run checkpoint/restore as non-root, > >> > >> If you need CAP_SYS_ADMIN anyway you're not gaining anything by > >> separating out CAP_RESTORE. > > > > No, as described we can checkpoint and restore a JVM with this patch and > > it also solves the problem the set_ns_last_pid fork() loop daemon tries > > to solve. It is not enough to support the full functionality of CRIU as > > map_files is also important, but we do not need CAP_SYS_ADMIN and > > CAP_RESTORE. Only CAP_RESTORE would be necessary. > > > > With a new capability users can enable checkpoint/restore as non-root > > without giving CRIU access to any of the other possibilities offered by > > CAP_SYS_ADMIN. Setting a PID and map_files have been introduced for CRIU > > and used to live behind CONFIG_CHECKPOINT_RESTORE. Having a capability > > for checkpoint/restore would make it easier for CRIU users to run it as > > non-root and make it very clear what is possible when giving CRIU the > > new capability. No other things would be allowed than necessary for > > checkpoint/restore. Setting a PID is most important for the restore part > > and reading map_files would be helpful during checkpoint. So it actually > > should be called CAP_CHECKPOINT_RESTORE as Christian mentioned in > > another email. > > Please if one is for checkpoint and one is for restore asking for a pair > of capabilities is probably more appropriate. I will send out a v2 with a renamed capability soon and also include map_files to be readable with that capability. > >> > but by applying this patch I can > >> > already checkpoint and restore processes as non-root. As there are > >> > already multiple workarounds I would prefer to do it correctly in the > >> > kernel to avoid that CRIU users are starting to invent more workarounds. > >> > >> You've presented a couple of really inappropriate implementations > >> that would qualify as workarounds. But the other two are completely > >> appropriate within the system security policy. They don't "get around" > >> the problem, they use existing mechanisms as they are intended. > > > > I agree with the user namespace approach to be appropriate, but not the > > CAP_SYS_ADMIN approach as CRIU only needs a tiny subset (2 things) of > > what CAP_SYS_ADMIN allows. > > > If we are only talking 2 things can you please include in your patchset > a patch enabling those 2 things? The two things are setting a PID via ns_last_pid/clone3() and reading map_files. > But even more than this we need a request that asks not for the least > you can possibly ask for but asks for what you need to do a good job. Also in this thread Kamil mentioned that they also need calling prctl with PR_SET_MM during restore in their production setup. > I am having visions of a recurring discussion that says can we add one > more permission check to CAP_RESTORE or CAP_CHECKPOINT when they are > things we could know today. I will prepare a new version of this patch using CAP_CHECKPOINT_RESTORE for ns_last_pid/clone3(), map_files, and prctl with PR_SET_MM. Adrian