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[23.128.96.18]) by mx.google.com with ESMTP id n8si7280498edo.580.2020.07.03.04.11.45; Fri, 03 Jul 2020 04:12:07 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@redhat.com header.s=mimecast20190719 header.b="B+7gZ8/b"; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726379AbgGCLLg (ORCPT + 99 others); Fri, 3 Jul 2020 07:11:36 -0400 Received: from us-smtp-2.mimecast.com ([205.139.110.61]:35059 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726022AbgGCLLf (ORCPT ); Fri, 3 Jul 2020 07:11:35 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1593774693; 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=F+dxHnBK5IM12q+1kQeLc827ddCTp+YxC832WaCEufM=; b=B+7gZ8/b9W7hYyAZlsoSQ1qdInLVQlcZcavK/8j0Hu/ScqLMArsHYXItJwPiRKyl5KgYbY 4u+tJKVWTXwp1D+Gn/B7uNoL/qGUDKdhBBCQEpd05v/nMCl8WbStJlJaJBd8MG4hHLi/l+ 0uaPIQ2yseZlR+cRuTLqXqvE1La7vdE= 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-170-GYAT4KpKM3-Nol6cdZloKQ-1; Fri, 03 Jul 2020 07:11:30 -0400 X-MC-Unique: GYAT4KpKM3-Nol6cdZloKQ-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 8EB76804003; Fri, 3 Jul 2020 11:11:26 +0000 (UTC) Received: from dcbz.redhat.com (ovpn-113-12.ams2.redhat.com [10.36.113.12]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B4B7419D7B; Fri, 3 Jul 2020 11:11:15 +0000 (UTC) Date: Fri, 3 Jul 2020 13:11:13 +0200 From: Adrian Reber To: Christian Brauner Cc: Eric Biederman , Pavel Emelyanov , Oleg Nesterov , Dmitry Safonov <0x7f454c46@gmail.com>, Andrei Vagin , Nicolas Viennot , =?utf-8?B?TWljaGHFgiBDxYJhcGnFhHNraQ==?= , Kamil Yurtsever , Dirk Petersen , Christine Flood , Casey Schaufler , 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 , linux-fsdevel@vger.kernel.org Subject: Re: [PATCH v4 1/3] capabilities: Introduce CAP_CHECKPOINT_RESTORE Message-ID: <20200703111113.GB243637@dcbz.redhat.com> References: <20200701064906.323185-1-areber@redhat.com> <20200701064906.323185-2-areber@redhat.com> <20200701082708.pgfskg7hrsnfi36k@wittgenstein> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200701082708.pgfskg7hrsnfi36k@wittgenstein> X-Operating-System: Linux (5.6.19-300.fc32.x86_64) X-Load-Average: 1.83 1.37 1.14 X-Unexpected: The Spanish Inquisition X-GnuPG-Key: gpg --recv-keys D3C4906A X-Url: Organization: Red Hat X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 01, 2020 at 10:27:08AM +0200, Christian Brauner wrote: > On Wed, Jul 01, 2020 at 08:49:04AM +0200, Adrian Reber wrote: > > This patch introduces CAP_CHECKPOINT_RESTORE, a new capability facilitating > > checkpoint/restore for non-root users. > > > > Over the last years, The CRIU (Checkpoint/Restore In Userspace) team has been > > asked numerous times if it is possible to checkpoint/restore a process as > > non-root. The answer usually was: 'almost'. > > > > The main blocker to restore a process as non-root was to control the PID of the > > restored process. This feature available via the clone3 system call, or via > > /proc/sys/kernel/ns_last_pid is unfortunately guarded by CAP_SYS_ADMIN. > > > > In the past two years, requests for non-root checkpoint/restore have increased > > due to the following use cases: > > * Checkpoint/Restore in an HPC environment in combination with a resource > > manager distributing jobs where users are always running as non-root. > > There is a desire to provide a way to checkpoint and restore long running > > jobs. > > * Container migration as non-root > > * We have been in contact with JVM developers who are integrating > > CRIU into a Java VM to decrease the startup time. These checkpoint/restore > > applications are not meant to be running with CAP_SYS_ADMIN. > > > > We have seen the following workarounds: > > * Use a setuid wrapper around CRIU: > > See https://github.com/FredHutch/slurm-examples/blob/master/checkpointer/lib/checkpointer/checkpointer-suid.c > > * Use a setuid helper that writes to ns_last_pid. > > Unfortunately, this helper delegation technique is impossible to use with > > clone3, and is thus prone to races. > > See https://github.com/twosigma/set_ns_last_pid > > * Cycle through PIDs with fork() until the desired PID is reached: > > This has been demonstrated to work with cycling rates of 100,000 PIDs/s > > See https://github.com/twosigma/set_ns_last_pid > > * Patch out the CAP_SYS_ADMIN check from the kernel > > * Run the desired application in a new user and PID namespace to provide > > a local CAP_SYS_ADMIN for controlling PIDs. This technique has limited use in > > typical container environments (e.g., Kubernetes) as /proc is > > typically protected with read-only layers (e.g., /proc/sys) for hardening > > purposes. Read-only layers prevent additional /proc mounts (due to proc's > > SB_I_USERNS_VISIBLE property), making the use of new PID namespaces limited as > > certain applications need access to /proc matching their PID namespace. > > > > The introduced capability allows to: > > * Control PIDs when the current user is CAP_CHECKPOINT_RESTORE capable > > for the corresponding PID namespace via ns_last_pid/clone3. > > * Open files in /proc/pid/map_files when the current user is > > CAP_CHECKPOINT_RESTORE capable in the root namespace, useful for recovering > > files that are unreachable via the file system such as deleted files, or memfd > > files. > > > > See corresponding selftest for an example with clone3(). > > > > Signed-off-by: Adrian Reber > > Signed-off-by: Nicolas Viennot > > --- > > I think that now looks reasonable. A few comments. > > Before we proceed, please split the addition of > checkpoint_restore_ns_capable() out into a separate patch. > In fact, I think the cleanest way of doing this would be: > - 0/n capability: add CAP_CHECKPOINT_RESTORE > - 1/n pid: use checkpoint_restore_ns_capable() for set_tid > - 2/n pid_namespace: use checkpoint_restore_ns_capable() for ns_last_pid > - 3/n: proc: require checkpoint_restore_ns_capable() in init userns for map_files > > (commit subjects up to you of course) and a nice commit message for each > time we relax a permissions on something so we have a clear separate > track record for each change in case we need to revert something. Then > the rest of the patches in this series. Testing patches probably last. Yes, makes sense. I was thinking about this already, but I was not sure if it I should do it or not. But I had the same idea already. Adrian