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Wed, 10 Jun 2020 15:41:36 +0000 Received: by smtp417.mail.ne1.yahoo.com (VZM Hermes SMTP Server) with ESMTPA ID b1c42b13e2ba96e7a3e09345eb0d59fe; Wed, 10 Jun 2020 15:41:32 +0000 (UTC) Subject: Re: [PATCH v2 1/3] capabilities: Introduce CAP_CHECKPOINT_RESTORE To: Andrei Vagin , Christian Brauner Cc: Adrian Reber , Eric Biederman , Pavel Emelyanov , Oleg Nesterov , Dmitry Safonov <0x7f454c46@gmail.com>, 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 , linux-fsdevel@vger.kernel.org, Casey Schaufler References: <20200603162328.854164-1-areber@redhat.com> <20200603162328.854164-2-areber@redhat.com> <20200609034221.GA150921@gmail.com> <20200609074422.burwzfgwgqqysrzh@wittgenstein> <20200609160627.GA163855@gmail.com> <20200609161427.4eoozs3kkgablmaa@wittgenstein> <20200610075928.GA172301@gmail.com> From: Casey Schaufler Autocrypt: addr=casey@schaufler-ca.com; 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WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: <20200610075928.GA172301@gmail.com> Content-Type: text/plain; charset=koi8-r Content-Transfer-Encoding: 7bit Content-Language: en-US X-Mailer: WebService/1.1.16072 hermes_yahoo Apache-HttpAsyncClient/4.1.4 (Java/11.0.6) Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: On 6/10/2020 12:59 AM, Andrei Vagin wrote: > On Tue, Jun 09, 2020 at 06:14:27PM +0200, Christian Brauner wrote: >> On Tue, Jun 09, 2020 at 09:06:27AM -0700, Andrei Vagin wrote: >>> On Tue, Jun 09, 2020 at 09:44:22AM +0200, Christian Brauner wrote: >>>> On Mon, Jun 08, 2020 at 08:42:21PM -0700, Andrei Vagin wrote: > ... >>>>> PTRACE_O_SUSPEND_SECCOMP is needed for C/R and it is protected by >>>>> CAP_SYS_ADMIN too. >>>> This is currently capable(CAP_SYS_ADMIN) (init_ns capable) why is it >>>> safe to allow unprivileged users to suspend security policies? That >>>> sounds like a bad idea. > ... >>> I don't suggest to remove or >>> downgrade this capability check. The patch allows all c/r related >>> operations if the current has CAP_CHECKPOINT_RESTORE. >>> >>> So in this case the check: >>> if (!capable(CAP_SYS_ADMIN)) >>> return -EPERM; >>> >>> will be converted in: >>> if (!capable(CAP_SYS_ADMIN) && !capable(CAP_CHECKPOINT_RESTORE)) >>> return -EPERM; >> Yeah, I got that but what's the goal here? Isn't it that you want to >> make it safe to install the criu binary with the CAP_CHECKPOINT_RESTORE >> fscap set so that unprivileged users can restore their own processes >> without creating a new user namespace or am I missing something? The >> use-cases in the cover-letter make it sound like that's what this is >> leading up to: >>>>>> * 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. >> But maybe I'm just misunderstanding crucial bits (likely (TM)). > I think you understand this right. The goal is to make it possible to > use C/R functionality for unprivileged processes. Y'all keep saying "unprivileged processes" when you mean "processes with less than root privilege". A process with CAP_CHECKPOINT_RESTORE *is* a privileged process. It would have different privilege from a process with CAP_SYS_ADMIN (the current case) but is not "unprivileged". > And for me, here are > two separate tasks. The first one is how to allow unprivileged users to > use C/R from the root user namespace. This is what we discuss here. > > And another one is how to allow to use C/R functionality from a non-root > user namespaces. The second task is about downgrading capable to > ns_capable for map_files and PTRACE_O_SUSPEND_SECCOMP. > > Thanks, > Andrei