linux-kernel - Re: [PATCH] capabilities: Introduce CAP

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Date:   Tue, 26 May 2020 10:09:22 +0100
From:   Radostin Stoyanov <rstoyanov1@...il.com>
To:     Jann Horn <jannh@...gle.com>, Adrian Reber <areber@...hat.com>
Cc:     Christian Brauner <christian.brauner@...ntu.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        Pavel Emelyanov <ovzxemul@...il.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Andrei Vagin <avagin@...il.com>,
        Nicolas Viennot <Nicolas.Viennot@...sigma.com>,
        Michał Cłapiński <mclapinski@...gle.com>,
        Kamil Yurtsever <kyurtsever@...gle.com>,
        Dirk Petersen <dipeit@...il.com>,
        Christine Flood <chf@...hat.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Serge Hallyn <serge@...lyn.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Sargun Dhillon <sargun@...gun.me>,
        Arnd Bergmann <arnd@...db.de>,
        Aaron Goidel <acgoide@...ho.nsa.gov>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        SElinux list <selinux@...r.kernel.org>,
        Eric Paris <eparis@...isplace.org>
Subject: Re: [PATCH] capabilities: Introduce CAP_RESTORE

On 25/05/2020 22:53, Jann Horn wrote:
> On Fri, May 22, 2020 at 7:55 AM Adrian Reber <areber@...hat.com> wrote:
>> This enables CRIU to checkpoint and restore a process as non-root.
>>
>> Over the last years CRIU upstream has been asked a couple of time if it
>> is possible to checkpoint and restore a process as non-root. The answer
>> usually was: 'almost'.
>>
>> The main blocker to restore a process was that selecting the PID of the
>> restored process, which is necessary for CRIU, is guarded by CAP_SYS_ADMIN.
> And if you were restoring the process into your own PID namespace, so
> that you actually have a guarantee that this isn't going to blow up in
> your face because one of your PIDs is allocated for a different
> process, this part of the problem could be simplified.
>
> I don't get why your users are fine with a "oh it kinda works 99% of
> the time but sometimes it randomly doesn't and then you have to go
> reboot or whatever" model.
Transparent checkpoint and restore of a process tree is not simple, 
especially when it is done entirely in user-space. To best of my 
knowledge, CRIU is the only tool out there that is able to achieve this, 
it is actively being tested and maintained, and it has been integrated 
into several container runtimes. Like any other software, CRIU has 
limitations but, as said in the README file, contributions are welcome.