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

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Message-ID: <CAG48ez3rh2a3PYRRkcu50LU9qPCaeOE8BJL=AmTwDD3qcA+xFA@mail.gmail.com>
Date:   Mon, 25 May 2020 23:53:10 +0200
From:   Jann Horn <jannh@...gle.com>
To:     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>,
        Radostin Stoyanov <rstoyanov1@...il.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 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.