linux-kernel - Re: [PATCH v2 1/3] capabilities: Introduce CAP_CHECKPOINT

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Message-ID: <20200609034221.GA150921@gmail.com>
Date:   Mon, 8 Jun 2020 20:42:21 -0700
From:   Andrei Vagin <avagin@...il.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>,
        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>,
        Casey Schaufler <casey@...aufler-ca.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>,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, selinux@...r.kernel.org,
        Eric Paris <eparis@...isplace.org>,
        Jann Horn <jannh@...gle.com>, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] capabilities: Introduce CAP_CHECKPOINT_RESTORE

On Wed, Jun 03, 2020 at 06:23:26PM +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.
> 
...
> 
> 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.

PTRACE_O_SUSPEND_SECCOMP is needed for C/R and it is protected by
CAP_SYS_ADMIN too.

Thanks,
Andrei