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Date:   Sun, 24 May 2020 19:01:54 -0700
From:   Casey Schaufler <>
To:     Andrei Vagin <>
Cc:     Adrian Reber <>,
        Christian Brauner <>,
        Eric Biederman <>,
        Pavel Emelyanov <>,
        Oleg Nesterov <>,
        Dmitry Safonov <>,
        Nicolas Viennot <>,
        Michał Cłapiński <>,
        Kamil Yurtsever <>,
        Dirk Petersen <>,
        Christine Flood <>,
        Mike Rapoport <>,
        Radostin Stoyanov <>,
        Cyrill Gorcunov <>,
        Serge Hallyn <>,
        Stephen Smalley <>,
        Sargun Dhillon <>,
        Arnd Bergmann <>,
        Aaron Goidel <>,,,,
        Eric Paris <>,
        Jann Horn <>,
        Casey Schaufler <>
Subject: Re: [PATCH] capabilities: Introduce CAP_RESTORE

On 5/22/2020 9:27 PM, Andrei Vagin wrote:
> On Fri, May 22, 2020 at 09:40:37AM -0700, Casey Schaufler wrote:
>> On 5/21/2020 10:53 PM, Adrian Reber wrote:
>>> There are probably a few more things guarded by CAP_SYS_ADMIN required
>>> to run checkpoint/restore as non-root,
>> If you need CAP_SYS_ADMIN anyway you're not gaining anything by
>> separating out CAP_RESTORE.
>>>  but by applying this patch I can
>>> already checkpoint and restore processes as non-root. As there are
>>> already multiple workarounds I would prefer to do it correctly in the
>>> kernel to avoid that CRIU users are starting to invent more workarounds.
>> You've presented a couple of really inappropriate implementations
>> that would qualify as workarounds. But the other two are completely
>> appropriate within the system security policy. They don't "get around"
>> the problem, they use existing mechanisms as they are intended.
> With CAP_CHECKPOINT_RESTORE, we will need to use the same mechanisms.

Then why call them out as objectionable "workarounds"?

> The problem is that CAP_SYS_ADMIN is too wide.

This is well understood, and irrelevant.

If we broke out CAP_SYS_ADMIN properly we'd have hundreds of
capabilities, and no one would be able to manage the capability
sets on anything. Just breaking out of CAP_SYS_ADMIN, especially
if the process is going to need other capabilities anyway, gains
you nothing.

>  If a process has
> CAP_SYS_ADMIN, it can do a lot of things and  the operation of forking a
> process with a specified pid isn't the most dangerous one in this case.
> Offten security policies don't allow to grant CAP_SYS_ADMIN to any
> third-party tools even in non-root user namespaces.

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