linux-kernel - Re: [RESEND RFC PATCH 0/1] CAP_SYS

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Date:   Mon, 18 Nov 2019 20:36:22 +0100
From:   Jann Horn <jannh@...gle.com>
To:     Prakash Sangappa <prakash.sangappa@...cle.com>
Cc:     kernel list <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Christian Brauner <christian@...uner.io>
Subject: Re: [RESEND RFC PATCH 0/1] CAP_SYS_NICE inside user namespace

On Mon, Nov 18, 2019 at 6:04 PM Prakash Sangappa
<prakash.sangappa@...cle.com> wrote:
> Some of the capabilities(7) which affect system wide resources, are ineffective
> inside user namespaces. This restriction applies even to root user( uid 0)
> from init namespace mapped into the user namespace. One such capability
> is CAP_SYS_NICE which is required to change process priority. As a result of
> which the root user cannot perform operations like increase a process priority
> using -ve nice value or set RT priority on processes inside the user namespace.
> A workaround to deal with this restriction is to use the help of a process /
> daemon running outside the user namespace to change process priority, which is
> a an inconvenience.

What is the goal here, in the big picture? Is your goal to allow
container admins to control the priorities of their tasks *relative to
each other*, or do you actually explicitly want container A to be able
to decide that its current workload is more timing-sensitive than
container B's?