linux-kernel - Re: [RFC PATCH] cpuset: Allow setscheduler regardless of manipulated task

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Message-ID: <YraNDoxU9IZaP3RV@mtj.duckdns.org>
Date:   Sat, 25 Jun 2022 13:20:30 +0900
From:   Tejun Heo <tj@...nel.org>
To:     Michal Koutný <mkoutny@...e.com>
Cc:     cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Waiman Long <longman@...hat.com>
Subject: Re: [RFC PATCH] cpuset: Allow setscheduler regardless of manipulated
 task

Hello,

On Thu, Jun 23, 2022 at 02:49:44PM +0200, Michal Koutný wrote:
> 1) The unified hierarchy attachment behavior -- is that the
>    right/consented model that migrated objects don't matter?

Yes.

> 2) If 1) is true, have I missed any danger in allowing cpuset'ing a
>    possibly privileged processes?

Given that the someone who has write perm on the cgroup or its
ancestors are allowed to change cpuset config itself, I have a hard
time imagining that check being all that useful as a security
mechanism.

> 2.2) cpuset may be in v2 mode even on v1 hierarchy with different
>    migration control rules (but checking migratee's creds in v1
>    eliminates effect of this patch).

Yeah, it should be fine to apply the change only to v2.

> 3) Alternative approach would be to allow cpuset migrations only when
>    nothing effectively changes (which is the case for parent->child
>    migration upon controller enablement).
> 
> 4) This is just idea draft, not tested in the real case.

Unless I'm missing something obvious, I don't see a reason to keep the
check, so please feel free to test and send a SOB'd patch.

Thanks.

-- 
tejun