linux-kernel - Re: [RFC PATCH] tmpfs: support user quotas

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Date:	Mon, 7 Nov 2011 15:27:36 +0100
From:	Kay Sievers <kay.sievers@...y.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Davidlohr Bueso <dave@....org>,
	Lennart Poettering <mzxreary@...inter.de>,
	Christoph Hellwig <hch@...radead.org>,
	Hugh Dickins <hughd@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	lkml <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: [RFC PATCH] tmpfs: support user quotas

On Mon, Nov 7, 2011 at 14:58, Alan Cox <alan@...rguk.ukuu.org.uk> wrote:
>> Right, rlimit approach guarantees a simple way of dealing with users
>> across all tmpfs instances.
>
> Which is almost certainly not what you want to happen. Think about direct
> rendering.
>
> For simple stuff tmpfs already supports size/nr_blocks/nr_inodes mount
> options so you can mount private resource constrained tmpfs objects
> already without kernel changes. No rlimit hacks needed - and rlimit is
> the wrong API anyway.

What part of the message did you read? This is about _per_user_
limits, not global limits!

Any untrusted user can fill /dev/shm today and DOS many services that
way on any machine out there. Same for /tmp when it's a tmpfs, or
/run/user. This is an absolutely unacceptable state and needs fixing.

I don't care about which interface it is, if someting else fits
better, let's discuss that, but it has surely absolutely noting to do
with size/nr_blocks/nr_inodes.

Kay
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