linux-kernel - Re: [PATCH -mm] vmscan: make mapped executable pages the first class citizen

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Date:	Thu, 7 May 2009 20:40:54 -0700
From:	Elladan <elladan@...imo.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	Christoph Lameter <cl@...ux.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Peter Zijlstra <peterz@...radead.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"tytso@....edu" <tytso@....edu>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Elladan <elladan@...imo.com>, Nick Piggin <npiggin@...e.de>,
	Johannes Weiner <hannes@...xchg.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Subject: Re: [PATCH -mm] vmscan: make mapped executable pages the first
	class citizen

On Thu, May 07, 2009 at 01:11:41PM -0400, Rik van Riel wrote:
> Christoph Lameter wrote:
>
>> We need some way to control this. If there would be a way to simply switch
>> off eviction of exec pages (via /proc/sys/vm/never_reclaim_exec_pages or
>> so) I'd use it.
>
> Nobody (except you) is proposing that we completely disable
> the eviction of executable pages.  I believe that your idea
> could easily lead to a denial of service attack, with a user
> creating a very large executable file and mmaping it.
>
> Giving executable pages some priority over other file cache
> pages is nowhere near as dangerous wrt. unexpected side effects
> and should work just as well.

I don't think this sort of DOS is relevant for a single user or trusted user
system.  

I don't know of any distro that applies default ulimits, so desktops are
already susceptible to the far more trivial "call malloc a lot" or "fork bomb"
attacks.  Plus, ulimits don't help, since they only apply per process - you'd
need a default mem cgroup before this mattered, I think.

Thanks,
Elladan

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