linux-kernel - Re: [PATCH 12/13] hrtimer: create a "timer

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Date:	Sun, 14 Sep 2008 09:04:08 -0700
From:	"Ulrich Drepper" <drepper@...il.com>
To:	"Pavel Machek" <pavel@...e.cz>
Cc:	"Arjan van de Ven" <arjan@...radead.org>,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	dwmw2@...radead.org, drepper@...hat.com, mingo@...e.hu,
	tglx@...x.de
Subject: Re: [PATCH 12/13] hrtimer: create a "timer_slack" field in the task struct

On Sun, Sep 14, 2008 at 8:57 AM, Pavel Machek <pavel@...e.cz> wrote:
>> LD_PRELOAD and other variables are ignored in security-relevant
>> contexts and environments are cleared in many situations.  Sure, you
>
> ...but that's okay, right? You would not want passwd to inherit huge
> slack specified by attacker...?

No, it's not OK.  There are enough apps which are privileged and need
to be handled this way.  Take the X server, for instance.

]
> Well, it is not too much, but... is the cost for userspace really
> significant? You'd clearly want it stored in environment, not
> filesystem...

You cannot really use the environment for anything meaningful.
Especially for this case, you couldn't change the setting for a
running process.  What a fully-userlevel implementation would have to
do is read the value from a file and monitor the file for changes for
every new poll/select call.  That's a huge cost.
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