linux-kernel - Re: [patch 2/2] ufd v1 - use unsequential O(1) fdmap

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Date:	Sun, 03 Jun 2007 13:46:21 -0700
From:	Ulrich Drepper <drepper@...hat.com>
To:	Davide Libenzi <davidel@...ilserver.org>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [patch 2/2] ufd v1 - use unsequential O(1) fdmap

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Davide Libenzi wrote:
>> If randomizing each allocator is too expensive then randomize at the
>> very least the number of the first descriptor you give out.
> 
> Can you tell me how this can be a problem, and in which way making a 
> random thing would help?

In attacking an application every bit of known data can be used in an
exploit.  Be it something as simple as having a predetermined value at a
certain point in the program since it loaded a file descriptor into a
register.

But what I'm mostly thinking about is the case where I/O could be
redirected.  The intruding program could call dup2() and suddenly the
program wanting to write a password to disk could be directed to send it
over a socket.  One could imagine countless such attacks.

I don't say such an attack exists today.  But this is no reason to not
implement these extra security measures.  The cost of a randomized star
base (offset from 2^30) should be zero.

- --
➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖
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