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

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Date:	Sun, 3 Jun 2007 16:01:52 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Ulrich Drepper <drepper@...hat.com>
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

On Sun, 3 Jun 2007, Ulrich Drepper wrote:

> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> 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.

Randomizing the base is not a problem. Should this be always, or flag 
driven?



- Davide


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