linux-kernel - Re: [Security] [PATCH] kernel: make /proc/kallsyms mode 400 to reduce ease of attacking

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Date:	Sun, 7 Nov 2010 13:32:32 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Willy Tarreau <w@....eu>
Cc:	Marcus Meissner <meissner@...e.de>, security@...nel.org,
	mort@....com, Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	fweisbec@...il.com, "H. Peter Anvin" <hpa@...or.com>,
	linux-kernel@...r.kernel.org, jason.wessel@...driver.com,
	tj@...nel.org, Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [Security] [PATCH] kernel: make /proc/kallsyms mode 400 to
 reduce ease of attacking


* Willy Tarreau <w@....eu> wrote:

> On Sun, Nov 07, 2010 at 01:12:35PM +0100, Ingo Molnar wrote:
> > 
> > * Willy Tarreau <w@....eu> wrote:
> > 
> > > [...]
> > >
> > > It's precisely because you're making a special case of the security bug that you 
> > > want to hide bugs from user-space by cheating on version.
> > 
> > You claimed this for the second time and i'm denying it for the second time.
> > 
> > The goal of fuzzing the version inforation is _not_ to 'hide bugs from user-space by 
> > cheating on version'. The goal is to introduce uncertainty to attackers, so that a 
> > honeypot silent alarm can warn the admin.
> 
> My interpretation of this mechanism is what I explained above. [...]

( Well, if it's "your interpretation" only then stop claiming that i said it. )

> [...] "Introducing uncertainty" means hiding a version so that the attacker 
> doesn't precisely know which one it is and has to send a few probes to guess it.

No. The 'exploit honeypot' mechanism i outlined is really simple, and it means what 
i explained already:

 - attacker breaks into unprivileged user-space

 - attacker runs exploit

 - exploit attempt gets detected by the 'exploit honeypot' kernel code and a 
   (silent) warning goes to the admin (via a syslog message for example)

 - attacker only sees that the attack did not succeed

This makes it _unsafe_ (for many types of attackers) to run an exploit locally.

> That's not much different than trying to fire the exploit itself. [...]

Erm, the difference is possible _detection_ via a silent alarm.

There's a huge difference between 'attempting an exploit and being caught' and 'not 
even trying the exploit because based on the kernel version the attacker knows it 
wont work'.

Thanks,

	Ingo
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