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 12:41:56 +0100
From:	Willy Tarreau <w@....eu>
To:	Ingo Molnar <mingo@...e.hu>
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

On Sun, Nov 07, 2010 at 12:27:09PM +0100, Ingo Molnar wrote:
> > I don't understand the point you're trying to make with this patch. [...]
> 
> It was a simple experiement to support my rather simple argument which you disputed.

OK

> > [...] Obviously we can pretend to be any version, [...]
> 
> Ok, it's a pretty cavalier style of arguing that you now essentially turn around 
> your earlier claim that the 'kernel version is needed at many places' and say what 
> i've been saying, prefixed with 'obviously' ;-)

Huh ?

> Yes, it's obvious that the kernel version is not needed for many functional purposes 
> on a modern distro - and that was my exact point.
> 
> I cannot think of a single valid case where the proper user-space solution to some 
> ABI compatibility detail is a kernel version check.

Ingo, I believe you did not read a single line of my previous mail, because I
precisely gave you counter-examples of that. The first use is simply the user
running "uname -a" to see if *he* can safely enable feature X or Y which is
known to be badly broken in some old versions.

> I'd even argue that we want to 
> keep unprivileged user-space from being able to implement such crappy version checks 
> ...

I'd say that *YOU* want that despite the fact that on mainstream distros, it
buys nothing since it's easy to guess the real version anyway as I showed you.
Don't forget that you proposed this in order to hide symbols from a small set
of well-known distro kernels. And the most important in my opinion is that it
does not bring anything to those who are currently victim of exploits : those
who don't upgrade, because their uptime alone is enough to *know* that the
vuln you want to exploit is still there.

At some places, your proposal would probably end up with uname being
chmoded +s so that users stop asking the admin for trivial things. That
really makes no sense.

Willy

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