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

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Date:	Fri, 5 Nov 2010 00:46:33 +0100
From:	Willy Tarreau <w@....eu>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	security@...nel.org, Marcus Meissner <meissner@...e.de>,
	mort@....com, Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	fweisbec@...il.com, jason.wessel@...driver.com,
	linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.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 Thu, Nov 04, 2010 at 11:35:26PM +0100, Willy Tarreau wrote:
> > The point is to make it riskier to run exploits - not to 'hide version because we 
> > are so buggy'. Unprivileged attackers wont be able to know whether a kernel is 
> > unpatched and wont know whether trying an actual exploit triggers a silent alarm or 
> > not.
> 
> In my opinion, hiding the distro-specific part of the version should not cause
> too much harm, but still I find this useless.

BTW, if you want to hide the kernel version for the 99% distro kernels,
there's a very simple way to do that : just don't bump EXTRAVERSION nor
the build date in official builds. Keep it the same for all the product's
life, and provide the real name in a /proc entry that is only readable by
root by default. This will solve your issue with the exact kernel version
revealing pointers/bugs without hurting compatibility with user space
tools.

That will not hide the hints I was talking about though (uptime, dir mod
time, ...) but it will provide you with a version unrelated to the bug
level.

Regards,
Willy

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