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

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Date:	Mon, 29 Nov 2010 14:21:33 -0500
From:	Eric Paris <eparis@...isplace.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Marcus Meissner <meissner@...e.de>,
	linux-kernel@...r.kernel.org, tj@...nel.org,
	akpm@...ux-foundation.org, w@....eu, alan@...rguk.ukuu.org.uk,
	serue@...ibm.com, LSM List <linux-security-module@...r.kernel.org>,
	James Morris <jmorris@...ei.org>
Subject: Re: [PATCH] kernel: make /proc/kallsyms mode 400 to reduce ease of attacking

On Mon, Nov 29, 2010 at 2:05 PM, H. Peter Anvin <hpa@...or.com> wrote:
> On 11/29/2010 10:04 AM, Ingo Molnar wrote:
>>
>> * Sarah Sharp <sarah.a.sharp@...ux.intel.com> wrote:
>>
>>> On Fri, Nov 26, 2010 at 08:48:09AM +0100, Ingo Molnar wrote:

>>>> Sarah,
>>>>
>>>> Does your system boot fine if we make /proc/kallsyms simply an empty file to
>>>> unprivileged users? Something like the (untested ...) patch below.
>>>
>>> Yes, that works.  The system boots as normal. `cat /proc/kallsyms`
>>> returns an empty file, and `sudo cat /proc/kallsyms` does not.
>>
>> Great! Marcus, mind respinning your patch with that approach?
>>
>
> Can we please not use CAP_SYS_ADMIN for this?  Relying on CAP_SYS_ADMIN
> is worse than anything else -- it is a fixed policy hardcoded in the
> kernel, with no ability for the system owner to delegate the policy
> outward, e.g. by adding group read permission and/or chgrp the file.
>
> Delegating CAP_SYS_ADMIN, of course, otherwise known as "everything", is
> worse than anything...

Serge just proposed a new CAP_SYSLOG

http://lwn.net/Articles/378472/

Which could probably still be renamed and used to cover this access as well....
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