linux-kernel - Re: [PATCH 1/2] procfs: restore 0400 permissions on /proc/*/{syscall,stack,personality}

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Message-ID: <524E118F.9080503@gmail.com>
Date:	Fri, 04 Oct 2013 10:53:35 +1000
From:	Ryan Mallon <rmallon@...il.com>
To:	Kees Cook <keescook@...omium.org>,
	Djalal Harouni <tixxdz@...ndz.org>
CC:	Al Viro <viro@...iv.linux.org.uk>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Solar Designer <solar@...nwall.com>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	George Spelvin <linux@...izon.com>
Subject: Re: [PATCH 1/2] procfs: restore 0400 permissions on /proc/*/{syscall,stack,personality}

On 04/10/13 10:41, Kees Cook wrote:
> On Wed, Aug 28, 2013 at 1:49 PM, Kees Cook <keescook@...omium.org> wrote:

<snip>

> 
> BTW, this just came to my attention:
> http://marc.info/?l=linux-kernel&m=138049414321387&w=2
> 
> Same problem, just for /proc/kallsyms. This would benefit from the
> open vs read cred check as well, I think.

I was actually just about to put together a repost of this. Sorry I
missed you off the original Cc list, get_maintainer didn't list you.

I wanted to at least change the comment mentioning "badly written"
setuid binaries. That isn't really true, as George Spelvin pointed out,
even a setuid binary which opens the file with dropped priviledges, but
reads it after re-elevating privileges will be susceptible to this.

Setuid apps could be more precautious by doing the open + read into
memory of user files with the privileges dropped, so that once
privileges are re-elevated only the in-memory copy is used.

I still think in-kernel fixing is a good idea too though, since it
hardens against user-space setuid apps that don't do this. This was just
the simplest approach to fixing the problem that I could think of. I'm
open to suggestions for a better solution.

~Ryan

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