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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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