Date: Thu, 21 Jun 2007 20:05:57 +0200
From: Adrian Bunk <bunk@stusta.de>
To: Alexander Wuerstlein <snalwuer@cip.informatik.uni-erlangen.de>
Cc: Alexander Wuerstlein <arw@arw.name>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] signed binaries support [0/4]
Message-ID: <20070621180557.GR12950@stusta.de>
References: <20070621155516.GA6838@faui01.informatik.uni-erlangen.de> <20070621161758.GP12950@stusta.de> <20070621162917.GB9741@cip.informatik.uni-erlangen.de> <20070621172344.GQ12950@stusta.de> <20070621173445.GF9741@cip.informatik.uni-erlangen.de>
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On Thu, Jun 21, 2007 at 07:34:45PM +0200, Alexander Wuerstlein wrote:
> On 070621 19:26, Adrian Bunk <bunk@stusta.de> wrote:
> > On Thu, Jun 21, 2007 at 06:29:17PM +0200, Alexander Wuerstlein wrote:
> > > On 070621 18:19, Adrian Bunk <bunk@stusta.de> wrote:
> > > > On Thu, Jun 21, 2007 at 05:55:16PM +0200, Johannes Schlumberger wrote:
> > > > 
> > > > > Hi,
> > > > 
> > > > Hi Johannes,
> > > > 
> > > > > We (two students of CS) built a system for signing binaries and verifying them
> > > > > before executing. Our main focus was to implement a way to inhibit execution
> > > > > of suid-binaries, which are not trustworthy (i.e. not signed).
> > > > >...
> > > > 
> > > > doesn't anyone who is able to install a not trustworthy suid-binary 
> > > > already have the priviliges to do anything he wants to without requiring 
> > > > an suid bit?
> > > 
> > > Yes, quite correct in most cases. But if you have taken control of a computer
> > > on of the more common ways to keep the control for some time is the
> > > installation of a suid-binary (e.g. as part of a rootkit). 
> > 
> > There are so many ways for manipulating a computer that controlling 
> > setuid binaries hardly brings a real security gain.
> 
> Even if it does not really improve security too much it can be helpful as a
> part of a larger system. For example around here we use a 'sbit-checker' that
> basically does a 'find' and 'chmod', which we would be able to replace by this
> patch.

Something that sounds as if it would increase security but doesn't 
really increase security is actually bad since it gives users a false 
impression of security.

> Also our patch is not solely about suid-binaries, we just implemented
> suid-checking because it seemed a simple and obvious thing to do.  Our real aim
> was to implement binary signatures, which can be used in numerous security
> related checks around the kernel. Btw. if you have any good ideas where one
> could use them, please tell us :)

Linux systems usually ship and heavily use interpreters like bash, perl 
or python.

Does writing an ELF loader in perl circumvent everything you want to do?

> Ciao,
> Alexander Wuerstlein.

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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