Subject: Re: [kernel-hardening] Re: [PATCH v2 1/1] Add Trusted Path
 Execution as a stackable LSM
From: Mimi Zohar <zohar@linux.vnet.ibm.com>
To: Matt Brown <matt@nmatt.com>, Kees Cook <keescook@chromium.org>
Cc: James Morris <james.l.morris@oracle.com>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-security-module <linux-security-module@vger.kernel.org>,
        "kernel-hardening@lists.openwall.com" 
        <kernel-hardening@lists.openwall.com>
Date: Fri, 09 Jun 2017 09:44:38 -0400
In-Reply-To: <e92c4476-8480-1f35-1777-b6fb1400c462@nmatt.com>
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         <94ba5ebb-952b-2037-799e-07306629a6f9@nmatt.com>
         <1497003507.21594.177.camel@linux.vnet.ibm.com>
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On Fri, 2017-06-09 at 09:18 -0400, Matt Brown wrote:
> On 6/9/17 9:16 AM, Mimi Zohar wrote:
> > On Fri, 2017-06-09 at 05:55 -0700, Kees Cook wrote:
> >> On Fri, Jun 9, 2017 at 3:18 AM, Mimi Zohar <zohar@linux.vnet.ibm.com> wrote:
> >>> On Thu, 2017-06-08 at 23:50 -0400, Matt Brown wrote:
> >>>>>>
> >>>>>> *  Issues:
> >>>>>>    *  Can be bypassed by interpreted languages such as python. You can run
> >>>>>>       malicious code by doing: python -c 'evil code'
> >>>>>
> >>>>> What's the recommendation for people interested in using TPE but
> >>>>> having interpreters installed?
> >>>>>
> >>>>
> >>>> If you don't need a given interpreter installed, uninstall it. While
> >>>> this is common sense system hardening it especially would make a
> >>>> difference under the TPE threat model.
> >>>>
> >>>> I don't have a knock down answer for this. Interpreters are a hard
> >>>> problem for TPE.
> >>>
> >>> You might be interested in the minor LSM named "shebang", that I
> >>> posted as a proof of concept back in January, which restricts the
> >>> python interactive prompt/interpreter, but allows the scripts
> >>> themselves to be executed.
> >>
> >> https://patchwork.kernel.org/patch/9547405/
> >>
> >> Maybe these could be merged and the interpreter string could be made
> >> into a configurable list?
> > 
> > I updated shebang, but didn't bother to post it, as nobody seemed to
> > be interested at the time.  The updated version already has support
> > for the configurable list. Re-posting ...
> > 
> 
> That would be awesome. I think it's the perfect complement to TPE as it
> protects a key hole in its current threat model.

Hm, I hadn't looked at it in since January.  It still needs to be
cleaned up and expanded a bit.  The original version used a pathname
for identifying the interpreter.  This version converts the list of
pathnames to a set of inodes, which is better, but now requires a
method for updating the inode number after a software update.

Please feel free to expand on it or re-use whatever you like.

Mimi