From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757161AbYEMNAK (ORCPT ); Tue, 13 May 2008 09:00:10 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756213AbYEMM7y (ORCPT ); Tue, 13 May 2008 08:59:54 -0400 Received: from bombadil.infradead.org ([18.85.46.34]:55413 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756621AbYEMM7x (ORCPT ); Tue, 13 May 2008 08:59:53 -0400 Subject: Re: System call audit From: David Woodhouse To: Mathieu Desnoyers Cc: linux-kernel@vger.kernel.org, mingo@redhat.com In-Reply-To: <20080513125120.GB29334@Krystal> References: <20080513000617.GA26009@Krystal> <1210670669.3582.219.camel@pmac.infradead.org> <20080513125120.GB29334@Krystal> Content-Type: text/plain Date: Tue, 13 May 2008 13:59:50 +0100 Message-Id: <1210683590.3582.242.camel@pmac.infradead.org> Mime-Version: 1.0 X-Mailer: Evolution 2.22.1 (2.22.1-2.fc9) Content-Transfer-Encoding: 7bit X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2008-05-13 at 08:51 -0400, Mathieu Desnoyers wrote: > * David Woodhouse (dwmw2@infradead.org) wrote: > > On Mon, 2008-05-12 at 20:06 -0400, Mathieu Desnoyers wrote: > > > Hi David, > > > > > > As I am looking into the system-wide system call tracing problem, I > > > start to wonder how auditsc deals with the fact that user-space could > > > concurrently change the content referred to by the __user pointers. > > > > In general we have to copy the content into kernel space, audit it, and > > then act on it from there. See the explanation on the IPC audit patch at > > http://lwn.net/Articles/125350/ for example. > > > > Auditing one thing and then acting on another would be simply broken. > > > > > This would be the case for execve. If we create a program with two > > > thread; one is executing execve syscalls and the other thread would be > > > modifying the userspace string containing the name of the program to > > > execute. > > > > I was going to suggest that that attack vector won't work, because > > execve() kills all threads. But all you have to do to avoid that is put > > the data in question into a shared writable mmap and modify it from > > another _process_. And in fact I suspect there's a combination of CLONE_ > > flags which would avoid the thread-killing behaviour anyway. > > > > Even better : if execve fails, it doesn't kill the threads. Therefore, > all we have to do is to busy-loop doing failing execve() calls and > atomically change the string to what we want to be executed. Can anyone > test the sample snippet in a context where executing /bin/bash is > disallowed on a SMP system ? I don't have a selinux setup handy. You were talking about audit earlier. Now you seem to be talking about selinux. -- dwmw2