From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261618AbTELAVK (ORCPT ); Sun, 11 May 2003 20:21:10 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261666AbTELAVJ (ORCPT ); Sun, 11 May 2003 20:21:09 -0400 Received: from crack.them.org ([146.82.138.56]:52101 "EHLO crack.them.org") by vger.kernel.org with ESMTP id S261618AbTELAUu (ORCPT ); Sun, 11 May 2003 20:20:50 -0400 Date: Sun, 11 May 2003 20:33:16 -0400 From: Daniel Jacobowitz To: Bernhard Kaindl Cc: Chuck Ebbert <76306.1226@compuserve.com>, Carl-Daniel Hailfinger , linux-kernel , Ingo Oeser Subject: Re: Problem: strace -ff fails on 2.4.21-rc1 Message-ID: <20030512003316.GA2167@nevyn.them.org> Mail-Followup-To: Bernhard Kaindl , Chuck Ebbert <76306.1226@compuserve.com>, Carl-Daniel Hailfinger , linux-kernel , Ingo Oeser References: <200305111140_MC3-1-385D-EEF@compuserve.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 12, 2003 at 01:50:01AM +0200, Bernhard Kaindl wrote: > On Sun, 11 May 2003, Chuck Ebbert wrote: > > Carl-Daniel Hailfinger wrote: > > > Chuck Ebbert wrote: > > > > I just found out minicom is spawing /sbin/lockdev which is setgrp > > > > 'lock'. Would that cause ptrace failure?? > > > > > > AFAIK that could have caused the failure. Please test 2.4.21-rc2 whcih > > > has fixes for many ptrace problems. > > > > I can now strace minicom and its children with 2.4.21-rc2-ac1 but it > > hangs on exit. Both child processes exit successfully: > > Very strange, does this work with 2.4.20? What's your version of strace? > > > However strace and minicom are hung up somehow and the screen is > > black with a blinking cursor at row 1 column 1. The other ttys all > > work OK and killing minicom cleans everything up. > > Hm, this sounds like there could be some error/loop opening the device, > which could be the effect of another side effect of the original ptrace > fix, which my fixes which are included in 2.4.21-rc2 don't fix. > > This side effect causes that if a system call needs a module loaded, > it is not loaded and only an error from request_module() is sent to > the kernel log. The attached patch on top of 2.4.21-rc2, fixes this > remaining problem. > > I'm not writing much info about it now, except that I think that it does > not open any securiy hole, but I would like to give it a little more > testing on SMP machines. On single CPU it fixed the "modprobe rejected" > problem fine for me, without sacrifying ptrace securitey. > > I'm uncertain if it would help in your case. > > In your first message, you wrote: > > > (BTW does minicom work for you on 2.5? It fails with the "No child > > processes" message on 2.5.6x here but works on 2.4 when it's not being > > traced. Just the very act of running it under strace on 2.4 makes it > > fail the same way it does on 2.5 here. And stracing it on 2.5.66 made > > it start working again! Something very strange is going on...) > > Very strange, maybe a "tail minicom.trc.*" at the time when it's hanging > helps to get some idea. > > Another note: suid is ignored when you are tracing the task which runs > exec() for a setuid program. > > So if minicom relies on having the setgid gid of /sbin/lockdev honored > has in your case, the only ways I can find to get it working inder strace are: > > - Change the locking config (temporary, for the debug) so that /sbin/lockdev > does not need to be setgid. > > - Don't have ptrace follow fork mode activated when forking the child > which exec()'s /sbin/lockdev. Run strace as root, and use strace -u? Then it should not remove the setuid-ness, I think. -- Daniel Jacobowitz MontaVista Software Debian GNU/Linux Developer