From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756504AbZE1C6s (ORCPT ); Wed, 27 May 2009 22:58:48 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753010AbZE1C6k (ORCPT ); Wed, 27 May 2009 22:58:40 -0400 Received: from mx2.redhat.com ([66.187.237.31]:38624 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751734AbZE1C6k (ORCPT ); Wed, 27 May 2009 22:58:40 -0400 Date: Thu, 28 May 2009 04:54:07 +0200 From: Oleg Nesterov To: Roland McGrath Cc: Christoph Hellwig , Ingo Molnar , linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 7/X] ptrace: mv task->parent ptrace_task->pt_tracer Message-ID: <20090528025407.GA22182@redhat.com> References: <20090525000016.GA2239@redhat.com> <20090525215903.GA9113@redhat.com> <20090527021131.4778BFC36B@magilla.sf.frob.com> <20090527224140.GC6770@redhat.com> <20090527230700.11F2DFC2BD@magilla.sf.frob.com> <20090527235936.GB12216@redhat.com> <20090528003256.86E4EFC2BD@magilla.sf.frob.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090528003256.86E4EFC2BD@magilla.sf.frob.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/27, Roland McGrath wrote: > > > OK, lets do this change later ;) > > Agreed. Damn. OTOH, it is so ugly to cache pid/uid for the very unlikely case. Roland, will you agree with the patch below? If yes, I'd like to send it separately. Oleg. ------------------------------------------------------------------- [PATCH -mm] ptrace: ptrace_signal: fix the usage of ->parent This patch complicates the code to fix the pure theoretical problems. But since we are going to change this code, it is better to fix them anyway. - If we are not traced any longer after ptrace_stop(), si_pid/si_uid are not necessary right. - It is not safe to dereference current->parent without tasklist or RCU lock. The tracer can detach and exit. ->siglock can't prevent this, and (in theory) local_irq_disable() doesn't imply RCU lock. Signed-off-by: Oleg Nesterov --- PTRACE/kernel/signal.c~PTRACE_SIGNAL 2009-05-28 04:12:02.000000000 +0200 +++ PTRACE/kernel/signal.c 2009-05-28 04:14:38.000000000 +0200 @@ -1770,11 +1770,22 @@ static int ptrace_signal(int signr, sigi specific in the siginfo structure then it should have updated *info via PTRACE_SETSIGINFO. */ if (signr != info->si_signo) { + struct task_struct *tracer; + info->si_signo = signr; info->si_errno = 0; info->si_code = SI_USER; - info->si_pid = task_pid_vnr(current->parent); - info->si_uid = task_uid(current->parent); + + rcu_read_lock(); + tracer = current->parent; + if (task_ptrace(current)) { + info->si_pid = task_pid_vnr(tracer); + info->si_uid = task_uid(tracer); + } else { + info->si_pid = 0; + info->si_uid = 0; + } + rcu_read_unlock(); } /* If the (new) signal is now blocked, requeue it. */