From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759437AbZE3Wnj (ORCPT ); Sat, 30 May 2009 18:43:39 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759185AbZE3Wm5 (ORCPT ); Sat, 30 May 2009 18:42:57 -0400 Received: from mx2.redhat.com ([66.187.237.31]:48855 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759224AbZE3Wm4 (ORCPT ); Sat, 30 May 2009 18:42:56 -0400 Date: Sun, 31 May 2009 00:38:24 +0200 From: Oleg Nesterov To: Roland McGrath Cc: Christoph Hellwig , Ingo Molnar , linux-kernel@vger.kernel.org Subject: [RFC PATCH 01/12 v3] ptrace: ptrace_signal: fix the usage of ->parent Message-ID: <20090530223824.GA30478@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline 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 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. Hopefully this "signr != info->si_signo" code will go away eventually. Signed-off-by: Oleg Nesterov --- kernel/signal.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) --- PTRACE/kernel/signal.c~01_PTRACE_SIGNAL 2009-05-30 21:30:04.000000000 +0200 +++ PTRACE/kernel/signal.c 2009-05-30 21:52:00.000000000 +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. */