From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756067AbZHMUCU (ORCPT ); Thu, 13 Aug 2009 16:02:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756056AbZHMUCQ (ORCPT ); Thu, 13 Aug 2009 16:02:16 -0400 Received: from kroah.org ([198.145.64.141]:41978 "EHLO coco.kroah.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932310AbZHMUAM (ORCPT ); Thu, 13 Aug 2009 16:00:12 -0400 X-Mailbox-Line: From gregkh@mini.kroah.org Thu Aug 13 12:51:34 2009 Message-Id: <20090813195134.782760213@mini.kroah.org> User-Agent: quilt/0.48-1 Date: Thu, 13 Aug 2009 12:50:44 -0700 From: Greg KH To: linux-kernel@vger.kernel.org, stable@kernel.org Cc: stable-review@kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Oleg Nesterov , Serge Hallyn , James Morris Subject: [patch 69/74] mm_for_maps: take ->cred_guard_mutex to fix the race with exec References: <20090813194935.985368088@mini.kroah.org> Content-Disposition: inline; filename=mm_for_maps-take-cred_guard_mutex-to-fix-the-race-with-exec.patch In-Reply-To: <20090813195705.GA22393@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2.6.30-stable review patch. If anyone has any objections, please let us know. ------------------ From: Oleg Nesterov commit 704b836cbf19e885f8366bccb2e4b0474346c02d upstream. The problem is minor, but without ->cred_guard_mutex held we can race with exec() and get the new ->mm but check old creds. Now we do not need to re-check task->mm after ptrace_may_access(), it can't be changed to the new mm under us. Strictly speaking, this also fixes another very minor problem. Unless security check fails or the task exits mm_for_maps() should never return NULL, the caller should get either old or new ->mm. Signed-off-by: Oleg Nesterov Acked-by: Serge Hallyn Signed-off-by: James Morris Signed-off-by: Greg Kroah-Hartman --- fs/proc/base.c | 22 +++++++++++----------- 1 file changed, 11 insertions(+), 11 deletions(-) --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -234,19 +234,19 @@ static int check_mem_permission(struct t struct mm_struct *mm_for_maps(struct task_struct *task) { - struct mm_struct *mm = get_task_mm(task); + struct mm_struct *mm; - if (mm && mm != current->mm) { - /* - * task->mm can be changed before security check, - * in that case we must notice the change after. - */ - if (!ptrace_may_access(task, PTRACE_MODE_READ) || - mm != task->mm) { - mmput(mm); - mm = NULL; - } + if (mutex_lock_killable(&task->cred_exec_mutex)) + return NULL; + + mm = get_task_mm(task); + if (mm && mm != current->mm && + !ptrace_may_access(task, PTRACE_MODE_READ)) { + mmput(mm); + mm = NULL; } + mutex_unlock(&task->cred_exec_mutex); + return mm; }