From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753908AbbIWJ5N (ORCPT ); Wed, 23 Sep 2015 05:57:13 -0400 Received: from mail-pa0-f53.google.com ([209.85.220.53]:34076 "EHLO mail-pa0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753014AbbIWJ5L (ORCPT ); Wed, 23 Sep 2015 05:57:11 -0400 Date: Wed, 23 Sep 2015 18:57:57 +0900 From: Sergey Senozhatsky To: Michal Hocko Cc: Vladimir Davydov , Sergey Senozhatsky , David Rientjes , Andrew Morton , Oleg Nesterov , Linus Torvalds , Kyle Walker , Christoph Lameter , Johannes Weiner , linux-mm , Linux Kernel Mailing List , Stanislav Kozina , Tetsuo Handa Subject: Re: [patch] mm, oom: remove task_lock protecting comm printing Message-ID: <20150923095757.GC640@swordfish> References: <20150923080632.GD12318@esperanza> <20150923091354.GA640@swordfish> <20150923093021.GE12318@esperanza> <20150923094358.GB8644@dhcp22.suse.cz> <20150923095022.GB640@swordfish> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150923095022.GB640@swordfish> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (09/23/15 18:50), Sergey Senozhatsky wrote: > On (09/23/15 11:43), Michal Hocko wrote: > [..] > > > > the previous name was already null terminated, > > > > > > Yeah, but if the old name is shorter than the new one, set_task_comm() > > > overwrites the terminating null of the old name before writing the new > > > terminating null, so there is a short time window during which tsk->comm > > > might be not null-terminated, no? > > > > Not really: > > case PR_SET_NAME: > > comm[sizeof(me->comm) - 1] = 0; > > if (strncpy_from_user(comm, (char __user *)arg2, > > sizeof(me->comm) - 1) < 0) > > return -EFAULT; > > > > So it first writes the terminating 0 and only then starts copying. > > right. ... no right. that should have been me->comm[sizeof(me->comm) - 1] = 0; to be save. no? > hm, shouldn't set_task_comm()->__set_task_comm() do the same? or something like this instead --- fs/exec.c | 1 + 1 file changed, 1 insertion(+) diff --git a/fs/exec.c b/fs/exec.c index b06623a..d7d2de0 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1072,6 +1072,7 @@ EXPORT_SYMBOL_GPL(get_task_comm); void __set_task_comm(struct task_struct *tsk, const char *buf, bool exec) { + tsk->comm[sizeof(tsk->comm) - 1] = 0; task_lock(tsk); trace_task_rename(tsk, buf); strlcpy(tsk->comm, buf, sizeof(tsk->comm));