From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756999AbZHGD0B (ORCPT ); Thu, 6 Aug 2009 23:26:01 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752166AbZHGD0A (ORCPT ); Thu, 6 Aug 2009 23:26:00 -0400 Received: from [222.73.24.84] ([222.73.24.84]:55464 "EHLO song.cn.fujitsu.com" rhost-flags-FAIL-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1751384AbZHGD0A (ORCPT ); Thu, 6 Aug 2009 23:26:00 -0400 Message-ID: <4A7B9E6B.2090202@cn.fujitsu.com> Date: Fri, 07 Aug 2009 11:24:27 +0800 From: Li Zefan User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1b3pre) Gecko/20090513 Fedora/3.0-2.3.beta2.fc11 Thunderbird/3.0b2 MIME-Version: 1.0 To: Steven Rostedt CC: Frederic Weisbecker , Ingo Molnar , LKML Subject: Re: [PATCH 3/3] tracing/filters: Support filtering for char * strings References: <4A7A72BD.5030201@cn.fujitsu.com> <4A7A72FA.9040102@cn.fujitsu.com> <4A7B8149.3070901@cn.fujitsu.com> <4A7B9BB5.3040005@cn.fujitsu.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Steven Rostedt wrote: > On Fri, 7 Aug 2009, Li Zefan wrote: >>> What protection is this giving us? >>> >> __field(char *) suggests it should be treated as plain pointer, >> while __field_ext(char *, FILTER_PTR_STR) suggests he's aware it's >> safe to dereference the pointer, for example the case in Frederic's >> blk events. >> >> In Frederic's initial version, "char *" field will always be >> attached to ptr_str filter function. This is unsafe, because for >> other fields defined as "char *" but not safe to dereference, >> a user still can do this: >> >> # echo 'name == abc' > filter >> >> Then we'll deref a pointer that can point to unsafe data. >> >> In this patch, this won't happen, as long as the developer is >> aware that his use of __field_ext(char *) is right. >> >> Otherwise, he will just use normal __field(char *) and print >> the pointer itself in TP_printk(). > > Ah, so the answer I'm looking for is: > > The filtering will not dereference "char *" unless the developer > explicitly sets FILTER_PTR_STR in __field_ext. > > Is this above statement correct? > Exactly. Sorry that I didn't explain it clearly in the first place. :)