From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753876AbcD1VSr (ORCPT ); Thu, 28 Apr 2016 17:18:47 -0400 Received: from mx1.redhat.com ([209.132.183.28]:44922 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753851AbcD1VSo (ORCPT ); Thu, 28 Apr 2016 17:18:44 -0400 Date: Thu, 28 Apr 2016 16:18:41 -0500 From: Josh Poimboeuf To: Jessica Yu Cc: Miroslav Benes , jikos@kernel.org, pmladek@suse.com, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: klp: make object/func-walking helpers more robust Message-ID: <20160428211841.46qvalvn6sxtrxig@treble> References: <1461854048-31473-1-git-send-email-mbenes@suse.cz> <20160428182131.GA22885@packer-debian-8-amd64.digitalocean.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20160428182131.GA22885@packer-debian-8-amd64.digitalocean.com> User-Agent: Mutt/1.6.0.1 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 28, 2016 at 02:21:31PM -0400, Jessica Yu wrote: > +++ Miroslav Benes [28/04/16 16:34 +0200]: > > Current object-walking helper checks the presence of obj->funcs to > > determine the end of objs array in klp_object structure. This is > > somewhat fragile because one can easily forget about funcs definition > > during livepatch creation. In such a case the livepatch module is > > successfully loaded and all objects after the incorrect one are omitted. > > This is very confusing. Let's make the helper more robust and check also > > for the other external member, name. Thus the helper correctly stops on > > an empty item of the array. We need to have a check for obj->funcs in > > klp_init_object() to make it work. > > > > The same applies to a func-walking helper. > > > > As a benefit we'll check for new_func member definition during the > > livepatch initialization. There is no such check anywhere in the code > > now. > > > > Signed-off-by: Miroslav Benes > > --- > > include/linux/livepatch.h | 6 ++++-- > > kernel/livepatch/core.c | 3 +++ > > 2 files changed, 7 insertions(+), 2 deletions(-) > > > > diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h > > index 0933ca47791c..a93a0b23dc8d 100644 > > --- a/include/linux/livepatch.h > > +++ b/include/linux/livepatch.h > > @@ -104,10 +104,12 @@ struct klp_patch { > > }; > > > > #define klp_for_each_object(patch, obj) \ > > - for (obj = patch->objs; obj->funcs; obj++) > > + for (obj = patch->objs; obj->funcs || obj->name; obj++) > > Remember that for patches to vmlinux, obj->name and obj->mod will also > both be NULL. So if someone happens to forget to fill in obj->funcs > for a vmlinux patch, we won't catch that case here. Perhaps we need a > better way of determining whether we've reached the end of the array, > or determining that the struct is truly empty.. That would be nice, but I'm not sure how we could do that. I suppose we could add a patch->nr_objs field. But that might arguably be even easier for the user to mess up. -- Josh