From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751522AbeBXWGE (ORCPT ); Sat, 24 Feb 2018 17:06:04 -0500 Received: from mx2.suse.de ([195.135.220.15]:47994 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751399AbeBXWGD (ORCPT ); Sat, 24 Feb 2018 17:06:03 -0500 Date: Sat, 24 Feb 2018 22:06:01 +0000 From: "Luis R. Rodriguez" To: Dan Carpenter Cc: "Luis R. Rodriguez" , linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org, cocci@systeme.lip6.fr Subject: Re: [PATCH] lib/test_kmod: Fix an integer overflow test Message-ID: <20180224220601.GG14069@wotan.suse.de> References: <20180122102754.GD23912@mwanda> <20180224025941.GB14069@wotan.suse.de> <20180224084516.pex3ogxzipzj2o5y@mwanda> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180224084516.pex3ogxzipzj2o5y@mwanda> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Feb 24, 2018 at 11:45:16AM +0300, Dan Carpenter wrote: > On Sat, Feb 24, 2018 at 02:59:41AM +0000, Luis R. Rodriguez wrote: > > On Mon, Jan 22, 2018 at 01:27:54PM +0300, Dan Carpenter wrote: > > > The main problem is that the parentheses are in the wrong place and the > > > unlikely() call returns either 0 or 1 so it's never less than zero. > > > > Doh, thanks, yes. Seems worth considering a grammar rule for it. > > > > > The other problem is that signed integer overflows like "INT_MAX + 1" are > > > undefined behavior. > > > > Likewise. > > > > This seems like another possible generic typo issue. But I would not resolve it > > the way you did, in this particular case below num_test_devs represents the > > number of already registered devs, before we increment. So the way to resolve > > this would be: > > > > if (num_test_devs + 1 == INT_MAX) > > > > I'll get this upstream, thanks! > > There is no issue if num_test_devs is INT_MAX. But capping it at > INT_MAX - 1 is also fine. If num_test_devs is INT_MAX, then doing num_test_devs + 1 overflows and as you noted that is undefined? Luis