Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751566AbdGaVSa (ORCPT ); Mon, 31 Jul 2017 17:18:30 -0400 Received: from mail-io0-f171.google.com ([209.85.223.171]:33658 "EHLO mail-io0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751017AbdGaVS3 (ORCPT ); Mon, 31 Jul 2017 17:18:29 -0400 MIME-Version: 1.0 In-Reply-To: References: <20170731065016.2947796-1-arnd@arndb.de> From: Kees Cook Date: Mon, 31 Jul 2017 14:18:27 -0700 X-Google-Sender-Auth: MQxTHuh8b1puWisDmqFaxWYTLwA Message-ID: Subject: Re: [PATCH] infiniband: avoid overflow warning To: Arnd Bergmann Cc: Moni Shoua , Doug Ledford , Sean Hefty , Hal Rosenstock , Daniel Micay , "Kalderon, Michal" , Ariel Elior , "David S. Miller" , Bart Van Assche , Parav Pandit , Noa Osherovich , linux-rdma , Linux Kernel Mailinglist Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1362 Lines: 32 On Mon, Jul 31, 2017 at 2:10 PM, Arnd Bergmann wrote: > On Mon, Jul 31, 2017 at 10:58 PM, Kees Cook wrote: >> On Mon, Jul 31, 2017 at 12:30 AM, Arnd Bergmann wrote: >>> On Mon, Jul 31, 2017 at 9:08 AM, Moni Shoua wrote: >>>>> break; >>>>> default: >>>>> return -EINVAL; >>>> what happens if you replace 16 with sizeof(struct in6_addr)? >>> >>> Same thing: the problem is that gcc already knows the size of the structure we >>> pass in here, and it is in fact shorter. >> >> So gcc is ignoring both the cast (to 16 byte struct in6_addr) and the >> caller's actual 128 byte struct sockaddr_storage, and looking only at >> struct sockaddr? That seems really weird. > > Using a sockaddr_storage on the stack would address the warning, but > the question was about just changing the hardcoded 16 to a sizeof() > operation, and that has no effect. Right, I didn't mean that; I was curious why the fortify macro resulted in an error at all. The callers are casting from struct sockaddr_storage (large enough) to struct sockaddr (not large enough), and then the inline is casting back to sockaddr_in6 (large enough). I would have expected fortify to check either sockaddr_storage or sockaddr_in6, but not sockaddr. -Kees -- Kees Cook Pixel Security