Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751707AbdGaVwK (ORCPT ); Mon, 31 Jul 2017 17:52:10 -0400 Received: from mail-oi0-f67.google.com ([209.85.218.67]:34991 "EHLO mail-oi0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751676AbdGaVwI (ORCPT ); Mon, 31 Jul 2017 17:52:08 -0400 MIME-Version: 1.0 In-Reply-To: References: <20170731065016.2947796-1-arnd@arndb.de> From: Arnd Bergmann Date: Mon, 31 Jul 2017 23:52:07 +0200 X-Google-Sender-Auth: t7rRacZZQAshRzpGKhwpGxX4KJ0 Message-ID: Subject: Re: [PATCH] infiniband: avoid overflow warning To: Kees Cook 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: 1711 Lines: 34 On Mon, Jul 31, 2017 at 11:18 PM, Kees Cook wrote: > 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. To clarify: this happens in inetaddr_event(), which has a sockaddr_in on the stack, not a sockaddr_storage. I tried casting the sockaddr_in pointer to sockaddr_storage, but that did not help. Changing the type of the stack variable to sockaddr_storage does help. Arnd