From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932168AbaJVCTz (ORCPT ); Tue, 21 Oct 2014 22:19:55 -0400 Received: from aserp1040.oracle.com ([141.146.126.69]:38587 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750731AbaJVCTy (ORCPT ); Tue, 21 Oct 2014 22:19:54 -0400 Message-ID: <54471438.1040907@oracle.com> Date: Tue, 21 Oct 2014 22:19:36 -0400 From: Sasha Levin User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.0 MIME-Version: 1.0 To: David Miller CC: a.ryabinin@samsung.com, pablo@netfilter.org, mschmidt@redhat.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org Subject: Re: [PATCH] netlink: don't copy over empty attribute data References: <1413924669-26732-1-git-send-email-sasha.levin@oracle.com> <20141021.213908.1088381802543942481.davem@davemloft.net> In-Reply-To: <20141021.213908.1088381802543942481.davem@davemloft.net> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit X-Source-IP: ucsinet21.oracle.com [156.151.31.93] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/21/2014 09:39 PM, David Miller wrote: > From: Sasha Levin > Date: Tue, 21 Oct 2014 16:51:09 -0400 > >> > netlink uses empty data to seperate different levels. However, we still >> > try to copy that data from a NULL ptr using memcpy, which is an undefined >> > behaviour. >> > >> > Signed-off-by: Sasha Levin > This isn't a POSIX C library, this it the Linux kernel, and as such > we can make sure none of our memcpy() implementations try to access > any bytes if the given length is NULL. We can make *our* implementations work around that undefined behaviour if we want, but right now our implementations is to call GCC's builtin memcpy(), which follows the standards and doesn't allow you to call it with NULL 'from' ptr. The fact that it doesn't die and behaves properly is just "luck". Thanks, Sasha