From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D856FC38A2A for ; Fri, 8 May 2020 11:17:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B50222070B for ; Fri, 8 May 2020 11:17:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="JwiGw3nb" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727768AbgEHLRU (ORCPT ); Fri, 8 May 2020 07:17:20 -0400 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:26347 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726792AbgEHLRU (ORCPT ); Fri, 8 May 2020 07:17:20 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1588936638; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=05yejxlqG112oAiJcuXsV6RzSLjBiSOJw5IfNxYWv1M=; b=JwiGw3nbXDuxXyg3t7wMggOazzBjmzo0NtTysF4pl+kjyuki+/xpKvcOJWvYMBI+Rs/A8q Fil/4WUu3EXo/f3PEvy9jiN2kMPpqyNl4yIp/Q1b3SAzS7QGRLrHQ556oUtpKoyznnVsFr x+NbSBgnqWrKrOgjDHpQBH686QnmoDI= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-441-6s15L47gOZeCdQrWo-lI9A-1; Fri, 08 May 2020 07:17:14 -0400 X-MC-Unique: 6s15L47gOZeCdQrWo-lI9A-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 57A49107ACF2; Fri, 8 May 2020 11:17:13 +0000 (UTC) Received: from madcap2.tricolour.ca (unknown [10.3.128.9]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B66526155F; Fri, 8 May 2020 11:17:03 +0000 (UTC) Date: Fri, 8 May 2020 07:17:00 -0400 From: Richard Guy Briggs To: "Gustavo A. R. Silva" Cc: Paul Moore , Eric Paris , linux-audit@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] audit: Replace zero-length array with flexible-array Message-ID: <20200508111700.4uwa7oizxqakbk3t@madcap2.tricolour.ca> References: <20200507185041.GA13930@embeddedor> <20200507215812.ksvwcykfged7ye2a@madcap2.tricolour.ca> <20200507224955.GA22343@embeddedor> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200507224955.GA22343@embeddedor> User-Agent: NeoMutt/20180716 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-05-07 17:49, Gustavo A. R. Silva wrote: > On Thu, May 07, 2020 at 05:58:13PM -0400, Richard Guy Briggs wrote: > > On 2020-05-07 13:50, Gustavo A. R. Silva wrote: > > > The current codebase makes use of the zero-length array language > > > extension to the C90 standard, but the preferred mechanism to declare > > > variable-length types such as these ones is a flexible array member[1][2], > > > introduced in C99: > > > > > > struct foo { > > > int stuff; > > > struct boo array[]; > > > }; > > > > > > By making use of the mechanism above, we will get a compiler warning > > > in case the flexible array does not occur last in the structure, which > > > will help us prevent some kind of undefined behavior bugs from being > > > inadvertently introduced[3] to the codebase from now on. > > > > > > Also, notice that, dynamic memory allocations won't be affected by > > > this change: > > > > > > "Flexible array members have incomplete type, and so the sizeof operator > > > may not be applied. As a quirk of the original implementation of > > > zero-length arrays, sizeof evaluates to zero."[1] > > > > > > sizeof(flexible-array-member) triggers a warning because flexible array > > > members have incomplete type[1]. There are some instances of code in > > > which the sizeof operator is being incorrectly/erroneously applied to > > > zero-length arrays and the result is zero. Such instances may be hiding > > > some bugs. So, this work (flexible-array member conversions) will also > > > help to get completely rid of those sorts of issues. > > > > > > This issue was found with the help of Coccinelle. > > > > > > [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html > > > [2] https://github.com/KSPP/linux/issues/21 > > > [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") > > > > > > Signed-off-by: Gustavo A. R. Silva > > > > Sounds reasonable to me. There's another in include/uapi/linux/audit.h > > Hi, Hello Gustavo, > I wouldn't advise to make any of these conversions in include/uapi/ > [1][2]. Ah-hah. Thanks for the contra-indicating supporting references. > > in struct audit_rule_data buf[0]. This alert also helped me fix another > > one in a patchset I'm about to post (and will probably cause a merge > > conflict but we can figure that out). > > Awesome. :) > > > Reviewed-by: Richard Guy Briggs > > Thanks > -- > Gustavo > > [1] https://lore.kernel.org/lkml/20200424121553.GE26002@ziepe.ca/ > [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=1e6e9d0f4859ec698d55381ea26f4136eff3afe1 > > > > --- > > > include/linux/audit.h | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/include/linux/audit.h b/include/linux/audit.h > > > index f9ceae57ca8d..2b63aee6e9fa 100644 > > > --- a/include/linux/audit.h > > > +++ b/include/linux/audit.h > > > @@ -19,7 +19,7 @@ > > > struct audit_sig_info { > > > uid_t uid; > > > pid_t pid; > > > - char ctx[0]; > > > + char ctx[]; > > > }; > > > > > > struct audit_buffer; > > > > - RGB - RGB -- Richard Guy Briggs Sr. S/W Engineer, Kernel Security, Base Operating Systems Remote, Ottawa, Red Hat Canada IRC: rgb, SunRaycer Voice: +1.647.777.2635, Internal: (81) 32635