From patchwork Thu Feb 13 15:24:16 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Gustavo A. R. Silva" X-Patchwork-Id: 1237574 X-Patchwork-Delegate: bpf@iogearbox.net Return-Path: X-Original-To: incoming-bpf@patchwork.ozlabs.org Delivered-To: patchwork-incoming-bpf@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=none (no SPF record) smtp.mailfrom=vger.kernel.org (client-ip=209.132.180.67; helo=vger.kernel.org; envelope-from=bpf-owner@vger.kernel.org; receiver=) Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=embeddedor.com Authentication-Results: ozlabs.org; dkim=fail reason="signature verification failed" (2048-bit key; unprotected) header.d=embeddedor.com header.i=@embeddedor.com header.a=rsa-sha256 header.s=default header.b=qUBPc+5f; dkim-atps=neutral Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 48JLSB3sZwz9sTQ for ; Fri, 14 Feb 2020 02:45:14 +1100 (AEDT) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729437AbgBMPpJ (ORCPT ); Thu, 13 Feb 2020 10:45:09 -0500 Received: from gateway31.websitewelcome.com ([192.185.143.43]:29973 "EHLO gateway31.websitewelcome.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729501AbgBMPpE (ORCPT ); Thu, 13 Feb 2020 10:45:04 -0500 X-Greylist: delayed 1401 seconds by postgrey-1.27 at vger.kernel.org; Thu, 13 Feb 2020 10:45:03 EST Received: from cm17.websitewelcome.com (cm17.websitewelcome.com [100.42.49.20]) by gateway31.websitewelcome.com (Postfix) with ESMTP id E956B494E for ; Thu, 13 Feb 2020 09:21:41 -0600 (CST) Received: from gator4166.hostgator.com ([108.167.133.22]) by cmsmtp with SMTP id 2GJBjQYpnAGTX2GJBjcaCO; Thu, 13 Feb 2020 09:21:41 -0600 X-Authority-Reason: nr=8 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=embeddedor.com; s=default; h=Content-Type:MIME-Version:Message-ID:Subject: Cc:To:From:Date:Sender:Reply-To:Content-Transfer-Encoding:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:In-Reply-To:References:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=tlzInWey23Efbti3IVI7QK7bG7x1edOF4vWB/j8UuCg=; b=qUBPc+5fDEGt6M5dgwJulMJp+G xcMtSAYOH/X0jV8IyUUPvs80Ttm+MXBgQ8qc27gOJWz05nEnxh4pFjiFklBTyOZgBCxQ0gkv0qNVU oKGPrxltSRC+XnaTwGk/xuX5mhgyFpgQdq+I4gqPpsSIi2DpRDoQCe55ho30GyrzWIqoyuzXhHiwE jyiSnpGoggRlGalXfSmMNqIutwrK5Wee4Z77OuIp/CvM13nU/t/nBmkfntKDkFRCSdgrqjor/APB0 5QE3/CkAoKBfUgQV9K5AT+4GfPe1H4rDZTWmD742+C+7oRRpkbCKEhX4WDPXJMHEDFtddVW2fo3hk OXEc0N7Q==; Received: from [200.68.140.15] (port=29529 helo=embeddedor) by gator4166.hostgator.com with esmtpa (Exim 4.92) (envelope-from ) id 1j2GJA-003BYr-8t; Thu, 13 Feb 2020 09:21:40 -0600 Date: Thu, 13 Feb 2020 09:24:16 -0600 From: "Gustavo A. R. Silva" To: Alexei Starovoitov , Daniel Borkmann , Martin KaFai Lau , Song Liu , Yonghong Song , Andrii Nakryiko Cc: netdev@vger.kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, "Gustavo A. R. Silva" Subject: [PATCH] bpf: queue_stack_maps: Replace zero-length array with flexible-array member Message-ID: <20200213152416.GA1873@embeddedor> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.9.4 (2018-02-28) X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - gator4166.hostgator.com X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - embeddedor.com X-BWhitelist: no X-Source-IP: 200.68.140.15 X-Source-L: No X-Exim-ID: 1j2GJA-003BYr-8t X-Source: X-Source-Args: X-Source-Dir: X-Source-Sender: (embeddedor) [200.68.140.15]:29529 X-Source-Auth: gustavo@embeddedor.com X-Email-Count: 29 X-Source-Cap: Z3V6aWRpbmU7Z3V6aWRpbmU7Z2F0b3I0MTY2Lmhvc3RnYXRvci5jb20= X-Local-Domain: yes Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org 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] 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 Acked-by: Andrii Nakryiko --- kernel/bpf/queue_stack_maps.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/bpf/queue_stack_maps.c b/kernel/bpf/queue_stack_maps.c index f697647ceb54..30e1373fd437 100644 --- a/kernel/bpf/queue_stack_maps.c +++ b/kernel/bpf/queue_stack_maps.c @@ -19,7 +19,7 @@ struct bpf_queue_stack { u32 head, tail; u32 size; /* max_entries + 1 */ - char elements[0] __aligned(8); + char elements[] __aligned(8); }; static struct bpf_queue_stack *bpf_queue_stack(struct bpf_map *map)