From patchwork Mon Mar 9 18:08:13 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: 1251758 Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@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=linux-ext4-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=nM5LyMf+; dkim-atps=neutral Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 48bnRp3dKLz9sPF for ; Tue, 10 Mar 2020 05:53:26 +1100 (AEDT) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727460AbgCISx0 (ORCPT ); Mon, 9 Mar 2020 14:53:26 -0400 Received: from gateway22.websitewelcome.com ([192.185.47.109]:20487 "EHLO gateway22.websitewelcome.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727334AbgCISxZ (ORCPT ); Mon, 9 Mar 2020 14:53:25 -0400 X-Greylist: delayed 1501 seconds by postgrey-1.27 at vger.kernel.org; Mon, 09 Mar 2020 14:53:24 EDT Received: from cm16.websitewelcome.com (cm16.websitewelcome.com [100.42.49.19]) by gateway22.websitewelcome.com (Postfix) with ESMTP id 7EBDB937A for ; Mon, 9 Mar 2020 13:05:05 -0500 (CDT) Received: from gator4166.hostgator.com ([108.167.133.22]) by cmsmtp with SMTP id BMm1jL3Ov8vkBBMm1jDv4i; Mon, 09 Mar 2020 13:05:05 -0500 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=M/+spNsZHyAg8E48D01jPchiqr2VpON3QaUIuLiE4zI=; b=nM5LyMf+ug8N0+yKKxSEt0RQFL yXvC+Ggrf0AssBa4PKtsX5zlzfSmlVZWeGIRVws/AdO6jkACKRjzCYJaVYgtdnYcWrCIMAep9T8X/ Fiqi4MBuKb3qgZuWMBUcT5ithvxtb5qt05qjwyM1sgwG5VhHYlllU1o2IRGeHh3kJKxrDPpuqWp9K lMRbNu4U059rr9yvP7gmuEtOKqrbZi4afar1Mpk1Xi/vUPJIlH2DH8FX1QNqXsh17b/LweyBXF3ar A081rcBuXV5DOte4jBE5L9iTIh7yZHMzskJiPNaye9VCR8CXAp3WQC32lmpnWuTrj+BpCOXEB+yoM UtHGmRAw==; Received: from [201.162.240.150] (port=3342 helo=embeddedor) by gator4166.hostgator.com with esmtpa (Exim 4.92) (envelope-from ) id 1jBMlw-004D0Z-Ry; Mon, 09 Mar 2020 13:05:01 -0500 Date: Mon, 9 Mar 2020 13:08:13 -0500 From: "Gustavo A. R. Silva" To: Theodore Ts'o , Andreas Dilger Cc: linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, "Gustavo A. R. Silva" Subject: [PATCH][next] ext4: xattr.h: Replace zero-length array with flexible-array member Message-ID: <20200309180813.GA3347@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: 201.162.240.150 X-Source-L: No X-Exim-ID: 1jBMlw-004D0Z-Ry X-Source: X-Source-Args: X-Source-Dir: X-Source-Sender: (embeddedor) [201.162.240.150]:3342 X-Source-Auth: gustavo@embeddedor.com X-Email-Count: 6 X-Source-Cap: Z3V6aWRpbmU7Z3V6aWRpbmU7Z2F0b3I0MTY2Lmhvc3RnYXRvci5jb20= X-Local-Domain: yes Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@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 --- fs/ext4/xattr.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/fs/ext4/xattr.h b/fs/ext4/xattr.h index f39cad2abe2a..ffe21ac77f78 100644 --- a/fs/ext4/xattr.h +++ b/fs/ext4/xattr.h @@ -48,7 +48,7 @@ struct ext4_xattr_entry { __le32 e_value_inum; /* inode in which the value is stored */ __le32 e_value_size; /* size of attribute value */ __le32 e_hash; /* hash value of name and value */ - char e_name[0]; /* attribute name */ + char e_name[]; /* attribute name */ }; #define EXT4_XATTR_PAD_BITS 2 @@ -118,7 +118,7 @@ struct ext4_xattr_ibody_find { struct ext4_xattr_inode_array { unsigned int count; /* # of used items in the array */ - struct inode *inodes[0]; + struct inode *inodes[]; }; extern const struct xattr_handler ext4_xattr_user_handler;