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=-13.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 7F122C38A24 for ; Thu, 7 May 2020 19:19:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4B1AC208E4 for ; Thu, 7 May 2020 19:19:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588879175; bh=pczH5X9hYaUj/TTXPQCiXcI3lnF49aDvEKo2rF2Bp8w=; h=Date:From:To:Cc:Subject:List-ID:From; b=F7rnkz6uU2f0Z2cvz4eg65fMxCszOKdKKuk6CejFkbrh9YMnuMJXlSOmkOWijGjXQ UdZEXkT+fp3f4pZE3JHD4ZUBYY5zCPt1Wh5vew2/JeQh8BK40iu6rbYuWvhfQ7Ru8i TddMLJIPrdED/zPnQ6yBa6zEAZ9Xy/HLqstKzV+E= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728396AbgEGTTe (ORCPT ); Thu, 7 May 2020 15:19:34 -0400 Received: from mail.kernel.org ([198.145.29.99]:41838 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726367AbgEGTTe (ORCPT ); Thu, 7 May 2020 15:19:34 -0400 Received: from embeddedor (unknown [189.207.59.248]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 2A4A3208D6; Thu, 7 May 2020 19:19:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588879173; bh=pczH5X9hYaUj/TTXPQCiXcI3lnF49aDvEKo2rF2Bp8w=; h=Date:From:To:Cc:Subject:From; b=k3mdqsLR5vUpLosWBY6qEvRB8OufNEEXlANpQ34GCGfE6VQlEmbyzweoctwr0x3dd UyjpfPMCEmfgjfO8B9sA5QvhWAfz7UcuUUAsun1i2yiyH4vh1MJZnSLd+2JzPbEoNX ttSVVxIatbKPn9dCuRBibZaJfGoOCwmzE8FyWAm0= Date: Thu, 7 May 2020 14:24:00 -0500 From: "Gustavo A. R. Silva" To: Phillip Lougher Cc: linux-kernel@vger.kernel.org Subject: [PATCH] Squashfs: Replace zero-length array with flexible-array Message-ID: <20200507192400.GA16423@embeddedor> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@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] 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 --- fs/squashfs/squashfs_fs.h | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) diff --git a/fs/squashfs/squashfs_fs.h b/fs/squashfs/squashfs_fs.h index 7187bd1a30ea..8d64edb80ebf 100644 --- a/fs/squashfs/squashfs_fs.h +++ b/fs/squashfs/squashfs_fs.h @@ -262,7 +262,7 @@ struct squashfs_dir_index { __le32 index; __le32 start_block; __le32 size; - unsigned char name[0]; + unsigned char name[]; }; struct squashfs_base_inode { @@ -327,7 +327,7 @@ struct squashfs_symlink_inode { __le32 inode_number; __le32 nlink; __le32 symlink_size; - char symlink[0]; + char symlink[]; }; struct squashfs_reg_inode { @@ -341,7 +341,7 @@ struct squashfs_reg_inode { __le32 fragment; __le32 offset; __le32 file_size; - __le16 block_list[0]; + __le16 block_list[]; }; struct squashfs_lreg_inode { @@ -358,7 +358,7 @@ struct squashfs_lreg_inode { __le32 fragment; __le32 offset; __le32 xattr; - __le16 block_list[0]; + __le16 block_list[]; }; struct squashfs_dir_inode { @@ -389,7 +389,7 @@ struct squashfs_ldir_inode { __le16 i_count; __le16 offset; __le32 xattr; - struct squashfs_dir_index index[0]; + struct squashfs_dir_index index[]; }; union squashfs_inode { @@ -410,7 +410,7 @@ struct squashfs_dir_entry { __le16 inode_number; __le16 type; __le16 size; - char name[0]; + char name[]; }; struct squashfs_dir_header { @@ -428,12 +428,12 @@ struct squashfs_fragment_entry { struct squashfs_xattr_entry { __le16 type; __le16 size; - char data[0]; + char data[]; }; struct squashfs_xattr_val { __le32 vsize; - char value[0]; + char value[]; }; struct squashfs_xattr_id {