From patchwork Mon Mar 9 20:24:49 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: 11428005 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 6C612139A for ; Mon, 9 Mar 2020 20:45:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4D4EF2464B for ; Mon, 9 Mar 2020 20:45:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=embeddedor.com header.i=@embeddedor.com header.b="Pz7R/rVH" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726118AbgCIUpw (ORCPT ); Mon, 9 Mar 2020 16:45:52 -0400 Received: from gateway30.websitewelcome.com ([192.185.149.4]:49648 "EHLO gateway30.websitewelcome.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725992AbgCIUpw (ORCPT ); Mon, 9 Mar 2020 16:45:52 -0400 X-Greylist: delayed 1452 seconds by postgrey-1.27 at vger.kernel.org; Mon, 09 Mar 2020 16:45:51 EDT Received: from cm14.websitewelcome.com (cm14.websitewelcome.com [100.42.49.7]) by gateway30.websitewelcome.com (Postfix) with ESMTP id BB96F2126F for ; Mon, 9 Mar 2020 15:21:38 -0500 (CDT) Received: from gator4166.hostgator.com ([108.167.133.22]) by cmsmtp with SMTP id BOuAjAxNCXVkQBOuAjTtmV; Mon, 09 Mar 2020 15:21:38 -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=KLV5yJSsYHCCLskrtRv6u1HK/r2QKBRZk7ghDZkHXAU=; b=Pz7R/rVH3x7D6lgGJyt/IlsXFD euImYoH8hRNDBfV4BZ1XYhTVwl1dQ3eFEbQSbi/XvbNTaWgdhpQkVllgtvc6mrbtk0f8EV+furKzM qooxbDinjvIfFFn0ZrfSsgA1m7ElwKde3cs6fLA91c77zfAkPGGBVrvCdO8pooJH2w3ZeHygnTMiO y9du0YzGWeBAKfUp4zXuBPrnBWAMzVLtzof7wUVSW038K0ArGnJ7dxtc4aRB3y7sRdseQSRsSIfyb MdUFhVvfrNsNxVXII1zwbitya6AEqT753Rh/rZ5yywk13JzP9MLorXZyUE/OetoKt2VztUICOHp89 PJvm55Jw==; Received: from [201.162.168.201] (port=20442 helo=embeddedor) by gator4166.hostgator.com with esmtpa (Exim 4.92) (envelope-from ) id 1jBOu8-000zkz-PA; Mon, 09 Mar 2020 15:21:37 -0500 Date: Mon, 9 Mar 2020 15:24:49 -0500 From: "Gustavo A. R. Silva" To: Alexander Viro Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, "Gustavo A. R. Silva" Subject: [PATCH][next] fs: select: Replace zero-length array with flexible-array member Message-ID: <20200309202449.GA9027@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: 201.162.168.201 X-Source-L: No X-Exim-ID: 1jBOu8-000zkz-PA X-Source: X-Source-Args: X-Source-Dir: X-Source-Sender: (embeddedor) [201.162.168.201]:20442 X-Source-Auth: gustavo@embeddedor.com X-Email-Count: 25 X-Source-Cap: Z3V6aWRpbmU7Z3V6aWRpbmU7Z2F0b3I0MTY2Lmhvc3RnYXRvci5jb20= X-Local-Domain: yes Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@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/select.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/fs/select.c b/fs/select.c index 11d0285d46b7..f38a8a7480f7 100644 --- a/fs/select.c +++ b/fs/select.c @@ -97,7 +97,7 @@ u64 select_estimate_accuracy(struct timespec64 *tv) struct poll_table_page { struct poll_table_page * next; struct poll_table_entry * entry; - struct poll_table_entry entries[0]; + struct poll_table_entry entries[]; }; #define POLL_TABLE_FULL(table) \ @@ -826,7 +826,7 @@ SYSCALL_DEFINE1(old_select, struct sel_arg_struct __user *, arg) struct poll_list { struct poll_list *next; int len; - struct pollfd entries[0]; + struct pollfd entries[]; }; #define POLLFD_PER_PAGE ((PAGE_SIZE-sizeof(struct poll_list)) / sizeof(struct pollfd))