From patchwork Thu May 7 18:57:10 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: 11534721 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 4615914B4 for ; Thu, 7 May 2020 18:52:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2F1D52495D for ; Thu, 7 May 2020 18:52:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877569; bh=P1BZoVC5niH/b6wY6lBALWnDN27yPCuxedD3vhCY58U=; h=Date:From:To:Cc:Subject:List-ID:From; b=2vlkvHl2U/VCjCq7TNXvkjGBTK8bTLLE1tXXg3rFVzUYL1CrYIJYQQ1qonkMat+37 GvBnysyIbnCP0u/rxV4GPod6b0EmtqUMONYeAwaAatnrNkW0OZiFkIrAv8PI94ZPnN DXTEhquFECNHJMgN3nVe+c90hjeunwerXv5Hf7dM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728486AbgEGSwp (ORCPT ); Thu, 7 May 2020 14:52:45 -0400 Received: from mail.kernel.org ([198.145.29.99]:53572 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728400AbgEGSwo (ORCPT ); Thu, 7 May 2020 14:52:44 -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 A4CAD2495D; Thu, 7 May 2020 18:52:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877564; bh=P1BZoVC5niH/b6wY6lBALWnDN27yPCuxedD3vhCY58U=; h=Date:From:To:Cc:Subject:From; b=zuE9YU9EaKifydGTMEqu4frQJYuioxYCSBuELZsfsf2e6pW6qHF9/oyv2U+rROTqD ZoM2JbXzngfjL3Mo2gOfa6Vsis4py0EZupTciFBJbfZQXSDlqdZJoQUG5914AUKeB5 lhwanVv7l7H5J4JI0atzEAi9nA3AeDAnI2Fy3CXg= Date: Thu, 7 May 2020 13:57:10 -0500 From: "Gustavo A. R. Silva" To: David Howells , Jarkko Sakkinen Cc: keyrings@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] KEYS: Replace zero-length array with flexible-array Message-ID: <20200507185710.GA14910@embeddedor> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.9.4 (2018-02-28) Sender: keyrings-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: keyrings@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 Reviewed-by: Jarkko Sakkinen --- include/keys/user-type.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/keys/user-type.h b/include/keys/user-type.h index be61fcddc02a..386c31432789 100644 --- a/include/keys/user-type.h +++ b/include/keys/user-type.h @@ -27,7 +27,7 @@ struct user_key_payload { struct rcu_head rcu; /* RCU destructor */ unsigned short datalen; /* length of this data */ - char data[0] __aligned(__alignof__(u64)); /* actual data */ + char data[] __aligned(__alignof__(u64)); /* actual data */ }; extern struct key_type key_type_user;