From patchwork Wed May 13 17:15:56 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: 1289533 X-Patchwork-Delegate: davem@davemloft.net Return-Path: X-Original-To: patchwork-incoming-netdev@ozlabs.org Delivered-To: patchwork-incoming-netdev@ozlabs.org Authentication-Results: ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=vger.kernel.org (client-ip=23.128.96.18; helo=vger.kernel.org; envelope-from=netdev-owner@vger.kernel.org; receiver=) Authentication-Results: ozlabs.org; dmarc=pass (p=none dis=none) header.from=kernel.org Authentication-Results: ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=default header.b=aEYGgg5i; dkim-atps=neutral Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by ozlabs.org (Postfix) with ESMTP id 49Mh6564PZz9sRf for ; Thu, 14 May 2020 03:11:25 +1000 (AEST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389507AbgEMRLV (ORCPT ); Wed, 13 May 2020 13:11:21 -0400 Received: from mail.kernel.org ([198.145.29.99]:45086 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727120AbgEMRLV (ORCPT ); Wed, 13 May 2020 13:11:21 -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 9C079205CB; Wed, 13 May 2020 17:11:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589389881; bh=uSkg61BwOrNifZEHey9E2g+dgeUJ0K29iZPqEkw2C1A=; h=Date:From:To:Cc:Subject:From; b=aEYGgg5i5me2qCi9VKCiX7P+P+teDthb9rpi5NS3rMap0eiPRldxu052rINx6puRk cUMxqvOGrSAgd1zvEq8OOca0UPW8wIXQLPLKJ8bD1F6q1K72+2MHVhWetq1h+pbeTh DqcRaC2GpB1t0kG9ksJDBkNz0PXOyfM/9GMdUCdI= Date: Wed, 13 May 2020 12:15:56 -0500 From: "Gustavo A. R. Silva" To: Marcel Holtmann , Johan Hedberg , "David S. Miller" , Jakub Kicinski Cc: linux-bluetooth@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, "Gustavo A. R. Silva" Subject: [PATCH] Bluetooth: L2CAP: Replace zero-length array with flexible-array Message-ID: <20200513171556.GA21969@embeddedor> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.9.4 (2018-02-28) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@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 --- include/net/bluetooth/l2cap.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/include/net/bluetooth/l2cap.h b/include/net/bluetooth/l2cap.h index dada14d0622c..8f1e6a7a2df8 100644 --- a/include/net/bluetooth/l2cap.h +++ b/include/net/bluetooth/l2cap.h @@ -499,7 +499,7 @@ struct l2cap_ecred_conn_req { __le16 mtu; __le16 mps; __le16 credits; - __le16 scid[0]; + __le16 scid[]; } __packed; struct l2cap_ecred_conn_rsp { @@ -507,13 +507,13 @@ struct l2cap_ecred_conn_rsp { __le16 mps; __le16 credits; __le16 result; - __le16 dcid[0]; + __le16 dcid[]; }; struct l2cap_ecred_reconf_req { __le16 mtu; __le16 mps; - __le16 scid[0]; + __le16 scid[]; } __packed; #define L2CAP_RECONF_SUCCESS 0x0000