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=-13.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,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 646D1C33CAA for ; Tue, 21 Jan 2020 05:54:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4187922314 for ; Tue, 21 Jan 2020 05:54:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728709AbgAUFy1 (ORCPT ); Tue, 21 Jan 2020 00:54:27 -0500 Received: from mail-wm1-f68.google.com ([209.85.128.68]:40811 "EHLO mail-wm1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725916AbgAUFy0 (ORCPT ); Tue, 21 Jan 2020 00:54:26 -0500 Received: by mail-wm1-f68.google.com with SMTP id t14so1617337wmi.5 for ; Mon, 20 Jan 2020 21:54:24 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:autocrypt :message-id:date:user-agent:mime-version:in-reply-to :content-language:content-transfer-encoding; bh=ZResEKvLOZfBbOB0xQdzNa77QXq6FAjHVNBvFSutmDQ=; b=URWH268gg+rPQvwFsclPqLjDjIgJS4skmqaJM572eV1GH3f4ne6QmDJAKt5J98nd30 7mkycjgW+HTZzXm8McIb4oiBi/DvH0C4OV7gZ5RFo2QcfMhUrf8slmu/dYJVWcAhhc0R n/+WScH5EnqJi/MnkLleueCzpoCFhImX60h8hRQvzSat7e/8zNQfH1FeIKdpeTODqxGF aWSKU0i4nh/x5tdWQ2/TkfKYU4+WblPgFQBZaPzMyxCQpsALYggmRbibHn4K+x12+obK OVrWEDF0WglxaB6OKRHz3kc/nOiaVUsm0oQjKcO3rs5bo7G+OLkKXli5txYSQO1lIJ7H kyWg== X-Gm-Message-State: APjAAAUiPzg8Iztml0g89inobUGccl0bBThMZvpPhm6gwnJTknr6opDi VhXjApHPhkY2ffL4Ec1qngo4P9ek8p8= X-Google-Smtp-Source: APXvYqwWGcHRrLRb9XgDoo6rcG8501kJURJy0Pj3Uf0k2cZrPw+W+YBvpBxBfy172ShrNaZTE0+J9w== X-Received: by 2002:a1c:16:: with SMTP id 22mr2445064wma.8.1579586063793; Mon, 20 Jan 2020 21:54:23 -0800 (PST) Received: from ?IPv6:2a0b:e7c0:0:107::49? ([2a0b:e7c0:0:107::49]) by smtp.gmail.com with ESMTPSA id c4sm2338963wml.7.2020.01.20.21.54.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 20 Jan 2020 21:54:23 -0800 (PST) Subject: Re: [PATCH] tty: n_hdlc: Use flexible-array member To: "Gustavo A. R. Silva" , Greg Kroah-Hartman Cc: linux-kernel@vger.kernel.org References: <20200120234528.GA26790@embeddedor.com> From: Jiri Slaby Autocrypt: addr=jslaby@suse.com; prefer-encrypt=mutual; keydata= mQINBE6S54YBEACzzjLwDUbU5elY4GTg/NdotjA0jyyJtYI86wdKraekbNE0bC4zV+ryvH4j rrcDwGs6tFVrAHvdHeIdI07s1iIx5R/ndcHwt4fvI8CL5PzPmn5J+h0WERR5rFprRh6axhOk rSD5CwQl19fm4AJCS6A9GJtOoiLpWn2/IbogPc71jQVrupZYYx51rAaHZ0D2KYK/uhfc6neJ i0WqPlbtIlIrpvWxckucNu6ZwXjFY0f3qIRg3Vqh5QxPkojGsq9tXVFVLEkSVz6FoqCHrUTx wr+aw6qqQVgvT/McQtsI0S66uIkQjzPUrgAEtWUv76rM4ekqL9stHyvTGw0Fjsualwb0Gwdx ReTZzMgheAyoy/umIOKrSEpWouVoBt5FFSZUyjuDdlPPYyPav+hpI6ggmCTld3u2hyiHji2H cDpcLM2LMhlHBipu80s9anNeZhCANDhbC5E+NZmuwgzHBcan8WC7xsPXPaiZSIm7TKaVoOcL 9tE5aN3jQmIlrT7ZUX52Ff/hSdx/JKDP3YMNtt4B0cH6ejIjtqTd+Ge8sSttsnNM0CQUkXps w98jwz+Lxw/bKMr3NSnnFpUZaxwji3BC9vYyxKMAwNelBCHEgS/OAa3EJoTfuYOK6wT6nadm YqYjwYbZE5V/SwzMbpWu7Jwlvuwyfo5mh7w5iMfnZE+vHFwp/wARAQABtBxKaXJpIFNsYWJ5 IDxqc2xhYnlAc3VzZS5jb20+iQI4BBMBAgAiBQJOkujrAhsDBgsJCAcDAgYVCAIJCgsEFgID AQIeAQIXgAAKCRC9JbEEBrRwSc1VD/9CxnyCYkBrzTfbi/F3/tTstr3cYOuQlpmufoEjCIXx PNnBVzP7XWPaHIUpp5tcweG6HNmHgnaJScMHHyG83nNAoCEPihyZC2ANQjgyOcnzDOnW2Gzf 8v34FDQqj8CgHulD5noYBrzYRAss6K42yUxUGHOFI1Ky1602OCBRtyJrMihio0gNuC1lE4YZ juGZEU6MYO1jKn8QwGNpNKz/oBs7YboU7bxNTgKrxX61cSJuknhB+7rHOQJSXdY02Tt31R8G diot+1lO/SoB47Y0Bex7WGTXe13gZvSyJkhZa5llWI/2d/s1aq5pgrpMDpTisIpmxFx2OEkb jM95kLOs/J8bzostEoEJGDL4u8XxoLnOEjWyT82eKkAe4j7IGQlA9QQR2hCMsBdvZ/EoqTcd SqZSOto9eLQkjZLz0BmeYIL8SPkgnVAJ/FEK44NrHUGzjzdkE7a0jNvHt8ztw6S+gACVpysi QYo2OH8hZGaajtJ8mrgN2Lxg7CpQ0F6t/N1aa/+A2FwdRw5sHBqA4PH8s0Apqu66Q94YFzzu 8OWkSPLgTjtyZcez79EQt02u8xH8dikk7API/PYOY+462qqbahpRGaYdvloaw7tOQJ224pWJ 4xePwtGyj4raAeczOcBQbKKW6hSH9iz7E5XUdpJqO3iZ9psILk5XoyO53wwhsLgGcrkCDQRO kueGARAAz5wNYsv5a9z1wuEDY5dn+Aya7s1tgqN+2HVTI64F3l6Yg753hF8UzTZcVMi3gzHC ECvKGwpBBwDiJA2V2RvJ6+Jis8paMtONFdPlwPaWlbOv4nHuZfsidXkk7PVCr4/6clZggGNQ qEjTe7Hz2nnwJiKXbhmnKfYXlxftT6KdjyUkgHAs8Gdz1nQCf8NWdQ4P7TAhxhWdkAoOIhc4 OQapODd+FnBtuL4oCG0c8UzZ8bDZVNR/rYgfNX54FKdqbM84FzVewlgpGjcUc14u5Lx/jBR7 ttZv07ro88Ur9GR6o1fpqSQUF/1V+tnWtMQoDIna6p/UQjWiVicQ2Tj7TQgFr4Fq8ZDxRb10 Zbeds+t+45XlRS9uexJDCPrulJ2sFCqKWvk3/kf3PtUINDR2G4k228NKVN/aJQUGqCTeyaWf fU9RiJU+sw/RXiNrSL2q079MHTWtN9PJdNG2rPneo7l0axiKWIk7lpSaHyzBWmi2Arj/nuHf Maxpc708aCecB2p4pUhNoVMtjUhKD4+1vgqiWKI6OsEyZBRIlW2RRcysIwJ648MYejvf1dzv mVweUa4zfIQH/+G0qPKmtst4t/XLjE/JN54XnOD/TO1Fk0pmJyASbHJQ0EcecEodDHPWP6bM fQeNlm1eMa7YosnXwbTurR+nPZk+TYPndbDf1U0j8n0AEQEAAYkCHwQYAQIACQUCTpLnhgIb DAAKCRC9JbEEBrRwSTe1EACA74MWlvIhrhGWd+lxbXsB+elmL1VHn7Ovj3qfaMf/WV3BE79L 5A1IDyp0AGoxv1YjgE1qgA2ByDQBLjb0yrS1ppYqQCOSQYBPuYPVDk+IuvTpj/4rN2v3R5RW d6ozZNRBBsr4qHsnCYZWtEY2pCsOT6BE28qcbAU15ORMq0nQ/yNh3s/WBlv0XCP1gvGOGf+x UiE2YQEsGgjs8v719sguok8eADBbfmumerh/8RhPKRuTWxrXdNq/pu0n7hA6Btx7NYjBnnD8 lV8Qlb0lencEUBXNFDmdWussMAlnxjmKhZyb30m1IgjFfG30UloZzUGCyLkr/53JMovAswmC IHNtXHwb58Ikn1i2U049aFso+WtDz4BjnYBqCL1Y2F7pd8l2HmDqm2I4gubffSaRHiBbqcSB lXIjJOrd6Q66u5+1Yv32qk/nOL542syYtFDH2J5wM2AWvfjZH1tMOVvVMu5Fv7+0n3x/9shY ivRypCapDfcWBGGsbX5eaXpRfInaMTGaU7wmWO44Z5diHpmQgTLOrN9/MEtdkK6OVhAMVenI w1UnZnA+ZfaZYShi5oFTQk3vAz7/NaA5/bNHCES4PcDZw7Y/GiIh/JQR8H1JKZ99or9LjFeg HrC8YQ1nzkeDfsLtYM11oC3peHa5AiXLmCuSC9ammQ3LhkfET6N42xTu2A== Message-ID: Date: Tue, 21 Jan 2020 06:54:22 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200120234528.GA26790@embeddedor.com> Content-Type: text/plain; charset=iso-8859-2 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 21. 01. 20, 0:45, Gustavo A. R. Silva wrote: > Old code in the kernel uses 1-byte and 0-byte arrays to indicate the > presence of a "variable length array": > > struct something { > int length; > u8 data[1]; > }; > > struct something *instance; > > instance = kmalloc(sizeof(*instance) + size, GFP_KERNEL); > instance->length = size; > memcpy(instance->data, source, size); > > There is also 0-byte arrays. Both cases pose confusion for things like > sizeof(), CONFIG_FORTIFY_SOURCE, etc.[1] Instead, the preferred mechanism > to declare variable-length types such as the one above is a flexible array > member[2] which need to be the last member of a structure and empty-sized: > > struct something { > int stuff; > u8 data[]; > }; > > Also, 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 > unadvertenly introduced[3] to the codebase from now on. > > [1] https://github.com/KSPP/linux/issues/21 > [2] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html > [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") > > Signed-off-by: Gustavo A. R. Silva > --- > drivers/tty/n_hdlc.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/tty/n_hdlc.c b/drivers/tty/n_hdlc.c > index 98361acd3053..b5499ca8757e 100644 > --- a/drivers/tty/n_hdlc.c > +++ b/drivers/tty/n_hdlc.c > @@ -115,7 +115,7 @@ > struct n_hdlc_buf { > struct list_head list_item; > int count; > - char buf[1]; > + char buf[]; > }; > > #define N_HDLC_BUF_SIZE (sizeof(struct n_hdlc_buf) + maxframe) Have you checked, that you don't have to "+ 1" here now? Other than that: Acked-by: Jiri Slaby thanks, -- js suse labs