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=-3.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 6D57DC433DF for ; Fri, 9 Oct 2020 20:39:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1EA2C22261 for ; Fri, 9 Oct 2020 20:39:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="bZz0eTFl" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390482AbgJIUjH (ORCPT ); Fri, 9 Oct 2020 16:39:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54634 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390305AbgJIUjG (ORCPT ); Fri, 9 Oct 2020 16:39:06 -0400 Received: from mail-il1-x131.google.com (mail-il1-x131.google.com [IPv6:2607:f8b0:4864:20::131]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 06E5BC0613D2 for ; Fri, 9 Oct 2020 13:39:05 -0700 (PDT) Received: by mail-il1-x131.google.com with SMTP id p16so1984456ilq.5 for ; Fri, 09 Oct 2020 13:39:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=hAe9ETz06pxyDt6Pbp5ekqxqf61u/LFZY9bHsqTAeHM=; b=bZz0eTFlbwNTQ0zP6oP3XKO9Q69ylukVJD2ZgHRuvbDjp2E1MflkC4uT+4mExaCLcD yxu4XuBvFDqsbqhgfU8liPtv55FYjYS2cIMK4uThPL4NwcMi56zkAYPREg1dU1hEhyWm 7FSVV4+kSNj4bZfdHhroNnQB594f0j6bUwlPwMR9k3TVnPbE2TkbNvgAxyz7c4GobzvN ul+E7bvVJjl/NwT96j3N3ycE0NCSzcLiMge0/CMWLmNwNGv1xJqIuBx7KrDf+m3Kq9Y/ yl4tQ27fzyMiPdkYeF8r91A3sedd5jYuLZmgQeIsxQz+oqwDYDjtREQKgs/fbR4Cj9jD RiCg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=hAe9ETz06pxyDt6Pbp5ekqxqf61u/LFZY9bHsqTAeHM=; b=EmgF0euxZAPlHtIecQ8RNfDTdCa4uQFjaRMwk0BC0XsRqCeDI2P4U19/EjIYsdt8F4 TjXqYuPSh5o2tLvuyMigiugrQCB/k1f+xcpV+Wxv4f6kNZMXVibXWtF8RtXZQ5DGBn+6 INloGzwn3bWVvfKn7O0W0RCMjX57aCunBsukTB7JGHxDGGHa/lpHWDs9fPWzORsF+Nfq T9wjjWBTXtGvZ5DPd4vtb3jd1p+cr4Y6s23PH9QgrRyJAJCjBeRyJDSmE/FJyRuMpLDh Ah+dJcOf4wQL2A7U4km3L1gE+mVMBK+j89kwQcZiO1g7Cw7UxupaIn7fO+KL4n8sLTUf TcCw== X-Gm-Message-State: AOAM530/+v47aGAy8pHMVANWXOCFKjCb6f2br5Viryn4aivXc+DktVwC QfP9J7vfvripzypP4Rba9BzWwxDaMd9k5vECG3I= X-Google-Smtp-Source: ABdhPJyuDTXYXxDnPIIJ98+H3bmNnm8khBa90M4qCm87WhQHpE/bdgr5AJLxiuNyBKxRE2peJO911JZM0yVBSMgAiIU= X-Received: by 2002:a92:d28a:: with SMTP id p10mr11892403ilp.22.1602275944165; Fri, 09 Oct 2020 13:39:04 -0700 (PDT) MIME-Version: 1.0 References: <20201008012154.11149-1-xiyou.wangcong@gmail.com> In-Reply-To: From: Cong Wang Date: Fri, 9 Oct 2020 13:38:52 -0700 Message-ID: Subject: Re: [Patch net] ip_gre: set dev->hard_header_len properly To: Xie He Cc: Willem de Bruijn , Network Development , syzbot , William Tu Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Fri, Oct 9, 2020 at 12:51 PM Xie He wrote: > > On Fri, Oct 9, 2020 at 12:41 PM Xie He wrote: > > > > Thanks. But there is still something that I don't understand. What is > > needed_headroom used for? If we are requesting space for t->encap_hlen > > and t->tun_hlen in hard_header_len. Do we still need to use > > needed_headroom? > > It seems to me that the original code includes t->encap_hlen, > t->tun_hlen, and the IP header length in needed_headroom. (Right?) If > we are including these in hard_header_len, we need to move them out of > needed_headroom. Interesting point. I think needed_headroom is 0 until we call ipgre_changelink(), but needed_headroom is already being used in multiple places for skb_cow_head() in the same file, I guess they should be replaced with hard_head_len because for GRE tunnel those are its link-layer header. What makes it more complicated is that header_ops is actually set conditionally, so should be hard_header_len/needed_head_room accordingly. Thanks.