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=-7.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 AD43BC433DF for ; Sat, 15 Aug 2020 22:01:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 91D2F2053B for ; Sat, 15 Aug 2020 22:01:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729708AbgHOWBD (ORCPT ); Sat, 15 Aug 2020 18:01:03 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45640 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728810AbgHOVvd (ORCPT ); Sat, 15 Aug 2020 17:51:33 -0400 Received: from shards.monkeyblade.net (shards.monkeyblade.net [IPv6:2620:137:e000::1:9]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C2D95C0612EF; Fri, 14 Aug 2020 20:41:22 -0700 (PDT) Received: from localhost (unknown [IPv6:2601:601:9f00:477::3d5]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) (Authenticated sender: davem-davemloft) by shards.monkeyblade.net (Postfix) with ESMTPSA id 7D1DC127C1D1F; Fri, 14 Aug 2020 20:24:36 -0700 (PDT) Date: Fri, 14 Aug 2020 20:41:21 -0700 (PDT) Message-Id: <20200814.204121.2301287009173291675.davem@davemloft.net> To: xie.he.0141@gmail.com Cc: kuba@kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-x25@vger.kernel.org, willemdebruijn.kernel@gmail.com, ms@dev.tdt.de, andrew.hendry@gmail.com Subject: Re: [PATCH net] drivers/net/wan/hdlc_x25: Added needed_headroom and a skb->len check From: David Miller In-Reply-To: <20200813181704.62694-1-xie.he.0141@gmail.com> References: <20200813181704.62694-1-xie.he.0141@gmail.com> X-Mailer: Mew version 6.8 on Emacs 26.3 Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.5.12 (shards.monkeyblade.net [149.20.54.216]); Fri, 14 Aug 2020 20:24:36 -0700 (PDT) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Xie He Date: Thu, 13 Aug 2020 11:17:04 -0700 > 1. Added a skb->len check > > This driver expects upper layers to include a pseudo header of 1 byte > when passing down a skb for transmission. This driver will read this > 1-byte header. This patch added a skb->len check before reading the > header to make sure the header exists. > > 2. Added needed_headroom and set hard_header_len to 0 > > When this driver transmits data, > first this driver will remove a pseudo header of 1 byte, > then the lapb module will prepend the LAPB header of 2 or 3 bytes. > So the value of needed_headroom in this driver should be 3 - 1. > > Because this driver has no header_ops, according to the logic of > af_packet.c, the value of hard_header_len should be 0. > > Reason of setting needed_headroom and hard_header_len at this place: > > This driver is written using the API of the hdlc module, the hdlc > module enables this driver (the protocol driver) to run on any hardware > that has a driver (the hardware driver) written using the API of the > hdlc module. > > Two other hdlc protocol drivers - hdlc_ppp and hdlc_raw_eth, also set > things like hard_header_len at this place. In hdlc_ppp, it sets > hard_header_len after attach_hdlc_protocol and before setting dev->type. > In hdlc_raw_eth, it sets hard_header_len by calling ether_setup after > attach_hdlc_protocol and after memcpy the settings. > > 3. Reset needed_headroom when detaching protocols (in hdlc.c) > > When detaching a protocol from a hardware device, the hdlc module will > reset various parameters of the device (including hard_header_len) to > the default values. We add needed_headroom here so that needed_headroom > will also be reset. > > Cc: Willem de Bruijn > Cc: Martin Schiller > Cc: Andrew Hendry > Signed-off-by: Xie He Applied, thanks.