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=-10.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 71A1FC433E0 for ; Tue, 4 Aug 2020 12:43:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5258B2067D for ; Tue, 4 Aug 2020 12:43:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728282AbgHDMnv (ORCPT ); Tue, 4 Aug 2020 08:43:51 -0400 Received: from host-88-217-225-28.customer.m-online.net ([88.217.225.28]:56536 "EHLO mail.dev.tdt.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726210AbgHDMnu (ORCPT ); Tue, 4 Aug 2020 08:43:50 -0400 Received: from mail.dev.tdt.de (localhost [IPv6:::1]) by mail.dev.tdt.de (Postfix) with ESMTP id 94668200F9; Tue, 4 Aug 2020 12:43:46 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Tue, 04 Aug 2020 14:43:46 +0200 From: Martin Schiller To: Xie He Cc: "David S. Miller" , Jakub Kicinski , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-x25@vger.kernel.org, Willem de Bruijn , Brian Norris , netdev-owner@vger.kernel.org Subject: Re: [net v3] drivers/net/wan/lapbether: Use needed_headroom instead of hard_header_len Organization: TDT AG In-Reply-To: <20200802195046.402539-1-xie.he.0141@gmail.com> References: <20200802195046.402539-1-xie.he.0141@gmail.com> Message-ID: X-Sender: ms@dev.tdt.de User-Agent: Roundcube Webmail/1.1.5 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-08-02 21:50, Xie He wrote: > In net/packet/af_packet.c, the function packet_snd first reserves a > headroom of length (dev->hard_header_len + dev->needed_headroom). > Then if the socket is a SOCK_DGRAM socket, it calls dev_hard_header, > which calls dev->header_ops->create, to create the link layer header. > If the socket is a SOCK_RAW socket, it "un-reserves" a headroom of > length (dev->hard_header_len), and assumes the user to provide the > appropriate link layer header. > > So according to the logic of af_packet.c, dev->hard_header_len should > be the length of the header that would be created by > dev->header_ops->create. > > However, this driver doesn't provide dev->header_ops, so logically > dev->hard_header_len should be 0. > > So we should use dev->needed_headroom instead of dev->hard_header_len > to request necessary headroom to be allocated. I'm not an expert in the field, but after reading the commit message and the previous comments, I'd say that makes sense. > > This change fixes kernel panic when this driver is used with AF_PACKET > SOCK_RAW sockets. Call stack when panic: > > [ 168.399197] skbuff: skb_under_panic: text:ffffffff819d95fb len:20 > put:14 head:ffff8882704c0a00 data:ffff8882704c09fd tail:0x11 end:0xc0 > dev:veth0 > ... > [ 168.399255] Call Trace: > [ 168.399259] skb_push.cold+0x14/0x24 > [ 168.399262] eth_header+0x2b/0xc0 > [ 168.399267] lapbeth_data_transmit+0x9a/0xb0 [lapbether] > [ 168.399275] lapb_data_transmit+0x22/0x2c [lapb] > [ 168.399277] lapb_transmit_buffer+0x71/0xb0 [lapb] > [ 168.399279] lapb_kick+0xe3/0x1c0 [lapb] > [ 168.399281] lapb_data_request+0x76/0xc0 [lapb] > [ 168.399283] lapbeth_xmit+0x56/0x90 [lapbether] > [ 168.399286] dev_hard_start_xmit+0x91/0x1f0 > [ 168.399289] ? irq_init_percpu_irqstack+0xc0/0x100 > [ 168.399291] __dev_queue_xmit+0x721/0x8e0 > [ 168.399295] ? packet_parse_headers.isra.0+0xd2/0x110 > [ 168.399297] dev_queue_xmit+0x10/0x20 > [ 168.399298] packet_sendmsg+0xbf0/0x19b0 > ...... Shouldn't this kernel panic be intercepted by a skb_cow() before the skb_push() in lapbeth_data_transmit()? > > Additional change: > When sending, check skb->len to ensure the 1-byte pseudo header is > present before reading it. > > Cc: Willem de Bruijn > Cc: Brian Norris > Signed-off-by: Xie He > --- > > Change from v2: > Added skb->len check when sending. > > Change from v1: > None > > --- > drivers/net/wan/lapbether.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/drivers/net/wan/lapbether.c b/drivers/net/wan/lapbether.c > index b2868433718f..8a3f7ba36f7e 100644 > --- a/drivers/net/wan/lapbether.c > +++ b/drivers/net/wan/lapbether.c > @@ -157,6 +157,9 @@ static netdev_tx_t lapbeth_xmit(struct sk_buff > *skb, > if (!netif_running(dev)) > goto drop; > > + if (skb->len < 1) > + goto drop; > + > switch (skb->data[0]) { > case X25_IFACE_DATA: > break; > @@ -305,6 +308,7 @@ static void lapbeth_setup(struct net_device *dev) > dev->netdev_ops = &lapbeth_netdev_ops; > dev->needs_free_netdev = true; > dev->type = ARPHRD_X25; > + dev->hard_header_len = 0; > dev->mtu = 1000; > dev->addr_len = 0; > } > @@ -331,7 +335,8 @@ static int lapbeth_new_device(struct net_device > *dev) > * then this driver prepends a length field of 2 bytes, > * then the underlying Ethernet device prepends its own header. > */ > - ndev->hard_header_len = -1 + 3 + 2 + dev->hard_header_len; > + ndev->needed_headroom = -1 + 3 + 2 + dev->hard_header_len > + + dev->needed_headroom; > > lapbeth = netdev_priv(ndev); > lapbeth->axdev = ndev;