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[209.85.217.52]) by smtp.gmail.com with ESMTPSA id f10sm1603252uad.5.2020.08.03.02.50.03 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 03 Aug 2020 02:50:04 -0700 (PDT) Received: by mail-vs1-f52.google.com with SMTP id p8so11436234vsm.12 for ; Mon, 03 Aug 2020 02:50:03 -0700 (PDT) X-Received: by 2002:a67:f454:: with SMTP id r20mr10240727vsn.20.1596448203263; Mon, 03 Aug 2020 02:50:03 -0700 (PDT) MIME-Version: 1.0 References: <20200802195046.402539-1-xie.he.0141@gmail.com> In-Reply-To: <20200802195046.402539-1-xie.he.0141@gmail.com> From: Willem de Bruijn Date: Mon, 3 Aug 2020 11:49:25 +0200 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [net v3] drivers/net/wan/lapbether: Use needed_headroom instead of hard_header_len To: Xie He Cc: "David S. Miller" , Jakub Kicinski , Network Development , linux-kernel , Linux X25 , Willem de Bruijn , Brian Norris Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Aug 2, 2020 at 9:51 PM 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. > > 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 > ...... > > 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 Overall, looks great. A few nits. It's [PATCH net v3], not [net v3] > 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; > + Might be worth a comment along the lines of: /* upper layers pass a control byte. must validate pf_packet input */ > 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; Technically not needed. The struct is allocated with kvzalloc, z for __GFP_ZERO. Fine to leave if intended as self-describing comment, of course. > 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; > -- > 2.25.1 >