linux-kernel - [PATCH net] drivers/net/wan/lapbether: Set network

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Date:   Tue, 25 Aug 2020 20:03:53 -0700
From:   Xie He <xie.he.0141@...il.com>
To:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-x25@...r.kernel.org
Cc:     Xie He <xie.he.0141@...il.com>, Martin Schiller <ms@....tdt.de>
Subject: [PATCH net] drivers/net/wan/lapbether: Set network_header before transmitting

Set the skb's network_header before it is passed to the underlying
Ethernet device for transmission.

This patch fixes the following issue:

When we use this driver with AF_PACKET sockets, there would be error
messages of:
   protocol 0805 is buggy, dev (Ethernet interface name)
printed in the system "dmesg" log.

This is because skbs passed down to the Ethernet device for transmission
don't have their network_header properly set, and the dev_queue_xmit_nit
function in net/core/dev.c complains about this.

Reason of setting the network_header to this place (at the end of the
Ethernet header, and at the beginning of the Ethernet payload):

Because when this driver receives an skb from the Ethernet device, the
network_header is also set at this place.

Cc: Martin Schiller <ms@....tdt.de>
Signed-off-by: Xie He <xie.he.0141@...il.com>
---
 drivers/net/wan/lapbether.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/wan/lapbether.c b/drivers/net/wan/lapbether.c
index cc297ea9c6ec..e61616b0b91c 100644
--- a/drivers/net/wan/lapbether.c
+++ b/drivers/net/wan/lapbether.c
@@ -210,6 +210,8 @@ static void lapbeth_data_transmit(struct net_device *ndev, struct sk_buff *skb)

 	skb->dev = dev = lapbeth->ethdev;

+	skb_reset_network_header(skb);
+
 	dev_hard_header(skb, dev, ETH_P_DEC, bcast_addr, NULL, 0);

 	dev_queue_xmit(skb);
-- 
2.25.1