netdev - [PATCH v2 2/2] wan/hdlc_x25: fix skb handling

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Message-Id: <20200114140223.22446-2-ms@dev.tdt.de>
Date:   Tue, 14 Jan 2020 15:02:23 +0100
From:   Martin Schiller <ms@....tdt.de>
To:     kubakici@...pl, khc@...waw.pl, davem@...emloft.net
Cc:     linux-x25@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Martin Schiller <ms@....tdt.de>
Subject: [PATCH v2 2/2] wan/hdlc_x25: fix skb handling

 o call skb_reset_network_header() before hdlc->xmit()
 o change skb proto to HDLC (0x0019) before hdlc->xmit()
 o call dev_queue_xmit_nit() before hdlc->xmit()

This changes make it possible to trace (tcpdump) outgoing layer2
(ETH_P_HDLC) packets

Additionally call skb_reset_network_header() after each skb_push() /
skb_pull().

Signed-off-by: Martin Schiller <ms@....tdt.de>
---
 drivers/net/wan/hdlc_x25.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wan/hdlc_x25.c b/drivers/net/wan/hdlc_x25.c
index 0479a2bf42f7..9eaad151c27f 100644
--- a/drivers/net/wan/hdlc_x25.c
+++ b/drivers/net/wan/hdlc_x25.c
@@ -71,11 +71,12 @@ static int x25_data_indication(struct net_device *dev, struct sk_buff *skb)
 {
 	unsigned char *ptr;
 
-	skb_push(skb, 1);
-
 	if (skb_cow(skb, 1))
 		return NET_RX_DROP;
 
+	skb_push(skb, 1);
+	skb_reset_network_header(skb);
+
 	ptr  = skb->data;
 	*ptr = X25_IFACE_DATA;
 
@@ -88,6 +89,13 @@ static int x25_data_indication(struct net_device *dev, struct sk_buff *skb)
 static void x25_data_transmit(struct net_device *dev, struct sk_buff *skb)
 {
 	hdlc_device *hdlc = dev_to_hdlc(dev);
+
+	skb_reset_network_header(skb);
+	skb->protocol = hdlc_type_trans(skb, dev);
+
+	if (dev_nit_active(dev))
+		dev_queue_xmit_nit(skb, dev);
+
 	hdlc->xmit(skb, dev); /* Ignore return value :-( */
 }
 
@@ -102,6 +110,7 @@ static netdev_tx_t x25_xmit(struct sk_buff *skb, struct net_device *dev)
 	switch (skb->data[0]) {
 	case X25_IFACE_DATA:	/* Data to be transmitted */
 		skb_pull(skb, 1);
+		skb_reset_network_header(skb);
 		if ((result = lapb_data_request(dev, skb)) != LAPB_OK)
 			dev_kfree_skb(skb);
 		return NETDEV_TX_OK;
-- 
2.20.1