[PATCH 2/2] wan/hdlc_x25: fix skb handling

Martin Schiller
2020-01-13T12:46:08Z

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

o use a copy of the skb for lapb_data_request() in x25_xmit()

This fixes the problem, that tracing layer3 (ETH_P_X25) packets
results in a malformed first byte of the packets.

Signed-off-by: Martin Schiller <ms@dev.tdt.de>
---
drivers/net/wan/hdlc_x25.c | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/drivers/net/wan/hdlc_x25.c b/drivers/net/wan/hdlc_x25.c
index b28051eba736..434e5263eddf 100644
--- a/drivers/net/wan/hdlc_x25.c
+++ b/drivers/net/wan/hdlc_x25.c
@@ -72,6 +72,7 @@ static int x25_data_indication(struct net_device *dev, struct sk_buff *skb)
unsigned char *ptr;

skb_push(skb, 1);
+ skb_reset_network_header(skb);

if (skb_cow(skb, 1))
return NET_RX_DROP;
@@ -88,6 +89,9 @@ 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);
+ dev_queue_xmit_nit(skb, dev);
hdlc->xmit(skb, dev); /* Ignore return value :-( */
}

@@ -95,16 +99,19 @@ static void x25_data_transmit(struct net_device *dev, struct sk_buff *skb)

static netdev_tx_t x25_xmit(struct sk_buff *skb, struct net_device *dev)
{
+ struct sk_buff *skbn;
int result;

/* X.25 to LAPB */
switch (skb->data[0]) {
case X25_IFACE_DATA: /* Data to be transmitted */
- skb_pull(skb, 1);
- if ((result = lapb_data_request(dev, skb)) != LAPB_OK)
- dev_kfree_skb(skb);
- return NETDEV_TX_OK;
+ skbn = skb_copy(skb, GFP_ATOMIC);
+ skb_pull(skbn, 1);
+ skb_reset_network_header(skbn);
+ if ((result = lapb_data_request(dev, skbn)) != LAPB_OK)
+ dev_kfree_skb(skbn);
+ break;

case X25_IFACE_CONNECT:
if ((result = lapb_connect_request(dev))!= LAPB_OK) {
--
2.20.1