[PATCH] drivers/net/wan/lapbether: Fixed the value of hard_header_len

From: Xie He
Date: Sat Jul 04 2020 - 01:13:07 EST


When transmitting data from upper layers or from AF_PACKET sockets,
this driver will first remove a pseudo header of 1 byte,
then the lapb module will prepend the LAPB header of 2 or 3 bytes,
then this driver will prepend a length field of 2 bytes,
then the underlying Ethernet device will prepend its own header.

So, the header length required should be:
-1 + 3 + 2 + "the header length needed by the underlying device".

This patch fixes kernel panic when this driver is used with AF_PACKET
SOCK_DGRAM sockets.

Signed-off-by: Xie He <xie.he.0141@xxxxxxxxx>
---
drivers/net/wan/lapbether.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wan/lapbether.c b/drivers/net/wan/lapbether.c
index e30d91a38cfb..3b5ed0928a4c 100644
--- a/drivers/net/wan/lapbether.c
+++ b/drivers/net/wan/lapbether.c
@@ -303,7 +303,6 @@ 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 = 3;
dev->mtu = 1000;
dev->addr_len = 0;
}
@@ -324,6 +323,8 @@ static int lapbeth_new_device(struct net_device *dev)
if (!ndev)
goto out;

+ ndev->hard_header_len = -1 + 3 + 2 + dev->hard_header_len;
+
lapbeth = netdev_priv(ndev);
lapbeth->axdev = ndev;

--
2.25.1