drivers/net/wan/lapbether: Fixed the value of hard_header_len

[ Upstream commit 9dc829a135fb5927f1519de11286e2bbb79f5b66 ]

When this driver transmits data,
  first this driver will 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@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/net/wan/lapbether.c b/drivers/net/wan/lapbether.c
index 6676607..f565778 100644 (file)
--- a/drivers/net/wan/lapbether.c
+++ b/drivers/net/wan/lapbether.c
@@ -308,7 +308,6 @@ static void lapbeth_setup(struct net_device *dev)
        dev->netdev_ops      = &lapbeth_netdev_ops;
        dev->destructor      = free_netdev;
        dev->type            = ARPHRD_X25;
-       dev->hard_header_len = 3;
        dev->mtu             = 1000;
        dev->addr_len        = 0;
 }
@@ -329,6 +328,14 @@ static int lapbeth_new_device(struct net_device *dev)
        if (!ndev)
                goto out;
 
+       /* When transmitting data:
+        * first this driver removes a pseudo header of 1 byte,
+        * then the lapb module prepends an LAPB header of at most 3 bytes,
+        * 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;
+
        lapbeth = netdev_priv(ndev);
        lapbeth->axdev = ndev;