[PATCH AUTOSEL 4.9 06/10] drivers/net/wan/lapbether: Fixed the value of hard_header_len

Sasha Levin
2020-07-14T14:40:33Z

From: Xie He <xie.he.0141@gmail.com>

[ 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>
---
drivers/net/wan/lapbether.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wan/lapbether.c b/drivers/net/wan/lapbether.c
index 6676607164d65..f5657783fad4e 100644
--- 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;

--
2.25.1