From: Xie He <xie.he.0141@gmail.com>
To: "David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
Madhuparna Bhowmik <madhuparnabhowmik04@gmail.com>,
Xie He <xie.he.0141@gmail.com>,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-x25@vger.kernel.org
Subject: [PATCH v2] drivers/net/wan/lapbether: Fixed the value of hard_header_len
Date: Sun, 5 Jul 2020 17:45:21 -0700 [thread overview]
Message-ID: <20200706004521.78091-1-xie.he.0141@gmail.com> (raw)
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>
---
Change in v2: added a comment in the code
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 e30d91a38cfb..284832314f31 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 +323,14 @@ 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
next reply other threads:[~2020-07-06 0:45 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-06 0:45 Xie He [this message]
2020-07-06 19:16 ` [PATCH v2] drivers/net/wan/lapbether: Fixed the value of hard_header_len David Miller
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