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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Martin Schiller <ms@dev.tdt.de>,
        Xie He <xie.he.0141@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.19 18/38] drivers/net/wan/lapbether: Make skb->protocol consistent with the header
Date:   Mon,  5 Oct 2020 17:26:35 +0200
Message-Id: <20201005142109.551212212@linuxfoundation.org>
In-Reply-To: <20201005142108.650363140@linuxfoundation.org>
References: <20201005142108.650363140@linuxfoundation.org>
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From: Xie He <xie.he.0141@gmail.com>

[ Upstream commit 83f9a9c8c1edc222846dc1bde6e3479703e8e5a3 ]

This driver is a virtual driver stacked on top of Ethernet interfaces.

When this driver transmits data on the Ethernet device, the skb->protocol
setting is inconsistent with the Ethernet header prepended to the skb.

This causes a user listening on the Ethernet interface with an AF_PACKET
socket, to see different sll_protocol values for incoming and outgoing
frames, because incoming frames would have this value set by parsing the
Ethernet header.

This patch changes the skb->protocol value for outgoing Ethernet frames,
making it consistent with the Ethernet header prepended. This makes a
user listening on the Ethernet device with an AF_PACKET socket, to see
the same sll_protocol value for incoming and outgoing frames.

Cc: Martin Schiller <ms@dev.tdt.de>
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 | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wan/lapbether.c b/drivers/net/wan/lapbether.c
index 15177a54b17d7..e5fc1b95cea6a 100644
--- a/drivers/net/wan/lapbether.c
+++ b/drivers/net/wan/lapbether.c
@@ -201,8 +201,6 @@ static void lapbeth_data_transmit(struct net_device *ndev, struct sk_buff *skb)
 	struct net_device *dev;
 	int size = skb->len;
 
-	skb->protocol = htons(ETH_P_X25);
-
 	ptr = skb_push(skb, 2);
 
 	*ptr++ = size % 256;
@@ -213,6 +211,8 @@ static void lapbeth_data_transmit(struct net_device *ndev, struct sk_buff *skb)
 
 	skb->dev = dev = lapbeth->ethdev;
 
+	skb->protocol = htons(ETH_P_DEC);
+
 	skb_reset_network_header(skb);
 
 	dev_hard_header(skb, dev, ETH_P_DEC, bcast_addr, NULL, 0);
-- 
2.25.1