netdev - [PATCH net-next] net/packet: Reset MAC header for direct packet transmission

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Message-Id: <20210326154835.21296-1-kurt@linutronix.de>
Date:   Fri, 26 Mar 2021 16:48:35 +0100
From:   Kurt Kanzenbach <kurt@...utronix.de>
To:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        netdev@...r.kernel.org, Kurt Kanzenbach <kurt@...utronix.de>
Subject: [PATCH net-next] net/packet: Reset MAC header for direct packet transmission

Reset MAC header in case of using packet_direct_xmit(), e.g. by specifying
PACKET_QDISC_BYPASS. This is needed, because other code such as the HSR layer
expects the MAC header to be correctly set.

This has been observed using the following setup:

|$ ip link add name hsr0 type hsr slave1 lan0 slave2 lan1 supervision 45 version 1
|$ ifconfig hsr0 up
|$ ./test hsr0

The test binary is using mmap'ed sockets and is specifying the
PACKET_QDISC_BYPASS socket option.

This patch resolves the following warning on a non-patched kernel:

|[  112.725394] ------------[ cut here ]------------
|[  112.731418] WARNING: CPU: 1 PID: 257 at net/hsr/hsr_forward.c:560 hsr_forward_skb+0x484/0x568
|[  112.739962] net/hsr/hsr_forward.c:560: Malformed frame (port_src hsr0)

The MAC header is also reset unconditionally in case of PACKET_QDISC_BYPASS is
not used.

Signed-off-by: Kurt Kanzenbach <kurt@...utronix.de>
---
 net/packet/af_packet.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 118d585337d7..6325c9b7df38 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -241,6 +241,7 @@ static void __fanout_link(struct sock *sk, struct packet_sock *po);
 
 static int packet_direct_xmit(struct sk_buff *skb)
 {
+	skb_reset_mac_header(skb);
 	return dev_direct_xmit(skb, packet_pick_tx_queue(skb));
 }
 
-- 
2.20.1