linux-kernel - [PATCH 3.16.y-ckt 066/126] net/core: Handle csum for CHECKSUM

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Message-Id: <1422361031-19364-67-git-send-email-luis.henriques@canonical.com>
Date:	Tue, 27 Jan 2015 12:16:11 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Jay Vosburgh <jay.vosburgh@...onical.com>,
	"David S. Miller" <davem@...emloft.net>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 066/126] net/core: Handle csum for CHECKSUM_COMPLETE VXLAN forwarding

3.16.7-ckt5 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jay Vosburgh <jay.vosburgh@...onical.com>

commit 2c26d34bbcc0b3f30385d5587aa232289e2eed8e upstream.

When using VXLAN tunnels and a sky2 device, I have experienced
checksum failures of the following type:

[ 4297.761899] eth0: hw csum failure
[...]
[ 4297.765223] Call Trace:
[ 4297.765224]  <IRQ>  [<ffffffff8172f026>] dump_stack+0x46/0x58
[ 4297.765235]  [<ffffffff8162ba52>] netdev_rx_csum_fault+0x42/0x50
[ 4297.765238]  [<ffffffff8161c1a0>] ? skb_push+0x40/0x40
[ 4297.765240]  [<ffffffff8162325c>] __skb_checksum_complete+0xbc/0xd0
[ 4297.765243]  [<ffffffff8168c602>] tcp_v4_rcv+0x2e2/0x950
[ 4297.765246]  [<ffffffff81666ca0>] ? ip_rcv_finish+0x360/0x360

	These are reliably reproduced in a network topology of:

container:eth0 == host(OVS VXLAN on VLAN) == bond0 == eth0 (sky2) -> switch

	When VXLAN encapsulated traffic is received from a similarly
configured peer, the above warning is generated in the receive
processing of the encapsulated packet.  Note that the warning is
associated with the container eth0.

        The skbs from sky2 have ip_summed set to CHECKSUM_COMPLETE, and
because the packet is an encapsulated Ethernet frame, the checksum
generated by the hardware includes the inner protocol and Ethernet
headers.

	The receive code is careful to update the skb->csum, except in
__dev_forward_skb, as called by dev_forward_skb.  __dev_forward_skb
calls eth_type_trans, which in turn calls skb_pull_inline(skb, ETH_HLEN)
to skip over the Ethernet header, but does not update skb->csum when
doing so.

	This patch resolves the problem by adding a call to
skb_postpull_rcsum to update the skb->csum after the call to
eth_type_trans.

Signed-off-by: Jay Vosburgh <jay.vosburgh@...onical.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 net/core/dev.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/core/dev.c b/net/core/dev.c
index 9785af6c54d4..a4ebbe7d4f15 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1686,6 +1686,7 @@ int __dev_forward_skb(struct net_device *dev, struct sk_buff *skb)
 
 	skb_scrub_packet(skb, true);
 	skb->protocol = eth_type_trans(skb, dev);
+	skb_postpull_rcsum(skb, eth_hdr(skb), ETH_HLEN);
 
 	return 0;
 }
-- 
2.1.4

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