[PATCH 3.13 038/212] mactap: Fix checksum errors for non-gso packets in bridge mode

Kamal Mostafa
2014-06-17T21:42:12Z

From: Vlad Yasevich <vyasevic@redhat.com>

[ Upstream commit cbdb04279ccaefcc702c8757757eea8ed76e50cf ]

The following is a problematic configuration:

VM1: virtio-net device connected to macvtap0@eth0
VM2: e1000 device connect to macvtap1@eth0

The problem is is that virtio-net supports checksum offloading
and thus sends the packets to the host with CHECKSUM_PARTIAL set.
On the other hand, e1000 does not support any acceleration.

For small TCP packets (and this includes the 3-way handshake),
e1000 ends up receiving packets that only have a partial checksum
set. This causes TCP to fail checksum validation and to drop
packets. As a result tcp connections can not be established.

Commit 3e4f8b787370978733ca6cae452720a4f0c296b8
macvtap: Perform GSO on forwarding path.
fixes this issue for large packets wthat will end up undergoing GSO.
This commit adds a check for the non-GSO case and attempts to
compute the checksum for partially checksummed packets in the
non-GSO case.

CC: Daniel Lezcano <daniel.lezcano@free.fr>
CC: Patrick McHardy <kaber@trash.net>
CC: Andrian Nord <nightnord@gmail.com>
CC: Eric Dumazet <eric.dumazet@gmail.com>
CC: Michael S. Tsirkin <mst@redhat.com>
CC: Jason Wang <jasowang@redhat.com>
Signed-off-by: Vlad Yasevich <vyasevic@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
drivers/net/macvtap.c | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index 2a89da0..73ffad8 100644
--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -315,6 +315,15 @@ static int macvtap_forward(struct net_device *dev, struct sk_buff *skb)
segs = nskb;
}
} else {
+ /* If we receive a partial checksum and the tap side
+ * doesn't support checksum offload, compute the checksum.
+ * Note: it doesn't matter which checksum feature to
+ * check, we either support them all or none.
+ */
+ if (skb->ip_summed == CHECKSUM_PARTIAL &&
+ !(features & NETIF_F_ALL_CSUM) &&
+ skb_checksum_help(skb))
+ goto drop;
skb_queue_tail(&q->sk.sk_receive_queue, skb);
}

--
1.9.1