Commit cbdb0427 authored Apr 29, 2014 by Vlad Yasevich Committed by David S. Miller Apr 30, 2014

mactap: Fix checksum errors for non-gso packets in bridge mode



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 3e4f8b78
	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>

parent fc9f3501

drivers/net/macvtap.c

+9 −0

Original line number	Diff line number	Diff line
		@@ -322,6 +322,15 @@ static rx_handler_result_t macvtap_handle_frame(struct sk_buff **pskb)
		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);
		}

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