mactap: Fix checksum errors for non-gso packets in bridge mode
authorVlad Yasevich <vyasevic@redhat.com>
Tue, 29 Apr 2014 14:09:50 +0000 (10:09 -0400)
committerDavid S. Miller <davem@davemloft.net>
Wed, 30 Apr 2014 20:12:22 +0000 (16:12 -0400)
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>
drivers/net/macvtap.c

index ff111a89e17f9c66561d79916d8d57e282c119d2..3381c4f91a8cc236df0df8be59bd586538480498 100644 (file)
@@ -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);
        }