I have an application that creates two pairs of veth devices.
a <-> b c <-> d
b and c have a raw packet socket opened on them and I 'bridge' frames
between b and c to provide network emulation (ie, configurable delay).
I put IP 1.1.1.1/24 on a, 1.1.1.2/24 on d, and then create a UDP connection
(using policy based routing to ensure frames are sent on the appropriate
interfaces).
This is user-space only app, and kernel in this case is completely unmodified.
The commit below breaks this feature: UDP frames are sniffed on both a and d
ports
(in both directions), but the UDP socket does not receive frames.
Using normal ethernet ports, this network emulation feature works fine, so it is
specific to VETH.
A similar test with just sending UDP between a single veth pair: e <-> f
works fine. Maybe it has something to do with raw packets?
The patch below is the culprit:
[greearb@ben-dt3 linux-2.6]$ git bisect bad
ce8c839b74e3017996fad4e1b7ba2e2625ede82f is the first bad commit
commit ce8c839b74e3017996fad4e1b7ba2e2625ede82f
Author: Vijay Pandurangan <vij...@vijayp.ca>
Date: Fri Dec 18 14:34:59 2015 -0500
veth: don’t modify ip_summed; doing so treats packets with bad checksums as
good.
Packets that arrive from real hardware devices have ip_summed ==
CHECKSUM_UNNECESSARY if the hardware verified the checksums, or
CHECKSUM_NONE if the packet is bad or it was unable to verify it. The
current version of veth will replace CHECKSUM_NONE with
CHECKSUM_UNNECESSARY, which causes corrupt packets routed from hardware to
a veth device to be delivered to the application. This caused applications
at Twitter to receive corrupt data when network hardware was corrupting
packets.
...
diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index 0ef4a5a..ba21d07 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -117,12 +117,6 @@ static netdev_tx_t veth_xmit(struct sk_buff *skb, struct
net_device *dev)
kfree_skb(skb);
goto drop;
}
- /* don't change ip_summed == CHECKSUM_PARTIAL, as that
- * will cause bad checksum on forwarded packets
- */
- if (skb->ip_summed == CHECKSUM_NONE &&
- rcv->features & NETIF_F_RXCSUM)
- skb->ip_summed = CHECKSUM_UNNECESSARY;
if (likely(dev_forward_skb(rcv, skb) == NET_RX_SUCCESS)) {
struct pcpu_vstats *stats = this_cpu_ptr(dev->vstats);
Any suggestions for how to fix this so that I get the old working behaviour and
the bug this patch was trying to fix is also resolved?
Thanks,
Ben
--
Ben Greear <gree...@candelatech.com>
Candela Technologies Inc http://www.candelatech.com
