From: David Miller <davem@xxxxxxxxxxxxx>
Date: Tue, 18 Apr 2017 15:07:08 -0400 (EDT)
> From: Andy Gospodarek <andy@xxxxxxxxxxxxx>
> Date: Tue, 18 Apr 2017 15:05:35 -0400
>
>> On Fri, Apr 14, 2017 at 05:59:51PM -0700, Alexei Starovoitov wrote:
>>> On Thu, Apr 13, 2017 at 04:23:15PM -0400, David Miller wrote:
>>> > +
>>> > + switch (act) {
>>> > + case XDP_TX:
>>> > + __skb_push(skb, skb->mac_len);
>>>
>>> s/skb->mac_len/mac_len/
>>>
>>
>> I was away from my keyboard for a few days, but was able to get some
>> time to test this today.
>>
>> When using this change above suggested by Alexei, XDP_DROP and XDP_TX
>> actions appear to work well with xdp1 and xdp2.
>>
>> I'm seeing some rather odd behavior with xdp_tx_tunnel so it might be
>> good to hold off on committing this just yet.
>>
>> At first glance, it looks like there is enough headroom for the new
>> frame, but the resulting packet data do not look right and I'm actually
>> seeing some data that may be left on the stack from a previous caller.
>
> Thanks for testing Andy, I'll take a look and see if I can figure it out.
Andy, I think we might be getting burnt by signedness issues in the
offset handling when the XDP program adjusts the packet data pointer.
In netif_receive_generic_xdp(), try changing the offset handling code to
read something like:
off = xdp.data - orig_data;
if (off > 0)
__skb_pull(skb, off);
else if (off < 0)
__skb_push(skb, -off);
If that doesn't work try adding:
__skb_cow(skb, XDP_PACKET_HEADROOM, 0);
right after the skb_linearize() call in that same function.
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