On Wed, 28 Sep 2016 16:43:38 +0200 Daniel Borkmann <dan...@iogearbox.net> wrote:
> Couldn't we end up with 1) for the act_vlan case when we'd have the
> offset-adjusted skb_vlan_push() fix from here, where we'd then redirect
> to ingress where skb_vlan_pop() would be called? If I'm not missing
> something, skb_vlan_push() would then point to the data location of 1)
> and with your other proposed direct netif_receive_skb() patch, no
> further skb->data adjustments would be done, right?
Right. Then skb_vlan_pop() should expect either (1) or (2).
> Another potential issue (but unrelated to this fix here) I just noticed
> is, whether act_vlan might have the same problem as we fixed in 8065694e6519
> ("bpf: fix checksum for vlan push/pop helper"). So potentially, we could
> end up fixing CHECKSUM_COMPLETE wrongly on ingress, since these 14 bytes
> are already pulled out of the sum at that point.
>
> > Should we adjust "offset" back, only if resulting offset is >=14 ?
>
> If also the checksum one might end up as an issue, maybe it's just best
> to go through the pain and do the push/pull for data plus csum, so both
> skb_vlan_*() functions see the frame starting from mac header temporarily?
Although not related to this specific fix, I see 2 ways addressing the
rcsum problem:
1. Per your suggestion, skb_vlan_*() to expect 'data' at mac_header
That would simplify things; for this suggested 'data unwind' fix as well
2. Within skb_vlan_*(), deduct (according to initial offset) whether
we're already "pulled out" of the rcsum, and not invoke the
skb_postpull/push_rcsum update.
Will meditate some more.
Thanks
Shmulik
