Re: [PATCH 2/3] net: UDP gro_receive accept csum=0

[Joseph Gasparakis <joseph.gasparakis@intel.com>]

On Thu, 13 Feb 2014, Tom Herbert wrote:

> >> > But even worse, is there a fundamental issue where udp4_csum_init is able
> >> > to change ip_summed to be CHECKSUM_UNNECESSARY (either check == 0
> >> > or ip_summed == CHECKSUM_UNNECESSARY) regardless of
> >> > skb->encapsulation, sending the packet into encap_rcv which could
> >> > ultimately incorrectly apply ip_summed on the inner TCP/UDP packet?
> >>
> >> By fundamental you mean performance issue or functionality issue (bug) or both?
> >>
> >
> > I would expect the check to be for ip_summed == CHECKSUM_UNNECESSARY. This
> > was the original thought behind commit:
> >
> > 0afb166 vxlan: Add capability of Rx checksum offload for inner packet
> 
> It looks like udp4_csum_init turns CHECKSUM_COMPLETE and check==0 into
> CHECKSUM_UNNECESSARY which could bypass the checksum validation for
> the encapsulated packet. This would be a significant functionality
> bug. Unfortunately udp4_csum_init writes ip_summed without regard to
> encapsulation.
> 
> Seems like the logic in the UDP rcv path should be:
> 
> if ip_summed == CHECKSUM_COMPLETE, ensure this is same value when
> calling encap_rcv
> if ip_summed == CHECKSUM_UNNECESSARY && !skb->encap change to
> CHECKSUM_NONE before calling encap_rcv
> if ip_summed == CHECKSUM_UNNECESSARY && skb->encap ip_summed value is okay
> 
> In any case, we need to consider the orignal ip_summed value from the
> driver, not the one that udp4_csum_init (udp_gro or anywhere else in
> the path) would set.
> 
> Also, udp_gro_receive should be able to handle the case where
> ip_summed == CHECKSUM_UNNECESSARY and !skb->encapsulation, that will
> be very common scenario. Probably CHECKSUM_NONE also.
> 

Yes, I now see your point and totaly agree. Thanks.