On 2021-01-08 22:35, Steffen Klassert wrote: > On Fri, Jan 08, 2021 at 09:52:28PM +0900, Dongseok Yi wrote: > > It is a workaround patch. > > > > UDP/IP header of UDP GROed frag_skbs are not updated even after NAT > > forwarding. Only the header of head_skb from ip_finish_output_gso -> > > skb_gso_segment is updated but following frag_skbs are not updated. > > > > A call path skb_mac_gso_segment -> inet_gso_segment -> > > udp4_ufo_fragment -> __udp_gso_segment -> __udp_gso_segment_list > > does not try to update any UDP/IP header of the segment list. > > > > It might make sense because each skb of frag_skbs is converted to a > > list of regular packets. Header update with checksum calculation may > > be not needed for UDP GROed frag_skbs. > > > > But UDP GRO frag_list is started from udp_gro_receive, we don't know > > whether the skb will be NAT forwarded at that time. For workaround, > > try to get sock always when call udp4_gro_receive -> udp_gro_receive > > to check if the skb is for local. > > > > I'm still not sure if UDP GRO frag_list is really designed for local > > session only. Can kernel support NAT forward for UDP GRO frag_list? > > What am I missing? > > The initial idea when I implemented this was to have a fast > forwarding path for UDP. So forwarding is a usecase, but NAT > is a problem, indeed. A quick fix could be to segment the > skb before it gets NAT forwarded. Alternatively we could > check for a header change in __udp_gso_segment_list and > update the header of the frag_skbs accordingly in that case.
Thank you for explaining. Can I think of it as a known issue? I think we should have a fix because NAT can be triggered by user. Can I check the current status? Already planning a patch or a new patch should be written?
