On Thu, Mar 25, 2021 at 1:24 PM Paolo Abeni <pab...@redhat.com> wrote: > > If NETIF_F_GRO_FRAGLIST or NETIF_F_GRO_UDP_FWD are enabled, and there > are UDP tunnels available in the system, udp_gro_receive() could end-up > doing L4 aggregation (either SKB_GSO_UDP_L4 or SKB_GSO_FRAGLIST) at > the outer UDP tunnel level for packets effectively carrying and UDP > tunnel header. > > That could cause inner protocol corruption. If e.g. the relevant > packets carry a vxlan header, different vxlan ids will be ignored/ > aggregated to the same GSO packet. Inner headers will be ignored, too, > so that e.g. TCP over vxlan push packets will be held in the GRO > engine till the next flush, etc. > > Just skip the SKB_GSO_UDP_L4 and SKB_GSO_FRAGLIST code path if the > current packet could land in a UDP tunnel, and let udp_gro_receive() > do GRO via udp_sk(sk)->gro_receive. > > The check implemented in this patch is broader than what is strictly > needed, as the existing UDP tunnel could be e.g. configured on top of > a different device: we could end-up skipping GRO at-all for some packets. > > Anyhow, the latter is a very thin corner case and covering it would add > quite a bit of complexity. > > v1 -> v2: > - hopefully clarify the commit message > > Fixes: 9fd1ff5d2ac7 ("udp: Support UDP fraglist GRO/GSO.") > Fixes: 36707061d6ba ("udp: allow forwarding of plain (non-fraglisted) UDP GRO > packets") > Signed-off-by: Paolo Abeni <pab...@redhat.com>
Reviewed-by: Willem de Bruijn <will...@google.com> Key is that udp tunnel GRO must take precedence over transport GRO, but the way the code is structured, the latter is tried first.