GRO currently ignores outer IPv4 header IDs for encapsulated packets
that have their don't-fragment flag set. GSO, however, always assumes
that outer IP IDs are incrementing. This results in GSO mangling the
outer IDs when they aren't incrementing. For example, GSO mangles the
outer IDs of IPv6 packets that were converted to IPv4, which must
have an ID of 0 according to RFC 6145, sect. 5.1.

GRO+GSO is supposed to be entirely transparent by default. GSO already
correctly restores inner IDs and IDs of non-encapsulated packets. The
tx-tcp-mangleid-segmentation feature can be enabled to allow the
mangling of such IDs so that TSO can be used.

This series fixes outer ID restoration for encapsulated packets when
tx-tcp-mangleid-segmentation is disabled. It also allows GRO to merge
packets with fixed IDs that don't have their don't-fragment flag set.

v2 -> v3:
 - Make argument const in fou_gro_ops helper
 - Rename SKB_GSO_TCP_FIXEDID_OUTER to SKB_GSO_TCP_FIXEDID
 - Fix formatting in selftest, gro_receive_network_flush and tcp4_gro_complete

v1 -> v2:
 - Add fou_gro_ops helper
 - Clarify why sk_family check works
 - Fix ipip packet generation in selftest

Links:
 - v1: https://lore.kernel.org/netdev/20250814114030.7683-1-richardbgobert@gmail.com/
 - v2: https://lore.kernel.org/netdev/20250819063223.5239-1-richardbgobert@gmail.com/

Richard Gobert (5):
  net: gro: remove is_ipv6 from napi_gro_cb
  net: gro: only merge packets with incrementing or fixed outer ids
  net: gso: restore ids of outer ip headers correctly
  net: gro: remove unnecessary df checks
  selftests/net: test ipip packets in gro.sh

 .../net/ethernet/mellanox/mlx5/core/en_rx.c   |  8 ++-
 drivers/net/ethernet/sfc/ef100_tx.c           | 12 ++--
 include/linux/netdevice.h                     |  9 ++-
 include/linux/skbuff.h                        |  6 +-
 include/net/gro.h                             | 43 ++++++--------
 net/core/dev.c                                |  7 +--
 net/ipv4/af_inet.c                            | 10 +---
 net/ipv4/fou_core.c                           | 32 +++++-----
 net/ipv4/udp_offload.c                        |  2 -
 net/ipv6/udp_offload.c                        |  2 -
 tools/testing/selftests/net/gro.c             | 58 ++++++++++++++-----
 tools/testing/selftests/net/gro.sh            |  5 +-
 12 files changed, 110 insertions(+), 84 deletions(-)

-- 
2.36.1

On Thu, 21 Aug 2025 09:30:42 +0200 Richard Gobert wrote:
> GRO currently ignores outer IPv4 header IDs for encapsulated packets
> that have their don't-fragment flag set. GSO, however, always assumes
> that outer IP IDs are incrementing. This results in GSO mangling the
> outer IDs when they aren't incrementing. For example, GSO mangles the
> outer IDs of IPv6 packets that were converted to IPv4, which must
> have an ID of 0 according to RFC 6145, sect. 5.1.
> 
> GRO+GSO is supposed to be entirely transparent by default. GSO already
> correctly restores inner IDs and IDs of non-encapsulated packets. The
> tx-tcp-mangleid-segmentation feature can be enabled to allow the
> mangling of such IDs so that TSO can be used.
> 
> This series fixes outer ID restoration for encapsulated packets when
> tx-tcp-mangleid-segmentation is disabled. It also allows GRO to merge
> packets with fixed IDs that don't have their don't-fragment flag set.


This series appears to break GSO_PARTIAL:

https://netdev-3.bots.linux.dev/vmksft-fbnic-qemu/results/263201/6-tso-py/stdout
-- 
pw-bot: cr