[PATCH bpf-next v5 0/6] bpf: decap flags and GSO state updates

Nick Hudson
2026-04-20T10:41:04Z

This series extends bpf_skb_adjust_room() with decapsulation-specific
flags and tunnel GSO state updates for decap use cases.

Motivation
----------

When BPF decapsulates tunneled packets, skb GSO state needs to be
updated to match the removed tunnel layer. This includes clearing the
corresponding tunnel GSO type bits and resetting encapsulation state
once no tunnel GSO flags remain.

Series Overview
---------------

- Name the adjust_room flag enum for CO-RE lookups.
- Refactor adjust_room helper masks for maintainable validation logic.
- Add new DECAP flags to UAPI.
- Add guard rails for incompatible/invalid decap flag combinations.
- Implement decap GSO flag clearing.
- Add selftests to validate decap GSO state transitions.

Changes v4 -> v5:
- Patch 5: Remove explicit clearing of encap_hdr_csum and
remcsum_offload on UDP decap, per review feedback.
- Patch 6: Remove SKB_GSO_TUNNEL_REMCSUM from SKB_GSO_UDP_TUNNEL_MASK
in selftests, and minor test improvements.

Changes v3 -> v4:
- Patch 5: drop SKB_GSO_TUNNEL_REMCSUM handling from this series.
- Patch 5: clear encap_hdr_csum and remcsum_offload directly on UDP
decap.

Changes v2 -> v3:
- Add a new selftests patch to validate decap GSO state behavior.
- Reorder the series so helper-mask refactoring precedes UAPI DECAP
flag additions.
- Refresh patch 2 and patch 3 split to keep refactoring
behavior-neutral.
- Patch 5: add decap tunnel GSO-state checks in "bpf: clear decap
tunnel GSO state in skb_adjust_room" (per Gemini/sashiko).

Changes v1 -> v2:
- Patch 3: decap flag acceptance intentionally remains L3-only while
adding helper masks.
- Patch 4: decap with L4/IPXIP support enabled with guard rails.

Co-developed-by: Max Tottenham <mtottenh@akamai.com>
Signed-off-by: Max Tottenham <mtottenh@akamai.com>
Co-developed-by: Anna Glasgall <aglasgal@akamai.com>
Signed-off-by: Anna Glasgall <aglasgal@akamai.com>
Signed-off-by: Nick Hudson <nhudson@akamai.com>

Nick Hudson (6):
bpf: name the enum for BPF_FUNC_skb_adjust_room flags
bpf: refactor masks for ADJ_ROOM flags and encap validation
bpf: add BPF_F_ADJ_ROOM_DECAP_* flags for tunnel decapsulation
bpf: allow new DECAP flags and add guard rails
bpf: clear decap tunnel GSO state in skb_adjust_room
selftests/bpf: tc_tunnel validate decap GSO state

include/uapi/linux/bpf.h | 36 +++++-
net/core/filter.c | 118 +++++++++++++++---
tools/include/uapi/linux/bpf.h | 36 +++++-
.../selftests/bpf/progs/test_tc_tunnel.c | 58 +++++++++
4 files changed, 225 insertions(+), 23 deletions(-)

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2.34.1