[PATCH bpf v3 0/2] bpf: Update transport_header when encapsulating UDP tunnel in lwt

[Leon Hwang <leon.hwang@linux.dev>]

Currently, bpf_lwt_push_ip_encap() does not update skb->transport_header.
When a driver, e.g. ice, reuses the stale skb->transport_header to
offload checksum computation to NIC hardware, VxLAN packets encapsulated
by bpf_lwt_push_encap() helper may be dropped due to incorrect checksum.

Update skb->transport_header in bpf_lwt_push_ip_encap() whenever the
encapsulated packet uses UDP, so checksum offload works correctly.

Changes:
v2 -> v3:
* Drop patch #1 and #2 of v2 that aim to resolve potential issues
  reported by sashiko (per Alexei).
* Check target IP version and UDP tunnel in test (per sashiko).
* v2: https://lore.kernel.org/bpf/20260529151351.69911-1-leon.hwang@linux.dev/

v1 -> v2:
* Address sashiko's reviews:
  * Fix TOCTOU issue in lwt to avoid changing hdr after checks.
  * Add check iph->ihl < 5 in lwt to avoid infinite-loop in MIPS driver.
  * Update comment style in selftests with BPF comment style.
* v1: https://lore.kernel.org/bpf/20260525142650.2569-1-leon.hwang@linux.dev/

Leon Hwang (2):
  bpf: Update transport_header when encapsulating UDP tunnel in lwt
  selftests/bpf: Add tests to verify the fix of encapsulating VxLAN in
    lwt

 net/core/lwt_bpf.c                            |  11 ++
 .../selftests/bpf/prog_tests/lwt_ip_encap.c   | 164 ++++++++++++++++++
 .../selftests/bpf/progs/test_lwt_ip_encap.c   | 112 ++++++++++++
 .../bpf/progs/test_lwt_ip_encap_fix.c         |  44 +++++
 4 files changed, 331 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/test_lwt_ip_encap_fix.c

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2.54.0