[PATCH net v2 0/2] net: psp: preserve SKB_EXT_PSP across packet scrubbing

[Wei Wang <weiwan@google.com>]

When a virtual interface such as netkit is associated with a PSP device
in another network namespace via PSP_CMD_DEV_ASSOC, incoming PSP packets
decapsulated on the physical device lose their SKB_EXT_PSP extension
when scrubbed during redirection (e.g. skb_do_redirect() or
netkit_xmit() calling skb_scrub_packet()). As a result,
__psp_sk_rx_policy_check() rejects incoming PSP-encrypted TCP data
segments at the socket layer.

This gap slipped through the existing psp.py selftests because both
_data_basic_send() and _data_basic_send_netkit_psp_assoc() only sent a
unidirectional data stream from the test socket to psp_responder; the
returning pure TCP ACKs had SKB_EXT_PSP stripped by skb_scrub_packet(),
but were still accepted by __psp_sk_rx_policy_check() while peer_tx was
unset.

Patch 1 (originally from Jakub Sitnicki's BPF skb extension series [1])
introduces skb_ext_scrub() to selectively preserve SKB_EXT_PSP during
skb_scrub_packet().

Patch 2 updates the psp.py selftests to exercise bidirectional PSP data
transfer using psp_responder's "data echo" command in both direct and
netkit dev-assoc test cases.

Changes in v2:
- Patch 1: Replace the skb_ext_del() loop in skb_ext_scrub() with
  skb_ext_reset() + skb_ext_add() (and a fast path when SKB_EXT_PSP is
  the only extension in the skb_ext buffer) so shared skb_ext buffers
  with refcounted extensions (SKB_EXT_SEC_PATH / SKB_EXT_MCTP) are not
  left half-deleted; clear skb->decrypted if skb_ext_add() fails.
- Patch 1: Make skb_ext_scrub() static in net/core/skbuff.c and drop
  EXPORT_SYMBOL() / public header prototype.

Link: https://lore.kernel.org/netdev/20260910-bpf-meta-inside-skb-ext-v2-3-0b21e42180b0@cloudflare.com/ [1]

Wei Wang (2):
  net: Make PSP skb extension survive packet scrubbing
  selftests/net: psp: test bidirectional data transfer

 net/core/skbuff.c                          | 31 ++++++++++++++++++++--
 tools/testing/selftests/drivers/net/psp.py |  8 ++++++
 2 files changed, 37 insertions(+), 2 deletions(-)

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2.56.0.317.g454f8302e1-goog