[PATCH bpf v4 0/2] bpf: Fix generic devmap egress skb sharing

[Sun Jian <sun.jian.kdev@gmail.com>]

Generic XDP devmap multi redirect can leave cloned skbs sharing packet
data. When a devmap egress program mutates packet data, another
destination sharing the same data may observe that mutation.

Fix this by making cloned skbs private before running the generic devmap
egress program. Add selftest coverage for the last-destination case,
where the final destination runs on the original skb while earlier
destinations use cloned skbs.

---

v4:

* Preserve mac_len after skb_copy().
* Separate errno return from XDP action output in
  dev_map_bpf_prog_run_skb().
* Zero-initialize net_config in the new selftest.

v3: https://lore.kernel.org/bpf/20260611043317.512843-1-sun.jian.kdev@gmail.com/T/#m77fde65437b0398cb470649d4f1feeb85bc134bc

* Split the kernel fix and selftest into separate patches.
* Move the private-copy logic into dev_map_bpf_prog_run_skb().
* Use deterministic DEVMAP_HASH keys in the last-destination selftest.
* Fix the Fixes tag.

v2: https://lore.kernel.org/bpf/08c35c70-a59e-4e0e-91db-22b5ec30b611@linux.dev/T/#m613671b243e8651c47f84bb329f0ea668974c549

* Move the private-copy step into dev_map_generic_redirect() so the
  last-destination path is covered as well.
* Use skb_copy() instead of skb_unshare() to keep caller ownership
  unchanged on allocation failure.
* Add a generic XDP last-destination selftest case.

v1: https://lore.kernel.org/bpf/CABFUUZFimdrZdq=NWi+N-0sJZWvMwY=f4iF6-3TVMS8=m07Zmw@mail.gmail.com/


Sun Jian (2):
  bpf: Run generic devmap egress prog on private skb
  selftests/bpf: Cover generic devmap egress last-dst rewrite

 kernel/bpf/devmap.c                           |  41 +++--
 .../selftests/bpf/prog_tests/test_xdp_veth.c  | 152 +++++++++++++++++-
 2 files changed, 180 insertions(+), 13 deletions(-)


base-commit: e7ae89a0c97ce2b68b0983cd01eda67cf373517d
-- 
2.43.0