A previous commit described in this topic
http://lore.kernel.org/bpf/20230523025618.113937-9-john.fastabend@gmail.com
directly updated 'sk->copied_seq' in the tcp_eat_skb() function when the
action of a BPF program was SK_REDIRECT. For other actions, like SK_PASS,
the update logic for 'sk->copied_seq' was moved to
tcp_bpf_recvmsg_parser() to ensure the accuracy of the 'fionread' feature.

That commit works for a single stream_verdict scenario, as it also
modified 'sk_data_ready->sk_psock_verdict_data_ready->tcp_read_skb'
to remove updating 'sk->copied_seq'.

However, for programs where both stream_parser and stream_verdict are
active(strparser purpose), tcp_read_sock() was used instead of
tcp_read_skb() (sk_data_ready->strp_data_ready->tcp_read_sock)
tcp_read_sock() now still update 'sk->copied_seq', leading to duplicated
updates.

In summary, for strparser + SK_PASS, copied_seq is redundantly calculated
in both tcp_read_sock() and tcp_bpf_recvmsg_parser().

The issue causes incorrect copied_seq calculations, which prevent
correct data reads from the recv() interface in user-land.

Modifying tcp_read_sock() or strparser implementation directly is
unreasonable, as it is widely used in other modules.

Here, we introduce a method tcp_bpf_read_sock() to replace
'sk->sk_socket->ops->read_sock' (like 'tls_build_proto()' does in
tls_main.c). Such replacement action was also used in updating
tcp_bpf_prots in tcp_bpf.c, so it's not weird.
(Note that checkpatch.pl may complain missing 'const' qualifier when we
define the bpf-specified 'proto_ops', but we have to do because we need
update it).

Also we remove strparser check in tcp_eat_skb() since we implement custom
function tcp_bpf_read_sock() without copied_seq updating.

Since strparser currently supports only TCP, it's sufficient for 'ops' to
inherit inet_stream_ops.

We added test cases for bpf + strparser and separated them from
sockmap_basic. This is because we need to add more test cases for
strparser in the future.

Fixes: e5c6de5fa025 ("bpf, sockmap: Incorrectly handling copied_seq")

---
v2-v3: save skb data offset for ENOMEM. (John Fastabend)
https://lore.kernel.org/bpf/20241209152740.281125-1-mrpre@163.com/#r

v1-v2: fix patchwork fail by adding Fixes tag

---
Jiayuan Chen (2):
  bpf: fix wrong copied_seq calculation
  selftests/bpf: add strparser test for bpf

 include/linux/skmsg.h                         |   2 +
 include/net/tcp.h                             |   1 +
 net/core/skmsg.c                              |   3 +
 net/ipv4/tcp.c                                |   2 +-
 net/ipv4/tcp_bpf.c                            | 108 +++++-
 .../selftests/bpf/prog_tests/sockmap_basic.c  |  53 ---
 .../selftests/bpf/prog_tests/sockmap_strp.c   | 344 ++++++++++++++++++
 .../selftests/bpf/progs/test_sockmap_strp.c   |  51 +++
 8 files changed, 507 insertions(+), 57 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/sockmap_strp.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_sockmap_strp.c


base-commit: 5a6ea7022ff4d2a65ae328619c586d6a8909b48b
-- 
2.43.5