Re: [PATCH bpf v5 1/3] bpf: fix wrong copied_seq calculation

On Thu, Jan 09, 2025 at 05:43 PM +08, Jiayuan Chen wrote:

'sk->copied_seq' was updated 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.

It 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.

We do not want to add new proto_ops to implement a new version of
tcp_read_sock, as this would introduce code complexity [1].

[1]: https://lore.kernel.org/bpf/20241218053408.437295-1-mrpre@163.com (local)
Fixes: e5c6de5fa025 ("bpf, sockmap: Incorrectly handling copied_seq")
Co-developed-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Jiayuan Chen <redacted>
---

No need to put me down as an author.
If you want you can me with a Suggested-by.

Also, please remove my Signed-off-by.
I will review these patches, but I haven't authored them.