linux-kernel - Re: [PATCH bpf v5 1/3] bpf: fix wrong copied

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Message-ID: <87o709eitp.fsf@cloudflare.com>
Date: Tue, 14 Jan 2025 12:27:46 +0100
From: Jakub Sitnicki <jakub@...udflare.com>
To: Jiayuan Chen <mrpre@....com>
Cc: bpf@...r.kernel.org,  john.fastabend@...il.com,  netdev@...r.kernel.org,
  martin.lau@...ux.dev,  ast@...nel.org,  edumazet@...gle.com,
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  shuah@...nel.org,  mykolal@...com,  jolsa@...nel.org,  haoluo@...gle.com,
  sdf@...ichev.me,  kpsingh@...nel.org,  linux-doc@...r.kernel.org
Subject: 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
> Fixes: e5c6de5fa025 ("bpf, sockmap: Incorrectly handling copied_seq")
> Co-developed-by: Jakub Sitnicki <jakub@...udflare.com>
> Signed-off-by: Jakub Sitnicki <jakub@...udflare.com>
> Signed-off-by: Jiayuan Chen <mrpre@....com>
> ---

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.