Re: [PATCH bpf v2 09/15] bpf, sockmap: Check the TCP state in recvmsg()

[Matthieu Baerts <matttbe@kernel.org>]

Hi Alexei, Chris,

Thank you for the fix!

On 02/11/2026 08:21, Alexei Starovoitov wrote:
> From: Chris Mason <mason@kernel.org>
> 
> With an sk_skb verdict prog, tcp_bpf_recvmsg_parser() copies data from the
> psock. Then it calls __tcp_cleanup_rbuf() to calculate the receive window
> and to send an ACK. The window and the ACK need a connection on the socket.
> But tcp_disconnect() keeps the socket in the sockmap and the data on the
> psock. For a TCP socket sock_map_redirect_allowed() rejects only
> TCP_LISTEN. Thus the psock can also get data after tcp_disconnect().
> 
> __tcp_select_window() divides by icsk_ack.rcv_mss, which can be 0 in
> TCP_CLOSE. In TCP_SYN_SENT the new peer can get an ACK with the sequence
> numbers of the old connection.
> 
> Call __tcp_cleanup_rbuf() only when tcp_can_send_ack() returns true.
> recvmsg() returns the data as before. Move tcp_can_send_ack() from MPTCP to
> tcp.h.

Good idea!

Acked-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>

Cheers,
Matt
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Sponsored by the NGI0 Core fund.