October 28, 2025 at 19:30, "Paolo Abeni" <[email protected]
mailto:[email protected]?to=%22Paolo%20Abeni%22%20%3Cpabeni%40redhat.com%3E >
wrote:
>
> On 10/23/25 2:54 PM, Jiayuan Chen wrote:
>
> >
> > When the server has MPTCP enabled but receives a non-MP-capable request
> > from a client, it calls mptcp_fallback_tcp_ops().
> >
> > Since non-MPTCP connections are allowed to use sockmap, which replaces
> > sk->sk_prot, using sk->sk_prot to determine the IP version in
> > mptcp_fallback_tcp_ops() becomes unreliable. This can lead to assigning
> > incorrect ops to sk->sk_socket->ops.
> >
> I don't see how sockmap could modify the to-be-accepted socket sk_prot
> before mptcp_fallback_tcp_ops(), as such call happens before the fd is
> installed, and AFAICS sockmap can only fetch sockets via fds.
>
> Is this patch needed?
"mptcp_fallback_tcp_ops" is only called during the accept process. However,
before that, for an already established TCP socket, its sk_prot is replaced via
the following path:
tcp_rcv_state_process()
tcp_init_transfer(BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB)
call bpf prog
bpf_sock_map_update(sk)
tcp_bpf_update_proto()
However, after discussing with Matthieu, we've concluded that this patch is
indeed no
longer necessary, as we have a simpler way to intercept the operation."
Thanks~
