Re: [PATCH net v3 1/3] net,mptcp: fix proto fallback detection with BPF sockmap

[Paolo Abeni]

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?

/P