Re: [PATCH net v5 0/3] mptcp: Fix conflicts between MPTCP and sockmap

[Matthieu Baerts]

Hi net and bpf-net maintainers,

On 11/11/2025 07:02, Jiayuan Chen wrote:
> Overall, we encountered a warning [1] that can be triggered by running the
> selftest I provided.
> 
> sockmap works by replacing sk_data_ready, recvmsg, sendmsg operations and
> implementing fast socket-level forwarding logic:
> 1. Users can obtain file descriptors through userspace socket()/accept()
>    interfaces, then call BPF syscall to perform these replacements.
> 2. Users can also use the bpf_sock_hash_update helper (in sockops programs)
>    to replace handlers when TCP connections enter ESTABLISHED state
>   (BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB/BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB)
> 
> However, when combined with MPTCP, an issue arises: MPTCP creates subflow
> sk's and performs TCP handshakes, so the BPF program obtains subflow sk's
> and may incorrectly replace their sk_prot. We need to reject such
> operations. In patch 1, we set psock_update_sk_prot to NULL in the
> subflow's custom sk_prot.
> 
> Additionally, if the server's listening socket has MPTCP enabled and the
> client's TCP also uses MPTCP, we should allow the combination of subflow
> and sockmap. This is because the latest Golang programs have enabled MPTCP
> for listening sockets by default [2]. For programs already using sockmap,
> upgrading Golang should not cause sockmap functionality to fail.
> 
> Patch 2 prevents the WARNING from occurring.

I think this series can be applied directly in 'net', if that's OK for
both of you.

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.