October 21, 2025 at 18:49, "Jakub Sitnicki" <[email protected]
mailto:[email protected]?to=%22Jakub%20Sitnicki%22%20%3Cjakub%40cloudflare.com%3E
> wrote:
>
> On Mon, Oct 20, 2025 at 02:04 PM +08, Jiayuan Chen wrote:
>
> >
> > MPTCP creates subflows for data transmission, and these sockets should not
> > be added to sockmap because MPTCP sets specialized data_ready handlers
> > that would be overridden by sockmap.
> >
> > Additionally, for the parent socket of MPTCP subflows (plain TCP socket),
> > MPTCP sk requires specific protocol handling that conflicts with sockmap's
> > operation(mptcp_prot).
> >
> > This patch adds proper checks to reject MPTCP subflows and their parent
> > sockets from being added to sockmap, while preserving compatibility with
> > reuseport functionality for listening MPTCP sockets.
> >
> > Fixes: 0b4f33def7bb ("mptcp: fix tcp fallback crash")
> > Signed-off-by: Jiayuan Chen <[email protected]>
> > ---
> > net/core/sock_map.c | 9 +++++++++
> > 1 file changed, 9 insertions(+)
> >
> > diff --git a/net/core/sock_map.c b/net/core/sock_map.c
> > index 5947b38e4f8b..da21deb970b3 100644
> > --- a/net/core/sock_map.c
> > +++ b/net/core/sock_map.c
> > @@ -535,6 +535,15 @@ static bool sock_map_redirect_allowed(const struct
> > sock *sk)
> >
> > static bool sock_map_sk_is_suitable(const struct sock *sk)
> > {
> > + if ((sk_is_tcp(sk) && sk_is_mptcp(sk)) /* subflow */ ||
> > + (sk->sk_protocol == IPPROTO_MPTCP && sk->sk_state != TCP_LISTEN)) {
> > + /* Disallow MPTCP subflows and their parent socket.
> > + * However, a TCP_LISTEN MPTCP socket is permitted because
> > + * sockmap can also serve for reuseport socket selection.
> > + */
> > + pr_err_once("sockmap: MPTCP sockets are not supported\n");
> > + return false;
> > + }
> > return !!sk->sk_prot->psock_update_sk_prot;
> > }
> >
> You're checking sk_state without sk_lock held. That doesn't seem right.
> Take a look how we always call sock_map_sk_state_allowed() after
> grabbing the lock.
> Same might apply to sk_is_mptcp(). Please double check.
>
Thank you for the suggestion. It seems more appropriate to place this logic
inside sock_map_sk_state_allowed().
