Re: [PATCH v1 net-next 7/8] sctp: Use sctp_clone_sock() in sctp_do_peeloff().

On Tue, Oct 21, 2025 at 2:44 PM Kuniyuki Iwashima <[email protected]> wrote:
>
> sctp_do_peeloff() calls sock_create() to allocate and initialise
> struct sock, inet_sock, and sctp_sock, but later sctp_copy_sock()
> and sctp_sock_migrate() overwrite most fields.
>
> What sctp_do_peeloff() does is more like accept().
>
> Let's use sock_create_lite() and sctp_clone_sock().
>
> Signed-off-by: Kuniyuki Iwashima <[email protected]>
> ---
>  net/sctp/socket.c | 36 +++++++++++++++---------------------
>  1 file changed, 15 insertions(+), 21 deletions(-)
>
> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> index 826f17747f176..60d3e340dfeda 100644
> --- a/net/sctp/socket.c
> +++ b/net/sctp/socket.c
> @@ -5671,11 +5671,11 @@ static int sctp_getsockopt_autoclose(struct sock *sk, int len, char __user *optv
>
>  /* Helper routine to branch off an association to a new socket.  */
>  static int sctp_do_peeloff(struct sock *sk, sctp_assoc_t id,
> -               struct socket **sockp)
> +                          struct socket **sockp)
>  {
>         struct sctp_association *asoc = sctp_id2assoc(sk, id);
> -       struct sctp_sock *sp = sctp_sk(sk);
>         struct socket *sock;
> +       struct sock *newsk;
>         int err = 0;
>
>         /* Do not peel off from one netns to another one. */
> @@ -5691,30 +5691,24 @@ static int sctp_do_peeloff(struct sock *sk, sctp_assoc_t id,
>         if (!sctp_style(sk, UDP))
>                 return -EINVAL;
>
> -       /* Create a new socket.  */
> -       err = sock_create(sk->sk_family, SOCK_SEQPACKET, IPPROTO_SCTP, &sock);
> -       if (err < 0)
> +       err = sock_create_lite(sk->sk_family, SOCK_SEQPACKET, IPPROTO_SCTP, &sock);
> +       if (err)
>                 return err;
>
> -       sctp_copy_sock(sock->sk, sk, asoc);
> -
> -       /* Make peeled-off sockets more like 1-1 accepted sockets.
> -        * Set the daddr and initialize id to something more random and also
> -        * copy over any ip options.
> -        */
> -       sp->pf->to_sk_daddr(&asoc->peer.primary_addr, sock->sk);
> -       sp->pf->copy_ip_options(sk, sock->sk);
> -
> -       /* Populate the fields of the newsk from the oldsk and migrate the
> -        * asoc to the newsk.
> -        */
> -       err = sctp_sock_migrate(sk, sock->sk, asoc,
> -                               SCTP_SOCKET_UDP_HIGH_BANDWIDTH);
> -       if (err) {
> +       newsk = sctp_clone_sock(sk, asoc, SCTP_SOCKET_UDP_HIGH_BANDWIDTH);
> +       if (IS_ERR(newsk)) {
>                 sock_release(sock);
> -               sock = NULL;
> +               *sockp = NULL;
> +               return PTR_ERR(newsk);
>         }
>
> +       lock_sock_nested(newsk, SINGLE_DEPTH_NESTING);
> +       __inet_accept(sk->sk_socket, sock, newsk);

Oh I assumed __inet_accept() was exported to MPTCP,
but it's built-in, and SCTP=m needs this.

diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index 77f6ae0fc231..ffd4d75d0a7a 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -788,6 +788,7 @@ void __inet_accept(struct socket *sock, struct
socket *newsock, struct sock *new

  newsock->state = SS_CONNECTED;
 }
+EXPORT_SYMBOL(__inet_accept);

 /*
  * Accept a pending connection. The TCP layer now gives BSD semantics.

--
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