netdev - Re: [PATCH net-next] sctp: add support for SCTP_REUSE

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Date:   Sun, 20 May 2018 12:44:58 -0700
From:   Tom Herbert <tom@...bertland.com>
To:     Xin Long <lucien.xin@...il.com>
Cc:     network dev <netdev@...r.kernel.org>,
        "linux-sctp @ vger . kernel . org" <linux-sctp@...r.kernel.org>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Neil Horman <nhorman@...driver.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH net-next] sctp: add support for SCTP_REUSE_PORT sockopt

On Sat, May 19, 2018 at 12:44 AM, Xin Long <lucien.xin@...il.com> wrote:
> This feature is actually already supported by sk->sk_reuse which can be
> set by SO_REUSEADDR. But it's not working exactly as RFC6458 demands in
> section 8.1.27, like:
>
>   - This option only supports one-to-one style SCTP sockets
>   - This socket option must not be used after calling bind()
>     or sctp_bindx().
>
> Besides, SCTP_REUSE_PORT sockopt should be provided for user's programs.
> Otherwise, the programs with SCTP_REUSE_PORT from other systems will not
> work in linux.
>
How is this different than SO_REUSEPORT?

> This patch reuses sk->sk_reuse and works pretty much as SO_REUSEADDR,
> just with some extra setup limitations that are neeeded when it is being
> enabled.
>
> "It should be noted that the behavior of the socket-level socket option
> to reuse ports and/or addresses for SCTP sockets is unspecified", so it
> leaves SO_REUSEADDR as is for the compatibility.
>
> Signed-off-by: Xin Long <lucien.xin@...il.com>
> ---
>  include/uapi/linux/sctp.h |  1 +
>  net/sctp/socket.c         | 48 +++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 49 insertions(+)
>
> diff --git a/include/uapi/linux/sctp.h b/include/uapi/linux/sctp.h
> index b64d583..c02986a 100644
> --- a/include/uapi/linux/sctp.h
> +++ b/include/uapi/linux/sctp.h
> @@ -100,6 +100,7 @@ typedef __s32 sctp_assoc_t;
>  #define SCTP_RECVNXTINFO       33
>  #define SCTP_DEFAULT_SNDINFO   34
>  #define SCTP_AUTH_DEACTIVATE_KEY       35
> +#define SCTP_REUSE_PORT                36
>
>  /* Internal Socket Options. Some of the sctp library functions are
>   * implemented using these socket options.
> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> index 1b4593b..8dfcc79 100644
> --- a/net/sctp/socket.c
> +++ b/net/sctp/socket.c
> @@ -4170,6 +4170,28 @@ static int sctp_setsockopt_interleaving_supported(struct sock *sk,
>         return retval;
>  }
>
> +static int sctp_setsockopt_reuse_port(struct sock *sk, char __user *optval,
> +                                     unsigned int optlen)
> +{
> +       int val;
> +
> +       if (!sctp_style(sk, TCP))
> +               return -EOPNOTSUPP;
> +
> +       if (sctp_sk(sk)->ep->base.bind_addr.port)
> +               return -EFAULT;
> +
> +       if (optlen < sizeof(int))
> +               return -EINVAL;
> +
> +       if (get_user(val, (int __user *)optval))
> +               return -EFAULT;
> +
> +       sk->sk_reuse = val ? SK_CAN_REUSE : SK_NO_REUSE;
> +
> +       return 0;
> +}
> +
>  /* API 6.2 setsockopt(), getsockopt()
>   *
>   * Applications use setsockopt() and getsockopt() to set or retrieve
> @@ -4364,6 +4386,9 @@ static int sctp_setsockopt(struct sock *sk, int level, int optname,
>                 retval = sctp_setsockopt_interleaving_supported(sk, optval,
>                                                                 optlen);
>                 break;
> +       case SCTP_REUSE_PORT:
> +               retval = sctp_setsockopt_reuse_port(sk, optval, optlen);
> +               break;
>         default:
>                 retval = -ENOPROTOOPT;
>                 break;
> @@ -7175,6 +7200,26 @@ static int sctp_getsockopt_interleaving_supported(struct sock *sk, int len,
>         return retval;
>  }
>
> +static int sctp_getsockopt_reuse_port(struct sock *sk, int len,
> +                                     char __user *optval,
> +                                     int __user *optlen)
> +{
> +       int val = 0;
> +
> +       if (len < sizeof(int))
> +               return -EINVAL;
> +
> +       len = sizeof(int);
> +       if (sk->sk_reuse != SK_NO_REUSE)
> +               val = 1;
> +       if (put_user(len, optlen))
> +               return -EFAULT;
> +       if (copy_to_user(optval, &val, len))
> +               return -EFAULT;
> +
> +       return 0;
> +}
> +
>  static int sctp_getsockopt(struct sock *sk, int level, int optname,
>                            char __user *optval, int __user *optlen)
>  {
> @@ -7370,6 +7415,9 @@ static int sctp_getsockopt(struct sock *sk, int level, int optname,
>                 retval = sctp_getsockopt_interleaving_supported(sk, len, optval,
>                                                                 optlen);
>                 break;
> +       case SCTP_REUSE_PORT:
> +               retval = sctp_getsockopt_reuse_port(sk, len, optval, optlen);
> +               break;
>         default:
>                 retval = -ENOPROTOOPT;
>                 break;
> --
> 2.1.0
>