netdev - Re: [PATCHv2 net-next] sctp: sctp should change socket state when shutdown is received

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Date:	Tue, 7 Jun 2016 19:03:55 +0800
From:	Xin Long <lucien.xin@...il.com>
To:	Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc:	network dev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org,
	Vlad Yasevich <vyasevich@...il.com>, daniel@...earbox.net,
	davem <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCHv2 net-next] sctp: sctp should change socket state when
 shutdown is received

On Sat, Jun 4, 2016 at 8:22 PM, Marcelo Ricardo Leitner
<marcelo.leitner@...il.com> wrote:
>
> Return error? Please don't. Adam Endrodi asked in May (linux-sctp@) a way to
> return the addresses used on such attempts and currently this address
> returned by accept() is the only one we can get.
[1] I've checked Adam's email, what he asked  was different case,  in
his case, the assoc
closed *after* sctp_accept, that's why he can catch the SCTP_COMM_UP event on
accept_sk but asoc is freed already.

[2] if assoc close *before* sctp_accept return, I mean asoc close
during sctp_accept schedule out.
listen sk will be the assoc's parent sk, in sctp_cmd_delete_tcb
(SCTP_CMD_DELETE_TCB):

        if (sctp_style(sk, TCP) && sctp_sstate(sk, LISTENING) &&
            (!asoc->temp) && (sk->sk_shutdown != SHUTDOWN_MASK))
                return;

assoc can't be freed. and the event skb will be appended to
listen_sk->sk_receive_queue
when sctp_accept schedule back, it will transfer to
accept_sk->sk_receive_queue. we can
still get the closed assoc information. until we call sctp_close:
                        if (sctp_state(asoc, CLOSED)) {
                                sctp_association_free(asoc);
                                continue;
                        }

and your suggestion to improve for his case [1] is to not schedule
SCTP_CMD_DELETE_TCB
(only for tcp style). right ?

if so, in the case [2] that assoc close *before* sctp_accept return,
we should also update
the newsk->sk_state, like:

--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -7565,10 +7565,12 @@ static void sctp_sock_migrate(struct sock
*oldsk, struct sock *newsk,
        /* If the association on the newsk is already closed before accept()
         * is called, set RCV_SHUTDOWN flag.
         */
-       if (sctp_state(assoc, CLOSED) && sctp_style(newsk, TCP))
+       if (sctp_state(assoc, CLOSED) && sctp_style(newsk, TCP)) {
+               newsk->sk_state = SCTP_SS_CLOSING;
                newsk->sk_shutdown |= RCV_SHUTDOWN;
+       } else
+               newsk->sk_state = SCTP_SS_ESTABLISHED;

-       newsk->sk_state = SCTP_SS_ESTABLISHED;

so that this two cases have the similar process, and wait for
sctp_close to clean assoc.
what do you think ?

>
>   Marcelo