sctp: Fix bundling of SHUTDOWN with COOKIE-ACK

When we start shutdown in sctp_sf_do_dupcook_a(), we want to bundle
the SHUTDOWN with the COOKIE-ACK to ensure that the peer receives them
at the same time and in the correct order. This bundling was broken by
commit 4ff40b8626 ("sctp: set chunk transport correctly when it's a
new asoc"), which assigns a transport for the COOKIE-ACK, but not for
the SHUTDOWN.

Fix this by passing a reference to the COOKIE-ACK chunk as an argument
to sctp_sf_do_9_2_start_shutdown() and onward to
sctp_make_shutdown(). This way the SHUTDOWN chunk is assigned the same
transport as the COOKIE-ACK chunk, which allows them to be bundled.

In sctp_sf_do_9_2_start_shutdown(), the void *arg parameter was
previously unused. Now that we're taking it into use, it must be a
valid pointer to a chunk, or NULL. There is only one call site where
it's not, in sctp_sf_autoclose_timer_expire(). Fix that too.

Fixes: 4ff40b8626 ("sctp: set chunk transport correctly when it's a new asoc")
Signed-off-by: Jere Leppänen <jere.leppanen@nokia.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sctp/sm_statefuns.c

@@ -1865,7 +1865,7 @@ static enum sctp_disposition sctp_sf_do_dupcook_a(
 		 */
 		sctp_add_cmd_sf(commands, SCTP_CMD_REPLY, SCTP_CHUNK(repl));
 		return sctp_sf_do_9_2_start_shutdown(net, ep, asoc,
-						     SCTP_ST_CHUNK(0), NULL,
+						     SCTP_ST_CHUNK(0), repl,
 						     commands);
 	} else {
 		sctp_add_cmd_sf(commands, SCTP_CMD_NEW_STATE,
@@ -5470,7 +5470,7 @@ enum sctp_disposition sctp_sf_do_9_2_start_shutdown(
 	 * in the Cumulative TSN Ack field the last sequential TSN it
 	 * has received from the peer.
 	 */
-	reply = sctp_make_shutdown(asoc, NULL);
+	reply = sctp_make_shutdown(asoc, arg);
 	if (!reply)
 		goto nomem;
 
@@ -6068,7 +6068,7 @@ enum sctp_disposition sctp_sf_autoclose_timer_expire(
 	disposition = SCTP_DISPOSITION_CONSUME;
 	if (sctp_outq_is_empty(&asoc->outqueue)) {
 		disposition = sctp_sf_do_9_2_start_shutdown(net, ep, asoc, type,
-							    arg, commands);
+							    NULL, commands);
 	}
 
 	return disposition;