sctp: Fix SHUTDOWN CTSN Ack in the peer restart case

stable inclusion
from linux-4.19.122
commit 9d0dc9fb94a564075403116591c728aedbe656d8

--------------------------------

commit 12dfd78e upstream.

When starting shutdown in sctp_sf_do_dupcook_a(), get the value for
SHUTDOWN Cumulative TSN Ack from the new association, which is
reconstructed from the cookie, instead of the old association, which
the peer doesn't have anymore.

Otherwise the SHUTDOWN is either ignored or replied to with an ABORT
by the peer because CTSN Ack doesn't match the peer's Initial TSN.

Fixes: bdf6fa52 ("sctp: handle association restarts when the socket is closed.")
Signed-off-by: NJere Leppänen <jere.leppanen@nokia.com>
Acked-by: NMarcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>
Signed-off-by: NLi Aichun <liaichun@huawei.com>
Reviewed-by: Nguodeqing <geffrey.guo@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

net/sctp/sm_make_chunk.c

@@ -871,7 +871,11 @@ struct sctp_chunk *sctp_make_shutdown(const struct sctp_association *asoc,
 	struct sctp_chunk *retval;
 	__u32 ctsn;
 
-	ctsn = sctp_tsnmap_get_ctsn(&asoc->peer.tsn_map);
+	if (chunk && chunk->asoc)
+		ctsn = sctp_tsnmap_get_ctsn(&chunk->asoc->peer.tsn_map);
+	else
+		ctsn = sctp_tsnmap_get_ctsn(&asoc->peer.tsn_map);
+
 	shut.cum_tsn_ack = htonl(ctsn);
 
 	retval = sctp_make_control(asoc, SCTP_CID_SHUTDOWN, 0,