sctp: use event->chunk when it's valid

Commit 52253db ("sctp: also point GSO head_skb to the sk when
it's available") used event->chunk->head_skb to get the head_skb in
sctp_ulpevent_set_owner().

But at that moment, the event->chunk was NULL, as it cloned the skb
in sctp_ulpevent_make_rcvmsg(). Therefore, that patch didn't really
work.

This patch is to move the event->chunk initialization before calling
sctp_ulpevent_receive_data() so that it uses event->chunk when it's
valid.

Fixes: 52253db ("sctp: also point GSO head_skb to the sk when it's available")
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sctp/ulpevent.c

@@ -702,14 +702,14 @@ struct sctp_ulpevent *sctp_ulpevent_make_rcvmsg(struct sctp_association *asoc,
 	 */
 	sctp_ulpevent_init(event, 0, skb->len + sizeof(struct sk_buff));
 
-	sctp_ulpevent_receive_data(event, asoc);
-
 	/* And hold the chunk as we need it for getting the IP headers
 	 * later in recvmsg
 	 */
 	sctp_chunk_hold(chunk);
 	event->chunk = chunk;
 
+	sctp_ulpevent_receive_data(event, asoc);
+
 	event->stream = ntohs(chunk->subh.data_hdr->stream);
 	event->ssn = ntohs(chunk->subh.data_hdr->ssn);
 	event->ppid = chunk->subh.data_hdr->ppid;