sctp: change to hold sk after auth shkey is created successfully

commit 25bff6d5 upstream.

Now in sctp_endpoint_init(), it holds the sk then creates auth
shkey. But when the creation fails, it doesn't release the sk,
which causes a sk defcnf leak,

Here to fix it by only holding the sk when auth shkey is created
successfully.

Fixes: a29a5bd4 ("[SCTP]: Implement SCTP-AUTH initializations.")
Reported-by:  <syzbot+afabda3890cc2f765041@syzkaller.appspotmail.com>
Reported-by:  <syzbot+276ca1c77a19977c0130@syzkaller.appspotmail.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Neil Horman <nhorman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

net/sctp/endpointola.c

@@ -126,10 +126,6 @@ static struct sctp_endpoint *sctp_endpoint_init(struct sctp_endpoint *ep,
 	/* Initialize the bind addr area */
 	sctp_bind_addr_init(&ep->base.bind_addr, 0);
 
-	/* Remember who we are attached to.  */
-	ep->base.sk = sk;
-	sock_hold(ep->base.sk);
-
 	/* Create the lists of associations.  */
 	INIT_LIST_HEAD(&ep->asocs);
 
@@ -165,6 +161,10 @@ static struct sctp_endpoint *sctp_endpoint_init(struct sctp_endpoint *ep,
 	ep->auth_hmacs_list = auth_hmacs;
 	ep->auth_chunk_list = auth_chunks;
 
+	/* Remember who we are attached to.  */
+	ep->base.sk = sk;
+	sock_hold(ep->base.sk);
+
 	return ep;
 
 nomem_hmacs: