Merge branch 'sctp-race-fix'

Xin Long says:

====================
sctp: fix the race condition in sctp_destroy_sock in a proper way

The original fix introduced a dead lock, and has to be removed in
Patch 1/2, and we will get a proper way to fix it in Patch 2/2.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sctp/socket.c

@@ -357,6 +357,18 @@ static struct sctp_af *sctp_sockaddr_af(struct sctp_sock *opt,
 	return af;
 }
 
+static void sctp_auto_asconf_init(struct sctp_sock *sp)
+{
+	struct net *net = sock_net(&sp->inet.sk);
+
+	if (net->sctp.default_auto_asconf) {
+		spin_lock(&net->sctp.addr_wq_lock);
+		list_add_tail(&sp->auto_asconf_list, &net->sctp.auto_asconf_splist);
+		spin_unlock(&net->sctp.addr_wq_lock);
+		sp->do_auto_asconf = 1;
+	}
+}
+
 /* Bind a local address either to an endpoint or to an association.  */
 static int sctp_do_bind(struct sock *sk, union sctp_addr *addr, int len)
 {
@@ -418,8 +430,10 @@ static int sctp_do_bind(struct sock *sk, union sctp_addr *addr, int len)
 		return -EADDRINUSE;
 
 	/* Refresh ephemeral port.  */
-	if (!bp->port)
+	if (!bp->port) {
 		bp->port = inet_sk(sk)->inet_num;
+		sctp_auto_asconf_init(sp);
+	}
 
 	/* Add the address to the bind address list.
 	 * Use GFP_ATOMIC since BHs will be disabled.
@@ -1520,9 +1534,11 @@ static void sctp_close(struct sock *sk, long timeout)
 
 	/* Supposedly, no process has access to the socket, but
 	 * the net layers still may.
+	 * Also, sctp_destroy_sock() needs to be called with addr_wq_lock
+	 * held and that should be grabbed before socket lock.
 	 */
-	local_bh_disable();
-	bh_lock_sock(sk);
+	spin_lock_bh(&net->sctp.addr_wq_lock);
+	bh_lock_sock_nested(sk);
 
 	/* Hold the sock, since sk_common_release() will put sock_put()
 	 * and we have just a little more cleanup.
@@ -1531,7 +1547,7 @@ static void sctp_close(struct sock *sk, long timeout)
 	sk_common_release(sk);
 
 	bh_unlock_sock(sk);
-	local_bh_enable();
+	spin_unlock_bh(&net->sctp.addr_wq_lock);
 
 	sock_put(sk);
 
@@ -4991,16 +5007,6 @@ static int sctp_init_sock(struct sock *sk)
 	sk_sockets_allocated_inc(sk);
 	sock_prot_inuse_add(net, sk->sk_prot, 1);
 
-	if (net->sctp.default_auto_asconf) {
-		spin_lock(&sock_net(sk)->sctp.addr_wq_lock);
-		list_add_tail(&sp->auto_asconf_list,
-		    &net->sctp.auto_asconf_splist);
-		sp->do_auto_asconf = 1;
-		spin_unlock(&sock_net(sk)->sctp.addr_wq_lock);
-	} else {
-		sp->do_auto_asconf = 0;
-	}
-
 	local_bh_enable();
 
 	return 0;
@@ -5025,9 +5031,7 @@ static void sctp_destroy_sock(struct sock *sk)
 
 	if (sp->do_auto_asconf) {
 		sp->do_auto_asconf = 0;
-		spin_lock_bh(&sock_net(sk)->sctp.addr_wq_lock);
 		list_del(&sp->auto_asconf_list);
-		spin_unlock_bh(&sock_net(sk)->sctp.addr_wq_lock);
 	}
 	sctp_endpoint_free(sp->ep);
 	local_bh_disable();
@@ -9398,6 +9402,8 @@ static int sctp_sock_migrate(struct sock *oldsk, struct sock *newsk,
 			return err;
 	}
 
+	sctp_auto_asconf_init(newsp);
+
 	/* Move any messages in the old socket's receive queue that are for the
 	 * peeled off association to the new socket's receive queue.
 	 */