Merge branch 'sctp-transport-races'

Xin Long says:

====================
fix the transport dead race check by using atomic_add_unless on refcnt

  sctp: fix the transport dead race check by using atomic_add_unless on
    refcnt
  sctp: hold transport before we access t->asoc in sctp proc
  sctp: remove the dead field of sctp_transport
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sctp/structs.h

@@ -756,7 +756,6 @@ struct sctp_transport {
 
 	/* Reference counting. */
 	atomic_t refcnt;
-	__u32	 dead:1,
 		/* RTO-Pending : A flag used to track if one of the DATA
 		 *		chunks sent to this address is currently being
 		 *		used to compute a RTT. If this flag is 0,
@@ -766,7 +765,7 @@ struct sctp_transport {
 		 *		calculation completes (i.e. the DATA chunk
 		 *		is SACK'd) clear this flag.
 		 */
-		 rto_pending:1,
+	__u32	rto_pending:1,
 
 		/*
 		 * hb_sent : a flag that signals that we have a pending
@@ -955,7 +954,7 @@ void sctp_transport_route(struct sctp_transport *, union sctp_addr *,
 void sctp_transport_pmtu(struct sctp_transport *, struct sock *sk);
 void sctp_transport_free(struct sctp_transport *);
 void sctp_transport_reset_timers(struct sctp_transport *);
-void sctp_transport_hold(struct sctp_transport *);
+int sctp_transport_hold(struct sctp_transport *);
 void sctp_transport_put(struct sctp_transport *);
 void sctp_transport_update_rto(struct sctp_transport *, __u32);
 void sctp_transport_raise_cwnd(struct sctp_transport *, __u32, __u32);

net/sctp/input.c

@@ -935,15 +935,22 @@ static struct sctp_association *__sctp_lookup_association(
 					struct sctp_transport **pt)
 {
 	struct sctp_transport *t;
+	struct sctp_association *asoc = NULL;
 
+	rcu_read_lock();
 	t = sctp_addrs_lookup_transport(net, local, peer);
-	if (!t || t->dead)
-		return NULL;
+	if (!t || !sctp_transport_hold(t))
+		goto out;
 
-	sctp_association_hold(t->asoc);
+	asoc = t->asoc;
+	sctp_association_hold(asoc);
 	*pt = t;
 
-	return t->asoc;
+	sctp_transport_put(t);
+
+out:
+	rcu_read_unlock();
+	return asoc;
 }
 
 /* Look up an association. protected by RCU read lock */
@@ -955,9 +962,7 @@ struct sctp_association *sctp_lookup_association(struct net *net,
 {
 	struct sctp_association *asoc;
 
-	rcu_read_lock();
 	asoc = __sctp_lookup_association(net, laddr, paddr, transportp);
-	rcu_read_unlock();
 
 	return asoc;
 }

net/sctp/proc.c

@@ -165,8 +165,6 @@ static void sctp_seq_dump_remote_addrs(struct seq_file *seq, struct sctp_associa
 	list_for_each_entry_rcu(transport, &assoc->peer.transport_addr_list,
 			transports) {
 		addr = &transport->ipaddr;
-		if (transport->dead)
-			continue;
 
 		af = sctp_get_af_specific(addr->sa.sa_family);
 		if (af->cmp_addr(addr, primary)) {
@@ -380,6 +378,8 @@ static int sctp_assocs_seq_show(struct seq_file *seq, void *v)
 	}
 
 	transport = (struct sctp_transport *)v;
+	if (!sctp_transport_hold(transport))
+		return 0;
 	assoc = transport->asoc;
 	epb = &assoc->base;
 	sk = epb->sk;
@@ -412,6 +412,8 @@ static int sctp_assocs_seq_show(struct seq_file *seq, void *v)
 		sk->sk_rcvbuf);
 	seq_printf(seq, "\n");
 
+	sctp_transport_put(transport);
+
 	return 0;
 }
 
@@ -489,12 +491,12 @@ static int sctp_remaddr_seq_show(struct seq_file *seq, void *v)
 	}
 
 	tsp = (struct sctp_transport *)v;
+	if (!sctp_transport_hold(tsp))
+		return 0;
 	assoc = tsp->asoc;
 
 	list_for_each_entry_rcu(tsp, &assoc->peer.transport_addr_list,
 				transports) {
-		if (tsp->dead)
-			continue;
 		/*
 		 * The remote address (ADDR)
 		 */
@@ -544,6 +546,8 @@ static int sctp_remaddr_seq_show(struct seq_file *seq, void *v)
 		seq_printf(seq, "\n");
 	}
 
+	sctp_transport_put(tsp);
+
 	return 0;
 }
 

net/sctp/sm_sideeffect.c

@@ -259,12 +259,6 @@ void sctp_generate_t3_rtx_event(unsigned long peer)
 		goto out_unlock;
 	}
 
-	/* Is this transport really dead and just waiting around for
-	 * the timer to let go of the reference?
-	 */
-	if (transport->dead)
-		goto out_unlock;
-
 	/* Run through the state machine.  */
 	error = sctp_do_sm(net, SCTP_EVENT_T_TIMEOUT,
 			   SCTP_ST_TIMEOUT(SCTP_EVENT_TIMEOUT_T3_RTX),
@@ -380,12 +374,6 @@ void sctp_generate_heartbeat_event(unsigned long data)
 		goto out_unlock;
 	}
 
-	/* Is this structure just waiting around for us to actually
-	 * get destroyed?
-	 */
-	if (transport->dead)
-		goto out_unlock;
-
 	error = sctp_do_sm(net, SCTP_EVENT_T_TIMEOUT,
 			   SCTP_ST_TIMEOUT(SCTP_EVENT_TIMEOUT_HEARTBEAT),
 			   asoc->state, asoc->ep, asoc,

net/sctp/transport.c

@@ -132,8 +132,6 @@ struct sctp_transport *sctp_transport_new(struct net *net,
  */
 void sctp_transport_free(struct sctp_transport *transport)
 {
-	transport->dead = 1;
-
 	/* Try to delete the heartbeat timer.  */
 	if (del_timer(&transport->hb_timer))
 		sctp_transport_put(transport);
@@ -169,7 +167,7 @@ static void sctp_transport_destroy_rcu(struct rcu_head *head)
  */
 static void sctp_transport_destroy(struct sctp_transport *transport)
 {
-	if (unlikely(!transport->dead)) {
+	if (unlikely(atomic_read(&transport->refcnt))) {
 		WARN(1, "Attempt to destroy undead transport %p!\n", transport);
 		return;
 	}
@@ -296,9 +294,9 @@ void sctp_transport_route(struct sctp_transport *transport,
 }
 
 /* Hold a reference to a transport.  */
-void sctp_transport_hold(struct sctp_transport *transport)
+int sctp_transport_hold(struct sctp_transport *transport)
 {
-	atomic_inc(&transport->refcnt);
+	return atomic_add_unless(&transport->refcnt, 1, 0);
 }
 
 /* Release a reference to a transport and clean up