sctp: hold transport before we access t->asoc in sctp proc

Previously, before rhashtable, /proc assoc listing was done by
read-locking the entire hash entry and dumping all assocs at once, so we
were sure that the assoc wasn't freed because it wouldn't be possible to
remove it from the hash meanwhile.

Now we use rhashtable to list transports, and dump entries one by one.
That is, now we have to check if the assoc is still a good one, as the
transport we got may be being freed.
Signed-off-by: NXin Long <lucien.xin@gmail.com>
Reviewed-by: NMarcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/sctp/proc.c

@@ -380,6 +380,8 @@ 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 +414,8 @@ 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;
 }
 
@@ -489,6 +493,8 @@ 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,
@@ -544,6 +550,8 @@ static int sctp_remaddr_seq_show(struct seq_file *seq, void *v)
 		seq_printf(seq, "\n");
 	}
 
+	sctp_transport_put(tsp);
+
 	return 0;
 }