[PATCH 3/3] net: fix iteration for sctp transport seq_files

[NeilBrown]

The sctp transport seq_file iterators take a reference to the transport
in the ->start and ->next functions and releases the reference in the
->show function.  The preferred handling for such resources is to
release them in the subsequent ->next or ->stop function call.

Since Commit 1f4aace60b0e ("fs/seq_file.c: simplify seq_file iteration
code and interface") there is no guarantee that ->show will be called
after ->next, so this function can now leak references.

So move the sctp_transport_put() call to ->next and ->stop.

Fixes: 1f4aace60b0e ("fs/seq_file.c: simplify seq_file iteration code and 
interface")
Reported-by: Xin Long <lucien....@gmail.com>
Signed-off-by: NeilBrown <ne...@suse.de>
---
 net/sctp/proc.c |   16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/net/sctp/proc.c b/net/sctp/proc.c
index f7da88ae20a5..982a87b3e11f 100644
--- a/net/sctp/proc.c
+++ b/net/sctp/proc.c
@@ -215,6 +215,12 @@ static void sctp_transport_seq_stop(struct seq_file *seq, 
void *v)
 {
        struct sctp_ht_iter *iter = seq->private;
 
+       if (v && v != SEQ_START_TOKEN) {
+               struct sctp_transport *transport = v;
+
+               sctp_transport_put(transport);
+       }
+
        sctp_transport_walk_stop(&iter->hti);
 }
 
@@ -222,6 +228,12 @@ static void *sctp_transport_seq_next(struct seq_file *seq, 
void *v, loff_t *pos)
 {
        struct sctp_ht_iter *iter = seq->private;
 
+       if (v && v != SEQ_START_TOKEN) {
+               struct sctp_transport *transport = v;
+
+               sctp_transport_put(transport);
+       }
+
        ++*pos;
 
        return sctp_transport_get_next(seq_file_net(seq), &iter->hti);
@@ -277,8 +289,6 @@ 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;
 }
 
@@ -354,8 +364,6 @@ static int sctp_remaddr_seq_show(struct seq_file *seq, void 
*v)
                seq_printf(seq, "\n");
        }
 
-       sctp_transport_put(transport);
-
        return 0;
 }