sctp: Fix the RTO-doubling on idle-link heartbeats

SCTP incorrectly doubles rto ever time a Hearbeat chunk
is generated.   However RFC 4960 states:

   On an idle destination address that is allowed to heartbeat, it is
   recommended that a HEARTBEAT chunk is sent once per RTO of that
   destination address plus the protocol parameter 'HB.interval', with
   jittering of +/- 50% of the RTO value, and exponential backoff of the
   RTO if the previous HEARTBEAT is unanswered.

Essentially, of if the heartbean is unacknowledged, do we double the RTO.

Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 17 insertions, 2 deletions

diff --git a/net/sctp/sm_sideeffect.c b/net/sctp/sm_sideeffect.c
index e1d6076b4f59..0146cfb1f182 100644
--- a/net/sctp/sm_sideeffect.c
+++ b/net/sctp/sm_sideeffect.c
@@ -461,9 +461,15 @@ static void sctp_do_8_2_transport_strike(struct sctp_association *asoc,
          * expires, set RTO <- RTO * 2 ("back off the timer").  The
          * maximum value discussed in rule C7 above (RTO.max) may be
          * used to provide an upper bound to this doubling operation.
+         *
+         * Special Case:  the first HB doesn't trigger exponential backoff.
+         * The first unacknowleged HB triggers it.  We do this with a flag
+         * that indicates that we have an outstanding HB.
          */
-        transport->last_rto = transport->rto;
-        transport->rto = min((transport->rto * 2), transport->asoc->rto_max);
+        if (transport->hb_sent) {
+                transport->last_rto = transport->rto;
+                transport->rto = min((transport->rto * 2), transport->asoc->rto_max);
+        }
 }
 
 /* Worker routine to handle INIT command failure.  */
@@ -621,6 +627,11 @@ static void sctp_cmd_transport_on(sctp_cmd_seq_t *cmds,
         t->error_count = 0;
         t->asoc->overall_error_count = 0;
 
+        /* Clear the hb_sent flag to signal that we had a good
+         * acknowledgement.
+         */
+        t->hb_sent = 0;
+
         /* Mark the destination transport address as active if it is not so
          * marked.
          */
@@ -657,6 +668,8 @@ static void sctp_cmd_transport_reset(sctp_cmd_seq_t *cmds,
 
         /* Mark one strike against a transport.  */
         sctp_do_8_2_transport_strike(asoc, t);
+
+        t->hb_sent = 1;
 }
 
 /* Helper function to process the process SACK command.  */
diff --git a/net/sctp/transport.c b/net/sctp/transport.c
index e745c118f239..5c29b14ee9af 100644
--- a/net/sctp/transport.c
+++ b/net/sctp/transport.c
@@ -79,6 +79,7 @@ static struct sctp_transport *sctp_transport_init(struct sctp_transport *peer,
         peer->rttvar = 0;
         peer->srtt = 0;
         peer->rto_pending = 0;
+        peer->hb_sent = 0;
         peer->fast_recovery = 0;
 
         peer->last_time_heard = jiffies;
@@ -608,6 +609,7 @@ void sctp_transport_reset(struct sctp_transport *t)
         t->flight_size = 0;
         t->error_count = 0;
         t->rto_pending = 0;
+        t->hb_sent = 0;
         t->fast_recovery = 0;
 
         /* Initialize the state information for SFR-CACC */