sctp: Correctly implement Fast Recovery cwnd manipulations.
Correctly keep track of Fast Recovery state and do not reduce
congestion window multiple times during sucht state.
Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Tested-by: Wei Yongjun <yjwei@cn.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sctp/transport.c b/net/sctp/transport.c
index 62082e7..9647fb2 100644
--- a/net/sctp/transport.c
+++ b/net/sctp/transport.c
@@ -79,6 +79,7 @@
peer->rttvar = 0;
peer->srtt = 0;
peer->rto_pending = 0;
+ peer->fast_recovery = 0;
peer->last_time_heard = jiffies;
peer->last_time_used = jiffies;
@@ -403,11 +404,16 @@
cwnd = transport->cwnd;
flight_size = transport->flight_size;
+ /* See if we need to exit Fast Recovery first */
+ if (transport->fast_recovery &&
+ TSN_lte(transport->fast_recovery_exit, sack_ctsn))
+ transport->fast_recovery = 0;
+
/* The appropriate cwnd increase algorithm is performed if, and only
- * if the cumulative TSN has advanced and the congestion window is
+ * if the cumulative TSN whould advanced and the congestion window is
* being fully utilized.
*/
- if ((transport->asoc->ctsn_ack_point >= sack_ctsn) ||
+ if (TSN_lte(sack_ctsn, transport->asoc->ctsn_ack_point) ||
(flight_size < cwnd))
return;
@@ -416,17 +422,23 @@
pmtu = transport->asoc->pathmtu;
if (cwnd <= ssthresh) {
- /* RFC 2960 7.2.1, sctpimpguide-05 2.14.2 When cwnd is less
- * than or equal to ssthresh an SCTP endpoint MUST use the
- * slow start algorithm to increase cwnd only if the current
- * congestion window is being fully utilized and an incoming
- * SACK advances the Cumulative TSN Ack Point. Only when these
- * two conditions are met can the cwnd be increased otherwise
- * the cwnd MUST not be increased. If these conditions are met
- * then cwnd MUST be increased by at most the lesser of
- * 1) the total size of the previously outstanding DATA
- * chunk(s) acknowledged, and 2) the destination's path MTU.
+ /* RFC 4960 7.2.1
+ * o When cwnd is less than or equal to ssthresh, an SCTP
+ * endpoint MUST use the slow-start algorithm to increase
+ * cwnd only if the current congestion window is being fully
+ * utilized, an incoming SACK advances the Cumulative TSN
+ * Ack Point, and the data sender is not in Fast Recovery.
+ * Only when these three conditions are met can the cwnd be
+ * increased; otherwise, the cwnd MUST not be increased.
+ * If these conditions are met, then cwnd MUST be increased
+ * by, at most, the lesser of 1) the total size of the
+ * previously outstanding DATA chunk(s) acknowledged, and
+ * 2) the destination's path MTU. This upper bound protects
+ * against the ACK-Splitting attack outlined in [SAVAGE99].
*/
+ if (transport->fast_recovery)
+ return;
+
if (bytes_acked > pmtu)
cwnd += pmtu;
else
@@ -502,6 +514,13 @@
* cwnd = ssthresh
* partial_bytes_acked = 0
*/
+ if (transport->fast_recovery)
+ return;
+
+ /* Mark Fast recovery */
+ transport->fast_recovery = 1;
+ transport->fast_recovery_exit = transport->asoc->next_tsn - 1;
+
transport->ssthresh = max(transport->cwnd/2,
4*transport->asoc->pathmtu);
transport->cwnd = transport->ssthresh;
@@ -586,6 +605,7 @@
t->flight_size = 0;
t->error_count = 0;
t->rto_pending = 0;
+ t->fast_recovery = 0;
/* Initialize the state information for SFR-CACC */
t->cacc.changeover_active = 0;