sctp: add the probe timer in transport for PLPMTUD

There are 3 timers described in rfc8899#section-5.1.1:

  PROBE_TIMER, PMTU_RAISE_TIMER, CONFIRMATION_TIMER

This patches adds a 'probe_timer' in transport, and it works as either
PROBE_TIMER or PMTU_RAISE_TIMER. At most time, it works as PROBE_TIMER
and expires every a 'probe_interval' time to send the HB probe packet.
When transport pl enters COMPLETE state, it works as PMTU_RAISE_TIMER
and expires in 'probe_interval * 30' time to go back to SEARCH state
and do searching again.

SCTP HB is an acknowledged packet, CONFIRMATION_TIMER is not needed.

The timer will start when transport pl enters BASE state and stop
when it enters DISABLED state.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

5 files changed, 93 insertions, 0 deletions

diff --git a/net/sctp/debug.c b/net/sctp/debug.c
index c4d9c7feffb9..ccd773e4c371 100644
--- a/net/sctp/debug.c
+++ b/net/sctp/debug.c
@@ -154,6 +154,7 @@ static const char *const sctp_timer_tbl[] = {
 	"TIMEOUT_T5_SHUTDOWN_GUARD",
 	"TIMEOUT_HEARTBEAT",
 	"TIMEOUT_RECONF",
+	"TIMEOUT_PROBE",
 	"TIMEOUT_SACK",
 	"TIMEOUT_AUTOCLOSE",
 };
diff --git a/net/sctp/sm_sideeffect.c b/net/sctp/sm_sideeffect.c
index ce15d590a615..b3815b568e8e 100644
--- a/net/sctp/sm_sideeffect.c
+++ b/net/sctp/sm_sideeffect.c
@@ -471,6 +471,38 @@ out_unlock:
 	sctp_transport_put(transport);
 }
 
+/* Handle the timeout of the probe timer. */
+void sctp_generate_probe_event(struct timer_list *t)
+{
+	struct sctp_transport *transport = from_timer(transport, t, probe_timer);
+	struct sctp_association *asoc = transport->asoc;
+	struct sock *sk = asoc->base.sk;
+	struct net *net = sock_net(sk);
+	int error = 0;
+
+	bh_lock_sock(sk);
+	if (sock_owned_by_user(sk)) {
+		pr_debug("%s: sock is busy\n", __func__);
+
+		/* Try again later.  */
+		if (!mod_timer(&transport->probe_timer, jiffies + (HZ / 20)))
+			sctp_transport_hold(transport);
+		goto out_unlock;
+	}
+
+	error = sctp_do_sm(net, SCTP_EVENT_T_TIMEOUT,
+			   SCTP_ST_TIMEOUT(SCTP_EVENT_TIMEOUT_PROBE),
+			   asoc->state, asoc->ep, asoc,
+			   transport, GFP_ATOMIC);
+
+	if (error)
+		sk->sk_err = -error;
+
+out_unlock:
+	bh_unlock_sock(sk);
+	sctp_transport_put(transport);
+}
+
 /* Inject a SACK Timeout event into the state machine.  */
 static void sctp_generate_sack_event(struct timer_list *t)
 {
@@ -1641,6 +1673,11 @@ static int sctp_cmd_interpreter(enum sctp_event_type event_type,
 			sctp_cmd_hb_timers_stop(commands, asoc);
 			break;
 
+		case SCTP_CMD_PROBE_TIMER_UPDATE:
+			t = cmd->obj.transport;
+			sctp_transport_reset_probe_timer(t);
+			break;
+
 		case SCTP_CMD_REPORT_ERROR:
 			error = cmd->obj.error;
 			break;
diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
index 4f30388a0dd0..3b99eda50618 100644
--- a/net/sctp/sm_statefuns.c
+++ b/net/sctp/sm_statefuns.c
@@ -1095,6 +1095,23 @@ enum sctp_disposition sctp_sf_send_reconf(struct net *net,
 	return SCTP_DISPOSITION_CONSUME;
 }
 
+/* send hb chunk with padding for PLPMUTD.  */
+enum sctp_disposition sctp_sf_send_probe(struct net *net,
+					 const struct sctp_endpoint *ep,
+					 const struct sctp_association *asoc,
+					 const union sctp_subtype type,
+					 void *arg,
+					 struct sctp_cmd_seq *commands)
+{
+	struct sctp_transport *transport = (struct sctp_transport *)arg;
+
+	/* The actual handling will be performed here in a later patch. */
+	sctp_add_cmd_sf(commands, SCTP_CMD_PROBE_TIMER_UPDATE,
+			SCTP_TRANSPORT(transport));
+
+	return SCTP_DISPOSITION_CONSUME;
+}
+
 /*
  * Process an heartbeat request.
  *
diff --git a/net/sctp/sm_statetable.c b/net/sctp/sm_statetable.c
index c82c4233ec6b..1816a4410b2b 100644
--- a/net/sctp/sm_statetable.c
+++ b/net/sctp/sm_statetable.c
@@ -967,6 +967,25 @@ other_event_table[SCTP_NUM_OTHER_TYPES][SCTP_STATE_NUM_STATES] = {
 	TYPE_SCTP_FUNC(sctp_sf_timer_ignore), \
 }
 
+#define TYPE_SCTP_EVENT_TIMEOUT_PROBE { \
+	/* SCTP_STATE_CLOSED */ \
+	TYPE_SCTP_FUNC(sctp_sf_timer_ignore), \
+	/* SCTP_STATE_COOKIE_WAIT */ \
+	TYPE_SCTP_FUNC(sctp_sf_timer_ignore), \
+	/* SCTP_STATE_COOKIE_ECHOED */ \
+	TYPE_SCTP_FUNC(sctp_sf_timer_ignore), \
+	/* SCTP_STATE_ESTABLISHED */ \
+	TYPE_SCTP_FUNC(sctp_sf_send_probe), \
+	/* SCTP_STATE_SHUTDOWN_PENDING */ \
+	TYPE_SCTP_FUNC(sctp_sf_timer_ignore), \
+	/* SCTP_STATE_SHUTDOWN_SENT */ \
+	TYPE_SCTP_FUNC(sctp_sf_timer_ignore), \
+	/* SCTP_STATE_SHUTDOWN_RECEIVED */ \
+	TYPE_SCTP_FUNC(sctp_sf_timer_ignore), \
+	/* SCTP_STATE_SHUTDOWN_ACK_SENT */ \
+	TYPE_SCTP_FUNC(sctp_sf_timer_ignore), \
+}
+
 static const struct sctp_sm_table_entry
 timeout_event_table[SCTP_NUM_TIMEOUT_TYPES][SCTP_STATE_NUM_STATES] = {
 	TYPE_SCTP_EVENT_TIMEOUT_NONE,
@@ -978,6 +997,7 @@ timeout_event_table[SCTP_NUM_TIMEOUT_TYPES][SCTP_STATE_NUM_STATES] = {
 	TYPE_SCTP_EVENT_TIMEOUT_T5_SHUTDOWN_GUARD,
 	TYPE_SCTP_EVENT_TIMEOUT_HEARTBEAT,
 	TYPE_SCTP_EVENT_TIMEOUT_RECONF,
+	TYPE_SCTP_EVENT_TIMEOUT_PROBE,
 	TYPE_SCTP_EVENT_TIMEOUT_SACK,
 	TYPE_SCTP_EVENT_TIMEOUT_AUTOCLOSE,
 };
diff --git a/net/sctp/transport.c b/net/sctp/transport.c
index bf0ac467e757..ca3343c2c80e 100644
--- a/net/sctp/transport.c
+++ b/net/sctp/transport.c
@@ -75,6 +75,7 @@ static struct sctp_transport *sctp_transport_init(struct net *net,
 	timer_setup(&peer->T3_rtx_timer, sctp_generate_t3_rtx_event, 0);
 	timer_setup(&peer->hb_timer, sctp_generate_heartbeat_event, 0);
 	timer_setup(&peer->reconf_timer, sctp_generate_reconf_event, 0);
+	timer_setup(&peer->probe_timer, sctp_generate_probe_event, 0);
 	timer_setup(&peer->proto_unreach_timer,
 		    sctp_generate_proto_unreach_event, 0);
 
@@ -131,6 +132,9 @@ void sctp_transport_free(struct sctp_transport *transport)
 	if (del_timer(&transport->reconf_timer))
 		sctp_transport_put(transport);
 
+	if (del_timer(&transport->probe_timer))
+		sctp_transport_put(transport);
+
 	/* Delete the ICMP proto unreachable timer if it's active. */
 	if (del_timer(&transport->proto_unreach_timer))
 		sctp_transport_put(transport);
@@ -207,6 +211,20 @@ void sctp_transport_reset_reconf_timer(struct sctp_transport *transport)
 			sctp_transport_hold(transport);
 }
 
+void sctp_transport_reset_probe_timer(struct sctp_transport *transport)
+{
+	int scale = 1;
+
+	if (timer_pending(&transport->probe_timer))
+		return;
+	if (transport->pl.state == SCTP_PL_COMPLETE &&
+	    transport->pl.probe_count == 1)
+		scale = 30; /* works as PMTU_RAISE_TIMER */
+	if (!mod_timer(&transport->probe_timer,
+		       jiffies + transport->probe_interval * scale))
+		sctp_transport_hold(transport);
+}
+
 /* This transport has been assigned to an association.
  * Initialize fields from the association or from the sock itself.
  * Register the reference count in the association.