[PATCH net] net: lapb: Add locking to the lapb module

[Xie He]

In the lapb module, the timers may run concurrently with other code in
this module, and there is currently no locking to prevent the code from
racing on "struct lapb_cb". This patch adds locking to prevent racing.

1. Add "spinlock_t lock" to "struct lapb_cb"; Add "spin_lock_bh" and
"spin_unlock_bh" to APIs, timer functions and notifier functions.

2. Add "bool t1timer_stop, t2timer_stop" to "struct lapb_cb" to make us
able to ask running timers to abort; Modify "lapb_stop_t1timer" and
"lapb_stop_t2timer" to make them able to abort running timers;
Modify "lapb_t2timer_expiry" and "lapb_t1timer_expiry" to make them
abort after they are stopped by "lapb_stop_t1timer", "lapb_stop_t2timer",
and "lapb_start_t1timer", "lapb_start_t2timer".

3. In lapb_unregister, change "lapb_stop_t1timer" and "lapb_stop_t2timer"
to "del_timer_sync" to make sure all running timers have exited.

4. In lapb_device_event, replace the "lapb_disconnect_request" call with
the content of "lapb_disconnect_request", to avoid trying to hold the
lock twice. When doing this, "lapb_start_t1timer" is removed because
I don't think it's necessary to start the timer when "NETDEV_GOING_DOWN".

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: Martin Schiller <ms@xxxxxxxxxx>
Signed-off-by: Xie He <xie.he.0141@xxxxxxxxx>
---
 include/net/lapb.h    |  2 ++
 net/lapb/lapb_iface.c | 54 +++++++++++++++++++++++++++++++++++++++----
 net/lapb/lapb_timer.c | 30 ++++++++++++++++++++----
 3 files changed, 78 insertions(+), 8 deletions(-)

diff --git a/include/net/lapb.h b/include/net/lapb.h
index ccc3d1f020b0..eee73442a1ba 100644
--- a/include/net/lapb.h
+++ b/include/net/lapb.h
@@ -92,6 +92,7 @@ struct lapb_cb {
 	unsigned short		n2, n2count;
 	unsigned short		t1, t2;
 	struct timer_list	t1timer, t2timer;
+	bool			t1timer_stop, t2timer_stop;
 
 	/* Internal control information */
 	struct sk_buff_head	write_queue;
@@ -103,6 +104,7 @@ struct lapb_cb {
 	struct lapb_frame	frmr_data;
 	unsigned char		frmr_type;
 
+	spinlock_t		lock;
 	refcount_t		refcnt;
 };
 
diff --git a/net/lapb/lapb_iface.c b/net/lapb/lapb_iface.c
index 40961889e9c0..ad6197381d05 100644
--- a/net/lapb/lapb_iface.c
+++ b/net/lapb/lapb_iface.c
@@ -122,6 +122,8 @@ static struct lapb_cb *lapb_create_cb(void)
 
 	timer_setup(&lapb->t1timer, NULL, 0);
 	timer_setup(&lapb->t2timer, NULL, 0);
+	lapb->t1timer_stop = true;
+	lapb->t2timer_stop = true;
 
 	lapb->t1      = LAPB_DEFAULT_T1;
 	lapb->t2      = LAPB_DEFAULT_T2;
@@ -129,6 +131,8 @@ static struct lapb_cb *lapb_create_cb(void)
 	lapb->mode    = LAPB_DEFAULT_MODE;
 	lapb->window  = LAPB_DEFAULT_WINDOW;
 	lapb->state   = LAPB_STATE_0;
+
+	spin_lock_init(&lapb->lock);
 	refcount_set(&lapb->refcnt, 1);
 out:
 	return lapb;
@@ -178,8 +182,8 @@ int lapb_unregister(struct net_device *dev)
 		goto out;
 	lapb_put(lapb);
 
-	lapb_stop_t1timer(lapb);
-	lapb_stop_t2timer(lapb);
+	del_timer_sync(&lapb->t1timer);
+	del_timer_sync(&lapb->t2timer);
 
 	lapb_clear_queues(lapb);
 
@@ -201,6 +205,8 @@ int lapb_getparms(struct net_device *dev, struct lapb_parms_struct *parms)
 	if (!lapb)
 		goto out;
 
+	spin_lock_bh(&lapb->lock);
+
 	parms->t1      = lapb->t1 / HZ;
 	parms->t2      = lapb->t2 / HZ;
 	parms->n2      = lapb->n2;
@@ -219,6 +225,7 @@ int lapb_getparms(struct net_device *dev, struct lapb_parms_struct *parms)
 	else
 		parms->t2timer = (lapb->t2timer.expires - jiffies) / HZ;
 
+	spin_unlock_bh(&lapb->lock);
 	lapb_put(lapb);
 	rc = LAPB_OK;
 out:
@@ -234,6 +241,8 @@ int lapb_setparms(struct net_device *dev, struct lapb_parms_struct *parms)
 	if (!lapb)
 		goto out;
 
+	spin_lock_bh(&lapb->lock);
+
 	rc = LAPB_INVALUE;
 	if (parms->t1 < 1 || parms->t2 < 1 || parms->n2 < 1)
 		goto out_put;
@@ -256,6 +265,7 @@ int lapb_setparms(struct net_device *dev, struct lapb_parms_struct *parms)
 
 	rc = LAPB_OK;
 out_put:
+	spin_unlock_bh(&lapb->lock);
 	lapb_put(lapb);
 out:
 	return rc;
@@ -270,6 +280,8 @@ int lapb_connect_request(struct net_device *dev)
 	if (!lapb)
 		goto out;
 
+	spin_lock_bh(&lapb->lock);
+
 	rc = LAPB_OK;
 	if (lapb->state == LAPB_STATE_1)
 		goto out_put;
@@ -285,6 +297,7 @@ int lapb_connect_request(struct net_device *dev)
 
 	rc = LAPB_OK;
 out_put:
+	spin_unlock_bh(&lapb->lock);
 	lapb_put(lapb);
 out:
 	return rc;
@@ -299,6 +312,8 @@ int lapb_disconnect_request(struct net_device *dev)
 	if (!lapb)
 		goto out;
 
+	spin_lock_bh(&lapb->lock);
+
 	switch (lapb->state) {
 	case LAPB_STATE_0:
 		rc = LAPB_NOTCONNECTED;
@@ -330,6 +345,7 @@ int lapb_disconnect_request(struct net_device *dev)
 
 	rc = LAPB_OK;
 out_put:
+	spin_unlock_bh(&lapb->lock);
 	lapb_put(lapb);
 out:
 	return rc;
@@ -344,6 +360,8 @@ int lapb_data_request(struct net_device *dev, struct sk_buff *skb)
 	if (!lapb)
 		goto out;
 
+	spin_lock_bh(&lapb->lock);
+
 	rc = LAPB_NOTCONNECTED;
 	if (lapb->state != LAPB_STATE_3 && lapb->state != LAPB_STATE_4)
 		goto out_put;
@@ -352,6 +370,7 @@ int lapb_data_request(struct net_device *dev, struct sk_buff *skb)
 	lapb_kick(lapb);
 	rc = LAPB_OK;
 out_put:
+	spin_unlock_bh(&lapb->lock);
 	lapb_put(lapb);
 out:
 	return rc;
@@ -364,7 +383,9 @@ int lapb_data_received(struct net_device *dev, struct sk_buff *skb)
 	int rc = LAPB_BADTOKEN;
 
 	if (lapb) {
+		spin_lock_bh(&lapb->lock);
 		lapb_data_input(lapb, skb);
+		spin_unlock_bh(&lapb->lock);
 		lapb_put(lapb);
 		rc = LAPB_OK;
 	}
@@ -435,6 +456,8 @@ static int lapb_device_event(struct notifier_block *this, unsigned long event,
 	if (!lapb)
 		return NOTIFY_DONE;
 
+	spin_lock_bh(&lapb->lock);
+
 	switch (event) {
 	case NETDEV_UP:
 		lapb_dbg(0, "(%p) Interface up: %s\n", dev, dev->name);
@@ -453,8 +476,30 @@ static int lapb_device_event(struct notifier_block *this, unsigned long event,
 		}
 		break;
 	case NETDEV_GOING_DOWN:
-		if (netif_carrier_ok(dev))
-			lapb_disconnect_request(dev);
+		switch (lapb->state) {
+		case LAPB_STATE_0:
+			break;
+
+		case LAPB_STATE_1:
+			lapb_dbg(1, "(%p) S1 TX DISC(1)\n", lapb->dev);
+			lapb_dbg(0, "(%p) S1 -> S0\n", lapb->dev);
+			lapb_send_control(lapb, LAPB_DISC, LAPB_POLLON, LAPB_COMMAND);
+			lapb->state = LAPB_STATE_0;
+			break;
+
+		case LAPB_STATE_2:
+			break;
+
+		default:
+			lapb_clear_queues(lapb);
+			lapb->n2count = 0;
+			lapb_send_control(lapb, LAPB_DISC, LAPB_POLLON, LAPB_COMMAND);
+			lapb_stop_t2timer(lapb);
+			lapb->state = LAPB_STATE_2;
+			lapb_dbg(1, "(%p) S3 DISC(1)\n", lapb->dev);
+			lapb_dbg(0, "(%p) S3 -> S2\n", lapb->dev);
+		}
+
 		break;
 	case NETDEV_DOWN:
 		lapb_dbg(0, "(%p) Interface down: %s\n", dev, dev->name);
@@ -489,6 +534,7 @@ static int lapb_device_event(struct notifier_block *this, unsigned long event,
 		break;
 	}
 
+	spin_unlock_bh(&lapb->lock);
 	lapb_put(lapb);
 	return NOTIFY_DONE;
 }
diff --git a/net/lapb/lapb_timer.c b/net/lapb/lapb_timer.c
index baa247fe4ed0..0230b272b7d1 100644
--- a/net/lapb/lapb_timer.c
+++ b/net/lapb/lapb_timer.c
@@ -40,6 +40,7 @@ void lapb_start_t1timer(struct lapb_cb *lapb)
 	lapb->t1timer.function = lapb_t1timer_expiry;
 	lapb->t1timer.expires  = jiffies + lapb->t1;
 
+	lapb->t1timer_stop = false;
 	add_timer(&lapb->t1timer);
 }
 
@@ -50,16 +51,19 @@ void lapb_start_t2timer(struct lapb_cb *lapb)
 	lapb->t2timer.function = lapb_t2timer_expiry;
 	lapb->t2timer.expires  = jiffies + lapb->t2;
 
+	lapb->t2timer_stop = false;
 	add_timer(&lapb->t2timer);
 }
 
 void lapb_stop_t1timer(struct lapb_cb *lapb)
 {
+	lapb->t1timer_stop = true;
 	del_timer(&lapb->t1timer);
 }
 
 void lapb_stop_t2timer(struct lapb_cb *lapb)
 {
+	lapb->t2timer_stop = true;
 	del_timer(&lapb->t2timer);
 }
 
@@ -72,16 +76,31 @@ static void lapb_t2timer_expiry(struct timer_list *t)
 {
 	struct lapb_cb *lapb = from_timer(lapb, t, t2timer);
 
+	spin_lock_bh(&lapb->lock);
+	if (timer_pending(&lapb->t2timer)) /* A new timer has been set up */
+		goto out;
+	if (lapb->t2timer_stop) /* The timer has been stopped */
+		goto out;
+
 	if (lapb->condition & LAPB_ACK_PENDING_CONDITION) {
 		lapb->condition &= ~LAPB_ACK_PENDING_CONDITION;
 		lapb_timeout_response(lapb);
 	}
+
+out:
+	spin_unlock_bh(&lapb->lock);
 }
 
 static void lapb_t1timer_expiry(struct timer_list *t)
 {
 	struct lapb_cb *lapb = from_timer(lapb, t, t1timer);
 
+	spin_lock_bh(&lapb->lock);
+	if (timer_pending(&lapb->t1timer)) /* A new timer has been set up */
+		goto out;
+	if (lapb->t1timer_stop) /* The timer has been stopped */
+		goto out;
+
 	switch (lapb->state) {
 
 		/*
@@ -108,7 +127,7 @@ static void lapb_t1timer_expiry(struct timer_list *t)
 				lapb->state = LAPB_STATE_0;
 				lapb_disconnect_indication(lapb, LAPB_TIMEDOUT);
 				lapb_dbg(0, "(%p) S1 -> S0\n", lapb->dev);
-				return;
+				goto out;
 			} else {
 				lapb->n2count++;
 				if (lapb->mode & LAPB_EXTENDED) {
@@ -132,7 +151,7 @@ static void lapb_t1timer_expiry(struct timer_list *t)
 				lapb->state = LAPB_STATE_0;
 				lapb_disconnect_confirmation(lapb, LAPB_TIMEDOUT);
 				lapb_dbg(0, "(%p) S2 -> S0\n", lapb->dev);
-				return;
+				goto out;
 			} else {
 				lapb->n2count++;
 				lapb_dbg(1, "(%p) S2 TX DISC(1)\n", lapb->dev);
@@ -150,7 +169,7 @@ static void lapb_t1timer_expiry(struct timer_list *t)
 				lapb_stop_t2timer(lapb);
 				lapb_disconnect_indication(lapb, LAPB_TIMEDOUT);
 				lapb_dbg(0, "(%p) S3 -> S0\n", lapb->dev);
-				return;
+				goto out;
 			} else {
 				lapb->n2count++;
 				lapb_requeue_frames(lapb);
@@ -167,7 +186,7 @@ static void lapb_t1timer_expiry(struct timer_list *t)
 				lapb->state = LAPB_STATE_0;
 				lapb_disconnect_indication(lapb, LAPB_TIMEDOUT);
 				lapb_dbg(0, "(%p) S4 -> S0\n", lapb->dev);
-				return;
+				goto out;
 			} else {
 				lapb->n2count++;
 				lapb_transmit_frmr(lapb);
@@ -176,4 +195,7 @@ static void lapb_t1timer_expiry(struct timer_list *t)
 	}
 
 	lapb_start_t1timer(lapb);
+
+out:
+	spin_unlock_bh(&lapb->lock);
 }
-- 
2.27.0