net: lapb: Add locking to the lapb module

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. Let lapb_unregister wait for other API functions and running timers
to stop.

4. The lapb_device_event function calls lapb_disconnect_request. In
order to avoid trying to hold the lock twice, add a new function named
"__lapb_disconnect_request" which assumes the lock is held, and make
it called by lapb_disconnect_request and lapb_device_event.

Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Cc: Martin Schiller <ms@dev.tdt.de>
Signed-off-by: Xie He <xie.he.0141@gmail.com>
Link: https://lore.kernel.org/r/20210126040939.69995-1-xie.he.0141@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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;
 };
 

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;
@@ -178,11 +182,23 @@ int lapb_unregister(struct net_device *dev)
 		goto out;
 	lapb_put(lapb);
 
+	/* Wait for other refs to "lapb" to drop */
+	while (refcount_read(&lapb->refcnt) > 2)
+		usleep_range(1, 10);
+
+	spin_lock_bh(&lapb->lock);
+
 	lapb_stop_t1timer(lapb);
 	lapb_stop_t2timer(lapb);
 
 	lapb_clear_queues(lapb);
 
+	spin_unlock_bh(&lapb->lock);
+
+	/* Wait for running timers to stop */
+	del_timer_sync(&lapb->t1timer);
+	del_timer_sync(&lapb->t2timer);
+
 	__lapb_remove_cb(lapb);
 
 	lapb_put(lapb);
@@ -201,6 +217,8 @@ 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 +237,7 @@ 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 +253,8 @@ 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 +277,7 @@ 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 +292,8 @@ 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;
@@ -285,24 +309,18 @@ int lapb_connect_request(struct net_device *dev)
 
 	rc = LAPB_OK;
 out_put:
+	spin_unlock_bh(&lapb->lock);
 	lapb_put(lapb);
 out:
 	return rc;
 }
 EXPORT_SYMBOL(lapb_connect_request);
 
-int lapb_disconnect_request(struct net_device *dev)
+static int __lapb_disconnect_request(struct lapb_cb *lapb)
 {
-	struct lapb_cb *lapb = lapb_devtostruct(dev);
-	int rc = LAPB_BADTOKEN;
-
-	if (!lapb)
-		goto out;
-
 	switch (lapb->state) {
 	case LAPB_STATE_0:
-		rc = LAPB_NOTCONNECTED;
+		return LAPB_NOTCONNECTED;
-		goto out_put;
 
 	case LAPB_STATE_1:
 		lapb_dbg(1, "(%p) S1 TX DISC(1)\n", lapb->dev);
@@ -310,12 +328,10 @@ int lapb_disconnect_request(struct net_device *dev)
 		lapb_send_control(lapb, LAPB_DISC, LAPB_POLLON, LAPB_COMMAND);
 		lapb->state = LAPB_STATE_0;
 		lapb_start_t1timer(lapb);
-		rc = LAPB_NOTCONNECTED;
+		return LAPB_NOTCONNECTED;
-		goto out_put;
 
 	case LAPB_STATE_2:
-		rc = LAPB_OK;
+		return LAPB_OK;
-		goto out_put;
 	}
 
 	lapb_clear_queues(lapb);
@@ -328,8 +344,22 @@ int lapb_disconnect_request(struct net_device *dev)
 	lapb_dbg(1, "(%p) S3 DISC(1)\n", lapb->dev);
 	lapb_dbg(0, "(%p) S3 -> S2\n", lapb->dev);
 
-	rc = LAPB_OK;
+	return LAPB_OK;
-out_put:
+}
+
+int lapb_disconnect_request(struct net_device *dev)
+{
+	struct lapb_cb *lapb = lapb_devtostruct(dev);
+	int rc = LAPB_BADTOKEN;
+
+	if (!lapb)
+		goto out;
+
+	spin_lock_bh(&lapb->lock);
+
+	rc = __lapb_disconnect_request(lapb);
+
+	spin_unlock_bh(&lapb->lock);
 	lapb_put(lapb);
 out:
 	return rc;
@@ -344,6 +374,8 @@ 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 +384,7 @@ 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 +397,9 @@ 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 +470,8 @@ 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);
@@ -454,7 +491,7 @@ 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);
+			__lapb_disconnect_request(lapb);
 		break;
 	case NETDEV_DOWN:
 		lapb_dbg(0, "(%p) Interface down: %s\n", dev, dev->name);
@@ -489,6 +526,7 @@ static int lapb_device_event(struct notifier_block *this, unsigned long event,
 		break;
 	}
 
+	spin_unlock_bh(&lapb->lock);
 	lapb_put(lapb);
 	return NOTIFY_DONE;
 }

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);
 }