[PATCH net v1 2/6] tipc: add subscription refcount to avoid invalid delete

[Parthasarathy Bhuvaragan <parthasarathy.bhuvaragan@ericsson.com>]

Until now, the subscribers keep track of the subscriptions using
reference count at subscriber level. At subscription cancel or
subscriber delete, we delete the subscription only if the timer
was pending for the subscription. This approach is incorrect as:
1. del_timer() is not SMP safe, if on CPU0 the check for pending
   timer returns true but CPU1 might schedule the timer callback
   thereby deleting the subscription. Thus when CPU0 is scheduled,
   it deletes an invalid subscription.
2. We export tipc_subscrp_report_overlap(), which accesses the
   subscription pointer multiple times. Meanwhile the subscription
   timer can expire thereby freeing the subscription and we might
   continue to access the subscription pointer leading to memory
   violations.

In this commit, we introduce subscription refcount to avoid deleting
an invalid subscription.

Reported-and-Tested-by: John Thompson <thompa.atl@gmail.com>
Acked-by: Ying Xue <ying.xue@windriver.com>
Acked-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: Parthasarathy Bhuvaragan <parthasarathy.bhuvaragan@ericsson.com>
---
 net/tipc/subscr.c | 124 ++++++++++++++++++++++++++++++------------------------
 net/tipc/subscr.h |   1 +
 2 files changed, 71 insertions(+), 54 deletions(-)

diff --git a/net/tipc/subscr.c b/net/tipc/subscr.c
index 0dd02244e21d..9d94e65d0894 100644
--- a/net/tipc/subscr.c
+++ b/net/tipc/subscr.c
@@ -54,6 +54,8 @@ struct tipc_subscriber {
 
 static void tipc_subscrp_delete(struct tipc_subscription *sub);
 static void tipc_subscrb_put(struct tipc_subscriber *subscriber);
+static void tipc_subscrp_put(struct tipc_subscription *subscription);
+static void tipc_subscrp_get(struct tipc_subscription *subscription);
 
 /**
  * htohl - convert value to endianness used by destination
@@ -123,6 +125,7 @@ void tipc_subscrp_report_overlap(struct tipc_subscription *sub, u32 found_lower,
 {
 	struct tipc_name_seq seq;
 
+	tipc_subscrp_get(sub);
 	tipc_subscrp_convert_seq(&sub->evt.s.seq, sub->swap, &seq);
 	if (!tipc_subscrp_check_overlap(&seq, found_lower, found_upper))
 		return;
@@ -132,30 +135,23 @@ void tipc_subscrp_report_overlap(struct tipc_subscription *sub, u32 found_lower,
 
 	tipc_subscrp_send_event(sub, found_lower, found_upper, event, port_ref,
 				node);
+	tipc_subscrp_put(sub);
 }
 
 static void tipc_subscrp_timeout(unsigned long data)
 {
 	struct tipc_subscription *sub = (struct tipc_subscription *)data;
-	struct tipc_subscriber *subscriber = sub->subscriber;
 
 	/* Notify subscriber of timeout */
 	tipc_subscrp_send_event(sub, sub->evt.s.seq.lower, sub->evt.s.seq.upper,
 				TIPC_SUBSCR_TIMEOUT, 0, 0);
 
-	spin_lock_bh(&subscriber->lock);
-	tipc_subscrp_delete(sub);
-	spin_unlock_bh(&subscriber->lock);
-
-	tipc_subscrb_put(subscriber);
+	tipc_subscrp_put(sub);
 }
 
 static void tipc_subscrb_kref_release(struct kref *kref)
 {
-	struct tipc_subscriber *subcriber = container_of(kref,
-					    struct tipc_subscriber, kref);
-
-	kfree(subcriber);
+	kfree(container_of(kref,struct tipc_subscriber, kref));
 }
 
 static void tipc_subscrb_put(struct tipc_subscriber *subscriber)
@@ -168,6 +164,59 @@ static void tipc_subscrb_get(struct tipc_subscriber *subscriber)
 	kref_get(&subscriber->kref);
 }
 
+static void tipc_subscrp_kref_release(struct kref *kref)
+{
+	struct tipc_subscription *sub = container_of(kref,
+						     struct tipc_subscription,
+						     kref);
+	struct tipc_net *tn = net_generic(sub->net, tipc_net_id);
+	struct tipc_subscriber *subscriber = sub->subscriber;
+
+	spin_lock_bh(&subscriber->lock);
+	tipc_nametbl_unsubscribe(sub);
+	list_del(&sub->subscrp_list);
+	atomic_dec(&tn->subscription_count);
+	spin_unlock_bh(&subscriber->lock);
+	kfree(sub);
+	tipc_subscrb_put(subscriber);
+}
+
+static void tipc_subscrp_put(struct tipc_subscription *subscription)
+{
+	kref_put(&subscription->kref, tipc_subscrp_kref_release);
+}
+
+static void tipc_subscrp_get(struct tipc_subscription *subscription)
+{
+	kref_get(&subscription->kref);
+}
+
+/* tipc_subscrb_subscrp_delete - delete a specific subscription or all
+ * subscriptions for a given subscriber.
+ */
+static void tipc_subscrb_subscrp_delete(struct tipc_subscriber *subscriber,
+					struct tipc_subscr *s)
+{
+	struct list_head *subscription_list = &subscriber->subscrp_list;
+	struct tipc_subscription *sub, *temp;
+
+	spin_lock_bh(&subscriber->lock);
+	list_for_each_entry_safe(sub, temp, subscription_list,  subscrp_list) {
+		if (s && memcmp(s, &sub->evt.s, sizeof(struct tipc_subscr)))
+			continue;
+
+		tipc_subscrp_get(sub);
+		spin_unlock_bh(&subscriber->lock);
+		tipc_subscrp_delete(sub);
+		tipc_subscrp_put(sub);
+		spin_lock_bh(&subscriber->lock);
+
+		if (s)
+			break;
+	}
+	spin_unlock_bh(&subscriber->lock);
+}
+
 static struct tipc_subscriber *tipc_subscrb_create(int conid)
 {
 	struct tipc_subscriber *subscriber;
@@ -177,8 +226,8 @@ static struct tipc_subscriber *tipc_subscrb_create(int conid)
 		pr_warn("Subscriber rejected, no memory\n");
 		return NULL;
 	}
-	kref_init(&subscriber->kref);
 	INIT_LIST_HEAD(&subscriber->subscrp_list);
+	kref_init(&subscriber->kref);
 	subscriber->conid = conid;
 	spin_lock_init(&subscriber->lock);
 
@@ -187,55 +236,22 @@ static struct tipc_subscriber *tipc_subscrb_create(int conid)
 
 static void tipc_subscrb_delete(struct tipc_subscriber *subscriber)
 {
-	struct tipc_subscription *sub, *temp;
-	u32 timeout;
-
-	spin_lock_bh(&subscriber->lock);
-	/* Destroy any existing subscriptions for subscriber */
-	list_for_each_entry_safe(sub, temp, &subscriber->subscrp_list,
-				 subscrp_list) {
-		timeout = htohl(sub->evt.s.timeout, sub->swap);
-		if ((timeout == TIPC_WAIT_FOREVER) || del_timer(&sub->timer)) {
-			tipc_subscrp_delete(sub);
-			tipc_subscrb_put(subscriber);
-		}
-	}
-	spin_unlock_bh(&subscriber->lock);
-
+	tipc_subscrb_subscrp_delete(subscriber, NULL);
 	tipc_subscrb_put(subscriber);
 }
 
 static void tipc_subscrp_delete(struct tipc_subscription *sub)
 {
-	struct tipc_net *tn = net_generic(sub->net, tipc_net_id);
+	u32 timeout = htohl(sub->evt.s.timeout, sub->swap);
 
-	tipc_nametbl_unsubscribe(sub);
-	list_del(&sub->subscrp_list);
-	kfree(sub);
-	atomic_dec(&tn->subscription_count);
+	if (timeout == TIPC_WAIT_FOREVER || del_timer(&sub->timer))
+		tipc_subscrp_put(sub);
 }
 
 static void tipc_subscrp_cancel(struct tipc_subscr *s,
 				struct tipc_subscriber *subscriber)
 {
-	struct tipc_subscription *sub, *temp;
-	u32 timeout;
-
-	spin_lock_bh(&subscriber->lock);
-	/* Find first matching subscription, exit if not found */
-	list_for_each_entry_safe(sub, temp, &subscriber->subscrp_list,
-				 subscrp_list) {
-		if (!memcmp(s, &sub->evt.s, sizeof(struct tipc_subscr))) {
-			timeout = htohl(sub->evt.s.timeout, sub->swap);
-			if ((timeout == TIPC_WAIT_FOREVER) ||
-			    del_timer(&sub->timer)) {
-				tipc_subscrp_delete(sub);
-				tipc_subscrb_put(subscriber);
-			}
-			break;
-		}
-	}
-	spin_unlock_bh(&subscriber->lock);
+	tipc_subscrb_subscrp_delete(subscriber, s);
 }
 
 static struct tipc_subscription *tipc_subscrp_create(struct net *net,
@@ -272,6 +288,7 @@ static struct tipc_subscription *tipc_subscrp_create(struct net *net,
 	sub->swap = swap;
 	memcpy(&sub->evt.s, s, sizeof(*s));
 	atomic_inc(&tn->subscription_count);
+	kref_init(&sub->kref);
 	return sub;
 }
 
@@ -288,17 +305,16 @@ static void tipc_subscrp_subscribe(struct net *net, struct tipc_subscr *s,
 
 	spin_lock_bh(&subscriber->lock);
 	list_add(&sub->subscrp_list, &subscriber->subscrp_list);
-	tipc_subscrb_get(subscriber);
 	sub->subscriber = subscriber;
 	tipc_nametbl_subscribe(sub);
+	tipc_subscrb_get(subscriber);
 	spin_unlock_bh(&subscriber->lock);
 
+	setup_timer(&sub->timer, tipc_subscrp_timeout, (unsigned long)sub);
 	timeout = htohl(sub->evt.s.timeout, swap);
-	if (timeout == TIPC_WAIT_FOREVER)
-		return;
 
-	setup_timer(&sub->timer, tipc_subscrp_timeout, (unsigned long)sub);
-	mod_timer(&sub->timer, jiffies + msecs_to_jiffies(timeout));
+	if (timeout != TIPC_WAIT_FOREVER)
+		mod_timer(&sub->timer, jiffies + msecs_to_jiffies(timeout));
 }
 
 /* Handle one termination request for the subscriber */
diff --git a/net/tipc/subscr.h b/net/tipc/subscr.h
index be60103082c9..ffdc214c117a 100644
--- a/net/tipc/subscr.h
+++ b/net/tipc/subscr.h
@@ -57,6 +57,7 @@ struct tipc_subscriber;
  * @evt: template for events generated by subscription
  */
 struct tipc_subscription {
+	struct kref kref;
 	struct tipc_subscriber *subscriber;
 	struct net *net;
 	struct timer_list timer;
-- 
2.1.4