tipc: fix unbalanced reference counter

When a topology subscription is created, we may encounter (or KASAN
may provoke) a failure to create a corresponding service instance in
the binding table. Instead of letting the tipc_nametbl_subscribe()
report the failure back to the caller, the function just makes a warning
printout and returns, without incrementing the subscription reference
counter as expected by the caller.

This makes the caller believe that the subscription was successful, so
it will at a later moment try to unsubscribe the item. This involves
a sub_put() call. Since the reference counter never was incremented
in the first place, we get a premature delete of the subscription item,
followed by a "use-after-free" warning.

We fix this by adding a return value to tipc_nametbl_subscribe() and
make the caller aware of the failure to subscribe.

This bug seems to always have been around, but this fix only applies
back to the commit shown below. Given the low risk of this happening
we believe this to be sufficient.

Fixes: commit 218527fe27ad ("tipc: replace name table service range
array with rb tree")
Reported-by: [e-mail]

Signed-off-by: Jon Maloy <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/tipc/name_table.c

···
 /**
  * tipc_nametbl_subscribe - add a subscription object to the name table
  */
-void tipc_nametbl_subscribe(struct tipc_subscription *sub)
+bool tipc_nametbl_subscribe(struct tipc_subscription *sub)
 {
 	struct name_table *nt = tipc_name_table(sub->net);
 	struct tipc_net *tn = tipc_net(sub->net);
 	struct tipc_subscr *s = &sub->evt.s;
 	u32 type = tipc_sub_read(s, seq.type);
 	struct tipc_service *sc;
+	bool res = true;
 
 	spin_lock_bh(&tn->nametbl_lock);
 	sc = tipc_service_find(sub->net, type);
···
 		pr_warn("Failed to subscribe for {%u,%u,%u}\n", type,
 			tipc_sub_read(s, seq.lower),
 			tipc_sub_read(s, seq.upper));
+		res = false;
 	}
 	spin_unlock_bh(&tn->nametbl_lock);
+	return res;
 }
 
 /**

net/tipc/name_table.h

···
 struct publication *tipc_nametbl_remove_publ(struct net *net, u32 type,
 					     u32 lower, u32 upper,
 					     u32 node, u32 key);
-void tipc_nametbl_subscribe(struct tipc_subscription *s);
+bool tipc_nametbl_subscribe(struct tipc_subscription *s);
 void tipc_nametbl_unsubscribe(struct tipc_subscription *s);
 int tipc_nametbl_init(struct net *net);
 void tipc_nametbl_stop(struct net *net);

net/tipc/subscr.c

···
 	memcpy(&sub->evt.s, s, sizeof(*s));
 	spin_lock_init(&sub->lock);
 	kref_init(&sub->kref);
-	tipc_nametbl_subscribe(sub);
+	if (!tipc_nametbl_subscribe(sub)) {
+		kfree(sub);
+		return NULL;
+	}
 	timer_setup(&sub->timer, tipc_sub_timeout, 0);
 	timeout = tipc_sub_read(&sub->evt.s, timeout);
 	if (timeout != TIPC_WAIT_FOREVER)