tipc: involve reference counter for node structure

TIPC node hash node table is protected with rcu lock on read side.
tipc_node_find() is used to look for a node object with node address
through iterating the hash node table. As the entire process of what
tipc_node_find() traverses the table is guarded with rcu read lock,
it's safe for us. However, when callers use the node object returned
by tipc_node_find(), there is no rcu read lock applied. Therefore,
this is absolutely unsafe for callers of tipc_node_find().

Now we introduce a reference counter for node structure. Before
tipc_node_find() returns node object to its caller, it first increases
the reference counter. Accordingly, after its caller used it up,
it decreases the counter again. This can prevent a node being used by
one thread from being freed by another thread.

Reviewed-by: Erik Hugne <erik.hugne@ericsson.com>
Reviewed-by: Jon Maloy <jon.maloy@ericson.com>
Signed-off-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 0 deletions

diff --git a/net/tipc/name_distr.c b/net/tipc/name_distr.c
index 506aaa565da7..41e7b7e4dda0 100644
--- a/net/tipc/name_distr.c
+++ b/net/tipc/name_distr.c
@@ -244,6 +244,7 @@ static void tipc_publ_subscribe(struct net *net, struct publication *publ,
 	tipc_node_lock(node);
 	list_add_tail(&publ->nodesub_list, &node->publ_list);
 	tipc_node_unlock(node);
+	tipc_node_put(node);
 }
 
 static void tipc_publ_unsubscribe(struct net *net, struct publication *publ,
@@ -258,6 +259,7 @@ static void tipc_publ_unsubscribe(struct net *net, struct publication *publ,
 	tipc_node_lock(node);
 	list_del_init(&publ->nodesub_list);
 	tipc_node_unlock(node);
+	tipc_node_put(node);
 }
 
 /**