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, 7 insertions, 2 deletions

diff --git a/net/tipc/node.h b/net/tipc/node.h
index 9629ecd..02d5c20 100644
--- a/net/tipc/node.h
+++ b/net/tipc/node.h
@@ -94,6 +94,7 @@ struct tipc_node_bclink {
 /**
  * struct tipc_node - TIPC node structure
  * @addr: network address of node
+ * @ref: reference counter to node object
  * @lock: spinlock governing access to structure
  * @net: the applicable net namespace
  * @hash: links to adjacent nodes in unsorted hash chain
@@ -115,6 +116,7 @@ struct tipc_node_bclink {
  */
 struct tipc_node {
 	u32 addr;
+	struct kref kref;
 	spinlock_t lock;
 	struct net *net;
 	struct hlist_node hash;
@@ -137,6 +139,7 @@ struct tipc_node {
 };
 
 struct tipc_node *tipc_node_find(struct net *net, u32 addr);
+void tipc_node_put(struct tipc_node *node);
 struct tipc_node *tipc_node_create(struct net *net, u32 addr);
 void tipc_node_stop(struct net *net);
 void tipc_node_attach_link(struct tipc_node *n_ptr, struct tipc_link *l_ptr);
@@ -171,10 +174,12 @@ static inline uint tipc_node_get_mtu(struct net *net, u32 addr, u32 selector)
 
 	node = tipc_node_find(net, addr);
 
-	if (likely(node))
+	if (likely(node)) {
 		mtu = node->act_mtus[selector & 1];
-	else
+		tipc_node_put(node);
+	} else {
 		mtu = MAX_MSG_SIZE;
+	}
 
 	return mtu;
 }