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>

6 files changed, 79 insertions, 30 deletions

diff --git a/net/tipc/bcast.c b/net/tipc/bcast.c
index 4289dd62f589..ae558dd7f8ee 100644
--- a/net/tipc/bcast.c
+++ b/net/tipc/bcast.c
@@ -329,13 +329,12 @@ static void bclink_peek_nack(struct net *net, struct tipc_msg *msg)
                 return;
 
         tipc_node_lock(n_ptr);
-
         if (n_ptr->bclink.recv_permitted &&
             (n_ptr->bclink.last_in != n_ptr->bclink.last_sent) &&
             (n_ptr->bclink.last_in == msg_bcgap_after(msg)))
                 n_ptr->bclink.oos_state = 2;
-
         tipc_node_unlock(n_ptr);
+        tipc_node_put(n_ptr);
 }
 
 /* tipc_bclink_xmit - deliver buffer chain to all nodes in cluster
@@ -466,6 +465,7 @@ void tipc_bclink_rcv(struct net *net, struct sk_buff *buf)
                         tipc_node_unlock(node);
                         bclink_peek_nack(net, msg);
                 }
+                tipc_node_put(node);
                 goto exit;
         }
 
@@ -570,6 +570,7 @@ receive:
 
 unlock:
         tipc_node_unlock(node);
+        tipc_node_put(node);
 exit:
         kfree_skb(buf);
 }
diff --git a/net/tipc/discover.c b/net/tipc/discover.c
index 169f3dd038b9..967e292f53c8 100644
--- a/net/tipc/discover.c
+++ b/net/tipc/discover.c
@@ -260,6 +260,7 @@ void tipc_disc_rcv(struct net *net, struct sk_buff *buf,
                 }
         }
         tipc_node_unlock(node);
+        tipc_node_put(node);
 }
 
 /**
diff --git a/net/tipc/link.c b/net/tipc/link.c
index f5e086c5f724..514466efc25c 100644
--- a/net/tipc/link.c
+++ b/net/tipc/link.c
@@ -854,6 +854,7 @@ int tipc_link_xmit(struct net *net, struct sk_buff_head *list, u32 dnode,
                 if (link)
                         rc = __tipc_link_xmit(net, link, list);
                 tipc_node_unlock(node);
+                tipc_node_put(node);
         }
         if (link)
                 return rc;
@@ -1116,8 +1117,8 @@ void tipc_rcv(struct net *net, struct sk_buff *skb, struct tipc_bearer *b_ptr)
                 n_ptr = tipc_node_find(net, msg_prevnode(msg));
                 if (unlikely(!n_ptr))
                         goto discard;
-                tipc_node_lock(n_ptr);
 
+                tipc_node_lock(n_ptr);
                 /* Locate unicast link endpoint that should handle message */
                 l_ptr = n_ptr->links[b_ptr->identity];
                 if (unlikely(!l_ptr))
@@ -1205,6 +1206,7 @@ void tipc_rcv(struct net *net, struct sk_buff *skb, struct tipc_bearer *b_ptr)
                 skb = NULL;
 unlock:
                 tipc_node_unlock(n_ptr);
+                tipc_node_put(n_ptr);
 discard:
                 if (unlikely(skb))
                         kfree_skb(skb);
@@ -2236,7 +2238,6 @@ int tipc_nl_link_dump(struct sk_buff *skb, struct netlink_callback *cb)
         msg.seq = cb->nlh->nlmsg_seq;
 
         rcu_read_lock();
-
         if (prev_node) {
                 node = tipc_node_find(net, prev_node);
                 if (!node) {
@@ -2249,6 +2250,7 @@ int tipc_nl_link_dump(struct sk_buff *skb, struct netlink_callback *cb)
                         cb->prev_seq = 1;
                         goto out;
                 }
+                tipc_node_put(node);
 
                 list_for_each_entry_continue_rcu(node, &tn->node_list,
                                                  list) {
@@ -2256,6 +2258,7 @@ int tipc_nl_link_dump(struct sk_buff *skb, struct netlink_callback *cb)
                         err = __tipc_nl_add_node_links(net, &msg, node,
                                                        &prev_link);
                         tipc_node_unlock(node);
+                        tipc_node_put(node);
                         if (err)
                                 goto out;
 
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);
 }
 
 /**
diff --git a/net/tipc/node.c b/net/tipc/node.c
index 5cc43d34ad0a..3e4f04897c03 100644
--- a/net/tipc/node.c
+++ b/net/tipc/node.c
@@ -42,6 +42,7 @@
 
 static void node_lost_contact(struct tipc_node *n_ptr);
 static void node_established_contact(struct tipc_node *n_ptr);
+static void tipc_node_delete(struct tipc_node *node);
 
 struct tipc_sock_conn {
         u32 port;
@@ -67,6 +68,23 @@ static unsigned int tipc_hashfn(u32 addr)
         return addr & (NODE_HTABLE_SIZE - 1);
 }
 
+static void tipc_node_kref_release(struct kref *kref)
+{
+        struct tipc_node *node = container_of(kref, struct tipc_node, kref);
+
+        tipc_node_delete(node);
+}
+
+void tipc_node_put(struct tipc_node *node)
+{
+        kref_put(&node->kref, tipc_node_kref_release);
+}
+
+static void tipc_node_get(struct tipc_node *node)
+{
+        kref_get(&node->kref);
+}
+
 /*
  * tipc_node_find - locate specified node object, if it exists
  */
@@ -82,6 +100,7 @@ struct tipc_node *tipc_node_find(struct net *net, u32 addr)
         hlist_for_each_entry_rcu(node, &tn->node_htable[tipc_hashfn(addr)],
                                  hash) {
                 if (node->addr == addr) {
+                        tipc_node_get(node);
                         rcu_read_unlock();
                         return node;
                 }
@@ -106,6 +125,7 @@ struct tipc_node *tipc_node_create(struct net *net, u32 addr)
         }
         n_ptr->addr = addr;
         n_ptr->net = net;
+        kref_init(&n_ptr->kref);
         spin_lock_init(&n_ptr->lock);
         INIT_HLIST_NODE(&n_ptr->hash);
         INIT_LIST_HEAD(&n_ptr->list);
@@ -120,16 +140,17 @@ struct tipc_node *tipc_node_create(struct net *net, u32 addr)
         list_add_tail_rcu(&n_ptr->list, &temp_node->list);
         n_ptr->action_flags = TIPC_WAIT_PEER_LINKS_DOWN;
         n_ptr->signature = INVALID_NODE_SIG;
+        tipc_node_get(n_ptr);
 exit:
         spin_unlock_bh(&tn->node_list_lock);
         return n_ptr;
 }
 
-static void tipc_node_delete(struct tipc_net *tn, struct tipc_node *n_ptr)
+static void tipc_node_delete(struct tipc_node *node)
 {
-        list_del_rcu(&n_ptr->list);
-        hlist_del_rcu(&n_ptr->hash);
-        kfree_rcu(n_ptr, rcu);
+        list_del_rcu(&node->list);
+        hlist_del_rcu(&node->hash);
+        kfree_rcu(node, rcu);
 }
 
 void tipc_node_stop(struct net *net)
@@ -139,7 +160,7 @@ void tipc_node_stop(struct net *net)
 
         spin_lock_bh(&tn->node_list_lock);
         list_for_each_entry_safe(node, t_node, &tn->node_list, list)
-                tipc_node_delete(tn, node);
+                tipc_node_put(node);
         spin_unlock_bh(&tn->node_list_lock);
 }
 
@@ -147,6 +168,7 @@ int tipc_node_add_conn(struct net *net, u32 dnode, u32 port, u32 peer_port)
 {
         struct tipc_node *node;
         struct tipc_sock_conn *conn;
+        int err = 0;
 
         if (in_own_node(net, dnode))
                 return 0;
@@ -157,8 +179,10 @@ int tipc_node_add_conn(struct net *net, u32 dnode, u32 port, u32 peer_port)
                 return -EHOSTUNREACH;
         }
         conn = kmalloc(sizeof(*conn), GFP_ATOMIC);
-        if (!conn)
-                return -EHOSTUNREACH;
+        if (!conn) {
+                err = -EHOSTUNREACH;
+                goto exit;
+        }
         conn->peer_node = dnode;
         conn->port = port;
         conn->peer_port = peer_port;
@@ -166,7 +190,9 @@ int tipc_node_add_conn(struct net *net, u32 dnode, u32 port, u32 peer_port)
         tipc_node_lock(node);
         list_add_tail(&conn->list, &node->conn_sks);
         tipc_node_unlock(node);
-        return 0;
+exit:
+        tipc_node_put(node);
+        return err;
 }
 
 void tipc_node_remove_conn(struct net *net, u32 dnode, u32 port)
@@ -189,6 +215,7 @@ void tipc_node_remove_conn(struct net *net, u32 dnode, u32 port)
                 kfree(conn);
         }
         tipc_node_unlock(node);
+        tipc_node_put(node);
 }
 
 /**
@@ -417,19 +444,25 @@ int tipc_node_get_linkname(struct net *net, u32 bearer_id, u32 addr,
                            char *linkname, size_t len)
 {
         struct tipc_link *link;
+        int err = -EINVAL;
         struct tipc_node *node = tipc_node_find(net, addr);
 
-        if ((bearer_id >= MAX_BEARERS) || !node)
-                return -EINVAL;
+        if (!node)
+                return err;
+
+        if (bearer_id >= MAX_BEARERS)
+                goto exit;
+
         tipc_node_lock(node);
         link = node->links[bearer_id];
         if (link) {
                 strncpy(linkname, link->name, len);
-                tipc_node_unlock(node);
-                return 0;
+                err = 0;
         }
+exit:
         tipc_node_unlock(node);
-        return -EINVAL;
+        tipc_node_put(node);
+        return err;
 }
 
 void tipc_node_unlock(struct tipc_node *node)
@@ -545,17 +578,21 @@ int tipc_nl_node_dump(struct sk_buff *skb, struct netlink_callback *cb)
         msg.seq = cb->nlh->nlmsg_seq;
 
         rcu_read_lock();
-
-        if (last_addr && !tipc_node_find(net, last_addr)) {
-                rcu_read_unlock();
-                /* We never set seq or call nl_dump_check_consistent() this
-                 * means that setting prev_seq here will cause the consistence
-                 * check to fail in the netlink callback handler. Resulting in
-                 * the NLMSG_DONE message having the NLM_F_DUMP_INTR flag set if
-                 * the node state changed while we released the lock.
-                 */
-                cb->prev_seq = 1;
-                return -EPIPE;
+        if (last_addr) {
+                node = tipc_node_find(net, last_addr);
+                if (!node) {
+                        rcu_read_unlock();
+                        /* We never set seq or call nl_dump_check_consistent()
+                         * this means that setting prev_seq here will cause the
+                         * consistence check to fail in the netlink callback
+                         * handler. Resulting in the NLMSG_DONE message having
+                         * the NLM_F_DUMP_INTR flag set if the node state
+                         * changed while we released the lock.
+                         */
+                        cb->prev_seq = 1;
+                        return -EPIPE;
+                }
+                tipc_node_put(node);
         }
 
         list_for_each_entry_rcu(node, &tn->node_list, list) {
diff --git a/net/tipc/node.h b/net/tipc/node.h
index 9629ecd2bdd8..02d5c20dc551 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;
 }