tipc: use node list lock to protect tipc_num_links variable

Without properly implicit or explicit read memory barrier, it's
unsafe to read an atomic variable with atomic_read() from another
thread which is different with the thread of changing the atomic
variable with atomic_inc() or atomic_dec(). So a stale tipc_num_links
may be got with atomic_read() in tipc_node_get_links(). If the
tipc_num_links variable type is converted from atomic to unsigned
integer and node list lock is used to protect it, the issue would
be avoided.

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

1 files changed, 11 insertions, 10 deletions

diff --git a/net/tipc/node.c b/net/tipc/node.c
index 85405a6e3076..1d3a4999a70f 100644
--- a/net/tipc/node.c
+++ b/net/tipc/node.c
@@ -47,10 +47,9 @@ static void node_established_contact(struct tipc_node *n_ptr);
 static struct hlist_head node_htable[NODE_HTABLE_SIZE];
 LIST_HEAD(tipc_node_list);
 static u32 tipc_num_nodes;
+static u32 tipc_num_links;
 static DEFINE_SPINLOCK(node_list_lock);
 
-static atomic_t tipc_num_links = ATOMIC_INIT(0);
-
 /*
  * A trivial power-of-two bitmask technique is used for speed, since this
  * operation is done for every incoming TIPC packet. The number of hash table
@@ -241,7 +240,9 @@ int tipc_node_is_up(struct tipc_node *n_ptr)
 void tipc_node_attach_link(struct tipc_node *n_ptr, struct tipc_link *l_ptr)
 {
         n_ptr->links[l_ptr->b_ptr->identity] = l_ptr;
-        atomic_inc(&tipc_num_links);
+        spin_lock_bh(&node_list_lock);
+        tipc_num_links++;
+        spin_unlock_bh(&node_list_lock);
         n_ptr->link_cnt++;
 }
 
@@ -253,7 +254,9 @@ void tipc_node_detach_link(struct tipc_node *n_ptr, struct tipc_link *l_ptr)
                 if (l_ptr != n_ptr->links[i])
                         continue;
                 n_ptr->links[i] = NULL;
-                atomic_dec(&tipc_num_links);
+                spin_lock_bh(&node_list_lock);
+                tipc_num_links--;
+                spin_unlock_bh(&node_list_lock);
                 n_ptr->link_cnt--;
         }
 }
@@ -393,18 +396,17 @@ struct sk_buff *tipc_node_get_links(const void *req_tlv_area, int req_tlv_space)
 
         spin_lock_bh(&node_list_lock);
         /* Get space for all unicast links + broadcast link */
-        payload_size = TLV_SPACE(sizeof(link_info)) *
-                (atomic_read(&tipc_num_links) + 1);
+        payload_size = TLV_SPACE((sizeof(link_info)) * (tipc_num_links + 1));
         if (payload_size > 32768u) {
                 spin_unlock_bh(&node_list_lock);
                 return tipc_cfg_reply_error_string(TIPC_CFG_NOT_SUPPORTED
                                                    " (too many links)");
         }
+        spin_unlock_bh(&node_list_lock);
+
         buf = tipc_cfg_reply_alloc(payload_size);
-        if (!buf) {
-                spin_unlock_bh(&node_list_lock);
+        if (!buf)
                 return NULL;
-        }
 
         /* Add TLV for broadcast link */
         link_info.dest = htonl(tipc_cluster_mask(tipc_own_addr));
@@ -432,6 +434,5 @@ struct sk_buff *tipc_node_get_links(const void *req_tlv_area, int req_tlv_space)
                 tipc_node_unlock(n_ptr);
         }
         rcu_read_unlock();
-        spin_unlock_bh(&node_list_lock);
         return buf;
 }