tipc: protect handler_enabled variable with qitem_lock spin lock

'handler_enabled' is a global flag indicating whether the TIPC
signal handling service is enabled or not. The lack of lock
protection for this flag incurs a risk for contention, so that
a tipc_k_signal() call might queue a signal handler to a destroyed
signal queue, with unpredictable results. To correct this, we let
the already existing 'qitem_lock' protect the flag, as it already
does with the queue itself. This way, we ensure that the flag
always is consistent across all cores.

Signed-off-by: Ying Xue <ying.xue@windriver.com>
Reviewed-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 3 deletions

diff --git a/net/tipc/handler.c b/net/tipc/handler.c
index b36f0fcd9bdf..e4bc8a296744 100644
--- a/net/tipc/handler.c
+++ b/net/tipc/handler.c
@@ -56,12 +56,13 @@ unsigned int tipc_k_signal(Handler routine, unsigned long argument)
 {
         struct queue_item *item;
 
+        spin_lock_bh(&qitem_lock);
         if (!handler_enabled) {
                 pr_err("Signal request ignored by handler\n");
+                spin_unlock_bh(&qitem_lock);
                 return -ENOPROTOOPT;
         }
 
-        spin_lock_bh(&qitem_lock);
         item = kmem_cache_alloc(tipc_queue_item_cache, GFP_ATOMIC);
         if (!item) {
                 pr_err("Signal queue out of memory\n");
@@ -112,10 +113,14 @@ void tipc_handler_stop(void)
         struct list_head *l, *n;
         struct queue_item *item;
 
-        if (!handler_enabled)
+        spin_lock_bh(&qitem_lock);
+        if (!handler_enabled) {
+                spin_unlock_bh(&qitem_lock);
                 return;
-
+        }
         handler_enabled = 0;
+        spin_unlock_bh(&qitem_lock);
+
         tasklet_kill(&tipc_tasklet);
 
         spin_lock_bh(&qitem_lock);