IB/mad: Fix null pointer dereference in local_completions()

handle_outgoing_dr_smp() can queue a struct ib_mad_local_private
*local on the mad_agent_priv->local_work work queue with
local->mad_priv == NULL if device->process_mad() returns
IB_MAD_RESULT_SUCCESS | IB_MAD_RESULT_REPLY and
(!ib_response_mad(&mad_priv->mad.mad) ||
!mad_agent_priv->agent.recv_handler).

In this case, local_completions() will be called with local->mad_priv
== NULL. The code does check for this case and skips calling
recv_mad_agent->agent.recv_handler() but recv == 0 so
kmem_cache_free() is called with a NULL pointer.

Also, since recv isn't reinitialized each time through the loop, it
can cause a memory leak if recv should have been zero.
Signed-off-by: Ralph Campbell <ralph.campbell@qlogic.com>

drivers/infiniband/core/mad.c

@@ -2356,7 +2356,7 @@ static void local_completions(struct work_struct *work)
 	struct ib_mad_local_private *local;
 	struct ib_mad_agent_private *recv_mad_agent;
 	unsigned long flags;
-	int recv = 0;
+	int free_mad;
 	struct ib_wc wc;
 	struct ib_mad_send_wc mad_send_wc;
 
@@ -2370,14 +2370,15 @@ static void local_completions(struct work_struct *work)
 				   completion_list);
 		list_del(&local->completion_list);
 		spin_unlock_irqrestore(&mad_agent_priv->lock, flags);
+		free_mad = 0;
 		if (local->mad_priv) {
 			recv_mad_agent = local->recv_mad_agent;
 			if (!recv_mad_agent) {
 				printk(KERN_ERR PFX "No receive MAD agent for local completion\n");
+				free_mad = 1;
 				goto local_send_completion;
 			}
 
-			recv = 1;
 			/*
 			 * Defined behavior is to complete response
 			 * before request
@@ -2422,7 +2423,7 @@ static void local_completions(struct work_struct *work)
 
 		spin_lock_irqsave(&mad_agent_priv->lock, flags);
 		atomic_dec(&mad_agent_priv->refcount);
-		if (!recv)
+		if (free_mad)
 			kmem_cache_free(ib_mad_cache, local->mad_priv);
 		kfree(local);
 	}